  In this paper we present a comparative study in order to specify the
influence of equalization enhanced phase noise (EEPN) for pre- and
post-compensation of chromatic dispersion in high capacity and high
constellation systems. This is - to our knowledge - the first detailed study in
this area for pre-compensation systems. Our main results show that the local
oscillator phase noise determines the EEPN influence in post-compensation
implementations whereas the transmitter laser determines the EEPN in
pre-compensation implementations. As a result of significance for the
implementation of practical longer-range systems it is to be emphasized that
the use of chromatic dispersion equalization in the optical domain - e.g. by
the use of dispersion compensation fibers - eliminates the EEPN entirely. Thus,
this seems a good option for such systems operating at high constellations in
the future.
