OFDM频域同步研究及在WLAN中的实现
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摘要
本文首先介绍了宽带无线接入和无线局域网的发展情况，阐述了OFDM原理和IEEE802.11a的物理层传输标准。接着重点分析了各种偏差对数据的影响，研究了基于导频的频域同步算法，包括频率偏移、采样钟频偏以及符号定时偏移的估计和补偿，并提出了频偏补偿和细符号补偿的改进算法，还提出了一种在估计整数倍频偏时用滤波器实现滑动相关的方法。经Simulink仿真验证，改进的算法可以降低系统的误码率，提高系统的性能。在算法仿真之后，选出了适合FPGA实现的算法，最后完成了电路的Quartus仿真和FPGA硬件电路的实现。实践证明，该电路可以稳定工作，改进的算法可以有效的降低实现复杂度，减少算法实现所需的逻辑单元。
First of all, this paper introduces the development of Broadband Wireless Access (BWA) and Wireless LAN (WLAN). The basic principles of Orthogonal Frequency Division Multiplexing (OFDM) and the Physical Layer (PHY) of IEEE802.11a standard are also expatiated. Then the quantitative analysis of synchronization error is given, and synchronization algorithms based on pilots in frequency-domain are studied, including the estimation and compensation of carrier frequency offset, sampling clock offset and symbol timing offset. New compensation methods of carrier frequency offset and symbol timing offset are proposed, an implementation method of correlation using filter is also proposed.The simulation with Simulink shows that the proposed methods can improve the performance of the system. After the simulation, suitable algorithms are selected as the scheme for FPGA design. This paper also implements the FPGA circuits with Quartus. The circuits work well in practice and the new methods can decrease the complexity of the implementation of the synchronization algorithms, and save the logic cells of FPGA.
First of all, this paper introduces the development of Broadband Wireless Access (BWA) and Wireless LAN (WLAN). The basic principles of Orthogonal Frequency Division Multiplexing (OFDM) and the Physical Layer (PHY) of IEEE802.11a standard are also expatiated. Then the quantitative analysis of synchronization error is given, and synchronization algorithms based on pilots in frequency-domain are studied, including the estimation and compensation of carrier frequency offset, sampling clock offset and symbol timing offset. New compensation methods of carrier frequency offset and symbol timing offset are proposed, an implementation method of correlation using filter is also proposed.The simulation with Simulink shows that the proposed methods can improve the performance of the system. After the simulation, suitable algorithms are selected as the scheme for FPGA design. This paper also implements the FPGA circuits with Quartus. The circuits work well in practice and the new methods can decrease the complexity of the implementation of the synchronization algorithms, and save the logic cells of FPGA.
引文
[1] 罗茜文，李进良“宽带无线接入的应用与发展”，电子商务世界，2004年第4期，P84-86
[2] 黄颖，李伟“无线局域网IEEE802.11a标准浅析”，赣南师范学院学报，2004年第6期，P60-61
[3] 覃焕勇“802.11a物理层OFDM解调系统的FPGA实现”，西北工业大学硕士学位论文，2005年3月
[4] 张辉，曹丽娜著，《现代通信原理与技术》，西安电子科技大学出版社，2002年1月版
[5] 佟学俭，罗涛著，《OFDM移动通信技术原理与应用》，人民邮电出版社，2003年6月版
[6] IEEE STD 802.11a, Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: High-speed Physical Layer in the 5GHz Band, 1999 Edition
[7] 杨晓“突发OFDM系统接收机同步算法设计及其FPGA实现”浙江大学硕士学位论文2005年4月
[8] Hanli Zou, McNair, B. Daneshrad, B., "An integrated OFDM Receiver for High-Speed Mobile Data Communication", Global Telecommunications Conference, 2001. GLOBECOM '01.IEEE, vol.5.25-29 Nov. 2001, P3090—3094
[9] Chayat, Naftali "Tentative Criteria for Comparison of Modulation Methods" IEEE P802.11-97-96, Sep, 1999
[10] 蔡天佑“无线局域网关键技术的研究—基于IEEE802.11a标准的OFDM系统同步技术研究”东南大学硕士学位论文2003年3月
[11] Bo Ai, Jian-hua Ge, Yong Wang, "Frequency Offset Estimation for OFDM in Wireless Communications" , Consumer Electronics, IEEE Transactions on Volume 50, Issue 1, Feb 2004 P73-77
[12] 陈宇“基于导频的多载波同步技术的研究”，西安电子科技大学硕士学位论文2002年4月
[13] Paul H. Moose, "A technique for orthogonal frequency division multiplexing frequency offset correction", IEEE Transactions on Commu.Vol.42, No.10, Oct.1994, P2908-2914
[14] 王洋“OFDM系统中的频率跟踪和信道估计”，北京邮电大学硕士学位论文2004年3月
[15] Shou-Yin Liu, Jong-Wha Chong "A Study of Joint Tracking Algorithms of Carrier Frequency Offset and Sampling Clock Offset for OFDM-based WLANs", Communications, Circuits and Systems and West Sino Expositions, IEEE 2002 International Conference on Volume 1, 29 June-1 July 2002 P109-113 vol. 1
[16] 樊春富，王保莲，“浅谈无线局域网技术”，信息技术，2005年第11期
[17] Kwonhue Choi, Joon-Ho Lee "Phase Discontinuity-Free Sampling Timing Control for IF Sampling Receiver", Signal Processing Letters, IEEE Volume 11, Issue 10, Oct. 2004 P810-812
[18] Chien-Fang Hsu, Yuan-Hao Huang and Tzi-Dar Chiueh, "Design of an OFDM Receiver For High-speed Wireless LAN", Circuits and Systems, 2001. ISCAS 2001. The 2001 IEEE International Symposium on Volume 4, 6-9 May 2001 P558-561 vol. 4
[19] 老元威“基于IEEE802.11a的OFDM传输系统的算法研究与部分硬件实现”，浙江大学硕士学位论文 2003年1月
[20] Baoguo Yang, Letaief, K. B., Cheng, R. S. and Zhigang Cao, "Timing recovery for OFDM transmission", Selected Areas in Communications, IEEE Journal on Volume 18, Issue 11, Nov. 2000 P2278-2291
[21] 陆震“OFDM无线传输中的同步技术”西安电子科技大学硕士学位论文，2004年1月
[22] H. Shafiee, B. Nourani, M.Khoshgard, "Estimation and Compensation of Frequency Offset in DAC/ADC Clocks in OFDM Systems", Communications, 2004 IEEE International Conference on Volume 4, 20-24 June 2004 P2397-2401 Vol. 4
[23] Minjian Zhao, Perliang Qiu, Jinhua Tang, "Sampling Rate Conversion and Symbol Timing for OFDM Software Receiver" Communications, Circuits and Systems and West Sino Expositions, IEEE 2002 International Conference on Volume 1, 29 June-1 July 2002 P 114-118 vol. 1
[24] 谢少枫“基于IEEE802.11a的OFDM传输系统的接收机算法研究与FPGA实现”浙江大学硕士学位论文 2005年4月
[25] 谭磊“宽带OFDM传输系统研究仿真与部分模块实现”浙江大学硕士学位论文 2005年4月
[26] 孙健“突发OFDM系统的同步技术研究”，浙江大学博士学位论文，2005年3月
[27] Victor P. Gil Jimenez, M. Julia Fernandez-Getino Garcia, Francisco J. Gonzalez Serrano "Design and Implementation of Synchronization and AGC for OFDM-based WLAN Receivers", Consumer Electronics, IEEE. Transactions on Volume 50, Issue 4, Nov. 2004 P1016-1025
[28] Baoguo Yang; Letaief, K. B.; Cheng, R. S.; Zhigang Cao; "An improved combined symbol and sampling clock synchronization method for OFDM systems", Wireless Communications and Networking Conference, 1999. WCNC. 1999 IEEE 21-24 Sept. 1999 P1153-1157 vol. 3
[29] Nguyen, V. D., "Channel Impulse Response Length Estimation and Interference Cancellation for OFDM Systems", Shaker Verlag Aachen, February 2004, ISBN 3-8322-2479-3.4
[30] SCbastien Simoens, VCronique Buzenac and Marc de Courville "A new method for Joint Cancellation of Clock and Carrier Frequency Offsets in OFDM receivers over Frequency Selective Channels" in Proc. IEEE VTC'00, Tokyo, Japan, May 2000, P390-394
[31] Weidong Xiang and Thomas Pratt "A Simple Cascade Carrier Frequency and Sampling Clock Offsets Estimation Method for OFDM Systems", Consumer Communications and Networking Conference, 2004. CCNC 2004. First IEEE 5-8 Jan. 2004 P718-720
[32] Chih-Peng Li, Po-Lin Chen, Tsui-Tsai Lin "Residual Carrier Frequency Offset Tracking for OFDM-Based Systems" Circuits and Systems, 2004 Proceedings. The 2004 IEEE Asia-Pacific Conference on Volume 2, 6-9 Dec. 2004 P989-992 vol. 2
[33] Hongbao Zhang, Zhongjun Wang, and Sista Satish Chandra "Implementation of Frequency Offset Correction Using Cordic Algorithm for 5GHz WLAN Applications" ICCS, vol. 2, P983-987, Nov. 2002.
[34] Essam Sourour, Hussein El-Ghoroury and Dale McNeill "Frequency Offset Estimation and Correction in the IEEE 802.11a WLAN" Vehicular Technology Conference, 2004. VTC2004-Fall. 2004 IEEE 60th Volume 7, 26-29 Sept.2004 P4923-4927 Vol. 7
[35] T. Pollet, M. V. Bladel and M.Moeneclaey, "BER Sensitivity of OFDM Systems to Carrier Frequency Offset and Wiener Phase Noise," IEEE Trans. Commun., vol. COM-43, NO.2/3/4, P191-193, Feb./Mar./Apr., 1995
[36] 李熠“无线局域网802.11a协议同步研究及嵌入式应用”浙江大学硕士学位论文 2003年3月
[37] 张绍军“OFDM全数字接收机的研究与设计”国防科学技术大学硕士学位论文 2002年11月
[38] 魏波“OFDM系统中的同步技术研究”电子科技大学硕士学位论文2004年2月
[39] 曾璐“基于OFDM技术的WLAN传输系统的同步与信道估计”西安电子科技 大学硕士学位论文 2003年1月
[40] Linling Kuang, Zuyao Ni, Jianhua Lu"A Time-Frequency Decision-Feedback Loop for Carrier Frequency Offset Tracking in OFDM Systems" Wireless Communications, IEEE Transactions on Volume 4, Issue 2, March 2005 P367-373
[41] 胡俊“IEEE80211a基带调制器的FPGA实现与降低信号峰平比的方法研究”浙江大学硕士学位论文 2005年1月
[42] 邝育军“OFDM无线传输系统中定时同步和信道估计的研究”北京邮电大学博士学位论文 2003年4月
[43] 周一青“OFDM系统的同步算法和信道估计算法的研究”东南大学硕士学位论文 2000年3月
[44] Canet, M. J., Vicedo, F., Almenar, V., "FPGA implementation of an IF transceiver for OFDM-based WLAN", Signal Processing Systems, 2004. SIPS 2004. IEEE Workshop on 2004 P227-232
[45] 吉训生，“基于FPGA的高速抽取过程的实现”，《现代电子技术》2004年第20期P71-73
[46] 张东玲，刘双平，金梁“数字化接收机中分数倍采样率转换的有效结构”，《无线通信技术》2002年第3期P24-26
[2] 黄颖，李伟“无线局域网IEEE802.11a标准浅析”，赣南师范学院学报，2004年第6期，P60-61
[3] 覃焕勇“802.11a物理层OFDM解调系统的FPGA实现”，西北工业大学硕士学位论文，2005年3月
[4] 张辉，曹丽娜著，《现代通信原理与技术》，西安电子科技大学出版社，2002年1月版
[5] 佟学俭，罗涛著，《OFDM移动通信技术原理与应用》，人民邮电出版社，2003年6月版
[6] IEEE STD 802.11a, Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: High-speed Physical Layer in the 5GHz Band, 1999 Edition
[7] 杨晓“突发OFDM系统接收机同步算法设计及其FPGA实现”浙江大学硕士学位论文2005年4月
[8] Hanli Zou, McNair, B. Daneshrad, B., "An integrated OFDM Receiver for High-Speed Mobile Data Communication", Global Telecommunications Conference, 2001. GLOBECOM '01.IEEE, vol.5.25-29 Nov. 2001, P3090—3094
[9] Chayat, Naftali "Tentative Criteria for Comparison of Modulation Methods" IEEE P802.11-97-96, Sep, 1999
[10] 蔡天佑“无线局域网关键技术的研究—基于IEEE802.11a标准的OFDM系统同步技术研究”东南大学硕士学位论文2003年3月
[11] Bo Ai, Jian-hua Ge, Yong Wang, "Frequency Offset Estimation for OFDM in Wireless Communications" , Consumer Electronics, IEEE Transactions on Volume 50, Issue 1, Feb 2004 P73-77
[12] 陈宇“基于导频的多载波同步技术的研究”，西安电子科技大学硕士学位论文2002年4月
[13] Paul H. Moose, "A technique for orthogonal frequency division multiplexing frequency offset correction", IEEE Transactions on Commu.Vol.42, No.10, Oct.1994, P2908-2914
[14] 王洋“OFDM系统中的频率跟踪和信道估计”，北京邮电大学硕士学位论文2004年3月
[15] Shou-Yin Liu, Jong-Wha Chong "A Study of Joint Tracking Algorithms of Carrier Frequency Offset and Sampling Clock Offset for OFDM-based WLANs", Communications, Circuits and Systems and West Sino Expositions, IEEE 2002 International Conference on Volume 1, 29 June-1 July 2002 P109-113 vol. 1
[16] 樊春富，王保莲，“浅谈无线局域网技术”，信息技术，2005年第11期
[17] Kwonhue Choi, Joon-Ho Lee "Phase Discontinuity-Free Sampling Timing Control for IF Sampling Receiver", Signal Processing Letters, IEEE Volume 11, Issue 10, Oct. 2004 P810-812
[18] Chien-Fang Hsu, Yuan-Hao Huang and Tzi-Dar Chiueh, "Design of an OFDM Receiver For High-speed Wireless LAN", Circuits and Systems, 2001. ISCAS 2001. The 2001 IEEE International Symposium on Volume 4, 6-9 May 2001 P558-561 vol. 4
[19] 老元威“基于IEEE802.11a的OFDM传输系统的算法研究与部分硬件实现”，浙江大学硕士学位论文 2003年1月
[20] Baoguo Yang, Letaief, K. B., Cheng, R. S. and Zhigang Cao, "Timing recovery for OFDM transmission", Selected Areas in Communications, IEEE Journal on Volume 18, Issue 11, Nov. 2000 P2278-2291
[21] 陆震“OFDM无线传输中的同步技术”西安电子科技大学硕士学位论文，2004年1月
[22] H. Shafiee, B. Nourani, M.Khoshgard, "Estimation and Compensation of Frequency Offset in DAC/ADC Clocks in OFDM Systems", Communications, 2004 IEEE International Conference on Volume 4, 20-24 June 2004 P2397-2401 Vol. 4
[23] Minjian Zhao, Perliang Qiu, Jinhua Tang, "Sampling Rate Conversion and Symbol Timing for OFDM Software Receiver" Communications, Circuits and Systems and West Sino Expositions, IEEE 2002 International Conference on Volume 1, 29 June-1 July 2002 P 114-118 vol. 1
[24] 谢少枫“基于IEEE802.11a的OFDM传输系统的接收机算法研究与FPGA实现”浙江大学硕士学位论文 2005年4月
[25] 谭磊“宽带OFDM传输系统研究仿真与部分模块实现”浙江大学硕士学位论文 2005年4月
[26] 孙健“突发OFDM系统的同步技术研究”，浙江大学博士学位论文，2005年3月
[27] Victor P. Gil Jimenez, M. Julia Fernandez-Getino Garcia, Francisco J. Gonzalez Serrano "Design and Implementation of Synchronization and AGC for OFDM-based WLAN Receivers", Consumer Electronics, IEEE. Transactions on Volume 50, Issue 4, Nov. 2004 P1016-1025
[28] Baoguo Yang; Letaief, K. B.; Cheng, R. S.; Zhigang Cao; "An improved combined symbol and sampling clock synchronization method for OFDM systems", Wireless Communications and Networking Conference, 1999. WCNC. 1999 IEEE 21-24 Sept. 1999 P1153-1157 vol. 3
[29] Nguyen, V. D., "Channel Impulse Response Length Estimation and Interference Cancellation for OFDM Systems", Shaker Verlag Aachen, February 2004, ISBN 3-8322-2479-3.4
[30] SCbastien Simoens, VCronique Buzenac and Marc de Courville "A new method for Joint Cancellation of Clock and Carrier Frequency Offsets in OFDM receivers over Frequency Selective Channels" in Proc. IEEE VTC'00, Tokyo, Japan, May 2000, P390-394
[31] Weidong Xiang and Thomas Pratt "A Simple Cascade Carrier Frequency and Sampling Clock Offsets Estimation Method for OFDM Systems", Consumer Communications and Networking Conference, 2004. CCNC 2004. First IEEE 5-8 Jan. 2004 P718-720
[32] Chih-Peng Li, Po-Lin Chen, Tsui-Tsai Lin "Residual Carrier Frequency Offset Tracking for OFDM-Based Systems" Circuits and Systems, 2004 Proceedings. The 2004 IEEE Asia-Pacific Conference on Volume 2, 6-9 Dec. 2004 P989-992 vol. 2
[33] Hongbao Zhang, Zhongjun Wang, and Sista Satish Chandra "Implementation of Frequency Offset Correction Using Cordic Algorithm for 5GHz WLAN Applications" ICCS, vol. 2, P983-987, Nov. 2002.
[34] Essam Sourour, Hussein El-Ghoroury and Dale McNeill "Frequency Offset Estimation and Correction in the IEEE 802.11a WLAN" Vehicular Technology Conference, 2004. VTC2004-Fall. 2004 IEEE 60th Volume 7, 26-29 Sept.2004 P4923-4927 Vol. 7
[35] T. Pollet, M. V. Bladel and M.Moeneclaey, "BER Sensitivity of OFDM Systems to Carrier Frequency Offset and Wiener Phase Noise," IEEE Trans. Commun., vol. COM-43, NO.2/3/4, P191-193, Feb./Mar./Apr., 1995
[36] 李熠“无线局域网802.11a协议同步研究及嵌入式应用”浙江大学硕士学位论文 2003年3月
[37] 张绍军“OFDM全数字接收机的研究与设计”国防科学技术大学硕士学位论文 2002年11月
[38] 魏波“OFDM系统中的同步技术研究”电子科技大学硕士学位论文2004年2月
[39] 曾璐“基于OFDM技术的WLAN传输系统的同步与信道估计”西安电子科技 大学硕士学位论文 2003年1月
[40] Linling Kuang, Zuyao Ni, Jianhua Lu"A Time-Frequency Decision-Feedback Loop for Carrier Frequency Offset Tracking in OFDM Systems" Wireless Communications, IEEE Transactions on Volume 4, Issue 2, March 2005 P367-373
[41] 胡俊“IEEE80211a基带调制器的FPGA实现与降低信号峰平比的方法研究”浙江大学硕士学位论文 2005年1月
[42] 邝育军“OFDM无线传输系统中定时同步和信道估计的研究”北京邮电大学博士学位论文 2003年4月
[43] 周一青“OFDM系统的同步算法和信道估计算法的研究”东南大学硕士学位论文 2000年3月
[44] Canet, M. J., Vicedo, F., Almenar, V., "FPGA implementation of an IF transceiver for OFDM-based WLAN", Signal Processing Systems, 2004. SIPS 2004. IEEE Workshop on 2004 P227-232
[45] 吉训生，“基于FPGA的高速抽取过程的实现”，《现代电子技术》2004年第20期P71-73
[46] 张东玲，刘双平，金梁“数字化接收机中分数倍采样率转换的有效结构”，《无线通信技术》2002年第3期P24-26