A multi-frame space-time coding method for the phase-coded signal in MIMO radars

Abstract

Code-division multiplexing (CDM) has become the focus of designing orthogonal waveforms of multiple-input multiple-output (MIMO) radars as it occupies fewer resources than time-division multiplexing (TDM) and frequency-division multiplexing (FDM). As one of the standard CDM waveforms, conventional inter-pulse phase-coded waveform possesses non-ideal diversity performance. That is, the orthogonality of the signals will reach the threshold after the codes extend to a certain length. To circumvent the coding restrictions, space-time coding (STC) makes use of spatial resources. This paper proposes a multi-frame STC method to improve the orthogonality among waveforms. Specifically, we first design the orthogonal transmitted signals and corresponding matched filters for MIMO radars. Then the signal expressions and the radar ambiguity function (AF) are deduced to verify the proposed method theoretically. Compared with conventional STC, such a method can save half of the time domain resources and make the most of coding resources. Furthermore, the output signal-to-noise ratio (SNR) is well improved as the proposed method effectively suppresses the cross-correlation energy of the waveform. The proposed multi-frame STC waveform can be easily implemented in practical radar applications because of its constant waveform amplitude. The theoretical analysis and simulation results demonstrate the effectiveness of the method.