Fractional Fourier domain hopped communication method based on chirp modulation for underwater acoustic channels

To improve the data rate of underwater acoustic frequency-hopped communications, frequency hopping is applied to different orders of fractional Fourier domain (FrFD), to enable non-intrusive, bandwidth-limited acoustic communications. An FrFD frequency-hopped communication method based on chirp modulation, namely multiple chirp shift keying-FrFD hopping (MCSK-FrFDH), is proposed for underwater acoustic channels. Validated by both simulations and experimental results, this method can reach a bandwidth efficiency twice more than conventional frequency-hopped methods with the same data rate and anti-multipath capability, suggesting that the proposed method achieves a better performance than the traditional frequency hopped communication in underwater acoustic communication channels. Results also show that in practical scenarios, the MCSK-FrFDH system with longer symbol length performs better at the low signal-to-noise ratio (SNR), while the system with larger frequency sweeping range performs better at a high SNR.

Research on reliability index of a large communication network with domain partition and interconnection

In order to indicate the performances of a large-scale communication network with domain partition and interconnection today, a kind of reliability index weighed by normalized capacity is defined. Based on the route rules of network with domain partition and interconnection, the interconnection indexes among the nodes within the domain and among the domains are given from several aspects. It is expatiated on that the index can thoroughly represent the effect on the reliability index of the objective factor and the subjective measures of the designer, which obeys the route rules of a network with domain partition and interconnection. It is discussed that the defined index is rational and compatible with the traditional index.

INTERFERENCE MITIGATING BASED ON FRACTIONAL FOURIER TRANSFORM IN TRANSFORM DOMAIN COMMUNICATION SYSTEM

The method of FRactional Fourier Transform (FRFT) is introduced to Transform Domain Communication System (TDCS) for signal transforming in the paper after theoretical analysis. The method yields optimal Basis Function (BF) by FRFT with optimal transform angle. The TDCS using the proposed method has wider usable spectrum, stronger robustness and better ability of anti non-stationary jamming than using usual methods, such as Fourier Transform (FT), Auto Regressive (AR), Wavelet Transform (WT), etc. The main simulation results are as follows. First, the Bit Error Rate (BER) Pb is close to theoretical bound of no jamming no matter in single tone or in linear chirp interference. Second, the interference-to-signal ratio J /E is at least 12dB more than that of Direct Spread Spectrum System (DSSS) under the same BER if the spectrum hopping-to-signal ratio is 1:20 in chirp plus hopping interfering. Third, the Eb /N 0(when estimation difference is 90% between trans- mitter and receiver) is about 3.5dB or about 0.5dB (when estimation difference is 10% between transmitter and receiver) more than that of theoretical result when no estimation difference un-der Pb=10-2.

Health Monitoring of Long-Haul Fiber Communication System Using Chaotic OTDR

A novel chaotic optical time-domain reflectometry(OTDR)-based approach was proposed for monitoring long-haul fiber communication systems with multiple fiber segments. The self-phase modulation and group velocity dispersion effects of the optical cable was considered in demonstrating the proof-of-concept experiment and simulation. In experiments, the correlation peaks are clearly obtained from the correlation trace between the reference and reflected(or scattered) light signals propagating in three optical-fiber segments. The technique affords a high spatial resolution of 2 m, and further long-haul fiber simulations indicate that the sensing distance can be more than 3300 km. Thus, the new proposed technique can be effectively applied for health monitoring of long-haul fiber communication systems.

Comparisons of Short-Prefix Based Channel Estimation in Single-Carrier Communication Systems

In this paper, we compare the performance between channel estimation based on compressed sensing (CS) and time-domain least square (LS) for single-carrier (SC) communication system. Unlike the conventional channel estimation techniques such as frequency domain LS which is used in the condition that the length of pilot sequence is equal to data sequence, the estimation scheme based on CS requires smaller length of pilot sequence. In this paper, the corresponding system structure is presented. Zadoff-Chu sequence is used to generate the pilot sequence, which is shown to perform better in forming measurement matrix of CS than pseudo random sequence. Simulation results demonstrate that channel estimation based on CS achieves a better bit error rate (BER) performance than time domain LS with a smaller pilot sequence and thus raising data rate of the SC communication system.

Integrating IPsec within OpenFlow Architecture for Secure Group Communication

Network security protocols such as IPsec have been used for many years to ensure robust end-to-end communication and are important in the context of SDN. Despite the widespread installation of IPsec to date, per-packet protection offered by the protocol is not very compatible with OpenFlow and tlow-like behavior. OpenFlow architecture cannot aggregate IPsee-ESP flows in transport mode or tunnel mode because layer-3 information is encrypted and therefore unreadable. In this paper, we propose using the Security Parameter Index （SPI） of IPsec within the OpenFlow architecture to identify and direct IPsec flows. This enables IPsec to conform to the packet-based behavior of OpenFlow architecture. In addition, by distinguishing between IPsec flows, the architecture is particularly suited to secure group communication.

Generic Framework for Context-Aware Communication Services in Visitor’s Guides

Ubiquitous computing plays an increasing role in our lives. Typically, applications in ubiquitous computing environ-ments are context aware, namely, they react to the situations of their users at a given moment in time. One example for such environment is visitor’s guides in cultural heritage sites, supporting visits of individuals or small groups, such as families or friends. In such environments, it is well known that interaction among visitors enhances the overall visit experience. Recently, some research prototypes of visitor’s guides have started supporting such interaction through textual communication services embedded in them. However, these applications have so far been developed separately in an ad-hoc manner, despite common features and infrastructures they share. The research described here generalizes communication services offered by different visitor’s guides and suggests a systematic and generic framework for developing context-aware communication services for visitor’s guides. The specific communication services are abstracted into a domain model, later used in practice for adapting and tailoring the different concepts to the specific requirements of the applications. The framework is demonstrated in the specific setting of a multi-agent museum visitor’s guide system. We also show that the suggested framework is not limited to the specific museum visitor’s guide system but may facilitate the development of context-aware communication applications in general.

Optimizing Parallel Kinetic Monte Carlo Simulation by Communication Aggregation and Scheduling

Kinetic Monte Carlo(KMC)algorithm has been widely applied for simulation of radiation damage,grain growth and chemical reactions.To simulate at a large temporal and spatial scale,domain decomposition is commonly used to parallelize the KMC algorithm.However,through experimental analysis,we find that the communication overhead is the main bottleneck which affects the overall performance and limits the scalability of parallel KMC algorithm on large-scale clusters.To alleviate the above problems,we present a communication aggregation approach to reduce the total number of messages and eliminate the communication redundancy,and further utilize neighborhood collective operations to optimize the communication scheduling.Experimental results show that the optimized KMC algorithm exhibits better performance and scalability compared with the well-known open-source library—SPPARKS.On 32-node Xeon E5-2680 cluster(total 640 cores),the optimized algorithm reduces the total execution time by 16%,reduces the communication time by 50%on average,and achieves 24 times speedup over the single node(20 cores)execution.

OTFS on Overspread Doubly Selective Channel

The orthogonal time frequency space(OTFS)modulation proposed in recent years is considered to have superior performance than orthogonal frequency division multiplexing(OFDM)for the doubly selective(DS)channels.The works in the existing literature on OTFS mainly focus on the cases where the channels are underspread(i.e.,the product of the delay spread and the Doppler spread is less than 1).In the scenario of overspread DS channel,which has large delay spread and severe Doppler spread,such as underwater acoustic(UWA)channel,the channel model in delay-Doppler(DD)Domain derived by existing work is no longer applicable.In this paper,we derive a more generalized expression of the channel model in delay-Doppler domain,which allows the product of the delay spread and Doppler spread to be larger than1.The result shows that the existing channel model is just a special case of the one we proposed.Using the proposed channel matrix in DD domain,we build the OTFS detectors with the minimum mean square error(MMSE)and message passing(MP)algorithms on overspread doubly selective channel.Finally,simulation results are presented to verify the theoretical derivation and the effectiveness of the detectors.

LAPPED TRANSFORM DOMAIN INTERFERENCE EXCISION USING MODIFIED MEDIAN FILTER

A novel communication receiver which uses lapped transform(LT) incorporating modified median filter(MMF) algorithm was designed for narrow band interference(NBI) excision.Comparing to traditional Fourier Transform,LT has longer basis vectors,less spectral leakage,thus better frequency resolution.The LT domain MMF algorithm takes full advantages of the direct sequence spread spectrum signal,as well as the characteristics of LT,performs the transform domain filtering twice.The first filtering locates the position of interference and mitigates most of them.The second filtering is performed in a small neighborhood of the located interference.So LT domain MMF algorithm can completely mitigate the interference without distorting the desired signal.The simulation results demonstrate the improved BER(Bit Error Rate)performance and increased robustness of our receiver.

Speech Encryption in Linear Canonical Transform Domain Based on Chaotic Dynamic Modulation

In order to transmit the speech information safely in the channel,a new speech encryp-tion algorithm in linear canonical transform(LCT)domain based on dynamic modulation of chaot-ic system is proposed.The algorithm first uses a chaotic system to obtain the number of sampling points of the grouped encrypted signal.Then three chaotic systems are used to modulate the corres-ponding parameters of the LCT,and each group of transform parameters corresponds to a group of encrypted signals.Thus,each group of signals is transformed by LCT with different parameters.Fi-nally,chaotic encryption is performed on the LCT domain spectrum of each group of signals,to realize the overall encryption of the speech signal.The experimental results show that the proposed algorithm is extremely sensitive to the keys and has a larger key space.Compared with the original signal,the waveform and LCT domain spectrum of obtained encrypted signal are distributed more uniformly and have less correlation,which can realize the safe transmission of speech signals.

Adaptive frequency domain pre-equalization for white-LED nonlinearity in OFDM-based visible light communication systems

In visible light communication, orthogonal frequency division multiplexing （OFDM） is an effective approach to improve the system speed. However, the nonlinearity of the light-emitting diode （LED） suppresses the trans- mission performance. The low-frequency part of the transmitted signal from LED suffers more from nonlinearity. Therefore, a pre-equalization scheme which suppresses the low frequency part of the OFDM signal and enhances the high frequency part can decrease the impact of LED nonlinearity. The experimental results show that the bit-error rate performance is largely enhanced by the pre-compensation.

An Algebraic Detection Approach for Control Systems under Multiple Stochastic Cyber-attacks

In order to compromise a target control system successfully, hackers possibly attempt to launch multiple cyberattacks aiming at multiple communication channels of the control system. However, the problem of detecting multiple cyber-attacks has been hardly investigated so far. Therefore, this paper deals with the detection of multiple stochastic cyber-attacks aiming at multiple communication channels of a control system. Our goal is to design a detector for the control system under multiple cyberattacks. Based on frequency-domain transformation technique and auxiliary detection tools, an algebraic detection approach is proposed. By applying the presented approach, residual information caused by different attacks is obtained respectively and anomalies in the control system are detected. Sufficient and necessary conditions guaranteeing the detectability of the multiple stochastic cyber-attacks are obtained. The presented detection approach is simple and straightforward. Finally, two simulation examples are provided, and the simulation results show that the detection approach is effective and feasible. © 2014 Chinese Association of Automation.

Multiple transformation analysis for interference separation in TDCS

Various types of interference signals limit the practical application of transform domain communication systems(TDCSs)in the severe electromagnetic field,an orthogonal basis learning method of transformation analysis(OBL-TA)is proposed to effectively address the problem of obtaining an optimal transform domain based on sparse representation.Then,the sparse availability is utilized to obtain the optimal transformation analysis by the iterative methods,which yields the sparse representation for transform domain(SRTD)in unrestricted form.In addition,the iterative version of SRTD(I-SRTD)in unrestricted form is obtained by decomposing the SRTD problem into three sub-problems and each sub-problem is iteratively solved by learning the best orthogonal basis.Furthermore,orthogonal basis learning via cost function minimization process is conducted by stochastic descent,which is assured to converge to a local minimum at least.Finally,the optimal transformation analysis is developed by the effectiveness of different transform domains according to the accuracy of the sparse representation and an optimal transformation analysis separately(OPTAS)is applied to the synthesized signal forms with conic alternatives,dualization,and smoothing.Simulation results demonstrate that the superiorities of the proposed methods achieve the optimal recovery and separation more rapidly and accurately than conventional methods.

THE STUDY OF A BOCC M-ARY SPREAD SPECTRUM SCHEME

M-ary spread spectrum technique has been found wide applications in wireless communications, but it needs too many orthogonal spreading codes and its despreading/demodulation is quite complex computationally, which limit its wider applications. This paper proposes a novel scheme for Code Division Multiple Access (CDMA) communication systems based on M-ary spread spectrum, where only one prototype spreading code is assigned to each user and the codes for different users are orthogonal or quasi-orthogonal with each other. The M spreading codes of each user to represent K bits data are generated by circularly shifting the assigned code and reversing its polarity. The spreading codes generated like that are called as BiOrthogonal Cyclic Codes (BOCCs). At the receiver of the system, a transform domain matched-filter implemented by means of Fast Fourier Transform (FFT) is employed to despread and demodulate the received signals, which has very low computational complexity. The results of simulation experiments and bit-error performance analysis show that the proposed scheme is practical and very useful in many cases.

A PMD-supported 100-Gb/s optical frequency-domain IM-DD transmission system

A novel method for distortion-free optical pulse transmission is theoretically proposed and simulated, in which two time lenses formed by dispersion fibers and quadratic phase modulations are utilized. One is used as an optical inverse Fourier transformation （OIFT） device to transform the initial time-domain data to frequency-domain one at the transmitter and the other as an optical Fourier transformation （OFT） device to recover the data at the receiver. By using the unchanged spectral envelope in linear optical fiber communication, the initial data can be recovered. Through simulations, a 10× 100 Gb/s intensity-modulated direct-detection （IM-DD） dense wavelength division multiplexing （DWDM） system over 20000 km transmission without the compensation for polarization mode dispersion （PMD） and dispersion slope is achieved, which can be used to upgrade the current 100Gb/s IM-DD system to a 100-Gb/s one directly.

基于神经网络的变换域通信系统接收技术

提出了一种不须要估计本地基函数的变换域通信系统接收机接收方法.详细分析了接收机的接收原理,以相关解调信号能量最大化为目标构建了接收机最优化接收模型,通过对模型求解得到了接收数据自协方差矩阵的最大特征值向量,此向量可作为接收端基函数实现最佳接收,从而引入基于Hebbian学习训练的神经网络完成最大特征值向量的自适应估计与数据接收.仿真结果表明:当算法收敛时,作为基函数估计的网络连接强度矢量与发送端基函数基本一致,并且当发送端改变基函数时,算法依然能够实现准确跟踪.系统的接收性能与收发两端基函数一致条件下的接收性能基本一致,当算法迭代次数为300,误码率为1×10-4时,系统的信噪比损失可小于1dB.

Distribution of a modulated squeezed state over a lossy channel

The distribution of a modulated squeezed state over a quantum channel is the basis for quantum key distribution（QKD） with a squeezed state. In this Letter, a modulated squeezed state is distributed over a lossy channel. The Wigner function of the distributed state is measured to observe the evolution of the quantum state over a lossy channel, which shows that the squeezing level and the displacement amplitude of the quantum state are decreased along with the increase of the channel loss. We also measure the squeezing level in the frequency domain by the frequency shift technique. The squeezing of the modulated squeezed state at the modulation frequency is observed in this way. The presented results supply a reference for a QKD with a squeezed state.

Compact triplexer in two-dimensional hexagonal lattice photonic crystals

We design a compact triplexer based on two-dimensional （2D） hexagonal lattice photonic crystals （PCs）. A folded directional coupler （FDC） is introduced in the triplexer beside the point-defect micro-cavities and line-defect waveguides. Because of the reflection feedback of the FDC, high channel drop efficiency can be realized and a compact size with the order of micrometers can be maintained. The proposed device is analyzed using the plane wave expansion method, and its transmission characteristics are calculated using the finite-difference time-domain method. The footprint of the triplexer is about 12 9 μm, and its extinction ratios are less than -20 dB for 1310 nm, approximately -20 dB for 1490 nm, and under -40 dB for 1550 nm, making it a potentially essential device in future fiber-to-the-home networks.

LDPC Coded TDS-OFDM for PLC Systems

Powerline communications （PLC） have drawn great interest in recent years. However, most PLC standards such as HomePlug AV use the cyclic-prefix OFDM （CP-OFDM） technology. This paper presents a broadband PLC system using low density parity check （LDPC） coded time domain synchronous OFDM （TDS-OFDM）, whose spectrum efficiency is about 10% higher than that of CP-OFDM. With the same bandwidth and the ability to combat the time delay spread as HomePlug AV, this system can provide a maximum throughput of 199.7 Mbps physical layer data rate. Simulations over the measured practical powerline channel in Beijing, China, show that LDPC in the TDS-OFDM system dramatically improves the bit error rate performance, and verify the feasibility and performance of the TDS-OFDM technology for PLC systems.