基于TDT的UWB系统非盲同步算法
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摘要
本文提出了一种基于估计理论的定时同步方案,它采用基于有噪模板的同步算法TDT与基于信号循环平稳特性的同步算法相结合的方法来实现同步。先利用TDT算法实现帧级的同步,然后对接收信号进行定时修正,接下来利用超宽带信号的循环平稳特性,进行一帧内的逐脉冲滑动相关实现脉冲级同步。该捕获方法继承了TDT算法的复杂度低、同步速度快的优点,在系统复杂度相对较低的情况下可以达到更高的脉冲级同步精度。对该同步方法进行了计算机仿真实验,其结果表明本文的算法更具有实用性和有效性。
本文还对非盲同步算法中训练序列的优化设计问题进行了研究。得到一个突发内的最佳训练脉冲数目和最佳的传信脉冲和训练脉冲的能量分配,这些参数不仅影响同步捕获性能,还影响到信道估计和数据解调性能,也影响到数据的传输速率。通过仿真实验验证了经过训练序列的优化设计后,系统的性能有一定的提高,不仅最小化了信道估计的均方误差MSE,而且最大化了系统的平均容量。
1. Introduction
Ultra-Wideband (UWB) technology becomes more and more attractive because of its advantages, such as high transmission rate, low power consumption, good security, robustness to multipath and low cost. UWB wireless communication technology uses the principle of overlapping to share the spectrum occupied, it is a novel short-distance wireless communication technique, in which data are transfered using non-sinusoidal pulses with very short duration, so it is fit for using in indoor environments which is a typical multipath environment. And it can be coexisted with the existing wireless communication systems at the same frequency band.
In digital communication systems, signal synchronization is essential to the system, and synchronization is the precondition of the transmission of information, the synchronized performance reduces can cause the communications system performance directly decline, even enables the system can’t normal work. So is the UWB receiver, the receiver needs to know the propagation delay of the received signal, and make local template signal synchronization with the received signal to accomplish despreading and demodulation. Further more synchronization is an especially difficult task in UWB system which employ spreading codes to distribute the transmitted signal energy over a wide bandwidth. Though synchronization is also a challenge in narrowband systems, its difficulty is accentuated in UWB due to the fact that the information-bearing waveforms are impulse-like and have low power. Moreover, the (oftentimes dense) multipath channel, through which these low-power narrow pulses propagate, is unknown at the receiver during the synchronization stage. These reasons explain why synchronization has received so much emphasis in UWB research.
Acquisition schemes for UWB systems can be broadly classified into those which follow detection-based approaches, and those which rely on estimation-theoretic strategies. And the estimation-based schemes can be broadly classified into data aided estimation and nondata aided estimation. Data aided estimation based on pilot symbol, which can lead to the waste of pilot width and power resource, thus decreases efficiency of the system; the nondata aided timing estimation exploit the signal structure inherent in UWB to estimate timing information of the received signal, which overcomes disadvantages of resources waste. In this paper, a estimation-based schemes is presented, and a design of training sequence for data aided estimation is provided.
2. A data-aided synchronization Algorithm based on TDT for UWB system
Conventional synchronization techniques based on pulse-rate sliding correlation are not only sub-optimum in the presence of dense multipath, but also very slow to converge, due to the prohibitively large number of fine bins (chips) to be searched over. This techniques is obviously acquiring very slowly, and the acquisition time is unacceptable and can not be used in practice. Therefore, we need a fast and effective way to solve the UWB system synchronization. In this paper, a synchronization algorithm for PAM-UWB system which adopts the method of combining the TDT algorithm and cyclostationary approach to achieve synchronization acquisition. Firstly, utilize the TDT algorithm to achieve frame-level synchronization acquisition, then carry on the timing compensation for the received signal, afterwards we apply the cyclostationarity-based timing estimation principle to achieve pulse-level synchronization.
Most existing synchronizers are based on the unique maximum of the received pulse’s autocorrelation function, which requires a“clean template”of the received pulse to be available. Evidently, the latter is not feasible when the multipath channel is unknown. TDT algorithm relies on the fact that the cross correlation of“dirty templates”extracted from the received waveform exhibits a unique maximum at the correct timing. In this scheme, a symbol length segment of the received waveform is used as a template and correlated with the subsequent symbol length segment, it makes use of cross correlations between adjacent symbols to estimate timing information of the received signal,the template signal is affected by the channel and noise. In the timing synchronization we don’t need to know the channel information, so the algorithm does not need to estimate the channel response, so it is low complexity, and is a fast synchronization algorithm. And after the timing compensation we apply the cyclostationarity-based timing estimation principle, we makes pulse-rate sliding correlation in one frame, relative to making pulse-rate sliding correlation in entire symbols the acquisition time is much more less. A symbol often constitutes with several to several dozens frames, the frame number is more, the advantages of this algorithm provided in this paper is more obvious. The proposed algorithm in this paper inherited TDT’s merit, such as lowly complexity, fast synchronous speed, in the case of relatively low complexity system could achieve a higher pulse synchronization accuracy. And the simulation results show that the algorithm is more practical and effective.
3. Design of training sequence for data aided estimation synchronization Algorithm
Data aided estimation based on training symbol,such as M sequence, Gold sequence and Barker Code. Compare to nondata aided estimation, data aided estimation has better acquisition performance, but the problem is the waste of pilot width and power resource, thus decreases efficiency of the system. So we should carry on the reasonable design to the training sequence length and the energy, then enhances the system performance. The good training sequence design may enhance the system synchronization capture accurate. To account for both performance and bandwidth efficiency, we design the training sequence to minimize the channel’s mean-square estimation error, and maximize the average capacity.
In the design, the question that we mainly considered is for any given size and energy of the burst, how to find out the optimal number of the training symbol and optimizing the training symbol energy. Not only, these parameters influence synchronization capture performance, but also affect the channel estimate and the data demodulation performance, also affect the data transmission speed. These parameter minimize the channel’s mean-square estimation error , moreover maximize the average capacity. And the simulation results show that after the training sequence optimized design, the system performance has certain enhancement.
本文还对非盲同步算法中训练序列的优化设计问题进行了研究。得到一个突发内的最佳训练脉冲数目和最佳的传信脉冲和训练脉冲的能量分配,这些参数不仅影响同步捕获性能,还影响到信道估计和数据解调性能,也影响到数据的传输速率。通过仿真实验验证了经过训练序列的优化设计后,系统的性能有一定的提高,不仅最小化了信道估计的均方误差MSE,而且最大化了系统的平均容量。
1. Introduction
Ultra-Wideband (UWB) technology becomes more and more attractive because of its advantages, such as high transmission rate, low power consumption, good security, robustness to multipath and low cost. UWB wireless communication technology uses the principle of overlapping to share the spectrum occupied, it is a novel short-distance wireless communication technique, in which data are transfered using non-sinusoidal pulses with very short duration, so it is fit for using in indoor environments which is a typical multipath environment. And it can be coexisted with the existing wireless communication systems at the same frequency band.
In digital communication systems, signal synchronization is essential to the system, and synchronization is the precondition of the transmission of information, the synchronized performance reduces can cause the communications system performance directly decline, even enables the system can’t normal work. So is the UWB receiver, the receiver needs to know the propagation delay of the received signal, and make local template signal synchronization with the received signal to accomplish despreading and demodulation. Further more synchronization is an especially difficult task in UWB system which employ spreading codes to distribute the transmitted signal energy over a wide bandwidth. Though synchronization is also a challenge in narrowband systems, its difficulty is accentuated in UWB due to the fact that the information-bearing waveforms are impulse-like and have low power. Moreover, the (oftentimes dense) multipath channel, through which these low-power narrow pulses propagate, is unknown at the receiver during the synchronization stage. These reasons explain why synchronization has received so much emphasis in UWB research.
Acquisition schemes for UWB systems can be broadly classified into those which follow detection-based approaches, and those which rely on estimation-theoretic strategies. And the estimation-based schemes can be broadly classified into data aided estimation and nondata aided estimation. Data aided estimation based on pilot symbol, which can lead to the waste of pilot width and power resource, thus decreases efficiency of the system; the nondata aided timing estimation exploit the signal structure inherent in UWB to estimate timing information of the received signal, which overcomes disadvantages of resources waste. In this paper, a estimation-based schemes is presented, and a design of training sequence for data aided estimation is provided.
2. A data-aided synchronization Algorithm based on TDT for UWB system
Conventional synchronization techniques based on pulse-rate sliding correlation are not only sub-optimum in the presence of dense multipath, but also very slow to converge, due to the prohibitively large number of fine bins (chips) to be searched over. This techniques is obviously acquiring very slowly, and the acquisition time is unacceptable and can not be used in practice. Therefore, we need a fast and effective way to solve the UWB system synchronization. In this paper, a synchronization algorithm for PAM-UWB system which adopts the method of combining the TDT algorithm and cyclostationary approach to achieve synchronization acquisition. Firstly, utilize the TDT algorithm to achieve frame-level synchronization acquisition, then carry on the timing compensation for the received signal, afterwards we apply the cyclostationarity-based timing estimation principle to achieve pulse-level synchronization.
Most existing synchronizers are based on the unique maximum of the received pulse’s autocorrelation function, which requires a“clean template”of the received pulse to be available. Evidently, the latter is not feasible when the multipath channel is unknown. TDT algorithm relies on the fact that the cross correlation of“dirty templates”extracted from the received waveform exhibits a unique maximum at the correct timing. In this scheme, a symbol length segment of the received waveform is used as a template and correlated with the subsequent symbol length segment, it makes use of cross correlations between adjacent symbols to estimate timing information of the received signal,the template signal is affected by the channel and noise. In the timing synchronization we don’t need to know the channel information, so the algorithm does not need to estimate the channel response, so it is low complexity, and is a fast synchronization algorithm. And after the timing compensation we apply the cyclostationarity-based timing estimation principle, we makes pulse-rate sliding correlation in one frame, relative to making pulse-rate sliding correlation in entire symbols the acquisition time is much more less. A symbol often constitutes with several to several dozens frames, the frame number is more, the advantages of this algorithm provided in this paper is more obvious. The proposed algorithm in this paper inherited TDT’s merit, such as lowly complexity, fast synchronous speed, in the case of relatively low complexity system could achieve a higher pulse synchronization accuracy. And the simulation results show that the algorithm is more practical and effective.
3. Design of training sequence for data aided estimation synchronization Algorithm
Data aided estimation based on training symbol,such as M sequence, Gold sequence and Barker Code. Compare to nondata aided estimation, data aided estimation has better acquisition performance, but the problem is the waste of pilot width and power resource, thus decreases efficiency of the system. So we should carry on the reasonable design to the training sequence length and the energy, then enhances the system performance. The good training sequence design may enhance the system synchronization capture accurate. To account for both performance and bandwidth efficiency, we design the training sequence to minimize the channel’s mean-square estimation error, and maximize the average capacity.
In the design, the question that we mainly considered is for any given size and energy of the burst, how to find out the optimal number of the training symbol and optimizing the training symbol energy. Not only, these parameters influence synchronization capture performance, but also affect the channel estimate and the data demodulation performance, also affect the data transmission speed. These parameter minimize the channel’s mean-square estimation error , moreover maximize the average capacity. And the simulation results show that after the training sequence optimized design, the system performance has certain enhancement.
引文
[1] 葛利嘉, 朱林, 袁晓芳, 陈帮富等译. 超宽带无线电基础. 电子工业出版社. 2005
[2] 葛利嘉, 曾凡鑫, 刘郁林, 岳光荣. 超宽带无线通信. 国防工业出版社. 2005
[3] M.K. Simon, J.K. Omura, R.A. Scholts. 扩频通信技术教程(英文版). 北京:人民邮电出版社, 2002:226~228.
[4] Zhang Z, Ge L J, Chen B F, et al. Differential Detection Acquisition in Multiple Access Time-Hopping Ultra-Wideband Communications. IEEE International Conference, Joint UWBST&IWUWBS 2004,2004:2442~2445.
[5] S. Vijayakumaran, T.F. Wong. Equal Gain Combining for Acquisition of UWB Signals. IEEE Military Communications Conference(MILCOM’03), 2003, 2 (10) :880~885.
[6] A. Rabbachin, J. Inatti. CLPDI Algorithm in UWB INITIAL Code Acquisition With Saleh-Valenzuela Modified Channel Models. Finnish Wireless Communications Workshop. 2003, 10 (16):102~104.
[7] S. Soderi, J. Iinatti, M. Hamalainen. CLPDI Algorithm in UWB Synchronization. Proc. of International Workshop on Ultra Wideband Systems, 2003, 6 (2) :759~763.
[8] Tian Zhi, G. B. Giannakis. Data-aided ML Timing Acquisition in Ultra-wideband Radios. UWBST2003, 2003:142~146.
[9] Sandeep R.Aedudodla,Saravanan Vijayakumaran.Timing Acquisition in Ultra-Wideband Communication Systems. Wireless Information Networking Group University of Florida,Mar 3,2005.
[10] 吴伟陵. 移动通信原理. 电子工业出版社. 2005:125~126.
[11] L. Henry, Bertoni. Radio Propagation for Modern Wireless Systems. Prentice Hall, Upper Saddle River, N.J., 2000.
[12] Rappaport T S. Wireless Communications Principles And Practice. Prentice Hall, Upper Saddle River, N.J., 1996.
[13] W.C. Jakes . Mobile Radio Propagation. Microwave Mobile Communications. (Jakes W.C.ed.), Wiley, 1974.
[14] H. T. Friis. A Note on a Simple Transmission Formula. Proc. IRE., 1946, Vol.34:254~256.
[15] 张在琛 , 毕国光. 超宽带室内信道模型. 电子电气教学学报. 2004,26 (10) :60~63
[16] A. Saleh, R. Valenzuela. A Statistical Model for Indoor Multipath.Propagation. IEEE J. Select. Areas Commun, SAC-5, 1987: 128~137.
[17] M.Z. WIN, R.A. SCHOLTZ and M.A. BARNES. Ultra-wide Bandwidth Signal Propagation for Indoor Wireless Communications. IEEE Int. Conf. on Commun, June 1997:56~60.
[18] J.R. Foerster, M. Pendergrass and A.F. Molisch. A Channel Model for Ultrawideband Indoor Communication. Mitsubishi. Eletric Research Laboratory, Inc. November 2003:TR-2003-7.
[19] J.Foerster. Path Loss Proposed Text and S-V Model Information. IEEE P802.15 Working Group For Wireless Personal Area Networks, submitted 4 September. 2002.
[20] J. Foerster. Channel Modeling Sub-committee Report Final. IEEE 802-15-SG3a02 /490,2003.
[21] M.L. Welborn. System Consideration for Ultra-Wideband Wireless Networks.Boston: Proc RAWCON. 2001:5~8.
[22] 查光明, 熊贤祚. 扩频通信.西安电子科技大学出版社 . 1990:66~70,132~135.
[23] J.K. Cavers. An Analysis of Pilot Symbol Assisted Modulation for Rayleigh Fading Channels. IEEE Trans. Veh. Technol, 1991, 40:686~693.
[24] R. Blazquez, P. Newaskar, and A. Chandrakasan.Coarse acquisition for ultrawide band digital receivers.Proc. 2003 IEEE Intl. Conf. Acoustics, Speech and Signal Proc., vol. 4, Apr. 2003:137~140.
[25] Homier E A,Scholtz R A.Rapid acquisition of Ultra-Wideband signals in the dense multipath channel. Ultra Wideband Systems and Technologies.Baltimore ,MD.2002:105~110
[26] Gezici S,Ffishler E,Kobayashi H,et a1.A rapid acquisition technique for impulse radio IEEE Pacific Rim Conf on Commun,Comp and Sig.Aug 2003:627~630.
[27] Aedudodla S,Vuayakumaran S,Wong T F.Rapid ultra-wideband signal acquisition.IEEE Wireless Commun and Networking Conf. Mar 2004:21~25.
[28] Z. Tian and V. Lottici. Efficient timing acquisition in dense multipath for UWB communications.in Proc. 2003 IEEE Vehicle Technology Conf.,2003:1318~1322.
[29] Z. Tian and G. B. Giannakis. A GLRT approach to data-aided timing acquisition in UWB radios—Part I: Algorithms.IEEE Trans. Wireless Commun., To appear.
[30] C. Carbonelli, U. Mengali, and U. Mitra. Synchronization and channel estimation for UWB signals. in Proc. 2003 IEEE Global Telecom. Conf.,vol. 6, Dec. 2003, 764~768.
[31] Z .Tian, GB.Giannakis. BER Sensitivity to mis-timing in UWB communications.IEEE Trans.On Signal Processing.2003, (01) :112~124.
[32] 刘磊, 向新, 田红心, 易克初. 一种适用于 PAM-UWB 系统的同步算法. 电子科技2006 年第 1 期.
[33] L. Yang and G. B. Giannakis.Timing Ultra-Wideband Signals with a dirty template. IEEE Transactions on communications,vol. 53.No.11,November 2005.
[34] L. Yang and G. B. Giannakis.Low-Complexity Training for Rapid Timing Acquisition in Ultra Wideband Communication.Globecom 2003.
[35] Z. Tian, L. Yang, and G. B. Giannakis.Symbol timing estimation in ultra widebandcommunications. in Proc. 2002 Asilomar Conf. Signals,Systems and Computers, 2002:. 1924~1928.
[36] L. Yang, Z. Tian, and G. B. Giannakis.Non-data aided timing acquisition of ultra-wideband transmissions using cyclostationarity. in Proc. 2003 IEEE Intl. Conf. Acoustics, Speech and Signal Proc., vol. 4, 2003: 121~124.
[37] Hoctor R,Tomlinson H. Delay-hopped transmitted RF communications.in Proc.IEEE UWBST2002,2002:265~269.
[38] L. Yang and G. B. Giannakis.Optimal Pilot Waveform Assisted Modulation for Ultrawide band Communications.IEEE Transactions on wireless communications,Vol.3,No.4,July 2004
[39] Cheng Xia, Dinh Anh. A synchronization technique for UWB systems using IEEE channel models.[C]//CCECE/CCGEI. Saskatcon, May 2005,1778~1781.
[40] I. Maravic, M. Vetterli, and K. Ramchandran. High resolution acquisition methods for wideband communication systems. in Proc. 2003 IEEE Intl.Conf. Acoustics, Speech and Signal Proc., vol. 4, Apr. 2003:133~136.
[41] Channel estimation and synchronizationwith sub-nyquist sampling and application to ultra-wideband systems,in Proc. 2004 Intl. Symp.Circuits and Systems, vol. 5, May 2004:381~384.
[42] I. Maravic, J. Kusuma, and M. Vetterli.Low-sampling rate UWB channel characterization and synchronization.J. Commun. Networks, vol. 5: 319~327, 2003.
[43] J. Zhang, R. A. Kennedy, and T. D. Abhayapala. Cramer-Rao lower bounds for the time-delay estimation of UWB signals. in Proc. 2004 IEEE Intl. Conf. Commun., vol. 6, Jun. 2004: 3424~3428.
[44] E. A. Homier and R. A. Scholtz. Rapid acquisition of ultra-wideband signals in the dense multipath channel. in Proc. 2002 IEEE Conf. Ultra Wideband Systems Technology, 2002:105~109.
[45] Hybrid fixed dwell time search techniques for rapid acquisition of ultra-wideband signals. in Proc. Intl.Workshop Ultra-Wideband Systems, Jun. 2003.
[46] A generalized signal flowgraph approach for hybrid acquisition for ultra-wideband signals. Intl. Journ. Wireless Inform. Networks, pp. 179–191, Oct. 2003.
[47] S. Vijayakumaran and T. F. Wong. Best permutation search strategy for ultra-wideband signal acquisition. in Proc. IEEE Veh. Technol. Conf., Sep. 2004. To appear in IEEE Trans. Commun.
[48] H. Bahramgiri and J. Salehi. Multiple-shift acquisition algorithm in ultrawide bandwidth frame time-hopping wireless CDMA systems. in Proc.13th IEEE Personal, Indoor and Mobile Radio Commun., vol. 4, Sep. 2002:1824~1828.
[49] S. Gezici, E. Fishler, H. Kobayashi, H. Poor, and A. Molisch. A rapid acquisition technique for impulse radio. in Proc. 2003 IEEE Pacific Rim Conf. Commun., Comp. and Signal Proc.,Aug. 2003:627~630.
[50] L. Reggiani and G. M. Maggio. A reduced-complexity acquisition algorithm for impulse radio. in Proc. 2003 IEEE Conf. Ultra Wideband Systems Technology, Nov. 2003: 131~135.
[51] S. Aedudodla, S. Vijayakumaran, and T. F. Wong. Ultra-wideband signal acquisition with hybrid DS-TH spreading. IEEE Trans. Wireless Commun., Jun. 2004. Submitted for publication. [Online]. Available:http://www.wireless.ece.ufl.edu/twong
[52] J. Furukawa, Y. Sanada, and T. Kuroda. Novel initial acquisition scheme for impulse-based UWB systems. in Proc. 2004 Intl. Workshop Ultra Wideband Systems, May 2004:278~282.
[53] S. Aedudodla, S. Vijayakumaran, and T. F. Wong. Rapid ultra-wideband signal acquisition. in Proc. 2004 IEEE Wireless Commun. and Networking Conf., vol. 2, Mar. 2004: 21~25.
[2] 葛利嘉, 曾凡鑫, 刘郁林, 岳光荣. 超宽带无线通信. 国防工业出版社. 2005
[3] M.K. Simon, J.K. Omura, R.A. Scholts. 扩频通信技术教程(英文版). 北京:人民邮电出版社, 2002:226~228.
[4] Zhang Z, Ge L J, Chen B F, et al. Differential Detection Acquisition in Multiple Access Time-Hopping Ultra-Wideband Communications. IEEE International Conference, Joint UWBST&IWUWBS 2004,2004:2442~2445.
[5] S. Vijayakumaran, T.F. Wong. Equal Gain Combining for Acquisition of UWB Signals. IEEE Military Communications Conference(MILCOM’03), 2003, 2 (10) :880~885.
[6] A. Rabbachin, J. Inatti. CLPDI Algorithm in UWB INITIAL Code Acquisition With Saleh-Valenzuela Modified Channel Models. Finnish Wireless Communications Workshop. 2003, 10 (16):102~104.
[7] S. Soderi, J. Iinatti, M. Hamalainen. CLPDI Algorithm in UWB Synchronization. Proc. of International Workshop on Ultra Wideband Systems, 2003, 6 (2) :759~763.
[8] Tian Zhi, G. B. Giannakis. Data-aided ML Timing Acquisition in Ultra-wideband Radios. UWBST2003, 2003:142~146.
[9] Sandeep R.Aedudodla,Saravanan Vijayakumaran.Timing Acquisition in Ultra-Wideband Communication Systems. Wireless Information Networking Group University of Florida,Mar 3,2005.
[10] 吴伟陵. 移动通信原理. 电子工业出版社. 2005:125~126.
[11] L. Henry, Bertoni. Radio Propagation for Modern Wireless Systems. Prentice Hall, Upper Saddle River, N.J., 2000.
[12] Rappaport T S. Wireless Communications Principles And Practice. Prentice Hall, Upper Saddle River, N.J., 1996.
[13] W.C. Jakes . Mobile Radio Propagation. Microwave Mobile Communications. (Jakes W.C.ed.), Wiley, 1974.
[14] H. T. Friis. A Note on a Simple Transmission Formula. Proc. IRE., 1946, Vol.34:254~256.
[15] 张在琛 , 毕国光. 超宽带室内信道模型. 电子电气教学学报. 2004,26 (10) :60~63
[16] A. Saleh, R. Valenzuela. A Statistical Model for Indoor Multipath.Propagation. IEEE J. Select. Areas Commun, SAC-5, 1987: 128~137.
[17] M.Z. WIN, R.A. SCHOLTZ and M.A. BARNES. Ultra-wide Bandwidth Signal Propagation for Indoor Wireless Communications. IEEE Int. Conf. on Commun, June 1997:56~60.
[18] J.R. Foerster, M. Pendergrass and A.F. Molisch. A Channel Model for Ultrawideband Indoor Communication. Mitsubishi. Eletric Research Laboratory, Inc. November 2003:TR-2003-7.
[19] J.Foerster. Path Loss Proposed Text and S-V Model Information. IEEE P802.15 Working Group For Wireless Personal Area Networks, submitted 4 September. 2002.
[20] J. Foerster. Channel Modeling Sub-committee Report Final. IEEE 802-15-SG3a02 /490,2003.
[21] M.L. Welborn. System Consideration for Ultra-Wideband Wireless Networks.Boston: Proc RAWCON. 2001:5~8.
[22] 查光明, 熊贤祚. 扩频通信.西安电子科技大学出版社 . 1990:66~70,132~135.
[23] J.K. Cavers. An Analysis of Pilot Symbol Assisted Modulation for Rayleigh Fading Channels. IEEE Trans. Veh. Technol, 1991, 40:686~693.
[24] R. Blazquez, P. Newaskar, and A. Chandrakasan.Coarse acquisition for ultrawide band digital receivers.Proc. 2003 IEEE Intl. Conf. Acoustics, Speech and Signal Proc., vol. 4, Apr. 2003:137~140.
[25] Homier E A,Scholtz R A.Rapid acquisition of Ultra-Wideband signals in the dense multipath channel. Ultra Wideband Systems and Technologies.Baltimore ,MD.2002:105~110
[26] Gezici S,Ffishler E,Kobayashi H,et a1.A rapid acquisition technique for impulse radio IEEE Pacific Rim Conf on Commun,Comp and Sig.Aug 2003:627~630.
[27] Aedudodla S,Vuayakumaran S,Wong T F.Rapid ultra-wideband signal acquisition.IEEE Wireless Commun and Networking Conf. Mar 2004:21~25.
[28] Z. Tian and V. Lottici. Efficient timing acquisition in dense multipath for UWB communications.in Proc. 2003 IEEE Vehicle Technology Conf.,2003:1318~1322.
[29] Z. Tian and G. B. Giannakis. A GLRT approach to data-aided timing acquisition in UWB radios—Part I: Algorithms.IEEE Trans. Wireless Commun., To appear.
[30] C. Carbonelli, U. Mengali, and U. Mitra. Synchronization and channel estimation for UWB signals. in Proc. 2003 IEEE Global Telecom. Conf.,vol. 6, Dec. 2003, 764~768.
[31] Z .Tian, GB.Giannakis. BER Sensitivity to mis-timing in UWB communications.IEEE Trans.On Signal Processing.2003, (01) :112~124.
[32] 刘磊, 向新, 田红心, 易克初. 一种适用于 PAM-UWB 系统的同步算法. 电子科技2006 年第 1 期.
[33] L. Yang and G. B. Giannakis.Timing Ultra-Wideband Signals with a dirty template. IEEE Transactions on communications,vol. 53.No.11,November 2005.
[34] L. Yang and G. B. Giannakis.Low-Complexity Training for Rapid Timing Acquisition in Ultra Wideband Communication.Globecom 2003.
[35] Z. Tian, L. Yang, and G. B. Giannakis.Symbol timing estimation in ultra widebandcommunications. in Proc. 2002 Asilomar Conf. Signals,Systems and Computers, 2002:. 1924~1928.
[36] L. Yang, Z. Tian, and G. B. Giannakis.Non-data aided timing acquisition of ultra-wideband transmissions using cyclostationarity. in Proc. 2003 IEEE Intl. Conf. Acoustics, Speech and Signal Proc., vol. 4, 2003: 121~124.
[37] Hoctor R,Tomlinson H. Delay-hopped transmitted RF communications.in Proc.IEEE UWBST2002,2002:265~269.
[38] L. Yang and G. B. Giannakis.Optimal Pilot Waveform Assisted Modulation for Ultrawide band Communications.IEEE Transactions on wireless communications,Vol.3,No.4,July 2004
[39] Cheng Xia, Dinh Anh. A synchronization technique for UWB systems using IEEE channel models.[C]//CCECE/CCGEI. Saskatcon, May 2005,1778~1781.
[40] I. Maravic, M. Vetterli, and K. Ramchandran. High resolution acquisition methods for wideband communication systems. in Proc. 2003 IEEE Intl.Conf. Acoustics, Speech and Signal Proc., vol. 4, Apr. 2003:133~136.
[41] Channel estimation and synchronizationwith sub-nyquist sampling and application to ultra-wideband systems,in Proc. 2004 Intl. Symp.Circuits and Systems, vol. 5, May 2004:381~384.
[42] I. Maravic, J. Kusuma, and M. Vetterli.Low-sampling rate UWB channel characterization and synchronization.J. Commun. Networks, vol. 5: 319~327, 2003.
[43] J. Zhang, R. A. Kennedy, and T. D. Abhayapala. Cramer-Rao lower bounds for the time-delay estimation of UWB signals. in Proc. 2004 IEEE Intl. Conf. Commun., vol. 6, Jun. 2004: 3424~3428.
[44] E. A. Homier and R. A. Scholtz. Rapid acquisition of ultra-wideband signals in the dense multipath channel. in Proc. 2002 IEEE Conf. Ultra Wideband Systems Technology, 2002:105~109.
[45] Hybrid fixed dwell time search techniques for rapid acquisition of ultra-wideband signals. in Proc. Intl.Workshop Ultra-Wideband Systems, Jun. 2003.
[46] A generalized signal flowgraph approach for hybrid acquisition for ultra-wideband signals. Intl. Journ. Wireless Inform. Networks, pp. 179–191, Oct. 2003.
[47] S. Vijayakumaran and T. F. Wong. Best permutation search strategy for ultra-wideband signal acquisition. in Proc. IEEE Veh. Technol. Conf., Sep. 2004. To appear in IEEE Trans. Commun.
[48] H. Bahramgiri and J. Salehi. Multiple-shift acquisition algorithm in ultrawide bandwidth frame time-hopping wireless CDMA systems. in Proc.13th IEEE Personal, Indoor and Mobile Radio Commun., vol. 4, Sep. 2002:1824~1828.
[49] S. Gezici, E. Fishler, H. Kobayashi, H. Poor, and A. Molisch. A rapid acquisition technique for impulse radio. in Proc. 2003 IEEE Pacific Rim Conf. Commun., Comp. and Signal Proc.,Aug. 2003:627~630.
[50] L. Reggiani and G. M. Maggio. A reduced-complexity acquisition algorithm for impulse radio. in Proc. 2003 IEEE Conf. Ultra Wideband Systems Technology, Nov. 2003: 131~135.
[51] S. Aedudodla, S. Vijayakumaran, and T. F. Wong. Ultra-wideband signal acquisition with hybrid DS-TH spreading. IEEE Trans. Wireless Commun., Jun. 2004. Submitted for publication. [Online]. Available:http://www.wireless.ece.ufl.edu/twong
[52] J. Furukawa, Y. Sanada, and T. Kuroda. Novel initial acquisition scheme for impulse-based UWB systems. in Proc. 2004 Intl. Workshop Ultra Wideband Systems, May 2004:278~282.
[53] S. Aedudodla, S. Vijayakumaran, and T. F. Wong. Rapid ultra-wideband signal acquisition. in Proc. 2004 IEEE Wireless Commun. and Networking Conf., vol. 2, Mar. 2004: 21~25.