This document summarizes a formal specification, verification, and simulation of the MACAW wireless LAN protocol. The specification formally models MACAW using communicating finite state machines and shared variables. The verification analyzes basic configurations of 2, 3, and 4 machines to check for errors like deadlocks, but does not verify all possible configurations. The simulation provides further insight into MACAW's performance and suggests areas for improvement. In summary, the work formally specifies MACAW, verifies parts of its behavior, and simulates its performance to evaluate and potentially enhance the protocol.
The document proposes a Power Controlled Dual Channel (PCDC) medium access protocol for wireless ad hoc networks that aims to increase channel utilization and network throughput while decreasing energy consumption. The protocol builds on IEEE 802.11 by allowing simultaneous transmissions in a neighborhood through dynamic power control based on directional and channel gain information from overheard RTS and CTS packets. Simulation results show the proposed protocol achieves significant increases in channel utilization and end-to-end throughput as well as significant decreases in total energy consumption compared to IEEE 802.11.
A DDRESSING T HE M ULTICHANNEL S ELECTION , S CHEDULING A ND C OORDINATION...pijans
We discuss a new multichannel coordination and sche
duling challenge called the Multichannel Scheduling
Cost (MSC). It is caused by the inability of the co
ntrol channel to schedule simultaneous transmission
s
resulting in data channels lying idle and their ban
dwidth underutilized. As a result, wasted bandwidth
increases as the number of data channels increases.
To address this challenge, a cyclic scheduling
Algorithm (CSA) is proposed. It employs one dedicat
ed signaling channel and 4 data channels. It is
premised on a proactive channel reservation scheme
which reduces the idleness of channels. The scheme
ensures that data channels are reserved while they
are still busy. The data channels are reserved whil
e
their remaining transmission duration is equal to t
he virtual carrier sensing duration. This gives the
next
pair sufficient time to reserve the current data ch
annel before it becomes available, limiting the MSC
to the
first cycle. The simulation results show a performa
nce benefit of the CSA scheme in addressing the eff
ects
of the MSC
11.a review of improvement in tcp congestion control using route failure det...Alexander Decker
This summary provides an overview of a document that reviews several algorithms aimed at improving TCP congestion control and addressing route failures in mobile ad hoc networks (MANETs).
The document begins with an introduction to MANETs and the issues they present for TCP, as TCP was designed for wired networks and interprets all packet losses as congestion. It then analyzes and compares five different algorithms that have been proposed to help TCP distinguish between losses due to route failures versus congestion. These algorithms aim to improve network performance metrics like throughput, packet delivery ratio, and end-to-end delay. The document concludes that while these algorithms approach the problem of route failures and TCP performance degradation in different ways, their overall goal is the
The three-way need for higher data rates, good quality of service and ubiquity in a converged all IP
communication cloud drives research in wireless communication. Wireless access networks are envisaged
candidates of the next generation wireless networks. The various access networks will be integrated with
other technologies including the wired backbone. The major issues in an all IP and converged networks
are: quality of service, seamless handover and network capacity. Emerging research seeks to address these
open research issues; for example the implementation of multi-channel and multi radio MAC protocols in
WMN. In this paper we analyze and evaluate the effectiveness of multi-channel and multi radio techniques
in WMN. The shortcomings of these schemes are highlighted and possible solutions are suggested. The
signalling delay metric is used for evaluation purposes. The focus is on the performance of the control
channel identified as the critical performance metric of multi-channel MAC protocols.
Mac protocols for ad hoc wireless networks Divya Tiwari
The document discusses MAC protocols for ad hoc wireless networks. It addresses key issues in designing MAC protocols including limited bandwidth, quality of service support, synchronization, hidden and exposed terminal problems, error-prone shared channels, distributed coordination without centralized control, and node mobility. Common MAC protocol classifications and examples are also presented, such as contention-based protocols, sender-initiated versus receiver-initiated protocols, and protocols using techniques like reservation, scheduling, and directional antennas.
- Mobile ad hoc networks (MANETs) are autonomous systems of wireless nodes that can dynamically change topology as nodes move. Routing must adapt to these changes.
- There are two main categories of routing protocols: table-driven protocols proactively maintain consistent, up-to-date routing tables whereas on-demand protocols only determine routes when needed.
- Examples of protocols include DSDV as a table-driven protocol and AODV as an on-demand protocol, with AODV using route requests and replies to discover routes only when transmitting data.
Some of the key driving forces behind the transition from the UMTS based cellular system to the Long Term Evolution Advanced (LTE-A) are to improve the mean and the cell-edge throughput, improve the user fairness, and improve the quality of service (QoS) satisfaction for all users. In the latter system, relays appear as one of the most prominent enabler for improving the cell-edge user experience while increasing the system’s fairness.
In this white paper, we present the basics of relay deployments in LTE-A networks. Moreover, we analyze resource allocation problem for Relay Nodes (RN) deployments and present some of the solutions for improvement in system resource usage and QoS satisfaction. Afterwards, we introduce the capabilities of NOMOR’s LTE-A system level simulator and evaluate the performance of LTE-A relay systems under the described solutions.
The document proposes a Power Controlled Dual Channel (PCDC) medium access protocol for wireless ad hoc networks that aims to increase channel utilization and network throughput while decreasing energy consumption. The protocol builds on IEEE 802.11 by allowing simultaneous transmissions in a neighborhood through dynamic power control based on directional and channel gain information from overheard RTS and CTS packets. Simulation results show the proposed protocol achieves significant increases in channel utilization and end-to-end throughput as well as significant decreases in total energy consumption compared to IEEE 802.11.
A DDRESSING T HE M ULTICHANNEL S ELECTION , S CHEDULING A ND C OORDINATION...pijans
We discuss a new multichannel coordination and sche
duling challenge called the Multichannel Scheduling
Cost (MSC). It is caused by the inability of the co
ntrol channel to schedule simultaneous transmission
s
resulting in data channels lying idle and their ban
dwidth underutilized. As a result, wasted bandwidth
increases as the number of data channels increases.
To address this challenge, a cyclic scheduling
Algorithm (CSA) is proposed. It employs one dedicat
ed signaling channel and 4 data channels. It is
premised on a proactive channel reservation scheme
which reduces the idleness of channels. The scheme
ensures that data channels are reserved while they
are still busy. The data channels are reserved whil
e
their remaining transmission duration is equal to t
he virtual carrier sensing duration. This gives the
next
pair sufficient time to reserve the current data ch
annel before it becomes available, limiting the MSC
to the
first cycle. The simulation results show a performa
nce benefit of the CSA scheme in addressing the eff
ects
of the MSC
11.a review of improvement in tcp congestion control using route failure det...Alexander Decker
This summary provides an overview of a document that reviews several algorithms aimed at improving TCP congestion control and addressing route failures in mobile ad hoc networks (MANETs).
The document begins with an introduction to MANETs and the issues they present for TCP, as TCP was designed for wired networks and interprets all packet losses as congestion. It then analyzes and compares five different algorithms that have been proposed to help TCP distinguish between losses due to route failures versus congestion. These algorithms aim to improve network performance metrics like throughput, packet delivery ratio, and end-to-end delay. The document concludes that while these algorithms approach the problem of route failures and TCP performance degradation in different ways, their overall goal is the
The three-way need for higher data rates, good quality of service and ubiquity in a converged all IP
communication cloud drives research in wireless communication. Wireless access networks are envisaged
candidates of the next generation wireless networks. The various access networks will be integrated with
other technologies including the wired backbone. The major issues in an all IP and converged networks
are: quality of service, seamless handover and network capacity. Emerging research seeks to address these
open research issues; for example the implementation of multi-channel and multi radio MAC protocols in
WMN. In this paper we analyze and evaluate the effectiveness of multi-channel and multi radio techniques
in WMN. The shortcomings of these schemes are highlighted and possible solutions are suggested. The
signalling delay metric is used for evaluation purposes. The focus is on the performance of the control
channel identified as the critical performance metric of multi-channel MAC protocols.
Mac protocols for ad hoc wireless networks Divya Tiwari
The document discusses MAC protocols for ad hoc wireless networks. It addresses key issues in designing MAC protocols including limited bandwidth, quality of service support, synchronization, hidden and exposed terminal problems, error-prone shared channels, distributed coordination without centralized control, and node mobility. Common MAC protocol classifications and examples are also presented, such as contention-based protocols, sender-initiated versus receiver-initiated protocols, and protocols using techniques like reservation, scheduling, and directional antennas.
- Mobile ad hoc networks (MANETs) are autonomous systems of wireless nodes that can dynamically change topology as nodes move. Routing must adapt to these changes.
- There are two main categories of routing protocols: table-driven protocols proactively maintain consistent, up-to-date routing tables whereas on-demand protocols only determine routes when needed.
- Examples of protocols include DSDV as a table-driven protocol and AODV as an on-demand protocol, with AODV using route requests and replies to discover routes only when transmitting data.
Some of the key driving forces behind the transition from the UMTS based cellular system to the Long Term Evolution Advanced (LTE-A) are to improve the mean and the cell-edge throughput, improve the user fairness, and improve the quality of service (QoS) satisfaction for all users. In the latter system, relays appear as one of the most prominent enabler for improving the cell-edge user experience while increasing the system’s fairness.
In this white paper, we present the basics of relay deployments in LTE-A networks. Moreover, we analyze resource allocation problem for Relay Nodes (RN) deployments and present some of the solutions for improvement in system resource usage and QoS satisfaction. Afterwards, we introduce the capabilities of NOMOR’s LTE-A system level simulator and evaluate the performance of LTE-A relay systems under the described solutions.
11.signal strength based congestion control in manetAlexander Decker
This document discusses several algorithms and approaches for improving TCP performance in mobile ad hoc networks (MANETs) using signal strength measurements:
1. TCP Venoplus is a cross-layer approach that uses signal strength information from the MAC layer to better distinguish between packet losses due to congestion versus random errors.
2. Other algorithms proposed include Link-RED and adaptive pacing to reduce the impact of wireless interference on TCP, as well as techniques to predict and avoid link failures before they occur such as gray zone prediction and multi-agent adaptive DSR.
3. Most of the algorithms aim to minimize unnecessary packet retransmissions when losses are due to non-congestion factors like mobility, thereby improving throughput
4..[26 36]signal strength based congestion control in manetAlexander Decker
This document discusses several algorithms and approaches for improving TCP performance in mobile ad hoc networks (MANETs) using signal strength measurements:
1. TCP Venoplus is a cross-layer approach that uses signal strength information from the MAC layer to better distinguish between packet losses due to congestion versus random errors.
2. Other algorithms proposed include Link-RED to tune wireless link drop probability, adaptive pacing to improve spatial reuse, and algorithms to predict link failures and find stable routes using signal strength measurements.
3. Received signal strength is also used in algorithms to minimize broadcast storms and adapt MAC layer retransmissions to distinguish true link failures from false ones caused by interference.
4. Gray zone prediction and
Signalling protocols in GSM networks include the Message Transfer Part (MTP) protocol stack and the Signalling System 7 (SS7) protocol stack. MTP has three levels that handle transport, routing, and error correction. Above MTP are protocols like SCCP and TCAP that establish connections and transport messages between applications. SS7 protocols include INAP, MAP, ISUP, and TUP that are used in different network elements for call setup and routing.
Dynamic Power Allocation for Mc-Cdma System Using Iterative Water Filling Alg...inventionjournals
ABSTRACT : Power control in Multi Carrier Code Division Multiple Access ( MCCDMA) based wireless cellular network is of great importance. The power allocation methodology to enhance the performance of the MCCDMA system by limiting interference noise is at the expense of signaling overhead due to sharing of Channel State Information (CSI). The distributed algorithms that manage the power level based on the user’s SINR requirements needs the complete knowledge of Channel State Information (CSI) .Since the CSI is subjected to the errors because of the imperfect channel estimation/measurement due to the time varying nature of the channels, the distributed power control algorithm is not globally optimum. The water filling algorithm is used to allocate proper power for every sub channel in order to improve channel capacity. The water filling algorithm distributes power among all users with the help of SINR that is received by the transmitter instead of getting full Channel State Information (CSI).
Simulation based Evaluation of a Simple Channel Distribution Scheme for MANETsIOSR Journals
This document presents a proposed multi-channel distribution scheme for mobile ad hoc networks (MANETs) and evaluates it through simulation. The proposed scheme assigns channels to nodes based on their node IDs to avoid control overhead from time synchronization. While neighboring nodes on the same channel is possible, the probability is low given random node distribution. The proposed scheme is compared to a single-channel scheme in ns-2 simulations. Results show the proposed technique has better performance.
Simulation and Performance Analysis of Long Term Evolution (LTE) Cellular Net...ijsrd.com
In the development, standardization and implementation of LTE Networks based on Orthogonal Freq. Division Multiple Access (OFDMA), simulations are necessary to test as well as optimize algorithms and procedures before real time establishment. This can be done by both Physical Layer (Link-Level) and Network (System-Level) context. This paper proposes Network Simulator 3 (NS-3) which is capable of evaluating the performance of the Downlink Shared Channel of LTE networks and comparing it with available MatLab based LTE System Level Simulator performance.
An energy efficient mac protocol for wirelessnabil_alsharafi
This document presents S-MAC, an energy-efficient MAC protocol designed for wireless sensor networks. S-MAC aims to reduce energy consumption through the use of synchronized duty cycles where nodes periodically listen and sleep. It also supports self-configuration. The paper describes the characteristics of WSNs that require a different MAC approach than IEEE 802.11. Experiments show that S-MAC achieves significant energy savings of around 98% compared to IEEE 802.11 through the use of duty cycles and avoiding overhearing. However, S-MAC can introduce increased latency and may not perform as well as other protocols under heavy traffic loads. Tradeoffs between energy consumption and latency can be tuned by adjusting the duty cycle parameters.
Managing Instantly Dense Hot Spot Regions in Wireless Cellular Communication ...Eswar Publications
In a wireless communication cellular network, call activity can be more intensive in some regions than others. These high-traffic regions are called hot spot regions. In typical deployments of wireless cellular networks, traffic hot spots can arise from the non-uniform geographic distribution of the mobile users, and the heavy-tailed nature of their network usage patterns. These hot spots of activity can degrade system performance, by increasing network utilization, wireless interference, call blocking, and even call dropping from failed handoffs for mobile users. In this paper, a hierarchical cellular communication wireless network is characterized by overlapping the service area for managing the new calls users having different mobility speed. The overlapping property of the hierarchical-network provides the advantages that share the traffic load to improve the performance of wireless
cellular networks in the highly populated area where both slow speed users and high speed users are available.
Picocells are created that are underlaid to two-tier networks for handling the slow or staying speed visitor (outside registered) users. The hierarchical-networks with picocells, microcells and macrocells provide the secondary resource, which provide the services to new calls as well as handoff calls with guard channels by overflow the slow speed visitor users in picocells, slow speed local users in macrocell by sharing the frequency in
vertical as well as in horizontal directions. The picocell is installed on four wheeler vehicle may be moved at any place as per necessity and may be utilized to create picocell to handle the load of hot spot area. Such kind of picocell is known as Portable-Picocell (P-Picocell/ P2cell). The call loss probability of new calls is developed through numerical analysis. The proposed schemes are compared with the existing schemes of CAC. Results show that new proposed schemes are more efficient and handle more visitor calls by redirecting calls and sharing of load in P2cell.
A Cross Layer Based Scalable Channel Slot Re-Utilization Technique for Wirele...csandit
Due to tremendous growth of the wireless based application services are increasing the demand
for wireless communication techniques that use bandwidth more effectively. Channel slot reutilization
in multi-radio wireless mesh networks is a very challenging problem. WMNs have
been adopted as back haul to connect various networks such as Wi-Fi (802.11), WI-MAX
(802.16e) etc. to the internet. The slot re-utilization technique proposed so far suffer due to high
collision due to improper channel slot usage approximation error. To overcome this here the
author propose the cross layer optimization technique by designing a device classification
based channel slot re-utilization routing strategy which considers the channel slot and node
information from various layers and use some of these parameters to approximate the risk
involve in channel slot re-utilization in order to improve the QoS of the network. The simulation
and analytical results show the effectiveness of our proposed approach in term of channel slot
re-utilization efficiency and thus helps in reducing latency for data transmission and reduce
channel slot collision.
A Survey of Various Routing and Channel Assignment Strategies for MR-MC WMNsijsrd.com
One fundamental problem of WMNs with a limited number of radio interfaces and orthogonal channels is that the performance degrades significantly as the network size grows. This results from increased interference between nodes and diminished spatial reuse over the network. A WMN node needs to share a common channel with each of its neighbours in the communication range, requiring it to set up a virtual link. Moreover, to reduce network interference, a node should minimize the number of neighbours that it shares a common channel with. The objective of a channel assignment strategy is to ensure efficient utilization of the available channels (e.g., by minimizing interference) while maximizing connectivity in the network. However, since these two requirements are conflicting with each other, the goal is to achieve a balance between these two. The major constraints which need to be satisfied by a channel assignment scheme include fixed number of channels in the network, limited number of radios in mesh nodes, common channel between two communicating nodes, and limited channel capacity. Also, a channel assignment scheme should take the amount of traffic load supported by each mesh node into consideration.
Heterogeneous LTE Networks and Inter-Cell Interference Coordination - Dec 201...Eiko Seidel
This document discusses heterogeneous LTE networks and inter-cell interference coordination (ICIC). It begins by explaining that initial LTE networks consisted of homogeneous macro cell deployments but that heterogeneous networks using smaller pico and femto cells are now being implemented to improve capacity and coverage. This introduces new interference challenges. The document then outlines various ICIC methods like frequency reuse and power control techniques that can help mitigate interference. It provides simulation results showing the benefits of heterogeneous networks and techniques like range expansion.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
we find out various power aware and data packet rate control with-collision-avoidance (CSMA/CA)-based ad hoc wireless network communication. And identifies that CSMA
Performance analysis of CSMA/CA and TDMA MAC protocols in Wireless Mesh Netw...Pranjal Das
This document summarizes a project presentation on analyzing the performance of CSMA/CA and TDMA MAC protocols in wireless mesh networks. It first provides background on wireless mesh networks and describes their architecture and characteristics. It then discusses CSMA/CA and TDMA protocols and how they work. The project involved simulating a wireless mesh network topology using NS-2 and evaluating the performance of the two protocols based on metrics like throughput, delay, and packet loss under varying conditions like number of hops and link distance. The results showed that TDMA performance was better than CSMA/CA. The conclusion recommends further analysis using directional antennas.
Multi-layer heterogeneous network layout including small cell base stations are considered to be the key to further enhancements of the spectral efficiency achieved in mobile communication networks. It has been recognized that inter-cell interference has become the limiting factor when trying to achieve not only high average user satisfaction, but a high degree of satisfaction for as many users as possible. Therefore, inter-cell interference coordination (ICIC) lies in the focus of researchers defining next generation mobile communication standards, such as LTE-A.
Building upon [1], this paper provides an overview over the background calling for ICIC in heterogeneous LTE-A networks. It outlines techniques standardized in Rel. 10 of LTE-A, discusses them showing their benefits and limitations by means of system-level simulations and motivates the importance of self optimizing network (SON) procedures for ICIC in LTE-A.
Efficient and Fair Bandwidth Allocation AQM Scheme for Wireless NetworksCSCJournals
Heterogeneous Wireless Networks are considered nowadays as one of the potential areas in research and development. The traffic management’s schemes that have been used at the fusion points between the different wireless networks are classical and conventional. This paper is focused on developing a novel scheme to overcome the problem of traffic congestion in the fusion point router interconnected the heterogeneous wireless networks. The paper proposed an EF-AQM algorithm which provides an efficient and fair allocation of bandwidth among different established flows. Finally, the proposed scheme developed, tested and validated through a set of experiments to demonstrate the relative merits and capabilities of a proposed scheme
International Journal of Engineering Research and Development (IJERD)IJERD Editor
This document summarizes a study that evaluates traffic load for multiple user types in mobile WiMAX networks. It begins with background on the growth of wireless broadband and the capabilities of mobile WiMAX technology. It then describes an algorithm to calculate the maximum number of subscribers a mobile WiMAX sector can support based on system parameters and traffic models. The algorithm calculates throughput by determining overhead values and available bandwidth for downlink and uplink transmissions separately. It accounts for factors like modulation distribution, frame structure, control signaling overhead from maps and ranging, and traffic from different applications. The method is intended to help network operators estimate infrastructure needs for deploying wide-area mobile WiMAX networks.
Investigation of Clock Synchronization Techniques and its Performance Impact ...ijctet
This document summarizes research on clock synchronization techniques in mobile ad hoc networks (MANETs). It begins by defining MANETs and explaining why time synchronization is important. It then discusses challenges in time synchronization due to clock imperfections and variable network delays. The document reviews existing clock synchronization methods like burst transmission and clock sampling. It also covers characteristics of MANETs like dynamic topology. Finally, it surveys previous research on time synchronization algorithms for MANETs, including a decentralized algorithm that achieves fast convergence times and high accuracy.
The document discusses issues with using TCP in ad hoc wireless networks and proposes solutions:
- TCP was designed for wired networks and faces challenges in ad hoc wireless networks due to characteristics like interference, dynamic topology, and packet loss.
- Existing TCP extensions and new transport protocols have been proposed to address issues like induced traffic, unfairness, power constraints, and congestion misinterpretation in ad hoc wireless networks.
- Solutions include splitting TCP functionality, adding awareness of lower layer conditions, and separating reliability, flow control and congestion control.
IRJET- QOS Aware Manet Routing Protocol for Multimedia Traffic in an Adaptive...IRJET Journal
This document proposes a modified AODV (M-AODV) routing protocol for transmitting multimedia traffic like video in mobile ad hoc networks (MANETs). The M-AODV protocol considers sending time, route stability, and bandwidth size to discover highly stable routes for transmitting video frames from source to destination nodes. It encodes the video at the source node and sends route requests with the required bandwidth. The performance is evaluated using NS3 simulation tools based on metrics like throughput, packet loss, and delay. The document also discusses research challenges for video streaming in MANETs like bandwidth usage and availability only when online, and identifies throughput, delay, and packet loss as key issues to address for video transmission in these networks.
Effective and Efficient Shape-Based Pattern Detection over Streaming Time Seriesambitlick
This article proposes a new distance measure called Spatial Assembling Distance (SpADe) to handle noisy, shifting, and scaling time series data. SpADe can effectively measure the similarity between time series that exhibit amplitude and temporal variations. The article also applies SpADe to the task of continuous pattern detection in streaming time series data and shows it achieves high accuracy and efficiency.
11.signal strength based congestion control in manetAlexander Decker
This document discusses several algorithms and approaches for improving TCP performance in mobile ad hoc networks (MANETs) using signal strength measurements:
1. TCP Venoplus is a cross-layer approach that uses signal strength information from the MAC layer to better distinguish between packet losses due to congestion versus random errors.
2. Other algorithms proposed include Link-RED and adaptive pacing to reduce the impact of wireless interference on TCP, as well as techniques to predict and avoid link failures before they occur such as gray zone prediction and multi-agent adaptive DSR.
3. Most of the algorithms aim to minimize unnecessary packet retransmissions when losses are due to non-congestion factors like mobility, thereby improving throughput
4..[26 36]signal strength based congestion control in manetAlexander Decker
This document discusses several algorithms and approaches for improving TCP performance in mobile ad hoc networks (MANETs) using signal strength measurements:
1. TCP Venoplus is a cross-layer approach that uses signal strength information from the MAC layer to better distinguish between packet losses due to congestion versus random errors.
2. Other algorithms proposed include Link-RED to tune wireless link drop probability, adaptive pacing to improve spatial reuse, and algorithms to predict link failures and find stable routes using signal strength measurements.
3. Received signal strength is also used in algorithms to minimize broadcast storms and adapt MAC layer retransmissions to distinguish true link failures from false ones caused by interference.
4. Gray zone prediction and
Signalling protocols in GSM networks include the Message Transfer Part (MTP) protocol stack and the Signalling System 7 (SS7) protocol stack. MTP has three levels that handle transport, routing, and error correction. Above MTP are protocols like SCCP and TCAP that establish connections and transport messages between applications. SS7 protocols include INAP, MAP, ISUP, and TUP that are used in different network elements for call setup and routing.
Dynamic Power Allocation for Mc-Cdma System Using Iterative Water Filling Alg...inventionjournals
ABSTRACT : Power control in Multi Carrier Code Division Multiple Access ( MCCDMA) based wireless cellular network is of great importance. The power allocation methodology to enhance the performance of the MCCDMA system by limiting interference noise is at the expense of signaling overhead due to sharing of Channel State Information (CSI). The distributed algorithms that manage the power level based on the user’s SINR requirements needs the complete knowledge of Channel State Information (CSI) .Since the CSI is subjected to the errors because of the imperfect channel estimation/measurement due to the time varying nature of the channels, the distributed power control algorithm is not globally optimum. The water filling algorithm is used to allocate proper power for every sub channel in order to improve channel capacity. The water filling algorithm distributes power among all users with the help of SINR that is received by the transmitter instead of getting full Channel State Information (CSI).
Simulation based Evaluation of a Simple Channel Distribution Scheme for MANETsIOSR Journals
This document presents a proposed multi-channel distribution scheme for mobile ad hoc networks (MANETs) and evaluates it through simulation. The proposed scheme assigns channels to nodes based on their node IDs to avoid control overhead from time synchronization. While neighboring nodes on the same channel is possible, the probability is low given random node distribution. The proposed scheme is compared to a single-channel scheme in ns-2 simulations. Results show the proposed technique has better performance.
Simulation and Performance Analysis of Long Term Evolution (LTE) Cellular Net...ijsrd.com
In the development, standardization and implementation of LTE Networks based on Orthogonal Freq. Division Multiple Access (OFDMA), simulations are necessary to test as well as optimize algorithms and procedures before real time establishment. This can be done by both Physical Layer (Link-Level) and Network (System-Level) context. This paper proposes Network Simulator 3 (NS-3) which is capable of evaluating the performance of the Downlink Shared Channel of LTE networks and comparing it with available MatLab based LTE System Level Simulator performance.
An energy efficient mac protocol for wirelessnabil_alsharafi
This document presents S-MAC, an energy-efficient MAC protocol designed for wireless sensor networks. S-MAC aims to reduce energy consumption through the use of synchronized duty cycles where nodes periodically listen and sleep. It also supports self-configuration. The paper describes the characteristics of WSNs that require a different MAC approach than IEEE 802.11. Experiments show that S-MAC achieves significant energy savings of around 98% compared to IEEE 802.11 through the use of duty cycles and avoiding overhearing. However, S-MAC can introduce increased latency and may not perform as well as other protocols under heavy traffic loads. Tradeoffs between energy consumption and latency can be tuned by adjusting the duty cycle parameters.
Managing Instantly Dense Hot Spot Regions in Wireless Cellular Communication ...Eswar Publications
In a wireless communication cellular network, call activity can be more intensive in some regions than others. These high-traffic regions are called hot spot regions. In typical deployments of wireless cellular networks, traffic hot spots can arise from the non-uniform geographic distribution of the mobile users, and the heavy-tailed nature of their network usage patterns. These hot spots of activity can degrade system performance, by increasing network utilization, wireless interference, call blocking, and even call dropping from failed handoffs for mobile users. In this paper, a hierarchical cellular communication wireless network is characterized by overlapping the service area for managing the new calls users having different mobility speed. The overlapping property of the hierarchical-network provides the advantages that share the traffic load to improve the performance of wireless
cellular networks in the highly populated area where both slow speed users and high speed users are available.
Picocells are created that are underlaid to two-tier networks for handling the slow or staying speed visitor (outside registered) users. The hierarchical-networks with picocells, microcells and macrocells provide the secondary resource, which provide the services to new calls as well as handoff calls with guard channels by overflow the slow speed visitor users in picocells, slow speed local users in macrocell by sharing the frequency in
vertical as well as in horizontal directions. The picocell is installed on four wheeler vehicle may be moved at any place as per necessity and may be utilized to create picocell to handle the load of hot spot area. Such kind of picocell is known as Portable-Picocell (P-Picocell/ P2cell). The call loss probability of new calls is developed through numerical analysis. The proposed schemes are compared with the existing schemes of CAC. Results show that new proposed schemes are more efficient and handle more visitor calls by redirecting calls and sharing of load in P2cell.
A Cross Layer Based Scalable Channel Slot Re-Utilization Technique for Wirele...csandit
Due to tremendous growth of the wireless based application services are increasing the demand
for wireless communication techniques that use bandwidth more effectively. Channel slot reutilization
in multi-radio wireless mesh networks is a very challenging problem. WMNs have
been adopted as back haul to connect various networks such as Wi-Fi (802.11), WI-MAX
(802.16e) etc. to the internet. The slot re-utilization technique proposed so far suffer due to high
collision due to improper channel slot usage approximation error. To overcome this here the
author propose the cross layer optimization technique by designing a device classification
based channel slot re-utilization routing strategy which considers the channel slot and node
information from various layers and use some of these parameters to approximate the risk
involve in channel slot re-utilization in order to improve the QoS of the network. The simulation
and analytical results show the effectiveness of our proposed approach in term of channel slot
re-utilization efficiency and thus helps in reducing latency for data transmission and reduce
channel slot collision.
A Survey of Various Routing and Channel Assignment Strategies for MR-MC WMNsijsrd.com
One fundamental problem of WMNs with a limited number of radio interfaces and orthogonal channels is that the performance degrades significantly as the network size grows. This results from increased interference between nodes and diminished spatial reuse over the network. A WMN node needs to share a common channel with each of its neighbours in the communication range, requiring it to set up a virtual link. Moreover, to reduce network interference, a node should minimize the number of neighbours that it shares a common channel with. The objective of a channel assignment strategy is to ensure efficient utilization of the available channels (e.g., by minimizing interference) while maximizing connectivity in the network. However, since these two requirements are conflicting with each other, the goal is to achieve a balance between these two. The major constraints which need to be satisfied by a channel assignment scheme include fixed number of channels in the network, limited number of radios in mesh nodes, common channel between two communicating nodes, and limited channel capacity. Also, a channel assignment scheme should take the amount of traffic load supported by each mesh node into consideration.
Heterogeneous LTE Networks and Inter-Cell Interference Coordination - Dec 201...Eiko Seidel
This document discusses heterogeneous LTE networks and inter-cell interference coordination (ICIC). It begins by explaining that initial LTE networks consisted of homogeneous macro cell deployments but that heterogeneous networks using smaller pico and femto cells are now being implemented to improve capacity and coverage. This introduces new interference challenges. The document then outlines various ICIC methods like frequency reuse and power control techniques that can help mitigate interference. It provides simulation results showing the benefits of heterogeneous networks and techniques like range expansion.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
we find out various power aware and data packet rate control with-collision-avoidance (CSMA/CA)-based ad hoc wireless network communication. And identifies that CSMA
Performance analysis of CSMA/CA and TDMA MAC protocols in Wireless Mesh Netw...Pranjal Das
This document summarizes a project presentation on analyzing the performance of CSMA/CA and TDMA MAC protocols in wireless mesh networks. It first provides background on wireless mesh networks and describes their architecture and characteristics. It then discusses CSMA/CA and TDMA protocols and how they work. The project involved simulating a wireless mesh network topology using NS-2 and evaluating the performance of the two protocols based on metrics like throughput, delay, and packet loss under varying conditions like number of hops and link distance. The results showed that TDMA performance was better than CSMA/CA. The conclusion recommends further analysis using directional antennas.
Multi-layer heterogeneous network layout including small cell base stations are considered to be the key to further enhancements of the spectral efficiency achieved in mobile communication networks. It has been recognized that inter-cell interference has become the limiting factor when trying to achieve not only high average user satisfaction, but a high degree of satisfaction for as many users as possible. Therefore, inter-cell interference coordination (ICIC) lies in the focus of researchers defining next generation mobile communication standards, such as LTE-A.
Building upon [1], this paper provides an overview over the background calling for ICIC in heterogeneous LTE-A networks. It outlines techniques standardized in Rel. 10 of LTE-A, discusses them showing their benefits and limitations by means of system-level simulations and motivates the importance of self optimizing network (SON) procedures for ICIC in LTE-A.
Efficient and Fair Bandwidth Allocation AQM Scheme for Wireless NetworksCSCJournals
Heterogeneous Wireless Networks are considered nowadays as one of the potential areas in research and development. The traffic management’s schemes that have been used at the fusion points between the different wireless networks are classical and conventional. This paper is focused on developing a novel scheme to overcome the problem of traffic congestion in the fusion point router interconnected the heterogeneous wireless networks. The paper proposed an EF-AQM algorithm which provides an efficient and fair allocation of bandwidth among different established flows. Finally, the proposed scheme developed, tested and validated through a set of experiments to demonstrate the relative merits and capabilities of a proposed scheme
International Journal of Engineering Research and Development (IJERD)IJERD Editor
This document summarizes a study that evaluates traffic load for multiple user types in mobile WiMAX networks. It begins with background on the growth of wireless broadband and the capabilities of mobile WiMAX technology. It then describes an algorithm to calculate the maximum number of subscribers a mobile WiMAX sector can support based on system parameters and traffic models. The algorithm calculates throughput by determining overhead values and available bandwidth for downlink and uplink transmissions separately. It accounts for factors like modulation distribution, frame structure, control signaling overhead from maps and ranging, and traffic from different applications. The method is intended to help network operators estimate infrastructure needs for deploying wide-area mobile WiMAX networks.
Investigation of Clock Synchronization Techniques and its Performance Impact ...ijctet
This document summarizes research on clock synchronization techniques in mobile ad hoc networks (MANETs). It begins by defining MANETs and explaining why time synchronization is important. It then discusses challenges in time synchronization due to clock imperfections and variable network delays. The document reviews existing clock synchronization methods like burst transmission and clock sampling. It also covers characteristics of MANETs like dynamic topology. Finally, it surveys previous research on time synchronization algorithms for MANETs, including a decentralized algorithm that achieves fast convergence times and high accuracy.
The document discusses issues with using TCP in ad hoc wireless networks and proposes solutions:
- TCP was designed for wired networks and faces challenges in ad hoc wireless networks due to characteristics like interference, dynamic topology, and packet loss.
- Existing TCP extensions and new transport protocols have been proposed to address issues like induced traffic, unfairness, power constraints, and congestion misinterpretation in ad hoc wireless networks.
- Solutions include splitting TCP functionality, adding awareness of lower layer conditions, and separating reliability, flow control and congestion control.
IRJET- QOS Aware Manet Routing Protocol for Multimedia Traffic in an Adaptive...IRJET Journal
This document proposes a modified AODV (M-AODV) routing protocol for transmitting multimedia traffic like video in mobile ad hoc networks (MANETs). The M-AODV protocol considers sending time, route stability, and bandwidth size to discover highly stable routes for transmitting video frames from source to destination nodes. It encodes the video at the source node and sends route requests with the required bandwidth. The performance is evaluated using NS3 simulation tools based on metrics like throughput, packet loss, and delay. The document also discusses research challenges for video streaming in MANETs like bandwidth usage and availability only when online, and identifies throughput, delay, and packet loss as key issues to address for video transmission in these networks.
Effective and Efficient Shape-Based Pattern Detection over Streaming Time Seriesambitlick
This article proposes a new distance measure called Spatial Assembling Distance (SpADe) to handle noisy, shifting, and scaling time series data. SpADe can effectively measure the similarity between time series that exhibit amplitude and temporal variations. The article also applies SpADe to the task of continuous pattern detection in streaming time series data and shows it achieves high accuracy and efficiency.
Mohan Pullabhatla is a production manager with over 19 years of experience in plastic injection moulding and profile extrusion. He has a Tier 2 General Dependent VISA valid until 2018 and is currently seeking new employment opportunities in the UK. His expertise includes process optimization, cost reduction, tool development, quality control, and implementing manufacturing best practices like SMED, 5S, and ISO standards.
This document provides information about the course ECON304 Introduction to Economic Statistics taught in the summer of 2016. The course is taught by Pairach Piboonrugnroj at Chiang Mai University in Thailand. It covers topics including index numbers, time series analysis, correlation, regression analysis, and the method of least squares. Students will be assessed through quizzes, midterm and final exams, a course project, and participation. Grades are based on thresholds without a curve.
The document discusses lightweight cryptography for constrained devices. It presents the objectives of designing a lightweight bit-permutation instruction called PERMS to accelerate cryptography in software, and a new lightweight block cipher called Khudra suitable for both FPGAs and ASICs. It also aims to analyze Khudra's security against cryptanalysis techniques. The PERMS instruction is based on bit swapping to achieve permutation efficiently in hardware using control bits.
The IP Landscape: Intellectual Property in Theme Parks and Attractions Jack Rouse Associates
JRA CEO/Owner Keith James discusses why attractions use intellectual property, as well as the design opportunities and challenges inherent in recreating cherished IP characters, themes and environments. As presented at the International Association of Amusement Parks and Attractions' 2015 Euro Attractions Show in Liseberg, Gothenburg Sweden on 7 October 2015. For more information, contact Shawn McCoy, VP of Marketing and Business Development, at smccoy@jackrouse.com, and for a transcript, visit www.jackrouse.com/blog.
ppl Internship report (Syed Wajih ul Hasnain)syedwajih
1. The document describes an internship report submitted by Syed Wajih-ul-Hasnain from the University of New South Wales (UNSW) during their internship at the Reservoir Engineering Department of Pakistan Petroleum Limited (PPL) from January to February 2015.
2. The report details the revision of core reservoir engineering concepts done during the internship such as fluid properties, material balance, decline curve analysis, and use of the MBAL reservoir modeling tool.
3. Key tasks accomplished included estimating original gas in place using pressure data from 2005-2014, decline curve analysis of a volatile oil well to determine remaining reserves and life, and decline curve analysis of a wet gas well. Estimates
Tagaytay Highlands aims to dominate the P1 billion niche market for upper class retirees seeking luxury residential properties with amenities. It positions itself as the only developer offering world-class golf clubs, country clubs, and post-sale services free with property purchases. The marketing plan involves targeting 45-70 year old entrepreneurs and retirees, strengthening direct sales, and leveraging discounts and freebies to promote its P5 million-plus lots located in Tagaytay City's recreational area featuring views of Taal Lake. The strategy is to focus on this niche market opportunity through differentiated amenities and services rather than competing directly with similar high-end developments.
The document is an internship report summarizing Zeehan Hyder Baloch's internship at the Kandhkot Gas Field operated by Pakistan Petroleum Limited. The report provides an overview of the gas field and its departments and processes. It describes the condensate recovery system, dehydration plant, and glycol regeneration unit. The dehydration plant removes water from the gas stream using glycol, then regenerates the glycol for reuse through a process involving flash separation, heating, and filtering.
The document provides tips for finding a research topic, including looking at keywords from favorite subjects and everyday life, reading academic papers and news, and focusing on important topics in economics. It suggests avoiding trendy but unimportant topics and government policies. The document also recommends standing on the shoulders of previous theses and papers, and searching databases like Scopus and the Thai Journal Citation Index for sample topics and papers. It emphasizes talking to others and potential advisors, and just getting started once a topic is chosen.
La rinitis alérgica es una inflamación de la mucosa nasal mediada por la respuesta de hipersensibilidad de tipo I e IgE. Afecta hasta el 20% de la población y se considera una enfermedad sistémica de la vía aérea. Su tratamiento incluye evitar los alérgenos, antihistamínicos, corticoesteroides intranasales y montelukast, e inmunoterapia para prevenir sensibilizaciones.
Cardiac MRI can be used to evaluate ischemic heart disease through various techniques:
1) Stress perfusion MRI can detect myocardial ischemia with high sensitivity and specificity compared to other modalities like SPECT.
2) Dobutamine stress MRI evaluates cardiac function and wall motion abnormalities under stress, identifying areas of ischemia.
3) Delayed enhancement MRI precisely determines infarct size and identifies viable versus non-viable tissue for evaluating prognosis and treatment.
Cardiac MRI provides a comprehensive non-invasive approach for assessing ischemic heart disease.
Este documento resume la insuficiencia respiratoria aguda, incluyendo su definición, tipos, causas, manifestaciones clínicas, criterios de diagnóstico, fisiopatología, exámenes auxiliares, manejo terapéutico e indicaciones para la ventilación mecánica. La IRA se define como una severa alteración en el recambio gaseoso pulmonar que resulta en hipoxemia con o sin hipercapnia. Sus principales tipos son la hipoxémica, hipercápnica y mixta, y puede ser causada
A privacy preserving framework for managing mobile ad requests and billing in...LeMeniz Infotech
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This document provides a progress report on research being conducted on energy management in wireless sensor networks using a modified MAC protocol. The report details work done so far, including modeling MAC protocols in OMNeT++, simulation results comparing BMAC, LMAC, and XMAC, and ongoing work to avoid collisions during packet transmission to improve energy efficiency. Future work includes further optimizing the modified MAC protocol and publishing results in peer-reviewed journals.
A CROSS-LAYER BASED SCALABLE CHANNEL SLOT RE-UTILIZATION TECHNIQUE FOR WIRELE...cscpconf
Due to tremendous growth of the wireless based application services are increasing the demand for wireless communication techniques that use bandwidth more effectively. Channel slot reutilization in multi-radio wireless mesh networks is a very challenging problem. WMNs have been adopted as back haul to connect various networks such as Wi-Fi (802.11), WI-MAX (802.16e) etc. to the internet. The slot re-utilization technique proposed so far suffer due to high collision due to improper channel slot usage approximation error. To overcome this here the author propose the cross layer optimization technique by designing a device classification based channel slot re-utilization routing strategy which considers the channel slot and node information from various layers and use some of these parameters to approximate the risk involve in channel slot re-utilization in order to improve the QoS of the network. The simulation and analytical results show the effectiveness of our proposed approach in term of channel slot re-utilization efficiency and thus helps in reducing latency for data transmission and reduce
channel slot collision.
The document discusses wireless and mobile computing, specifically focusing on MAC (media access control) layer protocols for wireless networks. It provides an overview of MAC layer issues for wireless networks, classifications of MAC protocols (including contention-based, reservation-based, and scheduling-based), and design goals of MAC protocols such as distributed operation, quality of service support, bandwidth efficiency, and minimizing hidden and exposed terminal problems.
A MAC PROTOCOL WITH DYNAMIC ALLOCATION OF TIME SLOTS BASED ON TRAFFIC PRIORIT...ijaia
In a wireless body area network (WBAN), wireless biomedical sensors are placed around, on, or inside the human body. Given specific requirements, WBANs can significantly improve healthcare, diagnostic monitoring, and other medical services. However, the existing standards such as IEEE 802.11 and IEEE 802.15.4 have some limitations to meet all the requirements of WBANs. Many medium access control (MAC) protocols have been studied so far, most of which are derived from the IEEE 802.15.4 superframe structure with some improvements and adjustments. However, the MAC protocols do not provide the required quality of service (QoS) for various types of traffic in a WBAN. In this paper, a traffic-aware MAC (TA-MAC) protocol for WBANs is proposed, in which time slots are dynamically allocated on the basis of traffic priority, providing the required QoS. According to the performance evaluation results, the proposed TA-MAC is better than IEEE 802.15.4 MAC and the conventional priority-based MAC in terms of transmission time, system throughput, energy efficiency, and collision ratio.
A MAC PROTOCOL WITH DYNAMIC ALLOCATION OF TIME SLOTS BASED ON TRAFFIC PRIORIT...IJCNCJournal
In a wireless body area network (WBAN), wireless biomedical sensors are placed around, on, or inside the human body. Given specific requirements, WBANs can significantly improve healthcare, diagnostic monitoring, and other medical services. However, the existing standards such as IEEE 802.11 and IEEE 802.15.4 have some limitations to meet all the requirements of WBANs. Many medium access control (MAC) protocols have been studied so far, most of which are derived from the IEEE 802.15.4 superframe structure with some improvements and adjustments. However, the MAC protocols do not provide the required quality of service (QoS) for various types of traffic in a WBAN. In this paper, a traffic-aware MAC (TA-MAC) protocol for WBANs is proposed, in which time slots are dynamically allocated on the basis of traffic priority, providing the required QoS. According to the performance evaluation results, the proposed TA-MAC is better than IEEE 802.15.4 MAC and the conventional priority
PERFORMANCE ANALYSIS OF CHANNEL ACCESS MODEL FOR MAC IN RANDOMLY DISTRIBUTED ...IJCNCJournal
Medium Access control (MAC) is one of the fundamental problems in wireless sensor networks. The performance of wireless sensor network depends on it. The main objective of a medium access control method is to provide high throughput, minimize the delay, and conservers the energy consumption by avoiding the collisions. In this paper, a general model for MAC protocol to reduce the delay, maximize throughput and conserve the energy consumption in channel accessing in high density randomly distributed wireless sensor network is presented. The proposed model is simulated using MATLAB. The simulation results show that the average delay for sensors with sufficient memory is lower than sensors without
memory. Further, the throughput of the channel access method with memory is better than without memory.
The document discusses the Minimum Cost Forwarding (MCF) routing protocol for wireless sensor networks. MCF establishes optimal routing paths with few message exchanges and is scalable and simple to implement. The authors formally model MCF as timed automata and use model checking to verify its properties. Their analysis identified weaknesses in MCF concerning equal-cost paths and node failures. The authors present improvements to address deficiencies in the original MCF protocol.
The Minimum Cost Forwarding Using MAC Protocol for Wireless Sensor NetworksIJMER
The document discusses the Minimum Cost Forwarding (MCF) routing protocol for wireless sensor networks. MCF establishes optimal routing paths with few message exchanges and is scalable and simple to implement. The authors formally model MCF as timed automata and use model checking to verify its properties. Their analysis identified weaknesses in MCF concerning equal-cost paths and node failures. The authors present improvements to address deficiencies in the original MCF protocol.
This document summarizes and compares various medium access control (MAC) protocols for wireless sensor networks. It begins by describing the properties and challenges of MAC layers in sensor networks, including sources of energy waste like idle listening, collisions, and overhearing. It then classifies and describes different types of MAC protocols for sensor networks, including contention-based, scheduling-based, and channel polling-based protocols. It also introduces cross-layer protocols and compares MAC protocols based on type, cross-layer support, and scheduling. Finally, it proposes future research directions for MAC protocol design in wireless sensor networks.
SLOTTED CSMA/CA BASED ENERGY EFFICIENT MAC PROTOCOL DESIGN IN NANONETWORKSijwmn
Devices in a beacon-enabled network use slotted CSMA/CA to contend for channel usage. Each node in the network competes for the channels when ready to transmit data. The slotted CSMA/CA mechanism based on the super-frame structure fairly provides communication chance for each node and makes a reasonable usage of the available energy in beacon-enabled Zigbee networks. When wireless nano-sensor nodes are implanted into the target human body area for detecting disease symptoms or virus existence, each node also requires a similar characteristic in channel sharing and in the transmission of event-driven data with a short length. In this paper, we suggest a wireless network model with nano-sensor nodes for the in-body application. We propose a novel MAC protocol derived from an existing Zigbee MAC protocol scheme and analyze the performance of energy usage with variable super-frame durations and packet sizes.
SLOTTED CSMA/CA BASED ENERGY EFFICIENT MAC PROTOCOL DESIGN IN NANONETWORKSijwmn
Devices in a beacon-enabled network use slotted CSMA/CA to contend for channel usage. Each node in the
network competes for the channels when ready to transmit data. The slotted CSMA/CA mechanism based
on the super-frame structure fairly provides communication chance for each node and makes a reasonable
usage of the available energy in beacon-enabled Zigbee networks. When wireless nano-sensor nodes are
implanted into the target human body area for detecting disease symptoms or virus existence, each node
also requires a similar characteristic in channel sharing and in the transmission of event-driven data with
a short length. In this paper, we suggest a wireless network model with nano-sensor nodes for the in-body
application. We propose a novel MAC protocol derived from an existing Zigbee MAC protocol scheme and
analyze the performance of energy usage with variable super-frame durations and packet sizes.
This document discusses an enhancement to the S-MAC protocol called Enhanced S-MAC. S-MAC is a MAC protocol for wireless sensor networks that aims to improve power efficiency. Enhanced S-MAC further improves power efficiency by allowing nodes to adaptively turn their receivers on and off based on traffic load. It also addresses issues with clock synchronization and overhearing in the original S-MAC protocol. The document outlines related work on MAC protocols, problems encountered with implementing S-MAC, and how Enhanced S-MAC addresses these issues through adaptive listening modes and an improved synchronization protocol. It proposes to simulate Enhanced S-MAC to demonstrate improved power efficiency over standard S-MAC.
This document summarizes research on congestion and fairness issues in wireless mesh networks. The researchers found that:
1) Wireless mesh networks using CSMA/CA MAC protocols can experience "starvation", where one-hop flows receive most bandwidth while competing multi-hop flows receive almost nothing.
2) Through experiments on an operational urban mesh network, they confirmed starvation occurs and isolated that only a one-hop TCP flow coupled with a two-hop TCP flow is needed to induce it.
3) They developed an analytical model to understand the causes of starvation as the interaction of MAC-layer biases, congestion control loops, and penalties of switching between network states.
4) Their model suggests a "
Performance of Vehicle-to-Vehicle Communication using IEEE 802.11p in Vehicul...IJNSA Journal
Traffic safety applications using vehicle-to-vehicle (V2V) communication is an emerging and promising area within the ITS environment. Many of these applications require real-time communication with high reliability. To meet a real-time deadline, timely and predictable access to the channel is paramount. The medium access method used in 802.11p, CSMA with collision avoidance, does not guarantee channel
access before a finite deadline. The well-known property of CSMA is undesirable for critical communications scenarios. The simulation results reveal that a specific vehicle is forced to drop over 80% of its packets because no channel access was possible before the next message was generated. To overcome this problem, we propose to use STDMA for real-time data traffic between vehicles. The realtime properties of STDMA are investigated by means of the highway road simulation scenario, with promising results.
This document compares the TDMA and CSMA access techniques for a linear topology of sensor nodes. It first provides background on wireless sensor networks and discusses applications that use a fixed chain topology. It then explains that TDMA is generally more suitable than CSMA for a linear chain topology with a large number of nodes, periodic traffic, and relatively high traffic. The document reviews several existing MAC protocols designed for chain topologies and discusses their advantages and disadvantages. It focuses on comparing the throughput and delay of nodes in a linear topology using TDMA versus CSMA.
Channel Aware Mac Protocol for Maximizing Throughput and FairnessIJORCS
The proper channel utilization and the queue length aware routing protocol is a challenging task in MANET. To overcome this drawback we are extending the previous work by improving the MAC protocol to maximize the Throughput and Fairness. In this work we are estimating the channel condition and Contention for a channel aware packet scheduling and the queue length is also calculated for the routing protocol which is aware of the queue length. The channel is scheduled based on the channel condition and the routing is carried out by considering the queue length. This queue length will provide a measurement of traffic load at the mobile node itself. Depending upon this load the node with the lesser load will be selected for the routing; this will effectively balance the load and improve the throughput of the ad hoc network.
General Model for Single and Multiple Channels WLANs with Quality of Service ...ijwmn
In this paper we develop an intergraded model for request mechanism and data transmission in the uplink phase in the presence of channel noise. This model supports quality of service. The wireless channel is prone to many impairments. Thus, certain techniques have to be developed to deliver data to the receiver. We calculated the performance parameters for single and multichannel wireless networks, like the requests throughput, data throughput and the requests acceptance probability and data acceptance probability. The proposed model is general model since it can be applied to different wireless networks such as IEEE802.11a, IEEE802.16e, CDMA operated networks and Hiperlan\2.
General Model for Single and Multiple Channels WLANs with Quality of Service...ijwmn
In this paper we develop an intergraded model for request mechanism and data transmission in the uplink
phase in the presence of channel noise. This model supports quality of service. The wireless channel is prone
to many impairments. Thus, certain techniques have to be developed to deliver data to the receiver. We
calculated the performance parameters for single and multichannel wireless networks, like the requests
throughput, data throughput and the requests acceptance probability and data acceptance probability. The
proposed model is general model since it can be applied to different wireless networks such as IEEE802.11a,
IEEE802.16e, CDMA operated networks and Hiperlan\2.
Elastic hybrid MAC protocol for wireless sensor networks IJECEIAES
This document summarizes an article that proposes an elastic hybrid medium access control (MAC) protocol for wireless sensor networks. The protocol aims to improve performance for diverse quality of service requirements by dynamically adapting between contention-based CSMA/CA and scheduled TDMA transmission schemes depending on traffic conditions. It allows nodes to transmit using CSMA/CA for low traffic, reserves more slots for TDMA scheduling as traffic increases, and provides an emergency contention-free period at the start of frames for urgent data. Simulation results showed improved performance over typical protocols in terms of queue delay, packet delivery ratio, and frame drops. The proposed elastic hybrid approach aims to balance efficiencies across various QoS metrics by flexibly distributing the transmission strategies in response
Performance Analysis of MAC Layer Protocols for WSN with Considering the Effe...BRNSSPublicationHubI
This document summarizes a research article that analyzed the performance of three MAC layer protocols (IEEE 802.11, IEEE 802.15.4, and TDMA) in a wireless sensor network considering the effects of the hidden node problem. Six performance metrics were evaluated: goodput, throughput, packet delivery ratio, residual energy, average delay, and node lifetime. The results showed that TDMA provided the best energy conservation and highest delay, while IEEE 802.11 gave the best throughput and goodput as well as lowest delay. IEEE 802.15.4 and TDMA were better than IEEE 802.11 at mitigating the hidden node problem.
Similar to Specifica‘tion, verification and simulation of a wireless lan (20)
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This document lists 15 potential 2013 IEEE NS2 project titles related to wireless networks and sensor networks. It includes projects on topics like capacity of hybrid wireless mesh networks, delay-optimal broadcast in multihop wireless networks, detection of spoofing attackers, and harvesting-aware energy management for wireless sensor networks. The document provides contact information for a company called Ambitlick Solutions that offers support and deliverables for IEEE projects, including project abstracts, papers, presentations, reports, and certification.
This document lists over 40 potential 2013 IEEE Java Dotnet project titles across various domains including wireless networks, mobile computing, network security, data mining, cloud computing, parallel and distributed computing, and multimedia/image processing. The projects focus on technical topics such as wireless sensor networks, wireless mesh networks, cognitive radio networks, mobile ad hoc networks, network coding, video streaming, machine learning, data warehousing, and more. Project deliverables include an abstract, IEEE paper, presentation, report, working prototype or proof of concept, and certification. Bulk older and new projects can be provided at a low cost.
Handling selfishness in replica allocationambitlick
The document discusses techniques for handling selfish nodes in replica allocation over mobile ad hoc networks. It aims to reduce traffic overhead while maintaining high data accessibility. The techniques include a selfish node detection algorithm that considers partial selfishness and novel replica allocation methods to address issues caused by selfish nodes hoarding replicas for their own benefit instead of sharing memory space. Simulations are used to evaluate the performance of these techniques in improving data delivery rates.
Mutual Distance Bounding Protocols enable entities to determine an upper bound on their physical distance and authenticate each other. They have been actively researched due to distance-based attacks on wireless systems like RFID. While most protocols provide unilateral authentication of a tag to a reader, one was proposed to provide mutual authentication with a lower false acceptance rate. However, this analysis is shown to overestimate security, as a new attack achieves a higher false acceptance rate. A method is also introduced to modify existing unilateral authentication protocols into mutual authentication protocols.
Moderated group authoring system for campus wide workgroupsambitlick
This paper describes a distributed authoring system for campus workgroups that allows group members to modify any document type using their own devices. Each member maintains an updatable copy of shared content, and read-only copies are distributed asynchronously based on wireless availability. Group members manually reconcile updates through moderation, merging changes from others into their copy. Over time, successive moderation converges all copies into a single version. An evaluation found the asynchronous update model effective and the moderation process intuitive for students.
Efficient spread spectrum communication without pre shared secretsambitlick
This document proposes a new mechanism called Time Reversed Message Extraction and Key Scheduling (TREKS) that allows for efficient spread spectrum communication without pre-shared secrets. TREKS is four orders of magnitude faster than previous solutions to this problem. It enables long-term spread spectrum communication with optimal energy costs, minimal storage overhead, and a computation cost at most twice traditional spread spectrum. The approach was evaluated through simulations and experiments sustaining 1Mbps communication spread over 100 Megachips per second using modest hardware.
The document lists 23 networking and mobile computing projects implemented in NS2. It includes projects on topics like mobility in wireless networks, intrusion detection, neighbor discovery, energy renewal with wireless power transfer, load balancing, and spectrum access control. Contact information is provided for those interested in the project reports, presentations, source code, or implementing new projects.
Adaptive weight factor estimation from user review 1ambitlick
This document proposes a novel technique called Adjacent Pair Priorities (APP) to estimate weight factors for quality of service parameters in vertical handoff decision algorithms. The APP technique allows users to set relative priority levels for adjacent pairs of QoS parameters in descending order using an exponential mapping. This adaptive approach controls the width of the weight distribution to provide flexibility for users. The document outlines the system requirements, block diagram, modules and references several research papers on vertical handoff decision schemes and network selection algorithms.
The document proposes an Integrated Institutional Portal that allows all colleges and institutions within a university or district to share information. [1] The portal would allow students and staff from different colleges to discuss and request information from one another through blogs, forums and by publishing notices. [2] Currently, each college maintains separate portals without a common forum for communication. [3] The proposed centralized portal managed by a super administrator would make all college information like results, events and departments accessible to benefit students and staff across institutions.
This document describes an Embassy Administration portal that aims to centralize and automate manual processes at a college. [1] The portal allows separate login access for staff, parents, students and other members of the college. [2] It displays student results, attendance, and performance for parents to view as well as enables communication between parents and faculty. [3] The system conducts model and unit examinations.
The document proposes a customer relationship management system (CRMS) to help space marketing executives, managers, and management interact and share information online. The existing CRMS is manual and DOS-based, which has disadvantages like a distributed database, obsolete technology, and low efficiency. The proposed system is a web-based online CRMS designed for the space marketing department. It allows monitoring executive calls, tracking performance, and sharing information among departments to improve customer relationships and business operations. The system has modules for corporate administration, regional management, center management, and executives to organize work and monitor progress at different levels.
Mutual Distance Bounding Protocols enable entities to determine an upper bound on their physical distance and authenticate each other. They have been actively researched due to distance-based attacks on wireless systems like RFID. While most protocols provide unilateral authentication of a tag to a reader, one was proposed to provide mutual authentication with a lower false acceptance rate. However, this analysis is shown to overestimate security, as a new attack achieves a higher false acceptance rate. A method is also introduced to modify existing unilateral authentication protocols into mutual authentication protocols.
Moderated group authoring system for campus wide workgroupsambitlick
This paper describes a distributed authoring system for campus workgroups that allows group members to modify any document type using their own devices. Each member maintains an updatable copy of shared content, and read-only copies are distributed based on wireless availability. Group members manually reconcile updates through moderation, merging changes from others into their copy. Over time, successive moderations converge the multiple versions into a single version. An evaluation found the asynchronous update propagation and moderation process intuitive for students.
Efficient spread spectrum communication without pre shared secretsambitlick
This document proposes a new mechanism called Time Reversed Message Extraction and Key Scheduling (TREKS) that allows for efficient spread spectrum communication without pre-shared secrets. TREKS is four orders of magnitude faster than previous solutions to this problem and enables long-term spread spectrum communication without establishing keys. It was evaluated through simulation and on a testbed and can sustain 1Mbps communication spread over a 100 Megachips bandwidth in real-time, with provably optimal energy cost and minimal storage overhead.
Comments on “mabs multicast authentication based on batch signature”ambitlick
This document summarizes and critiques the MABS-DSA protocol proposed by Zhou et al. for multicast authentication using batch verification. While MABS-DSA was intended to increase efficiency and security over other implementations, the author finds through reexamination of the arithmetic that the algorithm is actually incorrect and batch signature verification would fail almost always, even when individual packets were properly signed by an honest sender. The key issue is a flaw in protocol correctness rather than the intended security improvements.
Energy-Efficient Protocol for Deterministic and Probabilistic Coverage In Sen...ambitlick
The document proposes a new probabilistic coverage protocol (PCP) for sensor networks that can employ different sensing models. PCP aims to address the costly task of designing and testing different coverage protocols for each sensing model. It works with common disk sensing models as well as probabilistic sensing models with minimal changes. Simulation results show that PCP outperforms other deterministic and probabilistic protocols in terms of number of activated sensors, total energy consumed, and network lifetime while being robust against failures and inaccuracies.
Energy efficient protocol for deterministicambitlick
The document describes a new probabilistic coverage protocol (PCP) for sensor networks that can employ both deterministic and probabilistic sensing models. PCP works by activating sensors to construct an approximate triangular lattice over the monitored area. It is more energy efficient than previous protocols by reducing the number of activated sensors needed for coverage. Simulation results show PCP outperforms other protocols in terms of energy consumption and network lifetime while maintaining coverage under various conditions.
Estimating Parameters of Multiple Heterogeneous Target Objects Using Composit...ambitlick
This article proposes a method for estimating parameters of multiple heterogeneous target objects (objects with different sizes and shapes) using networked binary sensors. The sensors are simple and only report detections, but no individual sensor location is known. The method introduces "composite sensor nodes" containing multiple sensors in a fixed arrangement. This provides relative location information to help distinguish individual target objects. As an example, the article considers a composite node with two sensors on a line segment. Measures from these nodes can identify target shapes and estimate object parameters like radius and side lengths. Numerical tests demonstrate networked composite sensors can estimate parameters of multiple target objects.
How to Fix the Import Error in the Odoo 17Celine George
An import error occurs when a program fails to import a module or library, disrupting its execution. In languages like Python, this issue arises when the specified module cannot be found or accessed, hindering the program's functionality. Resolving import errors is crucial for maintaining smooth software operation and uninterrupted development processes.
A workshop hosted by the South African Journal of Science aimed at postgraduate students and early career researchers with little or no experience in writing and publishing journal articles.
This document provides an overview of wound healing, its functions, stages, mechanisms, factors affecting it, and complications.
A wound is a break in the integrity of the skin or tissues, which may be associated with disruption of the structure and function.
Healing is the body’s response to injury in an attempt to restore normal structure and functions.
Healing can occur in two ways: Regeneration and Repair
There are 4 phases of wound healing: hemostasis, inflammation, proliferation, and remodeling. This document also describes the mechanism of wound healing. Factors that affect healing include infection, uncontrolled diabetes, poor nutrition, age, anemia, the presence of foreign bodies, etc.
Complications of wound healing like infection, hyperpigmentation of scar, contractures, and keloid formation.
বাংলাদেশের অর্থনৈতিক সমীক্ষা ২০২৪ [Bangladesh Economic Review 2024 Bangla.pdf] কম্পিউটার , ট্যাব ও স্মার্ট ফোন ভার্সন সহ সম্পূর্ণ বাংলা ই-বুক বা pdf বই " সুচিপত্র ...বুকমার্ক মেনু 🔖 ও হাইপার লিংক মেনু 📝👆 যুক্ত ..
আমাদের সবার জন্য খুব খুব গুরুত্বপূর্ণ একটি বই ..বিসিএস, ব্যাংক, ইউনিভার্সিটি ভর্তি ও যে কোন প্রতিযোগিতা মূলক পরীক্ষার জন্য এর খুব ইম্পরট্যান্ট একটি বিষয় ...তাছাড়া বাংলাদেশের সাম্প্রতিক যে কোন ডাটা বা তথ্য এই বইতে পাবেন ...
তাই একজন নাগরিক হিসাবে এই তথ্য গুলো আপনার জানা প্রয়োজন ...।
বিসিএস ও ব্যাংক এর লিখিত পরীক্ষা ...+এছাড়া মাধ্যমিক ও উচ্চমাধ্যমিকের স্টুডেন্টদের জন্য অনেক কাজে আসবে ...
ISO/IEC 27001, ISO/IEC 42001, and GDPR: Best Practices for Implementation and...PECB
Denis is a dynamic and results-driven Chief Information Officer (CIO) with a distinguished career spanning information systems analysis and technical project management. With a proven track record of spearheading the design and delivery of cutting-edge Information Management solutions, he has consistently elevated business operations, streamlined reporting functions, and maximized process efficiency.
Certified as an ISO/IEC 27001: Information Security Management Systems (ISMS) Lead Implementer, Data Protection Officer, and Cyber Risks Analyst, Denis brings a heightened focus on data security, privacy, and cyber resilience to every endeavor.
His expertise extends across a diverse spectrum of reporting, database, and web development applications, underpinned by an exceptional grasp of data storage and virtualization technologies. His proficiency in application testing, database administration, and data cleansing ensures seamless execution of complex projects.
What sets Denis apart is his comprehensive understanding of Business and Systems Analysis technologies, honed through involvement in all phases of the Software Development Lifecycle (SDLC). From meticulous requirements gathering to precise analysis, innovative design, rigorous development, thorough testing, and successful implementation, he has consistently delivered exceptional results.
Throughout his career, he has taken on multifaceted roles, from leading technical project management teams to owning solutions that drive operational excellence. His conscientious and proactive approach is unwavering, whether he is working independently or collaboratively within a team. His ability to connect with colleagues on a personal level underscores his commitment to fostering a harmonious and productive workplace environment.
Date: May 29, 2024
Tags: Information Security, ISO/IEC 27001, ISO/IEC 42001, Artificial Intelligence, GDPR
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LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
environment for investigating the changes in vegetation cover dynamics. Our study utilizes
advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
centuries, evolving its structure over time and space. In the present era, these changes have
accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
diverse human activities.
Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
Leveraging Generative AI to Drive Nonprofit InnovationTechSoup
In this webinar, participants learned how to utilize Generative AI to streamline operations and elevate member engagement. Amazon Web Service experts provided a customer specific use cases and dived into low/no-code tools that are quick and easy to deploy through Amazon Web Service (AWS.)
Main Java[All of the Base Concepts}.docxadhitya5119
This is part 1 of my Java Learning Journey. This Contains Custom methods, classes, constructors, packages, multithreading , try- catch block, finally block and more.
How to Setup Warehouse & Location in Odoo 17 InventoryCeline George
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How to Make a Field Mandatory in Odoo 17Celine George
In Odoo, making a field required can be done through both Python code and XML views. When you set the required attribute to True in Python code, it makes the field required across all views where it's used. Conversely, when you set the required attribute in XML views, it makes the field required only in the context of that particular view.
This presentation includes basic of PCOS their pathology and treatment and also Ayurveda correlation of PCOS and Ayurvedic line of treatment mentioned in classics.
Specifica‘tion, verification and simulation of a wireless lan
1. SPECIFICA‘TION, VERIFICATION AND SIMULATION OF A WIRELESS LAN
PROTOCOL: MACAW
G M Lundy, M. Almquist, T. Oruk
U S Naval Postgraduate School
Monterey, CA 93943
ABSTRACT able to make some suggestions as to how it can be
A formal specification and verification of a wireless improved, and to give a fairly accurate indication of how
LAN protocol is given, and a simulation of the much the improvements will help performance.
protocol’s performance is also described. The
verification is a partial verification in that it does not MACAW -- Multiple Access, Collision Avoidance,
include a general verification of all possible Wireless -- was designed as an improvement upon an
configurations of the protocol; however; it does cover earlier protocol, called MACA [Karl. MACAW is based
the expected usage of ihe protocol, which is for a small on the same principle as is the cellular radio network for
number of users sharing a cell. The simulation provides automobiles. A set of base stations, which are ail
further insight into the protocol, especially concerning connected by a wired system, communicate via radio
its performance. Ba,sea! on the verification and signals with the user stations. The difference is that with
simulation, some sug,gestions are made which can MACAW, the base stations are connected by a local area
improve the protocol’s performance. network -- such as CSMACD -- rather than a telephone
type network covering a large area. The area around
I. INTRODUCTION each base station is called a cell; and the users
Wireless communications in various forms has been the communicate with the nearest base station. Another
subject of much attention and research in recent years. difference is in the cell size; here we are using cells
Wireless communications include the broadcast radio which are only a few meters in diameter, rather than
medium; terrestrial microwave[Mili]; satellite microwave miles across. A third difference is that the :stations are
in all its forms [Ha,Ree]; and the International Amateur not mobile, as are autos. The signals are relatively weak,
Radio Network, or “Ham Radio”[Bi]. Additionally , so that they should not penetrate beyond the “cell,” or
wireless communications includes acoustical (sound) its local area. However it is possible that some
communications, used by submarines for many years, interference between adjacent cells may occur. Other
and also for data communications, at least protocols for wireless and broadcast networks exist, and
experimentally [Rei]; and optical (visible) light have been in use for years; these are discussed in the
communications, which are still used by maritime references.
vessels. More recent fioms of wireless communications
includes wireless telephones; cellular telephones; air MACA (medium accessicollision avoidance) Karl,
phones, which enable the passenger aboard an airliner to MAC‘4W’s predecessor, used a sequence of three basic
connect to the long distance telephone system; and messages: request-to-send, clear-to-send, and DATA.
wireless computer networks. Pagers and remote control MACX used binary exponential backoff aligorithm to
devices might also be included, though these are very resolve collisions, the same type used in CSMA/CIl.
“low bandwidth” communications devices. Studies showed that the MACA protocol was not fair to
all stations on the network, and the throughput was not
In this paper we discuss a protocol suggested for wireless very high under conditions of imperfect channels [BD].
!oca1 computer networks, known as MACAW [BD]. This
protocol was suggested as an improved means to enable MACAW (MACA-wireless) improved upon IMACA by
computers in a local area to communicate with each adding to this message sequence. The request-to-send
other. The protocol is intended for a single channel (KTS) message from the sending station is followed by
packet radio network. This means that all stations use the the clear-to-send (CTS) from the receiver, as with
same channel (frequency), so that should more than one MACA; but the DATA is preceded by a short data-send
transmit at a time the signals may interfere. (DS) packet, which serves to alert the nearby stations that
a data packet is about to be transmitted, reducing the
Next we briefly describe MACAW. In section 2 , the probability of a collision. This is followed by an ACK
formal specification is summarized. Section 3 discusses packet from the receiver, through which reliability is
averification of the protocol.Further study of the enhanced. This means that MACAW is able to provide
protocol was carried out through a series of simulations; reliability at the MAC layer, where MACA co’uld not.
this is described in section 4. As a result of this work -
what we have learned through the formal specification MACAW also uses a different backoff algorithm than
process, the verification, and the simulation -- we are MACA. MACAW’S developers felt that the MACA
U.S. Government work not protected 565
by U S . copyright.
2. backoff algorithm oscillated too rapidly. Instead the predicate. The full specification is given in [All.
value of the backoff counter is increased by a factor of
1.5 (rather than 3) for each collision, and decreased by 111. VERIFICATION OF MACAW
1 for each success. This provided a gentler fluctuation A major benefit of formal specification of protocols or
in the backoff counter. computer programs is the potential for automated
generation and analysis. This automated analysis was
In this paper we show that MACAW is a reasonable conducted using the program developed in [Bu]. The
protocol for its intended purpose, however that it can be analysis is done by constructing a directed graph of
slightly refined and impioved. Our contributions states and the transitions between states.
include the formalizing of the protocol specification, its
verification, additional knowledge of its performance, Three basic configurations were analyzed with the
and suggested improvements. automated analysis. The number of machines was vaned
by using three input files with two, three and four
ECIFIC~~IO~ OF MACAW machines. Though it is possible to have more than four
MACAW is formally specified and analyzed using a machines in a single cell, this is unusual; a cell is only a
model called systems of communicating machines. This few meters in diameter. So, while our verification does
model, originally defined by Lundy and Miller[LM] has not cover all cases, it does cover the majority of
been used to analyze several communications protocols. practical cases.
Each machine is defined as a finite state machine with
variables. Communication between machines is done All of the the possible specified transitions of MACAW
through the use of shared variables. Local variables are were not always executed by all machines; in fact, for
used to maintain the state information for each machine, some cases, all transitions were not executed by any
and a predicate-action table serves to unify the state machines. At first glance this appeared as a protocol
machines and the variables. The goal of formal error -- an unexecutable transition but in fact was not.
specification is to determine if the protocol is free from It was simply a case in which the transition in question
errors, such as deadlock or unexecutable transitions, was not needed. For example, in the two machine
and if it possesses “liveness,” which is defined as the analysis, none of the quiet stare transitions were
ability to make positive progress. An additional benefit executed for the simple reason that there was no other
is identification of ambiguities in the protocol. machine causing interference.
A formal specification of MACAW was developed in With two machines: Machine 1 and machine 2 were run
[All, which includes a set of local variables, a set of in the two machine analysis. Both began in the IDLE
shared variables, used for communication, a finite state state and machine 1 had a message to send to machne
machine, and a predicate-action table. 2. Once machne 3 received the DATA message from
machine 1 it sent a DATA message to machinel.
The shared variables are channel.type, channel.DA, esn, (Machine 3’s action upon receiving a DATA message
channel-my-backoff, channel-local-backofS, and included writing a DATA type message to its own output
channel-retry-amount. These are used for buffer). No deadlock occurred and the total number of
communication between the nodes, and the names are system state generated was 69. The corresponding
descriptive of their uses global state analysis generated 275 states. One artificial
deadlock occurred in the global state analysis upon
The 1oca1 variables are inbuffer, outbuffer, backof, receipt by machine 2 of the ACK message from
my-backoff, local-backoff. Again, the names of the machinel. The deadlock happened as a result of
variables are descriptive of their uses. clearing the output buffers when an ACK message was
received. Essentially, both machines received their
The finite state machine diagram has 10 major states. respective DATA messages and no more data remained
These states are named IDLE, CONTEND, XMIT, to be transferred, thus causing a deadlock.
WFCTS, WFACK, WFDS, Q U E , WFDATA,
FCONTEND, CQNTEND2. Simulabons with 3 and 4 machines, which generated
many more states, are reported in [All.
The names of the states are descnptive; in IDLE, the
node has nothing to transmit. In CONTEND, the station IV. SIMULATION AND ANALYSIS OF MACAW
has a message to transmit and is trying to get the The purpose of the simulation is to determine the
channel; XMIT, is sending; “WF” signifies “Waiting behavior of the protocol under different operational
for,” as in WFACK, “waiting for acknowledgment.” conditions. Therefore, operational conditions are first
The initials CJTS signify “clear to send.” determined as test cases and simulations are performed
with these test cases. The results are analyzed and some
The predicate-action table unifies the finite-state suggestions to improve the protocol are given.
diagram with the local and shared variables. Each
transition in the diagram has an entry in the table, and The simulation model of the protocol was built using
for each entry there is an action and an enabling OPNET 2 . k from M I D , Inc. The OPNET design
566
3. environment greatly eiased the simulation process. These cases are also tested from 10% to 100% of the
total offered overlapping channel loads. An
A.Test Cases. The behaviors that we are interested in overlapping channel is the intersection of transmission
are the utilization of the channel and packet mean ranges of two (or more) non-communicating nodes
queue delay time. The usual performance measure for a where one’s transmission interferes with the other. .A
protocol is network utilization, but this does nut consider brief explanation of each case follows:
users of the network. ‘Therefore, mean queue delay time
is also considered as a performance measure of the Hidden node: While A is sending to B, C attempts to
protocol. These measures are related to the send to B also. In this scenario A and C are not aware of
Communication channel load. The load of the channel each other but affected from each other’s transmission,
depends on the number of the nodes that are sharing the so they are hidden from each other. &)osed node:
same transmission media (channel) and their (internal) While B is sending to C, , attempts to send 1.0 B. Here B
4
packet arrival rates. Besides these, the performance of is aware of A, thus B is exposed to -4’s transmissions.
the radio networks is greatly affected by hidden- Hidden and exposed nodes: While A and B are mutually
exposed nodeicell conditions [Karl. exchangmg data, C attempts to send to R. Here A and C
are hidden from each other and B is exposed to both A
With these consideratiions in mind, the test cases are and C. Hidden Cell: B and C are in different cells but
separated into two groups known as “load cases” and they can hear each other. Node . is not aware of the
4
“hidden-exposed nodei’cell cases.” In the load cases, it communication going on in the adjacent cell since it
is also determined whether the protocol acts in favor of cannot hear anything from that cell, it is hid’den from A,
any specific communication topology. For each test the same is true for node D. Exmsed Cell B and C are
case, communication scenarios are determined and, for in different cells but each can hear the other’s
each scenario, test cases are generated with different transmissions while they are communicating with other
numbers of nodes and packet arrival rates. nodes in their cells (A and D respectively). So they are
exposed to each other’s transmissions. ]Hidden and
With each load case, networks of up to four transmitting Exposed Cells: Node A does not hear any tiansmissions
nodes are built and each of these cases is tested from from the other cell xwhle node C is hearing node B. So
10% to 100% of the total offered channel loads. Having the adjacent cell is, hidden for A and exposed for C. All
up to four transmitting nodes for each load case in one: Heavy communication in both cells.
provided enough information about the behavior of .the
protocol under these conditions. Sample load case B. Performance Measure Criteria. As mentioned
scenarios are shown in Figure 1. The load case above, the performance measure also includes the mean
topologies of interest are as follows: delay time in addition to utilization. The resultant
formula is:
{a) reporting nodes with two, three and four transmitting
nodes; (b)one-wav communicating nodes with two, Total-Performance = utilization I mean-queue-delay
three and four transmitting nodes; (c)=
communicating nodes with one and two pairs mutually According to this formulation, if two utdizations are
communicating nodes; (d)ring communication with equal then the one with lesser mean delay time will have
three and four nodes. a better performance measure. For example, suppose
we have measured an utilization of 54% with a mean
delay time of 9 sec and for another case 54% Utilization
with a mean delay of 3 sec. Just looking at the
utilizations does not say anything about which one is
better. But when delay times are considcrcd, the first
case will have a performance measure of 0.54/9=0.06
while the second case will have a prformaiuce measure
of 0.%/3=0.18. This clearly shows that the second case
is better.
A performance measure should be independent of
transmission speed of the network in order to be used to
compare different protocols. Thus, delaiy time is
Figure 1: Sample load cases from each communication topology normalized to data packet length. This me.ans we can
tested. For all cases above, all nodes are in one cell, that is all can compare the performance of the protocol for networks
hear each other and arrows show the direction data streams. (a) four with different transmission speeds.
reporting nodes, (b) two 1-way nodes, (c) two pairs cmss-
communicating nodes, (d) ring communication with four nodes. C. Test Results. For all cases the Poisson distribution
function is used for the packet arrival distnbution. The
Hidden-exposed nodeicell cases are shown in [Or]. first test case, our base case, is chosen to determine the
567
4. maximum performance of the node that is running network increases, since per node utilization and data
MACAW protocol for a given arrival rate. This test is mean queue delay times does not change.
conducted with a network of one transmitter and one
receiver, and utilization is calculated. Data mean queue Hidden and Exposed Node/Cell Case Results In the
delay times are collected by OPNE3”s built-in utilities. hidden node case, due to the rapid increase of the
OPNEX calculates the delay times of the packets that backoff value of node B, performance is poor above
arrive to the queue during one unit of time and uses its 1 % of overlapping channel loads (load over node B).
0
mean (middle) value as a mean delay time of this time Channel access is fair, because both transmitters are
period. The simulation result of this base case and the using the same backoff value as in reporting nodes case
other cases are shown in detailed tables in [Or]. of load cases.
As seen from the table, the performance decreases In the exposed node case performance is fairly high
rapidly beyond 80% offered channel loads due the high compared to the hidden node case. However, above 80%
mean delay times. Maximum utilization observed for of offered overlapping channel loads, the behavior of
the protocol with given packet sizes (30B for control the network becomes similar to thc one way
packets, 520B for data packets), packet arrival communicating node cases of the load cases. The
distribution function and backoff limits is 66%. These “lucky” node gets the channel and keeps it.
results will be a base case to use in comparison with test
results. In the hidden and exposed node case , the hidden node
behavior is dominant. Due to the high delay times, the
Load Case Results For the load cases, channel performance decreases dramatically above 4%of
utilization almost never exceeds 50% for all simulations overlapping channel loads .
(the maximum utilization observed for the protocol was
66% with current parameters). The exceptions are the In the hidden cell case channel access of transmitter
base case and “one pair mutually communicating” nodes (node -4 and D) are always fair because the
network case. In the base case there is no interfering congestion levels at the receivers are similar. But due to
node against the transmitting node, so we should get the congestion at the receiver side data packet delay
“the most” from the protocol. The reason that one pair times in the transmitters are h g h so performance is low
mntually communicating network has high utilization for cell loads above 25%. Its behavior is the same as the
and low backoff values than the other simulation cases is hidden node case.
it has a slower rate of backoff increase for its remote
backoff values. Modified Protocol Simulations During the simulations it
was observed that the backoff increase rate is one of the
For high loads, one-way communicating nodes cases key factors that affects the performance of the MACAW
always violate the fairness of channel access. The protocol under moderate and high loads (40% and
backoff algorithm dictates that each node keeps track above). To further investigate, the same set of
of the congestion of the channel between itself and the simulations were run with a lower backoff increase rate.
neighboring nodes via backoff values. When a node As a result, for load cases with a small number of
attempts to communicate with one of its neighboring transmitting nodes, significant performance gains were
nodes, it uses the associated backoff value. These observed. These gains are due to the lower mean delay
backoff values are mutually exclusive. In a one way times rather than increased utilization. But as the
communicating network scenario when a “lucky” node number of the transmitting nodes increased, the
reaches the channel quicker than the others for a couple performance gain achieved by this modification
of consecutive times it gets and keeps the channel by degraded. No significant performance change was
h o w i n g other nodes have very high backoff values. observed in hidden-exposed nodeicell cases.
Reporting and ring cases have similar results. They both Another factor that affects the performance of the
have fair channel access during the simulations. But protocol is the nodes’ inability to determine whether the
both have high backoff values. To have high backoff channel is busy. According to the MACAW protocol,
value causes larger delay times on average therefore nodes behave purely in accordance with the received
reporting and ring cases have lower performance packet information. The keyword here is “received.”
measures. The MAC layer that runs the MACAW protocol does not
know that it is receiving a packet until the entire packet
The best performance measures observed during the has been transmitted. The probability of collision of two
simulations are around 20% channel load conditions for transmitting nodes is the probability of transmission of
three and four transmitting nodes cases. A s the number one node without recognizing (or before recognizing)
of transmitting nodes in the network increases, the effect that another node is transmitting. The transmission
of having high backoff values decreases (for low loads), probability of a node when it assumes that the channel is
because when the channel is free, the chance that there is available is based on the distribution function and its
a node ready to transmit is high. So idle times of the parameter value (in this case Poisson distribution with
channel are used and total performance measure of the
568
5. arrival rate value). The “recognition” period in the observed, which was caused by the rapid iiocrease of the
original MACAW protocol is the time that it takes for backoff increase rate for the small number of
control packet transmission plus propagation delay. transmitting nodes cases. 4 relation between the backoff
Thus, we haw a sample space of increase rate and the number of transmitting nodes was
time_slot+propugatic,n_clelay for a transmission event observed (but this needs to be investigated more
that may cause a collision. When carrier sensing is thoroughly). So, instead of using a linear increase rate
introduced to the protocol, this sample space shrinks to use of dynamic or exponential increase rates may give
one propagarion-delay ( assuming time-slot >> better results. The dynamic increase can bind to the
propagation delay). So, carrier sensing will decrease the number of transmitting nodes. For the fairness problem
probability of c:ollisions by a factor of in one-way communicating nodes cases more
time-slotlpropagatioi~z_delay. This is also what is fundamental changes should be made to the algorithm.
observed during the simulations of the MACAW That is, the backoff algorithm needs to be thoroughly
protocol with carrier sensing capability. Significant analyzed.
performance measure: increases observed for SO% and
above common channel loads. The source of gain is It is also observed that the channel acquisition with
lower mean delay times. While the greatest performance carrier sensing is superior to the original MACAW
gain is achieved in the hidden node case (for SO% protocol policy. This is quite significant for medium
offered load), no change was observed in the hidden cell and high loads. This contradicts the reasoning of the
case. In hidden cell case carrier sensing provides no help original MACAW protocol specification which says
to the network to improve its performance, because “...carrier sensing is inappropriate” [13D]. This
transmitters are out of range from each other (the only simulation is discussed in more detail in [Or] , as well as
time that a transmitter utilizes carrier sensing in this the remainder of the simulations which are omitted here
topology is to sense its receiver’s RRTS packet). due to lack of space.
.4nother improvement achieved by carrier sensing is V. CONCLUSIONS
fairer channel access of the transmitting nodes Uk described the: specification, verification, and
(compared to the original network) in the “hidden- simulation of MACAW. The specification uncovered
exposed cell” and “aill-in-one” network topologies. some ambiguities in the original specilfication. The
verification showed the protocol to be free of deadlocks,
In “hidden-exposed cell” network node C cannot get for most practical cases. Simulations gave further
the common channel1 as frequently as in the origmal confidence in the protocol and showed further possible
protocol. Now C should wait B to send a11 its packet and improvements in performance. We showed that the
act accordingly (nod,e C must understand what B is backoff algorithm is of major importance to the
“saying”). ’Ihis increases the performance of node A performance of the protocol, and topology is also
slightly, because backoff values are dominant for the critical. The protocol can also be improvled by adding
performance and here there is a big difference between carrier sensing. Simulations suggest that this could
congestion levels of the receivers (especially for high improve utilization under heavy load by about 5%.
loads).
REFERENCES
In “all-in-one” case fairness is achieved between inner [All Almquist, Marty, Formal Spec$cation and Analysis ~7f a
Wireless Media Access Protocol, MS Thesis, Department of
nodes. In the originail protocol for high loads (go%), Computer Science, Naval Postgraduate Schcol, Monterey, CA,
one of the inner noldes has much higher performance 1995.
measure than the other. Now with carrier sensing both [BDl Bharghavan, V., Demer;, A.. Sbenker. S. and Zhang, L.
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