Cooperative multiple access transmission using precoding vectors

We address in this paper the problem of transmitting data to multiple mobile stations (MS) using a decode-and-forward strategy. The links between the base station and relays are considered ideal and we study the downlink between relays and mobile stations. We propose a method to optimize the precoding vector in relays to cancel out multiple access interference and to maximize the signal to noise ratio at the mobile stations. Simulation results show that the maximum diversity advantage can be obtained, which is the product of the number of antennas at each relay by the number of relays minus the total number of system constraints. Furthermore, using Lagrange multipliers to optimize precoding vectors, we obtain a flexibility that enables us to consider different cases for signal to noise ratio at mobile stations.