United States Patent (19)
`Jalali et al.
`
`USOO5828662A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,828,662
`Oct. 27, 1998
`
`54 MEDIUM ACCESS CONTROL SCHEME FOR
`DATA TRANSMISSION ON CODE DIVISION
`MULTIPLE ACCESS (CDMA) WIRELESS
`SYSTEMS
`
`75 Inventors: Ahmad Jalali, Plano, Tex.; Witold
`Krzymien, Edmonton; Paul
`Mermelstein, Cote St. Luc, both of
`Canada
`
`73 Assignee: Northern Telecom Limited, Quebec,
`Canada
`
`Appl. No.: 666,828
`21
`22 Filed:
`Jun. 19, 1996
`(51) Int. Cl." ..................................................... H04B 71216
`52 U.S. Cl. .............................................................. 370/335
`58 Field of Search ..................................... 370/320, 321,
`370/324, 335, 337,342, 347, 350, 441;
`455/422
`
`56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,257.257 10/1993 Chen et al. ............................... 370/18
`5,260,967 11/1993 Schilling ..............
`... 370/342
`5,295,152 3/1994 Gudmundson et al. .................... 375/1
`5,309,474 5/1994 Gilhousen et al. ..................... 375/206
`5,394,391 2/1995 Chen et al. ............................... 370/18
`5,511,067 4/1996 Miller ........
`... 370/335
`5,586,120 12/1996 Cadd .........
`... 370/468
`5,603,081
`2/1997 Raith et al. .......
`... 455/435
`... 370/252
`5,604,730 2/1997 Tiedemann, Jr. .....
`5,640,414 6/1997 Blakeney, II et al. .................. 375/200
`
`5,673.259
`9/1997 Quick, Jr. ................................ 370/342
`FOREIGN PATENT DOCUMENTS
`O 564 937 A1 10/1993 European Pat. Off. .......... HO4B 7/26
`O 592 209 A1 4/1994 European Pat. Off. .......... H04B 7/26
`O 678 991 A2 10/1995 European Pat. Off. ......... HO4J 13/OO
`PCT/FI95/
`OO296 12/1995 WIPO.
`
`OTHER PUBLICATIONS
`Alfred Baier, Open Multi-Rate Radio Interface Architecture
`Based on CDMA, Phillips Kommunikations Industrie AG,
`Nurnberg, Germany, ICUPC 93, IEEE 1993, pp. 985–989.
`An Overview of the Application of Code Division Multiple
`Access (CDMA) to Digital Cellular Systems and Personal
`Cellular Networks, Qualcomm inc., Jun. 4, 1992, pp. 1-56.
`Primary Examiner Ajit Patel
`Attorney, Agent, Or Firm-Finnegan, HenderSon, Farabow,
`Garrett & Dunner, L.L.P.
`57
`ABSTRACT
`A Synchronous discontinuous transmission medium acceSS
`control (SDTX-MAC) method and apparatus for more effi
`ciently using existing uplink channels by Sharing these
`uplink channels between multiple terminals engaged in
`bursty data transmission. This is accomplished by assigning
`each mobile terminal an individual time slot and by not
`requiring each mobile terminal to broadcast its identity. This
`results in a reduction in the number of receivers on each base
`Station and a reduction in the length of the Synchronization
`meSSage.
`
`16 Claims, 5 Drawing Sheets
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`103
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`109
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`MOBILETERMINAL
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`BASE STATION
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`CONSTANTLY
`BROADCAST
`PILOT SIGNAL
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`RECEIVE ORIGINATION MESSAGE.
`ASSIGNSSRCTIMESLOT
`TOMOBILETERMINAL
`SEND SSRCASSGNMENT
`MESSAGE.
`
`107
`
`PAGING CHANNEL
`
`DETECTPACKETDATA CALL
`NITIATED BY USER.
`
`SEND ORGINATION MESSAGE
`SPECIFYING
`PACKETDATA CALL,
`
`RECEIVESSRC
`ASSIGNMENT MESSAGE.
`TUNE TO ASSIGNED SSRC, AND
`STORE SSRC ANDTIME
`SLOTIDENTIFIERS.
`
`IPR2018-01474
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`U.S. Patent
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`Oct. 27, 1998
`
`Sheet 1 of 5
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`5,828,662
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`|0ÅT INVISNOO
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`OHSS HAIBOEH60
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`U.S. Patent
`
`Oct. 27, 1998
`
`Sheet 2 of 5
`
`5,828,662
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`MOBILETERMINAL
`
`BASE STATION
`
`SET TRANSMITTER
`TO LOWEST
`POWER LEVEL
`
`201
`
`SEND SYNCH
`RONIZATION
`MESSAGEAT
`ASSIGNEDTIME
`SLOT ON SSRC.
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`START
`ACKNOWLEDGMENT
`TIMER.
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`205
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`ACKNOWLEDGMENT
`TIMER EXPRES,
`RESEND SYNCH
`RONIZATION
`MESSAGE AT NEXT
`POWER SETTING.
`
`RECEIVECHANNEL
`ASSIGNMENT
`MESSAGE.
`
`TUNE TO ASSIGNED
`TRAFFIC
`CHANNEL.
`
`SEND DATA FRAMES
`ONASSIGNED
`TRAFFIC CHANNELAT
`ASSIGNED SENDTIME.
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`RESPONSE
`RESERVATION
`CHANNEL
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`SYNCHRONIZATION
`MESSAGE
`NOTUNDERSTOOD
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`RECEIVE SYNCHRONIZATION
`MESSAGE SYNCHRONIZE
`TO MOBILETERMINAL USING
`SYNCHRONIZATION MESSAGE
`N PREAMBLE
`ASSIGN TRAFFIC CHANNEL
`SEND CHANNEL ASSIGNMENT
`MESSAGE.
`
`RECEIVE DATA FRAMES USING
`ALAYER TWOARQPROTOCOL.
`
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`US. Patent
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`Oct. 27, 1998
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`Sheet 3 0f 5
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`5,828,662
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`U.S. Patent
`
`Oct. 27, 1998
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`Sheet 4 of 5
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`5,828,662
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`REVERSE LINK CHANNELS
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`
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`ACCESS
`CH.1
`
`ACCESS TRAFFIC
`CH.
`CH.1
`
`TRAFFIC SSRC
`CHM
`CH.1
`
`SSRC
`CH.r
`
`4a
`
`
`
`SSRC 1
`SSRC 1
`FRAME FRAME 2
`
`SSRC
`FRAMES
`
`4b
`
`4C
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`U.S. Patent
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`Oct. 27, 1998
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`Sheet 5 of 5
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`5,828,662
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`09
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`1
`MEDIUM ACCESS CONTROL SCHEME FOR
`DATA TRANSMISSION ON CODE DIVISION
`MULTIPLE ACCESS (CDMA) WIRELESS
`SYSTEMS
`
`FIELD OF THE INVENTION
`The present invention relates to the use of code division
`multiple access to Support data transmission Systems. More
`particularly, the present invention relates to wireleSS acceSS
`Synchronization techniques to Support integrated Services in
`third generation personal communications Systems and as
`the wireleSS access technology for local area networkS.
`DESCRIPTION OF RELATED ART
`Code division multiple access (CDMA) systems, also
`known as CDMA wireleSS access Systems, are comprised of
`a plurality of base Stations interconnected by one or more
`Switching Systems. Each base Station Serves a particular
`geographic region referred to as a cell. Within each base
`station's cell are any number of mobile terminals. The
`function of each base Station is to transmit data between its
`respective Switching System and the mobile terminals
`assigned to its cell. The base Station transmits the data to the
`mobile terminal over radio channels, which are also known
`as downlinkS. Conversely, the mobile terminals communi
`cate with their assigned base Station over radio channels
`known as uplinkS.
`Typically, the base Station maintains track of its assigned
`mobile terminals by continuously transmitting a pilot Signal
`containing timing markers on a Specific downlink channel.
`This continuous transmission allows the base Station to
`maintain Synchronization with its assigned mobile terminals.
`Such synchronization in turn enables the base station to
`transmit data to any given mobile terminal as needed.
`In addition to achieving Synchronization on the downlink
`channel for Sending data, a base Station also Synchronizes
`with its assigned mobile terminals via the uplink channel to
`receive data by using a Synchronization message. Synchro
`nization messages are transmitted by a mobile terminal
`when it initiates a call. Like the pilot Signal, the Synchroni
`Zation message also contains timing markers to which the
`receiver on the assigned base Station Synchronizes at the
`beginning of a call. Once the uplink channel from the mobile
`terminal to the base Station is established, the base Station
`uses additional timing information contained in on-going
`transmissions from the connected mobile terminal to main
`tain Synchronization.
`The Synchronization requirements and the procedures
`discussed above are specified in EIA/TIA standard IS-95,
`which is discussed in detail in the 1992 Qualcomm Incor
`porated’s primer entitled “An Overview Of The Application
`Of Code Division Multiple Access (CDMA) To Digital
`Cellular Systems And Personal Cellular Networks.”
`One shortcoming of this widely used Synchronization
`Standard is that it only performs well in regard to voice
`Services. For example, Synchronization messages are inap
`plicable for other types of cellular Services because Such
`cellular Services do not maintain frequent enough contact
`with their respective base Station to maintain Synchroniza
`tion. Accordingly, if the System is used to provide packet
`data Services, or any other Services in which the mobile
`terminal to base Station transmissions are infrequent bursts,
`the base Station may lose Synchronization with its mobile
`terminals.
`Several methods have been proposed to avoid the loss of
`Synchronization at the base Station during packet data calls.
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`For example, in an article entitled “Open Multi-Rate Radio
`Interface Architecture Based On CDMA, Proc. of 2nd
`International Conference on Universal Personal
`Communications, pp. 985-89, October 1993, A. Baier dis
`closed a method in which mobile terminals continually
`transmit a low bit rate physical control Signal to the base
`station between data bursts. The base station would in turn
`use the physical control Signal to maintain Synchronization
`with the terminal between data bursts. This method is
`referred to in this patent application as the continuous
`transmission medium access control (CTX-MAC) scheme.
`However, the CTX-MAC scheme is not very practical in
`that it requires the reservation of an uplink channel for each
`mobile terminal engaged in bursty data transmission.
`Accordingly, even if a mobile terminals use of its assigned
`channel to transmit data burstS was very infrequent, the
`assigned channel could not be used by any other mobile
`terminal and in effect would be rendered useless whenever
`the assigned mobile terminal ceased transmitting.
`Additionally, the receiver on the base Station must remain
`active at all times for each “on-off Source. An “on-off
`Source is one that alternates between periods when it trans
`mits data and periods when it has no data to transmit.
`A variation of the CTX-MAC scheme which serves on-off
`Sources with Small duty cycles, i.e., the ratio of the on-period
`to the off-period, can achieve considerable Savings in base
`Station hardware, Such as eliminating individually assigned
`receivers, if the transmission from the individual mobile
`terminals is discontinued during the off-periods and the
`hardware is shared among different users. In order to imple
`ment this variation, which is known as the discontinuous
`transmission medium access control (DTX-MAC) scheme, a
`Synchronization message must be transmitted at the begin
`ning of each on-period to allow the base Station to acquire
`Synchronization with the transmitting mobile terminal. The
`Synchronization message also serves to inform the base
`Station that a particular mobile terminal intends to transmit.
`In this DTX-MAC scheme, all mobile terminals use the
`Same PN code to Send their Synchronization message on the
`Synchronization-reservation channel. Using the same PN
`code on the Synchronization-reservation channel avoids the
`need for a separate receiver assigned to receive communi
`cations from a mobile terminal even though that mobile
`terminal is in the off mode. Even though there may be a need
`for more than one Synchronization-reservation channel if the
`number of mobile terminals is large, the number of
`Synchronization-reservation channels should be kept as
`Small as possible in order to reduce complexity at the base
`station. Several protocols have been established to allow the
`Single receiver to accept and process the numerous Synchro
`nization messages originating from the numerous mobile
`terminals. For example, one approach allows the mobile
`units to Send Synchronization messages in an asynchronous
`fashion, which is also known as the ADTX-MAC scheme.
`However, one of the shortcomings of the ADTX-MAC
`Scheme is that collisions may occur among the numerous
`Synchronization messages Sent by their respective mobile
`terminals. At a given time only one mobile Station can
`attempt to access the uplink to establish Synchronization. If
`two or more mobile terminals transmit their Synchronization
`messages, which the IS-95 Standard refers to as a preamble,
`a collision occurs. If two or more of the mobile terminals
`have a relative delay of less than a chip duration, then
`destructive collisions occur and all terminals must retransmit
`at a later time. If all relative delays are greater than one chip
`duration, then depending on the receiver design used, the
`first arriving mobile terminal may be able to Successfully
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`3
`Synchronize but the Second arriving mobile terminal will not
`be able to Synchronize.
`One example of destructive collision is taught by U.S. Pat.
`No. 5,394,391 (Chen) and U.S. Pat. No. 5,257.257 (Chen2),
`both of which disclose a method of controlling the operation
`of a packet Switched CDMA telecommunication network.
`Both patents teach that the transmitting terminal begins its
`transmission routine by Sensing whether or not the receiving
`terminal is busy. If the receiving terminal is free, the
`transmitting terminal initiates its transmission. However,
`because this Sensing for activity is performed randomly, and
`accordingly So is the Subsequent transmission, if a Second
`mobile terminal begins transmitting at the same time, a
`destructive collision will most likely occur.
`One method to reduce the probability of destructive
`collisions is taught by U.S. Pat. No. 5,295,152
`(Gudmundson et al.). Although Gudmundson et al. teaches
`increasing the capacity of radiotelephone communication
`Systems by eliminating interference to communication traf
`fic caused by random access bursts from unconnected
`mobile Stations, it does So by interrupting the communica
`tion traffic of other mobile Stations using the same frequency
`at periodic intervals. Consequently, it does not allow mul
`tiple mobile transmitters to transmit in an orderly fashion.
`Another method to reduce the probability of destructive
`collisions functions by delaying the Synchronization mes
`Sage according to Some probabilistic rule. However, the
`initial delay tends to propagate additional Synchronization
`acquisition delayS. Also, for mobile terminals operating with
`relative delays from the base Station of more than a chip
`duration, the collision of the numerous Synchronization
`messages will also result in added interference. These Sec
`ondary interferences are referred to as interfering collisions.
`One additional shortcoming of CDMA Systems in general,
`and ADTX-MAC schemes in particular that must be
`resolved is that, because all the mobile terminals would use
`the same uplink channel, their Synchronization message
`must include a field identifying each individual transmitting
`mobile terminal. Because the base Station must then decode
`the identification field contained in the Synchronization
`message before Sending an acknowledgment to the Sending
`mobile terminal, there are certain repercussions on perfor
`mance. For example, the performance of the uplink is quite
`Sensitive to the closed-loop power control. Since closed
`loop power control is typically not established by the time
`the Synchronization message is transmitted, the error rate in
`decoding the identification part of the Synchronization mes
`Sage may be quite high. Consequently, the length of the
`Synchronization message must be long enough to ensure that
`the mobile terminal's identification field is correctly
`decoded by the base station.
`AS evidenced by the above discussion, there are Several
`interrelated shortcomings associated with the ADTX-MAC
`scheme. For example, the ADTX-MAC's performance
`depends on the number of Synchronization-reservation chan
`nels required to establish uplinks for all the mobile termi
`nals. In turn, the number of Synchronization-reservation
`channels required depends significantly on the Synchroniza
`tion message traffic generated by the mobile terminals.
`Because the number of Synchronization messages generated
`per unit of time by a given Source is difficult to characterize,
`the ADTX-MAC scheme is inherently unstable due to the
`potential for destructive or interfering collisions. As a result
`of this uncertainty in the amount of Synchronization traffic
`generated, not only is the System designer forced to under
`dimension the System as a whole, the design of the protocol
`needed to Stabilize the System also becomes more compli
`cated.
`
`4
`In light of the foregoing, there is a need for a method or
`apparatus that can make more efficient use of uplink chan
`nels by Sharing the uplink channels between Several mobile
`terminals engaged in bursty data transmission.
`
`SUMMARY OF INVENTION
`Accordingly, the present invention is directed to a method
`and apparatus to acquire Synchronization by a base Station
`with a mobile terminal at the beginning of the on-period on
`the uplink channel which Substantially overcomes one or
`more of the above mentioned problems arising from limi
`tations and disadvantages of the related art.
`To achieve these and other advantages and in accordance
`with the purpose of the invention, as embodied and broadly
`described, the invention is a method and apparatus for
`transmitting a Synchronization message on an uplink chan
`nel which not only reduces the number of receivers on the
`base Station but also avoids the need for identifying the
`mobile terminal transmitting the Synchronization message,
`which as a consequence avoids collisions among other
`mobile terminals in the same cell and reduces interference.
`It is to be understood that both the foregoing general
`description and the following descriptions are exemplary
`and explanatory and are intended to provide further expla
`nation of the invention as claimed.
`The accompanying drawings are included to provide a
`further understanding of the invention and are incorporated
`in and constitute a part of this Specification, illustrate one of
`many embodiments of the invention and together with the
`description Serve to explain the principles of the invention.
`
`BRIEF DESCRIPTION OF DRAWINGS
`FIG. 1 is a schematic representation of the establishment
`of a Synchronous Synchronization-reservation channel.
`FIG. 2 is a Schematic representation of a call initiation
`algorithm.
`FIG. 3 is a Schematic representation of a call termination
`algorithm.
`FIG. 4 is a schematic representation of the format of the
`Synchronization-reservation channel on the reverse link.
`FIG. 5 is a schematic representation of the format of the
`reservation response channel on the forward link.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`Reference will now be made in detail to the present
`preferred embodiment of the invention, an example of which
`is illustrated in the accompanying drawings. This embodi
`ment is a Synchronous approach to the transmission of a
`Synchronization message in order to overcome the short
`comings of the ADTX-MAC scheme described above. The
`preferred embodiment is Synchronous discontinuous trans
`mission MAC (SDTX-MAC)scheme in which a TDMA
`frame on a Synchronous Synchronization-reservation (SSR)
`channel on the reverse link is divided into Short time slots,
`and each time slot is assigned to a mobile terminal.
`The first step in establishing a SDTX-MAC scheme is
`depicted in FIG. 1. In such a depiction which, for example
`can be applied to a mobile telephone System, the base Station
`maintains constant contact with its assigned mobile termi
`nals by constantly broadcasting, as shown in Step 101, a pilot
`Signal on the downlink pilot channel. The user initiates, as
`shown in step 103, a transmission from the mobile terminal
`to the base Station by powering on the mobile terminal. Once
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`S
`powered on and the message is ready to be sent, the mobile
`terminal registers with the base Station by broadcasting, as
`shown in Step 105, an origination message on one of the
`uplink access channels. Upon receiving the origination
`message, the base Station broadcasts, as shown in Step 107,
`an assignment message to the mobile terminal on one of the
`downlink paging channels. This assignment message con
`Sists of an SSR channel assignment and an assigned time slot
`on the assigned SSR channel for use by the mobile terminal
`in communicating with the base Station.
`Upon receiving the assignment message, the mobile ter
`minal tunes its transmitter, as shown in step 109, to its
`assigned SSR channel, and stores both the SSR channel
`identifier and the time slot identifier in memory. The mobile
`terminal is now prepared to begin its data burst transmission
`to the base Station.
`FIG. 2 shows how a mobile terminal achieves packet data
`transmission on the uplink. AS depicted in FIG. 2, each
`mobile terminal is initially programmed to operate, as
`shown in Step 201, at its lowest power Setting. Then using
`the information contained in the assignment message, the
`mobile terminals transmitter broadcasts, as shown in Step
`203, a Synchronization message to the base Station on the
`assigned SSR channel at the assigned time slot.
`Once the mobile terminal broadcasts the Synchronization
`message, an acknowledgement timer begins to run as shown
`in step 205. If the base station does not send an acknowl
`edgement message within a period of time Set by the mobile
`terminal, as shown in Step 207, the acknowledgement timer
`expires. If the acknowledgement timer does expire as shown
`in step 209, the power setting of the mobile terminals
`transmitter is increased by X dB where (0<X-7) dB. After
`the power level is reset the message is rebroadcast, and the
`acknowledgement timer begins again.
`Once the base Station receives the Synchronization mes
`Sage it Synchronizes to the mobile terminal using the pre
`amble in the Synchronization message and then sends, as
`shown in Step 211, an acknowledgment to the mobile
`terminal. This acknowledgment is in the form of a channel
`assignment message containing a traffic channel and a Send
`time. The channel assignment message is then broadcast by
`the base Station to the mobile terminal on a response
`reservation channel (RR). Alternatively the paging channel
`could be used to broadcast the channel assignment message
`as well.
`Upon receiving the channel assignment message, the
`mobile terminal tunes its transmitter to the assigned traffic
`channel and at the assigned Send time transmits, as shown in
`Step 213, its data frames to the base Station on a reverse
`traffic channel. A layer two ARQ (Automatic Repeat
`reOuest) protocol may be used to ensure that the data frames
`are received correctly and in Sequence, as shown in Step 215.
`FIG. 3 depicts the call termination mode which begins
`with the mobile terminal using the time slot assigned in the
`assignment message to broadcast, as shown in Step 301, a
`Synchronization message on the SSR channel to the base
`Station. Once the base Station receives the Synchronization
`message, the base Station uses the preamble in the Synchro
`nization message broadcast by the mobile terminal to
`synchronize, as shown in step 303, with the mobile terminal.
`The base Station then assigns a traffic channel and a transmit
`time to the mobile terminal in a channel assignment mes
`Sage. This channel assignment message is Subsequently
`broadcast on a response reservation channel by the base
`Station to mobile terminal.
`Upon receiving the channel assignment message, the
`mobile terminal tunes its transmitter to the assigned traffic
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`channel and at the assigned Send time transmits its call
`termination message on a reverse traffic channel to the base
`station, as shown in step 305. Upon receiving the call
`termination message, the base Station broadcasts, as shown
`in Step 307, an acknowledgement message to the mobile
`terminal on a forward traffic channel, and then deletes both
`the traffic channel and the SSR channel time slot assign
`ments for that particular mobile terminal. Finally, upon
`receiving the message from the base Station acknowledging
`the receipt of the call termination message, the mobile
`terminal, as shown in step 309, turns off its transmitter and
`deletes both its SSR channel assignment and its time slot
`assignment, thereby terminating the call.
`Particular attention is now paid in FIG. 4 to the way the
`frames on the SSR channel are divided first into frames and
`then into time slots. For example, FIG. 4a depicts the format
`of all the reverse TDMA channels on which the mobile
`terminal can broadcast, including the r SSR channels. FIG.
`4b depicts the first SSR channel 401 further divided into S
`frames. FIG. 4c depicts the first frame of the first SSR
`channel 402 further divided into a series of t consecutive
`time slots.
`As discussed above, the preferred embodiment of the
`invention functions by assigning a time slot on a certain SSR
`channel to each mobile terminal during the call orientation
`period. It should be noted that the SSR channel frame
`repeats itself after t SSR channel time slots.
`An SSR channel PN code, or SSRC-PN, is assigned for
`each SSR channel in a sector of a given cell in which the
`mobile terminals are located. An SSRC-PN is a short code
`which is transmitted by the mobile terminal on its assigned
`SSR channel time slot. Because the same PN code is used on
`the SSR channel by all the mobile terminals in the same
`Sector, only one receiver is required for every SSR channel
`used.
`Since there is a one to one correspondence between the
`time slots of the SSR channel and the mobile terminals, it is
`not necessary that the mobile terminals identity be trans
`mitted in the time slot. Accordingly, the preamble transmit
`ted on the SSR channel by a mobile terminal only needs to
`be long enough to provide initial Synchronization. This
`results in the SSR channel time slots being long enough to
`allow k repetitions of the SSRC-PN in one time slot.
`Therefore, when the mobile terminal transmits its pre
`amble on its assigned SSR channel time slot, it will consist
`of k repetitions of the SSRC-PN. The reason for transmitting
`the preamble k times is to allow the base station to first
`detect energy on the SSR channel time slot So it can then
`acquire synchronization with the mobile terminal. Along PN
`code that differentiates different Sectors is used to mask the
`SSRC-PN before transmission of the preamble on the time
`slot.
`Once the base Station detects energy on a given SSR
`channel time slot, thereby determining that the correspond
`ing terminal is attempting to transmit data, the base Station
`in turn transmits a message on one of the reservation
`response (RR) channels. FIG. 5 is a representation of the
`breakdown of the typical channels found on a forward link.
`For example, FIG. 5a depicts the format of all the forward
`link channels, including the e RR channels on which the
`base stations can broadcast. FIG. 5b depicts the first RR
`channel 501 divided into f frames. FIG. 5c depicts the first
`frame of the first RR channel 502 further divided into a
`Series of g consecutive time slots.
`It should be noted that the number of time slots on an RR
`channel may be larger or Smaller than the number of time
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`IPR2018-01474
`Apple Inc. EX1024 Page 9
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`slots on the SSR channel. The mobile terminal is assigned to
`an RR channel time slot at the call Setup time, and is used
`by the base Station to respond to the reservation request Sent
`by the mobile terminal on the SSR channel time slot. The RR
`channel time slot can also be used by the base Station to
`inform the mobile terminal when there is a request on the
`network Side of the System for transmission of data to the
`terminal. Whenever the mobile terminal receives a message
`on the RR channel time slot, it knows to begin Sensing the
`traffic channel on the forward link based on information
`received in the message on the RR time slot.
`Note that the RR channel may be designed so that the base
`station only transmits k repetitions of an RR channel PN
`code (RRC-PN) so as to allow the terminal to receive energy
`on its assigned RR channel time slot which then directs the
`terminal to the forward link traffic channel to receive mes
`Sages. The RR channel may also be designed to include a
`Short message.
`As an example, consider an SSR channel which is 20
`msec long and is divided into 48 time slots. Assuming a PN
`code with period 128 is used, 32 periods of the PN code may
`be fit into one time slot. In order to take into account the
`round trip propagation delay between the mobile terminal
`and the base station unit, the PN code should be repeated 31
`times within the minislot.
`Simulation results indicate that 37% of the time the
`Synchronization delay is 20 msec (one transmission
`attempt), 36% of the time the synchronization delay is 40
`msec, 18% of the time the synchronization delay is 60 msec,
`6% of the time the synchronization delay is 80 msec, and 3%
`of the time the synchronization delay is 100 m.sec.
`Accordingly, the present invention has lower access delay,
`higher throughput, reduced base Station complexity, and is
`robust to traffic variations.
`Two types of handoffs may occur during a packet data
`call. If the terminal is in the process of data transmission and
`is put in Soft handoff with other cells/sectors or a hand
`handoff is carried out, the base Station will Send a new
`Synchronization channel assignment message to the terminal
`through the traffic channel. The message Specifies a new
`Synchronization channel, a time slot and a Sector by which
`the mobile terminal will make future access attempts. If the
`terminal is not on a traffic channel, i.e. it is in idle mode and
`carries out an idle handoff according to the IS-95 standard to
`another Sector, then the terminal will be required to relin
`quish both its Synchronization channel and its time slot on
`the old cell/Sector, and then obtain a new Synchronization
`channel and time slot on the new cell.
`It will be apparent to those skilled in the art that various
`modifications and variations can be made to the algorithm of
`the present invention without departing from the Spirit or
`Scope of the invention. Thus, it is intended that the present
`invention cover the modifications and variations of this
`invention provided they come within the scope of the
`appended claims and their equivalents.
`What is claimed:
`1. A code division multiple access (CDMA) communica
`tion System comprising a base Station and a plurality of
`assigned mobile terminals coupled at least one said base
`Station, wherein Said base Station communicates with Said
`plurality of assigned mobile terminals using at least one
`transmitter and at least one receiver to transfer at least one
`of many data bursts, and Said transmitter and receiver
`communicate using a plurality of communication channels
`comprising:
`forward link channels which include a pilot channel, a
`Synchronization channel, at least one paging channel, at
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`least one forward traffic channel, and at least one
`reservation response channel;
`reverse link channels which include at least one access
`channel, at least one reverse traffic channel, and at least
`one Synchronous Synchronization-reservation channel;
`and
`means for establishing a communication link between
`Said base Station and Said plurality of assigned mobile
`terminals.
`2. A code division multiple access (CDMA) communica
`tion System as recited in claim 1, wherein Said means for
`establishing a communication link further comprises:
`means for maintaining contact between Said base Station
`and a first of Said plurality of assigned mobile termi
`nals,
`means for Synchronizing transmissions between Said base
`Station and the first of Said plurality of assigned mobile
`terminals,
`means for adjusting the transmitting power of the first of
`Said plurality of assigned mobile terminals So as to
`allow the transfer o