AF/DF切替方式およびビットLLR合成受信による高信頼OFDM移動無線中継システム  [in Japanese] Reliable OFDM Mobile Radio Relaying Systems with AF/DF Switching Scheme and Bit LLR Combining Reception  [in Japanese]

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Abstract

本報告では,移動通信における中継システムとして,i)雑音が加わったアナログ信号を再送するAF(Amplify-and-Forward)と,ii)復号して再送するDF(Decode-and-Forward)を切替える方式を検討する.中継局において,CRC復号による判定誤りが検出された場合はAFを行い,誤りが検出されない場合にはDFを行う.さらに送信側とは異なる符号化を行いHARQ(Hybrid ARQ)と同様の高信頼化を図る.また,受信側で直接受信と中継局経由の受信信号の合成メトリックを求め,復号に必要なビット対数尤度比(LLR)を算出するために,まずプリアンブル信号を用いてチャネル推定とレプリカ誤差の平均電力推定を行い,合成メトリックの重み係数をレプリカ誤差の平均電力値から求める方法を提案する.マルチパスフェージング条件下でOFDM伝送の計算機シミュレーションを行い,i)切替方式はAFとDFよりも優れたパケット誤り率(PER)特性が得られ,ii)中継局での受信レベルが高く高符号化率の場合に異符号を用いる方式が効果があること,iii)準静的伝搬環境ではチャネル推定の精度による劣化が小さいことを明らかにする.

This report investigates a relaying system for mobile communications that switches between (i) Amplify-and-Forward (AF) to forward analog signals including noise and (ii) Decode-and-Forward (DF) to forward detected signals. The system selects AF and DF when a CRC decoder in the relay detects any errors and does not, respectively. In the case of DF, the relay also performs different decoding from that in the source, which is expected to bring about as high reliability as hybrid ARQ. On a receiver side, the destination needs to calculate log likelihood ratios (LLRs) of coded bits for decoding. To provide LLRs, a proposed scheme estimates channel impulse responses of desired signals and average powers of replica errors. Using these estimates, it obtains combining weights for metrics of received signals via the source and relay. Computer simulations of OFDM transmission under multipath fading conditions demonstrate the following three items: (i) the switching scheme outperforms AF and DF, (ii) the different decoding in the case of DF can be superior to the same decoding in packet error rate (PER) with high SNR at the relay and high coding rate, and (iii) degradation of PER by the channel estimation can be negligible under a quasi static channel condition.

Journal

  • IEICE technical report

    IEICE technical report 108(455), 31-36, 2009-02-23

    The Institute of Electronics, Information and Communication Engineers

References:  9

Codes

  • NII Article ID (NAID)
    110007327785
  • NII NACSIS-CAT ID (NCID)
    AN10013298
  • Text Lang
    JPN
  • Article Type
    ART
  • ISSN
    09135685
  • NDL Article ID
    10206505
  • NDL Source Classification
    ZN33(科学技術--電気工学・電気機械工業--電子工学・電気通信)
  • NDL Call No.
    Z16-940
  • Data Source
    CJP  NDL  NII-ELS 
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