Cooperative Orbital Angular Momentum Wireless Communications

TL;DR

This work tackles the challenge of hollow-divergence in orbital angular momentum (OAM) wireless communications by introducing Cooperative OAM Wireless (COW), which selects cooperative users to form aligned receive antennas for two OAM modes. It derives feasible radial and waist radii from the OAM intensity distribution, designs a cooperative formation protocol, and provides a closed-form probability for forming cooperative pairs, further enhanced by OAM beam steering to enlarge the feasible region. The analysis is complemented by a signal-model framework that quantifies the gains from beam steering, and simulations confirm that COW achieves higher spectrum efficiency than fixed-UCA OAM schemes, with the theoretical probability closely matching empirical results. Overall, COW offers a practical pathway to deploying high-spectral-efficiency OAM links in 6G/6G-like networks using size-limited user equipment and cooperative relays.

Abstract

Orbital angular momentum (OAM) mode multiplexing has the potential to achieve high spectrum-efficiency communications at the same time and frequency by using orthogonal mode resource. However, the vortex wave hollow divergence characteristic results in the requirement of the large-scale receive antenna, which makes users hardly receive the OAM signal by size-limited equipment. To promote the OAM application in the next 6G communications, this paper proposes the cooperative OAM wireless (COW) communication scheme, which can select the cooperative users (CUs) to form the aligned antennas by size-limited user equipment. First, we derive the feasible radial radius and selective waist radius to choose the CUs in the same circle with the origin at the base station. Then, based on the locations of CUs, the waist radius is adjusted to form the receive antennas and ensure the maximum intensity for the CUs. Finally, the cooperative formation probability is derived in the closed-form solution, which can depict the feasibility of the proposed COW communication scheme. Furthermore, OAM beam steering is used to expand the feasible CU region, thus achieving higher cooperative formation probability. Simulation results demonstrate that the derived cooperative formation probability in mathematical analysis is very close to the statistical probability of cooperative formation, and the proposed COW communication scheme can obtain higher spectrum efficiency than the traditional scheme due to the effective reception of the OAM signal.

Figures (11)

• Figure 1: The COW communications consist of the BS and multiple CPs. The zoomin figure at the bottom shows the detailed topology of a COW communication unit. The COW communications can be partitioned into a number of COW communication units. This implies that in the COW communication model, each user with size-limited equipment uniquely belongs to one COW communication unit.
• Figure 2: The demonstration of proposed COW communication scheme
• Figure 3: The minimum communication angle $\theta_\textup{min}(r_s)$ and maximum communication angle $\theta_\textup{max}(r_s)$
• Figure 4: The illustration of the selected CUs
• Figure 5: The cooperative formation probability versus BS coverage radius