Beam-selection performance analysis of a switched multibeam antenna system in mobile communications environments

The probability of incorrect beam selection (PIBS) with a switched multibeam antenna system is theoretically analyzed under power-limited and interference-limited mobile communication environments. Periodic transmission of a unique word sequence followed by the information symbol sequence is assumed. The model of beam selection used is based upon a simple three-stage mechanism: (1) signal validation; (2) averaging; and (3) selection of the largest output. Complex correlation peaks corresponding to the unique words, detected by the matched filter for the signal validation are averaged over several consecutive unique words, and a beam having the largest output is selected. Equally weighted noncoherent integration is assumed for the averaging process. The beam selection takes place frame-by-frame. The paper discusses the PIBS derivation for a simple switched two-beam antenna system. Numerical calculation results are then presented. It also investigates the impact of the incorrect beam selection on the overall average signal-to-noise (SNR) power ratio and signal-to-interference (SIR) power ratio. The amount of the overall SNR (or SIR) improvement over the omnidirectional antenna depends on the propagation conditions. In general, larger improvements can be achieved by smaller values of the PIBS.