Each Carrier Transmission Power Control with Antenna Carrier Diversity for OFDMDS-CDMA System

Abstract

In OFDM-DS/CDMA system, frequency distortion caused by multipath propagation occurs at different frequencies in the bandwidth and generally affects selected subcarriers within the larger bandwidth. It has been investigated that each carrier transmission power control is effective to compensate for subchannel variation due to multipath, by assigning different transmission power level to different subcarriers based on the attenuation level suffered by them. The effectiveness of power control is mainly affected by the accuracy of the transmission power adjustment at the transmitter. As a matter of fact, however, the dynamic range of transmission power is very limited, due to the restriction on power consumption of a mobile station (transmitter side of reverse link). When a subcarrier is subjected to strong fading, power control is not able to compensate for channel attenuation by transmitting signals with large power, and this condition is very potential to degrade system performance. In this paper, we propose to combine each carrier transmission power control with antenna-carrier diversity reception to lighten the burden imposed on power control. This system allows the base station (receiver side) to select the best combination among the carriers and antennas after receiving signals from mobile station (transmitter side), thus power control only compensates for smaller attenuation level. System performance is evaluated in terms of Bit Error Rate (BER) performance as a function of Doppler frequency, number of users, number of branches, updating period and dynamic range. The result of computer simulations clearly show that the proposed system reduces significantly the burden imposed on power control.