AU652431B2 - Communications system notably for use in air traffic control - Google Patents

Abstract

The invention relates to a digital communication system for a network operating in half-duplex mode and comprising a bus for speech and a bus for service messages. Since the latter are of considerable volume, it is advantageous to unburden the bus transporting the marshalling messages by sending a part of these messages via the speech bus and to thus ensure real-time transmission of the information. In order to be able to distinguish the two types of information on reception, the invention provides for the placing, at the level of each service message transmitted in place of a silence, of a recognition sign consisting of a code individual to the speech encoding law, and which is unobtrusive since it is unused or redundant as regards the transmission of speech. The invention provides preferentially for the use of the encoding law A which possesses not merely a redundancy, but what is more, a redundancy in the encoding of silences. The invention applies in particular to air traffic control. <IMAGE>

Description

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AUSTRALIA

PATENTS ACT 1990 0"052431 COMPLETE SPECIHC-ATION FQR A STANDARD PATENT

ORIGINAL

0 0 0 00 0 00 0 $0 00 C00 0 00 0 *o00 a 03 0 0 03 0000 0 0 00 0 Name and Address of Applicant: Actual Inventor(s): Address for Service: Thomson-CS F 51, Esplanade du General de Gaulle 92800 Puteaux

FRANCE

Georges Berry and Jean-Paul Woillez Spruson Ferguson, Patent Attorneys Level 33 St Martin& Tower, 31 Mariket Street Sydney, New South Wales, 2000, Australia Communications System Notably for Use in Air Traffic Control Invention Title: The following statemenit is a full description best method of performning It kilown to m/s.

of this invention, including the 5845/4 COM4UNtCTIONS SYSTEM NOTABLZY FOQR US~ INT ':RPAWICORL The present invention relates, to a cOMMuniations' SYStem, notably for use in air traffic Control..

e4 For this precise type of application, it is. known to employ distributed or non-distributed networks comprising a plurality ofinput-output pot.Tyialy h np3u-outpu*t 4, ports comprise a plurality of operator positions which communicate. with aircraft pilotsK a radio transmitter for providing such commnunications,, telephone sets, PABXs: (Private Automaticr 0Branch Exchanges), and sol on, this list not being exhaustive.

There are two types of information which travel within the network.

-data that is to be cornntnnicated, in other wards speech in the present applicationservice data or messages.

Bach type of information travols on *a different; transmissiona support, for example a -bus, Communication between traffic operators or controllers and aircraft pilots takes place differently depending *on the direction, more specifically in transmit/ receive mode in the operator-pilot direction, 2 with squelch operation being used in the pilot-operator direction. Communication is managed by service messages, such messages essentially corresponding to: start of transmit/receive mode operation when an i 5 operator starts to speak; end of transmit/receive mode operation when the operator stops speaking; start of transmit/receive mode operation inter-signal- SO o ing to indicate to the other operators that an operator has 10 started speaking; end of transmit/receive mode operation nter-signaling; start of squelch mode operation when an aircraft pilot starts speaking to the operators, S 15 end of squelch mode operation.

1 o The major problem that occurs in this type of network 0 0 resides in the significant volume of service messages which consequently leads to an increase in queuing time at the radio interface linking the traffic operators, to the transmitter.

In order to keep down the volume of data transmitted over the data bus, the use of silences or absence of speech in order to substitute certain data therefor, is known. The whole problem then resides in how to go about separating the two types of message at the receive end. What in fact is needed is. to code, at the transmitting end, the data being 3 transmitted in the place of silences, firstly, so as to be able to recognize it readily at the receive end and, secondly, in order not to cause any interference to speech transmission.

U One solution described in GB-A-I 013 447 consists in 5 replacing detected silences by data comprising a code which is forbidden in the speech coding law.

A solution similar to the preceding one is described in an article in IEEE Global Telecommunications Conference (vol.

3, no. 535 pages 1201 to 1206) in which the system employed i I 4 00 l0 consists in placing a specific flag in front of each item of 0 o data that is transmitted instead of a silence, said flag corresponding to a code which is not encountered in the codes used for speech.

The major disadvantage of this type of solution resides in the requirement of having two different sources of code at the input, so as to bo able to distinguish data from speech.

European Patent Application 0 082 333 discloses another t on j i solution in which the coding law selected for speech is such 1, that it is impossible to have, when transmitting speech alone, a given sequence of two coded words. It is then sufficient to transmit data in the place of silences detected using this precise sequence of two words in order to ensure that there will be distinction, at reception, between speech and data.

The disadvantage of this solution resides in the requirement of making means available in order to generate this sequence -4of two words and to insert the data therein.

The present invention sets out to overcome the above disadvantage through the provision of a system in which the data transmitted in the place of the detected silences can easily be identified.

More precisely the invention provides a digital communications system between a plurality of a digital communications system between a plurality of input and output ports mutually linked by a first speech transmission means for transmitting speech therebetween, said speech being transmitted in pulse coded form in accordance with a given coding law, said digital communications system being of the type in which codes relating to silences on said first speech transmission means are detected in order to carry service messages via said first speech transmission means, said digital communications system further including a transmission device provided with means which insert a recognition sign consisting of a given code from said coding law in each service message, and a reception device including means for recognising each recognition sign, and, when a recognition sign is encountered, separating, each transmitted service message from the transmitted speech.

The invention will be more readily understood from the description which follows with reference to the attached drawings, in which: Figure 1 illustrates a distributed digital network employed for air traffic control; Figure 2 illustrates implementation of the invention for communication between an operator and a pilot; o0 S,,4

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4 9 In:\libeOl0113:HRW Figure 3 represents a device forming part of an interface, which allows a signal simultaneously including speech and service messages to be transmitted; Figure 4 represents a receive device forming part of an interface enabling the two types of information to be separated from a signal generated as in Figure 3.

Figure 1 illustrates a distributed digital communications network employed for air traffic control purposes. The distributed architecture, in other words an architecture 'i 0 10 arranged so that each input-output port has its own interface, has the advantage of increasing information transfer as well as the security thereof when such information is being forwarded. The network in figure 1 consists of a plurality of input-output ports comprised of, for example, three operators 1, a transmitter 2, a PABX 3, a telephone set 4, a supervisory desk 5. As has been said above, each input-output port i, 2, V 3, 4, 5 has its own interface, 6, 7, 8, 9, 10 respectively.

Data is transmitted over two separate buses 11 and 12, bus ii being the speech transmission bus and bus 12 providing service o O 20 message transport.

Figure 2 illustrates operation of the invention for communication between an operator 1 and an aircraft pilot 19.

U The arrows consisting of solid lines represent communicaticn in the operator-pilot direction. Dashed line arrows indicate communication in the opposite direction. When an operator sends a spoken message to an aircraft pilot 19, the speech sent by operator 1 reaches the corresponding interface 6 in analog form. It is sampled and coded into binary form, for example on an eight-bit byte by means of the device 18 controlled by a microprocessor 14 which, for example, is a type 68000 microprocessor. The device 13 supplies a series of pulses 15 at its output, coded in accordance with a given coding law the special features of which will be indicated below, and containing the speech information.

ucrn o 10 In order to reduce the coding overhead at transmission, the system according to the invention is provided with means 0o 0 allowing a recognition sign to be assigned to each service 0 0 message, this recognition sign consisting of a particular code from the coding law employed for speech. In order not to interfere with transmission of speech, this special code is Ia preferably a code which has no use in speech, in other words 1 O one that is not employed for transmission of speech or is A 0 o redundant when transmitting a given item of speech information. One coding law which is of particular interest is A-law 20 coding.

Effectively, by using A-law coding for speech, it is silence, in other words absence of speech, that is represented by two codes 0+ and Such redundancy, which is of no use for the transmission of speech alone, will be employed, according to the invention, not only for transmitting over the i same support, in other words bus 11, speech and certain service messages, but also for providing a means of distinguishing between the two types of information, without service messages causing interference to speech transmission. In order to do this, the sequence of coded pulses 15 output from device 13 is processed by a further device 16, preferably a Digital Signal Processor (DSP) chosen for its speed of execution. Processing carried out on the sequence of coded 0.o o pulses 15 by device 16 is as follows, with reference to figure V'4o1 0. 6 10 3: in accordance with one possible implementation of the o 0 o invention, the device 16 for transmitting a signal which 00 r0 00 0 0 simultaneously includes speech and service messages, includes first means 17 which provide for detection of one of the redundant codes, for example 0+ as well as for systematic deletion of this code.

04 In parallel with this, the device 16 receives, from microprocessor 14, service messages coded on one byte, for 0 example a message indicating start of transmit/receive mode operation and start of transmit/receive mode operation inter- 00 0 04 20 signaling. The codes employed for coding such service messages are preferably selected from among codes that are representative of the lowest value speech signals in the coding law employed for speech, in order not to interfere with reception of speech should there be transmission of a service message at the same time as speech. This distinction is 8 created at device 16 by means of second means 18 which insert a flag, in other words a recognition signal, for example at the start of each service message. Advantageously, this recognition signal consists of the code that was deleted from the speech, in other words the code The signals output from, on the one hand, the first means 17 and, on the other hand from the means 18, are then multiplexed by a standard multiplexing device 20 before being transferred over speech 1 41 011100 bus 11.

auoo¢ Radio interface 7 in figure 2 hence receives a multio o 0 ~plexed signal which simultaneously contains speech and service 00 00 °0 messages. This signal is processed by device 21, preferably a SDSP, which is responsible for separating the two types of data as follows: in figure 4, device 21 for receiving the multiplexed signal includes first means 22 for detecting the code 0+.

4 00 If there is detection of second means 23 are responsible for isolating and saving the service message that is contained 0 in the byte that follows the 0+.

The recovered service message is then sent to microproo° 20 cessor 24 of radio interface 7 (see figure In parallel with this, third means 25 are responsible for deleting service messages in order to only preserve data relative to speech information. The information is then sent to a decoding device 26 (see figure 2) in order to extract the speech in analog form and to transmit it to the pilot 19 via the 9 transmitter 2 of figure 1.

For the sake of clarity, operation of the system according to the invention has been described using the example of simple communication between an operator 1 and an aircraft pilot 19. Obviously, the interest of this system resides in the fact that there are several operators 1, and hence several interface- 6 responsible for transferring signals that include two types of information to speech bus 11, in accordance with So" operation as illustrated in figure 3.

I S 10 In the same way, only communication in the operator-pilot direction (transmit/receive operation) has been deo (o scribed. Extension to the case of communication in the pi- 0 lot-operator direction is achieved by simply reversing the operation of the DSPs 16 and 21 as described above, and by making use of the part shown in dashed lines in figure 2.

I ,It is particularly advantageous to employ, for a given interface, one single DSP which makes it possible, depending on the direction of communication, to transmit a signal which simultaneously includes speech and service messages, or to o 20 separate the two types of information contained within such a received signal.

Moreover, the choice of the coding law is absolutely not limited to the A-law. Effectively, this law is practical in the sense that it introduces exploitable redundancy, and is of particular interest because such redundancy relates to the silences which it is necessary to detect. Nevertheless, the use of another coding law having a different sort of redundancy is absolutely by no means excluded, as is, yet again, regardless of the coding law, the use of some code which does not interfere too much with transmission.

The invention as described is not limited to radio communications between operators and aircraft pilots and can be extended to all types of digital communications networks employing several transmission channels.

1 0 Similarly, the distributed architecture of the network c does not constitute a condition necessary for implementing the system according to the invention.

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Claims (9)

1. A digital communications system between a plurality of input and output ports mutually linked by a first speech transmission means for transmitting speech therebetween, said speech being transmitted in pulse coded form in accordance with a given coding law, said digital communications system being of the type in which codes relating to silences on said first speech transmission means are detected in order to carry service messages via said first speech transmission means, said digital communications system further including a transmission device provided with means which insert a recognition sign consisting of a given code from said coding law in each io service message, and a reception device including means for recognising each recognition sign, and, when a recognition sign is encountered, separating each transmitted service message from the transmitted speech.

2. A digital communications system according to claim 1, wherein the transmission device further includes means for detecting and for deleting codes that is relate to silences, and a device for multiplexing signals output, firstly from said detection means and, secondly, from the means that insert said recognition sign.

3. A digital communications system according to claim 1 or 2, wherein said means included in the reception device consist of: first means for detecting said code constituting said recognition sign; second means for isolating and then saving the recognised service message; third means for deleting said service message in the transmitted speech.

4. A digital communications system according to any one of claims 1 to o* t3,, wherein said recognition sign is inserted at the begin:ing of the transmitted service message. S 25

5. A digital communications system according to any one of claims 1 to 004, wherein said given code from the coding law constituting said recognition sign is a a n code that is redundant within the coding law.

6. A digital communications system according to any one of claims 1 to wherein said coding law is A-law coding for which the redundant code is the code I 30 0+ or O- representing silences.

7. A digital communications system according to any one of claims 1 to 6, wherein the service messages transmitted are coded by means of codes representative of the weakest speech signals in the given coding law.

8. A digital communications system according to any one of claims 1 to 35 7, wherein the transmission and/or reception devices are digital signal processors (DSP). [n;\liboOO0113:HRW -12-

9. A digital conimunications system substantially as hereinbefore described with reference to the accompanying drawings. DATED this Sixteenth Day of June 1994 Thomson-CSF Patent Attorneys for the Applicant sPRTJSON FERGUSON i 9, t99~. 9 0 90 (C '9 I 599 9 1009 0 0 0 99 0009 9009 lm\IIbej00l 13!HRW ABSTRACT Communications System Notably for Use in Air Traffic Control A digital communication system is provided for a network employing transmit/receive mode operation and including a speech bus in which, a service message are transmitted over the speech bus (11) in the place of a silence, the two types of data being distinguished at reception, according to the invention, by the insertion, into each service message of a recognition sign consisting of a particular code taken from the speech coding law, said code through being unemployed or redundant for speech transmission causing no impairment of speech transmission. Use is preferably made of A-law coding which not only exhibits redundancy but moreover, has redundancy in the coding of silences, The invention is rn particularly applicable to air traffic control. o a 8 O Figure 2 Pt 0 ALB:6244N