Beam Drift in Millimeter Wave Links: Beamwidth Tradeoffs and Learning Based Optimization

Abstract

Millimeter wave (mmwave) communications, envisaged for the next generation wireless networks, rely on large antenna arrays and very narrow, high-gain beams. This poses significant challenges to beam alignment between transmitter and receiver, which has attracted considerable research attention. Even when alignment is achieved, the link is subject to beam drift (BD). BD, caused by non-ideal features inherent in practical beams and rapidly changing environments, is referred to as the phenomenon that the center of main-lobe of the used beam deviates from the real dominant channel direction, which further deteriorates the system's performance. To mitigate the BD effect, in this paper we first theoretically analyze the BD effect on the performance of outage probability as well as effective achievable rate, which takes practical factors (e.g., the rate of change of the environment, beam width, transmit power) into account. Then, different from conventional practice, we propose a novel design philosophy where multi-resolution beams with varying beam widths are used for data transmission while narrow beams are employed for beam training. Finally, we design an efficient learning based algorithm which can adaptively choose an appropriate beam width according to the environment. Simulation results demonstrate the effectiveness and superiority of our proposals.

Integrated Sensing and Communications: Toward Dual-Functional Wireless Networks for 6G and Beyond

“…3) Beamwidth Allocation: Beamwidth plays an important role in both S&C [191]. For faraway vehicles that are deemed to be point-like targets, the transmit beam can be made as narrow as possible, thus providing both high beamforming gain for communication and superior angular resolution for sensing.…”

Mobility management of multi-hop mobile integrated access and backhaul network

“…A tx node (e.g., a gNB or a parent MIAB node) and a rx node (e.g., a parent MIAB node or a child MIAB node) need beam alignment to obtain optimal directivity gain. If a parent MIAB node and its child MIAB node keep a beam pattern too long, the beam drift effect [30] occurs, which can reduce throughput. We define the average effective spectral efficiency (ESE) between node i and node j, ESE i,j as…”

“…Note that t w in ( 29) is changed to t h in (30). Therefore, the total UL CP data transmission delay from the child MIAB node to the gNB is the sum of ( 29) and (30):…”

Integrated Sensing and Communications: Towards Dual-functional Wireless Networks for 6G and Beyond

“…Beamwidth Allocation: Beamwidth plays an important role for both S&C [173]. For faraway vehicles that are deemed to be point-like targets, the transmit beam can be made as narrow as possible, thus providing both high beamforming gain for communication and superior angular resolution for sensing.…”