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It is said that 9600 bps is the data rate given and if each signal element represents 4 bits then what is frequency?
What I did since each signal element represents 4 bits then in a second (9600/4) 2400 signal elements per second gives a frequency of 2400 Hz.
How frequency is calculated when signal element represents more than 1 bit?
The data rate in any communication channel is equal to the Symbol Rate if there is 1 bit per symbol.
For any multi-level coded channel (where there is more than 1 bit per symbol), the symbol rate is simply the data rate / bits per symbol.
In this case, there are 4 bits per symbol, the data rate is 9600 bits per second and the symbol rate is therefore 2400 symbols per second assuming no channel overhead.
Note that Baud rate is one of the most misused terms in communications, because it does not equal the data rate unless there is only 1 bit per symbol but is often used in this context incorrectly.
There are numerous methods of encoding multiple bits per symbol.
If you have channel overhead (such as in an asynchronous channel over RS232), then the total symbol rate must include this.
If we have an ordinary channel (1 start bit, 1 stop bit, no parity, 8 data bits), then each data frame will contain 10 bits for a total data rate of 1.25 the raw data rate.
For a 9600 bps link (where the 9600 refers to the total data rate including framing overhead), the actual data rate (the number of bits conveying payload data) is 7680 bits per second.
In this case, if the full data rate (including overheads) is 9600 bits per second, then the symbol rate is, quite simply, 2400 per second. We rarely use the term Hertz when referring to data rates, incidentally.
All practical channels have some coding overhead (whether they be synchronous or asynchronous).
If each symbol represents four bits then the symbol rate is 2400 symbols per second. Lets assume we represent each symbol by a voltage level.
For such signals the "worst case fundamental" frequency is half the symbol rate or 1200 Hz. There will of course be harmonics beyond this but those harmonics are not vital to reconstructing the data stream.
