Analisys of frequency-correlation properties of multipath channel for encyprion key generation using samples of differential phase

Wireless Key Generation exploits randomness of fast fading of a multipath radio channel to create identical copies of a shared encryption key at two communication nodes. A promising way for creating a highly secure key is use of samples of differential phase, which allows to overcome short-term instability of frequency standards and to make key generation devices smaller. This study examines frequency-correlation properties of the multipath channel to justify a feasibility of encryption keys generation with the differential phase method. By computer simulation, frequency autocorrelation functions of the envelope and carrier phase of a multipath radio signal are obtained, and estimates of the channel coherence bandwidth are made for a typical urban propagation environment. For random variations of the differential phase of a two-sine probe signal, a probability distribution is analyzed, its uniformity tests are done, and estimates of Shannon entropy at various frequency separations of the two probing tones are made. An effect of the line-of-sight wave and the number of multipaths on the channel frequency-correlation function and on probabilistic properties of the differential phase is considered.