RETURN CHANNEL PROCESSING FOR A DIGITAL DATA COMMUNICATIONS SYSTEM

摘要

A user/subscriber set-top unit (42, 44) in a satellite TV system is associated with a modem (30) coupled to an input optical fiber interface network (12) via a relatively high attenuation unshielded twisted pair (UTP) link (24). The modem demodulates (36) a UTP-attenuated, CAP 16 modulated downstream main signal, and generates (38) a higher energy QPSK modulated upstream return signal. Return signal interference in the received main signal is attenuated (34) by subtracting a delayed, phase adjusted version of the modulated return signal from the main signal before the main signal is demodulated. Interference cancellation is accomplished by using a subtraction process rather than by using a frequency selective filtering process. Interference cancellation may also be accomplished (22) in the interface network (12) preceding the UTP link.