Baud
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- For the town in France, see Baud, Morbihan.
In telecommunications and electronics, baud (pronounced Template:IPA) is a measure of the "signaling rate" which is the number of distinct symbolic changes made to the transmission medium per second in a modulated signal. It is named after Émile Baudot, the inventor of the Baudot code for telegraphy.
For example: 250 baud means that 250 symbols are transmitted in one second. For instance, if 16 different symbols have been defined (each carries 4 bits of information), then in each second 1000 bits of information are transmitted, but with having to send only 250 actual symbols, rather than sending 1000 binary symbols (bits).
Note: Baud should not be confused with data rate (also called "bits per second", or bytes per second, etc.). Each signalling event transmitted can carry one or more bits (for example, 8 bits in 256-QAM modulation) of information. When each signalling event transmitted carries one bit the baud rate and the data rate are equal. However, it is more common to make better use of bandwidth by encoding multiple bits in one event. This reduces the time required for sending a given quantity of data.
Thus, a 2400 bit/s modem actually transmits at 600 baud (600 symbols/sec), where each quadrature amplitude modulation symbol carries four bits of information.
A clear example of the difference between the baud (or signalling rate) and the data rate (or bit rate) is a man using a single semaphore flag. He can move his arm to a new position once each second, so his signalling rate (or baud rate) is 1 per second. However, the flag can be held in one of eight distinct positions: Straight up, 45 degrees left, 90 degrees left, 135 degrees left, straight down (which is the rest state, where he is sending no signal), 135 degrees right, 90 degrees right, and 45 degrees right. This means each signal carries three bits of information, as it takes 3 binary digits to encode 8 distinct states – so the data rate is 3 bits per second.
Modems work in the same way – a 2400 bit/s modem will typically have a baud rate of 600 per second – but each signal carries 4 bits of information encoded within it, allowing a data rate of 2400 bit/s.
See also
External links
- {{cite web
| title=On the origins of serial communications and data encoding | url=http://www.compkarori.com/dbase/bu07sh.htm | accessdate=February 28 | accessyear=2006 }}
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