Target Range and Velocity Estimation for Joint Radar and Communications with Up and Down Chirps

This paper proposes joint radar and communications scheme based on chirp waveform diversity. A monostatic radar transmits a sequence of alternating up and down chirps to acquire target related information (TRI), while leveraging such waveform diversity to deliver data to another radar. This data can be TRI acquired in previous coherent pulse interval (CPI) or scheduling data, such as radar signal bandwidth, carrier frequency, and waveform parameters. We propose range and velocity estimation of multiple targets using dechirping and discrete Fourier transform (DFT). Given P chirps and N fast time samples, 2N DFTs, each of length $\frac{P}{2}$, are computed over slow time to locate peaks in the corresponding DFT amplitudes. The most frequently occurring peak locations are utilized for estimating target velocities, which, together with most frequently occurring peak locations in 2P DFTs, each of length $\frac{N}{2}$, computed over fast time, are then used for estimating target ranges. When compared to the standard range-Doppler processing, this method reduces computational complexity, and is motivated for improving robustness against noise. Computer simulations are used to show the performance of the proposed method in terms of the range and velocity estimation errors versus signal-to-noise ratio (SNR). Simulations show that the proposed method provides better range estimation than the method that uses only up or down chirps, especially when two targets are closely located. These results suggest that alternating up and down chirp-based transmission not only supports data transmission but also improves radar performance.