System and method for bridging an emergency call with an optimized satellite call

[0002] The present invention relates generally to telecommunications systems and methods for optimizing calls in a satellite network, and specifically to placing emergency calls within a satellite network.

[0003] Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.

[0004] With reference now to FIG. 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and a Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) 20 may move freely without having to send update location information to the MSC/VLR 14/16 that controls the LA 18. Each Location Area 12 is divided into a number of cells 22. Mobile Station (MS) 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless.

[0005] The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the geographical part of the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several BTS's 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.

[0006] With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.

[0007] The VLR 16 is a database containing information about all of the MS's 20 currently located within the MSC/VLR area 12. If an MS 20 roams into a new MSC/VLR area 12, the VLR 16 connected to that MSC 14 will request data about that MS 20 from the HLR database 26 (simultaneously informing the HLR 26 about the current location of the MS 20). Accordingly, if the user of the MS 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to reinterrogate the HLR 26. In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectively, contain various subscriber information associated with a given MS 20.

[0008] It should be understood that the aforementioned system 10, illustrated in FIG. 1, is a terrestrially-based system. In addition to the terrestrially-based systems, there are a number of satellite systems, which work together with the terrestrially-based systems to provide cellular telecommunications to a wider network of subscribers. This is due to the fact that the high altitude of the satellite makes the satellite visible (from a radio perspective) from a wider area on the earth. The higher the satellite, the larger the area that the satellite can communicate with.

[0009] Within a satellite-based network 205, as shown in FIG. 2 of the drawings, a system of geostationary satellites 200 in orbit are used to provide communication between MS's 20 and a satellite-adapted Base Station System (SBSS) 220, which is connected to an integrated Mobile Switching Center/Visitor Location Register (MSC/VLR) (hereinafter referred to collectively as reference number 14). The MS 20 communicates via one of the satellites 200 using a radio air interface. The satellite 200 in turn communicates with one or more SBSSs 220, which consist of equipment for communicating with the satellites 200 and through the satellites 200 to the MS's 20. The antennae and satellite tracking part of the system is the Radio Frequency Terminal (RFT) subsystem 230, which also provides for the connection of the communication path to the satellite 200.

[0010] In such satellite networks 205 using geostationary satellites 200, the coverage area for a satellite 200 can be (and usually is) very large. This area can be served by a number of MSC/VLRs 14 which are connected to Public Switched Telephone Networks (PSTNs) (wireline networks), PLMNs (cellular networks) and each other. The terrestrial interconnections (trunk circuits) to these MSC/VLRs 14 are expensive to install and maintain, especially in comparison to handling the traffic over the satellite 200. Since the distances within the area served by the satellite(s) 200 are typically very large, the costs for these circuits can be enormous. In particular, the costs can be considerable if the circuits must cross remote areas or oceans.

[0011] Therefore, calls within a geostationary satellite network 205 can be optimized such that a subscriber is reallocated to the MSC/VLR 14 that is the most optimal for a given call. For example, for calls from a calling MS 20 to another MS 20 within the satellite network 205, the calling MS 20 typically re-registers in the MSC/VLR 14 of the called MS 20. In this way, it is possible to make the connection directly over the satellite 200, avoiding the additional delay caused by a double satellite-hop. Thus, only one bi-directional path is required (MS-satellite-MS) instead of two (MS-satellite-SBSS-satellite-MS). However, when an MS 20 to MS 20 call is optimized, it is currently not possible for either MS 20 to establish an emergency call in parallel to the existing single-hop call. Thus, if one of the MS's 20 wants to establish an emergency call, the single-hop call must first be disconnected, and only one of the MS's can then be connected to the Emergency Call Center (ECC).

[0012] It is, therefore, an object of the present invention to allow an MS to complete an emergency call in parallel to a single-hop satellite call.

[0013] The present invention is directed to telecommunications systems and methods for allowing a mobile station involved in a single-hop satellite call to complete an emergency call. One of the mobile stations involved in the single-hop satellite call activates an emergency call feature, which triggers one or both of the mobile stations to perform a call release and call re-establishment procedure. When one or both of the mobile stations performs call re-establishment, the call is marked as an Emergency Call to prevent the mobile stations from being reconnected in a single-hop call. After re-establishment, the mobile station that activated the emergency call feature transmits an Emergency Setup message to the MSC/VLR, which initiates a call connection to the Emergency Call Center (ECC) . Once the MSC/VLR completes the call to the ECC, the MSC/VLR bridges all parties together in a conference call.

[0014] The disclosed invention will be described with reference to the accompanying drawings, which show important sample embodiments of the invention and which are incorporated in the specification hereof by reference, wherein:

[0015] FIG. 1 is block diagram of a terrestrially-based wireless telecommunications system;

[0016] FIG. 2 is a block diagram of a satellite telecommunications system;

[0017] FIG. 3 illustrates optimization of a call between mobile stations in a satellite network;

[0018] FIG. 4 illustrates establishing an emergency call in parallel to an existing optimized satellite call in accordance with preferred embodiments of the present invention;

[0019] FIG. 5 illustrates the steps for establishing the parallel emergency call shown in FIG. 4 of the drawings; and

[0020] FIG. 6 illustrates establishing an emergency call to the correct Emergency Call Center in parallel to an existing optimized satellite call in accordance with embodiments of the present invention.

[0021] The numerous innovative teachings of the present application will be described with particular reference to the presently preferred exemplary embodiments. However, it should be understood that this class of embodiments provides only a few examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily delimit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others.

[0022] With reference now to FIG. 3 of the drawings, when a calling Mobile Station (MS) 20acalls a called MS 20bwithin the area 205 visible to a satellite 200, a satellite-adapted Base Station System (SBSS) 220aserving the PLMN area 10athat the calling MS 20ais located in receives the Called Party Number (CPN) from the calling MS 20a.Thereafter, the SBSS 220asends the CPN to a serving Mobile Switching Center/Visitor Location Register (MSC/VLR) 14a.If the serving MSC/VLR 14adetermines that the CPN is not a number registered within the serving MSC/VLR 14a,the digit string for the CPN is sent to a Call Optimization Server (COS) 240 for pre-analysis. The COS 240 determines that the call is a MS 20ato MS 20bcall, queries a Home Location Register (HLR) 26 of the called MS 20bfor the current location of the called MS 20b,and assigns a transaction identifier to be used for making the connection between the two MSs (20a and 20b).

[0023] Thereafter, the COS 240 sends an Unstructured Supplementary Service Data (USSD) string to the calling MS 20a,which requests the calling MS 20ato re-register itself on an MSC/VLR 14bserving the called MS 20bvia an SBSS 220bserving the called MS 20b.The USSD string also includes the transaction identifier. In this way, satellite resources can be conserved by performing the connection for these calls using only the satellite 200, e.g., only one bi-directional path is required (MS-satellite-MS) instead of two (MS-satellite-SBSS-satellite-MS). This one bi-directional path connection is commonly known as a single-hop satellite call, whereas the two bi-directional path connection is referred to as a double-hop satellite call.

[0024] After re-registration in the desired MSC/VLR 14b,normal call setup procedures take place, with the addition of an indicator that this is a MS 20ato MS 20bcall and the transaction identifier. The MS 20ato MS 20bcall indicator is used to disable functions requiring terrestrial switch connections. The transaction identifier is used when channel assignments are done and the connection is made to ensure that the right channels can be connected with the satellite 200. Once the connection is made through the satellite 200, the transaction identifier is released.

[0025] However, when an MS 20ato MS 20bcall is optimized in the aforementioned manner, it is not possible for either MS 20aor 20bto place an emergency call in parallel to the optimized call. Therefore, as shown in FIG. 4 of the drawings, and in accordance with one preferred embodiment of the present invention, in order for either MS 20aor 20bto place an emergency call in parallel to an existing single-hop satellite call, one or both of the MSs 20 involved in the single-hop call must have an emergency call feature 40 associated therewith, which gives the MS 20aand/or 20bthe ability to establish an emergency call in parallel to a single-hop call. This emergency call feature 40 is preferably stored in a memory 45, such as a Subscriber Identity Module (SIM) card, in the MS 20aor 20b.

[0026] In a preferred embodiment, if both MSs 20aand 20bhave the emergency call feature 40, the parallel emergency call can be established by one of the MSs 20aor 20bactivating their emergency call feature 40. This feature 40 can be activated by pressing one or a sequence of emergency keys on a keypad 21 of the MS 20 or by using function keys 22 on the MS 20 to select the emergency call feature 40 from a menu of services displayed on a display 27 of the MS 20. Activating the emergency call feature 40 triggers both MSs 20aand 20bto perform a call release and call re-establishment procedure. After the call release, and during the call re-establishment procedure, the call is marked as an emergency call so that the MSs 20aand 20bare not reconnected again in a single-hop call. After re-establishment, the activating MS 20aor 20btransmits an Emergency Setup message 245 to the optimal MSC/VLR 14b,which initiates a connection to an Emergency Call Center (ECC) 50 within the area 10aserved by the optimal MSC/VLR 14b.When the call is completed to the ECC 50, all parties 20a,20band 50 are bridged together.

[0027] A sample call release and call re-establishment procedure is shown in FIG. 5 of the drawings. Upon activation of the emergency call feature 40, MS 20atransmits a DISCONNECT message 250 to the other MS 20b,which is relayed to the optimal MSC/VLR 14bvia satellite 200 (step 500). Upon receipt of the DISCONNECT message 250, MS 20btransmits a RELEASE message 260 to the other MS 20a,which is also relayed to the MSC/VLR 14bvia satellite 200 (step 510). To release the call, MS 20atransmits a RELEASE COMPLETE message 270 to the MSC/VLR 14bvia satellite 200 (step 520). When the call is released, both MS's 20aand 20bwill experience an interruption in voice communication until the call connection is re-established.

[0028] An indication 255 that each MS 20aand 20bhas the emergency call feature 40 can be included in a separate message or as a part of the DISCONNECT 250 and RELEASE 260 messages, respectively. In this case, both MSs 20aand 20bhave the emergency call feature 40, and therefore, both MSs 20aand 20bperform the call re-establishment procedure. The call re-establishment procedure is similar to normal GSM call re-establishment procedures, with minor modifications to allow for quicker call connection. Only the call re-establishment procedure for MS 20ais shown in FIG. 5 of the drawings. However, it should be understood that the call re-establishment procedure for MS 20bmirrors that of MS 20a.To begin call re-establishment, after the single-hop satellite call has been released, MS 20aautomatically transmits a re-establishment call setup message with an indication that the call should not be a single-hop call to the optimal MSC/VLR 14bvia satellite 200 (step 530). Thereafter, the optimal MSC/VLR 14brequests the SBSS 220bassociated with the optimal MSC/VLR 14bto assign a traffic channel to the MS 20a(step 540). The SBSS 220aassigns a channel and instructs the MS 20ato activate the traffic channel (step 550). Upon activation, the MS 20atransmits an assignment complete message to the MSC/VLR 14b(step 560). Once the MSC/VLR 14bhas received the assignment complete message from both MSs 20aand 20b,a double-hop satellite call connection is established (step 560) between MS 20aand MS 20b.The double-hop satellite call connection is from MS 20a,through the satellite 200, SBSS 220band MSC/VLR 14b,back through the SBSS 220b,and to MS 20bvia satellite 200. It should be understood that the SBSS 220 used by MS 20aand 20bcan be different.

[0029] Once the original call has been re-established (step 570), the original double-hop satellite call is put on hold, while the connection to the ECC 50 is initiated. It should be noted that the ECC 50 connection may be initiated as soon as MS 20afinishes the call re-establishment procedure. For example, once MS 20atransmits the Assignment Complete message (step 560), MS 20acan transmit the Emergency Setup message 245 to the optimal MSC/VLR 14b(step 580). The MSC/VLR 14bestablishes a call connection between the ECC 50 and MS 20a(step 590). After the call between MS 20aand MS 20bis completed, and the call between MS 20aand the ECC 50 is completed, the MSC/VLR 14bcan conference all parties together in a three-way call through a CCD device (conference circuit device) of the type known in the art within the MSC/VLR 14b(step 595).

[0030] In an alternative embodiment, if MS 20bdoes not support the emergency call feature, e.g., the indication 555 is not included in the RELEASE message 560, the MSC/VLR 14bcan either establish a normal emergency call between MS 20aand the ECC 50 (without conferencing MS 20b) or, after MS 20ahas completed call re-establishment, the MSC/VLR 14bcan page MS 20band establish a call connection between MS 20aand MS 20b.The decision to conference MS 20bcan be made by either MS 20aor the MSC/VLR 14b.For example, when MS 20areceives the RELEASE message 560 without the indication 555 from MS 20b,MS 20acan decide to release the call and transmit the Emergency Setup message 545 without initiating the call re-establishment. Alternatively, MS 20acan attempt to re-establish a double-hop satellite call connection with MS 20bby initiating the call re-establishment procedure. If MS 20aperforms the call re-establishment procedure, the MSC/VLR 14bcan decide to either page MS 20band attempt to complete the call or not allow MS 20ato re-establish a call connection with MS 20b.If the MSC/VLR 14bchooses the latter, the MSC/VLR 14bpreferably sends a message (not shown), such as a Short Message Service (SMS) message or Unstructured Supplementary Service Data (USSD), to MS 20ainforming MS 20athat the call to MS 20bcannot be re-established.

[0031] In some cases, if the MSC/VLR 14bconnects the emergency call to the ECC 50 in the PLMN 10bof the optimal MSC/VLR 14b,that ECC 50 may not be the correct ECC 50 for the type of emergency involved. For example, since MS 20ainitiates the emergency call, the ECC 50 in PLMN 10bmay be hundreds of miles away, and unable to render the appropriate emergency aid effectively.

[0032] Therefore, with reference now to FIG. 6 of the drawings, in an alternative embodiment, when MS 20aactivates the emergency call feature 40, the mobile subscriber associated with MS 20acan indicate whether the emergency relates to MS 20aor MS 20b.This emergency party information 248 can be included with the Emergency Setup message 245 sent by MS 20a.Thus, when the optimal MSC/VLR 14breceives the Emergency Setup message 245 and emergency party information 248, the MSC/VLR 14bcan determine the correct ECC 50 to connect the emergency call to.

[0033] For example, if MS 20ais the emergency party, the optimal MSC/VLR 14bcan determine the PLMN 10aof MS 20a,and route the call to the ECC 50 within PLMN 10a.It should be understood that each PLMN 10aand/or 10bcan contain more than one ECC 50, and therefore, the correct ECC 50 can be determined by ascertaining the Location Area, MSC/VLR area, cell or geographical location, e.g., X, Y coordinates, of the MS 20a.The connection to the correct ECC 50 can be completed directly from the optimal MSC/VLR 14bover trunk lines or through the SBSS 220aand MSC/VLR 14awithin the PLMN 10aof MS 20avia satellite 200.

[0034] As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed, but is instead defined by the following claims.