A design consideration on TDMA cellular radio

A time-division multiple access (TDMA) cellular system using QPSK (quadrature phase shift keying) with coherent detection is studied. The required guard time between TDMA bursts and the effect of the unbalanced characteristics of an IF filter on a detected signal are analyzed. An attempt is made to minimize the guard time between TDMA burst signals using a window which suppresses the signal at both edges. As a result, it was found that the required guard time can be reduced to a 2.3 symbol duration in a 3-km radius cell. If a conventional IF filter (which is designed for an analog terminal) is adapted to a digital terminal, in cases of 1 kHz variation of the center frequency intersymbol interference caused by the IF filter would be about -20 dB. It is concluded that more sophisticated IF filters are needed for digital cellular terminals are needed than for analog cellular terminals.<
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