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lteConvolutionalDecode

Convolutional decoding

Syntax

  • output = lteConvolutionalDecode(input)
    example

Description

example

output = lteConvolutionalDecode(input) performs convolutional decoding of the input data vector, input. The input data is assumed to be soft bit data that has been encoded by a tail-biting convolutional code with constraint length 7, coding rate 1/3, and octal polynomials G0 =133, G1 =171 and G2 =165. Since the code is tail-biting, output will be 1/3 of the length of the input. The input data vector is assumed to be structured as three encoded parity streams concatenated block-wise. For example, input is [D0 D1 D2], where D0, D1, and D2 are the separate parity streams resulting from the original encoding with individual polynomials G0, G1 and G2. The decoder uses a soft input Viterbi algorithm without any quantization.

Examples

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Convolutionally decode soft bits.

Generate random bits and convolutionally encode them. QPSK modulate the coded bits and add noise to the received symbols.

txBits = randi([0 1],1000,1);
codedData = lteConvolutionalEncode(txBits);

txSymbols = lteSymbolModulate(codedData,'QPSK');
noise = 0.5*complex(randn(size(txSymbols)),randn(size(txSymbols)));
rxSymbols = txSymbols + noise;

Show rxSymbols constellation, setting txSymbols as the reference constellation.

xylimits = [-2.5 2.5];
cdScope = comm.ConstellationDiagram('ReferenceConstellation',txSymbols,'XLimits',xylimits ,'YLimits',xylimits);
cdScope(rxSymbols)

Demodulate the noisy symbols to obtain soft bits. Convolutionally decode the soft bits. Display the number of erroneous bits.

softBits = lteSymbolDemodulate(rxSymbols,'QPSK','Soft');

rxBits = lteConvolutionalDecode(softBits);

numberErrors = sum(rxBits ~= int8(txBits))
numberErrors =

     0

Input Arguments

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Input data, specified as a column vector. The data is assumed to be soft bit data encoded by a tail-biting convolutional code with constraint length 7, coding rate 1/3 and octal polynomials G0=133, G1=171 and G2=165.

Output Arguments

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Convolutionally decoded data, specified as a column vector. The decoded data is 1/3 the length of the input input.

Data Types: int8

Introduced in R2014a

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