Ambiguity function and imaging performance of coded FMCW waveforms with fast 4D receiver processing in MIMO radar

Abstract In this paper, a novel design and processing of nearly orthogonal waveforms based on frequency modulated continuous wave (FMCW) signals for multiple-input, multiple-output (MIMO) radars is presented. The design, implementation and results of the complete system, capable of detection and imaging of radar targets, are here described. The orthogonality of sounding signals is critical for multi-channel radar applications since the interference between signals can significantly limit the radar's ability for observation of weak targets in presence of stronger targets and background clutter. The orthogonal waveforms are designed by coding consecutive complex FMCW signals in a frame so that they can be sent to the different transmit antennas of the radar allowing the simultaneous operation of all transmit channels. Unlike time division switching approaches, the orthogonality in the proposed architecture, is achieved by applying several coding techniques, at a symbol level: Golay complementary, Zadoff Chu, Direct Spread Spectrum (DSS), Space-Time Block Coded, Discrete Fourier Transform (DFT) and Costas based sequences. Moreover, a radar receiver processing, based on a complex frame based convolution between transmit and received waveforms together with 4-dimensional Fast Fourier Transform (4D-FFT) beamforming, is presented. This allows for a fast and complete sensing of range, azimuth, elevation and Doppler in a single frame. The performance of the proposed waveforms is evaluated through the analysis of their cross ambiguity functions and imaging capabilities, while the general performance of the radar's receiver processing is shown through the use of multiple radar images. The flexibility in generating such orthogonal coded waveforms and the proposed general receiver architecture are an important first step for developing a future software programmable MIMO radar.