WO2008069505A1 - Procédé et dispositif d'atténuation d'interférence intercellulaire - Google Patents

Procédé et dispositif d'atténuation d'interférence intercellulaire Download PDF

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Publication number
WO2008069505A1
WO2008069505A1 PCT/KR2007/006153 KR2007006153W WO2008069505A1 WO 2008069505 A1 WO2008069505 A1 WO 2008069505A1 KR 2007006153 W KR2007006153 W KR 2007006153W WO 2008069505 A1 WO2008069505 A1 WO 2008069505A1
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WO
WIPO (PCT)
Prior art keywords
channel
soft
soft decision
cell
outputs
Prior art date
Application number
PCT/KR2007/006153
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English (en)
Inventor
Junyoung Nam
Seong Rag Kim
Hyun Kyu Chung
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 KR1020070035859A external-priority patent/KR100932456B1/ko
Application filed by Electronics And Telecommunications Research Institute filed Critical Electronics And Telecommunications Research Institute
Publication of WO2008069505A1 publication Critical patent/WO2008069505A1/fr
Priority to US12/479,036 priority Critical patent/US8175071B2/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03171—Arrangements involving maximum a posteriori probability [MAP] detection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375—Passband transmission

Definitions

  • the present invention relates to an apparatus and a method for mitigating intercell interference in a mobile terminal having a single reception antenna in a multi-cell downlink of an Orthogonal Frequency Division Multiple Access (OFDMA) system.
  • OFDMA Orthogonal Frequency Division Multiple Access
  • Terminals with multiple reception antennas can relatively easily mitigate intercell interference using time/space diversity in a downlink of an OFDMA system.
  • intercell interference cancellation is a difficult task.
  • the intercell interference greatly deteriorates mobility and stability of a mobile communication system in a cell boundary area.
  • TDMA Time Division Multiple Access
  • Sequence Detection (MLSD) technique has been used to process, by joint detection, signals of several cells in a cell boundary area.
  • this technique uses a Viterbi algorithm for joint detection, it has a disadvantage in that the complexity increases exponentially with respect to the number of total users of all cells.
  • MMSE Multiuser Detection
  • CDMA Code Division Multiple Access
  • OFDMA Orthogonal Frequency Division Multiple Access
  • this technology also suffers from the problem of complexity in that an inverse of a matrix whose dimension is equal to the number (e.g., 1024) of multicarriers or arbitrary spreading elements should be calculated for every symbol.
  • an object of the present invention is to mitigate intercell interference in a terminal having a single reception antenna in a multi-cell downlink by applying an iterative reception technique using channel coding.
  • an intercell interference mitigation apparatus for use in a terminal having a single reception antenna in a multi-cell downlink of an OFDMA system, the apparatus comprising one or more parallel interference cancellers for canceling intercell interference by re- spreading soft decision values of cells other than a self cell; one or more LLR creation blocks for creating channel LLRs required for the soft decision for each of subcarriers, and producing channel soft outputs; one or more soft deciders for performing a soft decision of a self user symbol of the self cell in which interferences from other users are mitigated, and producing the soft decision values; and one or more channel estimation blocks for performing iterative channel estimation by respreading symbols of the soft decision values produced from the soft deciders.
  • An intercell interference mitigation method for use in a terminal having a single reception antenna in a multi-cell downlink of an OFDMA system, the method comprising canceling intercell interference by respreading soft decision values of cells other than a self cell; creating channel LLRs required for the soft decision for each of subcarriers to produce channel soft outputs; performing a soft decision of a self user symbol of the self cell, in which interferences from other users are mitigated, to produce the soft decision values; and performing iterative channel estimation by respreading symbols of the soft decision values produced in said performing the soft decision.
  • the present invention has an effect of greatly mitigating intercell interference by applying the iterative reception technique using the parallel interference cancellation to all cells of a terminal that has a single reception antenna in a multi-cell downlink.
  • FIGs. 1 and 2 are block diagrams illustrating an intercell interference mitigation apparatus in accordance with an embodiment of the present invention
  • FIG. 3 is a signal flow diagram illustrating a channel decoding and soft decision procedure in the intercell interference mitigation apparatus shown in Figs. 1 and 2;
  • FIG. 4 is a flowchart illustrating an iterative channel estimation procedure in the intercell interference mitigation apparatus shown in Figs. 1 and 2.
  • the present invention proposes an iterative reception technique using channel coding.
  • a reliability of Log-Likelihood Ratio (LLR) and a reception performance can be greatly enhanced by a channel coding gain obtained through the iterative reception technique using channel coding.
  • LLR Log-Likelihood Ratio
  • intercell interference is efficiently canceled in a downlink of an OFDMA system by employing an iterative reception technique.
  • a soft decision is used for the iterative reception technique of the present invention, and a soft decision value obtained through channel decoding is used under intercell cooperation in which user's channel code information is shared among all cells.
  • a transmit signal b of a qth cell of an OFDMA system that has L-number of sub- carriers and a multi-cell environment of Q-number of cells is expressed as in Eq. (1):
  • H Diag(H 0 , H 1 , ..., H L- i) is a diagonal matrix constituted by channel frequency responses, and n is a white Gaussian noise.
  • n a white Gaussian noise.
  • FIGs. 1 and 2 are block diagrams illustrating a receiving device for canceling intercell interference in a downlink in an OFDMA system in accordance with an embodiment of the present invention.
  • the following description will focus on the iterative reception technique in accordance with the present invention. Descriptions of well-known basic devices (for example, a discrete Fourier transformation device for transforming a reception signal of a time domain into that of a frequency domain, and a device for removing a cyclic prefix of a frequency-domain transformed signal) will be omitted for simplicity.
  • the intercell interference mitigation apparatus in accordance with the present invention includes parallel interference cancellers 110, 210, 310, and 410 for canceling intercell interference by respreading soft decision values of cells other than a self-cell; LLR creation blocks 120, 220, 320, and 420 for creating channel LLRs per each subcarrier required for the soft decision; de-interleavers 130, 230, 330, and 430 for canceling channel concentration errors of channel soft outputs produced from the LLR creation blocks 120, 220, 320, and 420; channel decoders 140, 240, 340, and 440 for decoding outputs from the de-interleavers 130, 230, 330, and 430 by channel decoding to thereby provide the decoded soft outputs; soft deciders 150, 250, 350, and 450 for performing soft decision on a self-user symbol of a self-cell in which interferences from other users is mitigated; and channel estimation blocks 160, 260, 360, and 460 for performing iterative
  • a reception signal of an lth subcarrier under an OFDMA environment having Q- number of cells is expressed by Eq. (3) as described above.
  • Ki Ki ⁇ Ki is a residual interference remaining after the interference cancellation is completed.
  • An LLR of a transmit signal x for a matching filter output y in a linear Gaussian or fading channel is expressed as in Eq. (5): [51] [52] Math Figure 5
  • a is equal to 1 in case of Gaussian channel, and is equivalent to a fading amplitude in case of fading channel. Since an output of a Maximum A Posteriori (MAP) channel decoder is based on channel coding, a more reliable LLR can be acquired therefrom.
  • MAP Maximum A Posteriori
  • Eq. (6) is a general LLR calculation formula for a matching filter output in a fading channel. From observation of the LLR, it can be appreciated that a single tap equalizer is included in a typical OFDMA receiver. [60] In Eq. (6), the variance
  • Eq. (11) can be expressed as in Eq. (12):
  • a is equal to 1 in case of Gaussian channel, and is equivalent to a fading amplitude in case of fading channel.
  • a second term of Eq. (12) corresponds to the LLR of Eq. (6). Since an output of a Maximum A Posteriori (MAP) channel decoder is based on channel coding, a more reliable LLR can be acquired therefrom.
  • MAP Maximum A Posteriori
  • a channel estimation method using a pilot symbol can be divided into a time-domain insertion type and a frequency-domain insertion type.
  • the following description of the present invention will focus on a time-domain pilot symbol method.
  • a receiver that considers intercell interference may be worse in performance than a conventional receiver that does not consider intercell interference.
  • EM Expectation Maximization
  • Fig. 3 illustrates an example of a channel decoding and soft decision procedure based on the EM algorithm in case of the intercell cooperation that user channel code information is shared among all cells; and Fig. 4 illustrates an example of iterative channel estimation procedure based on the EM algorithm.
  • the channel decoder 140 of Fig. 3 would be omitted. Further, in the following, only channel estimation of the self cell will be considered.
  • F ch h F ch h is established.
  • an LxN matrix F ch is a discrete Fourier Transformation matrix for obtaining a channel frequency response function, and is expressed as in Eq. (13):
  • ⁇ r, s ⁇ can be assumed to be a perfect data Z, and the EM algorithm can be constructed as follows.
  • step S501 shown in Fig. 4 is constructed (step S501 shown in Fig. 4) as an initial value vector in which a pilot symbol is inserted in a position of a pilot subcarrier and the remaining positions of sub- carriers are all filled with zero.
  • the initial value vector has a great influence on the performance of the EM algorithm. Therefore, a more dense pilot symbol is required for obtaining a better channel estimation value. Thus, in order to realize an efficient channel estimation technique, a pilot symbol deployment and the system efficiency should be compromised.
  • the channel estimation using the EM algorithm requires
  • an initial value b ( 1) is an initial value vector in which a pilot symbol is located in a position of a pilot subcarrier and zero is located in positions of other subcarriers.
  • the initial value vector has a great influence on a performance of the EM algorithm. Therefore, more dense pilot symbols are required to obtain a better channel estimation value.
  • step S503 an expectation expressed as in Eq. (17) is performed for obtaining the likelihood function for estimating the channel impulse response h on the assumption that the reception signal r, together with the to- be-detected symbol b, is given:
  • step S503 a resultant equation of the channel estimation value is calculated as in Eq. (19) to thereby update the estimation value of the channel impulse response:
  • step S504 is the diagonal matrix obtained in step S502, which is constituted of respread symbols of the soft decision value in a pth iterative reception.
  • the soft decision value corresponds to the soft decision of the channel soft output in a case where the intercell cooperation is weak; and corresponds to the soft decision of the decoded soft output in a case where the intercell cooperation is strong.
  • the channel frequency response estimation value is obtained in step S504 by transforming the channel impulse response using Eq. (20): [124] [125] Math Figure 20
  • step S505 it is checked whether or not p is smaller than P. Then, if the result is YES, the procedure is terminated; if otherwise, the procedure moves on to step S506. In step S506, the value of p is incremented by 1, and the procedure returns to the step S502.
  • the present invention has an effect of greatly mitigating intercell interference by applying the iterative reception technique using the parallel interference cancellation to all cells of a terminal that has a single reception antenna in a multi-cell downlink.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Probability & Statistics with Applications (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Noise Elimination (AREA)

Abstract

Dispositif d'atténuation d'interférence intercellulaire pour terminal à antenne de réception unique dans une liaison descendante multicellulaire de système MROF avec accès multiple. Le dispositif comprend un ou plusieurs annuleurs d'niterférences (intercellulaire) parallèles qui fonctionnent en annulation par ré-étalement de valeurs de décisions douces de cellules autres qu'une cellule propre à l'utilisateur; un ou plusieurs blocs de création de rapports de vraisemblance d'enregistrement (rapports LLR) pour la création des LLR de canal requis pour la décision souple correspondant à chaque sous-porteuse, et la production de sorties de canal douces; un ou plusieurs décideurs souples pour l'exécution d'une décision souple de symbole d'utilisateur propre correspondant à la cellule propre dans laquelle les interférences causées par d'autres utilisateurs sont atténuées, et la production des valeurs de décisions souples; et un ou plusieurs blocs d'estimation de canal pour la conduite d'estimation de canal itérative par ré-étalement de symboles des valeurs de décisions souples produites par les décideurs souples.
PCT/KR2007/006153 2006-12-05 2007-11-30 Procédé et dispositif d'atténuation d'interférence intercellulaire WO2008069505A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US12/479,036 US8175071B2 (en) 2006-12-05 2009-06-05 Intercell interference mitigation apparatus and method

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
KR20060122112 2006-12-05
KR10-2006-0122112 2006-12-05
KR10-2007-0035859 2007-04-12
KR1020070035859A KR100932456B1 (ko) 2006-12-05 2007-04-12 직교주파수분할다중접속 시스템의 셀간 간섭 완화 장치 및방법

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108712353A (zh) * 2018-03-29 2018-10-26 江苏中科羿链通信技术有限公司 软迭代信道估计方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040181744A1 (en) * 1999-12-02 2004-09-16 Nagabhushana Sindhushayana Method and apparatus for computing soft decision input metrics to a turbo decoder
JP2005236364A (ja) * 2004-02-17 2005-09-02 Tdk Corp マルチキャリア信号送受信機
US20060172716A1 (en) * 2003-03-14 2006-08-03 Matsushita Electric Industrail Co., Ltd. Ofdm reception device and ofdm reception method
US20060198292A1 (en) * 2003-03-28 2006-09-07 Isamu Yoshii Ofdm reception device and ofdm reception method

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040181744A1 (en) * 1999-12-02 2004-09-16 Nagabhushana Sindhushayana Method and apparatus for computing soft decision input metrics to a turbo decoder
US20060172716A1 (en) * 2003-03-14 2006-08-03 Matsushita Electric Industrail Co., Ltd. Ofdm reception device and ofdm reception method
US20060198292A1 (en) * 2003-03-28 2006-09-07 Isamu Yoshii Ofdm reception device and ofdm reception method
JP2005236364A (ja) * 2004-02-17 2005-09-02 Tdk Corp マルチキャリア信号送受信機

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108712353A (zh) * 2018-03-29 2018-10-26 江苏中科羿链通信技术有限公司 软迭代信道估计方法
CN108712353B (zh) * 2018-03-29 2021-05-11 江苏中科羿链通信技术有限公司 软迭代信道估计方法

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