Linear angular momentum multiplexing—conceptualization and experimental evaluation with antenna arrays

Abstract

Linear angular momentum multiplexing is a new method for providing highly spectrally efficient short-range communication between a transmitter and receiver, where one may move at speed transverse to the propagation. Such applications include rail, vehicle and hyperloop transport systems communicating with fixed infrastructure on the ground. This paper describes how the scientific concept of linear angular momentum multiplexing evolves from orbital angular momentum multiplexing. The essential parameters for implementing this concept are a long array at least at one of the ends of the link; antenna element radiation characteristics and the array element spacing relative to the propagation distance. These parameters are also backed by short-range measurements carried out at 2.4 GHz used to model the Rice fading channel and determine resilience to multipath fading.

Experimental evaluation of a linear angular momentum multiplexed radio link for moving platforms

“…Hence this would contribute to the reduction in Rician K-factor, where the resulting multi-path may have a negative effect. However, according to simulation results provided in [10], which show spectral efficiency for a 2 × 2 LAM link with Rician K-factor of 20 and 6, the spectral efficiency is shown to reduce only from 5 bits s Hz −1 to 4 bits s Hz −1 , with the exact performance being sensitive to d x /d y and showing variations of approximately ±10%. This indicates that the performance is sensitive to the link geometry.…”

“…Further work in developing the LAMM concept is suggested to focus on: exploring planar two-dimensional LAMM as described in [10], extending the system to support longer lateral movements, more modes, novel antenna designs and implementing dual polarization to provide additional minimization of crosstalk.…”

“…The SIR and spectral efficiency are analysed theoretically for two cases: (i) where the effect of antenna patterns of the patch antennas are excluded and, therefore, A(θ) = 1 for all angles defined as a 'top hat' antennas scenario; (ii) where the effect of the antenna patterns of the patch antennas are included and, therefore, A(θ ) as defined by (4.1) is subsequently used and can be considered as 'cosine' antennas. The subsequent channel coefficients can be computed as well as the LAMM pre-coded channels, as detailed in [10], assuming free space between the transmit and receive antennas.…”

“…However, in practice there would be some leakage due to the beamwidth of the elements' radiation patterns causing crosstalk, as indicated in figure 2. It is essential to ensure the topology is correctly set in order to have a viable link by carefully selecting the geometry determined by d x and d y , either to form a weak crosstalk link or a phase cancellation between the modes [10]. It is also determined by the level of leakage between feeder cables and devices used to create the required phase profile for the LAM modes.…”

“…Therefore, by selecting a low enough ratio of d x /d y it can create a substantial enough crosstalk without coding while applying the LAM pre-coding would counteract this. In this study a d x /d y ratio of 0.55 was chosen such that with the LAM pre-coding ( [10], fig. 7b) it will provide a maximum phase cancellation between the modes to maximize data throughput.…”