Front-end modeling of a space division multiple access receiver using a direct conversion architecture

Space Division Multiple Access (SDMA) is considered for achieving multi-user communication within an indoor wireless environment. Uplink communication is simulated between an eight-antenna SDMA receiver and four mobile terminals. Several system-level design considerations for the receiver are presented, including a strategy for modeling front-end impairments and the development of a novel AGC algorithm. A direct conversion architecture is selected for the receiver due to its potential for on-chip implementation. This necessitates the use of spread spectrum modulation, which is robust against certain impairments common in direct conversion receivers. Simulation results show that SDMA helps to overcome such impairments as quadrature mismatches, second-order nonlinearity and channel fading, while the use of spread spectrum modulation combats inter-symbol interference and phase noise. Also, a Verilog-AMS model demonstrates the performance of the full receiver, as well as the potential to expand the multiple access capability by combining SDMA with code division multiple access.