A convolutional weighting （CW） scheme applied to a half-wavelength spacing array was proposed for multi-user system to joint STBC （space time block ceding） and beam forming （BF）. The transmitting beam is equivalent to the product of two sub-beams. One is used to realize interference suppression, while the other is employed to form a couple of uncorrelated channels from base station （BS） to the desited user （to meet the requirement of STBC） and to maximize SINR （signal-to-interference-plus noise ratio） at the desired receiver. As an optimum combination of STBC and beam forming, the proposed scheme can achieve both full diversity order of STBC and array gain of BF. Meanwhile, it can also effec- tively restrain multi-user interference by nulling. Simulation results show that the proposed scheme can significantly improve the BER （Bit Error Rate） performance and enhance system capacity as compared with the conventional eigen-beamforming （EBF） technique applied to a half-wavelength spacing array.
All the parameters of beamforming are usually optimized simultaneously in implementing the optimization of antenna array pattern with multiple objectives and parameters by genetic algorithms （GAs）. Firstly, this paper analyzes the performance of fitness functions of previous algorithms. It shows that original algorithms make the fitness functions too complex leading to large amount of calculation, and also the selection of the weight of parameters very sensitive due to many parameters optimized simultaneously. This paper proposes a kind of algorithm of composite beamforming, which detaches the antenna array into two parts corresponding to optimization of different objective parameters respectively. New algorithm substitutes the previous complex fitness function with two simpler functions. Both theoretical analysis and simulation results show that this method simplifies the selection of weighting parameters and reduces the complexity of calculation. Furthermore, the algorithm has better performance in lowering side lobe and interferences in comparison with conventional algorithms of beamforming in the case of slightly widening the main lobe.
