Doppler Frequency Migration Effects Research Articles

Coherent Estimation of Three Positioning Measurements for Unknown Frequency-Hopping Signals in Passive Emitter Localization

Due to the superior anti-interception performance and inherent security features, the wide applications of frequency-hopping (FH) signals bring a great challenge to the reconnaissance and monitoring of FH emitters. This paper addresses the problem of positioning measurement estimation for unknown FH signals in passive localization, considering the range migration (RM) and Doppler frequency migration (DFM) of the maneuvering target within the observation time. A coherent range difference (RD), range rate difference (RRD) and acceleration difference (AD) estimation algorithm based on scaled Fourier transform and scaled non-uniform fast Fourier transform is proposed. This method can effectively remove RM and random DFM effects regardless of varied carrier frequency and achieve the coherent estimation of RD, RRD and AD. The whole estimation process can be easily implemented by complex multiplications combined with fast Fourier transform (FFT) and inverse FFT operations without any brute-force searching procedure. Numerical experiments demonstrate that the anti-noise performance of the proposed method is superior to several representative methods and comparable to the optimal maximum likelihood estimator with a much lower computational cost.

Analysis of the Code Phase Migration and Doppler Frequency Migration Effects in the Coherent Integration of Direct-Sequence Spread-Spectrum Signals

Coherent integration of direct-sequence spread-spectrum (DSSS) signals is a commonly used technique to improve receiver performance. However, this approach is susceptible to the code phase migration (CPM) and Doppler frequency migration (DFM) effects resulting from the relative motion between transmitter and receiver. In this paper, the CPM and DFM effects are explored and characterized. To evaluate the CPM effect, a simple analytic expression for the coherent integration results under motions of arbitrary orders is developed. In addition, the theoretically derived integration loss and time synchronization error caused by CPM are quantitatively examined. The DFM effect is evaluated under the motions of arbitrary orders by Fresnel integration and numerical fitting. The obtained closed-form expressions are verified by simulation and are shown to be useful for the performance analysis and the DSSS receiver design. The theoretical and the numerical results show that when the amount of CPM is larger than about one code chip duration, the signal-to-noise ratio gain obtained by coherent integration no longer increases because of the integration loss caused by CPM. In addition, the integration loss (in decibel units) caused by DFM is approximately inversely proportional to the square of the time-bandwidth product when the time-bandwidth product is small, and it is inversely proportional to the logarithm of the time-bandwidth product when this product is large.

Ground-Based Radar Detection for High-Speed Maneuvering Target via Fast Discrete Chirp-Fourier Transform

Detection of high-speed maneuvering targets has attracted a great deal of attention recently. There are two main problems to be solved: improving detection ability under the condition of complicated range migration and Doppler frequency migration effects, and reducing computational load. Different from most existing fast algorithms which are at the cost of detection ability, this paper devises a computationally attractive method with excellent detection performance. First, the keystone transform is carried out to remove linear range migration. Thereafter, a fast discrete chirp-Fourier transform (FDCFT) based on radix-4 decomposition is proposed to compensate the undersampled linear Doppler frequency migration and quadratic Doppler frequency migration. Because of exploiting inherent symmetry and periodicity as in the fast Fourier transform (FFT), the FDCFT can largely reduce the computational complexity without performance loss. The novelty of the proposed algorithm lies in combining linear transform with the concept of decimation-in-time FFT, which avoids the demanding multi-dimensional search and severe performance loss via introducing nonlinear transforms. It is shown that the proposed method has an approximately optimal detection performance but with relatively low computational cost.

Radon-S transform for hypersonic maneuvering target detection

Hypersonic maneuvering target can cause complex range migration and Doppler frequency migration effects even in a very short time. This brings a big challenge to the common long-time coherent integration based target detection methods. To solve this problem, a novel hypersonic maneuvering target detection method called Radon-S transform is proposed in this paper on the basis of Radon transform and S-transform. It performs the coherent integration along the target track on the time–range plane, and then performs the non-coherent integration along the time–frequency curve of target echo on the time–frequency plane. By combining the two energy integration processes, the signal-to-noise/clutter ratio can be effectively improved. The definition of Radon-S transform, the concrete realization of detection process, and the setting of correlative parameters are introduced in detail. Then the performance of Radon-S transform is analyzed in theory. Finally, numerical experiment results show that the proposed method is superior to some common long-time coherent integration methods in the hypersonic maneuvering target detection.

Effective coherent integration method for marine target with micromotion via phase differentiation and radon‐Lv's distribution

Effective detection of marine targets with low observability gives a severe challenge to radar signal processing. The micro-Doppler (m-D) signatures of marine target can provide extra information for non-stationary and time-varying signal analysis. Long-time integration is an effective way to strengthen the m-D signal and improve signal-to-clutter ratio. However, the performances are affected by the range across unit and Doppler frequency migration effects. In this study, m-D characteristics of marine target are studied and a novel representation, i.e. phase differentiation and Radon-Lv's distribution (PD-RLVD), is proposed to detect the m-D signal to realise the long-time coherent integration. The PD-RLVD can accurately and directly represent the m-D signal in the chirp rate and chirp change domain appearing as obvious peaks. The proposed method is simple not only because it only requires a 2D Fourier transform of the scaled Radon instantaneous auto-correlation function after PD, but also for not introducing any non-physical attributes. Relations between PD-RLVD and other integration methods are introduced as well. Experiments with real data show that the proposed method can achieve higher integration gain, detection probability, and accuracies of motion parameter estimation.

Radon-Linear Canonical Ambiguity Function-Based Detection and Estimation Method for Marine Target With Micromotion

Robust and effective detection of a marine target is a challenging task due to the complex sea environment and target's motion. A long-time coherent integration technique is one of the most useful methods for the improvement of radar detection ability, whereas it would easily run into the across range unit (ARU) and Doppler frequency migration (DFM) effects resulting distributed energy in the time and frequency domain. In this paper, the micro-Doppler (m-D) signature of a marine target is employed for detection and modeled as a quadratic frequency-modulated signal. Furthermore, a novel long-time coherent integration method, i.e., Radon-linear canonical ambiguity function (RLCAF), is proposed to detect and estimate the m-D signal without the ARU and DFM effects. The observation values of a micromotion target are first extracted by searching along the moving trajectory. Then these values are carried out with the long-time instantaneous autocorrelation function for reduction of the signal order, and well matched and accumulated in the RLCAF domain using extra three degrees of freedom. It can be verified that the proposed RLCAF can be regarded as a generalization of the popular ambiguity function, fractional Fourier transform, fractional ambiguity function, and Radon-linear canonical transform. Experiments with simulated and real radar data sets indicate that the RLCAF can achieve higher integration gain and detection probability of a marine target in a low signal-to-clutter ratio environment.