在短波跳频通信中OFDM与Turbo码技术的研究
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摘要
自1971年Weinstein和Ebert把离散复里叶变换DFT引入多载波传输系统并作为调制解调的一部分之后，正交频分复用(OFDM，Orthogonal Frequency Division Multiplexing)技术得到了广泛应用。OFDM技术特别适用于存在多径传播和多普勒频移的无线传输信道中传输高速数据。
而普通的短波跳频系统的信息传输速率一般较低，通常在2.4kbit／s左右，仅能传输语音信号，而要实现数据信号的传输，则必须提高数据传输率。本文针对短波跳频(FH)系统的性能特点和要求，并基于跳频速率为20跳／秒的短波跳频系统，提出了一种将OFDM用于短波跳频系统，并采用Turbo码作为信道编码的技术，使该系统的信息传输速率达20.48kbit／s，其中5.12kbit／s为导频信号，实际数据率为15.36kbit／s。
本文简要地介绍了短波信道的特点；简要地介绍了OFDM技术的原理，分析了OFDM技术应用到短波跳频通信中的特点；着重分析了OFDM调制时高峰均功率比PAPR(Peak-to-Average Power Ratio)产生的原因，并介绍了3种常用的降低PAPR的技术，在此基础上提出了改进方法，并作了数值仿真；着重介绍了OFDM技术应用到短波跳频通信中的导频子信道估计和信道内插算法以及均衡技术，并作了数值仿真；在此基础上，为了进一步降低短波跳频系统的比特误码率性能，保证信息的可靠传输，将Turbo码引入作为信道编码，并进行数值仿真，给出了短波跳频系统的误码性能曲线。
本文工作的独特之处在于：
(1)基于跳频速率为20跳／秒的短波跳频系统，提出了一种将OFDM和Turbo码结合的技术，用于提高短波跳频系统的数据传输率和降低短波跳频系统的比特误码率。在假设跳频能理想同步的前提下，数值仿真结果表明，该短波跳频系统采用这两种技术后更适于在短波瑞利衰落信道中应用。
(2)为了保证短波跳频系统的可实现性，本文针对OFDM有较高的PAPR这一基本问题，提出了一种改进方法，并进行了数值仿真，其结果表明，在OFDM中采用BPSK和QPSK映射时，改进的方法对于降低系统的PAPR具有很好的性能。
最后对全文进行了总结和展望。指出了如果能在短波频段全频段跳频，则可以提高跳频速率，进而提高短波跳频系统的信息传输速率和抗干扰能力；同时在OFDM调制时可以采用M-QAM映射方式，提高短波跳频系统的信息传输速率。
Since DFT was proposed as a part of the modulation and de-modulation in the multi-carrier transportation systems by 1971,OFDM(Orthogonal Frequency Division Multiplexing) has been applicated in many fields.OFDM is expecially applicable in wireless high information transportation with multi-path and Doppler shift.
However,the speed of the information transportation of ordinary short-wave frequency hopping systems is quite low.generally at 2.4kbit/s,and only tongue can be transported.Information transporting speed must be enhanced so that data can be transported.considering the characters and requirements of short-wave frequency hopping systems and based on the short-wave frequency systems with the hopping speed is 20hop/s,We introduced a technique which applicates OFDM and Turbo codes to the short-wave frequency hopping systems,so that the information transporting speed can reach 20.48kbit/s,including 5.12kbit/s pilot information and 15.36kbit/s data information.
The short-wave channel was briefly introduced,and the theory of OFDM was also briefly introduced.The characters of OFDM in short-wave frequency hopping systems was analyzed.The reason that cuases high PAPR was stressed analyzed and a new way to reduce PAPR was presented based on the three ordinary ways.The pilot channel estimation and other channels insertion and equalization is focoused on,and the value was simulated.Turbo codes was inducted as a channel coding.Finally,the curve of the system's error performance was presented.
The main points of this paper are:
(1)Based on the short-wave frequency hopping system with 20hop/s,we presented a technique with OFDM and Turbo codes,which can improve informations' transporting speed and depress the bit error rate. On the assumption that the synchronization of the frequency hopping system can be utility,the system with these techniques is more suitful for application in short-wave Reyleigh channel by simulation.
(2) For the sake of realization of the system,a upswing method for reducing the PAPR of the OFDM systems was presented.And simulation results shows that this method is effective for BPSK and QPSK mapping in OFDM modulation.
At the end of this thesis,the matter of this thesis is presented and new hopes are brought forward. Frequency hopping speed can be improved since the short-wave frequency domain can be used,which can improve data transportation speed and improve the system's anti-jamming performance.At the same time,M-QAM mapping can be used in OFDM for improving data transportation speed.
而普通的短波跳频系统的信息传输速率一般较低，通常在2.4kbit／s左右，仅能传输语音信号，而要实现数据信号的传输，则必须提高数据传输率。本文针对短波跳频(FH)系统的性能特点和要求，并基于跳频速率为20跳／秒的短波跳频系统，提出了一种将OFDM用于短波跳频系统，并采用Turbo码作为信道编码的技术，使该系统的信息传输速率达20.48kbit／s，其中5.12kbit／s为导频信号，实际数据率为15.36kbit／s。
本文简要地介绍了短波信道的特点；简要地介绍了OFDM技术的原理，分析了OFDM技术应用到短波跳频通信中的特点；着重分析了OFDM调制时高峰均功率比PAPR(Peak-to-Average Power Ratio)产生的原因，并介绍了3种常用的降低PAPR的技术，在此基础上提出了改进方法，并作了数值仿真；着重介绍了OFDM技术应用到短波跳频通信中的导频子信道估计和信道内插算法以及均衡技术，并作了数值仿真；在此基础上，为了进一步降低短波跳频系统的比特误码率性能，保证信息的可靠传输，将Turbo码引入作为信道编码，并进行数值仿真，给出了短波跳频系统的误码性能曲线。
本文工作的独特之处在于：
(1)基于跳频速率为20跳／秒的短波跳频系统，提出了一种将OFDM和Turbo码结合的技术，用于提高短波跳频系统的数据传输率和降低短波跳频系统的比特误码率。在假设跳频能理想同步的前提下，数值仿真结果表明，该短波跳频系统采用这两种技术后更适于在短波瑞利衰落信道中应用。
(2)为了保证短波跳频系统的可实现性，本文针对OFDM有较高的PAPR这一基本问题，提出了一种改进方法，并进行了数值仿真，其结果表明，在OFDM中采用BPSK和QPSK映射时，改进的方法对于降低系统的PAPR具有很好的性能。
最后对全文进行了总结和展望。指出了如果能在短波频段全频段跳频，则可以提高跳频速率，进而提高短波跳频系统的信息传输速率和抗干扰能力；同时在OFDM调制时可以采用M-QAM映射方式，提高短波跳频系统的信息传输速率。
Since DFT was proposed as a part of the modulation and de-modulation in the multi-carrier transportation systems by 1971,OFDM(Orthogonal Frequency Division Multiplexing) has been applicated in many fields.OFDM is expecially applicable in wireless high information transportation with multi-path and Doppler shift.
However,the speed of the information transportation of ordinary short-wave frequency hopping systems is quite low.generally at 2.4kbit/s,and only tongue can be transported.Information transporting speed must be enhanced so that data can be transported.considering the characters and requirements of short-wave frequency hopping systems and based on the short-wave frequency systems with the hopping speed is 20hop/s,We introduced a technique which applicates OFDM and Turbo codes to the short-wave frequency hopping systems,so that the information transporting speed can reach 20.48kbit/s,including 5.12kbit/s pilot information and 15.36kbit/s data information.
The short-wave channel was briefly introduced,and the theory of OFDM was also briefly introduced.The characters of OFDM in short-wave frequency hopping systems was analyzed.The reason that cuases high PAPR was stressed analyzed and a new way to reduce PAPR was presented based on the three ordinary ways.The pilot channel estimation and other channels insertion and equalization is focoused on,and the value was simulated.Turbo codes was inducted as a channel coding.Finally,the curve of the system's error performance was presented.
The main points of this paper are:
(1)Based on the short-wave frequency hopping system with 20hop/s,we presented a technique with OFDM and Turbo codes,which can improve informations' transporting speed and depress the bit error rate. On the assumption that the synchronization of the frequency hopping system can be utility,the system with these techniques is more suitful for application in short-wave Reyleigh channel by simulation.
(2) For the sake of realization of the system,a upswing method for reducing the PAPR of the OFDM systems was presented.And simulation results shows that this method is effective for BPSK and QPSK mapping in OFDM modulation.
At the end of this thesis,the matter of this thesis is presented and new hopes are brought forward. Frequency hopping speed can be improved since the short-wave frequency domain can be used,which can improve data transportation speed and improve the system's anti-jamming performance.At the same time,M-QAM mapping can be used in OFDM for improving data transportation speed.
引文
1．沈琪琪，朱德生，短波通信，西安：西安电子科技大学出版社，1997
2．及燕丽，王友村，沈其聪等，现代通信系统，北京：电子工业出版社，2001
3．戴耀森，高频时变信道，北京：人民邮电出版社，1985
4. Watterson.C,"Experimental Confirmation on HF Channel Model", IEEE T-COM, Vol.COM-18,1979:pp792-803
5. John.J.Lemmon,"Wideband Model of Man-made HF Noise and Interference",Radio Science,,Vol-32 No.1 March-April 1997:pp525-539
6. J.A.Hoffmeyer and L.E.Vogler,"A New Approach to HF Channel Modeling and Simulation",Vol.2 M ILCOM 1991 :pp60.2.1-60.2.10
7．李振玉等，扩频选址通信，北京：国防工业出版社，1988
8．查光明，熊贤祚，扩频通信，西安：西安电子科技大学出版社，2001
9．梅文华，杨义先，跳频通信地址编码理论，北京：国防工业出版社，1996
10. K.V.Cai,E.M.Jackson,R.W.Horner,"Advanced HF Anti-jam Network Architecture",Proceeding of MILCOM 1993:pp6.6.2-6.6.6
11．俞柏峰，短波FH／DQPSK系统信道模拟与监测及频率管理的研究，武汉大学硕士论文，2001．5
12．骆文，短波FH／DQPSK系统混沌跳频码发生器的研制与混沌初值的传送，武汉大学硕士论文，2001．5
13．易丹，基于混沌序列的短波跳频码与调制解调单元的实现，武汉大学硕士论文，2000．5
14．王文博，郑侃，宽带无线通信OFDM技术。北京：人民邮电出版社，2003
15．佟学俭，罗涛，OFDM移动通信技术原理与应用，北京：人民邮电出版社，2003
16．谢强，移动通信中OFDM技术的研究，南京理工大学硕士论文，2002．1
17．李斯伟，张建超，“正交频分复用(OFDM)的原理及应用”，《中国民航学院学报》，1999年10月，第17卷，第5期：pp35-39
18．张峻峰，“正交频分复用(OFDM)调制技术”，《天津通信技术》，1998年6月，第2期：pp1-5
19．金旗，裴昌幸，张振生，“OFDM技术的基本原理”，《通信技术》，2002年第6期：pp44-46
20．赵亚红，李伟华，吕伟陵，“正交多载波调制(OFDM)技术及应用”，《电讯技术》，2001年第1期：pp92-95
21．李引新，赵姚同，“正交频分多路(OFDM)的实现方式及性能分析”，《电讯技术》，1998年12月，第38卷第6期：pp10-15
22．宋铁成，“下一代移动通信系统中的OFDM技术”，《移动通信》，2001年第11期：pp20-23
23. Yun Hee Kim;Hong Gil Kim;Iickho Song;Min Joon Lee;Seok Ho Yoon,"A Coded OFDM System for Time-varing Multipath Rayleigh Fading Environment",MILCOM 97 Prceedings.Volume:2,2-5 Nov 1997:pp867-871
24. A.D.S,Jayalath,C.Tellambum,"Reducing the Peak-to-Average Power Ratio of Orthogonal Frequency Division Multiplexing Signal Through Bit or Symbol Interleaving[J]",Electronic Lertters,22nd June 2000,Vol.36,No.13
25. A.E,Jones:T.A.Wilknsom,"Combined Coding for Error Control and Increased Robustness to System Nonlinearities in OFDM",Vehicular Technology Conference,1996.'Mobile Technology for the Human Race'.IEEE 46th, Volume:2,28 April-1 May 1996:pp904-908
26. X.Li,and L.J.Cimini,"Effects of Clipping and Filtering on the Performance of OFDM",IEEE Commun.Left.,M ay 1998 :pp 131-133
27. Cinini,L.,Jr.,"Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing",IEEE Transcations on Communications,Vol.33,Jul 1955:pp665-675
28. Muller, S.H.;Huber, J.B.,"A Novel Peak Power Reduction Scheme for OFDM",Personal,Indoor and Mobile Radio Communications, 1997.'Waves of the Year 2000'.PIMRC'97.,The 8th IEEE International Symposium on,Volume:3,1-4 Sept. 1997:pp1090-1094
29. T.May, and H.Rohling ,"Reducing the Peak-to-Average Power Ratio in OFDM Radio Transmission Systems",in Proc.IEEE Veh.Techn.Conf.. 1998:pp2474-2478
30. Sathananthan K,Tellambura C.,"Coding to Reduce Both PAR and PICR of an OFDM Signal".IEEE Communications Letters,2002,6(8):pp316-318
31. Ochiai,H.;Imai,H.,"Forward Error Correction with Reduction of Peak to Average Power Ratio of QPSK Multicarrier Signals",Information Theory.1997.Proceedings.,1997 IEEE International Symposium on,29 June-4 July 1997:pp120
32. Tasadduq,l.A.;Rao,R.K.,"Weighted OFDM With Block Codes for Wireless Communication",Communications,Computers and Signal Proceeding,2001. PACRIM.2001 IEEE Pacific Rim Conference on,Volume:2,2001 :pp441-444
33. Heung-Gyoon Ryu;Kyoung-Jae Youn,"A New PAPR Reduction Scheme:SPW(Subbiock Phase Weighting)",Consumer Electronics,IEEE Transactions on,Volume:48,Issue:1,Feb.2002:81-89
34. Jayalath,A.D.S.;Tellambura,C.,"Adaptive PTS Approach for Redution of Peak-to-Average Power Ratio of OFDM Signal",Electronics Letters, Volume:36,Issue:14,6 July 2000:pp1226-1228
35. Hong Chen:Pottie,G.J.,"An Orthogonal Projection-Based approach for PAR Reduction in
OFDM",Communications Letters, IEEE,Volume:6 Issue:5,May 2002:pp169-171
36. Hill,G.;Faulkner, M.;Singh,J.,"Cyclic Shifting and Time Inversion of Partial Transmit Sequences to Reduce the Peak-to-Average Power Ratio in OFDM",Personal,Indoor and Mobile Radio Communications,2000.PIMRC 2000.The 11th IEEE International Symposiam on,Volume:2,18-21 Sept. 2000:pp 1256-1259
37. Ye Li,"Pilot-Symbol-Aided Channel Estimation for OFDM in Wireless Systems",Vehicular Technology, IEEE Transcations on,Volume:49,Issue:4, July 2000:pp 1207-1215
38. R.A.Strling-Gallacher and J.G.R Povey,"Performance of a Multi-carrier Code Division Multiple Access Frequency Domain Rake Receiver",Radio Receivers and Associated Systems,Sep. 1995 :pp86-90
39. Jae Kyoung Moon,Song In Chio,"Performance of Channel Estimation Methods for OFDM Systems in a Multipath Channels",Consumer Eletronics,IEEE Transactions on,2000:pp 161-170
40. Vittoria Mignone,Alberto MorelIo,"CD3-OFDM:A Novel Demodulation Scheme for Fixed and Mobile Receivers",IEEETrans.Commun.Vol.44, Sept, 1996:pp 1144-1151.
41. Ye(Gerffrey) Li,Leonard J. Cimini,Nelson R. Sollenberger,"Robust Channel Estimation for OFDM Systems with Rapid Dispersive Fading Channels",IEEE Trans.Commun.,Vol.46,July 1998:pp902-915
42. Baoguo Yang,Zhigang Cao,Letaief K.B.,"Analysis of Low-Complexity Windowed DFT-Based MMSE Channel Estimator for OFDM Systems", IEEE Trans.Commun., Vol.49,Nov 2001 :pp 1977-198
43. Jukka Rinne,Markku Renfors,"Pilot Spacing in Orthogonal Frequency Division Multiplexing Systems on Practical Channels",IEEE Trans. Consummer Electronics,Vol.42,No.4,Nov. 1996:pp959-962
44. Won Gi Jeon,Kyung Hi Chang,Yong Soo Che,"An Equalization Technique for Orthogonal Frequency Division Multiplexing Systems in Time-Variant Multipath Channels",IEEE Trans.commun.Vol.47,Jan. 1999:pp27-32
45. Seog Geun Kang,Yong Min Ha,Eon Kyeong Joo,"A Comparative Investigation on Channel Estimation Algorithms for OFDM in Mobile Communications",Broadcasting,IEEE Trans.on,Vol.49,Isue:2,June,2003:pp. 142-149
46．马新，葛临东，“OFDM中利用导频的一种信道估计算法”，《西安理工大学学报》，2002年第4期：pp403-406
47．束锋，罗琳，吴乐南，“OFDM通信系统中的一种通用的信道估计模型”，《电路与系统学报》，2001年6月，第2期：pp39-43
48. Berrou C.,Giavieux A.,Thitimajshima P.,"Near Shannon Limit Error Correcting Coding and Decoding:Turbo Codes",in Proc.of Int.Conf. On Comm,1993:pp1064-1070
49．肖东亮，“Turbo码技术及其应用研究”，武汉大学博士学位论文，2002．12
2．及燕丽，王友村，沈其聪等，现代通信系统，北京：电子工业出版社，2001
3．戴耀森，高频时变信道，北京：人民邮电出版社，1985
4. Watterson.C,"Experimental Confirmation on HF Channel Model", IEEE T-COM, Vol.COM-18,1979:pp792-803
5. John.J.Lemmon,"Wideband Model of Man-made HF Noise and Interference",Radio Science,,Vol-32 No.1 March-April 1997:pp525-539
6. J.A.Hoffmeyer and L.E.Vogler,"A New Approach to HF Channel Modeling and Simulation",Vol.2 M ILCOM 1991 :pp60.2.1-60.2.10
7．李振玉等，扩频选址通信，北京：国防工业出版社，1988
8．查光明，熊贤祚，扩频通信，西安：西安电子科技大学出版社，2001
9．梅文华，杨义先，跳频通信地址编码理论，北京：国防工业出版社，1996
10. K.V.Cai,E.M.Jackson,R.W.Horner,"Advanced HF Anti-jam Network Architecture",Proceeding of MILCOM 1993:pp6.6.2-6.6.6
11．俞柏峰，短波FH／DQPSK系统信道模拟与监测及频率管理的研究，武汉大学硕士论文，2001．5
12．骆文，短波FH／DQPSK系统混沌跳频码发生器的研制与混沌初值的传送，武汉大学硕士论文，2001．5
13．易丹，基于混沌序列的短波跳频码与调制解调单元的实现，武汉大学硕士论文，2000．5
14．王文博，郑侃，宽带无线通信OFDM技术。北京：人民邮电出版社，2003
15．佟学俭，罗涛，OFDM移动通信技术原理与应用，北京：人民邮电出版社，2003
16．谢强，移动通信中OFDM技术的研究，南京理工大学硕士论文，2002．1
17．李斯伟，张建超，“正交频分复用(OFDM)的原理及应用”，《中国民航学院学报》，1999年10月，第17卷，第5期：pp35-39
18．张峻峰，“正交频分复用(OFDM)调制技术”，《天津通信技术》，1998年6月，第2期：pp1-5
19．金旗，裴昌幸，张振生，“OFDM技术的基本原理”，《通信技术》，2002年第6期：pp44-46
20．赵亚红，李伟华，吕伟陵，“正交多载波调制(OFDM)技术及应用”，《电讯技术》，2001年第1期：pp92-95
21．李引新，赵姚同，“正交频分多路(OFDM)的实现方式及性能分析”，《电讯技术》，1998年12月，第38卷第6期：pp10-15
22．宋铁成，“下一代移动通信系统中的OFDM技术”，《移动通信》，2001年第11期：pp20-23
23. Yun Hee Kim;Hong Gil Kim;Iickho Song;Min Joon Lee;Seok Ho Yoon,"A Coded OFDM System for Time-varing Multipath Rayleigh Fading Environment",MILCOM 97 Prceedings.Volume:2,2-5 Nov 1997:pp867-871
24. A.D.S,Jayalath,C.Tellambum,"Reducing the Peak-to-Average Power Ratio of Orthogonal Frequency Division Multiplexing Signal Through Bit or Symbol Interleaving[J]",Electronic Lertters,22nd June 2000,Vol.36,No.13
25. A.E,Jones:T.A.Wilknsom,"Combined Coding for Error Control and Increased Robustness to System Nonlinearities in OFDM",Vehicular Technology Conference,1996.'Mobile Technology for the Human Race'.IEEE 46th, Volume:2,28 April-1 May 1996:pp904-908
26. X.Li,and L.J.Cimini,"Effects of Clipping and Filtering on the Performance of OFDM",IEEE Commun.Left.,M ay 1998 :pp 131-133
27. Cinini,L.,Jr.,"Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing",IEEE Transcations on Communications,Vol.33,Jul 1955:pp665-675
28. Muller, S.H.;Huber, J.B.,"A Novel Peak Power Reduction Scheme for OFDM",Personal,Indoor and Mobile Radio Communications, 1997.'Waves of the Year 2000'.PIMRC'97.,The 8th IEEE International Symposium on,Volume:3,1-4 Sept. 1997:pp1090-1094
29. T.May, and H.Rohling ,"Reducing the Peak-to-Average Power Ratio in OFDM Radio Transmission Systems",in Proc.IEEE Veh.Techn.Conf.. 1998:pp2474-2478
30. Sathananthan K,Tellambura C.,"Coding to Reduce Both PAR and PICR of an OFDM Signal".IEEE Communications Letters,2002,6(8):pp316-318
31. Ochiai,H.;Imai,H.,"Forward Error Correction with Reduction of Peak to Average Power Ratio of QPSK Multicarrier Signals",Information Theory.1997.Proceedings.,1997 IEEE International Symposium on,29 June-4 July 1997:pp120
32. Tasadduq,l.A.;Rao,R.K.,"Weighted OFDM With Block Codes for Wireless Communication",Communications,Computers and Signal Proceeding,2001. PACRIM.2001 IEEE Pacific Rim Conference on,Volume:2,2001 :pp441-444
33. Heung-Gyoon Ryu;Kyoung-Jae Youn,"A New PAPR Reduction Scheme:SPW(Subbiock Phase Weighting)",Consumer Electronics,IEEE Transactions on,Volume:48,Issue:1,Feb.2002:81-89
34. Jayalath,A.D.S.;Tellambura,C.,"Adaptive PTS Approach for Redution of Peak-to-Average Power Ratio of OFDM Signal",Electronics Letters, Volume:36,Issue:14,6 July 2000:pp1226-1228
35. Hong Chen:Pottie,G.J.,"An Orthogonal Projection-Based approach for PAR Reduction in
OFDM",Communications Letters, IEEE,Volume:6 Issue:5,May 2002:pp169-171
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