US006396827B1
`(10) Patent No:
`a2) United States Patent
`US 6,396,827 B1
`Paivikeetal.
`(45) Date of Patent:
`May28, 2002
`
`
`(54) MULTI-MODE MOBILE APPARATUS AND
`METHOD FOR CALCULATING
`FRAME/TIME SLOT OFFSETS, AND
`ALLOWING MOBILES TO SYNCHRONIZE
`WITH DIFFERENT MOBILE
`PROTOCOLS/SCHEMES
`
`(56)
`
`.
`
`olde
`
`tut
`
`-Ri
`
`References Cited
`US. PATENT DOCUMENTS
`5,329,530 A *
`7/1994 Kojima wo... ee 370/348
`3/1998 Hooperet al. 0.0.0.0... 455/434
`5,734,980 A
`
`8/1998 Janky et al... 370/321
`5,790,527 A *
`2/2001 LaDue ...... ee 370/329
`6,185,198 B1 *
`6,252,868 B1 *
`6/2001 Diachinaetal.
`
`1/2002 Owenset al. sce 380/255
`6,338,140 BL *
`Inventors: DaPalvineCoppel TX(US)
`(75)
`FOREIGN PATENT DOCUMENTS
`0818 938 A2
`1/1998
`EP
`(73) Assignee: Nokia Corporation, Espoo (FI)
`* cited by examiner
`(*) Notice:
`Subject to any disclaimer, the term of this
`Primary Examiner—David Vincent
`rec isexrendee “ adjusted under 35
`
`
`
`“oe by0days.(b) 74) Attorney, Agent, or Firm—Steven Shaw
`ys
`AS
`(21) Appl. No.: 09/205,539
`67)
`ABSTRACT
`(22)
`Filed:
`Dec. 3, 1998
`Apparatus, and an associated method, for a UWC-136 Hs
`communication system is provided. A synchronization sig-
`nal generated by the network infrastructure, constructed
`generally corresponding to the existing IS-136/136+ stan-
`dard is received by a mobile station operable, generally,
`pursuant to the timing scheme defined in a GSM system. A
`relative timing offset between the timing schemes of the
`respective communication system schemes is determined
`and thereafter utilized for purposes of synchronization.
`
`(60)
`
`Related U.S. Application Data
`Provisional application No. 60/089,412, filed on Jun. 16,
`1998,
`
`7
`te a ee370)aynace
`(52)
`Step IRIAEnInRInIIAEE 1347;
`i
`(58) Field of Seog33)3373aaS aeae oy
`
`506-7, 498, 509, 510, 512, 522
`
`22 Claims, 7 Drawing Sheets
`
`30
`
`START TIMING
`OFFSET+
`SEN FRAME NUMBER
`
`
`
`2)
`
`
`
`
`DETERMINER
`
`
`CONVERTER
`
`TIMING
`OFFSET
`CALCULATOR
`
`4) GSM FRAME NUMBER AND TIME SLOT
`
`PON=SS5
`
`ouUU
`
`CURRENTIS-136 FRAME NUMBER
`CURRENTIS-136 TIMESLOT NUMBER
`GSM FRAME NUMBER AT1)
`GSM FRAME NUMBER AND TIMESLOT ORIGINATE FROM TIMESLOT_ALLOCATION+
`TBF_STARTING_TIME PARAMETERS OF PACKET UPLINK OR DOWNLINK ASSIGNMENT MESSAGE
`=TIME DIFFERENCE BETWEEN 1)+2) AND 4)
`
`1
`
`APPLE 1012
`
`1
`
`APPLE 1012
`
`

`

`U.S. Patent
`
`May 28, 2002
`
`Sheet 1 of 7
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`US 6,396,827 B1
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`May28, 2002
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`May 28, 2002
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`U.S. Patent
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`May 28, 2002
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`Sheet 5 of 7
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`U.S. Patent
`
`May 28, 2002
`
`Sheet 6 of 7
`
`US 6,396,827 B1
`
`62
`
`CALCULATETHE IS-136
`FRAME NUMBER
`
`
`
`CALCULATE THE GSM FRAME
`NUMBER CORRESPONDING TO TBF
`STARTING TIME
`
`64
`
`66
`
`68
`
`72
`
`74
`
`DETERMINE THE
`IS-136 SEQUENCE NUMBER
`FROM THE FRAME NUMBER
`
`CONVERT THE IS-136
`SEQUENCE NUMBER TO
`A GSM FRAME NUMBER
`
`CALCULATE THE
`TIMING OFFSET
`
`FIG. 5
`
`7
`
`

`

`U.S. Patent
`
`May28, 2002
`
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`US 6,396,827 B1
`
`1
`MULTI-MODE MOBILE APPARATUS AND
`METHOD FOR CALCULATING
`FRAME/TIME SLOT OFFSETS, AND
`ALLOWING MOBILES TO SYNCHRONIZE
`WITH DIFFERENT MOBILE
`PROTOCOLS/SCHEMES
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`The present application claimsthe priority of provisional
`patent application No. 60/089,412, filed on Jun. 16, 1998,
`the contents of which are incorporated herein by reference.
`The present invention relates generally to a manner by
`which to synchronize a mobile station in a radio communi-
`cation system. More particularly,
`the present
`invention
`relates to apparatus, and an associated method, by which a
`synchronization signal generated by apparatus operable pur-
`suantto a first cellular communication standard can be used
`to synchronize a mobile station operable pursuant
`to a
`second cellular communication standard. An embodiment of
`
`the present invention is advantageously utilized in the imple-
`mentation of a so-called 3G (third generation) cellular
`communication system. The infrastructure of an existing
`IS-136 cellular communication system can be utilized to
`synchronize a mobile station which is operable pursuant to
`a time frame format defined in a GSM cellular communi-
`
`cation system.
`
`BACKGROUND OF THE INVENTION
`
`In recentyears, the utilization of wireless communication
`systems through which to communicate telephonically has
`achieved wide popularity. Conventional, voice communica-
`tions as well as data communications can be effectuated
`
`telephonically through the use of such wireless communi-
`cation systems.
`In a wireless communication system, the communication
`channel formed between a sending anda receivingstation is
`a radio channel, formed of a portion of the electromagnetic
`spectrum. A wire line connectionis not required to effectuate
`the communication of a communication signal between the
`sending and receiving stations. Thereby, communication by
`way of a wireless communication system is possible at a
`location to which formation of a wire line connection would
`
`be impractical or impossible.
`Cellular communication systems have been implemented
`using various communication schemes. Cellular communi-
`cation systems have been developed which utilize,
`for
`example, FDMA (frequency-division, multiple-access),
`TDMA (time-division, multiple-access), CDMA (code-
`division, multiple-access) techniques, and various combina-
`tions of such techniques.
`Acellular communication system includes network infra-
`structure which includes a plurality of spaced-apart base
`stations, formed of fixed-site radio transceivers. A user
`communicates with the infrastructure of a cellular commu-
`nication network through the use of a radio telephone,
`typically referred to as a mobile station. The mobile station
`receives downlink signals on a forward link and transmits
`uplink signals on a reverse link. Thereby, two-way commu-
`nications are provided between the infrastructure of the
`cellular communication network and the mobile station.
`
`With continued improvements in communication tech-
`nologies and the development of improved circuitry by
`which to implement such technologies, improvements to
`cellular communication systems have been proposed. Some
`
`2
`proposals pertain to a so-called 3G (third generation) cellu-
`lar communication standard. Such proposals for the 3G
`standard are intended to provide a cellular standard permit-
`ting universal implementation of a cellular system which
`shall be able to take advantage of the improved communi-
`cation technologies to provide a system permitting increased
`capacity levels of communications and which provide
`increased communication services.
`
`Onesuch proposal is the UWC-136 HS (Universal Wire-
`less Communications Consortium-136 High Speed) system.
`In this proposal, certain ones of the technologies and stan-
`dards promulgated in two existing cellular communication
`systems are integrated together. Namely,
`the proposed,
`UWC-136 HS system integrates together components, and
`operation, of the existing IS-136/136+ communication sys-
`tem and the GSM/GPRS/EDGE(global system for mobile
`communications/general packet radio service/enhanced data
`rates for GSM evolution) system.
`A problem associated with such integration is due to
`dissimilarities of the time frame structures defined in the
`
`the time frame structure of the
`systems. That is to say,
`IS-136/136+ system and the GSM system are dissimilar.
`Although both systems are TDMA(time-division, multiple-
`access) systems, the frames defined in the respective sys-
`tems are of dissimilar lengths. A frame is a group of time
`slots. Channels defined in a TDMAsystem are defined, in
`part, in termsof the time slots during which signal bursts are
`transmitted. Both of the systems also define superframes to
`be groups of frames, and hyperframes to be groups of
`superframes. But, the superframe lengths and hyperframe
`lengths are defined to be of dissimilar lengths in their
`respective systems.
`IS-136 and GSM standards define different signals to be
`used by the mobile in synchronization to the system. In
`GSM the common control channels are used for synchroni-
`zation. These channels are SCH (synchronization channel),
`FCCH (frequency correction channel) and (P)BCCH
`((Packet) Broadcast Control Channel). These common con-
`trol channels are sent in a GSM cell on downlink Carrier CO
`on its time slot 0. To enable synchronization and measure-
`ments by the mobile this carrier needs to be sent constantly
`at constant power by the base station.
`And, the signal bandwidths of signals generated in the
`different systems are of differing bandwidths. In the IS-136
`standard, channels are defined to be of 30 kilohertz band-
`widths. And, in the GSM standards, channel bandwidths are
`of 200 kilohertz bandwidths.
`
`When integrating the standards together to form the
`UWC-136 HS system, it would be beneficial if the IS-136
`DCCHsignal could be utilized in synchronization of the
`mobile to the 200 kHz GSM/GPRS/EDGEcarrier. Synchro-
`nization of the mobile station from IS-136 DCCHto the 200
`kHz carrier could be done quicker than by using the GSM
`synchronization signals. Also, existing plans for the imple-
`mentation of the UWC-136 HS system allocates only a
`limited portion of the electromagnetic spectrum within
`which to define radio channels. Implementation proposals
`for the United States, for instance, provide only one mega-
`hertz of spectrum, thus necessitating a high level of channel
`reuse, such as on a 1/3 cell reuse pattern. The common
`control channels set forth in the existing GSM standard
`when broadcast in a system utilizing a 1/3 cell reuse pattern
`mightresult in excessive levels of interference. A3G system
`necessitating a reduced level of signaling, relative to that
`utilized in a conventional GSM system, would be advanta-
`geous.
`
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`

`US 6,396,827 B1
`
`3
`Amannerby which to permit synchronization of a mobile
`station with the synchronization signals defined in the
`IS-136 system would advantageously permit synchroniza-
`tion to be performed more quickly and also obviate the need
`for certain of the synchronization signals utilized in a GSM
`communication system. The common control channels
`require bandwidth on the GSM carrier. In a low capacity
`initial deployment of 136HS it would be beneficial if this
`bandwidth could be used for packet data transfer. This
`capacity increase may be possible by using information
`present on the 30 kHz DCCH in synchronization to the
`GSM/GPRS/EDGEchannel.
`
`The UWC-136HS system will have both the EDGE
`coverage and 136 coverage in the area of the samecell. This
`means that the IS-136/136+ and GSM/EDGEbasestation
`transceivers will be located in the samecell site. From this
`perspective it does not seem reasonable that a mobile would
`needto use time to synchronize to a 200 kHzcarrier on a cell
`where it already has synchronized to the 30 kHz carrier. A
`faster way would be to utilize information on the 30 kHz
`channel to make synchronization to the 200 kHz carrier
`faster.
`
`is in light of this background material related to
`It
`synchronization between a mobile station and networkinfra-
`structure of a cellular communication system that the sig-
`nificant
`improvements of the present
`invention have
`evolved.
`
`SUMMARYOF THE INVENTION
`
`10
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`20
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`25
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`
`The present invention, accordingly, advantageously pro-
`vides apparatus, and an associated method, by which a
`synchronization signal generated by apparatus operable pur-
`suantto a first cellular communication standard can be used
`
`to synchronize a mobile station operable pursuant
`second cellular communication standard.
`
`to a
`
`35
`
`In one implementation, synchronization signals are gen-
`erated corresponding to standards set forth in the IS-136/
`136+ interim standard promulgated by the EIA/TIA,and the
`mobile station is constructed to be operable pursuant to the
`standards set forth in the GSM (global system for mobile
`communications) cellular communication standard. Another
`possible implementation is a multi-mode mobile station
`capable of operating both according to the IS-136 and/or
`GSMand/or GPRS and/or EDGE communication standards.
`Operation of an embodimentof the present invention deter-
`minesa relative time offset between a frame andtimeslot on
`the IS-136 DCCH and a frame and time slot on a GSM/
`GPRS/EDGEnetwork infrastructure. Responsive to deter-
`mination ofthe relative time offset, the mobile station can be
`placed in time synchronization with the signals generated by
`the GSM/GPRS/EDGEnetwork infrastructure.
`Such an implementation can be utilized, for instance, in
`the proposed, UWC-136 HS (Universal Wireless
`Consortium-136 High Speed) cellular communication
`system, a proposed 3G (third generation) cellular commu-
`nication system. The infrastructure of an existing IS-136
`cellular communication system can be utilized in the newly-
`proposed system in which the signals formed during opera-
`tion of the infrastructure correspond to a time frame format
`defined in the IS-136 communication system.
`By utilizing the synchronization signals generated upon
`the 30 kilohertz carriers defined in the IS-136 system,
`synchronization of a mobile station to GSM signals can be
`effectuated more quickly than through synchronization of
`the mobile station using the GSM, FCCH and SCH chan-
`nels. Also, through use of the signaling utilized in an IS-136
`
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`4
`system, lesser levels of co-channel interference are likely to
`occur, and smaller cluster sizes, such as those formed
`pursuant to 1/3 cell reuse patterns, are possible.
`Additionally, in the aforementioned, proposed UWC-136
`HSsystem, because control channels conventionally utilized
`in an existing GSM system are obviated,
`the bandwidth
`conventionally required to be reserved for signaling can be
`used for other purposes. Such channels can be reallocated
`and used, for example, instead to communicate packet data.
`An embodiment of the present invention takes advantage
`of the close relationship between the multi-frame timing of
`an IS-136 network and that of a GSM/GPRS/EGPRSnet-
`work.A period of time can be determined in which both the
`IS-136 and GSM multi-frames are recurrent. And,
`analogously, also, a period of time can be determined in
`which an IS-136 hyperframe and a GSM hyperframe are
`recurrent. Because of this recurrent relationship,
`timing
`differences between slots and frames of the two separate
`systemsare calculable. And, responsive to calculation of the
`timing differences, synchronization of a mobile station con-
`structed pursuant to the standards of a GSM system can be
`synchronized through the synchronization signals of the
`infrastructure constructed pursuant to the standards of the
`IS-136 system. That
`is to say, a mobile station that
`is
`“camping on” the DCCH ofan IS-136 base station can use
`the synchronization signal generated thereon to become
`synchronized to the GSM/GPRS/EGPRSchannels of the
`same cell. With only a few additions to the BCCH infor-
`mation on the DCCH,a mobilestation is able to calculate the
`timing differences between the slots and frames of the
`DCCH and the slots and frames of a GSM/GPRS/EDGE
`carrier and use such data for purposes of channel synchro-
`nization. Thereby, the FCCH and SCH control channels of
`a GSM system can be replaced with information generated
`on a DCCH defined in the IS-136 system.
`During operation of an embodiment of the present
`invention, advantage is taken of the fact
`that
`the GSM
`hyperframe length is an integral multiple of IS-136 hyper-
`frame length and that the GSM 26-multiframe length equals
`to the length of three IS-136 frames. These relationships
`make it easy to calculate the time difference from any given
`IS-136 frame-time slot to any given GSM frame/timeslot.
`This idea can be used in the context of a mobile station that
`needs to work according to both the GSM and IS-136
`standards. This will be the case in the UWC-136HS system
`where the base station will
`incorporate both GSM and
`IS-136 basestations. To use this idea synchronization of the
`GSMand IS-136 forward channels is needed on a cell site
`only (not network wide). Also,
`the IS-136 DCCH frame
`number is extended to count over GSM hyperframe. The
`same idea applies to any two TDMAsystems in case the
`hyperframe of one is an integral multiple of the hyperframe
`of the other.
`
`In these and other aspects, therefore, the apparatus, and an
`associated method,is providedfor calculating a relative time
`offset by which to offset a synchronization signal generated
`in a communication system by network infrastructure which
`is operable pursuant
`to a first TDMA (time-division,
`multiple-access) communication scheme havinga first time
`frame definition defined therein. The mobilestation is oper-
`able pursuant to a second TDMA communication scheme
`having a second time frame definition defined therein. A
`determiner is coupled to receive the synchronization signal
`and is operable responsive thereto. The determiner deter-
`mines an order number
`representative of a first-
`communication scheme time frame located within a
`
`sequenceof thefirst-communication-scheme time frame at a
`10
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`10
`
`

`

`US 6,396,827 B1
`
`6
`forward link signals 14 and reverse link signals 16 with the
`mobile station 18. The IS-41 network transceives commu-
`
`5
`selected determining time. A converter is operable respon-
`sive to the order number determined by the determiner. The
`nication signals, here forward link signals 20 and reverse
`converter converts the order number to a corresponding
`frame number of a second-communication-scheme time
`link signals 28 with the mobile station. Because no wire line
`connection is required to effectuate communications, com-
`frame number. A timing offset calculator is operable respon-
`munications effectuated by way of the communication sys-
`sive to a value representative of the second-communication-
`tem 10 are permitted irrespective of the availability of a wire
`scheme time frame number formed by the converter. The
`line connection at a location at which the mobilestation is
`timing offset calculator calculates a relative time offset
`positioned.
`between a first time frame of the sequence of the first-
`communication-scheme time frames in which the first-
`The UWC-136HSbasestation 36 has been defined here to
`communication-scheme time frame, the order number of
`include both an IS-136/136+ base station 34 and a GSM/
`EDGEbasestation 26. The GPRS network infrastructure 12
`which the determiner determines, is located, andafirst time
`frame of
`a corresponding sequence of second
`is here coupled to PSTN (public switched telephone
`communication-scheme time frames.
`network) 22. The GPRS network is shownto include a single
`SGSN(Serving GPRS Support Node) 30. Usually several
`SGSN’s and other network nodes are included. The IS-41
`network infrastructure 38 is here shownto include a single
`MSC 24. Usually several MSC’s and other infrastructure
`nodes are included.
`
`A more complete appreciation of the present invention
`and the scope thereof can be obtained from the accompa-
`nying drawings which are briefly summarized below, the
`following detailed description of the presently-preferred
`embodiments of the invention, and the appended claims.
`
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates a functional block diagram of a radio
`communication system in which an embodiment of the
`present invention is operable.
`FIG. 2 illustrates the timing scheme defined in an IS-136/
`136+ cellular communication system pursuant to which the
`network infrastructure of the communication system shown
`in FIG. 1 is operable pursuant to an embodiment of the
`present invention. 136+ refers here to the TIA TR 45.3
`GPRS-136 packet data proposal that adds GPRS protocols
`and 8-PSK modulation to the 136 standard.
`
`FIG. 3Aillustrates the timing scheme defined in a GSM
`cellular communication system pursuant
`to which the
`mobile station of the communication system shown in FIG.
`1 is operable in an embodiment of the present invention.
`FIG. 3B illustrates the relationship between a GSM hyper-
`frame and an IS-136 hyperframe and an SFN (start frame
`number) defined in the IS-136 interim standard.
`FIG. 4 illustrates the relationship between the timing
`definitions of the IS-136 system, shown in FIG. 2, and the
`timing definitions of the GSM system, shown in FIG. 3.
`FIG. 5 illustrates a method flow diagram whichlists the
`methodsteps of the method of an embodimentofthe present
`invention.
`
`FIG. 6 illustrates a functional block diagram of apparatus
`of an embodimentof the present invention which calculates
`a relative time offset between frames defined in the IS-136
`
`and GSM systems.
`DETAILED DESCRIPTION
`
`Referring first to FIG. 1, a radio communication system,
`showngenerally at 10, is operable to communicate commu-
`nication signals by way of radio communication channels
`defined upon the portion of the electromagnetic spectrum
`allocated to the communication system 10. The communi-
`cation system 10 is here exemplary of a UWC-136 HS
`communication system, a so-called 3G (third generation),
`cellular communication system. The UWC-136 HS system
`integrates together portions of existing, cellular communi-
`cation systems. Namely,
`the UWC-136 HS integrates
`together portions of an existing IS-136/136+ communication
`system and a GSM communication system.
`The communication system 10 includes IS-41 network
`infrastructure 38 and GPRSnetwork infrastructure 12. The
`
`GPRS network transceives communication signals, here
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`25
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`45
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`50
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`60
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`65
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`In the exemplary implementation in which the commu-
`nication system 10 forms a UWC-136 HS system,
`the
`network infrastructure 38 of the system is operable,
`generally, pursuant to the standards set forth in the IS-136/
`136+ specification promulgated by the EIA/TIA.
`In an
`IS-136/136+ system, channels are defined to be of 30
`kilohertz bandwidths and downlink signals 14 include syn-
`chronization signals which are used to synchronize mobile
`stations which receive such signals to the timing of the
`network infrastructure. When a mobile station becomes
`synchronized to the synchronization signals, signals trans-
`mitted and received by the mobile station are placed in time
`synchronization with the network infrastructure.
`to the
`The mobile station 18 is constructed pursuant
`standards set forth in both GSM specifications and in
`IS-136/136+ specifications. The MS can, however, receive
`only one forwardlink signal at a time. Eitherit receives the
`GSMforward link signal 14 or the IS-136/136+ forward link
`signal 20. Through the embodimentof the present invention,
`the MS can become synchronized to the GSM forward
`signal when it has first become synchronized to the IS-136
`forward signal. This synchronization to GSM forward signal
`can happen without the SCH, FCCH GSMcontrolsignals by
`utilizing the timing relationships between IS-136 and GSM
`time frames.
`
`In one implementation of an embodiment of the present
`invention,
`the mobile station 18 includes apparatus for
`calculating a relative time offset between time frames
`defined at the IS-136 base station forward signal and the
`GSMbasestation forward signal. In another embodiment,
`such apparatus is located at the network infrastructure and
`the relative time offset determined thereat is provided to the
`mobile station by way of a downlink signal.
`FIG. 2 illustrates the timing scheme, shown generally at
`42, defined in the IS-136/136+ communication system. The
`IS-136 communication system is a TDMA(time-division,
`multiple-access) system in which a channelis defined as a
`carrier frequency/time slot combination. The timing scheme
`42 indicates a manner by which a single carrier frequencyis
`time-divided. While not separately illustrated, additional
`carrier frequencies are analogously also divided into a
`plurality of time slots. Groups of sequentially-positioned
`time slots together form a frame. And, the Figure illustrates
`a plurality of frames 44, each formed of groups of
`sequentially-positioned time slots. Each of the frames 44 is
`defined by an IS-136 frame number. The IS-136 frame
`numberis defined here to be an integer number between zero
`11
`
`11
`
`

`

`US 6,396,827 B1
`
`7
`and 313343. This definition of IS-136 frame number has
`been done because 313344 IS-136 frames are exactly the
`length of one GSM hyperframe. The concept of a start frame
`number (SFN)is also made, as shown in FIG. 3B. The SFN
`defines the IS-136 frame numberofthat IS-136 frame during
`which the GSM frame with the GSM frame number0 starts,
`1.e., the GSM hyperframestarts.
`A group of three frames 44 defines a sequence 48 of three
`IS-136 frames 48. Each of the sequences 48 is defined by a
`sequence number (SN). A first sequence 48 starting at zero
`time 46 is defined by an SN=zero.
`FIG. 3 illustrates the timing scheme, shown generally at
`52, defined in the GSM specification. A GSM system is also
`a TDMAsystem, again in which a channelis defined by a
`time slot/carrier combination. While only a single carrier
`frequencyis illustrated in the Figure, other carrier frequen-
`cies can similarly be shown. Groups of sequentially-
`positioned timeslots defined in the GSM system form GSM
`frames 54, and groups of twenty-six frames 54 define a
`multi-frame 56. A time slot defined in the GSM system is of
`a duration of 15/26 ms, and a frame 54 is of a duration of
`120/26 ms. A superframe defined in the GSM system is
`formed of 26*51 GSM frames 54, and a hyperframe is
`defined to be 2,048 GSM superframes.
`FIG. 4 illustrates the timing scheme 42, shown in FIG. 2,
`together with the timing scheme 52, shown in FIG. 3. The
`timing scheme42 represents the timing scheme pursuant to
`which the IS-136 base station 34 is operable and the timing
`scheme 52 represents the timing scheme pursuant to which
`the GSMbasestation 26 is operable. A relative timing offset
`indicated by the line segment 62 is exemplary and repre-
`sentative of a relative time offset between the timing
`schemesof the IS-136 base station and the GSM base station
`belonging to the same UWC-136HSbasestation 36. Also,
`the symbolic value SFN (=start frame number) is exemplary
`and represents the value of the IS-136 frame number (0...
`313343) of that IS-136 frame during which the GSM frame
`with GSM frame number 0 starts (=the GSM hyperframe
`starts). Either of the following can be assumed:
`1) The IS-136 base station 34 and the GSM basestation
`26 are synchronized so that the start timing offset and the
`start frame number (SFN) have the same default values in
`every UWC-136HScell. If this is the case the start timing
`offset and start frame numbervalues do not need to be sent
`to the MS in the IS-136 forward channel 20. The most
`
`natural default values for both SFN and start timing offset
`would be zero but also other values are possible.
`. 313343
`2) The SENis an arbitrary number between 0. .
`and the start timing offset is an arbitrary number between
`0... 40000 microseconds. These values may vary from one
`UWC-136HScell to another.If this is the case both thestart
`frame numberandstart timing offset values need to be sent
`to the mobile station through the IS-136 forward channel 20
`of the UWC-136HSbasestation 36.
`
`In one embodimentof the present invention, the MS 18 is
`synchronized to the IS-136 forward DCCH signal of the
`UWC-136HSbasestation 36. The UWC-136HSbasestation
`
`assigns a temporary block flow on a GSM packettraffic
`channel to the MS by sendingto it a Packet Uplink Assign-
`ment or Packet Downlink Assignment message through he
`IS-136 forward DCCH 20. (These messages have been
`defined in GSM specification 04.60 Version 6.0.0.) The
`Packet Uplink or Downlink Assignment Message includes
`the following parameters:
`TBF_STARTING_TIME=Indicates the future GSM
`frame number at which the MSis supposed to start
`transmission/reception on the assigned GSM channel
`14/16
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`8
`TIMESLOT_ALLOCATION=The GSM timeslot allo-
`cated to the MS on the GSM channel
`
`PACKET_TIMING_ADVANCE=Timing advance that
`MSis supposed to use in transmission on the assigned
`GSM channel (for simplicity the timing advance is not
`dealt with in this example)
`The example embodimentof the present invention lets the
`MScalculate the time difference (=timing offset) from its
`current IS-136 frame/timeslot on IS-136 DCCHto the GSM
`frame/timeslot defined by the above parameters. Therest of
`this example deals with this calculation. For simplicity the
`PACKET_TIMING_ADVANCEis omitted.
`Additions to the BCCH information elements defined in
`the IS-136-A system are not required. The only alterations to
`existing standards are to add the GPRS Packet Uplink
`Assignment Message and Packet Downlink Assignment
`Message to IS-136 DCCH or to add corresponding infor-
`mation elements to existing messages on IS-136 DCCH.
`Also, the GSM BSIC (Base Station Identity Code) needs to
`be added to DCCH information elements. These additions
`will enable the MS 18 to synchronize from IS-136/136+
`DCCH to GSM/GPRS/EDGEpackettraffic channel.
`The mobile station 18is initially tuned, for instance, to the
`IS-136 DCCHat a particular IS-136 frame numberandat a
`particular IS-136 time slot, in which there are six time slots
`per frame. The mobile station 18 receives a packet uplink or
`downlink assignment message to a GSM/GPRS/EDGEcar-
`rier of the same cell together with frequency parameters, a
`TBFstarting time, and a GSM time slot of which there are
`eight time slots per frame. Responsive thereto, the mobile
`station 18 calculates the timing offset from the current
`IS-136 frame and time slots to a GSM timeslot and frame
`number corresponding to the TBFstarting time.
`FIG. 5 illustrates a method, shown generally at 62, by
`which the relative timing offset 56 (which equals time
`distance) between the current IS-136 frame number, time
`slot and the allocated GSM frame numbercorresponding to
`the TBS starting time and allocated GSM time slot
`is
`determined. (Viz., a constant known timing difference is
`assumed to exist between the start of GSM hyperframe and
`the start of the IS-136 frame during which the GSM hyper-
`frame starts. This item is called start timing offset. It may
`have a different value for each UWC-136HSbasestation or
`it may have a default value (e.g. 0) which is the same for
`each base station. This starting timing offset value is
`included as a parameter to the presented calculations in
`order to make them more general. The same applies to the
`SFNesstart frame number.) First, and as indicated by the
`block 64, the mobile station calculates the IS-136 frame
`numberfrom the information provided thereto on the DCCH
`burst and on the F-BCCH. The IS-136 frame number,
`1S136_FN,is calculated by the following equation:
`
`(IS136__FN)=CBN_high*8*12*2*16+EHFC*12*2*16+
`HFC*2*16+PSFI*16+SFP/2
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`5
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`wherein:
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`55
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`CBN_high is an optional information element on the
`IS-136 F-BCCH and counts when the extended hyper-
`frame counter wraps-around;
`EHFC is the extended hyperframe counter, also an
`optional information element on the IS-136 F-BCCH
`and counts when a hyperframe counter wraps-around;
`HFC is the hyperframe counter which is a mandatory
`information element on the IS-136 F-BCCH and counts
`
`hyperframes from zero to eleven;
`PSFI is a primary superframe indicator, a mandatory
`information element on the IS-136 F-BCCH which
`
`counts superframes zero... 1; and
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`12
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`12
`
`

`

`1S136_FNis the IS-136 frame number; and
`SEN is the start frame number,
`the above calculation
`being modulo 313344.
`Then, and