Browse Prior Art Database

Carrier Phase and Symbol Resynchronization

IP.com Disclosure Number: IPCOM000048362D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Godard, D: AUTHOR

Abstract

This article presents a signal processing algorithm for carrier phase and symbol resynchronization in a data receiver incorporating a decision feedback equalizer.

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Carrier Phase and Symbol Resynchronization

This article presents a signal processing algorithm for carrier phase and symbol resynchronization in a data receiver incorporating a decision feedback equalizer.

The figure shows a simplified block diagram of a data receiver including an ADC (analog to digital converter), AGC (automatic gain control) and HMF (Hilbert matched filter).

Denoting by y(k) the HMF output samples, the output signal of the forward equalizer takes the form of the given equation (see article) where c(k) are tap coefficients. The signal x(n) is rotated by an estimate (n) of carrier phase provided by the carrier-tracking loop. Previous decisions a(n-p), p equals 1,...,M, are linearly combined in the feedback part to form the input signal z(n) to the decision circuit.

Coefficients c and d as well as are adjusted to minimize the mean square error (see article) where E indicates expectation.

Assuming that past decisions are correct, this leads to gradient algorithms: (see article) where lambda(c), lambda(d) and lambda(phi) are positive step size parameters.

Attention must be paid to the relative values of lambda(c) and lambda(d). The ratio lambda(c)/ lambda(d) must be in the order of M E absolute value of a(n)/2//(1+N(1)+N(2) E absolute value of yn/2/.

It is important to note that joint solutions to (4) and (6) are not unique as in the case of transversal equalizers, but feedback coefficients converge to values independent of (n).

In the steady state, the output signal of the forward equalizer may be put into the general form of the given equation (see article) where w(n) represents noise, including residual intersymbol interference.

For resynchronization purpose, the transmitter sends alternations between data symbols A and B defined by A equals -3

B equals 3-3j

This article does not address carrier detection and clock phase processes which can be achieved through any known algorithm.

Once clock phase has been adjusted, the receiver waits for the forward equalizer to be filled with signal samples. It...