Performance Analysis of Amplify-and-Forward Wireless Relay Networks

Abstract

Wireless relay technology plays an important role in the next-generation mobile and wireless networks. It has been proposed as a cost effective solution to addressing a growing demand for high data rates and low power consumption. In the relay communication model, a source communicates to a destination through a wireless node(s) called a relay. There are two main relaying techniques: Decode-and-Forward (DF) and Amplify-and-Forward (AF). AF is the focus of this thesis. The AF relay networks provide considerable performance improvement in link reliability, Spectral Efficiency (SE), Energy Efficiency (EE) and Bit Error Rate (BER) performance. They also offer a low-complexity solution for practical relay networks that have critical energy constraints, as they enable the received signal to be amplified without the decoding process at the relays. This thesis proposes new methods of reducing the energy consumption and evaluating the error performance of AF relay networks, when the relay is either one-way (unidirectional) or two-way (bidirectional). The analysis is commenced by formulating the actual Signals-to-Noise Ratio (SNR) level, which corresponds to a low SNR level, in order to calculate the Exact Bit Error Rate (EBER) performance. Then, the approximated SNR, which refers to a high SNR level, is expressed and adopted to evaluate the Asymptotic Bit Error Rate (ABER). Another SNR level is presented in this work and defined as an optimal SNR level, which is obtained by optimal balancing of the SE and EE. The optimal SNR level allows evaluation of the ABER and the EBER of AF relay networks under optimal SNR conditions. Accordingly, a unifying BER evaluation at low, high, and optimal levels of AF relay networks is provided in this study. This thesis focuses on a high SNR level to derive an effective method for evaluating the ABER and EBER, whether in optimal or sub-optimal AF relay networks. The effectiveness of such a BER evaluation method is demonstrated by enhancing the ABER of AF relay networks at all SNR levels (i.e., low, high, optimal SNR levels). This is shown when disparity between the ABER and the EBER at a low SNR level is reduced, and this helps to calculate the accurate BER of AF relay networks under any SNR levels using either the ABER or EBER. The proposed methods are examined under different channels environments, as in practice the channel of each hop of an AF relay network can be located in a different environment. When both hops are located in the same environment, the fading channels of the hops are equal, while for different environments, the fading channels of the hops are different. Furthermore, relay location is also investigated for the aforementioned ABER and EBER, and a new method for determining the relationship between the EE and EBER with relay location is derived.