Modulation and demodulation system employing AM-PSK and QPSK communication system using digital signals

• US 5,084,903 A
• Filed: 12/21/1990
• Issued: 01/28/1992
• Est. Priority Date: 02/28/1989
• Status: Expired due to Fees

• Current Assignee: Future Technology Incorporated (Advanced Power Electronics Corp.)
• Original Assignee: First Pacific Networks, Inc.
• Inventors: Long, James C., Murphy, Timothy P., McNamara, Robert P.
• Primary Examiner(s): Safourek, Benedict V.
• Assistant Examiner(s): HSU, ALPUS
• Application Number:
  US07/631,760
• Time in Patent Office: 403 Days
• Field of Search: 370/11, 370/12, 370/19, 370/20, 370/50, 370/69.1, 370/71, 370/73, 370/124, 370/120, 370/121, 370/122, 370/24, 370/30, 370/85.1, 370/85.9, 370/85.11, 370/36, 370/76, 375/54, 375/38, 375/39, 375/41, 375/42, 375/52, 375/48, 375/86, 375/88, 375/18, 375/20, 375/53, 375/56, 340/825.58, 455/5
• US Class Current: 375/290
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04L 27/00 Modulated-carrier systems

Abstract

A communication network having a first broadband communications channel or transmitting bus and a second broadband communications channel or receiving bus, wherein the first broadband communications channel passes information upstream to a head end employing an offset quadrature phase shift keyed (OQPSK) modulator in bursts, and the second broadband communications channel passes information downstream from the head end to remote nodes in a continuous bit stream. All nodes of the system are coupled to both the first communications channel and the second communications channel. According to the invention, modulation of signals applied to the first communication channel is optimized for burst communication from a plurality of sources to central control at the head end, and modulation applied to the second communications channel is optimized for continuous communication from the central source to a target node. In one specific embodiment, the communication between the central unit (head end) and any one of a choice of target nodes through the second communication channel is by means of three-level class one partial response AM-PSK modulated onto a carrier, which is optimized for continuous operation.

Claims

1. A communication system comprising:

a head end device coupled to receive and translate bursts of information received in a partial response format into continuous information in a partial response format and to transmit said continuous information;

a first communications medium coupled to said head end device for conveying said bursts of information to said head end device;

a second communications medium coupled to said head end device for conveying said continuous information; and

a plurality of node devices, each one of said node devices having modulator means coupled to said first communications medium for transmitting signals upstream to said head end device and having demodulator means coupled to said second communications medium for receiving signals downstream from said head end device, each said modulator means comprising means for communicating bursts of information in an offset quadrature phase shift keyed (OQPSK) format, and each said demodulator means comprising means for receiving continuous information in an AM-PSK format.

2. The communication system of claim 1 wherein said modulator means comprises means for transmitting said bursts of information with an efficiency of one bit per Hertz.

3. The communication system of claim 2 wherein said head end device means comprises means for transmitting said continuous information with an efficiency of one bit per Hertz.

4. The communication system of claim 3 wherein said first communication medium is a first broadband communication medium and said second communication medium is a second broadband communication medium, wherein said first broadband communication medium and said second broadband communication medium are separate frequency channels on a single physical medium and said head end device includes a frequency translation means.

5. The communication system of claim 4 wherein said head end translating mean further comprises means for aligning in time a first bit pattern of said information of said OQPSK modulator means to synchronize said bit pattern of said information with a repetitive bit pattern in order to allow extracting of bits at an optimized time.

6. A method for transmitting information in a bit pattern from a source node to a target node in a communication system having a unidirectional transmitting medium terminating at a head end said information being translated at said head end onto a unidirectional receiving medium originating from said head end, comprising the steps of:

transmitting said information as an offset quadrature phase shift keyed (OQPSK) signal on a carrier on said transmitting medium from said source node;

receiving said OQPSK with an OQPSK receiver at said head end to obtain a received signal;

hard limiting said received signal with a limiter circuit means to obtain a limited signal within a defined dynamic range;

transmitting continuously a class one, three-level partial response signal on a continuous carrier on said receiving medium from said head end;

modulating said continuous carrier with said bit pattern of said information when said bit pattern of said information is present and modulating said continuous carrier with a repetitive bit pattern when said bit pattern of said information is not present;

receiving said continuous carrier at said target node on said receiving medium;

detecting said modulated continuous carrier with an envelope detector means; and

extracting said bit pattern of said information from said modulated continuous carrier by strobing said bit pattern in synchronism with a system clock.

7. The method of claim 6 further comprising the step of aligning in time said bit pattern of said information at said head end to synchronize said bit pattern of said information with said repetitive bit pattern in order to allow extracting of bits at an optimized time.

8. The method of claim 6 wherein said OQPSK signal transmitting step includes asynchronously transmitting said information in bursts.

9. A communication system for transmitting a unit of information in a bit pattern from a source node to a set of target nodes comprising:

a head end;

a unidirectional transmitting medium coupling each node in a source path to and terminating at said head end;

a unidirectional receiving medium originating from said head end and coupling to each said target node;

means at said source node for transmitting said information as an offset quadrature phase shift keyed (OQPSK) signal on a carried on a transmitting bus from said node;

said head end comprising;

a) head end receiving means at said head end for receiving said OQPSK signal with an OQPSK receiver at said head end to obtain a received signal, said head end receiving means including a limiter circuit means for hard limiting said received signal to obtain a limited signal within a defined range; and

b) head end translating means for transferring signals received at said head end of said transmitting medium to said receiving medium;

c) means for transmitting continuously a class one, three-level partial response signal on a continuous carrier on said receiving medium from said head end; and

d) means for modulating said continuous carrier with said bit pattern of said information when said bit pattern of said information is present and modulating said continuous carrier with a repetitive bit pattern when said bit pattern of said information is not present; and

target node receiving means for receiving said continuous carrier at said target node on said receiving medium, said target node receiving means including;

a) envelope detector means for detecting said modulated continuous carrier; and

b) analog to digital converting means for extracting said bit pattern of said information from said carrier by strobing said bit pattern in synchronism with a system clock.

10. The communication system of claim 9 wherein said head end translating means further comprises means for aligning in time a bit pattern of said information to synchronize said bit pattern of said information with said repetitive bit pattern in order to allow extracting of bits at an optimized time.

11. The communication system of claim 9 further comprising means, coupled to said source node, for digitizing a voice signal to produce said information.

12. The communication system of claim 11 wherein said transmitting medium and said receiving medium are separate frequency channels on a single physical medium and said translating means includes a frequency translator.

13. The communication system of claim 12 further comprising a plurality of transmitting and receiving channels on said physical medium, each of said nodes having means for transmitting and receiving on more than one channel.