Kazumitsu Sakamoto

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.

An SD Method Utilizing Null Dependency on Transmission Distance Due to Two-Ray Fading

A spatial division (SD) transmission method utilizing the characteristics of two-ray fading due to ground reflection with linear antenna arrays horizontal to the ground is proposed. Formulations of the optimum array arrangements as functions of the transmission distance and achievable channel capacity are clarified. For two- and three-element arrays, channel capacity is respectively doubled and tripled over that of free-space propagation. The proposed method provides increased capacity without the extra signal processing cost incurred when using conventional multiple-input-multiple-output (MIMO) transmission.

An SDM Method Utilizing Height Pattern Due to Two-Ray Fading Characteristics

A spatial division multiplexing (SDM) transmission method utilizing the characteristics of two-ray fading without relying on narrow beam of the antennas is introduced. This letter formulates the optimized array antenna arrangements and channel capacity as functions of the transmission distance and shows achievable channel capacity for two- and three-element antenna arrays. The letter also describes bandwidth dependency up to 15% bandwidth based on an assumed application to 60-GHz-band gigabit wireless systems. The proposed method provides increased capacity comparable to multiple-input–multiple-output (MIMO) transmission without the extra signal processing cost incurred when using conventional MIMO.

Dependency on Beamwidth in an SD Method Utilizing Two-Ray Fading Characteristics

Using ray-tracing propagation calculation, we clarify the dependency on antenna element beamwidth of the channel capacity of a spatial division (SD) transmission method utilizing the characteristics of two-ray fading. It was clarified that the SD transmission method can be effectively applied to microstrip antennas or horn antennas with beamwidth of more than 10 °, but that it is not effective when applied to narrow-beam antennas with less than 10 ° beamwidth. In such cases, simple parallel transmission is a better way to utilize the narrow beam to increase channel capacity .