Shohei Ishikawa

Millimeter-wave beam multiplexing method using hybrid beamforming

A millimeter-wave beam multiplexing method using a hybrid beamforming is proposed. We theoretically show that inter-subarray coding at the subarray type interleaved configuration can reduce interference and multiple beams of the same high gain as the full connection type. The condition that a hybrid beamforming of the subarray type can create the multiple high gain beams is clarified. For the case of beam multiplexing, the interleaved configuration with inter-subarray coding is confirmed to be robust for interference increasing by errors of beam direction estimation. Therefore, we think that the interleaved configuration is suitable for millimeter-wave beam multiplexing.

System validation of millimeter-wave beam multiplexing with interleaved hybrid beam-forming antennas

This paper describes beam division multiplexing at millimeter wave band using interleaved hybrid beam-forming (BF) antennas. The antenna elements are located alternately to make narrow beam-width of about 5 degrees, and the user multiplexing calculation on the digital signal processing part can suppress the undesired grating-lobe. The authors manufacture the interleaved hybrid beamforming antennas at 60GHz, and conduct antenna beam pattern measurements and transmission experiments. The measurement results show the desired-undesired ratio of 18dB after the suppression of the grating lobe by digital weight multiplication, and show good communication performance from the results of received constellation patterns of OFDM 16QAM modulation scheme.

Polarization diversity antenna with L-shaped slit for wireless sensor network

In this paper, a planar polarization diversity antenna with low correlation coefficient and low mutual coupling is developed for wireless sensor network system at UHF region. A slit, to eliminate mutual coupling between two antennas, inserted on ground plane of conventional diversity antenna is straight; this fact causes a restriction to layout of a PCB board at UHF region. To save a large area for the electric component, we employ an L-shaped slit which has an advantage of compact and same performance as straight slit. The prototype of diversity antenna has been developed and measured. The measured result obtained the very low correlation coefficient of 0.021 and very low mutual coupling about -20 dB at 1 GHz in this work.

Robust beamforming method for SDMA with interleaved subarray hybrid beamforming

This paper considers millimeter-wave access network systems with space division multiple access using an interleaved subarray hybrid beamforming structure, where antenna elements in each subarray scatter uniformly over the whole antenna array. The structure can provide high system capacity by multiplexing users in the space domain with narrow beams. However, imperfect user direction estimation might cause system capacity degradation due to interference between the beams. In particular, severe interference is experienced in the interleaved subarray configuration because many grating lobes are observed due to the wide element spacing in each subarray. Therefore, we propose a robust beamforming method in order to provide high system capacity even if user direction estimation is inaccurate. In the proposed method, multiple subarrays form beams to a common direction when the peaks of beams directed to the respective user directions are overlapped. We conduct computer simulations to evaluate the proposed method with a non-ideal beam search. The simulation results demonstrate that the proposed method can improve system capacity in the SDMA systems with the interleaved subarray hybrid beamforming structure.

Reducing technique of sidelobe in millimeter wave beam multiplexing system

In the millimeter wave beam multiplexing system, sidelobe decreases data-rate because data-rate is decided by signal to noise level (SINR), and sidelobe decides SINR. Sidelobe is decided by interference of coupling and phase error between RF channels, so suppress coupling and phase error is important to obtain high data-rate. Structures, such as cavity that silicon chip is placed in it to reduce length of bond-wire, grounded coplanar wave guide (CPWG), and higher positional accuracy of via, can obtain lower coupling and phase error. This paper describes effect of those structures to reduce coupling, and phase error example of manufactured RF board including beamforming antenna and silicon chips.

Polarization diversity antenna with current block element and open stub

In this paper, the design of a planar polarization diversity antenna with low mutual coupling is presented. A current block element is inserted between a RF module and a feed element of an inverted-F antenna to block the current on the nonactivated antenna induced by mutual coupling, and an open stub is inserted to cancel reactance, which is induced by mutual coupling. The prototype of diversity antenna has been developed and measured. The measured result demonstrated the very low correlation coefficient of 0.02 and very low mutual coupling about -15 dB at 1 GHz in this work.