mirror of https://github.com/drowe67/codec2.git
195 lines
6.8 KiB
Matlab
195 lines
6.8 KiB
Matlab
% ldpc.m
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%
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#{
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David Rowe 2013
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Octave functions for the CML LDPC library.
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To install and compile CML support:
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$ sudo apt-get install liboctave-dev
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$ git clone git@github.com:drowe67/cml.git
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$ cd cml
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$ make
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If you have configured codec2 with cmake -DUNITTEST=1, then you will
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already have CML (e.g. under build_linux/cml), as it is used to run unit tests.
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To use CML when running Octave simulations from the Octave CLI, set an
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environment variable for CML_PATH in your shell or in your
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codec2/octave/.octaverc file:
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setenv("CML_PATH",sprintf("%s/codec2/build_linux/cml",getenv("HOME")))
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#}
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1;
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function init_cml()
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currentdir = pwd;
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path_to_cml = getenv("CML_PATH");
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if exist(path_to_cml, 'dir') == 7
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cd(path_to_cml)
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CmlStartup
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cd(currentdir);
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else
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printf("\n---------------------------------------------------\n");
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printf("Can't start CML in path: %s\n", path_to_cml);
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printf("See CML_PATH instructions at top of this script (ldpc.m)\n");
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printf("-----------------------------------------------------\n\n");
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assert(0);
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end
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end
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% init using built in WiMax or DVSB2 code
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function code_param = ldpc_init_builtin(code, rate, framesize, modulation, mod_order, mapping, constellation)
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if strcmp(code,'wimax')
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[code_param.H_rows, code_param.H_cols, code_param.P_matrix] = InitializeWiMaxLDPC( rate, framesize, 0 );
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end
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if strcmp(code,'dvbs2')
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[code_param.H_rows, code_param.H_cols, code_param.P_matrix] = InitializeDVBS2( rate, framesize);
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end
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if nargin == 7
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code_param.S_matrix = constellation;
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else
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if length(mapping) == 0
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code_param.S_matrix = CreateConstellation( modulation, mod_order);
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else
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code_param.S_matrix = CreateConstellation( modulation, mod_order, mapping );
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end
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end
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code_param.bits_per_symbol = log2(mod_order);
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code_param.ldpc_data_bits_per_frame = length(code_param.H_cols) - length(code_param.P_matrix);
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code_param.ldpc_parity_bits_per_frame = framesize - code_param.ldpc_data_bits_per_frame;
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code_param.ldpc_coded_bits_per_frame = framesize;
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code_param.data_bits_per_frame = code_param.ldpc_data_bits_per_frame;
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code_param.coded_bits_per_frame = code_param.ldpc_coded_bits_per_frame;
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code_param.coded_syms_per_frame = code_param.coded_bits_per_frame/code_param.bits_per_symbol;
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endfunction
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% init using user supplied code
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function [code_param framesize rate] = ldpc_init_user(HRA, modulation, mod_order, mapping, constellation)
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[Nr Nc] = size(HRA);
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rate = (Nc-Nr)/Nc;
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framesize = Nc;
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[H_rows, H_cols] = Mat2Hrows(HRA);
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code_param.H_rows = H_rows;
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code_param.H_cols = H_cols;
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code_param.P_matrix = [];
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if nargin == 5
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code_param.S_matrix = constellation;
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else
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if length(mapping) == 0
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code_param.S_matrix = CreateConstellation( modulation, mod_order);
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else
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code_param.S_matrix = CreateConstellation( modulation, mod_order, mapping );
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end
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end
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code_param.bits_per_symbol = log2(mod_order);
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code_param.ldpc_data_bits_per_frame = length(code_param.H_cols) - length(code_param.P_matrix);
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code_param.ldpc_parity_bits_per_frame = framesize - code_param.ldpc_data_bits_per_frame;
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code_param.ldpc_coded_bits_per_frame = framesize;
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% these variables support 1's stuffing (not using all data bits to lower code rate)
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code_param.data_bits_per_frame = code_param.ldpc_data_bits_per_frame;
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code_param.coded_bits_per_frame = code_param.ldpc_coded_bits_per_frame;
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code_param.coded_syms_per_frame = code_param.coded_bits_per_frame/code_param.bits_per_symbol;
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endfunction
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function [codeword s] = ldpc_enc(data, code_param)
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if code_param.data_bits_per_frame != code_param.ldpc_data_bits_per_frame
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% optionally lower the code rate by "1's stuffing" - setting Nunused data bits to 1
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Nunused = code_param.ldpc_data_bits_per_frame - code_param.data_bits_per_frame;
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codeword = LdpcEncode([data ones(1,Nunused)], code_param.H_rows, code_param.P_matrix);
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% remove unused data bits from codeword, as they are known to the receiver and don't need to be transmitted
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codeword = [ codeword(1:code_param.data_bits_per_frame) codeword(code_param.ldpc_data_bits_per_frame+1:end) ];
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else
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codeword = LdpcEncode( data, code_param.H_rows, code_param.P_matrix );
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end
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s = Modulate( codeword, code_param.S_matrix );
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endfunction
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function [detected_data paritychecks] = ldpc_dec(code_param, max_iterations, ...
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demod_type, decoder_type, r, ...
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EsNo, fading)
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% handle "1's stuffing" case where we don't use all data bits
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Nunused = code_param.ldpc_data_bits_per_frame - code_param.data_bits_per_frame;
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symbol_likelihood = Demod2D( r, code_param.S_matrix, EsNo, fading);
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% initialize the extrinsic decoder input
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input_somap_c = zeros(1, code_param.ldpc_coded_bits_per_frame - Nunused);
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bit_likelihood = Somap( symbol_likelihood, demod_type, input_somap_c );
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input_decoder_c = bit_likelihood(1:(code_param.ldpc_coded_bits_per_frame-Nunused));
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% insert "very likely" LLRs for unused data bits (in 1's stuffing case)
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input_decoder_c = [input_decoder_c(1:code_param.data_bits_per_frame) ...
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100*ones(1,Nunused) ...
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input_decoder_c(code_param.data_bits_per_frame+1:end)];
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[x_hat paritychecks] = MpDecode( -input_decoder_c, code_param.H_rows, code_param.H_cols, ...
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max_iterations, decoder_type, 1, 1);
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[mx mx_ind] = max(paritychecks);
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detected_data = x_hat(mx_ind,:);
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endfunction
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% Packs a binary array into an array of 8 bit bytes, MSB first
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function packed = packmsb(unpacked)
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packed = zeros(1,floor(length(unpacked)+7)/8);
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bit = 7; byte = 1;
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for i=1:length(unpacked)
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packed(byte) = bitor(packed(byte), bitshift(unpacked(i),bit));
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bit--;
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if (bit < 0)
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bit = 7;
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byte++;
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end
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end
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endfunction
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% unpacks an array of 8 bit bytes into a binary array of unpacked bits, MSB first
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function unpacked = unpackmsb(packed)
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bit = 7; byte = 1;
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for i=1:length(packed)*8
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unpacked(i) = bitand(bitshift(packed(byte), -bit), 1);
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bit--;
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if (bit < 0)
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bit = 7;
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byte++;
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end
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end
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endfunction
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% symbol interleaver that acts on bits 2 at a time
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function y = interleave_bits(interleaver, x)
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y = zeros(1,length(x));
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for i = 1:length(interleaver)
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dst = interleaver(i);
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y(2*(dst-1)+1:2*dst) = x(2*(i-1)+1:2*(i));
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end
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endfunction
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% symbol de-interleaver
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function x = deinterleave_symbols(interleaver, y)
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for i = 1:length(interleaver)
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x(i) = y(interleaver(i));
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end
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endfunction
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