Abstract
Multiuser hybrid precoding in 5G NR mmWave communication system faces significant challenges such as establishing accurate directional radio links and maintaining links for mobile stations (MSs) moving in outdoor environments. A conventional solution relies on finite codebook-based beam sweeping for initial first-stage beam acquisition and subsequent second-stage beam tracking by sweeping adjacent beam pairs. However, such a conventional solution has inevitable residual AoA/AoD errors even after the best beam pair is established in the first stage and incurs nonnegligible overheads to sound adjacent beam pairs for maintaining the best beam pair in the second stage. To overcome these problems, a novel codebook-based two-stage solution that combines a novel beam tracking protocol with a low sounding overhead, a unique receiver structure employing a beam scheduler and a beam tester, and a fine accuracy residual AoA/AoD error estimation algorithm based on the monopulse ratio concept is proposed. The solution is unique because of the receiver structure for the residual AoA/AoD error estimation that exploits the cyclic prefix in OFDM systems, inspired by the monopulse ratio in radar systems. Moreover, it can be applied to MSs with a single RF chain. This solution, using the proposed receiver structure and algorithm, can establish a more accurate directional beam pair right after the initial beam sweeping in the first stage. For beam tracking in the second stage, it estimates the residual AoA/AoD errors of the current best beam pair rather than sweeping adjacent beam pairs, thereby reducing beam tracking overheads. Numerical evaluation and computer simulations show that the proposed solution offers more accurate beam acquisition (i.e., average array gain improvement of several dB) and costs considerably reduced beam sounding overheads compared to the conventional solution. Lastly, a ray-tracing tool is used to demonstrate that our solution is effective in practical channel parameters for outdoor environments.
Highlights
Millimeter wave band is highly anticipated for use in a mobile broadband radio access system
Remark 3: not explicitly shown in this paper because of space limitations, we can see from the simulation results that we can improve the performance of angle of arrival (AoA) error estimation in the low SNR region by adopting a moving average filter employing several OFDM symbols in the case where the AoA does not vary much during the averaging window
We proposed a novel solution for the two-stage multiuser hybrid precoding in mmWave OFDM systems such as 5G new radio (NR), which can achieve more accurate beam acquisition and lower sounding overheads in protocols than the conventional solution even for a single radio frequency (RF) chain mobile stations (MSs)
Summary
Millimeter wave (mmWave) band is highly anticipated for use in a mobile broadband radio access system. Multiuser hybrid precoding in the mmWave systems must overcome challenges so that beam acquisition is as accurate as possible and the beam tracking protocol is employed with sounding overheads as low as possible even for the MS with the single RF chain. To estimate the AoA error, the authors in [41] used phase difference across spatially separated receive subarrays along with multiple receive RF chains Their aim was to reduce RF beam codebook search complexity in single user and single carrier systems. Afterwards, the conventional solution is defined as the method that uses the DFT-based codebook for beam acquisition/tracking and does not estimate/compensate the residual AoA/AoD errors. The proposed solution consists of a novel beam tracking protocol, a unique receiver structure, and its algorithm to estimate the residual AoA/AoD error It works well for a single RF chain MS in both wideband multipath channels and timevarying angle conditions. An is a n-ary Cartesian power of a set A
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