Scrambling of the data involves reordering of the data symbols
in such a way that the chances of long strings of 1s or 0s occurring in the scrambled
waveform is minimized or eliminated. This process introduces a processing overhead and
also a latency in the encoding and decoding process which may introduce unacceptable time
delay in the communication process particularly if digital voice is being carried. In
most cases, a data encoding process is used in preference to scrambling, albeit at the
expense of occupied bandwidth in most cases. There are many data encoding schemes for
reducing the dc content of a data signal, the most common of which is Manchester encoding. It can be seen that compared with the original
non-return-to-zero (NRZ) data stream, the Manchester encoded
signal never contains long strings of 1s or 0s.
For a more detailed discussion of line coding techniques, see Haykin (1989).
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