AFC circuit with fast acquisition for a TDMA cellular mobile communication system

A novel AFC (automatic frequency control) circuit for a TDMA (time-division multiple-access) digital cellular mobile communication system with pi /4-shifted QPSK (quadrature phase-shift keying) modulation is described. The AFC circuit satisfies the two contradictory requirements of fast acquisition and stable operation even under low CNR (carrier-to-noise ratio) channel conditions, simultaneously. The performance of a 40-kb/s TDMA transmission system was measured to confirm the availability of the AFC circuit. An E/sub b//N/sub 0/ penalty of the differential demodulator is compressed to less than 0.1 dB by the AFC circuit when carrier frequency deviation is within +or-1 kHz. The results obtained show that the differential detection can be applied to a receiver of the TDMA digital cellular mobile communication system when the proposed AFC circuit is implemented.<
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