Lattice Reduction-Aided Uplink Multi-User MIMO in OFDM Cellular Systems

In cellular systems, multi-user multi-input multi-output (MIMO) multiplexing can increase the number of simultaneous users per cell; however co-channel interference (CCI) from other cells limits the number of users/cell (defined as the cellular capacity). The well-known zero-forcing detection (ZFD) and minimum mean square error detection (MMSED) are computationally efficient detection methods, but their diversity order decreases as the number of users increases. The multi-user signal detection method which has the full diversity order and less complexity is required in order to enhance the cellular capacity. In this paper, we introduce the lattice reduction (LR) aided ZFD and MMSED to the uplink multi-user MIMO using orthogonal frequency division multiplexing (OFDM) and investigate the uplink cellular capacity. LR using Lenstra-Lenstra-Lovasz (LLL) algorithm is a promising technique to improve the performance of ZFD and MMSED. We show that LR aided ZFD and MMSED can obtain larger uplink capacity than conventional ZFD and MMSED at the cost of relatively low increase of computational complexity.