GB2467854A

GB2467854A - Converting data to a format suitable for transmission by a Fixed Cellular Terminal (FCT)

Info

Publication number: GB2467854A
Application number: GB1002707A
Authority: GB
Inventors: Nigel Slater
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-02-17
Filing date: 2010-02-17
Publication date: 2010-08-18
Also published as: GB201002707D0; GB0902623D0

Abstract

A telecommunications apparatus comprises a wired telephone (5) connected to a Fixed Cellular Terminal (1), which connects the telephone. (5) to the PSTN via a wireless link. DTMF tones generated by the telephone cannot be reliably transmitted over a voice channel of the wireless link, so they are converted to signals compatible with the V.18 protocol (15,23) and then to signals compliant with the Cellular Text Modem (CTM) standard. Optionally the DTMF tones can be converted straight to CTM signals. The subscriber line interface circuit (SLIC,7) detects when DTMF pulses are present on the input from the telephone, and opens switch (9) to direct the pulses to the processing circuitry (15,19,21,23), which otherwise remains closed if normal voice communication only is input. Applications inlcude telecare systems connected to a remote monitoring centre.

Description

TELECOMMUNICATIONS APPARATUS

This invention relates to telecommunications apparatus, particularly but not exclusively to telecommunications apparatus for use in a telecommunications system that comprises a fixed cellular terminal configured for voice and data communications over a voice channel of a mobile telecommunications network.

So called "fixed cellular terminals" (FCT) (often generically known as PremicellTM terminals), an illustrative example of which is manufactured by Burnside Telecom (of IPR House, 37 Guildford Road, Lightwater, Surrey, GU18 55A, United Kingdom), are devices that act as an interface between a mobile telecommunications network and conventional touch tone telecommunications equipment of the type that would more usually be plugged directly into the Public Switched Telephone Network (PSTN) or into a Private Branch Exchange (PBX) that is in turn connected to the PSTN. Such devices enable a user to use their touch tone telephone, PBX or computer to make voice calls or access the Internet/email/PC fax over a mobile telecommunications network.

Fixed cellular terminals are popular devices for reducing the cost of communicating with mobile telephony terminals. A principal reason for this is that placing a call to a mobile terminal from a landline telephone will incur costs for use of the landline PSTN network as well as costs for use of the mobile telephone network for that mobile terminal. With a fixed cellular terminal, only the mobile telecommunications network is utilised when a call is placed to a mobile terminal and as such only one set of network charges are incurred.

Fixed cellular terminals are also effective solutions for providing telephony services in regions where there is no existing PSTN connection, or where the establishment of such a connection is not feasible or too expensive. Typical applications are boats, lifts, temporary offices, exhibitions, open air events, and outside broadcast events.

Another application for such devices is in the provision of telecare services by means of a telecare system. Telecare systems comprise a telephony terminal that is installed in the home, for example, of a vulnerable person such as an elderly or disabled person. The telephony terminal is operable as a conventional PSTN compatible touch tone telephone, and in addition can be controlled to operate in an assistance mode in the event of an emergency. For example if the person owning the telephone should become ill, they can press a button on the telephony terminal (or otherwise activate the terminal) that causes the terminal to make a telephone call over the PSTN to a remote monitoring centre, following which data (typically a relatively small amount of data such as an ID uniquely identifying the terminal and hence the person to whom it has been allocated) is transmitted to the remote monitoring centre. Once this data has been sent, the remote monitoring centre sends an acknowledgement and a voice connection is established with the telephony terminal to allow an operator at the remote monitoring centre to communicate, for example utilising speakerphone functionality built into the terminal, with the person to whom the terminal has been allocated, and if necessary take appropriate action to mitigate an emergency (for example by arranging for the emergency services to visit the person in question).

Such terminals can interface with security and safety devices, such as burglar or smoke alarms, to provide automatic notification of an event such as a break-in to a property or the occurrence of smoke that might be indicative of the start of a fire. The terminals can also typically interface with personal activation devices, such as a pendant worn round the neck, which include an emergency button that -when activated -wirelessly communicates with the terminal to cause the terminal to invoke the functionality described above. In such circumstances the data transferred to the remote monitoring centre on activation of the terminal may also indicate why the assistance mode has been activated (for example, because a button on a pendant has been pressed).

Such telecare telephony terminals can be plugged directly into the PSTN to provide an effective means for providing remote monitoring of the welfare of vulnerable persons. In addition, in circumstances where a direct connection to the PSTN is not possible or desirable, a fixed cellular terminal may be employed -either as an integral component of a telephony terminal or as an adaptor to which a telephony terminal is connected -to couple the telephony terminal to the remote monitoring centre via a mobile telecommunications network.

However, a problem with the latter arrangement is that it is conventional for telecare telephony terminals to utilise dual-tone multi-frequency (DTMF) signalling over a voice channel when exchanging data with a remote monitoring centre, and whilst DTMF signals can reliably be transmitted via the PSTN, problems arise when DTMF signals are transmitted to the remote monitoring centre via a fixed cellular terminal that interfaces with a mobile telecommunications network.

For example, it has been noted that DTMF tones are not reliably passed by the audio coders/decoders (codecs) of a mobile telecommunications network, and as a result the tones received by the remote processing centre can sometimes be garbled in transmission. It is also the case that some mobile telephone network operators detect DTMF tones and actively interfere with them to try to improve transmission reliability, but unfortunately these interferences more often than not tend to make matters worse.

Another associated problem is that as the time taken to acknowledge signalling from a telecare telephony terminal is invariably increased when communications are undertaken via an FCT and a mobile network (as compared with communications over the PSTN) it is not uncommon for telephony terminals to fail to receive an acknowledgement from the remote monitoring centre sufficiently quickly, following which the telephony terminal assumes that signalling with the remote monitoring centre has failed.

Clearly as telecare telephony terminals can be critical pieces of equipment, it would be advantageous if an arrangement could be devised that enabled such problems to be avoided or at least mitigated.

To this end a presently preferred embodiment of the present invention provides telecommunications apparatus for use in a telecommunications system that comprises a fixed cellular terminal configured for voice and data communications over a voice channel of a mobile telecommunications network; wherein the apparatus comprises a converter module configured for conversion of data signals between a first type that cannot reliably be transmitted via the voice channel of said mobile telecommunications network and a second type that can reliably be transmitted via the voice channel of said mobile telecommunications network.

In one embodiment, the apparatus further comprises a mobile network communications module coupled to said converter module and operable to transmit and receive voice and/or data traffic over the air interface of a mobile telecommunications network.

Preferably said mobile network communications module comprises an interface for communication with a subscriber identity module (SIM).

Preferably said mobile network communications module comprises an antenna.

Preferably said apparatus comprises an interface for coupling said apparatus to a telecommunications terminal, said converter module being coupled to said interface.

Preferably said converter module comprises a dual tone multi-frequency (DTMF) detector operable to detect DTMF tones in a signal received by said apparatus.

The DTMF detector may be configured to convert received analogue DTMF tones into a four bit digital signal.

Preferably the apparatus comprises a processor configured to convert four bit digital signals from said DTMF detector into a two-bit signal. The processor may comprise a CMOS integrated DTMF transceiver.

The processor may be configured to access a look-up table to convert received four bit digital signals into two bit digital signals.

The apparatus may comprise an FSK generator configured to receive two-bit digital signals from said processor and generate an analogue dual tone output signal that is V.18 compliant. The apparatus may comprise a digital signal processor configured to determine the pulse width and interval of DTMF signals received by said DTMF detector, and to information pertaining to the determined pulse width and interval of received DTMF signals to said FSK generator.

The apparatus may comprise a CTM conversion module coupled between said FSK generator and said mobile network communications module, said CTM conversion module being configured to convert V. 18 compliant FSK signals from said FSK generator into CTM compliant signals for onward transmission by said mobile network communications module.

The apparatus may comprise a CTM conversion module coupled between said FSK generator and said mobile network communications module, said CTM conversion module being configured to receive V. 18 compliant FSK signals and said information from said FSK generator into CTM compliant signals for onward transmission by said mobile network communications module.

The apparatus may comprise a CTM conversion module coupled between said processor and said mobile network communications module, said CTM conversion module being configured to convert two-bit digital signals from said processor into CTM compliant signals for onward transmission by said mobile network communications module.

The apparatus may comprise a processor that is configured to receive four-bit digital signals from said DTMF detector and convert said signals into a CTM compliant signal for onward transmission by said mobile network communications module.

The apparatus may comprise a DTMF generator operable to receive four-bit digital signals from said processor and to output DTMF tones representative of said digital signals to said interface.

The apparatus may comprise an interface for coupling said apparatus to the PSTN.

The converter module may comprise an FSK decoder operable to convert received CTM compliant signals into a digital signal. The apparatus may comprise a processor that is operable to convert two-bit digital signals from said FSK decoder into four-bit output signals. The apparatus may comprise a DTMF generator operable to convert four-bit digital signals from said processor into DTMF tones for transmission to an output interface for coupling said apparatus to monitoring centre equipment. The apparatus may comprise a DTMF detector operable to detect DTMF tones in signals received from said output interface and to convert said DTMF tones into four bit digital signals. Said processor may be configured to receive four bit digital signals from said DTMF detector and to generate a two-bit digital signal.

The apparatus may comprise an FSK generator operable to receive two-bit signals from said processor and to generate CTM compliant signals for transmission to the PSTN via said interface.

The apparatus may comprise a switch and a switch controller, said switch controller being operable to detect voice calls and to bypass said converter module by closing said switch.

In one implementation the first type of data signals comprise dual tone multi-frequency (DTMF) signals. In one implementation the second type of data signals V. 18 compliant signals. In another implementation the second type of data signals comprise cellular text modem (CTM) compliant signals.

Another aspect of the present invention provides a fixed cellular terminal comprising apparatus as described herein. Another aspect of the present invention provides a telecare system comprising a telecare terminal that includes, as an integral component thereof, a fixed cellular terminal as described herein.

The system may comprise an actuator configured to communicate with said telecare terminal. The actuator and the telecare terminal may each be configured for wireless telecommunications with one another.

The apparatus may comprise a sensor module configured for communication with said telecare terminal. The sensor module may be configured to communicate wirelessly with said telecare terminal. The sensor module may comprise a smoke detector. The sensor module may comprise an intruder detector such as a passive infrared sensor, pressure sensor or a vibration sensor.

Various aspects of the teachings of the present invention, and arrangements embodying those teachings, will hereafter be described by way of illustrative example with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of telecommunications apparatus according to a first embodiment of the present invention; Fig. 2 is a schematic representation of telecommunications apparatus according to a second embodiment of the present invention; Fig. 3 is a schematic representation of telecommunications apparatus according to a third embodiment of the present invention; Fig. 4 is a schematic representation of telecommunications apparatus according to a fourth embodiment of the present invention; and Fig. 5 is a schematic representation of an illustrative telecare terminal.

Preferred embodiments of the present invention will now be described with particular reference to a telecare system that includes a telecare telephony terminal which interfaces with an FCT for communication, via a wireless network and the PSTN, with a remote monitoring centre.

The teachings of the present invention have particular utility for such an application, but it will be appreciated that the teachings of the invention may be utilised for a variety of other applications, and as such the following description should be treated as being merely illustrative of the teachings of the invention and not a definitive limitation of the scope of the invention.

With the above proviso in mind, reference will now be made to Fig. 1 of the accompanying drawings in which there is provided a schematic representation of the components of telecommunications apparatus according to a first embodiment of the present invention.

However, before this first embodiment is described in detail it is useful at this juncture to devote a few paragraphs to a brief explanation of the particular features of a wireless telephony system that a convertor according to the teachings of the invention is configured to exploit.

In a system where a telecare telephony terminal is coupled directly to the PSTN, and through the PSTN to a remote monitoring centre, DTMF data signals can reliably be transmitted through the PSTN between the telecare telephony system and the monitoring centre. However, as aforementioned, when the PSTN is not directly accessible and an FCT is employed to provide access to the remote monitoring centre via a mobile telecommunications network, DTMF signals from the telecare telephony equipment tend to become garbled -typically because of the codecs conventionally employed in such mobile networks.

The problem of providing for reliable signalling between disparate items of equipment over a telelcommunications network is not a new one. For example, in the context of telecommunications devices for the deaf (TDD5), otherwise known as teletypewriter (TTY) terminals or textphones, interoperability and compatibility problems between terminals prompted the International Telecommunication Union (ITU) to develop various communications standards, culminating in the adoption of a frequency-shift keying (FSK) based communications standard known as V.18 -a dual standard in that it is both an umbrella protocol which enables recognition and interoperability of some of the most commonly used textphone protocols, as well as offering a native V.18 mode, which is an ASCII full-or half-duplex modulation method.

When the GSM (Groupe Special Mobile) mobile telecommunications network was designed it was anticipated that the use of textphone equipment over the air interface would be desirable, and as FSK based communications cannot reliably be passed over the in-band voice path of the network a new mechanism known as the Cellular Text Modem (CTM) was designed and standardised by ETSI, the European Telecommunications Standards Institute. In general terms, the CTM standard (as set out, inter alia, in ETSI Technical Specfication 123.226 and 126.226 -the contents of each of which are incorporated herein by reference) is a modulation and coding method which provides for the reliable transmission of a text telephone conversation alternating with a speech conversation through the existing speech communication paths in cellular mobile phone systems.

In general terms, the CTM standard provides a mechanism whereby V.18 compliant signalling from a first party's teletype terminal is converted by a CTM capable mobile terminal into CTM signalling for transmission over the air interface to a base station controller (BSC) and CTM adapter. The BSC and CTM adapter convert received CTM signalling back to V.18 compliant signalling for onward transmission via a mobile switching centre (MSC) to the PSTN, and via the PSTN ultimately to a second party that the first party wishes to communicate with. In another arrangement the BSC may communicate via the mobile network with a second party, thereby bypassing the PSTN.

The general concept embodied by the teachings of the present invention is that the CTM communications standard previously devised by ETSI can, in addition to a means for passing TTY signalling over the air interface, be utilised as an effective means for passing signalling of other types that are also not suitable for transmission over the air interface in their native form. To this end, the teachings of the present invention provide several embodiments whereby signalling from a telecare telephony terminal can utilise the CTM standard to pass through the air interface. For example, in one illustrative embodiment telecommunications apparatus is provided that is configured to convert DTMF signalling into CTM signalling for transmission over the air interface. As the CTM standard provides for reliable transmission of CTM protocol signals the CTM encoded DTMF signals can -in one illustrative arrangement -readily be converted back to DTMF signals for interpretation by a remote monitoring centre.

Referring now to Fig. 1 of the accompanying drawings, in a first embodiment there is provided telecommunications apparatus that comprises a fixed cellular terminal (FCT) 1 which includes an interface 3 (for example an RJ11 or BS6312 compliant socket interface) into which a conventional telecare telephony terminal 5 can be plugged. As aforementioned the telecare telephony terminal is configured to be capable of being activated to operate in an assistance mode where DTMF data signalling occurs between the terminal and a remote monitoring centre in the course of or before a voice call to the centre.

As will be appreciated by persons skilled in the art, other types of terminals that communicate with a remote terminal or centre by means of DTMF signalling could be plugged into the FCT, and as such the present invention should not be interpreted as being limited solely to a terminal for the provision of telecare functionality.

The interface 3 is coupled to a subscriber line interface circuit (SLIC) 7, the functionality and form of which are well known in the art. In general terms, the SLIC 7 emulates PSTN voltage levels, detects whether a connected telephony terminal is on-or off-hook, generates a ringing voltage (generally roughly 100V RMS AC in Europe) and a voltage of about -48 volt DC when the connected telephony terminal is on-hook, and fulfils many other functions the like of which are well known to persons of ordinary skill in the art.

The SLIC 7 is coupled to a conventional mobile network communications module 11 via a switch 9 that is opened and closed in response to a connected telephony terminal 5 switching between the transmission of DTMF data or audio signals.

The mobile network communications module 11 comprises known components for establishing a communications channel over an air interface with a mobile telecommunications network. The module includes, inter alia, a mobile transceiver, an aerial, a SIM interface, appropriate codecs and a controller.

For outbound communications (i.e. in this instance, from the telecare terminal 5 to the remote monitoring centre) a DTMF detector 13, the like and form of which are known in the art, is coupled to the SLIC 7. The DTMF detector monitors transmissions through the SLIC 7, and extracts from those signals the unique frequency pairs that characterise DTMF signals. The analogue DTMF tones input to the DTMF detector 13 are output as four bit digital signals (indicating which of the sixteen possible DTMF tones (representing 0-9 and A-F) the input signal includes) for conversion to a two bit digital signal (representative of two tones, typically 1400 and 1800 Hz) by a digital processor 15.

In one illustrative arrangement the digital processor 15 could comprise a CMOS integrated DTMF transceiver (such as the CM888818888-2 transceiver provided by California Micro Devices Corporation of 490 N. McCarthy Blvd., #100; Milpitas; California 95035; USA).

Conversion of input four bit digital signals to output two bit signals may be accomplished, in one illustrative embodiment, by providing an appropriate look-up table that enables the processor to select the appropriate output signal in dependence upon the identity of the input signal.

The two bit digital signals output by the digital processor 15 are, in this embodiment, passed to an FSK generator 17 which, in a known manner, encodes the two bit digital output of the digital conversion module, into for example a 1400/1 800 Hz dual tone signal. The FSK generator is configured to generate an analogue dual tone output signal in accordance with the V18 protocol, as set out for example in ITU-T Recommendation V.18 (11/2000). As is well known in the art, the V.18 standard covers issues such as transmission data rate, which FSK frequencies are used to represent 0 and 1 and the bit pattern required to represent a character or number. With this information to hand, a person skilled in the art is well able to implement the necessary conversion between the two bit digital representation of DTMF tones and the corresponding TTY V.18 compliant data stream, and vice versa.

The FSK analogue signals output by the FSK generator 17 are then passed to a CTM module 19 for conversion into a CTM compliant signal. CTM compliant signals are then passed from the CTM module 19 to the aforementioned mobile network communications module 11 for transmission over a mobile telecommunications network.

CTM modules are in themselves well known in the art, and could comprise for example a digital signal processor (DSP) executing appropriate software for conversion of FSK signals into CTM compliant signals in accordance with the appropriate international standards. One illustrative example of a DSP implemented software CTM is available from Illico of 765-82 San Antonio Avenue, Palo Alto, California 94303, United States of America.

The CTM conversion module 19 (or optionally the digital processor 15) is configured to control the aforementioned switch 9 via a control line 18 to open the switch in the event that DTMF signals are to be communicated, and to close the switch in the event that audio signals are to be communicated.

As is well known in the art, a bearer bit is set which indicates to the mobile network communications network that the appropriate resources should be available in the network to enable the mobile network communications module to use CTM for transmission of signals from the CTM module 19.

As will further be understood by persons skilled in the art, CTM signals are transmitted faithfully by the mobile network to which the FCT is connected, and are then converted by the mobile network to PSTN compliant signals, typically to V.18 compliant signals, for onward transmission to a remote monitoring centre via the PSTN (in circumstances where the remote monitoring centre is coupled to the mobile telecommunications network via the PSTN). In another contemplated arrangement, the remote monitoring centre may be directly coupled to the mobile communications network via the air interface, and in such an arrangement equipment at the remote monitoring centre would interface with a similar FCT to that depicted in Fig. 1.

For inbound communications to, in this instance, the telecare telephony terminal 5, the CTM conversion module 19 monitors signals received by the mobile network communications module 11 and in response to the detection of a bearer bit which identifies a given received signal as being a CTM compliant signal, converts the signal from a CTM compliant signal to an analogue V.18 FSK signal and passes the FSK signal to an FSK decoder 23. In the absence of a bearer bit, received signals are sent via the audio path to the SLIC.

The FSK decoder 23 retrieves a digital signal that is encoded within the analogue signals received from the CTM conversion module 19, and outputs a two bit digital representation of that encoded digital signal to the digital processor 15, which processor comprises a converter that is configured to convert received two-bit digital signals from the FSK decoder to a four-bit digital signal that is passed to a DTMF generator 21. As before, the processor 15 may be configured to access a look-up table for enabling the conversion of received two-bit signals to four-bit output signals.

The DTMF generator 21 receives the four-bit digital signal from the digital processor 15 and generates corresponding sinusoidal analogue DTMF compliant tones that are supplied to the SLIC 7 for transmission to the telecare telephony terminal 5 via the interface 3.

At the remote monitoring centre a variety of different approaches may be adopted. In one envisaged implementation the remote monitoring centre may opt to receive and directly process FSK V.18 signals from the PSTN. In another envisaged arrangement, the remote monitoring centre may wish to be presented with DTMF signalling, and for implementing this latter arrangement telecommunications apparatus comprising an adaptor 25 of the type depicted in Fig. 2 of the accompanying drawings may be employed.

Referring now to Fig. 2, the telecommunications apparatus of this embodiment comprises an adaptor 25 that is configured to function as an interface with the PSTN 27 and legacy monitoring centre equipment 29 -which equipment is configured to detect, decode and respond to received DTMF signalling.

For inbound communications, FSK V.18 compliant signals generated at the PSTN/mobile network interface of a mobile telecommunications network are transferred to the adaptor 25 via the PSTN 27 and an interface 31, which may comprise for example an RJ1 1 or BS6312 compliant socket interface.

A direct access arrangement (DAA) module 33 (typically embodied as a chip) is coupled to the interface 31 and has as one of its primary functions the isolation of the adaptor and equipment connected thereto from PSTN voltages. The DAA module 33 includes a ring detector and is configured to pass voice signals to and from the PSTN 27 and may also be configured to pass other telecommunications signals such as caller-ID signals. DAA modules are in themselves well known components of telecommunications systems, and any such device may in principle be utilised in the adaptor 25.

A switch 35 opens or closes an audio connection from the DAA 33 to a SLIC 37 when a call has been received and in dependence on whether FSK encoded DTMF signalling is detected. In one envisaged arrangement the DAA 33 may be configured to answer incoming calls before a ringing signal is presented to the SLIC 37 for detection by the connected monitoring centre equipment 29.

An FSK decoder 39, the like and form of which are known in the art, is coupled to the DAA 33 and is configured to monitor transmissions through the DAA 33. The FSK decoder extracts and decodes FSK encoded analogue signals passing through the DAA and generates a digital output signal corresponding to a digitised DTMF signal which is encoded within a carrier wave in the FSK signal received at the interface 31 from the PSTN 27.

The digital output signal from the FSK decoder 39 is converted from a two-bit digital signal to a four bit digital signal by a digital processor 41, which also controls operation of the switch 35 via control line 34. The four bit digital signal from the digital conversion module 41 is passed to a DTMF generator 43 that converts the received digital signals into analogue sinusoidal DTMF tones. The DTMF tones output by the DTMF generator 43 are passed to the SLIC and via an interface 45 to the monitoring centre equipment 29. As before, the processor 41 may be configured to access a look-up table for enabling the conversion of received two-bit signals to four-bit output signals.

As with the arrangement depicted in Fig. 1, the SLIC 37 emulates PSTN voltage levels, detects whether a telephony terminal is on-or off-hook and generates the ringing voltage (generally about 100V RMS AC in Europe).

For outbound signals, analogue DTMF signals from the monitoring centre equipment 29 are received by the SLIC 37 via the interface 45 to which that equipment 29 is connected.

A DTMF detector 47, the like and form of which are known in the art, is coupled to the SLIC 37. The DTMF detector 47 monitors transmissions through the SLIC 37, and extracts from those signals the unique frequency pairs that characterise DTMF signals output by the monitoring centre equipment 29. These analogue sinusoidal signals are converted by the DTMF detector 47 into four bit digital signals that are passed to the digital processor 41 for conversion into two-bit digital signals that are output to the FSK generator 49. As before, the DTMF detector and digital processor may be integrated in a single device that outputs digital signals which are representative of received analogue DTMF signals. For example a CMOS integrated DTMF transceiver (such as the CM888818888-2 transceiver provided by California Micro Devices Corporation of 490 N. McCarthy Blvd., #100; Milpitas; California 95035; USA) could be utilised in place of a separate DTMF detector and digital processor.

The FSK generator 49, in a known manner, modulates the two-bit digital output from the digital processor 41 with a carrier wave, for example a 1400/1800 Hz carrier wave. The FSK modulated digital signals are then passed to the DAA 33 for onward transmission via the PSTN 27.

It is apparent from the foregoing that the arrangement depicted in Fig. 2 provides an effective means to ensure that legacy monitoring centre equipment 29 receives signals that are of an appropriate format. In the context of a telecare system, those signals may comprise, for example, DTMF tones that are representative of data -for example an ID which uniquely identifies a given telecare terminal, and hence a person to whom that terminal has been allocated. The signals may also identify the reason for alarm activation -for example that the alarm has been activated by someone pressing a button on a pendant, or that the alarm has been activated by a smoke detector. The information encoded in DTMF tones may be supplemented by other items of information received from the PSTN, for example by caller-ID information indicating the telephone number of the incoming call.

In a modification of the arrangement depicted in Fig. 1, shown schematically in Fig. 3 (in which like components are designated with the reference numerals used in Fig. 1), the FCT 51 comprises a CTM conversion module 53 that is configured to convert digital signals received from the digital conversion module 15 into CTM compatible codes for transmission over the mobile network via the mobile network communications module 11. A modification of this embodiment could combine the digital processor with the CTM module and directly convert received four bit digital DTMF data into a CTM format digital code for transmission over the mobile network.

At the remote monitoring centre, the equipment may either be configured to recognise and act upon the codes (that are received as FSK V.18 signals from the PSTN), or in another embodiment an adaptor of the type depicted in Fig. 2 may be employed to present DTMF tones to the monitoring centre equipment 29.

Referring now to Fig. 4, there is depicted another embodiment of the present invention that is similar to the arrangement depicted in Fig. 1 (and in which like components are designated with the reference numerals used in Fig. 1). In this embodiment the telecommunications apparatus comprises an FCT 55 that includes a digital signal processor (DSP) 57 which is configured to determine the pulse width and interval of DTMF signals received by the SLIC 7 from the telecare terminal 5. The DSP 57 outputs a digital signal representation of the measured pulse width/interval to the FSK generator 17, and the FSK generator passes this information together with a generated FSK signal (representative of the received DTMF tones) to the CTM conversion module 19 for conversion into a CTM signal for transmission to the remote monitoring centre.

At the remote monitoring centre, the equipment may either be configured to recognise and act upon the codes received as FSK V.18 signals from the PSTN, or in another arrangement, an adaptor of the type depicted in Fig. 2 may be provided. In this instance the digital conversion module 41 is configured to generate a digital signal representative of the original pulse width/interval codes from information provided by the FSK decoder 39, and pass that digital signal to the DTMF generator 43 -the DTMF generator being configured to use the transmitted pulse width/interval information to generate corresponding DTMF codes having the same pulse width/interval as those received at the SLIC 7 from the connected telecare terminal 5.

The foregoing embodiments of the invention rely on the use of CTM for faithful transmission of DTMF tones over a mobile telecommunications network.

In a modification of the embodiment shown in Fig. 1 that also employs CTM for DTMF tone transmission, the digital processor 15 is configured -when the telecare terminal 5 goes off-hook -to provide a tone to the telecare terminal 5 (for example a calling tone) and control the mobile network communications module 11 to initiate a telecommunications session with a remote monitoring centre. The digital processor 15 then establishes a TTY FSK dialogue with the remote monitoring centre via the initiated telecommunications session, and if that dialogue should indicate that a reliable connection has been made to the remote monitoring centre, the digital processor 15 indicates to the telecare terminal that the call has been accepted by ceasing the tone and accepting signals from the telecare terminal for transmission to the remote monitoring centre. If a reliable connection cannot be established, the tone can be continued or an out of service tone presented to the telecare terminal, and in response to that out of service tone the telecare terminal may try again or dial an alternate number.

In one illustrative arrangement the digital processor could initially transmit a request for an acknowledgement signal to the remote monitoring centre. If an acknowledgement signal should be returned by the remote monitoring centre to the FCT, the digital processor 62 may then transmit an appropriate CTM encoded DTMF tone (or tones) to the remote monitoring centre, and the remote monitoring centre may interpret the received FSK TTY encoded DTMF tone, and then signal the digital processor with an indication of the identity of the received tone (or some other information characterising the received tone). The digital processor 62 may then determine whether the indication of the identity of the received tone returned by the remote monitoring centre matches the identity of the CTM encoded DTMF tone sent by the FCT, and if this determination should be positive the digital processor 15 may determine that a reliable connection has been achieved and proceed as outlined above.

As mentioned earlier, in this arrangement the remote monitoring centre equipment may be configured to receive and process FSK TTY signals from the PSTN.

In another envisaged arrangement, particularly suitable for legacy equipment, an adapter may be provided (for example an adaptor of the type shown in Fig. 2) to convert received FSK TTY signals into DTMF tones for presentation to the monitoring centre equipment.

In another aspect of the present invention there is provided telecommunications apparatus for addressing the problem of telecare equipment (or other equipment) timing out when communicating with a remote monitoring centre via a mobile network (where the time taken to receive an acknowledgement from the remote monitoring centre is typically much longer than that associated with a conventional PSTN connection).

In circumstances where equipment at a remote monitoring centre is capable of processing TTY FSK signals, the system may comprise an FCT of the type depicted in Fig. 1 (the remote monitoring centre equipment directly interfacing with the PSTN). In circumstances where the remote monitoring centre equipment is only capable of understanding DTMF signalling, an FCT of the type depicted in Fig. 1 may be provided for interfacing with the telecare terminal 5 and an adaptor of the type depicted in Fig. 2, with which the FCT communicates, may be provided for interfacing with the remote monitoring centre equipment.

In either case, when the digital processor 15 of the FCT 59 detects that the telecare terminal 5 has gone off-hook and receives DTMF signalling from the telecare terminal 5, the digital processor 15 issues an acknowledgement signal in response to the received DTMF signalling (which acknowledgement would normally, in previously proposed arrangements, have been issued by the remote monitoring centre equipment) to the telecare terminal 5 to thereby provide the telecare equipment 5 with an assurance that the DTMF signals from it have been received.

Once the digital processor 15 has acknowledged receipt of the DTMF signalling from the telecare terminal 5, it controls the mobile network communications module 11 to establish a communications session with the remote monitoring centre via the mobile network and transmits the DTMF signalling (utilising CTM for example) from the telecare terminal 5 to the remote monitoring centre.

As a result of this arrangement, the telecare terminal 5 more quickly receives an acknowledgement of receipt in response to issued DTMF signalling, and hence is less likely to time out as compared to a situations where signals are delayed by the air interface between the FCT and remote monitoring centre equipment.

In a related aspect of the present invention, that also addresses the fact that different telecare terminals may well expect different acknowledgement signals, the FCT could be capable of being placed in a learning mode so that the FCT automatically determines the appropriate acknowledgement codes and timing for a given connected telecare terminal 5. The learning mode could be invoked by presenting the FCT with a special code (for example by dialling the numbers corresponding to the code into the connected telecare terminal 5, or by transmitting the code to the FCT from the remote monitoring centre (or elsewhere)), or could be invoked automatically whenever a new SIM card is inserted into the mobile network communications module 11 of the FCT 59.

When the FCT is in the learning mode, the digital processor 15 controls the mobile network communications module 11 to send a signal to an adaptor 25 (for example an adaptor of the type depicted in Fig. 2) between the PSTN and the remote monitoring centre equipment, which signal advises the adaptor 25 that the FCT 59 is in learning mode.

In response to receipt of a learning mode signal, the digital processor 41 of the adaptor 25 generates a DTMF tone for presentation to the monitoring centre equipment 29. The monitoring centre equipment 29 issues a DTMF acknowledgement in response to the presented DTMF tone, following which the digital processor of the adaptor would determine the characteristics of that acknowledgement (for example, the DTMF code used, the duration of the DTMF code, and the time elapsed between the last DTMF character sent to the monitoring centre equipment 29 and the time at which the acknowledgement from the monitoring centre equipment is received by the adaptor), and signal the FCT with details of the acknowledgement issued by the remote monitoring centre equipment.

The digital processor 15 of the FCT 59 stores details of the acknowledgement code received from the adaptor to complete the learning process, and thereafter when the digital processor 15 receives DTMF tones from the connected telecare terminal it issues the appropriate acknowledgement DTMF tone to the connected telecare terminal that conforms to the stored details for the remote monitoring centre acknowledgement signals.

In another related aspect, the FCT may include a look up table of telecare terminals and associated acknowledgement codes for those terminals. The digital processor 15 may then be configured on receipt of a TTY code (for example from the remote monitoring centre, or from the telecare terminal 5 connected to the FCT) identifying the telecare terminal 5 connected to the FCT 59 to select the appropriate acknowledgement code for that particular terminal and to use that acknowledgement code to acknowledge receipt of DTMF from the telecare terminal 5.

In another aspect of the present invention that is also concerned with reducing delays associated with the issuance of an acknowledgement, remote monitoring centre equipment connected to an adaptor (for example of the type shown in Fig. 2) or to the PSTN and the remote monitoring centre equipment may utilise caller ID information associated with an incoming call and determine whether that caller ID information identifies the call as being associated with a mobile network or the PSTN, and by inference in this instance an FCT terminal or a PSTN connected telecare terminal. If the caller ID should indicate that the telecare terminal is directly connected to the PSTN, TTY to DTMF conversion may be avoided to thereby reduce the time taken to issue acknowledgement codes to connected telecare terminals. If the caller ID should indicate that the telecare terminal is connected to an FCT, any of the techniques hereinbefore described may be utilised.

In foregoing embodiments of the invention the FCT has been described as being a component into which a telecare terminal is plugged. It will be appreciated, however, that the components of an FCT according to any embodiment of the invention described herein may be incorporated into a telecare terminal to provide a particularly compact arrangement.

Such an arrangement is illustrated schematically in Fig. 5 of the accompanying drawings. In the arrangement of Fig. 5 there is depicted a telecare terminal 63 that is configured to generate DTMF or FSK signals for transmission via the PSTN. In an alternative arrangement the telecare terminal may generate CTM signals for transmission to the remote monitoring centre equipment.

Referring now to Fig. 5, the telecare terminal 63 includes a conventional telephony module 65 that comprises known components to enable the telecare terminal to be used as a telephone. The telephony module 65 is coupled to an FCT 67 of the type described herein that is configured to establish a mobile communications connection with a mobile communications network 69, and via the network 69 and the PSTN with a remote monitoring centre 71.

An alarm activation module 73 is provided and is configured, when activated in the event of an emergency, to communicate with the FCT 67 for the transmission of DTMF codes to the remote monitoring centre 71 via the PSTN or CTM encoded DTMF via mobile telecommunications network 69.

In this particular example, the alarm activation module 73 is coupled to a wireless interface 75 that is capable of communicating wirelessly with an alarm module 77, for example a pendant with an alarm activation button, that can be activated to signal the wireless interface and the connected alarm activation module 73 that an emergency has occurred.

As aforementioned, it is also conceivable for the remote monitoring centre equipment to be directly connected to a mobile telecommunications network, for example by means of an FCT. In such an arrangement an FCT of the type depicted in Fig. 1 could be provided for interfacing with the equipment at the remote monitoring centre.

It is apparent from the foregoing that various techniques have been described to address problems associated with signalling a remote monitoring centre over the air interface of a mobile telecommunications network.

It will also be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the scope of the appended claims.

For example, it may be desirable (for improving communications between legacy telecare equipment and FCTs) to provide an adaptor that interfaces with a telecare terminal and an FCT, and which is configured to convert (using any of the methods described above) DTMF signalling received from the telecare terminal to CTM signalling for onward transmission by the FCT. In such an arrangement the adaptor would comprise all of the components of the arrangement depicted in Fig. 1, apart from the mobile network communications module 11. The adaptor would, of course, need to inform the connected FCT that CTM protocol signals are to be transmitted, and to that end the firmware of the legacy FCT would need to be updated (in a known manner) so that the aforementioned bearer bit notifying the network that CTM signals are to be transferred could be set. Once updated the FCT could be switched into and out of a CTM transmission mode by means of appropriate signals from the digital processor of the adaptor.

It should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present invention is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed -irrespective of whether those features are associated with the same or different embodiments.

It will also be appreciated by persons skilled in the art that where functionality is mentioned herein as being embodied in software, that functionality could equally be provided by hardware (for example by means of one or more application specific integrated circuits (ASICs)) or a mix of hardware and software without departing from the scope of the present invention.

Lastly, whilst preferred embodiments of the invention are concerned with systems and devices that interface with a GSM mobile telecommunications network, it will be understood by persons skilled in the art that the teachings of the present invention may readily be applied, with appropriate modifications the like of which will immediately be apparent to persons skilled in the art, to other types of telecommunications network -for example a UMTS or PCS compatible network.

Claims

CLAIMS1. Telecommunications apparatus for use in a telecommunications system that comprises a fixed cellular terminal configured for voice and data communications over a voice channel of a mobile telecommunications network; wherein the apparatus comprises a converter module configured for conversion of data signals between a first type that cannot reliably be transmitted via the voice channel of said mobile telecommunications network and a second type that can reliably be transmitted via the voice channel of said mobile telecommunications network.
2. Apparatus according to Claim 1, further comprising a mobile network communications module coupled to said converter module and operable to transmit and receive voice and/or data traffic over the air interface of a mobile telecommunications network.
3. Apparatus according to Claim 2, wherein said mobile network communications module comprises an interface for communication with a subscriber identity module (SIM).
4. Apparatus according to Claim 2 or 3, wherein mobile network communications module comprises an antenna.
5. Apparatus according to any of Claims 2 to 4, comprising an interface for coupling said apparatus to a telecommunications terminal, said converter module being coupled to said interface.
6. Apparatus according to Claim 5, wherein said converter module comprises a dual tone multi-frequency (DTMF) detector operable to detect DTMF tones in a signal received by said apparatus.
7. Apparatus according to Claim 6, wherein said DTMF detector is configured to convert received analogue DTMF tones into a four bit digital signal.
8. Apparatus according to Claim 7, comprising a processor configured to convert four bit digital signals from said DTMF detector into a two-bit signal.
9. Apparatus according to Claim 8, wherein said processor comprises a CMOS integrated DTMF transceiver.
10; Apparatus according to Claim 8 or 9, wherein said processor is configured to access a look-up table to convert received four bit digital signals into two bit digital signals.
11. Apparatus according to any of claims 8 to 10, comprising an FSK generator configured to receive two-bit digital signals from said processor and generate an analogue dual tone output signal that is V.18 compliant.
12. Apparatus according to Claim 11, comprising a digital signal processor configured to determine the pulse width and interval of DTMF signals received by said DTMF detector, and to information pertaining to the determined pulse width and interval of received DTMF signals to said FSK generator.
13. Apparatus according to Claim 11, comprising a CTM conversion module coupled between said FSK generator and said mobile network communications module, said CTM conversion module being configured to convert V. 18 compliant FSK signals from said FSK generator into CTM compliant signals for onward transmission by said mobile network communications module.
14. Apparatus according to Claim 12, comprising a CTM conversion module coupled between said FSK generator and said mobile network communications module, said CTM conversion module being configured to receive V. 18 compliant FSK signals and said information from said FSK generator into CTM compliant signals for onward transmission by said mobile network communications module.
15. Apparatus according to any of Claims 8 to 10, comprising a CTM conversion module coupled between said processor and said mobile network communications module, said CTM conversion module being configured to convert two-bit digital signals from said processor into CTM compliant signals for onward transmission by said mobile network communications module.
16. Apparatus according to Claim 7, comprising a processor that is configured to receive four-bit digital signals from said DTMF detector and convert said signals into a CTM compliant signal for onward transmission by said mobile network communications module.
17. Apparatus according to any of Claims 8 to 10 when dependent on Claim 4, comprising a DTMF generator operable to receive four-bit digital signals from said processor and to output DTMF tones representative of said digital signals to said interface.
18. Apparatus according to Claim 1, comprising an interface for coupling said apparatus to the PSTN.
19. Apparatus according to Claim 18, wherein said converter module comprises an FSK decoder operable to convert received CTM compliant signals into a digital signal.
20. Apparatus according to Claim 19, comprising a processor that is operable to convert two-bit digital signals from said FSK decoder into four-bit output signals.
21. Apparatus according to Claim 20, comprising a DTMF generator operable to convert four-bit digital signals from said processor into DTMF tones for transmission to an output interface for coupling said apparatus to monitoring centre equipment.
22. Apparatus according to Claim 21, comprising a DTMF detector operable to detect DTMF tones in signals received from said output interface and to convert said DTMF tones into four bit digital signals.
23. Apparatus according to Claims 22 and 20, wherein said processor is configured to receive four bit digital signals from said DTMF detector and to generate a two-bit digital signal.
24. Apparatus according to Claim 23, comprising an FSK generator operable to receive two-bit signals from said processor and to generate CTM compliant signals for transmission to the PSTN via said interface.
25. Apparatus according to any preceding claim, comprising a switch and a switch controller, said switch controller being operable to detect voice calls and to bypass said converter module by closing said switch.
26. Apparatus according to any preceding claim, wherein said first type of data signals comprise dual tone multi-frequency (DTMF) signals.
27. Apparatus according to any preceding claim, wherein said second type of data signals V. 18 compliant signals.
28. Apparatus according to Claim 27, wherein said second type of data signals comprise cellular text modem (CTM) compliant signals.
29. A fixed cellular terminal comprising apparatus according to any preceding claim.
30. A telecare system comprising a telecare terminal that includes, as an integral component thereof, a fixed cellular terminal according to Claim 29.
31. A system according to Claim 30, comprising an actuator configured to communicate with said telecare terminal.
32 A system according to Claim 31, wherein said actuator and said telecare terminal are each configured for wireless telecommunications with one another.
33. A system according to any of Claims 30 to 32, further comprising a sensor module configured for communication with said telecare terminal.
34 A system according to Claim 33, wherein said sensor module is configured to communicate wirelessly with said telecare terminal.
35. A system according to Claim 34, wherein said sensor module comprises a smoke detector.
36. A system according to Claim 34, wherein said sensor module comprises an intruder detector such as a passive infrared sensor, pressure sensor or a vibration sensor.
37. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.