Multiplexing digital communication system

• US 6,667,994 B1
• Filed: 06/09/2000
• Issued: 12/23/2003
• Est. Priority Date: 06/09/2000
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Farhan, Forrest M.
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): PHAM, BRENDA H
• Application Number:
  US09/590,433
• Time in Patent Office: 1,292 Days
• Field of Search: 370/532-542, 370/503
• US Class Current: 370/535
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation
• CPC Class Codes: H04J 3/1605 Fixed allocated frame structures
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04N 21/242 Synchronization processes, e.g. processing of PCR [Program Clock References] arrangements for synchronising broadcast or distribution via plural systems in broadcast distribution systems H04H20/18
• CPC Class Codes: H04N 7/173 with two-way working, e.g. subscriber sending a programme selection signal

Abstract

A transmitter (501) for use in a communication system (500) includes clock input for receiving a clock signal and input ports (503, 510, 513) coupled to external signal sources for receiving input signals that are synchronously modulated at modulation frequencies rationally and fractionally related to the clock frequency and to each other. Additionally, the clock frequency should be greater than any of the modulation frequencies. An analog-to-digital converter (505) receives the analog input signals and converts them to a digital format, and a multiplexer (515) then processes the digital input signals and signals from the converter (505) to generate a single serial output signal. An output port of the transmitter (501) then transmits the single serial output signal as a digital signal having a bit rate equivalent to the number of input signals multiplied by the sampling frequency, plus additional overhead for optional framing and error correction.

Claims

1. A transmitter for use in a communication system, the transmitter comprising:

a clock input for receiving a clock signal having a sampling frequency;

input ports coupled to external signal sources for receiving input signals that are synchronously modulated at modulation frequencies rationally and fractionally related to the sampling frequency and to each other, wherein the sampling frequency is greater than any of the modulation frequencies;

an analog-to-digital converter (ADC) for receiving any input signals that in an analog format and converting the analog format to a digital format;

a multiplexer coupled to the input ports and the ADC for receiving the input signals in a digital format, the multiplexer comprising;

serializing means for serializing the input signals to generate a single serial output signal; and

an output port coupled to the serializing means for providing the single serial output signal at a bit rate equivalent to the number of input signals multiplied by the sampling frequency, plus additional overhead for optional framing and error correction; and

transmission means for transmitting the single serial output as a digital signal.

2. The transmitter of claim 1, wherein, when one of the input signals is an analog input signal, the analog input signal is modulated using bandlimited subcarrier analog modulation prior to reception by the ADC and the multiplexer.

3. The transmitter of claim 2, wherein the modulation frequency of the analog input signal is less than one-half of the sampling frequency.

4. The transmitter of claim 1, wherein, when one of the input signals is a digital input signal, the digital input signal is modulated using a digital baseband format prior to reception by the ADC and the multiplexer.

5. The transmitter of claim 4, wherein the modulation frequency of the digital input signal is related by a rational fraction to the sampling frequency.

6. The transmitter of claim 1, wherein the input signals may be modulated according to different modulation schemes prior to processing by the transmitter.

7. A broadband communication system, comprising:

a transmitter comprising;

a clock input for receiving a clock signal having a sampling frequency;

input ports coupled to external signal sources for receiving input signals that are synchronously modulated at modulation frequencies rationally and fractionally related to the sampling frequency and to each other, wherein the sampling frequency is greater than any of the modulation frequencies;

an analog-to-digital converter (ADC) for receiving any input signals that in an analog format and converting the analog format to a digital format;

a multiplexer coupled to the input ports and the ADC for receiving the input signals in a digital format, the multiplexer comprising;

serializing means for serializing the input signals to generate a single serial output signal; and

an output port coupled to the serializing means for providing the single serial output signal at a bit rate equivalent to the number of input signals multiplied by the sampling frequency, plus additional overhead for optional framing and error correction; and

transmission means for transmitting the single serial output as a digital signal; and

a receiver for receiving the digital signal.

8. The broadband communication system of claim 7, wherein, when one of the input signals to the transmitter is an analog input signal, the analog input signal is modulated using bandlimited subcarrier analog modulation prior to reception by the ADC and the multiplexer.

9. The broadband communication system of claim 8, wherein the modulation frequency of the analog input signal is less than one-half of the sampling frequency.

10. The broadband communication system of claim 7, wherein, when one of the input signals is a digital input signal, the digital input signal is modulated using a digital baseband format prior to reception by the ADC and the multiplexer.

11. The broadband communication system of claim 10, wherein the modulation frequency of the digital input signal is related by a rational fraction to the sampling frequency.

12. The broadband communication system of claim 7, wherein the input signals may be modulated according to different modulation schemes prior to processing by the transmitter.