一种非合作的跳频信号跳同步方法

针对跳频信号侦察中,在非合作条件下进行信号跳同步问题,提出利用跳信号分段频谱比较分析实现跳频信号跳变时刻同步的方法。该方法首先利用短时傅里叶变换和小波变换的方法有效估计跳频信号跳速率参数,在此基础上通过在一个跳周期内取三段信号进行频谱比较,并滑动调整时间参数的方法进行跳同步获取。实验证明该方法不仅可以有效实现跳频的跳同步,同时克服了跳速率估计精度不足的问题,且方法结构简单易于工程实现。     

一种慢跳频系统频率跳变时刻同步算法

提出一种盲接收环境下的慢跳频（SFH）系统频率跳变时刻同步算法。该算法针对慢跳频系统中1跳数据包含多个调制符号的特征,通过非线性变换得到包含离散谱线的信号。利用跳频信号在每1跳内能量恒定的特性,将1跳信号均匀划分为2段,提取分段信号非线性变换后离散谱线能量差异,作为调整频率跳变时刻的判决量,通过反馈环路实现盲接收环境下频率跳变时刻的精确同步。对典型慢跳频DPSK（SFH/DPSK）系统在盲接收环境下的同步性能进行仿真,在Eb/N0大于16 dB时,算法同步性能接近10-3,验证了算法的有效性。     

Frame synchronization of convolutionally coded systems for packettransmission

This letter proposes a decoder-assisted frame synchronization scheme for convolutionally encoded information packets. Rather than placing sync bits in a separate header, the sync bits are placed in a mid-amble and encoded as part of the information sequence, using the error correction encoder to resolve time ambiguities. This technique requires fewer bits for frame synchronization. The performance improvement over the conventional synchronization technique is explored via simulation     

Decoder-assisted frame synchronization for packet transmission

This paper proposes a novel frame synchronization methodology for packets with convolutionally encoded data. Rather than by placing sync bits in a separate header, the sync bits are placed in a midamble and encoded as part of the data sequence, using the error correction encoder to resolve time ambiguities. The scheme is based on the principle that an error in trellis termination may result in decoding a wrong information bit sequence, while the starting portion of the sequence can be decoded as error free. This frame synchronization technique is extended to the synchronization of turbo-coded systems using a list-based approach, where the first synchronizer provides a list of potential packet starting positions, and the following synchronizer makes the final decision. The performance improvement over conventional synchronization techniques is quantified via simulation     

基于FPGA的短波跳时跳频系统同步的实现

短波跳时跳频信号具有频率不断变化和发信时间随机的特性,能够很好地实现通信信号的隐蔽,具有较强的抗截获抗干扰能力,但是跳时技术会导致整体的发信时间被延长。为尽量缩短发信时间,对以往的同步序列+TOD信息的同步方法进行改进,提出一种帧同步序列与跳时跳频伪随机码一一对应,采用滑动窗相关检测进行同步的方法,在FPGA中实现了该同步系统,并对该系统进行了仿真。     

基于多通道数据融合的跳频信号频率跳变时刻估计算法

针对低信噪比条件下宽带高速跳频信号的参数估计问题,提出一种多通道数据融合跳频信号频率跳变时刻估计算法。该算法利用无盲区数字信道化预处理实现宽带跳频信号的全概率、全盲接收,通过数据融合得到一路包含全部频率跳变信息的参考信号,并利用该参考信号进行最大似然估计得到频率跳变时刻精确估计值。给出了所提出跳变时刻估计算法的Cramer-Rao下界并进行实验仿真。理论推导和仿真结果表明:针对一定的输入信噪比,适当选择信道化数和估计时间可实现较高的估计精度。在0dB信噪比条件下,采用16通道数字信道化处理,估计方差小于10-3。      

一种基于CORDIC算法的混合跳扩频跟踪同步方法

针对传统反馈环路补偿速度无法跟上目前混合跳扩频通信系统误差变化速度导致同步失败的问题,提出一种基于坐标旋转数字算法(Coordinate Rotation Digital Computer,CORDIC)的跟踪同步方法.该方法将系统载波同步误差和定时同步误差映射到相位上,利用二维旋转的方式对误差进行补偿,并根据二进制相移键控(Binary Phase Shift Keying,BPSK)调制的性质,确定最佳旋转位和补偿误差,实现系统同步.实验证明,此方法成功让具有跳频速率20000 hop/s、跳频带宽327.52 MHz的混合跳扩频通信系统实现了稳定同步,补偿性能相比于传统补偿技术具有明显优势.     

Preamble and embedded synchronization for RF carrier frequency-hopped OFDM

In this work, we apply RF carrier frequency hopping to orthogonal frequency-division multiplexing (FH-OFDM). Achievable hop rate and bandwidth efficiency are determined based on signal acquisition/synchronization and data demodulation performance in the presence of unknown time-frequency offsets, and channel gain/phase perturbations. We compare performance using two different data-aided synchronization approaches. The first method sends synchronization information in a preamble before the OFDM payload symbol, whereas the second method embeds the synchronization information directly into the OFDM symbol stream. In the embedded technique, superposition of the synchronization information causes interference onto the OFDM data information. Thus, the sync information must be removed before satisfactory bit-error rate (BER) performance can be achieved. Consequently, embedded interference cancellation (EIC) is utilized which requires accurate estimation of the synchronization offsets and channel perturbations. Using coherent quadrature phase-shift keying-OFDM modulation, performance comparisons are presented using the COST207 multipath fading channel model. Fading channel BER performance results indicate that the embedded technique incurs only a slight signal-to-noise ratio penalty (less than 1 dB) compared with the preamble method. However, the embedded method offers the potential for improved hop rate and bandwidth efficiency because no dedicated slot is required for a synchronization field.     

采用局部特征尺度分解的跳频信号参数盲估计算法

针对现有跳频信号参数盲估计算法存在时间分辨率和频率分辨率矛盾这一问题,提出了一种基于局部特征尺度分解的跳频信号参数估计新算法。该算法将跳频信号迭代地分解成若干个内禀尺度分量并进行降噪处理,然后对其最大瞬时幅度进行小波变换和傅里叶变换即可估计出跳频信号的跳变时刻和跳频周期,最后根据得到的跳变时刻和跳频周期可以进一步估计出跳频频率集。该算法不受时频不确定性原理的影响,能够在未知先验知识的条件下估计出跳频信号的跳周期、跳变时刻和跳频频率集。最后通过仿真验证了算法的有效性。      

强干扰下跳频信号的参数估计

针对通信对抗中跳频信号参数估计问题,考虑存在强干扰的情况下,提出了一种基于时频重心的跳频信号跳周期估计和基于跳频部分接收的跳时估计方法。对于跳周期估计,在短时傅里叶变换(STFT)时频变换的基础上提取信号随时间变化的时频重心,再结合小波变换和谱分析估计出跳频周期;对于跳时估计,采用跳频带宽的部分接收避开强干扰,构造含有跳变信息的参考信号,通过参考信号采用最大似然(ML)方法得到跳时的精确估计。仿真实验表明,算法运算复杂度低,跳频定位精度高,在强定频干扰的情况下仍能有效估计出跳频周期和起跳时刻。     

FH-OFDM系统同步算法研究与FPGA实现

研究了FH-OFDM系统的跳频同步方法和定时同步方法。跳频同步中利用GPS同步脉冲保证了接收机的时间基准。定时同步中使用了基于最小均方差的判决方法,对匹配滤波器进行了改进,有效地减少了载波频偏的干扰,并针对FPGA应用对算法进行了简化。对FH-OFDM同步系统进行了FPGA实现,性能测试结果表明该同步实现方法可以快速准确地检测到信号帧以及各个符号的起始位置。     

基于中国余数定理的跳频信号相时延估计方法

跳频信号每跳带宽窄且多跳间积累困难,利用传统方法对其时延估计精度都很低。针对该问题,该文充分挖掘跳频信号宽跳带的潜能,建立了多频点相时延估计模型,把时延估计问题转化为整周模糊求解问题;然后在解模糊过程中引入中国余数定理,针对非合作场景中模数无法选择的问题,提出一种基于虚拟频点的干涉相位外推方法,构造出鲁棒中国余数定理的适用条件;最后采用闭式鲁棒中国余数定理解算整周模糊,得到高精度的相时延。该方法具有精度高、运算量小、不依赖于信道衰落特性的优点。仿真结果验证了所提模型及方法的有效性和正确性。     

基于快速折叠算法和时频分析的LPI跳频信号截获

该文提出了一种新的低截获概率(LPI)跳频信号的截获方法,该方法基于快速折叠算法和时频分析。在低信噪比环境下,该方法能有效检测跳频信号;通过恰当地选择折叠周期范围和分辨率,能实现对跳频参数如跳频周期、跳变时刻和跳频频率的估计。仿真结果和性能分析表明,该方法能有效截获信噪比为0dB的跳频信号,与自适应门限检测方法相比具有更好的性能。     

Carrier initial phases estimation for single-channel adjacent-frequency mixture of digitally modulated signals

For single-channel mixture of adjacent-frequency digitally modulated signals which have the fixed frame length and sync codes in non-cooperative satellite communications,a carrier initial phases estimation algorithm which can be applied to both low-order and high-order digitally modulated mixtures was provided according to the differences of parameters in the source signals.The sync data eliminated the frequency offset was added in the interval of frame length firstly,then timing synchronization was accomplished for the added result in terms of power maximization rule,thus the initial phases information was derived.Moreover,the modified Cramer-Rao bound (MCRB) of carrier initial phases for single-channel mixture of adjacent-frequency digitally modulated signals was derived for comparison.Simulation results show that,difference between estimation performance of the proposed algorithm and MCRB becomes smaller with the increase in the number of added frames.     

基于单个FFT非线性早迟窗同步系统设计与实现

在传统的差分跳频早迟窗同步系统的基础上,采用单个FFT,通过FFT变换后提取早迟窗,大大降低了系统资源消耗。另外,采用非线性早迟窗,当跳沿时间误差相差过大时,采用粗调;当时间误差缩小时,改用细调,同时满足同步锁定时间和同步锁定精度。最后,以软件无线电思想,在现场可编程门阵列(FPGA)的Spartan6开发板上,采用Xilinx公司的System Generator工具进行建模设计仿真,验证方案的可行性和设计的正确性。     

TDS-OFDM系统中同步方法的研究

讨论了一种在TDS-OFDM系统中利用PN保护间隔进行系统同步的方法,用本地生成的PN序列和接收到的时域数据进行相关,找到相关峰位置,利用相关峰位置完成定时同步,同时采用二次相关完成载波频率同步.通过仿真证明本同步方案具有较好的同步性能.     

一种低功耗的多跳无线传感网时间同步算法

高精度低功耗的时间同步对于无线传感网络至关重要,文中重点分析了高精度时间同步算法,发现其在多跳网络时间同步过程中由于每跳范围内所有节点均要广播时间同步包,会产生大量的冗余信息。为降低同步功耗,提出了一种新方法,通过调节发射功率,筛选出每一跳范围内的周边节点,使其完成下一跳范围的时间同步,而非周边节点只接受却不发送时间同步包。最后,针对改进的算法在OMNet++上进行了仿真实验,仿真结果表明,改进后的算法能够有效地降低全网能量消耗。     

一种无线光通信中脉冲位置调制的符号同步方法

脉冲位置调制(pulse position modulation,PPM)是无线光通信的经典调制方式之一.符号同步是实现PPM正确解调的关键技术.在分析帧同步码型和长度要求的基础上,设计了一种PPM帧结构,提出了利用帧同步来实现PPM符号同步的方法.论述了其工作原理,并分析了其同步性能.结果表明该方法建立时间短,同步概率高,并具有自动调整功能,可实现性强.     

Frame synchronization in a photonic network of time multiplexedspace switches via a feedback scheme

A method for frame synchronization in a photonic network of time multiplexed space switches is presented. The method, which is based on a feedback scheme, is first introduced for frame synchronization in a single-switch configuration. The feedback scheme is then extended to both hierarchical (tree topology) and nonhierarchical (general topology) multiswitch configurations. Using this feedback scheme has the advantage of providing a mechanism for frame synchronization to be achieved initially, without the need for accurate transmission time measurements, and allowing synchronization to be maintained within very tight bounds. The methods presented require additional electronics at the switches, but electronics only for control purposes, not in the path of the information bits. However, optical delay elements are needed in the path of information bits on some links of the network. The proposed schemes also reduce the amount of synchronization equipment needed, compared to other methods     

基于YOLOX的跳频信号检测

现有跳频信号检测算法大多针对固定参数的跳频信号检测,而面对可变参数的跳频信号检测时,其每跳时长及带宽的不确定性导致这些算法的适用性下降。为此,提出了一种基于YOLOX的跳频信号检测算法。该算法适用于固定参数跳频信号和可变参数跳频信号,判断跳频信号的存在性。首先将观测时间内的信号进行短时傅里叶变换获得灰度时频谱图;然后将时频谱图经过目标检测网络YOLOX,获得各个信号的预测框;最后根据跳频信号各跳点的时间连续性,筛选出跳频信号各个跳点,根据连续跳点个数判断跳频信号的存在性。对算法的检测流程进行了仿真,以验证算法的可行性。实验结果表明,该算法可以较好地完成盲检测任务,且能够通过增加较少的先验信息以提高检测性能。