# White noise in communication channel

• LM741
In summary, the white noise in a communication channel is used to represent thermal noise and random bursts of noise. The DC component of the noise signal is irrelevant and can be ignored.

#### LM741

hi all - its been very long - hope everyone is well!

just a data comms related question:

When modelling a communication channel we normally include AWGN, that is, Additive white gaussian noise.

Can anybody tell me why we use white noise in the model. I know it has a constant power spectral density for all frequencies - but how does this help us or make things better?
Also, apperently the DC component( mean) of the noise signal is zero - is this because we use the Gaussian distribution? i.e. how to we get it to equal zero?

thanks very much

John

sqrt(4kTBR)=Vn

short answer: the noise is proportional to resistance, temp and bandwidth. you can get it equal by using a balanced circuit where these variables are the same and have common mode rejection reduce it to dc.

is my guess :tongue2:

Hello 741!

1) Thermal receiver noise is white, as mentioned above, and counts as part of the channel. Other noise, including that from motors, transmitters, lightning, etc. is random as well so, on average, at any time position and frequency, it's described well by Gaussian statistics.
2) DC is irrelevant to a high frequency communications system and isn't even picked up by the antenna or electronics. (Same is true of ethernet and other cabled digital channels.) Hence zero mean.

BTW, Did you figure out the sampled data/DFT stuff?

sup marcusl! thanks
ha ha - man can't believe you remember that stuff! yeah finaaly grabbed it by the horns and grasped it! actually ended up failing Signals and Systems 2 end of year - but there is a happy ending to the story - coz i qualified for a supp in January and passed - so thanks for all your help!
thanks ligh_bulb
so marcus - you telling me that the white noise is used to represent thermal noise and random amplidutes ( created by Gaussina) are used to repreent random bursts of noise - so in essence, we are represnting two types of noise? but what is so special about a CONSTANT power spectral density? thanks

Over large spans the noise power spectral density (PSD) can vary--it's different at 1MHz and 10GHz--but over any typical narrow channel it just doesn't vary much. For example, Verizon cell phones operate on a protocol called CDMA, occupying a 1.5 MHz channel located within one of Verizon's 5 MHz wide frequency allocations. Center frequency is 1.9GHz. Over this narrow channel a constant average PSD is a good approximation.

thanks
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## 1. What is white noise in communication channel?

White noise in communication channel refers to a random signal that contains an equal amount of energy at every frequency. It can be thought of as background noise that is present in all communication channels.

## 2. How does white noise affect communication?

White noise can interfere with the transmission and reception of information in a communication channel. It can reduce the signal-to-noise ratio, making it more difficult to distinguish the desired signal from the noise.

## 3. What causes white noise in communication channels?

White noise can be caused by a variety of factors, including atmospheric conditions, electronic interference, and thermal noise from electronic components. It can also be intentionally added to a signal to improve its quality.

## 4. How can white noise be reduced in a communication channel?

There are a few ways to reduce white noise in a communication channel. One method is to use filters to remove unwanted noise from the signal. Another approach is to increase the signal strength to improve the signal-to-noise ratio. Additionally, using error-correcting codes can help minimize the impact of white noise on the transmission of information.

## 5. Is white noise always undesirable in communication channels?

No, white noise is not always considered undesirable. In some cases, it can actually be beneficial for improving the quality of a signal. For example, adding a small amount of white noise to a signal can help reduce distortion and improve the overall fidelity of the signal.