EP1985134A2

EP1985134A2 - Wireless communication system, wireless communication unit and method for assigning an identifier

Info

Publication number: EP1985134A2
Application number: EP07717522A
Authority: EP
Inventors: Marlene Bloch
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2006-02-03
Filing date: 2007-02-02
Publication date: 2008-10-29
Also published as: WO2007092743A2; WO2007092743B1; GB2434940B; EP1985134A4; WO2007092743A3; GB2434940A; GB0602194D0

Abstract

A wireless communication system (100) comprises a plurality of serving wireless communication units (122-132) supporting communication in a respective plurality of location areas. A first serving wireless communication unit (126) of the plurality of serving wireless communication unit (122-132) is arranged to generate a temporary identifier for use by a migrating/roaming wireless communication unit (116) when the first serving wireless communication unit (126) is temporarily disconnected from the remote management logic (146).

Description

WIRELESS COMMUNICATION SYSTEM, WIRELESS COMMUNICATION UNIT AND METHOD FOR ASSIGNING AN IDENTIFIER

Field of the Invention

This invention relates to assigning an identifier to a migrating/roaming wireless communication unit to access a wireless communication system. The invention is applicable to, but not limited to, assigning an identifier to facilitate access to a communication site that is disconnected from portions of the communication system.

Background of the Invention

Wireless communication systems, for example cellular telephony or private mobile (two-way) radio communication systems, typically provide for radio telecommunication links to be arranged between a plurality of base transceiver stations (BTSs) and a plurality of subscriber units, often termed mobile stations (MSs) . The term mobile station generally includes both hand-portable and vehicular mounted radio units. Radio frequency (RF) transceivers (transmitters and receivers) are located in both BTSs and MSs in order to facilitate wireless communication between the communication units.

Wireless communication systems are distinguished over fixed communications systems, such as the public switched telephone networks (PSTN) (used for landline-to-MS calls) , principally in that mobile stations move between service providers (and/or different BTS) and in doing so encounter varying radio propagation environments. Connections between two TETRA systems will most likely use a dedicated (El) link for this purpose.

In two-way radio communications systems, communication between two radios often referred to as Mirect mode (DM) ' is performed either via point-to-point (otherwise referred to as individual calls) between two users, or point-to- multipoint (otherwise referred to as group calls) between possibly two or more users. As such, group call communication can be effected where users communicate to a number of other users in a particular communication group via a central controller, and using a central controller, the communication is often referred to as ^λtrunked mode' group call.

In a wireless communication system, each BTS has associated with it a particular geographical coverage area (or cell) , which is often referred to as a ^xlocation area' . A location area is an area in which MSs may roam, without updating the location registers stored within the system infrastructure. The coverage area defines a particular range that the BTS can maintain acceptable communications with MSs operating in its serving cell. Often these cells combine to produce an expanded system coverage area, with communications controlled by a central entity. A mobile station (MS) is allowed to roam/migrate to and register on a visiting system or site, i.e. via a BTS that it has not been assigned to or registered with, in order to travel across the expanded system coverage area. In general a MS will attempt to register with the system where system-wide services are available. System-wide services are generally broadcast over the air. When a MS registers on a network that is not its home system (often referred to as a ^Λforeign' system) , a temporary identifier (ID) that is unique to the foreign system, is assigned to the migrated MS. ID assignments are co-ordinated from an Operations and Management Centre (OMC) function, located centrally within the system. However, the System Operator/ Implementer may decide to distribute the ID range reserved for foreign users across several entities within the system to minimize fault scenarios. When a MS moves from one system to another in TETRA a MS ^λmigrates' and when the MS moves from one BTS/Location Area (LA) to another within the same system, the MS ^roams' .

One identified problem with migrating MSs is when the migrating MS registers onto a foreign system in a location/geographical area that is temporarily isolated from the rest of the system. In such a scenario, the BTS will not be able to connect to the OMC in the foreign system. For example, the disconnection may be due to wireless or landline components being disconnected or faulty, or links between core components in the system may not be operational.

Thus, the system's central management function is unable to allocate a temporary ID to the migrated MS that is unique to the foreign system. The TETRA Air Interface standard (EN 300 392-2 v2.5.2) states that when a system is temporarily isolated, the isolated base station is to broadcast a message that ^system wide services are temporarily not supported' . The MS will monitor this broadcast message to determine the status of the base stations within its receiving range.

However, the use of broadcasting 'system wide services temporarily not supported' is typically not used when core components of the system are not operational, for example when connection to OMC is unavailable. In such instances, the migrated MS will not be aware of any system failure.

The TETRA Voice and Data (V+D) , part 2: Air Interface standard (EN 300 392-2 v2.5.2), chapter 16.4.8 describes a mechanism for "Temporary Registration", i.e. how a MS registers on a part of the system that is temporary isolated from the rest of the TETRA system. The use of the "Temporary registration" acknowledge message is only supported in the case where the BTS is in the state "system wide services temporarily not supported". According to the TETRA standard, when the BTS is in this state and the MS has received a "Temporary registration" acknowledge, the MS assumes that its initial registration request has been accepted.

However, when the site reverts back to normal mode or the MS roams to a BTS in normal mode, the MS shall perform a periodic registration. Periodic registration will not result in a connection to the OMC to acquire a unique ID for the migrated MS. Thus, the inventor of the present invention has recognised and appreciated that, the MS is incapable of recognising that the ID provided to it by the foreign system is only a temporary roaming ID, and that a new ID should be requested by the MS when roaming off an isolated BTS or Location Area in the system, in order for it to be 'fully' registered with the (supported) foreign TETRA system.

This invention seeks to provide a wireless communication system, a wireless unit for use in the wireless communication system and a method of roaming in the wireless communication system which mitigate at least some of the above mentioned disadvantages .

Summary of the Invention

According to embodiments of the present invention there is provided a wireless communication system, a wireless communication unit, a serving wireless communication unit and a method for migrating/roaming in a wireless communication system are described, as claimed in the appended Claims.

Brief Description of the Drawings

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which. FIG. 1 shows a block diagram of a trunked radio communication system adapted to support embodiments of the present invention;

FIG. 2 shows a block diagram of a trunked radio communication unit adapted to support embodiments of the present invention;

FIG. 3 is a flow chart showing a method of operating at least one first radio unit in the communication system according to embodiments of the invention; and

FIG. 4 is a flow chart showing a method of operating at least one first radio unit in the communication system according to embodiments of the invention.

Description of Embodiments of the Invention

In summary, a wireless serving communication unit, such as a base station, is arranged to identify that it is isolated from the Operations and Management Centre (OMC) of the wireless communication system, and in response thereto configure itself to generate temporary IDs locally and assign these temporary IDs to migrating MSs. The migrated MS is arranged to interpret broadcast messages from the disconnected BTS and understand that during an initial registration an identifier (ID) allocated to the migrating MS is only a temporary ID that may not be unique within the wireless communication system, notably when a "Temporary registration" acknowledge is received in response to the initial registration. Although one embodiment of the present invention is described with reference to a TETRA private/public mobile radio system, it is envisaged that the inventive concept may^¬ be applied in any wireless cell-based communication system, such as the Global System for Mobile Communications (GSM) , otherwise referred to as a 2^nd Generation telecommunication system, a Universal Mobile Telecommunications System (UMTS) , otherwise referred to as a 3^rd Generation (3G) telecommunication system or other comparable wireless cell- based systems .

Referring first to FIG. 1, a trunked radio communications system 100, supporting a TErrestrial Trunked RAdio (TETRA) air-interface, is shown in outline, in accordance with one embodiment of the invention. The TETRA air-interface has been defined by the European Telecommunications Standards Institute (ETSI) . Generally, the air-interface protocol is administered from base transceiver sites that are geographically spaced apart - one base site supporting a cell (or, for example, sectors of a cell) .

A plurality of subscriber units, such as a mixture of MSs 112-116 and fixed terminals (not shown), communicate over the selected air-interface 118-120 with a plurality of serving wireless communication units, hereinafter referred to as base transceiver stations (BTSs), 122-132. A limited number of MSs 112-116 and BTSs 122-132 are shown for clarity purposes only.

The system infrastructure in a TETRA system is generally referred to as a switching and management infrastructure (SwMI) 110, which substantially contains all of the system elements apart from the mobile units. The BTSs 122-132 may be connected to a conventional public-switched telephone network (PSTN) 134 through base station controllers (BSCs) 136-140 and mobile switching centres (MSCs) 142-144.

Each BTS 122-132 is principally designed to serve its primary cell, with each BTS 122-132 containing one or more transceivers. The BTSs 122-132 may communicate 156-166 with the rest of the trunking system infrastructure via a frame relay interface.

Each BSC 136-140 may control one or more BTSs 122-132, with BSCs 136-140 generally interconnected through MSCs 142-144. Each BSC 136-140 is therefore able to communicate with one another, if desired, to pass system administration information therebetween, with BSCs 136-140 responsible for establishing and maintaining control channel and traffic channels to serviceable MSs 112-116 affiliated therewith. The interconnection of BSCs 136-140 therefore allows the trunked radio communication system to support handover of the MSs 112-116 between cells.

Each MSC 142-144 provides a gateway to the PSTN 134, with MSCs 142-144 interconnected through remote management logic (generally in the form of an operations and management centre (OMC) 146) that administers general control of the trunked radio system 100, as will be understood by those skilled in the art. The various system elements, such as BSCs 136-138 and OMC 146, include control logic 148-152, with the various system elements usually having associated memory 154 (shown only in relation to BSC 138 for the sake of clarity) . The memory typically stores historically compiled operational data as well as in-call data, system information and control algorithms.

In addition to administering general control of the trunked radio system 100, in accordance with one embodiment of the present invention, the OMC 146 contains an ID assignment function 155. The ID assignment function 155 allocates IDs and temporary IDs to BTSs within the system, for subsequent assignment to MSs and migrating MSs.

In one embodiment of the present invention, let us assume that BTS 126 is temporarily disconnected from the TETRA system. Thus, the site supported by BTS 126 is in a state where system wide services are temporarily unsupported.

Notably, BTS 126 may be in isolation for a variety of reasons. Whatever the reason, if the BTS 126 recognises that it is isolated, it broadcasts this information over the air-interface. As a consequence, all MSs are informed that the BTS is isolated. However, if other, e.g. landline links, are down between core parts of the system then a migrating/roaming MS will not be aware that the BTS is isolated when receiving a temporary ID.

Furthermore, let us assume that a migrated MS 116 migrates into an area where TETRA communication is supported by BTS 126. The migrated MS 116 requires an associated ID (Alias Short Subscriber Identity (ASSI) ) in order to operate on the ^xforeign' system supported by BTS 126. In this regard, the migrated MS 116 performs an ^initial registration' request procedure, transmitted to BTS 126, upon powering on or initial migration registration.

The BTS 126 comprises processing logic 127 that is arranged to identify that it is isolated from the rest of the system. The BTS 126 also comprises a transceiver (not shown) , that is operably coupled to the processing logic 127 and arranged to wirelessly receive the initial registration request from the migrated/roaming MS 116. The processing logic 127 is configured, in response thereto, to generate a temporary ID locally and assign this temporary ID to the migrated/roaming MS 116.

In one embodiment of the present invention, when roaming in a comparable GSM system, a roaming MS is assigned a Temporary Mobile Subscriber Identity (TMSI) or Local Mobile Station Identity (LMSI) by comparable processing logic, as would be appreciated by a skilled artisan.

The BTS 126 assigns the temporary ID such that it is only valid whilst the migrating/roaming MS 116 is registered within the location area supported by the BTS 126.

For completeness, it is understood that even though the BTS 126 indicates that system-wide services are not available; some communication services may still be available within the site or location area. By allowing the migrating/roaming MS 116 to register temporarily at the site, i.e. the site supported by BTS 126, the BTS 126 allows - li ¬

the migrating/roaming MS 116 to participate in whatever communication is permitted within the isolated area of the system.

In one embodiment of the present invention, when the roaming MS 116 roams out of the location area supported by BTS 126, for example into a location area supported by BTS 128, a new initial registration request is performed by the roaming MS 116. Such a new initial registration request is repeatedly performed by the roaming MS 116, until the registration request has been ^formally' accepted.

Alternatively, in one embodiment of the present invention, if the site/location area reverts to normal operation again, i.e. BTS 126 is re-connected to the TETRA system, then a new initial registration request is performed by the migrated/roaming MS 116 within the re-connected system. Notably, this request is re-transmitted until it is accepted normally.

In an alternative embodiment of the present invention, when applied to a GSM system and the roaming MS is registered at a site that is barred (according to the Barred Cell Broadcast information) , then the roaming MS again repeatedly re-invokes the same type of initial registration request upon each new required registration (e.g. roaming to a new site or location area or when the site reverts to "normal operation") until the registration request has been accepted normally. Referring now to FIG. 2, a block diagram of a wireless subscriber communication unit 200, otherwise referred to as a mobile station (MS) 116, is shown adapted to support embodiments of the present invention. MS 116 is a migrating MS and contains an antenna 202, coupled to a duplex filter or antenna switch 204, which provides isolation between receive chain 210 and transmit chain 220 within MS 116. The receiver chain 210 includes receiver front-end circuit 206 (effectively providing reception, filtering and intermediate or base-band frequency conversion) . The front-end circuit 206 scans signal transmissions from the BTS, e.g. BTS 126 whose location area the migrating/roaming MS has migrated/roamed into. The front-end circuit 206 is serially coupled to a signal processing function, generally realised by a digital signal processor (DSP), 208.

In accordance with one embodiment of the invention, the signal processing function 208 has been adapted to enable the MS 116 to receive and process a temporary ID sent by a temporarily unsupported BTS. In particular, the signal processing function 208 is arranged to recognise that the assigned temporary ID was generated locally by BTS 126, due to the fact that the response to the MS's initial registration was a "Temporary Registration" acknowledge message, and the MS understands that this message is a result of a broadcast message where system wide services not supported. An initial registration message may be required due to power-on of the MS, the MS being out of coverage for a long time or the MS migrating into a foreign system from another system. Thus, when MS 116 moves out of this location area, i.e. the area supported by BTS 126, the MS has to perform an initial registration again, as if it had just moved into a foreign system for the first time.

A controller 214 is operably coupled to the front-end circuitry 206 so that the receiver can calculate receive bit-error-rate (BER) or frame-error-rate (FER) or similar link-quality measurement data from recovered information via a received signal strength indication (RSSI) 212 function. The RSSI 212 function is operably coupled to the front-end circuit 206. The memory device 216 stores a wide array of MS-specific data, such as decoding/encoding functions and the like, as well as link quality measurement information to enable an optimal communication link to be selected.

A timer 218 is operably coupled to the controller 214 to control the timing of operations, namely the transmission or reception of time-dependent signals, within the MS 116. In the context of one embodiment of the present invention, timer 218 is used to synchronize the receiving MS 112 to the timing dictated by the associated BTS 126 (or the SwMI 110) of FIG. 1. As known in the art, received signals that are processed by the signal processing function 208 are typically input to an output device 210, such as a speaker or visual display unit (VDU) .

As regards the transmit chain 220, this essentially includes an input device such as a keypad, of the user interface 230. The user interface 230 is coupled in series via the signal processing function 208 through transmitter/ modulation circuitry 222 and a power amplifier 224 to the antenna 202. The transmitter/ modulation circuitry 222 and the power amplifier 224 are operationally responsive to the controller 214.

In one embodiment of the present invention, when a MS receives a temporary registration upon initial registration on a visited (foreign) system, it will know that the temporary ID received for this system is not unique and that it must request a new ID when roaming to a new site. This temporary ID will also allow for the MS to access services that are available within the isolated system.

It is envisaged that, in one embodiment of the present invention, the inventive concept described above may be supported by MSs that are allowed to migrate to a visited system without a pre-defined foreign ID programmed into the mobile. Thus, it is also supported in the infrastructure, when foreign MSs are allowed to register on the system, and these MSs are not pre-configured with an ID to operate in this system.

Referring now to FIG. 3, a flow chart 300 illustrates a method of migrating/roaming in a wireless communication system by assigning a temporary ID to a migrating/roaming wireless communication unit (MS) according to embodiments of the invention. The flowchart commences with the MS registering at a foreign site in a foreign system (that is not the MS' s home system), as shown in step 305. The BTS of the foreign system determines the type of registration message received from the migrated MS, in step 310. If the BTS of the foreign system determines that registration message received from the migrated MS in step 310 is an initial registration request, a determination is made by the BTS as to whether the migrated MS is allowed to register onto the system, as shown in step 315. If the migrated MS is not allowed to register onto the system in step 315, the BTS rejects the initial registration request, in step 320.

However, if the migrated MS is allowed to register onto the system in step 315, the BTS determines whether system-wide services are available in step 325. If the BTS determines that system-wide services are not available in step 325, the BTS determines whether it is able to assign a temporary operational ID to the migrated MS even though system-wide services are not available. If the BTS determines that it is unable to assign a unique, system-wide, temporary operational ID, even though system-wide services are unavailable, the BTS assigns a local temporary operational ID to the migrated MS and accepts a temporary registration of the MS, as shown in step 335.

However, if the registration is a non-initial registration type in step 310, or the BTS determines that system-wide services are available in step 325 or that the BTS is able to assign an unique, system-wide, operational ID (even though system-wide services are not available) in step 330, the BTS is able to accept or reject the registration request according to its existing operational procedures, as in step 340. Referring now to FIG. 4, a flow chart 400 illustrates a method of a MS operation in response to assignment of a temporary ID from a foreign BTS according to embodiments of the invention. The flowchart 400 commences with the MS migrating into a foreign system, as shown in step 405. The MS then determines whether it has previously been temporarily registered, in step 410. If the MS has previously been temporarily registered in step 410, the MS performs a new initial registration request, as shown in step 420. In TETRA, this initial registration request is an ^λITSI attach/ or ^Λmigration location update' or ^xcall restoration migration location update' message. If the MS has not previously been temporarily registered at that site in step 410, the MS uses the existing roaming registration procedures, as shown in step 415.

In this manner, a wireless communication system, a method of migrated/roaming therein, a wireless communication unit and a wireless serving communication unit are provided that mitigate one or more of the aforementioned disadvantages with present communications systems, methods or units.

Whilst specific embodiments of the present invention have been described, it is clear that one skilled in the art could readily apply further variations and modifications of such embodiments within the scope of the accompanying claims .

It will be appreciated that references to specific functional devices or elements are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization of components .

Aspects of the invention may be implemented in any suitable form. The elements and components of an embodiment of the invention may be physically, functionally and/or logically implemented in any suitable way. Indeed, the functionality of assigning the temporary ID by the BTS may be performed by another element in the system that is operably coupled to the BTS even though the BTS is not connected to the SwMI or the OMC.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ^comprising' does not exclude the presence of other elements or steps.

Furthermore, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to "a", "an", "first", "second", etc. do not preclude a plurality.

Claims

1. A wireless communication system (100) comprising remote management logic (146) operably coupled to a plurality of serving wireless communication units (122-132) supporting communication in a respective plurality of location areas, wherein the wireless communication system (100) is characterised in that a first serving wireless communication unit (126) of the plurality of serving wireless communication unit (122-132) is arranged to generate a temporary identifier for use by a migrating/roaming wireless communication unit (116) when the first serving wireless communication unit (126) is temporarily disconnected from the remote management logic (146) .

2. A wireless communication system (100) according to Claim 1 wherein the migrating/roaming wireless communication unit (116) is sent the temporary identifier by the first serving wireless communication unit (126) following transmission of an initial registration request to the first serving wireless communication unit (126) .

3. A wireless communication system (100) according to Claim 2 wherein the migrating/roaming wireless communication unit (116) comprises a signal processing function (208) configured to determine that the serving wireless communication unit (126) is disconnected from remote management logic (146) and that the temporary identifier was generated by the serving wireless communication unit (126) .

4. A wireless communication system (100) according to Claim 3 wherein the signal processing function (208) is arranged to re-transmit the initial registration request to a second serving wireless communication unit (128) when roaming into a location area supported by the second serving wireless communication unit (128) following receiving a temporary identifier from the first serving wireless communication unit (126) .

5. A wireless communication system (100) according to Claim 3 wherein the signal processing function (208) is arranged to re-transmit the initial registration request to the first serving wireless communication unit (126) in response to the first serving wireless communication unit (126) re-connecting to the remote management logic (146) .

6. A wireless communication system (100) according to Claim 3 wherein the wireless communication system wherein the wireless communication system (100) supports TETRA communication.

7. A wireless communication unit (116) comprising: a transceiver operably coupled to a signal processing function (208) , the transceiver arranged to transmit a registration request to a serving wireless communication unit (126) upon migrating/roaming into an area supported by the serving wireless communication unit (126) and in response thereto receive a temporary identifier, the wireless communication unit (116) characterised in that in response to receiving the temporary identifier the signal processing function

(208) is configured to determine that the serving wireless communication unit (126) is disconnected from remote management logic (146) and that the temporary identifier was generated by the serving wireless communication unit (126), and in response thereto the transceiver is arranged to either: re-transmit the registration request to a second serving wireless communication unit (128) when roaming into a location area supported by the second serving wireless communication unit (128) , or re-transmit the registration request to the first serving wireless communication unit (126) following determining that the first serving wireless communication unit (126) has re-connected to remote management logic (146) .

8. A wireless communication unit (116) according to Claim 7, wherein the wireless communication unit is capable of operating in a TETRA communication system (100) .

9. A serving wireless communication unit (126) comprising: a transceiver operably coupled to a processing function (127) and arranged to be operably coupled to remote management logic (146) and support communication to at least one migrating/roaming subscriber communication unit (116) migrating/roaming into a location area supported by the serving wireless communication unit (126) , wherein the serving wireless communication unit (126) is characterised in that the processing function (127) comprises identifier generation logic and is arranged to determine when the serving wireless communication unit (126) is not operably coupled to the remote management logic (146) and in response thereto the identifier generation logic generates a temporary identifier for transmitting to a migrating/roaming wireless communication unit (116) .

10. A serving wireless communication unit (126) according to Claim 9 wherein the migrating/roaming wireless communication unit (116) is sent the temporary identifier following receipt of an initial registration request sent from the migrating/roaming wireless communication unit (116) to the serving wireless communication unit (126) .

11. A serving wireless communication unit (126) according to Claim 10 wherein the serving wireless communication unit (126) supports TETRA communication.

12. A method for migrating/roaming in a wireless communication system (300, 400) comprising remote management logic operably coupled to a plurality of serving wireless communication units supporting communication in a respective plurality of location areas, wherein the method is characterised by the step of: determining (325) , by a first serving wireless communication units that it is disconnected from the remote management logic- generating (335) , by the first serving wireless communication units in response thereto, a temporary identifier; receiving a registration request (305) from a migrating/roaming wireless communication unit; and transmitting the temporary identifier to the migrating/roaming wireless communication unit in response thereto to enable the migrating/roaming wireless communication unit to communicate in a location area supported by the serving wireless communication unit.

13. A method for migrating/roaming in a wireless communication system (300, 400) according to Claim 12 further characterised by: determining (410) by the migrating/roaming wireless communication unit that the temporary identifier may not be unique; and in response thereto: re-transmitting the registration request to a second serving wireless communication unit (128) when roaming into a location area supported by the second serving wireless communication unit (128) ; or re-transmitting the registration request to the first serving wireless communication unit (126) following the first serving wireless communication unit (126) re-connecting to the at least one other of the plurality of serving wireless communication unit (122- 132) .