Optimum Resource Allocation for Multiple Access Fading Channels

We obtain the (Shannon) optimal power and rate allocation strategies for the uplink on single cell systems. For an N user system, we show that successive decoding which is independent of channel state is optimal in the Shannon sense. Using this result, we frame the resource allocation problem as a simple convex problem in N variables. We divide the vectors space formed by all possible channel states (RN+ ) into regions, and obtain expressions for the optimum power and rate allocation strategies in each region as explicit functions of the channel state. This solution for User i is found to depend only on his channel and the channels of the users decoded before and after (termed Users i 1 and i + 1 respectively), and is shown to be an increasing (waterfilling) in User i’s channel gain and decreasing in the channel gains of Users i 1 and i+ 1.