COMMUNICATIONS SYSTEM

FIELD OF THE INVENTION

The present invention relates to apparatus, methods, signals, and programs for a computer for supporting voice and data communications over a shared cryptographic communication unit, and systems incorporating the same.

BACKGROUND TO THE INVENTION

Cryptographic communications systems to provide secure voice and data communications in airborne, land, and marine environments are known. Such systems include, for example, the ITT Industries Airterm KY-100, which provides half-duplex narrowband/wideband communications links.

A problem with some such systems is that a human operator of the system must manually select a communication mode - voice or data communications - according to dynamically varying requirements. Such mode changes may, for example, be necessary many times during a single flight in an airborne application, adding to the operator's workload. In the case of the Airterm KY-100 switching is typically effected by means of a discrete switch separate from the KY-100 main terminal unit or its associated Remote Control Unit.

Referring to Figure 1 , known systems comprise a radio transceiver 100, coupled by a cryptographic data link 105 to a cryptographic communication unit (CCU) 110 which is coupled in turn via a data link 125 to a data subsystem 130 (comprising an Improved Data Modem (IDM) 131 and Host System 132) and via an audio link 126 to a voice subsystem 140 (comprising intercom unit 141 , audio interface 142 (comprising for example microphone and/or speakers)) and to both the IDM and the intercom unit by means of a common Press-to-talk (CPTT) link 128. A manual switch mechanism 150 is also provided to enable an operator to switch the CCU 110 between a data mode and an audio mode by means of a control link 127.

Data is transferred between the Host System and the IDM by means of a data link whilst voice is conveyed between the Audio interface and the Intercom over a Voice link. A Voice Press-to- TaIk (VPTT) link also connects the audio interface to the Intercom.

Referring now to Figure 2, the CCU 110 comprises a cryptographic coder/decoder 111 , a switch unit 1 12, and a digital-to-analogue converter / analogue-to-digital converter (DAC/ADC) 113.

The cryptographic coder/decoder sends/receives data to/from the radio 100 over a cryptographic data link 105; the digital-to-analogue converter 113 is selectively coupled via the switch unit to the cryptographic coder/decoder whereby to convey voice data over the voice link 126 (to and from the voice subsystem 140); data link 125 is also selectively coupled via the switch to the cryptographic coder/decoder whereby by to convey data to and from the data subsystem. The switch is controlled by signals received over control link 127 and CPTT link 128, and operates to switch traffic between the data subsystem (data mode) and the voice subsystem (voice mode).

In this arrangement the CCU, while receiving cypher text (CT) data from the Radio, ignores a mode change control signal received on link 127 unless it is accompanied by a recognised receipt of a Press-to-Talk signal received over the CPTT link 128.

In normal operation of such a CCU (for example a KY-100) the selection of traffic mode, as between receipt of data and voice traffic, is effected manually by a user by means of control signal to the KY100. When voice mode is selected, incoming signals are decrypted and directed to the voice output and hence to the Intercom for reception by the user; in data mode incoming traffic is directed instead solely to the data output for onward transmission to the IDM for processing, output of the decoded signal to the voice output being suppressed so as to avoid spurious audible noise being generated at the audio output caused by interpretation of incoming data as voice.

However a problem arises in such systems when the CCU is set in data reception mode but incoming voice traffic is received. No advance warning is received of a switch from incoming data traffic to incoming voice traffic. As a result, the received signal continues to be interpreted initially as if it were still data and the decrypted signal continues to be directed solely to the data output of the CCU.

During initial reception of the voice traffic, the IDM continues to attempt to interpret it as if it were data. After a period during which no identifiable data packets are received, the IDM times out and concludes that the incoming signal is in fact voice rather than data.

However since in the configuration shown the mode switching is effected manually by means of the Voice/Data Mode switch, and the user is unaware that the system is receiving voice, the control signal continues to be held to ground (0) until the user manually selects voice mode (open circuit) and no means is provided in such systems for the IDM to notify the CCU that the received signal now represents voice rather than data. Hence it is not possible to redirect the

incoming signal to the audio interface rather than the data interface. Consequently incoming voice communication is lost.

In an alternative embodiment the IDM is also coupled to the CCU via the control link, but by the time the IDM determines that the received signals are carrying voice, the CCU is already busy receiving signals from the Radio, and such control signals from the IDM are ignored by the CCU while in busy mode.

A corresponding problem also arises when the CCU is in data mode (sending data) and the local user wishes to transmit voice. Once again the request to transmit voice may not be recognised and no voice can be transmitted until the data transmission has been completed.

In operation it is however preferred practice that voice messages take precedence over data since voice messages - whether incoming or outgoing - may relate to important warnings or requests for urgent actions to be taken. Loss of such voice messages when the communications system is in data mode is therefore undesirable.

It is therefore desirable to provide a communications system in which voice traffic reliably takes precedence over data even when the system is initially in data mode. It is also desirable that genuine data traffic not be presented as audio noise to the audio interface since this would be distracting for the operator. It is also desirable to make use of existing equipment in service so as to minimise additional costs of replacement.

OBJECT OF THE INVENTION

The invention seeks to provide methods and apparatus for providing improved communication. The invention also seeks to make use of existing installed communication equipment, whereby to mitigate communication system upgrade costs.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a method of operating a communications unit, the unit comprising a data link for outputting both received voice and received data traffic, a voice link arranged to output received voice traffic, the method comprising ignoring voice signals received on the voice link and monitoring and forwarding only data and voice signals received via the data link.

In one embodiment the voice signals received via the data link are selectively forwarded along a voice link responsive to a control signal received on a control link.

In a further embodiment the control signal is issued responsive to an analysis of the signal received on the data link as to whether it comprises voice or data traffic.

In a further embodiment data signals received on the data link are not forwarded along the voice link.

In a further embodiment the communications unit is a cryptographic communications unit.

In a further embodiment the communications unit is an Airterm KY-100.

The invention is also directed to apparatus arranged to embody and/or support these methods.

In particular, according to a second aspect of the present invention there is provided a communications system having a data input interface, a data output interface, a voice output interface, and a control subsystem coupled to each of the interfaces and arranged selectively to couple signals received via the data input interface to the data output interface and the voice output interface.

In one embodiment the signals received via the data input interface are selectively coupled to the data output interface and the voice output interface responsive to receipt of a control signal received by the control subsystem at a control interface.

According to a third aspect of the present invention there is provided a method of operating a communications unit having a control interface and a common press to talk interface, the method comprising:

configuring the communications unit in a data mode by sending a first control signal indicative of such a mode to the control interface of the unit;

if the common press to talk interface is already carrying a press-to-talk signal, temporarily dropping the press-to-talk signal before reinstating it.

In one embodiment the communications unit is a cryptographic communications unit.

In a further embodiment the communications unit is an Airterm KY-100.

In a further embodiment the method further comprises the method of the first aspect.

The invention is also directed to apparatus arranged to embody and/or support these methods.

In particular, according to a fourth aspect of the present invention there is provided a communications unit having a data press to talk input and an audio press to talk input and a

common press to talk output, the unit being configured to selectively drop and reinstate a press to talk signal on the common press to talk output responsive to receipt of a press to talk signal on the audio press to talk input.

In one embodiment the common press to talk signal is dropped if a data press to talk signal was being received immediately prior to the time the voice press to talk signal was received.

Advantageously, by providing automated switching between data and audio modes, operator workload is reduced. The additional ADDI unit can be installed in-line between existing component units, thereby reducing installation complexity.

Advantageously the present system makes use of existing components with minimal changes, thereby minimising upgrade cost. In particular it obviates the need to provide two CCU's, one for voice and one for data communications. The ADDI unit is also potentially smaller and lighter than a second CCU. This may be particularly advantageous where system installation space may be limited for example within an aircraft cockpit.

The invention also provides for computer software in a machine-readable form and arranged, in operation, to carry out every function of the apparatus and/or methods.

The invention is also directed to signals employed by the other aspects of the invention.

The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to show how the invention may be carried into effect, embodiments of the invention are now described below by way of example only and with reference to the accompanying figures in which:

Figure 1 shows a schematic diagram of a communications system in accordance with the prior art;

Figure 2 shows a schematic diagram of a first embodiment of a communications system in accordance with the prior art;

Figure 3 shows a schematic diagram of communications system in accordance with the present invention;

Figure 4 shows a schematic diagram of a communications sub-system in accordance with the present invention.

DETAILED DESCRIPTION OF INVENTION

Referring now to Figure 3, a first embodiment of a modified system comprises a radio transceiver 100, coupled by a cryptographic data link 105 to a CCU 110. In this arrangement however an Audio Data Dynamic Interface (ADDI) unit 320 is located between the CCU 110 and the voice and data subsystems 130, 140, and no voice/data mode switch is required.

The CCU is coupled to the ADDI by a data link 125, voice link 126, control link 127, and common PTT link 128. the ADDI in turn is coupled to the IDM by means of a data link 125a and a Data Press-to-Talk (DPTT) link 128a; and the ADDI is coupled to the intercom 141 by means of a voice link 126a and a Voice Press-to-Talk (VPTT) link 128b, separate from the DPTT link.

As in the system of Figure 1 , data is transferred between the Host System and the IDM by means of a data link whilst voice is conveyed between the Audio interface and the Intercom over a voice link. However in this system the Voice Press-to-Talk (VPTT) link which connects the Intercom and ADDI is also monitored by the IDM in order to suppress data transmission to the ADDI during voice transmission.

Referring now to Figure 4, the ADDI comprises a mode control unit 129, a mixer 128, a Continuously Variable Slope Delta (CVSD) decoder 150, and a Voice Override Unit 400. The unit couples data link 125, for connection to the CCU, to data link 125a, coupling the IDM to the CCU and also to the CVSD. Voice link 126 to the CCU is coupled via the mixer to the voice link 126a, the mixer being operated, responsive to control signals received over control link 127a (and which are also fed to the mode control unit.

The voice override unit is coupled to both the Data PTT link 128a from the IDM and the Voice PTT link 128b from the Intercom to provide a common PTT signal to the Common PTT link to the CCU.

In operation the Voice Override Unit is arranged such that when a Data PTT is being received from the IDM over the DPTT link, this is passed through as a Common PTT signal over the CPTT link to the CCU. However if, while in this state, a Voice PTT signal is received from the intercom unit, the voice override unit temporarily stops transmitting the Common PTT signal over the CPTT link before reverting to sending the Common PTT signal, now indicative of the Voice PTT signal received. During this period the control signal is also overridden to voice mode. In this way the CCU detects both a change in control signal and a change in state of the

CPTT link, thereby prompting the CCU to update its state from Data mode to voice mode automatically.

The present inventors have observed that, in some CCU's in both voice and data receive modes, even when incoming voice traffic is switched to the voice link 126, the decrypted voice signals unexpectedly continue also to be output along data link 125. Consequently the decrypted incoming signal - whether carrying data or voice traffic - is always output on the data link 125.

The ADDI 320 takes advantage of this unexpected feature, receiving both the data and voice traffic on data link 125 and conveying both via link 125a to the IDM. The IDM monitors the content of the signals received over link 125 and interprets presence of signals which are not identifiable as data as denoting presence of voice traffic. If voice traffic is identified or suspected, then the IDM issues a control signal to the CVSD 150 of the ADDI, via control link 127a, whereby to cause the decrypted voice traffic to be coupled, as analogue audio signals, to the voice link 126a and hence to the audio subsystem 140 for presentation to the user. The ADDI makes no use of any audio signals received via link 126 from the CCU.

Elimination of data noise on the audio link 126a to the operator may be provided by the CVSD simply suppressing coupling of the signals received over "data" link 125 to voice link 126a while the IDM concludes that either data is being received or that no incoming transmissions - voice or data - are being received.

Regarding outgoing signals, outgoing data from the IDM is conveyed via link 125a to the ADDI where it is passed straight through, via link 125 to the CCU. Outgoing audio signals are coupled (not shown) to voice link 126 and hence to the CCU for onward encryption and transmission via radio unit 100.

So the ADDI receives all incoming data and audio traffic via the data link 125 from the CCU; but outgoing data is transmitted via the data link 125 and outgoing voice traffic is transmitted via voice link 126.

Regarding the sending of voice traffic, this is conventionally preceded by the operator pressing a Press to Talk (PTT) button. This causes a PTT signal to be sent over VPTT link 128b to the ADDI. Upon receipt at the ADDI the PTT signal is conveyed to the voice override unit 400 which in turn sends it onwards over control link 127 to the CCU. Upon receipt, the CCU couples the outgoing voice link to the cryptographic coder/decoder for onward transmission.

If however the voice control unit is already forwarding a data PTT signal from the IDM, then it first of all terminates sending the data PTT signal before sending the voice PTT signal. I n practice both of these signals are identical and it is necessary to let the first signal drop momentarily before sending the new voice PTT signal. In this way the temporary dropping of the PTT signal on the common PTT link 128 provides sufficient indication to the CCU that the control mode should be re-checked. At that juncture the CCU notes that voice mode has now been set by the ADDI on the Control link 127 in preference to the former data mode and so switches to voice transmission mode. As a result outgoing voice traffic always takes precedence over data traffic as required.

The IDM meanwhile monitors the Voice PTT link from the intercom unit to determine when voice is being sent and to suppress transmission of data while voice transmission is in progress.

In this way outgoing audio always takes immediate precedence over outgoing or incoming data upon operation of VPTT regardless of the CCU and IDM transmit/receive statuses. Indeed the system can be continually left in data mode by default since voice mode will always be automatically selected for outgoing voice traffic.

Overall, this arrangement allows existing CCU's to be operated in a manner which allows automatic switching between secure data and secure voice modes whereby both to reduce operator intervention in manually switching between modes, and also ensures that voice traffic, incoming or outgoing, automatically takes precedence over data traffic at all times. Important voice messages are therefore never missed even when the CCU itself is configured in data mode (provided the voice signals have sufficiently great signal strength to be successfully received by the radio receiver).

The system therefore enables efficient sharing of a single CCU (e.g. KY-100) for both secure data and secure voice communications.

Any range or device value given herein may be extended or altered without losing the effect sought, as will be apparent to the skilled person for an understanding of the teachings herein.