Christos V. Ilioudis

Fractional fourier based waveform for a joint radar-communication system

The increasing demand of spectrum resources and the need to keep the size, weight and power consumption of modern radar as low as possible, has led to the development of solutions like joint radar-communication systems. In this paper a novel Fractional Fourier Transform (FrFT) based multiplexing scheme is presented as a joint radar-communication technique. The FrFT is used to embed data into chirp sub-carriers with different time-frequency rates. Some optimisation procedures are also proposed, with the objective of improving the bandwidth occupancy and the bit rate and/or Bit Error Ratio (BER). The generated waveform is demonstrated to be robust to distortions introduced by the channel, leading to low BER, while keeping good radar characteristics compared to a widely used Linear Frequency Modulated (LFM) pulse with same duration and bandwidth.

Micro-Doppler Based Recognition of Ballistic Targets Using 2D Gabor Filters

The capability to recognize ballistic threats, is a critical topic due to the increasing effectiveness of resultant objects and to economical constraints. In particular the ability to distinguish between warheads and decoys is crucial in order to mitigate the number of shots per hit and to maximize the ammunition capabilities. For this reason a reliable technique to classify warheads and decoys is required. In this paper the use of micro-Doppler signatures in conjunction with the 2-Dimensional Gabor filter is presented for this problem. The effectiveness of the proposed approach is demonstrated through the use of real data.

Performance analysis of fractional waveform libraries in MIMO radar scenario

This paper presents the performance analysis of the novel constant envelope fractional waveforms in a distributed multiple input-multiple output radar system (DMRS) scenario. Waveform modulation is based on the Fractional Fourier Transform (FrFT) using the fractional order as a degree of freedom and a modified version of Gerchberg-Saxton Algorithm (GSA) to apply similarity and constant modulus constraints. Simulation and experimental results demonstrate the effectiveness of the novel technique and its capability to provide a reliable and robust waveform generation tool.

Reuse of fractional waveform libraries for MIMO radar and electronic countermeasures

A fundamental aspect in the hardware-software design of modern radar systems, for example MIMO or Low Probability of Intercept Radar, is to operate in electromagnetically crowded environments. Proper radar waveform design is central to effective solutions in such systems. In this paper cross-interference and waveform reuse for a set of waveform libraries based on the fractional Fourier transform are presented and analysed. The results demonstrate the potential of the novel libraries in increasing the number of available waveforms and for stealth transmissions.

Constant envelope fractional fourier transform based waveform libraries for MIMO radar

In this paper an efficient technique to generate novel libraries of phase-coded waveforms with constant envelope aimed at optimizing signal retrieval is presented. The modulation technique is based on the Fractional Fourier Transform (FrFT), where the signal waveforms retain their constant modulus. Reconstruction of sequences from the FrFT based waveforms is explored by means of the Error Reduction Algorithm (ERA), while the constant envelope property is kept unchanged. Additionally comparison between reconstructed and original sequences is also carried out in terms of performance and cross-correlation properties of the signals. Simulation results demonstrate the effectiveness of the novel waveform libraries considering design parameters such as resolution, interfering power, orthogonality and signal bandwidth.

On Model, Algorithms, and Experiment for Micro-Doppler-Based Recognition of Ballistic Targets

The ability to discriminate between ballistic missile warheads and confusing objects is an important topic from different points of view. In particular, the high cost of the interceptors with respect to tactical missiles may lead to an ammunition problem. Moreover, since the time interval in which the defense system can intercept the missile is very short with respect to target velocities, it is fundamental to minimize the number of shoots per kill. For this reason, a reliable technique to classify warheads and confusing objects is required. In the efficient warhead classification system presented in this paper, a model and a robust framework is developed, which incorporates different micro-Doppler-based classification techniques. The reliability of the proposed framework is tested on both simulated and real data.

GNSS based passive bistatic radar for micro-Doppler based classification of helicopters: Experimental validation

The capability of using illuminators of opportunity for target classification is of great interest to the radar community. In particular the alternative use of Global Navigation Satellite System (GNSS) has recently initiated a number of studies that aim to exploit this source of illumination for passive radar. We recently introduced the concept of a GNSS based passive radar for extraction of micro-Doppler signatures from helicopter rotor blades with the aim of identify these kind of targets. In this paper we present the experimental validation of our concept with real data from two different models of helicopter.

Fractional Fourier Transform Based Co-Radar Waveform: Experimental Validation

A Fractional Fourier Transform (FrFT) based waveform design for joint radar-communication systems (Co-Radar) that embeds data into chirp sub-carriers with different time-frequency rates has been recently presented. Simulations demonstrated the possibility to reach data rates as high as 3.660 Mb/s while maintaining good radar performance compared to a Linear Frequency Modulated (LFM) pulse that occupies the same bandwidth. In this paper the experimental validation of the concept is presented. The system is considered in its basic configuration, with a mono-static radar that generates the waveforms and performs basic radar tasks, and a communication receiver in charge of the pulse demodulation. The entire network is implemented on a Software Defined Radio (SDR) device. The system is then used to acquire data and assess radar and communication capabilities.

Waveform design for communicating radar systems using Fractional Fourier Transform

Abstract A novel waveform design technique for enabling a communication channel within a pulse radar is presented. The proposed waveform is composed of quasi-orthogonal chirp sub-carriers generated by means of the Fractional Fourier Transform (FrFT), with the aim of preserving the radar performance of a typical Linear Frequency Modulated (LFM) pulse while embedding data to be sent to a cooperative system. Waveform generation and demodulation are described, together with techniques aimed at optimising the design parameters and mitigating the Inter-Carrier Interference (ICI) caused by the quasi-orthogonality of the chirp sub-carriers. The proposed FrFT based communicating-radar (CoRadar) waveform design is compared with Orthogonal Frequency Division Multiplexing (OFDM) based CoRadar with respect to both radar and communication operations. Radar performance is evaluated through examination of the Ambiguity Function (AF) and by assessing the performance of a standard square law detector. Communication performance is shown in terms of Bit Error Ratio (BER) for different channel conditions. Results demonstrate that the proposed FrFT waveform presents performance close to a LFM pulse in terms of probability of detection and probability of false alarm, in exchange for slightly worse range and Doppler resolution. Furthermore, it is shown to maintain comparable communication performance with respect to the OFDM waveform. Finally, a hardware implementation is described that demonstrates the simultaneous radar and communication capabilities of the proposed system.

Ambiguity function for distributed MIMO radar systems

In this paper a multi-static ambiguity function (AF) based on the Kullback directed divergence (KDD) and a distributed multiple-input and multiple-output radar system (DMRS) framework is introduced. Additionally a mathematical analysis is used to derive the AF in terms of signal-to-noise ratios (SNRs) and matched filter outputs. This method manages to extract an upper bound and properly define an AF bounded from 0 to 1. Moreover, this method leads in avoidance of large matrices inversions allowing less complex and more accurate computations. Finally the performance of the proposed method in localisation problems is assessed by comparing the proposed AF with the squared summation of the matched filter outputs at each receiver at different SNR scenarios.