Real{time Smart Antenna Processing for Gsm1800

This work describes a direction of arrival DOA based smart antenna system for GSM The focus lies on the developed antenna array processor that performs real time adaptive beamforming in every GSM frame The smart antenna consists of a uniform linear array with M elements eight transceiver trains and the Adaptive Antenna Array Processor A P The system allows digital beamforming in uplink and in downlink The A P performs four main tasks DOA estimation From the received input data in the uplink the directions of the incoming waves are estimated with a high resolution estimator DOA classi cation This step identi es the wavefronts of the user First A P spatially resolves the wavefronts from the input data with a spatial pre lter A user identi cation based on a detector classi es the DOAs and decides whether a wavefront DOA belongs to a user or to an interferer Tracking and DOA selection A tracker follows each nominal DOA multipath component of the user This does not only include averaging of the DOAs but also measures the reliability of each multipath The main beam points into the direction of the strongest multipath which corresponds to angular selection diversity Selecting a multipath only when its reliability is large enough guarantees robust smart antenna processing Separate trackers are used for uplink and for downlink because the downlink requires averaging Signal reconstruction beamforming Finally a beamforming algorithm forms an antenna pattern with a main beam steered into the direction of the selected user multipath while simultaneously minimizing the in uence of the interfering wavefronts Placing broad nulls increases the robustness against a large angular spread and against inaccurate DOA estimates The key elements of a DOA based smart antenna are user identi cation and tracking To gether they provide very reliable decisions where the main beam should aim at resulting in an excellent interferer suppression even in low carrier to interference ratio C I environments The run time of A P is in the order of ms thus suitable for real time operation A P is optimized for spatial ltering for interference reduction SFIR operation but can be easily extended for space division multiple access SDMA operation The run time will only increase by for each additional user that is served in SDMA mode Experiments bear out the viability of DOA based processing A P achieves the expected enhancements but there are also nd some surprising results