【作者】 蒋光明；

【导师】 甘良才；

【作者基本信息】 武汉大学 ， 通信与信息系统， 2004， 硕士

【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。更多还原

【Abstract】 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.更多还原