A Study On The Beamforming Algorithm Of MIMO Smart Antenna Systems

In recent years, the development of mobile communication technology is rapid. How toovercome the constraints of the multipath fading channel to improve both information transfer rateand user capacity of the mobile communication is becoming current research hot spot. One of thekey research is combining space domain with time domain，or frequency domain or code domain，so that space domain plays its huge potential in the mobile communication. Multiple antennatechnology is just to make full use of space domain to improve both the information quality andchannel capacity of communication systems. Multiple antenna system includes Smart Antenna（SA）system and Multiple Input and Multiple Output antenna(MIMO)system. The core technology of thesmart antenna is beam-forming technology，which have a wide range of applications in fields ofcommunication and radar etc，and whose algorithm of selection determines the instantaneousresponse rate and the complexity of the circuit implementation. In the case of the multipath effect isslighter，the performance of SA is better, but in the other case ,its performance is worse. MIMOtechnology the combination of both antenna diversity and space-time processing technology, comesfrom the antenna diversity technology and SA, so it could be said that MIMO technology belongs tothe generalized SA category. MIMO technology uses multiple antenna both at the sender andreceiver，through which to improve the data transfer rate and transmission quality of system，butwithout increasing bandwidth. The performance of MIMO is better as the multipath effect is moreserious. So combination of SA with MIMO technology can more intelligent and efficient bring theirown advantages to improve the performance of system.This paper focus on the adaptive beamforming technology of smart antenna system and spacetime code technology of MIMO system，including the following content:(1)The basic principle of adaptive beamforming of smart antenna system was introduced, thenfive kinds of the receiving criteria which are commonly used were introduced. Based on thesecriteria, five kinds of typical adaptive beamforming algorithms were introduced, and theirbeamforming algorithms were simulated by MATLAB. Finally, based on the study of traditionallinear constrained least squares constant modulus (LCLSCMA) beamforming algorithm, aimproved algorithm- linear constrained least squares constant modulus algorithm based on subspace(LCLSCMA-SUB) was proposed in this paper. The result of simulation shows thatLCLSCMA-SUB can gain more 0.8dB than LCLSCMA，which is because of LCLSCMA-SUB canconstraint weight vector in signal subspace，and thus effectively eliminate the influence of noise subspace. The LCLSCMA-SUB beamforming algorithm proposed in this paper can effectivelyimprove the system performance.(2)The basic principle of the MIMO system was introduced, and based on Alamouti code,space-time block code technology with three transmitting antenna and four transmitting antennawas introduced respectively. Then the beamforming principle of MIMO system was introduced, inwhich the emphase is joint transmit-receive beamforming technology. Finally the similarities anddifferences of the beamforming technology of SA system and the beamforming technology ofMIMO system was analyzed, and based on this, the possibility of combination of both technologywas researched，and some existing scheme was introduced.(3)Aiming at the existence of the inter-symbol interference, the bit error rate of space-timecode technology is high in the frequency selective fading channel (FSFC), the system model andalgorithm of a quasi orthogonal space-time code (QSTBC) technology with four transmittingantenna of full rate and full spatial diversity gain combined with code filtering adaptive (CFA)beamforming algorithm was proposed in this paper, based on adaptive beamforming technology ofSA system has been researched,. The result of simulation of comparison CFA-QSTBC with STBCin flat fading channel (FFC) and FSFC respectively shows that the algorithm proposed in this papercan both improve the performance of bit error rate of users in FFC and FSFC，and play an importantrole both in theory and application.