Analysis of beamformer configurations for DS-CDMA systems

Two different beamformer configurations for the base station receiver in direct-sequence code-division multiple access (DS-CDMA) systems, namely, a chip-based and a symbol-based configuration, are studied. In the chip-based configuration, different interfering components are rejected based on the spatial distribution of their power. In the symbol-based configuration, spatial diversity is exploited after despreading and different interfering components are rejected based on their interfering strength, which depends on both their power and code correlation with the signal of interest. Thus, for the symbol-based configuration, more effort is applied to rejecting the interfering components with higher interfering strength and thus a more selective and efficient system is achieved. Detailed performance analysis and simulations show that in the presence of multiple-access interference, the symbol-based configuration can lead to a significant improvement in the signal-to-interference-plus-noise ratio relative to that achieved with the chip-based configuration for both asynchronous and synchronous DS-CDMA systems.