Multistage Interference Canceller Combined with Adaptive Array Antenna for DS-CDMA System

摘要

In order to increase the capacity of a DS-CDMA system, several kinds of interference suppression techniques have been studied, such as multiple access interference (MAI) cancellers and adaptive array antennas. However, their performance tends to degrade in high traffic-load situations. To compensate for the degradation, a receiver cascading an adaptive array antenna and a multistage parallel interference canceller (PIC) is studied in this paper. This receiver first uses an adaptive array antenna to suppress interference signals spatially, and uses a multistage PIC to suppress in-beam interference effectively. The performance of the cascaded receiver is evaluated with two schemes for antenna weight generation by computer simulations assuming a Rayleigh-distributed L-path channel. When antenna weights are generated for each user by an LMS algorithm, the cascaded receiver has shown better performance at the cost of a large number of pilot symbols and symbol by symbol weight update. Its performance degradation is 2.8 dB at the BER of 10~(-4) even when the number of users increases from one to 24. On the other hand, when antenna weights are generated for each path by a DMI algorithm, its performance is degraded due to the inaccurate weight generation which occurs when the SINR of the desired signal is small. This degradation can be mitigated by using all signals of the desired user received by all antenna patterns of desired user for RAKE combining when the difference among arrival angles of the paths of the desired user is small.