Multi-user Beam Alignment in Presence of Multi-path | IEEE Conference Publication | IEEE Xplore

Multi-user Beam Alignment in Presence of Multi-path


Abstract:

To overcome the high pathloss and the intense shadowing in millimeterwave (mmWave) communications, effective beamforming schemes are required which incorporate narrow bea...Show More

Abstract:

To overcome the high pathloss and the intense shadowing in millimeterwave (mmWave) communications, effective beamforming schemes are required which incorporate narrow beams with high beamforming gains. The mm Wave channel consists of a few spatial clusters each associated with an angle of departure (AoD). The narrow beams must be aligned with the channel AoDs to increase the beamforming gain. This is achieved through a procedure called beam alignment (BA). Most of the BA schemes in the literature consider channels with a single dominant path while in practice the channel has a few resolvable paths with different AoDs, hence, such BA schemes may not work correctly in the presence of multi-path or at the least do not exploit such multi path to achieve diversity or increase robustness. In this paper, we propose an efficient BA schemes in presence of multi-path. The proposed BA scheme transmits probing packets using a set of scanning beams and receives the feedback for all the scanning beams at the end of probing phase from each user. We formulate the BA scheme as minimizing the expected value of the average transmission beamwidth under different policies. The policy is defined as a function from the set of received feedback to the set of transmission beams (TB). In order to maximize the number of possible feedback sequences, we prove that the set of scanning beams (SB) has an special form, namely, Tulip Design. Consequently, we rewrite the minimization problem with a set of linear constraints and reduced number of variables which is solved by using an efficient greedy algorithm.
Date of Conference: 09-11 March 2022
Date Added to IEEE Xplore: 14 April 2022
ISBN Information:
Conference Location: Princeton, NJ, USA

I. Introduction

In pursuance of larger bandwidth that is required for realizing one of the main promises of 5G, i.e. enhanced mobile broad-band (eMBB), millimeter wave (mmWave) communications is a key technology due to abundance of unused spectrum available at mmWave frequency ranges [1]. However, high path loss and poor scattering associated with mm Wave communications leads to intense shadowing and severe blockage, especially in dense urban environments. These are among the major obstacles to increase data rate in such high frequency bands. To tackle these issues effective beamforming (BF) techniques are required to avoid the power leakage to undesired directions using directional transmission patterns, i.e., narrow beams [2]. Furthermore, several experimental results demonstrate that the mmWave channel usually consists of a few components (a.k.a spatial clusters) [3]. Therefore, it is essential to align the devised narrow transmission beams with the direction of the channel components. The problem of aligning the directions of the beams with the angle of departure (AoD) associated with clusters of the channel, is termed as the beam alignment (BA) problem. In the literature the beam alignment problem is also indexed as beam training or beam search. Devising effective beam alignment schemes is essential since a slight deviation of the transmitted beam AoDs from the mm Wave channel clusters may result in a severe drop in the beamforming gain [4] [5].

References

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