Upper and lower bound on signal-to-noise ratio gains for cooperative relay networks

Cooperative networking as a means of creating spatial diversity is used in order to mitigate the adverse effect of fading in a wireless channel and increase reliability of communications. We investigate signal-to-noise ratio (SNR) gain in wireless cooperative networks. We show that the differential SNR gain in the high data rate regime, which we refer to as SNR gain exponent ζ∞, is independent of the relaying strategy and only depends on the number of transmission phases used for communication. Furthermore, a straight-line upper and lower bound is derived based on geometric considerations. It is shown that the approximation error of the upper bound with respect to the exact SNR gain tends to zero for R → ∞. For the lower bound, the approximation error tends asymptotically to a constant factor δ for R → ∞. Both bounds are the best possible straight-line bounds with respect to absolute error.