Power Allocation for Wireless Communications Using Variable Time-Fraction Collaboration

In order to increase spatial diversity, collaborative protocols have recently been investigated. This allows nodes not equipped with multiple transmit antennas the ability to achieve high levels of diversity. In previous works, the authors proposed and analyzed a collaborative protocol using variable time-fraction. In this paper, the scheme is further expanded to include the case where the transmitting nodes have access to the channel state information (CSIT). The outage probability of such a scenario is obtained. In order to exploit the CSIT, an optimal Power Allocation Algorithm (OPAA) is proposed. Furthermore, we present a simpler, more robust suboptimal PAA. An upper bound on the Frame Error Rate is obtained and the different PAAs are analyzed. The OPAA shows a gain of 3 dB compared to a non CSIT scheme. The results also show the advantages of using PAA with a variable time-fraction for any relay location.