Frequency-hopping code optimization for MIMO radar using the hit-matrix formalism

There has been a recent interest in the application of multiple-input multiple-output (MIMO) communication concepts to radars. While traditional phased-array radars transmit coherent waveforms from their many antenna elements, MIMO radars transmit incoherent waveforms from their transmitters, which offer additional benefits like spatial diversity and spatial resolution. In recent literature, the optimization of orthogonal frequency-hopping waveforms for MIMO radars has been discussed. This optimization is done using a ‘cost function’ derived from a newly formulated MIMO radar ambiguity function. In our paper, we extend the scope of this ambiguity function to large values of target Doppler. We also propose the use of the ‘hitmatrix’ as a tool to optimize frequency-hopping codes under the large Doppler scenario, since it results in a cost function with a significantly lower computational complexity. The hit-matrix is a generalization of the hit-array, which has been used in the context of frequency-hopping waveforms for phased-array radars.