Closed-loop power control algorithms in soft handover for WCDMA systems

Abstract

Closed-loop fast power control algorithms in a WCDMA system is discussed, dealing also with the special requirements set by using these algorithms when the mobile station is connected to more than one base station, i.e. in soft handover. The starting point for the discussion is the SIR-based algorithm, where the reliability of the decrease/increase-power command is evaluated from the SIR level. This algorithm was also the basis for 3GPP standardization work for WCDMA. A new method for establishing the reliability of the TPC command is introduced, where the soft symbol of the TCP command itself is directly used as a reliability indicator. In addition to the new reliability estimation, the concept of parallel use of TPC algorithms is presented, with a new TPC algorithm based on integrating TPC commands over a period of a few slots. The results show that the soft symbol reliability estimation decreases the Tx power levels with 0.5 dB, thus providing a useful capacity gain. The parallel use of 2 to 4 algorithms is also shown to decrease the sensitivity of the algorithms to the algorithm thresholds used, and thus increase the feasibility of the algorithms in a real-world network. The soft symbol reliability estimation for closed-loop power control was accepted by the 3GPP as a part of the WCDMA standard.