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

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`33H 5-51 10—ZOO4*0089937
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`ANNOUNCEMENT
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`RADIO RESOURCE RELEASE
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`04168
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`(19) 0
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`European Patent Office
`Office européen des brevets
`
`Iiiiliillllillilllllililililllillilliiiilliiillilllllli
`
`EP 1 496 639 A2
`
`(11)
`
`(12)
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`EUROPEAN PATENT APPLICATION
`
`(43) Date ofpubncation:
`12.01 .2005 Bulletin 2005/02
`
`(51) IntCI.7: H04L 1/18
`
`(21) Application number: 040152910
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`(22) Date of filing: 30.06.2004
`
`(84) Designated Contracting States:
`AT BE BG CH CY CZ DE DK EE ES FI FR GB GR
`HU lE IT LI LU MC NL PL PT RO SE SI SK TR
`Designated Extension States:
`AL HR LT LV MK
`
`. Cai, Liyu, CTO, Alcatel Shanghai Bell Co., Ltd.
`201206 Shangai (CN)
`- Pengpeng, Song, CTO,
`Alcatel Shan. Bell Co., Ltd.
`201206 Shangai (CN)
`
`(30) Priority: 08.07.2003 CN 03141448
`
`(71) Applicant: ALCATEL
`75008 Paris (FR)
`
`(74) Representative:
`Dreiss, Fuhlendorf, Steimle & Becker
`Patentanwalte,
`Postfach 10 37 52
`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
`
`The present invention provides a HARQ (Hy-
`(57)
`brid Automatic Repeat Request) combining method in
`an OFDM (Orthogonal Frequency Division Multiplexing)
`system, which adopts improved Chase combining meth-
`
`od weighted by SNR and variance of SNR to realize
`HARQ combining. The method canimprove system per—
`formance in processing power and time delay, particu~
`larly in low SNR environment. and will not make the sys-
`tem more complex.
`
`Receiver
`
`HARQ
`Combin—
`ing Unit
`
`Fig.1
`
`Printed by Jouve. 75001 PARIS (FR)
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`04175
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`EP 1 496 639 A2
`
`Description
`
`FIELD OF THE INVENTION
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`[0001] The present invention generally relates to a mobile communication system and particularly to a HARQ (Hybn'd
`Automatic Repeat Request) combining method in an OFDM (Orthogonal Frequency Division Multiplexing) system.
`
`BACKGROUND OF THE lNVENTION
`
`[0002] Existing simple combining techniques use Chase combining weighted by SNR (signal—to-noise ratio) to realize
`HARQ combining. Here. SNR is an average value over a period of time (for example, a data frame).
`[0003] There are two cases in relatively low SNR environment: 1) van‘ance of SNR may be relatively high over the
`same period of time; 2) variance of SNR may be relatively low over the same period of time. The first 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 combining at the receiver side may be reduced if only Chase combining weighted by SNR
`is simply adopted to realize HARQ combing.
`
`SUMMARY OF THE INVENTION
`
`[0004] The object of the present invention is to provide a HARQ combining method in an OF DM system, which can
`solve problems existing in the prior art. improve system performance in throughput and time delay, and reduce the
`system retransmission times at the same time.
`[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 receiver in 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 processing the stored final data to determine whether the received data frames are
`correct;
`
`b. If the 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 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 receives an ACK indicator. 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 NACK indicator, 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 same time, storing the combined data as final
`data in the buffer of the HARQ combining unit. then the receiver processing the combined final data to determine
`whether the combined data frames are 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]
`some processes including CRC appending. encoding and OFDM modulating in turn. and at the same time storing the
`data after CRC appending and before encoding in a TX buffer as final data in order to 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 NACK indicator 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 data in itself. whereas when said TX buffer receives a
`NACK indicator. it will hold on'ginal 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 combined final data. including in turn soft decoding and CRC checking. and then
`
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`EP 1 496 639 A2
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`obtaining an ACK or NACK indicator based on the determining whether the combined data frames are 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:
`
`1O
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`wherei indicates the i—th retransmission, and i2 0;
`
`Nm‘mn; indicates the retransmission times of a transmission block, and 1 s Mum",s s Nma,‘ ;
`Nma,‘ 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(r) indicates SNR of the i—th estimation;
`SNRmmsnord indicates the threshold of SNR:
`OSNRU) indicates variance of SNR of the i-th estimation;
`cumshom 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: it 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 on its SNR
`and variance of SNR, and combining the weighted retransmission data with the data stored in the buffer of said
`HARQ combining unit and storing the combined data as final data in the butter of said HARQ combining unit.
`
`[0011] The present invention implements a hybrid automatic repeat request combining method in an OFDM system
`by means of improved Chase combining weighted by SNR and variance of SNR. The method improves system per-
`tormance in throughput and time delay. particularly in low SNR environment. and will not make the system more com~
`plex.
`
`B RIEF DESCRIPTION OF THE DRAWINGS
`
`[0012] The present invention will now be further described in combination with the attached drawings and exemplary
`embodiments of the present invention.
`
`Fig. 1 is a schematic illustrating relevant structure of the receiver and transmitter for pertorming 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 ofSNR - System Throughput in which the HARQ combining method of the present
`invention is compared with normal Chase combining method and non-weighted data combining method; and
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`EP 1 496 639 A2
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`Fig. 4 is a simulation curve chart ofSNR ~ Time Delay in which the HARQ combining method of the present invention
`is compared with normal Chase combining method and non-weighted data combining method.
`
`DESCRIPTION OF THE PREFERRED EMBODIMENTS
`
`[0013] Vifith reference to the attached drawings and preferred embodiments, the present invention will now be further
`described.
`
`Fig. 1 is a schematic illustrating related structure of the receiver and transmitter for performing the HARQ
`[0014]
`combining method of the present invention in an OFDM system. As shown in Fig. 1 , at the side of Transmitter 10, firstly,
`CRC Appending Unit 11 of Transmitter 1O appends CRC to 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 user data inputted from TX Buffer 12 and outputs the result to OFDM
`Modulation Unit 14. And later. OFDM Modulation Unit 14 transmits the OFDM-modulated user data to a transmission
`unit of Transmitter 10 (not shown in Fig. 1) , which transmits the user data to radio channels (not shown in Fig. 1).
`[0015] At the side of Receiver 20. firstly, after a receiving unit of Receiver 20 (not shown in Fig. 1) receives the user
`data transmitted from Transmitter 10 from radio channels, OFDM Demodulation Unit 21 OFDM-demodulates the re—
`ceived user data and inputs the result, i.e.. user data 5(0) to HARQ Combining Unit 23 and SNR Estimation Unit 22,
`respectively. SNR Estimation Unit 22 SNR-estimates the user data 8(0) to get estimation values of SNR and variance
`of SNR. i,e., SNR__est(0) and os~R(0), of the user data 8(0). Then SNR_est(0) and os~R(0) are inputted together into
`HARQ Combining Unit 23. HARQ Combining Unit 23 weights the user data 8(0) based on estimated SNR and Variance
`of SNR, i.e.. SNR_est(0) and OSNR(0) to get weighted user data R(O). and stores the result. i.e.. weighted user data
`R(O) as final user data in the buffer of HARQ Combining Unit 23. And later, HARQ Combining Unit 23 inputs the user
`data R(O) to Soft Decoder 24, in which the inputted user data R(O) 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]
`If 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 ACK indicator, 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 ACK indicator, respectively.
`so the ACK indicator 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 ACK indicator,
`the operating procedures for transmitting user data at the 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), and stores it as final user data. Then the stored user data is transmitted to radio channels (not shown in Fig.
`1) via a transmission unit (not shown in Fig. 1) after encoded and OFDM modulated by Transmitter 10. Receiver 20
`receives the new user data transmitted by Transmitter 10 from radio channels (not shown in Fig. 1) and processes the
`received new user data, including OFDM demodulating, SNR estimating and weighting in turn, and at the same time
`storing weighted new user data as final user data in the buffer of HARQ Combining Unit 23. And later, 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 NACK indicator. 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 NACK indicator,
`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 modulate it. After that, the user data is transmitted to radio channels
`(not shown in 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 8(1) and inputs the retransmission date 5(1) into SNR Estimation Unit 22 and HARQ
`Combining Unit 23, respectively. SNR Estimation Unit 22 SNR-estimates the retransmission data S(1) to get its esti-
`mation values of SNR and Variance of SNR, i.e.. 8NR_est(1) and os~R(1). and inputs the estimated 8NR_est(1) and
`OSNRU) together into HARQ Combining Unit 23. HARQ Combining Unit 23 weights the inputted retransmission data
`8(1) based on its SNR_est(1) and 031m“): then gets user data R(1) by combining the weighted retransmission data
`and final user data 8(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
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`[0020] Then. HARQ Combining Unit 23 inputs the combined user data R(1) into Soft Decoder 24 to decode it. Soft
`Decoder 24 outputs soft—decoded data to CRC Checking Unit 25 to determine whether the received retransmission
`user data is correct. If the received retransmission user data is not correct, Receiver 20 feeds back a NACK indicator
`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 NACK indicator. 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. That is. after encoded and OFDM modulated by Transmitter 10. the final user data in TX
`Buffer 12 is retransmitted to radio channels (not shown in 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 gets
`retransmission data 5(2) by OFDM demodulation. and then gets SNR_est(2) and GSNR(2) by SNR-estimating the
`retransmission data 8(2). HARQ Combining Unit 23 weights the inputted retransmission data 8(2) based on inputted
`SNR_est(2) and oS~R(2), and then combines the weighted retransmission data with the final user data 5(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. And later. R(2) is soft decoded and C RC—checked by Receiver 20 to determine whether the received
`new retransmission user data is correct. If the received retransmission user data is not correct. Receiver 20 feeds back
`a NACK indicator 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 according to the following formula:
`
`E's“) . SNR _ est (1‘)
`R“) = 1-0”
`SNR f2:((3
`.
`i-o
`”SN: (0
`”2.50) ' SNR _ e:r(i)
`
`R(i) = "‘°N
`i-O
`fSNR _ e:t(i)
`
`’
`
`,
`
`SNR __ 95‘ (i) < SNRtlruIiolJ
`
`and
`
`65m (0 > alllrnhald
`
`I
`
`SNR __ est (1‘) 2 SNR "mm,
`
`or a”, (i) 5 0mm,“
`
`Where i indicates the i-th retransmission and i2 0;
`Nmmns indicates the retransmission times of a transmission block. and 1 g Nmmns s Nmax;
`Nmax indicates the maximum retransmission times of a transmission block;
`R(i) indicates the data after the i—th combining;
`S(f) indicates the data before the i-th combining;
`SNR_est(i) indicates the SNR of the i-th estimation;
`SNanmsnald indicates the threshold of SNR;
`OSNRU) indicates variance of SNR of the i—th estimation;
`olhmmom 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 present invention can be
`summarized as the following steps:
`
`a. A transmitter transmits data to a receiver in a unit of frame, then the receiver weights the received data based
`on its SNR and variance of SNR and stores the weighted data as final data in a buffer of a HARQ combining unlt,
`and later, the receiver processes the stored final data to determine whether the received data frames are correct;
`
`b. if the data frames are correct. the receiver will output the final data and feed back an ACK indicator 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 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 receive an ACK indicator. the process returns
`to step a. until all data has been transmitted;
`
`d. When the HARQ combining unit of the receiver and the transmitter receive a NACK indicator, 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 same time, stores the combined data as final
`data in the buffer of the HARQ combining unit, then the receiver processes the combined final data to determine
`whether the combined data frames are correct, after that, the proceSS returns to Step b.
`
`[0023] At the same time, from the above embodiment the receiver in the OFDM system of the present invention will
`be achieved, which includes:
`
`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 its 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 determination whether the re—
`ceived data frames are 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 and vari-
`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 combined data as final data in the buffer of said HARQ combining unit.
`
`[0024] The transmitter and other function modules of the receiver in the OFDM system can be realized by existing
`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:
`
`no.2... 5U) . SNR ._ es!(i)
`R ' = "0
`05”,, (i)
`Ni SNR ._ est“)
`0)
`
`iaO
`N"-
`
`USN; (i)
`
`,
`
`SNR est(i) < SNR, mg
`_
`I.
`n Id
`
`and a
`
`(r') > 0' m a
`it
`A Id
`
`SNR
`
`I
`
`2 3(1') ' SNR _ emu)
`R(i) = —"“:—v——-—-.
`fSNR _est(i)
`(:0
`
`SNR _ 951(1') 2 5NR,.,..,..u 0' <75" (1') 5 0mm,“
`
`Where i indicates the i-th retransmission and i2 0:
`Nmmms indicates the retransmission times of a transmission block, and 1 S Mama"s S Nmax;
`me 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(i) indicates the SNR of the i-th estimation;
`SNRthnshold indicates the threshold of SNR;
`OSNRU) indicates variance of SNR of the i-th estimation;
`Gama,“ 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 b3 indicate the simulation curves when employing normal Chase combining method weighted by SNR. and curves
`c1. c2. and 03 indicate the simulation curves when employing improved Chase combining method weighted by SNR
`and van‘ance of SNR of the present invention.
`[0027] The simulation curves shown in 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 120km/h; coding mode is 1/3 Turbo coding; modulation mode is 160AM; CRC is 24-bit; channel
`estimation and SNR estimation are ideal; the simulation point is 10240'150; and the maximum retransmission times
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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 present invention improves not only the performance of BER, but also system performance in throughput
`and time delay. And in relatively low SNR (less than 11dB) environment, the improvement of system performance in
`throughput and time delay of the method is remarkable. Thus. the improved Chase combining method weighted by
`SNR and variance of SNR of the present invention has more advantages. particularly in low 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 understood that the invention is not limited to the specific embodiments
`thereof except as defined in the appended claims.
`
`Claims
`
`1. A Hybrid Automatic Repeat Request (HARQ) combining method in an Orthogonal Frequency Division Multiplexing
`(OFDM) system, comprising steps of:
`
`a. a transmitter transmitting data to a receiver in 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 processing the stored final 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 unit of the receiver and the transmitter receiving a NACK indicator, 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 same time. storing the combined
`data as final data in the buffer of the HARQ combining unit, then the receiver processing the combined final
`data to determine whether the combined data frames are 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 receiver in unit of frame. the data needs to undergo processes of CRC appending. coding and OFDM mod—
`ulating in turn, and at the same time storing the data after CRC appending and before coding as final data in a TX
`buffer in order to facilitate possible retransmission.
`
`3. The HARQ combining method according to Claim 2, wherein in said 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.
`
`4. The HARQ combining method according to Claim 3. wherein in said step a, the receiver processes stored final
`data including soft decoding and CRC checking in turn, and then obtaining an ACK or NACK indicator based on
`the determination whether the received data is correct by CRC checking.
`
`5. The HARQ combining method according to Claim 1. wherein in said step b. the ACK or NACK indicator fed back
`to the transmitter is inputted to the TX buffer. and if said TX buffer receives an ACK indicator, it will store new data
`as final data in 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 variance of SNR. the receiver has to
`OFDM-demodulate the received retransmission data.
`
`7. The HARQ 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 checking in turn, and then obtaining an ACK or NACK indicator based
`on the determination whether the combined data frames are correct by CRC checking.
`
`The HARQ combining method according to Claim 1, wherein the process of said Receiver forweighting the received
`data and weighted combining said retransmission data is implemented according to the following formula:
`
`.
`R“) =
`
`RU) -_.
`
`HEM
`
`no
`
`-
`5U) ‘ SNR _e(s.l)(1)
`
`i-
`0’ -
`l
`0”
`SNR - 2:7“)
`as”: (i)
`N
`
`fsfi) ‘ SNR _ es! (i)
`N...
`"'°
`1:0
`2 SNR __ 2:1(i)
`
`‘
`.
`SNR _esl(i) < SNR,,,,DW and as” (1) > Ulhruhuhl
`
`I
`
`SNR _ 25:0) 2 SNRmmW or a," (i) 5 0M,“
`
`,
`
`_
`
`where i indicates the i-th retransmission. and i.>_ 0; Nmm,“ indicates the retransmission times of a transmission
`block, and 1 S NM,ans 5 NM“;
`Nmu indicates the maximum retransmission times of a transmission block:
`RU) indicates the data after the i-th combining;
`S(i) indicates the data before the i-th combing;
`SNR__est(i) indicates the SNR of the i—th estimation;
`SNRmnshom indicates the threshold of SNR;
`OSNRU) indicates variance of SNR of the i-th estimation;
`owflhom indicates the threshold of variance of SNR.
`
`10. A receiver in an OFDM system, comprising:
`
`a SNR estimation unit for SNR-estimating demodulated data to obtain estimated SNR and variance of SNR
`and outputting them;
`
`a HARQ combining unit for receiving the output from the SNR estima