A novel approach for designing diversity radar waveforms that are orthogonal on both transmit and receive

In this paper, we present an approach to the design of orthogonal, Doppler tolerant waveforms for diversity waveform radar (e.g. MIMO radar). Previous work has given little consideration to the design of radar waveforms that remain orthogonal when they are received. Our research is focused on: (1) developing sets of waveforms that are orthogonal on both transmit and receive, and (2) ensuring that these waveforms are Doppler tolerant when properly processed. Our proposed solution achieves the above mentioned goals by incorporating direct sequence spread spectrum (DSSS) coding techniques on linear frequency modulated (LFM) signals. We call it Spread Spectrum Coded LFM (SSCL) signaling. Our transmitted LFM waveforms are rendered orthogonal with a unique spread spectrum code. At the receiver, the echo signal will be decoded using it's spreading code. In this manner, transmitted orthogonal waveforms can be match filtered only with the intended received signals. From analytical expressions of the waveforms we have designed and from simulation results, we found that: (a) cross-ambiguity function of two LFM spread spectrum coded (orthogonal) waveforms is small for all delays and Dopplers (i.e. transmit and receive signals satisfy the orthogonality constraint), (b) The length and type of the spread spectrum code determines amount of suppression (i.e. complete orthogonal or near orthogonal of the received signal), (c) We can process the same received signal in two different ways; one method can provide LFM signal resolution and the other method can provide ultra high resolution.