Robert Anthony Manning

US Patent:

7190741, Mar 13, 2007

Filed:

Oct 21, 2002

Appl. No.:

10/274756

Inventors:

Robert M. Manning - Strongsville OH, US

Assignee:

The United States of America as represented by the Administrator of the National Aeronautics and Space Administration - Washington DC

International Classification:

H04L 27/00
H04Q 1/20
H04B 1/10

US Classification:

375324, 375227, 375254, 375285

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 θ(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 θ(t), θ(t),. . . , θ(t) is obtained from the composite input signal subtending a time interval Δt=t−twhose 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.