One-Bit Massive MIMO: Channel Estimation and High-Order Modulations (1504.04540v2)

Abstract: We investigate the information-theoretic throughout achievable on a fading communication link when the receiver is equipped with one-bit analog-to-digital converters (ADCs). The analysis is conducted for the setting where neither the transmitter nor the receiver have a priori information on the realization of the fading channels. This means that channel-state information needs to be acquired at the receiver on the basis of the one-bit quantized channel outputs. We show that least-squares (LS) channel estimation combined with joint pilot and data processing is capacity achieving in the single-user, single-receive-antenna case. We also investigate the achievable uplink throughput in a massive multiple-input multiple-output system where each element of the antenna array at the receiver base-station feeds a one-bit ADC. We show that LS channel estimation and maximum-ratio combining are sufficient to support both multiuser operation and the use of high-order constellations. This holds in spite of the severe nonlinearity introduced by the one-bit ADCs.

• The paper analyzes how one-bit massive MIMO systems handle channel estimation and high-order modulations, demonstrating their capability even with low-resolution receivers.
• The research demonstrates that massive MIMO systems can sustain high spectral efficiency with one-bit receivers and high-order modulations, particularly with a large number of base station antennas.
• Numerical simulations reveal complex behaviors, like constellation collapse, and show that high-order constellations can outperform QPSK under certain conditions, suggesting spatial oversampling benefits.

An Analysis of Channel Estimation and High-Order Modulations in One-Bit Massive MIMO Systems

The paper at hand explores the performance of one-bit quantized receivers in the context of massive multiple-input multiple-output (MIMO) systems, particularly focusing on their efficacy in channel estimation and modulation. The primary goal of this investigation is to evaluate how such receivers, often limited by their low-resolution analog-to-digital converters (ADCs), manage channel estimation and high-order constellations in a fading communication environment where neither the transmitter nor the receiver has prior information on channel state realizations.

Key Contributions and Findings

1. SISO Channel Capacity: The paper first examines the capacity achievable in a single-user single-input single-output (SISO) scenario where the receiver employs one-bit ADCs. Notable is the finding that least-squares (LS) channel estimation, when combined with joint pilot-data (JPD) processing, achieves the theoretical channel capacity. This result is significant as it underscores the adequacy of LS estimates even in a quantization-limited regime, which defies conventional expectations of sophisticated channel estimation algorithms being necessary.
2. Multichannel MIMO Capacity and Limitations: Extending the analysis to the uplink in a massive MIMO configuration, the paper explores achievable rates with multi-user interference and high-order modulation schemes such as 16-QAM. Even with the inherent nonlinearity introduced by one-bit quantizers at the receiver, the research demonstrates that such systems can sustain high spectral efficiency, particularly when the quantity of antennas at the base station is large. The findings indicate that massive MIMO setups can indeed capitalize on spatial diversity to mitigate quantization-induced losses.
3. Numerical Simulations Across Various Conditions: Through comprehensive simulation experiments, the paper provides comparative analyses across different system parameters, including coherence time, SNR levels, and antenna array sizes. Interesting phenomena such as the collapse of constellations into circular shapes at high SNRs are observed, which stress the complex interplay between noise resilience and multi-user interference in such constrained receiver architectures. Furthermore, the paper empirically establishes scenarios where high-order constellations outperform traditional QPSK modulations, highlighting the potential for spatial oversampling in massive antenna layouts to substitute for temporal oversampling.
4. Theoretical and Practical Implications: The work has several critical implications. On a theoretical level, it contributes insights into the rate-distortion characteristics of one-bit quantized systems in the absence of prior CSI, presenting a novel perspective on the feasibility of simplistic estimation techniques in complex environments. Practically, it offers guidance on the design of energy-efficient, low-complexity receivers suitable for future wideband and millimeter-wave applications, where the need for power-efficient components is paramount.

Looking into the future, the implications of this research are extensive. The capability of one-bit massive MIMO systems to sustain high-order modulations paves the way toward realizing scalable, cost-effective network designs that meet the bandwidth demands of next-generation wireless systems. However, additional research is required to tackle challenges such as interference management, further refinement of coding schemes, and possible improvements through AI-driven signal processing. This paper sets the foundation for such explorative endeavors, challenging existing paradigms about ADC quantization and pushing the boundaries of what minimalistic hardware can achieve in complex signal processing tasks.