Influence of user spatial separation on the uplink performance of a TD-CDMA mobile radio system with smart antennas

Smart antennas for base stations (BS) of cellular mobile radio systems are expected to be one of the most important means to increase capacity. The smart antenna concept followed in this paper takes advantage of the directional inhomogeneity of the mobile radio channel by applying direction-finding (DF) and beamforming (BF) algorithms in conjunction with filtering in the time domain. This concept is applied to a time division (TD)-CDMA mobile radio system, which has been selected by ETSI (European Telecommunications Standards Institute) in January 1998 to form part of the UMTS (Universal Mobile Telecommunications System) air interface standard, and can be split up into a novel channel estimator and joint data detector which explicitly incorporate the information about the directions of arrival (DOAs) of signals emerging from users assigned to the considered BS. In this paper, the influence of the spatial separation of users assigned to the considered BS on the link level performance of a TD-CDMA mobile radio system is investigated by Monte Carlo simulations of data transmission in a single cell. Average bit error rates versus the average signal-to-noise ratio at the receiver input are presented for the uplink of a TD-CDMA mobile radio system in the rural propagation environment. The system performance is evaluated and compared for different scenarios of the user spatial separation and for two receiver structures, i.e., the conventional receiver, which does not use the information of the DOAs of user signals, and the enhanced receiver, which explicitly incorporates this knowledge.