SYSTEM AND METHOD FOR TRANSMITTING DATA ON RETURN PATH OF A CABLE TELEVISION SYSTEM

• US 20070277213A1
• Filed: 08/13/2007
• Published: 11/29/2007
• Est. Priority Date: 12/13/1999
• Status: Active Grant

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Finisar Corporation (II-VI Incorporated)
• Inventors: Mostert, Willem, Sage, Gerald, Lawson, Arthur, Levinson, Frank
• Granted Patent: US 7,529,487 B2
• Time in Patent Office: Days
• US Class Current: 725/121
• CPC Class Codes: H04N 21/615 Signal processing at physical level signal processing in analog two-way television systems H04N7/173
• CPC Class Codes: H04N 21/6168 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications
• CPC Class Codes: H04N 7/22 Adaptations for optical transmission

Abstract

An optical signal return path system includes a transmitter having a sample clock generator for generating a sample clock and an RF signal receiver for receiving and converting an analog RF data signal into a first data stream of digitized RF data samples at a rate determined by the sample clock. Supplemental channel circuitry provides a second data stream. A multiplexor receives and combines the first data stream and second data stream, and an optical transmitter converting the combined data stream into a serialized optical data signal for transmission over an optical fiber. The second data stream may contain maintenance data reflecting an operational state of the transmitter. A receiver receives the optical data signal and recovers therefrom a digital data stream and an associated first clock having an associated first clock rate. The data stream is stored in a memory device at the first clock rate. A clock generator generates a second clock having an associated second clock rate that is adjusted in accordance with a clock control signal. A control circuit reads data from the memory device at a rate corresponding to the second clock rate and generates a fullness signal that indicates whether the memory device is more full than a predefined threshold fullness level. A clock speed adjusting circuit generates the clock control signal in accordance with the fullness signal.

Claims

1. A return path transmitter for use in conjunction with a local system that generates an analog RF data signal to be conveyed to a head end system, the return path transmitter comprising:

an optical signal receiver configured to receive a digital optical signal and generate therefrom a first digitized RF data stream and a sample clock;

an RF signal receiver, coupled to the optical signal receiver, configured to receive and convert the analog RF data signal into a second digitized RF data stream of digitized RF data samples at a rate determined by the sample clock;

a summing circuit configured to mathematically sum the first and second digitized RF data streams so as to generate a third digitized RF data stream; and

an optical transmitter configured to convert an output data stream into a serialized optical data signal for transmission over an optical fiber, the output data stream including the third digitized RF data stream.

2. The return path transmitter of claim 1, wherein:

the optical signal receiver is configured to demultiplex data within the received digital optical signal into a first digitized RF data stream and a first non-RF data stream; and

the return path transmitter includes;

a data port for receiving a second non-RF data stream from a digital data source external to the return path transmitter, the second non-RF data stream having a data rate of at least 5 Mb/s;

a full duplex drop and add circuit for extracting a portion of the first non-RF data stream and for replacing the extracted portion of the first non-RF data stream with the second non-RF data stream so as to generate a third non-RF data stream;

a multiplexor coupled to the summing circuit and the full duplex drop and add circuit to receive the third digitized RF data stream and the third non-RF data stream and to output a combined data stream; and

the output data stream converted by the optical transmitter includes the combined data stream.

3. A method for transmitting data representing an analog RF signal generated at a local system, the method comprising:

receiving a digital optical signal and generating therefrom a first digitized RF data stream and a sample clock having an associated sample rate;

receiving and converting the analog RF signal into a second digitized RF data stream of digitized RF data samples at a rate determined by the sample clock;

mathematically summing the first and second digitized RF data streams so as to generate a third digitized RF data stream; and

converting an output data stream into a serialized optical data signal for transmission over an optical fiber, the output data stream including the third digitized RF data stream.

4. The method of claim 3, including:

demultiplexing data within the received digital optical signal into a first digitized RF data stream and a first non-RF data stream;

receiving a second non-RF data stream from a digital data source external to the return path transmitter, the second non-RF data stream having a data rate of at least 5 Mb/s;

extracting a portion of the first non-RF data stream and replacing the extracted portion of the first non-RF data stream with the second non-RF data stream so as to generate a third non-RF data stream; and

combining the third digitized RF data stream and the third non-RF data stream and generate a combined data stream;

wherein the output data stream includes the combined data stream.