Resource allocation and scheduling schemes for WCDMA downlinks
R. Vaanithamby, Elvino Silveira Sousa · 2002
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 (/spl sigma/=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.