United States Patent
`US 6,400,699 B1
`(10) Patent No.:
`(12)
`Airyet al.
`(45) Date of Patent:
`Jun. 4, 2002
`
`
`US006400699B1
`
`(54) TRANSMISSION SCHEDULER FOR A
`MULTIPLE ANTENNA WIRELESS
`CELLULAR NETWORK
`
`(75)
`
`Inventors: Manish Airy, San Jose; Baraa
`Al-Dabagh, Sunnyvale; Jose Tellado,
`Stanford; Partho Mishra, Cupertino;
`hn
`Fan,
`Palo Alto: P
`K.
`Johnyan, M.owatainView.
`Arogyaswami J. Paulraj, Stanford, all
`of CA (US)
`
`(73) Assignee:
`
`(*) Notice:
`
`Iospan Wireless, Inc., San Jose, CA
`(US)
`Subject to any disclaimer, the term of this
`tent is
`extended
`djusted
`under
`35
`USCc ‘154(b)by 38‘ ” coun
`—
`y
`ys:
`
`(21) Appl. No.: 09/660,246
`44.
`(22)
`Filed:
`Sep. 12, 2000
`(SL) Ute C0 eeeeccccccsteseeseeseereereeeeeseeseesees H04Q 7/00
`(52) U.S. Che cece 370/329; 370/334; 370/474
`(58) Field of Search
`370/310, 310.1
`370/310.2311. 328. 329-348 468 369.
`370-375 474
`™”
`,
`,
`;
`References Cited
`U.S. PATENT DOCUMENTS
`
`(56)
`
`7/1992 Bruckert ....... cesses 375/1
`5,128,959 A *
`4/1996 Kay et AL.
`soeesseeeseessees 370/95.3
`5,513,183 A *
`3,oon Senoenieltl Ale sees 370/329
`5,742,592 “
`eres A * Lov1908 Raithetal .ove 370/347
`5,933,421 A
`8/1999 Alamoutiet al.
`5,970,062 A * 10/1999 Bauchot oo... 370/345
`6,058,105 A
`5/2000 Hochwald
`6,064,662 A
`5/2000 Gitlin etal.
`6,081,536 A *
`6/2000 Gorsuch etal. «0.0... 370/468
`ene “ isoo un tal
`aleL
`et al.
`6.192.026 Bl
`2/2001 Pollack et al.
`........ 370/329
`6,236,656 B1 *
`5/2001 Westerberg et al.
`6,317,435 Bl * 11/2001 Tiedemann, Jr. et al.
`... 370/441
`
`WO
`wo
`WO
`
`FOREIGN PATENT DOCUMENTS
`98/09385
`3/1998
`WO098/09381
`5/1998
`00/79722
`12/2000
`
`OTHER PUBLICATIONS
`vel
`fi
`ing
`f
`Paulray. A. Z
`i
`aulraj,
`A., Taxonomy of space-time processing for wireless
`networks, IEE Proc—Radar Sonar navig., vol. 145, No. 1,
`Feb. 1998.
`* cited by examiner
`
`Primary Examiner—David Vincent
`(74) Attorney, Agent, or Firm—Brian R. Short
`(57)
`ABSTRACT
`The invention includes an apparatus and method for sched-
`uling wireless transmission of data blocks between at least
`one antenna of a base transceiver station and multiple
`subscriber units. The scheduling can be based on the quality
`of a transmission link betweenthe base station antennas and
`the subscriber units, the amount of data requested by the
`subscriber units, and/or the type of data requested by the
`Subscriber units. The scheduling generally includes assign-
`ing frequency blocks and timeslots to each of the subscriber
`units for receiving or transmitting data blocks. The invention
`includes a method for transmitting data streams between a
`base transceiver station and a plurality of subscribers. The
`method includes receiving protocol data units from a
`network, creating sub-protocol data units from the protocol
`data units, and once per a frame of time, generating a
`schedule that designates time slots and pre-defined fre-
`quency blocks in which each one of the plurality of sub-
`scribersis to receive each of the sub-protocol data units from
`a plurality of base station transceiver antennas. The inven-
`tion can further include transmitting the schedule to each of
`the subscribers, and the plurality of base station transceiver
`antennas transmitting the sub-protocol data units according
`to the schedule. The invention can further include selecting
`at least one transmission mode for each subscriber. The
`transmission mode dictating the type of modulation and/or
`coding used during transmission of the sub-protocol data
`1
`units.
`
`33 Claims, 15 Drawing Sheets
`
`[ers||410
`
`
`
`tt
`CREATE SUB-PROTOCOL DATA
`UNITS FROM PDU'S
`
`|_¢~420
`
`BUFFER THE SUB-PROTOCOL
`DATA UNITS
`
`430
`
`
`
`
`_—___Y.
`ASSIGN TIME SLOTS ANO FREQUENCY
`BLOCKS TO RECEIVER UNITS (SCHEDULE)
`
`TRANSMIT SCHEDULE TO|¢~ 450
`RECEIVER UNITS
`
`
`TRANSMIT SUB-PROTOCOL DATA|5-460
`UNITS TO THE RECEIVER UNITS
`
`
`
`
`
`
`1
`1
`
`DELL EX. 1010
`
`440
`
`DELL EX. 1010
`
`

`

`U.S. Patent
`
`Jun. 4, 2002
`
`Sheet 1 of 15
`
`US 6,400,699 B1
`
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`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 2 of 15
`
`US 6,400,699 B1
`
`220
`
`FIGURE2(PRIORART)
`
`
`TRANSMITTERANTENNA ~ 210
`
`
`
`
`
`
`
`3
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 3 of 15
`
`US 6,400,699 B1
`
`Gee
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`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 4 of 15
`
`US 6,400,699 B1
`
`RECEIVE PDU'S
`
`410
`
`CREATE SUB-PROTOCOL DATA
`UNITS FROM PDU'S
`
`DATA UNITS
`
`BUFFER THE SUB-PROTOCOL
`
`420
`
`430
`
`ASSIGN TIME SLOTS AND FREQUENCY
`
`440
`
`BLOCKS TO RECEIVER UNITS (SCHEDULE)
`RECEIVER UNITS
`UNITS TO THE RECEIVER UNITS
`
`TRANSMIT SCHEDULE TO
`
`450
`
`TRANSMIT SUB-PROTOCOL DATA
`
`460
`
`FIGURE 4A
`
`5
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 5 of 15
`
`US 6,400,699 B1
`
`POWER UP SUBSCRIBER UNIT
`
`SYNCHRONIZE WITH SYSTEM
`
`415
`
`425
`
`DECODE TRANSMITTER MAP
`
`435
`
`RANGE TO DETERMINE DELAY BETWEEN
`
`445
`
`TRANSMITTER AND SUBSCRIBER UNIT
`DETERMINE RANGING OFFSET
`
`DECODE SUBSEQUENT MAP TO
`
`455
`
`INTRODUCE OFFSET TO
`SUBSCRIBER UNIT TRANSMISSIONS
`
`CONTEND FOR DATA REQUESTS
`
`465
`
`475
`
`
`
` RECEIVE MAP WITH BLOCK ALLOCATIONS
`
`48
`
`FIGURE 4B
`
`6
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 6 of 15
`
`US 6,400,699 B1
`
`= Te.
`— [ho
`
`SCHEDULER
`
`MAP
`
`530
`
`540
`
`a a a a a a
`
`—____>
`
`—__—_——_»
`
`SERVICE FLOW QUEUES
`
`FIGURE 5A
`
`7
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 7 of 15
`
`US 6,400,699 B1
`
`555
`
`SCHEDULER
`
`wap
`
`515
`
`525
`
`“Us
`
`a a a a a a
`
`545
`
`SERVICE FLOW QUEUES
`
`FIGURE 5B
`
`8
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 8 of 15
`
`US 6,400,699 B1
`
`BANDWIDTH
`
`FREQUENCY AVAILABLE
`
`JNUId
`
`FIGURE6
`
`9
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 9 of 15
`
`US 6,400,699 B1
`
`TIME
`
`SLOT
`
`01d
`ADNANOAYS
`
`FIGURE7A
`
`AINANDIYS
`
`10
`
`10
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 10 of 15
`
`US 6,400,699 B1
`
`YANNdf
`
`YNIT~
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`Oed
`
`JWIL
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`AQNANDIY
`
`11
`
`11
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 11 of 15
`
`US 6,400,699 B1
`
`Ald
`
`83uNOls
`
`AWIL ANTNMOG
`umn|ma|wTSas|S
`©Wno|we|WOTS|ws|e||acowaisis|1HoaMyoTa|INAWNOKSYadON|szs3nandss|as|
`YNITdn
`
`OZAMNOSIS
`
`AININDAYS
`
`12
`
`12
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 12 of 15
`
`US 6,400,699 B1
`
`NO
`
`NO
`
`ADDRESS SERVICE FLOW THAT
`
`CONTAINS SUB-PROTOCOL DATA UNITS
`
`
`
`IF THERE IS DATA TO SEND, THEN
`ASSIGN PRESENT SERVICE FLOW TO
`
`
`ONE OR MORE BLOCKS BASED ON
`MODE, BW, AND SYSTEM MODE
`
`
`
`910
`
`920
`
`UPDATE SERVICE FLOW QUEUE
`
`930
`
`INCREMENT BLOCK COUNT
`
`
`
`
`
`BLOCK COUNT
`
`
`LESS THAN N?
`
`
`950
`
`YES
`
`
`
`
`FINISHED WITH FRAME,
`
`READY TO TRANSMIT
`
`960
`
`FIGURE 9
`
`13
`
`13
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 13 of 15
`
`oO
`
`Od
`
`Oo°|—
`
` 1 SUB-
`
`DATA UNIT
`
`1 BLOCK
`
`oF&S2Speaa5a0
`
`ake
`
`14
`
`

`

`U.S. Patent
`
`Jun.4, 2002
`
`Sheet 14 of 15
`
`US 6,400,699 B1
`
`1110
`
`FIGURE11
`
`ADNANOSYA
`
`15
`
`15
`
`

`

`U.S. Patent
`
`US 6,400,699 B1
`
`
`
`Jun.4, 2002
`
`Sheet 15 of 15
`
`FIGURE 12
`
`16
`
`16
`
`

`

`US 6,400,699 B1
`
`1
`TRANSMISSION SCHEDULER FOR A
`MULTIPLE ANTENNA WIRELESS
`CELLULAR NETWORK
`
`FIELD OF THE INVENTION
`
`The invention relates generally to wireless communica-
`tions. Moreparticularly, the invention relates to scheduling
`of data wirelessly transmitted between a base controlstation
`having multiple antennas, and subscriber units.
`
`BACKGROUND OF THE INVENTION
`
`Wireless communication systems commonly include
`information carrying modulated carrier signals that are wire-
`lessly transmitted from a transmission source (for example,
`a base transceiver station) to one or more subscribers (for
`example, subscriber units) within an area or region.
`
`SPATIAL MULTIPLEXING
`
`Spatial multiplexing is a transmission technology that
`exploits multiple antennae at both the base transceiver
`station and at the subscriber units to increase the bit rate in
`
`a wireless radio link with no additional power or bandwidth
`consumption. Undercertain conditions, spatial multiplexing
`offers a linear increase in spectrum efficiency with the
`number of antennae. The substreams occupy the same
`channel of a multiple access protocol, the same time slot in
`a time-division multiple access protocol, the same frequency
`slot in frequency-division multiple access protocol, the same
`code sequence in code-division multiple access protocol or
`the same spatial target location in space-division multiple
`access protocol. The substreamsare applied separately to the
`transmit antennae and transmitted through a radio channel.
`Due to the presence of various scattering objects in the
`environment, each signal experiences multipath propaga-
`tion.
`
`The composite signals resulting from the transmission are
`finally captured by an array of receiving antennae with
`random phase and amplitudes. At the subscriber array, a
`spatial signature of each of the received signals is estimated.
`Based on the spatial signatures, a signal processing tech-
`nique is applied to separate the signals, recovering the
`original substreams.
`FIG. 1 showsthree transmitter antenna arrays 110, 120,
`130. The transmitter antenna arrays 110, 120, 130 transmit
`data symbols to a subscriber antenna array 140. Each
`transmitter antenna array includes spatially separate anten-
`nae. A subscriber connected to the subscriber antenna array
`140 separates the received signals.
`FIG. 2 shows modulated carrier signals traveling from a
`transmitter 210 to a subscriber 220 following manydifferent
`(multiple) transmission paths.
`Multipath can include a composition of a primary signal
`plus duplicate or echoed images caused by reflections of
`signals off objects between the transmitter and subscriber.
`The subscriber may receive the primary signal sent by the
`transmitter, but also receives secondary signals that are
`reflected off objects located in the signal path. The reflected
`signals arrive at the subscriber later than the primary signal.
`Due to this misalignment, the multipath signals can cause
`intersymbolinterference or distortion of the received signal.
`The actual received signal can include a combination of a
`primary and several reflected signals. Because the distance
`traveled by the original signal is shorter than the reflected
`signals, the signals are received at different times. The time
`difference between the first received and the last received
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`signal is called the delay spread and can be as great as
`several microseconds.
`
`The multiple paths traveled by the modulated carrier
`signal typically results in fading of the modulated carrier
`signal. Fading causes the modulated carrier signal to attenu-
`ate in amplitude when multiple paths subtractively combine.
`COMMUNICATION DIVERSITY
`
`Antennadiversity is a technique used in multiple antenna-
`based communication system to reduce the effects of multi-
`path fading. Antennadiversity can be obtained by providing
`a transmitter and/or a subscriber with two or more antennae.
`These multiple antennae imply multiple channels that suffer
`from fading in a statistically independent manner. Therefore,
`when onechannelis fading due to the destructive effects of
`multipath interference, another of the channels is unlikely to
`be suffering from fading simultaneously. By virtue of the
`redundancy provided by these independent channels, a sub-
`scriber can often reduce the detrimental effects of fading.
`Wireless systems generally require scheduling of infor-
`mation transmitted between base transceiver stations and
`subscriber units. The bandwidth of the available transmis-
`
`the transmission
`sion frequencies is limited. Therefore,
`between multiple transceiver stations and subscriber units
`generally requires time, frequency, or some other type of
`multiplexing. The larger the numberof basestation trans-
`ceivers and subscriber units, the more complex the sched-
`uling. Additionally, the above-described spatial multiplexing
`and communication diversity add complexity to the sched-
`uling.
`An individual transmission link exists between each indi-
`vidual base transceiver station antenna and a subscriber unit
`in communication with the base transceiver station. The
`
`previously described spatial multiplexing and communica-
`tion diversity require multiple antennas to each havetrans-
`mission links with a single subscriber unit. Optimally, the
`base transceiver station can schedule data transmission
`accordingto the transmission link quality between each base
`transceiver station antenna the subscriber unit. That is, the
`amountof information that can be transmitted between the
`individual base transceiver station antennas and the sub-
`
`scriber unit is base upon the quality of the transmission
`links. Ideally, the scheduling of the transmission of infor-
`mation between the base station transceiver and the sub-
`scriber units is dependent upon the quality of the individual
`transmission links.
`
`is desirable to have an apparatus and method that
`It
`provides scheduling of transmission of data blocks between
`base station transceiver antennas and subscribers
`(subscriber) units.
`It
`is desirable that
`the scheduling be
`adaptive to the quality of transmission links between the
`base station transceiver antennas and each of the subscribers
`(subscriber) units. It is additionally desirable that the appa-
`ratus and method allow for spatial multiplexing and com-
`munication diversity.
`SUMMARYOF THE INVENTION
`
`The invention includes an apparatus and a method for
`scheduling wireless transmission of data blocks between at
`least one antenna of a base transceiver station and multiple
`subscriber units. The scheduling can be based on the quality
`of a transmission link between the base station antennas and
`the subscriber units, the amount of data requested by the
`subscriber units, and/or the type of data requested by the
`subscriber units. The scheduling generally includes assign-
`ing frequency blocks and timeslots to each of the subscriber
`units for receiving or transmitting data blocks.
`
`17
`
`17
`
`

`

`US 6,400,699 B1
`
`4
`FIG. 7C showsa frame structure that include an up link
`map transmitted at a first
`time, and a down link map
`transmitted at a second time.
`
`FIG. 8 shows an example of a service flow table.
`FIG. 9 shows a flow chart of steps included within an
`embodimentof a scheduler according to the invention.
`FIG. 10 depicts several modes of block transmission
`according to the invention.
`FIG. 11 showsa framestructure that includes a code that
`
`distinguishes the blocks of the frame from blocks of other
`frames having a different code,
`thereby providing code
`division multiple access (CDMA).
`FIG. 12 showsa structure of a map messagethat is sent
`once per frame.
`DETAILED DESCRIPTION
`
`As shownin the drawings for purposesofillustration, the
`invention is embodied in an apparatus and a method for
`scheduling wireless transmission of data blocks between at
`least one antenna of a base transceiver station and multiple
`subscriber units. The scheduling can be based on the quality
`of a transmission link between the base station antennas and
`the subscriber units, the amount of data requested by the
`subscriber units, and/or the type of data requested by the
`subscriber units. The scheduling generally includes assign-
`ing frequency blocks and timeslots to each of the subscriber
`units for receiving or transmitting data blocks.
`As previously described, the invention includes wireless
`communication betweenat least one base transceiver station
`
`3
`A first embodimentof the invention includes a method for
`transmitting data streams between a base transceiverstation
`and a plurality of subscribers. The method includes receiv-
`ing protocol data units from a network, creating sub-
`protocol data units from the protocol data units, and once per
`a frame of time, generating a schedule that designates time
`slots and pre-defined frequency blocks in which each one of
`the plurality of subscribers is to receive each of the sub-
`protocol data units from a plurality of base station trans-
`ceiver antennas.
`A second embodiment of the invention is similar to the
`first embodiment. The second embodimentfurther includes
`
`transmitting the schedule to each of the subscribers, and the
`plurality of base station transceiver antennas transmitting the
`sub-protocol data units according to the schedule.
`A third embodimentis similar to the second embodiment.
`The third embodiment includesselecting at least one trans-
`mission mode for each subscriber. The transmission mode
`
`dictating the type of modulation and/or coding used during
`transmission of the sub-protocol data units. The transmis-
`sion mode selection can be dependent upon a quality of
`transmission link between the base station transceiver and
`
`the subscribers, and/or a quality of service requested by the
`subscribers.
`A fourth embodimentis similar to the first embodiment.
`
`10
`
`15
`
`20
`
`25
`
`For the third embodiment, generating a schedule that des-
`ignates time slots and pre-defined frequency blocks includes
`receiving service flow requests from the subscribers. The
`service flow requests indicating demands for data by the
`subscribers. Generating a schedule can further include
`receiving an information size request from the subscribers,
`and/or receiving a block weight for each of the service flow
`requests, wherein the block weight is dependent upon a
`priority of each of the service flow request. The block weight
`determines how many consecutive time slots and frequency
`blocks are transmitted to each subscriber.
`
`Other aspects and advantagesof the present invention will
`become apparent from the following detailed description,
`taken in conjunction with the accompanying drawings,
`illustrating by way of example the principles of the inven-
`tion.
`
`40
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`and subscriber units. The communicationsis two-way. That
`is,
`information is transmitted from the base transceiver
`station to the subscriber units (downlink transmission), and
`information is transmitted from the subscriber units to the
`base transceiver station (up link transmission).
`The transmission can be time division duplex (TDD).
`That is, the down link transmission can occupy the same
`channel
`(same transmission frequency) as the up link
`transmission, but occur at different times. Alternatively, the
`transmission can be frequency division duplex (FDD). That
`is, the downlink transmission can beat a different frequency
`than the up link transmission. FDD allows down link trans-
`mission and up link transmission to occur simultaneously.
`The following discussion of the invention generally includes
`45
`FIG. 1 showsaprior art wireless system that includes
`FDD. However, it should be understood that a TDD imple-
`mentation is feasible.
`spatially separate transmitters.
`FIG. 2 showsaprior art wireless system that includes As previously discussed, multiple subscriber units are in
`
`communication with at least once base transceiver station
`multiple paths from a system transmitter to system sub-
`scriber.
`antenna. Multi-point wireless communication systems like
`FIG. 3 shows an embodiment of the invention.
`this, can include time division multiplexing (TDM), fre-
`quency division multiplexing (FDM), code division multi-
`plexing (CDM),spatial division multiplexing (SDM),or any
`combination thereof, for communicating with multiple units.
`The following discussion of the invention includes a TDM-
`FDM combination. However,
`it is to be understood that
`other combinations of the above describe multiplexing
`schemes can be implemented.
`FIG. 3 shows an embodiment of the invention. The
`embodiment includes a base station transceiver receiving
`standard protocol data units (PDU’s). The PDU’s are
`divided into smaller sub-protocol data units that are stored in
`memory. A schedule is generated that designates time slots
`and frequency blocks in which the sub-protocol data units
`are to be transmitted to each of the subscriber units, and time
`slots and frequency blocks in which other sub-protocol data
`units are to be transmitted from the subscriber units to the
`base station transceiver.
`
`FIG. 4A showsa flow chart of steps included within an
`embodimentof the invention.
`
`FIG. 4B show another flow chart of steps included within
`another embodiment of the invention.
`
`FIG. 5A showsa set of service flow requests that indicate
`demands for data by subscriber units.
`FIG. 5B showsa setof estimated service flow buffer sizes
`
`that indicate demands for up link data by subscriber units.
`FIG. 6 showsa frequency spectrum of OFDM sub-carrier
`signals.
`FIG. 7A shows a frame structure depicting blocks of
`transmission data defined by transmission time and trans-
`mission frequency.
`FIG. 7B showsa framestructure that includes an up link
`map transmitted at one frequency band, and a downlink map
`transmitted at another frequency band.
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`whatfrequency data blocks requested by the subscriber unit
`will be transmitted, and when and at what frequency data
`blocks can be transmitted from the subscriber unit. The
`
`frameincludes a predetermined numberof sub-protocol data
`units as will be described later. An implementation of the
`framing unit 340 will be discussed later.
`The framed sub-protocol data units are received by
`coding, diversity processing, multi-carrier modulation units
`350, 360, 370. The coding within the units 350, 360, 370 will
`be discussed later. The units 350, 360, 370 can include
`diversity processing of the sub-protocol units. Diversity
`communications and processing is well knowninthe field of
`communications.
`
`5
`A media access control (MAC) adaptation unit 310
`receives the protocol data units from a standard computer
`network. The protocol data units can be Ethernet or ATM
`frames, or Internet protocol (IP) or frame relay packets. The
`MACadaptation unit 310 divides the protocol data units into
`smaller sub-protocol data units that are more adaptable for
`transmission within wireless communication systems. The
`smaller sub-protocol data units facilitate moreefficient error
`recovery through retransmission. Wireless channels tend to
`vary often. The smaller size of the sub-protocol data units
`makes it more likely that the data units will experience a
`steady channel during transmission.
`The digital circuitry or software required to divide or
`break large groups of data into smaller groups of data is well
`Multi-carrier modulator units 350, 360, 370 cach generate
`knownin the art of digital circuit and software design.
`a plurality of multiple-carrier modulated signals. Each
`multi-carrier modulator 350, 360, 370 receives a processed
`The sub-protocoldata units are stored within sub-protocol
`(coding and/or diversity processing) sub-protocol data unit
`data buffers 320. The sub-protocol data buffers 320 provide
`stream and generates a multiple-carrier modulated signal
`a scheduler 330 with easy access to the sub-protocol data.
`based on the corresponding processed sub-protocol data unit
`The scheduler 330 generates a map or schedule of when
`stream. The multiple-carrier modulated signals are fre-
`the sub-protocol data units are to be transmitted, which
`quency up-converted and amplified as is well known in the
`sub-protocol data units are to be received by which sub-
`art of communication systems.
`scriber unit, and when and at what frequency band the
`An output of a first multi-carrier modulator 350 is con-
`subscriber units can transmit sub-protocol data units back to
`
`the base station transceiver. The map is transmitted to the nected toafirst transmit antenna 375. An output of a second
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`subscriber units so that each subscriber unit knows when to
`multi-carrier modulator 360 is connected to a second trans-
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`receive and transmit sub-protocol units. Amapis transmitted
`once per unit of time. The unit of time is generally referred
`to as a frame. The time duration of a frameis variable.
`
`The scheduler 330 receives information regarding the
`quality of transmission links between the base station trans-
`ceiver and the subscriber units. The quality of the links can
`be used to determine whether the transmission of data
`should include spatial multiplexing or communication diver-
`sity. Additionally, the scheduler 330 receives data requests
`from the subscriber units. The data requests include infor-
`mation regarding the size and data type of data to be
`transmitted. The scheduler utilizes the link quality
`information,
`the data size, and the data type (including
`priority and requisite quality of service (QoS)) for generat-
`ing the schedule. A detailed discussion of an implementation
`of the scheduler will follow.
`
`A spatial multiplexing/diversity/neither block 335 has
`been included within FIG. 3. The spatial multiplexing/
`diversity/neither block 335 is included to show that a
`decision is made whetherto include spatial multiplexing or
`diversity based upon the quality of the transmission link
`parameters between the base transceiver station and a sub-
`scriber unit. The decision process can be located within the
`scheduler 330 or even within the subscriber unit.
`
`The scheduling decisions that are based upon the trans-
`mission quality between a base transceiver station and
`subscriber unit can be made at either the base station
`transceiver or the subscriber unit. The scheduling decisions
`can be made for both down link transmission and up link
`transmission. It is essential that both the base transceiver
`
`station and the subscriber unit be aware of the scheduling,
`spatial multiplexing and diversity decisions that are made
`base upon the quality of the transmission link.
`The scheduler 330 accesses the sub-protocol data units
`within the sub-protocol data buffers 320. Each data request
`can have a dedicated buffer within the sub-protocol data
`buffers 320. A predetermined number of sub-protocol data
`units are retrieved by the scheduler 330 and ordered within
`a frame within a framing unit 340. A mapof the schedule is
`included within every frame for the purpose of indicating to
`each subscriber unit when (that is, which time slot) and at
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`mit antenna 385. An output of a third multi-carrier modu-
`lator 370 is connected to a third transmit antenna 395. The
`first transmit antenna 375, the second transmit antenna 385,
`and the third transmit antenna 395 can be located within an
`antennaarray at a single base station. Alternatively, the first
`transmit antenna 375, the second transmit antenna 385, and
`the third transmit antenna 395 can each be located at
`
`separate base stations. The first transmit antenna 375, the
`second transmit antenna 385, and the third transmit antenna
`395 can have different polarization states, and be either
`physically co-located at a single base station, or each located
`at separate base stations. Circuitry associated with the trans-
`mit chains can be separately located with the antennas 375,
`385, 395.
`The embodimentof FIG. 3 includes three transmit anten-
`nas. It is to be understoodthat the invention can include two
`or more transmit antennas. The additional antennas can be
`
`driven by additional multi-carrier modulators that each
`include separate corresponding processed sub-protocol data
`unit streams.
`The embodimentof FIG. 3 can further include subscribers
`units 397, 399. The subscribers units 397, 399 can include
`multiple spatially separate subscriber antennae.
`Multiple transmitter antennae and multiple subscriber
`antennae allow the wireless communication system to
`include spatial multiplexing and communication diversity.
`As described earlier, spatial multiplexing and communica-
`tion diversity can improve the capacity of the communica-
`tion system and reducethe effects of fading and multi-path
`resulting in increased capacity.
`The scheduler 330 can support the processing required for
`spatial multiplexing. That is, the scheduler can direct sub-
`protocol data units to be transmitted from multiple base
`transceiver antennae (single base or multiple bases) so that
`transmission to a particular subscriber unit includes spatial
`multiplexing. For spatial multiplexing, more sub-protocol
`data units are scheduled for transmission. The number of
`
`sub-protocol data units scheduled for transmission is depen-
`dent upon the spatial multiplexing order.
`Radio Frequency (RF) signals are coupled between the
`transmitter antennae and the subscriber antennae. The RF
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`signals are modulated with data streams comprising the
`transmitted symbols. The signals transmitted from the trans-
`mitter antennae can be formed from different data streams
`(spatial multiplexing) or
`from one data stream
`(communication diversity) or both.
`Down Link Transmission
`
`FIG. 4A showsa flow chart of steps included within an
`embodiment of the invention. A first step 410 includes
`receiving the PUD’s. A second step 420 includes creating
`sub-protocol data units from the PUD’s. A third step 430
`includes storing the sub-protocol data units in sub-protocol
`data unit buffers. A fourth step 440 includes scheduling time
`slots and frequency block to each of the subscriber units. A
`fifth step 450 includes transmitting the schedule to the
`subscriber units. A sixth step 460 includes transmitting the
`sub-protocol data units to the subscribers. It is to be under-
`stood that the steps of the flow chart of FIG. 4A are not
`necessarily sequential.
`Up Link Transmission
`FIG. 4B show another flow chart of steps included within
`another embodiment of the invention. This embodiment
`includes the up link transmission procedures.
`A first step 415 includes powering up a subscriber unit.
`Asecond step 425 includes synchronizing the subscriber
`unit with frames being transmitted being transmitted from a
`base transceiver station. The base transceiver station trans-
`mits information within the framesthat allows the subscriber
`units to phase-lock or synchronize with the base transceiver
`station. Generally, all base transceiver stations of a cellular
`system are synchronized with a common reference clock
`signal.
`A third step 425 includes decoding a map transmitted
`within the base transceiver station. The transmitted map
`allows identification of ranging blocks and contention
`blocks that the subscriber can use for transmitting informa-
`tion to the base transceiver station.
`
`A fourth step 445 includes the subscriber unit sending
`ranging information. The ranging information is sent for
`estimating the propagation delay between the subscriber unit
`and the base transceiver station. The estimated delay is used
`for ensuring that transmit timing of the subscriber unit is
`adjusted to compensate for the propagation delay.
`A fifth step 455 includes decoding a map that is subse-
`quently sent by the base transceiver station for determining
`a ranging offset. The ranging offset can be used for future
`transmission by the subscriber unit.
`Asixth step 465 includes introducing the ranging offset in
`future subscriber unit transmissions.
`
`Aseventh step 475 includes contending for data requests
`with other subscriber units.
`
`An eighth step 485 includes receiving a map with block
`allocations in which data requests (up link) can be sent by
`the subscriber unit to the base transceiverstation.
`Service Flows
`
`Aservice flow request represents a bidirectional demand
`for data (up stream and down stream) between a base
`transceiver station and a subscriber unit, with an associated
`set of quality of service parameters. Generally,there are two
`types of service flow requests, constant bit rate (CBR) and
`unrestricted bit rate (UBR).
`The CBR service flow requests include the scheduler
`scheduling the subscribers to receive or
`transmit sub-
`protocol data units periodically. The period can be a prede-
`termined number of times per frame. Once a service flow
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`the up link and down link bandwidth
`is made,
`request
`allocation is periodic. Information is transmitted to and from
`the subscriber units without the subscriber units having to
`send information size requests. Up link allocations are
`periodically scheduled without solicitation by the subscriber
`unit.
`
`The UBRservice flow requests include the scheduler
`scheduling the up link and downlink scheduling based upon
`information size requests by the subscribers. The down link
`map allocations are made based upon the amountof data in
`the associated service flow buffers. The up link map allo-
`cations are made based upon the information size requests
`sent by the subscriber units. Each information size request
`updates the scheduler estimate of the amount of data in an
`associated service flow buffer.
`
`Down Link Service Flow Request
`FIG. 5A showsa set of service flow buffers 510, 520, 530,
`540 that contain sub-protocol data units for subscriber units.
`The scheduler uses the service flow buffers 510, 520, 530,
`540 to generate