timetr.m

GPS software toolbox for GPS receiver development

%                             timetr.m
%  Scope:   This MATLAB macro computes GPS time of transmission from time of
%           measurement (reception) for a satellite pseudorange measurement; 
%           WGS-84 constants are used.
%  Usage:   xoutput = timetr(tmeas,toc,af,pr)
%  Description of parameters:
%           tmeas    - input, time of measurement (reception), in seconds
%           toc      - input, reference time of clock (from ephemeris data), in
%                      seconds
%           af       - input, array containing ephemeris satellite clock
%                      parameters af0 --> af(1), af1 --> af(2) and af2 --> af(3) 
%           pr       - input, satellite pseudorange, in meters
%           xoutput  - output, time of transmission, in seconds
%  Remark:  The relativistic correction term given by
%                    delta_tr = F * e * sqrt(a) * sin(Ek)
%           where   
%                 F = -4.442807633*10^(-10) sec/(meters)^0.5   in WGS-84 
%                 e  is the satellite eccentricity
%                 a  is the satellite semi-major axis
%                 Ek is ecentric anomaly (time dependent)
%           can be added to delta_ts to improved the computational accuracy.
%  External Matlab macros used:  wgs84con
%  Last update:  04/16/00
%  Copyright (C) 2000 by LL Consulting. All Rights Reserved.

function   xoutput = timetr(tmeas,toc,af,pr)

wgs84con;
% global constants used: c_speed

%  Compute the predicted satellite clock error at time of measurement 
%  (reception)

temp = tmeas - toc;
delta_ts = af(1) + (af(2) + af(3)*temp)*temp; 

%  Compute the time of transmission

xoutput = tmeas - pr/c - delta_ts;