Signal-to-noise ratio gains for cooperative relaying strategies

We study signal-to-noise ratio (SNR) gains for two different cooperation strategies that are applied to networks consisting of one source, one destination, and one or two relays, respectively. The first strategy is called orthogonal decode-and-forward where all transmit terminals transmit interference free in orthogonal time slots. The second strategy is called nonorthogonal decode-and-forward where all relays transmit simultaneously by applying space-time block coding. We demonstrate that the SNR gain ¿_¿ is proportional to K+1¿(1/p_out ^K) with K representing the number of relays. We further define the SNR gain exponent as a new criterion to evaluate the asymptotic behavior of SNR gain for high-rate regimes. It will be demonstrated that the SNR gain exponent only depends on the number of transmission phases.