A combined antenna array and multi-user detection DS-CDMA receiver in single-path and multi-path fading channels

摘要

An adaptive antenna array is incorporated into a decorrelating multi-user detector to effectively increase the DS-CDMA system capacity. Capacity improvement is due to beamforming gain, spatial diversity gain (assuming large angle spread), and the decorrelating effect. The receiver has been analyzed for the cases of sufficiently and insufficiently spaced receiving antennas. The receiver consists of a front-end beamformer for every user in the cell and has knowledge of all users' signature sequences. The beamformer estimates the desired user channel vector, enhancing its signal and reducing the co-channel interference from other directions. The multi-user detection, exploiting knowledge of other users, rejects those interferers whose arrival angles are close to that of the desired user. The average uncoded Bit Error Rate (BER) as a function of the number of in-beam active users, the average antenna Signal-to-Noise Ratio (SNR), and the number of receiving antennas is examined in both single-path and multi-path Rayleigh fading channels. Analysis shows an increase in system capacity proportional to the number of receiving antennas.