Orthogonalized spatial multiplexing for MIMO WCDMA downlink over frequency-selective Rayleigh fading channels
D. Tujkovic, Emiliano Sottani · 2003
Abstarct: Exploiting the good correlation properties of the Walsh-Hadamard spreading codes to orthogonalize spatially multiplexed signals at the transmitter a new scheme was proposed in this paper that considerably enhances the throughput in MIMO WCDMA downlink systems over frequency selective Rayleigh fading channels. The delayed version of the same spreading code is applied to different individual or groups of transmit antennas which is denoted as the orthogonalized spatial multiplexing with the resolution of one (OSM-1) or two (OSM-2), respectively. The newly introduced method preserves the allocated number of spreading codes and enables a simple detection just with the use of matched filtering. Since the signals are separated already at the transmitter there are no restrictions in the terms of the minimum required number of receiver antennas. The diversity level of the system is proportional to the number of employed receive antennas. As we will show the number of antennas at the receiver is determined by the level of interference in the system and the desired system performance and is typically lower than in VBLAST and its generalizations. I.