# How can telecommunication system know which part is signal and which is noise? [closed]

When signal is received how can receiver know which part of received signal is signal and which part is noise??

To elaborate on MM's answer just a little bit. Unless the receiver has some sort of expectation of the nature of the signal there is no way to tell. With an expectation (for instance a pure tone), only a best estimation can be made with the rest assumed to be noise. With something like serial communication a voltage past a threshold is considered a "1" and no (or low) voltage is considered a "0". In noisy channels, parity bits (or error correcting codes) are used to ensure "what was sent". There are many possibilities, but the receiver has to know the nature of is being sent, which seems to be the answer you are fishing for.

They don't know.

They use estimation to figure out what was sent. Noise is everything random that disturbs that.

• But how can receiver know what was sent?? – user48391 Aug 4 '18 at 10:04
• I answered that. It doesn't know. It estimates. It's all an estimation problem. – Marcus Müller Aug 4 '18 at 10:06
• We can't remove noise completely in practical system than how signal is generated at receiver completely in presence of noise?? – user48391 Aug 4 '18 at 10:06
• We can't remove noise completely in practical system than how signal is generated at receiver completely in presence of noise?? – user48391 Aug 4 '18 at 10:06
• Please read my comments before answering to them. Thank you, and have a nice day. – Marcus Müller Aug 4 '18 at 10:07

I agree with Marcus Mueller, the receiver doesn't know. It uses a decision rule that was designed to minimize the probability that an error occurred in the received message given known and assumed characteristics of the signals that transport the message and the known and assumed characteristics of the noise. Noise can be many things, including other interacting transmitters and receivers.

The receiver doesn't know. It makes a "best" guess. The transmitter doesn't know if the message was received either. In many circumstances, feedback can improve the probability that messages have low probability of error.

There are other kinds of channels outside of this model such as the erasure channel where messages are lost between transmitter and receiver.

It is proven that all noise combined will form a distribution of gaussian function hence most of the receivers are designed with what you can call a matched filter what it does is reverse and shift by bit interval(tb) and integrate it & sample at which it has highest snr (of course it is at tb) but for real time application we use threshold detection and fec(forward error correction) and digital system we even have repeaters that placed bw tx &rx to minimize noise and if you use ofc it not effected by external noise so I suggest to read at least the basic block diagram of digital communication

• What about analog signal degraded by noise very heavily if two waves are mixed no one can differentiate their components than how receiver knows how much component is of signal and how much component of noise how receiver knows this much is signal power and this much is of noise – user48391 Aug 8 '18 at 12:28
• @user48391 there is nowhere telling which is noise and which is signal in analog communication but if you want to minimize the noise in analog communication then you can use FM(frequency modulation) because it has constant amplitude hence any amplitude changes can be considered as noise but the telecommunication uses digital modulation technique namely PCM(pulse code modulation)or even advanced techniques so your comment is not valid – Ch.Siva Ram Kishore Aug 8 '18 at 17:16
• @user48391 how often do you think repeating "how does the receiver tell noise from signal" will you need until you finally believe one of us that says "it cannot tell noise from signal". You've literally been told this seven times now (under your question here). Maybe you could start believing it! – Marcus Müller Aug 9 '18 at 9:45

Your question is too general, you need to specify a few and ask a targeted question but this doesn't mean that your question isn't good, so let me give you an answer to your question. You question concern the signal postprocessing and processing parts of a telecommunication system (transmitter and receiver). In the receiver channel, we found many components like LNA(Low Noise Amplifier) and then we find filtering operation to keep the desired frequencies. Pulsed radar, for example, use the matched filter (correlation) to detect the targeted signal in a noise Hope I gave you a good answer Good luck

• But filters are not ideal and we don't know characteristics of random noise how can receiver judge between signal and noise – user48391 Aug 4 '18 at 16:38
• you're just repeating your question, @user48391. Read Cedron's answer! The receiver can't "judge". It does a "as good as possible guess", based on the signal it receives. That's what receivers do. All receivers. How they do that completely depends on what kind of signal we're talking about, and what kind of receiver for that signal. – Marcus Müller Aug 4 '18 at 18:24