WO2000049706A1

WO2000049706A1 - Method and system for accelerating real time data transmission

Info

Publication number: WO2000049706A1
Application number: PCT/FR2000/000327
Authority: WO
Inventors: Jean-Michel Reibel
Original assignee: Info Telecom
Priority date: 1999-02-17
Filing date: 2000-02-10
Publication date: 2000-08-24
Also published as: FR2789830A1; FR2789830B1

Abstract

The invention concerns a method for accelerating data transmission in real time, wherein data are transmitted from at least a fixed station by radiofrequency channel subcarriers using asynchronous transmission by frames each containing a predetermined number of elementary lines. In transmission, the data are arranged in packets comprising lines of a first type containing data bits, parity bits and error-correcting bits, and lines of a second type containing parity bits inserted between the first-type lines. At least one first-type line is provided with predetermined arbitrary data, the second-type lines being calculated from the first-type lines. In reception, proper data transmission is verified by means of the parity bits of the second-type lines.

Description

METHOD AND SYSTEM FOR ACCELERATING REAL-TIME DATA TRANSMISSION

The invention relates to the transmission of digital information between at least one transmitting station and a plurality of receivers, using sub-carriers of radio frequency channels as well as an asynchronous packet transmission protocol each containing a predetermined number of elementary blocks of data.

A person skilled in the art already knows such a transmission protocol, in particular from the document pr ETS 300 751 (May 1997 version), entitled "Radiobroadcast Systems; System for Wireless Infotainment Forwarding and Teledistribution (SWIFT)", available from the secretariat of ETSI in Sophia Antipolis (France), and hereinafter referred to as "SWIFT document".

Currently, this type of asynchronous transmission protocol is used for the transfer of files intended for a group of users, and in particular for radio frequency broadcasting of written newspapers.

As opposed to an asynchronous transmission protocol, such as that provided by the RDS (Radio Data System) transmission standard, and in which the various transmission frames are synchronized on a perfectly defined time clock, an asynchronous transmission protocol does not is, by definition, not synchronized on a predetermined time basis. Consequently, the information receivers operating on this type of asynchronous protocol must remain permanently on so as to be able to acquire, at any time, which by definition is not known in advance, the digital information which their are intended.

_ The SWIFT document provides for different types of packets for data transmission. The QA packet includes 190 data blocks comprising actual data, correction bits and horizontal parity bits, followed by 82 vertical parity blocks. However, almost 30% of the transmission time is spent on vertical parity blocks. Such a packet is unsuitable for real-time data transmission because the AQ packet can only be transmitted after calculation of the vertical parity blocks which depend on the content of the data blocks. No data is transmitted during the transmission of the vertical parity blocks.

The A _j packet also includes 190 data blocks similar to those of the AQ packet followed by 82 vertical parity blocks in the middle of which 12 real time information blocks are inserted. This pack includes 284 blocks which differentiates it from other generally used packets with a length of 272 blocks and makes it very difficult to synchronize the awakening of information receivers which is carried out after a period of sleep allowing to reduce their electrical consumption and thus increase their autonomy. In practice, the Al package is hardly usable.

Package B comprises 272 blocks, the information blocks and the vertical parity blocks being interleaved which allows excellent continuity of the transmission of information but is not suitable for the transmission of real-time information since everything vertical parity block whatever its rank in the packet depends on data present in the data blocks whatever their ranks in the packet.

Package C includes 272 information blocks and has no vertical parity blocks. Its throughput performance is excellent and this packet is perfectly suited for real-time data transmission. However, its security is low since no error correction is possible, which is a major drawback when it is desired to transmit large files for which the probability of error is high. Of course, any insertion of vertical parity blocks implies a delay in transmission because the coder of the transmitting station will have to collect the data, calculate the vertical parity blocks and then insert them into the packet. Such a delay is obviously harmful when it is desired to transmit the information in real time. The present invention aims to remedy the drawbacks of existing methods.

The object of the present invention is to propose a method in which the continuity and the security of information transmission is satisfactory, the transmission of real-time information is easy and the synchronization of the waking of the receivers is possible.

The method according to the invention is intended to accelerate the transmission of data in real time. The information is transmitted from at least one fixed station by sub-carriers of radio frequency channels using an asynchronous transmission protocol by frames each containing a predetermined number of elementary lines. In transmission, data is arranged in packets comprising lines of a first type comprising data bits, parity bits and error detection bits, and lines of a second type comprising parity bits , the second type lines being inserted between the first type lines, and calculated from the first type lines and allowing the correction of errors on the data bits. At least one line of the first type is provided with predetermined arbitrary data, the lines of the second type being calculated from the lines of the first type. On reception, the correct data transmission is checked by means of the parity bits of the second type lines.

Distributed vertical parity bit line packets allow better continuity of information transmission. However, conventionally this type of packet prohibits the transmission of real-time information. The insertion of arbitrary lines of prerecorded data into a transmission means and into the receivers makes it possible to transmit real time information in this type of packet.

Advantageously, after calculation of the lines of the second type, the arbitrary data are replaced by real-time data and one issues the packet. In reception, it is possible to extract the real-time data, replace the real-time data with the arbitrary data, and verify the correct transmission of the data by means of the parity bits of the second type lines. In one embodiment of the invention, the rank of the line of arbitrary data in the packet is constant and predetermined.

In one embodiment of the invention, the rank of the line of arbitrary data is stored in a transmission means and in a reception means.

In another embodiment of the invention, the transmission of information is ensured by the rank of the line of arbitrary data in the packet.

The rank of the arbitrary data line can be determined in transmission as a function of information to be transmitted, the arbitrary data line being transmitted with the packet, the other lines of the first type being shifted in a corresponding manner, and the rank of the line of arbitrary data can be identified on reception by comparison with stored data to deduce said information.

Advantageously, the arbitrary data are stored in a transmission means and in a reception means.

The present invention also relates to a digital information transmission system, comprising at least one fixed station transmitting the information by sub-carriers of radio frequency channels using an asynchronous packet transmission protocol each containing a predetermined number of elementary blocks , and several receivers comprising means for radio frequency reception and means for processing the data received. The station includes generation means capable of generating, within the transmission protocol conveyed by at least one specific identifiable transmission network materialized by at least one specific transmission channel selected from said radio frequency channels, successive transmission packets each comprising a predetermined number of elementary lines, the means of generation being able to dispose of the data in packets comprising lines of a first type comprising data bits, parity bits and error detection bits, and lines of a second type comprising parity bits , the second type lines being interposed between the first type lines and calculated from the first type lines and allowing the correction of errors on the data bits, at least one first type line being provided with predetermined arbitrary data, the second type lines being calculated from the first type lines. The receiver processing means are capable of verifying the correct transmission of the data by means of the parity bits of the second type lines.

Thus, the invention makes it possible to combine the qualities of continuity, safety and standard format of the packet B and the adaptation to the real-time data transmission of the packet C by overcoming their respective drawbacks. Real-time data is transmitted without loss of time while non-real-time data benefits from vertical parity blocks which allow their correction in the event of errors. Other advantages and characteristics of the invention will appear on examining the detailed description of an embodiment taken by way of nonlimiting example and illustrated by the appended drawings in which:

FIG. 1 schematically represents a structure of elementary blocks usable according to the invention in accordance with a SWIFT transmission protocol,

- Figure 2 schematically shows the structure of a frame according to the invention; and

- Figure 3 very schematically illustrates the internal architecture of a receiver.

Although the invention is not limited thereto, we will now rely in the example which will be described, on an asynchronous transmission protocol of the type described in the document.

SWIFT. Indeed, such a transmission protocol allows a high net speed of information transmission, typically between 6 kilobits / s and 10 kilobits / s, which is particularly useful for the transmission of voice messages.

Those skilled in the art know the characteristics of such an asynchronous packet transmission protocol each containing a predetermined number of elementary blocks. We recall here the essential characteristics relating in particular to the structure of these elementary blocks. Those skilled in the art may possibly, for more details, refer to the aforementioned SWIFT document, the content of which is, for all intents and purposes, incorporated into the present description. According to this transmission protocol, each elementary block

BLC comprises (FIG. 1) a BIC identifier followed by an AND header indicating the type of the block. The header is followed by a useful part DU containing the data proper of the BLC block. This useful part DU is followed by CRC error detection bits and PRY parity bits. Each of these blocks comprises a total of 288 bits. These blocks are combined in packets of 272 blocks and these packets are transmitted one after the other asynchronously, that is to say without it being possible to determine the times of transmission temporally and in advance. of these packages. The transmission time of a packet is typically of the order of 5 seconds.

This asynchronous transmission protocol is carried by a subcarrier (centered around 76 kHz) of radio frequency channels, typically located in the FM band. To convey the asynchronous transmission protocol according to the invention, at least one specific identifiable transmission network is materialized by selecting from said radiofrequency channels at least one specific channel. Of course, a transmission network can use several radio frequency channels. Likewise, several identifiable transmission networks can be defined.

FIG. 2 shows the structure of a packet of data blocks in accordance with the invention, and comprising 190 blocks of information and 82 blocks of vertical parity, ie a total of 272 blocks. Among the data blocks, a certain number of so-called real-time blocks have been selected which will be assigned to the transmission. information in real time. In the example illustrated, an information block every sixteen information blocks is dedicated to this use. Before the real-time information is received by the transmitting station and inserted into the packet, the real-time information blocks, that is to say the blocks of rank 16 and multiple of 16, are provided with arbitrary data prerecorded both in the transmitting station and in each receiver of the information transmission network.

After the installation of the non-real time information blocks of rank 1 to 15, 17 to 31, etc., the transmitting station calculates the vertical parity blocks from all the data blocks whatever their rank including therefore the non-real-time data blocks and the arbitrary blocks of rank 16 and multiple of 16. Before the transmission of this packet, if real-time data must be transmitted, one or more arbitrary blocks of rank 16 or multiple of 16 by real time data blocks. The packet is then transmitted, which is received by all of the receivers in the active state.

The receivers for which this packet is intended first of all extract the real time data located in the blocks of rank 16 and multiple of 16 in order to be able to display or use said real time data immediately. Then, processing means of each receiver replace the real-time data blocks by the prerecorded arbitrary blocks identical to those used in the transmitting station for the calculation of the vertical parity blocks. These arbitrary blocks are stored in a memory of the receiver. The processing means then carry out the verification of the vertical parity and if necessary the correction of the erroneous bits of the non-real-time data blocks.

If we now refer more particularly to FIG. 3 which represents the internal architecture of an RC receiver, it can be seen that this receiver, for example an autonomous portable paging receiver, is equipped with a reception antenna receiving the SRF radio frequency signal. This antenna is connected to reception means 1 comprising, at the head, a high frequency stage 10, followed by a specific filtering circuit 1 1 making it possible to extract the SWIFT subcarrier. This filtering stage is itself connected to a decoder, for example that marketed by the Japanese company OKI under the reference MSM 9553 and capable of delivering at output, after error correction and parity check, the elementary blocks freed in particular of CRC and PRY bits.

The reception means also comprise a specific circuit, not shown here for the purposes of simplification, research and automatic control of the frequency of the carrier signal, so as to be able to lock onto one of the transmission channels.

The output of the reception means is connected to processing means 2 incorporating a microprocessor 20, for example 8 bits, associated, via a communication bus, with a random access memory 21 and a read-only memory 22. Means control 3 are able to temporarily activate the reception means and the processing means by respectively delivering to these two means corresponding control instructions. These control means can be incorporated in a conventional manner within the microprocessor 20, or can be produced by a specific conventional external circuit.

These control means are consequently able to put the receiver, either in an active state in which it is capable of receiving and processing the data contained in the carrier signal, or in a state of rest. The entire receiver is supplied by power supply means 4 comprising a cell element associated with a DC - DC converter used to raise the voltage of this cell element to that necessary for the operation of the microprocessor.

Various indications relating to the network and necessary for its operation are stored in the receiver's read-only memory, as well as the arbitrary blocks which have to replace the real-time data blocks after their extraction. Extraction and replacement will be carried out by the decoder.

The transmitting station will essentially comprise means of insertion, produced for example by software within a PC type microcomputer and receiving for a designated receiver the various indications necessary for its operation and transmission. The means of insertion then hampered the headers and the useful parts of different elementary blocks which make up the packets for you. All these elements are then transmitted to an encoder, for example that marketed by the Swedish company SECTRA under the reference TSE 760 which completes the shaping of these blocks, by adding in particular the CRC error detection and parity blocks. Then all of these blocks gathered in packets, are transmitted within the signal. The replacement of the arbitrary blocks pre-recorded by blocks of real time data will be carried out by the coder.

The invention is particularly well suited to paging networks, for example of the Mobidarc type or to differential global positioning by satellite (GPS) applications using a satellite, a fixed reference and a mobile transmitter.

In a variant, for example intended for an interactive televised game, one could foresee that a response considered as good on the part of a viewer causes the blocking of the receivers of the other players thanks to the real time data. In this variant, the information to be transmitted is known following the correct response from a viewer, but the receiver does not know the instant of transmission.

In each packet, space is reserved, for example a block, for said predetermined information. In the absence of said predetermined information, provision is made to issue a negative arbitrary pattern occupying the same place. When it is desired to transmit said predetermined real-time data, it is substituted for one or more blocks of data which is or are delivered to the space reserved for the negative arbitrary pattern.

It is thus possible to transmit real-time information with a delay reduced to a minimum while maintaining the transmission of non-real-time data and this without modifying the parity blocks which will be calculated on the basis of the non-real-time data and the negative arbitrary pattern. On reception, the receiver will receive said data predetermined real time and will then carry out the planned operations such as a blocking or neutralization of an external command and / or a corresponding display. The receiver after extraction of the real-time data will replace these in the packet with the predetermined negative arbitrary pattern and will then be able to perform the parity check. The double transmission of real-time data and non-real-time data is thus preserved while giving absolute priority to the transmission of predetermined real-time data.

Claims

1. Method for accelerating the transmission of data in real time, in which the information is transmitted from at least one fixed station by sub-carriers of radio frequency channels using an asynchronous transmission protocol by frames each containing a predetermined number of elementary lines , characterized in that, in transmission, data are arranged in packets comprising lines of a first type comprising data bits, parity bits and error detection bits, and lines of a second type comprising parity bits, the second type lines being inserted between the first type lines, and calculated from the first type lines and allowing the correction of errors on the data bits, that at least one line of the first type is provided with predetermined arbitrary data, the lines of the second type being calculated from the lines of the first type, and that 'on reception, the correct data transmission is checked by means of the parity bits of the second type lines.

2. Method according to claim 1, in which after calculation of the lines of the second type, the arbitrary data are replaced by real-time data and the packet is transmitted.

3. Method according to claim 2, in which, on reception, the real time data are extracted, the real time data are replaced by the arbitrary data, and the correct transmission of the data is verified by means of the parity bits of the second lines. type.

4. Method according to any one of the preceding claims, characterized in that the rank of the line of arbitrary data in the packet is constant and predetermined.

5. Method according to claim 4, characterized in that the rank of the line of arbitrary data is stored in a transmission means and in a reception means.

6. Method according to claim 1, in which the transmission of information is ensured by the rank of the line of arbitrary data in the packet.

7. The method as claimed in claim 6, in which the rank of the arbitrary data line is determined in transmission as a function of information to be transmitted, the arbitrary data line being transmitted with the packet, the other first type lines being shifted. correspondingly, and the rank of the line of arbitrary data is identified on reception by comparison with stored data to deduce said information.

8. Method according to any one of the preceding claims, characterized in that the arbitrary data are stored in a transmission means and in a reception means.

9. Digital information transmission system, comprising at least one fixed station transmitting the information by sub-carriers of radio frequency channels using an asynchronous packet transmission protocol each containing a predetermined number of elementary blocks, and several receivers comprising radiofrequency reception means and means for processing the received data, characterized in that the station includes generation means capable of generating, within the transmission protocol carried by at least one specific identifiable transmission network materialized by at least one specific transmission channel selected from said radiofrequency channels, successive transmission packets each comprising a predetermined number of elementary lines, the generation means being able to dispose of the data in packets comprising lines of a first type comprising data bits, parity bits and error detection bits, and lines of a second type comprising parity bits, the lines of the second type being inserted between the lines of the first type, and calculated from the first type lines and allowing the correction of errors on the data bits, at least one first type line being provided with predetermined arbitrary data, the second type lines being calculated from the first lines type, the receiver processing means being able to verify the correct transmission of the data by means of the parity bits of the second type lines.