Switching considerations to combat spectral pollution in TDMA for satellite broadcasting

A better switching technique for combating spectral pollution i.e. spectral spreading of burst time-division multiple access (TDMA) digital FM and pi /4-QPSK (quadrature phase-shift keying) systems, is proposed. The effects of rectangular, linear, and raised cosine ramp on/off switching are examined for two prototypes using both hardware experimental methods and computer simulation for different gating rates, duty cycles, roll-off factors of transmitter filter and ramp on/off times. The measures results agree with the computer simulation results and indicate that the adjacent channel interference (ACI) caused by the burst operating in TDMA pi /4-QPSK is significantly reduced by raised cosine switching in comparison with other types of switching.<
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