Thursday, September 11, 2014

Types of Conversions Cont


   Return to Zero (RZ)
o    Any time, data contains long strings of 1's or 0's, Rx can loose its timing
o    In  unipolar,  we  have  seen  a  good  solution  is  to  send  a  separate  timing
signal but this solution is both expensive and full of error
o    A better solution is to somehow include synch in encoded signal somewhat
similar to what we did in NRZ-I but it should work for both strings of 0 &
1
o    One solution is RZ encoding which uses 3 values : Positive, Negative and
Zero
o    Signal changes not b/w bits but during each bit
o    Like NRZ-L , +ve voltage means 1 and a -ve voltage means 0, but unlike
NRZ-   L, half way through each bit interval, the signal returns to zero
o    A 1 bit is represented by positive to zero and a 0 is represented by negative
to zero transition
o    The only problem with RZ encoding is that it requires two signal changes
to encode one bit and therefore occupies more BANDWIDTH
o    But of the 3 alternatives we have discussed, it is most effective
     Biphase Encoding
o    Best existing solution to the problem of Synchronization
o    Signal changes at the middle of bit interval but does not stop at zero
o    Instead it continues to the opposite pole


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