I have to admit, I haven’t thought about baud rate in quite some time. In my daily work I have moved ‘up the stack,’ and can safely assume that someone else has done the work to ensure that the information I send between software components gets to its destination as intended. It’s good, however, to understand how this reliability comes about, and a basic understanding of the role baud rate and bit rate helps.
Digital communication relies on sending and receiving data by encoding information in binary digits or bits. Two key metrics for measuring digital communication speeds are baud rate and bit rate. While these terms are sometimes used interchangeably they actually refer to different things. This article will explain what baud rate and bit rate mean, how they relate, and when you need to know the difference.
What is Baud Rate?
Baud rate refers to the number of signaling elements or symbols that are transmitted each second during communications A symbol represents one or more bits of data The term comes from the last name of Émile Baudot, who developed an early digital communications code.
For example, a baud rate of 2400 means 2400 symbols are transmitted per second. The baud unit is similar to cycles per second or hertz.
Originally, baud rate was used in telegraph systems, referring to the number of dot/dash code elements sent. Today it still indicates the switching speed of a communication channel to update or change the state of the signal.
Higher baud rates allow more information to be encoded and carried over communication links. But the baud rate does not always equal the bit rate.
What is Bit Rate?
Bit rate describes the number of binary bits transmitted each second during digital communications. This directly indicates the actual data throughput rate.
Common measures include kbps (kilobits per second), Mbps (megabits per second) and Gbps (gigabits per second).
Bit rate depends on three factors:
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The baud rate
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The number of bits encoded in each symbol
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Any overhead bits being transmitted along with the data payload
When there are more bits encoded per baud, the bit rate increases accordingly. The relationship between baud rate and bit rate is:
Bit rate = Baud rate x (Bits per symbol)
Baud Rate vs Bit Rate Example
For example, let’s say a modem has a baud rate of 2400. By default, each symbol represents 1 bit using simple binary encoding. Therefore, the bit rate is:
2400 baud x 1 bit per symbol = 2400 bits/second
Now let’s change the encoding to represent 2 bits per symbol. The baud rate is still 2400. But the bit rate doubles to:
2400 baud x 2 bits per symbol = 4800 bits/second
This shows why bit rate can be higher than baud rate – multiple bits are squeezed into each symbol. The baud rate stays the same, but more information transmits each second at a higher bit rate.
When Bit Rate Equals Baud Rate
In the simplest case, each symbol represents one binary bit. This is used in basic modulation schemes like on-off keying. Then the bit rate equals the baud rate, since they directly correspond.
Baud rate = bit rate when using:
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Binary frequency shift keying (2FSK)
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Binary phase shift keying (BPSK)
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Simple non-return-to-zero binary encoding (NRZ)
Keys for Remembering the Difference
Here are some simple ways to remember whether baud rate or bit rate is the right term:
- Baud rate refers to symbols per second
- Bit rate tells actual throughput in bits per second
- Baud rate measures signaling rate on the channel
- Bit rate depends on bits encoded in each symbol
- For simple modulation using 1 bit per baud, they are equal
- Baud rate stays constant while bit rate can vary
Why the Distinction Matters
Understanding the difference between baud rate and bit rate is essential for choosing modems and setting up communications links properly.
For instance, a 2400 baud modem can’t handle an arbitrary 2400 kbps bit rate. It may require a higher baud rate modem, or a multi-bit encoding scheme.
Matching the baud rate of modems or other equipment with channel bandwidth is critical. A faster bit rate may require upgrading baud rate to support more symbols per second.
And when quantifying throughput for networking capacity planning, bit rate gives the usable data rate, while baud rate refers to just the underlying signaling rate.
Real-World Applications
Let’s look at some examples of different baud rates and bit rates in real communications systems:
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Telephone modems often used 2400 or 56k baud rates, with each symbol mapping to 1 bit for 2400 or 56k bits/sec throughput.
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Digital TV uses a technique called 8-VSB encoding about 10,760,000 baud per channel, with 3 bits per symbol, achieving a bitrate of 32.4 Mbps.
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DOCSIS cable modems use QAM encoding, with typical symbol rates of 5120 kHz to 6952 kHz baud, and anywhere from 1 to 10 bits encoded per baud depending on configuration.
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5G NR mobile technology defines modulation schemes with 15 kHz to 480 kHz subcarriers, and 2 to 256 QAM encoding (2 to 8 bits per symbol per subcarrier).
To summarize, baud rate describes the symbol signaling rate per second for digital communications. Bit rate indicates the actual throughput in bits per second. When each symbol maps to a single binary bit, they are equal. But as modulation schemes encode more bits per symbol, bit rate increases relative to baud rate. Understanding this key difference allows matching of modem equipment, utilization of channel capacity, and accurate networking performance measurement.
Frequency of Entities:
geeksforgeeks.org:
baud rate: 20
bit rate: 17
electronicdesign.com:
baud rate: 13
bit rate: 12
The Challenge of Streaming 1s and 0s from Point A to Point B
It turns out that getting a signal from one end of a piece of wire or fiber to the other is pretty tricky, especially with increasing line length and transmission rate. The important thing to know is that the signal that comes of the line is not exactly the same as the signal that went in. See the figure below:
From the figure we can see that the cooper cable of the transmission line is a lot more complex than a straight connection. The length of the cable adds resistance, induction, and capacitance components which distort the signal as it travels.
In the case of optical fibre, the multiple paths photons can travel (even with single mode fibre) have different lengths, stretching and distorting the signal. The output signal shown is smaller and less defined than the source signal and it is delayed with respect to the timing grid.
The big advantage that optical technologies have over copper technologies, apart from lower loss for a given length, is less electromagnetic interference. Any single electrical signal flowing down a wire will emit some of the signal as electromagnetic energy, which can be picked up by other conductors (wires) and converted back into an electrical signal. This means that foreign signals may also be present on the transmission line, as well as the original signal. A key requirement is to be able to ensure the required signal can be distinguished from the unwanted signals (also known as “noise”) at the receiving end.
The “Symbolic” Nature of Data on the Wire
The challenge with data transmission is to get a signal from point A to point B, carrying as much information as possible, in a reliable manner. Note that the 1s and 0s we send as application developers may have different representations while they are in transit or ‘on the wire.’ For that reason when talking about baud rate we talk about symbols and not bits. Symbol rate is effectively the baud rate. I’ll explain the conversion from bit rate below, but with that in mind, the encoding process needs provide the following functions:
- End-to-end timing to ensure the receiver samples the signal at the correct time to reliably detect the transmitted symbols.
- Maximize the signal-to-noise ratio so that the signal is recoverable at the receiver.
- Reduce the symbol rate (baud rate)
- Minimize signal bandwidth
- Maximize signal bit rate
Baud rate, then, is the measure of the number of changes to the signal (per second) that propagate through a transmission medium. The baud rate may be higher or lower than the bit rate, which is the number of bits per second that the user can push through the transmission system. Bits will be converted into baud for transmission at the sender side and the reverse conversion will happen at the receiver end so that the user receives the bit stream that was sent. A few simple definitions before we move ahead:
- Bit rate – the number of binary ‘bits’, 1s or 0s to be transmitted per second
- Baud rate – the number of line ‘symbols’ transmitted per second
- Channels – the number of transmission channels
So to convert bit rate to baud rate you multiple baud rate by the number of bits per symbol by the number of channels being used:
Bit rate = baud rate * bits per symbol * Channels
Next I’ll explain how baud rate and bit rate apply to Solace appliances.
What is Bit Rate vs. Baud Rate?
FAQ
How fast is 115200 baud?
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Transmission Speed
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115200 bauds
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115200 bits/s
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14400 bytes/s
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230400 bauds
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230400 bits/s
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28800 bytes/s
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460800 bauds
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460800 bits/s
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57600 bytes/s
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576000 bauds
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576000 bits/s
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72000 bytes/s
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How do I set baud rate?
The UART baud rate is determined by the overflow rate of Timer 1. Specifically, the UART baud rate is equal to the Timer 1 overflow frequency divided by 2. For example, to configure the UART for a baud rate of 9600 bps, you would configure the overflow rate of Timer 1 to equal 9600 * 2 = 19.2 kHz. Related Articles. UART Maximum Baud Rate. Baud Rate Configuration for N/16 UARTs
What does baud rate stand for?
What does baud rate stand for? The baud rate is the rate at which information is transferred in a communication channel. In the serial port context, “9600 baud” means that the serial port is capable of transferring a maximum of 9600 bits per second. At baud rates above 76,800, the cable length will need to be reduced.
What is the default baud rate?
The 74880 on esp8266 is an artifact of the crystal speed (if you use a 40MHz crystal the baud rate is 115200, but everyone uses 26MHz crystals so it’s proportionally lower.) On ESP32 the default baud rate is 115200 regardless of crystal clock rate.
What is baud rate do you use?
The “baud” rate is a unit used to describe the speed of serial communications between two electronic devices. The exact meaning of this unit is often clout in confusion. What exactly is “baud”? The baud rate (the symbol is “Bd”) is unit we use to describe the “speed” of communication between the two electronic devices.
