Research On The Performance Of Multiuser Opportunistic Beamforming

In order to combat multi-path fading and improve performance of the radio link, the modern wireless communication system uses a variety of diversity techniques. The principle of classical and modern diversity and combination is that, two or more channels carry copies of the signal which are to be combined to increase the overall received signal-noise ratio.Multi-user diversity gain is determined by the distribution of the fluctuations of the channel gain, the greater and faster of the fluctuations, the more suitable for accessing multi-user diversity gain. In the actual system, the lack of scattering in the environment and the existence of straight path will reduce the fluctuations of the channel; if the rate of the channel fading is too slow compared with the delay constraints, the transmission can not wait for the channel reaching its peak.Multi-antenna array using the singular value decomposition teconology can form independent parallel channels to improve throughput, but it requires the transmitter to obtain accurate channel state information, and it is not easy to carry out. The opportunistic beamforming uses multi-user diversity to achieve the similar throughput with the singular value decomposition teconology, amd it has been widely concerned.This paper introduces the opportunistic beamforming on the base of beam-forming. Opportunistic beamforming teconology weights the transmission signal to get rich scattering channel environment, and artificially amplify the speed and magnitude of the fluctuation to get independent channels, resulting in multi-user diversity gain in the slow-fading channel environment, and improving transmission reliability.In order to enhance the selectivity of beam and improve the matching of beam with the user, we introduced the concept of micro-slots opportunity beamforming, and further improved the system performance. We know the power distribution with water principle is the best strategy, but it is too complicated to applicate. In the opportunity beamforming system, the communication channels have been truncated when the base station select users for each beam, so we can use truncated channel inversion to allocate power for system. This principle will decline the channel capacity a little compared with water principle power allocation, but it only needs to carry out an operation of eigenvalue decomposition, with greatly reducing system complexity.