Toshimitsu Tsubaki

Performance measurement of broadband simple decoding in short-range MIMO

In a short-range multiple-input and multiple-output (SR-MIMO) transmission system that relies on line-of-sight (LOS) propagation, the channel matrix is determined by the antenna geometry, hence radio frequency (RF) signal processing by using an analog matrix circuit is a valid means of separating spatially-multiplexed multiple signal streams. To date several simple decoding methods utilizing this feature for SR-MIMO transmission have been proposed and demonstrated at one frequency point. This paper presents a demonstration of a simple decoding method for two-branch SR-MIMO transmission in a broadband with eight percent relative bandwidth, which corresponds to two-channel usage in the 60-GHz band. An experimental evaluation of the method was performed after prototyping the array antenna and weight matrix circuit. The evaluation results showed signal separation performance of 15 dB was obtained through the frequency range of 24.0-26.0 GHz. Bit error rate (BER) was simulated using measured transmission characteristics and we determined that 16 QAM signals at this band can be transmitted in the prototype system.

A Novel ZF-Based Fast Beamforming Method for Short-Range MIMO Transmission

Millimeter-wave short-range multiple-input multiple-output (SR-MIMO) transmission employing zero-forcing beamforming (ZF-BF) at the information kiosk side can improve transmission rate without increasing mobile terminal power consumption for MIMO signal processing. However, processing delay for ZF weight generation is large, so the effects of time-varying channels due to the users hand jiggling, which cause performance degradation, cannot be ignored. In this letter, a novel fast beamforming method is described with which ZF-based weight can be generated with low delay by utilizing the relationship of channel variation and ZF weight variation. Simulation results show that the method can achieve better performance than ZF-BF.