Secure information transmission for mobile radio

A new technique for secure information transmission in a mobile environment is described. While the method may be used for secure cryptographic key distribution, it also enables the transmission of information in a secure manner without resort to any cryptographic techniques. This is achieved by using the short term reciprocity of the mobile radio channel to communicate in a two step process. In the first step, the phase response of the channel is probed, and in the second step the information bearing signal is modified to pre-compensate for the phase effects of the channel. Since the channel impulse response between two users is different from the channel impulse responses between the users and an adversary, the method is secure