on November 15, 2009 by denpras in Transmission, Comments (0)
Baud Rate not Bit Rate ??
We try to discuss more about tranmission system. When we send our information data to destination through transmission network we require sufficient transmission bandwidth to accommodate the spectrum of the signal. If not we face about signal distortion.
I refresh that communication signal is a quantity that is always changing with time. We can map it into time domain and frequency domain. We know for terminology spectrum in frequency domain, and for time domain we know for totalling sinusoidal spectrum. For analyze that, we have to know more about Fourier formula.
If we see deeper, a pulse signal in time domain and frequency domain can be shown in this picture :
For example, if pulse duration T = 1 miliseconds (ms), we have strongest spectrum of signal in 1 Khz (1/T = 1/1 ms = 1,000 1/s = 1 kHz). In other words, we can send 1000 pulse in 1 seconds ( 1 / 1000 sec = 1 ms ) in bandwidth 1 Khz, it is same with biner signal with rate 1 Kbps.
To increase data rate, we have to reduce the duration of pulse width of the spectrum, but the consequences will increase and thus require a wider bandwidth. So if we want to increase data rate to be 10 times, we should use pulse time 10 times shorter and need bandwidth 10 times wider.
We can say that is a major limiting factor for the transmission of the data, and then there is relationship between data rate with bandwidth needed. Reducing data rate will increase network capacity.
In telephone line implementation, we do the voice coding to reduce data rate transmission to make higher quality transmission in fixed bandwidth.
In fact, every transmision channel have a limited bandwidth. When data rate increase, digital pulse duration will be shorter, the result is increasing consuming bandwidth. When a signal changes rapidly change from the time spectrum it will be widened so that we say that the signal has large bandwidth.
It means signal transmission with high data rate transmission channel must use a wide bandwidth. I must be taken to get rid from error detection reading the bit symbol, we know as an ISI ( Intersymbol Interference ) effect.
The baseband transmission of a digital signal which consisting of r symbols per second required transmission bandwidth in unit Hertz : B >= r/2.
So we have to say date rate for sending symbol per second is baud rate not bit rate !
Clearly, in data tranmission with 1000 baud ( symbol / second ) is same with sending data with bit rate 2000 bit / second if using QPSK modulation.
Now, we’ve already known about bit rate and baud rate..the relation between them will be discussed in next posting.
Keep smiling !
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Tags: Telecommunication, Transmission
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