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Analysis of quantisation effects in adaptive array antennas

Adaptive antennas are used to increase the spectral efficiency in mobile telecommunication systems. The precision required in the beamforming and in the calibration process is evaluated by simulations and verified by measurements on an adaptive antenna testbed. As a performance measure, the carrier to interference ratio (CIR) on adaptive antenna output is used. A theoretical expression for the output CIR is derived and compared with simulations and measurements. The testbed is designed for the DCS-1800 system and operates in the uplink only. It uses the hybrid-digital-analog beamformer, where the weights are computed in a DSP, but the beamforming is performed on RF or IF frequency using analog phase-shifters and attenuators. We show how the simulation tool can be used to make the design balanced and thus avoiding overor under-dimensioning of hardware parameters such as weight accuracy and calibration accuracy. This is important for the system-designer, and can be used to find performance bottlenecks.