Jianxin Yi

Experimental Research for CMMB-Based Passive Radar Under a Multipath Environment

China mobile multimedia broadcasting (CMMB) is a digital television standard that works in a single-frequency network (SFN) at the ultrahigh frequency band and adopts orthogonal frequency division multiplex modulation with a cyclic prefix (CP-OFDM). This paper investigates the practical feasibility of a CMMB-based passive radar (CPR) in the multipath propagation environment. First, several aspects involving system considerations induced by propagation conditions and radar signal characteristics are analyzed, including power budget, dynamic range requirement, clutter rejection metrics, and ambiguity function analysis. Then targeting the problems caused by multipath signals in the complex propagation environment and corresponding processing techniques are discussed, covering reference signal extraction and clutter rejection, as well as, tracking and localization. The highlight is clutter rejection with subcarrier-based spatial adaptive processing (SSAP), which is matched with the features of CP-OFDM. The applicability of SSAP under severe channel response spread mainly contributed by SFN is specially considered. Last, a description of the experiments and the CPR systems developed by Wuhan University is given, together with results from previous field trials for low-altitude aircraft and ship detection.

Computationally Efficient RF Interference Suppression Method With Closed-Form Maximum Likelihood Estimator for HF Surface Wave Over-The-Horizon Radars

Among all types of unwanted signals in high-frequency (HF) surface wave (HFSW) over-the-horizon (OTH) radars, radio-frequency interference (RFI) is dominant since HF band is shared by many radio services. In observation data, there are two types of common RFI. The most common one is the conventional RFI which presents vertical stripe paralleling to range axis in range-Doppler spectrum (RDS) and has been exhaustively reported by previous papers. Meanwhile, a new type of RFI characterized by sloping stripes (called RFISS) in RDS is also frequently observed. This work concentrates on the new RFISS and establishes a unified model for the above two types of RFI. Based on this generalized model, a time-domain RFI suppression algorithm is proposed here. Benefiting from a closed-form approximate maximum likelihood estimator, the proposed algorithm exhibits excellent performance and is computationally efficient. Its operational performance is evaluated using the field data recorded by experimental HFSW OTH radar of Wuhan University.

MIMO Passive Radar Tracking Under a Single Frequency Network

In conventional MIMO radars, transmitting waveforms are usually assumed to be mutually orthogonal. This is also the case for MIMO passive radar when the transmitters occupy non-overlapping frequency channels, such as the FM-based MIMO passive radar. For the single frequency network (SFN)-based MIMO passive radar (SMPR), all illuminators transmit the same content at the same frequency simultaneously, that makes the signal indistinguishable. Therefore, one has to solve the measurement-to-transmitter association herein in addition to the standard measurement-to-target association in conventional MIMO radars. This paper investigates the non-standard target tracking for SMPR. A novel approach is proposed to achieve real-time operation as well as nearly optimal performance. Simulation results show comparable performance to the case with known association. Moreover, the feasibility of the proposed approach is demonstrated using field experimental data.

Deghosting for target tracking in single frequency network based passive radar

Nowadays most of modern digital TV and broadcast systems adopt a novel network technology, namely single frequency network (SFN). In SFN the same data stream is broadcasted from multiple transmitters in the same frequency band. Thus SFN-based passive radar (SPR) could generate multiple simultaneous measurements from the same target, introducing a measurement-to-transmitter association ambiguity (MTAA). False association could lead to ghosts. In this paper, we present a solvability analysis for MTAA under 2-dimensional (2-D) space and well-separated targets case. The purpose of this solvability analysis is to obtain the simplest sufficient condition for resolving MTAA. Besides, an association hypothesis decision (AHD) method is proposed for deghosting. Numerical simulations demonstrate that AHD is an effective method against ghosts under the SPR scenario.

Side Peak Interference Mitigation in FM-Based Passive Radar Via Detection Identification

In frequency-modulation (FM)-based passive radar, the strong side peaks randomly appearing in the ambiguity function will generate a false alarm of target detection. To mitigate this side peak interference, this paper starts with a detailed analysis of the structure and ambiguity function of FM stereo signal. Then, it expounds the formation and characteristics of side peaks, together with a side peak identification method, which identifies and discards the false detections of the same range and Doppler caused by side peaks, respectively. The performance analysis, conducted using both simulated data and real recorded datasets, proves that the proposed method can eliminate the false targets caused by side peaks thus improving the detection performance in FM-passive radar.

A parallel processing algorithm for multipath clutter cancellation in passive radar

The multipath clutter cancellation, the most computationally demanding part of signal processing in passive bistatic radar (PBR), is a key challenge in real time processing. However the previous Extensive Cancellation Algorithm (ECA) versions have their limitations in parallel implementation. In this paper an advanced version of ECA is proposed for multipath clutter cancellation in passive radar. Validated by simulation and theoretical analysis, the proposed algorithm can improve the computation efficiency with an excellent cancelling capability, which provides a valuable basis for real time signal processing in PBR.

Receiver placement in multistatic passive radars

It is well known that geometry is of significance to the performance of multistatic radars. In multistatic passive radars the receiver placement is especially critical since the transmitters of opportunity are beyond control of radar designer. Instead of considering a single objective, we suggest to implement the receiver placement by using multiobjective optimization in this paper. Specifically, three objectives with clear physical meaning are constructed. Then optimal operating points are explored through Pareto optimization. The receiver placement approach is demonstrated via a numerical example.

Joint Optimization of Receiver Placement and Illuminator Selection for a Multiband Passive Radar Network

The performance of a passive radar network can be greatly improved by an optimal radar network structure. Generally, radar network structure optimization consists of two aspects, namely the placement of receivers in suitable places and selection of appropriate illuminators. The present study investigates issues concerning the joint optimization of receiver placement and illuminator selection for a passive radar network. Firstly, the required radar cross section (RCS) for target detection is chosen as the performance metric, and the joint optimization model boils down to the partition p-center problem (PPCP). The PPCP is then solved by a proposed bisection algorithm. The key of the bisection algorithm lies in solving the partition set covering problem (PSCP), which can be solved by a hybrid algorithm developed by coupling the convex optimization with the greedy dropping algorithm. In the end, the performance of the proposed algorithm is validated via numerical simulations.

Joint Placement of Transmitters and Receivers for Distributed MIMO Radars

Geometry configuration is crucial to the system performance in distributed multiple-input–multiple-output (MIMO) radars. Sensor placement in distributed MIMO radars is different from the conventional sensor placement problem as transmitters and receivers need to cooperate with each other to perform sensing. In this paper, we establish a combinatorial optimization model for the joint placement of transmitters and receivers. The proposed algorithm first transforms the original model into an equivalent model with convex constraints via convex relaxation. Then, the nonconvex objective function is further replaced with a new convex surrogate. The surrogate is shown to converge to a good approximation of the original optimal solution. The performance of the proposed algorithm is validated using numerical simulations.

Noncooperative registration for multistatic passive radars

Multistatic passive radars localize targets by using multiple bistatic range measurements. Multistatic localization requires all range measurements to be unbiased. It is proved by real data processing that registration is an important topic to be addressed. Traditionally, atomic clocks or GPS are used to achieve unbiased measurements. However, these approaches are unattainable under the case of multistatic passive radars as the transmitters of opportunity are beyond control. This paper proposes a novel registration method using noncooperative targets. The global convergence and accuracy of the proposed algorithm are obtained analytically. Computer simulations and experimental data are used to verify that the proposed algorithm possesses a good global convergence behavior and the performance can approach the Craḿer-Rao bound (CRB).