Baud

For the common Frenchwoman of the Morbihan, to see Baud. ----

Measure

In the field of the Telecommunications, the baud (symbol data base ) is a measurement of the number of symbols transmitted by second by a modulated signal, that is to say the modulation rate . It is named according to Emile Baudot, the inventor of the Code Baudot used in Télégraphie.

According to the Theorem of sampling of Nyquist-Shannon, the sampling rate of a signal must be at least the double of the maximum frequency of this signal. Example:

In telephony, for example, the spectrum is included/understood between 300 and 3400 hertz, the sampling rate must be at least of 6800 Hz. In practice, it is worth 8 Khz.

The binary debit is equal to the sampling rate, that is to say here 8 Kb/s.

If the bits are transmitted one by modulation rate is equal to binary debit but expresses themselves in baud.

If the bits are gathered in words of 2,3,…, N bits before being transmitted the modulation rate will be divided by N.

In this case the modulation rate and the binary debit do not have the same value.

The term baud is thus sometimes used wrongly to mean bits by second : this is true only when the signal is bivalent (only 2 values, 0 or 1, Valence =2).

Although it is possible to transmit a bit by symbol, one uses usually the Band-width in a more effective way by transmitting several bits by event. For example, a Modem of 1200 bit/s transmits to 1200 bauds; with the Amplitude modulation in squaring of phase, a technique which employs a combination of amplitude and phase modulation, it is possible to transmit several bits to each period of the signal.

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