Distributed space-time coding for multihop networks

Cooperation among mobile users in a wireless network can be exploited to induce diversity and/or rate gain, using distributed space-time coding. In this work we consider a distributed block Alamouti scheme, valid for frequency selective channels, where we take explicitly into account the errors in the source-relay link and we derive a closed form expression for the bit error rate in the simple case of BPSK transmission. Building on such derivations, we show how to allocate the power among source and relay terminals in order to minimize the average bit error rate. Since cooperation inevitably requires a proper allocation of resources between source and relay nodes, we show the final balance in terms of rate and diversity gain, incorporating the rate loss due to the exchange of information between source and relays.