Dual tone pair modulation for narrow-band data transmission

Waveshaping of data bits is used in many digital modulation techniques to control transmission bandwidth. For 99% power-in-channel bandwidth, minimum shift keying (MSK) achieves a channel bandwidth utilization of approximately 1.2 Hz/BPS. While transmitting a message at R_b bits per second, MSK produces a constant-envelope, continuous-phase, FSK waveform by utilizing a modulating tone of plus or minus 1/4 R_b Hertz about an apparent carrier signal. This paper describes a modulation method that utilizes both ± 1/2 R_b and ± 1/4 R_b tones to provide continuous phase of the signaling waveforms, while exhibiting low apparent carrier signal induced by the signaling message. Dual tone pair modulation (DTPM) is a non-constant envelope, linear modulation method achieving a channel bandwidth utilization of 0.66 Hz/BPS. Since DTPM has low apparent carrier, sub-earner signal injection is used to provide a stable phase reference for coherent detection. This paper describes the DTPM method and provides a DTPM performance measure for bit error rate (BER) in an AWGN channel.