Title of Invention	COMMUNICATION METHOD AND APPARATUS
Abstract	(57) Abstract: A network station 4 receives a principal sisal S and data D. When the principal signal S is present or contains information it is transmitted to a receiving station 6 through a communication channel. When the principal signal S is absent or does not have a significant information content, the network station 4 transmits the data D through the same communication channel in a format such that the data D is received and output by a further receiving station 8. PRICE: THIRTY RUPEES

Title of Invention

COMMUNICATION METHOD AND APPARATUS

Abstract

(57) Abstract: A network station 4 receives a principal sisal S and data D. When the principal signal S is present or contains information it is transmitted to a receiving station 6 through a communication channel. When the principal signal S is absent or does not have a significant information content, the network station 4 transmits the data D through the same communication channel in a format such that the data D is received and output by a further receiving station 8. PRICE: THIRTY RUPEES

Full Text	The present invention relates to a method and an apparatus for radio-frequency communication to separate first and second mobile terminals and particularly but not exclusively to apparatus for providing data communication over a radio frequency channel in addition to voice, image or other data communication. In a known radio frequency communication system, for example the INMARSAT-A (TM) Satellite Communication System, as described for example in "Satellite Communications: Principles and Applications", Calcutta and Tetley, 1st edition 1994, users are connected to a public service telephone network (PSTN) through a satellite link to provide voice, facsimile and circuit switched data communication services. Attempts have been made to add a packet switched data service, in which users share a single channel, to the existing services available through IKNIARSAT-A. However, this requires the allocation of additional traffic channels, which adds to the cost of the system. The document GB-A-2 232 562 describes a digital mobile telephone system with a data communications function. If a data communication is asymmetric, time slots, which are not needed for communication in one direction, are reassigned for data transmission in the opposite direction. The time slots may be reassigned to a different data terminal. However, such a system requires reallocation of part of a physical channel assigned for communication in one direction so as to change the direction and/or data terminal to which that part is assigned. According to one aspect of the present invention there is provided a communication system in which a first station is arranged selectively to transmit a principal signal and a data signal. The first station establishes a communication channel to a second station and begins to transmit the principal signal to the second earth station. However, during a period in which no information can be transmitted to the second station, the first station transmits the data signal in such a way that it may be decoded by a third station and may also be received by the second station without affecting the information decoded by the second station. During voice communication, a proportion of the time during which a channel is kept open is unused, for example when a user is listening without talking, so that the user's transmit channel carries only noise. Likewise, in a facsimile communication, a terminal, which > receives facsimile data only transmits during the handshaking phases of the communication; at other times its transmit channel is unused. In embodiments of the invention the available bandwidth of the communication channel is used with greater efficiency, and a data communication service may be provided concurrently with another service. Preferably, the principal signal comprises a voice or facsimile signal. Where the principal signal is a voice signal the data signal is transmitted during periods of silence. The first earth station may transmit a silence code which is decoded by the second earth station to reproduce silence or low- level noise during a voice communication. Preferably, the third earth station interprets the silence code as a signal to receive data. Alternatively, the first earth station may transmit a signal which is reproduced by the second earth station as acceptable (e.g. low-level) noise or silence but which is decoded by the third earth station as data, during the periods of silence. l Where the principal signal is a facsimile signal, the first station may detect whether the second earth station is facsimile data and therefore does not need to receive anvil facsimile data. The first station transmits the signal including the data signal in such a way tilt it does not activate the facsimile terminal at the second earth station, but activates the third earth station to receive data. By the above measures, tile second and third stations may receive data concurrently, with the second earth station only decoding the principal signal and the third earth station only decoding the data, but without interference between the signals. This aspect of the present invention extends in particular to the first station, the third station, apparatus within the first or third station which implement the essential features of the present invention and any method performed by such apparatus. According to another aspect of the present invention, there is provided a method of encoding data not derived from a voice signal such that it appears to relate to a voice signal to a voice decoder but can be decoded to reproduce the data by a data decoder, and apparatus for performing said method. According to another aspect of the present invention, there is provided a method in which a duplex channel assigned to a facsimile communication is shared so teat, when a facsimile terminal is transmitting facsimile data in one direction, data is transmitted in the other direction for decoding by a data decoder in such a way that the facsimile terminal is not interrupted by the data. Accordingly the present invention provides a method of radio-frequency communication to separate first and second mobile terminals, the method comprising storing data (D) for transmission to said second mobile terminal, setting up a communication (S) with said first mobile terminal via a radio-frequency channel; detecting an absence of information in said communication (S); and transmitting one or more data packets derived from said data (D) and addressed to said second mobile terminal in said radio-frequency channel during said absence. The present invention also provides an apparatus for radio-frequency communication to separate first and second mobile terminals, comprising storing means for storing data (D) for transmission to said second mobile terminal; set-up means for setting up a communication (S) with said first mobile terminal via a radio-frequency channel (C): detecting means for detecting an absence of information in said communication (S); and transmitting means for transmitting one or more data packets derived from said data (D) and addressed to said second mobile terminal in said radio-frequency channel during said absence. Specific embodiments of the present invention will now be described with reference to the accompanying drawings in which Figure 1 is a diagram showing the logical connection between earth stations in embodiments of the present invention: Figure 2 is a functional block diagram of a land earth station according to a first embodiment; Fieure 3 is a block diagram of a voice codec according to the first embodiment; Figure 4 is a flowchart of the operation ofithe land earth station; Figure 5 is a functional block diagram of a second mobile earth station; Figure 6 is a flowchart of the operation of the second mobile earth station; Figure 7 shows the format of a packet transmitted by the land earth station according to the first embodiment; Figure 8 is a functional block diagram of fa packet data interface unit according to a second embodiment;. Figure 9 is a block diagram of the packet data interface unit including a PCM codec; Figure 10 is a schematic diagram of an APC loder and decoder; { Figure 11 is a functional block diagram of a land earth station according to a third embodiment; Figure 12 is a flowchart of the operation of the land earth station according to the third embodiment; Figure 13 is a diagram of the packet forrtiat of a signal transmitted by the land earth stacion according to the third embodiment of the present invention. Modes for Carrying Out the Invention Figure 1 shows schematically a communication system in which a network station, such as a land earth station (LE;S) 4 is connected to a public service telephone network (PSTN) 2. The LES 4 is arranged to provide a satellite link between a number of users connected to the PSTN 2 and a number of user terminals, such as mobile earth stations (MES) which are able to receive and decode signals S transmitted by the LES 4 via a satellite, and to encode and transm.it signals to the LES 4 via the satellite. Figure 1 shows a first MES 6 and a second MES 8, both in com.munication with the LES 4 by means of a single channel r' K’ . Tne nature of the channel C d'::;:p6-nds '::n the addr’essing technique used. For example, in a Single clianriel per carrier (SCPC) system, a channel corresponds to a single carrier frequency in a half duplex syst:,i;!m or a pair of carrier frequencies in a full duplex, system. In a TDMA system, a channel corresponds to a predetermined time slot in a repeating time frame of a tranainission at a particular frequency or set of frequencies. In .a CDMA syestem, a channel corresponds to a transmission encoded with a predetermined code. The present invention does not depend on the addressing system used. The LES 4 also receives data D, addressed to the second MES 8, from the PSTN 2. The data D is stored at the LES 4 until it can be transmitted. Th(3 data D may alternatively have been entered directly at the LES 4 or previously received from an MES. In order to establish a communications link with the first MES 6, the LES 4 transmits a predetermined calling code identifying the first MES 6 on an LES signalling channel. The calling code includes a service--ty]:)e code which identifies whether a voice, facsimile or data transmission is to follow. The first MES 6 acknowledges the calling code on an MES signalling channel if it is ready to communicate. A communications link is then allocated by an independent network control station. If the LES 4 receives data D addressed to the second MES 8, it transmits a predetermined data addressing code on the LES signalling channel and the second MES 8 acknowledges the data addressing code if it is ready to receive the data. The data addressing code includes information on the communications link which will be used for data transmission. A first embodiment of the present invention will be described with reference to Figures 1 to 7. In this embodiment, a packet switched data service is provided in addition to a voice communication service such as the INMARSAT-M (TM) system as also described .::: the Calcutt and Tetley reference above. First, a call is sec up between the LES 4 and the first MES 6 (step 102) . The call may be initiated by either the LES 4 or the first MES 6. During the call, a voice signal V is receivad from the PSTN 2 by a codec 10 of the LES 4. Details of the codec 10 used in the INMARSAT-M (TM) system are described for example in the Calcutt and Tetley reference. This codec 10 uses an Improved Multi-Band Excitation (IMBE) algorithm, shown schematically in Figure 3. The voice signal V is analysed by a pitch estimation stage 46 which estimates the fundamental frequency of the voice signal V. A voiced/unvoiced determination stage 4 8 evaluates the voicing measure of each of a number of non-overlapping frequency bands of the voice spectrum and generates a set of decisions Vj’ as to whether the voice signal. V is voiced or unvoiced in each band. A spectral amplitude estimation stage 50 determines the spectral envelope M, of each frequency band according to whether the band is determined to be voiced or unvoiced. The values ui’, V,,, M’ are encoded for each 20 ms frame of speech to form a series of vectors Uo to U7. Error correction information is added prior to radio frequency modulation and transmission. However, if the codec 10 does not: detect any vocal characteristics in the voice signal V, i \: sets the first six bits of vector UQ to 110010 (decimal .50) to form a silence code. In the first MES 6, another coderc 52 decodes the values of w’, V’. and M’ and synthesises unvoiced and voiced speech signals at unvoiced speech synthesizer 54 and voiced speech synthesizer 56 respectively. The outputs of the synthesizers 54 and 56 are added to produce a synthesised speed signal Vg. Alternatively, if the codec 52 receives the silence code, it generates low level "comfort" noise and does not decode any other information. The LES 4 includes a packet data interface unit 12 which normally receives encoded dal:a froni the codec 10 and sends the encoded data (step 106) to a raiio frequency (RF) modulator 14 for transmission by an antenna 16 to a WE CLAIM : 1. A method of radio-frequency communication to separate first and second mobile terminals (6 8), the method comprising storing data (D) for transmission to said second mobile terminal, setting up a communication (S) with said first mobile terminal (6) via a radio-frequency channel; detecting an absence of information in said communication (S); and transmitting one or more data packets (20) derived from said data (D) and addressed to said second mobile terminal (8) in said radio-frequency channel during said absence. 2. The method as claimed in claim 1, wherein the one or more data packets (20) are transmitted with a predetermined code (SC) indicative of said absence of information. 3. The method as claimed in claim 1, wherein the one or more data packets include data representative of said absence of information in a format arranged for decoding by the first mobile terminal (6). 4. The method as claimed in any preceding claim, wherein said communication is a voice communication (V). 5. The method as claimed in claim 1, wherein said channel is a duplex channel (C) and the transmitting step comprises transmitting (124) said one or more data packets (20) while the first mobile terminal (6) is in a transmit-only state. 6. The method as claimed in claim 5, wherein the transmit-only state of the first mobile terminal (6) is determined by detecting (122) a signal transmitted by the first mobile terminal (6), said signal being indicative of said transmit-only state. 7. The method as claimed in claim 5, wherein the transmit-only state of the first mobile terminal (6) is determined by detecting (122) a command signal transmitted to the first mobile terminal (6), which commands the mobile terminal (6) to enter said transmit-only state. 8. The method as claimed in any of claims 1 or 5 to 7, wherein said communication is a facsimile communication (F). 9. The method as claimed in any preceding claim, wherein said one or more data packets are transmitted with a predetermined identifying code (ID) associated with said second mobile terminal (8). 10. The method as claimed in any preceding claim, wherein said radio-frequency channel (C) is transmitted via satellite. 11. The method as claimed in any one of claims 1 to 9, wherein said radio-frequency channel (C) is a terrestrial cellular channel. 12. Apparatus for radio-frequency communication to separate first and second mobile terminals (6, 8), comprising storing means for storing data (D) for transmission to said second mobile terminal (8); set-up means torr setting up a communication (S) with said first mobile terminal (6) via a radio-frequency channel (C); detecting means for detecting an absence of information in said communication (S); and transmitting means (12) for transmitting one or more data packets (20) derived from said data (D) and addressed to said second mobile terminal (8) in said radio-frequency channel during said absence. 13. Apparatus as claimed in claim 12, wherein said transmitting means (12) is configured to output said one or more data packets (20) together with a pre-determined code (SC) indicative of said absence of information. 14. Apparatus as claimed in any one of claims 12 or 13, wherein said radio frequency communication is a voice-type communication (V). 15. Apparatus as claimed in claim 12, wherein a state detecting means (38) is provided for detecting a transmit-only state of the first mobile terminal (6), the transmitting means (12) has a switch (40) for outputting the one or more data packets (20) in response to detection of the transmit-only state by the state detecting means (38). 16. Apparatus as claimed in claim 15, wherein the state detecting means (38) is configured to identify said transmit-only state by detecting a signal indicative of said transmit-only state, which is transmitted by the first mobile terminal (6). 17. Apparatus as claimed in claim 15, wherein the state detecting means (38) is configured to identify said transmit-only state by detecting a command signal which is transmitted to the first mobile terminal (6) to command the first mobile terminal (6) to enter said transmit-only state. 18. Apparatus as claimed in any one of claims 12 or 15 to 17, wherein said radio fi-equency communication is a facsimile communication (F). 19. Apparatus as claimed in any one of claims 12 to 18, wherein said one or more data packets (20) has a predetermined identifying code (ID) associated with said second mobile terminal (8). 20. Apparatus as claimed in any one of claims 12 to 19, wherein the radio fi-equency channel (C) is a satellite channel. 21. Apparatus as claimed in any one of claims 12 to 19, wherein the radio frequency channel (C) is a terrestrial cellular channel (C). 22. A method of radio-frequency communication to separate first and second mobile terminals substantially as herein described with reference to the accompanying drawings. 23. Apparatus for radio-frequency communication to separate first and second mobile terminals substantially as herein described with reference to the accompanying drawings.

Full Text

The present invention relates to a method and an apparatus for radio-frequency communication to separate first and second mobile terminals and particularly but not exclusively to apparatus for providing data communication over a radio frequency channel in addition to voice, image or other data communication.
In a known radio frequency communication system, for example the INMARSAT-A (TM) Satellite Communication System, as described for example in "Satellite Communications: Principles and Applications", Calcutta and Tetley, 1st edition 1994, users are connected to a public service telephone network (PSTN) through a satellite link to provide voice, facsimile and circuit switched data communication services. Attempts have been made to add a packet switched data service, in which users share a single channel, to the existing services available through IKNIARSAT-A. However, this requires the allocation of additional traffic channels, which adds to the cost of the system.
The document GB-A-2 232 562 describes a digital mobile telephone system with a data communications function. If a data communication is asymmetric, time slots, which are not needed for communication in one direction, are reassigned for data transmission in the opposite direction. The time slots may be reassigned to a different data terminal. However, such a system requires reallocation of part of a physical channel assigned for communication in one direction so as to change the direction and/or data terminal to which that part is assigned.
According to one aspect of the present invention there is provided a
communication system in which a first station is arranged selectively to transmit
a principal signal and a data signal. The first station establishes a
communication channel to a second station and begins to

transmit the principal signal to the second earth station. However, during a period in which no information can be transmitted to the second station, the first station transmits the data signal in such a way that it may be decoded by a third station and may also be received by the second station without affecting the information decoded by the second station.
During voice communication, a proportion of the time during which a channel is kept open is unused, for example when a user is listening without talking, so that the user's transmit channel carries only noise. Likewise, in a facsimile communication, a terminal, which > receives facsimile data only transmits during the handshaking phases of the communication; at other times its transmit channel is unused.
In embodiments of the invention the available bandwidth of the communication channel is used with greater efficiency, and a data communication service may be provided concurrently with another service.
Preferably, the principal signal comprises a voice or facsimile signal.
Where the principal signal is a voice signal the data signal is transmitted during periods of silence. The first
earth station may transmit a silence code which is decoded

by the second earth station to reproduce silence or low-

level noise during a voice communication. Preferably, the
third earth station interprets the silence code as a signal to receive data.
Alternatively, the first earth station may transmit a
signal which is reproduced by the second earth station as
acceptable (e.g. low-level) noise or silence but which is
decoded by the third earth station as data, during the
periods of silence. l
Where the principal signal is a facsimile signal, the first station may detect whether the second earth station is facsimile data and therefore does not need to receive anvil facsimile data. The first station transmits

the signal including the data signal in such a way tilt it does not activate the facsimile terminal at the second earth station, but activates the third earth station to receive data.
By the above measures, tile second and third stations may receive data concurrently, with the second earth station only decoding the principal signal and the third earth station only decoding the data, but without interference between the signals. This aspect of the present invention extends in particular to the first station, the third station, apparatus within the first or third station which implement the essential features of the present invention and any method performed by such apparatus.
According to another aspect of the present invention, there is provided a method of encoding data not derived from a voice signal such that it appears to relate to a voice signal to a voice decoder but can be decoded to reproduce the data by a data decoder, and apparatus for performing said method.
According to another aspect of the present invention, there is provided a method in which a duplex channel assigned to a facsimile communication is shared so teat, when a facsimile terminal is transmitting facsimile data in one direction, data is transmitted in the other direction for decoding by a data decoder in such a way that the facsimile terminal is not interrupted by the data.

Accordingly the present invention provides a method of radio-frequency communication to separate first and second mobile terminals, the method comprising storing data (D) for transmission to said second mobile terminal, setting up a communication (S) with said first mobile terminal via a radio-frequency channel; detecting an absence of information in said communication (S); and transmitting one or more data packets derived from said data (D) and addressed to said second mobile terminal in said radio-frequency channel during said absence.
The present invention also provides an apparatus for radio-frequency communication to separate first and second mobile terminals, comprising storing means for storing data (D) for transmission to said second mobile terminal; set-up means for setting up a communication (S) with said first mobile terminal via a radio-frequency channel (C): detecting means for detecting an absence of information in said communication (S); and transmitting means for transmitting one or more data packets derived from said data (D) and addressed to said second mobile terminal in said radio-frequency channel during said absence.
Specific embodiments of the present invention will now be described with reference to the accompanying drawings in which
Figure 1 is a diagram showing the logical connection between earth stations in embodiments of the present invention:
Figure 2 is a functional block diagram of a land earth station according to a first embodiment;
Fieure 3 is a block diagram of a voice codec according

to the first embodiment;
Figure 4 is a flowchart of the operation ofithe land earth station;
Figure 5 is a functional block diagram of a second mobile earth station;
Figure 6 is a flowchart of the operation of the second mobile earth station;
Figure 7 shows the format of a packet transmitted by the land earth station according to the first embodiment;
Figure 8 is a functional block diagram of fa packet data interface unit according to a second embodiment;.
Figure 9 is a block diagram of the packet data interface unit including a PCM codec;
Figure 10 is a schematic diagram of an APC loder and
decoder; {
Figure 11 is a functional block diagram of a land earth station according to a third embodiment;
Figure 12 is a flowchart of the operation of the land earth station according to the third embodiment;
Figure 13 is a diagram of the packet forrtiat of a signal transmitted by the land earth stacion according to the third embodiment of the present invention. Modes for Carrying Out the Invention
Figure 1 shows schematically a communication system in which a network station, such as a land earth station (LE;S) 4 is connected to a public service telephone network (PSTN) 2. The LES 4 is arranged to provide a satellite link between a number of users connected to the PSTN 2 and a number of user terminals, such as mobile earth stations (MES) which are able to receive and decode signals S transmitted by the LES 4 via a satellite, and to encode and transm.it signals to the LES 4 via the satellite. Figure 1 shows a first MES 6 and a second MES 8, both in com.munication with the LES 4 by means of a single channel
r' K’ .
Tne nature of the channel C d'::;:p6-nds '::n the addr’essing technique used. For example, in a Single clianriel per

carrier (SCPC) system, a channel corresponds to a single carrier frequency in a half duplex syst:,i;!m or a pair of carrier frequencies in a full duplex, system. In a TDMA system, a channel corresponds to a predetermined time slot in a repeating time frame of a tranainission at a particular frequency or set of frequencies. In .a CDMA syestem, a channel corresponds to a transmission encoded with a predetermined code. The present invention does not depend on the addressing system used.
The LES 4 also receives data D, addressed to the second MES 8, from the PSTN 2. The data D is stored at the LES 4 until it can be transmitted. Th(3 data D may alternatively have been entered directly at the LES 4 or previously received from an MES.
In order to establish a communications link with the first MES 6, the LES 4 transmits a predetermined calling code identifying the first MES 6 on an LES signalling channel. The calling code includes a service--ty]:)e code which identifies whether a voice, facsimile or data transmission is to follow. The first MES 6 acknowledges the calling code on an MES signalling channel if it is ready to communicate. A communications link is then allocated by an independent network control station.
If the LES 4 receives data D addressed to the second MES 8, it transmits a predetermined data addressing code on the LES signalling channel and the second MES 8 acknowledges the data addressing code if it is ready to receive the data. The data addressing code includes information on the communications link which will be used for data transmission.
A first embodiment of the present invention will be described with reference to Figures 1 to 7. In this embodiment, a packet switched data service is provided in addition to a voice communication service such as the INMARSAT-M (TM) system as also described .::: the Calcutt and Tetley reference above.
First, a call is sec up between the LES 4 and the

first MES 6 (step 102) . The call may be initiated by either the LES 4 or the first MES 6.
During the call, a voice signal V is receivad from the PSTN 2 by a codec 10 of the LES 4. Details of the codec 10 used in the INMARSAT-M (TM) system are described for example in the Calcutt and Tetley reference. This codec 10 uses an Improved Multi-Band Excitation (IMBE) algorithm, shown schematically in Figure 3. The voice signal V is analysed by a pitch estimation stage 46 which estimates the fundamental frequency of the voice signal V. A voiced/unvoiced determination stage 4 8 evaluates the voicing measure of each of a number of non-overlapping frequency bands of the voice spectrum and generates a set of decisions Vj’ as to whether the voice signal. V is voiced or unvoiced in each band. A spectral amplitude estimation stage 50 determines the spectral envelope M, of each frequency band according to whether the band is determined to be voiced or unvoiced. The values ui’, V,,, M’ are encoded for each 20 ms frame of speech to form a series of vectors Uo to U7. Error correction information is added prior to radio frequency modulation and transmission.
However, if the codec 10 does not: detect any vocal characteristics in the voice signal V, i \: sets the first six bits of vector UQ to 110010 (decimal .50) to form a silence code.
In the first MES 6, another coderc 52 decodes the values of w’, V’. and M’ and synthesises unvoiced and voiced speech signals at unvoiced speech synthesizer 54 and voiced speech synthesizer 56 respectively. The outputs of the synthesizers 54 and 56 are added to produce a synthesised speed signal Vg. Alternatively, if the codec 52 receives the silence code, it generates low level "comfort" noise and does not decode any other information.
The LES 4 includes a packet data interface unit 12 which normally receives encoded dal:a froni the codec 10 and sends the encoded data (step 106) to a raiio frequency (RF) modulator 14 for transmission by an antenna 16 to a

WE CLAIM :
1. A method of radio-frequency communication to separate first and second mobile terminals (6 8), the method comprising storing data (D) for transmission to said second mobile terminal, setting up a communication (S) with said first mobile terminal (6) via a radio-frequency channel; detecting an absence of information in said communication (S); and transmitting one or more data packets (20) derived from said data (D) and addressed to said second mobile terminal (8) in said radio-frequency channel during said absence.
2. The method as claimed in claim 1, wherein the one or more data packets (20) are transmitted with a predetermined code (SC) indicative of said absence of information.
3. The method as claimed in claim 1, wherein the one or more data packets include data representative of said absence of information in a format arranged for decoding by the first mobile terminal (6).
4. The method as claimed in any preceding claim, wherein said communication is a voice communication (V).
5. The method as claimed in claim 1, wherein said channel is a duplex channel (C) and the transmitting step comprises transmitting (124) said one or more data packets (20) while the first mobile terminal (6) is in a transmit-only state.

6. The method as claimed in claim 5, wherein the transmit-only state of the first mobile terminal (6) is determined by detecting (122) a signal transmitted by the first mobile terminal (6), said signal being indicative of said transmit-only state.
7. The method as claimed in claim 5, wherein the transmit-only state of the first mobile terminal (6) is determined by detecting (122) a command signal transmitted to the first mobile terminal (6), which commands the mobile terminal (6) to enter said transmit-only state.
8. The method as claimed in any of claims 1 or 5 to 7, wherein said communication is a facsimile communication (F).
9. The method as claimed in any preceding claim, wherein said one or more data packets are transmitted with a predetermined identifying code (ID) associated with said second mobile terminal (8).
10. The method as claimed in any preceding claim, wherein said radio-frequency channel (C) is transmitted via satellite.
11. The method as claimed in any one of claims 1 to 9, wherein said radio-frequency channel (C) is a terrestrial cellular channel.
12. Apparatus for radio-frequency communication to separate first and second mobile terminals (6, 8), comprising storing means for storing data

(D) for transmission to said second mobile terminal (8); set-up means torr setting up a communication (S) with said first mobile terminal (6) via a radio-frequency channel (C); detecting means for detecting an absence of information in said communication (S); and transmitting means (12) for transmitting one or more data packets (20) derived from said data (D) and addressed to said second mobile terminal (8) in said radio-frequency channel during said absence.
13. Apparatus as claimed in claim 12, wherein said transmitting means (12) is configured to output said one or more data packets (20) together with a pre-determined code (SC) indicative of said absence of information.
14. Apparatus as claimed in any one of claims 12 or 13, wherein said radio frequency communication is a voice-type communication (V).
15. Apparatus as claimed in claim 12, wherein a state detecting means (38) is provided for detecting a transmit-only state of the first mobile terminal (6), the transmitting means (12) has a switch (40) for outputting the one or more data packets (20) in response to detection of the transmit-only state by the state detecting means (38).
16. Apparatus as claimed in claim 15, wherein the state detecting means (38) is configured to identify said transmit-only state by detecting a signal indicative of said transmit-only state, which is transmitted by the first mobile terminal (6).
17. Apparatus as claimed in claim 15, wherein the state detecting means (38) is configured to identify said transmit-only state by detecting a command

signal which is transmitted to the first mobile terminal (6) to command the first mobile terminal (6) to enter said transmit-only state.
18. Apparatus as claimed in any one of claims 12 or 15 to 17, wherein said
radio fi-equency communication is a facsimile communication (F).
19. Apparatus as claimed in any one of claims 12 to 18, wherein said one or
more data packets (20) has a predetermined identifying code (ID)
associated with said second mobile terminal (8).
20. Apparatus as claimed in any one of claims 12 to 19, wherein the radio fi-equency channel (C) is a satellite channel.
21. Apparatus as claimed in any one of claims 12 to 19, wherein the radio frequency channel (C) is a terrestrial cellular channel (C).
22. A method of radio-frequency communication to separate first and second mobile terminals substantially as herein described with reference to the accompanying drawings.
23. Apparatus for radio-frequency communication to separate first and
second mobile terminals substantially as herein described with reference
to the accompanying drawings.

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Patent Number

193869

Indian Patent Application Number

707/MAS/1996

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

Date of Filing

30-Apr-1996

Name of Patentee

INTERNATIONAL MOBILE SATELLITE ORGANIZATION

Applicant Address

INTERNATIONAL ORGANIZATION ESTABLISHED UNDER THE INMARSAT CONVENTION 99 CITY ROAD, LONDON EC1Y 1AX,

Inventors:

#	Inventor's Name	Inventor's Address
1	FELDMAN, HOWARD	82 ALICIA GARDENS, KENTON, MIDDLESEX HA3 8JE,

PCT International Classification Number

H04L 1/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA