Shunsuke Fujio

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.

Energy-efficient hybrid beamforming in millimeter-wave communications using FDMA

This paper considers millimeter-wave access network systems using a hybrid beamforming structure, which is a combination of digital and analog beamformers. To multiplex mobile stations in the frequency domain along with the space and time domain improves a system capacity for the following reasons: it exploits frequency diversity, accommodates mobile stations that can only use a limited bandwidth in the same time slot, and increases uplink transmission power density. Therefore, we propose a hybrid beamforming method that provides high beamforming gain to more mobile stations multiplexed in the space and frequency domain than radio frequency (RF) chains of a base station by using multi-peak beams. Assuming a mobile station cannot receive a full bandwidth signal, we conduct downlink system-level simulations to which a millimeter-wave channel model proposed by MiWEBA is applied. The results demonstrate that the proposed method can provide almost the same throughput with 25% fewer RF chains.

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.

Energy saving effect of solar powered repeaters for cellular mobile systems

In this paper, a low-energy cellular mobile system assisted by multiple solar powered full-duplex relays is proposed. In the proposed system, many relays are scattered over the cell area so that all users in the cell can enjoy higher-quality links. In other words, base stations can save energy consumption by reducing their transmission powers without degrading the experiences of wireless communications. Because inter-relay interference is caused when multiple full-duplex relays transmit signals simultaneously, it is very important to mitigate interference in order to improve the quality of communication. Moreover, to improve the reliability of the system, it is necessary to reduce the energy consumption of relays. Therefore, we applied to the system a new inter-relay interference mitigation method based on power control that considers the path-loss between relays together with a new battery power-control method. The energy saving performance of the system and the system reliability are verified by performing system level simulations.