Millimeter Wave Beam-Selection Using Out-of-Band Spatial Information (1702.08574v1)

Abstract: Millimeter wave (mmWave) communication is one feasible solution for high data-rate applications like vehicular-to-everything communication and next generation cellular communication. Configuring mmWave links, which can be done through channel estimation or beam-selection, however, is a source of significant overhead. In this paper, we propose to use spatial information extracted at sub-6 GHz to help establish the mmWave link. First, we review the prior work on frequency dependent channel behavior and outline a simulation strategy to generate multi-band frequency dependent channels. Second, assuming: (i) narrowband channels and a fully digital architecture at sub-6 GHz; and (ii) wideband frequency selective channels, OFDM signaling, and an analog architecture at mmWave, we outline strategies to incorporate sub-6 GHz spatial information in mmWave compressed beam selection. We formulate compressed beam-selection as a weighted sparse signal recovery problem, and obtain the weighting information from sub-6 GHz channels. In addition, we outline a structured precoder/combiner design to tailor the training to out-of-band information. We also extend the proposed out-of-band aided compressed beam-selection approach to leverage information from all active OFDM subcarriers. The simulation results for achievable rate show that out-of-band aided beam-selection can reduce the training overhead of in-band only beam-selection by 4x.

• The paper introduces an OOB-aided beam-selection framework using weighted sparse signal recovery to reduce mmWave training overhead.
• It employs sub-6 GHz spatial information to design structured precoders/combiners and simulates frequency-dependent channel behaviors.
• Simulation results demonstrate a fourfold training overhead reduction, offering tangible benefits for high-mobility applications like V2X communications.

An Overview of Millimeter Wave Beam-Selection Using Out-of-Band Spatial Information

The paper "Millimeter Wave Beam-Selection Using Out-of-Band Spatial Information" by Anum Ali, Nuria González-Prelcic, and Robert W. Heath Jr. addresses a significant challenge in millimeter wave (mmWave) communication: reducing the overhead in configuring mmWave links through effective beam-selection. The authors propose utilizing spatial information extracted from sub-6 GHz channels to facilitate this process, thereby reducing the training burden traditionally associated with in-band mmWave link establishment.

Key Contributions and Methodology

The research offers several key methodological contributions:

• Multi-Band Frequency Dependent Channels: The paper reviews frequency-dependent channel behavior, proposing simulation strategies for generating multi-band frequency dependent channels. The authors elaborate on channel characteristics across different frequencies, acknowledging spatial congruence between sub-6 GHz and mmWave channels.
• OOB-Aided Beam-Selection Framework: The core proposition is leveraging out-of-band (OOB) sub-6 GHz spatial information in mmWave beam-selection. The problem is cast as a weighted sparse signal recovery, with weights derived from the OOB information. The authors extend their approach to include structured precoder/combiner design and leveraging all active OFDM subcarrier information.
• Simulation Results for Rate Performance: Simulations demonstrate that the proposed OOB-aided beam-selection approach can decrease the training overhead by a factor of four compared to methods relying solely on in-band information. This reduction is particularly advantageous in high-mobility scenarios, such as vehicular-to-everything (V2X) communications and next-generation cellular systems.

Numerical Results and Implications

The numerical results from simulations indicate that the proposed methodology effectively reduces the training overhead, achieving a fourfold reduction compared to in-band-only approaches. The authors point out that the structured codebook design and weighted sparse recovery improve the effectiveness of beam-selection in terms of achievable rate.

This work has both theoretical and practical implications. Theoretically, it suggests that substantial spatial congruence between sub-6 GHz and mmWave channels can be exploited to enhance mmWave communication without incurring prohibitive overhead. Practically, this could lead to tangible improvements in V2X communications and future outdoor cellular systems, where the dynamic link reconfiguration is frequent and costly in terms of time and resources.

Future Directions

The research opens pathways for further investigation, particularly in the context of hybrid analog/digital and fully digital mmWave architectures. Future work could explore broader array geometries beyond uniform linear arrays, implement this approach in real-world scenarios, and refine the correlation models between sub-6 GHz spatial characteristics and mmWave performance metrics. Enhanced joint channel modeling and more robust correlation strategies could refine the congruence insights gained in this paper.

In summary, the paper offers a comprehensive framework to improve mmWave beam-selection efficiency using out-of-band spatial information, with significant implications for high-speed mobile communications.