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I am currently researching existing literature for my master thesis about passive sensing using different radio-wave-modules (e.g. UWB and WiFi).

The question I would like to research is whether higher bandwidth (= UWB) leads to better passive sensing (e.g. human detection / location / counting) than WiFi (which has like 1/3rd of the bandwidth).

What is the theory behind higher bandwidth that could actually explain if this is true?

My primitive idea is that the carrier frequency of the signal is most important because the higher frequency the smaller the wavelength which is equal to higher "resolution", e.g. if a wave is 50cm long it might pass directly through a human body and we don't see anything on the resulting change of the channel, whereas a 10cm long wave gets irritated by a human body and therefore we see a change in the channel information.

How does bandwidth come into play here? Why would it be beneficial to transfer data via 500MHz of bandwidth rather than 160 MHz of bandwidth (except higher data rates with less energy consumption) for passive sensing?

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  • \$\begingroup\$ You might be confusing the concepts of detection, and location. It's worth tabulating all the different mechanisms by which each is done (timing, triangulation etc). \$\endgroup\$
    – Neil_UK
    May 7, 2023 at 8:49
  • \$\begingroup\$ What you are describing IS NOT passive sensing. \$\endgroup\$
    – Andy aka
    May 7, 2023 at 9:05
  • \$\begingroup\$ "radio-wave-modules" is not a term that you'd find in literature. UWB is a statement on the relation of bandwidth to carrier frequency, and WiFi is a set of complex communications standards, so "UWB" and "WiFi" don't even come from the same category of terms. I think you might need to go back and untangle a bit of basics. \$\endgroup\$ May 7, 2023 at 9:48
  • \$\begingroup\$ @MarcusMüller I mean, WiFi is not commonly refered to as ultra-wideband so there is a distinction with respect to bandwidth. That's what I meant \$\endgroup\$ May 7, 2023 at 11:28

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As commenters have suggested already, you would be wise to study the basics of radio based detection and ranging (i.e. radar) before jumping to technology buzzwords like WiFi and UWB. They've also pointed out that passive sensing means different things to different people, but it seems to me you're talking about radar-style detection of objects.

You are correct that shorter wavelengths help with resolution in several ways: first, a given object has a larger effective cross section at higher frequencies, bouncing more of the radio wave back which improves sensitivity; second, for a given antenna size, the radar beam can be made narrower at higher frequencies, allowing you to better determine the angular position and even the shape and size of the object (providing you have a way to steer that beam).

The reason bandwidth is important is that the radio wave must be modulated in order to detect the distance to the object. When you modulate a radio wave, you increase its bandwidth. Originally radars transmitted a short pulse (a few microseconds), and the length of the pulse determined the distance resolution. Newer radars transmit continuously and modulate the frequency of the wave instead, but the same principle applies: the faster the modulation (and therefore the wider the bandwidth) the better the resolution in distance.

Your thesis should begin with a section demonstrating a thorough understanding of basic principles like these.

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If you're asking about radar, the ability to resolve something in distance depends on how fast the modulation changes longitudinally (along the direction of propagation). In the extreme case of a monochromatic waveform, you broadcast a perfect sin wave and have no way to know which cycle is which when they reflect and so no idea how far the reflector is. For a broadband waveform, the modulation changes faster and you have better distance range resolution.

Conversely the ability to focus a beam in the transverse dimension depends only on the center wavelength and not the bandwidth of the modulation. Consider something like a laser door sensor. This has no modulation at all by can precisely measure when something passes the exact edge of the door because optical frequencies have very short wavelengths.

Consider as an example a radar system at 2.4 GHz with a 100 MHz bandwidth and a lidar system at 240 THz (infrared) with a 100 MHz modulation. Both systems have the same bandwidth and so the same distance resolution. But the lidar system has 100,000 times shorter wavelength, so if scanned it will focus down to a spot ~ 100,000^2 as small and so have much better transverse resolution.

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