lp_filter.m

包括载波跟踪和伪码相位跟踪

%%低通滤波器
function [signal_I,signal_Q,signal_I_noise,signal_Q_noise]=LP_filter(N,M,code_cycle,fs,Rece_Signal_Quan_down_I,Rece_Signal_Quan_down_Q,Rece_Signal_Quan_down_I_noise,Rece_Signal_Quan_down_Q_noise,EmulateIndex)      %进过低通滤波器

global filter_previous_I;
global filter_previous_Q;
global filter_previous_I_noise;
global filter_previous_Q_noise;

%%下变频后通过低通滤波器
  
    freq_replace=58.08e6;
    wp = code_cycle*2/fs;                  % 归一化数字截止频率
    b = fir1(10,wp);                  % 11个系数，即10阶海明窗FIR通滤波 
    b=round(b*2^8);
%       滤波器系数量化
%       b_bit=8;
%       b_step=1/(2^7);
%       b=round(b/b_step);
if 1==mod(EmulateIndex,M)
    Rece_Signal_Quan_down_I=[0 0 0 0 0 0 0 0 0 0 Rece_Signal_Quan_down_I];
    Rece_Signal_Quan_down_Q=[0 0 0 0 0 0 0 0 0 0 Rece_Signal_Quan_down_Q];
    Rece_Signal_Quan_down_I_noise=[0 0 0 0 0 0 0 0 0 0 Rece_Signal_Quan_down_I_noise];
    Rece_Signal_Quan_down_Q_noise=[0 0 0 0 0 0 0 0 0 0 Rece_Signal_Quan_down_Q_noise];

else
    Rece_Signal_Quan_down_I=[filter_previous_I Rece_Signal_Quan_down_I];
    Rece_Signal_Quan_down_Q=[filter_previous_Q Rece_Signal_Quan_down_Q];
    Rece_Signal_Quan_down_I_noise=[filter_previous_I_noise Rece_Signal_Quan_down_I_noise];
    Rece_Signal_Quan_down_Q_noise=[filter_previous_I_noise Rece_Signal_Quan_down_Q_noise];

end
    signal_I_filter = filter(b,1,Rece_Signal_Quan_down_I);
    signal_Q_filter= filter(b,1,Rece_Signal_Quan_down_Q);
    signal_I_nosie_filter = filter(b,1,Rece_Signal_Quan_down_I_noise);
    signal_Q_nosie_filter = filter(b,1,Rece_Signal_Quan_down_Q_noise);
  
    signal_I_filter=round(signal_I_filter/2^9);
    signal_Q_filter=round(signal_Q_filter/2^9);  
    signal_I_nosie_filter=round(signal_I_nosie_filter/2^9);
    signal_Q_nosie_filter=round(signal_Q_nosie_filter/2^9);

    signal_I=signal_I_filter(11:(N+10));
    signal_Q=signal_Q_filter(11:(N+10));
    signal_I_noise=signal_I_nosie_filter(11:(N+10));
    signal_Q_noise=signal_Q_nosie_filter(11:(N+10));

    filter_previous_I=Rece_Signal_Quan_down_I((N+1):(N+10));
    filter_previous_Q=Rece_Signal_Quan_down_Q((N+1):(N+10));
    filter_previous_I_noise=Rece_Signal_Quan_down_I_noise((N+1):(N+10));
    filter_previous_Q_noise=Rece_Signal_Quan_down_Q_noise((N+1):(N+10));