摘要
跳频技术是扩频技术的一种,跳频通信具有良好的抗干扰性,低截获概率及组网能力,因此跳频技术一出现,便在军事领域得到了极大的发展。采用跳频技术的短波超短波电台在军事通信中得到了广泛应用,极大地提高了军事装备的抗截获和抗干扰能力,保证了军事指挥系统的安全性和有效性。
目前,军事通信传递的信息,已从发送简单的指挥命令发展到诸如雷达探测的数据、高速图像传真信息和数字话音加密信息等一些要求较高的数字数据信息。传统调制方式由于频谱利用率不高而不适合跳频系统的高速数据传输。因而研究适合于跳频通信特点的具有高效频谱利用率的调制方式具有重要的意义。
在各种调制方式中,高斯最小频移键控(Gaussian Minimum Shift Keying)具有极好的频谱利用率、功率效率和可以采用非相干解调等优点,已经广泛应用于无线通信系统,尤其是移动通信领域。本文在介绍几种数字调制技术的基础上,讨论了GMSK调制技术的产生、解调方法及其特性,并设计了基于GMSK调制的跳频调制系统模型;然后,针对信道的特点,对跳频下GMSK的非相干解调方法进行了分析,最后通过建立MATLAB系统仿真模型,对该方案的性能进行了分析。经过仿真结果证明,GMSK跳频系统在没有差错控制的条件下可以获得较好的传输效果,也说明了GMSK调制方式应用于跳频系统的可行性。
Frequency-Hopping(FH) is a novel spread spectrum communication technique which develops very fast in military field due to its Low Probability of Intercept Detection of properties and immunity against interferences , The extensive application of HF/VHF (high frequency/vey high frequency)frequency-hopping radio in military has greatly enhanced ability of military equipment against jamming and interception and ensure the safety and validity of chain of military command.
At present, many military information had developed from simple commanding order to radar detecting data、computer calculating result、high-speed image fax and so on ,Modern FH communication system need transmit a mass of data, traditional modulation are no longer suitable for high–speed data transmitting in FH system due to low spectrum efficiency, Therefore it has a practical significance to develop some fit methods of modulation with high spectrum efficiency of FH communication system.
In all kinds of modulation, with the advantage of good spectrum utilization and power efficiency as well as noncoherent demodulation can be employed. GMSK(Gaussian Minimum Shift Keying)has been widely applied in the wireless system .It will be introduced for FH to implement high-speed data transmitting in this paper. Firstly, base on some digital modulation techniques used in FH system, main research is made on the principle, the method of generation and demodulation, characteristic of GMSK signal ,Secondly, according to the feature of FH channel, Finally, take full use of Simulink module in MATLAB to build computer simulation model, The simulation results show that, GMSK frequency hopping systems in the absence of errors control of the transmission can get better results,it is feasible to introduce the GMSK into the FH communication.
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