Complexity reduced zero-forcing beamforming in massive MIMO systems

Data gathering is one of the most popular applications in multi-hop wireless sensor networks. Since resources are limited, it is important to efficiently allocate the resource Massive multi-input multi-output (m-MIMO) systems can provide a high degree of freedom in signal transmission, enabling to simultaneously serve a number of users with high transmission capacity. Conventional zero-forcing beamforming (ZFBF) techniques can transmit multi-user signal while completely canceling out interbeam interference. However, they may have implementation difficulty when applied to m-MIMO systems mainly due to hugh processing complexity. In this paper, we design a complexity reduced ZFBF scheme by means of sequential interference cancellation. We first determine the beam weight according to the use of conventional maximum ratio transmission (MRT) scheme and calculate the corresponding interbeam interference. We calculate so-called an interference cancellation vector by sequentially cancelling out a predetermined number of interference sources in an order of the strongest interference. Finally, we determine the beam weight by adding the interference cancellation vector to the MRT beam weight. The number of interbeam interferences to be cancelled out can be pre-determined taking into consideration of the processing complexity and required performance. As the number of interbeam interferences to be cancelled out increases, the performance of the proposed scheme approaches to that of ZFBF. The numerical and simulation results show that the proposed scheme can achieve about 90 % capacity of ZFBF while requiring 2~7% processing complexity of ZFBF in various operating environments with the use of 32 128 transmit antennas.