On the Spectral Efficiency of Indoor Wireless Networks with a Rotary Uniform Linear Array

TL;DR

This work addresses indoor MU-MIMO by introducing a Rotary Uniform Linear Array (RULA) at the access point to rotate its orientation and exploit channel variation for performance gains. The rotation is optimized using position estimates through a location-based beamforming approach and a brute-force search over the angular position, assuming full-LoS propagation to predict the per-user mean spectral efficiency $\bar{R}$. Through a spatially correlated Rician channel model and comparisons of MRC, ZF, and MMSE receivers, the study demonstrates substantial SE gains from rotation, especially in LoS-dominant scenarios and when $M$ is close to $K$, with robustness to reasonable positioning errors. The proposed low-complexity rotation strategy offers a practical, cost-efficient alternative to movable antennas for indoor deployments and highlights the potential of angular reconfiguration in enhancing uplink SE.

Abstract

Contemporary wireless communication systems rely on Multi-User Multiple-Input Multiple-Output (MU-MIMO) techniques. In such systems, each Access Point (AP) is equipped with multiple antenna elements and serves multiple devices simultaneously. Notably, traditional systems utilize fixed antennas, i.e., antennas without any movement capabilities, while the idea of movable antennas has recently gained traction among the research community. By moving in a confined region, movable antennas are able to exploit the wireless channel variation in the continuous domain. This additional degree of freedom may enhance the quality of the wireless links, and consequently the communication performance. However, movable antennas for MU-MIMO proposed in the literature are complex, bulky, expensive and present a high power consumption. In this paper, we propose an alternative to such systems that has lower complexity and lower cost. More specifically, we propose the incorporation of rotation capabilities to APs equipped with Uniform Linear Arrays (ULAs) of antennas. We consider the uplink of an indoor scenario where the AP serves multiple devices simultaneously. The optimal rotation of the ULA is computed based on estimates of the positions of the active devices and aiming at maximizing the per-user mean achievable Spectral Efficiency (SE). Adopting a spatially correlated Rician channel model, our numerical results show that the rotation capabilities of the AP can bring substantial improvements in the SE in scenarios where the line-of-sight component of the channel vectors is strong. Moreover, our proposed system is robust against imperfect positioning estimates.

Figures (7)

• Figure 1: Illustration of the considered system model for $l=100$ m and $K=16$.
• Figure 2: Illustration of a RULA, its distance and its angular position with respect to an active device.
• Figure 3: Predicted per-user mean achievable SE versus angular position of the RULA, for $M=16$, $K=16$ and $l=50$ m.
• Figure 4: Per-user mean achievable SE versus number of antennas, for $K=4$, $\kappa=10$ dB and $\sigma_e^2=-10$ dB.
• Figure 5: Per-user mean achievable SE versus number of active devices, for $M=16$, $\kappa=10$ dB and and $\sigma_e^2=-10$ dB.