Differences between return-to-zero and non-return-to-zero signals

[dervast]

Hi i want to find and read about the return to zeroes and non return to zeroes. What are the differences betwwen them ? Advantages Disadvantages>?

 

[chroot]

http://en.wikipedia.org/wiki/Non-return-to-zero

Do you have a specific question?

- Warren

 

[dervast]

Yes i have and i really hope u are an expert in the field..
I want to ask why the RZ signals requires the twice the bandwidth of an NRZ data signal operatin at the same bit rate

 

[chroot]

RZ signals invovle a periodic return to a "zero" signal value. This zero signal value carries no information, and thus decreases the symbol rate of the transmission.

- Warren

 

[dervast]

Thx a lot of your answer but i can understand how the symbol rate of the transmission is connected with the bandwidth i have asked... I have a big missunderstanding of these things and perhaps u can help me understand them :)

 

[bobill]

I'm not sure if this is the textbook answer, but from what it seems, RZ requires twice the sampling rate as NRZ, simply in that it needs to move from one point to the next twice as many times as NRZ. It makes sense, then, that to maintain the same symbol rate, you must double the bandwidth. Does that make sense?

 

[vk6kro]

If you send a series of 10 1's you have the choice of sending a rising edge, then a falling edge, then a rising edge etc.
Or you could send a rising edge then keep it high until there is a zero. Thus a falling edge implies a zero and staying low implies more zeros. A rising edge implies a 1 and successive high level implies more 1s.
If you are clocking it, you can tell how many 1's the high level, or zeros the low level, represents.

Suppose you did send 10 ones followed by 10 zeros, and used the second scheme, can you see that this involves a square wave of about 1/10th the frequency of the alternative waveform?
So, it must involve about 1/10th of the bandwidth.

On average, you wouldn't be lucky enough to have 10 1s followed by 10 zeros very often and the worst case would be continuous 1-0-1-0 sequences. What the saving is for doing this depends on the data, but it could be something like 50%.

This is actually the system used in Barcodes and it used to be used for putting data onto recording tapes.