may i know what is the difference between bit rate and baud rate ??

 

Baud rate is the rate at which bits are placed in the line. Bit rate is the rate at which actual data is sent. Typical UART protocol sends 10 bits on the line for each 8-bit byte of data, so the bit rate is only 80% of the baud rate.

 

Baud = number of symbols per second

Since, baud is already a rate, saying "baud rate" is grammatically incorrect. However, "baud rate" is frequently used.

Bit rate = bits per second

In single bit digital serial transmission, baud and bit rate are the same.
In multi-bit transmission such as audio and digital encoding, there could be N bits per symbol.

If R = bit rate
and fs = sample frequency or baud

then
R = N x fs

 

Baud = number of symbols per second

Since, baud is already a rate, saying "baud rate" is grammatically incorrect. However, "baud rate" is frequently used.

Bit rate = bits per second

In single bit digital serial transmission, baud and bit rate are the same.
In multi-bit transmission such as audio and digital encoding, there could be N bits per symbol.

If R = bit rate
and fs = sample frequency or baud

then
R = N x fs

This is correct, and to add a bit more (those puns just come without being bidden) by way of elucidation...

What is called Baud Rate is more rigorously called Symbol Rate which is measure in baud (abbreviated Bd but rarely seen). Baud is symbols per second. To transmit data requires a state change and a symbol is that change of state. Each symbol can transmit one or more bits depending on the degrees of freedom it has.

For example, if you had a light that could be on of off, using it to transmit symbols with its one degree of freedom limits you to one bit of information per symbol. You can image it to be 1 for on and 0 for off. This is simple. But, if we take the light and add the ability to have it red, green, 50% bright, or 100% bright we have two bits per symbol because of the two degrees of freedom: color and intensity.

Clever use of phase angle in modulating phone lines when voice line modems were standard was able to achieve a bit rate of 9600bps using the maximum symbol rate of of only 2400Bd. This was possible using QAM (Quadrature Amplitude Modulation) which relies on manipulating phase relationships.

More complicated versions of QAM are used in digital radio communications and fiber optic data transmission to maximized the bits per symbol and move data faster. Keep in mind that a lot of high throughput technologies that achieve bit rates in the multi-gigabit range have symbol rates considerably slower.

The practical effect of this is when thinking about transfer times you have to account for the fact that multiple bits are sent at once, it’s not a simple continuous stream of bits at the specified rate. For applications with critical latency concerns, this can matter.

 

We were using 8PSK for digital data on UHF stacom analog audio bandwidth (6kHz per allotted transponder slot) transponders in the 70's.

 

Baud does not seem to be much used any more when discussing data rates, at least I haven't seen it.

 

Baud (rate) is the most common way to specify the data clock for RS-232 and similar transmission standards.

 

Baud does not seem to be much used any more when discussing data rates, at least I haven't seen it.

That's because it isn't as misleading as it used to be.

Back when signaling was done using binary modulation, the baud was higher than the data rate, and marketing types always like to claim bigger numbers, whether they mean what they are implying or not.

But as soon as you move to multibit symbols, the opposite happens, so now you talk about bit rate at the next higher level (ignoring the fact that a lot of those bits are dedicated to communication overhead).

Of course, a lot of this is lost in the general lack of comprehension on both sides of the conversation about any of this -- and why it is so common to see bits and bytes used interchangeably in such discussions, even in official literature and advertising campaigns.

But baud rate is still a fundamental concept when you are talking about physical layer implementations.

 

Baud (rate) is the most common way to specify the data clock for RS-232 and similar transmission standards.

Well, I don't think RS-232 is used much anymore either.

 

Well, I don't think RS-232 is used much anymore either.

Even if we accept that baud is the most common way to specify one thing, that does NOT imply anything about how commonly baud is used for anything else.

Most digital communication systems pack several bits into each symbol to improve spectral efficiency, so there is a significant difference between the baud rate and the (gross) bit rate of these systems.

ADSL used up to 32768 points in it's constellation (15 bits per symbol) -- though I don't know that "constellation" is really the proper term since ADSL is tone based -- numerous systems use 1024-, 2048- or 4096-QAM and QAM64 is extremely widely employed.

 

Well, I don't think RS-232 is used much anymore either.

RS-232 levels may not be so common these days, but TTL serial using UART/USB converters are probably more prevalent than ever! Ask anyone who uses an Arduino, ESP8266 or ESP32.

Arduino had sold 10 million boards by 2021 and clones have likely far-outpaced that. Each Arduino or clone has a USB-UART converter chip.

 

Well, I don't think RS-232 is used much anymore either.

You would be surprised at the level of serial comm port usage at the industrial level on modern equipment (including out of band secure computer admin connections) and much of that serial data still uses RS232 as the physical signal level specification.

 

I used UART at TTL levels to link an LCD status display for a machine controller running state-machine code. One byte embedded 2 bits as 1 of 4 units and 6 bits for message token. It runs at 460.8 kbps just fine on a 12" cable. Async may be old but Very handy and easy. Signalling level standard depend on length & speed.