Sub-Chain Beam for mmWave Devices: A Trade-off between Power Saving and Beam Correspondence

TL;DR

This paper introduces sub-chain beam codebook design methods for mmWave devices to balance power efficiency and beam correspondence, addressing challenges when DL and UL configurations differ.

Contribution

It proposes novel sub-chain beam codebook design techniques to maintain beam correspondence while reducing power consumption in mmWave devices.

Findings

Sub-chain beam can approximate DL beam patterns with lower power.

Trade-off methods improve power saving without significantly losing beam correspondence.

The approach enhances beam management efficiency in asymmetric DL-UL configurations.

Abstract

Beam correspondence, or downlink-uplink (DL-UL) beam reciprocity, refers to the assumption that the best beams in the DL are also the best beams in the UL. This is an important assumption that allows the existing beam management framework in 5G to rely heavily on DL beam sweeping and avoid UL beam sweeping: UL beams are inferred from the measurements of the DL reference signals. Beam correspondence holds when the radio configurations are symmetric in the DL and UL. However, as mmWave technology matures, the DL and the UL face different constraints often breaking the beam correspondence. For example, power constraints may require a UE to activate only a portion of its antenna array for UL transmission, while still activating the full array for DL reception. Meanwhile, if the UL beam with sub-array, named as sub-chain beam in this paper, has a similar radiation pattern as the DL beam, the beam correspondence can still hold. This paper proposes methods for sub-chain beam codebook design to achieve a trade-off between the power saving and beam correspondence.