伪噪声时频编码通信信号LPI/AJ性能分析

在基于时频编码抗衰落通信的基础上,把噪声编码通信技术运用到时频编码中,提出了采用随机的比特流实现多个PN码、多个频率、多个时隙的伪噪声时频编码的新途径,显著地提高了伪噪声时频编码信号抗干扰、低截获概率性能。在进行伪噪声时频编码信号设计的同时,给出信号性能详尽论述和数学分析,并通过计算机仿真验证了该方法的可行性和正确性。     

Jointly optimizing sensing time and resource allocation in multichannel cognitive radio networks

Spectrum sensing is a key technique for determining the spectrum available in cognitive radio (CR) networks. In this paper, we study how to jointly optimize sensing time and resource allocation to maximize the sum transmission rate of all CR users of a multichannel CR network. We take into consideration the transmission power and interference constraints to protect primary users from harmful interference, as well as constraints of detection probability and false alarm probability. Under these constraints, we propose an asymptotically optimal resource allocation algorithm. The optimal sensing time can be obtained using the traditional one‐dimensional exhaustive search. However, owing to the high complexity of searching for the sensing time, we propose a simplified method to get the optimal sensing time under the assumption that false alarm probability is small. Simulation results show that the simplified method can obtain the optimal sensing time efficiently under strict constraint of false alarm probability. Copyright © 2012 John Wiley & Sons, Ltd.     

一种跳频同步的抗干扰方法

提出了一种跳频模式同步系统的有效抗干扰措施。该方法综合利用了纠错编码技术和直接序列扩谱技术对TOD同步信息进行处理,对单频干扰和跟踪式干扰均有较好的对抗能力,提高了系统性能。     

Joint design of precoder and receiver in cognitive radio networks using an MSE criterion

We consider a single-user multiple-input multiple output (MIMO) transmission from secondary base station (SBS) in cognitive radio network where there is one primary user to which spectrum is licensed. It is assumed that coexistence of secondary network is allowed if interference power from the secondary network measured at primary user (PU) can be kept below a given threshold. In this paper, joint design problem of precoder and receiver is treated using mean-squared error (MSE) criterion between transmitted signal and its estimate at the receiver. Due to constraint on interference power measured at the PU, it is not possible to find an optimal solution in closed form. Therefore, a suboptimal solution with low complexity is proposed in closed form. Simulation results show that the MSE and bit error rate (BER) performances of the proposed scheme are 1.5-4.0 dB better than those of a conventional capacity-maximization scheme when the received signal-to-noise ratio (SNR) is high, and they converge to their lower bounds, i.e., those of an MSE-based scheme without considering the PU interference constraint, as the received SNR increases.     

认知网络主用户吞吐量受限下的传输半径分析与仿真

该文针对认知无线电中认知用户对主用户接收机造成的并发通信干扰问题,采用信息论的观点,在主用户吞吐量门限和主用户通信中断概率的限制条件下,首先分析了认知用户对主用户接收机的干扰功率,并引用马尔科夫不等式,推导出主用户传输半径范围,同时数值分析表明：在其他条件一定时,主用户平均吞吐量、认知用户接入数目和主用户传输半径之间是相互量化制约的关系。其次,改进开发了一个基于中断概率的认知无线电网络仿真平台,分析了在不同认知用户密度下,主用户吞吐量和传输半径之间的实际作用关系,验证了所提模型的合理性和正确性。     

联合迭代解调译码算法的短波FH/OFDM系统的性能分析

该文提出了一种基于联合迭代解调译码的短波跳频OFDM系统,并在其接收端采用非相干序列检测和迭代译码相结合的联合迭代解调译码算法。该联合迭代解调译码算法可以降低差分检测时所导致的性能损失,同时,也可以提高短波FH/OFDM系统的可靠性。仿真结果表明：该方法可使其系统在短波信道中获得较好的比特误码性能,当Eb/N0＝5.5 dB时,其系统的比特误码率可达到10-5,数据传输速率达到8.912 kb/s,显然,该联合迭代译码解调算法是适合短波FH/OFDM系统的。     

基于时频联合估计的短波OFDM的检测算法

针对短波信道的特点,该文提出了一种OFDM同步检测方案。方案采用m序列调制导频符号,利用时频偏移联合估计得到m序列的相关峰来实现同步检测。该文理论分析了方案中判决门限区间的选取。蒙特卡罗仿真表明,该方案在低信噪比(-10dB)下性能良好,有可靠的同步概率和小的虚警概率。     

Improving FH and FH/PN spread spectrum communications through PN M-ary phase sequences and signal editing

Pseudo-noise (PN) or direct sequence (DS) modulation, frequency hopping (FH) and their combination (i.e. the hybrid FH/PN approach) are common spread spectrum (SS) communications techniques used to achieve anti-jamming (AJ) and/or low probability of intercept (LPI). This study investigates the following FH and FH/PN related issues: (i) derive and apply M-ary phases of PN sequences to increase the AJ and transmission efficiency, (ii) use of erasure channel to reduce received errors and unreliable data, (iii) employ error correction coding and signal editing (SE) to improve communication surviv-ability, and (iv) adopt surface acoustic wave (SAW) devices to simplify the synchronization procedure in PN correlation. A special example is also given to illustrate the potential AJ improvement when an SS communications system employs both concatenated coding and concatenated SE techniques.     

A high sensitivity and wide dynamic range zero-IF RF receiver for cognitive radio application

This paper presents an RF receiver of zero-Intermediate Frequency (IF) architecture for Cognitive Radio (CR) communication systems. Zero-IF architecture reduce the image reject filter and IF filter, so it is excellent in low cost, compact volume, and low power dissipation. The receiver employs three digital attenuator and a high gain, high linearity low noise amplifier to achieve wide dynamic range of 70 dB and high receiving sensitivity of −81 dBm. A fully balanced I/Q demodulator and a differential Local Oscillator (LO) chips are used to minimize the negative effects caused by second-order distortion and LO leakage. In order to select an 8 MHz-channel from 14 continuous ones located in UHF band (694–806 MHz) accurately, approach of channel selectivity circuits is proposed. The RF receiver has been designed, fabricated, and test. The measured result shows that the noise figure is 3.4 dB, and the error vector magnitude is 7.5% when the input power is −81 dBm.     

一种新的部分频带噪声干扰模型下的FH/MFSK系统性能分析

部分频带噪声干扰(PBNJ)是一种主要的窄带干扰,它对通信系统性能的影响十分突出。该文针对FH/ MFSK系统中,传统的部分频带干扰模型的干扰带宽最小分辨率是一个跳频子带带宽(即MFSK信号的带宽),研究了更具有实际价值的新的部分频带干扰模型,即将干扰带宽最小分辨率精确到MFSK信号带宽的1/M。该文推导了莱斯衰落信道下的误比特率(BER)公式,给出了其闭合表达式,并通过计算机仿真验证了理论推导的正确性。理论分析与仿真结果表明,M,Nh,越小,传统与新PBNJ模型下FH/MFSK信号的BER性能差异就越大。     

认知无线电网络的物理层安全研究及其鲁棒性设计

该文从用户服务质量(QoS)的角度研究了多输入单输出(MISO)认知无线电网络的物理层安全问题。通过在次用户的发送信号中加入适当功率的人为噪声,能够有效地提高网络的物理层安全性能。经过适当的变换,将次用户的安全优化问题转化为一个半定规划,从而可以有效地求得次用户的最优发射方案。另外,针对信道状态信息不确定性的问题,在假设已知信道状态信息误差范围的前提下,采用最差性能最优的方法对系统进行鲁棒性设计,以保证即使在信道状态信息误差最大的情况下,依然可以满足系统的约束条件。最后,通过仿真验证了算法的有效性。     

基于信道分类和自适应调制编码的认知无线电决策引擎

在多径信道条件下,针对单载波频域均衡(SC-FDE)认知系统不能通过多目标优化策略进行决策的问题,该文提出一种基于信道分类和自适应调制编码(AMC)的认知无线电决策引擎。该决策引擎首先对当前信道进行分类,确定当前信道状态;然后根据当前信道状态下的策略切换表选取最优传输策略(MCS),并计算该策略的使用时长(MCSD)。一旦当前策略的持续时间超过了其使用时长,认知决策引擎就会对最优策略进行更新。仿真结果表明,该决策引擎能够提供最优的传输策略以提高频谱效率,使SC-FDE认知系统更好地适应无线信道复杂的电磁环境。     

噪声功率不确定性区间估计和降低SNR WALL恶化的能量检测算法

能量检测是认知无线电系统中广泛采用的空闲频谱检测方案,但其性能受到噪声功率不确定性(NPU)的严重影响。该文提出一种新颖的复杂度较低的NPU区间估计算法,并且从理论上分析了估计的噪声功率对能量检测信噪比墙(SNR WALL)恶化的影响,得出了SNR WALL恶化性定理。进一步基于门限修正提出一种改进的能量检测算法以消除SNR WALL恶化。仿真结果表明,该算法能较为精确地估计NPU区间,并且验证了SNR WALL恶化性定理的正确性;同时,改进的能量检测算法性能要优于稳健的统计方案(RSA)能量检测的结果,并且改进后降低了SNR WALL恶化,提高了检测的鲁棒性。     

一种低轨双星高脉冲重复频率雷达信号的定位模糊消除算法

针对低轨(LEO)双星到达时间差(TDOA)定位系统中雷达信号的定位模糊问题,该文分析了高重频信号的模糊特性,演示了虚假定位点的产生过程,提出一种基于时差序列变化趋势匹配(VTMT)的定位模糊消除算法。在测量时差序列与定位结果对应的理论时差序列之间的残差近似服从正态分布的条件下,通过两个序列的欧式距离作为相似程度衡量依据,筛选出测量时差线与理论时差线最为接近的定位点作为目标辐射源真实位置。校验台测试信号验证了该算法的有效性。仿真结果表明,该算法能够显著提高无模糊定位概率,对长基线时差定位系统中雷达信号的定位具有较高的应用价值。     

星基增强系统接收机中的导航比特同步设计与性能仿真

星基增强系统(SBAS)中导航电文速率为500符号/秒,针对其弱信号时找导航比特边界难的特点,提出了基于最大似然算法的比特同步算法,给出了在SBAS接收机中比特同步的应用公式和实现方法,并进一步创新性地设计了包含有软判决和多次判决的比特同步综合流程;最后在多种导航比特分布的情形下,对最大似然比特同步算法进行了不同载噪比下的性能仿真,确认了此算法在接收信号很弱时仍然有效。     

Future IoT‐enabled threats and vulnerabilities: State of the art,challenges, and future prospects

In the recent era, the security issues affecting the future Internet‐of‐Things (IoT) standards has fascinated noteworthy consideration from numerous research communities. In this view, numerous assessments in the form of surveys were proposed highlighting several future IoT‐centric subjects together with threat modeling, intrusion detection systems (IDS), and various emergent technologies. In contrast, in this article, we have focused exclusively on the emerging IoT‐related vulnerabilities. This article is a multi‐fold survey that emphasizes on understanding the crucial causes of novel vulnerabilities in IoT paradigms and issues in existing research. Initially, we have emphasized on different layers of IoT architecture and highlight various emerging security challenges associated with each layer along with the key issues of different IoT systems. Secondly, we discuss the exploitation, detection, and defense methodologies of IoT malware‐enabled distributed denial of service (DDoS), Sybil, and collusion attack capabilities. We have also discussed numerous state‐of‐the‐art strategies for intrusion detection and methods for IDS setup in future IoT systems. Third, we have presented a brief classification of existing IoT authentication protocols and a comparative analysis of such protocols based on different IoT‐enabled cyber attacks. For conducting a real‐time future IoT research, we have presented some emerging blockchain solutions. We have also discussed a comparative examination of some of the recently developed simulation tools and IoT test beds that are characterized based on different layers of IoT infrastructure. We have also outlined some of the open issues and future research directions and also facilitate the readers with broad classification of existing surveys in this domain that addresses several scopes related to the IoT paradigm. This survey article focuses in enabling IoT‐related research activities by comparing and merging scattered surveys in this domain.     

A new feature extraction and attacking node classification framework using PDCFE‐HPSMM model in cognitive radio networks

The increasing demand of wireless communication introduces a challenge to an effective spectrum utilization. In wireless communication systems, the Cognitive Radio (CR) has emerged as a new key technology to address this issue, which allows an opportunistic access to the spectrum. The CRs form a CRN by extending the radio link features to network layer functions. The existing CR based wireless communication techniques has some drawbacks such as, inability to differentiate interference or noise from primary signals, it does not distinguish the different types of noise, low performance, not effective in spread spectrum detection, long observation time and high computational cost. To overwhelm these disadvantages, a novel method, namely, partial distribution based cyclostationary feature extraction–hidden probability state Markov model (PDCFE‐HPSMM) is proposed in this work. The main intention of this technique is to extract the node features, classify the attacker nodes and predict the licensed and unlicensed bandwidth. At first, the CRN is formed with some set of CR nodes, and the communication links between the nodes are estimated. Then, the node features are extracted by employing the PDCFE technique. After that, the attacking nodes are classified based on those features with the help of a HPSMM classification technique. If the attacker is present in the network, the link between the attacking nodes to other nodes is disconnected; otherwise, the communication link is updated. In this work, the Rayleigh channels are used to predict the licensed and unlicensed bandwidth. Again, the HPSMM model is employed to optimally select the channel, and the scheduling technique is implemented to check the status of the channel for message transmission. If the channel is not busy, the message signals are multiplexed and transmitted to the receiver via the selected channel. The novel concept of this paper is, the proposed PDCFE technique extracts the features of the nodes in CRN; based on these features, the attacker nodes in the network are classified with the help of HPSMM technique. Moreover, the HPSMM is used to select the optimal channel for message transmission. The experimental results evaluate the performance of the proposed system in terms of bit error rate (BER), error rate, relay, false detection rate (FDR) and cumulative distribution function (CDF). Copyright © 2016 John Wiley & Sons, Ltd.