Resource allocation and scheduling schemes for WCDMA downlinks

We analytically derive the appropriate rates and optimum transmit power levels that need to be allocated for high data rate services in downlinks of a WCDMA system with a time-slotted structure consisting of variable-length time slots and frames. It is shown that the average throughput decreases by 90% and average delay increases ten-fold in a severe shadowing environment (σ=8 dB) compared to no shadowing. However, by introducing an outage probability of 0.05 as opposed to serving all the mobiles, the average system throughput can be increased six-fold and the average delay can be reduced by about 80% in such channel conditions. We analyze the trade-off between the throughput and delay performance of the system and the operating point of the outage. We consider two modes of transmission: a uni-access mode in which only one user is allowed to access the channel at a time, and a multi-access mode in which multiple users are allowed. We compare the performance of four scheduling schemes such as round-robin and fastest-first schemes that are appropriate for the uni-access mode, and equal-rate and equal-weight schemes that are for multi-access mode transmission. Simulation results show that the system employing the uni-access mode schemes performs better than one with multi-access mode schemes in terms of the average delay, and performs worse in terms of fair allocation of data rates