# How the bit rate is related to channel bandwith?

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#### magnetra

##### Full Member level 5
Bandwidth

This is in reference to a section in Modern Digital and Analog communication by B.P Lathi.

The author states, in digital communication, fundamental basis of determining bandwith is "Two signals without error can be transmitted per sec per Hz"

In fact I'm confused how the bit rate is related to channel bandwith in Digital Communication? Anyone please explain.

Magnetra

#### sameerbabu

##### Member level 3
Re: Bandwidth

According to Nyquist theorem
theoretical maximum u can transmit is 1 symbol/s in 1 Hz band

u may be knowig symbol/s and bps relation

#### magnetra

##### Full Member level 5
Re: Bandwidth

Hmm the Bandwidth required in Digital communication doesn't seem to be related to the message as in case of Analog Comm'n. But I don't understand how the bandwidthis determined in Digital commn
Any place on the net which has a good explanation.?

Magnetra

#### magnetra

##### Full Member level 5
Bandwidth

Is the question too trival to be bothered about or is it a tricky one??

Magnetra

#### rednewguy

##### Full Member level 2
Re: Bandwidth

in digital communication, the channel bandwidth only depends upon the bit rate. take u r going to represent 0 and 1 using NRZ coding. 0 with negative pulse and 1 with positive pulse.

the frequency domain characteristic of a rectangular pulse is sinc, which means u need frequencies of (- infinity to + infinity) ---> infinite bandwidth

in practice we use raised cosine to represent 0\1s which takes only main lobe of the sinc function.

reduce the pulse width(increase bit rate), main lobe size increases(increased bandwidth)

#### mro83

##### Member level 5
Bandwidth

in the information theory u have the Shannon's theorems.
it states:
C = BW. log(1+SNR) i.e; capacity of the channel is related to bandwidth and SNR of the signal and noise.
and capacity is related to Hs (Antrpy of the source ) and Rs (Symbol rate).
for more detailed discussion refer to "digital communication " books. or the essay in this link :
https://www.edaboard.com/viewtopic.php?t=143493&highlight=

cheers

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