The difference between bit rate, baud rate and data transmission rate

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The difference between bit rate, baud rate and data transmission rate [Copy link]

1. Bit rate

　　Bit rate is also called signaling rate or information transmission rate (abbreviated as information rate). Its definition is: the amount of information transmitted per unit time (per second) of a communication line (or system), that is, the number of binary bits that can be transmitted per second, usually expressed as Rb, and its unit is bit/second (bit/s or b/s, abbreviated as bps in English).

　　In a binary system, the information rate (bit rate) is equal to the signal rate (baud rate). For example, when the system transmits 50 binary symbols per second, the information rate is 50 bit/s and the signal rate is also 50 Bd (baud). In the absence of modulation, the bit rate is equal to the baud rate; when phase modulation technology is used, the bit rate is not equal to the baud rate. The transmitting and receiving devices of the communication system must work at the same baud rate, otherwise frame synchronization errors will occur.

2. Baud rate

　　Baud rate is also called code rate, symbol transmission rate (symbol rate for short), signal transmission rate (signaling rate for short) or modulation rate. Its definition is: the number of symbols (pulses) transmitted per unit time (per second) of a communication line (or system); or the number of changes in the modulated signal waveform per unit time during signal modulation, usually expressed in RB, and the unit is baud (Bd or Baud, the former is the standard). If 1 symbol is transmitted per second, it is called 1Bd; if the duration of 1 symbol is 200ms, 5 symbols can be transmitted per second, then the symbol rate (baud rate) is 5Bd.

　　The baud rate (symbol rate) does not limit the symbol base, so the symbol base must be specified when the baud rate is given. For M-base symbols, the relationship between the bit rate (information rate) Rb and the baud rate (symbol rate) RB is
　　Rb=RB·lbM
　　, where lbM=log2M, which represents the logarithm of M with base 2. Obviously, for binary symbols, since lb2=1, Rb=RB, that is, the baud rate and the bit rate are equal in value, but the units are different, that is, the meanings of the two are different.

　　For example, if the baud rate is 600 Bd, then in binary, the bit rate is also 600 bit/s; in quaternary, since lb4=2, the bit rate is 1200 bit/s. It can be seen that multiple bits can be transmitted in one code element.

3. Data transfer rate

　　Data transfer rate is also called data transmission rate or data transfer rate. Its definition is: the number of characters transmitted per unit time (per second) of a communication line (or system); or the number of code groups (word blocks) or bits transmitted per unit time (per second). Its unit is character/second; or code group/second, bit/second (it can be seen that when the data transmission rate is expressed in "bit/s", it is equal to the bit rate).

　　For example, in a certain computer asynchronous serial communication system, the data transmission rate is 960 characters/s, each character includes 1 start bit, 8 data bits, and 1 stop bit, then the corresponding bit rate is 10×960 bits/s=9600 bits/s=9600bit/s; because it is binary encoding, the corresponding baud rate is also 9600Bd.

4. Baud, code element, bit

　　Baud (Bd) is a unit of measurement used to measure the number of signal changes per second for devices such as modems, that is, the number of times the state of the communication line changes per second, rather than the amount of data transmitted. The word "baud" comes from the name of a Frenchman - Baudot. He developed a coding scheme for the French telegraph system in 1877. If the modem transmits 1 bit of data for each signal change, then the bit rate (information rate) of the system is the same as the baud rate (symbol rate). However, after using coding technology, 1Bd (1 signal change) can represent 2 bits or more. Each baud represents 2 bits, which is called double-bit coding, and each baud represents 3 bits, which is called triple-bit coding. In other words, a change in the voltage (or current) waveform may include several bits of data, so the baud rate and bit rate cannot be confused; the former refers to the number of voltage (or current) changes (the amount of change), and the latter refers to the amount of data transmitted.

A code cell is a digital unit that carries information. It refers to a waveform symbol that transmits a digital signal in a digital channel, that is, "a signal coding unit on the time axis." A code cell can be binary or multi-ary.

　　Bit is the unit of measurement for "amount of information". The amount of information carried by 1 binary digit is 1 bit. For example, 10010110 is an 8-bit binary digit, and the amount of information it carries is 8 bits.