Application of arbitrary pulse width and position trains for the correlation sidelobes reduction for narrowband transducers

Abstract

Novel excitation technique is suggested which allows to reduce the correlation function sidelobes in case of narrowband channel. Application is planned for time of flight estimation using air coupled narrowband transducers. Time of flight is estimated by using the correlation function peak position. Narrowband signal has high level of correlation function sidelobes and therefore large signal to noise ratio cannot be fully exploited. Our investigation aimed to reduce the sidelobes by optimizing the signal. Novelty of the approach is that trains of arbitrary width and position square pulses are used. Such signals are easy to generate and to simulate in digital domain. The excitation signal spectrum was allowed to span beyond the passband, improving the envelope bandwidth in such way. The signal energy loss is caused by the attenuation of the out-of-band portion of the signal. Optimal balance between the energy loss and the sidelobes reduction had to be found. To predict the signal performance, the AC response of the transmission channel was measured and then used in simulation to predict the candidate signal’s performance: the expected sidelobes’ level and the energy. Monte Carlo technique was used to generate the candidate signals’ parameters for the simulation. The relative noise margin was suggested as optimum criteria to balance the loss of the energy and the sidelobes reduction. Performance of the optimal signals obtained in simulation was verified experimentally. It was concluded that reduction of the sidelobes’ is possible even for narrowband channel if some energy loss can be tolerated. An increase of 40% in relative noise margin, compared to the same length CW burst signals was achieved.