coarse_sync_block.m

一个UWB仿真程序包

function [coarse_sync_index, corr_overlap] = coarse_sync_block(rx_down,corr_overlap,corr_template,thld,...
                                     blocks_per_code_symbol,N,PLOT_DEBUG)

% %generate sequence to correlate with
% blocks_per_code_symbol = L * TC / (T_INT * N_INT );
% corr_template = reshape( ... 
%   repmat(abs(len31_preamble_code(CODE_ID)),blocks_per_code_symbol, 1), ...
%   1,31*blocks_per_code_symbol);
% 
% %repeat correlation template G times
% corr_template = repmat(corr_template,1,G);
corr_tmpl_len = length(corr_template);

%do the correlation
corr = conv(rx_down, fliplr(corr_template));

%cut out the piece that is usable
corr = corr(corr_tmpl_len:end-corr_tmpl_len+1);

%pad the overlap from the last run
corr = [corr_overlap corr];
overlap_len = length(corr_overlap);

%store the overlap for the next run
%determine start of overlap
blcl = blocks_per_code_symbol * 31;
corr_len = length(corr);
overlap_start = max(1,(floor(corr_len/blcl)-(N-1))*blcl+1);
corr_overlap = corr(overlap_start:end);

%coarse synchronization

% %analytical calculation of thld and noise floor, in a real system the noise
% %comes from our components, so we know the noise_var and can thus always compute
% %these thresholds
% noise_floor = noise_var * T_INT * 2 * RX_BW * N_INT * G * ...
%   blocks_per_code_symbol * 16; %16 is due to the fact that out of the 31 code
% %symbols 16 are non-zero
% thld = noise_var * chi2inv(THLD_PROBA, (T_INT * 2* RX_BW) * N_INT * G * ...
%   blocks_per_code_symbol * 16);

%downsample correlation for coarse sync
corr_sampled = downsample(corr,blocks_per_code_symbol);
%pad the end with zeros so that we can do the reshape
if(~isempty(corr_sampled))
    corr_sampled = zero_pad_reshape(corr_sampled,31);
    corr_sampled_mat = reshape(corr_sampled,31,length(corr_sampled)/31);
    %check against threshold, set values lower than thld to zero
    corr_sampled_mat(corr_sampled_mat < thld) = 0;
    [m max_slots] = max(corr_sampled_mat);
    clear corr_sampled_mat; %free memory

    %find N consecutive identical values (and make sure they don't correspond to a
    %slot that was below the thld i.e. that are zero)
    test_slot_no = -1; %this is to remember which of the 31 slots created the last max
    no_consecutive = 0; %how many consecutive maxes do we have for this slot
    corr_sampled_coarse_sync_index = 0;%index into corr_sampled of the sync point
    for i=1:length(max_slots)
        current_slot_no = max_slots(i);
        if(m(i)~= 0) %is not zero
            if(test_slot_no == current_slot_no)
                no_consecutive = no_consecutive + 1;
            else
                test_slot_no = current_slot_no;
                no_consecutive = 1;
            end
            if(no_consecutive == N)
                corr_sampled_coarse_sync_index = (i-1)*31 + test_slot_no;
                break;
            end
        else
            test_slot_no = -1;
            no_consecutive = 0;
        end
    end
    %coarse sync index is now 0 if not successful, otherwise equals number of
    %128ns block of starting point in corr_sampled
    %corr_sampled_coarse_sync_index
else
    corr_sampled_coarse_sync_index = 0;
end
if(corr_sampled_coarse_sync_index ~= 0)
    %find the corresponding index into corr (the one not sampled)
    corr_coarse_sync_index = ...
        (corr_sampled_coarse_sync_index-1)*blocks_per_code_symbol+1;
    
    %find the corresponding index into the received signal
    coarse_sync_index = corr_coarse_sync_index-overlap_len;% - (length(corr_template)-1);
    
    if(PLOT_DEBUG)
        figure
        plot(corr_sampled)
        hold on
        %plot(noise_floor*ones(1,length(corr)),'r')
        plot(thld*ones(1,length(corr_sampled)),'m')
        line([corr_sampled_coarse_sync_index corr_sampled_coarse_sync_index],[0 max(corr_sampled)],'Color','y')
        
        figure
        plot(corr)
        hold on
        %plot(noise_floor*ones(1,length(corr)),'r')
        plot(thld*ones(1,length(corr)),'m')
        line([corr_coarse_sync_index corr_coarse_sync_index],[0 max(corr)],'Color','y')
    end
    
else
    coarse_sync_index = 0;
end
    
return;