Research On Multi-user Joint Detection Based On Smart Antennas Technology

With the demand increase of the capacity to mobile communication systems and scarce spectrum resources, Smart antennas are used to resolve co-channel interference, multiple access interference, multipath fading and other issues, as a new application to airspace resource development. But most of the adaptive beamforming algorithms in smart antennas are of low spatial resolution with an increase of user number, and the resulting multi-access interference degrade the performance of multi-user detection. For the above, we learn the smart antenna basic structure, principle, classification and beamforming, study various adaptive beamforming guidelines, and simulate least mean squares(LMS) adaptive beamforming algorithm and recursive least squares(RLS) adaptive beamforming algorithm. A new multi-user detection algorithm based on pseudo-inverse method is proposed, then the smart antennas combined with joint detection technology also is used for detection. Theoretical analysis and simulation results show that the new method can effectively improve the detection performance of the multi-user system. The main contents of this thesis are as follows:1. The basic structure and working principle of smart antennas are concisely described. The beamforming technology based on smart antennas is especially presented. The effect of relevant parameters on system performance is simulated and analyzed.2. Four common adaptive beamforming guidelines of smart antennas are studied, including the minimum mean square error criterion, the maximum signal to noise ratio criterion, the linear constrained minimum variance criterion and the least square criterion, and a simple comparison to four adaptive beamforming guidelines is provided. The classical LMS adaptive beamforming algorithms and RLS adaptive beamforming algorithms are introduced in detail, and the performance is analyzed by simulating the relevant parameters.3. For the case where multi-access interference still exists in multiuser beamforming system, some detection algorithms are studied, for instance, zero forcing detection algorithm, minimum mean square error detection algorithm, successive interference cancellation, parallel interference cancellation and the successive interference cancellation based on QR decomposition detection algorithm. The pseudo-inverse method from the multi-beam forming is used to receive and separate the target user signal, and an improved algorithm combined with parallel interference cancellation technology is proposed, simulation results show that the detection performance of the improved method is greatly improved.4. The beamforming technology is used to detect multiuser signal in smart antenna, and then the spatial correlation matrix derived after beamforming is processed to detect multi-user signal with zero-forcing detection, minimum mean square error detection and other joint detection technology. The bit error rate performance is further improved followed by parallel interference cancellation technology. Furthermore, the successive interference cancellation based on QR decomposition is proposed to detect multiuser. The improved algorithm is simulated in flat fading channel and frequency selective fading channel, and the BER performance of improved algorithm is closed to the border of ideal performance to single-user.