The generalized sinusoidal frequency modulated waveform for continuous active sonar

Abstract

Continous Active Sonar (CAS) system are bi-static systems that transmit high duty cycle waveforms so as to constantly process target echoes and revisit the target scene more frequently than conventional Pulsed Active Sonar (PAS) systems. This paper presents novel pulse train waveforms and adaptive processing methods for CAS systems. The pulse trains are composed of Generalized Sinusoidal Frequency Modulated (GSFM) waveforms that are nearly orthogonal to each other even when occupying the same band of frequencies. Additionally, three processing methods are introduced that trade off Coherent Processing Interval (CPI) with target acceleration tolerance while revisiting the target scene every Pulse Repetition Interval (PRI). Simulations demonstrate the pulse trains waveform designs and processing methods and show that certain pulse train designs also mitigate interference from the transmitted acoustic signal, known as the Direct Blast (DBL).

Integrated waveform for continuous active sonar detection and communication

“…The GSFM signal proposed by Hague and Buck [20, 21] modifies a sinusoidal frequency‐modulated waveform using an instantaneous frequency (IF) function that resembles a frequency‐modulated chirp waveform. Thus, GSFM has a frequency modulation waveform expressed as follows: where is the rectangular function, T is the signal duration time, is the phase modulation function, and is the centre frequency.…”

“…Continuous active sonar (CAS) is a bi‐static system that transmits high duty cycle waveforms. It has a higher target revisit rate and better tracking recognition than conventional pulse active sonar [16–20]. Moreover, CAS‐IDC systems have a good communication rate.…”

“…Generalised sinusoidal frequency‐modulated (GSFM) signals are nearly orthogonal to each other, even when occupying the same band of frequencies, and they have an approximate thumbtack AF. Furthermore, GSFM can achieve the minimum estimation variance for the time delay and Doppler shift, and have an optimal resolution of closely spaced targets in range and Doppler shift [20, 21]. Due to the low mutual interference and the high range and velocity resolution, GSFM pulses have been applied in CAS systems [20].…”

Experimental Results of Underwater Acoustic Communication with Nonlinear Frequency Modulation Waveform

“…However, it contains many high sidelobes in the ACF due to the periodicity of the IF. For this reason, generalized sinusoidal frequency modulation (GSFM) was suggested to eliminate the drawbacks of the SFM [15,16]. The GSFM waveform is a generalized form of the SFM waveform and uses a variable exponent parameter.…”

“…Unlike the SFM waveform, the broadband ambiguity function (AF) of this variant GSFM waveform has a distinct mainlobe centered at the origin without a peak sidelobe, and the AF is very similar to a thumbtack. Designing GSFM waveforms with different parameter values (determined by the user) can produce a family of waveforms that occupy the same band of frequencies and are nearly orthogonal to each other [15]. For this reason, the GSFM waveform was recently researched in active sonar by Hague and Buck [16].…”