Optimum Power Distribution for Uplink Channel in a Cooperative Wireless CDMA Network

This paper studies power distribution in the uplink channel of a wireless CDMA network, where peer stations cooperatively relay traffic for each other, and the destination, i.e., the base station (BS), combines signals received from both the source station (SS) and the relay station (RS). Two different cooperative schemes are presented. In the first scheme, the SS transmits packets in all time slots, and two RSs forward received signals from the SS to the BS in odd and even time slots alternatively. In the second scheme, the SS transmits in the odd time slots, and a single RS receives from the SS in the odd time slots and forwards to the BS in the even time slots. Two forwarding techniques, i.e., decode-and-forward (DF) and amplify-and-forward (AF), are considered. For each of the cooperation scheme and forwarding technique combinations, an optimization problem is formulated with an objective to minimize the total transmission power subject to the average transmission rate and signal-to-interference-plus-noise ratio (SINR) requirement of the user traffic. Our results show that by appropriately selecting the RSs and forwarding techniques, cooperative communications in a CDMA network can significantly reduce the communication outage probability and save total transmission power.