Agenda

PhD Thesis Defence

• Wednesday, 1 April 2020
• 15:00-17:30

Reconfigurable Range-Doppler Processing and Interference Mitigation for FMCW Radars.

Deramping Frequency Modulated Continuous Wave (FMCW) radars with chirp-sequence waveforms are widely used in numerous applications. The research objective behind this dissertation was to develop methods and waveforms for the operational enhancement of that class of radars. This is in the sense that there was a desire to take FMCW radars beyond their existing state of the art performance limitations, and increase their resistance to interference. To achieve these objectives, the following research questions were addressed:
Is there a way to mitigate FMCW radar interferences where the developed mitigation method restores any SNR loss due to the interference and/or the mitigation technique itself? Can the method be evaluatable in performance in the range-Doppler domain (as opposed to only in a range-profile)? Is there a way to decouple the Doppler velocity ambiguity interval -- defined by the PRF -- from parameters like the maximum operational range, range resolution, all while maintaining the same transmitted chirp-rate? Would it be possible to liberate the radar from the design/operational trade-offs associated with these parameters? Particularly in the scenario in which the PRF is to be increased for the observation of fast(er) moving targets. Is there a way to overcome the existence of the transient (fly-back) region in deramping FMCW radar beat-signals? This is in the sense that its existence limits the maximum observation time in a single sweep. Would manoeuvring it then allow the coherent chaining of beat-signals -- from multiple sweeps -- in a way that could improve the {target response function width}? {Could it also improve the SNR}? And since the beginning of a sweep and the transient region are related -- and therefore the Doppler velocity ambiguity interval is related too in de facto -- could overcoming the presence of the transient region then allow for Doppler processing PRFs that are different from the transmitted PRF?

The novelty, main results and implications of the research presented are:
• A method was developed to mitigate FMCW radar interferences. The method restored any SNR loss due to the interference, and was evaluatable in performance in the range-Doppler domain (as opposed to only in a range-profile). It was {the first ever} interference mitigation method for deramping FMCW radar receivers via {model-based} beat-signals interpolation in the time-frequency domain. It allowed the introduction of an optional linear prediction interpolation coefficients reconfigurable estimation mode for CPI processing. Coefficients are estimated for the current observation scene using a known single interference-free sweep. These coefficients are then reused for the restoration of subsequent interference-contaminated sweeps in the CPI. It was also suitable for real-time implementation, with a predictable execution delay (latency), based on FT banks and fixed-length extrapolation filters, as opposed to iterative methods relying on algorithm convergence. The evaluation of the method's performance was done in the range-Doppler domain. The aim was to additionally showcase the maintenance of the radar's coherence over a CPI after interference mitigation.
• A method was developed to decouple the Doppler ambiguity interval -- defined by the PRF -- from parameters like the maximum operational range and range resolution, all while maintaining the same transmitted chirp-rate. It was the first ever processing method for the coherent integration of frequency multiplexed chirps within one sweep/PRI -- for deramping FMCW radar in the time-frequency domain. It constructed a single fast-time slow-time matrix -- with an extended Doppler ambiguity interval, while maintaining the range resolution and CPI processing gain -- in one go. It did not use iterative algorithms with unpredictable latencies, nor requires any detection or a-priori information about the observed scene, and is applicable to very-extended targets like rain/clouds.
• A method was developed to overcome the existence of the transient (fly-back) region in FMCW radar. It was the first ever method for deramping FMCW radar sweeps coherent concatenation in the time-frequency domain. It allowed for {target response function width} improvement without transmitting additional bandwidth. It offered the ability to -- in parallel -- generate different size fast-time slow-time matrices, and allowed for Doppler processing PRFs that are different from the transmitted PRF, without compromising on the total CPI processing gain. This offered the ability to observer different unambiguous Doppler velocity intervals in one CPI.

Overview of PhD Thesis Defence