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TCP-group 1995


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NRZ/NRZI




Greetings Apostolos,

Quoting from a old paper I have here on PCM modulation schemes.


     NRZ-C     Non-return-to-zero-change
   also   NRZ-L           "      level
   also NRZ (ambiguous)

A ONE bit is represented by one signal level, a ZERO bit is
represented by a different signal level.


     NRZ-M     Non-return-to-zero-mark
   also   NRZ-I   Non-return-to-zero-index (NOT INVERT!)

A ONE bit is represented by a change in signal level, a ZERO bit is
represented by no change in signal level.

     NRZ-S     Non-return-to-zero-space

A ONE bit is represented by no change in signal level, a ZERO bit is
represented by a change in signal level.

All three modulation schemes exhibit the same bandwidth
characteristics DC to half the bit rate.  However NRZ-C requires you
to know which signal level represents a ONE and which signal level
represents a ZERO.  With NRZ-M and NRZ-S it is only necessary to know
that a ONE is represented by a change (or vice-versa).

Regards


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