TELECOMMUNICATION SYSTEMS WITH CALL DROP-OUT MESSAGING ACTIVATION

Abstract: When a telephone link is established between a mobile station, such as a mobile handset (1) for example over a satellite link (2, 3) through a telephone network (6) to a telephone (7), a messaging service is offered in the event of a call dropout, so that one party can record a message, which is retrieved by the other party after the dropout.

Description: Telecommunication Systems with Call Drop-out Messaging Activation Field of the invention i This invention relates to the provision of a telecommunication link between a first and second telecommunication station, with an improved messaging service. The invention finds particular but not exclusive application to satellite communication systems for providing telecommunication coverage to mobile stations, such as mobile telephone handsets. 10 Background A number of different mobile telecommunication systems have been proposed that utilise satellite communication links between mobile handsets and conventional terrestrial networks, such as landline networks or conventional i} cellular mobile telephone networks. One system, as proposed in e.g. US Patent No. 5 394 561 (Motorola) makes use of a constellation of so-called low earth orbit (LEO) satellites, which typically have an orbital radius of 7-800 km. Mobile handsets for this 20 system are configured to establish a link to an overhead orbiting satellite, from which a call can be directed to another satellite in the constellation and then typically to a ground station which is connected to conventional land- based networks. 5 Alternative schemes which make use of so-called middle earth orbit (MEO) satellite constellation have been proposed with an orbit radius in the range of 10-20,000 km and reference is directed to Walker J.G. "Satellite Patterns for Continuous Multiple Whole Earth Coverage" Royal Aircraft Establishment, pp 119-122 (1977). These systems are also known as intermediate earth orbit 0 (IEO) or intermediate constellations (ICO). With these systems, the satellite communication link does not permit communication between adjacent satellites and instead, a signal from a mobile handset is directed firstly to the satellite and then direct to a ground based transmission station, connected to conventional land-based telephone system. This has the advantage that many components of the system are compatible with known digital terrestrial cellular technology, and it also permits simpler satellite communication techniques to be used. A problem arises with all satellite based systems in that there is a risk that the communication path between the satellite and the mobile handset will become obscured by buildings or other objects during a call, with a result that the communication link drops out and the call is interrupted. Also, the handset may move out of range for the satellite. Dropout can also arise in conventional terrestrial mobile systems either due to the communication path becoming blocked by buildings or other objects, or as a result of the mobile station moving out of range of the area covered by the mobile network. In a conventional terrestrial mobile system, such as the Global System Mobile (GSM) mobile telecommunication system, a voicemail facility is usually provided so that if a user's mobile handset is switched off, the caller is offered the facility so that a recorded voice message can be left. The recorded message can then be retrieved by the user of the mobile handset when the user decides to interrogate the mailbox. Summary of the invention The present invention includes from a first aspeα, a method of providing a telecommunication link between a first and a second telecommunication station, including offering a messaging service for use by a party at one of said stations in the event that the link drops out during use thereof, so as to permit a message to be stored and retrieved by another party after the dropout. Thus, in accordance with the invention, one of the parties can record a message by means of the service in the event of the dropout, and the other party can then retrieve the message after the dropout. The method according to the invention has particular application to satellite global mobile systems, which may be prone to dropout, and offers a convenient way for a terminating message for the call to be left, in the event that a dropout occurs. The method according to the invention also may be used with conventional terrestrial mobile system, in the event of a dropout. In the event that the telecommunication link is initiated by a calling party at the first station, the messaging service is offered to the calling party in the event that the link drops out. In these circumstances, the calling party may be billed for both the call over the link and the use of the messaging service. In the event that the link is initiated by a calling party at the mobile station, the messaging service is offered to the called party at the first station in the event that the link drops out. In these circumstances, the calling party is billed for the call over the link and the called party may be billed for the messaging service although other billing options for the messaging service may be provided. The invention also includes a telecommunication system for providing a telecommunication link between a first station and a second mobile station, the system including means for providing a messaging service for use by a party at one of said stations in the event that the link drops out during use thereof, so as to permit a message to be stored and retrieved by the other party after the dropout. The system may include means responsive to dropout of the link for rendering the messaging service operative during the dropout. Means may be included for signalling subsequent to the dropout, that a message has been recorded and is available for retrieval. The second station may comprise a mobile station, such as a mobile telephone handset, j The system may include a plurality of geographically spaced transmission stations for selectively establishing a communication path with the mobile station. The transmission stations may be interconnected by a network. Gateway means may be provided for coupling the first station to the network, io for example through conventional land-based telecommunication networks. A network control means may be provided for routing a telecommunication link through the network between the gateway means and the transmission station appropriate for establishing the communication path for the mobile station. The messaging service may comprise a voicemail facility coupled to the a network. The network control means may include location register means for keeping a record of the location of the mobile station for routing the telecommunication link through the network between the gateway means and the transmission 20 station appropriate for establishing the communication path for the mobile station. The location register means may comprise a plurality of visitor location registers associated with the transmission stations respeαively, for keeping a record of the mobile stations within the operational range thereof, and a home location register that receives data from the visitor location registers. The transmission stations may comprise satellite access nodes for establishing a communication path with the mobile station via at least one satellite. The o satellite access nodes may be operative to communicate with a constellation of MEO satellites in intermediate earth orbits. Alternatively, the transmission stations may be operative to communicate with a constellation of satellites in low earth orbits or geostationary orbits. Alternatively, for a land-based system according to the invention, the transmission stations may comprise base stations of a GSM mobile telephone system or other digital network. The invention also extends to a mobile station, such as a mobile telephone handset, for use in a telecommunication system which provides a telecommunication link therewith and another party, the mobile station being operative to communicate with a messaging service provided by the system in the event of dropout of the link, to receive an indication that the message has been recorded in the service as a result of dropout, and to retrieve the recorded message. Brief description of the drawings In order that the invention may be more fully understood an embodiment thereof relating to a MEO satellite system, will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic block diagram of a mobile telecommunication system in accordance with the invention; Figures 2a to 2e illustrate how the voicemail is used in the event of a drop our for a call initiated by a land-based subscriber; and Figures 3a to 3e illustrate how the voicemail is used in the event of a dropout for a call initiated from a mobile handset. Detailed description Referring to Figure 1, a schematic block diagram of a satellite mobile telecommunication system is shown. A mobile station 1 in the form of a mobile telephone handset can communicate on a radio channel over a communication path 2, 3 via an earth orbiting satellite 4, with a satellite access node SAN2. As shown schematically in Figure 1, the SAN is provided with an antenna which can track the orbiting satellite. A number of the satellite access nodes, SANl, 2 etc are connected together in a network 5, which is connected through a number of gateways GW1, 2 etc to conventional earth based telephone networks. For example, considering the gateway GWl, it is connected to a land-based public switch telephone network (PSTN) 6, which permits connection to be made to a conventional telephone set 7. The gateways may additionally be connected to other networks such as public switch data networks (PSDNs) for carrying digital data, and to public land mobile networks (PLMNs) such as conventional analogue or digital cellular telephone networks including Global System Mobile (GSM) networks, Digital American Mobile Phone Systems (DAMPS), or the Japanese Personal Handiphone Systems (PHS) and Personal Digital Communications (PDC) network. The system is designed to provide worldwide coverage, and the satellite 4 forms one part of a constellation of satellites, which may be arranged in several orbits. In one example, two orbits of five satellites are used, which can be shown to provide coverage of a major part of the surface of the earth, in which for a 10° satellite elevation angle , one satellite can be accessed by the mobile handset all of the time and two satellites can be accessed for at least 80% of the time, thereby providing system redundancy. Additional satellites may be included in the constellation in order to provide additional redundancy. The satellites are typically arranged in a MEO constellation, for example with an orbital radius of 10,355 km, although the invention is not restriαed to a particular orbital radius, as will be explained hereinafter. In this embodiment, the satellites orbit the earth and are consequently tracked by the antenna of each SAN. The SANs are spaced around the earth in order to provide continuous coverage. In the example shown, SANl may be located in Europe, whereas SAN2 may be located in Africa, other SANs are located in the American continents and elsewhere. Each satellite, such as satellite 4, is provided with a multiple beam forming antenna which transmits a plurality of spaced beams towards the earth, typically at different frequencies, the beams providing adjacent cellular areas, which correspond to the cells of a conventional land-based mobile telephone system. An antenna may use a beam former that utilises a Butler matrix device as described in GB 9407669.2. The antenna may be provided with a beam steering arrangement in order to keep the cellular pattern located in a constant geographical area for given periods, as the satellite orbits the earth. For further details of an example of a satellite system antenna, reference is direαed to WO 93/09614. In order to keep track of the location of the various mobile telephone handsets, such as handset 1, each SAN has an associated visitor location register (VLR) which operates in a similar manner to the visitor location register of a conventional GSM terrestrial mobile telephone system. Thus, VLR1 keeps a record of the handsets, such as handset 1, within the operational range of SANl. To this end, the handset 1 periodically transmits an identification signal which is deteαed at SANl and the presence of handset 1 is then recorded in VLR1. Information from the visitor location registers VLR1, 2 etc associated with each SAN is periodically fed through the network 5 to a home location register (HLR). The HLR operates in a similar way to a conventional GSM home location register and permits calls to be routed to the current location of the mobile handset. Also, the network performs a number of administration funαions, such as accumulating data concerning calls made by the subscribers, and their billing addresses so that bills can be sent to each subscriber. This is conduαed at an administration data centre ADC. Also, information concerning new users, derived from point of sale operators may be entered into the HLR at the ADC. When it is desired to make a telephone call from the conventional handset 7 to the mobile handset 1 via the satellite 4, the user at handset 7, dials the number of the mobile handset and the call is direαed by PSTN 6 to the gateway GWl and then on to SANl. The gateway GW1 may be operated by a land-based telephone operator and may typically comprise a conventional land-based international access node, for which the network 5 has an individual international dialling code. The current location of the handset 1 is determined by SANl requesting the information from the HLR. The call is then routed to the SAN appropriate for the current handset location. In this example, the call is routed to SAN2 from which it is routed over communication path 3 to the satellite 4, and then re-transmitted by the satellite on path 2, to the handset 1. The path 2 comprises one of the plurality of beams transmitted from the multibeam antenna of the satellite 4. The paths 2, 3 are bidireαional. SAN2 monitors the duration of the call and sends timing information to the ADC for billing purposes. Those skilled in the art will appreciate that the described call routing system is similar to conventional land-based GSM systems, in which the base stations (BSs) and mobile switching centres (MSCs) are replaced by the SANs and the satellite constellation. Calls from the mobile handset 1 to a conventional land-based telephone are set up in an inverse manner to the process just described. The system can also provide a link between more than one mobile handset at different locations around the world, in which case the call may be routed from SAN2 to another SAN, e.g. SANl shown in Figure 1. The network may also include a voicemail facility which is used to receive and store messages from callers who attempt to make calls to satellite mobile telephone users at times when an initiated call cannot be conneαed, when the handset 1 is switched off, or the handset is in a place to which calls cannot be delivered, or the handset is configured for another purpose e.g. sending facsimile transmissions, or the handset 1 is engaged on another call. Thus, for example, when the caller on handset 7 is unable to make a conneαion to mobile handset 1 for any of the aforementioned reasons, the voicemail facility VM allows a voice message to be left in a mailbox for the handset 1. When a voicemail message is left in the mailbox, the user of handset 1 is notified by means of an appropriate display on the display panel la of the handset terminal. The notification message may tell the user of the number of unread messages in the voice box. The handset terminal may confirm receipt of the notification message, back to the network 5. The HLR may also operate as the HLR and voicemail facility for a land-based digital network, such a GSM network (not shown) conneαed to the HLR as shown schematically by line 9. Thus, the voicemail funαions may be shared by the satellite and GSM networks. On receiving a notification message, the user of handset 1 may then make a call to the voicemail box and listen to the recorded message. This may require the user to key in a PIN number, and a voice menu may then allow the user via the keypad 16 of the handset 1, to read, erase or save messages. The voice menu for the system may be offered in a number of different languages, to take account of the international nature of the mobile satellite system. Furthermore, in accordance with the invention, the voicemail facility is offered in the event of a call dropout. With a satellite mobile telecommunication system, there is a risk that communication path 2 may become broken as a result of the handset 1 loosing its "line of sight" to the satellite, for instance due to the movement of the mobile user or the satellite, behind a building or some other obstruαion, causing call dropout. This will now be described in more detail with reference to Figure 2, for a situation in which a call is initiated from the handset 7. Referring to Figure 2a, this shows schematically a call that has been set up by a subscriber at handset 7, to the mobile handset 1. In Figure 2b, the conneαion is lost as a result of path 2 being broken. This may occur as a result of the satellite moving behind a building 8 or due to the user moving the handset 1 behind the building. The call dropout is deteαed at SAN2 and the voicemail facility VM is made available to the subscriber at handset 7 so as to give the caller the option of leaving a voicemail message. This is shown schematically in Figure 2c. A message is then recorded in the mailbox of handset 1, by the user of handset 7 as shown in Figure 2d. The use of the mailbox is billed to the user of handset 7. After the voicemail facility has been used, the conneαion to handset 7 is terminated. The message can be read by the user of the handset 1 after the call dropout, when the handset 1 is next used to make contaα with the network, to the voicemail facility VM, transmits a message via SAN2 to the handset 1 to provide a display that there is an unread message in the voicemail box. This is shown schematically in Figure 2e. The user of the handset can then access the mailbox and retrieve the recorded message in the manner previously described, by operation of the keypad lb. Referring now to Figure 3, this shows the procedure adopted when a dropout occurs after a call has been initiated from the handset 1 (rather than the land- based handset 7). Figure 3a shows the call being initially set up from the handset 1 to the handset 7, in the manner previously described. Figure 3b shows the effeα of the communication path 2 being interrupted by the effeα of a building or similar obstruαion. Then, referring to Figure 3c, the SAN2, signals to the voicemail facility VM (Figure 1) that the call has been interrupted as a result of a dropout, and the voicemail facility VM offers its service to the user of handset 7, giving the option of leaving a voicemail message. The announcement provided by the voicemail facility VM indicates the charging details for the voicemail message, which will depend upon the system configuration seleαed by the network operator. Normally, the charge for the voicemail message will be billed to the user of handset 7, whereas the call itself, prior to the dropout, will be billed to the user of handset 1. Alternatively, the announcement may indicate that the voicemail facility may be used at no cost to the user. Further billing regimes will be apparent to those skilled in the art. Referring to Figure 3d, the user at handset 7 may then leave a message in the mailbox for the handset 1. This message can be read by the user of handset 1 at the end of the call dropout. Referring to Figure 3e, when the handset is next used to make contaα with the network the voicemail facility VM provides a signal to the handset 1 via SAN2 and satellite 4, that a message is available for retrieval. The user of the handset 1 may then access the mailbox using the keypad lb, in the manner previously described. The described mailbox facility has the advantage that if the call drops out, the party at handset 7 can leave a message to enable the telephone conversation to be "rounded off" in the event that the unexpeαed dropout occurs at an inopportune moment in the telephone conversation. It will be appreciated that the voicemail facility as previously described can be adapted for use when a call is made between two mobile stations via the satellite link. The voicemail facility may be offered to the handset which does not suffer dropout of its associated satellite communication path, to enable a voicemail message to be recorded and subsequently retrieved by the other handset. Furthermore, although the invention has been described in relation to a MEO satellite constellation, it is also applicable to a LEO constellation, in which communication links are established from a ground station to a first satellite and then to a second satellite before being direαed earthward to a mobile station. It is also applicable to use with a geostationary satellite. Also, the invention is applicable to conventional land-based mobile telephone systems, for example a conventional GSM system in order to provide a voicemail facility in the event of a call dropout, for example when the use of a handset moves inside a building or into a tunnel, or some other region which produces a call dropout. Whilst the described example of the mobile station comprises a mobile handset, it could comprise a vehicle based station or other mobile device. Furthermore, the mobile station could aαually be located at a fixed, or semi¬ fixed location such as a boat or other maritime location. The described example of the invention uses a voicemail facility, but other messaging services could be used, for example data, graphical or text based e.g. facsimile systems.

Claims: Claims 1. A method of providing a telecommunication link between a first and a second telecommunication station, including offering a messaging service for use by a party at one of said stations in the event that the link drops out during use thereof, so as to permit a message to be stored and retrieved by another party after the dropout. 2. A method according to claim 1 wherein one of said parties records a message by means of said service in the event of the dropout, and the other paπy retrieves the message after the dropout. 3. A method according to claim 2 including signalling to the other party that a message is available for retrieval subsequent to the end of the dropout. 4. A method according to any preceding claim wherein the second station is a mobile station. 5. A method according to claim 4, wherein the link is initiated by a calling party at the first station, and the messaging service is offered to the calling party in the event that the link drops out. 6. A method according to claim 5 wherein the calling party is billed for both the call over the link and use of the messaging service in the event that the link drops out. 7. A method according to claim 4, wherein the link is initiated by a calling party at the mobile station that calls a called party at the first station, and the messaging service is offered to the called party in the event that the link drops out. 8. A method according to claim 7 wherein the calling party is billed for the call over the link and the called party is billed for use of the messaging service. 9. A method according to any preceding claim wherein the link is established via a satellite. 10. A method according to claim 9 wherein the link includes a signal communication path between a satellite access node, the satellite and the mobile station, said messaging service being made available in the event of dropout of the signal communication path. 11. A telecommunication system for providing a telecommunication link between a first and a second telecommunication station, the system including means for providing a messaging service for use by a party at one of said stations in the event that the link drops out during use thereof, so as to permit a message to be stored and retrieved by another party after the dropout. 12. A system according to claim 11, configured to produce the link for which the second station is a mobile station. 13. A system according to claim 11 or 12 including means responsive to dropout of the link for rendering the messaging service operative during the dropout. 14. A system according to claim 11, 12 or 13 including means for signalling subsequent to the dropout that a message has been recorded and is available for retrieval. 15. A system according to claim 12, including a plurality of geographically spaced transmission stations for seleαively establishing a communication path with the mobile station. 16. A system according to claim 15 including a network interconneαing the transmission stations, coupling means for coupling the first station to the network, and network control means for routing the telecommunication link through the network between the coupling means and the transmission station appropriate for establishing the communication path for the mobile station. 17. A system according to claim 16 wherein the messaging service comprises a voicemail facility coupled to the network. 18. A system according to claim 16 or 17 wherein the network control means includes location register means for keeping a record of the location of the mobile station relative to the transmission stations, for routing the telecommunication link through the network between the coupling means and the transmission station appropriate for establishing the communication path for the mobile station. 19. A system according to claim 18 wherein the location register means comprises a plurality of visitor location registers associated with the transmission stations respeαively for keeping a record of mobile stations within the operational range thereof, and a home location register that receives data from visitor location registers. 20. A system according to any one of claims 12 to 19 wherein the means providing the messaging service is operative to offer the service to the calling party in the event that the link drops out after the telecommunication link was initiated by a calling party at the first station. 21. A system according to claim 20 including means for billing the calling party for both the call over the link and use of the messaging service. 22. A system according to any one of claims 12 to 21 wherein the means providing the messaging service is operative to offer the service to the called party in the event that the link drops out after the link being initiated by a calling party at the mobile station that calls a called party at the first station. j 23. A system according to claim 22 including means for billing the calling party for the call over the link, and the called party for use of the messaging service. o 24. A system according to any one of claims 15 to 23 wherein the transmission stations comprise satellite access nodes for establishing a communication path with the mobile station via at least one satellite. 25. A system according to claim 24 wherein said transmission stations are 5 operative to communicate with a constellation of satellites in medium earth orbits. 26. A system according to claim 24 wherein said transmission stations are operative to communicate with a constellation of satellites in low earth orbits. 27. A system according to claim 24 wherein the satellite is in a geostationary orbit. 28. A system according to any one of claims 15 to 23 wherein the transmission stations comprise stations of a GSM, DAMPS, PHS or PDC mobile telephone system. 29. A mobile station configured for use in a method as claimed in any one claims 1 to 10 or for use in a system as claimed in any one of claims 11 to 28. 30. A mobile station for use in a telecommunications system which provides a telecommunication link therewith and another party, the mobile station being operative to communicate with a messaging service provided by the system in the event of dropout of the link, to receive an indication that a message has been recorded in the service during the dropout, and to retrieve the recorded message. 31. A mobile station according to claim 30 that comprises a mobile telephone handset.

Inventors: CHAMBERS PAUL, GREEN JEREMY, SHEPHERD PHILIP, CHAMBERS, PAUL, GREEN, JEREMY, SHEPHERD, PHILIP
Applicants: CHAMBERS PAUL, GREEN JEREMY, ICO SERVICES LTD, SHEPHERD PHILIP, CHAMBERS, PAUL, GREEN, JEREMY, ICO SERVICES LTD., SHEPHERD, PHILIP
Application year: 1996
Main classification: H04B7
IPC codes: H04B7, H04M3, H04W4