Orbital-Angular-Momentum-Embedded Massive-MIMO: Achieving Multiplicative Spectrum Efficiency for 6G Communications

By enabling very high bandwidth for radio communications, the millimeter wave (mmWave), which can easily be integrated with massive multiple input multiple output (massive-MIMO) due to small antenna size, has been attracting growing attention as a candidate for the sixth-generation (6G) wireless communication networks. On the other hand, the communication over the orthogonal states/modes of orbital angular momentum (OAM) is a subset of the solutions offered by massive-MIMO communications. Traditional massive-MIMO-based mmWave communications did not concern the potential spectrum efficiency gain (SE gain) offered by orthogonal states of OAM. However, the highly expected maximum SE gain for OAM and massive-MIMO communications is the product of SE gains offered by OAM and massive MIMO. In this chapter, we propose the OAM-embedded-MIMO (OEM) communication framework to obtain the multiplicative SE gain for joint OAM and massive-MIMO-based mmWave wireless communications. We design the parabolic antenna for each uniform circular array antenna to converge OAM signals. Then, we develop the mode-decomposition and multiplexing-detection schemes to obtain the transmit signal on each OAM mode of each transmit antenna. Also, we develop the OEM-water-filling power allocation policy to achieve the maximum multiplicative SE gain for OEM communications. The extensive simulations obtained validate and evaluate our developed parabolic antenna-based converging method, mode-decomposition and multiplexing-detection schemes, and an OEM-water-filling policy, showing that our proposed OEM mmWave communications can significantly increase the SE as compared with traditional massive-MIMO-based mmWave communications.