Differential codec for pragmatic PSK TCM schemes

• US 6,304,614 B1
• Filed: 11/03/1998
• Issued: 10/16/2001
• Est. Priority Date: 11/04/1997
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Fonnesbeck, Dale D., Abbaszadeh, Ayyoob D.
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Nguyen, Dung X.
• Application Number:
  US09/185,210
• Time in Patent Office: 1,078 Days
• Field of Search: 375/279, 375/265, 375/280, 375/340, 375/147, 375/265.RC
• US Class Current: 375/279
• CPC Class Codes: H03M 13/25 Error detection or forward error correction by signal space coding, i.e. adding redundancy in the signal constellation, e.g. Trellis Coded Modulation [TCM] modulation codes H03M13/31
• CPC Class Codes: H03M 13/256 with trellis coding, e.g. with convolutional codes and TCM
• CPC Class Codes: H04L 1/006 Trellis-coded modulation
• CPC Class Codes: H04L 27/186 in which the information is carried by both the individual signal points and the subset to which the individual signal points belong, e.g. coset coding or related schemes

Abstract

A system including coding and decoding circuits provides for resolution of the phase ambiguities in pragmatic trellis-coded PSK modulation transmissions. An error correcting coder, such as a convolutional encoder, precedes the modulator for reducing the effect of noise in inducing phase errors. A corresponding decoder appears at the reception end of the communication system. A differential encoder and decoder automatically remove the possible phase ambiguities, and operate in conjunction with the error correcting encoder and decoder. Each of the ambiguity-removal differential encoder and the decoder act as an operator upon its input signal. In order that both the error correcting encoder and the ambiguity encoder immediately precede the modulator, the ambiguity removal circuitry is placed between the error correcting encoder, and is constructed as a combination of differential encoder and inverse differential encoder. The use for ambiguity removal of both the differential encoder and the inverse differential encoder operates to remove the phase ambiguity while making the ambiguity operation transparent to the output of the error correction encoder. This retains the benefit of placing the error correcting encoder immediately before the modulator.

Claims

1. An error correction phase-shift-keying communication system with removal of phase ambiguities, comprising:

a communication channel having a phase modulator at an input side of the channel and a phase demodulator at an output side of the channel;

a signal preprocessor and a differential encoder, the preprocessor comprising an error correction unit for correction of errors in signal generation, the differential encoder being connected between an output terminal of the preprocessor and an input terminal of the modulator;

a signal post processor and a differential decoder, the differential decoder being connected between an output terminal of the demodulator and an input terminal of the post processor; and

wherein an operational function of the differential decoder is inverse to an operational function of the differential encoder to provide for removal of a phase ambiguity produced within the signal channel; and

the processor of each of said preprocessor and said post processor comprises a one-dimensional coder and a convolutional encoder serially connected to each other for processing a least significant bit of an input signal of said processor to provide an output digit of an output signal of said processor; and

logic means including a full adder responsive to the output signal of said convolutional encoder and the next more significant bit of the input signal of said processor to provide a further digit of the output signal of said processor.

2. A system according to claim 1 further comprising:

a first compensation unit located in said preprocessor and having an operational function inverse to the operational function of said differential encoder to provide for a virtual direct connection between said error correction unit and said modulator;

a second compensation unit located in said post processor and having an operational function inverse to the operational function of said first compensation unit; and

wherein said second compensation unit is operative to remove a signal perturbation introduced by said first compensation unit.

3. An error correction phase-shift-keying communication system with removal of phase ambiguities, comprising:

a communication channel having a phase modulator at an input side of the channel and a phase demodulator at an output side of the channel;

a first error correction unit for correction of errors in signal generation, the error correction unit preceding said modulator, a second error correction unit for correction of errors in signal generation, said second error correction unit following said demodulator;

a first phase ambiguity resolving means interconnecting said correction unit with said modulator and having a first operator, and a second phase ambiguity resolving means interconnecting said second correction unit with said demodulator and having a second operator inverse to said first operator, each of said operators comprising means for performing logic operations of a mapping process including a combination of an input signal of said operator with a delayed signal wherein said delayed signal is the input signal of said operator or an output signal of said operator; and

wherein said first error correction unit and said first phase ambiguity resolving means constitute a first ambiguity resolving circuit, and said second error correction unit and said second phase ambiguity resolving means constitute a second ambiguity resolving circuit, each of said resolving circuits comprising a one-dimensional coder and a convolutional encoder serially connected to each other for processing a least significant bit of an input signal of said resolving circuit to provide an output digit of an output signal of said resolving circuit; and

logic means including a full adder responsive to the output signal of said convolutional encoder and the next more significant bit of the input signal of said resolving circuit to provide a further digit of the output signal of said resolving circuit.

4. A system according to claim 3 wherein, in said first operator, said delayed signal is a delayed replica of the output signal of said first operator.

5. A system according to claim 4 wherein, in said second operator, said delayed signal is a delayed replica of the input signal of said second operator.

8. A system according to claim 3 wherein said first error correction unit is an encoder and said second error correction unit is a decoder.

9. A system according to claim 8 wherein, in said first operator, said delayed signal is a delayed replica of the output signal of said first operator.

10. A system according to claim 9 wherein, is said second operator, said delayed signal is a delayed replica of the input signal of said second operator.

11. A system according to claim 10 wherein said second ambiguity resolving circuit comprises a one-dimensional decoder coupled to an input terminal of said resolving circuit for processing a least significant bit of an input signal of said resolving circuit to provide an output digit of an output signal of said resolving circuit.

6. An error correction phase-shift-keying communication system with removal of phase ambiguities, comprising:

a communication channel having a phase modulator at an input side of the channel and a phase demodulator at an output side of the channel;

an error correction unit for correction of errors in signal generation, the error correction unit preceding said modulator;

phase ambiguity resolving means interconnecting said correction unit with said modulator, and comprising an operator for performing logic operations of a mapping process including a combination of an input signal of said operator with a delayed replica of output signal of said operator; and

wherein said error correction unit and said phase ambiguity resolving means constitute an ambiguity resolving circuit comprising a one-dimensional encoder and a convolutional encoder coupled to an output terminal of said one-dimensional decoder for processing a least significant bit of an input signal of said resolving circuit to provide an output digit of an output signal of said resolving circuit; and

logic means including a full adder responsive to the output signal of said convolutional decoder and the next more significant bit of the input signal of said resolving circuit to provide a further digit of the output signal of said resolving circuit.

7. A system according to claim 6 wherein said logic means includes OR means for combining an encoded replica of a third digit of the input signal of said resolving circuit with an output signal of said full adder to provide a further digit of the output signal of said resolving circuit.

12. An error correction phase-shift-keying communication system with removal of phase ambiguities, comprising:

a communication channel having a phase modulator at an input side of the channel and a phase demodulator at an output side of the channel;

a first error correction unit for correction of errors in signal generation, the first error correction unit preceding said modulator, and a second error correction unit for correction of errors in signal generation, said second error correction unit following said demodulator;

a first phase ambiguity resolving means interconnecting said correction unit with said modulator and having a first operator, and a second phase ambiguity resolving means interconnecting said second correction unit with said demodulator and having a second operator inverse to said first operator, each of said operators comprising means for performing logic operations of a mapping process including a combination of an input signal of said operator with a delayed signal wherein said delayed signal is the input signal of said operator or an output signal of said operator;

wherein said first error correction unit is an encoder and said second error correction unit is a decoder, said delayed signal for said first operator is a delayed replica of the output signal of said first operator, said delayed signal for said second operator is a delayed replica of the input signal of said second operator;

said second error correction unit and said second resolving means constitute an ambiguity resolving circuit comprising a one-dimensional decoder coupled to an input terminal of said resolving circuit for processing a least significant bit of an input signal of said resolving circuit to provide an output digit of an output signal of said resolving circuit;

said one-dimensional decoder is a first one-dimensional decoder, the system further comprising;

logic means including a full adder, and a second one-dimensional decoder and a convolutional encoder coupled to an output terminal of said second one-dimensional decoder for processing the least significant bit of the input signal of said resolving circuit to provide a clock input to said full adder; and

wherein said logic means includes OR means for combining more significant bits of the input signal of said resolving circuit for application to said adder to provide a further digit of the output signal of said resolving circuit.