baud

[After Jean Maurice Emile Baudot (1845-1903), French engineer.]

The signaling rate of a line, which is the number of transitions (voltage or frequency changes) that are made per second. The term has often been erroneously used to specify bits per second. However, only at very low speeds is baud equal to bps; for example, 300 baud is the same as 300 bps. Beyond that, one baud can be made to represent more than one bit. For example, a V.22bis modem generates 1,200 bps at 600 baud.

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Measurement of the speed of a modem, specifically the number of times per second a communications channel changes the carrier signal it sends on the phone line. A 56,000-baud (56K) modem changes the signal 56,000 times a second. Baud is often confused with bits per second (Bps); technically, they are different measurements.

[simplified from its technical meaning] n. Bits per second. Hence kilobaud or Kbaud, thousands of bits per second. The technical meaning is level transitions per second; this coincides with bps only for two-level modulation with no framing or stop bits. Most hackers are aware of these nuances but blithely ignore them.

Historical note: baud was originally a unit of telegraph signalling speed, set at one pulse per second. It was proposed at the November, 1926 conference of the Comité Consultatif International Des Communications Télégraphiques as an improvement on the then standard practice of referring to line speeds in terms of words per minute, and named for Jean Maurice Emile Baudot (1845-1903), a French engineer who did a lot of pioneering work in early teleprinters.

[Etymology: J. M. E. Baudot; France 1845-1903] electromagnetics, informatics In telegraphy and other digital signalling, the time between representative samplings of the signal, during which any transition of signal state occurs, for example a hundredth of a second. A transmission line with such a rate of transition/reading would invariably be called a ‘100-baud’ line; in such an expression the baud becomes a rate rather than the original time element. Since virtually all telegraphy and most similar transmission until recently used only two levels for transition, each baud accommodated just 1 bit; hence a 100-baud line was often referred to as being of 100 bits per second. In reality, most lines of such magnitude dissipate from 10 to over 30% of their capacity on asynchronous signal control, so the translation to bits is quite exaggerated to the user. Modern high-speed circuits dissipate very little, so the nominal figure is not significantly misleading; however, its transition/reading scheme may be very different, with perhaps eight levels communicating three bits per baud on a ‘4 800-baud’ line (i.e. sampled every ¹/₄₈₀₀ s = 208.33~ μs), giving 14.4 kilobits per second (numerically far in excess of the 4 000 Hz bandwidth usually provided for a standard telephone circuit). More levels, and hence greater multiplication from baud rate to bit rate, are increasingly common as greater transmission rates are pursued. There is no absolute limit to the number of discernible transitions (hence bits per baud) or to the number of bauds or samples per second for any line circuit. The quality of the circuit and its equipment is the sole arbiter. Higher rates often involve error detection/correction techniques that reduce the effective transfer rate through both control and re-transmission, but often use data compression techniques that enhance the effective rate even more.

See also kibi-.

It has been suggested that this article or section be merged with Symbol rate. (Discuss)

For the town in France, see Baud, Morbihan.

In telecommunications and electronics, baud (pronounced /ˈbɔːd/, 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 T_s can be calculated as:

where f_s 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 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.

The baud unit is named after Emile Baudot, the inventor of the Baudot code for telegraphy, and is represented as SI units are. 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.

Contents 1 Relationship to gross bit rate 2 See also 3 References 4 External links

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 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. In more advanced modems and data transmission techniques, a symbol may have more than two states, so it may represent more than one binary bit (a binary bit 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 can be calculated as:

In that case M=2^N 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. In a line code, these may be M different voltage levels.

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^[1] constructed a measure of the gross bitrate R as:

See also

• Bandwidth
• Bitrate
• Constellation diagram, which shows (on a graph or 2D oscilloscope image) how a given signal state (a symbol) can represent three or more bits at once.
• Modulation
• Modem
• Nyquist rate
• Symbol rate
• List of device bandwidths
• PCM

References

1. ^ D. A. Bell (1962). Information Theory; and its Engineering Applications (3rd ed. ed.). New York: Pitman. 

External links

• "On the origins of serial communications and data encoding". http://www.compkarori.com/dbase/bu07sh.htm. Retrieved January 4 2007. 

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Dansk (Danish)
n. - baud

idioms:

• baud rate    baudhastighed

Nederlands (Dutch)
1 bit per seconde (computer)

Français (French)
n. - baud

idioms:

• baud rate    vitesse en bauds

Deutsch (German)
n. - Baud, (Einheit der Telegraphiergeschwindigkeit)

idioms:

• baud rate    Baudrate

Ελληνική (Greek)
n. - μονάδα ταχύτητας μετάδοσης δεδομένων

idioms:

• baud rate    ταχύτητα μετάδοσης δεδομένων

Italiano (Italian)
unità di trasmissione dati

Português (Portuguese)
n. - baud (medida de transmissão de dados) (Inf.)

Русский (Russian)
бод

Español (Spanish)
n. - baudio

idioms:

• baud rate    velocidad de transmisión de datos (en baudios)

Svenska (Swedish)
n. - baud (måttenhet för överföringshastighet)

中文（简体）(Chinese (Simplified))
波特

idioms:

• baud rate    传输速率

中文（繁體）(Chinese (Traditional))
n. - 波特

idioms:

• baud rate    傳輸速率

한국어 (Korean)
n. - 보드(데이터 처리 속도의 단위)

日本語 (Japanese)
n. - ボー

العربيه (Arabic)
‏(الاسم) وحدة قياس, الأرسال التلغرافي‏

עברית (Hebrew)
n. - ‮באוד (יחידת מהירות) - סיבית לשניה‬

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