Synchronous quantized subcarrier multiplexer for digital transport of video, voice and data

• US 4,999,831 A
• Filed: 10/19/1989
• Issued: 03/12/1991
• Est. Priority Date: 10/19/1989
• Status: Expired due to Fees

• Current Assignee: Telecommunications Systems Incorporated
• Original Assignee: Telecommunications Systems Incorporated
• Inventors: Grace, Martin K.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): HSU, ALPUS
• Application Number:
  US07/423,374
• Time in Patent Office: 509 Days
• Field of Search: 370/69.1, 370/70, 370/76, 370/120, 370/50, 370/3, 370/118, 370/110.1, 375/25, 375/61, 375/43, 358/11-13, 358/15, 358/21 R, 358/335, 358/343, 358/141-143, 455/109, 332/167
• US Class Current: 370/481
• CPC Class Codes: H04B 10/504 using direct modulation
• CPC Class Codes: H04J 14/0298 with sub-carrier multiplexing [SCM]

Abstract

This invention addresses the digital transmission of wideband video, narrowband audio, and digital information over information networks. More specifically, the invention involves synchronous quantized subcarrier multiplexing (quantized-SCM) which results in purely electronic multiplexing of voice, data and multiple channel full bandwidth NTSC video for digital transmission over a communcation line and recovery of same signals at a receiving station.

Claims

1. A method of transmitting at least two information bearing signals over a communication link comprising the steps of

a. mixing a first signal having a bandwidth B₁ with a local carrier signal having a frequency F₁ ;

b. mixing a second signal having a bandwidth B₂ with a second local carrier signal having a frequency F₂ which is greater than F₁ such that F₂ -B₂ exceeds F₁ +B₁ ;

c. multiplexing the carriers to form a composite signal;

d. synchronously sampling the composite signal at a sampling rate F_S where F_S is equal to 2 times F₂ and converting the composite signal to a digital signal representative thereof;

e. applying said digital signal to the communication link;

f. receiving said digital signal at a receiver connected with said link in a manner such that F_S is recoverable at the receiver and converting said digital signal to a reconstructed composite signal substantially identical to the first named composite signal; and

g. recovering the first and second signals from said reconstructed signal.

2. A method as in claim 1, including the steps of:

generating a base band analog signal having a bandwidth B₀ such that B₀ is less than F₁ -B₁ ;

multiplexing said base band signal with said carriers; and

recovering said base band signal from said reconstructed composite signal.

3. The method as in claim 2, wherein said base band signal is recovered by low pass filtering.

4. A method of transmitting at least two information bearing signals over a communication link comprising the steps of:

a. accepting a baseband signal having bandwidth B₀ ;

b. accepting a second signal with bandwidth B₁ and mixing it with a local carrier signal having a frequency of F₁, where F₁ -B₁ exceeding B₀ ;

c. accepting additional signals with bandwidth B_n and mixing it (them) with local carrier signal(s) having frequency of F_n, where F_n is the maximum carrier frequency, B_n is the maximum bandwidth and n is an integer greater than or equal to 1, where F_n is greater than F(n-1) such that (F_n -B_n) exceeds (F(n-1)+B(n-1));

d. multiplexing the signals with bandwidth B₀ through B_n to form a composite signal;

e. synchronously sampling the composite signal at a sampling rate F_S where F_S is equal to 2 times F_n and converting the composite signal to a digital signal representative thereof;

f. applying said digital signal to the communication link;

g. assuring the line data rate of transmission F_L =F_S (N+X) bits/sec. where N is the bit resolution of a uniform characteristic A/D converter resulting in a 2ⁿ =M quantization levels, and where X equals the number of overhead bits required for framing and synchronization;

h. receiving said digital signal at a receiver connected with said link in a manner such that F_S is recoverable at the receiver and converting said digital signal to a reconstructed analog composite signal substantially identical to the first named composite signal.

5. A method as in claim 4, including the steps of:

a. Demultiplexing said reconstructed composite signal resulting in the same number of separate information bearing signals as were present prior to multiplexing;

b. Each signal containing substantially identical information as its corresponding original signal.

6. A method as in claim 5, wherein said information contained on said baseband signal is recovered by low pass filtering.

7. A method as in claim 5, wherein said information contained on said signals with bandwidth B₁, through B_n are recovered using homodyne detection and low pass filtering technique on each of the remaining signals.