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