Mode S Technology In digital communications, modulation is the
process in which a bitstream is converted to a waveform
compatible with a transmission channel. Some design choices,
such as modulation, were indirectly affected by the need for
interoperability. Modulation is the process by which a signal is
encoded for transfer over a data link, and demodulation is the
process by which it is decoded upon receipt for further
processing. Different modulation schemes have varying abilities
to deal with noise and interference. In the case of Mode S, the
choice of using interoperable frequencies affected modulation
because interference became a large concern. However, the
easiest way to ensure backwards compatibility was to make as few
equipment changes as possible. This approach was also endorsed
by the contractors that would eventually manufacture the
equipment since it required fewer changes to their production
and testing facilities. In the end, a compromise was reached
that utilized a combination of old and new