On the Mean Square Error Optimal Estimator in One-Bit Quantized Systems

TL;DR

This paper analyzes the mean square error optimal estimator in one-bit quantized systems, compares it with the Bussgang estimator, and proposes an optimal pilot sequence with closed-form MSE expressions, revealing insights into quantized channel estimation.

Contribution

It establishes the relationship between the CME and Bussgang estimator, derives a new closed-form MSE for an optimal pilot sequence, and provides asymptotic analysis for large pilot numbers.

Findings

Bussgang estimator equals CME in certain cases

Derived closed-form MSE for the optimal pilot sequence

Quantified the stochastic resonance effect in quantized systems

Abstract

This paper investigates the mean square error (MSE)-optimal conditional mean estimator (CME) in one-bit quantized systems in the context of channel estimation with jointly Gaussian inputs. We analyze the relationship of the generally nonlinear CME to the linear Bussgang estimator, a well-known method based on Bussgang's theorem. We highlight a novel observation that the Bussgang estimator is equal to the CME for different special cases, including the case of univariate Gaussian inputs and the case of multiple pilot signals in the absence of additive noise prior to the quantization. For the general cases we conduct numerical simulations to quantify the gap between the Bussgang estimator and the CME. This gap increases for higher dimensions and longer pilot sequences. We propose an optimal pilot sequence, motivated by insights from the CME, and derive a novel closed-form expression of the MSE for that case. Afterwards, we find a closed-form limit of the MSE in the asymptotically large number of pilots regime that also holds for the Bussgang estimator. Lastly, we present numerical experiments for various system parameters and for different performance metrics which illuminate the behavior of the optimal channel estimator in the quantized regime. In this context, the well-known stochastic resonance effect that appears in quantized systems can be quantified.