%                                   pradr.m
%  Scope:   This MATLAB macro computes pseudorange and accumulated delta range for a
%           specified satellite. WGS-84 constants are used.
%  Usage:   [pr,adr] = pradr(upos,uposlla,uelaz,svpos,tsim,step,svid,flags)
%  Description of parameters:
%           upos    - input, user position in ECEF, the components are in meters
%           uposlla - input, user position in geodetic coordinates (latitude/longitude/
%                     altitude above ellipsoid), the components are in radians, radians,
%                     and meters (optional, it is needed when iono correction flag is set)
%           uelaz   - input, elevation and azimuth angles as follows
%                     uelaz(1) - elevation angle, in radians
%                     uelaz(2) - azimuth angle, in radians
%           svpos   - input, ECEF satellite position, the components in meters
%           tsim    - input, simulation time (time of week), in seconds
%           step    - input, step number; the value is used when when one of the following 
%                     are applied: SA, multipath, user clock, pseudorange noise,
%                     ambiguity, delta range noise
%           svid    - input, satellite id
%           flags   - input, flags with the following meaning 
%                     flags(1)  =  0  iono error is not used
%                              !=  0  iono error is used; the coefficients alpha and beta
%                                     should be initialized before calling this module
%                     flags(2)  =  0  tropo error is not used
%                              !=  0  tropo error is used; geoid heights data file (e.g. 
%                                     tgeoid84.dat) should be loaded before calling this 
%                                     module
%                     flags(3)  =  0  SA error is not used
%                              !=  0  SA error is used; SA data file (e.g.  safile.mat)
%                                     should be loaded before calling this module
%                     flags(4)  =  0  multipath is not used
%                              !=  0  multipath is used; multipath data file (e.g. mpfile.
%                                     mat) should be loaded before calling this module
%                     flags(5)  =  0  user clock bias is not used
%                              !=  0  user clock bias is used; user clock bias data file
%                                     (e.g. ucbfile.mat) should be loaded before calling 
%                                     this module 
%                     flags(6)  =  0  earth rotation error is not used
%                              !=  0  earth rotation error is used
%                     flags(7)  =  0  pseudorange noise is not used
%                              !=  0  pseudorange noise is used; prnoise(nrstep,svid) 
%                                     should be generated in the main program 
%                     flags(8)  =  0  carrier phase is not generated
%                              !=  0  carrier phase is generated; ambiguity data file 
%                                     (e.g. ambfile.mat) file should be loaded before 
%                                     calling this module 
%                     flags(9)  =  0  delta range noise is not used
%                              !=  0  delta range noise is used;  adrnoise(nrstep,svid) 
%                                     should be generated in the main program                                
%            pr     - output, pseudorange, in meters
%            adr    - output, accumulated delta range, in meters (optional)
%            Note that some data are transmitted by using global variables, namely alpha 
%            and beta coefficients for iono correction, geoid height data, SA data, 
%            multipath data, user clock bias data, ambiguity constants, pseudorange noise,
%            accumulated delta range noise, and lambda.
%  Remark:  It is assumed that the satellite is visible.
%  External Matlab macros used:  ionoc, tropoc1, uercor, wgs84con
%  Last update:  01/20/01
%  Copyright (C) 1999-01 by LL Consulting. All Rights Reserved.

function    [pr,adr] = pradr(upos,uposlla,uelaz,svpos,tsim,step,svid,flags)

wgs84con;
% global constants used:  rot_rate, c_speed

global  alpha  beta  tgeoid  sa  mpath  ucbias  ambig   prnoise  adrnoise lambda

mpfactor = 0.005*lambda;      %  multipath scaling factor used in adr determination

%  Determine iono error

if  flags(1) ~= 0
   ionoerr = ionoc(uposlla(1),uposlla(2),uelaz(1),uelaz(2),tsim,alpha,beta);
else
   ionoerr = 0.;
end

%  Determine tropo error

if  flags(2) ~= 0
   tropoerr = tropoc1(uposlla(1),uposlla(2),uposlla(3),uelaz(1),tgeoid);
else
   tropoerr = 0.;
end

%  Determine SA error

if  flags(3) ~= 0
   saerr = sa(step,svid);
else
   saerr = 0.;
end

%  Determine multipath error

if  flags(4) ~= 0
   mperr = mpath(step,svid);
else
   mperr = 0.;
end

%  Determine user clock bias 

if  flags(5) ~= 0
   ucberr = ucbias(step,1);    %  data for the first receiver
else
   ucberr = 0.;
end

%  Determine earth rotation correction

if  flags(6) ~= 0
   grange = norm(upos - svpos);
   dt = grange / c_speed;
   ererr = uercor(upos,dt);
else
   ererr = 0.;
end

%  Determine pseudorange noise

if  flags(7) ~= 0
   prnerr = prnoise(step,svid);
else
   prnerr = 0.;
end

%  Determine the adjusted geometric range

grange = norm(upos + ererr - svpos);
pr = grange;      

%  Computation of pseudorange

pr = grange + ionoerr + tropoerr + saerr + mperr + ucberr + prnerr;

%  Computation of accumulated delta range

if  flags(8) ~= 0
   
   adr =  grange - ionoerr + tropoerr + saerr + mpfactor*mperr + ucberr - lambda*ambig(svid);
%   adr =  grange - ionoerr + tropoerr + saerr + mpfactor*mperr + ucberr - ambig(svid);
   if flags(9) ~= 0
       adr = adr + adrnoise(step,svid);
   end   

end