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WO2007066984A1 - Appareil et procede de correction iterative des frequences et phases residuelles dans un systeme mrof turbocode - Google Patents

Appareil et procede de correction iterative des frequences et phases residuelles dans un systeme mrof turbocode Download PDF

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Publication number
WO2007066984A1
WO2007066984A1 PCT/KR2006/005259 KR2006005259W WO2007066984A1 WO 2007066984 A1 WO2007066984 A1 WO 2007066984A1 KR 2006005259 W KR2006005259 W KR 2006005259W WO 2007066984 A1 WO2007066984 A1 WO 2007066984A1
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WO
WIPO (PCT)
Prior art keywords
frequency
phase
soft
iterative
symbols
Prior art date
Application number
PCT/KR2006/005259
Other languages
English (en)
Inventor
Sun-Heui Ryoo
Kwon-Hue Choi
Do-Seob Ahn
Original Assignee
Electronics And Telecommunications Research Institute
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from KR1020060048235A external-priority patent/KR100728221B1/ko
Application filed by Electronics And Telecommunications Research Institute filed Critical Electronics And Telecommunications Research Institute
Priority to US12/094,282 priority Critical patent/US8036289B2/en
Publication of WO2007066984A1 publication Critical patent/WO2007066984A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0045—Arrangements at the receiver end
    • H04L1/0047—Decoding adapted to other signal detection operation
    • H04L1/005—Iterative decoding, including iteration between signal detection and decoding operation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0064—Concatenated codes
    • H04L1/0066—Parallel concatenated codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H04L27/266—Fine or fractional frequency offset determination and synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2673—Details of algorithms characterised by synchronisation parameters
    • H04L27/2676—Blind, i.e. without using known symbols
    • H04L27/2679—Decision-aided

Definitions

  • the present invention relates to an apparatus and method for correcting an iterative residual frequency and phase in a turbo coded OFDM system in a low power environment, and a method thereof; and more particularly, to an iterative residual frequency and phase compensation apparatus for estimating and compensating the phase of a carrier wave iteratively using the soft-decision reliability of a channel decoder in a digital communication system using an OFDM modulation scheme, and a method thereof.
  • Portable mobile satellite communication has been receiving an attention as a next generation mobile communication, and many related technologies have been actively researched and developed.
  • the portable mobile satellite communication uses a high frequency band, for example, higher than 10 GHz. Since the high frequency band is easily attenuated by wind or rain, various problems may be arisen.
  • the portable mobile satellite communication requires a high design cost to sustain the receiving power level at an uplink similar to the receiving power level of a terrestrial wave because of the structural limitation of a portable terminal and the large power attenuation characteristic of satellite communication. Therefore, a synchronization unit of a portable mobile satellite MODEM must be designed to operate in a low signal- to-noise ratio (SNR).
  • SNR signal- to-noise ratio
  • the iterative phase synchronization method uses phase error information obtained from one codeword only for decoding a corresponding code. Therefore, a delay problem caused by an unnecessary loop that is a feedback based synchronizing algorithm is not arisen in the iterative phase synchronization method.
  • the iterative phase synchronization method assumes that a phase error is constant in a codeword, the phase errors of codewords are estimated based on the constant phase error at every iteration stages. Accordingly, the conventional iterative phase synchronization method cannot be used when a phase rotates in a codeword due to a residual frequency. Because the iterative phase synchronization method seriously degraded the performance thereof if the residual frequency error is present.
  • the residual frequency error is commonly generated in a codeword by a Doppler in the mobile communication environment. Although the Doppler is not present, the residual frequency error is generated when a preceding frequency synchronizing algorithm is not perfect. If the length of a codeword is comparatively short although the residual frequency error is generated, it is possible to assume a phase error as a constant in a codeword. However, since the length of a codeword having a high coding gain such as a turbo code or low-density parity-check (LDPC) is generally long, it is unreasonable to assume the phase error as the constant. As described above, to assume the phase error as a constant is very strict assumption. Therefore, the conventional iterative phase synchronization method has restricted applicability.
  • LDPC low-density parity-check
  • the iterative phase synchronization method can be applicable.
  • the code symbols are transmitted with different subcarrier waves as many as the number of the subcarrier waves. That is, the code symbols are grouped into N groups, where N denotes the number of subcarrier waves in the OFDM system.
  • the OFDM system transmits the code symbols sequentially in each subcarrier wave and transmits the code symbols with subcarrier waves in parallel.
  • the subcarrier waves have different initial phase errors due to a timing error, a timing jitter and fading. It means that the phases of each subcarrier wave must be estimated independently. That is, a frequency and phase restoring method for a single carrier wave system must be modified to be suitable to the characteristics of the OFDM modulation method.
  • an object of the present invention to provide an iterative residual frequency and phase compensation apparatus and a method thereof for effective synchronization in a low power environment by estimating and compensating the phase of a carrier wave iteratively using the soft-decision reliability of a channel decoder in a digital communication system using an OFDM modulation scheme.
  • an iterative frequency and phase compensation apparatus for in an OFDM communication system including a OFDM demodulator and an iterative decoder, including: a first classifying unit for classifying OFDM demodulated symbol sequences by each subcarrier wave according to a location in a frame of a corresponding data symbol; a soft-decision calculating unit for calculating a soft-decision value of a data symbol using a soft- decision reliability obtained from iterative decoding performed by the iterative decoder; a second classifying unit for receiving the soft-decision values from the soft- decision calculating unit and classifying the received soft-decision values by a carrier wave; a frequency estimating unit for estimating a residual frequency error of each carrier wave for symbols of each carrier wave inputted from the first classifying unit using the soft-decision value of each carrier wave inputted from the second classifying unit; a phase estimating unit for estimating an average residual phase error of carrier waves for symbols of each carrier wave inputted
  • an iterative frequency and phase compensation method for an OFDM communication system including an OFDM demodulator and an iterative decoder, the method including the steps of: a) calculating a soft-decision value using soft-decision reliability obtained at a l ' decoding stage; b) arranging symbols of each subcarrier wave according to a location in an OFDM frame of a corresponding data symbol; c) estimating a frequency error and a phase error for the arranged symbol of each subcarrier wave using the calculated soft-decision value; d) compensating frequencies and phases of all code symbols in a corresponding carrier wave using the estimated frequency error and the estimated phase error; e) rearranging updated sample values of each frequency and phase compensated code symbol according to an order of original code symbol sequence and inputting the rearranged sample values to the iterative decoder; and f) performing the steps a) to e) until the number of decoding stage reaches at a predetermined iterative
  • An iterative residual frequency and phase compensation apparatus and a method thereof according to the present invention can merge the iterative decoding of a single OFDM frame with the estimation and compensation of a frequency and a phase of each carrier wave in a multi carrier waves system for high data transmission, and can effectively remove residual frequency and phase from a comparative low energy region. Therefore, the system performance thereof can be improved.
  • Fig. 1 is a layout of a code symbol in a typical OFDM frame
  • Fig. 2 is a view for describing the initial residual frequency error and a residual phase error of a channel receiving signal
  • FIG. 3 is a block diagram illustrating an iterative frequency and phase compensation apparatus in accordance with an embodiment of the present invention.
  • FIG. 4 is a flowchart of an iterative frequency and phase compensation method in accordance with an embodiment of the present invention.
  • Fig. 1 is a layout of a code symbol in a typical OFDM frame.
  • An orthogonal frequency division multiplexing (OFDM) system simultaneously transmits N code symbols using N subcarrier wave, when the length of a codeword is L
  • each of the subcarrier waves transmits
  • Fig. 2 is a view for describing the initial residual frequency error and a residual phase error of a channel receiving signal.
  • ⁇ f denotes an initial frequency error
  • ⁇ (n) denotes the initial phase error of an n subcarrier wave allocated for code transmission.
  • ⁇ (n) is independent from n and ⁇ (n) has uniform distribution in [- ⁇ , ⁇ ].
  • the residual phase errors of each carrier wave are max max
  • FIG. 3 is a block diagram illustrating an iterative frequency and phase compensation apparatus in accordance with an embodiment of the present invention.
  • the iterative frequency and phase compensation apparatus arranges OFDM modulated symbol sequences in serial and inputs the serial symbol sequence to a turbo iterative decoder 308 at the first decoding stage. After the first decoding stage, the iterative frequency and phase compensation apparatus corrects the input symbols of a preceding decoding stage based on a phase error and frequency error estimated at the preceding decoding stage. Then, the iterative frequency and phase compensation apparatus inputs the corrected symbols to the turbo iterative decoder 308.
  • An OFDM demodulator 301 demodulates input symbol sequences, and a parallel/ serial converter 302 serializes the demodulated symbol sequence from the OFDM demodulator 301.
  • a first classifying unit 304 receives the selected serial symbol sequence from the symbol sequence switching unit 303 and classifies the received serial symbol sequence by a carrier wave. After classifying, the first classifying unit 304 outputs the classified symbol sequences to a frequency estimating unit 311, a phase estimating unit 312, and a frequency and phase compensating unit 305. That is, the first classifying unit 304 rearranges the symbol sequences of each carrier wave in a time domain according to a location in the OFDM frame of corresponding data symbol and outputs the rearranged symbol sequences to the frequency estimating unit 311, the phase estimating unit 312 and the frequency and phase compensator 305.
  • a soft-decision calculator 309 calculates and outputs the soft-decision value a (m) of a m data symbol as a soft-decision reliability obtained from a current decoding stage, that is, a / * decoding stage.
  • the soft-decision calculator 309 may be embodied using a tanh calculator and calculate the soft-decision value as like a following Eq. 1.
  • L (m) denotes the log likelihood ratio (LLR) of an m data symbol when a subcarrier wave is a BPSK modulation.
  • L l,in (m) and L l.quad ⁇ (m) denote the soft-decision reliabilities of a real part and an imaginary part in a m data symbol when a subcarrier wave is the BPSK modulation.
  • a second classifying unit 310 receives the calculated soft-decision values from the soft-decision calculator 309 and classifies the received soft-decision values by a carrier wave. After classifying, the second classifying unit 310 provides the classified soft- decision values to the frequency estimating unit 311 and the phase estimating unit 312.
  • the frequency estimating unit 311 estimates a residual frequency error for the
  • the phase estimating unit 312 estimates an average residual phase error for the symbol sequences of each carrier wave inputted from the first classifying unit 304 using the soft-decision value inputted from the second classifying unit 310.
  • the frequency and phase compensating unit 305 compensates the frequencies and the phases of all code symbols in a corresponding carrier wave inputted from the first classifying unit 304 using the average residual phase error and the residual frequency error of the carrier wave, which are estimated carrier wave at the frequency estimating unit 311 and the phase estimating unit 312.
  • a symbol sorter 306 rearranges the compensated symbol sequence from the
  • the compensated symbol sequence is also buffered at the input buffer 308 for the next decoding stage.
  • the operation for compensating the frequency and the phase of each carrier wave will be described in detail.
  • the frequency and phase compensating unit 305 compensates the phase error of an m* data symbol value y (m) using a soft-decision value obtained from the soft-decision calculator 309 as shown in Eq. 2.
  • a residual phase error and a residual frequency error of each subcarrier wave are estimated using the phase of compensated symbol s (m) in Eq. 2. Since codewords are transmitted by a plurality of subcarrier waves in the OFDM system, the residual phase error and the residual frequency error must be estimated independently for each carrier wave.
  • the first classifying unit 304 rearranges the compensated symbols S (m) by each subcarrier wave in a time domain according to the location in an OFDM frame of a corresponding data symbol. Using rearranged samples of S (m), the frequency estimating unit 311 and the phase estimating unit 312 estimate the residual frequency error and the residual phase error.
  • the ave)rage residual phase error of n* carrier waves can be obtained using Eq. 3.
  • J denotes the number of data symbols in each carrier wave.
  • J is given as Eq. 4.
  • a frequency can be estimated using three methods shown in Eq. 5.
  • T denotes an OFDM symbol interval
  • r denotes a code rate.
  • the first method estimates the frequency by obtaining the means of phase variation.
  • the second method estimates the frequency by obtaining a phase after adding the results of conjugate multiplication between symbols.
  • the third method estimates the frequency by obtaining a phase difference after adding all front symbol and rear symbols separated at a symbol interval d. Since the third method requires only two operations for estimating phases and adding complex numbers, the computation complex of the third method is lower than other two methods.
  • the reliability of estimating frequency error is improved using the average value of estimated frequency errors of each subcarrier wave as the final frequency error.
  • the frequency and phase compensating unit 305 compensates the frequencies and the phases of all code symbols belonging to a corresponding carrier wave.
  • the symbol sorter 306 After compensating the frequency and the phase of each carrier wave, the symbol sorter 306 transforms the updated sample values
  • the currently inputted codeword is decoded with the frequency error and the phase error compensated by recursively repeating the iterative decoding stage until the number of performing the decoding reaches to a predetermined iterative number.
  • FIG. 4 is a flowchart of an iterative frequency and phase compensation method in accordance with an embodiment of the present invention.
  • an initializing operation is performed at step S401. That is, the number of iterative decoding stage / is initialized as T parallel symbol sequences demodulated at an OFDM demodulator are serialized, the serial symbol sequences are classified by a carrier wave, and the classified symbol sequences are inputted to the iterative decoder at step S401.
  • step S403 the symbols of each subcarrier wave are sorted in a time domain
  • the first method estimates the frequency error by obtaining the means of phase variation.
  • the second method estimates the frequency error by obtaining a phase after adding the results of conjugate multiplication between symbols.
  • the third method estimates the frequency error by obtaining a phase difference after adding all front symbol and rear symbols separated at a symbol interval d.
  • step S404 the frequency and the phase of all code symbols in a corresponding carrier wave are corrected using the estimated frequency error and the estimated phase error of each carrier wave.
  • the updated sample value of each code symbol is transformed according to the order of original code symbol sequence for iterative decoding, and the transformed sample value is inputted to the iterative decoder.
  • the / * iterative decoding stage is completely finished with the frequency and phase compensation.
  • step S405 it determines whether the number of performing the iterative
  • decoding / reaches to a predetermined iterative decoding number or not. If not, the number of performing the iterative decoding / increases by one at step S406, and the step S402 for calculating the soft-decision value is repeatedly performed. If the number of performing the iterative decoding / reaches to the predetermined iterative decoding number, it determines that the iterative decoding for the current codeword is completely finished with the frequency and phase error compensation.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Error Detection And Correction (AREA)

Abstract

L'invention porte sur un appareil de compensation itérative des fréquences et phases résiduelles pour système OFDM, et procédé associé. L'appareil comporte: Une première unité de classement par sous-porteuse de séquences de symboles; une unité de calcul à décision douce de la valeur d'un symbole de données utilisant une fiabilité de décision douce obtenue par un décodage itératif exécuté par le décodeur itératif; une unité de classement par porteuse des valeurs de décision douce; une unité d'estimation de l'erreur sur la fréquence résiduelle pour chaque porteuse utilisant la valeur de détection douce; une unité d'estimation de l'erreur moyenne sur la phase résiduelle utilisant la valeur de détection douce; une unité de compensation de la phase et de la fréquence des symboles introduits de chaque porteuse utilisant l'erreur estimée de fréquence et l'erreur estimée de phase; et un tampon stockant temporairement les symboles compensés et les transférant à la première unité de classement.
PCT/KR2006/005259 2005-12-08 2006-12-07 Appareil et procede de correction iterative des frequences et phases residuelles dans un systeme mrof turbocode WO2007066984A1 (fr)

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Application Number Priority Date Filing Date Title
US12/094,282 US8036289B2 (en) 2005-12-08 2006-12-07 Apparatus and method for correcting iterative residual frequency and phase in turbo coded OFDM system

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
KR10-2005-0119681 2005-12-08
KR20050119681 2005-12-08
KR1020060048235A KR100728221B1 (ko) 2005-12-08 2006-05-29 터보부호 ｏｆｄｍ 시스템용 반복적 잔류 주파수 위상 보정장치 및 그 방법
KR10-2006-0048235 2006-05-29

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014058674A1 (fr) * 2012-10-09 2014-04-17 Nec Laboratories America, Inc. Modulation codée ldpc pour un transport optique à ultra haute vitesse en présence de bruit de phase
WO2014100699A1 (fr) * 2012-12-20 2014-06-26 Qualcomm Incorporated Systèmes et procédés d'atténuation de bruit de phase

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR19990058954A (ko) * 1997-12-30 1999-07-26 구자홍 디지털 방송수신 방법
US6219334B1 (en) * 1997-03-14 2001-04-17 Kabushiki Kaisha Toshiba Receiving apparatus for receiving orthogonal frequency division multiplexing signal and receiving method thereof
US6289000B1 (en) * 2000-05-19 2001-09-11 Intellon Corporation Frame control encoder/decoder for robust OFDM frame transmissions
WO2003058904A1 (fr) * 2001-12-27 2003-07-17 Bermai, Inc. Egalisation, demapping pondere et correction d'erreur de phase conjoints dans un systeme sans fil a diversite de reception

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6219334B1 (en) * 1997-03-14 2001-04-17 Kabushiki Kaisha Toshiba Receiving apparatus for receiving orthogonal frequency division multiplexing signal and receiving method thereof
KR19990058954A (ko) * 1997-12-30 1999-07-26 구자홍 디지털 방송수신 방법
US6289000B1 (en) * 2000-05-19 2001-09-11 Intellon Corporation Frame control encoder/decoder for robust OFDM frame transmissions
WO2003058904A1 (fr) * 2001-12-27 2003-07-17 Bermai, Inc. Egalisation, demapping pondere et correction d'erreur de phase conjoints dans un systeme sans fil a diversite de reception

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014058674A1 (fr) * 2012-10-09 2014-04-17 Nec Laboratories America, Inc. Modulation codée ldpc pour un transport optique à ultra haute vitesse en présence de bruit de phase
US9036992B2 (en) 2012-10-09 2015-05-19 Nec Laboratories America, Inc. LDPC-coded modulation for ultra-high-speed optical transport in the presence of phase noise
WO2014100699A1 (fr) * 2012-12-20 2014-06-26 Qualcomm Incorporated Systèmes et procédés d'atténuation de bruit de phase
US9137065B2 (en) 2012-12-20 2015-09-15 Qualcomm Incorporated Systems and methods to mitigate phase noise

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