Combined scrambler-encoder for multilevel digital data

• US 3,925,611 A
• Filed: 08/12/1974
• Issued: 12/09/1975
• Est. Priority Date: 08/12/1974
• Status: Expired due to Term

• Current Assignee: Thomas Mann Dennis
• Original Assignee: Thomas Mann Dennis
• Inventors: Dennis, Thomas Mann
• Primary Examiner(s): Hubler, Malcolm F.
• Assistant Examiner(s): Birmiel, H. A.
• Application Number:
  US05/496,529
• Time in Patent Office: 484 Days
• Field of Search: 178/22,68 325/38A 340/347DD,146.1AL
• US Class Current: 380/31
• CPC Class Codes: H03M 5/00 Conversion of the form of the representation of individual digits
• CPC Class Codes: H04L 25/4917 using multilevel codes

Abstract

A high-speed digital data transmission system combines quadrature amplitude modulation with scrambling-descrambling, differential amplitude coding-decoding, and Gray-to-rotational coding-decoding of multilevel data symbols channeled at baseband, i.e., including frequencies extending down to zero, onto parallel bit streams with a minimization of error multiplication. Scrambling and descrambling facilitate timing recovery and equalizer adjustment. Differential and rotational encoding and decoding compensate for phase ambiguities in the signal constellation, i.e., points on a space diagram representative of the tips of multilevel symbol vectors.

Claims

1. In combination with a synchronous digital data transmission system in which multilevel symbols plottable as points on a twodimensional four-quadrant signal space diagram are encoded on parallel bit streams, a transmitting terminal comprising:

means for differentially encoding at least the parallel streams representing the most significant bits of said multilevel symbols by continuously augmenting the last-transmittted bits by the increment between such last-transmitted bits and incoming bits therein, and means for rotationally encoding other parallel streams representing bits of lesser significance in said multilevel symbols from a uniform rotational Gray coding format throughout all quadrants of said signal space diagram to a bilaterally symmetric relationship.

2. The combination defined in claim 1 in which said differential encoding means comprises means for delaying by one synchronous symbol interval each differentially encoded bit, and means for combining each incoming bit with the previous bit from said delaying means to form differentially encoded bits.

3. The combinatin defined in claim 1 in which said rotational encoding means comprises means for detecting the simultaneous occurrence of bits of complementary types in parallel data streams, and means responsive to a determination that the current multilevel symbol is encoded in a predetermined quadrant for complementing the bits detected by said detecting means.

4. In combination with a synchronous digital data transmission system in which multilevel symbols plottable as points on a two-dimensional four-quadrant signal space diagram are encoded on parallel bit streams, a receiving terminal including means for decoding such parallel bit streams comprising means for rotationally decoding preselected parallel bit streams representing received multilevel symbols of one degree of significance arranged in bilaterally symmetric coding format into a uniform rotational Gray coding relationship, and means for differentially decoding at least the parallel streams representing the most significant bits of received multilevel symbols by continuously determining the increment between consecutive bits therein.

5. The combination defined in claim 4 in which said rotational decoding means comprises means for detecting the simultaneous occurrence of bits of complementary type in parallel data streams, and means responsive to a determination that the current multilevel symbol is encoded in a predetermined quadrant for complementing the bits detected by said detecting means.

6. The combination defined in claim 4 in which said differential decoding means comprises means for delaying by one synchronous symbol interval each bit to be differentially decoded, and means for combining directly received bits with previous bits from said delaying means to form differentially decoded bits.

7. In combination with a synchronous digital data transmission system in which multilevel symbols are plottable as points on a two-dimensional four-quadrant signal space diagram are encoded on parallel bit streams, a transmitting terminal comprising means responsive to one of said parallel streams for generating a pseudorandom key signal and combining said key signal with said one parallel bit stream to form a first scrambled bit stream, means for joining one or more of said other parallel bit streams with said first scrambled bit stream after discrete synchronous delay intervals to form additional scrambled bit streams, means for differentially encoding at least the parallel streams representing the most significant bits of said multilevel symbols by continuously augmenting the last-transmitted bits by the increment between such last-transmitted bits and incoming bits in such streams, and means for rotationally encoding other parallel streams representing Bits of lesser significance in said multilevel symbols from a uniform rotational Gray-code format throughout all quadrants of said signal diagram to a bilaterally symmetric relationship.

8. In combination with a synchronous digital data transmission system in which multilevel symbols plottable as points on a two-dimensional four-quadrant signal space diagram have been encoded on parallel bit streams partially as augmentations of the last-transmitted values and the increments between such last-transmitted and incoming absolute values and partially from a conversion between uniform Gray-code rotational symmetry and bilateral symmetry through all quadrants of said space diagram, a receiving terminal comprising means responsive to those bit streams encoded with respect to rotational symmetry pattern for complementing bits therein exhibiting a complementary symmetry relationship when the received multilevel symbol falls in an even-ordered quadrant of said space diagram thereby transforming those bit streams exhibitng bilateral symmetry into said rotational symmetry, means responsive to the one of said parallel streams from which the scrambling key signal was derived after subjection to said complementing means for generating a pseudorandom descrambling key signal and combining said descrambling key signal with said last-mentioned parallel stream to form a first descrambled bit stream, means for differentially decoding at least the received parallel streams representing the most significant bits of said multilevel symbols by continuously combining consecutive bits in such streams to reconstruct absolute valued bit streams, and means for joining said bit stream from which said key signal was derived after subjection to said complementing means and after discrete synchronous delay intervals with others of said decoded parallel bit streams to form additional descrambled bit streams.

9. In combination with a synchronous digital data transmission system in which multilevel symbols plottable as points on a two-dimensional four-quadrant signal space diagram are encoded on parallel bit streams including a transmitting terminal, a transmission channel and a receiving terminal:

at said transmitting terminal including means for applying modulated signals to said channel, means for differentially encoding at least the parallel streams representing the most significant bits of said multilevel symbols by continuously augmenting the last-transmitted bits by the increments between such last-transmitted bits and incoming bits therein, and means for converting other parallel streams representing bits of lesser significance in said multilevel symbols from a uniform rotational Gray-code format throughout all quadrants of said signal space diagram to a bilaterally symmetric relationship suitable for said transmission channel, at said receiving terminal including means for demodulating signals from said channel, means for reconverting certain parallel bit streams representing received multilevel symbols of lesser significance arranged in a bilaterally symmetrical relationship into a uniform rotational Gray-code format throughout all quadrants, and means for differentially decoding at least the parallel streams representing the most significant bits of received multilevel symbols by continuously determining the increment between consecutive bits therein.

10. In combination with a synchronous digital data transmission system in which multilevel symbols plottable as points on a two-dimensional four-quadrant signal space diagram are encoded on parallel bit streams including a transmitting terminal, a transmission channel and a receiving terminal:

at said transmitting terminal including means for applying modulated signals to said channel, means responsive to one of said parallel streams for generating a pseudorandom key signal and combining said key signal with said one parallel bit stream to form a first scrambled bit stream, means for joining one or more of said other parallel bit streams with said first parallel bit stream after discrete synchronous delay intervals to form additional scrambled bit streams, means for differentially encoding at least the parallel streams representing the most significant bits of said multilevel symbols by continuously augmenting the last-transmitted bits by the increment between such last-transmitted bits and incoming bits, and means for rotationally encoding other parallel streams representing bits of lesser significance in said multilevel symbols from a uniform rotational Gray-code format throughout all quadrants of said signal diagram to a bilaterally symmetric relationship, at said receiving terminal including means for demodulating signals from said channel, means responsive to those bit streams encoded with respect to rotational symmetry pattern for complementing bits therein exhibiting a complementary symmetry relationship when the received multilevel symbol falls in an even-ordered quadrant of said space diagram thereby transforming those bit streams exhibiting bilateral symmetry into said rotational symmetry, means responsive to the one of said parallel streams from which the scrambling key signal was derived at said transmitting terminal after subjection to said complementing means for generating a pseudorandom descrambling key signal and combining said descrambling key signal with said last-mentioned parallel stream to form a first descrambled bit stream, means for differentially decoding at least the received parallel streams representing the most significant bits of said multilevel symbols by continuously combining consecutive bits in such streams to reconstruct absolute-valued bit streams, and means for joining said bit stream from which said key signal was derived after subjection to said complementing means and after discrete synchronous delay intervals with others of said decoded parallel bit streams to form additional descrambled bit streams.