A novel low data rate speech communications system

This dissertation presents research results for methods that reduce RF channel bandwidth requirements for low data rate speech communications systems. To achieve low bandwidth speech communications, both the speech coder design and the RF channel modulator design are equally important. The speech coder must convert speech into the fewest digital states needed to convey intelligible speech. The channel modulator must convert the speech coder states to radio frequency energy that occupies the least amount of the RF spectrum. The speech coding and the channel modulation methods must be jointly considered if minimal channel bandwidth is to be achieved. This dissertation presents a novel method to code speech and a novel method to modulate the speech data onto the RF channel. The speech coder utilizes solutions of a second-order differential equation having periodic coefficients to code speech data for time frames of variable length. The channel modulator utilizes non-orthogonal, continuous-phase signaling states to convey the speech data while utilizing less bandwidth than traditional methods. The research outcomes presented in this dissertation describe new concepts in narrowband speech transmission, a topic that remains an active area of research within academia and industry.