AU752659B2

AU752659B2 - Device for time resetting in digital signal transmission for networks

Info

Publication number: AU752659B2
Application number: AU48788/99A
Authority: AU
Inventors: Gerard Faria
Original assignee: Harris Corp
Current assignee: Harris Corp
Priority date: 1998-09-17
Filing date: 1999-09-17
Publication date: 2002-09-26
Anticipated expiration: 2019-09-17
Also published as: JP2000174716A; FR2783657B1; EP0987845A1; AU4878899A; CA2282839A1; FR2783657A1

Description

P00011 Regulation 3.2 Revised 2/98

AUSTRALIA

Patents Act, 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT *r

U

TO BE COMPLETED BY THE APPLICANT NAME OF APPLICANT: HARRIS CORPORATION ACTUAL INVENTOR: ADDRESS FOR SERVICE: INVENTION TITLE: DETAILS OF ASSOCIATED APPLICATION NO: Peter Maxwell Associates Level 6 60 Pitt Street SYDNEY NSW 2000 DEVICE FOR TIME RESETTING IN DIGITAL SIGNAL TRANSMISSION FOR

NETWORKS

98 11642 17 September 1998 France The following statement is a full description of this invention including the best method of performing it known to us:- DEVICE FOR TIME RESETTING IN DIGITAL SIGNAL TRANSMISSION

NETWORKS

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to digital type transmission networks and, more particularly, in such networks, to a device to reset the time at which the information is transmitted to the receivers.

In analog type transmission networks, the periods of transmission of the analog signals are brief and are practically not detectable by a radio station listener or a television station viewer.

In the case of digital type transmission networks, whether these are radio or television networks, the analog signals are encoded in binary numbers on which a certain number of digital processing operations are carried out. These C processing operations give rise to delays which accumulate from the beginning to the end of the transmission chain or sequence.

.2Q. 2. Description of the Prior Art Figure 1 is a drawing of a digital type transmission sequence that begins with radio or television studios 10, 20 and whose audio and/or video analog signals are encoded in binary numbers by encoders 12, 22 and 32 respectively. These binary codes come from the studios 10, 20 and 30 and are transmitted e to a multiplexing site 40 by means of collection networks 14, 24, and 34.

e In the multiplexing site 40, the binary codes coming from the different studios are "mixed" to form what is called a digital "bouquet". This bouquet is distributed to transmission sites 16, 26 and 36 by means of a distribution network 42 known as a "primary" network. In these transmission sites 16, 26 and 36, each of which includes a modulator/transmitter assembly 18, 28 and 38, the bouquet is sent to the receivers of the users of the radio or television broadcasting network by a distribution network known as a o secondary network.

In one structure according to the drawing of Figure 1, each encoding, multiplexing and transmission site carries out a digital processing operation whose duration is not negligible while each primary distribution, secondary distribution and collection network introduces a variable delay that too is not negligible.

The adding up of these digital processing periods and these transmission periods leads to a time lag between the instant at which the sound or the image is picked up and the instant at which this sound or this image is received by the user's receiver.

Furthermore, the new radio or television RF digital broadcasting standards stipulate the integration, into the bouquets, of service information in addition to the audio and/or video programs. Now this service information, known as SI, includes the date and time which is usually introduced into the studio 10, 20, 30 or by the operator of the multiplexing site 40 using information given by a receiver known as the GPS (Global Positi6ning System) receiver.

This information given by the GPS receiver includes a onee• pulse-per-second time reference, a frequency reference given by a 10 MHz frequency signal and the UTC date and time information, UTC being the acronym for Universal Time e Coordinated or Greenwich Mean Time using the Julian calendar.

Furthermore, to take account of the fact that the UTC information corresponds to the Greenwich Mean Time, the time lag or time offset between the Greenwich meridian and the zone served by the bouquet is taken into account by using the local time information given by the "LTO" (Local Time Offset) signal.

When this date and time information reaches the user's receiver, the earlier it has been introduced into the transmission sequence, the more erroneous will it be.

The aim of the present invention therefore is to obtain a device that can be used to reset the information on time that is transmitted to the user's receiver so that it corresponds to the real time of the place of reception.

This aim is achieved by implementing a time-resetting device positioned in each transmission site 16, 26 and 36 and more particularly at the input of the modulator of each site, this time-resetting device using the UTC information given by the GPS receiver as well as the information on the duration of processing in the transmission site and on the duration of transmission to the user's receiver.

SUMMARY OF THE INVENTION The invention therefore relates to a device for resetting the time in a digital signal transmission network, the network comprising studio digital encoding sites, collection networks, a multiplexing site that sets up the "digital bouquet", a network for the primary distribution of the digital bouquet and transmission sites, each transmission site comprising a modulator, a radiofrequency amplifier and a W GPS receiver, wherein the time-resetting device is positioned in the modulator and comprises: means for computing the time to be transmitted to the users, oo2 means for extracting the time in the digital bouquet, and means for substituting the computed time for the extracted time.

S- BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention shall appear from the following description of a particular embodiment, said description being made with reference to the appended drawings, of which: Figure 1 is a drawing of a structure of a digital type transmission system to which the invention can be applied, Figure 2 is a functional drawing of a modulator/transmitter comprising a time-resetting device according to the invention, Figure 3 is a functional drawing of the time-resetting device according to the invention, Figure 4 is a functional drawing showing the computation of the time that will be transmitted to the user, and Figure 5 is a functional drawing of the substitution module 72 of Figure 3.

MORE DETAILED

DESCRIPTION

Each transmission site 16, 26 or 36 respectively comprises a modulator/transmitter 18, 28 or 38 which consists (Figure 2) of a modulator 50, a transmitter 52, a transmission antenna 54 and a GPS receiver 56. The transmitter comprises a power amplifier 66 and, as the case may be, a filter 68. In the S known way, the modulator 50 comprises an input interface 58 for the input of the digital signal given by the primary distribution network 42, an OFDM (Orthogonal Frequency Division Multiplex) type modulator 60 proper that carries out baseband modulation and a frequency converter 62 that carries out a baseband frequency change.

According to the invention, a time-resetting device 63 is "i positioned between the input interface 58 and the modulator and carries out a resetting of the time contained in the digital signal of the distribution network by introducing the current time or real time after having corrected it by the duration of processing in the transmission site.

The GPS receiver 56 gives the modulator 50 the following information in order that it may be used in a manner that is known: the one-pulse-per-second time reference information and the 10 Mhz frequency reference information. According to the invention, the GPS receiver furthermore gives the UTC time information which is used only by the time-resetting device 64.

The time-resetting device 64 comprises (Figure 3) a module to compute the time information to be transmitted on the basis of the UTC time information, the one-pulse-per-second time information elements given by the GPS receiver 56 and the information on duration of processing Td in the transmission site. This corrected time information replaces the information contained in the digital signal of the bouquet in a module 72.

The time information of the bouquet is localized in the input digital signal by the modules 74 and 76, the module 74 being used to localize the Service Information elements SI while the module 76 is used for the demarcation, in these Service Information elements SI, of those information elements that correspond to the information of the received bouquet.

As can be seen in Figure 4, the module 70 comprises a first register 78 for the memorizing, at each second, of the real UTC time information, a second register 80 for the memorizing of the processing duration Td of the transmission site considered, an adder 82 to add up the contents of the first and second registers 78, 80 and a third register 84 to store S* the result of the addition which constitutes the substitution Q time information.

The modules 74 and 76 are adapted to the digital signals of the bouquet to be broadcast. This bouquet is given to the modulator in a form known as the "transport multiplex" which is defined by the ETI standard (ETS 300 799) for digital *2 audio broadcasting (DAB) and by the MPEG-TS (ISO/IEC 13818-1) e standard for digital video broadcasting television

(DVB-T)

The Service Information elements SI and their transport S envelope are constituted by information elements that are defined by the ETS standard 300 401 for digital audio broadcasting (DAB) and by the ETS standard 300 468 for digital video broadcasting

(DVB-T)

The localizing module 74 is designed to identify the envelope of the Service Information elements SI in the transport multiplex. For digital audio broadcasting, the envelope is conveyed by the frame ETI to a fixed location. For digital video broadcasting, the transport envelope is defined by a TDT (Time and Date Table) that is conveyed in packets provided with an identifier having the value 14.

The UTC time demarcation module is designed for the identification in the envelope SI, localized beforehand by the module 74, of the information element conveying the UTC time. For digital audio broadcasting, this is a group having the identifier 0/9 (FIG 0/9, FIG being the acronym for "Fast Information Group"). For digital video broadcasting, it is a TDT table having the identifier The substitution module 72 essentially comprises a multiplexer 86 that is controlled by a substitution signal given by the localizing module 74. This substitution module 72 replaces the UTC bytes of the distribution network by the bytes of the UTC value computed by the module The description that has just been given of the invention shows that the time-resetting device comprises: C means 70 to compute the time to be transmitted to the users, means 74 and 76 to extract the time in the digital bouquet, *pW and means 72 to substitute the computed time for the extracted time.

C..

C

Claims

1. A device for resetting the time in a digital signal transmission network, said network comprising studio digital encoding sites, collection networks, a multiplexing site that sets up the "digital bouquet", a network for the primary distribution of the digital bouquet and transmission sites, each transmission site comprising a modulator, a radiofrequency amplifier and a GPS receiver, wherein the time-resetting device is positioned in the modulator and comprises: means to compute the time to be transmitted to the users, means to extract the time in the digital bouquet, and means to substitute the computed time for the extracted time. J

2. A time-resetting device according to claim 1, wherein the computation means comprise: a module to memorize the UTC time given by the GPS receiver a module to memorize the delay introduced by the concerned transmission site, a module to add up the UTC time memorized by the module and the delay memorized by the module, and a module to memorize the computed time.

3. A time-resetting device according to claim 1 or 2, wherein the means for the extraction of the time in the digital bouquet comprise: a localization module to identify the envelope of the Service Information elements, and a demarcation module for the identifying, in the envelope of the Service Information elements, of that information element which conveys the UTC time.

4. A time-resetting device according to claim 1, 2 or 3, wherein the substitution means comprise a multiplexer.