Research Of Multiple Beamforming Techniques For TD-SCDMA System

In modern mobile communications, the performance of communication systems is severely limited by fading effects of the wireless channel. Therefore how to overcome the channel fading and improve the spectrum efficiency and data rate becomes a very important research topic. Multiple-antennas techniques have received wide interests in recent years due to its high data rate, high spectrum efficiency, strong abilities of suppressing the interference and so on. Multiple antennas techniques can be classified into two categories, one is the so call smart antennas, another is the spatial diversity approach. Smart antennas system, which introduces advanced adaptive array processing, produces space beams with main beam directing at the direction of desired user and null steering beams directing at the directions of interfers, thus suppressing or canceling the interfering signals. Therefore, it can improve the signal-to-interference ratio to enlarge the system capacity. Spatial diversity takes advantage of the irrelevant among individual antennas to combate against the multi-path fading, however it is another multiple antennas constructions.Time division synchronous code division multiple access (TD-SCDMA) system is a 3rd Generation communication standard put forward independently by China. Smart Antenna has considerd to be an effient technology in this system. In this paper, spatial diversity is proposed to combined with smart antennas in the TD-SCDMA system tegother, which can take advantage of the space-time channel characteristic to eliminate multiple access interference, as well as multi-path interference.The primary works are as follows:1) A space-time coded two-beams transmit diversity schemes is presented for TD-SCDMA system. The two-beams are based on one circular array with 4-unit antennas. Compared with the traditional signal beamforming in TD-SCDMA system, the new scheme has better performance on the same antenna array.2) In additionally, two-beams can be generated by two independent circular arrays. This scheme is successful implemented in this paper. The modified schemes which employed by two independent beams, obtains diversity gain which improves the performance of system.3) Based on the TD-SCDMA standard and channel parameters, simulations are carried out by Matlab software and the results show that the new schemes are effective.