Radar waveform design in spectrum sharing environment: Coexistence and cognition

The proliferation of mobile devices of late has been exponential in numbers as well as heterogeneity, which gives rise to a great increase in the demand of spectral resources. Researchers have suggested that in order to solve the spectrum crisis, future spectrum users will be required to be frequency-flexible and cognitive, and spectrum sharing protocols on communication system have thus been studied. Radars, in the present form, are spectrum users which have fixed operating frequencies, high power and tendency to interfere with other users. Because of these characteristics, conventional radar will have difficulty in cooperating with spectrum sharing communication systems. Though the idea of combining radar and communication has been around for a long time, few have considered operating a radar in the communication band until recently. In order to make radar and communication systems coexist in the same band, one must maintain the quality of communication links. Additionally, radar should also be cognitive to benefit from the knowledge provided by the communication systems. In this paper, we investigate how future radars respond to spectrum sharing environment and derive optimal waveforms satisfying the spectral requirement.