基于DSP的流星信道模拟器设计

讨论了流星突发通信欠密类余迹的信道特性及其模型。以TMS320VC5509 DSP为核心设计了流星信道模拟器系统，并给出模拟器在实验室流星突发通信自适应变速率系统设计中的测试应用。     

流星突发通信中的信道估计研究

在流星突发通信中,大部分流星余迹反射接收信号功率呈指数衰减,所以采用自适应变速率传输可以充分利用信道容量。动态信道估计技术是流星突发通信中自适应变速率的关键,通过实时地计算接收信号的信噪比决定此时的发端速率。通过Matlab仿真比较了两种适合D-BPSK信号差分相干解调的信噪比估计算法。     

链路自适应技术在流星余迹通信中的应用

流星余迹通信具有其他通信系统无法比拟的优点,如:大跨距、抗干扰、低截获概率特性和抗毁性等特点,使得这种通信方式的应用范围越来越广泛,尤其是支援短波通信及用作卫星通信的替补手段。但是流星余迹信道又是一种典型的突发信道,通信容量小和实时性差。为了最大限度地利用短暂的流星余迹信道,人们设计了链路自适应技术。此技术能够根据信道状况自动调整发射机和接收机的参数,使得流星余迹信道资源得到最大限度的利用。     

流星余迹通信最佳传输帧长设计

在分析流星余迹通信原理及其传输信道物理特性基础上,根据流星余迹电子线密度的分布特性,构建出流星余迹信号初始接收功率的概率密度函数.针对以信号帧为单位的自适应变速率传输机制,推导出欠密类余迹平均信息通过量与传输帧长的关系,提出最佳帧长设计原则,得到自适应传输帧长的理论最佳值.仿真结果表明,在满足通信可靠性及实时性的要求下,所得最佳帧长能使系统平均信息通过量达到最大,有效提高流星余迹信道利用率.     

流星余迹通信信道统计特性及模型仿真

流星余迹通信不同于传统的通信,它是低速率通信,具有突发、不连续以及不定时的特性。流星余迹通信的复杂性要求有必要对其通信信道进行研究。可用流星率、占空比、平均持续期、等待时间和通信通过量是影响流星余迹通信信道性能的重要参数。根据偶发流星日心空间和地心空间的几何关系,得到了流星突发通信信道参数预测模型;并对流星通信链路观测的数据进行统计分析,得到流星余迹通信信道的各参数,预测结果和通信链路观测结果比较一致,为流星通信系统的建立提供了技术支持。     

流星余迹通信技术特征及影响

流星余迹通信利用流星电离余迹进行通信,它是一种突发的通信方式。流星余迹通信方式特殊,它具有很好的隐蔽性、很强的抗干扰能力,使其成为一种受到物理或电子攻击时的有效通信保障手段。这里给出描述流星余迹信道参数（流星达到率、可用时间比、平均持续期等）的数学表达及实测结果。制订2种流星突发通信的握手协议,并基于该协议和信道实测结果,估算得到流星突发通信的通过量和突发等待时间。     

流星突发通信中的变速率编码方案研究

流星突发通信是一种利用流星余迹进行通信的短时、突发通信方式。如何在较短通信时间内尽可能多的实现数据的可靠传输,始终是研究者关注的问题。传统的固定速率编码方案无法很好地适应信道变化,因此提出变速率编码以提高系统性能。通过对两种方案研究,对变速率编码算法进行了改进。仿真结果表明,改进后的变速率编码方案可明显改善系统性能。     

流星余迹通信变速率编码研究

流星余迹通信是一种利用流星电离余迹反射电波实现数据传输的通信方式。衡量流星余迹通信系统性能的指标之一是所采用编码的数据包正确传输概率。通常采用的编码方式为固定速率编码,这种编码数据包传输正确概率较低,系统性能较差。变速率编码根据流星余迹通信信道特点,通过改变数据包中各个码字的码率,提高数据包正确传输概率,改善系统性能。理论分析和仿真结果表明,采用变速率编码系统性能提高。     

流星余迹通信信道季节变化模型与仿真

流星余迹通信不同于传统的通信,它是低速率通信,具有突发、不连续、不定时的特性。因此,流星余迹通信的复杂性要求有必要对其通信信道进行建模。根据流星轨道分布的特点,推导出轨道-辐射的转换,得到流星分布和通信链路的关系,建立了流星余迹通信信道季节变化预测模型,并将预测模型应用于流星余迹通信链路。预测的结果和中纬度雷达观测结果比较一致,为建立流星余迹通信系统提供了技术支持。     

一种基于流星突发通信的分组无线网

流星余迹信道短时突发的特点使得流星突发通信呈现间歇性,在等待一颗适合的流星出现前往往需要等待很长的时间,同时由于流星突发通信的"足迹"和"热点"特性,使其通信距离受到限制。为解决上述问题,提出一种基于流星余迹通信的无线分组网,首先针对流星余迹信道特点给出了适合该网络的路由选择策略,其次介绍了工作流程,最后对分组长度进行了分析,并给出了仿真结果。     

基于TPC-RS的自适应编码流星余迹通信系统

 针对流星余迹通信系统原理及信道特点,研究了基于自适应编码机制的流星余迹通信系统．根据流星余迹信道能量随时间呈指数变化的规律,在系统误比特率的约束条件下,通过实时估计出的流星信号接收信噪比,动态地改变系统TPC-RS编码的码率冗余,实现信息速率的自适应变化,有效提高了流星余迹信道的利用率．仿真结果和分析表明,在相同信道条件下,采用自适应编码较固定编码传输效率在误比特率为2×10^-4时可获得3.68dB系统增益,数据通过量提高了一倍,验证了该方案的有效性和可行性．     

Coding for meteor burst communications

The use of error correction coding for meteor burst communications is discussed. The cutoff rate is derived for a meteor burst channel model which assumes that the received signal amplitude decays exponentially. The message error rate of a coded system, obtained by means of computer simulation, is compared to that of an uncoded system. A tight upper bound on the performance of the coded system is presented. It is shown that coding can reduce the signal-to-noise ratio (SNR) required for reliable communications via meteor bursts by many decibels. The coding gain is larger at shorter communication ranges where meteor trails, decay faster. It is also shown that the additional improvement achieved by providing the decoder with side information on the instantaneous level of the received signal is small     

An adaptive receiver of joint data and channel estimation for meteor burst communications

In view of the characteristics of the meteor burst channel, the variable rate data transmission should be adopted to improve the system average throughput, which results in channel tracing and equalization problems at the receiver. Although the joint data and channel estimation of maximum likelihood sequence detection performing the principle of per‐survivor processing (PSP) is considered as an optimal detection scheme, its great computational complexity is a major problem and can hardly agree with the decreasing of the meteor channel. Based on the estimation of the system parameters, an adaptive state reduction of the PSP (ASRP) algorithm with only a few states in the trellis diagram is employed, while these states are chosen by the time‐varying threshold according to the exponential decay of meteor channels. It is shown that, ASRP can make a good tradeoff between the performance and the computational complexity, and provides reliable data transmission for adaptive modulation and coding of the meteor burst communication system. Computer simulation results and performance analysis are also included to support our developments. Copyright © 2010 John Wiley & Sons, Ltd.     

流星突发通信在军事通信中的应用分析

简述了流星突发通信的原理、工作方式,介绍了流星突发通信在在国外中的应用和发展现状,根据流星突发通信具有较好的低截获、抗干扰能力和受自然环境影响较小的特点,对流星突发通信在军事方面的应用环境进行了分析。通过分析可以看出,流星突发通信在军事应用上具有特殊的地位,在可能出现的现代战争中,流星突发通信为一种最终的通信保障之一,它是一种不可缺少的应急和辅助的远距离通信手段。     

An efficient convolutional coding/decoding strategy for channelswith memory

Many digital communication channels are affected by errors that tend to occur in bursts. A great deal of work has been devoted to finding good burst-error-correcting codes and developing burst-error-correcting schemes. However, burst-error-correcting codes are generally not effective for long bursts. Some burst-error-correcting schemes suffer long delay in decoding. Others are very sensitive to random errors in the guard space. Most of these schemes are not adaptive to channel conditions. A new adaptive scheme is proposed to overcome these drawbacks. The scheme employs a combination of two complementary punctured convolutional (CPC) codes. One of the codes is used for burst detection and for channel state estimation, and both codes are used for error correction. The proposed scheme is analyzed over a two state Markov chain channel model. Unlike existing burst-error-correcting schemes, it is shown that the proposed scheme is adaptive to channel conditions and less sensitive to errors in the guard space. For the same delay, the proposed scheme offers better performance than the interleaving schemes. When the channel is heavily corrupted by bursts, the improvement is even more pronounced     

流星余迹信道建模与仿真分析

为检验流星余迹通信设备及软件在实战化环境中的应用效能,针对流星余迹通信信道规律复杂、实测代价高等问题,建立流星余迹信道仿真模型。通过对典型数学模型的深入研究,以欠密类流星余迹和过密类流星余迹信道模型为基础,融入了欠密类流星簇和多径信道两种特殊类型,按照概率论原理,建立了流星余迹信道混合模型,并结合流星余迹到达间隔模型,利用C++实现了流星余迹信道混合模型的仿真。该模型可生成包含单颗欠密类、单颗过密类、欠密类流星簇和多径信道等多种类型的复杂信道。仿真结果表明,所产生的流星余迹信道特征与实际信道基本相符,验证了该模型的可用性和合理性。