Takenori Ohshima

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.

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.

A phase and power difference detection technique using symmetric mixer with input level switching for millimeter-wave phased-array calibration

Methods for detecting phase and power difference by using a mixer configured with two symmetrically connected unit mixers with delay lines are proposed. The mixer having two detection curves achieves highly accurate phase detection for all phases, compared with a conventional mixer that has the stationary points 0 and π. The accuracy is demonstrated with a 77GHz 2-ch phased array in 65-nm CMOS. The mixer can also detect the power difference with input level switching in the reverse phase.