coarse_sync.m

一个UWB仿真程序包

function [coarse_sync_index] = coarse_sync(rx_down,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);

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

%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
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

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 - (length(corr_template)-1);
    
    if(PLOT_DEBUG)
        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;