A Highly Efficient Secure Communication Interface : Collision - Free Frequency Hopping ( CFFH )

Frequency hopping systems have been widely used in military communications to prevent hostile jamming, interception and detection. In traditional frequency hopping (FH) systems, the transmitter hops in a pseudo-random manner among available frequencies according to a pre-specified algorithm, and the receiver operates accordingly in exact synchronization with the transmitter's hopping pattern. In multiple access systems, a collision may happen when more than one users transmit in the same frequency band simultaneously. Two major limitations with the conventional frequency hopping systems are: strict requirement on frequency acquisition/synchronization, and very low spectral efficiency due to inefficient utilization of the available bandwidth. In this paper, we introduce a new conceptcollisionfree frequency hopping (CFFH). Based on the OFDM framework and the secure subcarrier assignment algorithm, the proposed CFFH system can achieve high information capacity through collision-free multiple access, and can successfully resolve the strict synchronization limitation. At the same time, as each user still transmits through a pseudo-random frequency hopping scheme, CFFH can maintain the inherent anti-jamming, antiinterception security features of the conventional FH system. The proposed CFFH scheme can be used for both civilian and military applications where secure high speed information transmission is needed.