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Relationship between baud and characters-per-second? Other questions too.

Hi:

What is the relationship between baud, bits-per-character, and characters-per-second?

Carrying more bits-per-symbol saves bandwidth as opposed to using more bauds-per-symbol.

Does carrying more bits-per-character use up less bandwidth than carrying more characters-per-bit?

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?Conveying more than one bit per symbol has advantages. It reduces the time required to send a given quantity of data, and allows modern modems, FDDI and 100/1000 Mbit/s Ethernet LANs, and others, to achieve high data rates. An optimal symbol set design takes into account channel bandwidth, desired information rate, noise characteristics of the channel and the receiver, and receiver and decoder complexity. A typical

2400-bit/s modem transmits at 600 baud (600 symbol/s), where each quadrature amplitude modulation symbol carries four bits of information. 1000 Mbit/s Ethernet LAN cables use many wire pairs and many bits per symbol to encode their data payloads. 1000BASE-T uses four wire pairs and two data bits per symbol to get a symbol rate of 125MBd.?

?Representing one bit by many symbols overcomes signal noise like radio jamming, and is common in military radio and CDMA radio, including cell phones, despite using more bandwidth to carry the same bit rate. In these systems, each signal is called a "chip" and the baud the "chip rate".?

Unfortunately I don?t think this answers my question. Unless of course, if symbols and characters are the same thing.

Are ?bits-per-symbol? and ?bits-per-character? the same thing? I did a Google search for ?bits-per-character? and ?characters-per-second? but didn?t see much in terms of telecommunications, baud and modems.

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OTOH, ?bits-per-symbol? gave tons of links about telecommunications, baud and modems.

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Thanks,

Radium

Reply to
Green Xenon [Radium]
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[snip]

Are you trying to get some homework done or do you really want to understand these concepts? It seems from your post that it's the former.

Either way, here are the basics. From this you should be able to deduce the answers you seek.

A symbol can represent one or more bits. For example, if you decide to transmit data using only two signal level regions (e.g. 3.3V LVTTL -- where a low = -0.5V to 0.8V and a high = 2.0V to 3.8V) then each symbol will carry one bit of information. However, what if you allowed sixteen different signal level regions instead of only two? Then, each symbol will carry four bits of information. It mostly depends on the transmission path as to how many bits you can represent with each symbol. If you're sending data through a digital IC then you can only get one bit per symbol, but if you're sending data through some type of analog medium then you can get more than one bit (i.e. two signal levels) through the channel.

A baud is equal to the number of symbols sent per second.

A "character" can be made up of as many bits as is required. Typically, a character (like an ASCII character) is eight bits.

Think about this for a while until it makes sense to you.

Bob

Reply to
Bob

It's just simple math. You haven't thought l "Give a man a fire and he'll be warm for a day. Set a man afire and he'll be warm for the rest of his life."

Bob

Bob

Reply to
Bob

No. It's the latter.

Okay.

Thanks.

Yes.

What about characters-per-second?

Most of it does make sense, except for the characters-per-second.

If there is a difference between "characters-per-second" and "symbols-per-second", what is this difference?

Reply to
Green Xenon [Radium]

simple maths

char/sec = (sym/sec) / (sym/char)

Are you *sure* this isn't homework?

Reply to
_

Baud refers to how often the actual line signal changes state; the same as symbols per second. Bits per character is really an animal of a different color, and depends on the original encoding. For ASCII, a common value is 8 bits per character. For instance, the 8 bit ASCII code for the numeral 1 is

00110001. For 8 bit encoding the number of characters per second is 1/8 th the bits per second, but usually not 1/8 the symbols/second. I am ignoring any extra bits and characters which are often added.

Suppose you transmit a 4 level signal. Call these A,B,C, and D. Suppose the bits are packed into the symbols so that A=00, B=01, C=10, and D=11. You can see that each symbol carries 2 bits, so that the baud rate would be 1/2 the bit rate. For a 16 level signal, each symbol carries 4 bits.

Baud is symbols/second. Any time you increase the baud rate you increase the bandwidth.

You will have to work this out, but having LESS bits per character reduces the bits per second and bandwidth. The original Teletype code used 5 bits per character. This only allows for 32 characters, so, one of the characters was a SHIFT character.

Tam

Reply to
Tam/WB2TT

On Sep 13, 4:00 am, _ wrote in

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:

What about char/bit?

char/bit = ?

Yes.

Reply to
Green Xenon [Radium]

On Sep 13, 8:25 am, "Tam/WB2TT" wrote in

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:

1/8 th > the bits per second, but usually not 1/8 the symbols/second. I am ignoring > any extra bits and characters which are often added.

Why not 1/8 the symbols/seconds? Wouldn?t using fewer symbols-per-second make it easer to transmit/receive in high-speed? The less symbols-per-second, the less bandwidth is used, regardless of the amount of bits-per-symbol.

1/2 the > bit rate. For a 16 level signal, each symbol carries 4 bits.

Okay.

Yes.

If you have more bits-per-character but less characters-per-second, would this be more efficient in terms of bandwidth usage?

I ask because I am aware that more bits-per-symbol but fewer symbols-per-second makes better use of bandwidth. So I am guessing that this is analogous.

Reply to
Green Xenon [Radium]

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:

If you want to keep the overall data rate the same, then if you go to 1/8 as many symbols/second as before you now need to have 8X as many bits per symbol as before. Actually, this kind of thing is done, but there is a limit as to how far you can go because every time you increase the bits/symbol, the effective signal to noise ratio gets worse unless you increase the power. For ATSC HDTV they go 3 bits/symbol for over the air transmission; that means each symbol can have one of 8 values (2**3=8). If you wanted to have 8 bits/symbol then each symbol must be capable of having one of 256 values (2**8 = 256). If you keep the power the same, then the resultant signal will be 256 times more susceptible to noise than straight binary.

Tam

Reply to
Tam/WB2TT

Ignoring the SNR, is there a physical limit to how many bits-per-symbol a device can transmit/receive/process/record/playback if the symbol rate is only 1 baud [1 symbol per second]?

Is it possible to have only 1-symbol-per-second but

1-billion-bits-per-symbol?

Also, my previous question -- [*most important and interesting to me*]:

If you have more bits-per-character but less characters-per-second, would this be more efficient in terms of bandwidth usage?

I ask because I am aware that more bits-per-symbol but fewer symbols-per-second makes better use of bandwidth. So I am guessing that this is analogous.

Reply to
Green Xenon [Radium]

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