Two-ray ground reflection model has been widely used as the propagation model to investigate the
performance of an ad hoc network. But two-ray model is too simple to represent a real world network. A
more realistic model namely shadowing propagation model has been used in this investigation. Under
shadowing propagation model, a mobile node may receive a packet at a signal level that is below a
required threshold level. This low signal level affects the routing protocol as well as the medium access
control protocol of a network. An analytical model has been presented in this paper to investigate the
shadowing effects on the network performance. The analytical model has been verified via simulation
results. Simulation results show that the performance of a network becomes very poor if shadowing
propagation model is used in compare to the simple two-ray model. Two solutions have also been proposed
in this paper to overcome the effects of shadowing. One solution is a physical layer solution and the other
one is a Medium Access Control (MAC) layer solution. Simulation results show that these two solutions
reduce the shadowing effect and improve network performance.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
OPTIMUM NEIGHBORS FOR RESOURCECONSTRAINED MOBILE AD HOC NETWORKSijasuc
This paper presents an investigation on the optimum number of neighbors for mobile ad hoc networks
(MANETs). The MANETs are self-configuring and self-organizing networks. In such a network, energyconstrained mobile nodes share limited bandwidth to send their packets to the destinations. The mobile nodes
have a limited transmission range and they rely on their neighbors to deliver their packets. Hence, the mobile
nodes must be associated with the required (i.e., optimum) number of neighbors. As the number of neighbors
is varied, a trade-off exists between the network connectivity and available bandwidth per mobile node. To
investigate this issue, we consider Dynamic Source Routing (DSR) as the routing protocol and IEEE 802.11
as the MAC layer protocol in this work. We consider both static and dynamic scenarios in this work. We
simulated the ad hoc networks via network simulator (NS-2) and the simulation results show that there exists
an optimum number of neighbors for the static case. We also show that mobility has a grave impact on the
performance of the MANETs in terms of network throughput, end-to-end delay, energy consumption, and
packet loss. Hence, we need to increase the number of neighbors under mobility conditions. However, there
is no global optimum number of neighbors for the mobility case.
Reduction of Topology Control Using Cooperative Communications in ManetsIJMER
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
Design and implementation of new routingIJCNCJournal
Energy consumption is a key element in the Wireless Sensor Networks (WSNs) design. Indeed, sensor nodes are really constrained by energy supply. Hence, how to improve the network lifetime is a crucial and challenging task. Several techniques are available at different levels of the OSI model to maximize the WSN lifetime and especially at the network layer which uses routing strategies to maintain the routes in the network and guarantee reliable communication. In this paper we intend to propose a new protocol called
Combined Energy and Distance Metrics Dynamic Routing Protocol (CEDM-DR). Our new approach considers not only the distance between wireless sensors but also the energy of node acting as a router in order to find the optimal path and achieve a dynamic and adaptive routing.
The performance metrics exploited for the evaluation of our protocol are average energy consumed, network lifetime and packets lost. By comparing our proposed routing strategy to protocol widely used in WSN namely Ad hoc On demand Distance Vector(AODV), simulation results show that CEDM-DR strategy might effectively balance the sensor power consumption and permits accordingly to enhance the network
lifetime. As well, this new protocol yields a noticeable energy saving compared to its counterpart.
MULTI-HOP BANDWIDTH MANAGEMENT PROTOCOL FOR MOBILE AD HOC NETWORKSIJMIT JOURNAL
An admission control scheme should play the role of a coordinator for flows in a data communication network, to provide the guarantees as the medium is shared. The nodes of a wired network can monitor the medium to know the available bandwidth at any point of time. But, in wireless ad hoc networks, a node must consume the bandwidth of neighboring nodes, during a communication. Hence, the consumption of bandwidth by a flow and the availability of resources to any wireless node strictly depend upon the neighboring nodes within its transmission range. We present a scalable and efficient admission control scheme, Multi-hop Bandwidth Management Protocol (MBMP), to support the QoS requirements
in multi-hop ad hoc networks. We simulate several options to design MBMP and compare the performances of these options through mathematical analysis and simulation results, and compare its effectiveness with the existing admission control schemes through extensive simulations.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
OPTIMUM NEIGHBORS FOR RESOURCECONSTRAINED MOBILE AD HOC NETWORKSijasuc
This paper presents an investigation on the optimum number of neighbors for mobile ad hoc networks
(MANETs). The MANETs are self-configuring and self-organizing networks. In such a network, energyconstrained mobile nodes share limited bandwidth to send their packets to the destinations. The mobile nodes
have a limited transmission range and they rely on their neighbors to deliver their packets. Hence, the mobile
nodes must be associated with the required (i.e., optimum) number of neighbors. As the number of neighbors
is varied, a trade-off exists between the network connectivity and available bandwidth per mobile node. To
investigate this issue, we consider Dynamic Source Routing (DSR) as the routing protocol and IEEE 802.11
as the MAC layer protocol in this work. We consider both static and dynamic scenarios in this work. We
simulated the ad hoc networks via network simulator (NS-2) and the simulation results show that there exists
an optimum number of neighbors for the static case. We also show that mobility has a grave impact on the
performance of the MANETs in terms of network throughput, end-to-end delay, energy consumption, and
packet loss. Hence, we need to increase the number of neighbors under mobility conditions. However, there
is no global optimum number of neighbors for the mobility case.
Reduction of Topology Control Using Cooperative Communications in ManetsIJMER
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
Design and implementation of new routingIJCNCJournal
Energy consumption is a key element in the Wireless Sensor Networks (WSNs) design. Indeed, sensor nodes are really constrained by energy supply. Hence, how to improve the network lifetime is a crucial and challenging task. Several techniques are available at different levels of the OSI model to maximize the WSN lifetime and especially at the network layer which uses routing strategies to maintain the routes in the network and guarantee reliable communication. In this paper we intend to propose a new protocol called
Combined Energy and Distance Metrics Dynamic Routing Protocol (CEDM-DR). Our new approach considers not only the distance between wireless sensors but also the energy of node acting as a router in order to find the optimal path and achieve a dynamic and adaptive routing.
The performance metrics exploited for the evaluation of our protocol are average energy consumed, network lifetime and packets lost. By comparing our proposed routing strategy to protocol widely used in WSN namely Ad hoc On demand Distance Vector(AODV), simulation results show that CEDM-DR strategy might effectively balance the sensor power consumption and permits accordingly to enhance the network
lifetime. As well, this new protocol yields a noticeable energy saving compared to its counterpart.
MULTI-HOP BANDWIDTH MANAGEMENT PROTOCOL FOR MOBILE AD HOC NETWORKSIJMIT JOURNAL
An admission control scheme should play the role of a coordinator for flows in a data communication network, to provide the guarantees as the medium is shared. The nodes of a wired network can monitor the medium to know the available bandwidth at any point of time. But, in wireless ad hoc networks, a node must consume the bandwidth of neighboring nodes, during a communication. Hence, the consumption of bandwidth by a flow and the availability of resources to any wireless node strictly depend upon the neighboring nodes within its transmission range. We present a scalable and efficient admission control scheme, Multi-hop Bandwidth Management Protocol (MBMP), to support the QoS requirements
in multi-hop ad hoc networks. We simulate several options to design MBMP and compare the performances of these options through mathematical analysis and simulation results, and compare its effectiveness with the existing admission control schemes through extensive simulations.
PERFORMANCE STUDY AND SIMULATION OF AN ANYCAST PROTOCOL FOR WIRELESS MOBILE A...ijwmn
This paper conducts a detailed simulation study of stateless anycast routing in a mobile wireless ad hoc
network. The model covers all the fundamental aspects of such networks with a routing mechanism using
a scheme of orientation-dependent inter-node communication links. The simulation system Winsim is used
which explicitly represents parallelism of events and processes in the network. The purpose of these
simulations is to investigate the effect of node’s maximum speed, and different TTL over the network
performance under two different scenarios. Simulation study investigates five practically important
performance metrics of a wireless mobile ad hoc network and shows the dependence of this metrics on
the transmission radius, link availability, and maximal possible node speed
Advancement in VANET Routing by Optimize the Centrality with ANT Colony Approachijceronline
In a wireless ad hoc network, an opportunistic routing strategy is a strategy where there is no predefined rule for choosing the next node to destination (as it is the case in conventional schemes such as OLSR, DSR or even Geo-Routing). A popular example of opportunistic routing is the “delay tolerant” forwarding to VANET network when a direct path to destination does not exist. Conventional routing in this case would just “drop” the packet. With opportunistic routing, a node acts upon the available information, In this thesis optimize the routing by centrality information then refine by ant colony metaheuristics. In this method validate our approach on different parameter like overhead, throughput.
Clustering effects on wireless mobile ad hoc networks performancesijcsit
A new era is dawning for wireless mobile ad hoc networks where communication will be done using a
group of mobile devices called cluster, hence clustered network. In a clustered network, protocols used by
these mobile devices are different from those used in a wired network; which helps to save computation
time and resources efficiently. This paper focuses on Cluster-Based Routing Protocol and Dynamic Source
Routing. The results presented in this paper illustrates the implementation of Ad-hoc On-Demand Distance
Vector routing protocol for enhancing mobile nodes performance and lifetime in a clustered network and to
demonstrate how this routing protocol results in time efficient and resource saving in wireless mobile ad
hoc networks.
Improvement at Network Planning using Heuristic Algorithm to Minimize Cost of...Yayah Zakaria
Wireless Mesh Networks (WMN) consists of wireless stations that are connected with each other in a semi-static configuration. Depending on the configuration of a WMN, different paths between nodes offer different levels of efficiency. One areas of research with regard to WMN is cost minimization. A Modified Binary Particle Swarm Optimization (MBPSO) approach was used to optimize cost. However, minimized cost does not
guarantee network performance. This paper thus, modified the minimization function to take into consideration the distance between the different nodes so as to enable better performance while maintaining cost balance. The results were positive with the PDR showing an approximate increase of 17.83% whereas the E2E delay saw an approximate decrease of 8.33%.
EFFICIENT ANALYSIS OF THE ERGODIC CAPACITY OF COOPERATIVE NON-REGENERATIVE RE...ijwmn
In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the
cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight
approximate moment generating function (MGF) of end-to-end signal-to-noise ratio of 2-hop multi-relay
system, which is In this paper, we proposed a novel efficient method of analyzing the ergodic channel
capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a
very tight approximate moment applicable to myriad of fading environments including mixed and
composite fading channels. Three distinct adaptive source transmission policies were considered in our
analysis namely: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate
adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). The proposed frame
work based on the novel approximate MGF method is sufficiently general to encapsulate all types of fading
environments (especially for the analysis of the mixed fading case)and provides significant advantage to
model wireless system for mixed and composite fading channel. In addition to simplifying computation
complexity of ergodic capacity for CAF relaying schemes treated in literature, we also derive closed form
expressions for the above three adaptive source transmission policies under Nakagami-m fading with i.n.d
statistics. The accuracy of our proposed method has been validated with existing MGF expressions that are
readily available for specific fading environments in terms of bounds, and via Monte Carlo simulations.
International Journal of Engineering Research and Development (IJERD)IJERD Editor
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
Efficient and stable route selection by using cross layer concept for highly...Roopali Singh
Efficient and stable route selection by using cross layer concept for highly mobile network with predictive features by Rupali Singh, Gajendra Singh Dhakad
published in International Journal of Research & Technology, Volume 3, Issue 4_November_2015
A FASTER ROUTING SCHEME FOR STATIONARY WIRELESS SENSOR NETWORKS - A HYBRID AP...ijasuc
A wireless sensor network consists of light-weight, low power, small size sensor nodes. Routing in wireless
sensor networks is a demanding task. This demand has led to a number of routing protocols which
efficiently utilize the limited resources available at the sensor nodes. Most of these protocols are either
based on single hop routing or multi hop routing and typically find the minimum energy path without
addressing other issues such as time delay in delivering a packet, load balancing, and redundancy of data.
Response time is very critical in environment monitoring sensor networks where typically the sensors are
stationary and transmit data to a base station or a sink node. In this paper a faster load balancing routing
protocol based on location with a hybrid approach is proposed.
Optimum Neighbors for Resource-Constrained Mobile Ad Hoc Networksijasuc
This paper presents an investigation on the optimum number of neighbors for mobile ad hoc networks
(MANETs). The MANETs are self-configuring and self-organizing networks. In such a network, energyconstrained mobile nodes share limited bandwidth to send their packets to the destinations. The mobile nodes
have a limited transmission range and they rely on their neighbors to deliver their packets. Hence, the mobile
nodes must be associated with the required (i.e., optimum) number of neighbors. As the number of neighbors
is varied, a trade-off exists between the network connectivity and available bandwidth per mobile node. To
investigate this issue, we consider Dynamic Source Routing (DSR) as the routing protocol and IEEE 802.11
as the MAC layer protocol in this work. We consider both static and dynamic scenarios in this work. We
simulated the ad hoc networks via network simulator (NS-2) and the simulation results show that there exists
an optimum number of neighbors for the static case. We also show that mobility has a grave impact on the
performance of the MANETs in terms of network throughput, end-to-end delay, energy consumption, and
packet loss. Hence, we need to increase the number of neighbors under mobility conditions. However, there
is no global optimum number of neighbors for the mobility case.
OPTIMUM NEIGHBORS FOR RESOURCECONSTRAINED MOBILE AD HOC NETWORKSijasuc
Wireless networking has been an active research focus since the early days of the packet radio
network introduced by the Defense Advanced Research Project Agency (DARPA) [1]. Recent
developments in wireless devices have made laptop computers, personal digital assistants (PDA),
pagers, and cellular telephones portable. Now, users can carry these devices to any place at any
time. Hence, there is a need for a network that can be deployed at any place at any time without
any infrastructure support. In some cases, an infrastructure-based network is hard to build.
Networks used by the soldiers on the battlefield are worthwhile to mention here. In some cases,
infrastructures may not exist due to natural calamities such as cyclones, tsunami, and tornados.
Hence, there is always a need for setting up a temporary network among a group of users without
any pre-existing infrastructure and centralized administration. Mobile Ad hoc Networks
(MANETs) are considered suitable solutions for these kinds of temporary networks. MANETs
consist of a group of mobile nodes, which have limited battery and limited processing power.
MANETs are self-organizing and self-configuring networks and they can be deployed without any
infrastructure support. Numerous groundbreaking applications have been proposed based on
MANETs. These applications include disaster management, search and recovery, remote
International Journal of Ad hoc, Sensor & Ubiquitous Computing (IJASUC) Vol.12, No.2, April 2021
2
healthcare, tele-geoprocessing, education, traffic management, process control, and security [2].
These applications impose diversified design and performance constraints on the MANETs.
OPTIMUM NEIGHBORS FOR RESOURCECONSTRAINED MOBILE AD HOC NETWORKSijasuc
This paper presents an investigation on the optimum number of neighbors for mobile ad hoc networks
(MANETs). The MANETs are self-configuring and self-organizing networks. In such a network, energyconstrained mobile nodes share limited bandwidth to send their packets to the destinations. The mobile nodes
have a limited transmission range and they rely on their neighbors to deliver their packets. Hence, the mobile
nodes must be associated with the required (i.e., optimum) number of neighbors. As the number of neighbors
is varied, a trade-off exists between the network connectivity and available bandwidth per mobile node. To
investigate this issue, we consider Dynamic Source Routing (DSR) as the routing protocol and IEEE 802.11
as the MAC layer protocol in this work. We consider both static and dynamic scenarios in this work. We
simulated the ad hoc networks via network simulator (NS-2) and the simulation results show that there exists
an optimum number of neighbors for the static case. We also show that mobility has a grave impact on the
performance of the MANETs in terms of network throughput, end-to-end delay, energy consumption, and
packet loss. Hence, we need to increase the number of neighbors under mobility conditions. However, there
is no global optimum number of neighbors for the mobility case.
Analysis of Neighbor Knowledge Based Bcast Protocol Performance For Multihop ...pijans
Reliable group communication is a challenging issue for most Mobile Ad-hoc Networks (MANETs) due to
dynamic nature of wireless mobile nodes, group key establishment and management, ensuring secure
information exchange and Quality of Service (QoS) in data transfer. Recently multicast and broadcast
routing protocols are emerging for supporting QoS aware group communication. In MANETs QoS
requirements can be quantified by a set of measurable pre-specified service attributes such as packet
delivery ratio, end-to-end delay, packet loss probability, network control overhead, throughput,
bandwidth, power consumption, service coverage area etc. In this paper, the performance of a neighbor
knowledge based broadcast protocol is analyzed using different QoS metrics (packet delivery ratio, end-toend delay, packet loss probability and network control overhead). BCAST is used as broadcast protocol.
The performance differentials are analyzed using NS-2 network simulator for varying number of data
senders (multicast group size) and data sending rate (offered traffic to the network) over QoS aware group
communication. Simulation results show that BCAST performs well in most cases and provides robust
performance even with high traffic environments.
Analysis of Neighbor Knowledge Based Bcast Protocol Performance For Multihop ...pijans
Reliable group communication is a challenging issue for most Mobile Ad-hoc Networks (MANETs) due to
dynamic nature of wireless mobile nodes, group key establishment and management, ensuring secure
information exchange and Quality of Service (QoS) in data transfer. Recently multicast and broadcast
routing protocols are emerging for supporting QoS aware group communication. In MANETs QoS
requirements can be quantified by a set of measurable pre-specified service attributes such as packet
delivery ratio, end-to-end delay, packet loss probability, network control overhead, throughput,
bandwidth, power consumption, service coverage area etc. In this paper, the performance of a neighbor
knowledge based broadcast protocol is analyzed using different QoS metrics (packet delivery ratio, end-toend delay, packet loss probability and network control overhead). BCAST is used as broadcast protocol.
The performance differentials are analyzed using NS-2 network simulator for varying number of data
senders (multicast group size) and data sending rate (offered traffic to the network) over QoS aware group
communication. Simulation results show that BCAST performs well in most cases and provides robust
performance even with high traffic environments.
Secure data storage over distributed nodes in network through broadcast techn...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
A Low Overhead Reachability Guaranteed Dynamic Route Discovery Mechanism for ...ijasuc
A crucial issue for a mobile ad hoc network is the handling of a large number of nodes. As more nodes join
the mobile ad hoc network, contention and congestion are more likely. The on demand routing protocols
which broadcasts control packets to discover routes to the destination nodes, generate a high number of
broadcast packets in a larger networks causing contention and collision. We propose an efficient route
discovery protocol, which reduces the number of broadcast packet, using controlled flooding technique.
The simulation results show that the proposed probabilistic flooding decreases the number of control
packets floating in the network during route discovery phase, without lowering the success ratio of path
discoveries. Furthermore, the proposed method adapts to the normal network conditions. The results show
that up to 70% of control packet traffic is saved in route discovery phase when the network is denser.
EFFICIENT ANALYSIS OF THE ERGODIC CAPACITY OF COOPERATIVE NON-REGENERATIVE RE...ijwmn
In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the
cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight
approximate moment generating function (MGF) of end-to-end signal-to-noise ratio of 2-hop multi-relay
system, which is In this paper, we proposed a novel efficient method of analyzing the ergodic channel
capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a
very tight approximate moment applicable to myriad of fading environments including mixed and
composite fading channels. Three distinct adaptive source transmission policies were considered in our
analysis namely: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate
adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). The proposed frame
work based on the novel approximate MGF method is sufficiently general to encapsulate all types of fading
environments (especially for the analysis of the mixed fading case)and provides significant advantage to
model wireless system for mixed and composite fading channel. In addition to simplifying computation
complexity of ergodic capacity for CAF relaying schemes treated in literature, we also derive closed form
expressions for the above three adaptive source transmission policies under Nakagami-m fading with i.n.d
statistics. The accuracy of our proposed method has been validated with existing MGF expressions that are
readily available for specific fading environments in terms of bounds, and via Monte Carlo simulations.
PERFORMANCES OF AD HOC NETWORKS UNDER DETERMINISTIC AND PROBABILISTIC CHANNEL...IJCNCJournal
Deterministic channel models have been widely used in simulation and modeling of ad hoc network for a long time. But, deterministic channel models are too simple to represent a real-world ad hoc network scenario. Recently, random channel models have drawn considerable attention of the researchers in this field. The results presented in the literature show that random channel models have a grave impact on the
performance of an ad hoc network. A comprehensive investigation on this issue is yet to be available in the
literature. In this investigation, we consider both deterministic and random channel models to investigate their effects on ad hoc networks. We consider two different types of routing protocols namely single path and multipath routing protocols. We choose Destination Sequence Distance Vector (DSDV), Dynamic Source Routing Protocol (DSR), and Ad-hoc On-Demand Distance Vector (AODV) as the single path routing protocols. On the other hand, we choose Ad-hoc On-Demand Multiple Path Distance Vector (AOMDV) as the multipath routing protocol. The results show that some single path routing protocol can outperform multipath routing protocol under both deterministic and random channel conditions. These results surprisingly contradict the popular claim that multipath routing protocol always outperforms single path routing protocol. A guideline for choosing an appropriate routing protocol for adhoc network has also been provided in this work.
PERFORMANCE STUDY AND SIMULATION OF AN ANYCAST PROTOCOL FOR WIRELESS MOBILE A...ijwmn
This paper conducts a detailed simulation study of stateless anycast routing in a mobile wireless ad hoc
network. The model covers all the fundamental aspects of such networks with a routing mechanism using
a scheme of orientation-dependent inter-node communication links. The simulation system Winsim is used
which explicitly represents parallelism of events and processes in the network. The purpose of these
simulations is to investigate the effect of node’s maximum speed, and different TTL over the network
performance under two different scenarios. Simulation study investigates five practically important
performance metrics of a wireless mobile ad hoc network and shows the dependence of this metrics on
the transmission radius, link availability, and maximal possible node speed
Advancement in VANET Routing by Optimize the Centrality with ANT Colony Approachijceronline
In a wireless ad hoc network, an opportunistic routing strategy is a strategy where there is no predefined rule for choosing the next node to destination (as it is the case in conventional schemes such as OLSR, DSR or even Geo-Routing). A popular example of opportunistic routing is the “delay tolerant” forwarding to VANET network when a direct path to destination does not exist. Conventional routing in this case would just “drop” the packet. With opportunistic routing, a node acts upon the available information, In this thesis optimize the routing by centrality information then refine by ant colony metaheuristics. In this method validate our approach on different parameter like overhead, throughput.
Clustering effects on wireless mobile ad hoc networks performancesijcsit
A new era is dawning for wireless mobile ad hoc networks where communication will be done using a
group of mobile devices called cluster, hence clustered network. In a clustered network, protocols used by
these mobile devices are different from those used in a wired network; which helps to save computation
time and resources efficiently. This paper focuses on Cluster-Based Routing Protocol and Dynamic Source
Routing. The results presented in this paper illustrates the implementation of Ad-hoc On-Demand Distance
Vector routing protocol for enhancing mobile nodes performance and lifetime in a clustered network and to
demonstrate how this routing protocol results in time efficient and resource saving in wireless mobile ad
hoc networks.
Improvement at Network Planning using Heuristic Algorithm to Minimize Cost of...Yayah Zakaria
Wireless Mesh Networks (WMN) consists of wireless stations that are connected with each other in a semi-static configuration. Depending on the configuration of a WMN, different paths between nodes offer different levels of efficiency. One areas of research with regard to WMN is cost minimization. A Modified Binary Particle Swarm Optimization (MBPSO) approach was used to optimize cost. However, minimized cost does not
guarantee network performance. This paper thus, modified the minimization function to take into consideration the distance between the different nodes so as to enable better performance while maintaining cost balance. The results were positive with the PDR showing an approximate increase of 17.83% whereas the E2E delay saw an approximate decrease of 8.33%.
EFFICIENT ANALYSIS OF THE ERGODIC CAPACITY OF COOPERATIVE NON-REGENERATIVE RE...ijwmn
In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the
cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight
approximate moment generating function (MGF) of end-to-end signal-to-noise ratio of 2-hop multi-relay
system, which is In this paper, we proposed a novel efficient method of analyzing the ergodic channel
capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a
very tight approximate moment applicable to myriad of fading environments including mixed and
composite fading channels. Three distinct adaptive source transmission policies were considered in our
analysis namely: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate
adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). The proposed frame
work based on the novel approximate MGF method is sufficiently general to encapsulate all types of fading
environments (especially for the analysis of the mixed fading case)and provides significant advantage to
model wireless system for mixed and composite fading channel. In addition to simplifying computation
complexity of ergodic capacity for CAF relaying schemes treated in literature, we also derive closed form
expressions for the above three adaptive source transmission policies under Nakagami-m fading with i.n.d
statistics. The accuracy of our proposed method has been validated with existing MGF expressions that are
readily available for specific fading environments in terms of bounds, and via Monte Carlo simulations.
International Journal of Engineering Research and Development (IJERD)IJERD Editor
journal publishing, how to publish research paper, Call For research paper, international journal, publishing a paper, IJERD, journal of science and technology, how to get a research paper published, publishing a paper, publishing of journal, publishing of research paper, reserach and review articles, IJERD Journal, How to publish your research paper, publish research paper, open access engineering journal, Engineering journal, Mathemetics journal, Physics journal, Chemistry journal, Computer Engineering, Computer Science journal, how to submit your paper, peer reviw journal, indexed journal, reserach and review articles, engineering journal, www.ijerd.com, research journals,
yahoo journals, bing journals, International Journal of Engineering Research and Development, google journals, hard copy of journal
Efficient and stable route selection by using cross layer concept for highly...Roopali Singh
Efficient and stable route selection by using cross layer concept for highly mobile network with predictive features by Rupali Singh, Gajendra Singh Dhakad
published in International Journal of Research & Technology, Volume 3, Issue 4_November_2015
A FASTER ROUTING SCHEME FOR STATIONARY WIRELESS SENSOR NETWORKS - A HYBRID AP...ijasuc
A wireless sensor network consists of light-weight, low power, small size sensor nodes. Routing in wireless
sensor networks is a demanding task. This demand has led to a number of routing protocols which
efficiently utilize the limited resources available at the sensor nodes. Most of these protocols are either
based on single hop routing or multi hop routing and typically find the minimum energy path without
addressing other issues such as time delay in delivering a packet, load balancing, and redundancy of data.
Response time is very critical in environment monitoring sensor networks where typically the sensors are
stationary and transmit data to a base station or a sink node. In this paper a faster load balancing routing
protocol based on location with a hybrid approach is proposed.
Optimum Neighbors for Resource-Constrained Mobile Ad Hoc Networksijasuc
This paper presents an investigation on the optimum number of neighbors for mobile ad hoc networks
(MANETs). The MANETs are self-configuring and self-organizing networks. In such a network, energyconstrained mobile nodes share limited bandwidth to send their packets to the destinations. The mobile nodes
have a limited transmission range and they rely on their neighbors to deliver their packets. Hence, the mobile
nodes must be associated with the required (i.e., optimum) number of neighbors. As the number of neighbors
is varied, a trade-off exists between the network connectivity and available bandwidth per mobile node. To
investigate this issue, we consider Dynamic Source Routing (DSR) as the routing protocol and IEEE 802.11
as the MAC layer protocol in this work. We consider both static and dynamic scenarios in this work. We
simulated the ad hoc networks via network simulator (NS-2) and the simulation results show that there exists
an optimum number of neighbors for the static case. We also show that mobility has a grave impact on the
performance of the MANETs in terms of network throughput, end-to-end delay, energy consumption, and
packet loss. Hence, we need to increase the number of neighbors under mobility conditions. However, there
is no global optimum number of neighbors for the mobility case.
OPTIMUM NEIGHBORS FOR RESOURCECONSTRAINED MOBILE AD HOC NETWORKSijasuc
Wireless networking has been an active research focus since the early days of the packet radio
network introduced by the Defense Advanced Research Project Agency (DARPA) [1]. Recent
developments in wireless devices have made laptop computers, personal digital assistants (PDA),
pagers, and cellular telephones portable. Now, users can carry these devices to any place at any
time. Hence, there is a need for a network that can be deployed at any place at any time without
any infrastructure support. In some cases, an infrastructure-based network is hard to build.
Networks used by the soldiers on the battlefield are worthwhile to mention here. In some cases,
infrastructures may not exist due to natural calamities such as cyclones, tsunami, and tornados.
Hence, there is always a need for setting up a temporary network among a group of users without
any pre-existing infrastructure and centralized administration. Mobile Ad hoc Networks
(MANETs) are considered suitable solutions for these kinds of temporary networks. MANETs
consist of a group of mobile nodes, which have limited battery and limited processing power.
MANETs are self-organizing and self-configuring networks and they can be deployed without any
infrastructure support. Numerous groundbreaking applications have been proposed based on
MANETs. These applications include disaster management, search and recovery, remote
International Journal of Ad hoc, Sensor & Ubiquitous Computing (IJASUC) Vol.12, No.2, April 2021
2
healthcare, tele-geoprocessing, education, traffic management, process control, and security [2].
These applications impose diversified design and performance constraints on the MANETs.
OPTIMUM NEIGHBORS FOR RESOURCECONSTRAINED MOBILE AD HOC NETWORKSijasuc
This paper presents an investigation on the optimum number of neighbors for mobile ad hoc networks
(MANETs). The MANETs are self-configuring and self-organizing networks. In such a network, energyconstrained mobile nodes share limited bandwidth to send their packets to the destinations. The mobile nodes
have a limited transmission range and they rely on their neighbors to deliver their packets. Hence, the mobile
nodes must be associated with the required (i.e., optimum) number of neighbors. As the number of neighbors
is varied, a trade-off exists between the network connectivity and available bandwidth per mobile node. To
investigate this issue, we consider Dynamic Source Routing (DSR) as the routing protocol and IEEE 802.11
as the MAC layer protocol in this work. We consider both static and dynamic scenarios in this work. We
simulated the ad hoc networks via network simulator (NS-2) and the simulation results show that there exists
an optimum number of neighbors for the static case. We also show that mobility has a grave impact on the
performance of the MANETs in terms of network throughput, end-to-end delay, energy consumption, and
packet loss. Hence, we need to increase the number of neighbors under mobility conditions. However, there
is no global optimum number of neighbors for the mobility case.
Analysis of Neighbor Knowledge Based Bcast Protocol Performance For Multihop ...pijans
Reliable group communication is a challenging issue for most Mobile Ad-hoc Networks (MANETs) due to
dynamic nature of wireless mobile nodes, group key establishment and management, ensuring secure
information exchange and Quality of Service (QoS) in data transfer. Recently multicast and broadcast
routing protocols are emerging for supporting QoS aware group communication. In MANETs QoS
requirements can be quantified by a set of measurable pre-specified service attributes such as packet
delivery ratio, end-to-end delay, packet loss probability, network control overhead, throughput,
bandwidth, power consumption, service coverage area etc. In this paper, the performance of a neighbor
knowledge based broadcast protocol is analyzed using different QoS metrics (packet delivery ratio, end-toend delay, packet loss probability and network control overhead). BCAST is used as broadcast protocol.
The performance differentials are analyzed using NS-2 network simulator for varying number of data
senders (multicast group size) and data sending rate (offered traffic to the network) over QoS aware group
communication. Simulation results show that BCAST performs well in most cases and provides robust
performance even with high traffic environments.
Analysis of Neighbor Knowledge Based Bcast Protocol Performance For Multihop ...pijans
Reliable group communication is a challenging issue for most Mobile Ad-hoc Networks (MANETs) due to
dynamic nature of wireless mobile nodes, group key establishment and management, ensuring secure
information exchange and Quality of Service (QoS) in data transfer. Recently multicast and broadcast
routing protocols are emerging for supporting QoS aware group communication. In MANETs QoS
requirements can be quantified by a set of measurable pre-specified service attributes such as packet
delivery ratio, end-to-end delay, packet loss probability, network control overhead, throughput,
bandwidth, power consumption, service coverage area etc. In this paper, the performance of a neighbor
knowledge based broadcast protocol is analyzed using different QoS metrics (packet delivery ratio, end-toend delay, packet loss probability and network control overhead). BCAST is used as broadcast protocol.
The performance differentials are analyzed using NS-2 network simulator for varying number of data
senders (multicast group size) and data sending rate (offered traffic to the network) over QoS aware group
communication. Simulation results show that BCAST performs well in most cases and provides robust
performance even with high traffic environments.
Secure data storage over distributed nodes in network through broadcast techn...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
A Low Overhead Reachability Guaranteed Dynamic Route Discovery Mechanism for ...ijasuc
A crucial issue for a mobile ad hoc network is the handling of a large number of nodes. As more nodes join
the mobile ad hoc network, contention and congestion are more likely. The on demand routing protocols
which broadcasts control packets to discover routes to the destination nodes, generate a high number of
broadcast packets in a larger networks causing contention and collision. We propose an efficient route
discovery protocol, which reduces the number of broadcast packet, using controlled flooding technique.
The simulation results show that the proposed probabilistic flooding decreases the number of control
packets floating in the network during route discovery phase, without lowering the success ratio of path
discoveries. Furthermore, the proposed method adapts to the normal network conditions. The results show
that up to 70% of control packet traffic is saved in route discovery phase when the network is denser.
EFFICIENT ANALYSIS OF THE ERGODIC CAPACITY OF COOPERATIVE NON-REGENERATIVE RE...ijwmn
In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the
cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight
approximate moment generating function (MGF) of end-to-end signal-to-noise ratio of 2-hop multi-relay
system, which is In this paper, we proposed a novel efficient method of analyzing the ergodic channel
capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a
very tight approximate moment applicable to myriad of fading environments including mixed and
composite fading channels. Three distinct adaptive source transmission policies were considered in our
analysis namely: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate
adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). The proposed frame
work based on the novel approximate MGF method is sufficiently general to encapsulate all types of fading
environments (especially for the analysis of the mixed fading case)and provides significant advantage to
model wireless system for mixed and composite fading channel. In addition to simplifying computation
complexity of ergodic capacity for CAF relaying schemes treated in literature, we also derive closed form
expressions for the above three adaptive source transmission policies under Nakagami-m fading with i.n.d
statistics. The accuracy of our proposed method has been validated with existing MGF expressions that are
readily available for specific fading environments in terms of bounds, and via Monte Carlo simulations.
PERFORMANCES OF AD HOC NETWORKS UNDER DETERMINISTIC AND PROBABILISTIC CHANNEL...IJCNCJournal
Deterministic channel models have been widely used in simulation and modeling of ad hoc network for a long time. But, deterministic channel models are too simple to represent a real-world ad hoc network scenario. Recently, random channel models have drawn considerable attention of the researchers in this field. The results presented in the literature show that random channel models have a grave impact on the
performance of an ad hoc network. A comprehensive investigation on this issue is yet to be available in the
literature. In this investigation, we consider both deterministic and random channel models to investigate their effects on ad hoc networks. We consider two different types of routing protocols namely single path and multipath routing protocols. We choose Destination Sequence Distance Vector (DSDV), Dynamic Source Routing Protocol (DSR), and Ad-hoc On-Demand Distance Vector (AODV) as the single path routing protocols. On the other hand, we choose Ad-hoc On-Demand Multiple Path Distance Vector (AOMDV) as the multipath routing protocol. The results show that some single path routing protocol can outperform multipath routing protocol under both deterministic and random channel conditions. These results surprisingly contradict the popular claim that multipath routing protocol always outperforms single path routing protocol. A guideline for choosing an appropriate routing protocol for adhoc network has also been provided in this work.
Fault tolerant routing scheme based onIJCNCJournal
Most routing protocols designed for wireless sensor networks used the unit disk graph model (UGD) to
represent the physical layer. This model does not take into account fluctuations of the radio signal. Therefore, these protocols must be improved to be adapted to a non-ideal environment. In this paper, we used the lognormal shadowing (LNS) model to represent a non-ideal environment. In this model, the probability of successful reception is calculated according to the link quality. We evaluated LEACH’s performance with LNS model to illustrate the effects of radio signal. Unfortunately, our findings showed that the fluctuations of signal radio have a significant impact on protocol performance. Thereby, we
proposed a Fault-Tolerant LEACH-based Routing scheme (FTLR scheme) to improve the performance of LEACH in a non-ideal environment. Simulation results proved that our contribution provides good performance over the ideal model in terms packet loss rate and energy consumption.
PERFORMANCE ANALYSIS OF OLSR PROTOCOL IN MANET CONSIDERING DIFFERENT MOBILITY...ijwmn
A Mobile Ad Hoc Network (MANET) is created when an independent mobile node network is connected
dynamically via wireless links. MANET is a self-organizing network that does not rely on pre-existing
infrastructure such as wired or wireless network routers. Mobile nodes in this network move randomly,
thus, the topology is always changing. Routing protocols in MANET are critical in ensuring dependable
and consistent connectivity between the mobile nodes. They conclude logically based on the interaction
between mobile nodes in MANET routing and encourage them to choose the optimum path between source
and destination. Routing protocols are classified as proactive, reactive, or hybrid. The focus of this project
will be on Optimized Link State Routing (OLSR) protocol, a proactive routing technique. OLSR is known as
the optimized variant of link state routing in which packets are sent throughout the network using the
multipoint relay (MPR) mechanism. This article evaluates the performance of the OLSR routing protocol
under condition of changing mobility speed and network density. The study's performance indicators are
average packet throughput, packet delivery ratio (PDR), and average packet latency. Network Simulator 2
(NS-2) and an external patch UM-OLSR are used to simulate and evaluate the performance of such
protocol. As a result of research, the approach of implementing the MPR mechanism are able to minimise
redundant data transmission during the normal message broadcast. The MPRs enhance the link state
protocols’ traditional diffusion mechanism by selecting the right MPRs. Hence, the number of undesired
broadcasts can be reduced and limited. Further research will focus on different scenario and environment
using different mobility model
PERFORMANCE ANALYSIS OF OLSR PROTOCOL IN MANET CONSIDERING DIFFERENT MOBILITY...ijwmn
A Mobile Ad Hoc Network (MANET) is created when an independent mobile node network is connected dynamically via wireless links. MANET is a self-organizing network that does not rely on pre-existing infrastructure such as wired or wireless network routers. Mobile nodes in this network move randomly, thus, the topology is always changing. Routing protocols in MANET are critical in ensuring dependable and consistent connectivity between the mobile nodes. They conclude logically based on the interaction between mobile nodes in MANET routing and encourage them to choose the optimum path between source and destination. Routing protocols are classified as proactive, reactive, or hybrid. The focus of this project will be on Optimized Link State Routing (OLSR) protocol, a proactive routing technique. OLSR is known as the optimized variant of link state routing in which packets are sent throughout the network using the multipoint relay (MPR) mechanism. This article evaluates the performance of the OLSR routing protocol under condition of changing mobility speed and network density. The study's performance indicators are average packet throughput, packet delivery ratio (PDR), and average packet latency. Network Simulator 2 (NS-2) and an external patch UM-OLSR are used to simulate and evaluate the performance of such protocol. As a result of research, the approach of implementing the MPR mechanism are able to minimise redundant data transmission during the normal message broadcast. The MPRs enhance the link state protocols’ traditional diffusion mechanism by selecting the right MPRs. Hence, the number of undesired broadcasts can be reduced and limited. Further research will focus on different scenario and environment using different mobility model.
A FASTER ROUTING SCHEME FOR STATIONARY WIRELESS SENSOR NETWORKS - A HYBRID AP...ijasuc
A wireless sensor network consists of light-weight, low power, small size sensor nodes. Routing in wireless
sensor networks is a demanding task. This demand has led to a number of routing protocols which
efficiently utilize the limited resources available at the sensor nodes. Most of these protocols are either
based on single hop routing or multi hop routing and typically find the minimum energy path without
addressing other issues such as time delay in delivering a packet, load balancing, and redundancy of data.
Response time is very critical in environment monitoring sensor networks where typically the sensors are
stationary and transmit data to a base station or a sink node. In this paper a faster load balancing routing
protocol based on location with a hybrid approach is proposed.
A FASTER ROUTING SCHEME FOR STATIONARY WIRELESS SENSOR NETWORKS - A HYBRID AP...ijasuc
A wireless sensor network consists of light-weight, low power, small size sensor nodes. Routing in wireless
sensor networks is a demanding task. This demand has led to a number of routing protocols which
efficiently utilize the limited resources available at the sensor nodes. Most of these protocols are either
based on single hop routing or multi hop routing and typically find the minimum energy path without
addressing other issues such as time delay in delivering a packet, load balancing, and redundancy of data.
Response time is very critical in environment monitoring sensor networks where typically the sensors are
stationary and transmit data to a base station or a sink node. In this paper a faster load balancing routing
protocol based on location with a hybrid approach is proposed.
Route Stability in Mobile Ad-Hoc Networksarpublication
A Mobile Ad Hoc Network (MANET) is a wireless network consisting of mobile nodes, which can communicate with each other without any infrastructure support. In these networks, nodes typically cooperate with each other, by forwarding packets for nodes which are not in the communication range of the source node. A fundamental issue arising in mobile ad-hoc networks (MANETs) is the selection of the optimal path between any two nodes. A method that has been advocated to improve routing efficiency is to select the most stable path so as to reduce the latency and the overhead due to route reconstruction. In this work we study the stability of a routing path, which is subject to link failures caused by node mobility, and we consider as metrics of interest the duration and the availability of a path. Moreover, using the results on path duration and availability, we show how to determine the optimal path in terms of route stability, under the Random Direction mobility models.
An Analytical Analysis Of Neighbour And Isolatednodefor Geocast Routing In Va...pijans
Geocasting is a special variant of multicasting, where data packet or message is transmitted to a predefined
geographical location i.e., known as geocast region. The applications of geocasting in VANET are to
disseminate information like, collision warning, advertising, alerts message, etc. The topology of VANET
changes frequently and rapidly due to the fast movement of vehicles. Therefore, the link time between two
neighbouring vehicles exist for a short span of time. This makes delivery of messages to a geocast region
most challenging issue in VANET. In this paper, we have proposed a probabilisticanalytical model based
on neighbour node and isolatednode on the highway. Where highway is divided in to cells.For the better
network connectivity in multi hop vehicular ad hoc network each cell should have at least one node. The
numerical results show how connectivity between nodes depends on the transmission range, network
density and total network area.
Comparative Review for Routing Protocols in Mobile Ad-Hoc Networksijasuc
Wireless Mobile Ad-Hoc Networks is one of the attractive research field that growing exponentially in the
last decade. it surrounded by much challenges that should be solved the improve establishment of such
networks. Failure of wireless link is considered as one of popular challenges faced by Mobile Ad-Hoc
Networks (MANETs). As this type of networks does not require any pre-exist hardware. As well as, every
node have the ability of roaming where it can be connected to other nodes dynamically. Therefore, the
network internal structure will be unpredictably changed frequently according to continuous activities
between nodes that simultaneously update network topology in the basis of active ad-hoc nature. This
model puts the functionality of routing operation in crucial angle in the area of research under mobile adhoc
network field due to highly dynamic nature. Adapting such kernel makes MANET indigence new
routing techniques to settle these challenges. Thereafter, tremendous amount of routing protocols proposed
to argue with ad-hoc nature. Thus, it is quite difficult to specify which protocols operate efficiently under
different mobile ad-hoc scenarios. This paper examines some of the prominent routing protocols that are
designed for mobile ad-hoc networks by describing their structures, operations, features and then
comparing their various characteristics.
Comparative Review for Routing Protocols in Mobile Ad-Hoc Networksjake henry
Wireless Mobile Ad-Hoc Networks is one of the attractive research field that growing exponentially in the
last decade. it surrounded by much challenges that should be solved the improve establishment of such
networks. Failure of wireless link is considered as one of popular challenges faced by Mobile Ad-Hoc
Networks (MANETs). As this type of networks does not require any pre-exist hardware. As well as, every
node have the ability of roaming where it can be connected to other nodes dynamically. Therefore, the
network internal structure will be unpredictably changed frequently according to continuous activities
between nodes that simultaneously update network topology in the basis of active ad-hoc nature. This
model puts the functionality of routing operation in crucial angle in the area of research under mobile adhoc
network field due to highly dynamic nature. Adapting such kernel makes MANET indigence new
routing techniques to settle these challenges. Thereafter, tremendous amount of routing protocols proposed
to argue with ad-hoc nature. Thus, it is quite difficult to specify which protocols operate efficiently under
different mobile ad-hoc scenarios. This paper examines some of the prominent routing protocols that are
designed for mobile ad-hoc networks by describing their structures, operations, features and then
comparing their various characteristics.
A Proactive Greedy Routing Protocol Precludes Sink-Hole Formation in Wireless...ijwmn
The International Journal of Wireless & Mobile Networks (IJWMN) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of Wireless & Mobile Networks. The journal focuses on all technical and practical aspects of Wireless & Mobile Networks. The goal of this journal is to bring together researchers and practitioners from academia and industry to focus on advanced wireless & mobile networking concepts and establishing new collaborations in these areas.
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SHADOWING EFFECTS ON ROUTING PROTOCOL OF MULTIHOP AD HOC NETWORKS
1. International Journal of Ad hoc, Sensor & Ubiquitous Computing ( IJASUC ), Volume 1, Number 1, March 2010
DOI : 10.5121/ijasuc.2010.1102 12
SHADOWING EFFECTS ON ROUTING
PROTOCOL OF MULTIHOP AD HOC
NETWORKS
Md. Anwar Hossain, Mohammed Tarique and Rumana Islam
Faculty of Engineering, American International University-Bangladesh
anwar94113@aiub.edu
ABSTRACT
Two-ray ground reflection model has been widely used as the propagation model to investigate the
performance of an ad hoc network. But two-ray model is too simple to represent a real world network. A
more realistic model namely shadowing propagation model has been used in this investigation. Under
shadowing propagation model, a mobile node may receive a packet at a signal level that is below a
required threshold level. This low signal level affects the routing protocol as well as the medium access
control protocol of a network. An analytical model has been presented in this paper to investigate the
shadowing effects on the network performance. The analytical model has been verified via simulation
results. Simulation results show that the performance of a network becomes very poor if shadowing
propagation model is used in compare to the simple two-ray model. Two solutions have also been proposed
in this paper to overcome the effects of shadowing. One solution is a physical layer solution and the other
one is a Medium Access Control (MAC) layer solution. Simulation results show that these two solutions
reduce the shadowing effect and improve network performance.
KEYWORDS
Ad hoc networks, shadowing, link distance, probability, delivery ratio, signal-to-interference-plus-noise
power ration (SINR), MAC layer, and transmission power.
1. INTRODUCTION
Mobile Ad hoc Network (MANET) is a highly appealing means of providing network support to
a group of people without the aid of any infrastructure support. MANET consists of a group of
mobile nodes that may not be within the range of each other. Necessary controls and networking
functions are performed by using of a distributed control algorithm. MANET is characterized as a
multihop communication network unlike a cellular mobile network where each mobile node is
connected to a nearest base station based on a single hop connection. In MANET, a mobile node
forwards packet for other mobile nodes in addition to transmit its own packet. Dynamic topology
is another important characteristic of MANET [1]. Mobile nodes may join or leave a network at
any time. In order to maintain network connectivity under a dynamic topological condition an
efficient routing protocol is very essential for MANET. Existing routing protocols like
Destination Sequence Distance Vector (DSDV) [2], Dynamic Source Routing (DSR) [3] and Ad-
hoc On-Demand Distance Vector (AODV) [4] consist of two main mechanisms namely route
discovery and route maintenance. A mobile node discovers a route or a set of routes to a
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destination mobile node by using a route discovery mechanism. On the other hand, a mobile node
detects any network topology change by using the route maintenance mechanism. While using
any of these two mechanisms, a routing protocol relies on mobile radio channel. Mobile radio
channel places a fundamental limitation on the performance of a MANET. The transmission path
between a transmitter and a receiver can vary from simple line-of-sight to one that is severely
obstructed by buildings, trees, road signs, mountains, and other objects. Hence mobile radio
channel is extremely random unlike its wired counterpart. Different propagation models have
been proposed in the literatures to predict the signal attenuation that occurs between two mobile
nodes separated by a distance. The ground reflection model or two-ray propagation model is
widely used in the test bed and also in the simulation model [10-17]. Tworay propagation model
assumes that there is a line-of-sight path and a ground reflected propagation path between a
transmitter and a receiver. This model has been found to be reasonably accurate for predicting the
large-scale signal strength over distances of several kilometers for mobile radio system. This
model characterizes signal propagation in an isolated area with few reflectors such as rural road
or highways. It is not typically a good channel model for a real world mobile communication
system especially when the system is deployed in an urban area. Because this model does not
consider the fact that the surrounding environment of a network is always changing. In a real
world situation, the surrounding environmental cluster is always changing. This leads to a signal
level that can vary vastly across a given distance. The short-term variations in the signal strength
can be as high as 10-20 dB from the mean value of the signal. Measurements have shown that at
any given distance, the path loss at a particular distance is random and distributed log-normally
about a mean value [5]. The log-normal distribution describes the random shadowing effects
which occur over a large number of measurements locations that have the same separation
distance. This adverse effect of shadowing on the routing protocol has been investigated in this
paper.
One of the first papers related to connectivity issues in wireless multihop network was [18]. The
authors studied the percolation of a broadcast in a multihop radio network modeled by a spatial
Poisson process. The effect of station density and transmission radius on the extent of broadcast
percolation was examined. The results presented in this paper shows that in optimizing
transmission radius as a function of communication performance measures, the choice of radius
may be bounded from below by the need to maintain a desired network connectivity. Another
early paper [19] addressed connectivity issues for mobile nodes that are randomly distributed
according to a uniform probability distribution on a one-dimensional line segment. More recently
another work [20] performed a fundamental study on the connectivity of uniformly distributed
mobile nodes on a circular area. According to [20] mobile nodes should adjust transmission
power to a level that is just enough to maintain connectivity in a network provided a mobile node
cooperates with other mobile node to route packet. Further analytical investigations of the
connectivity in bounded areas were made in [21- 22]. In [21] the authors analyzed the critical
transmission range for connectivity in wireless ad hoc networks. The authors first considered the
connectivity problem for stationary network and provided an upper and lower bound on the
critical transmission range for one dimensional network. The authors evaluated the relationship
between the critical transmission range and the minimum transmission range that ensured
formation of a connected component containing a large fraction (i.e., 90%) of the nodes. The
authors then extended this work to a mobility condition where mobile nodes were allowed to
move during a time interval. In [22] the authors considered a ddimensional region, with 1=d=3
and they presented an analysis to determine the transmission range that ensure the resulting
network is connected with a high probability. Based on the bounds of node density the authors
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concluded that, as compared to the deterministic case, a probabilistic solution to this range
assignment problem achieves substantial energy savings. A framework for the calculation of
stochastic connectivity properties of wireless multihop network has been presented in [23]. In
fact, the connectivity problem has been solved for the general case of a k-connected network
accounting for the robustness against node failures. These issues were studied for uniformly
distributed nodel, Gaussian distributed nodes, and nodes that move according to the commonly
used random waypoint mobility model. A large scale network with low node density has been
investigated in [25]. The author studied the connectivity for both purely ad hoc network and
hybrid network. In hybrid network, base stations were placed in a network. Mobile node
communicates with other mobile node through the base stations. The authors obtained an
analytical expression for the probability of connectivity in one dimensional network. They
showed that bottlenecks are unavoidable in a low density sparse network. Most of the works
mentioned so far assume idealized radio propagation model without considering fading and
shadow effects. One of the earliest papers that considered fading and shadowing is [26]. The
authors claim that many well designed protocols will fail simply because of fading and
shadowing experienced in a realistic wireless environment. The authors have shown that fading
and shadowing can have significant influence on network performance. They studied three
different systems namely (1) a multichannel CDMA system, (2) a pure CDMA system, and (3) a
contention based system. They also show that the multichannel CDMA system outperform the
pure CDMA system as well as the contention based system under fading and shadowing
environments. The connectivity of multihop radio networks in a log-normal shadow fading
environment has been investigated in [27]. Assuming the mobile nodes have equal transmission
capabilities and are randomly distributed according to a homogenous Poisson process, the authors
provided a tight lower bound for the minimum node density that is necessary to obtain an almost
surely connected subnetwork on a bounded area of given size. The authors also provided an
insight into how fading affects the topology of multihop networks. The connectivity of a network
from a layered perspective has been investigated in [28]. The authors first pointed out how the
transmission range affects the end-to-end connection probability in a long-normal shadowing
model and compared the results to theoretical bound and measurements in the path loss model.
The authors then showed how connectivity issues behave in 802.11 and IP based networks if
fading effects increases. The authors came up with an analytical model for the link probability in
log-normal shadowing environments as a function of the number of nodes, network area,
transmission range, path loss and shadowing deviation.
A probabilistic analysis of the shadowing effects on the signal level variations has also been
presented in this paper. While investigating the impact of shadowing on the network
performance, the delivery ratio has been considered as a performance metric. The delivery ratio is
defined as the ratio between the number of packets received at a destination and the number of
packets that was sent by a source to that destination. Hence the packet delivery ratio indicates
how many packets were lost in a network. An analytical model to estimate packet losses in a
given network has been presented in this paper. This analytical model has also been verified via
simulation results. In order to investigate the shadowing effects on a routing protocol, we selected
Dynamic Source Routing (DSR)[3] protocol as the candidate. A brief description of the DSR
protocol has been provided in the following section for the completeness of this work. The effects
of shadowing on the DSR protocol have been explained in the section III. The shadowing has
grave effects on a medium access control scheme. Since IEEE 802.11 MAC layer protocol has
been used in this paper, section IV contains a brief description of IEEE 802.11 MAC layer
protocol and section V shows the effects of shadowing on IEEE 802.11 MAC layer protocal.
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Using a derived probability density function based on the results published in [6], the mean value
of the link distances has been derived in section VI. The probability that the received signal level
will be greater than a threshold level has also been derived in the same section. Simulation
models and results have been presented in section VII. Two solutions of shadowing problem have
been presented in the same section. Finally, we conclude this paper in the last section.
2. THE DSR PROTOCOL
The DSR [3] protocol consists of two basic mechanisms: (1) route discovery, and (2) route
maintenance. Route discovery is the mechanism by which a source node discovers a route to a
destination. When a source node wants to send a data packet, it first looks into its route cache to
find a route. If a source cannot find a route in its route cache, it initiates a route discovery
mechanism by broadcasting a request packet to its neighbours. When a neighbour of a source
receives a request packet, it first checks whether the request packet is intended for it or not. If a
neighbour discovers that it is the destination, it sends a reply back to the source after copying the
accumulated routing information contained in the route request packet into a route reply packet.
If a neighbour discovers that it is not the destination of this request packet, it checks for a route in
the route cache for that destination. If this neighbour is neither a destination nor it has a route in
the route cache to that destination, it appends its address in the route request packet and re-
broadcasts the route request packet to its neighbours. This process continues until a route request
packet reaches at the destination node. Then the destination node replies all route requests that it
receives. When a source node receives a route reply packet, it starts sending data packets using
the route indicated in the reply packet. If multiple paths are discovered, it chooses a path that is
the shortest one.
Figure1. Route discovery mechanism of DSR protocol
A typical route discovery mechanism of DSR protocol is illustrated in Figure 1. In this scenario,
mobile node ‘1’ is the source and mobile node ‘5’ is the destination. Mobile node ‘1’ does not
have any route in its cache to this destination. Hence it initiates the route discovery mechanism
by broadcasting a request packet. When some neighbouring nodes like mobile node ‘2’ and ‘6’
receive the request packet, they put their addresses in the request packet and re-broadcast that
request message. Similarly mobile nodes ‘3’,’4’ and ‘7’ also rebroadcast that request packet until
the destination node ‘5’ receives it. The destination node ‘5’ then replies back to the source node
‘1’ by using a route reply packet. The route reply packet contains the information of the route that
has been just discovered. After receiving the route reply packet, mobile node ‘1’ records all the
routes in its route cache. In this simple scenario, two routes namely ’1-2-3-4-5’ and ‘1-6-7-5’ are
discovered. According to the routing algorithm, mobile node ‘1’ should select the shortest path
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between these two paths. In this case, the shortest path is ‘1-6-7-5’. After selecting this shortest
path, the source node starts sending data packet by using the route ‘1-6-7-5’.
Figure 2. Route maintenance mechanism of DSR protocol
Route maintenance is the mechanism by which a node is able to detect any change in the network
topology. When a node detects a ’broken’ link, for example, by using missing MAC layer
acknowledgments, it removes the link from its route cache and sends a route error message to
each node that has sent packets over that link. A typical route maintenance mechanism is shown
in Figure 2. Let us assume that the link between mobile node ‘3’ and ‘4’ is ‘broken’ due to
battery exhaustion of mobile node ‘4’. Mobile node ‘3’ detects that the mobile node ‘4’ is
unreachable by using a MAC layer mechanism. Mobile node ‘3’ then creates a route error
message and sends it to the source. A route error message contains the information of the faulty
link (i.e., 3-4). After receiving the route error message, the source mobile node ‘1’ marks the
route ‘1-2-3-4-5’ as invalid route and tries to find an alternative route from its route cache. Since
an alternative route ‘1-6-7-5’ is there in the route cache, the source mobile node should select that
route and start using this new route.
3. EFFECTS OF SHADOWING ON ROUTING PROTOCOL
In the route discovery and route maintenance operation of the DSR protocol, it is assumed that
the link between two nodes is stable and the variation of signal level only depends on the distance
between them. That means a neighbouring node is always ‘reachable’ unless this neighbour is not
out of battery or it has moved out of the reach. But shadowing effect assumes that the signal level
can vary widely for a given distance between two nodes. This increases the probability that the
signal level may go below a certain required level called a ‘threshold’ level. In this case, a
receiving mobile node may not successfully receive a packet. Hence the following problems may
arise:
(a) The route request packet may not reach all the neighbours. Hence there is a probability of an
unsuccessful route discovery. That means the route request packet may not reach to a destination.
(b) The route discovery mechanism may not be an efficient one. The route discovery mechanism
of the DSR protocol aims to discover as many paths as possible. The reason is that if one path
fails, a source can selects an alternative path instantly. But this kind of flexibility may be lost
under shadowing condition. Since only a few number of paths are discovered, there is a
probability that a source may not find any other alternative route once a current route fails.
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(c) Once some routes are discovered and a source mobile node starts sending data packets using
one of the discovered routes, a neighbouring node may not receive that data packet because of the
wide variation of signal. Hence a data packet may be lost at an intermediate node.
(d) The route maintenance operation of the DSR protocol also may not work properly because
there is a probability that a route error message may be lost during its way to a source mobile
node. If a source does not receive the route error message, it cannot detect a link breakage. The
source continues sending data packet using the route that contains the broken link. All these data
packets will be lost at the broken link.
The shadowing not only affects a routing protocol but also makes problems for a medium access
control scheme. In all the simulation results presented in this paper, IEEE 802.11 has been chosen
as the medium access protocol. A brief description of IEEE 802.11 MAC layer has been
described in the following section.
4. IEEE 802.11 MAC LAYER
Like other IEEE 802.x protocol, the IEEE 802.11 protocol defines the Medium Access Control
(MAC) and physical layers. The IEEE 802.11 MAC layer defines two different access methods
namely Distribution Coordination Function (DCF) and Point Coordination Function (PCF). We
will now only describe DCF based MAC protocol since PCF based MAC protocol cannot be used
in an ad hoc network. The basic access mechanism of DCF based MAC protocol is basically a
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). The main mechanism of
CSMA/CA protocol is as follows: a mobile node senses the medium before transmitting its
packet. If it finds that the medium is free, it transmits its packet. But if the medium if busy, a
mobile node defers its transmission to a later time which is chosen randomly. IEEE 802.11
protocol includes both physical carrier sensing and virtual carrier sensing.
Physical carrier sensing is used to detect other mobile nodes operating in the same network by
analyzing all detected packets. It also helps to detect activities in the channel via relative signal
strength from other sources. Virtual carrier sensing is performed by sending MPDU duration
information in the header of Request-to-Send (RTS), Clear-to-Send (CTS), and data frames as
shown in Figure 3. In addition to header information, payload and a 32-bits CRC, MPDU also
contains a duration field. The duration field contains information of the time duration that will
take this data or management frame to complete transmission. Other mobile stations in the same
area use this information to adjust their Network Allocation Vector (NAV), which indicates the
amount of time that must elapse until the current transmission session is completed and the
channel can be sampled again for idle status. The channel is marked busy if either the physical or
virtual carrier sensing mechanism indicates the channel is busy. Priority access to the wireless
medium is controlled through the use of Inter-Frame Space (IFS) time intervals between the
transmissions of frames. Two IFS intervals are specified in IEEE 802.11 standard (a) Short Inter-
frame Space (SIFS) and, (b) DCF Inter-Frame Space (DIFS). The SIFS is the smallest IFS after a
DIFS as shown in Figure 3. When a station senses the medium and finds it is idle, it has to wait
for a DIFS period to sense the medium again. If the channel is still idle, the mobile station
transmits its MPDU. Upon receiving the MPDU, a receiver checks the checksum to determine
whether a packet was received correctly or not. If a packet is received correctly, a receiver waits
for a SIFS time period and sends a positive acknowledgement (ACK) to the transmitting station
to indicate that the transmission was successful. If an acknowledgement is not received within a
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given time period, another attempt is made to send a packet again. The number of times a source
attempts to send a packet is determined by an important parameter named ‘Long Retry Limit’.
Figure 3. Carrier sensing in IEEE 802.11
When the number of attempts exceeds this limit, a source discards a packet permanently. Since
each mobile node has a limited buffer to store packet, this ‘Long Retry Limit’ parameter helps a
mobile node to operate with a limited packet buffer size. In order to reduce collision and save
channel bandwidth, Request-to-Send (RTS) and Clear-to- Send (CTS) are also used in IEEE
802.11 layer. RTS and CTS control frames are used by a station to reserve channel bandwidth
prior to the transmission of MPDU. The timing diagram of RTS and CTS packets are shown in
Figure 4. The RTS control frame is first transmitted by a source mobile. All other stations in a
given area read the duration field and set their NAVs accordingly. The destination station
responds to the RTS packet with a CTS packet after an SIFS idle period has elapsed. Mobile
stations hearing the CTS packet look at the duration field and again update their NAV. Upon
successful reception of the CTS, the source station is virtually assured that the medium is stable
and reserved for successful transmission of the MPDU. In this way, the mobile stations update
their NAVs based on the information contents of RTS and CTS packets, which helps to combat
‘hidden terminal’ problem. The collision avoidance portion of CSMA/CA is performed through a
random back-off procedure. If a mobile station with a frame to transmit senses the channel and
finds the medium is busy, then the mobile node waits for a DIFS period. At the end of the DIFS
period, the mobile station computes a random period of time called back-off period. In IEEE
802.11, time is slotted in time periods that corresponds to a time unit called slot time. The
random back-off time is an integer value that corresponds to a number of time slots. Initially, the
mobile station computes a back-off time in the range of 0-31. This period is called the contention
window as shown in figure 4. After this contention period, a mobile node again senses the
medium. If it finds the medium busy again, it goes for longer contention period. On the other
hand, if it finds the medium free, it waits for DIFS period to make sure no other mobile node is
transmitting. If no other mobile node transmits during that period, a mobile node starts
transmitting its own packet.
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Figure 4. Transmission of MPDU with RTS and CTS
5. EFFECTS OF SHADOWING ON MAC LAYER
The CSMA/CA based multi-access technique assumes that the medium is an intermittent
synchronous multi-access bit pipe on which idle periods can be distinguished from packet
transmission periods. If nodes can detect idle periods quickly, it is reasonable to terminate idle
periods quickly and to allow nodes to initiate packet transmission after such idle detections. This
is the philosophy of a CSMA/CA based multiple access technique. Shadowing effects may put
hurdle on the normal operation of IEEE 802.11 MAC layer operation in the following ways: (a)
as mentioned in the earlier section that IEEE 802.11 carrier sensing is performed at both the air
interface, which is referred to as physical carrier sensing and at the MAC sub-layer referred to as
virtual carrier sensing. Physical sensing may not work properly due to shadowing because signal
level may go below a threshold level so that it cannot be detected. Hence both physical carrier
sensing and virtual carrier sensing may not work properly, (b) a source station performs virtual
carrier sensing by sending MPDU duration information in the header of RTS, CTS and data
packets. Stations in a given area use this information in the duration field to adjust their Network
Allocation Vector (NAV). The NAV indicates the amount of time that must elapse until the
current transmission session is complete and the channel can be sampled again for idle status.
The stations in a given area may not be able to recover the bit duration information from the
packet because of the poor signal level arisen from the shadowing effects. Hence the adjustment
of NAV cannot work properly, (c) The RTS and CTS frame exchanging between a source station
and a destination station may not be successful due to variation of signal level. If the destination
station does not receive RTS packet due to signal variation, it does not reply that RTS by sending
a CTS packet. Since a source station cannot send a data packet unless it receives a CTS packet
from the destination, a source station has to keep the data packet in the buffer for longer period of
time. Similarly, if the CTS packet is not successfully received by a source station due to signal
variation, a source station also delays its transmission. Hence unsuccessful reception of RTS and
CTS packets can cause unnecessary delaying of a packet transmission, (d) according to IEEE
802.11 after receiving a data packet, a source station sends an acknowledgement. A destination
station may not receive a data packet successfully due to variation of the signal strength. Hence a
source station has to resend a data packet several times. These redundant packets will occupy
channel unnecessarily and waste scarce channel bandwidth. On the other hand, a destination may
successfully receive a packet, but the acknowledgement packet sent by that destination may be
lost due to shadowing effects. Since a source node does not receive an ACK packet, it keeps
sending the data packet repeatedly. According to IEEE 802.11 MAC layer, a source has the
opportunity to resend a packet for seven times after that it will assume that the destination is
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unreachable and it drops the packet. Hence there will be a large number of packet losses in a
network due to unsuccessful reception of an ACK.
6. DERIVATION OF EXPRESSION
If we do not consider the shadowing effects, then the quality of each link should remain constant
during the operation of the network. But this is not a valid assumption under a shadowing
condition. Shadowing causes a wide range variation of the received signal. It increases the
probability that the received signal goes below a threshold level. Hence a packet may not be
correctly received by a receiver. The analytical model presented in this section is based on the
following assumptions: (1) all link distances are uniform within a rectangular service area, (2) the
characteristic of the channel is almost same over the whole rectangular service area (i.e., the
whole network has shadowing effect), (3) the node density (i.e., number of nodes per square
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meter) is kept constant when network size is varied, and (4) once a packet is successfully
received, the receiving mobile node re-transmits that packet at the same power level at which the
previous node has transmitted the same packet to itself. Shadowing effect states that at any given
distance d from a transmitter, the path loss PL(d) at a particular location is random and
distributed log-normally (normal in dB) about the mean distance-dependent value [5]. Therefore,
path loss and received power at d meter from the transmitter is modelled as follows:
Figure 6. Comparison results of probability density functions of path loss at d = 4 , 40, 80, and 186m
The probability density functions for path loss using Equation (4) is a Gaussian log-normal
distribution. The distance dependent mean values of path losses at d = 4,40,80, and 186 meter far
from the receiver is 50, 80, 88, and 100 dBm respectively shown in the Figure 6.
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Figure 7. Probability of received power greater than threshold power level with respect to distance d and
circular area πd2
Based on the analysis presented in [5], the probability that the received signal level will be
greater than the threshold power Pth can be expressed as
7. SIMULATION MODEL AND RESULTS
To investigate the effects of shadowing on the performance of an ad hoc network, a network
consists of 30 mobile nodes was created and tested via Network Simulator (NS-2) [9]. These
nodes were placed randomly over an area of 400m´ 300m area. Five connections were randomly
set up in the network. While setting up each connection of the DSR protocol was used as the
routing algorithm. Once a connection is set-up, Constant Bit Rate (CBR) agent was used to
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generate packets. Each CBR connection started at random period of time. Once a CBR
connection started, it continued generating packet till the end of the simulation.
Table 1: Simulation parameters
The packet generation rate was 1 packet per second. Each simulation was tested for 250 seconds
simulation time. IEEE 802.11 MAC layer was used as the MAC layer. The network size was then
increased to 400m x 400m, 500m x 400m, 500m x 500m, 600m x 500m, 600m x 600m, 700m x
600m and 700m x 700m by keeping the node density constant so that the network connectivity is
not affected. That means there are 40, 50, 62, 75, 90, 105 and 122 mobile nodes were deployed
over the network area when the network sizes were 400m x 400m, 500m x 400m, 500m x 500m,
600m x 500m, 600m x 600m, 700m x 600m and 700m x 700m respectively. The total number of
data packets generated in the network at the source mobile nodes and the total number of data
packets delivered to the destination mobile nodes were monitored during each simulation. The
delivery ratio is the ratio defined by . For a given area, ten different topologies
were created and tested by using different seeds. Ten simulation results were then averaged. The
other simulation parameters are shown in Table I. The transmission range is 250 meter with the
given transmission power level of 24.50 dBm and the threshold power of -64.38 dBm. These are
the default values of these two parameters in Network Simulator (NS-2) [9].
The two-ray model has been used as the propagation model. As mentioned in the previous section
that two-ray model is too simple to represent a real world scenario. The two-ray reflection model
assumes that there are two paths between a source and a destination. One path is the line-of-sight
path and the other one is the reflected path from the ground. The variation of the signal strength
follows the following rule [5]
where Gt and Gr are the transmitting antenna gain and receiving antenna gain, ht and hr are the
transmitting and receiving antenna heights, Pt is the transmitting power and Pr is the receiving
power, and d is the distance between the transmitter and the receiver. Based on the two-ray model
the received signal variation is illustrated in the upper graph of Figure 8.
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Figure 8. Delivery ratio of simplest two-ray channel model with respect to rectangular area
The figure shows that the received power level remains above a threshold power level Pth unless
the distance between a transmitter and a receiver is 160 meter. After that the received signal level
goes below a threshold level. Hence there will be packet losses in the network if a network is
large enough to have average link distance greater than 160 meter. Since each mobile node uses
the same power level to transmit all kinds of packets (i.e., route discovery, route maintenance and
data packets), the link up to 160 meter is considered stable in this case. That means once a route
is discovered, the qualities of all links lying along that route do not change over the time. Hence
there is almost no packet loss. The lower graph of Figure 8 also depicts the simulation results. It
shows that the delivery ratio for two-ray model is almost 100%. That means a negligible number
of packets has been lost. This figure shows that the delivery ratio is 100% under different
network size. Because the average link distance is those simulated networks is less than 160
meter. The above mentioned simulations were repeated with shadowing propagation model by
keeping other parameters mentioned in Table I same. The simulation results with that of the
probabilistic analytic model are shown in the Figure 9. It is depicted that the delivery ratio is
almost 100% when network area is less than or equal to 1.6 x 105
square meter.
Figure 9. Comparison of simulated delivery ratios of two-ray channel model and shadowing model and
theoretical probabilistic analytic result of shadowing model
After that the delivery ratio decreases exponentially as the network gets larger. The delivery ratio
decreases exponentially to almost 15% when the network size was 700m x 700m. This
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exponential drop in the delivery ratio complies with the theoretical model derived in section VI
where it was shown that the probability of the received power is greater than the threshold power
level. In order to successfully receive a packet, the received signal level should be greater than
the threshold value defined by the parameter ( i.e. Pth ), which is listed in Table 1. The decision of
successfully received a packet is determined by the probability defined as Pr ( Pr (d) > Pth) since
successfully received packets solely depend on the received power that is a random variable for
shadowing model. This probability is directly proportional to the delivery ratio within the same
rectangular area where link distance is almost linearly increased with the rectangular area, i.e.,
Delivery ratio = k Pr (Pr (d) > Pth ) (7)
where k is a scaling factor constant. Both the theoretical and simulation results of shadowing
model are shown in Figure 9. In addition to these results, simulation result of two-ray model is
also plotted in the same graph to show the difference between the network performance under
two-ray model and shadowing model. Two methods that can reduce the shadowing effects
suggested in this paper are: (1) by increasing the transmission power, and (2) by increasing the
retry-limit of MAC layer protocol. The first solution is a physical layer solution. This solution of
reducing shadowing effects is to increase the transmission power level. As shown in Equation (3)
that the received signal level at a given distance will increase if the transmission power Pt is
increased.
To investigate how a higher transmission power can reduce the shadowing effect the previous
simulations have been repeated here. But the transmission power is increased to 0.58432 watts
(or 27.67 dBm). This transmission range of a mobile for this new transmission power is 300
meter (if two-ray model is used). The network performance in terms of delivery ratio under a
shadowing condition but with the increase in transmission power is shown in Figure 10 labelled
as high transmission power.
Figure 10. Comparison results of delivery ratio in shadowing environment using different Techniques
The figure shows that the delivery ratio can be improved if a higher transmission power is used.
For example, when the network area is 500m x 500m, the delivery ratios are 40% and 55% for
the transmission power of 24.5 dBm and 27.67 dBm respectively. But the improvement in
delivery ratio is less when the network size is small. The higher transmission power level not
only increases the probability of improving the signal level. But it also helps to reduce the
15. International Journal of Ad hoc, Sensor & Ubiquitous Computing ( IJASUC ), Volume 1, Number 1, March 2010
26
number of hops that a packet travels from a source to a destination. Hence there is less
probability of packet loss. Although the higher transmission power improves delivery ratio, it
may not be a good choice to increase the transmission power to reduce shadowing effect. High
transmission power will increase interference level in a network. Another alternative solution to
reduce the shadowing effect is to modify the MAC layer protocol. As mentioned previously that
an important parameter of IEEE 802.11 MAC layer is ‘Long Retry Limit’. By default the ‘Long
Retry Limit is set to 7. That means after 7 attempts, a mobile node discards a packet permanently
by assuming that the next hop is unreachable. But under a shadowing condition 7 attempts are not
enough. A mobile node may not successfully receive a packet from its previous hop due to poor
signal level in 7 attempts. In order to increase the probability of successfully receiving a packet
the ‘Long Retry Limit’ was increased to a higher value of 12. That means a mobile node has 5
additional attempts to send a packet successfully to its next hop. The simulation result for this
MAC layer solution is shown in shown in Figure 10 labelled as ‘MAC Layer’. This figure shows
that delivery ratio is improved compared to that of a shadowing. Although the amount of
improvement in MAC layer solution is less in compare to its higher transmission power counter
part, but still the packet loss can be reduced in a network. The figure shows that an average
almost of 10% packet loss can be reduced in a network if MAC layer is modified as mentioned
above.
8. CONCLUSIONS
In this paper, the shadowing effects on the performance of an ad hoc network have been
investigated. Although two-ray model is widely used as a propagation model in ad hoc network
simulation, but this model does not represent a real world network propagation model because the
surrounding environment of a network is always changing. It is shown that the performance of a
network deteriorate very quickly if the shadowing effects are taken into account. The main
reasons for this degraded performance resulted from the fact that there will be a large variation of
the received signal level for a given link distance. Hence a packet (routing packet or MAC
packet) may not be received successfully by a mobile node due to poor signal level. This causes
problem to the normal operations of a routing protocol as well as the MAC protocol. One of the
solutions of reducing showing effect suggested in this paper is to increase the transmission power
level. The simulation result shows that the delivery ratio can be improved by almost 40% on
average if the transmission power is increased from 24.5 dBm to 27.67 dBm. But higher
transmission power increases the interference level in a network. Another alternative MAC
solution has been suggested in this paper. This alternative solution is based on a modification of
MAC layer protocol parameter. In this solution the number of packet transmission attempts was
increased. The simulation result shows that this solution also improves the network performance.
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AUTHORS
Md. Anwar Hossain received the B.Sc. degree in Electrical and Electronic
Engineering from Rajshahi University of Engineering & Technology, RUET in 2001
and M.Sc. Engineering degree in Information and Communication Technology from
Asian Institute of Technology, AIT in 2006. He had worked as a lecturer in
Electrical and Electronic Engineering Department at Rajshahi University of
Engineering & Technology, RUET. Recently, he is working as an Assistant
Professor at American International University-Bangladesh. His research interests
are in Ad hoc networks, CDMA, OFDM and MIMO-OFDM Systems.
Mohammed Tarique received B.Sc. degree in Electrical and Electronics from
Bangladesh University of Engineering and Technology (BUET) in 1992. He has
worked in Beximco corporation for 6 years as a Senior Engineer. He received his
Master of Business Administration (MBA) degree from the Institute of Business
Administration (IBA), Dhaka. He also received his Master of Science (MS) degree
from Lamar University, Texas, USA and Ph.D. degree from University of Windsor,
Ontario, Canada. He is currently working in American International University-
Bangladesh as an assistant Professor. His research interests are in wireless
communication, sensor network, ad hoc network and mesh networks. He has presented his research works
in the conferences held in Europe, USA and Canada. He has published several papers in the top tier
journals.
Rumana Islam completed her Master of Science (M.Sc.) in Biomedical
Engineering from Wayne State University, Michigan, USA in 2005 and her B.Sc.
Engineering degree in Electrical and Electronic Engineering from Bangladesh
University of Engineering and Technology (BUET) in 1995. She is currently with
the Department of Electrical and Electronic Engineering of American International
University-Bangladesh. She has 7 years of professional experience in reputed
public and private sectors. Her research interests are in Biomedical sensor design,
sensor networks, ad hoc networks and Signal Processing.