摘要
随着通信技术的发展,短距离无线通信技术近年来发展迅速,给人们带来了越来越多的便捷。作为短距离无线通信技术中最具有前景的技术,UWB(超宽带,Ultra-Wide-Band)无线电技术近年来受到了广泛而深刻的关注。它具有极高的带宽和数据速率,而且抗多径能量特别强,因此特别适合室内密集多径环境,具有其它无线技术无法比拟的优势。
论文首先介绍了UWB无线电技术的概念、特点和研究现状。接着介绍了超宽带的脉冲形成方式、调制方式、收发机系统结构、信号衰减模型、室内多径信道模型以及各种多址系统,为后面的章节做好铺垫。
常见的UWB多址系统有2PPM-TH-UWB、2PAM-TH-UWB和DS-UWB系统。一方面由于上述三种多址系统有其自身的不足,另一方面由于用户需求的多样性,可变速率将是未来通信系统的一个基本需求。针对这些问题,本文提出了一种新颖的基于OVSF码(正交可变扩频因子码,Orthogonal Variable Spread Factor code)和TH码(跳时码,Time Hopping code)的混合OVSF-TH-UWB通信系统。利用OVSF码的正交性来降低各个用户之间的干扰,利用TH码的随机性将冲突随机分散在时域上面。从理论上分析了其抗AWGN(加性高斯白噪声, Additive White Gaussian Noise)噪声以及抗多用户干扰的性能,并且通过仿真实验进行了验证。
超宽带直接发射脉冲,具有非常高的时间分辨率,从而可以精确估计信号传输时延,比较适应精确定位。但是在实际应用中,在合理的时间内估计信号传输时延是一个难题,因为传统的滑动相关是一个非常耗时的工作。本文提出了一种分步的快速时延估计算法,该算法分为两个步骤:首先通过RSSI(接收信号强度指示,Received Signal Strength Indication)进行粗粒度的时延估计,得出时延大概在哪个分块里面。然后通过基于符号采样率的相关运算估计精确的时延。在理论上该算法的时延估计可以达到一个码片时间的精度。
Along with the development of communication technology, short distance wireless communication develops fast in resent years, and brings conveniences to people. UWB has attracted profound and comprehensive interests. It has a very broad bandwidth, very high data rate, and is suitable for the indoor multipath environment. It is superior to other wireless technologies.
This paper first introduces the conception, the characteristic and the present research status of UWB radio. Then introduces the pulse waveform, the architecture of the UWB transceiver, the fading models of the signal, the indoor channel models, at last some multiple access systems are presented as follow.
The current UWB multiple access communication systems, such as 2PPM-TH-UWB, 2PAM-TH-UWB, DS-UWB have some drawbacks and do not provide the variable rate service. However, in the next generation communication systems, the variable rate is a basic need. Thus, the hybrid OVSF-TH-UWB is proposed to address the above problems, and a corresponding correlation mask is designed. It uses the OVSF code to reduce the interference and uses the TH code to disperse the collision in time domain. Because UWB transmits the pulses immediately, so it can estimate the time
delay accurately. This makes it suitable for accurate positioning. But it still remains a difficult problem to estimate the time delay in an appropriate time interval. The accustomed method to estimate the delay is sliding correlation, but it is very time-consuming to implement. To improve the sliding correlation method, this paper presents the two-step rapid method to estimate the time delay. First step is to use the RSSI to implement the coarse-grained estimate, and then use the sliding correlation method to implement the fine-grained estimate. In theory, this algorithm can achieve the accuracy of one chip time.
引文
[1] R. A. Scholtz. Multiple-access with time-hopping impulse modulation. Proc MILCOM, 1993, 2(10): 447-450
[2] M. Z. Win, R. A. Scholtz. Ultra-wide bandwidth time-hopping spread- spectrum impulse radio for wireless multiple-access communications. IEEE Trans, 2000, 48(4): 679-691
[3] Julius P.Knapp. Testimony of FCC's Julius Knapp. www.fcc.gov/ Speeches/misc/statements/knapp060502.pdf , 2002
[4] Maria-Gabriella, Di Benedetto, Guerino Giancola 著. 葛利嘉等译. 超宽带无线电基础. 北京: 电子工业出版社, 2005
[5] Joseph Mitola. Software radios--survey, critical evaluation and future directions. IEEE Aerospace and Electronie Systems Magazine, 1993, 8(4): 25-36
[6] Joseph Mitola. Cognitive radio for flexible mobile multimedia communicatiom. Mobile Networks and Applications,2001,6(5):435-441
[7] Joseph Mitola. Cognitive radio--making soft radios more personal. IEEE Personal Communications,1999,6(4): 13-18
[8] Lansford. UWB Coexistence and Cognitive Radio. Ultra Wideband Systems. Joint UWBST & IWUWBS 2004 International Workshop, 2004 :18-21
[9] Granelli F, Honggang Zhang. Cognitive ultra wide band radio: a research vision and its open challenges. Networking with Ultra Wide Band and Workshop on Ultra Wide Band for Sensor Networks, 2005.,55-59
[10] WU X R,TIAN Z. Optimal waveform design for UWB radios. In: IEEE International Conference on Acoustics, Speech, and Signal Processing. Montreal, 2004
[11] 张洪欣,吕英华,贺鹏飞等. 一种基于脉冲压缩的 UWB 成形脉冲设计方法. 北京邮电大学学报,2007,29(1):117-120
[12] 邹卫霞,聂晶,周正. UWB 脉冲的优化设计. 北京邮电大学学报, 2006, 29(4):69-72
[13] PARR B, CHO B L, WALLACE K, et al. A novel ultra wideband pulse design algorithm. IEEE Communications Letters,2003,7(5):219-221
[14] LUO Z D, GAO H, Liu Y N, et al. A new UWB pulse design method for narrowband interference suppression. In: IEEE Global Telecommunications Conference(GLOBECOM 2004).Dallas,USA,2004, 3488-3492
[15] Theodore S.Rappaport 著. 蔡涛,李旭等译. 无线通信原理与应用. 北京: 电子工业出版社, 1999
[16] 景振海. 超宽带理论及其性能仿真分析:[电子科技大学硕士学位论文]. 西安:西安电子科技大学通信与信息系统,2006
[17] A.F. Molisch, D. Cassioli, C.C. Chong, et al. A Comprehensive Standardized Model for Ultrawideband Propagation Channels. IEEE Transactions on Antennas and Propagation (S0018-926X), 2006, 54(11): 3151-3166
[18] Ghassemzadeh S, Jana R, Rice C W, et al. Measurement and Modeling of an Ultra-Wide Bandwidth Indoor Channel . IEEE Trans on Comm, 2004, 52(10): 1786-1796
[19] Thomas Gigl, Gerard J.M. Janssen, et al. Analysis of a UWB Indoor Positioning System Based on Received Signal Strength. 4th Workshop on Positioning, Navigation and Communication 2007 (WPNC'07), 2007,97-101
[20] GHASSEMZADEH S, JANA R, RICE C, et al. A Statistical Path Loss Model for In-Home UWB Channels . IEEE UWBST,2002,59-64
[21] 何灿芝,吴俊杰. 概率论与数量统计. 长沙:湖南科学技术出版社,2002
[22] 于 进 刚 , 卢 爱 华 . UWB 信 道 模 型 简 介 . 西 安 邮 电 学 院 学 报 , 2006 ,11(01):29-32
[23] 汪洋,张乃通,唐珣等. UWB 室内视距环境多径传播模型. 通信学报,2005,26(10):24-28
[24] A.Saleh, A. Valenzuela. A Statistical Model for Indoor Multipath Propagation. Selected Areas in Communications,1987,5(2):128-137
[25] Tesi, R Hamalainen, M Iinatti, et al. On the multi-user interference study for ultra wideband communication systems in AWGN and modified Saleh-Valenzuela channel. In: Ultra Wideband Systems Joint with Conference on Ultrawideband Systems and Technologies,2004:91-95
[26] 张陆勇,周正 . UWB 室内外信道模型分析 . 无线电通信技术, 2004, 30(2):13-16
[27] 郝润芳,闫永梅,王华奎. 基于修正 S-V 信道模型的多脉冲超宽带系统性能分析. 太原理工大学学报, 2007, 38(5):385-387
[28] G. Durisi, S. Benedetto. Performance evaluation of PPM-TH UWB systems in the presence of multiuser interference . In: IEEE Commun. Lett,2003,224-226
[29] Wei Chiang Wu. Multiuser detection of time-hopping PPM UWB system in the presence of multipath fading. AEU-International Journal of Electronics and Communications,2007,61(1):22-29
[30] 吴建军,陈江, 蒋伟等. TH-PPM UWB 系统的多址干扰模型改进及误码性能分析. 北京大学学报(自然科学版),2007,43(1):113-117
[31] Vojcic, B.R.Pickholtz. Direct-sequence code division multiple access for ultra-wide bandwidth impulse radio. In: Military Communications Conference,2003,898-902
[32] Xiang-Ning Fan, Yong-Fu Huang, Guang-Guo Bi. Closed BER Expression of multi-user DS UWB Systems in Indoor Fading Channel. Journal of Southeast University (English Edition),2006,22(3):16-20
[33] Rahman.M.A, Sasaki.S., Jie Zhou, Kikuchi.H., Error Analysis for a Hybrid DS/TH Impulse Radio UWB Multiple Access System . In: Ultra-Wideband, 2005 IEEE International Conference,2005,5-8
[34] Zhang Peng, Liu Hao, Hu Jianhao. A Novel Multiple-Access Scheme for Chirp UWB . In: Wireless Communications and Networking Conference, WCNC 2007. IEEE,2007,1631-1635
[35] Hwang, Jun Hyeok Kim, Suk Chan et al. Performance Analysis of PO-THMA UWB System Using Mutually Orthogonal MHP Pulses. Consumer Electronics, 2007, ICCE 2007,Digest of Technical Papers,International Conference,2007, 1-2
[36] 赵立昕, 赵成林, 周正. 一种基于完备互补码的 UWB 多址接人方式. 北京邮电大学学报, 2005, 28(6):65-68
[37] Shayesteh, M.G. Nasiri-Kenari. A new TH/DS-UWB scheme for UWB communication systems and its performance analysis. Iran Radio and Wireless Symposium,2006
[38] 王辉宇, 张钦宇, 张乃通等. 码间干扰效应对 I-UWB 频谱效率的限制作用. 吉林大学学报(工学版),2007, 37(1):198-201
[39] Hasam Cam. Non-blocking OVSF codes and enhancing network capacity for 3G wireless and beyond systems. Computer Communications , 2003, 26(17): 1907-1917
[40] T. Minn, K.Y. Siu. Dynamic assignment of orthogonal variable spreading factor codes in WCDMA . IEEE Journal on Selected Areas in Communications,2000, 18(8): 1429-1440
[41] R.G. Cheng, P. Lin. OVSF code channel assignment for IMT-2000 . In: Proceedings of VTC’2000 . Tokyo,2000, 2188– 2192
[42] John G. proakis 著.张力军,张宗橙等译. 数字通信(第四版). 北京:电子工业出版社, 2003
[43] V.S. Somayazulu, J.R. Foerster, S. Roy. Design challenges for very high data rate UWB systems. In: Conference record of the thirty-sixth asilomar conference on signals, systems and computers. Piscataway (NJ,USA):IEEE Press,2002,717-721
[44] Luca Reggiani, Gian Mario Maggio. Rapid Search Algorithms for Code Acquisition in UWB Impulse Radio Communications. IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, 2005,23( 5):898-908
[45] HOMIER E A, SCHOLTZ R A. Rapid acquisition of ultra-wideband signals in the dense multipath channel. IEEE Conf Ultra-Wideband Syst & Technol. Redondo Beach ,2002,105-110
[46] 周先军,胡修林,张蕴玉等. UWB 定时信号的一种快速捕获算法. 通信学报,2006,27(5):126-129
[47] L.Yang, G.B.Giannakis. Blind timing ultra-wideband signals with dirty templates. Communications IEEE Transactions,2004,53(11):1952-1963
[48] 徐巧勇, 陈浩珉,王宗欣. DS-UWB 定位系统传输时延估计. 复旦大学大学学报(自然科学版),2004, 43(1):92-96
[49] Sinan Gezici,Zafer Sahinoglu,Andreas Molisch,etc. A two step time of arrival estimation algorithm for impulse radio ultra wideband systems. In: 13thEuropean Signal Processing Conference. Atalya: EUSIPCO Press,2005