Millimeter Wave MIMO with Lens Antenna Array: A New Path Division Multiplexing Paradigm (1507.01699v1)

Abstract: Millimeter wave (mmWave) communication is a promising technology for 5G cellular systems. To compensate for the severe path loss in mmWave systems, large antenna arrays are generally used to achieve significant beamforming gains. However, due to the high hardware and power consumption cost associated with radio frequency (RF) chains, it is desirable to achieve the large-antenna gains, but with only limited number of RF chains for mmWave communications. To this end, we study in this paper a new lens antenna array enabled mmWave MIMO communication system. We first show that the array response of the proposed lens antenna array at the receiver/transmitter follows a "sinc" function, where the antenna with the peak response is determined by the angle of arrival (AoA)/departure (AoD) of the received/transmitted signal. By exploiting this unique property of lens antenna arrays along with the multi-path sparsity of mmWave channels, we propose a novel low-cost and capacity-achieving MIMO transmission scheme, termed \emph{orthogonal path division multiplexing (OPDM)}. For channels with insufficiently separated AoAs and/or AoDs, we also propose a simple \emph{path grouping} technique with group-based small-scale MIMO processing to mitigate the inter-path interference. Numerical results are provided to compare the performance of the proposed lens antenna arrays for mmWave MIMO system against that of conventional arrays, under different practical setups. It is shown that the proposed system achieves significant throughput gain as well as complexity and hardware cost reduction, both making it an appealing new paradigm for mmWave MIMO communications.

• The paper introduces Orthogonal Path Division Multiplexing (OPDM) that exploits lens antenna arrays to transform mmWave MIMO by significantly lowering RF chain requirements.
• It demonstrates that each propagation path acts as an individual AWGN sub-channel when angles of arrival and departure are sufficiently separated, enabling efficient spatial multiplexing.
• Numerical results reveal substantial throughput gains and hardware cost reductions compared to traditional uniform planar arrays, offering practical benefits for 5G networks.

Overview of Millimeter Wave MIMO with Lens Antenna Array: A New Path Division Multiplexing Paradigm

The paper entitled "Millimeter Wave MIMO with Lens Antenna Array: A New Path Division Multiplexing Paradigm" by Yong Zeng and Rui Zhang presents an innovative approach to millimeter wave (mmWave) MIMO systems by leveraging lens antenna arrays. This work is situated in the context of enhancing fifth-generation (5G) cellular systems, particularly in harnessing the mmWave spectrum range of 30-300 GHz, which is largely underutilized. The primary objective is to achieve significant beamforming gains while reducing the high hardware and power consumption typically associated with numerous RF chains required in traditional MIMO setups.

Key Contributions and Findings

The research introduces a paradigm termed Orthogonal Path Division Multiplexing (OPDM), which exploits the unique properties of lens antenna arrays combined with the inherent multi-path sparsity of mmWave channels. OPDM allows for multiple data streams to be transmitted simultaneously over different propagation paths, requiring only per-path signal processing at both the transmitter and receiver. This approach is distinguished by:

• The lens antenna arrays' ability to translate signals from antenna space to a beamspace with reduced dimensions, significantly cutting the number of RF chains needed.
• The demonstration that each path can behave as an individual AWGN sub-channel under sufficiently separated angle of arrivals (AoA) and departures (AoD), enabling spatial multiplexing without the usual complexity.
• The proposed lens configuration yielding a "sinc" function array response, centered around the AoA/AoD, facilitating energy focusing capabilities not inherent to conventional arrays.

Numerical Results and Implications

Through simulations, the lens MIMO system evidenced substantial throughput gains and reductions in complexity and hardware costs when juxtaposed with traditional uniform planar arrays (UPAs). The findings illuminate the potential of lens antenna arrays in mmWave MIMO systems to achieve high directional gains and capacity maximization with minimal RF hardware, making such systems more feasible for integration into future 5G networks.

Theoretical and Practical Implications

Theoretically, this paradigm shift supports a refined understanding of mmWave propagation characteristics, thereby opening avenues for further exploration into high-capacity wireless communication models. Practically, the reduction in RF chain requirements addresses one of the significant barriers to the deployment of mmWave technology, namely, the cost and complexity associated with large-scale MIMO implementations. Moreover, the proposed OPDM and related techniques underscore the potential for efficient signal processing strategies that can be adapted to varying channel conditions, further amplifying the versatility of mmWave communications in real-world applications.

Speculation on Future Developments

Moving forward, the field may witness augmented attention to multi-user settings and dynamic antenna array configurations incorporating lens technologies, particularly those considering elevation data in multi-dimensional beamforming scenarios. Additionally, advances in adaptive beam selection methodologies could further streamline the use of lens antenna arrays, enhancing their applicability in dense urban environments or other challenging propagation conditions where mmWave frequencies are deployed.

In summary, the work of Zeng and Zhang provides a compelling framework for advancing mmWave MIMO communication systems, with impactful implications for both existing and emerging wireless networks. The lens antenna array offers a transformative potential for achieving high spectral efficiency with reduced system complexity, positioning it as a critical technological foundation for the next generation of wireless communication systems.