Interference suppression in CDMA mobile stations using multiple antennas

The link level performance gain of using multiple antennas in CDMA mobile stations is theoretically investigated and the corresponding capacity gain is evaluated by means of system level simulations. Depending on the channel model, the maximum ratio combiner improves the performance by 4-6 dB when the number of antennas is increased from one to two, and by another 3-5 dB when the number of antennas is increased from two to four. The resulting capacity gain is close to a direct translation of the link level gain. The optimum combiner is capable of completely suppressing a number of interfering rays equal to the number of antennas minus one. In contrast to the uplink, the downlink can greatly benefit from the suppression of a few interfering rays, leading to an additional substantial gain in downlink capacity.