Throughput Improvement Technique Using Adaptive Control of Perturbation Interval for Downlink Multi-User MIMO Based on Vector Perturbation

In a downlink multi-user multiple-input multiple-output (MU-MIMO) system, the vector perturbation (VP) method, which is one of the non-linear precoding methods, is a promising technique with which to maximize the channel capacity. In the VP method, the receiver requires the modulo operation to remove the perturbation signal added at the transmitter. However, owing to noise, the modulo operation may not run correctly which makes the soft demapper produce unreliable log-likelihood ratios (LLRs), resulting in a degradation of system throughput. To enhance the throughput performance, we propose a method that expands the basic perturbation interval and adaptively controls the expansion rate according to the modulation and coding scheme (MCS). The optimum expansion rate is derived by link-level simulation and the system throughput is measured by system-level simulation. The system-level simulation results show that the proposed VP method can obtain higher throughput than the conventional VP method.