On the performance of spatial-multiplexing MIMO-CDMA downlink receivers based on chip rate equalization and despreading

This paper is devoted to the performance analysis of downlink MIMO-CDMA receivers based on a chip rate MIMO equalizer followed by despreading. The various transmit antennas send independent streams and the spreading codes are scrambled Walsh-Hadamard sequences, the various transmit antennas being allocated different scrambling codes. The behaviour of the SINR provided by the receiver is first studied when the spreading factor and the number of users per antenna converge to +infin at the same rate. It is shown that the SINR converges towards a simple expression depending on the particular realization of the frequency selective channel between the base station and the mobile of interest. In order to get more insights on the long term performance, the ergodic sum-capacity delivered by the system is evaluated in the large number of antennas regime in the case the impulse response taps of the channel are Gaussian random matrices. A simple expression is obtained. It appears to be quite reliable for a realistic number of antennas, and is discussed in order to get some insights on the overall performance.