12. Interference & Noise

 

12. Interference & Noise



17.12.2018

Interference & Noise – Video: Register for Course


Interference & Noise – Transcript:

Noise

  • Noise is an additive „signal” added on top of the useful signal – that makes it distorted with constructive or destructive alternatives
  • This makes the signal level fluctuating thus the reception can be missed as the decision thresholds may be passed wrongly.
  • The noise power depends on the temperaturę and system BW and on the noise figure (the lower the value the better precision of the receiver electronic elements)
  • The received signal level should be larger than the noise-floor that is defined by the thermal noise power shown in the table. The wider the system BWs the more noise power it is expected – thus the wider the BW the more useful signal power should be delivered.

Interference Channel Disortion

  • Other type of distortion is interference
  • When we transmit a useful signal on a given frequency and of given BW – it has certain character – e.g. wifi signal
  • Then we have other similiar systems working on the same carrier frequency (e.g. channel 1 at 2.4Ghz) between aps and STAs,
  • The character of the signal is similiar – same BW and freq response
  • This interferes with our useful signal over the whole BW
  • Then there are other systems that could work in the same spectrum range, but being of a different character – that is e.g. a sensor / bluetooth, microwave oven etc. Using the same frequencies, but the signal looks different – the frquency response, BW, burstiness or constant signal – all that matters for the interference character, and how the signal distorts our useful signal

Interference Dominant

  • There are at least two types of interference : dominant vs non-dominant
  • The first one covers the situation, that there is a single cochannel signal that is strong (i.e. received at our STA) at the level that can be seen as of similiar amplitudę / power than the useful signal. In this case the received signal is changing its character and is strongly destroyed – but on the other hand if we know that this is a certain type of transmission, there are methods to cope with this by means of e.g. succesive interference cancellation
  • On the other end if there are no dominant interferenrs, the signals from multiple sources that are of lower values of power (and more than one of them), the resulting signal is impaired by an interference that looks similiar to noise – as the character of the interference is of random nature

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