Experimental evaluation of combined effect of coherent rake combining and SIR-based fast transmit power control for reverse link of DS-CDMA mobile radio

The combined effect of coherent Rake combining using the weighted multislot averaging (WMSA) channel estimation biter and closed-loop fast transmit power control (TPC) in the 4.096 Mchip/s direct sequence code division multiple access (DS-CDMA) mobile radio reverse link is experimentally evaluated. The WMSA channel estimation filter utilizes periodically transmitted pilot symbols (four pilot symbols are time-multiplexed in each 40-symbol time slot). Its observation period is extended to 2-K slots in order to improve the accuracy of the channel estimation. The fast TPC is based on the measurement of signal-to-interference plus background noise ratio (SIR) using pilot symbols. Laboratory experiments show that the use of the K = 2 WMSA channel estimation filter reduces the required E-b/I-0 at the average BER of 10(-3) by approximately 0.5 dB compared to use of the linear interpolation filter, and that the required E-b/I-0 is minimized when the SLR measurement interval is M = 10 symbols (one slot TPC delay). It was also clarified that SIR-based TPC works satisfactorily when two users with different information data rates, i.e., SF, independently employ fast TPC. Field experimental results conducted in an area nearby Tokyo showed that the average BER of 10-3 is achieved at the target E-b/I-0 per antenna of approximately 2.5 dB by using four-finger/branch Rake and two-branch antenna diversity. Although the target E-b/I-0 to achieve same BER, when there is one interfering user with a fourfold greater transmit power than that of the desired user that independently employs fast TPC, is almost the same as that in the single-user case, the mobile transmit power is increased by 1.0-2.0 dB due to the increased MAI. These results indicate that the combination of coherent Rake combining and fast TPC works well in practical multipath fading channels.