An Efficient Track-Before-Detect Algorithm Based on Complex Likelihood Ratio in Radar Systems

In this paper, we presented a track-before-detect (TBD) method which can cope with range-Doppler ambiguity for medium pulse repetition frequency (MPRF) radars. The target state evolutions in the ambiguous range-Doppler domain are considered as a hybrid system with the range- Doppler ambiguous number deemed as mode variable. Phase information of measurement is used to provide a detection sensitivity improvement, and the reduction of computation is acquired by using complex likelihood instead of the envelope likelihood. Finally, a dynamic programming algorithm is used to estimate target state and ambiguous number of every PRF, and the true trajectory of target is backtracked after resolving the ambiguity. Simulation results show that the proposed method achieves 1.2 dB performance improvement at 50 % detection rate compared with the present method

Focusing High-Resolution Highly-Squinted Airborne SAR Data with Maneuvers

Maneuvers provide flexibility for high-resolution highly-squinted (HRHS) airborne synthetic aperture radar (SAR) imaging and also mean complex signal properties in the echoes. In this paper, considering the curved path described by the fifth-order motion parameter model, effects of the third- and higher-order motion parameters on imaging are analyzed. The results indicate that the spatial variations distributed in range, azimuth, and height directions, have great impacts on imaging qualities, and they should be eliminated when designing the focusing approach. In order to deal with this problem, the spatial variations are decomposed into three main parts: range, azimuth, and cross-coupling terms. The cross-coupling variations are corrected by polynomial phase filter, whereas the range and azimuth terms are removed via Stolt mapping. Different from the traditional focusing methods, the cross-coupling variations can be removed greatly by the proposed approach. Implementation considerations are also included. Simulation results prove the effectiveness of the proposed approach

The Dynamic Sea Clutter Simulation of Shore-Based Radar Based on Stokes Waves

The sea clutter model based on the physical sea surface can simulate radar echo at different times and positions and is more suitable for describing dynamic sea clutter than the traditional models based on statistical significance. However, when applying the physical surface model to shore-based radar, the effects of wave nonlinearity, breaking wave, shadow, and radar footprint size must be considered. In this paper, a dynamic sea clutter simulation scheme based on a nonlinear wave is proposed that uses random Stokes waves instead of linear superposition waves to simulate the nonlinear dynamic sea surface and then calculates echo in the form of scattering cells. In this process, the relationship between wind speed and the nonlinear factor of the Stokes wave is derived, a simple model of shadow modulation is provided, and a method for appending the sea clutter spikes formed by breaking waves is developed. The experimental results show that the simulated sea clutter and the real measured clutter have good consistency in intensity, amplitude statistical distribution, Doppler spectrum, and spatiotemporal correlation. The proposed scheme is suitable for the sea clutter simulation of shore-based radar and can also adjust the relevant parameters to extend to other types of sea clutter simulation

Computationally Efficient Direction-of-Arrival Estimation Based on Partial A Priori Knowledge of Signal Sources

A computationally efficient method is proposed for estimating the directions-of-arrival (DOAs) of signals impinging on a uniform linear array (ULA), based on partial a priori knowledge of signal sources. Unlike the classical MUSIC algorithm, the proposed method merely needs the forward recursion of the multistage Wiener filter (MSWF) to find the noise subspace and does not involve an estimate of the array covariance matrix as well as its eigendecomposition. Thereby, the proposed method is computationally efficient. Numerical results are given to illustrate the performance of the proposed method.</p

Design of Integrated Radar and Communication Signal Based on Multicarrier Parameter Modulation Signal

Communication signals are vital to the implementation of integrated radar and communication, which is an effective way to reduce platform volume and electromagnetic interference. In this paper, an integrated radar and communication signal based on multicarrier parameter modulation chirp signal is proposed. Its main carrier adopts the unique chirp signal to implement radar function, while communication information is modulated by the subcarrier with different chirp rates and initial frequency chirp signal. The signal property is analyzed by ambiguity function, and the processing and system performance are studied. Finally, simulation results demonstrate that the proposed sharing signal has a low symbol error rate and high robustness, and communication data transmission can be implemented by slightly degrading the radars performance

Moving Multitarget Detection Using a Multisite Radar System with Widely Separated Stations

This study investigates the detection problem of multiple moving targets using a multisite radar system with widely separated stations. Spatial mapping is presented to integrate the observation data of a moving target from different angles into a spatial resolution cell (SRC). However, data association errors occur in some SRCs in this way, which causes extra false alarm, called the “ghost target”. Therefore, an interference discriminator-based detector is developed. In this way, the background interference is discriminated between “ghost target” and pure noise, and then the final decision is made based on the generalized likelihood ratio test. Statistical analyses are provided to discuss the achievable performance. Simulation results show that the proposed algorithm can accurately detect multiple moving targets while suppressing the “ghost target”

An Oblique Projection-Based Beamforming Method for Coherent Signals Receiving

Within a complex sea or ground surface background, multipath signals are strongly correlated or even completely coherent, which leads to signal cancellation when conventional optimal beamforming is performed. Aiming at the above problem, a coherent signal-receiving algorithm is proposed based on oblique projection technology in this paper. The direction of arrival (DOA) of incident signals is estimated firstly by the space smoothing-based MUSIC method. The composite steering vector of multipath coherent signals is then obtained utilizing the oblique projection matrix constructed with the estimated angles. The weight vector is thereby derived with the minimum variance distortionless response criteria. The proposed oblique projection-based beamformer can receive the multipath coherent signals effectively. Moreover, the proposed beamformer is more robust and converges to optimal beamformer rapidly without aperture loss. The theoretical analysis and simulation verify the validity and superiority of the proposed coherent signal beamformer

Orthogonal frequency‐division multiplexing‐based signal design for a dual‐function radar‐communications system using circulating code array

Abstract In this study, a dual‐function radar‐communications (DFRC) system based on the circulating code array is presented to address the contradiction between radar and communications system in beam scanning and beam coverage. Processed orthogonal frequency‐division multiplexing (OFDM) signal is transmitted by the circulating code array as the base signal to improve the data rate. Following the spatial angle of the communication receiver, the communication symbols are modulated to part of OFDM signal subcarriers occupying a specific frequency band. A significant property of the circulating code array, which provides a relationship between the baseband frequency of the base signal and the spatial angles, implements a basis for safe telecommunication transmission towards the cooperative receiver and demodulation. Moreover, the circulating code array transmits the same signal and introduces the same time interval between adjacent array elements. Therefore, the complex problems of multi‐dimensional orthogonal signal design in the traditional multiple‐input‐multiple‐output‐based DFRC system design are transformed into a simple base signal design. Finally, an omnidirectional coverage pattern is obtained. Thus, whether the communication receiver is in the mainlobe or the sidelobe of the radar beam, the communication connection can be established between the designed DFRC system and the communication users. The performance of the described DFRC system is verified through theoretical analysis and simulations