Constrained Phase Noise Estimation in OFDM Using Scattered Pilots Without Decision Feedback

TL;DR

This paper introduces a novel phase noise estimation method for OFDM systems that uses only scattered pilots without decision feedback, employing a convex optimization approach to improve accuracy and reduce errors.

Contribution

It proposes a constrained optimization framework for phase noise estimation in OFDM that avoids decision feedback and leverages phase noise geometry for enhanced accuracy.

Findings

Improved bit-error-rate performance at high SNRs.

Thinner tails in phase noise estimation error distribution.

Convex dual problem solution for non-convex optimization.

Abstract

In this paper, we consider an OFDM radio link corrupted by oscillator phase noise in the receiver, namely the problem of estimating and compensating for the impairment. To lessen the computational burden and delay incurred onto the receiver, we estimate phase noise using only scattered pilot subcarriers, i.e., no tentative symbol decisions are used in obtaining and improving the phase noise estimate. In particular, the phase noise estimation problem is posed as an unconstrained optimization problem whose minimizer suffers from the so-called amplitude and phase estimation error. These errors arise due to receiver noise, estimation from limited scattered pilot subcarriers and estimation using a dimensionality reduction model. It is empirically shown that, at high signal-to-noise-ratios, the phase estimation error is small. To reduce the amplitude estimation error, we restrict the minimizer to be drawn from the so-called phase noise geometry set when minimizing the cost function. The resulting optimization problem is a non-convex program. However, using the S-procedure for quadratic equalities, we show that the optimal solution can be obtained by solving the convex dual problem. We also consider a less complex heuristic scheme that achieves the same objective of restricting the minimizer to the phase noise geometry set. Through simulations, we demonstrate improved coded bit-error-rate and phase noise estimation error performance when enforcing the phase noise geometry. For example, at high signal-to-noise-ratios, the probability density function of the phase noise estimation error exhibits thinner tails which results in lower bit-error-rate.