mirror of https://github.com/PentHertz/srsLTE.git
82 lines
2.7 KiB
Matlab
82 lines
2.7 KiB
Matlab
function [coarse_start freq_offset] = find_coarse_time_and_freq_offset(in, N_cp_l_else)
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% Decompose input
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in_re = real(in);
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in_im = imag(in);
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abs_corr = zeros(1,960);
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for(slot=0:10)
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for(n=1:40:960)
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corr_re = 0;
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corr_im = 0;
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for(z=1:N_cp_l_else)
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index = (slot*960) + n-1 + z;
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corr_re = corr_re + in_re(index)*in_re(index+128) + in_im(index)*in_im(index+128);
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corr_im = corr_im + in_re(index)*in_im(index+128) - in_im(index)*in_re(index+128);
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end
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abs_corr(n) = abs_corr(n) + corr_re*corr_re + corr_im*corr_im;
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end
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end
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% Find first and second max
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abs_corr_idx = zeros(1,2);
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for(m=0:1)
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abs_corr_max = 0;
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for(n=1:480)
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if(abs_corr((m*480)+n) > abs_corr_max)
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abs_corr_max = abs_corr((m*480)+n);
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abs_corr_idx(m+1) = (m*480)+n;
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end
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end
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end
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% Fine correlation and fraction frequency offset
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abs_corr = zeros(1,960);
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corr_freq_err = zeros(1,960);
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for(slot=1:10)
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for(idx=1:2)
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if((abs_corr_idx(idx) - 40) < 1)
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abs_corr_idx(idx) = 41;
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end
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if((abs_corr_idx(idx) + 40) > 960)
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abs_corr_idx(idx) = 960 - 40;
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end
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for(n=abs_corr_idx(idx)-40:abs_corr_idx(idx)+40)
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corr_re = 0;
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corr_im = 0;
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for(z=1:N_cp_l_else)
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index = (slot*960) + n-1 + z;
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corr_re = corr_re + in_re(index)*in_re(index+128) + in_im(index)*in_im(index+128);
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corr_im = corr_im + in_re(index)*in_im(index+128) - in_im(index)*in_re(index+128);
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end
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abs_corr(n) = abs_corr(n) + corr_re*corr_re + corr_im*corr_im;
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corr_freq_err(n) = corr_freq_err(n) + atan2(corr_im, corr_re)/(128*2*pi*(0.0005/960));
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end
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end
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end
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% Find first and second max
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abs_corr_idx = zeros(1,2);
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for(m=0:1)
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abs_corr_max = 0;
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for(n=1:480)
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if(abs_corr((m*480)+n) > abs_corr_max)
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abs_corr_max = abs_corr((m*480)+n);
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abs_corr_idx(m+1) = (m*480)+n;
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end
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end
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end
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% Determine frequency offset FIXME No integer offset is calculated here
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freq_offset = (corr_freq_err(abs_corr_idx(1))/10 + corr_freq_err(abs_corr_idx(2))/10)/2;23
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% Determine the symbol start locations from the correlation peaks
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% FIXME Needs some work
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tmp = abs_corr_idx(1);
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while(tmp > 0)
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tmp = tmp - 2192;
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end
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for(n=1:7)
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coarse_start(n) = tmp + (n*2192);
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end
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end |