Dynamical effects of time delays and time delay compensation in power controlled DS-CDMA

Transmission power control is essential in WCDMA in order to optimize the bandwidth utilization which is critical when variable data rates are used. One remaining problem is oscillations in the output powers due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete-time describing functions, which are introduced and applied. More importantly, Time Delay Compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm operates more stable, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved and thus less fading margin is needed. The latest news from standardization is to try to operate without additional delay when close to a base station. Nevertheless, there will still be more distant mobile stations for which TDC will be beneficial.