A robust DOA-based smart antenna processor for GSM base stations

We present a robust smart antenna processor that is based on directions-of-arrival (DOA) estimation at the uplink. For optimum BER performance in a cellular mobile radio environment we resolve all relevant paths for the intended user, not only a single one. To increase the system's reliability, we apply separate trackers for uplink and downlink and use a beamforming algorithm that places broad nulls to suppress interferers as they appear realistically in the mobile radio channel. A performance evaluation of the eight-element array based on a semi-stochastic directional channel model shows that the DOA estimation accuracy is not of great concern, but estimation robustness strongly influences the BER. By adaptation within every GSM frame, the processor yields a mean noise and interference ratio (SNIR) improvement of up to 35 dB in an interference limited mobile radio macro-cell environment. The tracking algorithm gains 10 dB in mean input SNIR at a raw BER of 1%. Our beamformer with broad nulls has up to an order of magnitude better BER performance than a conventional beamformer that places sharp nulls. Angular diversity in the uplink and spatial interleaving in the downlink are implemented to improve the link quality.