On the performance of multistage cooperative networks

We propose a decode-and-forward (DF) multistage cooperation protocol wherein the transmission between source and destination takes place in T ≥ 2 equal duration and orthogonal time phases with the help of relays. In the first time phase, the source broadcasts its message which is received by all potential relays. During subsequent time phases, the relays that have successfully decoded the message using information from all previous transmitting relays, transmit a space-time code for the source´s message. The non-decoding relays keep accumulating information and transmit in the later stages when they are able to decode the message. This process continues for T cooperation stages. We develop an analytical expression for end-to-end outage probability which is valid for any number of stages and relays. We consider a relay placement scenario where relays are placed at equal intervals along the straight line between source and the destination. We investigate an interesting tradeoff between an increased SNR and decreased spectral efficiency as the number of cooperation stages is increased. It is also observed that the largest multistage cooperation gain is obtained in the low and moderate SNR regime.