Throughput maximization in CDMA uplinks using adaptive spreading and power control

We formulate the throughput maximization problem for CDMA uplinks as an optimization problem in terms of the spreading gains (equivalently transmission bit rates) and transmit powers of the users, and solve it using a nonlinear programming approach. In nearly all cases, the solution is to give a rate of W to the highest-path-gain user in each cell and virtually nothing to the others. This approach maximizes total throughput at the expense of fairness. We then extend the notion of one-user-at-a-time by assuming all users get served on a time-sharing basis. The result is a considerable gain in fairness, with a modest loss in total throughput. The average user throughput (per timeslot) now ranges from W near the base to ~0.4 W near the cell boundaries, and the average cell throughput drops by 33%. Also, compared to rate-control-only (no power control), we show that optional power allocation considerably improves both average cell throughput and transmit power usage at the terminals