• Title/Summary/Keyword: MPSK

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BER Performance of an Offset Stacked Spreading CDMA System Based on Orthogonal Complementary Codes (직교 상보코드 기반의 옵셋누적 확산 CDMA 시스템의 비트오율 성능)

  • Kim, Myoung-Jin
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.46 no.3
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    • pp.1-8
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    • 2009
  • DS-CDMA system has very low bandwidth efficiency, hence it is difficult to maintain high spreading gain for high speed data transmission. Offset stacked spreading CDMA(OSS-CDMA) is a transmission scheme where spreading codes with chip offsets are overlapped, then transmitted. This kind of system requires a code set that guarantees orthogonality between codes in the set of any cjip offset. An orthogonal complementary code set has a property that the crosscorrelation function between codes in the group is zero for all shifts, hence it can be used for an OSS-CDMA system. In an OCC-OSS CDMA system each user is assigned an orthogonal complementary code group. User data bit is spread by the given codes and overlapped, and the code sequences are transmitted with multicarrier. However, the offset stacked spread sequences are multilevel, and the number of symbol levels is increases as the spreading efficiency is increased. When the OSS sequence is transmitted with MPSK mapping, the signal constellation becomes dense, and the system is easily affected by channel impairments. In this paper, we propose a level clipping scheme on OSS sequence before MPSK modulated. Simulations have been carried out to investigate the BER performance of the OCC-OSS CDMA system in AWGN environment. The results show that proposed scheme outperform the scheme without level clipping.

The MSDD Diversity Receiver Algorithm for a High Speed Burst Modem (고속 버스트 모뎀을 위한 MSDD Diversity 수신 알고리즘)

  • 김재형;이영철
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.8 no.2
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    • pp.281-288
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    • 2004
  • In this paper, we consider the diversity combining method for multiple symbol differential detection (MSDD) over the slow fading diversity channel. Though the performance of the optimum maximum-likelihood sequence estimator for MSDD approaches the performance of maximal-ratio combining with differential encoding, the complexity increases exponentially as the size of MSDD block is increased. This new pre-combining method can make use of the efficient MSDD algorithm that has a complexity increasing linearly with the block length or MSDD. Thus, in many wireless scenarios where it is not possible to perform coherent detection. this pre-combined diversity MSDD can be applied to obtain substantial gain compare to conventional differential detection.