(12)
`
`United States Patent
`Esteves et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,245,594 B1
`Jul. 17, 2007
`
`US007245594B1
`
`(54) METHOD AND APPARATUS FOR FAST
`CLOSED-LOOP RATE ADAPTATION IN A
`HIGH RATE PACKET DATA TRANSMISSION
`(75) Inventors: Eduardo A. S. Esteves, San Diego, CA
`(US); Rashid A. Attar, San Diego, CA
`(US); Nagabhushana T.
`s
`Sindhushayana, San Diego, CA (US)
`
`(73) Asigne gullsen incorporated, San Diego,
`(US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/570,210
`
`May 12, 2000
`
`(22) Filed:
`51) Int. C
`nt. C.
`(2006.01)
`H04B 7/22
`(52) U.S. Cl. ....................... 370/322; 370/348; 370/443
`(58) Field of Classification Search ............. 370/395.2,
`370/442,232, 243, 230.1, 352,252,253,
`370/335, 340, 412,337, 450, 451, 454, 458,
`370/459, 468,452,322, 348, 347,524; 375/225,
`375/133,227, 222 455/69, 62, 67.11. 67.13.
`455/452.2, 450, 436,509, 519; 340/502,
`34O7825.25
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
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`9, 1989 Williams et al.
`5,038,399 A * 8, 1991 Bruckert .................. 455, 67.11
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`5,172.375 A 12, 1992 Kou ........................... 370,322
`5,203,008 A * 4, 1993 Yasuda et al. ........... 455,452.2
`5,227,775 A * 7/1993 Bruckert et al. ....... 340,825.25
`5,287,544. A * 2/1994 Menich et al. .............. 455,436
`
`5,295,140 A * 3/1994 Crisler et al. ............... 370,458
`5,303,234. A
`4, 1994 Kou ........................... 370,459
`5,377,192 A * 12/1994 Goodings et al. ........... 370,348
`ck
`5,396,516 A
`3/1995 Padovani et al. ............. 455.69
`5.483,676 A *
`1/1996 Mahany et al. ............. 370/468
`5,790,533 A * 8/1998 Burke et al. .................. 455.69
`5,881,061 A * 3/1999 Iizuka et al. ................ 370/468
`6,005,856 A * 12/1999 Jensen et al. ............... 370,337
`6,034,952. A * 3/2000 Dohi et al. ................. 370,252
`6,154.450 A * 1 1/2000 Wallentin et al. ........... 370,311
`6, 192,029 B1* 2/2001 Averbuch et al. ........... 370,230
`6.219,528 B1 *
`4/2001 Wright et al................ 370,318
`6,400,701 B2
`6/2002 Lin et al. .................... 455,450
`
`(Continued)
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`O65268O
`
`5, 1995
`
`Continued
`(Continued)
`Primary Examiner Doris H. To
`Assistant Examiner Phuongchau Ba Nguyen
`(74) Attorney, Agent, or Firm Thomas R. Rouse; Thien T.
`Nguyen; Kyong H. Macek
`
`(57)
`
`ABSTRACT
`
`In a high data rate communication system capable of vari
`able rate transmission, an open loop rate control can be
`adjusted with a closed loop rate control to maximize
`throughput. An access point generates interleaved multi-slot
`packets that allow an access terminal to transmit indicator
`messages to the access point in accordance with recently
`received data carried within slots of the multi-slot packets.
`
`18 Claims, 4 Drawing Sheets
`
`
`
`Access Point
`
`700
`
`
`
`Scheduler
`
`SNR
`estimation
`
`OuterLoop
`Rate
`Control
`
`Closed Loop
`Rite
`Control
`FCL)
`
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`US 7,245,594 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`6,661,774 B1* 12/2003 Laufenburger et al. . 370/395.2
`2002fO198O12 A1* 12/2002 Vukovic et al.
`
`- - - - - - - - - - - - 455,509
`
`- - - - - - 375/225
`
`FOREIGN PATENT DOCUMENTS
`
`11, 1998
`7/1997
`8, 1998
`11, 1999
`12/2000
`
`6.426,971
`6.459,901
`6,501,785
`6,539,033
`6,574,211
`6,584,116
`6,587,443
`6,603,797
`6,608,821
`
`7, 2002 Wu et al. .............
`B1
`10, 2002 Chawla et al. .
`B1
`... 455,67.13
`B1* 12/2002 Chang et al. .........
`O876008
`B1* 3/2003 Kamperschroer et al. ... 455/450
`97.25827
`370,347 W
`B2
`6, 2003 Padovani et al.
`9837713
`B1* 6/2003 Gourgue et al. ..
`... 370/442
`WO
`996O742
`B1
`7, 2003 Dutta ............
`... 370,322
`WO
`OOT6233
`B1
`8, 2003 Zeira et al. ....
`... 455,522
`* cited by examiner
`B1
`8/2003 Gendel .................
`
`- - - - - - 375/133
`
`EP
`
`
`
`- - - - - - 370/468
`
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`U.S. Patent
`
`Jul. 17, 2007
`
`Sheet 1 of 4
`
`US 7,245,594 B1
`
`-
`
`- - - - - - - -
`
`-
`
`a as a a m - - - - - - - - C----------
`
`100
`
`n
`
`n+1 n+2 n+3 n-4 n+5 n+6 n+7 n+8
`
`X /N
`
`n-2 n-1
`
`FORWARD
`
`
`
`REVERSE
`
`FIG. 1
`
`
`
`FORWARD
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`REVERSE
`
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`Ix
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`
`
`
`
`
`
`- m - m
`
`- - -e as a
`
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`
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`up ru
`
`FIG. 2
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`U.S. Patent
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`Jul. 17, 2007
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`Sheet 2 of 4
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`US 7.245,594 B1
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`REVERSE
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`U.S. Patent
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`Jul. 17, 2007
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`Sheet 3 of 4
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`US 7.245,594 B1
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`n
`
`n-2 n-1
`
`X
`
`
`
`REVERSE Drd
`
`n+1 n+2 n+3 n+4 n+5 n-6 n+7 n--8
`
`X
`
`X
`
`
`
`FIG. 4
`
`500
`------------------------------ -?---------
`n-2 n-1
`n
`n+1 - n+2 n+3 n+4 n+5 n+6 n+7 n+8
`
`*-
`
`
`
`FORWARD !
`
`REVERSE
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`510
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`520
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`530
`
`2
`
`:
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`U.S. Patent
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`Jul. 17, 2007
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`Sheet 4 of 4
`
`245,594 B1
`US 7
`
`9
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`doOT JØjnO
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`US 7,245,594 B1
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`1.
`METHOD AND APPARATUS FOR FAST
`CLOSED-LOOP RATE ADAPTATION IN A
`HIGH RATE PACKET DATA TRANSMISSION
`
`BACKGROUND OF THE INVENTION
`
`2
`traffic data or voice data is partitioned into code channel
`frames which are 20 msec wide with data rates as high as
`14.4 Kbps.
`A significant difference between Voice services and data
`services is the fact that the former imposes Stringent and
`fixed delay requirements. Typically, the overall one-way
`delay of speech frames must be less than 100 m.sec. In
`contrast, the data delay can become a variable parameter
`used to optimize the efficiency of the data communication
`system. Specifically, more efficient error correcting coding
`techniques which require significantly larger delays than
`those that can be tolerated by voice services can be utilized.
`An exemplary efficient coding scheme for data is disclosed
`in U.S. patent application Ser. No. 08/743,688, entitled
`SOFT DECISION OUTPUT DECODER FOR DECOD
`ING CONVOLUTIONALLY ENCODED CODEWORDS.”
`filed Nov. 6, 1996, now U.S. Pat. No. 5,933.462, issued Aug.
`3, 1999, assigned to the assignee of the present invention and
`incorporated by reference herein.
`Another significant difference between voice services and
`data services is that the former requires a fixed and common
`grade of service (GOS) for all users. Typically, for digital
`systems providing Voice services, this translates into a fixed
`and equal transmission rate for all users and a maximum
`tolerable value for the error rates of the speech frames. In
`contrast, for data services, the GOS can be different from
`user to user and can be a parameter optimized to increase the
`overall efficiency of the data communication system. The
`GOS of a data communication system is typically defined as
`the total delay incurred in the transfer of a predetermined
`amount of data, hereinafter referred to as a data packet.
`Yet another significant difference between the voice ser
`vices and data services is that the former requires a reliable
`communication link which, in the exemplary CDMA com
`munication system, is provided by soft handoff. Soft handoff
`results in redundant transmissions from two or more base
`stations to improve reliability. However, this additional
`reliability is not required for data transmission because the
`data packets received in error can be retransmitted. For data
`services, the transmit power used to Support Soft handoff can
`be more efficiently used for transmitting additional data.
`The transmission delay required to transfer a data packet
`and the average throughput rate of a communication system
`are parameters that measure the quality and effectiveness of
`the data communication system. Transmission delay does
`not have the same impact in data communication as it does
`for voice communication, but it is an important metric for
`measuring the quality of the data communication system.
`The average throughput rate is a measure of the efficiency of
`the data transmission capability of the communication sys
`tem.
`It is well known that in cellular systems, the signal-to
`interference-and-noise ratio (SINR) of any given user is a
`function of the location of the user within the coverage area.
`In order to maintain a given level of service, time division
`multiple access (TDMA) and frequency division multiple
`access (FDMA) systems resort to frequency reuse tech
`niques, i.e. not all frequency channels and/or time slots are
`used in each base station. In a CDMA system, the same
`frequency allocation is reused in every cell of the system,
`thereby improving the overall efficiency. The SINR mea
`Sured at any given user's mobile station determines the
`information rate that can be supported for this particular link
`from the base station to the user's mobile station. Given the
`specific modulation and error correction method used for the
`transmission, a given level of performance is achieved at a
`corresponding level of SINR. For an idealized cellular
`
`10
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`15
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`25
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`
`I. Field of the Invention
`The present invention relates to data communication.
`More particularly, the present invention relates to a novel
`and improved method and apparatus for performing fast
`closed-loop rate adaptation in a high rate packet data trans
`mission.
`II. Description of the Related Art
`Mobile computing and data access is steadily becoming
`available to an increasing number of users. The development
`and introduction of new data services and technologies that
`will provide continuous data connectivity and full access to
`information is presently occurring. Users can now use a
`variety of electronic devices to retrieve voice or data infor
`mation stored on other electronic devices or data networks.
`Some of these electronic devices can connect to data
`resources through wires and some can connect to data
`resources through wireless Solutions. As used herein, an
`access terminal is a device providing data connectivity to a
`user. An access terminal may be coupled to a computing
`device, such as a desktop computer, a laptop computer, or a
`personal data assistant (PDA), or it may be physically
`incorporated into any Such devices. An access point is
`equipment that provides data connectivity between a packet
`Switched data network and access terminals.
`An example of an access terminal that can be used to
`provide wireless connectivity is a mobile telephone that is
`part of a communication system capable of Supporting a
`variety of applications. One Such communication system is
`a code division multiple access (CDMA) system which
`conforms to the “TIA/EIA/IS-95 Mobile Station-Base Sta
`tion Compatibility Standard for Dual-Mode Wideband
`Spread Spectrum Cellular System', hereinafter referred to as
`the IS-95 standard. The CDMA system allows for voice and
`data communications between users over a terrestrial link.
`The use of CDMA techniques in a multiple access commu
`nication system is disclosed in U.S. Pat. No. 4,901.307.
`entitled 'SPREAD SPECTRUM MULTIPLE ACCESS
`45
`COMMUNICATION SYSTEM USING SATELLITE OR
`TERRESTRIAL REPEATERS, and U.S. Pat. No. 5,103,
`459, entitled “SYSTEMAND METHOD FOR GENERAT
`ING WAVEFORMS IN A CDMA CELLULAR TELE
`PHONE SYSTEM, both assigned to the assignee of the
`50
`present invention and incorporated by reference herein. It
`should be understood that the present invention is equally
`applicable to other types of communication systems. Sys
`tems utilizing other well-known transmission modulation
`schemes such as TDMA and FDMA as well as other spread
`spectrum systems may employ the present invention.
`Given the growing demand for wireless data applications,
`the need for very efficient wireless data communication
`systems has become increasingly significant. The IS-95
`standard is capable of transmitting traffic data and Voice data
`over the forward and reverse links. A method for transmit
`ting traffic data in code channel frames of fixed size is
`described in detail in U.S. Pat. No. 5,504,773, entitled
`METHOD AND APPARATUS FOR THE FORMATTING
`OF DATA FOR TRANSMISSION,” assigned to the
`65
`assignee of the present invention and incorporated by ref
`erence herein. In accordance with the IS-95 standard, the
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`3
`system with hexagonal cell layouts and utilizing a common
`frequency in every cell, the distribution of SINR achieved
`within the idealized cells can be calculated.
`In a system that is capable of transmitting data at high
`rates, which will be referred to hereafter as a High Data Rate
`(HDR) system, an open-loop rate adaptation algorithm is
`used to adjust the data rate of the forward link. An exemplary
`HDR system is described in U.S. patent application Ser. No.
`08/963,386, entitled “METHOD AND APPARATUS FOR
`HIGH RATE PACKET DATA TRANSMISSION, now
`10
`U.S. Pat. No. 6,574,211, issued Jun. 3, 2003, assigned to the
`assignee of the present invention and incorporated herein by
`reference. The open-loop rate adaptation algorithm adjusts
`the data rate in accordance with the varying channel condi
`tions typically found in a wireless environment. In generally,
`an access terminal measures the received SINR during
`periods of pilot signal transmissions on the forward link. The
`access terminal uses the measured SINR information to
`predict the future average SINR over the next data packet
`duration. An exemplary prediction method is discussed in
`U.S. patent application Ser. No. 09/394.980, entitled, “SYS
`TEMAND METHOD FOR ACCURATELY PREDICTING
`SIGNAL TO INTERFERENCE AND NOISE RATIO TO
`IMPROVE COMMUNICATIONS SYSTEM PERFOR
`MANCE, now U.S. Pat. No. 6,426,971, issued Jul. 30,
`25
`2002, assigned to the assignee of the present invention and
`incorporated herein by reference. The predicted SINR deter
`mines the maximum data rate that can be supported on the
`forward link with a given probability of success. Hence, the
`open-loop rate adaptation algorithm is the mechanism by
`which the access terminal requests an access point to trans
`mit the next packet at the data rate determined by the
`predicted SINR. The open-loop rate adaptation method has
`proven to be very effective in providing a high throughput
`packet data system even in adverse wireless channel condi
`tions, such as a mobile environment.
`However, the use of an open-loop rate adaptation method
`is impaired by the implicit feedback delay associated with
`the transmission of the rate request feedback to the access
`point. This implicit delay problem is exacerbated when
`40
`channel conditions change rapidly, thus requiring the access
`terminal to update its requested data rate several times per
`second. In a typical HDR system, the access terminal would
`make approximately 600 updates per second.
`Other reasons exist for not implementing a pure open
`loop rate adaptation method. For example, the open-loop
`rate adaptation method is highly dependent upon the accu
`racy of the SINR estimate. Hence, imperfect SINR mea
`Surements would prevent the access terminal from making a
`precise characterization of the underlying channel statistics.
`One factor that would lead to imprecise channel statistics is
`the feedback delay discussed above. Due to the feedback
`delay, the access terminal must predict a Supportable data
`rate in the near future using past and present noisy SINR
`estimates. Another factor that would lead to imprecise
`channels statistics is the unpredictable, bursty nature of
`received data packets. In a packet data cellular system, Such
`bursts cause Sudden changes in the interference levels seen
`at the access terminal. The unpredictability of the interfer
`ence levels cannot be efficiently accounted for by a pure
`open-loop rate adaptation scheme.
`Another reason for not implementing a pure open-loop
`rate adaptation method is an inability to minimize the effects
`of errors. For example, when the prediction error for an
`estimated SINR is large, as in the case of some mobile
`environments, the access terminal will transmit a conserva
`tive data rate request in order to ensure a low packet error
`
`4
`probability. A low packet error probability will provide low
`overall delays in the transmission. However, it is probable
`that the access terminal could have Successfully received a
`higher data rate packet. There is no mechanism in the
`open-loop rate adaptation method to update a data rate
`request based on estimated channel statistics with a data rate
`based on the actual channel statistics during the transmission
`of a data packet. Hence, the open-loop rate adaptation
`method would not provide a maximized throughput rate
`when the prediction error for an estimated SINR is large.
`Another example in which the open-loop rate adaptation
`method fails to minimize the effects of an error is the
`instance when the access terminal has incorrectly decoded a
`received packet. The Radio Link Protocol (RLP) requires a
`retransmission request when the access terminal incorrectly
`decodes a packet, but the retransmission request is generated
`only after detecting a gap in the received sequence number
`space. Therefore, the RLP protocol requires the processing
`of a Subsequent received packet after the incorrectly
`decoded packet. This procedure increases the overall trans
`mission delay. Some mechanism is needed to implement a
`quick retransmission of some or all of the code symbols
`contained in the data packet, wherein the mechanism would
`enable the access terminal to correctly decode the packet
`without incurring excessive delays.
`Hence, there exists a present need to modify the open
`loop rate adaptation method in order to minimize transmis
`sion delays and to maximize the throughput rate as discussed
`above.
`
`SUMMARY
`
`The present invention is directed to a novel and improved
`method and apparatus for modifying an open-loop rate
`adaptation algorithm to produce a hybrid open loop/closed
`loop rate adaptation scheme. An access point advanta
`geously generates a time interleaved structure for slots in
`data packets, allowing an access terminal to transmit indi
`cator messages to the access point during periods associated
`with gaps inserted into the interleaved structure.
`In one aspect of the invention, the periods associated with
`the interleaved gaps are of sufficient duration to allow the
`access terminal to decode the data carried in the slots and to
`send an indicator message based on the decoded data. In an
`alternative aspect of the invention, the indicator messages
`are based on an estimated signal-to-interference-and-noise
`level.
`In another aspect of the invention, the indicator messages
`are one bit long, which is interpreted by the access point in
`accordance with the timing of the arrival of the bit.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features, objects, and advantages of the present
`invention will become more apparent from the detailed
`description set forth below when taken in conjunction with
`the drawings in which like reference characters identify
`correspondingly throughout and wherein:
`FIG. 1 is a diagram of an exemplary one-slot gap inter
`laced structure for multi-slot packets;
`FIG. 2 is a diagram of an exemplary uniform N-slot gap
`interlaced structure for multi-slot packets;
`FIG. 3 is a diagram of an exemplary non-uniform N-slot
`gap interlaced structure for multi-slot packets;
`FIG. 4 is a diagram of an exemplary STOP control
`indication for a multi-slot packet;
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`5
`FIG. 5 is a diagram of an exemplary EXTEND control
`indication for a multi-slot packet; and
`FIG. 6 is a block diagram of an exemplary embodiment of
`the invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`6
`data rate control channel (hereinafter referred to as the DRC
`channel). The DRC message can contain the requested data
`rate, or alternatively, the quality of the forward link channel
`(e.g., the SINR measurement itself, the bit-error-rate, or the
`packet-error-rate). In the exemplary embodiment, the access
`terminal can direct the transmission of the DRC message to
`a specific access point by the use of a Walsh code that
`uniquely identifies the access point. The DRC message
`symbols are exclusively OR'ed (XOR) with the unique
`Walsh code. Since each access point in the active set of the
`access terminal is identified by a unique Walsh code, only
`the selected access point which performs the identical XOR
`operation as that performed by the access terminal, with the
`correct Walsh code, can correctly decode the DRC message.
`The access point uses the rate control information from each
`access terminal to efficiently transmit forward link data at
`the highest possible rate.
`At each time slot, the access point can select any of the
`paged access terminals for data transmission. The access
`point then determines the data rate at which to transmit the
`data to the selected access terminal based on the most recent
`value of the DRC message received from the access termi
`nal. Additionally, the access point uniquely identifies a
`transmission to a particular access terminal by appending an
`identifying preamble to a data packet directed to an access
`terminal. In the exemplary embodiment, the preamble is
`spread using a Walsh code that uniquely identifies the access
`terminal.
`In the exemplary embodiment, the forward link capacity
`of the data transmission system is determined by the data
`rate requests of the access terminals. Additional gains in the
`forward link capacity can be achieved by using directional
`antennas and/or adaptive spatial filters. An exemplary
`method and apparatus for providing directional transmis
`sions are disclosed in copending U.S. patent application Ser.
`No. 08/575,049, entitled “METHOD AND APPARATUS
`FOR DETERMINING THE TRANSMISSION DATA
`RATE IN A MULTI-USER COMMUNICATION SYS
`TEM, filed Dec. 20, 1995, now U.S. Pat. No. 5,857,147,
`issued Jan. 5, 1999, and U.S. patent application Ser. No.
`08/925,521, entitled “METHOD AND APPARATUS FOR
`PROVIDING ORTHOGONAL SPOT BEAMS, SECTORS,
`AND PICOCELLS, filed Sep. 8, 1997, now U.S. Pat. No.
`6,285,655, issued Sep. 4, 2001, both assigned to the assignee
`of the present invention and incorporated by reference
`herein.
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`In an exemplary embodiment of a data communication
`system, forward link data transmission occurs from one
`access point to one or more access terminals at the data rate
`requested by the access terminal(s). Reverse link data com
`munication can occur from one access terminal to one or
`more access points. Data is partitioned into data packets,
`with each data packet being transmitted over one or more
`time slots. At each time slot, the access point can direct data
`transmission to any access terminal in communication with
`the access point.
`Initially, the access terminal establishes communication
`with an access point using a predetermined access proce
`dure. In this connected State, the access terminal can receive
`data messages and control messages from the access point,
`and is able to transmit data messages and control messages
`to the access point. The access terminal then monitors the
`forward link for transmissions from the access points in the
`active set of the access terminal. The active set contains a list
`of access points in communication with the access terminal.
`Specifically, the access terminal measures the signal-to
`interference-and-noise ratio (SINR) of the forward link pilot
`from the access points in the active set, as received at the
`access terminal. If the received pilot signal is above a
`predetermined add threshold or below a predetermined drop
`threshold, the access terminal reports this to the access point.
`Subsequent messages from the access point direct the access
`terminal to add or delete the access point to or from its active
`set, respectively.
`If there is no data to send, the access terminal returns to
`an idle State and discontinues transmission of data rate
`information to the access point(s). While the access terminal
`is in the idle state, the access terminal periodically monitors
`the control channel from one or more access points in the
`active set for paging messages.
`If there is data to be transmitted to the access terminal, the
`data is sent by a central controller to all access points in the
`active set and stored in a queue at each access point. A
`45
`paging message is then sent by one or more access points to
`the access terminal on the respective control channels. The
`access point may transmit all Such paging messages at the
`same time across several access points in order to ensure
`reception even when the access terminal is Switching
`between access points. The access terminal demodulates and
`decodes the signals on one or more control channels to
`receive the paging messages.
`Upon decoding the paging messages, and for each time
`slot until the data transmission is completed, the access
`terminal measures the SINR of the forward link signals from
`the access points in the active set, as received at the access
`terminal. The SINR of the forward link signals can be
`obtained by measuring the respective pilot signals. The
`access terminal then selects the best access point based on a
`set of parameters. The set of parameters can comprise the
`present and previous SINR measurements and the bit-error
`rate or packet-error-rate. For example, the best access point
`can be selected based on the largest SINR measurement. The
`access terminal then identifies the best access point and
`transmits to the selected access point a data rate control
`message (hereinafter referred to as the DRC message) on the
`
`50
`
`55
`
`60
`
`65
`
`Fast Closed-Loop (FCL) Rate Control Adaptation
`
`In an HDR system, an open-loop rate adaptation scheme
`uses a fast feedback channel to allow a transmission of a
`DRC message from an access terminal to an access point
`while the access point concurrently transmits a data packet
`to the access terminal on the forward data link. Hence, the
`access terminal can command the access point to either
`terminate or extend the current transmission in accordance
`with actual SINR conditions at the receiving access termi
`nal. In an exemplary embodiment, the fast feedback channel
`is used to carry extra information as described below.
`The forward link data rates in an HDR system vary from
`38.4 kbps to 2.456 Mbps. The duration of each packet
`transmission in number of slots as well as other modulation
`parameters are described in Table 1. In this embodiment, a
`slot corresponds to a period of 1.666 ms, or equivalently,
`2048 chips transmitted at the chip rate 1.2288 Mcps.
`
`IPR2018-1556
`HTC EX1013, Page 9
`
`

`

`US 7,245,594 B1
`
`7
`
`TABLE 1.
`
`Forward Link Modulation Parameters
`
`Data Rate
`number
`
`Data Rate Number Bits per
`(kbps)
`of Slots Packet Code Rate Modulation
`
`1
`2
`3
`4
`5
`6
`7
`8
`9
`10
`11
`
`38.4
`76.8
`102.4
`153.6
`204.8
`3.07.2
`614.4
`921.6
`1228.8
`1843.2
`2457.6
`
`16
`8
`6
`4
`3
`2
`1
`2
`1
`1
`1
`
`1024
`1024
`1024
`1024
`1024
`1024
`1024
`3072
`2048
`3072
`4096
`
`/4
`/4
`/4
`/4
`/4
`/4
`/4
`3/8
`A.
`A.
`A.
`
`QPSK
`QPSK
`QPSK
`QPSK
`QPSK
`QPSK
`QPSK
`QPSK
`QPSK
`8PSK
`16QAM
`
`10
`
`15
`
`8
`error. Hence, if the access terminal determines that channel
`conditions are not favorable, the access terminal will trans
`mit a DRC message requesting a data rate below 614.4 kbps.
`The access point will then transmit multi-slot packets in
`accordance with the structure described in FIG.1. However,
`if the actual channel conditions improve so that the access
`terminal needs fewer repeated code symbols than originally
`specified by the open-loop rate adaptation algorithm, the
`structure described in FIG. 1 will allow the access terminal
`to transmit an indicator message. Such as a STOP indicator
`message, on the reverse link feedback channel.
`FIG. 2 is a diagram that illustrates the use of a STOP
`indicator message. An access point transmits a data packet
`200 in accordance with the interleaved structure of FIG. 1.
`Slots n, n+2, and n+4 are slots carrying data. A DRC
`message 210 is received during slot period n-1, so that data
`in slots n, n+2, n+4, and n+6 are scheduled for transmission
`in accordance with the requested data rate. A STOP indicator
`message 220 is transmitted by the access terminal because
`the access terminal has received enough repetitions of the
`code symbols in slots n, n+2, and n+4 to determine the
`complete data without receiving any more repetitions carried
`by n+6. Hence, the access terminal is ready to receive new
`data. STOP indicator message 220 is received by the access
`point during slot n+5. Upon receiving the STOP indicator
`message 220, the access point will cease transmitting rep
`etitions in the remaining allocated data slot n+6 and begin
`the transmission of a new data packet in slot n+6. Unused
`allocated slots can be reassigned to another packet trans
`mission directed toward any access terminal. In this manner,
`a closed loop rate adaptation can be performed to optimize
`resources when actual channel conditions allow for a higher
`data rate than the one specified in the original DRC message
`based on estimated channel conditions. In the example
`above, an effective data rate is 4/3 times higher than the
`original requested data rate is achieved by sending the STOP
`indication.
`In another aspect of this embodiment, an indicator mes
`sage can be sent from the access terminal to the access point
`to enable more repetitions of the code symbols whenever the
`actual channel conditions are worse than the estimated
`channel conditions. The indicator message can be referred to
`as an EXTEND indicator message. Another use for an
`EXTEND indicator message arises when a one slot packet is
`incorrectly decoded by the access terminal. In this case, the
`access terminal may transmit an EXTEND indicator mes
`sage requesting the retransmission of the data carried in a
`specified slot. The structure of FIG. 1 allows the access point
`to retransmit the data on the very next slot, referred to herein
`as an extended data slot, following the decoding of the
`EXTEND indicator message. FIG. 3 is an illustration of this
`use for an EXTEND indicator message. Data packet 300 is
`constructed in accordance with the structure of FIG. 1, so
`that alternating slots are designated gap slots. A DRC
`message 310 is received by the access point that provides the
`preferred rate for data transmitted in data slot n. Data is also
`transmitted in slot n+2 in accordance with the requested data
`rate. However an EXTEND indicator message 320 is
`received by the access point that orders data repetition at
`data slot n+4 due to an error in decoding the data carried in
`slot n+2.
`In another aspect of this embodiment, single-slot packets
`may be requested when the estimated SINR indicates a
`reduced probability of packet success, for example, a prob
`ability of packet success of 80-90%. Based on the received
`single-slot packet, the access terminal can send an EXTEND
`indicator to the access point, requesting retransmission of
`
`25
`
`In an exemplary embodiment, the structure of the multi
`slot packets is modified to carry data in predetermined data
`slots, but not in predetermined gap slots. When the multi-slot
`packets are structured in accordance with the exemplary
`embodiment, the access terminal that is receiving the multi
`slot packet can utilize the duration of the predetermined gap
`slots for other purposes. For example, the access terminal
`can use the time between the data slots to decide if the packet
`can be correctly decoded with the soft code symbols accu
`mulated thus far. The access terminal can use various
`methods for determining whether the data slots have been
`correctly decoded, these methods including, but not limited
`to, checking the CRC bits associated with the data or
`30
`estimating a predicted SINR based on received SINR of
`pilot and traffic symbols.
`FIG. 1 is a diagram of an exemplary one-slot gap inter
`laced structure for multi-slot packets, wherein the predeter
`mined data slots and the predetermined gap slots are inter
`laced in an alternating pattern. This embodiment will be
`referred to hereafter as a one-slot gap pattern. Multi-slot
`packet 100 is transmitted from an acce