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In this article, we propose the utilization of chaos-based frequency modulated (CBFM) waveforms for joint monostatic and bistatic radar-communication systems. Short-duration pulses generated via chaotic oscillators are used for wideband radar imaging, while information is embedded in the pulses using chaos shift keying (CSK). A self-synchronization technique for chaotic systems decodes the information at the communication receiver and reconstructs the transmitted waveform at the bistatic radar receiver. Using a nonlinear detection scheme, we show that the CBFM waveforms closely follow the theoretical bit-error rate (BER) associated with bipolar phase-shift keying (BPSK). We utilize the same nonlinear detection scheme to optimize the target detection at the bistatic radar receiver. The ambiguity function for both the monostatic and bistatic cases resembles a thumbtack ambiguity function with a pseudo-random sidelobe distribution. Furthermore, we characterize the high-resolution imaging capability of the CBFM waveforms in the presence of noise and considering a complex target.

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Reverse-time chaos can be used to realise hardware chaotic systems that can operate at speeds equivalent to existing state-of-the-art while requiring significantly less complex circuitry. Unlike traditional chaotic systems, which require significant analogue hardware that is difficult to realise at high speed, the reverse-time system can be realised with a field programmable gate array calculating a digital iterated map. The resulting output forgoes the need for digital-to-analogue conversion by directly driving a series RLC filter. Since the dynamics of this system are determined by an iterated map, precise control of this system is possible by adjusting the map's initial condition. Hardware results for the controllable reverse-time system demonstrate chaotic behaviour at an operating frequency of 1.8 MHz and show promise for extension to higher frequencies.Introduction: Chaotic electronic systems have been previously investigated for their potential utility in many applications including communication [1] and radar [2]. Previous work has shown that such systems can be constructed and tuned, such that they possess dynamics advantageous for their specific application [3]. Control schemes have also been devised that can maintain these systems on desired trajectories while in operation [4]. By combining these characteristics with matched filter decoding [5], many of the necessary components for a modern high-performance communication system or radar may be realised with chaotic dynamics.Actually realising physical systems that exhibit the chaotic dynamics necessary for these applications has long proven to be a difficult task. Although surprisingly simple systems constructed from both familiar [6] and exotic [7] components have been shown to behave chaotically, such systems do not readily lend themselves to control. Simulations have shown that hardware can be developed for a potentially controllable chaotic system with an exact solution [8], but this hardware relies on many analogue components that are not expected to scale well with high-speed operation.Reverse-time chaos provides a potential solution for realising chaos in hardware with both solvable and controllable properties without sacrificing the ability to scale in frequency. First proposed by Corron et al. in [9], reverse-time chaos describes behaviour that differs from traditional chaos by using the current state of the system to represent all of its past states instead of all of its future states. Despite this difference, reversetime chaos retains a positive Lyapunov exponent and a corresponding sensitivity to initial conditions that defines traditional chaotic systems.

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The use of reverse time chaos allows the realization of hardware chaotic systems that can operate at speeds equivalent to existing state of the art while requiring significantly less complex circuitry. Matched filter decoding is possible for the reverse time system since it exhibits a closed form solution formed partially by a linear basis pulse. Coefficients have been calculated and are used to realize the matched filter digitally as a finite impulse response filter. Numerical simulations confirm that this correctly implements a matched filter that can be used for detection of the chaotic signal. In addition, the direct form of the filter has been implemented in hardware description language and demonstrates performance in agreement with numerical results.

We show examples of dynamical systems that can be solved analytically at any point along a period doubling route to chaos. Each system consists of a linear part oscillating about a set point and a nonlinear rule for regularly updating that set point. Previously it has been shown that such systems can be solved analytically even when the oscillations are chaotic. However, these solvable systems show few bifurcations, transitioning directly from a steady state to chaos. Here we show that a simple change to the rule for updating the set point allows for a greater variety of nonlinear dynamical phenomena, such as period doubling, while maintaining solvability. Two specific examples are given. The first is an oscillator whose set points are determined by a logistic map. We present analytic solutions describing an entire period doubling route to chaos. The second example is an electronic circuit. We show experimental data confirming both solvability and a period doubling route to chaos. These results suggest that analytic solutions may be a more useful tool in studying nonlinear dynamics than was previously recognized.