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WO1993015563A1 - Transmission de signal d'essai entre des stations afin de mesurer le temps de propagation d'un groupe - Google Patents

Transmission de signal d'essai entre des stations afin de mesurer le temps de propagation d'un groupe Download PDF

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Publication number
WO1993015563A1
WO1993015563A1 PCT/GB1993/000178 GB9300178W WO9315563A1 WO 1993015563 A1 WO1993015563 A1 WO 1993015563A1 GB 9300178 W GB9300178 W GB 9300178W WO 9315563 A1 WO9315563 A1 WO 9315563A1
Authority
WO
WIPO (PCT)
Prior art keywords
signal
station
transition
test signal
test
Prior art date
Application number
PCT/GB1993/000178
Other languages
English (en)
Inventor
John David Brownlie
Original Assignee
British Telecommunications Public Limited Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by British Telecommunications Public Limited Company filed Critical British Telecommunications Public Limited Company
Publication of WO1993015563A1 publication Critical patent/WO1993015563A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/46—Monitoring; Testing
    • H04B3/462—Testing group delay or phase shift, e.g. timing jitter

Definitions

  • the present invention is concerned with modems, that is to say, modulation/demodulation apparatus by means of 5 which digital signals to be transmitted control one or more of the properties (phase, frequency, amplitude) of a carrier, and digital signals to be received are recovered from an incoming modulated carrier.
  • modulation/demodulation apparatus by means of 5 which digital signals to be transmitted control one or more of the properties (phase, frequency, amplitude) of a carrier, and digital signals to be received are recovered from an incoming modulated carrier.
  • modulation/demodulation apparatus by means of 5 which digital signals to be transmitted control one or more of the properties (phase, frequency, amplitude) of a carrier, and digital signals to be received are recovered from an incoming modulated carrier.
  • modulation/demodulation apparatus by means of 5 which digital signals to be transmitted control one or more of the properties (phase, frequency, amplitude) of a carrier, and digital signals to be received are recovered from an incoming modulated carrier.
  • the precise form of modulation to be used is not however critical to the
  • a transmission link comprising two simple modems connected by a transmission path requires little preparation before data can be sent; however where-as is common - adaptive echo cancellers are used to improve the quality of transmission it
  • start-up procedures may include provision for measuring other characteristics of the path to enable decisions to be made as to (for example) the bit-rate that may be used, or the optimum transmission powers to be employed (for example as described in our UK patent application no. 8628656). Also
  • commencement of a ⁇ eriod of transmission will first be described.
  • the start up procedure will include provision for echo canceller training;., but this and •other conventional parts of the procedure will not be described.
  • the object of the sequence now to be described is (a) to determine the signal-to-noise ratio of the transmission path at different frequencies.
  • the variation of group delay across the signal bandwidth of interest may also be measured.
  • the echo duration may be such as to render the use of a single echo canceller uneconomic and the known expedient of employing a first echo canceller to deal with short-term echo and a second canceller (receiving the locally transmitted signal via a delay line) to deal with long-term echo may be employed, in which case the round-trip delay measurement (c) is needed in order that the delay line may be appropriately adjusted.
  • the other measurements may be used so that the modems (usually in concert) may determine the symbol rate and/or power and/or portion of the available bandwidth to be used (truncation may be desirable if for example the signal- to-noise ratio or group delay characteristics are particularly unsatisfactory close to the band limits).
  • a timing chart is shown in figure 2.
  • station 2 transmits a multi-frequency probing signal PI which is analysed at station 1 to provide measurements (a). It also repeats this signal at reduced powers (P2, P3) to permit measurements (b) by station 1.
  • the delay measurements necessitate transmission by one station to be acknowledged by the other and station 1 therefore also transmits a signal Q which may be a single frequency tone, or possibly another ultitone signal.
  • the signal Q should be such as to minimise crosstalk with the probing signal. Supposing that the latter contains components at odd multiples of 50Hz then the frequency of the former would ideally be an even multiple (or even multiples) of 50Hz. A single tone of 600Hz is assumed for the purposes of description.
  • station 1 begins transmitting unmodulated carrier at 600Hz and station 2 begins transmitting probing signal PI at maximum power.
  • Station 1 receive the probing signal PI and performs signal- to-noise ratio measurements on the various frequency components.
  • station 1 signals to station 2 at time t2 by a suitable modulation of its 600Hz carrier (eg. by a simple phase reversal indicated as " ⁇ " in figure 2).
  • This transition is received by station 2 (after a delay ⁇ l equal to the transmission delay from station 1 to station 2) at time t3.
  • Station 2 responds (following a fixed delay ⁇ 2) by transmitting the probing signal at reduced power (e. g -1.5dB).
  • station 1 For the purposes of round trip delay and group delay measurement, station 1 must recognise this event; in principle it could do this on the basis of the power change, but, in order that the timing of this event be accurately observed at station 1 it is preferred that it be accompanied by a phase reversal. Thus at time t4 stations 2' s transmission of probing signals PI is replaced by transmission of probing signals P2 which, relative to PI, are phase reversed and 1.5dB down.
  • station 1 can then analyse the received signal P2 in the same manner as for PI.
  • station 2 If it is required that station 2 also make a round- trip determination then this can be achieved by providing that station 1, at time t6 (a fixed delay 5 following time t4) execute a further phase reversal of its carrier, which is then recorded at station 2, ⁇ 6 later, at time t7.
  • a further probing signal P3 at a further reduced power may then be transmitted by station 2 (at time t8) and analysed by station 1 as for PI and P2.
  • Signal P3 may be phase-reversed if this is found desirable to ensure that station 1 does not commence measurement until it is known that signals P3 have commenced.
  • FIG. 3 is a block diagram of station 1 (station 2 being identical).
  • Data received at an input 100 feeds a modulator 101 of conventional construction, its modulated output passing via an electronic changeover switch 102, controllable attenuator phase reversal unit 103 and hybrid circuit 104 to the line 3.
  • the changeover switch is switchable to receive signals from the signals from the modulator 101, a 600Hz tone generator 105 or a probing signal generator 106 (eg. constructed as described in our above- noted patent application) .
  • a probing signal generator 106 eg. constructed as described in our above- noted patent application
  • the signals pi etc may be formed as the sum of several signals generated as described in the earlier patent application. In this case, the signal Q would preferably lie in one of the larger intervals of this spectrum.
  • Received signals from the line 2 pass via the hybrid 104 to a receiver 107 (which may contain equalisation and/or carrier recovery circuits). Its output passes via short-term and long-term echo cancellers 108, 109 (fed with transmitted signal directly and via a delay line 110 respectively) and thence to a demodulator 111 and a data output 112.
  • the received signals from the receiver 107 are also fed to a phase detector 113 (for detecting phase reversals of 600Hz carrier) and a signal-to-noise ratio measuring unit 114 (for measuring the SNR of received probing signals).
  • a control unit 115 is provided to control the sequence of operations in accordance with figure 2 (specifically the choice of transmission (line 120)), and to receive the outputs of the phase detector 113 and SNR measurement 114. It has control outputs 122, 123 to set the delay value of the line 110, and transmitted power and phase and outputs 124, 125 to control the data rates of the modulator and demodulator. Further connections 126, 127, permit the control unit to communicate signalling data; for example station 2 could sent to station 1 at time t9 a signal SR indicating the symbol rate, carrier frequency and amplitude to be used for subsequent high speed transmission.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

Les modems 1 et 2 se chargent d'une séquence de démarrage au cours de laquelle le modem 1 émet un premier signal d'essai multifréquence; le modem 2 mesure le rapport signal-bruit du premier signal d'essai; le modem 2 transmet une référence temporelle au modem 1; le modem 1 répond en effectuant une commutation entre le premier signal d'essai et un second signal analogue d'une puissance différente du premier; le modem 2 mesure le rapport signal/bruit et reconnaît également la synchronisation de la transition de puissance afin de déterminer la durée du temps de propagation entre la référence temporelle et la transition.
PCT/GB1993/000178 1992-01-28 1993-01-28 Transmission de signal d'essai entre des stations afin de mesurer le temps de propagation d'un groupe WO1993015563A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9201737.5 1992-01-28
GB929201737A GB9201737D0 (en) 1992-01-28 1992-01-28 Data transmission

Publications (1)

Publication Number Publication Date
WO1993015563A1 true WO1993015563A1 (fr) 1993-08-05

Family

ID=10709340

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1993/000178 WO1993015563A1 (fr) 1992-01-28 1993-01-28 Transmission de signal d'essai entre des stations afin de mesurer le temps de propagation d'un groupe

Country Status (2)

Country Link
GB (1) GB9201737D0 (fr)
WO (1) WO1993015563A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2155454C2 (ru) * 1996-06-17 2000-08-27 Моторола, Инк. Устройство, способ и программный модем для использования характеристик искажения, обусловленного групповой задержкой, для определения скорости передачи символов и частоты несущей для пересылки данных

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1178681A (en) * 1964-04-16 1970-01-21 Tavkozlesi Ki Improvements in Methods for Measuring Group Delay Time
US3970926A (en) * 1974-06-03 1976-07-20 Hewlett-Packard Limited Method and apparatus for measuring the group delay characteristics of a transmission path
WO1986007223A1 (fr) * 1985-05-20 1986-12-04 Telebit Corporation Structure modem d'ensemble pour milieux de transmission imparfaite
EP0397535A2 (fr) * 1989-05-12 1990-11-14 Codex Corporation Modem

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1178681A (en) * 1964-04-16 1970-01-21 Tavkozlesi Ki Improvements in Methods for Measuring Group Delay Time
US3970926A (en) * 1974-06-03 1976-07-20 Hewlett-Packard Limited Method and apparatus for measuring the group delay characteristics of a transmission path
WO1986007223A1 (fr) * 1985-05-20 1986-12-04 Telebit Corporation Structure modem d'ensemble pour milieux de transmission imparfaite
EP0397535A2 (fr) * 1989-05-12 1990-11-14 Codex Corporation Modem

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
IEEE INSTRUMENTATION AND MEASUREMENT TECHNOLOGY CONFERENCE April 1989, WASHINGTON,US; pages 467 - 470 VAN WASSENHOVE ET AL 'GROUP DELAY MEASUREMENTS OF A TRANSMISSION LINE USING SINGLE CHANNEL MEASUREMENTS' *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2155454C2 (ru) * 1996-06-17 2000-08-27 Моторола, Инк. Устройство, способ и программный модем для использования характеристик искажения, обусловленного групповой задержкой, для определения скорости передачи символов и частоты несущей для пересылки данных

Also Published As

Publication number Publication date
GB9201737D0 (en) 1992-03-11

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