GB2366950A

GB2366950A - Transmission of inactivity registration removal mechanism data

Info

Publication number: GB2366950A
Application number: GB0022931A
Authority: GB
Inventors: Mark Shahaf; Nimrod Glazer; Rafael Carmon
Original assignee: Motorola Israel Ltd
Current assignee: Motorola Solutions Israel Ltd
Priority date: 2000-09-19
Filing date: 2000-09-19
Publication date: 2002-03-20
Anticipated expiration: 2020-09-19
Also published as: GB2366950B; GB0022931D0

Abstract

In a wireless communications system, the mechanism by which the registration of a mobile station is cancelled is transmitted to registered mobile stations. The arrangement reduces the number of unnecessary registration requests received from a mobile station after is has regained radio contact with the system. The removal mechanisms may include the expiry of a duration of time since the last communication and a predetermined number of unsuccessful pages to the mobile station. The registration removal mechanism data may be transmitted as a broadcast message.

Description

<Desc/Clms Page number 1> WIRELESS COMMUNICATION SYSTEM, COMMUNICATION UNIT AND METHOD OF REGISTRATION

Field of the Invention This invention relates to registration requirements in wireless communications systems. The invention is applicable to, but not limited to the re-registration requirements if a remote or mobile station was to temporarily lose contact with the system. Background of the Invention Wireless communications systems, for example cellular telephony or private mobile radio communications systems, typically provide for radio telecommunication links to be arranged between a plurality of base transceiver stations (BTSs) and a plurality of subscriber units. The subscriber units are typically either vehicuiar-mounted Amobile' or 'hand-portable' radio or cellular units. Henceforth, the term mobile station (MS) will be used for all such subscriber units. Wireless communications systems are distinguished over fixed communications systems, such as the public switched telephone networks (PSTN), principal'.y in that mobile stations move between service providers (and/or different

BTS) and in doing so encounter varying radio propagation environments. The communication link from a BTS to a MS is generally referred to as a down-link channel. Conversely, the communication link from a MS to a BTS is generally referred to as an up-link channel. Multiple access techniques permit simultaneous transmissions from several MS to a single BTS over a plurality of communications channels. Some channels are used for carrying traffic whilst other channels (which may be logical or dedicated channels) are used for transferring control information, such as call paging, between the base transceiver stations and subscriber units. Examples of multiple access techniques include: frequency division multiple access (FDMA), time division multiplexing/ multiple access (TDM, TDMA) and code division multiple access (CDMA). In wireless communication systems subscribers have to register with the system's system management infrastructure (often termed the main control sub-system) in order to gain access to various system services. This is particularly the case in cell-based communication systems where MSs have to inform the system management about their presence, and furthermore about their general location, typically within a particular cell in the network. Such location information reduces the system management's computational load (signalling traffic in

the system control channels) in searching for particular MSs within the respective coverage area(s).

In a wireless communications system, each BTS has associated with it a particular geographical coverage area (or cell). 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, and MSs therefore may move within and between coverage areas serviced by different BTSs.

Furthermore, these cells are often grouped (or divided) into Location Areas for the purposes of tracking a MS within the coverage area, whilst attempting to minimise any location-updating signalling. One facet of MSs moving between cells (serving BTSs) is that the MS needs to re-register with each new serving BTS, before service provision can continue.

Therefore, whenever the mobile station moves from one service area to another service area, the main control sub-system is updated with regard to the MS's new location. The number of MS registrations, and consequently control traffic load, is thereby reduced to the case where a MS crosses cell boundaries. The search for a MS can then be limited to the cells/BTS sites that belong to a particular area/region.

Whenever a MS is fully powered down, it often performs a de-registration procedure in order to inform the main control unit within network. The reason for this is to reduce obsolete messages addressed to non-operating MSs. This allows the better use of valuable system control resources. In addition to a MS being fully powered-down, a further scenario exists where a MS may not receive a message that has been addressed to it. The MS may have moved outside the effective coverage area of the radio network, without informing the main control sub-system of its movements beforehand. Such a scenario frequently happens due to the MSs moving into bridges, tunnels, underground parking, etc, that are effectively outside the normal coverage area. In the above cases, the main control sub-system monitors the system level inactivity of the MS in order to identify the loss of a communication link. This procedure may be based on unsuccessful attempts to page certain MS for a pre-defined period. After the inactivity period has expired, the main control subsystem will remove the MS record from the "active MS" database and will not search for the MS for paging purposes until the MS re-registers onto the system with the previous serving BTS or an alternative BTS. Typically, a MS may move outside of the coverage area of the network for a sufficiently long enough time that the

MS realises the communication link has been lost, but is unaware of whether or not the respective "inactivity period" has expired. The MS, on re-entering the network at say, the same location, has to perform a registration procedure. Such a requirement is due to the MS not having any knowledge whether system has removed it from its database or not. In summary, in order to ensure service any time after a temporary system loss, the MS has to re-register. The impact of re-registration requirements on control channel traffic becomes more severe when a MS has the capability of multi-system operation. With such multisystem opportunities, a MS may intentionally leave one system for a service provided by another system. Each system change will require a re-registration procedure, even if the topographical location of the MS remains unchanged. A yet further example of the registration and reregistration requirements of a MS can be found in the TErrestrial Trunked R_Adio (TETRA) system. In a TETRA system there is a mode of operation that is required to support Direct Mode communications (direct communications between MSs without usage of system resources). Such a mode of operation is offered in parallel to normal private mobile radio (PMR) or cellular-like operation with the network. Here, an individual or group of MSs within a particular geographical area may leave the network to participate in a Direct Mode call and

subsequently return to the network, perhaps in the same Location Area that it left. It is clear that the aforementioned re-registration requirement of cellular and PMR systems creates an abnormal and undesirable load on the control channel(s) in that Location Area, as well as using up valuable processing resource to continually update the main control sub-system databases. Thus there currently exists a need to provide a communication system, a communication unit and method of registration wherein the abovementioned disadvantage(s) may be alleviated. Statement of Invention In accordance with the present invention there is provided a communication system, as claimed in claim 1. In accordance with the present invention there is provided a communication unit as claimed in claim 4 In accordance with the present invention there is provided a broadcast transmission message as claimed in claim 8 In accordance with the present invention there is provided a wireless serving communication unit in

accordance with claim 9, adapted to transmit the broadcast transmission message of claim 8. In accordance with the present invention there is provided a method of registration as claimed in claim 10. Brief Description of the Drawings Exemplary embodiments of the present invention will now be described, with reference to the accompanying drawings, in which: FIG. 1 shows a block diagram of a trunked radio communications system that can be adapted to support the various inventive concepts of a preferred embodiment of the present invention; FIG. 2 shows a block diagram of a subscriber unit adapted to support the inventive concepts of the preferred embodiments of the present invention; FIG. 3 shows a flowchart of the decision making process for cell registration in accordance with a preferred embodiment of the invention; and FIG. 4 shows a timing diagram illustrating an example of the timing processes when employing the inventive concepts of a preferred embodiment of the invention.

Description of Preferred Embodiments

In current wireless communication systems, a serving cell periodically broadcasts general system information, for example details identifying each BTS's neighbouring cells. In this field of endeavour, a MS will always have to acquire synchronisation to its serving BTS, or a neighbouring BTS if its communication link is being handed over. Furthermore, the MS needs to register with such serving or neighbouring BTS, before being able to initiate a communication link. A preferred embodiment of the invention provides a mechanism for each network to broadcast a new set of operational parameters, namely operational parameters identifying the network's respective MS inactivity removal mechanism. This communication from a wireless serving communication unit, such as a BTS or BSC, will allow at least one of a plurality of MSs an opportunity to update their internal registration mechanisms and determine whether they need to make a re-registration transmission to one or more serving networks (or BTSs) after a lapse in communication activity. Amongst other benefits, this mechanism significantly reduces the amount of signalling traffic on the system's control channel. FIG. 1 shows, in outline, a trunked radio communications system 10 supporting a TErrestrial Trunked RAdio (TETRP,) air-interface in accordance with a preferred 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 sites that are geographically spaced apart - one base site supporting a cell or sectors of a cell. A plurality of subscriber units, such as a mixture of MSs 12-16 and fixed terminals (not shown), communicate over a selected air-interface 18-20 with a plurality of base transceiver stations (BTS) 22-32. The BTSs 22-32 may be connected to a conventional public-switched telephone network (PSTN) 34 through base station controllers (BSCs) 36-40 and mobile switching centres (MSCs) 42-44. Each BTS 22-32 is principally designed to serve its primary cell, with each BTS 22-32 containing one or more transceivers. Each BSC 36-40 may control one or more BTSs 22-32, with BSCs 36-40 generally interconnected through MSCs 42-44. Each BSC 36-40 is therefore able to communicate with one another, if desired, to pass system administration information therebetween, with BSCs responsible for establishing and maintaining control channel and traffic channels to serviceable MSs affiliated therewith. The interconnection of BSCs therefore allows the trunked radio communication system to support handover of the MSs between cells.

Each MSC 42-44 provides a gateway to the PSTN 34, with MSCs interconnected through an operations and management centre (OMC) 46 that administers general control of the trunked radio system 10, as will be understood by those skilled in the art. The various system elements, such as BSCs 36-38 and OMC 46, will include control logic 48-52, with the various system elements usually having associated memory element 54 (shown only in relation to BSC 38 for the sake of clarity). The memory element 54 typically stores historically compiled operational data as well as in-call data, system information and control algorithms. In the context of the present invention, the OMC 46, or one or more of the BSCs 36-40 or MSCs 42-44 maintain a database of "active MSs", namely MSs that are believed to be contactable at any particular time. Furthermore, the OMC 46 broadcasts information relating to the inactivity removal mechanism of each of its cells/BTSs. The broadcast information is contained in a broadcast field, preferably in a broadcast transmission message on a system control channel. The broadcast field identifies the respective inactivity removal mechanism employed in that Location Area, for that particular BTS or system, and may encompass one or more of the following: (i) timer information for each of the systems or Location Areas in one particular system that employ

different time factors for their respective inactivity removal mechanisms; (ii) details of how many unsuccessful pages to a MS will be attempted before a MS is removed from an active- MS database; and/or (iii) timing information related to periods between successive inactivity removal broadcast transmissions. Turning now to FIG. 2, there is shown a block diagram of a MS 100 adapted to support the inventive concepts of the preferred embodiments of the present invention. The MS 100 contains an antenna 102 preferably coupled to a duplex filter or circulator 104 that provides isolation between receive and transmit chains within the MS 100. The receiver chain includes scanning receiver front-end circuitry 106 (effectively providing reception, filtering and intermediate or base-band frequency conversion). The scanning front-end circuit 106 is serially coupled to a signal processing function 108. In accordance with a preferred embodiment of the invention, the receiver chain receives broadcast transmissions from each of its serving BTS, on one or more systems. The signal processing function 108, coupled to a memory function 116 via a controller 114 has been adapted, in accordance with the present invention, to track and identify the inactivity removal mechanism data broadcast from each of its serving BTSs. The memory element stores the inactivity removal mechanism data of

each BTS. Therefore, each MS 100 shall know exactly how and when it will be removed from an "active MS database" on that particular system. With such knowledge the MS will be able to determine whether it should re-register on any particular serving system (BTS), should the MS 100 lose contact with the system for a period of time. It should be noted that the inactivity removal mechanism may well be different for different systems. In addition, it is within the contemplation of the invention that the periods where the inactivity removal mechanism is broadcast within a single system may not be fixed. The timing of such broadcast transmissions could be adaptively controlled dependent upon the system (or site) control channel loading. The controller 114 may calculate receive bit-error-rate (BER) or frame-error-rate (FER) data from recovered information via a received signal strength indication (RSSI) 112 function. The RSSI 112 function is operably coupled to the scanning front-end circuit 106. The memory device 116 also stores a wide array of MS-specific data, such as decoding/encoding functions and the like, as well as system inactivity removal mechanism data associated with each serving BTS/system. A timer 118 is operably coupled to the controller 114 to control the timing of operations (transmission or reception of time-dependent signals) within the MS. In the context of the preferred embodiment of the oresent

invention, timer 118 may include a number of timer functions in order to track the timing of system inactivity broadcast transmissions and periods of time where the MS has lost a communication link with each respective serving BTS or system. As known in the art, an output from the signal processing function is typically provided to a suitable output device 110, such as a speaker or visual display unit (VDU). As regards the transmit chain, this essentially includes an input device 120, such as a transducer or other manmachine interface (e.g. a keypad), coupled in series through transmitter/modulation circuitry 122 and a power amplifier 124. The transmitter/modulation circuitry 122 and the power amplifier 124 are operationally responsive to the controller, with an output from the power amplifier coupled to the duplex filter or circulator 104. In the context of the preferred embodiment of the present invention, the transmitter chain is utilised to implement re-registration procedures, if such is required, under guidance of the signal processing function 108 and controller 114. Of course, the various components within the MS 100 can be realised in discrete or integrated component form, with an ultimate structure therefore being merely an arbitrary selection. Furthermore, a substantially

similar circuit arrangement is found in each of the associated BTSs. In operation, upon power-on of MS 100, the MS 100 will search for all systems on which it expects or desires to operate. Once the systems have been found, using the scanning receiver front-end circuitry 106, the signal processor function 108 will extract the appropriate system inactivity removal mechanism data. Preferably, this scanning operation is performed during an idle mode of operation, namely when the MS 100 listens to the paging channels whilst awaiting service. The memory element (116) will store (or alternatively, if stored information exists, may decide to update if the data is different) respective inactivity removal mechanism data of one or more BTSs or communication systems. The signal processing function 108 will initiate the inactivity time measurement of the timer(s) as soon as a respective system activity is lost. Each time a communication link takes place in a particular network, for example even if only receiving a paging message, the corresponding timer is reset to an appropriate value for that network. When the MS 100 commences service in a particular network, it leaves all other networks for the time period of the service. During this time period, the inactivity

timer(s) continue to increment (or decrement if the timer is set to reduce). Upon service completion, the MS 100 will return to an idle state of operation, restoring links to other networks. At this stage the MS 100 will examine each network to determine whether: first of all the Location Area has changed or secondly, whether the inactivity timer has expired for each particular network (or network's BTS). Whenever appropriate, MS 100 will re-register with these networks. Turning now to FIG. 3, a flow-diagram is shown, in accordance with a preferred embodiment of the invention, In the example shown, it is assumed that the MS is a multi-system TETRA subscriber which can access "k" systems including a TETRA trunked mode (cellular-like) operation, and a TETRA Direct mode of operation. The TETRA Direct mode of operation is assumed to be the "k"th system in the flowchart. The MS is powered on in step 200, and as a consequence camps on the systems/BTS that it is arranged to communicate on, as shown in step 202. During the MS's wake up procedure, the MS extracts inactivity timer information from all of the systems and/or BTSs that it communicates with, as shown in step 204, and initializes the respective timer, or timers, as in step 206. The MS starts in an idle mode on all "k" systems but, for example, generally camped on its preferred TETRA trunked cel''Lular net-work, as shown in step 208. Whilst in an

idle mode it simultaneously monitors the other systems/BTS including both the direct mode channel and the paging channel of the cellular system. If the MS is paged by one of the systems, for example system "k", as shown in step 207, it resets the corresponding timer of this system "k", as in step 216. It is within the contemplation of the invention that such paging mechanisms may include the inactivity removal mechanism data. Further, if this paging was a "call setup", as in step 218, it leaves all other cellular systems to participate in that call. For example, in the preferred embodiment of at least a TETRA trunked and direct mode network, this could be a Direct Mode communication call set-up. The direct mode call set up on the direct mode communication system is initiated, as in step 210, and continues until the call is completed, as shown in step 212. Upon direct mode call completion, the MS returns to its preferred TETRA trunked cellular system and if either location has changed or the MS determines that the system inactivity timer has expired during its direct mode call, in step 213, it will re-register on at least the trunked system, as shown in step 214. The MS then returns to an idle mode of operation until a communication is requested by or with the MS, in any of its "k" serving systems or BTSs.

Turning now to FIG. 4, a timing diagram is shown indicating an example of a broadcast field in accordance with a preferred embodiment of the invention. The timing diagram is an example of the MS operation and shows the timing of an MS monitoring two networks (network "'l" and network "2"). The timing diagram shows a MS initially in an idle mode of operation during timing period 400. During an idle mode of operation, the MS monitors broadcast inactivity mechanism transmissions from network "1", broadcast at a period value "N", and network "2", broadcast at a period value "M" (i.e. asynchronous). Whilst in this idle mode of operation, both networks are paging the MS. Preferably the MS has two separate timer functions, one for each network (T1 and T2). Upon receiving a paging message from network "l"' at time period 402, without the message indicating a call set-up needs to be initiated, timer T1 is preset by the MS. Upon receiving a paging message from network "2" at time period 404, without the message indicating a call set-up needs to be initiated, timer T2 is preset by the MS. When a paging message is received by the MS to initiate a call set-up on network "2", as shown at timing position 406, the MS is forced to abandon monitoring network "l", for the duration of the call 408.

At the end of the call on network "2", indicated by timing position 410, timer Tl of the MS has measured a time T from the last paging of network "l", as shown. if the value of "T" is greater then the broadcast inactivity period of "N" of network "l". then the MS needs to reregister on network "1", as indicated at timing position 412. Otherwise, no re-registration on network "1" is required, provided the location area of the MS has not changed. Clearly, if the location area has changed, a registration on the new serving BTS or system, as compared to a re-registration on the previous system, is effected. It will be understood that the communication system, communication unit and method of registration described above provides at least the following advantages: (i) Network operators can support multi network capable subscribers without a substantial penalty of increasing the amount of re-registration procedures on their system; (ii) A mobile station is now aware of whether it is registered on one or more systems after a period of inactivity and can independently determine whether one or more re-registration procedures is/are required; and (iii) The number of re-registration procedures performed in single-cell or multi-cell systems is reduced. This is particularly the case in layered cells where different

services and/or features are provided in different layers of the cell, e.g. in pico- and micro-cellular systems. Although the invention has been described in general with reference to the TETRA communication specification, utilising a TDMA access protocol, the inventive concepts contained herein are clearly suitable to alternative radio communications system technologies operating similar or alternative access protocols. Clearly only one system needs to be operating the inactivity removal mechanism to fall within the scope of the present invention. If the communication unit initiates a call on an alternative system, whether such a system employs an inactivity removal mechanism or not, the communication unit only needs to measure the time period elapsed whilst on that alternative communication system. The communication unit compares the call (and elapsed time) with the extracted inactivity removal period broadcast on the first system, in order to determine whether the unit needs to re-register on that first system after the call on the alternative system has been completed. It is also within the contemplation of the invention that alternative inactivity removal mechanisms, and associated data, can be accommodated for within the inventive concepts described herein. The invention is therefore not limited to inactivity removal mechanism data comprising solely of timer information for each of the

systems or details of how many unsuccessful pages to a MS will be attempted before a MS is removed from an active- MS database. The inventive concepts described herein will clearly operate with any type of inactivity removal data. Within, at least, the TETRA Standard, the requirement to register or re-register after loss of system coverage, is assumed to be unavoidable. Therefore, it is notable that the inventors of the present invention have recognised the deficiencies in the proposed standard in that the requirement to register or re-register after loss of system coverage, in all cases, may be detrimental to the performance of the communications system. Thus a wireless communication system, a communication unit and method of registration have been provided that addresses the registration and re-registration problems, as previously described in relation to the prior art.

Claims

Claims

1. A wireless communication system having at least one wireless serving communication unit serving a plurality of remote units with a communication resource, the at least one wireless serving communication unit comprising a transmitter for transmitting operational data, the wireless communications system characterised by said transmitter transmitting inactivity removal mechanism data to at least one of the plurality of remote units to facilitate the at least one remote unit determining whether to re-register with at least one wireless serving communication unit after a lapse in communication activity. 2. The wireless communication system according to claim 1, the wireless communication system further characterised by said inactivity removal mechanism data being transmitted in a broadcast field of the communications resource. 3. The wireless communication system according to claim 1 or claim 2, the wireless communication system further characterised by said inactivity removal mechanism data including at least one of the following: at least one timer, a number of unsuccessful pages to remote communications units before the unit is removed from an active database and timing information related to periods between successive inactivity removal broadcast transmissions.

<Desc/Clms Page number 22>

4. A communication unit comprising a receiver operably coupled to a signalling processing function and a memory element, wherein the communication unit is characterised by said receiver receiving inactivity removal mechanism data from at least one wireless serving communications unit, said signalling processing function identifying said inactivity removal mechanism data as being transmitted from said at least one wireless serving communications unit and said memory element storing said inactivity removal mechanism data of said at least one wireless serving communications unit. S. The communication unit in accordance with claim 4, wherein said receiver is a scanning receiver such that upon power-up of the communication unit, said scanning receiver scans transmissions from at least one wireless communication system to receive and extract respective inactivity removal mechanism data of said at least one wireless communication system. 6. The communication unit in accordance with claim 4 or claim 5, wherein the communications unit includes at least one timer operably coupled to said signalling processing function, said timer adapted to measure an elapsed time between receiving inactivity removal mechanism data transmissions from said at least one wireless serving communications unit.

<Desc/Clms Page number 23>

7. The communication unit in accordance with any one of claims 4 to 6, wherein the communications unit is further characterised by a controller, operably coupled to said signalling processor function and said memory element to determine, after said communication unit has completed a communication with said at least one wireless serving communication unit, whether a registration or reregistration procedure needs to be performed with any other of said at least one wireless serving communication unit in response to the measured elapsed time. 8. A broadcast transmission message broadcast from a wireless serving communication unit to at least one of a plurality of communication units on a wireless communication system, said broadcast transmission message including inactivity removal mechanism data. 9. A wireless serving communication unit adapted to transmit the broadcast transmission message of claim 8.

<Desc/Clms Page number 24>

10. A method of registration on a wireless communication system, said method characterised by the steps of: transmitting inactivity removal mechanism data of at least one wireless serving communications unit to at least one of a plurality of remote communications unit that are being served; receiving said inactivity removal mechanism data at said at least one remote communications unit; and determining, at said at least one remote communications unit, whether a registration procedure is required to access or regain access to said communications system. 11. The method of registration on a wireless communication system according to claim 10, wherein the communication unit includes at least one timer and is capable of communicating with a number of wireless communication systems and/or wireless serving communication units, the method further characterised by the step of: extracting inactivity timer information from a number of said wireless communication systems and/or wireless serving communication units; communicating in a call, between said communication unit and one wireless communication system or wireless serving communication units; and resetting at 'east one timer in said communication unit, relating to respective said at least one wireless communication systems and/or wireless serving communication units, once said call has completed.

<Desc/Clms Page number 25>

12. The method of registration on a wireless communication system according to claim 10 or claim 11, the method further characterised by the step of reregistering on at least one wireless communication systems and/or wireless serving communication units in response to said determination that a registration procedure is required. 13. A wireless communication system substantially as hereinbefore described with reference to, and/or as illustrated by, FIG. 1 of the accompanying drawings. 14. A communication unit substantially as hereinbefore described with reference to, and/or as illustrated by, FIG. 2 of the accompanying drawings. 15. A method of registration of a communication unit on a wireless communication system, substantially as hereinbefore described with reference to, and/or as illustrated by, FIG. 3 of the accompanying drawings.