  Joint radar-communication (JRC) waveform can be used for simultaneous radar
detection and communication in the same frequency band. However, radar
detection processing requires the prior knowledge of the waveform including the
embedded information for matched filtering. To remove this requirement, we
propose a unimodular JRC waveform based on composite modulation where the
internal modulation embeds information by mapping the bit sequence to different
orthogonal signals, and the external modulation performs phase modulation on
the internal waveform to satisfy the demand of detection. By adjusting the
number of the orthogonal signals, a trade-off between the detection and the
communication performance can be made. Besides, a new parameter, dissimilarity,
is defined to evaluate the detection performance robustness to unknown embedded
information. The numerical results show that the SER performance of the
proposed system is similar to that of the multilevel frequency shift keying
system, the ambiguity function resembles that of the phase coded signal, and
the dissimilarity performance is better than other JRC systems.
