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Convolutional Codes in Phase Modulation Communication Systems

IP.com Disclosure Number: IPCOM000086688D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Digeon, A: AUTHOR [+2]

Abstract

The data stream to be transmitted is divided into groups of two consecutive bits. Each is encoded into a group of three bits (tribits) by means of a (3,2) convolutional code. Each tribit is encoded as a carrier-phase change in accordance with conventional 8-phase-modulation technique, and the modulated carrier is sent over the channel. At the receiver, demodulation provides the received tribits, which are decoded in a soft-decision Viterbi decoder. The decoded data are provided to the user unit. Coding: The following (3, 2) convolutional codes gave good results. Encoding constraint length n = 4 ; free distance d = 5.

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Convolutional Codes in Phase Modulation Communication Systems

The data stream to be transmitted is divided into groups of two consecutive bits. Each is encoded into a group of three bits (tribits) by means of a (3,2) convolutional code. Each tribit is encoded as a carrier-phase change in accordance with conventional 8-phase-modulation technique, and the modulated carrier is sent over the channel. At the receiver, demodulation provides the received tribits, which are decoded in a soft-decision Viterbi decoder. The decoded data are provided to the user unit.

Coding: The following (3, 2) convolutional codes gave good results. Encoding constraint length n = 4 ; free distance d = 5.

Generator matrix :

1 0 1 1 0 1 1 1 0

0 1 1 1 1 1 0 1 1

Parity polynomials :

1 0 1 0 1

1 1 0 0 1

1 0 1 1 1

Encoding constraint length n = 6 ; free distance d = 7. Generator matrix :

1 0 1 1 1 1 0 1 1 1 0 1

0 1 1 1 1 1 1 0 0 0 1 1

Parity polynomials :

1 1 0 0 1 0 1

1 1 1 0 0 1 1

1 0 0 0 1 0 1.

Decoding : Decoding was performed with the Viterbi algorithm, by minimizing the Euclidean distance between the paths corresponding to the received and the possible transmitted signals. The chosen decoding constraint length was equal to 4 n.

Results : Assuming additive white Gaussian noise, a bit error probability P=2.0410/-4/ was achieved with an average power-signal-to-noise ratio SNR = 9dB with the 8-phase coded system, instead of SNR = 11 dB, to achieve P =
2.04.10/-4/, with a 4-phase system transmi...