ABSTRACT
Cooperative diversity in both cellular and ad hoc networks has been the subject of great research interest in the past years. This method makes use of available mobile terminals as relays that cooperate together to form a virtual antenna array. In this chapter, we consider an intuitive measure of diversity gains achievable in such networks, which is defined as the number of independent fading channels that can be averaged over to detect symbols. First, geometry-based channel models are
proposed to describe the topology of a generalized distributed antenna system with cooperative users (GDAS-CU). The system architecture is comprised of M largely separated access points (APs) at one side of the link, and N geographically closed user terminals (UTs) at the other side. The UTs are operating in cooperative mode to enhance the system performance, where an idealized message sharing among the UTs is assumed. The mean cross-correlation coefficients (MCCCs) of signals received from noncollocated APs and UTs is calculated based on the network topology and the correlation models derived from the empirical data. The analysis is also extendable to more general scenarios where the APs are placed in a clustered form. Subsequently, a generalized pathloss model based on stochastic ray tracing (SRT) theory is proposed where propagation environments are suitable to be described by stochastic structures rather than being deterministically characterized. The derived model consists of two dominant terms: a logarithmic function and a power function of the distance between the transmitter and the receiver. It is shown that the proposed pathloss law which is generalized from several physically inspired SRT models, exhibits better agreement with the experimental data as compared to other existing models. Armed with the cross-correlation and pathloss model preliminaries, we investigate the diversity gains obtainable from a GDAS-CU network, which would provide critical insight into the degree of possible performance improvementwhen combining multiple copies of the received signal in such systems.
