Spectrally Efficient Spread Spectrum System Design: Message-Driven Frequency Hopping

Originally developed for secure communications in military applications, frequency hopping systems possess anti-jamming and anti-interception features by exploiting time- frequency diversity over large spectrum. However, the spectral efficiency of existing FH systems is very low due to inappropriate use of the total available bandwidth. To improve the system capacity, in this paper, we propose an innovative message-driven frequency hopping (MDFH) scheme. Unlike in traditional FH systems where the hopping pattern of each user is determined by a pre-assigned pseudo-random (PN) sequence, in MDFH, part of the message stream will be acting as the PN sequence for hopping frequency selection. Essentially, transmission of information through hopping frequency control introduces another dimension to the signal space, and the corresponding coding gain increases system efficiency by multiple times. The MDFH scheme can be further enhanced by allowing simultaneous transmissions over multiple frequency bands. Including both MDFH and OFDM as special cases, the enhanced MDFH scheme, named E-MDFH, can achieve high spectral efficiency while providing excellent design flexibility. E-MDFH can readily be extended to a FH-based collision-free multiple access scheme.