Browse Prior Art Database

Decision Directed Method for Timing Recovery in PAM Data Signal Receivers

IP.com Disclosure Number: IPCOM000083907D
Original Publication Date: 1975-Aug-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Ungerboeck, G: AUTHOR

Abstract

A receiver for synchronous pulse-amplitude modulated (PAM) data signals has to deal with a signal of the form: (Image Omitted) where a(n) are the discrete symbol amplitudes carrying the information, s (t) is the elementary symbol waveform, T denotes the elementary symbol spacing, and w (t) may be additive noise.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 55% of the total text.

Page 1 of 3

Decision Directed Method for Timing Recovery in PAM Data Signal Receivers

A receiver for synchronous pulse-amplitude modulated (PAM) data signals has to deal with a signal of the form:

(Image Omitted)

where a(n) are the discrete symbol amplitudes carrying the information, s (t) is the elementary symbol waveform, T denotes the elementary symbol spacing, and w (t) may be additive noise.

In carrier-modulated systems z(t) may be complex (representing the in phase and quadrature components converted to the baseband as real and imaginary parts, respectively). In a well-equalized system, s(t) closely looks like the familiar sin (x)/x form shown in Fig. 1.

Many recent schemes for timing recovery employ a voltage-controlled oscillator (VCO) in a phase-locked loop (PLL) arrangement. The various approaches differ in their manner of deriving a phase-control signal for the VCO. In the so-called "decision directed receivers", the phase-control signal is derived with the aid of decisions made by the receiver.

In many modern receivers, especially for data transmission over telephone channels where data rates are moderate and signal distortion can be severe, adaptive digital filtering techniques are employed. In this case, only sample values of z (t) are available at rate f(T). Timing must be controlled at the analog/digital (A/D) converter prior to the equalizer. A time derivative of z (t) is then not readily available, or can be provided only at considerable additional expense.

It is then still desirable to have a timing-recovery scheme comprising a phase-locked loop arrangement, but the scheme should work without time derivatives. The proposed method eliminates this need and, furthermore, does not require multiplication of analog quantities, as is the case in most prior receivers.

The proposed scheme is seen in Fig. 2. Here the voltage-controlled oscillator (VCO) is controlled according to:

(Image Omitted)

In order to visualize the effect of this method, the expectation of the phase- control in...