【作者】 屈晓旭；

【导师】 王殊；

【作者基本信息】 华中科技大学 ， 信息与通信工程， 2011， 博士

【摘要】 短波通信是实现超视距通信的重要手段之一,由于短波信道可用带宽窄且存在严重的时变和多径衰落问题,长期以来实现高速可靠的短波数据传输一直是军事通信领域关注的热点之一。差分跳频技术的提出为提高短波通信速率提供了一条全新的思路。目前在差分跳频抗干扰抗截获技术方面的研究仍存在明显不足。在抗干扰技术方面,由于差分跳频是一种宽带异步跳频体制,需要在整个跳频频率集内进行频点能量检测,因此部分频带干扰会显著削弱差分跳频系统性能,已有的信号检测和译码算法有各自的性能局限性。在抗截获性能方面,已有研究表明,差分跳频并非一种低截获概率通信方式,任何第三方通过侦听差分跳频信号都可获得频率转移矩阵,而通过发射具有相同频率转移矩阵的差分跳频干扰信号可严重破坏差分跳频通信系统性能。因此研究差分跳频的抗截获技术是有必要的。另外,差分跳频具有高速数据传输能力,这使基于差分跳频的短波猝发通信成为可能,但差分跳频及猝发通信的特点决定了必须考虑其抗干扰设计问题。基于上述考虑,本文围绕差分跳频抗干扰抗截获技术展开研究,论文主要研究内容及结论包括：(1)提出了一种新的基于噪声归一化合并技术的差分跳频抗部分频带干扰接收机模型,推导了无衰落信道、瑞利衰落信道及Nakagami-m衰落信道下系统的误符号性能,并研究了非理想噪声功率估计对系统性能的影响。研究结果表明在非最坏部分频带干扰下,除信道衰落较弱且干扰能量较为分散的特殊情况外,噪声归一化差分跳频接收机性能总是优于线性合并和乘积合并差分跳频接收机,且干扰越集中性能优势越明显；在最坏部分频带干扰下,在所考察的各种衰落条件下均有噪声归化差分跳频接收机的抗部分频带干扰性能优于线性合并和乘积合并差分跳频接收机,与信道衰落程度及干扰带宽因子取值无关；在噪声估计不存在严重偏差时(估计误差因子满足0.1<λ<3),噪声归一化合并差分跳频接收机在最坏部分频带干扰下的性能优于乘积合并和线性合并差分跳频接收机,且当噪声估计值略低于理想估计值时(0.2<λ<0.6),系统误符号率低于理想噪声估计条件下的误符号率。(2)研究了差分跳频系统的抗截获设计原则及各项抗截获性能指标的检测方法,分类研究了应用不同G函数的差分跳频系统的抗截获性能,证明了普通差分跳频系统不可能具有良好的二维连续性,进而给出了两种改善差分跳频系统抗截获性能的新方法：基于时变G函数(Time Varying G-Function, TVG)的抗截获设计方法和将常规跳频与差分跳频结合在一起的FH/DFH抗截获方法。对于TVG方法,给出了其优化准则并证明了依据该准则的TVG差分跳频系统具有长观测周期意义上的优良二维连续性。对于FH/DFH抗截获方法,在给出系统模型的基础上理论分析了其一维均匀和二维连续性。理论和仿真结果表明,采用这两种方法能够在不增加差分跳频译码复杂度的情况下有效改善差分跳频系统的抗截获性能,相对于TVG方法,FH/DFH方法在二维连续性和随机性方面都有更好的性能,但其系统复杂度略高。(3)为了缩短发射机信号辐射时间,猝发通信中一般不能如常规差分跳频系统一样进行自适应频率集优化,而为了提高通信隐蔽性又必须保留差分跳频的宽带跳频特性,这就使跳频带宽内会以较大概率存在干扰信号。为了克服此问题,提出了一种适用于单站发射,多站守听的特定场景下隐蔽通信的抗干扰分集猝发差分跳频通信方法,利用空间分集技术实现干扰抑制。分别推导了无干扰和有干扰存在时系统的误符号性能,得到了多重求和形式的误符号率表达式,该结果便于采用数值方法求解。研究结果表明,在给定的跳频频率集中有一半的频点上存在与跳频信号瞬时功率相当的干扰信号时,采用分集阶数不低于4的分集猝发差分跳频系统仍可保证系统误符号率接近10-4。该技术是实现短波猝发通信的一种新思路。更多还原

【Abstract】 Shortwave communication is one of the important ways to achieve over the horizon communication. As the shortwave channel is often corrupted by some poor properties such as multi-path fading and serious time-varying and the available bandwidth is relatively small, to achieve high data transmission speed has long been a hot concern in military communications. Differential frequency hopping (DFH) technology offers a new way of improving the rate of short-wave communication. Researches on anti-jamming and anti-interception technologies for DFH system are still inadequate. DFH is a wideband asynchronously receiving frequency hopping scheme and power detection is performed over all the frequencies of the hopping frequency set, therefore partial-band jamming may reduce the performance of DFH system severely. Signal detection and decoding algorithms proposed nowadays have their individual limitations. In terms of anti-interception, it is shown by related researches that DFH is not a communication scheme with low probability of interception (LPI). Any third party interception receivers can obtain the frequency transition matrix through the intercepted frequency sequence and jamming signal generated with the same frequency transition matrix may seriously damage the performance of DFH system. Studies on methods of improving the anti-interception performance of DFH system are necessary therefore. In addition, high data transmission speed capability of DFH system makes it a potential for shortwave burst communication, but anti-jamming design must be considered seriously for the special characteristics and requirements of DFH and burst communication.This paper focuses on studies on anti-jamming and anti-interception technologies used for DFH system. The main research contents and conclusions are listed as follows.(1) A novel anti partial band jamming (PBJ) DFH receiver based on noise normalization combining (NNC) is proposed. Symbol error rate (SER) of NNC-DFH receiver is derived with multiple fading conditions considered including non-fading, Rayleigh fading and the more general Nakagami-m fading. The inevitable non-ideal noise power estimation and its influence on system performance are also considered. It is shown that when jammed by non-worstcase jamming, NNC-DFH receiver is superior to linear combining (LC) receiver and product combining (PC) receiver except for the special condition when channel fading is weak and the jamming power is dispersed and the superiority increases with the concentration of the jamming power. When suffering worstcase jamming, NNC-DFH receiver is always superior to LC and PC DFH receiver over the studied fading conditions for any jamming bandwidth ratio. It is shown that when noise power estimation error is not great (0.1<λ<3,λis the estimation error factor), NNC-DFH receiver is superior to LC and PC DFH receiver when corrupted by worstcase PBJ. System with noise power a little lower estimated (0.2<λ< 0.6) outperforms that with ideal noise power estimation.(2) Anti-interception design criterions and the evaluation methods of vary anti-interception performance indexes are studied first. G-functions proposed by literates are classified and anti-interception performances of DFH systems applying different G-function are studied. After proving that normal DFH system can not achieve good two-dimensional continuity performance, two methods of improving anti-interception performance of DFH system are proposed including time varying G-Function (TVG) method and FH/DFH method which combines traditional frequency hopping with DFH. For TVG, an optimization criterion is provided and it is proved that DFH system using TVG method has good two-dimensional continuity performance in long observing period sense. For FH/DFH, after description of system model, one-dimensional uniformity and two-dimensional continuity performance is analyzed theoretically. Theoretical and simulation results validate the effectiveness of these two proposed methods in improving the anti-interception performance of DFH system. Comparing with TVG method, FH/DFH method is superior in two-dimensional continuity and randomness performance with the cost of inceread complexity of implementation.(3) To reduce the signal radiation time as much as possible, adaptive frequency set optimization are not applied in burst communication although which is often used in normal DFH system. On the other hand, wideband property should be reserved to enhance the communication concealment, but which will make many interferer signals unavoidable. An anti-jamming method based on multi antenna diversity is used in burst DFH communication system, which is suitable for the special application scene where there are single transmitter and multiple receivers. SERs of this system (jammed or not) are deduced in multi-dimensional addition style, which is easy to be evaluated. It is shown by these analyses that even when half of the frequencies are jammed with jamming power equal to the instantaneous signal power, a 10-4 SER can be obtained with the proposed system with diversity order not less than 4. This is a new approach of designing of shortwave burst communication system.更多还原