CODING AND DECODING SYSTEM WITH MULTI-LEVEL FORMAT

• US 3,760,277 A
• Filed: 05/17/1971
• Issued: 09/18/1973
• Est. Priority Date: 05/17/1971
• Status: Expired due to Term

• Current Assignee: Racal Data Communications Incorporated
• Original Assignee: Sang Y. Whang
• Inventors: Whang, Sang Y.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Sloyan, Thomas J.
• Application Number:
  US05/143,762
• Time in Patent Office: 855 Days
• Field of Search: 325/38A,42,65 178/68 340/347DD 235/154 333/15,18
• US Class Current: 375/293
• CPC Class Codes: H04L 25/4919 using balanced multilevel codes H04L25/4927 takes precedence

Abstract

The present invention is directed to a method and apparatus for coding and decoding data so that it may be transmitted from point to point in either a baseband system or in a carrier system. The method and apparatus involves forming a multi-bit group of binary signals (bits) and transmitting such signals with at least one bit and a fractional part of another bit of the group in an encoding period. In a preferred embodiment of my invention a pair of adjacent encoding periods are employed to fully identify all of the bits of a multi-bit group. My format requires less bandwidth than prior art binary formats. Furthermore, my format, when employed with a three level system, also requires less bandwidth than any known prior art three level system. The invention also includes an inherent error detection capability. Such inherent error detection is utilized at the receiver to automatically emit a decoded signal which has a high probability of being the correct signal that was transmitted. In addition, the invention readily provides a signal of a unique characteristic from which a decoding clock can be simply and easily derived.

Claims

1. A data transmission system having a carrier signal to be transmitted over a communication link, said system comprising:

means at a transmitter for grouping, into a multi-bit word, input binary data having a data rate defined by a given number of input bit periods per second with one data bit represented in each input bit period;

means responsive to said grouping means for generating a discrete signal level during at least a pair of modulation periods per multi-bit word for representing the identity of the multi-bit word, said signal generating means characterized by emitting a signal having a data bit-to-baud ratio of a mixed number and by emitting said discrete signal levels in a continuous sequence that represents a plurality of adjacent ones of said multi-bit data words;

means for modulating said carrier signal with said signal from said generating means; and

means at a receiver for deriving a clock signal from said signal modulated carrier, which clock signal is synchronized in time with the baud rate of said generating means at said transmitter.

2. A system in accordance with claim 1 wherein each multi-bit word comprises three binary bits and said mixed number bit-to-baud ratio is 1.5.

3. A system in accordance with claim 2 wherein the bits of binary values are identified by occupying one of two possible signal levels during sequentially-appearing input bit periods, and said generating means comprises an encoder employing a trinary format which comprises three signal levels and a modulation period equal to 1 1/2 bit periods;

said system comprising;

means modulating said carrier with a discrete signal level during a first modulation period of a pair of adjacent modulation periods for partially identifying the bits for a multi-bit word to be represented in that modulation period; and

means modulating a given signal level during the second modulation period of said pair for completing the identity of the bits of said multi-bit word.

4. A system in accordance with claim 3 and wherein said generating means comprises:

means for selecting a given amplitude level from levels of 0, +Y, or -Y, where Y is a predetermined voltage for said discrete signal level in said first and second modulation periods of said pair; and

means for amplitude modulating said carrier with said selected amplitude levels.

5. A system in accordance with claim 3 and wherein said generating means comprises:

means for selecting a given phase angle from three different substantially equally separated phase angle amounts for said discrete signal levels in said first and second modulation periods of said pair; and

means for differentially phase modulating said carrier with said selected phase angle amounts in said pair of modulation periods.

6. A system in accordance with claim 4 wherein a word comprised of three binary bits represents eight possibilities and means in said encoder for assigning each possibility one matrix position from the nine possible matrix positions for identifying the signal levels in a Trit Pair.

7. A system in accordance with claim 6 wherein the one unused data-representing possibility of the matrix is assigned by Said possibility assigning means to have signal values for adjacent Trit Pairs such that a random string of binary data yields a trinary format signal having signal energy distribution including a frequency of 1/2 T where T is the modulation period for a Trit, and said system comprising a demodulator adapted for connection to said communication link said demodulator comprising:

means for receiving said trinary format modulated carrier signal including at least one Trit Pair;

means connected to said clock signal deriving means and responsive thereto for sampling the signal levels of said Trit Pair; and

means associated with said sampling means for emitting the multi-bit binary bit word identified by the signal levels sampled from said Trit Pair.

8. A system in accordance with claim 7 wherein said input binary data has a bit rate of about 7,200 bits per second and said transmitter further comprises:

timing means for assigning a baud rate for said trinary format of about 4,800, and said signal level modulated carrier has a bandwidth of 1/2 T where T is the modulation period;

means for adding a pilot tone to said signal level modulated carrier; and

means for applying the pilot tone and the signal level modulated carrier as a vestigial sideband carrier to a communication link.

9. A system in accordance with claim 8 including at said receiver:

means for removing said pilot tone from the vestigial sideband carrier received over said link.