Hybrid Modulated Signal Research Articles

Sub-Nyquist sampling and parameter measurement of LFM-BPSK hybrid modulated signal

The linear frequency modulation-binary phase shift keying (LFM-BPSK) hybrid modulated signal combines the advantages of linear frequency modulation (LFM) and binary phase shift keying (BPSK). It has been extensively applied in the field of integrated radar communication. For the parameters estimation problem of LFM-BPSK signal, the traditional technologies based on the Nyquist theorem will bring a huge quantities of sample data with heavy data handling burden. This paper has presented a dual-channel cooperative sub-Nyquist sampling system for LFM-BPSK hybrid modulated signal. In the main channel, a time-interleaved sub-Nyquist sampling structure is proposed to resolve the frequency ambiguity problem caused by low sampling rate. In the other channel, a time-interleaved sub-Nyquist sampling structure based on self-mixing is proposed to estimate the phases of binary symbols and the positions of discontinuities from the low-rate samples. Simulation results have demonstrated the effectiveness and anti-noise performance of the proposed system.

Parameters estimation of hybrid modulated signal combining BPSK and LFM Based on Born-Jordan Distribution

Aiming at the problem of the estimation of hybrid modulated signal combining Binary Phase Shift Keying and Linear Frequency Modulation (LFM-BPSK), the existing methods have low estimation accuracy in low SNR. To solve this problem, the algorithm based on Born-Jordan time-frequency distribution (BJD) is proposed, which uses the Hough transform (HT) to estimate the initial frequency and chirp rate of LFM-BPSK signal, and then estimates the code element width by dimensionality reduction time-domain signal. Finally, simulation experiments show that the parameter estimation accuracy of the proposed algorithm under low SNR is significantly better than that of existing algorithms, and the performance is close to MCRLB.

An Improved Adjustable Modulation Strategy for Three-Level NPC Inverters Considering Dynamic Loading Applications

Three-level neutral-point-clamped (NPC) inverters are being widely adopted in low-voltage low-power applications. For an intended application, the modulation strategy and the operating conditions are the two key factors that highly influence the major performance indices of the NPC inverter, such as efficiency, harmonic distortion, and voltage oscillations at neutral point (NP). Considering dynamic loading applications where the operating point varies significantly, this paper proposes an improved adjustable pulsewidth modulation (PWM) strategy for a three-level NPC inverter that can alter its modulation pattern to meet desired performance objectives for the full operation range. It has been shown that by varying two control parameters namely discontinuity control parameter and bias control parameter, the proposed modulation strategy changes its pattern between the most efficient generalized discontinuous PWM to NP oscillations-free partial dipolar PWM strategy. Additionally, to obtain a tradeoff between the performance parameters-efficiency, NP oscillations, and waveform quality-The proposed strategy has the ability to settle at the intermediate modulation patterns by transforming into a hybrid modulation signal. Furthermore, considering NP voltage unbalance mitigation as major technical challenge in adjustable modulation strategy, a voltage unbalance compensator that exhibits satisfactory balancing performance for the entire variations of modulation patterns and operating conditions has also been presented. The performance of the proposed modulation strategy in conjunction with voltage unbalance compensator has been evaluated in simulation by widely varying the speed and load of induction motor, and verified in experimentation.

Nyquist Zone Index and Chirp Rate Estimation of LFM Signal Intercepted by Nyquist Folding Receiver Based on Random Sample Consensus and Fractional Fourier Transform.

The Nyquist folding receiver (NYFR) can achieve a high-probability interception of an ultra-wideband (UWB) signal with fewer devices, while the output of the NYFR is converted into a hybrid modulated signal of the local oscillator (LO) and the received signal, which requires the matching parameter estimation methods. The linear frequency modulation (LFM) signal is a typical low probability of intercept (LPI) radar signal. In this paper, an estimation method of both the Nyquist Zone (NZ) index and the chirp rate for the LFM signal intercepted by NYFR was proposed. First, according to the time-frequency characteristics of the LFM signal, the accurate NZ and the rough chirp rate was estimated based on least squares (LS) and random sample consensus (RANSAC). Then, the information of the LO was removed from the hybrid modulated signal by the known NZ, and the precise chirp rate was obtained by using the fractional Fourier transform (FrFT). Moreover, a fast search method of FrFT optimal order was presented, which could obviously reduce the computational complexity. The simulation demonstrated that the proposed method could precisely estimate the parameters of the hybrid modulated output signal of the NYFR.

Estimation of both Nyquist zone index and code rate for BPSK radar signal intercepted by Nyquist folding receiver

Nyquist folding receiver (NYFR) can realize the wideband receiving with a small amount of equipment. As a tradeoff between the amount of equipment and the complexity of the signal processing, the NYFR output is usually a hybrid modulated signal. Therefore, it is necessary to investigate the parameter estimation method of the signal intercepted by the NYFR. Binary phase shift keying (BPSK) signal is a typical low probability of intercept radar signal and the authors focus on the parameter estimation of the BPSK radar signal intercepted by the NYFR. Firstly, matching component function is proposed to obtain Nyquist zone (NZ) index. Then, the Hankel-singular value decomposition (SVD) method is introduced to estimate the code rate of the BPSK signal. The efficacy of the Hankel-SVD method is proved in a mathematical way. Several numerical simulations demonstrate the merits of the proposed approach and finally, a brief investigation for case of the multiple BPSK signals intercepted by the NYFR is given. For NZ index estimation, the computational complexity of the matching component function is low and it has no need to use squaring process. In addition, the code rate estimation using the Hankel-SVD method is more accurate compared with the wavelet transform.

A parameter estimation algorithm for LFM/BPSK hybrid modulated signal intercepted by Nyquist folding receiver.

Nyquist folding receiver (NYFR) is a novel ultra-wideband receiver architecture which can realize wideband receiving with a small amount of equipment. Linear frequency modulated/binary phase shift keying (LFM/BPSK) hybrid modulated signal is a novel kind of low probability interception signal with wide bandwidth. The NYFR is an effective architecture to intercept the LFM/BPSK signal and the LFM/BPSK signal intercepted by the NYFR will add the local oscillator modulation. A parameter estimation algorithm for the NYFR output signal is proposed. According to the NYFR prior information, the chirp singular value ratio spectrum is proposed to estimate the chirp rate. Then, based on the output self-characteristic, matching component function is designed to estimate Nyquist zone (NZ) index. Finally, matching code and subspace method are employed to estimate the phase change points and code length. Compared with the existing methods, the proposed algorithm has a better performance. It also has no need to construct a multi-channel structure, which means the computational complexity for the NZ index estimation is small. The simulation results demonstrate the efficacy of the proposed algorithm.

An Estimation Method for number of carrier frequency

This paper proposes a method that utilizes AR model power spectrum estimation based on Burg algorithm to estimate the number of carrier frequency in single pulse. In the modern electronic and information warfare, the pulse signal form of radar is complex and changeable, among which single pulse with multi-carrier frequencies is the most typical one, such as the frequency shift keying (FSK) signal, the frequency shift keying with linear frequency (FSK-LFM) hybrid modulation signal and the frequency shift keying with bi-phase shift keying (FSK-BPSK) hybrid modulation signal. In view of this kind of single pulse which has multi-carrier fre- quencies, this paper adopts a method which transforms the complex signal into AR model, then takes power spectrum based on Burg algorithm to show the effect. Experimental results show that the estimation method still can determine the number of carrier frequencies accurately even when the signal noise ratio (SNR) is very low.

The Recognition and Parameter Estimation of Hybrid Modulation Signal Combined with FSK and BPSK

The Recognition and Parameter Estimation of Hybrid Modulation Signal Combined with FSK and BPSK

Gear Fault Diagnosis Methods Based on EMD and HMM

Due to the feature and the forms of motion of the gears, the vibration signal of the gear is mainly the frequency modulation, amplitude modulation, or hybrid modulation signal corresponding to the gear-mesh frequency and its double frequency signal. When faults arise on the gears, the number and shape of the modulation sideband will be changed. The structures and forms of the FM composition differ according to the type of faults. According to the above mentioned characteristic, this essay raises a method to disassemble the gear vibrate signal, points out the formulas to build up characteristic vector, on that basis, the essay raised a gear fault diagnosis method based on EMD and Hidden Markov Model (HMM), this method can identify the working condition of the normal gears, snaggletooth gears, and pitting gears.