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With the increase in demand for spectral resources and bandwidth constraints, efficient solutions for the coexistence of radar and communication systems are needed. Simultaneously, the development of multifunctional radio frequency (RF) systems with less hardware have received considerable attention. Most previous work on coexistence has focused on hardware design and mitigation of interference between radar and communication systems. This work proposes, a novel method for controlling a chaotic trajectory, which allows for the coexistence of both radar and communication systems. Binary information can be encoded in a chaotic state by adjusting its trajectory. In this approach, a state variable is selected to control the trajectory and generate a controlled chaos-based frequency modulated (CCBFM) waveform for joint radar-communication system signal transmission. We also design a communication receiver to decode the information and a radar receiver that extracts the signature of the target are designed accordingly. The performance of the controlled chaotic communication system is assessed in terms of the bit error ratio (BER). The analysis of the communication system shows that the CCBFM receiver performs reasonably well compared to a half-sine pulse frequency modulated (HSPFM) receiver. Analysis of the radar system performance is assessed using the entropy of the target's signature. The use of a CCBFM waveform leads to accurate target detection and classification for a signal-to-noise ratio as low as −30 dB. These analyses demonstrate that a CCBFM waveform can be successfully used for joint radar-communication systems in a shared spectrum. INDEX TERMS Controlled chaos, chaotic systems, joint radar-communication systems, Lorenz oscillator, radar imaging. Research (ONR) launched an Advanced Multifunction RF Systems (AMRFS) program [3] to develop a single system that performs multiple operations such as sensing, communication, electronic warfare, etc. Numerous studies have been dedicated to integrating radar and communication subsystems into a single system [4]-[8]. In spite of advances, the challenge of designing a singlewaveform transmission approach for joint radar and communication (RadCom) system remains [9]. The use of a single waveform for both radar sensing and communication data transmission is desirable to avoid multiple expensive RF transmitters [4]. A dual-function system that adopts this fixed signal approach would, of course, require a trade-off between its radar and communication performance [10]. For instance,

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We explore the characteristics of chaos for wideband radar imaging. Chaos can be generated via nonlinear functions that produce statistically independent samples with invariant probability density functions. By feeding this type of chaos to the input of a voltage-controlled oscillator, a stochastic frequency modulated signal with fractal features is generated. The FM signal is an ergodic and stationary process with initial random phase. The power spectral density of such signal is typically broadband. We show that the time autocorrelation associated with the FM signal provides high range resolution for zero Doppler and dies out rapidly for increasing Doppler shifts. Furthermore, we show that a set of realizations of the signal can be processed into a set of ambiguity surfaces that when averaged yield a low self-noise pedestal.

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