Phase and frequency offset compensation in a telecommunications receiver

摘要

A modem (55) including receive circuitry (30) implemented by way of a digital signal processor (32, 32') is disclosed. The receive circuitry (30) operates according to a receive clock (CLKr) that is based upon the output of a free run oscillator (50). An incoming frequency multiplexed signal (f(t)) is sampled by an analog-to-digital converter (31) and demodulated by way of a Fast Fourier Transform function (36). After such demodulation, a phase rotation function (40) applies a phase shift to the demodulated signal corresponding to an estimated phase offset (&tgr;) between the receive clock (CLKr) and a pilot signal (P) transmitted by the transmitting modem; a finite impulse response filter function (42) applies a digital filter to the demodulated signal to correct for phase error based upon an estimated frequency offset (DELTA). According to another disclosed embodiment, a pre-emphasis FIR filter function (52) and a pre-emphasis phase rotation function (54) are applied to an upstream singal, based upon the estimated phase offset (eta) and frequency offset (DELTA).