gnss 并行码捕获-matlab

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已于 2024-05-26 02:06:48 修改

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分类专栏： GNSS 文章标签： GPS L1 GPS捕获 Matlab-GPS捕获代码 BDS B1I 并行码捕获

于 2021-05-10 11:38:31 首次发布

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本文链接：https://blog.youkuaiyun.com/qq_42263796/article/details/116590979

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1 GPS捕获原理

首先是正交混频，剥离载波，CA码不做介绍（参考谢钢那本GPS原理和接收机设计）。将CA码重采样，对于GPS L1CA，考虑计算量，采用2倍采样率，即2.046MHz。利用matlab的xcorr做1ms并行相关，N次相干积分，M次非相干积分，寻找大于阈值的非相干结果的峰值，即可实现捕获。

2 Matlab代码

gnss_main.m

%%
clear
close all

%% gps L1 bds B1I prn and doppler
% 4 7 8 9 16 21 26 27
% -2272 3143 777 -385 -1963 3126 -2332 -1556
% 1 2 3 4 5 6 7 9 10 16 27 30
% 10 -4 24 25 4 -1021 -138 -446 -60 -1019 -1255 1757

%% datapath and read data
ifdata_path     = 'IFData\\';
codepath        = 'OutCACodeResult\\';
pathname        = 'ifdata_2bit_20ms.txt';
dataformat      = 2; %% 1: txt IQ, with header, 2: txt no header
system_type     = 1; %% 0: GPS L1CA 1: BDS: B1I

%% read raw ifdata
switch dataformat
    case 1
        filename        = [ifdata_path,pathname];
        readdata        = importdata(filename);
        gnss_ifdata     = readdata.data;
    case 2
        filename        = [ifdata_path,pathname];
        readdata        = importdata(filename);
        gnss_ifdata     = readdata;
end

%% read code data
switch system_type
        case 0
            filename1   = 'GPSCACode.txt';
            f1          = [codepath,filename1];
            gnss_code   = importdata(f1); 
        case 1
            filename1   = 'BDSCACode.txt';
            f1          = [codepath,filename1];
            gnss_code   = importdata(f1); 
        case 2
            disp("error system!!!")
        case 3
            disp("error system!!!")
        otherwise
            disp("error system!!!")
end
%% gnss config init
gnss_config     = set_gnss_config(system_type);
%% acq
tic
acq_result      = gnss_acq(gnss_config.acq_config, gnss_ifdata, gnss_code);
toc

if acq_result.acq_status == 1
    %% show result
    dop_list            = gnss_config.acq_config.acq_fre_min : gnss_config.acq_config.acq_fre_step : gnss_config.acq_config.acq_fre_max;
    code_phase_step     = gnss_config.acq_config.code_phase_step;
    system_name         = gnss_config.acq_config.system_name;
    x                   = acq_result.acq_check_list{
   1,1}.x * code_phase_step;
    acq_noncoh_result   = acq_result.acq_check_list{
   1,1}.temp_noncoh_result;
    PRN                 = acq_result.acq_check_list{
   1,1}.prn;
    
    %% 2D plot
    figure(1)
    plot(x, acq_noncoh_result(:, acq_result.acq_check_list{
   1, 1}.acq_check_result.dop_cnt))
    xlabel('Codephase/chip')
    ylabel('Amplitude')
    titlename = [system_name, ' PRN-', num2str(PRN),' ','Result'];
    title(titlename)
    grid on
    
    % 3D plot, note: gnss_acq not save result, please config
    if 1
        h = figure(2);
        mesh(dop_list, x, acq_noncoh_result)
        titlename = [system_name, ' PRN-', num2str(PRN),' '