Baud
Encyclopedia
In telecommunications and electronics
, baud (ˈ, unit symbol "Bd") is synonymous to symbols per second or pulses per second. It is the unit of symbol rate
, also known as baud rate or modulation rate; the number of distinct symbol changes (signaling events) made to the transmission medium per second
in a digitally modulated
signal or a line code
. The baud rate is related to but should not be confused with gross bit rate expressed in bit/s.
The symbol duration time, also known as unit interval
, can be directly measured as the time between transitions by looking into an eye diagram of an oscilloscope
. The symbol duration time Ts can be calculated as:
where fs is the symbol rate.
The baud unit is named after Émile Baudot
, the inventor of the Baudot code
for telegraphy
, and is represented as SI units
. That is, the first letter of its symbol is uppercase (Bd), but when the unit is spelled out, it should be written in lowercase (baud) except when it begins a sentence.
The term baud rate has sometimes incorrectly been used to mean bit rate, since these rates are the same in old modem
s 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. In more advanced modems and data transmission techniques, a symbol may have more than two states, so it may represent more than one bit (a bit (binary digit) always represents one of exactly two states).
If N bits are conveyed per symbol, and the gross bit rate is R, inclusive of channel coding overhead, the symbol rate fs can be calculated as:
In that case M=2N different symbols are used. In a modem, these may be sinewave tones with unique combinations of amplitude, phase and/or frequency. For example, in a 64QAM modem, M=64, and so the bit rate is N=6 times the baud rate. In a line code, these may be M different voltage levels.
The ratio might not even be an integer; in 4B3T
coding, the bit rate is 4/3 the baud rate. (A typical basic rate interface
with a 160 kbit/s raw data rate operates at 120 kbaud.) On the other hand, Manchester coding has a bit rate equal to 1/2 the baud rate.
By taking information per pulse N in bit/pulse to be the base-2-logarithm
of the number of distinct messages M that could be sent, Hartley
constructed a measure of the gross bitrate R as:
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
, baud (ˈ, unit symbol "Bd") is synonymous to symbols per second or pulses per second. It is the unit of symbol rate
Symbol rate
In digital communications, symbol rate is the number of symbol changes made to the transmission medium per second using a digitally modulated signal or a line code. The Symbol rate is measured in baud or symbols/second. In the case of a line code, the symbol rate is the pulse rate in pulses/second...
, also known as baud rate or modulation rate; the number of distinct symbol changes (signaling events) made to the transmission medium per second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
in a digitally modulated
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
signal or a line code
Line code
In telecommunication, a line code is a code chosen for use within a communications system for baseband transmission purposes...
. The baud rate is related to but should not be confused with gross bit rate expressed in bit/s.
The symbol duration time, also known as unit interval
Unit interval (data transmission)
The unit interval is the minimum time interval between condition changes of a data transmission signal, also known as the symbol duration time....
, can be directly measured as the time between transitions by looking into an eye diagram of an oscilloscope
Oscilloscope
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical or 'Y' axis, plotted as a function of time,...
. The symbol duration time Ts can be calculated as:
where fs is the symbol rate.
- A simple 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 modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
, 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.
The baud unit is named after Émile Baudot
Émile Baudot
Jean-Maurice-Émile Baudot , French telegraph engineer and inventor of the first means of digital communication Baudot code, was one of the pioneers of telecommunications...
, the inventor of the Baudot code
Baudot code
The Baudot code, invented by Émile Baudot, is a character set predating EBCDIC and ASCII. It was the predecessor to the International Telegraph Alphabet No 2 , the teleprinter code in use until the advent of ASCII. Each character in the alphabet is represented by a series of bits, sent over a...
for telegraphy
Telegraphy
Telegraphy is the long-distance transmission of messages via some form of signalling technology. Telegraphy requires messages to be converted to a code which is known to both sender and receiver...
, and is represented as SI units
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...
. That is, the first letter of its symbol is uppercase (Bd), but when the unit is spelled out, it should be written in lowercase (baud) except when it begins a sentence.
Relationship to gross bit rate
The symbol rate is related to but should not be confused with gross bit rate expressed in bit/s.The term baud rate has sometimes incorrectly been used to mean bit rate, since these rates are the same in old modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s 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. In more advanced modems and data transmission techniques, a symbol may have more than two states, so it may represent more than one bit (a bit (binary digit) always represents one of exactly two states).
If N bits are conveyed per symbol, and the gross bit rate is R, inclusive of channel coding overhead, the symbol rate fs can be calculated as:
In that case M=2N different symbols are used. In a modem, these may be sinewave tones with unique combinations of amplitude, phase and/or frequency. For example, in a 64QAM modem, M=64, and so the bit rate is N=6 times the baud rate. In a line code, these may be M different voltage levels.
The ratio might not even be an integer; in 4B3T
4B3T
4B3T stands for 4 Binary 3 Ternary, a line encoding scheme used for ISDN BRI interface. 4B3T represents four binary bits using three pulses.It uses three states:* + ,* 0 , and* − ....
coding, the bit rate is 4/3 the baud rate. (A typical basic rate interface
Basic rate interface
Basic Rate Interface is an Integrated Services Digital Network configuration intended primarily for use in subscriber lines similar to those that have long been used for plain old telephone service...
with a 160 kbit/s raw data rate operates at 120 kbaud.) On the other hand, Manchester coding has a bit rate equal to 1/2 the baud rate.
By taking information per pulse N in bit/pulse to be the base-2-logarithm
Logarithm
The logarithm of a number is the exponent by which another fixed value, the base, has to be raised to produce that number. For example, the logarithm of 1000 to base 10 is 3, because 1000 is 10 to the power 3: More generally, if x = by, then y is the logarithm of x to base b, and is written...
of the number of distinct messages M that could be sent, Hartley
Ralph Hartley
Ralph Vinton Lyon Hartley was an electronics researcher. He invented the Hartley oscillator and the Hartley transform, and contributed to the foundations of information theory.-Biography:...
constructed a measure of the gross bitrate R as:
See also
- BandwidthBandwidth (computing)In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
- BitrateBitrateIn telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
- Constellation diagramConstellation diagramA constellation diagram is a representation of a signal modulated by a digital modulation scheme such as quadrature amplitude modulation or phase-shift keying. It displays the signal as a two-dimensional scatter diagram in the complex plane at symbol sampling instants...
, which shows (on a graph or 2D oscilloscope image) how a given signal state (a symbol) can represent three or more bits at once. - ModulationModulationIn electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
- ModemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
- Nyquist rateNyquist rateIn signal processing, the Nyquist rate, named after Harry Nyquist, is two times the bandwidth of a bandlimited signal or a bandlimited channel...
- Symbol rateSymbol rateIn digital communications, symbol rate is the number of symbol changes made to the transmission medium per second using a digitally modulated signal or a line code. The Symbol rate is measured in baud or symbols/second. In the case of a line code, the symbol rate is the pulse rate in pulses/second...
- List of device bandwidths
- PCM