Preamble Design with HFMs for Underwater Acoustic Communications

Hyperbolic frequency modulation (HFM) is Doppler insensitive. Therefore, HFM has been widely used in underwater acoustic communications as a preamble where wideband Doppler insensitivity is highly required. Based on this, we propose a new waveform named up-down-sweeping HFM (UMD-HFM). It combines an up-sweeping HFM and a down-sweeping HFM and leaves a span which is a little longer than delay spread of channel. UMD-HFM not only preserves the Doppler invariance, but also can be used to estimate the instantaneous Doppler scale for underwater communication. With this simple coding structure, UMD-HFM can also demonstrate a better detection performance.