Power-efficient beam tracking during connected mode DRX in mmWave and sub-THz systems

Abstract

Discontinuous reception (DRX), wherein a user equipment (UE) temporarily disables its receiver, is a critical power saving feature in modern cellular systems. DRX is likely to be aggressively used at mmWave and sub-THz frequencies due to the high front-end power consumption. A key challenge for DRX at these frequencies is blockage-induced link outages: A UE will likely need to track many directional links to ensure reliable multi-connectivity, thereby increasing the power consumption. In this paper, we explore reinforcement learning-based link tracking policies in connected mode DRX that reduce power consumption by tracking only a fraction of the available links, but without adversely affecting the outage and throughput performance. Through detailed, system level simulations at 28 GHz (5G) and 140 GHz (6G), we observe that even sub-optimal link tracking policies can achieve considerable power savings with relatively little degradation in outage and throughput performance, especially with digital beamforming at the UE. In particular, we show that it is feasible to reduce power consumption by 75% and still achieve up to 95% (80%) of the maximum throughput using digital beamforming at 28 GHz (140 GHz), subject to an outage probability of at most 1%.

Power-Efficient Beam Tracking During Connected Mode DRX in mmWave and Sub-THz Systems

“…In [8]. For the expressions of each of these quantities, we refer the reader to to [33,Appendix], which is an unabridged version of this paper. Based on Table I, we make the following remarks: Remark 1 (Digital beamforming with low-resolution ADCs).…”

“…, using Bayes' rule [36] {This updates the posterior distribution ofγn(t) based on the measured γn(t) in A(t−1). See [33], [36] for update rules for specific choices of ζn).} Finally, we consider a policy with one-step memory (i.e., s = t − 1 in (2)), which is a modified version of the policy presented in [1].…”

“…• Go back to Operation codebook based on the steering vector of a UPA, such that the main lobes of the beam patterns cover the hemisphere, equally spaced in both azimuth and elevation. We refer the reader to [33] for the expressions of f…”

“…and v(.) denote the UPA steering vectors at the UE and gNB, respectively [33]. ẋ UE denotes the UE speed, f c the carrier frequency and c the speed of light.…”

“…Hence, we consider L m = 3L/4 for each case from here on. For a detailed discussion on parameter tuning for each of the policies, see [33].…”