Outage Probability Analysis of Cooperative Communications over Asymmetric Fading Channel

Abstract

Cooperative relaying is a promising technology for future wireless communications. It is mostly applicable to the small dimensional and limited power devices, which cannot use the conventional multiple input multiple output (MIMO) technology to obtain the advantages of MIMO. It can benefit most of the leverages of MIMO such as array gain, diversity gain, spatial multiplexing gain and interference reduction without using the conventional MIMO technology Liu et al. (2009); Laneman et al. (2004); Paulraj et al. (2004). Since the original signal is forwarded by relay nodes, the performance of the relaying network depends on the relaying process of the relay nodes and fading characteristic of their links. Classically, relay network has three links source-destination (S-D), source-relay (S-R) and relay-destination (R-D) and the relaying processes are classified as amplify-and-forward (AF), decode-andforward (DF) and compress-and-forward (CF) Krikidis & Thompson (2008); Nosratinia et al. (2004). The diversity of the relaying network depends on the degree of freedom of the network. For repetition-based relaying, the degree of freedom increases with the number of relay nodes when the system is an half duplex and use a time division duplex Zhao et al. (2005, 2007). However, it suffers spectral efficiency with increase in the number of relay nodes in the network. On the other hand, opportunistic relaying uses only one relay node to forward source data to the destination and its degree of freedom is two. It has higher spectral efficiency and better outage performance than that of repetition-based relaying. The performance of the relaying network depends on the fading characteristic of S-D, S-R and R-D links, i.e. diversity of the relaying networks depends on the location of the relay nodes and its surrounding environment. In practice, cooperative nodes are usually located in different geographical locations and at different distances with respect to S and D. The signal in one link may be in line of sight (LOS) situation and other links may be in NLOS situation. For example, fixed relay nodes are used for forwarding source’s data to a specific region (e.g. tunnel, behind of the building) and they often use directional antennas, so the RD link is likely to be a LOS situation. However, we cannot assume such scenario for other links specially when D is in a shadowing region with respect to S. In other words, one link may undergo Rician fading channel and others links may undergo Rayleigh fading channel. Such scenario is refereed to as asymmetric fading channel. This channel scenario can also be