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Imagine we have an ultrasonic sensor that transmits a multiple cycles of sinusoidal signal/waveform that can travel up to a specific distance/range.

Can we achieve more distance coverage using more number of cycles in the input signal (at the same frequency) or this change can not affect the coverage?

I understand that more number of cycles will result in more signal energy. Does that mean that having more energy in the signal will result in less signal deterioration when SNR goes down in longer distances due to attenuation?

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    $\begingroup$ In general, higher frequencies suffer larger attenuation/path loss en.wikipedia.org/wiki/Attenuation. For long range communications, low frequencies are prefered. If you want higher SNR, it is better keeping carrier frequency unchanged and increasing TX power. $\endgroup$ – AlexTP Aug 15 '17 at 14:48
  • $\begingroup$ 'If you want higher SNR, it is better keeping carrier frequency unchanged and increasing TX power.' does this mean using higher number of cycles or trying to amplify the signal for more power? $\endgroup$ – S Fateri Aug 15 '17 at 14:52
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    $\begingroup$ @AlexTP by more cycles, he probably refers to longer duration at the same frequency, rather than higher frequency (more cycles per second)... He should clarify it better. $\endgroup$ – Fat32 Aug 15 '17 at 15:00
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    $\begingroup$ Yes, using longer duration (by adding more number of cycles) at the same frequency. So, to reconfirm, do you mean adding more number of cycles (longer duration) will have no affect on signal coverage? $\endgroup$ – S Fateri Aug 15 '17 at 15:50
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    $\begingroup$ ok. So it's better if you edit your quesiton to reflect this important detail. $\endgroup$ – Fat32 Aug 15 '17 at 16:29
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So yes, increasing the duration of the transmitted sinusoidal pulse (by increasing the number of cycles transmitted) will provide improved detection at the same SNR.

This is equivalent to a brute force bit duplication used to decrease the bit error rate (hence improve the reliable communication) at a given SNR. Note, however, that you will be transmitting at a slower rate than a shorter window.

So in effect, this method of longer window will compromise transmission rate vs improved detection at longer distance (lower SNR).

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  • $\begingroup$ As you rightly identified this method is known as repetition coding But I do not agree to the fact that it will improve the SNR. The reason being SNR = (Signal Power)/(Noise Power). Since signal power (energy per cycle) and noise statistics(Power Spectral Density) remain the same there is no change to SNR. $\endgroup$ – AnVij Oct 15 '17 at 13:20
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    $\begingroup$ ok thanks. But I don't say it would improve SNR anywhere in the answer? All I say is: it will decrease error rate at a given SNR.. therefore you have to upvote now! :-) $\endgroup$ – Fat32 Oct 15 '17 at 13:38

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