Optimum Power Allocation in Cooperative Networks

Cooperation among network users provides transmit diversity in cases where wireless transmitters, due to size and power limitation, cannot support multiple antennas. We consider cooperation between M users, where each user achieves space-time diversity by using other users’ antennas as relays. Cooperation among users has been shown to achieve impressive gains as compared to a non-cooperative system while maintaining the same information rate, transmit power, and bandwidth [1], [2], [3], [4]. This paper formulates an optimum power allocation scheme appropriate for a cooperative network using transparent relaying. It will be shown that the proposed allocation scheme significantly outperforms the equal power allocation scheme, e.g., by up to 7 dB at a bit error rate of 10−3. The results presented here may serve as bounds for the performance assessment of sub-optimal (but practical) algorithms.