Digital transmission using multimode phase-continuous chirp signals

In a spread-spectrum system the transmitted signal is spread over a wide frequency band, often much wider than the minimum bandwidth needed for the information to be conveyed. The concept of varying the modulation index of a continuous phase FSK (i.e. CPFSK) waveform is applied to digital transmission using chirp signals. These multimode chirp waveforms are described and their ability to perform over the coherent Gaussian channel is examined. It is shown that the dual-mode phase-continuous chirp signals out perform monomode signals by nearly 0.8 dB, when corresponding high-SNR 5-bit optimum minimum-bit-error-probability receivers are employed. A low-complexity suboptimum average matched filter receiver for multimode chirp signals is examined and explicit expressions for its performance are given