Have You Used Comm.SphereDecoder System Object For Soft Output?

2013 6 8
1 个回答
更新时间：2015 11 16
7 次查看（30 天）

0 个投票

Hi I am Using Comm.SphereDecoder System Object for a simulation. I am using Viterbi Decoder System Object To Decode the Soft Bits.
But BER is Coming Like 0.49.
Anyone is here Experienced the same Problem? Or Any Suggestion? I am Adding my Code Here.
M = 16;
k = log2(M);
nBits = 1e3*log2(M);
noiseVariance = 1e-2;
EbNo = 4;
symMap = [11 10 14 15 9 8 12 13 1 0 4 5 3 2 6 7];
BitTable = de2bi(symMap, log2(M), 'left-msb');
codeRate = 1/2;
constlen = 7;
codegenpoly = [171 133];
tblen = 32;
trellis = poly2trellis(constlen, codegenpoly);
hConvEnc = comm.ConvolutionalEncoder(trellis);
trellis = poly2trellis(7, [171 133])
hMod = comm.RectangularQAMModulator('BitInput', true, ...
'ModulationOrder', M, 'NormalizationMethod', 'Average power',...
'SymbolMapping', 'Custom', 'CustomSymbolMapping', symMap);
hAWGN = comm.AWGNChannel('NoiseMethod', ...
'Signal to noise ratio (SNR)',...
'SNR',10);
hMIMO = comm.MIMOChannel('MaximumDopplerShift', 0, ...
'NumTransmitAntennas', 4, ...
'NumReceiveAntennas', 4, ...
'TransmitCorrelationMatrix', eye(4), ...
'ReceiveCorrelationMatrix', eye(4), ...
'PathGainsOutputPort', true);
hSpDec = comm.SphereDecoder('Constellation', constellation(hMod),...
'BitTable', BitTable, 'DecisionType', 'Soft');
hVitDecSD = comm.ViterbiDecoder(trellis, ...
'InputFormat', 'Unquantized', 'TracebackDepth', tblen);
hBER = comm.ErrorRate;
data = randi([0 1], nBits, 1);
encodedData = step(hConvEnc, data);
yMod = step(hMod, encodedData);
yTx = reshape(yMod, [], 4);
[yFad, yPG] = step(hMIMO, yTx);
yRec = step(hAWGN, yFad);
rxBits = step(hSpDec, yRec, squeeze(yPG));
decDataSD = step(hVitDecSD, rxBits(:));
ber = step(hBER, data, decDataSD);
disp(ber(1));

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回答（1 个）

Amit Kansal
Amit Kansal 2015-11-16
编辑：Walter Roberson 2015-11-16

1 个投票

Couple of issues with the code. The Viterbi Decoder is set to the continuous operation which introduces a delay of tblen bits which is not accounted for in the comparison.
Also, the bit polarity assumed by the SphereDecoder is opposite of that used by the Viterbi Decoder.
Update above respective lines to :
hBER = comm.ErrorRate('ReceiveDelay', tblen);
decDataSD = step(hVitDecSD, -rxBits(:));
to get better ber values.

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