期刊
IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY
卷 70, 期 11, 页码 11748-11760出版社
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TVT.2021.3113983
关键词
Mode division multiplexing; multiple-input multiple-output systems; orbital angular momentum; spatial multiplexing; uniform circular antenna array; zero-forcing
资金
- U.K. Engineering and Physical Sciences Research Council (EPSRC) [EP/P000673/1]
- U.K. Research and Innovation Future Leaders Fellowships [MR/T019980/1]
- Department for the Economy Northern Ireland under the US-Ireland Research and Development Partnership Programme
- European Research Council (ERC) under the European Union's Horizon 2020 research, and innovation programme [101001331]
- EPSRC [EP/P000673/1] Funding Source: UKRI
Due to the spatial orthogonality of different OAM modes, MDM using OAM has been explored as a new wireless transmission technique. However, the presence of OAM mode offset can lead to inter-mode interference, impacting the spectral efficiency of line-of-sight free-space wireless communication systems. A theoretical analysis and practical communication experiment were conducted to evaluate the impact and propose solutions for improving system efficiency.
Thanks to its low transceiver complexity, mode division multiplexing (MDM) using orbital angular momentum (OAM) has been recently investigated as a new physical layer wireless transmission technique. This is due to the fact that different OAM modes are spatially orthogonal to each other, thus, perfectly suitable for spatial multiplexing and/or diversity. The orthogonality amongst different OAM modes is achieved in the absence of any mode offset between the transceivers' phase-shifting feeding networks. However, the inherent presence of OAM mode offset destroys the orthogonality between different modes, which gives rise to inter-mode interference (IMI). Therefore, in this paper, in order to theoretically analyze the negative impact of OAM mode offset of MDM-OAM systems on the spectral efficiency of line-of-sight free-spacewireless communication systems, an explicit signal-to-interference-plus-noise ratio expression for each OAM mode is derived, through which the spectral efficiency degradation is evaluated. Furthermore, in order to support our theoretical analysis, a 9 x 9 MDM-OAM practical communication experiment for different OAM mode settings is carried out at a microwave frequency of 5.8 GHz. In addition, by leveraging the fact that all circulant matrices always have the same eigendirections, regardless of the entries of the matrix, a low-complexity optimal OAM mode selection scheme is proposed which significantly improves the spectral efficiency of the system. Finally, in order to completely null-out the impact of OAM mode offset, a baseband zero-forcing stage is embedded at the receiver.
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