SIR estimation for fast power control for FDD-UMTS

The control of transmission power is essential in third generation systems for several reasons. The fast power control (or closed-loop power control) is intended to track the fast fading of the channel. Therefore, the received SIR (signal-to-interference ratio) has to be estimated. This paper investigates the requirements for SIR estimation when used in fast power control. It is explained that delay is more critical than low exactness of the estimate. Then, it is derived that the SIR estimation problem can be reduced to the problem of signal power estimation. Different simple estimation methods give insight into the performance of SIR estimation. Moreover, a new estimation algorithm is derived that takes sent TPC (transmit power control) bits into account to improve SIR estimation. Finally, simulation results highlight the derived results.