FR2860383A1 - Improved cellular mobile telephone system inter cellular transfer method having transfer execution request adapted indicating whether service transfer - Google Patents

Abstract

The inter cellular mobile telephone transfer system has transmission to another mobile radio communications network, and having a request for execution of the intercellular transfer. The request is adapted to indicate if the intercellular transfer is requested for service reasons.

Description

METHOD FOR IMPROVING INTER-CELL TRANSFERS IN

  CELLULAR MOBILE RADIOCOMMUNICATION SYSTEMS

  The present invention generally relates to mobile radio systems.

  In general, mobile radio systems are subject to standardization, and for more information reference can be made to the corresponding standards issued by the corresponding standardization bodies.

  The general architecture of a mobile radio system is briefly recalled in connection with FIG. 1. The system comprises a mobile radio network 1 communicating with mobile terminals 2 and with external networks (not specifically illustrated). The mobile radio network 1 itself comprises a radio access network 3 (or Radio Access Network) mainly responsible for the transmission and management of radio resources on the radio interface between the network and the mobile terminals, and a Core Network 4 (or Core Network) primarily responsible for routing and communications management.

  Changes in needs and technologies generally lead to distinguishing different types of systems, including second generation systems and third generation systems.

  A typical example of a second-generation system is Global System for Mobile Communication (GSM), which uses FDMA / TDMA (Frequency Division Multiple Access) radio access technology. In a GSM type system, the mobile terminal is called MS (Mobile Station) and the radio access network is also called BSS (Base Station Subsystem).

  A typical third-generation system is the Universal Mobile Telecommunication System (UMTS), using W-CDMA (Wideband - Code Division Multiple Access) radio access technology. In a UMTS type system, the mobile terminal is called UE (User Equipment), and the radio access network is also called UMTS Terrestrial Radio Access Network (UTRAN).

  It will be recalled that, in general, in these systems, cell change mechanisms are provided. In the following, we focus more particularly on the mechanisms of handover or handover. In general, the handover process is broken down into two stages: a preparation step (during which it is decided whether a cell change is possible and desirable, according to different criteria or causes, and if so to which cell , or target cell, it should be done and during which the network and radio resources necessary to ensure continuity of communication are reserved) and an execution step (or switching to the selected target cell). A handover decision is generally made by the network, generally on the basis of results of radio measurements reported to the network by the mobile terminal, and of any other criterion such as in particular the traffic load. Handover execution is the switching of mobile and network resources to the target cell.

  From a system architecture point of view, we can distinguish different types of handovers, depending on whether the initial cell and the target cell use the same radio access technology or not. The initial cell and target cell case using different radio access technologies is also called inter-system handover, or inter-RAT (for inter-radio access technology).

  At least in their initial phase of deployment, third-generation networks will rely on existing second-generation infrastructures. In other words, second-generation cells (in particular GSM) will be able to coexist with third-generation cells (in particular UMTS). This allows, especially for services supported jointly by these two generations, such as telephony-like services, to extend the radio coverage of a third-generation network, while benefiting from the existing radio coverage provided by a network of second generation.

  An inter-system handover may then be necessary for reasons of lack of radio coverage, in order to avoid loss of calls, which would be very badly perceived by the users.

  Inter-system handover may also be desired for other reasons, especially for service reasons, for example, from the operators' point of view, so that connections for telephony type services are preferably established via GSM cells, in order to free the resources available in the UMTS cells, for services available only in these cells.

  Figure 2 shows the main steps of an inter-system handover for service-based handover, as an example of UMTS to GSM, in the current state of the standard represented in particular, for the UMTS system, by the specification 3GPP TS 25.413 relating to the RANAP protocol (Radio Access Network Application Part) on the interface read between UTRAN and core network (noted CN) and, for the GSM system, the specification 3GPP TS 48.008 relating to the BSSMAP protocol (BSS Management Application Part) on the interface A between BSS and core network (noted MSC, for Mobile Switching Center).

  It is recalled that the service-based handover concept from UMTS to GSM is defined in 3GPP specification TS 25.413. The GSM-UMTS servicebased handover concept is defined in 3GPP TS 08.08.

  As illustrated in 5, it is considered that a set of procedures is in progress, in a UMTS cell, between UE / MS, UTRAN and CN (where UE / MS designates a dual-mode mobile terminal UMTS / GSM), including in particular a Radio Access Bearer (RAB) procedure, this procedure allocates resources for a connection between UE / MS and CN, taking into account the required service.

  In a step 6, CN sends the UTRAN a request to set up RAB in an RAB Assignment Request message. According to the specification 3GPP TS 25.413, this message may include an information element, or IE (Information Element) called Service Handover. If this IE Service handover is included, it indicates whether the RAB should or should not be transferred, as soon as possible, to the GSM, from the point of view of the NAS (Non Access Stratum) protocol, in charge of all aspects related to the services. In other words, the IE Service Handover in the RAB Assignment Request message indicates whether an inter-system handover is desired for service reasons.

  In a step 7, a handover decision is made by the UTRAN. The final decision is indeed made by UTRAN who can decide either not to initiate handover, or to initiate a handover during the signaling phase relating to the establishment of the connection (this type of handover is also called 2860383 4 directed retry) to initiate a handover as soon as the RAB is established. In the example illustrated, it is considered that the final decision taken by UTRAN is to initiate such a handover to GSM.

  The method then comprises a set of steps corresponding to the execution of this handover, these steps including, among others: a step 8 corresponding to the sending by the UTRAN to CN of a message Relocation Required, - a step 9 corresponding to the sending by the MSC to the BSS of a Handover Request message, - a step 10 decision of allocation of resources, by the BSS, in the target cell.

  It is recalled that in a third generation system such as in particular UMTS, a relocation may be required, in particular for the following reasons.

  Systems such as UMTS use the technique known as macro-diversity transmission (or else sort-handover), in which a UE is connected simultaneously to several Node B (or base stations), that is to say is served simultaneously by several waiter cells. The different Nodes B to which a UE is connected may or may not be controlled by the same RNC (Radio Network Controller) If they are controlled by different RNCs, one of these RNCs has an SRNC (Serving RNC) role, and the Node B connected to the EU and not controlled by the SRNC communicate with the SRNC via the RNCs that control them, also called DRNC (Drift RNC) .With the displacements of the EU, the role of SRNC may have to be transferred to a another RNC, this is achieved by means of a relocation procedure.

  The relocation procedure is initiated by the sending by the radio access network entity corresponding to the initial SRNC (i.e., before relocation) to the appropriate core network entity of a Relocation Required message. .

  As recalled by way of step 8 of FIG. 2, the procedure for sending a Relocation Required message is also used to initiate the execution of an inter-system handover, from UMTS to another system such as in particular GSM.

  It is also recalled that in a second generation system such as in particular GSM, in the case of external handover, that is to say such that the initial cell and the target cell are not controlled by the same element of the network. radio access, a Handover Request message is transmitted from the core network entity in charge of the target cell to the radio access network entity in charge of the target cell, following the reception by the entity core network manager in charge of the initial cell of a Handover Required message transmitted by the radio access network entity in charge of the initial cell.

  As recalled by means of step 9 of FIG. 2, the procedure for sending such a message Handover Request is also used for the execution of an inter-system handover towards the GSM, from another system such as UMTS, following receipt of a Relocation Request message as recalled earlier.

  The RANAP Relocation Required message transmitted in step 8 contains, according to 3GPP specification TS 25.413, an IE called Cause Value.

  The Cause Cause Value included in the RANAP Relocation Required message is relayed by the core network to the BSS in the BSSMAP Handover Request message defined in the 3GPP TS 48.008 specification.

  However, as the Applicant has observed, in the current state of the standard, there is no cause value indicating whether it is a handover for service reasons (or service). -based handover). The BSS can not then distinguish between a desirable handover for service reasons, and in particular, an emergency handover or loss of radio coverage needed to avoid loss of call. This can result in congestion in the BSS, due to an excess of handovers from UMTS to GSM for service reasons, which makes it impossible for the BSS to accept emergency handovers or loss of radio coverage. . It can then result in a loss of calls, which will be very poorly perceived by users. Calls whose handovers for service reasons have been rejected are not lost but continue to be served by the UTRAN.

  In other words, in the current state of the standard, the case of inter-system handover is not treated optimally, in relation to the concept of handover for service reasons (or service-based handover) , and results in performance degradation, especially in terms of quality of service.

  As the applicant has also observed, similar problems may arise, at least for certain services, in the case of inter-system handover from GSM to UMTS.

  As the applicant has also observed, similar problems may also arise for any radio access technology, other than the GSM and UMTS technologies considered above by way of example, for example another access technology. third generation radio such as radio access technology used in CDMA 2000 type systems; similar problems can arise for example in the case of inter-system handover between GSM and CDMA 2000, or between UMTS and CDMA 2000.

  As the applicant has also observed, similar problems may also arise in the case of handover infra-system (for example an inter-RNC handover, from UMTS to UMTS), in a system in which the services may not be uniform in all cells, even if these cells use the same radio access technology, in case an intra-system handover for service reasons is also defined.

  The present invention is intended in particular to solve all or part of these problems, and / or to avoid all or part of these disadvantages. More generally, it is an object of the present invention to improve the performance and quality of service in these systems.

  One of the objects of the present invention is a method as defined in the claims.

  Another object of the present invention is a radio access network entity for a mobile radio network, comprising means for carrying out such a method.

  Another object of the present invention is a core network entity for a mobile radio network, comprising means for implementing such a method.

  Another object of the present invention is a mobile radio system comprising at least one such mobile radio network entity.

  Other objects and features of the present invention will appear on reading the following description of exemplary embodiments, with reference to the appended figures in which: FIG. 1 is intended to recall the general architecture of a Mobile radio cellular system, FIG. 2 is intended to illustrate an example of an inter-system handover method according to the prior art, FIG. 3 is intended to illustrate an example of an intersystem handover method according to the invention.

  The invention will be more particularly described in the following, by way of example, for the case of inter-system handover UMTS to GSM. However, as indicated above, the invention is not limited to such an example.

  As previously explained, in the current state of the standard, there is no cause value that indicates, in the RANAP Relocation Required and BSSMAP Handover Request messages, whether it is a required handover for service reasons. Thus, the BSS can not distinguish between a handover desirable for service reasons, and, in particular, an emergency handover necessary to avoid loss of call. This can result in congestion in the BSS due to excessive handovers from UMTS to GSM for service reasons, which makes it impossible for the BSS to accept emergency handovers. This can result in a loss of calls, which will be very poorly perceived by users.

  It would therefore be useful to make such a distinction because it would then be possible to perform different admission controls with different thresholds for these different kinds of handover, in particular to reserve resources for the case of emergency handover or for lack of radio coverage, rejecting an excess of handovers for service reasons. In other words, this would avoid possible congestion in the BSS, due to excessive handovers for service reasons.

  The invention suggests, in particular, to provide for the IE Cause Value in the RANP Relocation Required message, a specific cause value corresponding to the handover case for service-based handover reasons, this cause being noteworthy. handover service, or any equivalent rating. This cause value can then be relayed by the core network to the BSS in the BSSMAP Handover Request message.

  An example of a method according to the invention is illustrated in FIG. 3. Elements that may be common to FIGS. 2 and 3 have in this case been noted with the same references.

  The method illustrated in FIG. 3 comprises a step 8 'which differs from step 8 of FIG. 2 in that the value of VIE Cause Value in the RANAP Relocation Required message corresponds to the service handover cause. This value is relayed by the core network to the BSS in the BSSMAP Handover Request message, as illustrated in step 9 'of FIG.

  In the step noted 10 'in Figure 3, the BSS is then able to distinguish between handovers for service reasons and other handovers, and can for example perform different admission checks with different thresholds. This can be used to reserve resources for certain handovers, including rejecting certain handovers for service reasons and accepting emergency handovers or lack of radio coverage. Calls for which service handouts have been rejected are not lost but continue to be served by UTRAN.

  As indicated above, the present invention is also applicable to the case of inter-system handover from GSM to UMTS. However, in this case, unlike the case of inter-system handover from UMTS to GSM, if the required service can not be supported by the GSM, or even maintained with a lower quality of service, then the call may be lost.

  Recall that the service-based handover concept from GSM to UMTS is defined in 3GPP specification TS 48.008.

  For the service-based handover case from GSM to UMTS, an example of a method would be of the same type as that illustrated in FIG. 3, replacing: the RAB Assignment Request message transmitted from CN to UTRAN by an Assignment Request message transmitted from MSC to BSS, the Relocation Required message transmitted from UTRAN to CN by a Handover Required message transmitted from BSS to MSC, the Handover Request message transmitted from MSC to BSS by a Relocation Request message transmitted from CN to UTRAN.

  The present invention also relates to a radio access network entity for a mobile radio network, comprising means for implementing a method according to the invention.

  The present invention also relates to a core network entity 5 for mobile radio network, comprising means for implementing a method according to the invention.

  For example, in the case of inter-system handover, from UMTS to GSM: in the UMTS system, a radio access network or UTRAN entity, such as in particular an RNC (Radio Network Controller) type entity, comprises means for transmit to a core network entity of this system, such as in particular a 3G-MSC type entity (3d Generation Mobile Switching Center), with a request relating to the execution of a handover, at least one information capable of indicating whether handover is required for service reasons; such means may in particular comprise means for transmitting, in a Relocation Required message, an IE Cause Value having a cause value specific to the inter-system handover case for service reasons, - in the GSM system, a network entity core, such as in particular a 2G-MSC type entity (2 "d Generation - Mobile Switching Center) can include, in particular, means for transmitting to a radio access network entity or BSS, such as including a type entity BSC (Base Station Controller), with a request relating to the execution of a handover, at least one information capable of indicating whether the handover is required for reasons of service, such means may include means for transmitting, in particular a Handover Request message, an IE Cause Value having a cause value specific to the inter-system handover for service reasons.

  For example, in the case of inter-system handover, from UMTS to GSM: in the GSM system, a radio access network or BSS entity, such as in particular a BSC (Base Station Controller) type entity, comprises means to use said information able to indicate whether the handover is required for service reasons, to distinguish between handovers for service reasons and handovers for other reasons, so as to optimize the management of radio resources in the target cell ; such means may in particular comprise means for implementing different admission controls with different thresholds for handovers for reasons of service and for handovers for other reasons.

  Since the particular embodiment of such means does not present any particular difficulty for a person skilled in the art, such means do not need to be described here in more detail than what has been done previously, by their function.

2860383 11

Claims (12)

  A method for improving inter-cellular transfers in cellular mobile radio systems, the method comprising at least one step in which a mobile radio network entity transmits to another mobile radio network entity, with a request relating to the executing a handover, at least one information capable of indicating whether said handover is required for service reasons.   2. Method according to claim 1 wherein said intercellular transfer corresponds to an inter-system intercell transfer.   3. Method according to one of claims 1 or 2, comprising, for an inter-system handoff, a first system using a third generation radio access technology to a second system using another radio access technology at least one step in which a radio access network entity of the first system transmits to a core network entity of the first system, with a relocation / handover request, at least one information capable of indicating whether said handover is required for service reasons.   4. Method according to claim 3, comprising, for an inter-system handoff, a first UMTS type system to a second GSM type system, at least one step in which a radio access network entity of the first system transmits to a core network entity of the first system, in a Relocation Required message, an information item corresponding to a cause value, said cause value having a specific value for the handover case for reasons of service.   5. Method according to one of claims 1 to 4, comprising, for an inter-system handover, to a second system using a second generation radio access technology from a first system using another technology of radio access, at least one step in which a core network entity of the second system transmits to a radio access network entity of the second system, with an inter-cellular transfer request, at least one information capable of indicating whether said transfer Intercellular is required for service reasons.   6. The method as claimed in claim 5, comprising, for an inter-system handoff, a first UMTS type system to a second GSM type system, at least one step in which a core network entity of the second system transmits to a radio access network entity of the second system, in a Handover Request message, an information element corresponding to a cause value, said cause value having a specific value for the handover case for reasons of service.   7. The method of claim 1 wherein said intercellular transfer corresponds to an intrasystem transfer.   8. Method according to one of claims 1 to 7, wherein said information capable of indicating whether the handover is required for service reasons is used in a radio access network entity in charge of the target cell, to distinguish between handoffs for service reasons and handoffs for other reasons, so as to optimize the management of radio resources in the target cell.   9. The method of claim 8, wherein said information able to indicate whether the handover is required for service reasons is used to implement different admission controls with different thresholds for intercellular transfers for service reasons and for intercellular transfers for other reasons.   10. Radio access network entity for a mobile radio network, comprising means for implementing a method according to one of claims 1 to 9.   11. Heart network entity for a mobile radiocommunications network, comprising means for implementing a method according to one of claims 1 to 9.   Mobile radio system, comprising at least one mobile radio network entity according to one of claims 10 or 11.