Decentralized Reduced-Rank Multiuser Relaying for Cooperative Uplink CDMA Networks

We examine a cooperative uplink CDMA network where multiple sources simultaneously access the cooperative channel using different spreading codes and compete for the resources at the relays. To efficiently utilize the limited energy and bandwidth resources at the relays, we propose in this work a decentralized reduced-rank multiuser relaying (RR-MUR) where the data received at each relay is compressed into a limited number of dimensions and forwarded with optimal power allocation among the different dimensions. The proposed scheme follows upon our previous work where a centralized strategy has been proposed. Specifically, we propose the minimum mean square error principle component analysis (MMSE-PCA) approach that can be used to design the relay precoders in a decentralized manner. We show that the MMSE-PCA scheme is the optimal relay precoder design when only one relay exists in the network. Through numerical simulations, we show that the proposed scheme outperforms the Q-selection scheme, where only a selected group of sources are served by each relay.