United States Patent 19
`Andersson et al.
`
`||||||||||||||
`US005604744A
`11
`Patent Number:
`5,604,744
`(45) Date of Patent:
`Feb. 18, 1997
`
`54). DIGITAL CONTROL CHANNELS HAVING
`LOGICAL CHANNELS FOR MULTIPLE
`ACCESS RADIOCOMMUNICATION
`75 Inventors: Håkan C. Andersson, Ekerö, Sweden;
`John W. Diachina, Garner, N.C.; Bengt
`Persson, Djursholm, Sweden; Alex K.
`Raith, Durham; Anthony J.
`Sammarco, Garner, both of N.C.;
`Francois Sawyer, St-Hubert, Canada
`73) Assignee: Telefonaktiebolaget LM Ericsson,
`Stockholm, Sweden
`
`21 Appl. No.: 331,703
`
`22 Filed:
`
`56)
`
`
`
`9/1991 European Pat. Off..
`4.45887
`56. E. Ea Ea. 3.
`uropean Pat. Oft. .
`WO92/10042 6/1992 WIPO
`WO92/14308 8/1992 WIPO
`OTHER PUBLICATIONS
`Supplementary European Search Report No. EP9590 1121
`Date of Completion of search: 31 Oct. 1995.
`(List continued on next page.)
`Primary Examiner-Douglas W. Olms
`Assistant Examiner-Ajit Patel
`Attorney, Agent, or Firm-Burns, Doane, Swecker &
`Mathis, L.L.P.
`ABSTRACT
`57
`Oct. 31, 1994
`A communications system in which information is transmit
`ted in successive time slots grouped into a plurality of
`Related U.S. Application Data
`superframes which are, in turn, grouped into a plurality of
`hyperframes. A remote station is assigned to one of the time
`63 Continuation-in-part of Ser. No. 147,254, Nov. 1, 1993, and
`slots in each of the superframes for paging the remote
`a continuation-in-part of Ser. No. 956,640, Oct. 5, 1992, Pat.
`station, each hyperframe including at least two superframes,
`No. 5,404,355.
`and the information sent in the assigned time slot in one
`(51) Int. Cl." ......................... H04J 3/16
`superframe in each hyperframe is repeated in the assigned
`52 U.S. Cl
`370/347
`trir time slot in the other superframe(s) in each hyperframe.
`58) Field of Search ...
`... 370/95.1, 95.3,
`Each superframe can include a plurality of time slots used
`370/85.7, 82,99, 110.1; 455/34.1, 118,
`for sending paging messages to remote stations, grouped
`33.1, 54.1, 32.1, 38.1, 379/59, 60,340/825.44;
`into a plurality of successive paging frames, and the time
`371/69.1, 67.1, 70
`slot to which the remote station is assigned is included once
`in every paging frame. Also, each superframe may include
`time slots comprising a logical channel for broadcast control
`References Cited
`information and time slots comprising a logical paging
`channel. Information sent in the assigned time slot may
`U.S. PATENT DOCUMENTS
`direct the remote station to read the broadcast control
`E. E. E. M. E. information, and the information may have been encoded
`according to an error correcting code and include a plurality
`... 455/33
`5,081,704 1/1992 Umeda et al. .....
`of bits having polarities that are inverses of cyclic redun
`455/33.1
`5,127,100 6/1992 D'Amico et al. ...
`5,193,091
`3/1993 Crisler et al. ......
`370/95.1
`dancy check bits produced by the encoding. Also, the
`5,228,030 7/1993 Dresher ..........
`370/100.1
`broadcast control information may comprise special mes
`5,325,088 6/1994 Willard et al. .....
`... 3401825.2
`sages that are included in respective time slots comprising a
`5,353,332 10/1994 Raith et al. ............................... 379/59
`logical special message channel, the time slots of the special
`message channel may be grouped in successive SMS
`FOREIGN PATENT DOCUMENTS
`frames, and the SMS frames may be synchronized to start
`with a start of a superframe.
`240073 10/1987 European Pat. Off..
`291068 11/1988 European Pat. Off..
`321454 6/1989 European Pat. Off. .
`
`39 Claims, 9 Drawing Sheets
`
`130
`
`150
`
`CHANNEL
`TRANSCEIVER
`
`140
`- A -
`
`| CONTROL
`AN)
`SC -
`PROCESSING!
`NT
`
`160
`--
`\/
`conTROL
`HCHANNE---
`TRANSCEIVER
`
`BASE SATION
`--
`-110
`
`I
`
`v
`
`---------
`woICE AND CONTROL 170
`: I CANNEL TRANSCEIVER
`
`-------
`PROCESSNG UNIT s -
`
`---
`MOBILE
`{{20
`
`ypeffairie C
`uportiuns 0.
`mary
`O
`
`Suportrame t
`secondary
`
`Hyperfrare :
`Supdf fi?ne 2
`primary
`
`-----
`
`s° spachfessPacifies spaca
`
`F - F-3CCH
`E - E-8CCH
`S - S-BCCH
`SPACH - PCH cr ARCH or Sischi
`
`IPR2020-00038
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`
`

`

`5,604,744
`Page 2
`
`OTHER PUBLICATIONS
`
`B. Walke et al., "Cellpac: A Packet Radio Protocol Applied
`to the Cellular GSM Mobile Radio Network', 41st IEEE
`Vehicular Technology Conference Gateway to the Future.
`Technology in Motion (19-22 May 1991).
`
`"A New Standard for North American Digital Cellular",
`Magnus Isaksson et al., Ericsson Review, No. 2, 1994.
`
`“Cellular System Dual-Mode Mobile Station-Base Station
`Compatibility Standard”, EIA/TIA Interim Standard,
`IS-54-B, pp. 101-106; 109-116; 139–140; and 163-166
`(Apr., 1992).
`"Radio Link Control Techniques for Digital Cellular Sys
`tems', Seizo Onoe et al., NNT Review, vol. 4, No. 1, pp.
`47-54 (Jan. 1992).
`"Call Setup Strategy Tradeoffs for Universal Digital Por
`table Communications', Yurdaer N. Doganata et al., Com
`puter Networks and ISDN Systems, vol. 20, No. 1/5, pp.
`455-464, (Dec. 1990).
`
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`
`

`

`5,604,744
`
`Isllertt o»
`9
`
`-t5
`
`一Ls. latent
`
`Fdb. p
`
`BURST
`CHANNEL
`
`BURST
`CHANNEL
`
`BURST
`CHANNEL
`
`BURST
`CHANNEL
`
`BURST
`CHANNEL
`
`BURST
`CHANNEL
`
`BURST
`CHANNEL
`
`15 CHANNEL
`
`BURST
`
`FRAME
`LAYER 2
`
`FRAME
`LAYER 2
`
`FRAME
`LAYER 2
`
`FRAME
`LAYER 2
`
`FRAME
`LAYER 2
`
`FRAME
`LAYER 2
`
`FRAME
`LAYER 2
`
`^ FRAME
`13 LAYER 2
`
`MESSAGE
`LAYER 3
`
`MESSAGE
`LAYER 3
`
`MESSAGE
`LAYER 3
`
`11
`
`PRIOR ART
`Fig. 1
`
`IPR2020-00038
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`
`

`

`U.S. Patent
`
`Feb. 18, 1997
`
`Sheet 2 of 9
`
`5,604,744
`
`TDMA Frame
`
`TOMA Block
`
`to ea.
`
`Time Time Time Time Time Time Time Time Time Time Time Time Time
`Slot
`Slot Slot Slot Slot
`Slot Slot Slot
`Slot
`Slot
`Slot Slot
`Slot
`2
`3
`4
`5
`6
`2
`3
`4
`5
`6
`
`
`
`
`
`ecchipch arch. . .
`— superframe --
`
`FG. 2
`
`Hyperframe 0
`Superframe 0
`primary
`
`
`
`Superframe 1
`Secondary
`
`Hyperframe 1
`Superframe 2
`primary
`
`
`
`If E°s spacHF EssPacHF EssPACH
`
`
`
`F - F-BCCH
`
`E = E-BCCH
`
`S - S-BCCH
`
`-
`
`SPACH - PCH or ARCH or SMSCH
`
`F.G. 5
`
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`

`

`산요 Patent
`
`Feb. 대， 1997
`
`U.S. Patent
`
`Feb. 18, 1997
`
`Sheet 3 of 9
`
`
`
`Sheet 3 of 9
`5,604,744
`
`S，6H744
`
`(H
`
`09
`
`0Ç
`
`욧
`
`〆I j
`
`i-v
`_ K
`
`OF
`
`'•i
`
`00
`CD
`ir
`
`유
`
`IPR2020-00038
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`
`

`

`U.S. Patent
`Feb. 18, 1997
`FG. 4
`
`Sheet 4 of 9
`
`5,604,744
`
`
`
`
`
`
`
`
`
`
`
`
`
`CONTROL
`AND
`PROCESSING
`UNIT
`
`WOCE
`CHANNEL
`TRANSCEIVER
`
`
`
`CONTROL
`CHANNEL
`TRANSCEIVER
`
`BASE STATION
`
`10
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`VOICE AND CONTROL
`CHANNEL TRANSCEIVER
`
`PROCESSING UNIT
`
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`
`

`

`U.S. Patent
`
`Feb. 18, 1997
`
`Sheet 5 of 9
`
`5,604,744
`
`DCC
`
`
`
`downlink
`
`RACH
`
`SPACH
`
`BCCH
`
`Reserved
`
`
`
`
`
`
`
`F-BCCH
`
`E-BCCH
`
`S-BCCH
`
`Fig. 6
`
`One Frame = 1944 bits (972 Symbols) = 40 ms. (25 frames per second)
`
`slot
`
`slot 2
`
`slot a
`
`slot 4
`
`slot 5
`
`slot
`
`One Slot
`
`Fig. 7
`
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`

`

`U.S. Patent
`
`Feb. 18, 1997
`
`Sheet 6 of 9
`
`5,604,744
`
`6 6
`
`16
`
`28
`
`122
`
`24
`
`an PREAM SYNC DATA
`
`SYNC-
`
`122
`
`DATA
`
`FG. 8a
`
`6 6
`
`16
`
`28
`
`122
`
`24
`
`78
`
`44
`
`an PREAM SYNC DATA
`
`SYNC--
`
`DATA
`
`F.G. 8b
`
`28
`
`3
`
`3
`
`6
`
`130
`
`12
`
`130
`
`3
`
`2
`
`5
`
`2
`
`sync balancPE DatacsFloata balancPE Insvo
`
`FIG. 8C
`
`Abbrew i at 8 d Guard Time
`AG
`= Busy I Rese rved I de l n dic at Or
`BR
`CSFP = CO ded Super Frame Phase
`DATA = | n for rn at On b t S
`G
`= Guard Time
`CPE
`= CO ded Part i a
`PREAM = Preamb e
`R
`Ramp Time
`R 1 N
`= Re C e i v e di NO t Re C e i v ed
`RSWD = Reserved field, set t 0 1 1
`SYNC = Synchronization
`SYNC + = Add it iOn a Synch r Onization
`
`E Ch 0
`
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`

`

`U.S. Patent
`
`Feb. 18, 1997
`
`Sheet 7 of 9
`
`5,604,744
`
`6
`5
`4
`3
`2
`O
`HF
`sFol 1 2 3 4 56789 10111213
`PF, p. sp. sp. sp. sp. sps ps
`PFaps -- Ips - I - Ips - I - Ips
`PFaps -
`-
`-
`- Ips - - -
`- ps
`PFaps - - - - - - Ips - - - -
`
`PF
`
`
`
`PFa—-
`PF -
`
`-
`
`HF = Hyperframe
`SF = Superframe
`PF = Paging frame
`P = Primary PCHs
`S = Secondary PCHs
`FIG. O
`
`109/10 1/79
`
`6
`
`5
`
`FG. 9
`
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`

`

`U.S. Patent
`
`Feb. 18, 1997
`
`Sheet 8 of 9
`
`5,604,744
`
`-— SMS frame = 24 Superframes = 15.36 s —-
`O
`1
`2
`...
`23
`
`Superfr.
`
`F.G. 11
`
`S-BCCH: SMS(1)
`SPACH: TF(2
`)
`
`F.G. 12
`
`
`
`
`
`
`
`(3) TF(4)
`TF(3) TF(4
`
`TF(
`)
`
`
`
`
`
`
`
`
`) TF(3
`
`. . .
`
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`

`

`U.S. Patent
`
`Feb. 18, 1997
`
`Sheet 9 of 9
`
`5,604,744
`
`SCS
`=X
`
`BC
`=0
`
`L3LI L3DATA BE
`=1
`=X..X
`=X..X
`8
`
`FILLER
`=o..o
`
`FIG. 13a.
`
`SCS
`=x
`
`BC
`=0
`1
`FIG. 13b
`
`L3 니 L3DATA BE
`=X..X
`=0
`=X..X
`8
`
`L3 니
`X..X
`8
`
`L3DATA
`X..X
`
`SCS
`=x
`
`BC
`=1
`
`C 니 L3DATA BE
`X.X =X..X
`=1
`
`FILLER
`0..0
`
`FIG. 13c
`
`CRC
`X..X
`16
`
`CRC
`X..X
`16
`
`CRC
`=x..x
`16
`
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`

`5,604,744
`
`1
`DIGITAL CONTROL CHANNELS HAVING
`LOGICAL CHANNELS FOR MULTIPLE
`ACCESS RADIOCOMMUNICATION
`
`This application is a continuation in part of U.S. patent
`application Ser. No. 08/147.254 entitled "A Method for
`Communicating in a Wireless Communication System',
`which was filed on Nov. 1, 1993, and which is incorporated
`in this application by reference. This application is also a
`continuation in part of U.S. patent application Ser. No.
`07/956,640 entitled "Digital Control Channel', which was
`filed on Oct. 5, 1992, now U.S. Pat. No. 5,404,355 and
`which is incorporated in this application by reference.
`
`10
`
`2
`described in more detail below, digital control channels
`(DCCs) can also be provided for communicating control
`signals, and such a DCC is a logical channel formed by a
`succession of usually non-consecutive time slots on the
`radio carrier.
`According to IS-54B, each TDMA frame consists of six
`consecutive time slots and has a duration of 40 milliseconds
`(msec). Thus, each radio channel can carry from three to six
`DTCs (e.g., three to six telephone conversations), depending
`on the source rates of the speech coder/decoders (codecs)
`used to digitally encode the conversations. Such speech
`codecs can operate at either full-rate or half-rate, with
`full-rate codecs being expected to be used until half-rate
`codecs that produce acceptable speech quality are devel
`oped. A full-rate DTC requires twice as many time slots in
`a given time period as a half-rate DTC, and in IS-54B, each
`radio channel can carry up to three full-rate DTCs or up to
`six half-rate DTCs. Each full-rate DTC uses two slots of
`each TDMA frame, i.e., the first and fourth, second and fifth,
`or third and sixth of a TDMA frame's six slots. Each
`half-rate DTC uses one time slot of each TDMA frame.
`During each DTC time slot, 324 bits are transmitted, of
`which the majorportion, 260 bits, is due to the speech output
`of the codec, including bits due to error correction coding of
`the speech output, and the remaining bits are used for guard
`times and overhead signalling for purposes such as synchro
`nization.
`It can be seen that the TDMA cellular system operates in
`a buffer-and-burst, or discontinuous-transmission, mode:
`each mobile station transmits (and receives) only during its
`assigned time slots. At full rate, for example, a mobile
`station might transmit during slot 1, receive during slot 2,
`idle during slot 3, transmit during slot 4, receive during slot
`5, and idle during slot 6, and then repeat the cycle during
`succeeding TDMA frames. Therefore, the mobile station,
`which may be battery-powered, can be switched off, or
`sleep, to save power during the time slots when it is neither
`transmitting nor receiving. In the IS-54B system in which
`the mobile does not transmit and receive simultaneously, a
`mobile can sleep for periods of at most about 27 msec (four
`slots) for a half-rate DTC and about 7 msec (one slot) for a
`full-rate DTC.
`In addition to voice or traffic channels, cellular radio.com
`munication systems also provide paging/access, or control,
`channels for carrying call-setup messages between base
`stations and mobile stations. According to IS-54B, for
`example, there are twenty-one dedicated analog control
`channels (ACCs), which have predetermined fixed frequen
`cies for transmission and reception located near 800 MHz.
`Since these ACCs are always found at the same frequencies,
`they can be readily located and monitored by the mobile
`stations.
`For example, when in an idle state (i.e., switched on but
`not making or receiving a call), a mobile station in an IS-54B
`system tunes to and then regularly monitors the strongest
`control channel (generally, the control channel of the cell in
`which the mobile station is located at that moment) and may
`receive or initiate a call through the corresponding base
`station. When moving between cells while in the idle state,
`the mobile station will eventually "lose' radio connection on
`the control channel of the 'old' cell and tune to the control
`channel of the "new" cell. The initial tuning and subsequent
`re-tuning to control channels are both accomplished auto
`matically by scanning all the available control channels at
`their known frequencies to find the "best" control channel.
`When a control channel with good reception quality is
`found, the mobile station remains tuned to this channel until
`
`15
`
`20
`
`25
`
`30
`
`35
`
`BACKGROUND
`Applicants' invention relates generally to radiocommu
`nication systems that use digital control channels in a
`multiple access scheme and more particularly to cellular
`TDMA radiotelephone systems having digital control chan
`nels.
`The growth of commercial radiocommunications and, in
`particular, the explosive growth of cellular radiotelephone
`systems have compelled system designers to search for ways
`to increase system capacity without reducing communica
`tion quality beyond consumer tolerance thresholds. One way
`to increase capacity is to use digital communication and
`multiple access techniques such as TDMA, in which several
`users are assigned respective time slots on a single radio
`carrier frequency.
`In North America, these features are currently provided by
`a digital cellular radiotelephone system called the digital
`advanced mobile phone service (D-AMPS), some of the
`characteristics of which are specified in the interim standard
`IS-54B, “Dual-Mode Mobile Station-Base Station Compat
`ibility Standard', published by the Electronic Industries
`Association and Telecommunications Industry Association
`(EIA/TIA). Because of a large existing consumer base of
`equipment operating only in the analog domain with fre
`quency-division multiple access (FDMA), IS-54B is a dual
`mode (analog and digital) standard, providing for analog
`compatibility in tandem with digital communication capa
`bility. For example, the IS-54B standard provides for both
`FDMA analog voice channels (AVC) and TDMA digital
`traffic channels (DTC), and the system operator can dynami
`cally replace one type with the other to accommodate
`fluctuating traffic patterns among analog and digital users.
`The AVCs and DTCs are implemented by frequency modu
`lating radio carrier signals, which have frequencies near 800
`50
`megahertz (MHz) such that each radio channel has a spectral
`width of 30 kilohertz (KHZ).
`In a TDMA cellular radiotelephone system, each radio
`channel is divided into a series of time slots, each of which
`contains a burst of information from a data source, e.g., a
`digitally encoded portion of a voice conversation. The time
`slots are grouped into successive TDMA frames having a
`predetermined duration. The number of time slots in each
`TDMA frame is related to the number of different users that
`can simultaneously share the radio channel. If each slot in a
`TDMA frame is assigned to a different user, the duration of
`a TDMA frame is the minimum amount of time between
`successive time slots assigned to the same user.
`The successive time slots assigned to the same user, which
`are usually not consecutive time slots on the radio carrier,
`constitute the user's digital traffic channel, which may be
`considered a logical channel assigned to the user. As
`
`40
`
`45
`
`55
`
`60
`
`65
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`5,604,744
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`3
`the quality deteriorates again. In this way, mobile stations
`stay "in touch” with the system. The ACCs specified in
`IS-54B require the mobile stations to remain continuously
`"awake' (or at least for a significant part of the time, e.g.
`50%) in the idle state, at least to the extent that they must
`keep their receivers switched on.
`While in the idle state, a mobile station must monitor the
`control channel for paging messages addressed to it. For
`example, when an ordinary telephone (land-line) subscriber
`calls a mobile subscriber, the call is directed from the public
`switched telephone network (PSTN) to a mobile switching
`center (MSC) that analyzes the dialed number. If the dialed
`number is validated, the MSC requests some or all of a
`number of radio base stations to page the called mobile
`station by transmitting over their respective control channels
`paging messages that contain the mobile identification num
`ber (MIN) of the called mobile station. Each idle mobile
`station receiving a paging message compares the received
`MIN with its own stored MIN. The mobile station with the
`matching stored MIN transmits a page response over the
`particular control channel to the base station, which for
`wards the page response to the MSC.
`Upon receiving the page response, the MSC selects an
`AVC or a DTC available to the base station that received the
`page response, switches on a corresponding radio trans
`ceiver in that base station, and causes that base station to
`send a message via the control channel to the called mobile
`station that instructs the called mobile station to tune to the
`selected voice or traffic channel. A through-connection for
`the call is established once the mobile station has tuned to
`the selected AVC or DTC.
`When a mobile subscriber initiates a call, e.g., by dialing
`the telephone number of an ordinary subscriber and pressing
`the "send' button on the mobile station, the mobile station
`transmits the dialed number and its MIN and an electronic
`serial number (ESN) over the control channel to the base
`station. The ESN is a factory-set, "unchangeable' number
`designed to protect against the unauthorized use of the
`mobile station. The base station forwards the received
`numbers to the MSC, which validates the mobile station,
`selects an AVC or DTC, and establishes a through-connec
`tion for the call as described above. The mobile may also be
`required to send an authentication message.
`It will be understood that a communication system that
`uses ACCs has a number of deficiencies. For example, the
`format of the forward analog control channel specified in
`IS-54B is largely inflexible and not conducive to the objec
`tives of modern cellular telephony, including the extension
`of mobile station battery life. In particular, the time interval
`between transmission of certain broadcast messages is fixed
`and the order in which messages are handled is also rigid.
`Also, mobile stations are required to re-read messages that
`may not have changed, wasting battery power. These defi
`ciencies can be remedied by providing a DCC having new
`formats and processes, one example of which is described in
`U.S. patent application Ser. No. 07/956,640 entitled "Digital
`Control Channel', which was filed on Oct. 5, 1992, and
`which is incorporated in this application by reference. Using
`such DCCs, each IS-54B radio channel can carry DTCs only,
`DCCs only, or a mixture of both DTCs and DCCs. Within
`the IS-54B framework, each radio carrier frequency can
`have up to three full-rate DTCs/DCCs, or six half-rate
`DTCs/DCCs, or any combination in-between, for example,
`one full-rate and four half-rate DTCs/DCCs. As described in
`this application, a DCC in accordance with Applicants'
`invention provides a further increase in functionality.
`65
`In general, however, the transmission rate of the DCC
`need not coincide with the half-rate and full-rate specified in
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`IS-54B, and the length of the DCC slots may not be uniform
`and may not coincide with the length of the DTC slots. The
`DCC may be defined on an IS-54B radio channel and may
`consist, for example, of every n-th slot in the stream of
`consecutive TDMA slots. In this case, the length of each
`DCC slot may or may not be equal to 6.67 msec, which is
`the length of a DTC slot according to IS-54B. Alternatively
`(and without limitation on other possible alternatives), these
`DCC slots may be defined in other ways known to one
`skilled in the art.
`As such hybrid analog/digital systems mature, the number
`of analog users should diminish and the number of digital
`users should increase until all of the analog voice and control
`channels are replaced by digital traffic and control channels.
`When that occurs, the current dual-mode mobile terminals
`can be replaced by less expensive digital-only mobile units,
`which would be unable to scan the ACCs currently provided
`in the IS-54B system. One conventional radiocommunica
`tion system used in Europe, known as GSM, is already an
`all-digital system, in which 200-KHz-wide radio channels
`are located near 900 MHz. Each GSM radio channel has a
`gross data rate of 270 kilobits per second and is divided into
`eightfull-rate traffic channels (each traffic time slot carrying
`116 encrypted bits).
`In cellular telephone systems, an air-interface communi
`cations link protocol is required in order to allow a mobile
`station to communicate with the base stations and MSC. The
`communications link protocol is used to initiate and to
`receive cellular telephone calls. As described in U.S. patent
`application Ser. No. 08/047,452 entitled "Layer 2 Protocol
`for the Random Access Channel and the Access Response
`Channel,” which was filed on Apr. 19, 1993, and which is
`incorporated in this application by reference, the communi
`cations link protocol is commonly referred to within the
`communications industry as a Layer 2 protocol, and its
`functionality includes the delimiting, or framing, of Layer3
`messages. These Layer 3 messages may be sent between
`communicating Layer 3 peer entities residing within mobile
`stations and cellular switching systems. The physical layer
`(Layer 1) defines the parameters of the physical communi
`cations channel, e.g., radio frequency spacing, modulation
`characteristics, etc. Layer 2 defines the techniques necessary
`for the accurate transmission of information within the
`constraints of the physical channel, e.g., error correction and
`detection, etc. Layer 3 defines the procedures for reception
`and processing of information transmitted over the physical
`channel.
`Communications between mobile stations and the cellular
`switching system (the base stations and the MSC) can be
`described in general with reference to FIGS. 1 and 2. FIG.
`1 schematically illustrates pluralities of Layer 3 messages
`11, Layer 2 frames 13, and Layer 1 channel bursts, or time
`slots, 15. In FIG. 1, each group of channel bursts corre
`sponding to each Layer 3 message may constitute a logical
`channel, and as described above, the channel bursts for a
`given Layer 3 message would usually not be consecutive
`slots on an IS-54B carrier. On the other hand, the channel
`bursts could be consecutive; as soon as one time slot ends,
`the next time slot could begin.
`Each Layer 1 channel burst 15 contains a complete Layer
`2 frame as well as other information such as, for example,
`error correction information and other overhead information
`used for Layer 1 operation. Each Layer 2 frame contains at
`least a portion of a Layer 3 message as well as overhead
`information used for Layer 2 operation. Although not indi
`cated in FIG. 1, each Layer 3 message would include various
`information elements that can be considered the payload of
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`the message, a header portion for identifying the respective
`message's type, and possibly padding.
`Each Layer 1 burst and each Layer 2 frame is divided into
`a plurality of different fields. In particular, a limited-length
`DATA field in each Layer 2 frame contains the Layer 3
`message 11. Since Layer 3 messages have variable lengths
`depending upon the amount of information contained in the
`Layer 3 message, a plurality of Layer 2 frames may be
`needed for transmission of a single Layer 3 message. As a
`result, a plurality of Layer 1 channel bursts may also be
`needed to transmit the entire Layer 3 message as there is a
`one-to-one correspondence between channel bursts and
`Layer 2 frames.
`As noted above, when more than one channel burst is
`required to send a Layer 3 message, the several bursts are not
`usually consecutive bursts on the radio channel. Moreover,
`the several bursts are not even usually successive bursts
`devoted to the particular logical channel used for carrying
`the Layer 3 message. Since time is required to receive,
`process, and react to each received burst, the bursts required
`for transmission of a Layer 3 message are usually sent in a
`staggered format, as schematically illustrated in FIG. 2 and
`as described above in connection with the IS-54B standard.
`FIG. 2 shows a general example of a forward (or down
`25
`link) DCC configured as a succession of time slots 1, 2, ..
`., N, ... included in the consecutive time slots 1, 2, ... sent
`on a carrier frequency. These DCC slots may be defined on
`a radio channel such as that specified by IS-54B, and may
`consist, as seen in FIG. 2 for example, of every n-th slot in
`a series of consecutive slots. Each DCC slot has a duration
`that may or may not be 6.67 msec, which is the length of a
`DTC slot according to the IS-54B standard.
`As shown in FIG. 2, the DCC slots may be organized into
`superframes (SF), and each superframe includes a number of
`logical channels that carry different kinds of information.
`One or more DCC slots may be allocated to each logical
`channel in the superframe. The exemplary downlink super
`frame in FIG. 2 includes three logical channels: a broadcast
`control channel (BCCH) including six successive slots for
`overhead messages; a paging channel (PCH) including one
`slot for paging messages; and an access response channel
`(ARCH) including one slot for channel assignment and other
`messages. The remaining time slots in the exemplary super
`frame of FIG.2 may be dedicated to other logical channels,
`such as additional paging channels PCH or other channels.
`Since the number of mobile stations is usually much greater
`than the number of slots in the superframe, each paging slot
`is used for paging several mobile stations that share some
`unique characteristic, e.g., the last digit of the MIN.
`For purposes of efficient sleep mode operation and fast
`cell selection, the BCCH may be divided into a number of
`sub-channels. U.S. patent application Ser. No. 07/956,640
`discloses a BCCH structure that allows the mobile station to
`read a minimum amount of information when it is switched
`on (when it locks onto a DCC) before being able to access
`the system (place or receive a call). After being switched on,
`an idle mobile station needs to regularly monitor only its
`assigned PCH slots (usually one in each superframe); the
`mobile can sleep during other slots. The ratio of the mobile's
`time spent reading paging messages and its time spent asleep
`is controllable and represents a tradeoff between call-set-up
`delay and power consumption.
`Since each TDMA time slot has a certain fixed informa
`tion carrying capacity, each burst typically carries only a
`portion of a Layer 3 message as noted above. In the uplink
`direction, multiple mobile stations attempt to communicate
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`with the system on a contention basis, while multiple mobile
`stations listen for Layer 3 messages sent from the system in
`the downlink direction. In known systems, any given Layer
`3 message must be carried using as many TDMA channel
`bursts as required to send the entire Layer 3 message.
`Digital control and traffic channels are desirable for these
`and other reasons described in U.S. patent application Ser.
`No. 08/147,254, entitled "A Method for Communicating in
`a Wireless Communication System', which was filed on
`Nov. 1, 1993, and which is incorporated in this application
`by reference. For example, they support longer sleep periods
`for the mobile units, which results in longer battery life.
`Although IS-54B provides for digital traffic channels, more
`flexibility is desirable in using digital control channels
`having expanded functionality to optimize system capacity
`and to support hierarchical cell structures, i.e., structures of
`macrocells, microcells, picocells, etc. The term "macrocell"
`generally refers to a cell having a size comparable to the
`sizes of cells in a conventional cellular telephone system
`(e.g., a radius of at least about 1 kilometer), and the terms
`"microcell' and "picocell” generally refer to progressively
`smaller cells. For example, a microcell might cover a public
`indoor or outdoor area, e.g., a convention center or a busy
`street, and apicocell might cover an office corridor or a floor
`of a high-rise building. From a radio coverage perspective,
`macrocells, microcells, and picocells may be distinct from
`one another or may overlap one another to handle different
`traffic patterns or radio environments.
`FIG. 3 is an exemplary hierarchical, or multi-layered,
`cellular system. An umbrella macrocell 10 represented by a
`hexagonal shape makes up an overlying cellular structure.
`Each umbrella cell may contain an underlying microcell
`structure. The umbrella cell 10 includes microcell 20 rep
`resented by the area enclosed within the dotted line and
`microcell 30 represented by the area enclosed within the
`dashed line corresponding to areas along city streets, and
`picocells 40, 50, and 60, which cover individual floors of a
`building. The intersection of the two city streets covered by
`the microcells 20 and 30 may be an area of dense traffic
`concentration, and thus might represent a hot spot.
`FIG. 4 represents a block diagram of an exemplary
`cellular mobile radiotelephone system, including an exem
`plary base station 110 and mobile station 120. The base
`station includes a control and processing unit 130 which is
`connected to the MSC 140 which in turn is connected to the
`PSTN (not shown). General aspects of such cellular radio
`telephone systems are known in the art, as described by the
`above-cited U.S. patent applications and by U.S. Pat. No.
`5,175.867 to Wejke et al., entitled “Neighbor-Assisted
`Handoff in a Cellular Communication System,” and U.S.
`patent application Ser. No. 07/967,027 entitled "Multi-mode
`Signal Processing,” which was filed on Oct. 27, 1992, both
`of which are incorporated in this application by reference.
`The base station 110 handles a plurality of voice channels
`through a voice channel transceiver 150, which is controlled
`by the control and processing unit 130. Also, each base
`station includes a control channel transceiver 160, which
`may be capable of handling more than one control channel.
`The control channel transceiver 160 is controlled by the
`control and processing unit 130. The control channel trans
`ceiver 160 broadcasts control information over the control
`channel of the base station or cell to mobiles locked to that
`control channel. It will be understood that the transceivers
`150 and 160 can be implemented as a single device, like the
`voice and control transceiver 170, for use with DCCs and
`DTCs that share the same radio carrier frequency.
`The mobile station 120 receives the information broadcast
`on a control channel at its voice and control channel trans
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`ceiver 170. Then, the processing unit 180 evaluates the
`received control channel information, which includes the
`characteristics of cells that are candidates for the mobile
`station to lock on to, and determines on which cell the
`mobile should lock. Advantageously, the received control
`channel information not only includes absolute information
`concerning the cell with which it is associated, but also
`contains relative information concerning other cells proxi
`mate to the cell with which the control channel is associated,
`as described in U.S. Pat. No. 5,353,332 to Raith et al.,
`entitled "Method and Apparatus for Communication Control
`in a Radiotelephone System," which is incorporated in this
`application by reference.
`As noted above, one of the goals of a digital cellular
`system is to increase the user's "talk time', i.e., th