Dynamic Subarrays for Hybrid Precoding in Wideband mmWave MIMO Systems (1606.08405v1)

Abstract: Hybrid analog/digital precoding architectures can address the trade-off between achievable spectral efficiency and power consumption in large-scale MIMO systems. This makes it a promising candidate for millimeter wave systems, which require deploying large antenna arrays at both the transmitter and receiver to guarantee sufficient received signal power. Most prior work on hybrid precoding focused on narrowband channels and assumed fully-connected hybrid architectures. MmWave systems, though, are expected to be wideband with frequency selectivity. In this paper, a closed-form solution for fully-connected OFDM-based hybrid analog/digital precoding is developed for frequency selective mmWave systems. This solution is then extended to partially-connected but fixed architectures in which each RF chain is connected to a specific subset of the antennas. The derived solutions give insights into how the hybrid subarray structures should be designed. Based on them, a novel technique that dynamically constructs the hybrid subarrays based on the long-term channel characteristics is developed. Simulation results show that the proposed hybrid precoding solutions achieve spectral efficiencies close to that obtained with fully-digital architectures in wideband mmWave channels. Further, the results indicate that the developed dynamic subarray solution outperforms the fixed hybrid subarray structures in various system and channel conditions.

• The paper presents a dynamic subarray technique that leverages long-term channel statistics for optimizing hybrid precoding in wideband mmWave MIMO systems.
• It extends traditional fully-connected approaches to partially-connected subarray architectures, achieving spectral efficiencies close to fully-digital systems.
• Numerical evaluations demonstrate that dynamic subarrays outperform fixed configurations, suggesting significant potential for improved hardware implementations.

Dynamic Subarrays for Hybrid Precoding in Wideband mmWave MIMO Systems

The paper addresses the design challenges of hybrid analog/digital precoding architectures in wideband millimeter wave (mmWave) multiple-input multiple-output (MIMO) systems. Such architectures aim to balance achievable spectral efficiency with power consumption, a critical consideration as mmWave systems demand extensive antenna arrays at both the transmitter and receiver. Unlike previous research, which predominantly focused on narrowband channels and fully-connected hybrid structures, this paper advances a comprehensive solution applicable to wideband, frequency-selective environments.

Key Contributions

1. Hybrid Precoding Design: The authors derive a closed-form solution for fully-connected orthogonal frequency-division multiplexing (OFDM)-based hybrid precoding in wideband mmWave channels. The solution extends to partially-connected architectures where each radio frequency (RF) chain interfaces with a specific subset of antennas rather than all antennas. The presented methodologies offer insight into the design of hybrid subarray structures and propose a dynamically adaptive solution based on long-term channel characteristics.
2. Dynamic Subarray Technique: A novel dynamic approach is introduced, enabling the construction of adaptive hybrid subarrays. This method exploits long-term channel statistics to adjust the subarray structure dynamically. The implementation of such dynamic subarrays intends to optimize system performance beyond the static configuration limits typically imposed in fixed subarray designs.
3. Numerical Evaluation: Simulation results demonstrate the proposed hybrid precoding solutions achieving spectral efficiencies close to those attainable with fully-digital architectures, even in complex wideband mmWave channels. In conditions where the number of RF chains is greater than or equal to the number of channel paths, the hybrid precoding strategies achieve efficiencies on par with those of unconstrained fully-digital precoders.

Strong Numerical Results

• The dynamic subarray solution outperforms fixed subarray configurations across various system settings, highlighting the potential advantages of the dynamic approach in versatile channel environments.
• The paper provides evidence that dynamic subarrays can adaptively maximize spectral efficiency in response to changing channel conditions, offering a practical enhancement over static subarrays.

Theoretical and Practical Implications

Theoretically, the findings make a significant contribution to the understanding of hybrid precoding in wideband mmWave systems, demonstrating that adaptive subarray structures can significantly boost system throughput. Practically, the research implications suggest hardware development directions for implementing dynamic switching mechanisms in mmWave antennas.

Future Directions

Future work might focus on optimizing the complexity of implementing dynamic subarrays, assessing trade-offs between energy efficiency and spectral performance. Additionally, exploring the integration of these solutions in multi-user frameworks and larger-scale arrays could provide further insights into maximized performance in next-generation mmWave communications.

In conclusion, this paper indicates a promising trajectory toward more efficient and adaptable hybrid precoding schemes in wideband mmWave MIMO systems, setting a foundation for future innovations in communication technologies.