Mobile Communication System In The Digital Beamforming Technology

The demand for the wireless communication service has been increased rapidly and this requires higher system capacities while improving the quality of service for the mobile user. The adaptive antenna array is one of the advanced techniques which could be implemented in the mobile telecommunications systems to achieve high system capacity. This thesis places emphasis on one of the key techniques ofsmart antenna ------beamforming and its application in the mobiletelecommunications systems. A new algorithm is going to be presented. With this algorithm, the physical limit of array can be broken and the number of the beams formed can exceed the number of antenna sensors. This makes possible forming beams with relative less antenna sensors. Thus the cost is reduced.Based on a large volume of reference books and articles, the first step is reviewing conventional methods of beamforming, including MVDR, SMI, steepest-descent method, LMS, RLS, CMA, etc. The Second one, recent beamforming methods in the mobile telecommunications systems are studied, including the algorithm based on Lagrange formula and least-squares despread respread multitarget array algorithm. These beamforming techniques have used the signal characteristics, such as constant modulus, PN spread code, or spread gain.A new technique, which virtually increases the number of antenna sensors, is presented. This new technique utilizes the characteristics of finite alphabets and constant modulus of communication signals. BPSK signals, for example, has only two values , +1 and -1. The 3rd power of these signals equal to themselves, thus the dimension of the received signal data matrix can be extended from M to 3M-5 virtually. Using the new matrix to form beams is just like virtually increasing the number of antenna sensors from M to 3M-5. The feasibility of this method is proved by both computer simulation and theoretical deduction. Combining the constant modulus of communication signals, the beamforming algorithm with virtual array is given,2D-RAKE receiver used in communications system is discussed and itsperformance is analyzed. Computer simulations of 2D-RAKE receiver with parameter errors and array errors are given, in order to shed light on the influence of each parameter error.