Real-time signal-to-noise ratio (SNR) estimation for BPSK and QPSK modulation using the active communications channel

US7190741B1 · kind B1 · utility

Assignee

• The United States of America as represented by the Administrator of the National Aeronautics and Space Administration · US

Inventor

• Robert M. Manning · Weymouth, US

Key dates

• Filing date: Oct 21, 2002
• Grant date: Mar 13, 2007
• Expiry date: Nov 11, 2024

Classification

• Technology area (CPC H): Electricity
• CPC primary: H04L27/2332
• WIPO field: Telecommunications
• WIPO sector: Electrical engineering

Abstract

Method and apparatus for estimating signal-to-noise ratio (SNR) γ of a composite input signal e(t) on a phase-modulated (e.g., BPSK) communications link. A first demodulator receives the composite input signal and a stable carrier signal and outputs an in-phase output signal; a second demodulator receives the composite input signal and a phase-shifted version of the carrier signal and outputs a quadrature-phase output signal; and phase error θE(t) contained within the composite input signal e(t) is calculated from the outputs of the first and second demodulators. A time series of statistically independent phase error measurements θE(t1), θE(t2), . . . , θE(tk) is obtained from the composite input signal subtending a time interval Δt=tk−t1 whose value is small enough such that γ(t) and σ(t) can be taken to be constant in Δt. A biased estimate γ* for the signal-to-noise ratio (SNR) γ of the composite input signal is calculated using maximum likelihood (ML) estimation techniques, and an unbiased estimate {circumflex over (γ)} for the signal-to-noise ratio (SNR) γ of the composite input signal is determined from the biased estimate γ*, such as by use of a look-up table.