Abstract
Electromagnetic waves carrying orbital angular momentum (OAM) have been used for mode division multiplexing in free-space communication systems to increase both the capacity and the spectral efficiency. In the case of conventional wireless communication links using non-OAM beams, multipath effects caused by beam spreading and reflection from the surrounding objects affect the system performance. This paper presents the results of analysis, simulations, and measurements of multipath effects in a millimetre-wave communication link using OAM multiplexing at 28 GHz. Multipath-induced intra- and inter-channel crosstalk, which are caused by specular reflection from a plane parallel to the propagation path, are analysed and measured. Both the simulation and the experimental results show that an OAM channel with a high OAM number ℓ tends to suffer from both strong intra-channel crosstalk and strong inter-channel crosstalk with other OAM channels. Results of the analysis show that this observation can be explained on the basis of both the properties of OAM beam divergence and the filtering effect at the receiver, which is associated with the spiral wavefront of OAM beams.
Highlights
There are many compelling applications for high-spectral-efficiency and high-transmission-capacity point-to-point free-space line-of-sight (LoS) communication links, including indoor, data centre, front-haul, and back-haul systems[1,2]
Results of the analysis and measurement show that orbital angular momentum (OAM) channels with high values of l tend to suffer from both strong intra-channel crosstalk and strong inter-channel crosstalk with other channels
Due to the unique intensity and phase structure of OAM beams, the analysis is different from the traditional multipath effects
Summary
We investigated the multipath-induced intra- and inter-channel crosstalk effects in a millimetre-wave communications link using OAM multiplexing. The multipath OAM channels with higher values tend to have stronger intra-channel crosstalk. OAM channels with higher l values cause an increase in the inter-channel crosstalk with the other OAM channels in the presence of multipath effects. The results of our investigation primarily focus on the fundamental effect of multipath in an OAM multiplexing scenario and consider a single specular reflector. This scenario is practically relevant as being similar to a ground/wall reflection and provides insights into the interaction between the direct and the reflected components. Further work may investigate the combined impact of multiple reflectors and diffused reflectors and diffused reflection, and explore using digital signal processing (such as using an equalizer) to mitigate multipath effects[23]
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