WO2000049759A1

WO2000049759A1 - Method for reducing the duration of activity in digital data receivers and digital data transmission system

Info

Publication number: WO2000049759A1
Application number: PCT/FR2000/000324
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: FR2789833B1; FR2789833A1

Abstract

The invention concerns a method for reducing the duration of activity in digital data receivers with an active state and an inactive state, wherein data are transmitted from at least one fixed station (ST) by radiofrequency channel subcarriers using an asynchronous transmission protocol by packets each containing a predetermined number of elementary blocks. In transmission, data are arranged in packets comprising blocks of a first type comprising data bits, parity bits and error-detecting bits, and blocks of a second type comprising parity bits, the second-type blocks being calculated from the first-type blocks and enabling to correct errors on the data bits. In reception, the absence of errors in the blocks is verified block by block in the first-type block using the error-detecting bits, the absence or presence of error is stored, and in the event of absence of error, the receiver is reverted into inactive state as soon as said receiver has received the data addressed to it.

Description

Method for reducing the duration of activity of digital information receivers and digital information transmission system.

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 by document pr ETS 300751 (May 1997 version), entitled "Radio broadcast 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 transferring files intended for a group of users, and in particular for radiofrequency broadcasting of written logs. As opposed to a synchronous transmission protocol, such as that provided for 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, digital information which are for them. This poses a significant problem of autonomy for receivers operating on their own power supply, for example portable microcomputers operating on batteries or accumulator. The invention aims to provide a solution to this problem. The method according to the invention is intended to reduce the duration of activity of digital information receivers having an active state and an inactive state, in which the information is transmitted from at least one fixed station by subcarriers of radio frequency channels using an asynchronous packet transmission protocol each containing a predetermined number of elementary blocks. In transmission, data is arranged in packets comprising blocks of a first type comprising data bits, parity bits and error detection bits, and blocks of a second type comprising parity bits , the second type blocks being calculated from the first type blocks and allowing the correction of errors on the data bits. On reception, the absence of error in the first type blocks is checked block by block by means of the error detection bits, the absence or the presence of error is memorized, and in the absence of error it is reset the receiver in the inactive state as soon as said receiver has received the data intended for it. The duration of activity of the receiver is thus reduced, hence a reduction in the consumption of electrical energy supplied by batteries of the receiver and an increase in its autonomy.

Advantageously, said receiver is returned to the inactive state before the end of the transmission of the current packet.

In one embodiment of the invention, the blocks of second type being arranged at the end of the packet, in the absence of error on the blocks of first type, said receiver is returned to the inactive state before the transmission of the blocks of the second type.

In another embodiment of the invention, the second type blocks being inserted between the first type blocks, in the absence of error on the blocks at the start of the packet, said receiver is returned to the inactive state before the transmission of the blocks at the end of the packet, the blocks at the start of the packet being so numerous in relation to the total number of blocks in the packet that the blocks at the end of the packet can be reconstituted from the blocks at the start of the packet. Advantageously, in the presence of an error, said receiver is maintained in the active state until the end of the packet, thus allowing the correction of the error (s).

In one embodiment of the invention, after putting a packet in the inactive state during transmission, said receiver is returned to the active state during the next normal cycle of returning to the active state.

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 blocks. The generation means are able to dispose of the data in packets comprising blocks of a first type comprising data bits, parity bits and error detection bits, and blocks of a second type comprising parity bits, the second type blocks being calculated from the first type blocks and allowing the correction of errors on the data bits. The processing means of each receiver are able to check the absence of error in the first type blocks block by block by means of the error detection bits, to memorize the absence or the presence of error, and in the absence of error in returning the receiver to the inactive state as soon as said receiver has received the data intended for it. Advantageously, the processing means are able to return the said receiver to the inactive state before the end of the transmission of the current packet. It thus succeeds in reducing the duration of activity of the receptors. On average, a receiver can be returned to the inactive state after the transmission of half a packet. Overall, we will be able to reduce this duration of activity by around 50%, hence a considerable increase in receiver autonomy.

The invention will be better understood and other advantages will appear on reading the detailed description of a particular embodiment taken by way of nonlimiting example and illustrated by the appended drawings, in which:

- Figures 1 to 4 very schematically represent a structure of elementary blocks usable according to the invention, in accordance with a SWIFT transmission protocol;

- Figure 5 very schematically illustrates the internal architecture of a receiver according to the invention;

- Figure 6 is a first diagram of the organization of the blocks of a packet; and

- Figure 7 is a second diagram of the organization of the blocks of a packet. 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 SWIFT document. Indeed, such a transmission protocol allows a high net bit rate of information, 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 correction 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. others asynchronously, that is to say without it being possible to determine temporally and in advance the times of transmission of these packets.

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.

It is then possible to define, for this transmission protocol according to the invention, a transmission frame comprising a predetermined number of successive packets, for example sixteen packets. A specific block for BLTS packet identification (FIG. 3) identified by a specific digital word ET2 (for example on five bits) is then inserted into each packet of the frame, preferably at the start of each packet. head AND. This BLTS identification block contains, in the useful part

DU, an IR identifier making it possible to identify the rank of this packet, in other words its position, in the frame. Thus, this IR rank identifier will make it possible to designate a group of receptors. Likewise, provision can advantageously be made for the useful part DU to include a binary word MSF making it possible to designate, within the group of receptors, subgroups of receptors.

BLNS network signaling blocks (FIG. 2) are also inserted in the successive frames, the type of which is identified by a specific word ET1 in the header ET. This BLNS block contains at least one NWD network identifier defining the characteristics of the transmission network and in particular the frequency of the transmission channel.

These BLNS blocks are inserted by the transmitting station in the successive transmission frames, so that they are mutually spaced from a maximum number of elementary blocks of any type, whether they are blocks of BLC type, BLTS blocks or others block types. This maximum number corresponding to a predetermined maximum spacing duration, typically 0.5 seconds, less than the duration of transmission of a packet. The spacing time between two consecutive BLNS blocks may vary provided that it remains less than the maximum duration. It is in fact the means of insertion of the station which decide on the insertion of these BLTS blocks in the successive frames. It should therefore be noted here that the insertion of BLNS blocks takes place in a completely asynchronous manner with respect to the insertion of BLTS blocks. The invention also provides for using another specific BLMS elementary block which is in fact a message signaling block (FIG. 4) and whose type ET3 appears in the AND header. This BLMS block contains in the useful part DU the address ADR of the receiver for which a message is intended, as well as a time indication DFS relative to the instant of start of message. If the message is transmitted in the same packet as that containing the BLMS block, this DFS indication defines for example the rank of the first block of the message proper, intended for the receiver, relative to the start of the packet. This DFS time indication can also indicate that the actual message intended for the receiver will be transmitted not in the packet containing this BLMS block, but in a subsequent packet.

If we now refer more particularly to FIG. 5 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 12, for example that marketed by the Japanese company OKI under the reference MSM 9553 and capable of delivering as output, after error correction and parity check, the elementary blocks cleared in particular 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.

Control means 3 are capable of momentarily activating the reception means 1 and the processing means 2 by delivering respectively to these two means corresponding control pulses. These control means 3 can be incorporated in a conventional manner within the microprocessor 20, or can be produced by a specific conventional external circuit. These control means 3 are therefore able to put the RC 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 rest state.

The entire receiver is supplied by supply means 4 comprising a battery element associated with a DC-DC converter used to raise the voltage of this battery element to that necessary for the operation of the microprocessor. In the read-only memory 22 of the RC receiver is stored an indication of network IDRR, an indication of group IDG corresponding to a rank of packet in said frame, an indication of subgroup IDSG corresponding to the subgroup to which the receiver belongs, as well as the receiver's actual ADD address. The transmitting station, not shown, essentially comprises insertion means, produced for example in software within a PC type microcomputer and receiving for example for a designated receiver, on the one hand its ADD address , its indication of group IDG, of subgroup IDSG and of network IDRR, and on the other hand, the data relating to the message proper which is intended for it. These insertion means then generate the headers and the useful parts DU of the various elementary blocks which will constitute the packets and in particular those relating to the blocks of identification of packets, network signaling, and message signaling. 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 formatting of these blocks, by adding in particular the blocks for detecting CRC errors and PRY parity. Then, all of these BL blocks, gathered in packets, are transmitted within the SRF signal. The packages we use can have different structures. The packet represented in FIG. 6, called "A ₀ ", can comprise 190 data blocks comprising a 16-bit BIC block identification code, a 16-bit header, a useful part of 160 bits, 14 bits CRC error detection and 82 horizontal parity bits, and 82 vertical parity blocks calculated from the 190 information blocks.

The packet of type "B", the structure of which is illustrated in FIG. 7, also includes 190 blocks of information whose structure is similar to those of packet A ₀ and 82 blocks of vertical parity. The difference between packet A ₀ and packet B lies in the fact that in packet A _Q , the vertical parity blocks are transmitted after the information blocks, while in packet B, the vertical parity blocks are inserted between information blocks, which ensures better continuity of information transmission.

The vertical parity blocks ensure a redundancy of the information with respect to the information blocks and thus allow by calculation to entirely find a block of information which would contain errors detected thanks to the bits of detection of errors CRC or which does not would not have been received by a receiver.

In practice, all the receivers of the same group will wake up, that is to say go into their active state, at each instant of reception of a packet comprising at the head the BLTS packet identification block whose l IR rank indication corresponds to their group.

A receiver which searches for an appropriate transmission channel, waits for the reception of a BLNS block and if said channel is appropriate, the processing means of the receiver will then analyze the rank identifier

IR contained in the next BLTS packet identification block. When the BLTS block is acquired, the processing means analyze the content of said BLTS block, and in particular analyze the IR rank identifier that it contains. If this IR rank identifier corresponds to the group indication IDG, or IDSG sub-group if applicable, stored in the receiver, the control means 3 of the receiver will then automatically synchronize the passages of the receiver in its active state in time at successive instants separated from the initial acquisition time the BLTS block of an integer multiple of the duration of the packet.

If the IR identifier does not correspond to the IDG group indication, the receiver control means will then put the latter in its idle state and then determine the occurrence of the BLTS identification block whose rank corresponds to the group of the receiver and then synchronize the alarm clocks of the receiver from this moment, taking into account the duration of the packets. Time synchronization of successive alarms of the receiver is then carried out.

When a receiver receives a packet of type A ₀ or B and all the blocks of the current packet have been properly received, that is to say have been checked by means of the CRC error detection bits, an operation which is performed by the decoder 12 of the RC receiver, the control means 3 put the receiver in its inactive state. On the contrary, if the decoder 12 detects one or more errors on the blocks already transmitted and this up to the last block intended for said receiver, then the control means of said receiver keep it in the active state to allow reception of the end of the packet and the use of vertical parity blocks to correct erroneous information blocks.

For example, in the case of an A _Q type packet, if the first ten information blocks are intended for a given receiver and these are received without error, the receiver will immediately reset to inactive state. If the last ten blocks of information in a packet are intended for a given receiver, this latter will remain in the active state until the end of the transmission of these last ten blocks of information. The decoder will check by means of the CRC error detection bits that the ten blocks intended for the receiver have been received without error and the control means will then be able to put the receiver in the inactive state for the duration of the transmission of the parity blocks. vertical. On the contrary, if an error has been detected in the ten blocks of information intended for the receiver, the latter will remain active until the end of the transmission of the packet. In the case of a type B package, the operation will be similar, that is to say that the receiver will be put into the inactive state after checking the reception without error of the blocks of information intended for it. To further reduce the activity time of the receivers, the redundancy properties of the vertical parity blocks are used. In fact, the vertical parity blocks are calculated from the information blocks and allow them to be found in the event of an error.

In the case of a type B packet, a receiver having received satisfactorily, that is to say without error detected by decoding of the CRC error detection bits the first n blocks, is capable of finding the others blocks of rank between n + 1 and 272 by a mathematical processing carried out by the processing means. The number n depends on the type of coding carried out to obtain the vertical parity blocks.

In other words, if the first n blocks of a packet B have been received satisfactorily, the receiver is capable of reconstructing the other blocks and can therefore be put into the inactive state after checking the satisfactory reception of said n -first blocks. We can thus put a receiver in the inactive state even when the information blocks intended for it are the last of a packet B. We thus reduce even more the duration of activity of a receiver. The receiver will be returned to the active state according to its normal wake-up cycle.

When all the blocks of a packet are intended for a receiver, the latter remains in the active state during a satisfactory transmission, until the verification of the last block of information for a packet A ₀ , and until verification of the n ^th block of information for a packet B, which allows, in practice, a reduction in the duration of activity of the receivers of the order of 25 to 30%. This reduction will be greater when only part of a packet is intended for a receiver.

Claims

1. Method for reducing the duration of activity of digital information receivers having an active state and an inactive state, in which the information is transmitted from at least one fixed station (ST) by sub-carriers of radio frequency channels using an asynchronous packet transmission protocol each containing a predetermined number of elementary blocks, characterized in that, on transmission, data is arranged in packets comprising blocks of a first type comprising data bits, parity bits and error detection bits, and blocks of a second type comprising parity bits, the blocks of second type being calculated from the blocks of first type and allowing the correction of errors on the data bits, and by the fact that on reception, the absence of error in the first type blocks is checked block by block by means of the error detection bits, the absse is memorized nce or the presence of error, and in the absence of error the receiver is returned to the inactive state as soon as said receiver has received the data intended for it.

2. The method of claim 1, wherein said receiver is returned to the inactive state before the end of the transmission of the current packet.

3. Method according to claim 1 or 2, wherein, the blocks of second type being arranged at the end of the packet, in the absence of error on the blocks of first type, said receiver is returned to the inactive state before the transmission of blocks of the second type.

4. The method of claim 1 or 2, wherein, the blocks of second type being interposed between the blocks of first type, in the absence of error on the blocks at the start of the packet, said receiver is returned to the inactive state before the transmission of the blocks of the end of the packet, the blocks of the beginning of the packet being in such a number compared to the total number of blocks of the packet that the blocks of the end of the packet can be reconstituted from the blocks of the start of the package.

5. Method according to any one of the preceding claims, in which in the presence of an error, said receiver is kept in the active state until the end of the packet.

6. Method according to any one of the preceding claims, in which, after putting a packet into the inactive state during transmission, said receiver is returned to the active state during the next normal cycle of delivery into the active state.

7. A digital information transmission system, comprising at least one fixed station (ST) 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 (RC) comprising radio frequency reception means (1) and processing means (2) of the received data, characterized in that the station comprises generation means (MIS) 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 radio frequency channels, successive transmission packets each comprising a predetermined number of elementary blocks, the generation means (MIS) being able to have data in packets comprising blocks of a first type comprising data bits, parity bits and error detection bits, and blocks of a second type comprising parity bits, the blocks of second type being calculated from blocks of first type and allowing the correction of errors on the data bits, the processing means (2) of each receiver being able to verify the absence of error in the first type blocks block by block by means of the error detection bits , to memorize the absence or presence of error, and in the absence of error to return the receiver to the inactive state as soon as said receiver has received the data intended for it.

8. System according to claim 7, characterized in that the processing means (2) are able to return said receiver to the inactive state before the end of the transmission of the current packet.