Power and Weight Distribution Design Criteria for Cooperative Diversity Channels

The paper considers the single relay orthogonal cooperative diversity decode and forward scenario as a block fading channel model. A closed form expression for the pairwise error probability is derived which leads to design criteria for full diversity and coding gain. Furthermore, the power distribution between the source and relay units is introduced as a design parameter. Fixed power distribution allocation has the potential of improving performance with no increase in the system complexity. Several techniques for improving the coding gain are given based on the power distribution during the cooperation phase of the transmission. As an example, the (1,7/5) convolutional code was considered. Simulation results for this example show that a 1 dB performance gain can be achieved by modifying the power distribution of the source and relay. For the code considered, the equal power allocation method most commonly used gave the worst performance. The best performance was achieved when the source was silent during the cooperation phase. This observation simplifies protocol design.