Bounds on ergodic capacity of multirelay cooperative links with channel state information

Cooperation among users of wireless networks has been lately presented as a suitable technique to obtain reliable communications and capacity gains over fading environments. This paper studies the impact that mutual relaying has over the ergodic capacity of wireless networks when full channel state information (CSI) is available at both receiver and transmitter side, and at the relay nodes. Upper and lower bounds are derived for the ergodic capacity of multiple relay, half-duplex, decode-and-forward Gaussian channels with CSI, assuming Rayleigh flat fading and random relay positions, and a short-term power constraint. Both bounds show spectral efficiency gains growing with the logarithm of the total number of network users, and better performance of cooperative links in the low SNR regime. Likewise, it is shown that the proposed bounds approach the ergodic capacity as SNR diminishes