Optimal Power Allocation for Pilot Channel Assisted Multi-User CDMA

This paper examines the performance of a conventional direct sequence-code division multiple access (DS-CDMA) receiver, a two-stage multi-user receiver that does not employ channel fading estimation in the interference cancellation process and a two-stage multi-user receiver that uses the channel fading estimation when cancelling the multiple access interference. The optimal power allocation to the pilot and data channels is also determined for different numbers of users, processing gains and signal-to-noise ratios by finding out the power ratio of the data bit to the pilot bit that minimizes the probability of error. It has been observed that the optimal power allocation to the pilot signal varies from 20 to 30% of the total power depending on the number of users, processing gain and signal-to-noise ratio. Increasing the power allocated to the pilot requires a corresponding decrease in power to the data channel. The bit error rate degradation caused by allocating more power to the pilot outweighs the benefits obtained by more accurate channel estimates when we attempt to allocate more than 30% of the power to the pilot stream. Simulations have also shown the two-stage multi-user receiver that employs the channel estimates for interference cancellation consistently outperforms the other two receivers.