تشخیص چندکاربره وفقی مبتنی بر SVD برای یک سیستم طیف گسترده با رشته‌های آشوبی بهینه‌شده
محورهای موضوعی : مهندسی برق و کامپیوترسعید شعرباف تبریزی 1 * , سيدعلیرضا سیدین 2
1 - دانشگاه فردوسی مشهد
2 - دانشگاه فردوسی مشهد
کلید واژه: مخابرات پهن‌باند مولد آشوبی DS-CDMA SVD تشخیص چندکاربره کانال چندمسیره الگوریتم ژنتیک,
چکیده مقاله :
طراحی ساختارهای مخابراتی پهن‌باند که از سیگنال‌های آشوبی برای ارسال اطلاعات استفاده می‌کنند، به یکی از زمینه‌های پرکاربرد در زمینه مخابرات طیف گسترده بدل گردیده است. در این میان، محدوده وسیعی از مطالعات به طراحی رشته‌های شبه‌نویز آشوبی به‌عنوان جایگزین برای کدهای گسترش متداول در سیستم‌های DS-CDMA متمرکز گردیده که با وجود برخی مزایای قابل توجه چون غیر متناوب بودن، امکان پیاده‌سازی آنالوگ و نیز امکان توسعه آسان برای تعداد کاربران زیاد، هنوز با مشکلاتی چون خطای نسبتاً بالا در کانال‌های با سیگنال به نویز کم و یا کانال‌های دارای تداخل چندمسیره دست به گریبان هستند. در این مقاله با هدف بهبود عملکرد سیستم‌های طیف گسترده آشوبی، از دو ایده بهینه‌سازی فرآیند تولید کد و کاهش تداخل بین کاربری استفاده شده که بدین منظور ابتدا روشی مبتنی بر الگوریتم ژنتیک، برای تولید مولدهای آشوبی بهینه در فرستنده پیشنهاد می‌گردد و در ادامه طرحی متکی بر تبدیل SVD برای تشخیص چندکاربره و کاهش وفقی اثر تداخل کاربران، در گیرنده پیاده‌سازی خواهد شد. نتایج شبیه‌سازی برای شرایط مختلف کانال و تعداد کاربران متفاوت، نشان از بهبود قابل توجه عملکرد سیستم طیف گسترده آشوبی معرفی‌شده در حضور نویز کانال و اعوجاج چندمسیره، نسبت به ساختارهای آشوبی اولیه و نیز سیستم‌های طیف گسترده معمول که از رشته‌های حداکثر طول استفاده می‌کنند، دارد.
In recent years, chaotic signals have created a new area in the designation of wideband communication systems. Most of the activity has focused on DS-CDMA systems, in which the conventional pseudo-noise sequences will be replaced by binary chaotic sequences. Unfortunately, despite the advantages of chaotic systems such as aperiodicity, low cost generation and noise-like spectrum, the performance of most of such designs is not still suitable for multiuser wireless channels. In this paper, we propose a novel method based on singular value decomposition for adaptive multiuser detection in chaos-based DS-CDMA systems. We also propose a new genetic algorithm-based method for the optimal generation of chaotic sequences in such systems. Simulation results show that our proposed nonlinear receiver with optimized chaotic sequences outperforms the conventional DS-CDMA systems with “maximal length” codes as well as non-optimized chaos-based DS-CDMA systems in all channel condition, particularly for under-loaded CDMA condition, which the number of active users is less than processing gain.
[1] A. Cambel, Applied Chaos Theory - A Paradigm for Complexity, San Diego, CA: Academic Press, 1993.
[2] L. Pecora and T. Caroll, "Synchronization in chaotic systems," Phys. Rev. Lett, vol. 64, no. 2, pp. 821-823, Jan. 1990.
[3] M. H. Elmirghani and R. A. Cryan, "Communication using chaotic masking," IEE Colloquium on Exploiting Chaos in Signal Processing, vol. 5, no. 2, pp. 121-126, 1994.
[4] H. Leung and J. Lam, "Design of demodulator for the chaotic modulation communication system," IEEE Trans. Circuits and Systems I: Fundamental Theory and Applications, vol. 44, no. 3, pp. 262-267, Mar. 1997.
[5] A. Abel and W. Schwarz, "Chaos communications, principles, schemes, and system analysis," in Invited Paper in IEEE Proc., vol. 90, no. 5, pp. 253-305, May 2002.
[6] G. Kolumban, B. Vizvari, W. Schwarz, and A. Abel, "Differential chaos shift keying: a robust coding for chaotic communication," in Proc. of the 4th Int. Workshop on Nonlinear Dynamics of Electronic Systems, pp. 87-92, Jun. 1996.
[7] J. M. H. Elmirghani and R. A. Cryan, "New chaotic based communication technique with multiuser provision," IEEE Electronics Letters, vol. 30, no. 15, pp. 1206-1207, Jul. 1997.
[8] J. M. H. Elmirghani and R. A. Cryan, "Point - to - point and multi-user communication based on chaotic sequences," in Proc. IEEE ICC Colloquium on Exploiting Chaos in Signal Processing, vol. 1, pp. 582-584, 1995.
[9] N. Xie and H. Leung, "An analog multi - user spread spectrum technique for wireless home automation," IEEE Trans. Consumer Electronics, vol. 48, no. 4, pp. 1016-1025, Nov. 2002.
[10] Y. Lau and Z. Hussain, "Chaos shift keying spread spectrum with multicarrier modulation for secure digital communication," WSEAS Trans. on Communications, vol. 4, no. 1, pp. 47-77, Jan. 2005.
[11] Y. Lau and Z. Hussain, "Chaotic-based CDMA versus PN-based CDMA for digital secure communications: a comparative study," in Proc. Australian Telecommunications Networks and Applications Conf., pp. 99-103, Sydney, Australia, Dec. 2004.
[12] Y. Lau and Z. Hussain, "Chaotic - based OFDM - CDMA for secure digital communications: performance comparison with PN - based OFDM - CDMA," in Proc. 3rd Workshop on Telecommunications and Signal Processing, WITSP'04, Adelaide, Australia, Dec. 2004.
[13] A. Tsuneda, D. Yoshioka, and T. Hadate, "Design of spreading sequences with negative auto - correlations realizable by nonlinear feedback shift registers," in Proc. IEEE 8th In. Symp. on Spread Spectrum Techniques and Applications, vol. 4, pp. 330-334, May 2004.
[14] M. Latva, Advanced Receivers for Wideband CDMA Systems, Department of Electrical Engineering University of Oulu, Finland, Ph.D. Thesis, 1999.
[15] J. Wehinger, Iterative Multi User Receivers for CDMA Systems, Vienna University of Technology, Ph.D. Thesis, 2005.
[16] M. Juntti, "Performance analysis of linear multisensor multiuser receivers for CDMA in fading channels," IEEE J. Sel. Areas in Communication, vol. 18, no. 7, pp. 1221-1229, Jul. 2000.
[17] P. Stavroulakis, Chaos Application in Telecommunication, Taylor & Francis Press, 2006.
[18] M. Gotz and A. Abel, "Design of infinite chaotic polyphase sequences with perfect correlation properties," in Proc. IEEE Int. Symp. Circuits and Systems, ISACS'98, vol. 3, pp. 279-282, 31 May-3 Jun. 1998.
[19] J. Krupar and W. Schwarz, "A performance estimation method for chaotic spread spectrum clock process," in Proc. Proc. IEEE Int. Symp. Circuits and Systems, ISACS'05, vol. 4, pp. 3383 - 3386, 23-26 May 2005.
[20] S. Verdú, "Minimum probability of error for asynchronous gaussian multiple - access channels," IEEE Trans. on Information Theory, vol. 32, no. 1, pp. 85-96, Jan. 1986.
[21] S. Verdu, Multiuser Detection, Cambridge University Press, 1998.
[22] B. Xu, C. Yang, and S. Mao, "An improved blind adaptive multiuser detector in multipath CDMA channels based on subspace estimation," in Proc. IEEE 55th Vehicular Technology Conf., vol. 2, pp. 285-288, 6-9 May 2002.
[23] X. Wang and H. Vincent Poor, "Blind multiuser detection: a subspace approach," IEEE Trans. on Information Theory, vol. 44, no. 2, pp. 677-690, Mar. 1998.
[24] X. Wang and H. Vincent Poor, "Subspace methods for blind joint channel estimation and multiuser detection in CDMA systems," Wireless Networks, vol. 6, no. 1, pp. 59-71, 2000.
[25] G. Cai, D. Yu, and W. Song, "An subspace - based blind multiuser detection in dispersive CDMA channels," in Proc. IEEE 6th Symp. on Emerging Techonlogies: Mobile and Wireless Communications, vol. 4, pp. 779-782, Shanghai, China, Jun. 2004.
[26] H. Zamiri-Jafarian and G. Gulak, "Adaptive channel SVD estimation for MIMO-OFDM systems," in Proc. IEEE 61st Vehicular Technology Conf., vol. 1, pp. 552-556, Stockholm, Sweden, 30 May-1 Jun. 2005.