Time Bandwidth Research Articles

Photonic Generation of a Phase-Coded Chirp Microwave Waveform With Increased TBWP

Photonic generation of a phase-coded chirped microwave waveform with an increased time bandwidth product (TBWP) using a frequency-tunable optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The frequency-tunable OEO is implemented using a tunable laser source (TLS), a phase modulator (PM), a phase-shifted fiber Bragg grating, and a photodetector (PD), with the frequency tuning realized by tuning the wavelength of the TLS. A frequency-tunable optical sideband with a frequency that is equal to that of the optical carrier plus the OEO oscillation frequency is generated by the OEO, which is then orthogonally polarization multiplexed with the optical carrier from the TLS at a polarization beam combiner, and applied to a polarization modulator, to which a binary phase-coded parabolic electrical signal is applied. By beating the two orthogonally polarized optical signals at a PD, a phase-coded chirped microwave waveform is generated. The TBWP is significantly increased due to the increase of the temporal duration of the microwave waveform. The proposed approach is experimentally demonstrated. Two phase-coded chirped microwave waveforms with TBWPs of 58.5 and 80 000 using two phase coding signals corresponding to a 13 Barker code and a 20480-bit pseudorandom sequence are generated.

SECURE HYBRID ENCRYPTION USING ECC IN CLOUDS

The evolution of the cloud computing furnishes a better way for the data storage. ABE with delegation is accustomed for accessing the data and keep it confidential. But this scheme faces some limitations like the cloud servers can replace the cipher text with some malignant intent. They may also cheat the eligible users as unauthorized ones. The cloud servers even face external threats like the security attacks. So, to protect against the security attacks and to preserve the data integrity in the cloud, a hybrid encryption with VD scheme is proposed by Xu et al. Even this scheme faces the challenges like having larger keys, more computational time and vulnerability to man-in-the-middle attacks. A secure Hybrid Encryption using ECC in clouds is proposed to overcome these problems. The application of Elliptic Curve Cryptography and its algorithms in the proposed work provides a greater security because of the Elliptic Curve Discrete Logarithm Problem. The proposed work ensures greater security with the aid of a smaller key size. It also ensures less computational time, less memory and communication bandwidth

Container-as-a-Service at the Edge: Trade-off between Energy Efficiency and Service Availability at Fog Nano Data Centers

In the last few years, we have witnessed the huge popularity of one of the most promising technologies of the modern era: the Internet of Things. In IoT, various smart objects (smart sensors, embedded devices, PDAs, and smartphones) share their data with one another irrespective of their geographical locations using the Internet. The amount of data generated by these connected smart objects will be on the order of zettabytes in the coming years. This huge amount of data creates challenges with respect to storage and analytics given the resource constraints of these smart devices. Additionally, to process the large volume of information generated, the traditional cloud-based infrastructure may lead to long response time and higher bandwidth consumption. To cope up with these challenges, a new powerful technology, edge computing, promises to support data processing and service availability to end users at the edge of the network. However, the integration of IoT and edge computing is still in its infancy. Task scheduling will play a pivotal role in this integrated architecture. To handle all the above mentioned issues, we present a novel architecture for task selection and scheduling at the edge of the network using container-as-a-service (CoaaS). We solve the problem of task selection and scheduling by using cooperative game theory. For this purpose, we developed a multi-objective function in order to reduce the energy consumption and makespan by considering different constraints such as memory, CPU, and the user's budget. We also present a real-time internal and external container migration technique for minimizing the energy consumption. For task selection and scheduling, we have used lightweight containers instead of the conventional virtual machines to reduce the overhead and response time as well as the overall energy consumption of fog devices, that is, nano data centers (nDCs). Our empirical results demonstrate that the proposed scheme reduces the energy consumption and the average number of SLA violations by 21.75 and 11.82 percent, respectively.

AutoMigrate: a framework for developing intelligent, self-managing cloud services with maximum availability

Cloud services are on-demand services provided to end-users over the Internet and hosted by cloud service providers. A cloud service consists of a set of interacting applications/processes running on one or more interconnected VMs. Organizations are increasingly using cloud services as a cost-effective means for outsourcing their IT departments. However, cloud service availability is not guaranteed by cloud service providers, especially in the event of anomalous circumstances that spontaneously disrupt availability including natural disasters, power failure, and cybersecurity attacks. In this paper, we propose a framework for developing intelligent systems that can monitor and migrate cloud services to maximize their availability in case of cloud disruption. The framework connects an autonomic computing agent to the cloud to automatically migrate cloud services based on anticipated cloud disruption. The autonomic agent employs a modular design to facilitate the incorporation of different techniques for deciding when to migrate cloud services, what cloud services to migrate, and where to migrate the selected cloud services. We incorporated a virtual machine selection algorithm for deciding what cloud services to migrate that maximizes the availability of high priority services during migration under time and network bandwidth constraints. We implemented the framework and conducted experiments to evaluate the performance of the underlying techniques. Based on the experiments, the use of this framework results in less down-time due to migration, thereby leading to reduced cloud service disruption.

Passively mode-locked soliton femtosecond pulses employing graphene saturable absorber

We demonstrate a passively mode-locked fiber laser incorporating graphene thin film (GTF) as saturable absorber (SA). The SA is fabricated by sandwiching the GTF between two single mode fiber ferrules through a fiber adaptor. The transmission loss at 1560nm and non-linear saturation absorption modulation depth for GTF-SA are 0.8dB and 2.90%, respectively. An erbium-doped fiber laser cavity is constructed to verify the functionality of GTF-SA and is designed to have net anomalous dispersion. It generates large spectral width of 4.99nm with pulse repetition rate of 9.655MHz and pulse width of 670fs. Net anomalous dispersion and time bandwidth product higher than the sech2 transform-limited pulse validate the experimental result. In short, we demonstrate high performance GTF-SA that is able to generate ultrafast pulse duration in femtosecond range effortlessly with simple and green SA fabrication procedures.

Filter-Based Design of Noise Radar Waveform With Reduced Sidelobes

Noise radars possess several advantageous properties, including low probability of detection and identification, especially when working in continuous-wave mode. One of the main drawbacks of such radars is the occurrence of the masking effect, when a weak target echo is masked by the sidelobes of a strong target echo. The sidelobes of the ambiguity function emerge on the level of the time–bandwidth product below the main peak and are spread in the entire range–Doppler plane. While most approaches to mitigate the masking effect focus on the processing of the received signal, it is possible to move the computation burden to the waveform design phase. This paper describes a filter-based method of creating noise-like waveforms that have very low sidelobes in the area of certain range and Doppler shifts. Both theoretical analysis and measurement results are presented and compared with the lattice filter method of masking effect cancellation.

The Dependence of Signal Coherence on Sea-Surface Roughness for High and Low Duty Cycle Sonars in a Shallow-Water Channel

It is anticipated that high duty cycle (HDC) sonars will typically maintain the same bandwidth as the pulsed active sonars (PASs) that they might replace. This will significantly increase their time–bandwidth product, but may not produce the increased gain anticipated, if there are coherence limitations of the acoustic channel. To compare performance of HDC with conventional PAS in the littorals, a set of experiments was conducted as part of the Target and Reverberation Experiment in spring 2013 (TREX13). This paper presents the results of an examination of short-range single surface-reflection echoes, and longer range target echoes from an air hose. The Pearson product–moment correlation coefficient (Pearson's $R$ ) was used to confirm significance of the results. Measurements showed that for an 18-s HDC pulse, the mean (coherent) component of the specular arrival decreased by as much as 5 dB as root mean square (rms) surface roughness increased, whereas the 0.5-s PAS pulse echoes showed no correlation with roughness. The standard deviations of the mean levels were used to examine the incoherent (scattered) component of the specular arrivals. The incoherent component of the specular arrival increased with the product of the surface correlation length and the square of the rms roughness, for both HDC and PAS, with the PAS data having a 1-dB higher standard deviation. A normal mode propagation model and a rough surface scattering model used in conjunction with a simple model that accounts for coherence loss from the matched filter were successfully used to interpret the results.

Adaptive non-uniform photonic time stretch for blind RF signal detection with compressed time-bandwidth product

Photonic time stretch significantly extends the effective bandwidth of existing analog-to-digital convertors by slowing down the input high-speed RF signals. Non-uniform photonic time stretch further enables time bandwidth product reduction in RF signal detection by selectively stretching high-frequency features more. However, it requires the prior knowledge of spectral-temporal distribution of the input RF signal and has to reconfigure the time stretch filter for different RF input signals. Here we propose for the first time an adaptive non-uniform photonic time stretch method based on microwave photonics pre-stretching that achieves blind detection of high-speed RF signals with reduced time bandwidth product. Non-uniform photonic time stretch using both quadratic and cubic group delay response has been demonstrated and time bandwidth product compression ratios of 72% and 56% have been achieved respectively.

Efficient forward-looking imaging via synthetic bandwidth azimuth modulation imaging radar for high-speed platform

This paper deals with the forward-looking imaging problem under high-speed platform for the airborne single-channel forward-looking radar (ASFLR). Biphase-based synthetic bandwidth azimuth modulation imaging radar (Bi-SBAMIR) can be used to increase the azimuth resolution. However, the performance degrades significantly when the velocity of the platform is high. To solve this problem, a more generalized SBAMIR framework based on linear frequency modulation (LFM) waveform (LFM-SBAMIR) is proposed. The LFM waveform is more Doppler tolerant than the biphase waveform, which makes it a good choice for high speed platform. In LFM-SBAMIR, the synthetic bandwidth of the received signal has two parts: the modulation bandwidth and the Doppler bandwidth. Therefore, large synthetic bandwidth can be achieved by increasing the modulation bandwidth even in the case of small Doppler bandwidth, and high azimuth resolution can be achieved after matched filtering. Moreover, it is firstly proved that the azimuth resolution is proportional to the time bandwidth product (TBP) of the modulated LFM waveform. Finally, the azimuth resolution performance under different TBPs, SNRs and velocities are analyzed. The performance assessment conducted by resorting to simulated data, also in comparison to the previously proposed Bi-SBAMIR method, has confirmed the effectiveness of the newly proposed algorithm in high-speed platform scenarios.

Privacy-area Aware All-dummy-based Location Privacy Algorithms for Location-based Services

Location-Based Services (LBSs) have become one of the most popular activities in our daily life. With the rapid advance of LBSs, there are more threats to users’ privacy. For this reason, while enjoying the convenience provided by LBSs, we have to protect our location privacy. In this paper, we propose two all-dummy-based location privacy algorithms to achieve k-anonymity for privacy-area aware users in LBSs. Different from previous work, on the client side, our method can prevent the center attack and border attack through transforming the actual location to an anchor and the request we send to the LBSs doesn’t contain the actual location of the user. On the server side, we use a rough query before precise query to reduce the processing time and transmission bandwidth. It only returns the results that the client needs. Evaluation results show that our methods can provide more effective privacy protection and lower computation and communication cost.

Giant pulses of the Crab Nebula pulsar as an indicator of a strong electromagnetic wave

The spectra and visibility functions of giant pulses of the Crab Nebula pulsar derived from VLBI observations carried out through the “RadioAstron” project in 2015 are analyzed. Parameters of the scattering of the pulses in the interstellar medium are measured, namely, the scattering time and decorrelation bandwidth. A comparative analysis of the shapes of the spectra and visibility functions of giant pulses obtained in real observations and via modeling of their scattering is carried out. The results suggest the presence of short bursts (dt < 30 ns) in the structure of the giant pulses at 1668 MHz, whose brightness temperatures exceed 1038 K. These pulses propagate in the pulsar magnetosphere in a strong electromagneticwave regime, leading to the generation of additional radiation perpendicular to the direction of propagation of the giant pulses. This radiation may be associated with anomalous components of the mean pulse profile observed at frequencies above 4 GHz.

Piecewise Nonlinear Frequency Modulation Waveform for MIMO Radar

We propose a piecewise nonlinear frequency modulation (PNLFM) waveform for a multiple-input multiple-output (MIMO) radar. Each subpulse in the waveform set is divided into three segments. The first and the third segments are linear frequency modulation (LFM) signals, whereas the second segment is a nonlinear frequency modulation (NLFM) signal. The bandwidths and durations of subpulses are the same, whereas they can be different for each segment in the subpulse. In addition, the nonlinear time–frequency function of the second segment is controlled to improve the range and Doppler sidelobe suppression. A genetic algorithm is implemented to optimize the performance by maximally suppressing the autocorrelation sidelobe and cross correlation in range, Doppler, and angle. The MIMO radar performance is demonstrated via computation of the ambiguity function, autocorrelation function, and cross-correlation function. Numerical results are presented to show waveform properties and to compare with some existing MIMO radar waveforms. The proposed PNLFM waveform has low autocorrelation sidelobes and low cross correlation in range and Doppler, which sits at a level determined largely by the chosen time–bandwidth product.

S&lt;SUP align="right"&gt;3&lt;/SUP&gt;R: storage-sensitive services redeployment in the cloud

Services redeployment is one of the critical techniques for energy-efficiency in cloud data centres. In recent years, cloud providers have been providing local storage for cloud services, since it offers a better performance with identified price. Nevertheless, most existing work did not consider the problems introduced by utilising local storage, e.g., migrating much more data, and therefore consuming much more migration time and network bandwidth. Meanwhile, instance migration is a costly operation, the number of migrated instances must be considered. However, the data size and the number of instances on servers are not often accordant, and therefore a tradeoff should be made. To address this problem, this paper proposes S3R, a storage-sensitive services redeployment approach. S3R firstly builds a tradeoff model to estimate the release cost for each server, and then adopts a FFD-based heuristic algorithm to migrate/redeploy instances. Evaluation results on production traces demonstrate the effectiveness of S3R.

S&lt;SUP align="right"&gt;3&lt;/SUP&gt;R: storage-sensitive services redeployment in the cloud

Services redeployment is one of the critical techniques for energy-efficiency in cloud data centres. In recent years, cloud providers have been providing local storage for cloud services, since it offers a better performance with identified price. Nevertheless, most existing work did not consider the problems introduced by utilising local storage, e.g., migrating much more data, and therefore consuming much more migration time and network bandwidth. Meanwhile, instance migration is a costly operation, the number of migrated instances must be considered. However, the data size and the number of instances on servers are not often accordant, and therefore a tradeoff should be made. To address this problem, this paper proposes S3R, a storage-sensitive services redeployment approach. S3R firstly builds a tradeoff model to estimate the release cost for each server, and then adopts a FFD-based heuristic algorithm to migrate/redeploy instances. Evaluation results on production traces demonstrate the effectiveness of S3R.

Bandwidth extension, linearity enhancement, and cost reduction techniques for continuous‐time channel‐select filters

SummaryAchieving a wide bandwidth in a conventional active‐RC filter requires large power consumption and is often accompanied by significant performance degradation. In this paper, a new structure to implement active‐RC continuous‐time filters and also a new frequency compensation scheme for the operational amplifiers that are the main building blocks of active‐RC filters are proposed. Exploiting these techniques increases the maximum possible bandwidth with lower power consumption in comparison with the conventional architectures, reduces die area, and enhances the dynamic range. The effectiveness of these methods has been verified by analysis and simulation of the conventional and proposed filters under identical conditions. Both the analytical investigations and extensive simulation results prove that the adopted techniques improve the performance of continuous‐time filters considerably in terms of bandwidth and linearity while reducing the die area. Simulations have been carried out in a standard 90‐nm CMOS process by using Advanced Design System (ADS), and the proposed filter features 11.08‐dB spurious‐free dynamic range improvement and 5.9 times bandwidth enhancement. Also, the total on‐chip capacitance is made 2.4 times smaller by using the new biquad structure. Copyright © 2016 John Wiley &amp; Sons, Ltd.

80 GHz AlGaInAs/InP colliding-pulse mode-locked laser with high pulse power

We theoretically analyze the impact of a saturable absorber (SA) length on the pulse power of a semiconductor mode-locked laser and find that in the range of the SA length from 1.5 to 7%, a laser with a longer SA can generate pulses with a higher power. Based on the simulation, we demonstrate a colliding-pulse mode-locked laser with an 80 µm SA. The device generates pulses at 80 GHz, with a pulse width of 1.75 ps, peak power of 188 mW, pulse energy of 0.33 pJ, and time–bandwidth product of 0.51. The results provide new possibilities for the design of high-repetition frequency high-pulse power mode-locked lasers.

Effect of Laser Modulation on Dispersion Induced Chirp Microwave Signal Generation by Using Temporal Pulse Shaping Technique

A photonic approach for generating an arbitrary chirp microwave waveform using optical coupler of different length is proposed and experimentally demonstrated. The chirp microwave waveform can be used in Radar system to improve its range Doppler resolution. The paper give the specific details about various performance parameters like input signal frequency and power, output signal parameters viz output frequency, chirp rate, chirp bandwidth and time bandwidth product etc. In this proposed approach two single mode optical fibers of different lengths are used to create the phase variation of the light coming from the continuous wave laser. The overall model and its performance parameters are computed on optiwave software and compared with experimental results carried out in lab which shows the validity of our experimental setup.

Enhanced processing gain via pulse polarity switching in an RF photonic phase filter.

Fast pulse polarity switching is proposed and demonstrated to enhance processing gain in a comb-based radio-frequency photonic phase filter. The polarity switching scheme overcomes previous limits on time bandwidth product and processing gain based on the number of optical frequency comb lines. In an experiment with broadband jamming noise, the peak signal-to-noise ratio of compressed RF output pulses is improved by ~30 dB compared to the input average signal-to-noise ratio.

Load Frequency Control with Communication Topology Changes in Smart Grid

In this paper, the quality of service of communication infrastructure implemented in multiarea power system for load frequency control application is assessed in smart grid environment. In this study, network induced effects time delay, packet loss, bandwidth, quantization, and change in communication topology (CT) has been addressed to examine the system performance in closed loop. Uncertainty in time delay is approximated using deterministic and stochastic models. The network is modeled considering different network configurations, i.e., change in CT. The modeled communication network guarantees control relevant properties, i.e., stability. The decentralized controller and linear matrix inequality-based linear quadratic regulator is implemented to reduce the dynamic performance (mean square error of states variables) of power system as CT changes. Simulation results suggest that the proposed scheme of networked control is superior with respect to other design methods available in the literature, and thus robust to communication imperfections.

Detecting pulsars with interstellar scintillation in variance images

Pulsars are the only cosmic radio sources known to be sufficiently compact to show diffractive interstellar scintillations. Images of the variance of radio signals in both time and frequency can be used to detect pulsars in large-scale continuum surveys using the next generation of synthesis radio telescopes. This technique allows a search over the full field of view while avoiding the need for expensive pixel-by-pixel high time resolution searches. We investigate the sensitivity of detecting pulsars in variance images. We show that variance images are most sensitive to pulsars whose scintillation time-scales and bandwidths are close to the subintegration time and channel bandwidth. Therefore, in order to maximise the detection of pulsars for a given radio continuum survey, it is essential to retain a high time and frequency resolution, allowing us to make variance images sensitive to pulsars with different scintillation properties. We demonstrate the technique with Murchision Widefield Array data and show that variance images can indeed lead to the detection of pulsars by distinguishing them from other radio sources.