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12th International Conference on Transparent Optical Networks (ICTON)

作者： Dang, Ngoc T. Pham, Anh T. Univ Aizu Comp Commun Lab Aizu Wakamatsu Fukushima 9658580 Japan

ISBN: (纸本)9781424477982

A new modulation scheme for 2-D OCDMA systems named multi-code modulation (MCM) is proposed in this paper. The key advantage of MCM over the conventional ones is the ability of mitigating simultaneously both multiple access interference and dispersion. We also propose to combine MCM with heterodyne detection, a powerful technique to relax optical beating interference, to obtain better performance. The numerical results show that the proposed system allows for lower bit error rate, lower required power, and higher user's bit rate than that of conventional ones using other modulation schemes such as on-off keying modulation, pulse amplitude modulation, and pulse position modulation.

关键词： two-dimensional OCDMA multi-code modulation pulse position modulation heterodyne detection

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Preceding for minimization of envelope variations in multicode DS-CDMA systems

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WIRELESS PERSONAL COMMUNICATIONS 2000年第1-2期13卷 57-78页

作者： Ottosson, T Chalmers Univ Technol Dept Signals & Syst Commun Syst Grp SE-41296 Gothenburg Sweden

A multicode direct-sequence code-division multiple-access system experiences large envelope variations as a result of a sum of many independently spread signals. However, large envelope variations is problematic because it reduces the spectral efficiency, the efficiency of the power amplifiers and the performance. All these effects depend on the non-linear amplifiers that generally are used in handsets. It would of course be possible to use a linear amplifier but then the power efficiency is drastically reduced. In this paper we analyze the envelope variations of a multicode signal in terms of the crest factor and find that it increases as the square root of the number of used codes. As a consequence it is only possible to use the multicode scheme for a few parallel codes. To reduce the envelope variations a precoder is introduced. This precoder is a non-linear high-rate block code especially designed for the set of spreading codes used. However, the precoder can be made independent of the spreading codes if a user-specific spreading code is concatenated with a set of Hadamard or Conference sequences. The resulting spreadig codes are orthogonal. Also, the precoder is independent of the user-specific spreading code, and can thus be used for all users. After precoding the crest factor is significantly reduced and the performance, due to introduced coding gain, improved. Algorithms for the design of precoders with both reduced envelope variation and good performance are presented. Furthermore, simulations show that a preceded multicode system outperforms an uncoded multicode system in a single-user as well as in a multiuser environment.

关键词： crest factor direct-sequence code-division multiple-access (DS-CDMA) envelope variations multi-code modulation multirate systems multimedia systems precoding

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Performance of parallel combinatorial CDMA systems with side information

Performance of parallel combinatorial CDMA systems with side...

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IEEE 5th International Symposium on Spread Spectrum Techniques and Applications

作者： Sasaki, S Kikuchi, H Marubayashi, G Niigata Univ Dept Elect & Elect Engn Niigata 9502181 Japan

ISBN: (纸本)078034281X

This paper investigates the effects of using error-and-erasure decoding in coded parallel combinatorial spread spectrum (PC/SS) systems over Rayleigh fading channels. The PC/SS system is an advanced multi-code direct sequence spread spectrum system for high-speed data transmission. Our previous works have shown that the Reed-Solomon (RS) coded PC/SS systems provide significant improvement in error rate performance over conventional DS/SS systems. To achieve further performance improvement in the PC/SS systems, error-and-erasure decoding techniques are implemented in the RS coded PC/SS receiver. To obtain the erasure location information, a threshold for the signal-to-noise ratio is set at the correlator output. Numerical results show that the coded PC/SS systems with error-and-erasure decoding provides significant improvement in the bit error rate (BER). With errors-only decoding, the PC/SS systems cannot improve the error rate performance because of large SNR penalty introduced by coding. On the contrary, error-and erasure decoding still improves the performance of PC/SS systems under multiple access environment.

关键词： spread spectrum multi-code modulation Reed-Solomon code errors-only decoding error-and-erasure decoding

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