Browse Prior Art Database

DELAY MEASUREMENT METHOD USING OOK

IP.com Disclosure Number: IPCOM000006705D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-24
Document File: 2 page(s) / 110K

Publishing Venue

Motorola

Related People

Pedro T Figueredo: AUTHOR [+3]

Abstract

For various systems it is necessary to measure the delay that signals will experience as they traverse vari- ous communications paths. The path may involve tele- phone twisted pairs, radio frequency transmission and reception, splitters, nonanalog transmission media (i.e. digitized analog facilities), etc. The delay measurement is usually performed as a loop back type of operation.

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MOTOROLA INC. Technical Developments Volume 17 December 1992

DELAY MEASUREMENT METHOD USING OOK2

by Pedro T Figueredo, Dimitrios Nikas and Gregory L. Cannon

  For various systems it is necessary to measure the delay that signals will experience as they traverse vari- ous communications paths. The path may involve tele- phone twisted pairs, radio frequency transmission and reception, splitters, nonanalog transmission media (i.e. digitized analog facilities), etc. The delay measurement is usually performed as a loop back type of operation.

  In order to perform this measurement, the source sends a known sequence. At some point in the sequence a timer is started. It is stopped when the same point in the sequence is received.

  Digital communications over telephony type media usually employ frequency shi keying for data rates up to 2400 baud. Signals sent over these paths will how- ever exhibit frequency dependent propagation times. Although bit states may be recoverable, accurate timing of the received bit stream delay may not be due to the uncertainty of the exact switching points.

  Above 2400 baud, phase shifting of a single Sequency is offen used. This avoids the different delays due to using multiple frequencies, but it is even more dil?icult to derive a precise switching point due to the phase discontinuities.

  Amplitude modulation also has the advantage of using a single frequency. In telephony applications, ampli- tude modulation is not generally used for modems because the change from one amplitude to another is a discontinuity which generates higher frequencies. The phone lines however act as low pass filters. The result is a ringing which decays with time. The problem then is to differentiate the true end of the signal from the decaying transient response. One approach is to use a curve known as the raised cosine when switching from on to off or off to on. By not producing a sharp discontinuity, the received signal on properly conditioned lines is very close in form to that transmitted. The difference between the full ampli- tude cycle and the transition cycle can be determined by simple comparisons ofthe amplitudes.

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  A problem, however, exists on limes which have a large mismatch and/or are heavily capacitively and/or inductively loaded. Instead of a low level transient sig- nal occurring, a slowly decaying transient signal is observed. In this case, the determination of the signal end by rolloff is difficult, if not impossible. In this...