Solution to the most common confusion : BAUD RATE Vs BIT RATE/Data RATE

Yesterday while tinkering over some serial communication projects, We found a problem of baud rate mismatching of two devices. Thinking as a noob, Baud rate seems to be same as bit rate, tried something and again faced that problem. After some googling and reading stuff we concluded to a simple definition which can easily differentiate between Baud Rate and Bit Rate.

Baud rate is the number of change in signal-state/ pulse/symbol per second in a communication channel.

For example :-  A baud rate of 1 kBd = 1,000 Bd is synonymous to a symbol rate of 1,000 symbols per second. In case of a modem, this corresponds to 1,000 tones per second, and in case of a line code, this corresponds to 1,000 pulses per second. The symbol duration time is 1/1,000 second = 1 millisecond.

Also if any circuit shows a baud rate of 9600, that means circuit changes its signal-state 9600 times in a second. Signal-State change can include 0 to 1 or vice versa.

The symbol rate is related to but should not be confused with gross bit rate expressed in bit/s.

Bit Rate is the number of data bits (i.e. ‘0’ or ‘1’) transferred per second in a communication channel.

For example :- A bit rate of 2400 means there are 2400 ‘0’s or ‘1’s to be transmitted across communication channel in 1 second.

The main difference between the two is that one change of state can transmit one bit, or slightly more or less than one bit, that depends on the modulation technique used. So the bit rate (bps) and baud rate (baud per second) have this connection:

bps = baud per second X the number of bit per baud

The term baud rate has sometimes incorrectly been used to mean bit rate, since these rates are the same in old modems as well as in the simplest digital communication links using only one bit per symbol, such that binary “0” is represented by one symbol, and binary “1” by another symbol.

The modulation technique determines the number of bit per baud. Here are two examples:

When FSK (Frequency Shift Keying, a transmission technique) is used, each baud transmits one bit. Only one change in state is required to send a bit. Thus, the modem’s bps rate is equal to the baud rate. When a baud rate of 2400 is used, a modulation technique called phase modulation that transmits four bits per baud is used.

So:          2400 baud x 4 bits per baud = 9600 bps

Such modems are capable of 9600 bps operation.

If you want to share more knowledge about baud rate and bit rate, feel free to share it with us.