METHOD FOR IMPROVING INTERCELLULAR TRANSFERS IN CELLULAR MOBILE RADIO COMMUNICATION SYSTEMS
The present invention relates generally to mobile radio communication systems.
Generally speaking, mobile radio communication systems are covered by standards, and for more information reference may be made to the corresponding standards published by the corresponding standardization organizations.
The general architecture of such systems is described briefly with reference to figure 1. Such systems include a mobile radio communication network 1 communicating with mobile terminals 2 and with external networks (not specifically shown). The network 1 itself includes a radio access network (RAN) 3, primarily responsible for transmission and radio resource management at the radio interface between the network and the mobile terminals, and a core network (CN) 4, primarily responsible for routing and call management.
Changes in requirements and in technology generally lead to making a distinction between different types of radio access technologies and/or radio access networks. Examples of radio access technologies and/or radio access networks that may be cited include: TDMA (Time Division Multiple Access), W-CDMA (Wideband - Code Division Multiple Access), TD-SCDMA (Time Division - Synchronous Code Division Multiple Access), OFDM (Orthogonal Frequency Division Multiple Access), I-WLAN (Interworking Wireless Local Access Network), GAN (Generic Access Network), LIMA (Unlicensed Mobile Access), etc.
Generally speaking, a distinction may be made between different types of radio access technologies and/or radio access networks according to whether or not they are capable of supporting a plurality of simultaneous services per user, i.e. according to whether or not they are capable of processing a plurality of radio access bearers (RAB) in parallel. Examples of simultaneous services that may be cited include in particular voice services, data services, circuit type services and packet type services.
Examples of systems capable of supporting a plurality of simultaneous sen/ices per user that may be cited include in particular the Universal Mobile Telecommunication System (UMTS).

Examples of systems that are not capable of supporting a plurality of simultaneous services per user that may be cited include the Global System for Mobile communication (GSM) in certain circumstances.
Moreover, in the case of systems such as the GSM/GPRS (Global System for Mobile communication/General Packet Radio Service), it is possible to use additional functions, such as the DIM (Dual Transfer Mode) function in particular, simultaneously supporting circuit services and packet services for the same user. It should be emphasized that the terminal of the user must also support the DIM function for the simultaneity of services to be operational.
Accordingly, generally speaking, in cellular mobile radio communication systems a distinction can be made between cells in which a plurality of simultaneous services per user are supported (corresponding to the situation of cells and terminals supporting appropriate additional functions and/or radio access technologies) and cells in which a plurality of simultaneous sen/ices per user are not supported (corresponding to the situation of cells or terminals not supporting appropriate additional functions and/or radio access technologies).
It must also be remembered that cell changing mechanisms are generally provided in these cellular systems. Of more particular interest hereinafter are intercellular transfer (handover) mechanisms.
Moreover, in systems including cells capable of supporting a plurality of simultaneous services per user and cells not capable of supporting a plurality of simultaneous services per user, intercellular transfers may be provided between the different cell types.
In this context, as the applicant has noticed, problems can arise that for the sake of simplicity may be illustrated by means of an example.
Consider by way of example intersystem handover from a UMTS cell to a GSM/GPRS cell.
It will be remembered that in a GSM/GPRS type system a mobile terminal is called a mobile station (MS), the radio access network (RAN) is made up of subsystems called base station subsystems (BSS) and the core network (CN) includes, in particular, for the circuit switching domain (CS domain), 2G-MSC (2nd Generation Mobile Switching Center) type network elements and, for the packet switching domain (PS domain), 2G-SGSN (2nd

Generation Serving GPRS Support Node) type network elements.
It will be remembered that in a UMTS type system a mobile terminal is called a user equipment (UE), the radio access network (RAN) is called the UMTS terrestrial radio access network (UTRAN), and the core network (CN) includes in particular, for the circuit switching domain (CS domain), 3G-MSC (3rd Generation Mobile Switching Center) type network elements and, for the packet switching domain (CS domain), 3G-SGSN (3rd Generation Serving GPRS Support Node) type network elements.
The principal steps of an intersystem handover, for example from a UMTS cell to a GSM/GPRS cell, are shown in figure 2.
In a step 5, a handover decision is taken by the UTRAN.
The method then includes a set of steps including, among others:
- a step 6 corresponding to the sending by the UTRAN to the CN of a
"Relocation Required" message,
- a step 7 corresponding to the sending by the MSC to the BSS of a
"Handover Request" message,
- a step 8 of deciding to allocate resources, by the BSS, in the target
cell.
It will be remembered that in a system such as the UMTS in particular a relocation procedure is initiated by the sending of a "Relocation Required" message by the radio access network entity responsible for the call (the serving radio network controller (SRNC)) to the appropriate core network (CN) entity, using the RANAP (Radio Access Network Application Part) protocol as defined in the 3GPP Technical Specification TS 25.413.
As illustrated by the step 6 in figure 2, the procedure of sending a "Relocation Required" message is used to initiate the execution of an intersystem handover from the UMTS to another system such as the GSM/GPRS in particular.
It will also be remembered that in a system such as the GSM/GPRS in particular, in the case of "external" handover, i.e. when the original cell and the target cell are not controlled by the same radio access network element, a "Handover Request" message is transmitted from the core network entity (MSC) responsible for the target cell to the radio access network entity (BSS) responsible for the target cell, following the reception by the core network entity responsible for the original cell of a "Handover

Required" message transmitted by the radio access network entity responsible for the original cell, using the BSSMAP (Base Station Subsystem Management Application Part) protocol as defined in the 3GPP Technical Specification TS 48.008.
As indicated by the step 7 in figure 2, the procedure of sending a "Handover Request" message is used to execute an intersystem handover to the GSM/GPRS from another system such as the UMTS following the reception of a "Relocation Required" message as indicated above.
As the applicant has noticed, a new problem arises in this context, which may be stated in the following terms, for example.
If, because of lack of UMTS coverage, for example, handover to a GSM/GPRS cell is decided on by the UTRAN, under the present version of the standard there is no way for the BSS to determine if the user is simultaneously using a plurality of services, for example if the user is engaged in a circuit call and one or more packet sessions or only in a circuit call. In fact, according to the 3GPP Technical Specifications TS 23.009 and TS 25.413, the UTRAN initiates a handover for a circuit connection (CS handover) and if the user is engaged simultaneously in one or more packet sessions the packet session(s) (PS sessions) is or are taken over at the initiative of the mobile terminal in the GSM/GPRS network.
However, if the mobile terminal and/or the BSS do not support the DTM function, the packet session(s) cannot normally be taken over before terminating the circuit call. The packet session(s) can, however, be taken over before terminating the circuit connection if UMTS coverage resumes and a handover to the UMTS is then decided on by the BSS.
However, as indicated above, under the present version of the standard the BSS does not know if the user is engaged only in a circuit call or simultaneously in a circuit call and one or more packet sessions. Consequently, the decision taken by the BSS (for this handover to the UMTS) is not the optimum. For example, if the user is engaged only in a circuit call, it may be preferable for the mobile terminal to remain in the GSM network to minimize the number of handovers. On the other hand, if the user is simultaneously engaged in a circuit call and in one or more packet sessions, it may be preferable to effect a handover to the UMTS to enable the user to resume simultaneously the circuit call and the packet session(s).

In other words, under the present version of the standard the situation of intersystem handover is not dealt with optimally, in particular for the reasons explained above by means of an example, and this results in degraded performance, in particular in terms of quality of service.
As the applicant has also noticed, this type of problem arises for any handover from a first cell in which a plurality of simultaneous services per user is supported to a second cell in which a plurality of simultaneous services per user is not supported.
A particular object of the present invention is to solve some or all of the above problems and/or to avoid some or all of the above drawbacks. More generally, one object of the present invention is to improve performance and quality of service in such systems.
One aspect of the present invention is a method for improving intercellular transfers in cellular mobile radio communication systems, said method including at least one step in which a mobile radio communication network entity sends another mobile radio communication network entity, for an intercellular transfer from a first cell in which a plurality of simultaneous services per user are supported to a second cell in which a plurality of simultaneous services per user are not supported, at least one information item for indicating simultaneity of services.
Another aspect of the present invention is a radio access network entity for a mobile radio communication network, including means for implementing the above kind of method.
A further aspect of the present invention is a core network entity for a mobile radio communication network, including means for implementing the above kind of method.
A further aspect of the invention is a mobile radio communication system including at least one of said mobile radio communication network entities.
Other aspects and features of the present invention will become apparent on reading the following description of embodiments of the invention given with reference to the appended figures, in which:
- figure 1 is intended to outline the general architecture of a cellular
mobile radio communication system,
- figure 2 is intended to show one example of a prior art intersystem

handover method,
- figure 3 is intended to show one example of an intersystem handover method of the invention.
The invention is more particularly described hereinafter, by way of example, in the situation of intersystem handover from a UMTS cell to a GSM/GPRS cell and in the case of simultaneous services corresponding to circuit type services and packet type services. However, as indicated above, the invention is not limited to this kind of example.
One example of a method according to the invention is shown in figure 3. Elements that may be common to figures 2 and 3 have here been denoted by the same reference numbers.
The method shown in figure 3 includes a step 6' which differs from the step 6 of figure 2 in that an information item, for example a "PS session indication" that indicates if the user is engaged only in a circuit call or simultaneously in a circuit call and one or more packet sessions, is sent in the RANAP "Relocation Required" message. This information item is relayed by the core network to the BSS in the BSSMAP "Handover Request" message, as shown in the step 7' in figure 3.
For example, this information item could be contained in an information element (IE) such as the "Old BSS to New BSS information" IE, for example, or any other container for transferring information from the UTRAN to the BSS in a manner that is transparent for the core network. In the case of intersystem handover, the "Old BSS to New BSS information" IE is contained in the "Relocation Required" message as defined in the 3GPP Technical Specification TS 25.413 and in the "Handover Request" message as defined in the 3GPP Technical Specification TS 48.008.
In the step denoted 8' in figure 3, the BSS is then capable of taking a better decision regarding handover to the UMTS if UMTS coverage resumes afterwards.
Another aspect of the present invention is a radio access network entity including means for implementing a method according to the invention. •
A further aspect of the present invention is a core network entity including means for implementing a method according to the invention.
In the case of intersystem handover, for example, from a first cell

corresponding to a UMTS cell to a second cell corresponding to a GSM/GPRS cell, and for the situation of simultaneous services corresponding to circuit type services and packet type services:
- in the UMTS, a UTRAN or radio access network entity, such as in
particular an RNC (Radio Network Controller) type entity, responsible for the
first cell, may include means for sending a core network entity of that system,
such as in particular a 3G-MSC (3rd Generation Mobile Switching Center)
type entity, responsible for the first cell, at least one information item for
indicating if the user is engaged only in a circuit call or simultaneously in a
circuit call and in one or more packet sessions. Such means may in particular
include means for sending this kind of information item in a "Relocation
Required" message as defined in the 3GPP Technical Specification TS 25.413,
in particular in an information element of this kind of message corresponding
to the "Old BSS to New BSS information" IE or any other container for
transferring information from UTRAN to BSS in a manner that it is transparent
for the core network.
For example, in the case of handover from a first cell corresponding to a GSM/GPRS cell adapted to support a plurality of simultaneous services per user to a second cell corresponding to a GSM/GPRS cell, and for the situation of simultaneous services corresponding to circuit type services and packet type services:
- in the GSM/GPRS system, a BSS or radio access network entity, such
as in particular a BSC (Base Station Controller) type entity, responsible for the
first cell, may include means for sending a core network entity of this system,
such as in particular a 2G-MSC (2nd Generation Mobile Switching Center)
type entity, at least one information item for indicating if the user is engaged
only in a circuit call or simultaneously in a circuit call and in one or more
packet sessions. Such means may in particular include means for sending
this kind of information item in a "Handover Required" message as defined in
the 3GPP Technical Specification TS 48.008, in particular in an information
element of this kind of message corresponding to the "Old BSS to New BSS
information" IE.
For example, in the case of handover from a first cell that may correspond to a UMTS cell or to a GSM/GPRS cell adapted to support a plurality of simultaneous services per user to a second cell corresponding to

a GSM/GPRS cell and for the situation of simultaneous services corresponding to circuit type services and packet type services:
- in the GSM/GPRS system, a core network entity, such as in
particular a 2G-MSC (2nd Generation Mobile Switching Center) type entity,
responsible for the second cell, may include, in particular, means for sending
a BSS or radio access network entity, such as in particular a BSC (Base Station
Controller) type entity, responsible for the second cell, at least one
information item for indicating if the user is engaged only in a circuit call or
simultaneously in a circuit call and in one or more packet sessions. Such
means may in particular include means for sending such information in a
"Handover Request" message, in particular in an information element of this
kind of message corresponding to the "Old BSS to New BSS information " IE or
any other container for transferring information from UTRAN to BSS in a
manner that is transparent for the core network.
For example, in the case of handover from a first cell that may correspond to a UMTS cell or to a GSM/GPRS cell adapted to support a plurality of simultaneous services per user to a second cell corresponding to a GSM/GPRS cell and for the situation of simultaneous services corresponding to circuit type services and to packet type services:
- in the GSM/GPRS system, a BSS or radio access network entity, such
as in particular a BSC (Base Station Controller) type entity, responsible for the
second cell, may include means for processing at least one information item
received from a core network entity such as in particular a 2G - 2nd
Generation Mobile Switching Center) type entity, responsible for the second
cell, and for indicating if the user is engaged only in a circuit call or
simultaneously in a circuit call and in ones or more packet sessions, to decide
afterwards on possible handover to a cell adapted to support a plurality of
simultaneous services per user.
The particular implementation of such means presenting no particular difficulty to the person skilled in the art, such means need not be described here in more detail than by their function, as above.

CLAIMS
1. Method for improving intercellular transfers in cellular mobile radio
communication systems, said method including at least one step in
which a mobile radio communication network entity sends another
mobile radio communication network entity, for an intercellular transfer
from a first cell in which a plurality of simultaneous services per user are
supported to a second cell in which a plurality of simultaneous services
per user are not supported, at least one information item for indicating
simultaneity of services.
2. Method according to claim 1, including, in the case of a first cell of UMTS
type, respectively of GSM/GPRS type supporting a plurality of
simultaneous services per user, at least one step in which a radio access
network entity responsible for the first cell sends a core network entity
responsible for the first cell, in a "Relocation Required" type message as
defined in the; RANAP protocol, respectively a "Handover Required" type
message as defined in the BSSMAP protocol, an information element
containing an information item for indicating simultaneity of services.
3. Method according to claim 2, wherein said information element
corresponds to the "Old BSS to new BSS information" IE or to any other
container for transferring information from UTRAN to BSS in a manner that
is transparent for the core network.
4. Method according to claim 1, including, in the case of a second cell of
GSM type, at least one step in which a core network entity responsible
for the second cell sends a radio access network entity responsible for
the second cell, in a "Handover Request" type message as defined in the
BSSMAP protocol, an information element containing an information
item for indicating simultaneity of services.
5. Method according to claim 4, wherein said information element
corresponds to the "Old BSS to new BSS information" IE.
6. Method according to any one of claims 1 to 5, wherein said information
item for indicating simultaneity of services is used, in a radio access
network entity responsible for the second cell, for deciding afterwards on
a possible transfer to a cell supporting a plurality of simultaneous services
per user.
7. Radio access network entity for a mobile radio communication network,
including means for implementing a method according to any one of

claims 1 to 6.
8. Mobile radio communication network radio access network entity
including means for sending a core network entity, for an intercellular
transfer from a first cell capable of supporting a plurality of simultaneous
services per user to a second cell not capable of supporting a plurality
of simultaneous services per user, at least one information item for
indicating simultaneity of services.
9. Radio access network entity according to claim 8, including means for
sending a core network entity, in a "Relocation Required" type message
as defined in the RANAP protocol, respectively a "Handover Required"
type message as defined in the BSSMAP protocol, at least one
information item for indicating simultaneity of services.
10. Entity according to claim 9, wherein said information item is sent in an
information element corresponding to the "Old BSS to new BSS
information" IE or any other container for transferring information from
UTRAN to BSS in a manner that is transparent for the core network.
11. Core network entity for a mobile radio communication network,
including means for implementing a method according to any one of
claims 1 to 6.
12. Mobile radio communication network core network entity including
means for sending a radio access network entity, for an intercellular
transfer from a first cell capable of supporting a plurality of simultaneous
services per user to a second cell not capable of supporting a plurality
of simultaneous services per user, at least one information item for
indicating simultaneity of services.
13. Entity according to claim 12, including means for sending a radio access
network entity, in a "Handover Request" type message as defined in the
BSSMAP protocol, at least one information item for indicating
simultaneity of services.
14. Entity according to claim 13, wherein said information item is transmitted
in an information element corresponding to the "Old BSS to new BSS
information" IE or any other container for transferring information from
UTRAN to BSS in a manner that is transparent for the core network.
15. Mobile radio communication network radio access network entity
including means for processing at least one information item for
indicating simultaneity of services received from a core network entity,

for an intercellular transfer from a first cell capable of supporting a plurality of simultaneous services per user to a second cell not capable of supporting a plurality of simultaneous services per user, to decide afterwards on possible intercellular transfer to a cell able to support a plurality of simultaneous services per user.
16. Mobile radio communication system including at least one mobile radio communication network entity according to any one of claims 7 to 15.