HUT Communications Lab. / Timo O. Korhonen
3
Why to apply digital transmission?
nDigital communication withstands
channel noise and distortion better that analog system. For instance in
PSTN inter-exchange STP-links NEXT (Near-End Cross-Talk) produces several
interference.
For analog systems interference must be below 50 dB whereas in
digital system 20 dB is enough. With this respect digital systems
can utilize lower quality cables than analog systems
nRegenerative repeaters can
be used. Note that generally cleaning of analog-signals repeatedly is not very
successful
nDigital HW implementation is
straight forward
nCircuits can be easily reconfigured
by DSP techniques (an application: software radio)
nDigital signals can be coded
to yield very low error rates
nDigital communication enables
efficient exchanging of SNR to BW-> easy adaptation into different
channels
nThe cost of digital HW
continues to halve every two or three years
STP: Shielded twisted pair