04167
`
`Ex. 2001
`T-Mobile USA, Inc. v. Intellectual Ventures II LLC
`IPR2018-01775
`
`

`

`SISA 10-2004-0089937
`
`
`RADIO RESOURCE RELEASE
`
`
` DATA TRANSFER
`
`multicast mode bearer setup
`
`204
`
`205
`
`207
`
`208
`
`SUBSCRIPTION
`
`ANNOUNCEMENT
`
`201
`
`202
`
`203
`
`04168
`
`

`

`
`
`
`
`310RRCCONNECTIONSETUP[MBMSID]
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`310RECOUNTING
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`oH 10-2004-0089937
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`NBO_1*10ms
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`
`for
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`635|630ACCESSCONTROL[newPmbms]
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`UEsinacellandjoinedaMBMSserviceNodeBRNC
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`
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`
`04171
`
`04171
`
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`
`

`

`SIHS 1 10-2004-0089937
`
`
`
`Get RACH tx contro! parameters
` NOTE: MAC - c/sh receives RACHtx controlparameters
`from RRC: Mmax,Naotmin, Nsotmx
`from RRC with CMAC- CONFIG- Req primitive
`
`,set of ASC parameters , P mbms
`whenever one of the parameters ts updated
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`
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`counter M
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`730
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`
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`at
`B
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`Wait expiry
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`tx control
`Timer T,(10 ms)
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`parameters
`including
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`
`04172
`
`04172
`
`

`

`BISA 10-2004-0089937
`
`Pabms 1E= ea A= Oi AL AL al
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`04173
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`

`

`SIHSGl 10-2004-0089937
`
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`04174
`
`04174
`
`

`

`(19)
`
`(12)
`
`
`
`0,
`
`EuropeanPatent Office
`Office européen des brevets
`
`ee MAACACER
`
`(11)
`
`EP 1 496 639 A2
`
`EUROPEAN PATENT APPLICATION
`
`(43) Date of publication:
`12.01.2005 Bulletin 2005/02
`
`(21) Application number: 04015291.0
`
`(51) intci7: HO4L 1/18
`
`(22) Date of filing: 30.06.2004
`(84) Designated Contracting States:
`* Cai, Liyu, CTO, Alcatel Shanghai Bell Co., Ltd.
`AT BE BG CH CY CZ DE DK EE ES FI FRGB GR
`201206 Shangai (CN)
`HU IE IT LILU MC NL PL PT RO SE SISK TR
`« Pengpeng, Song, CTO,
`Designated Extension States:
`Alcatel Shan. Bell Co., Ltd.
`AL HR LT LV MK
`201206 Shangai (CN)
`
`(30) Priority: 08.07.2003 CN 03141448
`
`(71) Applicant: ALCATEL
`75008 Paris (FR)
`
`(74) Representative:
`Dreiss, Fuhlendorf, Steimle & Becker
`Patentanwiilte,
`Postfach 10 37 62
`70032 Stuttgart (DE)
`
`(72) Inventors:
`* Wan, Yan, CTO, Alcatel Shanghai Bell Co., Ltd.
`201206 Shangai (CN)
`
`
`(54)
`
`Hybrid automatic repeat request combining method and system in orthogonal frequency
`division multiplexing system
`
`(57)—The present invention provides a HARQ (Hy- od weighted by SNR and variance of SNR to realize
`
`brid Automatic Repeat Request) combining method in
`HARQ combining. The method can improve system per-
`an OFDM (Orthogonal FrequencyDivision Multiplexing)
`formance in processing powerandtime delay, particu-
`system, which adopts improved Chase combining meth-
`larly in fow SNR environment, and will not makethe sys-
`tem more complex.
`
`Receiver
`
`Fig.1
`
`Printed by Jouve, 75001 PARIS (FR)
`
`04175
`
`EP1496639A2
`
`04175
`
`

`

`EP 1 496 639 A2
`
`Description
`
`FIELD OF THE INVENTION
`
`{0001] The presentinvention generally relates to a mobile communication system and particularly to a HARQ (Hybrid
`Automatic Repeat Request) combining method in an OFDM (Orthogonal!Frequency Division Multiplexing) system.
`
`BACKGROUNDOF THE INVENTION
`
`[0002] Existing simple combining techniques use Chase combining weighted by SNR(signal-to-noiseratio) to realize
`HARQ combining. Here, SNR is an average value over a period oftime (for example, a data frame).
`[0003] There are twocasesin relatively low SNR environment: 1) variance of SNR mayberelatively high over the
`sameperiodof time; 2) variance of SNR mayberelatively low over the sameperiod of time. Thefirst case indicates
`that time selective fading of the signal is very serious. The effect of fast fading in time domain may be neglected and
`the performance of HARQ combiningat the receiver side may be reduced if only Chase combining weighted by SNR
`is simply adopted to realize HARQ combing.
`
`SUMMARYOF THE INVENTION
`
`Theobjectof the presentinventionis to provide a HARQ combining method in an OFDMsystem, which can
`[0004]
`solve problems existing in the prior art, improve system performance in throughput and time delay, and reduce the
`system retransmission times at the sametime.
`[0005] The HARQ combining method in an OFDM system according to the present invention comprises the following
`steps:
`
`a. A transmitter transmitting data to a receiverin a unit of frame, then the receiver weighting the received data
`based on its SNR and variance of SNR andstoring the weighted data asfinal datain a buffer ofa HARQ combining
`unit, and later, the receiver processing the stored final data to determine whether the received data frames are
`correct;
`
`b. Ifthe data frames are correct, the receiver outputting the final data and feeding back an ACK indicator respec-
`tively to the HARQ combining unit of the receiver and the transmitter, and if the data frames are not correct, the
`receiver feeding back a NACKindicator respectively to the HARQ combining unit of the receiver and the transmitter,
`
`c. When the HARQ combining unit of the receiver and the transmitter receives an ACKindicator, the process
`returning to step a, until all data has been transmitted;
`
`d. When the HARQ combining unit of the receiver and the transmitter receives a NACKindicator, the transmitter
`retransmitting original data to the receiver, then the HARQ combining unit of the receiver weighting the received
`retransmission data based on its SNR and variance of SNR, and combining the weighted retransmission data with
`the data stored in the buffer of the HARQ combining unit, and at the sametime, storing the combined data as final
`data in the buffer of the HARQ combining unit, then the receiver processing the combinedfinal data to determine
`whether the combined data framesare correct, and returning to step b.
`
`in step a, before the transmitter transmits data to the receiver in a unit of frame, the data needs to undergo
`[0006]
`someprocessesincluding CRC appending, encoding and OFDM modulatingin turn, and at the sametime storing the
`data after CRC appending and before encoding in a TX bufferasfinal data in orderto facilitate possible retransmission.
`In step a, before the receiver weights the received data based on its SNR and variance of SNR,the receiver has to
`OFDM-demodulate the received data. In step a, the receiver processes the stored final data, including in turn soft
`decoding and CRC checking, and then obtaining an ACK or NACK indicator based on the determining whether the
`received data is correct by CRC checking.
`[0007]
`In step b, the ACK or NACKindicator fed back to the transmitter is inputted to the TX buffer. When said TX
`buffer receives an ACK indicator,it will store new data as final datain itself, whereas when said TX buffer receives a
`NACK indicator,it will hold original final data unchanged.
`[0008]
`In step d, before the HARQ combining unit of the receiver weights the received retransmission data based
`on its SNR and variance of SNR, the receiver has to OFDM-demodulate the received retransmission data. In step d,
`the receiver SNR-estimates the OFDM-demodulated retransmission data to obtain its SNR and variance of SNR.In
`Step d, the receiver processes the combinedfinal data, including in turn soft decoding and CRC checking, and then
`
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`EP 1 496 639 A2
`
`obtaining an ACK or NACKindicator based on the determining whether the combined data framesare correct by CRC
`checking.
`[0009] Here, in the receiver of the present invention, the processes for weighting the received data and weighted
`combining the retransmission data can be realized according to the following formula:
`
`= s(i)* SNR _ est (é)
`=
`i)
`.
`
`
`
`Ri) = — SNR_est ANE Oguef) > FireS sua (i » (i) < SNR geo
`
`x
`SNR _ est(i)
`(4)
`—
`()
`threshoid
`sve @)
`threshoid
`10
`o sua Cf)
`7-0
`,
`5"s(é) * SNR _ est (i)
`
`R(i) = 2
`
`SNR _est(i) = SNR presto
`
`OF
`
`OF sya (8) S SO trresnors
`
`,
`
`
`
`»
`
`15
`
`S*SNR _ est (i)
`inQ
`
`20
`
`256
`
`30
`
`35
`
`40
`
`45
`
`wherei indicates the i-th retransmission, and i 2 0;
`Nretrans indicates the retransmission times of a transmission block, and 1 < Nyetrans S Nmax
`N,nax indicates the maximum retransmissiontimes of a transmission block;
`R(i) indicates the data after the i-th combining;
`S(i) indicates the data before the i-th combining;
`SNR_est(i) indicates SNR of the i-th estimation;
`SNRinreshoid indicates the threshold of SNR;
`Sswali) indicates variance of SNR ofthe i-th estimation;
`Sthreshola indicates the threshold of variance of SNR.
`[0010] The receiver in the OFDM system of the present invention comprises:
`
`a SNR estimation unit for SNR-estimating the demodulated data to obtain estimated SNR and variance of SNR
`and outputting them;
`
`a HARQ combining unit for receiving the output from the SNR estimation unit, weighting inputted demodulated
`data based on inputted SNR and variance of SNR, and storing the weighted data as final data in a buffer of said
`HARQ combining unit, then determining whether to execute the combining based on determining whether the
`received data frames are correct: if the received data frames are correct, not executing the combining. if the re-
`ceived data frames are not correct, weighting the inputted demodulated retransmission data based onits SNR
`and variance of SNR, and combining the weighted retransmission data with the data storedin the buffer of said
`HARQ combining unit and storing the combined data asfina! data in the buffer of said HARQ combiningunit.
`
`[0011] The present invention implements a hybrid automatic repeat request combining method in an OFDM system
`by meansof improved Chase combining weighted by SNR and variance of SNR. The method improves system per-
`formancein throughput and time delay,particularly in !ow SNR environment, and will not makethe system more com-
`plex.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0012] The presentinventionwill now be further described in combination with the attached drawings and exemplary
`embodiments of the present invention.
`
`Fig. 1 is a schematicillustrating retevant structure of the receiver and transmitter for performing the HARQ com-
`bining method of the present invention in an OFDM system;
`
`55
`
`Fig. 2 is a simulation curve chart of SNR - Bit Error Ratio (BER) in which the HARQ combining method of the
`present invention is compared with normal Chase combining method and non-weighted data combining method;
`
`Fig. 3.is a simulation curve chart of SNR - System Throughputin which the HARQ combining method of the present
`invention is compared with normal Chase combining method and non-weighted data combining method; and
`
`04177
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`04177
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`

`

`EP 1 496 639 A2
`
`Fig. 4 is a simulation curve chart of SNR- Time Delayin which the HARQ combining methodofthe present invention
`is compared with normal Chase combining method and non-weighted data combining method.
`
`DESCRIPTION OF THE PREFERRED EMBODIMENTS
`
`[0013] With reference to the attached drawings and preferred embodiments, the presentinvention will now be further
`described.
`[0014]
`Fig. 1 is a schematic illustrating related structure of the receiver and transmitter for performing the HARQ
`combining methodofthe presentinvention in an OFDM system. As shownin Fig. 1, at the side of Transmitter 10, firstly,
`CRC Appending Unit 11 of Transmitter 10 appends CRCto inputted user data in unit of frame and stores the appended
`user data with CRC bit as final user data in TX Buffer (transmitter buffer) 12. Then, TX Buffer 12 transmits the stored
`user data to Encoder 13, which encodes the userdata inputted from TX Buffer 12 and outputs the result to OFDM
`Modulation Unit 14. And later, OFDM Modulation Unit 14 transmits the OFDM-modulated userdata to a transmission
`unit of Transmitter 10 (not shown in Fig. 1), which transmits the user data to radio channels (not shownin Fig. 1).
`[0015] Atthe side of Receiver20,firstly, after a receiving unit of Receiver 20 (not shownin Fig. 1) receives the user
`data transmitted from Transmitter 10 from radio channels, OFDM Demodulation Unit 21 OF DM-demodulates the re-
`ceived user data and inputs the result, i.e., user data $(0) to HARQ Combining Unit 23 and SNR Estimation Unit 22,
`respectively. SNR Estimation Unit 22 SNR-estimates the user data S(0) to get estimation values of SNR and variance
`of SNR,i.e., SNR_est(0) and Ggya(0), of the user data S(0). Then SNR_est{0) and ogy,a{0) are inputted togetherinto
`HARQ Combining Unit 23. HARQ Combining Unit 23 weights the user data $(0) based on estimated SNR and Variance
`of SNR,i.@., SNR_est(0) and Ggyp(0) to get weighted user data R(0), and stores the result, i.e., weighted user data
`R(0) as final user data in the buffer of HARQ Combining Unit 23. And later, HARQ Combining Unit 23 inputs the user
`data R(0) to Soft Decoder 24, in which the inputted user data R(0) is soft decoded and outputted to CRC Checking
`Unit 25. CRC Checking Unit 25 determines whether the user data frames received by Receive 20 are correct and then
`gets an ACK or NACK indicator accordingly.
`[0016]
`!f CRC Checking Unit 25 determines the user data received by receiver 20 are correct, CRC Checking Unit
`25 will output the user data after CRC checking and issue an ACKindicator, which is fed back respectively to HARQ
`Combining Unit 23 of Receiver 20 and TX Buffer 12 of Transmitter 10. There should be a certain time delay before
`HARQ Combining Unit 23 of Receiver 20 and TX Buffer 12 of Transmitter 10 receive the ACKindicator, respectively,
`so the ACKindicator issued from CRC Checking Unit 25 of Receiver 20 is delayed by Time Delay Unit 26 of Receiver
`20 before fed back to HARQ Combining Unit 23 of Receiver 20 and TX Buffer 12 of Transmitter 10, respectively.
`{0017] When TX Buffer 12 of Transmitter 10 and HARQ Combining Unit 23 of Receiver 20 receive an ACKindicator,
`the operating proceduresfor transmitting user data atthe side of the transmitter and for receiving user data at the side
`of the receiver are repeated. That is, TX Buffer 12 of Transmitter 10 gets new user data after CRC appending(in unit
`of frame), andstoresit as final user data. Thenthestored userdatais transmitted to radio channels (not shownin Fig.
`1) via a transmission unit (not shownin Fig. 1) after encoded and OFDM modulated by Transmitter 10. Receiver 20
`receives the new userdata transmitted by Transmitter 10 from radio channels (not shownin Fig. 1) and processes the
`received new userdata,including OFDM demodulating, SNR estimating and weighting in turn, and at the sametime
`storing weighted new userdataasfinal user data in the buffer of HARQ Combining Unit 23. Andlater, the stored user
`data is soft decoded and CRC checked to determine whether the received new user data frames are correct. If the
`received new user data frames are correct, Receiver 20 outputs the user data after CRC checking and feeds back an
`ACK indicator to HARQ Combining Unit 23 of Receiver 20 and TX Buffer 12 of Transmitter 10 simultaneously. Thus,
`all these processes form a loop.
`[0018]
`If CRC Checking Unit 25 determines the received user data frames are not correct, CRC Checking Unit 25
`of Receiver 20 will issue a NACKindicator. In the same way, the NACK indicator is also delayed by Time Delay Unit
`26 and fed back to HARQ Combining Unit 23 of Receiver 20 and TX Buffer 12 of Transmitter 10, respectively.
`[0019] When HARQ Combining Unit 23 of Receiver 20 and TX Buffer 12 of Transmitter 10 receive a NACKindicator,
`TX Buffer 12 of Transmitter 10 does not get new user data, and retransmits the stored final user data to Encoder 13
`and OFDM Modulation Unit 14 to encode and modulateit. After that, the user data is transmitted to radio channels
`(not shownin Fig. 1) via the transmission unit (not shown in Fig. 1). After receiving the user data retransmitted by
`Transmitter 10 from radio channels (not shown in Fig.1), Receiver 20 OFDM-demodulates the retransmission user
`data to get retransmission data $(1) and inputs the retransmission data $(1} into SNR Estimation Unit 22 and HARQ
`Combining Unit 23, respectively. SNR Estimation Unit 22 SNR-estimates the retransmission data S(1) to getits esti-
`mation values of SNR and Variance of SNR,i.e., SNR_est(1) and osya(1), and inputs the estimated SNR_est(1) and
`Sswri1) together into HARQ Combining Unit 23. HARQ Combining Unit 23 weights the inputted retransmission data
`S(1) based on its SNR_est{(1) and ogyp(t), then gets user data R(1) by combining the weighted retransmission data
`and final user data S(0) stored in the buffer of HARQ Combining Unit 23, and at the same time stores the combined
`user data R(1) as final user data in the buffer of HARQ Combining Unit 23.
`
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`EP 1 496 639 A2
`
`(0020) Then, HARQ Combining Unit 23 inputs the combined user data R(1) into Soft Decoder 24 to decodeit. Soft
`Decoder 24 outputs soft-decoded data to CRC Checking Unit 25 to determine whetherthe received retransmission
`user data is correct.If the received retransmission user data is not correct, Receiver 20 feeds back a NACKindicator
`to HARQ Combining Unit 23 of Receiver 20 and TX Buffer Unit 12 of Transmitter 10, respectively. When HARQ Com-
`bining Unit 23 of Receiver 20 and TX Buffer Unit 12 of Transmitter 10 receive the NACKindicator, the operating pro-
`cedures for retransmitting user data at the side of the transmitter and for receiving retransmitted user data at the side
`of the receiver are repeated. Thatis, after encoded and OFDM modulated by Transmitter 10, the final user data in TX
`Buffer 12 is retransmitted to radio channels (not shownin Fig. 1) via the transmission unit (not shownin Fig. 1). After
`receiving the user data retransmitted by Transmitter 10 from radio channels (not shownin Fig. 1), Receiver 20 gets
`retransmission data $(2) by OFDM demodulation, and then gets SNR_est{(2) and ogyp(2) by SNR-estimating the
`retransmission data $(2). HARQ Combining Unit 23 weights the inputted retransmission data S(2) based on inputted
`SNR_est(2) and Ogypl2), and then combines the weighted retransmission data with the final user data $(1) in the
`buffer of HARQ Combining Unit 23 to get user data R(2), which is stored as final user data in the buffer of HARQ
`Combining Unit 23. Andlater, R(2) is soft decoded and CRC-checked by Receiver 20 to determine whetherthe received
`new retransmission userdata is correct.If the received retransmission userdata is not correct, Receiver 20 feeds back
`a NACKindicator respectively to HARQ Combining Unit 23 of Receiver 20 and TX Buffer 12 of Transmitter 10, thus
`constituting a loop. The loop will go on until the received new retransmission user data is correct. Then Receiver 20
`outputs the retransmission user data and feeds back an ACK indicator respectively to HARQ Combining Unit 23 of
`Receiver 20 and TX Buffer 12 of Transmitter 10 simultaneously.
`[0021] The above weighted combining process can be realized accordingto the following formula:
`
`5 si) ~ SNR: _ est (i)
`R(i) = =<
`SNR -o ,
`_
`iso
`So swe (@)
`"FPsci) * SNR _est(i)
`
`Ri) =
`S*SNR _ est (i)
`iad
`
`,
`
`SNR _ est(#) < SNR renee EOsup (1) > ©ereeshowa
`
`’
`
`SNR _est(i) 2 SNR ihrestoia
`
`9% SF syn @) SF thresh
`
`Wherei indicates the i-th retransmission and i 2 0;
`Nretrans indicates the retransmission times of a transmission block, and 1S Nyetrans & Nmax?
`Ninax indicates the maximum retransmission times of a transmission block;
`R(i) indicates the data after the i-th combining;
`S(/) indicates tie data before the i-th combining,
`SNR_est(i) indicates the SNR ofthe i-th estimation;
`SNRinresnoid indicates the threshold of SNR;
`Ssnrti indicates variance of SNRofthei-th estimation;
`Srhreshold indicates the threshold of variance of SNR.
`{0022} According to above detailed description of the embodiment, the HARQ (Hybrid Automatic Repeat Requests )}
`combining method in an OFDM (Orthogonal Frequency Division Multiplexing ) System of the presentinvention can be
`summarized as the following steps:
`
`a. A transmitter transmits data to a receiverin a unit of frame, then the receiver weights the received data based
`on its SNR and variance of SNR andstores the weighted data asfinal data in a buffer of a HARQ combining unit,
`andlater, the receiver processesthe storedfinal data to determine whether the received data frames are correct;
`
`b. If the data framesare correct, the receiverwill output the final data and feed back an ACKindicator respectively
`to the HARQ combining unit of the receiver and the transmitter, and if the data frames are not correct, the receiver
`will feed back a NACKindicator respectively to the HARQ combining unit of the receiver and the transmitter;
`
`c. When the HARQ combining unit of the receiver and the transmitter receive an ACKindicator, the process retums
`to step a, until all data has been transmitted;
`
`d. When the HARQ combining unit of the receiver and the transmitter receive a NACKindicator, the transmitter
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`EP 1 496 639 A2
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`retransmits original data to the receiver, then the HARQ combining unit of the receiver weights the received re-
`transmission data based on its SNR and variance of SNR, and combines the weighted retransmission data with
`the data stored in the buffer of the HARQ combining unit, and at the sametime, stores the combined dataas final
`data in the buffer of the HARQ combining unit, then the receiver processes the combinedfinal data to determine
`whether the combined data framesare correct, after that, the process returns to Step b.
`
`[0023] Atthe sametime, from the above embodimentthe receiver in the OFDM system of the present invention will
`be achieved, which includes:
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`10
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`15
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`20
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`25
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`a SNRestimation unit for SNR-estimating the demodulated data to obtain estimated SNR and variance of SNR
`and outputting them;
`
`a HARQ combining unit for receiving the output from the SNR estimation unit, weighting inputted demodulated
`data based onits SNR and variance of SNR, and storing the weighted data asfinal data in a buffer of said HARQ
`combining unit, then determining whether to execute the combining based on the determination whetherthe re-
`ceived data framesare correct: if the received data frames are correct, not executing the combining; if the received
`data frames are not correct, weighting the inputted demodulated retransmission data based on its SNR andvari-
`ance of SNR and combining the weighted retransmission data with the data in the buffer of said HARQ combining
`unit, and at the same time, storing the combineddata asfinal data in the buffer of said HARQ combining unit.
`
`Thetransmitter and other function modulesof the receiver in the OFDM system can berealized by existing
`[0024]
`technologies. Thus, their description are omitted here.
`[0025] Herein, in the receiver of the present invention, the process of the HARQ combining unit for weighting the
`received data and weighted combining the retransmission data based on its SNR and variance of SNR respectively
`can be realized according to the following formula:
`
`Nseem
`
`°
`
`SF sa EO
`30
`
`Ri) = 2 SNR_est(i) <SNR seers NEOug1) > F stresteO svn!
`
`(i) = SNR _ est(i)
`~
`Areshold
`INR
`threshold
`So syr (*)
`#20
`S$s(i)* SNR _est(i)
`RG) ==, SNR _ est(i) 2 SNR weston
`SNR _ est(i)
`is
`
`35
`
`‘
`
`OF
`
`OF svn C1) SO reshots
`
`40
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`45
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`50
`
`55
`
`Wherei indicates the i-th retransmission and j2 0;
`Nretrans indicates the retransmission times of a transmission block, and 4 < Nrerrans = Nmax?
`Ninax indicates the maximum retransmission times of a transmission block;
`R(i) indicates the data after the i-th combining;
`S(i) indicates the data before the i-th combining:
`SNR_est{/) indicates the SNR of the i-th estimation;
`SNRehreshoig indicates the threshold of SNR;
`Ssnrt) indicates variance of SNRofthe i-th estimation;
`Sthreshota indicates the threshold of variance of SNR.
`[0026]
`Figures 2, 3, and 4 show the simulation curve chart of SNR-BER (Bit Error Ratio), SNR-Throughput and
`SNR-Time Delay according to comparing examples of the present invention, respectively. As show in Figures 2-4,
`curves a1, a2, and a3 indicate the simulation curves when employing non-weighted combining method, curves b1, b2,
`and b3indicate the simulation curves when employing normal Chase combining method weighted by SNR,and curves
`c1, 2, and c3 indicate the simulation curves when employing improved Chase combining method weighted by SNR
`and variance of SNRofthe presentinvention.
`[0027] The simulation curves shownin Figures 2-4 are obtained in the following simulation environments: in an
`OFDM system; the carrier frequency is 3.2GHz; the channel is an outdoor multipath channel A with AWGN+UMTS;
`the mobile speed is 120kmv/h; coding modeis 1/3 Turbo coding; modulation mode is 16QAM; CRCis 24-bit; channel
`estimation and SNRestimation are ideal; the simulation point is 10240*150; and the maximum retransmission times
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`EP 1 496 639 A2
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`are set to 5. According to Figures 2, 3, and 4, the improved Chase combining method weighted by SNR and variance
`of SNR of the presentinvention improvesnotonly the performance of BER, but also system performancein throughput
`and time delay. And in relatively low SNR(less than 11dB) environment, the improvementof system performancein
`throughput and time delay of the method is remarkable. Thus, the improved Chase combining method weighted by
`SNR and vanance of SNRofthe present invention has more advantages, particularly in !ow SNR environment, which
`is the common condition in mobile communication systems.
`[0028] As many apparently widely different embodiments of the present invention can be made without departing
`from the spirit and scope thereof, it is to be understoodthatthe invention is not limited to the specific embodiments
`thereof except as defined in the appended ciaims.
`
`Claims
`
`1. AHybrid Automatic Repeat Request (HARQ) combining methodin an Orthogonal Frequency Division Muitiplexing
`(OFDM) system, comprising steps of:
`
`a. a transmitter transmitting data to a receiverin a unit of frame, then the receiver weighting the received data
`based on its SNR and variance of SNR and storing the weighted data as final data in a buffer of a HARQ
`combining unit, and later, the receiver processingthestoredfinal data to determine whether the received data
`frames are correct;
`
`if the data frames are correct, the receiver outputting the final data and feeding back an ACK indicator
`b.
`respectively to the HARQ combining unit of the receiver and the transmitter, and if the data frames are not
`correct, the receiver feeding back a NACK indicator respectively to the HARQ combining unit of the receiver
`and the transmitter;
`
`c. when the HARQ combining unit of the receiver and the transmitter receiving an ACK indicator, the process
`returning to step a, until all data has been transmitted;
`
`d. when the HARQ combining unitof the receiver and the transmitter receiving a NACKindicator, the transmitter
`retransmitting originat data to the receiver, then the HARQ combining unitof the receiver weighting the received
`retransmission data based on its SNR and variance of SNR, and combining the weighted retransmission data
`with the data stored in the buffer of the HARQ combining unit, and at the same time, storing the combined
`data asfinal data in the buffer of the HARQ combining unit, then the receiver processing the combined final
`data to determine whether the combined data framesare correct, after that, the process returning to step b.
`
`2. The HARQ combining method according to Claim 1, wherein in said step a, before the transmitter transmits data
`to the receiverin unit of frame, the data needs to undergo processes of CRC appending, coding and OFDM mod-
`ulating in turn, and at the sametimestoring the data after CRC appending and before coding as final data in a TX
`buffer in orderto facilitate possible retransmission.
`
`3. The HARQ combining method accordingto Claim 2, whereinin said step a, before the receiver weights the received
`data based on its SNR and variance of SNR, the receiver has to OFDM-demcdulate the received data.
`
`4. The HARQ combining method according to Claim 3, wherein in said step a, the receiver processesstoredfinal
`data including soft decoding and CRC checking in turn, and then obtaining an ACK or NACKindicator based on
`the determination whether the received data is correct by CRC checking.
`
`5. The HARQ combining method according to Ciaim 1, wherein in said step b, the ACK or NACKindicator fed back
`to the transmitteris inputted to the TX buffer, and if said TX buffer receives an ACKindicator,it will store new data
`as final datain itself, and if said TX buffer receives a NACK indicator, it will hold the final data unchanged.
`
`6. The HARQ combining method according to Claim 4, wherein in said step d, before the HARQ combining unit of
`the receiver weights the received retransmission data based on its SNR and varianceof SNR,the receiver has to
`OFDM-demodulate the received retransmission data.
`
`7. The HARG combining method according to Claim 6, wherein in said step d, the SNR and variance of SNR of the
`retransmission data are obtained by the receiver by SNR-estimating the received OFDM-demodulated retrans-
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`mission data.
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`EP 1 496 639 A2
`
`The HARQ combining method according to Claim 7, wherein in said step d, the receiver processes the combined
`final data including soft decoding and CRC checkingin turn, and then obtaining an ACK or NACKindicator based
`onthe determination whether the combined data frames are correct by CRC checking.
`
`The HARQ combining method according to Claim 1, wherein the processof said Receiverfor weighting the received
`data and weighted combining said retransmission data is implemented according to the following formula:
`
`.
`R() =
`
`x
`S ociys SNR West (i)
`te
`SF vr Gi)
`o
`SNR ost (i)
`i=0
`o sur (8)
`nN
`sti) * SNR _ est(i)
`
`Dy ere
`Ri) =
`D, SNR _ est (i)
`=O
`
`,
`
`,
`
`.
`.
`SNR _est(i) < SNRureshuts OE OCsyn (4) > Otrresrot
`
`é
`
`SNR _ est(i) 2 SNR aresmoen
`
`OF Fyn CE) S O rertratd
`
`wherei indicates the i-th retransmission, and i> 0; Nyerrans indicates the retransmission times of a transmission
`block, and 1 < Nretrans = Nmaxi
`Nmax indicates the maximum retransmission times of a transmission block;
`R(A indicates the data after the i-th combining;
`S(/ indicates the data before the i-th combing:
`SNR_est(/) indicates the SNR of the i-th estimation;
`SNRihreshotd indicates the threshold of SNR;
`Sgwali) indicates variance of SNRofthei-th estimation;
`Sinrashola indicates the threshold of variance of SNR.
`
`40. Areceiver in an OFDM system, comprising:
`
`a SNRestimation unit for SNR-estimating demodulated data to obtain estimated SNR and variance of SNR
`and outputting them;
`
`a HARQ combiningunit for receiving the output from the SNRestimation unit, weighting inputted demodulated
`data based on inputted SNR and variance of SNR, and storing the weighted data as final data in a buffer of
`said HARQ combining unit, then determining whether to execute the combining based on the de