Fade Duration
Exercise
A subscriber of an analog NMT cellular system (900 MHz)
connects a 1200 bit/s modem to his cellular phone.
He drives his car at 36 km/h. The signal experiences
wide-sense stationary noise.
Experiment with the Javascript
spreadsheet
to find the fade margin required to
ensure an average nonfade duration enough to
pass 600 bits uninterrupted.
Answer
36 km/h equals 10 meter/sec.
600 bits at 1200 bit/s take half a second to transmit.
By trial and error we find that an
average nonfade duration of 0.5 sec is achieved for
a fade margin of 31.5 dB.
