(12) United States Patent
`Faerber et al.
`
`(10) Patent N0.:
`
`(45) Date of Patent:
`
`US 6,944,453 B2
`Sep. 13,2005
`
`US006944453B2
`
`5,978,679 A * 11/1999 Agre ........................ .. 455/442
`6,377,804 B1 *
`4/2002 Lintulampi
`455/435.2
`. . . . .
`6,850,540 B1 *
`2/2005 Peisa et al.
`. . . .. 370/468
`2001/0022782 A1 *
`9/2001 Steudle . . . . . . .
`. . . . .. 370/335
`2001/0043576 A1 * 11/2001 Terry . . . . . . .
`. . . . .. 370/328
`2002/0085531 A1 *
`7/2002 Hermann et al.
`370/338
`..
`2002/0136181 A1 *
`9/2002 Belaiche et al.
`.......... .. 370/337
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`WO
`
`98/59513
`
`12/1998
`
`OTHER PUBLICATIONS
`
`3rd Generation Partnership Project; Technical Specification
`Group Radio Access network; Multiplexing and channel
`coding (TDD) 3G TS 25.212 Version 3.1.0, Dec. 1999.
`3rd Generation Partnership Project; Technical Specification
`Group Radio Access network; Multiplexing and channel
`coding (FDD) 3G TS 25.222, Version 3.1.0, Dec. 1999.
`Universal Mobile Telecommunications System (UMTS);
`RRC Protocol Specification (3G TS 25.331 Version 3.1.0
`(ETSI TS 125 331 v3.1.0), Jan. 2000.
`
`* cited by examiner
`
`Primary Examiner—Joseph Mancuso
`Assistant Examiner—Ariel Balaoing
`(74) Attorney, Agent, or Firm—Staas & Halsey LLP
`
`(57)
`
`ABSTRACT
`
`According to the invention, a reduced set of transport format
`combinations is signalled to a subscriber station which has
`established a link to a second radio communication system
`in a second signalling channel of said second radio com-
`munication system. The transport format indicator is then
`selected from the reduced set of transport format combina-
`tions and used to initiate a link transfer to the first signalling
`channel of a first radio communication system. A full set of
`transport format combinations is subsequently signalled to
`the subscriber station in the first signalling channel.
`
`(54) METHOD FOR CONTROLLING AN
`INTERSYSTEM LINK TRANSFER
`
`(75)
`
`Inventors: Michael Faerber, Wolfratshausen (DE);
`Kenneth Isaacs, Dorset (GB); David
`Wynne Thomas, GB-Hampshire (GB);
`Jean-Michel Traynard, Miinchen (DE)
`
`(73) Assignee: Siemens Aktiengesellschaft, Munich
`(DE)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 473 days.
`
`(21) Appl. No.:
`
`10/220,860
`
`(22) PCT Filed:
`
`Mar. 6, 2001
`
`(86) PCT No.:
`
`PCT/EP01/02508
`
`§ 371 (C)(1),
`(2), (4) Date: Oct. 22, 2002
`
`(87) PCT Pub. No.: W001/67795
`
`PCT Pub. Date: Scp. 13, 2001
`
`(65)
`
`Prior Publication Data
`
`US 2003/0153313 A1 Aug. 14, 2003
`
`(30)
`
`Foreign Application Priority Data
`
`Mar. 6, 2000
`
`(EP) .......................................... .. 00301815
`
`Int. Cl.7 ................................................ .. H04Q 7/20
`(51)
`(52) U.S. Cl.
`...................................... .. 455/436; 370/335
`(58) Field of Search ............................... .. 455/436, 443;
`370/335
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,878,349 A
`
`3/1999 Dufour et al.
`
`............ .. 455/438
`
`7 Claims, 1 Drawing Sheet
`
`APPLE 1012
`
`APPLE 1012
`
`1
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`

`
`U.S. Patent
`
`Sep. 13,2005
`
`US 6,944,453 B2
`
`855
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`_‘OE
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`2
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`

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`US 6,944,453 B2
`
`1
`METHOD FOR CONTROLLING AN
`INTERSYSTEM LINK TRANSFER
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`This application is based on and hereby claims priority to
`European Application No. 00301815 .7 filed on Mar. 6, 2000,
`the contents of which are hereby incorporated by reference.
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The invention relates to a method for the control of an
`intersystem handover, in particular the handover between a
`GSM- and a UMTS mobile radio system.
`2. Description of the Related Art
`Reference is made to the UMTS standardization docu-
`
`ments 3GPP: 3G TS 25.212 V3.1.1, 1999-12, Multiplexing
`and channel coding (FDD), 3GPP: 3G TS 25.222 V3.1.1,
`1999-12, Multiplexing and channel coding (TDD), and
`3GPP: 3G TS 25.331 V3.1.0, 2000-01, RRC Protocol Speci-
`fication as the state of the art for the UMTS mobile radio
`
`system. For descriptions of the mobile radio system of the
`second generation GSM,
`the book by J. Biala, “Mobile
`Radio and Intelligent Networks”, Vieweg Verlag, is taken as
`a basis for the general state of the art.
`In radio communication systems, for example the Euro-
`pean mobile radio system of the second generation GSM
`(Global System for Mobile Communications), information
`such as speech, image information or other data are trans-
`mitted by electromagnetic waves over a radio interface. At
`the radio interface, one or more connections are set up
`between a base station and plural subscriber stations; the
`subscriber stations can be, for example, mobile stations or
`stationary radio stations. The radiation of the electromag-
`netic waves takes place at carrier frequencies which are
`situated in a frequency band provided for the respective
`system. For
`future radio communication systems, for
`example, the UMTS (Universal Mobile Telecommunication
`System) or other systems of the third generation, frequencies
`in the frequency band of about 2,000 MHz are provided. For
`the third mobile radio generation UMTS, two modes are
`provided, one mode being termed a FDD (Frequency Divi-
`sion Duplex) operation and the other mode being termed a
`TDD operation (Time Division Duplex) operation. These
`modes find their application in different frequency bands;
`both modes support a so-called CDMA (Code Division
`Multiple Access) subscriber separation method.
`Based on a parallel existence and a desired harmonization
`between the radio communication systems of the second and
`third generation, subscriber stations which have set up a
`connection in a radio communication system are to be given
`the possibility of handing the connection over to a further
`radio communication system, which as the case may be
`supports another transmission mode. Such an intersystem
`handover assumes, besides a synchronization of the sub-
`scriber station with the radio communication system which
`is to take over the connection, the knowledge of the transport
`format used. Here, according to the referenced state of the
`art of base stations of the UMTS mobile radio system, a
`subscriber station signals, during a connection setup, a
`so-called set of transport format combinations TFCS
`(Transport Format Combination Set). With a change of the
`transport format used at
`the time, a so-called Transport
`Format Combination Identifier TFCI is subsequently sig-
`naled to the subscriber station, and states which transport
`format is used out of the set of possible transport format
`combinations.
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`The signaling of the set of transport format combinations
`TFCS would have a length of up to 200 8-bit bytes,
`depending on the number of possible TFCIs in a known
`GSM signaling channel. This length is very disadvantageous
`because of the only limited capacity available on the usable
`GSM signal channels.
`SUMMARY OF THE INVENTION
`
`The invention has as its object to propose a method or
`respectively a communication system station which makes
`possible a small loading of the signaling channel of at least
`one of the systems during the signaling of an intersystem
`handover.
`
`According to the invention, the set of transport format
`combinations is reduced, and in the reduced form is used for
`transmission to a subscriber station on a signaling channel,
`for example, a GSM mobile radio system. In order to be able
`to work with data of the reduced data set, the subscriber
`stations and corresponding network stations suitable for this
`method have a memory region with corresponding data.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`These and other objects and advantages of the present
`invention will become more apparent and more readily
`appreciated from the following description of the preferred
`embodiments, taken in conjunction with the accompanying
`drawings of which:
`FIG. 1 is a block circuit diagram of two neighboring radio
`communication systems, a subscriber station being situated
`in their overlapping radio cells.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`Reference will now be made in detail to the preferred
`embodiments of the present invention, examples of which
`are illustrated in the accompanying drawings, wherein like
`reference numerals refer to like elements throughout.
`According to the invention, two exemplary cases of a
`handover can be distinguished for a subscriber station in the
`region of two radio systems. It is assumed below that the
`handover is from a GSM to a UMTS mobile radio system,
`the implementation in the reverse direction also being pos-
`sible in principle.
`According to a first case, during a connection setup
`procedure in a GSM mode, a service is requested by the
`subscriber station which cannot be made available by the
`GSM system or by a GSM transmission channel (so-called
`bearer). In this case, the necessity exists for a service-based
`connection handover from the GSM- to the UMTS mobile
`
`radio system.
`In this phase, only a first signaling channel SDCCH
`(Stand-Alone Dedicated Control Channel) is set up as an
`independent, fixedly allocatable control channel. The trans-
`mission capacity of the SDCCH however appears insuffi-
`cient for the transmission of the whole of the TFCS
`
`information, which in the present example can amount to up
`to 200 8-bit bytes. In this phase, however, no service is set
`up. The problem is therefore solved according to the inven-
`tion in that the handover is limited to a signaling channel. in
`the simplest form of the method,
`for example, only a
`transport format indicator TFCI is used for the handover to
`the UMTS system over the GSM signaling channel GSM-
`SDCCH. Here an a priori knowledge of the transport format
`indicator TFCI to be used must be present.
`After a successful handover to a UMTS signaling
`channel, the negotiation over the service to be used can be
`
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`

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`US 6,944,453 B2
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`3
`concluded within the UMTS system, the transport format
`indicator TFCI being signaled to the subscriber station from
`the then completely available set of transport format com-
`binations TFCS for the traffic channel within a so-called
`UMTS radio bearer configuration information.
`In order to make greater flexibility possible, a set of
`UMTS signaling channels can be defined. This enables
`access to the network by reduced signaling on these signal-
`ing channels. In an exemplary set of 32 TFCI, the reduced
`signaling can be transmitted, for example, by a simple
`bitmap coding of 5 bits within a signaling channel SDCCH.
`In a second exemplary case, a stabilized connection to the
`GSM mobile radio system already exists, and the setup of a
`further service is requested which can only be made avail-
`able by the UMTS system. The standardization of the UMTS
`system at the present time, Release 99, assumes solely the
`possibility of setting up a switched service (CS—Circuit
`Switched). Nevertheless this leads to an enlarged possibility
`of combination.
`
`If it is assumed, as described, that the detailed TFCI or
`TFCS processing takes place within the UMTS system, then
`at least a combination of a signaling channel and a CS
`service is possible.
`The advantage of the present state of the art according to
`Release 99 is that a handover of transmission channels with
`
`plural services and different qualities of service can be
`ignored on a GSM transmission channel;
`the concept of
`signaling by reduced data sets or counting of indicators can
`be expanded in the same manner to such procedures.
`Because of this, a complete flexibility in the TFCI coding
`within the signaling phase can be dispensed with.
`If for example 64 to 128 combination possibilities are
`assumed between a required CS transmission channel and a
`signaling channel, the TFCI coding can be reduced to this
`required volume. The selection is limited to a predefined list
`of possible TFCI, which represent the respectively possible
`combinations, instead of to the complete set of possible
`TFCI. A coding of the combination possibilities can take
`place, as in the case first considered, by a bitmap coding of,
`for example, 7 bits.
`Summarizing, the concept embraces a substitution of the
`complete TFCS signaling by a reduced set of combinations,
`which is known in both the subscriber station and the
`network. The reduced signaling makes possible a first han-
`dover to a UMTS signaling and data channel, or to a UMTS
`signaling channel, which is subsequently used for passing on
`the connection setup or service setup, making use of the then
`completely available flexibility of the TFCI coding.
`FIG. 1 shows, as a version of the first embodiment of the
`embodiment example, respective sections of two mobile
`radio systems RS1, RS2 as an example of radio communi-
`cation systems, e.g., a GSM and a UMTS mobile radio
`system. A mobile radio system typically has numerous
`mobile switching centers MSC or UMSC (Mobile Switching
`Center or UMTS Mobile Switching Center), which belong
`to a switching network SSS (Switching SubSystem) and are
`networked together or produce the access to a fixed network,
`and of respectively one or more base station systems BSS
`(Base Station Subsystem) connected to these mobile switch-
`ing centers MSC, UMSC. A base station system BSS fi1r-
`thermore has at least one BSC (Base Station Controller) or
`RNC (Radio Network Controller) device for the allocation
`of radio-technical resources, and also at
`least one base
`station BTS (Base Transceiver Station) or NB (node B),
`respectively connected thereto.
`Abase station BTS, NB can set up, over a radio interface,
`connections to subscriber stations UE (User Equipment),
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`such as for example mobile stations or other mobile and
`stationary terminal devices. At least one radio cell is formed
`by each base station BTS, NB. The size of the radio cell is
`as a rule determined by the range of a general signaling
`channel BCH (Beacon Channel) or BCCH (Broadcast Con-
`trol Channel), which is transmitted from the base stations
`BTS, NB at a respectively higher transmitting power than
`that of the traffic channels. With sectorization or with
`
`hierarchical cell structures, even plural radio cells can be
`provided for per base station BTS, NB. The fiinctionality of
`this structure can be transferred to other radio communica-
`tion systems in which the invention can be used, in particular
`for subscriber access networks with wireless subscriber
`connection.
`
`The example of FIG. 1 shows a subscriber station UE,
`which is embodied as a mobile station and which is situated
`
`in a coverage area, and also a first mobile radio system RS1
`which supports a UMTS standard, and in addition a second
`mobile radio system RS2,which supports a GSM standard.
`The subscriber station UE has set up a connection to the base
`station BTS, shown by way of example, of the second
`mobile radio system RS2.
`During the connection, the subscriber station UE periodi-
`cally evaluates the transmission conditions of the radio
`interface to the base stations surrounding it, such as for
`example the indicated base station NB of the first mobile
`radio system RS1, in order, for example with a worsening of
`the transmission quality to the base station BTS of the
`second mobile radio system RS2, or with an additional
`setting up of a service, to instigate a handover to the base
`station NB of the first mobile radio station RS1. The same
`
`method is also used, for example, with hierarchical network
`structures, when a connection is handed over between dif-
`ferent hierarchy planes, for example, from a micro-cell to a
`macro-cell, which operate in respectively different
`fre-
`quency bands.
`For performing a handover, signal channels SIG.CH1 or
`SIG.CH2 are used as independent control channels which
`can be fixedly allocated, as has been described hereinabove
`in the context of the preferred signaling procedures. In a
`UMTS system,
`the set of transport format combinations
`TFCS (Transport Format Combination Set)
`is used for
`signaling a handover. This has many of the transport format
`combination identifiers TFCI, which are signaled to the
`subscriber station. If the subscriber station UE is connected
`
`to the GSM network RS2 at a first time, then as explained
`hereinabove, the reduced set of transport format combina-
`tions TFCS is used for initiating a handover. After the setting
`up of a corresponding connection to the first communication
`system, the complete set of transport format combinations
`TFCS is used.
`
`According to a modified embodiment, in particular the
`signaling of the reduced information set can take place over
`different signaling channels, e.g., over the message control
`channel BCCH already existing for other control and sig-
`naling purposes. The broadcasting of the reduced set of
`transport format combinations TFCS can thus in particular
`take place over the radio channel or message channel
`BCCH. A dedicated transport format combination identifier
`TFCI is signaled and allocated, e.g., over the signaling
`channel SIG.CH, to the subscriber station UE, in common
`with the handover command.
`
`This handover is to be capable of being performed in
`future radio communication systems, such as for example
`the UMTS mobile radio system, and also between radio
`communication systems which support different transmis-
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`

`
`US 6,944,453 B2
`
`5
`sion methods. Further scenarios of the handover between
`
`like or different systems and transmission methods are
`conceivable.
`
`The invention has been described in detail with particular
`reference to preferred embodiments thereof and examples,
`but it will be understood that variations and modifications
`
`can be effected within the spirit and scope of the invention.
`What is claimed is:
`
`1. A method of controlling an intersystem handover
`between first and second radio communication systems
`having first and second signaling channels, respectively,
`comprising:
`signaling to a subscriber station a reduced set of transport
`format combinations related to setting up a connection
`to the second radio communication system, in one of a
`dedicated second signaling channel and a radio channel
`of the second radio communication system;
`selecting a transport format indicator from the reduced set
`of transport format combinations for initiation of a
`handover to at least one of a first signaling channel and
`a data channel of the first radio communication system;
`and
`
`signaling a complete set of transport format combinations
`to the subscriber station in the first signaling channel.
`2. A method according to claim 1, further comprising
`initiating the handover to a signaling and/or data channel of
`the first radio communication system.
`3. A method according to claim 2, further comprising
`coding the transport format indicator by bitmap coding.
`4. A method according to claim 3, wherein the first radio
`communication system is a UMTS mobile radio system and
`the second radio communication system is a GSM mobile
`radio system.
`5. A method according to claim 4, wherein the second
`signaling channel of the second radio connnunication sys-
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`tem is one of a stand-alone dedicated control channel and a
`radio control channel.
`6. A communication system subscriber station for use in
`an intersystem handover between first and second radio
`communication systems having first and second signaling
`channels, respectively, comprising:
`a memory to store data of a reduced set of transport format
`combinations related to setting up a connection to the
`second radio communication system, in one of a dedi-
`cated second signaling channel and a radio channel of
`the second radio communication system; and
`a processor, coupled to said memory, to select a transport
`format
`indicator from the reduced set of transport
`format combinations for initiation of a handover to at
`
`least one of a first signaling channel and a data channel
`of the first radio communication system; and to receive
`a complete set of transport format combinations to the
`subscriber station via the first signaling channel.
`7. A communication system network station for use in an
`intersystem handover between first and second radio com-
`munication systems having first and second signaling
`channels, respectively, comprising:
`a memory to store data of a reduced set of transport format
`combinations related to setting up a connection to the
`second radio communication system, in one of a dedi-
`cated second signaling channel and a radio channel of
`the second radio communication system; and
`a processor, coupled to said memory, to select a transport
`format
`indicator from the reduced set of transport
`format combinations for initiation of a handover to at
`
`least one of a first signaling channel and a data channel
`of the first radio communication system; and to receive
`a complete set of transport format combinations to the
`subscriber station via the first signaling channel.
`
`5