Abstract: A high speed bidirectional cable transmission system for CATV and other television systems includes unidirectional transmission of video signals from a head end unit to a plurality of transceivers or subscribers connected to a transmission line. The head end unit encodes voice data using QPSK encoding and time division multiplexing of the encoded data in a plurality of frequency bands to the subscribers. Each subscriber attached to the cable for receiving continuous transmission of voice and video data is assigned an identification number and at least one voice channel for selectively accessing data. Each subscriber includes a transmitter for transmitting voice data on the cable to the head end unit using time division multiple access transmission of bursts of data in a plurality of frequency bands.

Abstract: A method is presented for efficient VLSI implementation of a narrowband BPSK or QPSK demodulator which minimizes filter processing requirements. The demodulator implements a digital filter which spans a time duration of 8 symbols to realize a square root of raised cosine filter. The disadvantage of a conventional FIR filter, is that it requires a fixed ratio between the input sample rate and the FIR filter output rate. The subject invention employs a unique, flexible digital filter which provides one output per symbol while the input sample rate may vary from a low rate approaching two samples per symbol to over 128 samples per symbol. A key element of this approach is the digital phase locked loop used for symbol tracking which employs a direct digital synthesizer (DDS) as the frequency control element. In addition to providing symbol timing to the accuracy of the sample clock, the DDS also provides a fine measure of symbol timing phase at each sample clock.