Joint Resource Allocation and Interference Mitigation Techniques for Cooperative Wireless Networks

Introduction

Multiple-antenna wireless communication systems can exploit the spatial diversity in wireless channels, mitigating the effects of fading and enhancing their performance and capacity. Due to the size and cost of mobile terminals, it is considered impractical to equip them with multiple antennas. However, spatial diversity gains can be obtained when single-antenna terminals establish a distributed antenna array via cooperation (Sendonaris, Erkip, & Aazhang, 2003; Laneman & Wornell, 2004). The use of cooperative strategies can lead to several types of gains (Dohler & Li, 2010; Pabst, et al., 2004), namely, pathloss, diversity, and multiplexing gains. Pathloss gains allow a significant reduction in the transmitted power for an equivalent performance, can increase the coverage (Ettefagh, Kuhn, Hammerstrom, & Wittneben, 2006) and enhance the interference suppression capability (Dohler & Li, 2010; Pabst, et al., 2004). The diversity gains improve the performance of the wireless system with respect to the probability of error because the transmission of multiple copies of the signals reduce the probability that the message will not be received correctly. The multiplexing gains (So & Liang, 2005), which correspond to the additional number of bits that the system can transmit as compared to a single-antenna link, can be obtained when a designer can use relays to form independent channels and increase the rate of communication.

Despite the many advantages in terms of gains as previously outlined, cooperative communications also entail some disadvantages such as signalling overheads (Pabst, et al., 2004), more computationally complex scheduling algorithms (Dohler & Li, 2010) and increased latency (Lu, Steenkiste, & Chen, 2007). For this reason, it is important to weigh the pros and cons of cooperative techniques prior to their adoption and consider the practical scenarios of interest (Kyritsi, et al., 2007). Motivated by their performance and diversity gains, cooperative techniques are now being considered for the next generation of mobile networks (Scaglione, Goeckel, & Laneman, 2006; Fan & Thompson, 2007; Peters, Panah, Truong, & Heath, 2009). In cooperative systems, terminals or users relay signals to each other in order to propagate redundant copies of the same signals to the destination user or terminal. To this end, the designer must resort to a cooperation protocol such as Amplify-and-Forward (AF) (Laneman & Wornell, 2004), Decode-and-Forward (DF) (Laneman & Wornell, 2004; Huang, Hong, & Kuo, 2007), and Compress-and-Forward (CF) (Kramer, Gastpar, & Gupta, 2005).

In order to obtain the benefits of cooperative techniques, designers must address a number of problems that are encountered in cooperative wireless systems. These problems include physical-layer strategies such as synchronization, interference mitigation, and parameter estimation. However, designers also have to consider a number of associated problems that belong to higher protocol layers and include the allocation of resources such as power, relays and rate. These tasks present an opportunity to perform cross-layer design and to obtain very significant gains in performance and capacity for cooperative wireless networks. This chapter is concerned with cross-layer design techniques for cooperative wireless networks and investigates the benefits of approaches that jointly mitigate interference and perform resource allocation.