54 research outputs found
Truncated-ARQ aided adaptive network coding for cooperative two-way relaying networks: cross-layer design and analysis
Network Coding (NC) constitutes a promising technique of improving the throughput of relay-aided networks. In this context, we propose a cross-layer design for both amplifyand- forward (AF-) and decode-and-forward two-way relaying (DF-TWR) based on the NC technique invoked for improving the achievable throughput under specific Quality of Service (QoS) requirements, such as the maximum affordable delay and error rate.We intrinsically amalgamate adaptive Analog Network Coding (ANC) and Network Coded Modulation (NCM) with truncated Automatic Repeat reQuest (ARQ) operating at the different OSI layers. At the data-link layer, we design a pair of improved NC-based ARQ strategies based on the Stop-andwait and the Selective-repeat ARQ protocols. At the physical layer, adaptive ANC/NCM are invoked based on our approximate packet error ratio (PER). We demonstrate that the adaptive ANC design can be readily amalgamated with the proposed protocols. However, adaptive NC-QAM suffers from an SNR-loss, when the transmit rates of the pair of downlink (DL) channels spanning from the relay to the pair of destinations are different. Therefore we develop a novel transmission strategy for jointly selecting the optimal constellation sizes for both of the relay-to-destination links that have to be adapted to both pair of channel conditions. Finally, we analyze the attainable throughput, demonstrating that our truncated ARQ-aided adaptive ANC/NCM schemes attain considerable throughput gains over the schemes dispensing with ARQ, whilst our proposed scheme is capable of supporting bidirectional NC scenarios
Cooperative diversity techniques for future wireless communications systems.
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.Multiple-input multiple-output (MIMO) systems have been extensively studied in the past
decade. The attractiveness of MIMO systems is due to the fact that they drastically reduce
the deleterious e ects of multipath fading leading to high system capacity and low error rates.
In situations where wireless devices are restrained by their size and hardware complexity, such
as mobile phones, transmit diversity is not achievable. A new paradigm called cooperative
communication is a viable solution. In a cooperative scenario, a single-antenna device is
assisted by another single-antenna device to relay its message to the destination or base
station. This creates a virtual multiple-input multiple-output (MIMO) system.
There exist two cooperative strategies: amplify-and-forward (AF) and decode-and-forward
(DF). In the former, the relay ampli es the noisy signal received from the source before forwarding
it to the destination. No form of demodulation is required. In the latter, the relay
rst decodes the source signal before transmitting an estimate to the destination. In this
work, focus is on the DF method. A drawback of an uncoded DF cooperative strategy is
error propagation at the relay. To avoid error propagation in DF, various relay selection
schemes can be used. Coded cooperation can also be used to avoid error propagation at
the relay. Various error correcting codes such as convolutional codes or turbo codes can
be used in a cooperative scenario. The rst part of this work studies a variation of the
turbo codes in cooperative diversity, that further reduces error propagation at the relay,
hence lowering the end-to-end error rate. The union bounds on the bit-error rate (BER) of
the proposed scheme are derived using the pairwise error probability via the transfer bounds
and limit-before-average techniques. In addition, the outage analysis of the proposed scheme
is presented. Simulation results of the bit error and outage probabilities are presented to
corroborate the analytical work. In the case of outage probability, the computer simulation
results are in good agreement with the the analytical framework presented in this chapter.
Recently, most studies have focused on cross-layer design of cooperative diversity at the
physical layer and truncated automatic-repeat request (ARQ) at the data-link layer using the
system throughput as the performance metric. Various throughput optimization strategies
have been investigated. In this work, a cross-relay selection approach that maximizes the
system throughput is presented. The cooperative network is comprised of a set of relays and
the reliable relay(s) that maximize the throughput at the data-link layer are selected to assist
the source. It can be shown through simulation that this novel scheme outperforms from
a throughput point of view, a system throughput where the all the reliable relays always
participate in forwarding the source packet.
A power optimization of the best relay uncoded DF cooperative diversity is investigated.
This optimization aims at maximizing the system throughput. Because of the non-concavity
and non-convexity of the throughput expression, it is intractable to derive a closed-form
expression of the optimal power through the system throughput. However, this can be done
via the symbol-error rate (SER) optimization, since it is shown that minimizing the SER of
the cooperative system is equivalent to maximizing the system throughput. The SER of the
retransmission scheme at high signal-to-noise ratio (SNR) was obtained and it was noted that
the derived SER is in perfect agreement with the simulated SER at high SNR. Moreover, the
optimal power allocation obtained under a general optimization problem, yields a throughput
performance that is superior to non-optimized power values from moderate to high SNRs.
The last part of the work considers the throughput maximization of the multi-relay adaptive
DF over independent and non-identically distributed (i.n.i.d.) Rayleigh fading channels,
that integrates ARQ at the link layer. The aim of this chapter is to maximize the system
throughput via power optimization and it is shown that this can be done by minimizing the
SER of the retransmission. Firstly, the closed-form expressions for the exact SER of the
multi-relay adaptive DF are derived as well as their corresponding asymptotic bounds. Results
showed that the optimal power distribution yields maximum throughput. Furthermore,
the power allocated at a relay is greatly dependent of its location relative to the source and
destination
Queueing analysis for cross-layer design with adaptive modulation and coding
PhDWith the development of wireless networks, Quality of Service (QoS) has become one of the most important mechanisms to improve the system performance such as loss, delay and throughput. Cross-layer design is seen as one of the main approaches to achieve QoS provisioned services in contrast to the well-adopted TCP/IP network model. This thesis focuses on the cross-layer design incorporating queueing effects and adaptive modulation and coding (AMC), which operates at both the data-link layer and the physical layer, to obtain the performance analyses on loss, delay and throughput using the matrix geometric method. More specifically, this thesis explores the potential to extend the cross-layer analysis, at the data-link and the physical layer respectively.
At the data-link layer, since the traffic types such as voice, video and data are proven to be bursty, and the well-adopted Poisson arrivals fail to capture the burstiness of such traffic types, the bursty traffic models including ON-OFF and aggregated ON-OFF arrivals are introduced in the cross-layer analysis. This thesis investigates the impact of traffic models on performance analysis, identifying the importance of choosing the proper traffic model for cross-layer analysis.
At the physical layer, IEEE 802.11ac standard is adopted for the cross-layer analysis. In order to meet the specifications of 802.11ac with higher-order Modulation and Coding Schemes (MCS), wider channel bandwidth and more spatial streams, the Signal-to-Noise Ratio (SNR) thresholds are re-determined for the AMC; in addition, a single user (SU) multiple in multiple out (MIMO) spatial multiplexing system with zero-forcing (ZF) detector is adopted for the cross-layer analysis. Furthermore, this thesis explores the impact of antenna correlations on the system performance.
All of the work done in this thesis aims at obtaining more practical performance analysis on the cross-layer design incorporating queueing effects and AMC. The proposed cross-layer analysis is quite general, so that it’s ready to be applied to any QoS provisioned networks
Cooperative Diversity and Partner Selection in Wireless Networks
Next generation wireless communication systems are expected to provide a variety
of services including voice, data and video. The rapidly growing demand for these services
needs high data rate wireless communication systems with reliability and high user
capacity. Recently, it has been shown that reliability and achievable data rate of wireless communication systems increases dramatically by employing multiple transmit and receive antennas. Transmit diversity is a powerful technique for combating multipath
fading in wireless communications. However, employing multiple antennas in a mobile
terminal to achieve the transmit diversity in the uplink is not feasible due to the limited
size of the mobile unit.
In order to overcome this problem, a new mode of transmit diversity called cooperative
diversity (CD) based on user cooperation, was proposed very recently. By user cooperation, it is meant that the sender transmits to the destination and copies to other users, called partners, for relaying to the destination. The antennas of the sender and the partners together form a multiple antenna situation. CD systems are immuned not only against small scale channel fading but also against large scale channel fading. On the other hand, CD systems are more sensitive to interuser (between sender and partner) transmission errors and user mobility.
In this dissertation, we propose a bandwidth and power efficient CD system which could be accommodated with minimal modifications in the currently available direct or
point-to-point communication systems. The proposed CD system is based on quadrature
signaling (QS). With quadrature signaling, both sender’s and partners’ information
symbols are transmitted simultaneously in his/her multiple access channels. It also reduces the synchronization as well as the interference problems that occur in the schemes reported in the literature.
The performance of the proposed QS-CD system is analyzed at different layers. First, we study the bit error probability (BEP) of the QS-CD system for both fixed and adaptive
relaying at the partner. It is shown from the BEP performance that the QS-CD system can
achieve diversity order of two. Then, a cross-layer communication system is developed
by combing the proposed QS-CD system at the physical layer and the truncated stop-and-
wait automatic repeat request (ARQ) at the data link layer. The performance of the cross-layer system is analyzed and compared with existing schemes in the literature
for performance metrics at the data link layer and upper layers, i.e., frame error rate, packet loss rate, average packet delay, throughput, etc. In addition, the studies show that the proposed QS-CD-ARQ system outperforms existing schemes when it has a good partner. In this respect, the proposed system is fully utilizing the communication channel and less complex in terms of implementation when compared with the existing systems.
Since the partner selection gives significant impact on the performance of the CD systems, partner selection algorithms (PSAs) are extensively analyzed for both static and
mobile user network. In this case, each individual user would like to take advantage
of cooperation by choosing a suitable partner. The objective of an individual user may conflict with the objective of the network. In this regard, we would like to introduce a PSA which tries to balance both users and network objectives by taking user mobility into consideration. The proposed PSA referred to as worst link first (WLF), to choose the best partner in cooperative communication systems. The WLF algorithm gives priority to the worst link user to choose its partner and to maximize the energy gain of the radio cell. It is easy to implement not only in centralized networks but also in distributed networks with or without the global knowledge of users in the network. The proposed WLF matching algorithm, being less complex than the optimal maximum weighted (MW) matching and the heuristic based Greedy matching algorithms, yields performance characteristics close to those of MW matching algorithm and better than the Greedy matching algorithm in both static and mobile user networks. Furthermore, the proposed matching algorithm provides around 10dB energy gain with optimal power allocation over a non-cooperative system which is equivalent to prolonging the cell phone battery recharge time by about ten times
Cooperative Diversity and Partner Selection in Wireless Networks
Next generation wireless communication systems are expected to provide a variety
of services including voice, data and video. The rapidly growing demand for these services
needs high data rate wireless communication systems with reliability and high user
capacity. Recently, it has been shown that reliability and achievable data rate of wireless communication systems increases dramatically by employing multiple transmit and receive antennas. Transmit diversity is a powerful technique for combating multipath
fading in wireless communications. However, employing multiple antennas in a mobile
terminal to achieve the transmit diversity in the uplink is not feasible due to the limited
size of the mobile unit.
In order to overcome this problem, a new mode of transmit diversity called cooperative
diversity (CD) based on user cooperation, was proposed very recently. By user cooperation, it is meant that the sender transmits to the destination and copies to other users, called partners, for relaying to the destination. The antennas of the sender and the partners together form a multiple antenna situation. CD systems are immuned not only against small scale channel fading but also against large scale channel fading. On the other hand, CD systems are more sensitive to interuser (between sender and partner) transmission errors and user mobility.
In this dissertation, we propose a bandwidth and power efficient CD system which could be accommodated with minimal modifications in the currently available direct or
point-to-point communication systems. The proposed CD system is based on quadrature
signaling (QS). With quadrature signaling, both sender’s and partners’ information
symbols are transmitted simultaneously in his/her multiple access channels. It also reduces the synchronization as well as the interference problems that occur in the schemes reported in the literature.
The performance of the proposed QS-CD system is analyzed at different layers. First, we study the bit error probability (BEP) of the QS-CD system for both fixed and adaptive
relaying at the partner. It is shown from the BEP performance that the QS-CD system can
achieve diversity order of two. Then, a cross-layer communication system is developed
by combing the proposed QS-CD system at the physical layer and the truncated stop-and-
wait automatic repeat request (ARQ) at the data link layer. The performance of the cross-layer system is analyzed and compared with existing schemes in the literature
for performance metrics at the data link layer and upper layers, i.e., frame error rate, packet loss rate, average packet delay, throughput, etc. In addition, the studies show that the proposed QS-CD-ARQ system outperforms existing schemes when it has a good partner. In this respect, the proposed system is fully utilizing the communication channel and less complex in terms of implementation when compared with the existing systems.
Since the partner selection gives significant impact on the performance of the CD systems, partner selection algorithms (PSAs) are extensively analyzed for both static and
mobile user network. In this case, each individual user would like to take advantage
of cooperation by choosing a suitable partner. The objective of an individual user may conflict with the objective of the network. In this regard, we would like to introduce a PSA which tries to balance both users and network objectives by taking user mobility into consideration. The proposed PSA referred to as worst link first (WLF), to choose the best partner in cooperative communication systems. The WLF algorithm gives priority to the worst link user to choose its partner and to maximize the energy gain of the radio cell. It is easy to implement not only in centralized networks but also in distributed networks with or without the global knowledge of users in the network. The proposed WLF matching algorithm, being less complex than the optimal maximum weighted (MW) matching and the heuristic based Greedy matching algorithms, yields performance characteristics close to those of MW matching algorithm and better than the Greedy matching algorithm in both static and mobile user networks. Furthermore, the proposed matching algorithm provides around 10dB energy gain with optimal power allocation over a non-cooperative system which is equivalent to prolonging the cell phone battery recharge time by about ten times
Cross-layer design for the transmission of multimedia traffic over fading channels.
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.Providing guarantees in the Quality of Service (QoS) has become essential to the
transmission of multimedia traffic over wireless links with fading channels. However this
poses significant challenges due to the variable nature of such channels and the diverse QoS
requirements of different applications including voice, video and data. The benefits of
dynamic adaptation to system and channel conditions have been accepted, but the true
potential of optimized adaptation is lost if the layers operate independently, ignoring possible
interdependencies between them. Cross-layer design mechanisms exploit such
interdependencies to provide QoS guarantees for the transmission of multimedia traffic over
fading channels.
Channel adaptive M-QAM schemes are examples of some of the earliest works in the area of
cross-layer design. However, many of the original schemes use the assumption that
thresholds designed for AWGN channels can be directly applied to slow-fading channels.
The thresholds are calculated with a commonly used approximation bit error rate (BER)
expression and the first objective of the thesis was to study the accuracy of this commonly
used expression in fading channels. It is shown that that the inaccuracy of the expression
makes it unsuitable for use in the calculation of the threshold points for an adaptive M-QAM
system over fading channels. An alternative BER expression is then derived which is shown
to be far more accurate than the previous one. The improved accuracy is verified through
simulations of the system over Nakagami-m fading channels.
Many of the cross-layer adaptation mechanisms that address the QoS provisioning problem
only use the lower layers (physical and data link) and few explore the possibility of using
higher layers. As a result, restrictions are placed on the system which introduces functional
limitations such as the inability to insert more than one class of traffic in a physical layer
frame. The second objective in this thesis was to design a physical and application layer
cross-layer adaptation mechanism which overcomes this limitation. The performance results
of the scheme in both AWGN and fading channels show that the cross-layer mechanism can
be efficiently utilized for the purposes of providing error rate QoS guarantees for multimedia
traffic transmissions over wireless links
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