محاسبه كارآيي تكنيك دنباله مستقيم فراپهن باند در کانالهاي محوشدگي چند مسيره
محورهای موضوعی : مهندسی برق و کامپیوترمینا دشتی 1 * , محمد ابطحي 2 , شهريار شيرواني مقدم 3
1 - دانشگاه آزاد اسلامی واحد تهران جنوب
2 - مركز تحقيقات مخابرات ايران
3 - دانشگاه تربیت دبیرشهید رجایی
کلید واژه: دنباله مستقيمطيف گستردهگيرنده RAKE و UWB,
چکیده مقاله :
سيستمهاي رادیویی فراپهن باند (UWB) به دليل توانايي ارائه نرخ بيت بسيار بالا و توان مصرفي بسيار پايين به عنوان نامزد مناسبي براي مخابرات بيسيم چندكاربره، مورد توجه واقع شدهاند. اين سيستمها به جاي استفاده از حاملهاي سينوسي براي انتقال سيگنال، پالسهاي بسيار باريكي ارسال ميكنند كه داراي پهناي باند بسيار وسيعي هستند. اين مقاله به بررسي تكنيك دنباله مستقيم فراپهن باند با مدولاسيون آنتي پودال ميپردازد. ابتدا كارايي سيستم DS-UWB و TH-UWB در محيط دسترسي چندگانه و در كانال AWGN بررسي شده است. نتايج شبيهسازي نشان ميدهد که عملكرد سيستم DS-UWB بهتر از TH-UWB است. علاوه بر اين، كارايي سيستم DS-UWB در محيطهاي دسترسي چندگانه و در كانال محوشدگي شديد با استفاده از گيرنده PRAKE بررسي و شبيهسازي شده است. نتايج حاصل از شبيهسازيهاي اين تحقيق نشان ميدهد كه سيستم DS-UWB حتي در محيطهاي محوشدگي شديد نيز قادر است به احتمال خطاي 5-10 دست يابد و با افزايش تعداد شاخههاي گيرنده به 10 ميتوان عملكرد آن را تا dB 12 بهبود بخشيد.
Ultra Wideband (UWB) technology has attracted considerable interest in the research and standardization communities, due to its promising ability to provide high data rate at low cost with relatively low power consumption. UWB is characterized by transmitting extremely short duration radio impulses. The signal energy is thus spread over a band of frequencies up to a few GHz. In this paper we outline the attractive features of direct sequence ultra wideband systems employing antipodal signaling (DS_BPSK). First, we compare TH_PPM and DS_UWB in terms of their multiple access performance in AWGN environment. Compared with TH_UWB, results show that DS_UWB supports a larger number of users communicating at higher data rates. Then, we evaluate the multiple access performance of DS_UWB in multipath fading channels. We consider partial Rake receiver structure with different number of Rake fingers. Results show that DS-UWB system using Rake receiver is able to sustain BER less than 10e-5 even in channels suffering from severe multipath fading. Using 10 fingers Rake receiver, about 12 dB improvement in performance of system can be achieved.
[1] A. R. Forouzan and M. Abtahi, "Convolutioally encoded M-ary PPM ultrawideband time-hopping spread-spectrum systems," in Proc. European Conf. Wireless Technology, ECWT'02, pp. 79-82, Milan, Italy, Sep. 2002.
[2] A. R. Forouzan and M. Abtahi, "Application of convolutional error correcting codes in ultrawideband M-ary PPM signaling," IEEE Microwave and Wireless Components Letters, vol. 13, no. 8, pp. 308 -310, Aug. 2003.
[3] G. Durisi and S. Benedetto, "Performance evaluation and comparison of different modulation schemes for UWB multiaccess systems," in Proc. IEEE Int. Conf., ICC’03, vol. 3, pp. 2187-2191, May 2003.
[4] V. S. Somayazulu, "Multiple access performance in UWB systems using time hopping vs. direct sequence spreading," in Proc. IEEE Wireless Communications and Networking Conf., vol. 2, pp. 522-525, Mar. 2002.
[5] M. Hamalainen, R. Tesi, and J. Linatti, "On the UWB system performance studies signals in AWGN channel with interference in UMTS Band," in Proc. IEEE Conf. on Ultra Wideband Systems and Technologies, pp. 321-326, 2002.
[6] M. Hamalainen, V. Hovinen, and J. Linatti, "Performance comparison between various UWB signals in AWGN channel in the presence of multitone interference at the GSM downlink band," in Proc. WPM01 Conf., pp. 449-453, 2001.
[7] M. Z. Win and R. A. Scholtz, "Ultra-wide bandwidth time-hopping spread-spectrum impulse radio for wireless multiple-access communications," IEEE Trans. Commun., vol. 48, no. 4, pp. 679-690, Apr. 2000.
[8] مينا دشتي، تكنيك دنباله مستقيم فرا پهن باند (DS-UWB) در مخابرات بي سيم، پايان نامة كارشناسي ارشد، دانشكده تحصيلات تكميلي ، واحد تهران جنوب دانشگاه آزاد اسلامي، تابستان 1383
[9] D. Cassioli, M.Z. Win, and A.F. Molisch, "Ultra wide bandwidth indoor channel: from statistical model to simulations," IEEE Commun., vol. 20, no. 5, pp. 1247-1257, Aug. 2002.
[10] A. R. Forouzan and M. Abtahi, "Performance evaluation of uncoded and coded pulse position modulation time hopping ultra wideband systems in indoor multipath fading channels," Report Number:82G02R06, Wireless LAN Group, Mobile Communications Division, Iran Telecom Research Center, 2003.
[11] D. Cassioli, M. Z. Win, F. Vatalaro, and A. F. Molisch, "Performance of low-complexity rake reception in a realisticUWB channel," in Proc. IEEE Intl. Conf. on Communications, ICC’2002, vol. 2, pp. 763-767, Apr. 2002.