This document discusses mobile and wireless computing and networking basics. It covers the seven layers of the OSI model and their functions. It also describes various techniques for multiplexing wireless channels, including space, time, frequency and code division multiplexing. Challenges like hidden and exposed terminals that arise with using CSMA in wireless networks are also summarized. The document concludes by stating the course will focus on studying routing protocols for mobile ad hoc networks.
This document presents a master's thesis that compares the non-orthogonal waveforms FBMC and UFMC to OFDM for 5G. The thesis was completed at the University of Applied Sciences Rosenheim in Germany. It includes simulations in MATLAB to characterize the waveforms using metrics like error vector magnitude, power spectral density, and complementary cumulative distribution function. FBMC uses a prototype filter and polyphase network to eliminate interference between subcarriers while UFMC filters blocks of subcarriers. Both waveforms are compared to OFDM and simulated over an AWGN channel with channel estimation techniques. The thesis provides background on the waveforms and details of the MATLAB simulations and analysis to meet the objectives of characterizing and comparing the 5G candidate waveforms
This document summarizes a seminar presentation on Optical Code Division Multiple Access (OCDMA). OCDMA allows multiple users to transmit simultaneously over the same bandwidth using unique optical codes. It provides advantages over TDMA and FDMA such as supporting more users and asynchronous transmission without packet collisions. The presentation describes OCDMA network implementation using optical orthogonal codes assigned to transmitters and receivers for communication. It also discusses enhanced security provided by OCDMA through increasing the signal-to-noise ratio required for eavesdropping.
Implementation and Study of Universal Filtered Multi Carrier under Carrier Fr...Editor IJAIEM
Sathiyapriya N.S
PG Student, Dept. of ECE, Periyar Maniammai University Thanjavur, Tamilnadu, India
ABSTRACT
OFDM is a matured technology and applied in various wireless standards. However they are not suitable for Uplink and this
technology is replaced by SC FDMA in 4G standards. Similarly Universal Filtered Multicarrier Communication (UFMC) is
another suitable technology for Multi user Uplink and for applications like cognitive radio. UFMC is a new, non-orthogonal,
waveform designed by Alcatel Lucent Labs which provide a much more efficient way of enabling networks to serve both
broadband users and very narrowband “short data” devices such as any embedded sensor or M2M module. In UFMC the
filtering of waveform is done on a group of subcarriers. In OFDM it is done on the whole subcarriers together. This reduces
the side lobe levels, inters carrier interference (ICI) and requires reduced filter length. Moreover Internet-of-Things where
Machine-Machine communication and applications where very tight response in time requirements are needed, OFDM
miserably fails. We examine impact of carrier frequency offset on the performance of the proposed scheme and compare the
results performance of cyclic prefix based orthogonal frequency division multiplexing(CP-OFDM) system.-
Key words: ICI,CFO,OFDM,UFMC
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
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.
This document summarizes a research paper that proposes novel modem structures for GFDM (generalized frequency division multiplexing) to reduce implementation complexity. The proposed transmitter is based on modulating matrix sparsification using FFT. A unified demodulator structure is derived for matched filter, zero forcing, and minimum mean square error receivers. The demodulation techniques exploit the block circulant property of matrices to reduce computational cost. The complexity of the proposed techniques is analyzed and shown to provide substantial reductions compared to existing solutions.
This document describes a PhD thesis on designing unipolar orthogonal codes for optical code division multiple access (CDMA) networks. The research involves developing algorithms to generate sets of 1D and 2D unipolar orthogonal codes with maximum size and orthogonality. Two algorithms are proposed for generating maximal clique sets of 1D codes based on generating all possible codes in a difference of positions representation and using correlation constraints to identify orthogonal code sets. Computational complexity analysis shows the algorithms may have polynomial runtime complexity for certain code parameter ranges. The thesis will evaluate the proposed algorithms and compare results to hypothetical ideal schemes.
Techniques for Improving BER and SNR in MIMO Antenna for Optimum PerformanceIJMTST Journal
The use of multiple antennas for diversity, including MIMO (Multiple Input Multiple Output) is one of the most promising wireless technologies for broadband communication applications. This antenna system is a vital study in today’s wireless communication system especially when the signal propagates through some corrupted environments. In our paper new techniques of improving bit error ratio and signal to noise ratio are discussed. Inter symbol interference is a major limitation of wireless communications. It degrades the performance significantly if the delay spread is comparable or higher than the symbol duration. To remove ISI, equalization needs to be included at the receiver end. This paper discusses the merits of the MIMO system and the techniques used for improving BER performance and SNR. In MIMO wireless communication, an equalizer is used to recover a signal that suffers from Inter symbol Interference (ISI) and the BER characteristics is improved and a good SNR can be obtained. Different equalization techniques are discussed in this paper.
This document presents a master's thesis that compares the non-orthogonal waveforms FBMC and UFMC to OFDM for 5G. The thesis was completed at the University of Applied Sciences Rosenheim in Germany. It includes simulations in MATLAB to characterize the waveforms using metrics like error vector magnitude, power spectral density, and complementary cumulative distribution function. FBMC uses a prototype filter and polyphase network to eliminate interference between subcarriers while UFMC filters blocks of subcarriers. Both waveforms are compared to OFDM and simulated over an AWGN channel with channel estimation techniques. The thesis provides background on the waveforms and details of the MATLAB simulations and analysis to meet the objectives of characterizing and comparing the 5G candidate waveforms
This document summarizes a seminar presentation on Optical Code Division Multiple Access (OCDMA). OCDMA allows multiple users to transmit simultaneously over the same bandwidth using unique optical codes. It provides advantages over TDMA and FDMA such as supporting more users and asynchronous transmission without packet collisions. The presentation describes OCDMA network implementation using optical orthogonal codes assigned to transmitters and receivers for communication. It also discusses enhanced security provided by OCDMA through increasing the signal-to-noise ratio required for eavesdropping.
Implementation and Study of Universal Filtered Multi Carrier under Carrier Fr...Editor IJAIEM
Sathiyapriya N.S
PG Student, Dept. of ECE, Periyar Maniammai University Thanjavur, Tamilnadu, India
ABSTRACT
OFDM is a matured technology and applied in various wireless standards. However they are not suitable for Uplink and this
technology is replaced by SC FDMA in 4G standards. Similarly Universal Filtered Multicarrier Communication (UFMC) is
another suitable technology for Multi user Uplink and for applications like cognitive radio. UFMC is a new, non-orthogonal,
waveform designed by Alcatel Lucent Labs which provide a much more efficient way of enabling networks to serve both
broadband users and very narrowband “short data” devices such as any embedded sensor or M2M module. In UFMC the
filtering of waveform is done on a group of subcarriers. In OFDM it is done on the whole subcarriers together. This reduces
the side lobe levels, inters carrier interference (ICI) and requires reduced filter length. Moreover Internet-of-Things where
Machine-Machine communication and applications where very tight response in time requirements are needed, OFDM
miserably fails. We examine impact of carrier frequency offset on the performance of the proposed scheme and compare the
results performance of cyclic prefix based orthogonal frequency division multiplexing(CP-OFDM) system.-
Key words: ICI,CFO,OFDM,UFMC
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
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.
This document summarizes a research paper that proposes novel modem structures for GFDM (generalized frequency division multiplexing) to reduce implementation complexity. The proposed transmitter is based on modulating matrix sparsification using FFT. A unified demodulator structure is derived for matched filter, zero forcing, and minimum mean square error receivers. The demodulation techniques exploit the block circulant property of matrices to reduce computational cost. The complexity of the proposed techniques is analyzed and shown to provide substantial reductions compared to existing solutions.
This document describes a PhD thesis on designing unipolar orthogonal codes for optical code division multiple access (CDMA) networks. The research involves developing algorithms to generate sets of 1D and 2D unipolar orthogonal codes with maximum size and orthogonality. Two algorithms are proposed for generating maximal clique sets of 1D codes based on generating all possible codes in a difference of positions representation and using correlation constraints to identify orthogonal code sets. Computational complexity analysis shows the algorithms may have polynomial runtime complexity for certain code parameter ranges. The thesis will evaluate the proposed algorithms and compare results to hypothetical ideal schemes.
Techniques for Improving BER and SNR in MIMO Antenna for Optimum PerformanceIJMTST Journal
The use of multiple antennas for diversity, including MIMO (Multiple Input Multiple Output) is one of the most promising wireless technologies for broadband communication applications. This antenna system is a vital study in today’s wireless communication system especially when the signal propagates through some corrupted environments. In our paper new techniques of improving bit error ratio and signal to noise ratio are discussed. Inter symbol interference is a major limitation of wireless communications. It degrades the performance significantly if the delay spread is comparable or higher than the symbol duration. To remove ISI, equalization needs to be included at the receiver end. This paper discusses the merits of the MIMO system and the techniques used for improving BER performance and SNR. In MIMO wireless communication, an equalizer is used to recover a signal that suffers from Inter symbol Interference (ISI) and the BER characteristics is improved and a good SNR can be obtained. Different equalization techniques are discussed in this paper.
A Discrete-Time Polynomial Model of Single Channel Long-Haul Fiber-Optic Comm...West Virginia University
The document presents a discrete-time polynomial model for single channel long-haul fiber-optic communication systems. It simplifies previous models by reducing a triple integral to a simple integral for Gaussian pulses, providing computational advantages over split-step Fourier methods while maintaining accuracy. The model accounts for fiber loss, chirp, and photodetection ignored in prior work, and can be extended to multichannel and polarization cases. It is intended to enable digital signal processing for optical communications.
1) The document discusses channel estimation techniques for 4G wireless networks using OFDM modulation.
2) Channel estimation is important for coherent detection and diversity techniques in wireless systems, which have time-varying channels. Accurate channel estimation allows techniques like maximal ratio combining.
3) OFDM divides the channel into multiple sub-carriers to combat multipath fading and make channel equalization easier compared to single carrier systems. Channel estimation is needed to characterize the time-varying frequency response of the wireless channel.
Different Issues and Survey of Proposed Solutions in TCP over Wireless Enviro...Ranjeet Bidwe
This document discusses issues with using TCP in wireless networks and proposed solutions. The main issues are higher bit error rates, lower bandwidth, mobility, and longer round trip times in wireless networks compared to wired networks. TCP was designed for wired networks and assumes packet loss is always due to congestion, but in wireless networks loss can occur for other reasons like bit errors, handoffs, or disconnections. This wrong assumption causes TCP to reduce its window size unnecessarily, degrading performance. The document surveys proposed solutions like Snoop to cache packets at base stations to hide losses from the sender, and Explicit Congestion Notification to signal congestion before queue overflows.
https://www.ijmst.com/
IJMST Volume 1 Issue 1, Manuscript 4
As the popularity of mobile devices and wireless networks significantly increased over the
past years. The wireless adhoc network has now become one of the most vibrant and active
fields of communication and networking research. These networks are a new generation of
networks offering unrestricted mobility without any underlying infrastructure. As their
principle application is in disastrous environments, security is critical. Various challenges are
faced in the adhoc environment, mostly due to the resource poorness of these networks. One
man confront in the design of these networks is their vulnerability to security attacks. The
solutions for conventional networks are usually not sufficient to provide efficient adhoc
operations. Just because of its wireless nature of communication and lack of any security
infrastructure raise several security problems and threats.
In this paper, we briefly review the threats an adhoc network faces and the security goals to
be achieved. Moreover, it also presents existing security schemes used in wireless adhoc
networks in order to handle security threats.
This paper modifies the DYMO protocol and develops the AIS-DYMO protocol that is
capable to handle the network layer attack. It means the performance of the network doesn’t get
degraded under the attack. Various immune algorithms can be used to enhance the performance of
the DYMO protocol, but the clonal selection algorithm is used in this work to enhance the
performance of the DYMO protocol. Overall the DYMO protocol is modified to handle the network
layer attacks by using the clonal selection immune algorithm.
The document analyzes the performance of IEEE 802.16d under the Stanford University Interim (SUI) channel model. It investigates the bit error rate of IEEE 802.16d using different SUI channel models and digital modulations like BPSK and QPSK. The results show the BER performance for different SUI channel models and modulations.
1) The document describes a model for a wireless communication channel with multiple transmit and receive antennas, known as a MIMO channel. It accounts for multipath propagation through multiple propagation paths.
2) The capacity of the MIMO channel is analyzed. It is shown that multipath can substantially improve capacity over SISO, SIMO, and MISO channels if the number of multipath components exceeds a certain value. In this case, the capacity slope can be proportional to the number of antennas.
3) Two coding structures, STVC and DMMT, are proposed to achieve the MIMO channel capacity. STVC has very high complexity while DMMT has reduced complexity but can still achieve full channel capacity asymptot
The document discusses concepts and models of computer communication. It defines the basic components of a communication system including the source, transmitter, transmission system, receiver, and destination. It also discusses transmission media, data representation, parallel vs serial transmission, and asynchronous transmission. The key aspects are models for computer communication, basic communication components, and differences between parallel and serial transmission.
ESTIMATION AND COMPENSATION OF INTER CARRIER INTERFERENCE IN WIMAX PHYSICAL L...ijngnjournal
WiMAX is Wireless Interoperability for Microwave Access has emerged as a promising solution for transmission of higher data rates for fixed and mobile applications. IEEE 802.16d and e are the standards proposed by WiMAX group for fixed and mobile. As the wireless channel have so many limitation Such as Multipath, Doppler spread, Delay spread and Line Of Sight (LOS)/Non Line Of Sight (NLOS) components. To attain higher data rates the Multi Carrier System with Multiple Input and Multiple Output (MIMO) is incorporated in the WiMAX. The Orthogonal Frequency Division Multiplexing (OFDM) is a multi carrier technique used with the WiMAX systems. In OFDM the available spectrum is split into numerous narrow band channels of dissimilar frequencies to achieve high data rate in a multi path fading environment. And all these sub carriers are considered to be orthogonal to each other. As the number of sub carriers is increased there is no guarantee of sustained orthogonality, i.e. at some point the carriers are not
independent to each other, and hence where the orthogonality can be loosed which leads to interference and also owing to the synchronization between transmitter and receiver local oscillator, it causes interference known as Inter Carrier Interference (ICI). The systems uses MIMO-OFDM will suffer with the effects of ICI and Carrier Frequency Offset (CFO) “ε”. However these affect the power leakage in the midst of sub carriers, consequently degrading the system performance. In this paper a new approach is proposed in order to reduce the ICI caused in WiMAX and improve the system performance. In this scheme at the transmitter side the modulated data and a few predefined pilot symbols are mapped onto the non
neighboring sub carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols the frequency offset is exactly estimated by using Maximum Likelihood Estimation (MLE) and hence can be minimized. At demodulation stage the received signals are linearly combined along with their weighted
coefficients and pilot symbols, called as Pilot Aided Self Cancellation Method (PASCS). And also to realize the various wireless environments the simulations are carried out on Stanford University Interim (SUI) channels. The simulation results shows that by incorporating this method into WiMAX systems it performs better when the Line Of Sight (LOS) component is present in the transmission and also it improves the Bit Error Rate (BER) and Carrier to Interference Ratio (CIR). The CIR can be improved 20 dB. In this paper the effectiveness of PASCS scheme is compared with the Self Cancellation Method (SCM). It provides accurate estimation of frequency offset and when residual CFO is less significant the ICI can be diminished successfully.
The document summarizes routing security in ad hoc wireless networks. It discusses the characteristics of ad hoc wireless networks and routing protocols used, including proactive, reactive, and hybrid protocols. It then covers various security attacks on routing protocols like passive attacks, active attacks, impersonation attacks, and attacks using modification or fabrication. Finally, it discusses some security mechanisms and routing protocols that aim to provide security, such as SEAD, Ariadne, SAR, and SRP.
This document outlines the teaching and examination scheme for the subject of Computer Networks. It includes 3 hours of theory and 2 hours of practical classes per week. The theory exam will be worth 100 marks and include two tests worth 25 marks each. The objectives are to understand computer network concepts, topologies, devices, transmission media, and models like OSI and TCP/IP. The practical focuses on skills like network installation, configuration, and troubleshooting. Five recommended textbooks are provided for additional learning resources.
The document provides an overview of communication and network concepts. It discusses what a network is, the need for networking, and the evolution of networking from ARPANET in 1969 to the modern Internet. It also describes switching techniques, data communication terminology, transmission media including guided cables and unguided waves, common network devices, network topologies, types of networks including LANs and WANs, and protocols such as FTP and TCP/IP.
Multiplexing allows the simultaneous transmission of multiple signals across a single data link. There are several types of multiplexing employed in telecommunications, including frequency-division multiplexing (FDM), wavelength-division multiplexing (WDM), and time division multiplexing (TDM). FDM uses different carrier frequencies to transmit separate signals. WDM takes advantage of the high data capacity of fiber-optic cables. TDM divides the transmission time into time slots and allots one slot for each message. Within TDM, synchronous TDM gives each device a fixed time slot while asynchronous TDM dynamically allocates slots.
An ad hoc network is a type of wireless network that does not require a central router or base station. Nodes communicate directly with each other or through intermediate nodes in a multi-hop fashion without any fixed infrastructure. Routing and resource management are distributed. Common types include wireless mesh networks, wireless sensor networks, and hybrid wireless networks. Ad hoc networks face challenges related to medium access, routing, security, and resource constraints due to the lack of centralized control.
The document discusses optical network survivability, which refers to a network's ability to continue operating during failures. It outlines existing techniques for survivability, including predesigned protection which reserves backup resources in advance, and restoration which chooses backup resources in real-time. The document also compares approaches like shared path protection, traffic control, hybrid preplanned and real-time allocation, and dual homing. It proposes an algorithm for best-effort fast lightpath routing to improve survivability.
Iaetsd comparative study mimo ofdm, cdma-sdmaIaetsd Iaetsd
This document compares and contrasts MIMO OFDM, CDMA-SDMA, and multi-user detection techniques for wireless communication systems. It discusses how MIMO OFDM can achieve high data rates with frequency and antenna diversity. Space division multiple access (SDMA) is introduced as an application of MIMO that improves spectral efficiency by multiplexing signals based on spatial signatures. The document also examines multi-user detection methods like linear detection, minimum mean square error, and successive interference cancellation that are needed for robust SDMA performance as the number of users increases.
PERFORMANCE IMPROVEMENT OF PAPR REDUCTION FOR OFDM SIGNAL IN LTE SYSTEMijwmn
This document discusses performance improvement of peak-to-average power ratio (PAPR) reduction for orthogonal frequency division multiplexing (OFDM) signals in long-term evolution (LTE) systems. It proposes an improved amplitude clipping and filtering method for PAPR reduction that shows significant improvement over existing methods, with a slight increase in bit error rate. The document provides background on OFDM, PAPR issues in OFDM, and motivations for reducing PAPR such as improving power amplifier efficiency.
This document discusses optimization techniques for designing ultra-wideband planar monopole antennas. It presents two powerful design methodologies: size optimization using design of experiments, and topology optimization using binary particle swarm optimization. Size optimization is a systematic approach that varies geometric parameters to achieve design goals with a small number of simulations. Topology optimization determines the optimal metal distribution within the design area without a predefined shape using an automatic approach. These techniques are demonstrated by designing UWB antennas and band-notched UWB antennas, improving efficiency over trial-and-error approaches.
This document provides an introduction to the course CS144: An Introduction to Computer Networks at Stanford University. It discusses the 4-layer model of computer networks, including the application, transport, network and link layers. It explains how each layer communicates with its peer layer and how encapsulation works, with one layer serving as a payload for the layer below it. The document also provides an outline of topics to be covered in the course, including what the Internet is and a brief history of networking and the development of the Internet.
The document discusses Personal Communication Services (PCS) and provides examples of different wireless communication systems, including cellular and cordless systems. It describes key aspects of cellular systems like Advanced Mobile Phone Service (AMPS), Global System for Mobile Communications (GSM), EIA/TIA IS-136, and EIA/TIA IS-95 standards. These include multiple access techniques, frequency bands, channel structures, features supported, and mobility management protocols. PCS networks integrate these wireless systems to provide mobile communication services connected to the public switched telephone network.
This document provides an overview of key concepts in computer networks and communication. It defines what a network is, discusses the need for networking and sharing of resources, and outlines the evolution of early networks like ARPANET and NSFNET into the modern Internet. It also covers network topologies, transmission media, switching techniques, common network devices, and communication protocols.
Stoe Noll Westin Data Transmission PresentationJennifer Stoe
The document summarizes various methods of data transmission throughout history including Morse code, telegraphs, telephones, computers, and modern wireless technologies. It describes how data is encoded and transmitted through different channels like wired, wireless, satellite, and cellular networks. The key technologies discussed are analog and digital transmission, protocols, wired connections like Ethernet and USB, and wireless standards like Bluetooth, WiFi, WiMAX, and cellular networks.
A Discrete-Time Polynomial Model of Single Channel Long-Haul Fiber-Optic Comm...West Virginia University
The document presents a discrete-time polynomial model for single channel long-haul fiber-optic communication systems. It simplifies previous models by reducing a triple integral to a simple integral for Gaussian pulses, providing computational advantages over split-step Fourier methods while maintaining accuracy. The model accounts for fiber loss, chirp, and photodetection ignored in prior work, and can be extended to multichannel and polarization cases. It is intended to enable digital signal processing for optical communications.
1) The document discusses channel estimation techniques for 4G wireless networks using OFDM modulation.
2) Channel estimation is important for coherent detection and diversity techniques in wireless systems, which have time-varying channels. Accurate channel estimation allows techniques like maximal ratio combining.
3) OFDM divides the channel into multiple sub-carriers to combat multipath fading and make channel equalization easier compared to single carrier systems. Channel estimation is needed to characterize the time-varying frequency response of the wireless channel.
Different Issues and Survey of Proposed Solutions in TCP over Wireless Enviro...Ranjeet Bidwe
This document discusses issues with using TCP in wireless networks and proposed solutions. The main issues are higher bit error rates, lower bandwidth, mobility, and longer round trip times in wireless networks compared to wired networks. TCP was designed for wired networks and assumes packet loss is always due to congestion, but in wireless networks loss can occur for other reasons like bit errors, handoffs, or disconnections. This wrong assumption causes TCP to reduce its window size unnecessarily, degrading performance. The document surveys proposed solutions like Snoop to cache packets at base stations to hide losses from the sender, and Explicit Congestion Notification to signal congestion before queue overflows.
https://www.ijmst.com/
IJMST Volume 1 Issue 1, Manuscript 4
As the popularity of mobile devices and wireless networks significantly increased over the
past years. The wireless adhoc network has now become one of the most vibrant and active
fields of communication and networking research. These networks are a new generation of
networks offering unrestricted mobility without any underlying infrastructure. As their
principle application is in disastrous environments, security is critical. Various challenges are
faced in the adhoc environment, mostly due to the resource poorness of these networks. One
man confront in the design of these networks is their vulnerability to security attacks. The
solutions for conventional networks are usually not sufficient to provide efficient adhoc
operations. Just because of its wireless nature of communication and lack of any security
infrastructure raise several security problems and threats.
In this paper, we briefly review the threats an adhoc network faces and the security goals to
be achieved. Moreover, it also presents existing security schemes used in wireless adhoc
networks in order to handle security threats.
This paper modifies the DYMO protocol and develops the AIS-DYMO protocol that is
capable to handle the network layer attack. It means the performance of the network doesn’t get
degraded under the attack. Various immune algorithms can be used to enhance the performance of
the DYMO protocol, but the clonal selection algorithm is used in this work to enhance the
performance of the DYMO protocol. Overall the DYMO protocol is modified to handle the network
layer attacks by using the clonal selection immune algorithm.
The document analyzes the performance of IEEE 802.16d under the Stanford University Interim (SUI) channel model. It investigates the bit error rate of IEEE 802.16d using different SUI channel models and digital modulations like BPSK and QPSK. The results show the BER performance for different SUI channel models and modulations.
1) The document describes a model for a wireless communication channel with multiple transmit and receive antennas, known as a MIMO channel. It accounts for multipath propagation through multiple propagation paths.
2) The capacity of the MIMO channel is analyzed. It is shown that multipath can substantially improve capacity over SISO, SIMO, and MISO channels if the number of multipath components exceeds a certain value. In this case, the capacity slope can be proportional to the number of antennas.
3) Two coding structures, STVC and DMMT, are proposed to achieve the MIMO channel capacity. STVC has very high complexity while DMMT has reduced complexity but can still achieve full channel capacity asymptot
The document discusses concepts and models of computer communication. It defines the basic components of a communication system including the source, transmitter, transmission system, receiver, and destination. It also discusses transmission media, data representation, parallel vs serial transmission, and asynchronous transmission. The key aspects are models for computer communication, basic communication components, and differences between parallel and serial transmission.
ESTIMATION AND COMPENSATION OF INTER CARRIER INTERFERENCE IN WIMAX PHYSICAL L...ijngnjournal
WiMAX is Wireless Interoperability for Microwave Access has emerged as a promising solution for transmission of higher data rates for fixed and mobile applications. IEEE 802.16d and e are the standards proposed by WiMAX group for fixed and mobile. As the wireless channel have so many limitation Such as Multipath, Doppler spread, Delay spread and Line Of Sight (LOS)/Non Line Of Sight (NLOS) components. To attain higher data rates the Multi Carrier System with Multiple Input and Multiple Output (MIMO) is incorporated in the WiMAX. The Orthogonal Frequency Division Multiplexing (OFDM) is a multi carrier technique used with the WiMAX systems. In OFDM the available spectrum is split into numerous narrow band channels of dissimilar frequencies to achieve high data rate in a multi path fading environment. And all these sub carriers are considered to be orthogonal to each other. As the number of sub carriers is increased there is no guarantee of sustained orthogonality, i.e. at some point the carriers are not
independent to each other, and hence where the orthogonality can be loosed which leads to interference and also owing to the synchronization between transmitter and receiver local oscillator, it causes interference known as Inter Carrier Interference (ICI). The systems uses MIMO-OFDM will suffer with the effects of ICI and Carrier Frequency Offset (CFO) “ε”. However these affect the power leakage in the midst of sub carriers, consequently degrading the system performance. In this paper a new approach is proposed in order to reduce the ICI caused in WiMAX and improve the system performance. In this scheme at the transmitter side the modulated data and a few predefined pilot symbols are mapped onto the non
neighboring sub carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols the frequency offset is exactly estimated by using Maximum Likelihood Estimation (MLE) and hence can be minimized. At demodulation stage the received signals are linearly combined along with their weighted
coefficients and pilot symbols, called as Pilot Aided Self Cancellation Method (PASCS). And also to realize the various wireless environments the simulations are carried out on Stanford University Interim (SUI) channels. The simulation results shows that by incorporating this method into WiMAX systems it performs better when the Line Of Sight (LOS) component is present in the transmission and also it improves the Bit Error Rate (BER) and Carrier to Interference Ratio (CIR). The CIR can be improved 20 dB. In this paper the effectiveness of PASCS scheme is compared with the Self Cancellation Method (SCM). It provides accurate estimation of frequency offset and when residual CFO is less significant the ICI can be diminished successfully.
The document summarizes routing security in ad hoc wireless networks. It discusses the characteristics of ad hoc wireless networks and routing protocols used, including proactive, reactive, and hybrid protocols. It then covers various security attacks on routing protocols like passive attacks, active attacks, impersonation attacks, and attacks using modification or fabrication. Finally, it discusses some security mechanisms and routing protocols that aim to provide security, such as SEAD, Ariadne, SAR, and SRP.
This document outlines the teaching and examination scheme for the subject of Computer Networks. It includes 3 hours of theory and 2 hours of practical classes per week. The theory exam will be worth 100 marks and include two tests worth 25 marks each. The objectives are to understand computer network concepts, topologies, devices, transmission media, and models like OSI and TCP/IP. The practical focuses on skills like network installation, configuration, and troubleshooting. Five recommended textbooks are provided for additional learning resources.
The document provides an overview of communication and network concepts. It discusses what a network is, the need for networking, and the evolution of networking from ARPANET in 1969 to the modern Internet. It also describes switching techniques, data communication terminology, transmission media including guided cables and unguided waves, common network devices, network topologies, types of networks including LANs and WANs, and protocols such as FTP and TCP/IP.
Multiplexing allows the simultaneous transmission of multiple signals across a single data link. There are several types of multiplexing employed in telecommunications, including frequency-division multiplexing (FDM), wavelength-division multiplexing (WDM), and time division multiplexing (TDM). FDM uses different carrier frequencies to transmit separate signals. WDM takes advantage of the high data capacity of fiber-optic cables. TDM divides the transmission time into time slots and allots one slot for each message. Within TDM, synchronous TDM gives each device a fixed time slot while asynchronous TDM dynamically allocates slots.
An ad hoc network is a type of wireless network that does not require a central router or base station. Nodes communicate directly with each other or through intermediate nodes in a multi-hop fashion without any fixed infrastructure. Routing and resource management are distributed. Common types include wireless mesh networks, wireless sensor networks, and hybrid wireless networks. Ad hoc networks face challenges related to medium access, routing, security, and resource constraints due to the lack of centralized control.
The document discusses optical network survivability, which refers to a network's ability to continue operating during failures. It outlines existing techniques for survivability, including predesigned protection which reserves backup resources in advance, and restoration which chooses backup resources in real-time. The document also compares approaches like shared path protection, traffic control, hybrid preplanned and real-time allocation, and dual homing. It proposes an algorithm for best-effort fast lightpath routing to improve survivability.
Iaetsd comparative study mimo ofdm, cdma-sdmaIaetsd Iaetsd
This document compares and contrasts MIMO OFDM, CDMA-SDMA, and multi-user detection techniques for wireless communication systems. It discusses how MIMO OFDM can achieve high data rates with frequency and antenna diversity. Space division multiple access (SDMA) is introduced as an application of MIMO that improves spectral efficiency by multiplexing signals based on spatial signatures. The document also examines multi-user detection methods like linear detection, minimum mean square error, and successive interference cancellation that are needed for robust SDMA performance as the number of users increases.
PERFORMANCE IMPROVEMENT OF PAPR REDUCTION FOR OFDM SIGNAL IN LTE SYSTEMijwmn
This document discusses performance improvement of peak-to-average power ratio (PAPR) reduction for orthogonal frequency division multiplexing (OFDM) signals in long-term evolution (LTE) systems. It proposes an improved amplitude clipping and filtering method for PAPR reduction that shows significant improvement over existing methods, with a slight increase in bit error rate. The document provides background on OFDM, PAPR issues in OFDM, and motivations for reducing PAPR such as improving power amplifier efficiency.
This document discusses optimization techniques for designing ultra-wideband planar monopole antennas. It presents two powerful design methodologies: size optimization using design of experiments, and topology optimization using binary particle swarm optimization. Size optimization is a systematic approach that varies geometric parameters to achieve design goals with a small number of simulations. Topology optimization determines the optimal metal distribution within the design area without a predefined shape using an automatic approach. These techniques are demonstrated by designing UWB antennas and band-notched UWB antennas, improving efficiency over trial-and-error approaches.
This document provides an introduction to the course CS144: An Introduction to Computer Networks at Stanford University. It discusses the 4-layer model of computer networks, including the application, transport, network and link layers. It explains how each layer communicates with its peer layer and how encapsulation works, with one layer serving as a payload for the layer below it. The document also provides an outline of topics to be covered in the course, including what the Internet is and a brief history of networking and the development of the Internet.
The document discusses Personal Communication Services (PCS) and provides examples of different wireless communication systems, including cellular and cordless systems. It describes key aspects of cellular systems like Advanced Mobile Phone Service (AMPS), Global System for Mobile Communications (GSM), EIA/TIA IS-136, and EIA/TIA IS-95 standards. These include multiple access techniques, frequency bands, channel structures, features supported, and mobility management protocols. PCS networks integrate these wireless systems to provide mobile communication services connected to the public switched telephone network.
This document provides an overview of key concepts in computer networks and communication. It defines what a network is, discusses the need for networking and sharing of resources, and outlines the evolution of early networks like ARPANET and NSFNET into the modern Internet. It also covers network topologies, transmission media, switching techniques, common network devices, and communication protocols.
Stoe Noll Westin Data Transmission PresentationJennifer Stoe
The document summarizes various methods of data transmission throughout history including Morse code, telegraphs, telephones, computers, and modern wireless technologies. It describes how data is encoded and transmitted through different channels like wired, wireless, satellite, and cellular networks. The key technologies discussed are analog and digital transmission, protocols, wired connections like Ethernet and USB, and wireless standards like Bluetooth, WiFi, WiMAX, and cellular networks.
This document discusses the challenges faced when using TCP in mobile ad hoc networks (MANETs). Some key challenges include: media access control issues like hidden terminals; power constraints of mobile nodes; frequent topology changes due to node mobility; multipath fading increasing the likelihood of path breaks; and misinterpreting packet losses as congestion rather than broken routes. TCP was designed for wired networks and assumes packet losses are always due to congestion, which does not hold in MANETs where losses can be from broken routes. Overall, TCP performs poorly in MANETs due to these challenges.
The document discusses computer networks and networking concepts. It defines what a network is and explains the need for networking. It describes the components of a network including nodes, servers, network interface units. It covers the evolution of networks from ARPANET to the internet. It discusses different types of networks including LAN, MAN, WAN and their characteristics. It also covers topics like communication media, switching techniques, wireless networking and networking terms.
This document provides an overview of computer networks. It defines what a network is and discusses the need for networking. It describes the key components of a network including nodes, servers, network interface units. It also covers the evolution of networks from ARPANET to the modern Internet. It defines different types of networks including LANs, MANs, and WANs. Finally, it discusses various networking topics such as transmission media, switching techniques, wireless networks and common terminology.
The document discusses free computer science eBooks and technology news that are being provided. It includes links to blogs sharing this free content and encourages clicking on advertisements to support their work. It then discusses the topics of wireless technologies and Wi-Fi networks in particular, covering introductions, architectures, elements, how they work, topologies and configurations.
What is a network?
Need for networking
Components of Network
Types of Network
Evolution of Networking
Communication media
Data Communication Terminologies
Switching Techniques
Digital and Analog Transmission
Network Topology
Network Devices
Communication Protocols
Wireless/Mobile Computing
This document provides an overview of computer networks. It discusses what a network is and the need for networking. The key components of a network are workstations/nodes, servers, and network interface units. Networks have evolved over time from early networks like ARPANET to today's internet. Various transmission media and technologies are used for data communication across networks, including cables, wireless transmission, and satellite communication. The document also covers network devices, topologies, and protocols.
A network connects two or more computers. Common network types are local area networks (LANs), which connect computers in a small area like a building, and wide area networks (WANs), which connect computers over a large geographical area through multiple LAN connections. Networks can be configured using different topologies like bus, star, or ring and use protocols like Ethernet or Token Ring to transmit data. Common network devices include hubs, switches, routers, and firewalls. Networks can be categorized based on their topology, protocols, and architecture.
A network is two or more computers connected together. The document discusses different types of networks including local area networks (LANs), wide area networks (WANs), intranets, and extranets. It also covers network topologies like bus, star, and ring as well as protocols like Ethernet and TCP/IP. Key networking hardware is described such as hubs, routers, bridges, and gateways. Communication media including twisted pair cable, coaxial cable, fiber optic cable, and wireless options are also summarized.
This document provides an overview of advanced networking concepts. It begins with learning objectives around data communication, network devices, protocols, topologies and network types. It then defines key networking components like switches, routers, and firewalls. It discusses different network topologies, media like Ethernet and wireless, and various network types including LAN, WAN, SAN and more. The document is intended to help readers understand fundamental networking concepts.
A computer network allows devices to communicate with each other over a transmission medium. There are two main types of networks: local area networks (LANs) which connect devices within a limited geographic area like an office, and wide area networks (WANs) which interconnect multiple LANs across an unlimited geographic area. Common topologies for LANs include bus, star, and ring configurations. Network devices like switches and routers allow communication within and between LANs and WANs.
This document provides an overview of implementing and evaluating wireless local area networks (WLANs). It discusses topics such as the wireless spectrum, physical impairments like noise and interference, medium access control, security, the IEEE 802.11 standard, and transport control protocols. The objectives are to demonstrate the implementation of a WLAN topology and evaluate its performance under various conditions using tools like Wireshark.
The document provides information about different types of computer network topologies. It describes bus, star, ring, mesh, tree and hybrid topologies. For each topology, it outlines the basic structure, advantages and disadvantages. Bus topology connects all nodes to a single cable. Star topology connects each node to a central hub. Ring topology connects each node in a continuous loop. Mesh topology connects each node to every other node. Tree topology connects nodes in a hierarchical manner with a root node at the top. Hybrid topologies combine two or more standard topologies.
This document summarizes a research paper that evaluates the performance of wired and wireless local area networks using simulation. It describes simulating Ethernet and IEEE 802.11 wireless LANs in OPNET with varying numbers of users. Key performance metrics for wired networks like collision count, throughput, and delay were analyzed. For wireless, metrics like data dropped, throughput, and access delay were studied. As the number of users increased, throughput decreased more for wireless than wired due to transmission limitations in wireless. The paper concludes wireless performs better than wired for small user numbers but degrades more with increasing loads.
The document discusses different techniques for multiplexing, which is the sharing of a transmission medium by multiple signals. It describes frequency division multiplexing (FDM), time division multiplexing (TDM) including synchronous and statistical TDM, wavelength division multiplexing (WDM), and code division multiplexing (CDM). TDM techniques like T-1 and ISDN use synchronous multiplexing to transmit multiple digital signals over a single circuit simultaneously.
The document discusses different types of multiplexing techniques used to share transmission mediums. It describes frequency division multiplexing which assigns different non-overlapping frequency ranges to signals transmitted simultaneously. It also describes synchronous and statistical time division multiplexing which divide transmission time among users in a continuous or variable manner. Finally, it briefly mentions wavelength division multiplexing which assigns different wavelengths to signals on fiber optics and code division multiplexing used in mobile communications.
The document discusses computer networks and networking concepts. It begins by outlining the course content, which includes network types, uses of networks, network media, threats, and cloud computing. It then defines what a computer network is and describes common networking devices like switches, routers, and firewalls. The document discusses different network types including LANs, WANs, MANs, and VPNs. It also covers topics like network protocols, wireless networks, and network media such as copper cable, fiber optic cable, and wireless.
This document provides an overview of computer networks and networking concepts. It begins by covering basic network types like LANs, WANs, and the Internet. It then discusses common networking components like switches, routers, and firewalls. Various network topologies are described along with physical network media like Ethernet cables and wireless technologies. Communication protocols and standards for networking are also outlined. The document provides a comprehensive introduction to computer networks, networking hardware and software, and fundamental networking concepts.
Andreas Schleicher presents PISA 2022 Volume III - Creative Thinking - 18 Jun...EduSkills OECD
Andreas Schleicher, Director of Education and Skills at the OECD presents at the launch of PISA 2022 Volume III - Creative Minds, Creative Schools on 18 June 2024.
How to Manage Reception Report in Odoo 17Celine George
A business may deal with both sales and purchases occasionally. They buy things from vendors and then sell them to their customers. Such dealings can be confusing at times. Because multiple clients may inquire about the same product at the same time, after purchasing those products, customers must be assigned to them. Odoo has a tool called Reception Report that can be used to complete this assignment. By enabling this, a reception report comes automatically after confirming a receipt, from which we can assign products to orders.
How to Setup Default Value for a Field in Odoo 17Celine George
In Odoo, we can set a default value for a field during the creation of a record for a model. We have many methods in odoo for setting a default value to the field.
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إضغ بين إيديكم من أقوى الملازم التي صممتها
ملزمة تشريح الجهاز الهيكلي (نظري 3)
💀💀💀💀💀💀💀💀💀💀
تتميز هذهِ الملزمة بعِدة مُميزات :
1- مُترجمة ترجمة تُناسب جميع المستويات
2- تحتوي على 78 رسم توضيحي لكل كلمة موجودة بالملزمة (لكل كلمة !!!!)
#فهم_ماكو_درخ
3- دقة الكتابة والصور عالية جداً جداً جداً
4- هُنالك بعض المعلومات تم توضيحها بشكل تفصيلي جداً (تُعتبر لدى الطالب أو الطالبة بإنها معلومات مُبهمة ومع ذلك تم توضيح هذهِ المعلومات المُبهمة بشكل تفصيلي جداً
5- الملزمة تشرح نفسها ب نفسها بس تكلك تعال اقراني
6- تحتوي الملزمة في اول سلايد على خارطة تتضمن جميع تفرُعات معلومات الجهاز الهيكلي المذكورة في هذهِ الملزمة
واخيراً هذهِ الملزمة حلالٌ عليكم وإتمنى منكم إن تدعولي بالخير والصحة والعافية فقط
كل التوفيق زملائي وزميلاتي ، زميلكم محمد الذهبي 💊💊
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THE SACRIFICE HOW PRO-PALESTINE PROTESTS STUDENTS ARE SACRIFICING TO CHANGE T...indexPub
The recent surge in pro-Palestine student activism has prompted significant responses from universities, ranging from negotiations and divestment commitments to increased transparency about investments in companies supporting the war on Gaza. This activism has led to the cessation of student encampments but also highlighted the substantial sacrifices made by students, including academic disruptions and personal risks. The primary drivers of these protests are poor university administration, lack of transparency, and inadequate communication between officials and students. This study examines the profound emotional, psychological, and professional impacts on students engaged in pro-Palestine protests, focusing on Generation Z's (Gen-Z) activism dynamics. This paper explores the significant sacrifices made by these students and even the professors supporting the pro-Palestine movement, with a focus on recent global movements. Through an in-depth analysis of printed and electronic media, the study examines the impacts of these sacrifices on the academic and personal lives of those involved. The paper highlights examples from various universities, demonstrating student activism's long-term and short-term effects, including disciplinary actions, social backlash, and career implications. The researchers also explore the broader implications of student sacrifices. The findings reveal that these sacrifices are driven by a profound commitment to justice and human rights, and are influenced by the increasing availability of information, peer interactions, and personal convictions. The study also discusses the broader implications of this activism, comparing it to historical precedents and assessing its potential to influence policy and public opinion. The emotional and psychological toll on student activists is significant, but their sense of purpose and community support mitigates some of these challenges. However, the researchers call for acknowledging the broader Impact of these sacrifices on the future global movement of FreePalestine.
Level 3 NCEA - NZ: A Nation In the Making 1872 - 1900 SML.pptHenry Hollis
The History of NZ 1870-1900.
Making of a Nation.
From the NZ Wars to Liberals,
Richard Seddon, George Grey,
Social Laboratory, New Zealand,
Confiscations, Kotahitanga, Kingitanga, Parliament, Suffrage, Repudiation, Economic Change, Agriculture, Gold Mining, Timber, Flax, Sheep, Dairying,
1. Mobile and Wireless Computing
Networking basics
Courtesey of Abdus Salam International Centre for Theoretical Physics, Trieste
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
2. Mobile and Wireless Computing
Physical Layer
This layer is concerned with the transmission of
bits.
Some of the issues handled in this layer are :
how many volts for 0, how many for 1; number of
bits per second to be transmitted; whether it is a
one-way or two-way communication etc.
Many standards have been developed, e.g., RS-
232 for serial communication lines.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
3. Mobile and Wireless Computing
Data Link Layer
This layer groups bits into frames and ensures
their correct delivery.
It adds some bits at the beginning and end of
each frame plus the checksum. Receiver of the
frame verifies the checksum and requests
retransmission if the checksum is not correct.
This layer consists of two sublayers.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
4. Mobile and Wireless Computing
Logical Link Control and Medium Access Control
The LLC defines how data is transferred over
the network medium (e.g., cables) and provides
data link service to the higher layers.
The Medium Access Control (MAC) layer defines
who can use the network medium when multiple
computers are trying to access it simultaneously.
For example, token passing or CSMA/CD for
Ethernet.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
5. Mobile and Wireless Computing
Network Layer
This layer is concerned with the transmission of
packets. It takes routing decisions, e.g., the best
path to send a packet.
The network layer may be quite complex in a
large network, e.g., the Internet.
Most protocols are connection oriented (packets
are sent when the destination accepts a
connection) or connection-less, like IP.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
6. Mobile and Wireless Computing
Transport Layer
This layer ensures reliable service and deals
with lost messages.
It breaks the messages into smaller packets,
assigns sequence number and sends them.
Reliable transport connections are built on top of
X.25 or IP.
Examples are TCP (Transfer Control Protocol),
TCP/IP, UDP etc.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
7. Mobile and Wireless Computing
Sessions Layer
Very few applications use this layer. It is mostly
an enhanced version of the transport layer.
It facilitates dialog control and synchronization.
Many network implementations do not support it.
For example, Internet suite does not support this
layer.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
8. Mobile and Wireless Computing
Presentation Layer
Very few applications use this layer. This layer is
concerned with the semantics of the bits.
It defines records and fields in them. The sender
can tell the receiver about the format.
It makes machines with different internal
representations to communicate. It is the best
layer for implementing cryptographic services.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
9. Mobile and Wireless Computing
Application Layer
This is a collection of miscellaneous protocols
for high level applications.
Typical services are electronic mail, file transfer,
connecting remote terminals etc.
FTP, telnet, HTTP, NFS etc.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
10. Mobile and Wireless Computing
Multiplexing
In a mobile and wireless network, the wireless
medium is shared by many nodes.
Hence, multiple use of a shared medium is a
major challenge in wireless networking.
Most decisions for accessing the wireless
medium is made in the MAC layer.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
11. Mobile and Wireless Computing
Multiplexing
The wireless channels can be multiplexed (used
by multiple machines) in four dimensions :
– Space (s)
– Time (t)
– Frequency (f)
– Code (c)
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
12. Mobile and Wireless Computing
Space multiplexing : Cellular Networks
Same frequency can be
reused when the base
stations are separated in
space.
The reuse of frequencies
depend on signal
propagation range.
Example : fixed frequency
assignment for reuse with
distance 2.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
13. Mobile and Wireless Computing
Frequency Division Multiplex (FDM)
The whole spectrum is
separated into smaller
frequency bands.
A band is allocated to a
channel for the whole
f
time.
This is somewhat
inflexible if the traffic is
non-uniform.
An example is radio or TV
broadcast. The bandwidth
is wasted if a station is off
the air. t
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
14. Mobile and Wireless Computing
Time Division Multiplex (TDM)
A channel gets the whole
frequency spectrum for a
certain amount of time.
Only one user for the f
medium at a time.
Usually the throughput is
high even with many
users.
However, no two users
should use the medium at
the same time. Precise
synchronization is t
needed.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
15. Mobile and Wireless Computing
An example of TDM
Ethernet uses a protocol called CSMA/CD
Carrier Sense Multiple Access with Collision
Detection
When a node wants to broadcast, it checks
whether any other node is broadcasting (senses
the carrier).
A node broadcasts when no other node is
broadcasting. Otherwise, it tries later at a
random interval.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
16. Mobile and Wireless Computing
CSMA Problems in Wireless Medium
Collision detection is easy in wired networks but
difficult in wireless medium.
With only one antenna, nodes can only listen or
send.
Full duplex radios are extremely expensive.
CSMA gives rise to hidden terminal and exposed
terminal problems.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
17. Mobile and Wireless Computing
Hidden Terminal Problem
Wireless transmission is usually short range.
Even if the medium is free near the transmitter, it
may not be free near the intended receiver.
A B C
Collision
at B
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
18. Mobile and Wireless Computing
Exposed Terminal Problem
Even if the medium is busy near the transmitter,
it may be free near the intended receiver.
A B C D
C cannot transmit because B is transmitting.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
19. Mobile and Wireless Computing
Message Loss due to Collision
Using CSMA in wireless medium results in
message loss and requires retransmission of
lost messages.
A node spends much more energy while
receiving or transmitting messages. Hence,
retransmission wastes a lot of energy.
The other alternative is to use a reservation
based TDM protocol.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
20. Mobile and Wireless Computing
Demand Assignment Multiple Access (DAMA)
In a DAMA protocol, nodes first reserve slots
which they intend to use for broadcasting.
Each round of broadcast is preceded by a
reservation round.
DAMA protocols are widely used in satellite
communication and increasingly being used in
wireless networking.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
21. Mobile and Wireless Computing
Code Division Multiplex (CDM)
Each channel uses a
unique code for c
transmitting.
All channels use the
same frequency
spectrum at the same
time. t
f
However, signal
regeneration is very
complex and requires
complex HW/SW support.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
22. Mobile and Wireless Computing
Code Division Multiplexing
CDMA has ben adopted for the 3G mobile phone
technology.
CDMA is not very suitable for ad hoc networking
as we cannot expect specialized
hardware/software support at the nodes.
TDMA and its variations are most suitable for ad
hoc networking.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)
23. Mobile and Wireless Computing
The Organization of the Course
We will mainly study routing protocols in this
course.
Routing messages is the most important issue in
any network. Conventional protocols for wired
networks do not work well for ad hoc networks.
We will study routing protocols both for ad hoc
mobile networks and mobile IP.
Institute for Computer Science, University of Freiburg
Western Australian Interactive Virtual Environments Centre (IVEC)