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

Optimum Design of Spectral Efficient Green Wireless Communications

This dissertation focuses on the optimum design of spectral efficient green wireless communications. Energy efficiency (EE), which is defined as the inverse of average energy required to successfully deliver one information bit from a source to its destination, and spectral efficiency (SE), which is defined as the average data rate per unit bandwidth, are two fundamental performance metrics of wireless communication systems. We study the optimum designs of a wide range of practical wireless communication systems that can either maximize EE, or SE, or achieve a balanced tradeoff between the two metrics. There are three objectives in this dissertation. First, an accurate frame error rate (FER) expression is developed for practical coded wireless communication systems operating in quasi-static Rayleigh fading channels. The new FER expression enables the accurate modeling of EE and SE for various wireless communication systems. Second, the optimum designs of automatic repeat request (ARQ) and hybrid ARQ (HARQ) systems are performed to by using the EE and SE as design metrics. Specifically, a new metric of normalized EE, which is defined as the EE normalized by the SE, is proposed to achieve a balanced tradeoff between the EE and SE. Third, a robust frequency-domain on-off accumulative transmission (OOAT) scheme has been developed to achieve collision-tolerant media access control (CT-MAC) in a wireless network. The proposed frequency domain OOAT scheme can improve the SE and EE by allowing multiple users to transmit simultaneously over the same frequency bands, and the signal collisions at the receiver can be resolved by using signal processing techniques in the physical layer

Some fundamental issues in receiver design and performance analysis for wireless communication

Ph.DDOCTOR OF PHILOSOPH