IES80779B2 - A method for signalling between an analogue pulse coded modulation modem and a digital pcm modem - Google Patents

A method for signalling between an analogue pulse coded modulation modem and a digital pcm modem

Info

Publication number
IES80779B2
IES80779B2 IES980667A IES80779B2 IE S80779 B2 IES80779 B2 IE S80779B2 IE S980667 A IES980667 A IE S980667A IE S80779 B2 IES80779 B2 IE S80779B2
Authority
IE
Ireland
Prior art keywords
symbols
pcm modem
sequences
analogue
transmitted
Prior art date
Application number
Inventor
Michael Joseph Mclaughlin
Original Assignee
Fernway Ltd
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 Fernway Ltd filed Critical Fernway Ltd
Priority to IE980667 priority Critical patent/IES80779B2/en
Publication of IES980667A2 publication Critical patent/IES980667A2/en
Publication of IES80779B2 publication Critical patent/IES80779B2/en

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/24—Testing correct operation
    • H04L1/242—Testing correct operation by comparing a transmitted test signal with a locally generated replica
    • H04L1/243—Testing correct operation by comparing a transmitted test signal with a locally generated replica at the transmitter, using a loop-back
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
    • H04L25/40—Transmitting circuits; Receiving circuits
    • H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
    • H04L25/4917—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using multilevel codes
    • H04L25/4927—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using multilevel codes using levels matched to the quantisation levels of the channel

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Telephonic Communication Services (AREA)
  • Communication Control (AREA)

Abstract

A method for detecting impairments present in digital signals transmitted by a digital PCM modem, comprises the steps of sequentially transmitting a plurality of descriptions of sequences of symbols S 1 ,S 2 ...S L an analogue PCM modem to the digital PCM modem, and requesting the digital PCM modem to transmit respective corresponding sequences of symbols. The received sequences of symbols (Fig.2) are compared by the analogue PCM modem with the requested sequences of symbols and stored for cross referencing during subsequent communication. Each described sequence of symbols is transmitted to detect at least one impairment in the corresponding sequence of symbols transmitted by the digital PCM modem, and each described sequence of symbols is transmitted for detecting an impairment different to the impairments to be detected by the other transmitted descriptions of sequences of symbols.

Description

A method for signalling between an analogue pulse coded modulation modem and a digital PCM modem The present invention relates to a method for signalling between an analogue pulse coded modulation (PCM) modem and a digital PCM modem for detecting impairments present in digital signals transmitted by the digital PCM modem.
In telecommunications transmissions between an analogue PCM modem and a digital PCM modem impairments are common in the signals transmitted by the digital PCM modem. Typically, these impairments affect symbols transmitted by the digital PCM modem. Accordingly, before communication can be established between an analogue PCM modem and a digital PCM modem, it is important that such impairments are detected. This, typically, requires the analogue PCM modem to transmit a relatively long description of the sequence of symbols to the digital PCM modem, which are symbols which the analogue PCM modem expects to receive from the digital PCM modem. The sequence of symbols transmitted by the analogue PCM modem is accompanied by a request to the digital PCM modem to transmit a corresponding sequence of symbols. The received symbols from the digital PCM modem are compared by the analogue PCM modem with the requested symbols and cross referenced so that meaningful communication can then continue. However, because of the relatively large number of different types of digital impairment and the different aspects of signal impairment which can arise in telecommunications between an analogue PCM modem and a digital PCM modem, known methods for detecting the impairments tend to be relative slow and inefficient.
There is therefore a need for an improved method for signalling between an analogue PCM modem and a digital PCM modem for detecting impairments present in digital signals transmitted by the digital PCM modem.
The present invention is directed towards providing such a method.
According to the invention there is provided a method for signalling between an analogue PCM modem and a digital PCM modem for detecting impairments present in digital signals transmitted by the digital PCM modem, the method comprising the steps of sequentially transmitting a plurality of descriptions of sequences of symbols from the analogue PCM modem to the digital PCM modem, requesting the digital PCM modem to transmit respective sequences of symbols corresponding to the described sequences, reading the received sequences of symbols, comparing the received sequences of symbols with the requested sequences of symbols, and storing the received and requested sequences of symbols in the analogue PCM modem in a form which permits ready cross reference by the analogue PCM modem between each requested symbol and its corresponding received symbol, each described sequence of symbols being transmitted to detect at least one impairment in the corresponding sequence of symbols received from the digital PCM modem, and each described sequence of symbols being transmitted for detecting an impairment different to the impairments to be detected by the other described sequences of symbols.
In one embodiment of the invention each transmitted described sequence of symbols is provided with a header. Preferably, the header of each described sequence of symbols transmitted indicates the number of symbols in that sequence. Advantageously, each described sequence of symbols is divided into a plurality of mini-periods, each mini-period comprising a plurality of symbols, and the header indicates the number of symbols in each mini-period.
In one embodiment of the invention at least some of the mini-periods in each described sequence of symbols are repeated. Preferably, the repeat of each repeated mini-period is provided immediately after the original mini-period.
In one embodiment of the invention the repeat of each mini-period is inverted. Preferably, the header indicates if the mini-periods are repeated in inverted form, and advantageously the header contains a one bit flag which is set to indicate inversion of the repeated mini-periods .
Ideally, the header indicates the number of times each mini-period in a described sequence of symbols is repeated.
In one embodiment of the invention each described sequence of symbols is not transmitted until the received sequence of symbols corresponding to the previously transmitted described sequence of symbols has been received by the analogue PCM modem.
Alternatively, the described sequences of symbols are continuously transmitted without interruption until all the described sequences of symbols have been transmitted. Ideally, the header indicates the number of descriptions of sequences being transmitted.
The invention will be more clearly understood from the following description of some preferred embodiments thereof which are given by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of one description of a sequence of symbols of a plurality of descriptions of sequences of symbols which are transmitted by an analogue PCM modem in the signalling method according to the invention, Fig. 2 is a schematic representation of a received sequence of symbols of a plurality of received sequences of symbols received by the analogue PCM modem from a digital PCM modem in the signalling method according to the invention, and Fig. 3 is a schematic representation of a plurality of descriptions of sequences of symbols which are transmitted by an analogue PCM modem in the signalling method according to another embodiment of the invention.
Referring to Figs. 1 and 2 of the drawings a method according to the invention for signalling between an analogue PCM modem and a digital PCM modem for detecting impairments and aspects of impairment present in digital signals transmitted by the digital PCM modem will now be described. The analogue PCM modem prepares a plurality of descriptions of sequences of symbols which it requires to receive in digital signal form from the digital PCM modem. Fig 1 illustrates a description of a sequence of symbols which is transmitted by the analogue PCM modem. The analogue PCM modem transmits the descriptions of the sequences of symbols sequentially to the digital PCM modem with a request that sequences of symbols corresponding to the described sequence of symbols be transmitted by the digital PCM modem to the analogue PCM modem. Fig. 2 illustrates a corresponding received sequence of symbols transmitted by the digital PCM modem in response to the transmitted described sequence of Fig. 1. Each described sequence of symbols comprises different symbols to the other sequences, and the symbols of each described sequence are selected for detecting one impairment in the corresponding sequence of symbols received from the digital PCM modem. Additionally, each described sequence of symbols is prepared by the analogue PCM modem for detecting a different impairment to the impairments to be detected by the other sequences of symbols.
Each transmitted described sequence of symbols comprises the symbols Slz S2 to SL and each described sequence of symbols comprises a header which comprises identification of various aspects of the sequence.
The headers include the letters L, Μ, N, I and P in the header. L indicates the number of symbols Si to SL in the sequence. Each described sequence is subdivided into mini-periods, and the letter P in the header indicates the number of symbols in each miniperiod. The mini-periods are repeated in the sequence of symbols and the letter N in the header represents the number of times each mini-period is repeated. Typically, the symbols of each mini-period are repeated immediately after the corresponding miniperiod, and additionally, each mini-period of P symbols may be repeated in inverted form. I which is a one bit flag in the header is set to indicate whether the mini-periods of P symbols are repeated in inverted form. A symbol is inverted by computing its negative value. In the event that each mini-period is inverted, the length of a mini-period and its inverted form is 2P, and the mini-period and its inverted form are then repeated N times as a sub-sequence. M indicates the number of times the sub-sequence is repeated to provide the complete sequence. If the flag I is set to indicate inversion of each miniperiod, then the complete sequence has an null at DC.
Fig. 2 illustrates the corresponding sequence of symbols, which is received from the digital PCM modem by the analogue PCM modem in response to the transmitted described sequence of symbols of Fig. 1.
In this case the flag I in the transmitted sequence of symbols of Fig. 1 is set to indicate immediate repetition of each mini-period in inverted form.
As each received sequence of symbols is received by the analogue PCM modem it is compared with the corresponding transmitted described sequence of symbols requested, and the corresponding requested and received sequences of symbols are stored in the analogue PCM modem for ready cross reference of the requested and the received symbols by the analogue PCM modem during communication between the analogue PCM modem and the digital PCM modem.
In this embodiment of the invention the analogue PCM modem awaits receipt of the sequence of symbols transmitted by the digital PCM modem before transmitting the next description of sequence of symbols. This has the advantage that each subsequent description of sequence of symbols can be formulated after analysis of the received sequences already received, and additionally, the number of descriptions of sequences of symbols can be decided in real time rather than prior to commencement of transmission of the descriptions of sequences of symbols. However, a disadvantage of awaiting the received sequences of symbols before transmitting the next description of sequence of symbols is that extra round trip delays occur and an information channel of an appropriate type is required from the analogue PCM modem to the digital PCM modem for each sequence.
Fig. 3 illustrates an alternative method for signalling according to the invention in which the descriptions of sequences of symbols are transmitted sequentially and uninterrupted, and there is no delay between the transmission of each described sequence awaiting a corresponding received sequence from the digital PCM modem. In Fig. 3 the letter J indicates the number of descriptions of sequences of the type which are illustrated in Fig. 1 which are to be transmitted by the analogue PCM modem. The letters Lk, Mk, Nk, Ik and Pk are the same as L, Μ, N, I and P as in Fig. 1 but for the sequence of the type shown in Fig. 1. Q is the sum of 1¾ for k = 1 to J. In this way, J descriptions of sequences are sent uninterrupted, each description of sequence having different symbols and parameters, and each description of sequence is prepared to detect a different impairment and aspect of impairment to that which is to be detected by the other descriptions of sequences.
In response to the transmitted sequences of Fig. 3 the digital PCM modem transmits J corresponding sequences of symbols, each sequence being in the form set out in Fig. 2 which are received by the analogue PCM modem, and the received sequences of symbols which are received by the analogue PCM modem are compared and stored with the requested sequences of symbols, and are cross referenced for ready cross referencing of the requested and the received symbols by the analogue PCM modem for subsequent use during communications between the analogue PCM modem and the digital PCM modem.

Claims (5)

1. A method for signalling between an analogue PCM modem and a digital PCM modem for detecting impairments present in digital signals transmitted by the digital PCM modem, the method comprising the steps of sequentially transmitting a plurality of descriptions of sequences of symbols from the analogue PCM modem to the digital PCM modem, requesting the digital PCM modem to transmit respective sequences of symbols corresponding to the described sequences, reading the received sequences of symbols, comparing the received sequences of symbols with the requested sequences of symbols, and storing the received and requested sequences of symbols in the analogue PCM modem in a form which permits ready cross reference by the analogue PCM modem between each requested symbol and its corresponding received symbol, each described sequence of symbols being transmitted to detect at least one impairment in the corresponding sequence of symbols received from the digital PCM modem, and each described sequence of symbols being transmitted for detecting an impairment different to the impairments to be detected by the other described sequences of symbols.
2. A method as claimed in Claim 1 in which each » transmitted described sequence of symbols is provided with a header, the header of each described sequence of symbols transmitted indicating the number of symbols in that sequence.
3. A method as claimed in Claim 2 in which each described sequence of symbols is divided into a plurality of mini-periods, each mini-period comprising a plurality of symbols, and the header indicates the number of symbols in each mini-period, at least some of the mini-periods in each described seguence of symbols being repeated, the repeat of each mini-period being inverted, and the header indicating if the miniperiods are repeated in inverted form.
4. A method as claimed in any preceding Claim in which each described seguence of symbols is not transmitted until the received sequence of symbols corresponding to the previously transmitted described sequence of symbols has been received by the analogue PCM modem.
5. A method for signalling between an analogue PCM modem and a digital PCM modem for detecting impairments present in digital signals transmitted by the digital PCM modem, the method being substantially as described herein with reference to and is illustrated in the accompanying drawings.
IE980667 1997-08-12 1998-08-11 A method for signalling between an analogue pulse coded modulation modem and a digital pcm modem IES80779B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
IE980667 IES80779B2 (en) 1997-08-12 1998-08-11 A method for signalling between an analogue pulse coded modulation modem and a digital pcm modem

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IE970593 1997-08-12
IE980667 IES80779B2 (en) 1997-08-12 1998-08-11 A method for signalling between an analogue pulse coded modulation modem and a digital pcm modem

Publications (2)

Publication Number Publication Date
IES980667A2 IES980667A2 (en) 1999-01-10
IES80779B2 true IES80779B2 (en) 1999-02-10

Family

ID=11041563

Family Applications (1)

Application Number Title Priority Date Filing Date
IE980667 IES80779B2 (en) 1997-08-12 1998-08-11 A method for signalling between an analogue pulse coded modulation modem and a digital pcm modem

Country Status (2)

Country Link
GB (1) GB2331209B (en)
IE (1) IES80779B2 (en)

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2466144B1 (en) * 1979-09-18 1986-11-07 Lignes Telegraph Telephon METHOD FOR TESTING A LINE FOR TRANSMITTING DIGITAL DATA BETWEEN TWO MODEMS AND DEVICE IMPLEMENTING THIS METHOD
US6061391A (en) * 1997-02-28 2000-05-09 Fujitsu Limited Error indicator, and data modulator-demodulator and indicating method of light emitter therein

Also Published As

Publication number Publication date
GB2331209A9 (en)
GB2331209B (en) 2002-08-28
IES980667A2 (en) 1999-01-10
IE980666A1 (en) 1999-02-24
GB2331209A (en) 1999-05-12
GB9817477D0 (en) 1998-10-07

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FK9A Application deemed to have been withdrawn section 23(9)
FD4E Short term patents deemed void under section 64