Spectrum and Energy Efficient Beamspace MIMO-NOMA for Millimeter-Wave Communications Using Lens Antenna Array (1707.06740v1)

Abstract: The recent concept of beamspace multiple input multiple output (MIMO) can significantly reduce the number of required radio-frequency (RF) chains in millimeter-wave (mmWave) massive MIMO systems without obvious performance loss. However, the fundamental limit of existing beamspace MIMO is that, the number of supported users cannot be larger than the number of RF chains at the same time-frequency resources. To break this fundamental limit, in this paper we propose a new spectrum and energy efficient mmWave transmission scheme that integrates the concept of non-orthogonal multiple access (NOMA) with beamspace MIMO, i.e., beamspace MIMO-NOMA. By using NOMA in beamspace MIMO systems, the number of supported users can be larger than the number of RF chains at the same time-frequency resources. Particularly, the achievable sum rate of the proposed beamspace MIMO-NOMA in a typical mmWave channel model is analyzed, which shows an obvious performance gain compared with the existing beamspace MIMO. Then, a precoding scheme based on the principle of zero-forcing (ZF) is designed to reduce the inter-beam interferences in the beamspace MIMO-NOMA system. Furthermore, to maximize the achievable sum rate, a dynamic power allocation is proposed by solving the joint power optimization problem, which not only includes the intra-beam power optimization, but also considers the inter-beam power optimization. Finally, an iterative optimization algorithm with low complexity is developed to realize the dynamic power allocation. Simulation results show that the proposed beamspace MIMO-NOMA can achieve higher spectrum and energy efficiency compared with existing beamspace MIMO.

• The paper introduces beamspace MIMO-NOMA, integrating NOMA with beamspace MIMO to enhance spectrum and energy efficiency by serving multiple users per beam.
• Interference mitigation is managed via ZF-based precoding, and dynamic power allocation optimizes performance while adhering to a total power constraint.
• Simulation results demonstrate the proposed beamspace MIMO-NOMA scheme achieves superior spectrum and energy efficiency, including approximately a 25% improvement in energy efficiency.

Overview of Beamspace MIMO-NOMA in mmWave Communications

The paper "Spectrum and Energy Efficient Beamspace MIMO-NOMA for Millimeter-Wave Communications Using Lens Antenna Array" introduces an innovative transmission scheme to address the limitations inherent in traditional beamspace multiple-input multiple-output (MIMO) systems for millimeter-wave (mmWave) communications. The authors propose integrating non-orthogonal multiple access (NOMA) with beamspace MIMO to enhance spectrum and energy efficiencies.

Key Contributions

1. Concept Introduction: The paper presents the concept of beamspace MIMO-NOMA, which allows more than one user to be simultaneously served within each beam, thereby increasing the potential number of users relative to the number of RF chains. This is in contrast to conventional beamspace MIMO, where each beam serves at most one user.
2. Interference Mitigation Through Precoding: The research utilizes a zero-forcing (ZF)-based precoding approach to mitigate inter-beam interference. Two methods are highlighted: one based on the strongest user channel and the other leveraging singular value decomposition (SVD) of the beamspace channel matrices.
3. Dynamic Power Allocation: An iterative power allocation algorithm is introduced, designed to optimize both intra-beam and inter-beam power levels. This dynamic adjustment aims to maximize the system's achievable sum rate while adhering to a total power constraint.
4. Simulation Results: Through simulations, the beamspace MIMO-NOMA scheme demonstrates superior performance in both spectrum and energy efficiencies compared to traditional beamspace MIMO and MIMO-OMA systems. Notably, the proposed system achieves around 25% improvement in energy efficiency.

Numerical and Practical Implications

• Energy Efficiency: The proposed system reduces the energy consumption associated with RF chains, which is substantial in traditional MIMO systems given each antenna's direct RF chain connection.
• Spectrum Efficiency: By utilizing NOMA's power domain for user multiplexing, the scheme improves the data rate per bandwidth, essential for the anticipated mmWave communication demands in future networks.

Theoretical Insights and Future Directions

The integration of NOMA with beamspace MIMO explores the field of exploiting power domain multiplexing to enhance mmWave system capabilities, offering an alternative to further physical layer complexity. Beamspace MIMO-NOMA showcases potential by allowing greater channel utilization than traditional MIMO configurations, breaking the presumed limitations where user numbers are bound by available RF chains.

Going forward, effective user pairing or clustering strategies could be examined to maximize performance in ultra-dense network environments. Additionally, exploring more sophisticated forms of inter-beam interference management and alternative precoding techniques could further optimize system effectiveness.

In conclusion, this paper paves the way for enhanced capacity and connectivity in next-generation wireless networks by bridging theoretical advances with practical design optimizations. While the proposed beamspace MIMO-NOMA extension presents complexities in implementation, it offers a substantial promise for the growing demands of modern communications infrastructure.