Embedding Communication Symbols Into Radar Waveform With Orthogonal FM Scheme

In this paper, we investigate an approach for embedding communication symbols into radar waveform while holding constant envelope with spectral containment. To achieve this approach, a new frequency modulation (FM) scheme is proposed, where the proposed FM is the addition of a communication FM term (CFMT) and the base radar FM. For communication information modulation, the CFMT is designed to be a linear combination of multiple sub-FM terms, and the information-bearing communication symbols are carried out by the coefficients of different sub-FM terms. This technique is based on these sub-FM terms comprising of the CFMT mathematically orthogonal to each other in the inner product domain. In addition, in order to mitigate the interference caused by the radar FM on the demodulation procedure, the CFMT is designed mathematically orthogonal to the radar FM. Therefore, the resulting FM of emission is actually a group of orthogonal FM terms. Besides, a weighted coefficient is introduced to make a tradeoff between the degrees of range sidelobe modulation and the communication bit error rate (BER) performance. The performance of the designed radar-embedded communication waveform, including ambiguity function, spectral, weighted coefficient design, and the demodulation procedure, is analyzed. The results show that the satisfactory communication BER performance can be achieved without sacrificing the radar performance.