(12) United States Patent
`Chung et al.
`
`USOO6741862B2
`(10) Patent No.:
`US 6,741,862 B2
`(45) Date of Patent:
`May 25, 2004
`
`(56)
`
`(54) ENHANCED REVERSE-LINK RATE
`CONTROL IN WIRELESS
`COMMUNICATION
`
`(75) Inventors: Sae-Young Chung, Waltham, MA (US);
`Dae-Young Kim, Lexington, MA (US)
`
`(73) Assignee: Airvana, Inc., Chelmsford, MA (US)
`(*) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/778,668
`(22) Filed:
`Feb. 7, 2001
`(65)
`Prior Publication Data
`US 2002/0151310 A1 Oct. 17, 2002
`(51) Int. Cl. ............................. H04Q 7/20; H04B 1/00
`(52) U.S. Cl. .......................................... 455/452; 455/63
`(58) Field of Search ................................. 455/452, 453,
`455/458, 226.3, 226.2, 63, 67.1, 67.4, 562;
`370/252, 335, 458, 468, 328, 329, 229,
`230, 232, 233,234, 235; 375/225
`
`
`
`12
`
`52 Claims, 5 Drawing Sheets
`
`2-1 :
`
`e OZ, Jaa-SeO
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,548.812 A * 8/1996 Padovani et al. ........... 370/332
`5,774,808 A * 6/1998 Sarkioja et al.............. 370/332
`5,790,551 A
`8/1998 Chan .......................... 370/458
`6,023,625 A * 2/2000 Myers, Jr. ................... 455/446
`6,088,335 A
`7/2000 I et al. ....................... 370/252
`6,101,392 A
`8/2000 Corriveau ................... 455/458
`6,122,516 A : 9/2000 Thompson et al. ......... 455/450
`ls R : i.S. his G - - - - - a-Bellido 455/561
`et al. .......................... 370/331
`6,373,878 B1 * 4/2002 Palenius et al. ............ 370/335
`* cited by examiner
`Primary Examiner Nguyen T. Vo
`ASSistant Examiner-Sheila B. Smith
`(74) Attorney, Agent, or Firm-Fish & Richardson P.C.
`(57)
`ABSTRACT
`By controlling reverse rates among mobile Stations to reduce
`reverse-link interference, reverse-link throughput can be
`increased.
`
`Ex. 1005 - Sierra Wireless, Inc.
`Sierra Wireless, Inc., et al. v. Sisvel S.P.A., IPR2021-01141
`Page 1 of 16
`
`

`

`U.S. Patent
`
`May 25, 2004
`
`Sheet 1 of 5
`
`US 6,741,862 B2
`
`
`
`FIG. 1
`
`Ex. 1005 - Sierra Wireless, Inc.
`Sierra Wireless, Inc., et al. v. Sisvel S.P.A., IPR2021-01141
`Page 2 of 16
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`

`

`U.S. Patent
`
`May 25, 2004
`
`Sheet 2 of 5
`
`US 6,741,862 B2
`
`BS1 MS MS2
`FIG 2
`
`BS2
`
`Ex. 1005 - Sierra Wireless, Inc.
`Sierra Wireless, Inc., et al. v. Sisvel S.P.A., IPR2021-01141
`Page 3 of 16
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`

`

`U.S. Patent
`
`May 25, 2004
`
`Sheet 3 of 5
`
`US 6,741,862 B2
`
`20
`
`5
`
`
`
`
`
`
`
`15
`
`1 O
`
`5
`
`O
`
`FIG. 3
`
`-10
`
`-5
`
`O
`
`5
`
`10
`
`15
`
`20
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`Sierra Wireless, Inc., et al. v. Sisvel S.P.A., IPR2021-01141
`Page 4 of 16
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`

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`U.S. Patent
`
`May 25, 2004
`
`Sheet 4 of 5
`
`US 6,741,862 B2
`
`At the MS, measure its forward-link SlR -40
`
`At the MS, calculate DRC using the SIR value and send
`the DRC value and its current queue size to the BS
`
`2
`
`
`
`At the BS, calculate desired reverse-link rate for the MS that
`depends on the DRC value and calculate the next reverse-link 44
`rate for the MS according to the calculated desired reverse
`link rate and the current queue size of the MS
`
`At the BS, send the rate to the MS
`
`46
`
`At the MS, transmit its data using the rate
`
`48
`
`FIG. 5
`
`Ex. 1005 - Sierra Wireless, Inc.
`Sierra Wireless, Inc., et al. v. Sisvel S.P.A., IPR2021-01141
`Page 5 of 16
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`

`

`U.S. Patent
`
`May 25, 2004
`
`Sheet 5 of 5
`
`US 6,741,862 B2
`
`At the MS, measure its forward-link SlR -50
`
`At the MS, calculate DRC using the SIR value and send 52
`the DRC value and its Current reverse rate to the BS
`
`
`
`At the BS, Calculate desired reverse-link rate for the MS that
`depends on the DRC value and estimate the rate limit for the
`MS according to the calculated desired reverse-link rate and
`the past history of reverse-link traffic pattern of the MS
`observed from the MS's reported rate values
`
`At the BS, send the rate limit to the MS
`
`56
`
`At the MS, in it its reverse rate to the rate limit
`
`58
`
`F.G. 6
`
`Ex. 1005 - Sierra Wireless, Inc.
`Sierra Wireless, Inc., et al. v. Sisvel S.P.A., IPR2021-01141
`Page 6 of 16
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`

`

`US 6,741,862 B2
`
`1
`ENHANCED REVERSE-LINK RATE
`CONTROL IN WIRELESS
`COMMUNICATION
`
`BACKGROUND
`We use the following acronyms in our discussion:
`
`1xEV-DO
`1xEV-DV
`3GPP2
`BS
`CDMA
`CDMA-2OOO
`DRC
`HDR
`IS-95
`MS
`psd
`RA
`RAE
`SIR
`SNR
`TDMA
`
`1xEV-Data Only
`1xEV-Data and Voice
`3' Generation Partnership Project 2
`Base Station
`Code Division Multiple Access
`A CDMA standard for voice and data
`Data Rate Control
`High Data Rate
`TIA/EIA Interim Standard 95
`Mobile Station
`Power Spectral Density
`Reverse Activity
`Reverse Activity Bit
`Signal-to-Interference Ratio
`Signal-to-Noise Ratio
`Time Division Multiple Access
`
`We use the following notations in our discussion.
`
`ai
`CR
`b
`B
`dR
`E.
`Eb
`F
`G
`Si
`I
`Io
`Io;
`I
`N
`Nth
`P
`R
`R
`S
`S.
`W
`
`path gain from the i-th sector to a MS
`relative data power over pilot for reverse rate R
`path gain from a MS to the i-th sector
`interference factor
`minimum required E/I for reverse rate R
`energy per bit
`energy per bit for the i-th MS
`base station noise figure
`processing gain = WR
`path gain from the i-th MS to the BS
`psd of interference from other sectors
`psd of thermal noise and interference
`psd of thermal noise and interference for the i-th MS
`psd of the total received power at the BS
`number of mobile stations in a sector
`psd of thermal noise
`pilot transmission power of the i-th MS
`reverse rate
`reverse rate of the i-th MS
`received signal power
`received pilot power of the i-th MS
`system bandwidth
`
`FIG. 1 shows a general configuration of cellular wireleSS
`communication Systems. A large geographic area is divided
`into cells 10. Each cell can be further divided into sectors 12.
`Typically three Sectors per cell are used as shown in the
`figure. We will use the term sector even when there is only
`one sector per cell. In each cell, a BS 14, 20, 22 serves three
`sectors and communicates with multiple MS's 16, 18 in its
`cell.
`High Data Rate (HDR) is an emerging mobile wireless
`access technology that enables personal broadband Internet
`Services which can be accessed from anywhere, anytime.
`Developed by Qualcomm, HDR is a new air interface
`optimized for IP packet data services. HDR can deliver a
`shared forward link transmission rate of up to 2.4576 Mbit/s
`per sector using only (1x) 1.25 MHz of spectrum. HDR has
`been adopted by TIA as a new standard in the CDMA2000
`family, an EVolution of the current 1xRTT standard for
`high-speed data-only (DO) services, formally referred to as
`1xEV-DO or IS-856.
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`IS-856 defines AN, AT, and sector as follows:
`Access Network (AN): The network equipment providing
`data connectivity between a packet Switched data network
`(typically the Internet) and the access terminals. An access
`network is equivalent to a base station in the CDMA-2000
`Standard.
`Access Terminal (AT): A device providing data connec
`tivity to a user. An acceSS terminal may be connected to a
`computing device Such as a laptop personal computer or it
`may be a Self-contained data device Such as a personal
`digital assistant. An access terminal is equivalent to a mobile
`station in the CDMA-2000 standard.
`Sector: The part of the acceSS network that provides one
`CDMA channel.
`We will use BS and AN interchangeably and MS and AT
`interchangeably.
`In HDR, the forward-link channel is time-shared among
`MS’s. Actual forward throughput becomes smaller than the
`instantaneous rates if there are more than one MS.
`The MS periodically monitors the quality of its forward
`channels by measuring the forward-link SIR values from
`Several Sectors. The MS chooses the Sector among active
`Sectors whose SIR is the highest and calculates the maxi
`mum possible forward-link rate Supported at this SIR. The
`MS then sends a DRC value in every slot (one slot is 1.66
`msec) that indicates this rate to the BS. The following table
`shows the DRC value and the corresponding rate in Kbps.
`Packet length shows how many slots a forward packet needs
`at each rate.
`
`DRC value
`
`Rate (kbps)
`
`Packet Length
`in slots
`
`1.
`2
`3
`4
`5
`6
`7
`8
`9
`1O
`11
`12
`
`38.4
`76.8
`153.6
`3.07.2
`3.07.2
`614.4
`614.4
`921.6
`1228.8
`1228.8
`1843.2
`2457.6
`
`16
`8
`4
`2
`4
`1.
`2
`2
`1.
`2
`1.
`1.
`
`In HDR, the reverse link (from MS to BS) can support bit
`rates 9.6, 19.2, 38.4, 76.8, and 153.6 Kbps in a 1.25 MHz
`spectrum (no overlap with the forward-link spectrum). Since
`the reverse link is shared using CDMA, these are the actual
`rates each MS can get.
`A MS can communicate with several Sectors. A MS is in
`Soft handoff if decoding of the reverse packet is done at
`Several Sectors and an error-free frame, if any, is finally
`chosen. A MS is in Softer handoff, if several sectors in the
`Same cell jointly decode the reverse packet.
`Due to the unpredictable nature of the reverse traffic and
`delay, it is difficult to schedule individual reverse traffic
`together at the BS. As we will show later, there is a limit on
`the aggregate reverse rate in each Sector at which MSS can
`send data reliably. Therefore, it is important to be able to
`control the reverse rate of each MS So that their aggregate
`rate rarely exceed the limit. We briefly describe how this is
`done in HDR.
`In HDR, there are four variables for reverse rate control,
`i.e., MaxRate, CurrentRate, Combinded BusyBit, and Cur
`
`Ex. 1005 - Sierra Wireless, Inc.
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`Page 7 of 16
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`

`

`3
`rentRateLimit. CurrentRate is the actual rate at which a MS
`sent data last time. The BS can send broadcast (to all MS's
`in the sector) or unicast (to a specific MS) RateLimit
`messages. After receiving the RateLimit message (unicast or
`broadcast), the MS sets its CurrentRateLimit equal to the
`RateLimit value. CurrentRateLimit is initially 9.6 Kbps.
`The BS can send another broadcast control signal, RAB
`(reverse activity bit), to all active MS’s. The MS collects all
`RAB's from active base stations and determines Combined
`BusyBit. The Combined BusyBit is 1 if any of these RAB’s
`is 1 and is 0 otherwise. The MS then computes the MaxRate
`with a certain probability depending on the Combined
`BusyBit. This probability is a function of both the Curren
`tRate and the Combined BusyBit. The MS then chooses a
`rate that does not exceed either of MaxRate or CurrentRate
`Limit. The rate is also limited by the transmission power of
`the MS (in general more power is needed for transmitting at
`a higher rate). If the payload size is Small enough to be
`transmitted using a lower rate, then the MSchoose the lower
`rate. The following Summarizes the reverse rate variables:
`CurrentRateLimit
`
`15
`
`1. initially 9.6 Kbps
`2. after receiving broadcast or unicast RateLimit message,
`an MS updates it as follows:
`a.. if the Rate Limit <= Current Rate Limit, set
`CurrentRateLimit=RateLimit immediately.
`b. if the Rate Limita Current Rate Limit, set
`CurrentRate Limit=Rate Limit after one frame (16
`slots).
`Combined BusyBit
`1 if and only if any RAB is 1 from any sector.
`MaxRate
`2.0*CurrentRate if Combined BusyBit=0 and with prob
`ability X.
`0.5* CurrentRate if Combined BusyBit=1 and with prob
`ability X.
`MaxRate cannot be set to 0 in any case.
`MaxRate cannot exceed 153.6 Kbps.
`MS selects a transmission rate (becomes CurrentRate)
`Such that
`1. rate.<=MaxRate
`2. rate.<=CurrentRateLimit
`3. rate.<=highest rate that can be accommodated by the
`transmission power
`4. rate.<=highest rate Such that the number of minimum
`payload bits is less than the number of bits to send.
`Default values of the transition probability X are:
`
`Combined BusyBit
`O
`O
`O
`O
`1.
`1.
`1.
`1.
`
`CurrentRate
`9.6 kbps
`19.2 kbps
`38.4 kbps
`76.8 kbps
`19.2 kbps
`38.4 kbps
`76.8 kbps
`153.6 kbps
`
`Max Rate
`19.2 kbps
`38.4 kbps
`76.8 kbps
`153.6 kbps
`9.6 kbps
`19.2 kbps
`38.4 kbps
`76.8 kbps
`
`Default probability
`0.75
`0.25
`O.125
`O.125
`0.25
`0.25
`0.5
`1.
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`SUMMARY
`In general, in one aspect, the invention features a method
`that includes (a) at a mobile wireless communication device
`
`65
`
`US 6,741,862 B2
`
`4
`operating in a cell, transmitting data to Sectors, and (b) at the
`base Station controlling the reverse data rate of the mobile
`device based on an estimated amount of interference the
`mobile device is causing to other Sectors. Implementations
`of the invention may include one or more of the following
`features. The estimated amount of interference is based on a
`forward-link SIR for the mobile device. The forward-link
`SIR is averaged over a period of time. The estimated amount
`of interference is based on pilot power from the mobile
`device received at the base Station or on total power received
`from the mobile device at the base station or on the mobile
`device's request forward-link data rate. The request data rate
`is averaged over a certain period of time. The reverse rate of
`the mobile device is set by the base station. The reverse rate
`is Set as a target rate based on the queue Status of the mobile
`device or on the status of the sector in which the mobile
`device is operating. The Status of the Sector comprises a
`number of mobile devices or a reverse rate of other devices
`operating in the Sector. The reverse rate of the mobile device
`is set by the mobile device. The reverse rate is set based on
`a determined rate limit. The rate limit is communicated to
`the mobile device from the base station. The reverse rate is
`limited by sending rate control bits from the base station to
`the mobile device. The mobile device sets a value of
`MaxRate according to a message from the base Station, the
`MaxRate being dependent on the current rate of the mobile
`device and given transition probabilities. The mobile device
`Sets a MaxRate deterministically. The aggregate rate from all
`mobile devices in all SectorS is maximized. The rate of each
`mobile device is restricted by a condition. The condition
`includes fairness among the mobile devices.
`In general, in another aspect, the invention features a
`method that includes (a) generating one or more reverse rate
`control bit or bits for each of several mobile devices oper
`ating in a Sector of a cell, and controlling the reverse rates
`of the respective mobile devices based on the reveres rate
`control bits.
`In general, in another aspect, the invention features a
`method that includes (a) at a mobile wireless communication
`device operating in a Sector of a cell, transmitting data to the
`base station in the Sector, and (b) controlling its reverse data
`rate based on an estimated amount of interference the mobile
`device is causing to base Stations in other Sectors. Imple
`mentations of the invention may include one or more of the
`following features. The estimated amount of interference is
`based on its forward-link SIR. The estimated amount of
`interference is based on its forward-link rate. The estimated
`amount of interference is based on its request forward-link
`data rate. The estimated amount of interference is based on
`the received power from the base station. The reverse rate is
`limited by a command from the base Station.
`Other advantages and features will become apparent from
`the following description and from the claims.
`DESCRIPTION
`FIG. 1 shows cells and sectors.
`FIG. 2 shows two BSS and two MSS.
`FIGS. 3 and 4 are correlation diagrams.
`FIGS. 5 and 6 are process flow diagrams.
`Compared to IS-95 or CDMA-2000, it is possible to
`achieve about two to three times more aggregate throughput
`in the forward link in HDR using the same 1.25 MHz
`Spectrum. In addition to employing higher order modulation,
`such as 8PSK and 16QAM, the increase in throughput is
`attributable the following.
`Delay Sensitive voice traffic requires the same average
`rate among MS’s which forces the BS to increase its
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`

`

`S
`transmission power when a MS's forward channel degrades
`(for example, when the MS is moving away from the BS).
`To guarantee the same rate for all MS’s independent of their
`channel condition, a MS operating in a bad channel condi
`tion takes up a lot of resources (i.e., power in the case of
`CDMA systems such as IS-95 and CDMA-2000), and this
`results in lower aggregate throughput. By contrast, a HDR
`System in which all MS’s get about the same resources (i.e.,
`time in the case of TDMA systems such as in the HDR
`forward link) independent of their respective channel con
`ditions can achieve higher aggregate throughput because a
`MS operating in a good channel condition gets higher
`throughput. In this case, the forward-link rate becomes a
`function of the forward-link SIR that the MS is experienc
`ing.
`HDR gets similar reverse-link rates compared to IS-95 or
`CDMA-2000 and thus fails to achieve the two to three times
`throughput improvement of the forward-link. Throughput
`can be improved using enhanced reverse link rate control
`schemes. We first show how to improve reverse link
`throughput of a HDR System using the control Signals and
`messages defined in HDR standard. We also show how to
`improve reverse link throughput in cellular Systems includ
`ing HDR by adding new control Signals in the Standard.
`1. Reverse Link Capacity
`We first calculate the reverse link capacity of a HDR
`System using the same method described in K. I. Kim,
`Handbook of CDMA System Design, Engineering, and
`Optimization, Prentice Hall, 2000 to calculate the reverse
`link capacity of IS-95. E., is the energy per bit and Io is the
`power spectral density of the combined thermal noise N.,
`and interference. Since the spectral efficiency of the channel
`is very low, we are operating in a power-limited regime. In
`this case, the channel capacity is nearly proportional to the
`SNR. We assume that at least E/I=d is required for
`error-free transmission. For example, if a convolutional code
`is used, then we use d=7 dB. If a more powerful turbo code
`is used, then we use d=3 dB.
`The receiver at the base Station introduces Some addi
`tional noise, which effectively magnifies N., by F. For now,
`we assume that the received power S for each MS is the
`same, which is the case when the uplink rate of each MS is
`the same and when the reverse link power control is perfect.
`Similarly, we assume R is the common bit rate of each MS.
`If there are N MS’s in a cell, then the in-cell interference
`comes from N-1 of the MS’s. Let B denote the interference
`factor from MS’s in other sectors/cells, i.e., the total inter
`ference from other SectorS/cells is B times the total in-cell
`interference. For example, B=0.6 can be used for a single
`sector cell and B=0.85 can be used for a sectored cell.
`Finally, let W denote the system bandwidth and let G denote
`the processing gain defined as W/R.
`Using these quantities, we can calculate the E/I value as
`follows.
`
`15
`
`25
`
`35
`
`40
`
`45
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`50
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`55
`
`US 6,741,862 B2
`
`6
`Similarly, the rate R is upper-bounded by the following:
`
`sRmax - FN, WA (1
`
`SW
`
`(N - 1)Sg
`
`5
`
`ASSuming the mobile Stations have unlimited power, we
`can simplify the above two bounds, because we can ignore
`the thermal noise, i.e.,
`
`G
`
`(2)
`
`This capacity is called the pole point or power pole. Note
`that (N-1) and R are inversely proportional to each other
`when the inequalities are met with equality.
`For example, if N=10, W=1.25 MHz, d=3 dB, B=0.85,
`then R is equal to about 37 kbps. N.
`for the same
`parameter becomes about 3.2, 5.4, 9.8, 18.6, and 36.2 for
`R=153.6, 76.8, 38.4, 19.2, and 9.6 kbps, respectively.
`Using the definition of N in (2), we get from (1)
`
`fix
`
`fix
`
`Sai - -
`T (1 + f3)(Ninax-N)
`
`(3)
`
`Therefore, the received power needs to be increased as N
`increases.
`In the following section, we consider the case when MS's
`can have different rates and there is Some overhead in
`Sending pilots.
`2. Users with Different Rates
`If MS's have different rates, i.e., R for MS i, then the
`above bounds can be modified as follows. Let g be the path
`gain from the i-th MS to the BS. Let P be the pilot
`transmission power from MS i and let C be the relative data
`power over the pilot power when the rate is R. In this case,
`we get the i-th MS’s SNR E/I as follows:
`
`|
`lo;
`
`2
`
`2 dr;,
`g; Par, W/ R.
`-
`(FN, + 1) W + X. giP. (1 + ar)
`i=1,...i-fi
`
`where d is the minimum required SNR for rate R, and I is
`the psd of the interference from other sectors. Let S=g.P. be
`the received pilot psd from MS i and let I,-(FN+I)+X-
`Ng, P(1+c)/W be the total received psd. If r is defied as
`the ratio of the received pilot pSci and the total received pSci,
`I.C.,
`
`Eb
`Io
`
`S
`= G
`Sf R
`(1 + f3)(N - 1)S TFN, W + (1 + f3)(N - 1)S
`
`(1)
`
`Since E/Ioad, we have an upper bound on N, i.e.,
`
`Ns Nina = a
`
`G
`
`FN, W
`+1 -
`as
`
`60
`
`65
`
`In general, r is a function of the rate R. If r is not a
`constant, then the outer-loop power control needs to know
`the instantaneous reverse rate R, which may increase the
`complexity and introduce Some delayS. For optimal power
`
`Ex. 1005 - Sierra Wireless, Inc.
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`US 6,741,862 B2
`
`7
`allocation, CS and r’s need to be optimized dynamically
`among all MS’s, which is even more complex to do. One
`Simple way to avoid this problem is to Set r equal to a
`constant ro for all MS’s, which will force the received pilot
`power the same for all MS’s in the sector. To maintain the
`minimum required SNR for the pilot, we need to set ro
`higher than the SNR. Once the value of ro is determined, C.
`can be calculated as follows:
`
`1 fro-1
`CR
`T 1 + W / RdR
`
`(4)
`
`Note that if we want to keep the ratio fo of the pilot psd
`S, and the interference psc (FN+I)+X-1,g°P(1+c), W
`15
`the same for all MS’s at the receiver, then we get different
`C’s as follows:
`
`CR
`
`(5)
`
`8
`ence to neighboring cells. However, there is no explicit
`signaling information that enables the BS to know what the
`MS's transmit power is nor its location within the cell. One
`possible approach is to make the reverse rate roughly
`proportional to the corresponding forward-link rate, which
`will be as fair as the forward link. To demonstrate how this
`Scheme can reduce the interference to other cells/Sectors, we
`first consider the following example.
`ASSume there are two base stations 30, 36 in FIG. 2
`separated by distance 1, and two MS’s are located 0.2 (MS
`1, 32) and 0.4 (MS 2, 34) from the first base station 30 on
`the line connecting the two base Stations. ASSume that the
`MS's transmission power is proportional to its reverse rate.
`If MS 2's reverse rate is 10 times MS 1's reverse rate, then
`MS 2s transmission power is
`
`43.5
`10x
`0.23.5
`
`as 113
`
`The difference in C's in (4) and (5) should be small since
`ro-1 and W/Rd.>> 1 in a HDR System. In any case, C.
`should not be larger than a certain number So that the
`minimum pilot power corresponding to the rate can be
`maintained.
`3. Basic Rate Control Scheme
`Because RateLimit meSS ages consume a significant por
`tion of the forward traffic channel bandwidth, it is not
`desirable to send them every time we want to control the
`reverse-link rates. Instead, we need to rely on RABs for
`Short-term rate control. One way to do this is to use a
`RateLimit message when a new MS is entered or a MS is
`moved out and to use RABS for controlling the rate assum
`ing the number of MS’s is fixed. We can also use RateLimit
`messages when the rates need to be decreased quickly.
`The value of RateLimit depends on the reverse traffic
`pattern. If each MS's queue is always fall, then RateLimit
`can be set to be slightly larger than the maximum average
`per-user rate R. If the reverse traffic is lightly loaded, then
`we need to increase RateLimit more So that high-rate bursty
`reverse data can be transmitted. Because RateLimit is
`discrete, if we set all MS's RateLimit to be equal, then we
`cannot fine tune the total RateLimit. In this case, we may
`want to Send unicast RateLimit messages to Set RateLimits
`differently among MS's so that the total RateLimit can be
`the desired number. The actual value of R will depend on
`B and the number of MS’s in Soft and softer handoff, but it
`will not change much normally.
`One possible control scheme for RAB is to set it to 1 if the
`total rate measured for a certain period of time is greater than
`a threshold and to 0 otherwise. This threshold should be
`Smaller than capacity; otherwise it could cause many frame
`COS.
`4. Rate Control Based on Forward Traffic Rate
`To achieve a certain rate, the received power of a MS at
`the BS should be the same independent of the MS's location.
`Therefore, a MS far from the base station has to increase its
`transmission power. Furthermore, its pilot arrives at the base
`Station with equal power among MS's assuming the power
`control Scheme in Section 2 is used.
`A MS far from the serving BS is near to the neighboring
`BS's (compared to a MS near to the serving BS) and causes
`more interference. Therefore, a plausible Strategy is to
`allocate less rate (as a result, lowering its transmission
`power) for those MS's who should transmit at higher power
`So that they do not become significant Sources of interfer
`
`times MS 1's transmission power. Let P be MS 1's trans
`mission power. Then the interference to the base Station 2 is
`equal to
`
`25
`
`P
`to: --
`
`= 678Po,
`
`where C. is a constant.
`If we exchange MS 1 and 2's reverse rates, then the
`transmission power of MS 1 becomes 10 P and the trans
`mission power of MS 2 becomes 11.3 P. The total reverse
`throughput is unchanged. However, the interference to the
`base Station 2 now becomes
`
`( 1OP
`C 0.83.5 --
`
`11.3P
`)= 89 Pa,
`0.63.5
`
`which reduces the interference by about 9 dB.
`This can be easily implemented in an HDR system based
`on our observation that the amount of interference a MS is
`causing to other base Stations can be estimated Somewhat
`accurately from its forward-link SIR. Each BS knows the
`forward-link data rate of each MS as reported by a DRC
`value from each MS. This information can be used to adjust
`the reverse-link data rate as a function of the corresponding
`forward-link rate of the MS. The initial reverse link rate of
`a MS when it makes a connection can be set using the pilot
`Strength field in Route update message.
`Let a, and b, be the forward and reverse link path gains
`(including path loss and fading) from/to the i-th Sector
`to/from a MS of interest, respectively. Let i=0 be the sector
`that is Serving the MS (Sending and receiving data to and
`from the MS). We will describe later the case when sectors
`Sending and receiving data to and from the MS are different
`and also the case when the MS is in Soft or Softer handoff.
`Let M be the total number of sectors. Then, the forward-link
`SIR SIR is defined as follows (ignoring thermal noise at the
`MS):
`
`SIR = S. C
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Ex. 1005 - Sierra Wireless, Inc.
`Sierra Wireless, Inc., et al. v. Sisvel S.P.A., IPR2021-01141
`Page 10 of 16
`
`

`

`Similarly, we can define reciprocal reverse-link SIR SIR as
`follows:
`
`US 6,741,862 B2
`
`10
`To control the reverse rate R of the MS depending on how
`much interference it is causing to other Sectors, we can
`estimate
`
`1O
`
`15
`
`25
`
`Note that this is not the actual reverse-link SIR. It is only
`defined for convenience to represent how much reverse
`interference the MS’s are generating: When SIR is smaller,
`more interference is generated by MSs.
`The wireleSS channel is modeled using three components:
`path loss, Shadow fading, and fast fading (a.k.a. Rayleigh
`fading) (See T. S. Rappaport, Wireless Communications,
`Principles and Practice, Prentice Hall 1996.) The path loss
`and shadowing of forward link and reverse link is about the
`Same when the carrier frequencies of the forward link and
`the reverse link are about the same. Fast fading is the part
`that can be quite different for forward and reverse links.
`When a MS is moving at high speed, Rayleigh fading will
`have only an average effect and the forward and reverse
`links will have similar path loss, i.e., asb, for i=0,..., M.
`Therefore, in this case, SIR, and SIR will be similar.
`If a MS is stationary or is moving very slowly, the two
`linkS could have quite different instantaneous Rayleigh
`fading values, which makes the prediction of the reverse
`link path loSS based on the forward-link path loSS leSS
`accurate than the other case. In this case, SIR, and SIR can
`be significantly different, because their numerators can be
`very different although the difference in their denominators
`are expected to be Smaller due to the law of large numbers.
`In the next Section, through Simulation, we show the
`accuracy in predicting the total amount of interference a MS
`35
`is causing to other base Stations in these two cases. For the
`first case, we will assume that there is no Rayleigh fading but
`there is only 1/d path loss and shadow fading that are the
`Same for forward and reverse linkS. For the Second case, we
`will assume there is Rayleigh fading that is independent in
`forward and reverse links.
`Let P be the pilot transmission power and let R be the
`reverse rate of this MS. Then, the total interference this MS
`is causing to other BSS is equal to
`
`40
`
`45
`
`i
`Xb P1 + a R).
`
`i=l
`
`(6)
`
`is almost proportional to R, to reduce this
`Since C
`interference, we can assign higher rates for MS's that cause
`lower interference and assign lower rates for MS’s that
`cause higher interference. Therefore, it is necessary to
`measure the interference for each MS.
`However, direct measurement of (6) is difficult, because
`every BS has to measure each term of (6) and needs to send
`the information to the BS that is serving the MS (BS0 in this
`case).
`ASSuming SIR is similar to SIR, we can use the
`following relationship to estimate (6):
`
`50
`
`55
`
`60
`
`65
`
`and use it to control R. Using the above approximation, we
`can represent this as follows:
`
`biP
`SIR
`
`(7)
`
`This estimation requires SIR, and boP. boP can be
`calculated at the BS by measuring either the received pilot
`power or the received total power from the MS. The BS can
`estimate SIR from the DRC value it is receiving from the
`MS. The uncertainty in (7) can be reduced by averaging
`SIR for Some time period. In the following Section, we
`show how to assign reverse rates depending on the above
`estimate and show how much gain we can obtain in the
`reverse-link throughput.
`When a MS is in Soft handoff, the BS sending the forward
`traffic to the MS could be different from the BS that can
`decode the reverse traffic with the least probability of error.
`In this case, we assume the following approximation holds:
`
`(8)
`
`where k is the index of the BS that can decode the reverse
`traffic with the least probability of error. Approximation (8)
`seems to be far less accurate than (7) when the forward and
`reverse channels are very different. However, our simulation
`results in Section 7 shows that this is good enough for
`improving the reverse-link rate.
`Since it is not always possible to decide which BS can
`decode the reverse traffic with the least probability of error,
`we may choose one of BS’s that decoded the reverse traffic
`correctly most recently.
`Now, our goal is to minimize the aggregate interference
`these MS’s are causing to other BS’s (defined as all BS’s
`except the one that decodes the reverse traffic of the MS with
`the least probability of error) while maintaining the same
`aggregate rate. Equivalently and more desirably, we can
`maximize the aggregate rate while maintaining the same
`per-Sector aggregate interference to other BSS. Without any
`other restriction, the solution to this problem will be to
`allocate the maximum rate to the user in each Sector who is
`causing the least interference to other BS’s. However, this is
`not fair.
`Furthermore, it would be difficult to do global optimiza
`tion among all BS’s, Since it requires So much exchange of
`information. Instead, we can maximize the rate in each
`Sector Separately while maintaining the same interference to
`other BS’s. Since the amount of interference to other BS’s
`remains the Same in this case, the global optimization is
`equivalent to the distributed optimization.
`To introduce Some fairness, we consider the following.
`Let be the ratio of predicted reverse and forward data rates
`of the i-th MS. For example, will be close to one if the
`traffic is two-way communication Such as audio or video
`streams. It will be less than one for f