Echo canceller having FIR and IIR filters for cancelling long ta

Details Echo canceller having FIR and IIR filters for cancelling long ta Echo canceller having FIR and IIR filters for cancelling long ta

1990-02-23

1992-01-28

Olms, Douglas W.

Multiplex communications

Wide area network

Packet switching

379406, 379410, 379411, H04B 323

Patent

active

050848658

ABSTRACT:
An echo canceller comprises a finite impulse response filter (6) connected to the incoming port of a hybrid (1), and a tail canceller (7) which includes an infinite impulse response filter (24; 40) having a multiplier (14; 33) for recursively multiplying an output digital symbol from the tapped-delay line (8) of the FIR filter with an attenuation coefficient R. A digital symbol from the IIR filter or one from the tapped-delay line (8) is multiplied with a tap-weight coefficient C.sub.1 and summed with the outputs of tap-weight multipliers of the FIR filter to produce a replica of an echo symbol, which is subtracted from a digital symbol y.sub.n from the outgoing port of the hybrid (1), producing a residual echo symbol e.sub.n. The coefficient C.sub.1 is derived from correlation between residual echo e.sub.n and a symbol from the tapped-delay line. In one embodiment, symbol from the tapped-delay line is further delayed (17) for a unit interval on the one hand, and multiplied (18) with coefficient R on the other, the difference between them being detected (19) and multiplied (20) with a coefficient K, which is either sgn(C.sub.1) or 1/C.sub.1, to generate a multiplied difference. Correlation is detected (22) between the difference and residual echo e.sub.n to derive the coefficient R. In a second embodiment, symbol from the tapped-delay line is further delayed (36) for a unit interval and multiplied (37) with K to produce a delayed-multiplied symbol. Correlation is detected (35) between it and residual echo e.sub.n to derive the coefficient R.

REFERENCES:
patent: 4007341 (1977-02-01), Sourgens et al.
patent: 4087654 (1978-05-01), Mueller
patent: 4707824 (1987-11-01), Kanemasa
patent: 4862449 (1989-08-01), Hoefkens et al.
patent: 4965823 (1990-10-01), Nakagawa et al.

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