We propose analytical formulations, approximations, upper and lower bounds for the angle sweep of maximum magnitude of fractional Fourier transform of mono- and multicomponent linear frequency ...modulated (LFM) signals. We employ a successive coarse-to-fine grid-search algorithm to estimate the chirp rates of multicomponent nonseparable LFM signals. Extensive numerical simulations show the validity of analytical formulations and performance of the proposed estimator. Obtained analytical results may also find themselves other application areas, where nonstationary signals are of interest.
A microwave photonic multiple-input and multiple-output (MIMO) radar is proposed and demonstrated to implement high-resolution imaging. In the proposed system, multiple orthogonal linearly frequency ...modulated (LFM) signals are generated by heterodyning between two optical frequency combs, which enables a MIMO transmitting array with a simple and reconfigurable structure. The receiving array uses photonic frequency mixing to implement multiple channel separation and de-chirp processing simultaneously. This microwave photonic MIMO radar can have a large operation bandwidth and a large equivalent aperture, which helps to achieve high-resolution imaging in both range and azimuth directions. In the experiment, a microwave photonic <inline-formula><tex-math notation="LaTeX">\text{4}\times \text{8}</tex-math></inline-formula> MIMO radar is established with a 2-GHz bandwidth in each channel. Based on this MIMO radar, high-resolution back-projection (BP) imaging with a theoretical range resolution of 7.5 cm and azimuth resolution of 1.85° is demonstrated. The experimental results can verify the feasibility of the proposed MIMO radar, which is a good solution to high-resolution radar imaging by combining microwave photonic and MIMO technologies.
Simultaneous generation of linear frequency-modulated (LFM) and phase-coded LFM microwave waveform with a large time-bandwidth-product (TBWP) based on an improved frequency-sweeping optoelectronic ...oscillator (OEO) is proposed and experimentally demonstrated. The key significance of the frequency-sweeping OEO is that a near-zero-dispersion single-mode-fiber (SMF) is introduced into the loop, which can not only avoid the limitation of high frequency oscillation caused by dispersion, but also construct long OEO delay loop to realize large temporal duration. A fiber-Bragg-grating Fabry–Perot (FBG-FP) with large reflection bandwidth is also adopted to construct microwave photonic filter (MPF) with wide tuning range of central frequency. Thus, the limitations on temporal duration and oscillation frequency are solved and a LFM microwave waveform with large TBWP can be generated. Simultaneously, by modulating the optical sideband from the MPF and beating the phase-modulated signal with a portion of frequency-sweeping laser light, a phase-coded LFM microwave waveform can be generated. In the experimental demonstration, a LFM microwave waveform with a chirp rate of 0.736 GHz∕μs and a large TBWP of 173,856 is generated, and reconfiguring central frequency and bandwidth is also completed. Simultaneously, a phase-coded LFM microwave waveform with a bandwidth of 8 GHz and a TBWP of 173,856 is also experimentally demonstrated.
This paper investigated a Subsample Time delay Estimation (STE) algorithm based on the amplitude of cross-correlation function to improve the estimation accuracy. In this paper, a rough time delay ...estimation is applied based on traditional cross correlator, and a fine estimation is achieved by approximating the sampled cross-correlation sequence to the amplitude of the theoretical cross-correlation function for linear frequency modulation (LFM) signal. Simulation results show that the proposed algorithm outperforms existing methods and can effectively improve time delay estimation accuracy with the complexity comparable to the traditional cross-correlation method. The theoretical Cramér-Rao Bound (CRB) is derived, and simulations demonstrate that the performance of STE can approach the boundary. Eventually, four important parameters discussed in the simulation to explore the impact on Mean Squared Error (MSE).
With the increase of radar signal bandwidth and the application of RF directing sampling technology, wideband radars are facing greater pressures for data transmission, storage, and processing. Based ...on the relationship between linear frequency modulation (LFM for short) signal and LFM-stepped signal, synthesis method of high-resolution range profile (HRRP for short) for LFM step signal can be applied to LFM signal. Combining the synthesis method of HRRP for LFM signal with compressed sensing theory, this study proposes a new compression method for wideband radar echo with LFM signal style based on random segment selection and analyses the constraint conditions of the proposed data compression method. Finally, the validity and practicability of the proposed data compression method are verified from two aspects: simulation experiment and actual data processing.
•A review of frequency regulation in power system with/without renewable energy.•Frequency regulation aspects with a complete outlook of state-of-the-art of development.•Comprehensive review of ...different controllers for load frequency management.•Review of latest soft computing techniques for load frequency management.•An outlook of future research scope regarding the LFM controller and algorithmic techniques.
Load frequency management (LFM) has become more significant in modern power systems due to variation demand and generation profiles. Further, integration of renewable energy resources (RSs) into the power systems makes LFM job more challenging. To this end, the concept of secondary frequency control, or LFM, objective is introduced to single and multi-area power systems to manage the power mismatch of the particular power system. This helps regulate the system frequency for single/multi area systems and schedule tie-line power exchange for multi area systems. To control and reduce the system frequency deviation, load frequency controllers are introduced. However, to achieve optimal power management, intelligent soft computing techniques that take different controllers into account are utilized. This paper aims to provide a review of different controllers utilized in traditional as well as renewable energy-based power system for LFM such as; classical controllers, fractional order controllers, cascaded controllers, sliding mode controller (SMC), tilt-integral-derivative controllers, H-infinity controller and other recently developed controllers. Some popular and recently adopted soft-computing tools for power management such as; genetic algorithm, particle swarm optimization, firefly, cuckoo search techniques, fuzzy tuning tool, model predictive technique and other newer once have been explored. Finally, the paper concludes by highlighting some future scope in the field of LFM.
•Introduce a methodology to determine and deliver optimal flexibility to the distribution network.•Maximize social welfare within the local flexibility market.•Integrate the innovative concept of the ...value of flexibility loss in the local flexibility market.•Propose a linear programming model to optimize flexibility in local flexibility markets.•Enable flexibility exchange (import and export) with the Transmission System Operator.
The increasing integration of Renewable Energy Sources (RESs) poses challenges due to their unpredictable nature. To address these challenges, flexible Distributed Energy Resources (DERs), such as Distributed Generators (DGs), Flexible Loads (FLs), and Energy Storage Systems (ESSs), have emerged in distribution networks. This paper proposes a linear programming formulation for optimizing flexibility provision in the Local Flexibility Market (LFM) to maximize Social Welfare (SW), contrasting with existing literature. The concept of the Value of Flexibility Loss (VOFL) is introduced to enable the Distribution System Operator (DSO) to optimize flexibility procurement, ensuring economic profitability for both providers and consumers. Additionally, the DSO can interchange flexibility with the Transmission System Operator (TSO) based on economic incentives. Numerical results demonstrate the accuracy and efficiency of the proposed model.
•The proposed method effectively reduces the number of redundant calculations.•A reasonable search strategy is formulated.•An efficient method based on FRFT domain filter is proposed to separate the ...multi-component LFM signal.•The CRLB is derived for the unbiased estimation error of LFM signal parameters.•The estimation of parameters is achieved with high accuracy even in low SNR.
In this paper, an efficient and robust algorithm for fast parameter estimation and separation of multi-component LFM signals is proposed, which is suitable for processing overlapping and intersect LFM signals in the time-frequency plane. First, the key innovative idea of the algorithm is to use the fourth-order origin moment of fractional Fourier transform spectrum to formulate a reasonable search strategy for the optimal rotation order to achieve parameter estimation, and propose a step-by-step filtering technique for signals in the fractional Fourier domain achieve the signal separation we are interested in. Then, the proposed algorithm overcomes the problems of low estimation accuracy and large computational of traditional two-dimensional search and time-frequency analysis methods by virtue of good impulse characteristics and anti-noise performance. Different from existing solutions, the method avoid interference problems between multiple signals with close time-frequency distance, overlapping and cross components. Moreover, the error analysis of the linear frequency modulation signal is carried out, and the Cramer-Rao lower bound for the unbiased estimation of the parameters is derived. Finally, the simulation results demonstrate the accuracy and effectiveness of the proposed method in noisy environments by comparing with traditional methods and existing methods.
•Developing an integrated framework of a local flexibility market design as well as a flexibility allocation process.•Being compatible with the wholesale energy market based on a fair and competitive ...mechanism.•Suggesting a rational formulation for the flexibility price.•Proposing a linear optimization problem for each market player’s participation in the wholesale energy and local flexibility markets.
With the high penetration of Renewable Energy Resources (RERs) into power systems, distribution systems are facing various challenges due to their intermittency and uncertainty. One of the ways to cope with uncertainty and variability of the RERs is utilizing flexibility by market tools to enable active system management. Local Flexibility Markets (LFMs) provide opportunities to trade flexibility among distribution system operators and other participants (e.g., aggregators) in an economically efficient way. This research proposes an interactive framework for prosumers by a market-based platform to utilize and trade flexibility. The suggested framework comprises a novel flexibility allocation process which is performed through a Day-Ahead (DA) flexibility market mechanism. In the proposed process, market participants adjust their flexibility bids, which is done under a fair and competitive market mechanism. The results of the simulation validate the major features of the proposed framework and satisfy DSO’s purposes in congestion management.
Linear frequency modulation (LFM) signals are widely used in modern radar systems owing to their intrinsic pulse compression capability but are restricted due to a limited range-Doppler resolution. ...On the other hand, dual- or cross-LFM signals have complementary LFM waveforms at the same time instant that reduces the range-Doppler coupling and thus improving range-Doppler resolution. We propose a simple microwave-photonic-based approach to generate multiband dual- and cross-LFM waveforms using only a single dual-drive Mach–Zehnder modulator (DDMZM). A theoretical analysis is carried out, which is modeled and verified through experiments. Dual- and cross-LFM waveforms at a carrier frequency of 6 GHz and 18 GHz with a bandwidth of 2 GHz is generated by controlling the DC and RF bias of the DDMZM. The tunability of the carrier frequency from 3 GHz to 9 GHz is also verified. A range resolution of 6.3 cm for dual- and cross-LFM waveforms, is obtained with a time-bandwidth-product (TBWP) of 20,000. The proposed technique is a promising solution for dual- and cross-LFM waveform generation in two-band multipurpose radar systems.
•Dual- or cross-LFM waveform generation with only a single dual-drive Mach-Zehnder modulator at a single DC bias setpoint.•Cross-LFM generation is achieved by using a simple electronic time-shift.•Spectral bandwidth doubling resulting in improved range resolution by a factor of ‘2’.•Multiband dual- or cross-LFM generation by only increasing the power (modulation index) of the RF carrier.
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