Detailed explanation of 19 dimensional integrated navigation module sinsgps in psins (time synchronization part)

Time synchronization part

Time asynchronous error principle

See chart 7.3.2, In inertia / In the integrated satellite navigation system , The time when the integrated navigation computer obtains the navigation information of the two types of sensors is often not the time when the actual information of the sensors is collected (A and B), There is a certain time lag between sensor information acquisition and integrated navigation calculation ﹐ For example, after the satellite receiver collects the radio signal ﹐ A series of solutions are needed first , Then it is sent to the integrated navigation computer through the communication port . The time lag of inertial and satellite sensors is generally different , The relative lag between the two is recorded as time asynchronous error delta t. When comparing integrated navigation information , The time synchronization error must be estimated or compensated .

When analyzing the time synchronization error , It is assumed that the rod arm error between inertial navigation and satellite navigation has been corrected . Pictured 7.3.2 Shown , The relationship between inertial navigation speed and satellite speed should be

Time out of sync error code

function [kgps, dt] = imugpssyn(k0, k1, ForB)
% SIMU & GPS time synchronization. A schematic diagram for time  
% relationship between SIMU & GPS looks like
%                 k0               k1
%  imu_t:    -----|------*---|-----|--------
%                         <---dt--->     (Forward)
%                 <--dt-->               (Backward)
%  gps_t:    ------------|------------------
%                       kgps
%     where k0,k1 for SIMU data log index and kgps for GPS data log index.
% 
% Prototype: [kgps, dt] = imugpssyn(k0, k1, ForB)
% Usages:
%   For initialization:  imugpssyn(imut, gpst)
%       where imut is SIMU time array, gpst is GPS time array
%   For synchrony checking: [kgps, dt] = imugpssyn(k0, k1, ForB)
%       It checks if there is any GPS sample between SIMU time interval
%       imut(k0) and imut(k1), if exists, return the GPS index 'kgps'
%       and time gap 'dt'. 
%       ForB='F' for forward checking,
%       ForB='B' for backward checking, 
%       ForB='f' for re-setting from the first one,
%       ForB='b' for re-setting from the last one. 
%
% See also  insupdate, kfupdate, POSProcessing, combinedata, combinet, igsplot.

% Copyright(c) 2009-2014, by Gongmin Yan, All rights reserved.
% Northwestern Polytechnical University, Xi An, P.R.China
% 03/02/2014
global igaln
    if nargin==2  % initialization: imugpsaln(imut, gpst)
        igaln.imut = k0; igaln.gpst = k1;
        igaln.glen = length(igaln.gpst);
        igaln.kgps = 1;
        return;
    end
    k0 = k0-1;
    if k0==0, k0 = 1; end
    t0 = igaln.imut(k0); t1 = igaln.imut(k1);
    kgps = 0; dt = 0;
    if ForB=='F'  % Forward search
        while igaln.gpst(igaln.kgps)<t0 
            igaln.kgps = igaln.kgps + 1;
            if igaln.kgps>igaln.glen
                igaln.kgps = igaln.glen;
                break;
            end
        end
        tg = igaln.gpst(igaln.kgps);
        if t0<tg && tg<=t1
            kgps = igaln.kgps; dt = t1 - tg;
        end
    elseif ForB=='B' % Backward search
        while igaln.gpst(igaln.kgps)>t1 
            igaln.kgps = igaln.kgps - 1;
            if igaln.kgps==0
                igaln.kgps = 1;
                break;
            end
        end
        tg = igaln.gpst(igaln.kgps);
        if t0<=tg && tg<t1
            kgps = igaln.kgps; dt = tg - t0;
        end
    elseif ForB=='f'  % Forward re-intialization, set to the first one
        igaln.kgps = 1;
    elseif ForB=='b'  % Backward re-intialization, set to the last one
        igaln.kgps = igaln.glen;
    end

Time out of sync initialization

1.imugpssyn(imu(:,end), gps(:,end)); Initialize the module for parameters with time out of sync , the imu and gps The time of is assigned to the global variable
2. [kgps, dt] = imugpssyn(k, k1, 'F'); This code block in the subsequent code , Is to look for gps The time is imu In the middle of two moments ：
imu Time is t0,t1;gps Time is tg; if t0<tg<t1, be dT=t1-tg;