To provide an inexpensive modem that supplies high accuracy to communication in frequency multiplex communication.
A modem 55 includes a reception circuit 30 executed by a digital signal processor 32'. The reception circuit 30 is operated by a received clock (CLKr) on the basis of an output of a free-run oscillator. An A/D converter 31 samples an input frequency multiplex signal (f(t)) and a fast Fourier transform function 36 demodulates the sampled signal. After the demodulation above, a phase rotation function 40 applies phase shift to a demodulation signal corresponding to an estimated phase offset between the received clock and a pilot signal P sent by the transmission modem. A definite impulse response filter function 52 applies digital filtering to the demodulation signal to correct a phase error on the basis of the estimated frequency offset Δ.
GARCIA DOMINGO G
POLLEY MICHAEL O
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