Advantages/disadvantages of NonReturnToZero, Manchester, Miller, 4 levels coding (data transmission/line code)?

Question

ok, so I had this laboratory about the line codes (baseband) and the teacher told us about the optimum signal feats:

1. no use of DC & large components @ low freq. in the spectrum
2. small bandwidth
3. protection against noise
4. good sync. between the receiver & transmitter clocks
5. no necesity for the receiving device to determine the absolute polarity of the signal

We studied the following signals: Non Return to Zero, Differential Non Return to Zero (Inverted), Manchester, Differential Manchester, Miller & 4 levels encoding.

So the question is: At what of the 5 criterions is each encoding better (and at what worse)? Why is that?

As an example I can say that differential signals gain an advantage in the 5th criterion as they are not affected by polarity problems.Or that Manchester is better than NRZ because it has no DC component & has many transitions, but has a larger bandwidth and worst protection against noise.

Please do explain your answer :)

Thanks!

Answer 1

For most of these you are trading off bandwidth for no DC component.



If you have a DC component (i.e. NRZ), you must preserve it and therefore your transmission channel must have a DC (galvanic) path. Try that with a satellite! That's a pretty long cable out into space. There are work-arounds; DC restorers and such for NRZ signals, but there must still be limits placed on the amount of zeros that can be transmitted at-a-time.



Coding schemes that have a clock embedded into the signal (i.e. manchester) have no DC component but require a higher bandwidth channel because both the signal and the clock take up bandwidth. These signals can be passed through transformers, AC coupled amplifiers, and other non-galvanic paths. This is important if you need isolation (i.e. for safety) or if the transmitter and receiver are at locations where different power sources exist (common mode rejection). AC coupled amplifiers are almost always cheaper than DC coupled amplifiers.



Embedded clocks provide very good sync between Tx and Rx, because you can extract the exact clock you need tor the signal. NRZ does not have an embedded clock so it is difficult to regenerate a clock at the Rx end. Miller coding also contains an embedded clock, but uses only half the bandwidth as manchester coding.



In general the differential types offer better noise immunity than the non-differential types. The drawback is that you need differential Tx and Rx amplifiers, which are generally more expensive.





That's a few of things I can think of, off the top-of-my-head.



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Answer 2

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Answer 3

The Main problem with NRZ Encoding occurs when the sender and receiver clocks are not synchronized. The Receiver Doesn't know when one bit has ended and the next n bit is starting. One solution is the return-to-zero(RZ) scheme, which uses three variables: positive,negative, and zero. In RZ, the signal changes not between bits but during the bit.