Hybrid Architectures with Few-Bit ADC Receivers: Achievable Rates and Energy-Rate Tradeoffs (1605.00668v2)

Abstract: Hybrid analog/digital architectures and receivers with low-resolution analog-to-digital converters (ADCs) are two low power solutions for wireless systems with large antenna arrays, such as millimeter wave and massive MIMO systems. Most prior work represents two extreme cases in which either a small number of RF chains with full-resolution ADCs, or low resolution ADC with a number of RF chains equal to the number of antennas is assumed. In this paper, a generalized hybrid architecture with a small number of RF chains and finite number of ADC bits is proposed. For this architecture, achievable rates with channel inversion and SVD based transmission methods are derived. Results show that the achievable rate is comparable to that obtained by full-precision ADC receivers at low and medium SNRs. A trade-off between the achievable rate and power consumption for different numbers of bits and RF chains is devised. This enables us to draw some conclusions on the number of ADC bits needed to maximize the system energy efficiency. Numerical simulations show that coarse ADC quantization is optimal under various system configurations. This means that hybrid combining with coarse quantization achieves better energy-rate trade-off compared to both hybrid combining with full-resolutions ADCs and 1-bit ADC combining.

• The paper proposes a hybrid architecture that balances the trade-off between RF chain count and ADC resolution to optimize system performance.
• It derives closed-form expressions indicating that intermediate ADC resolutions (4-5 bits) achieve superior energy-rate trade-offs compared to 1-bit or full-resolution ADCs.
• Numerical simulations confirm that the proposed system attains nearly full-resolution performance at low-to-medium SNRs while enhancing overall energy efficiency.

Hybrid Architectures with Few-Bit ADC Receivers: Achievable Rates and Energy-Rate Tradeoffs

The research paper addresses the challenges and potential solutions in the development of energy-efficient wireless communication systems employing hybrid analog/digital architectures with low-resolution ADCs—particularly within massive MIMO and mmWave systems. These architectures, characterized by their capacity to reduce both hardware complexity and power consumption, have significant implications for future wireless networks where large antenna arrays are prevalent.

Summary of Contributions

The researchers propose a generalized hybrid architecture that balances the trade-offs between the number of RF chains and ADC resolution, aiming to optimize both resource allocation and system performance. Their approach bridges the gap between existing architectures that either employ a small number of RF chains with full-resolution ADCs, or utilize numerous RF chains with extremely low-resolution ADCs.

The paper presents the following key contributions:

1. Achievable Rate Analysis: The researchers derive closed-form expressions for achievable rates employing channel inversion and singular value decomposition (SVD) based transmission methods within their proposed architecture. The results reveal that, particularly at low-to-medium SNRs, the architecture can achieve rates comparable to those of systems with full-resolution ADC receivers.
2. Energy-Rate Trade-off: They devise a framework to paper the trade-offs between achievable rates and power consumption for configurations with varying ADC bit resolutions and RF chain counts. Their findings suggest that intermediate ADC resolutions, typically around 4-5 bits, provide an optimal balance, achieving superior energy efficiency across diverse system configurations compared to both 1-bit and full-resolution ADC scenarios.
3. Numerical Simulations: To complement their theoretical findings, the researchers conduct numerical simulations demonstrating that hybrid combining with coarse quantization offers more favorable energy-rate trade-offs than configurations using either full-resolution ADCs or only 1-bit ADCs.
4. Upper and Lower Bounds of Rates: The paper also establishes upper and lower bounds on achievable rates, particularly focusing on one-bit quantization scenarios. These benchmarks elucidate the efficacy of proposed methods in relation to theoretical limits and help delineate optimal system configurations.

Implications and Future Directions

The implications of this research extend to both theoretical and practical domains within wireless communication technology. By mapping out the potential advantages of using few-bit ADCs in hybrid architectures, the researchers provide insight into designing energy-efficient systems without substantially compromising on performance. This becomes especially relevant for mmWave communication, where the balance between power consumption and spectral efficiency is crucial.

Envisioning future directions, further exploration could revolve around adaptive strategies that dynamically optimize ADC resolution and RF chain allocation in accordance with evolving channel conditions and user requirements. Additionally, research can extend to hybrid architectures with digital-to-analog converters (DACs) also operating at reduced resolutions.

This paper offers a foundational step in understanding the trade-offs inherent in hybrid architecture configurations, encouraging the design of adaptable systems that efficiently manage the pivotal balance between power consumption and achievable rates as the demand for higher data throughput and energy-efficient communications proliferates in wireless networks.