Symbol Error Rate Analysis in Cooperative Transmission: AF Relaying Scenarios and Optimal Power Allocations

In this paper, we study three cooperative transmission schemes by use of amplify-and-forward (AF) relaying strategies. It is assumed that there is one source, one destination and several AF-relays. First, a parallel-relay strategy is considered wherein the transmitted message from the source is received by each relay independently. Th en, the relay retransmit the message by use of AF relaying to the destination. Next, we consider the case where the message is being sent through the whole relays sequentially to the destination. Finally, we consider a general case, where we have multi-branches such that on each branch, there exist several relays sequentially cooperating to transmit the message to the destination. For each cooperative transmission scheme, we are looking for minimizing the symbol-error rate (SER) subject to sum-relay power (SRP). Hence, for each cooperative transmission schemes, we analyze the optimization problem and analytically derive the optimal power allocation at the relays to minimize the SER. Finally, we numerically show that when the SRP is low, we can optimize the number of active relays. Th at is, at low SRP increasing number of relays does not monotonically decrease the SER. On the other hand, at high SRP, employing more number of relays is more beneficial than allocating more power to a limited number of relays.