#define _CRT_SECURE_NO_DEPRECATE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#include <omp.h>
#ifdef _WIN32
#include "getopt.h"
#else
#include <unistd.h>
#endif

#ifndef bool
typedef int bool;
#define true 1
#define false 0
#endif

/*! \brief Maximum length of a line in a text file (RINEX, motion) */
#define MAX_CHAR (100)

/*! \brief Maximum number of satellites in RINEX file */
#define MAX_SAT (32)
/*! \brief Maximum number of channels we simulate */
#define MAX_CHAN (16)

/*! \brief Maximum number of user motion waypoints */
#define USER_MOTION_SIZE (3000) // max 300 sec at 10Hz

/*! \brief Number of subframes */
#define N_SBF (51) // 6 seconds per subframe, 6 sec * 51 = 306 sec (max)

/*! \brief Number of words per subframe */
#define N_DWRD_SBF (10) // 10 word per subframe

/*! \brief Number of words */
#define N_DWRD (N_SBF*N_DWRD_SBF) // 10 word per subframe

/*! \brief C/A code sequence length */
#define CA_SEQ_LEN (1023)

#define SECONDS_IN_WEEK 604800.0
#define SECONDS_IN_HALF_WEEK 302400.0
#define SECONDS_IN_DAY 86400.0
#define SECONDS_IN_HOUR 3600.0
#define SECONDS_IN_MINUTE 60.0

#define POW2_M5  0.03125
#define POW2_M19 1.907348632812500e-6
#define POW2_M29 1.862645149230957e-9
#define POW2_M31 4.656612873077393e-10
#define POW2_M33 1.164153218269348e-10
#define POW2_M43 1.136868377216160e-13
#define POW2_M55 2.775557561562891e-17

// Conventional values employed in GPS ephemeris model (ICD-GPS-200)
#define GM_EARTH 3.986005e14
#define OMEGA_EARTH 7.2921151467e-5
#define PI 3.1415926535898

#define WGS84_RADIUS	6378137.0
#define WGS84_ECCENTRICITY 0.0818191908426

#define R2D 57.2957795131

#define SPEED_OF_LIGHT 2.99792458e8
#define LAMBDA_L1 0.190293672798365

/*! \brief GPS L1 Carrier frequency */
#define CARR_FREQ (1575.42e6)
/*! \brief C/A code frequency */
#define CODE_FREQ (1.023e6)
#define CARR_TO_CODE (1.0/1540.0)

// Sampling data format
#define SC08 (8)
#define SC16 (16)

int sinTable512[] = {
	   2,   5,   8,  11,  14,  17,  20,  23,  26,  29,  32,  35,  38,  41,  44,  47,
	  50,  53,  56,  59,  62,  65,  68,  71,  74,  77,  80,  83,  86,  89,  91,  94,
	  97, 100, 103, 105, 108, 111, 114, 116, 119, 122, 125, 127, 130, 132, 135, 138,
	 140, 143, 145, 148, 150, 153, 155, 157, 160, 162, 164, 167, 169, 171, 173, 176,
	 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, 205, 207,
	 209, 210, 212, 214, 215, 217, 218, 220, 221, 223, 224, 225, 227, 228, 229, 230,
	 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 241, 242, 243, 244, 244, 245,
	 245, 246, 247, 247, 248, 248, 248, 249, 249, 249, 249, 250, 250, 250, 250, 250,
	 250, 250, 250, 250, 250, 249, 249, 249, 249, 248, 248, 248, 247, 247, 246, 245,
	 245, 244, 244, 243, 242, 241, 241, 240, 239, 238, 237, 236, 235, 234, 233, 232,
	 230, 229, 228, 227, 225, 224, 223, 221, 220, 218, 217, 215, 214, 212, 210, 209,
	 207, 205, 204, 202, 200, 198, 196, 194, 192, 190, 188, 186, 184, 182, 180, 178,
	 176, 173, 171, 169, 167, 164, 162, 160, 157, 155, 153, 150, 148, 145, 143, 140,
	 138, 135, 132, 130, 127, 125, 122, 119, 116, 114, 111, 108, 105, 103, 100,  97,
	  94,  91,  89,  86,  83,  80,  77,  74,  71,  68,  65,  62,  59,  56,  53,  50,
	  47,  44,  41,  38,  35,  32,  29,  26,  23,  20,  17,  14,  11,   8,   5,   2,
	  -2,  -5,  -8, -11, -14, -17, -20, -23, -26, -29, -32, -35, -38, -41, -44, -47,
	 -50, -53, -56, -59, -62, -65, -68, -71, -74, -77, -80, -83, -86, -89, -91, -94,
	 -97,-100,-103,-105,-108,-111,-114,-116,-119,-122,-125,-127,-130,-132,-135,-138,
	-140,-143,-145,-148,-150,-153,-155,-157,-160,-162,-164,-167,-169,-171,-173,-176,
	-178,-180,-182,-184,-186,-188,-190,-192,-194,-196,-198,-200,-202,-204,-205,-207,
	-209,-210,-212,-214,-215,-217,-218,-220,-221,-223,-224,-225,-227,-228,-229,-230,
	-232,-233,-234,-235,-236,-237,-238,-239,-240,-241,-241,-242,-243,-244,-244,-245,
	-245,-246,-247,-247,-248,-248,-248,-249,-249,-249,-249,-250,-250,-250,-250,-250,
	-250,-250,-250,-250,-250,-249,-249,-249,-249,-248,-248,-248,-247,-247,-246,-245,
	-245,-244,-244,-243,-242,-241,-241,-240,-239,-238,-237,-236,-235,-234,-233,-232,
	-230,-229,-228,-227,-225,-224,-223,-221,-220,-218,-217,-215,-214,-212,-210,-209,
	-207,-205,-204,-202,-200,-198,-196,-194,-192,-190,-188,-186,-184,-182,-180,-178,
	-176,-173,-171,-169,-167,-164,-162,-160,-157,-155,-153,-150,-148,-145,-143,-140,
	-138,-135,-132,-130,-127,-125,-122,-119,-116,-114,-111,-108,-105,-103,-100, -97,
	 -94, -91, -89, -86, -83, -80, -77, -74, -71, -68, -65, -62, -59, -56, -53, -50,
	 -47, -44, -41, -38, -35, -32, -29, -26, -23, -20, -17, -14, -11,  -8,  -5,  -2
};

int cosTable512[] = {
	 250, 250, 250, 250, 250, 249, 249, 249, 249, 248, 248, 248, 247, 247, 246, 245,
	 245, 244, 244, 243, 242, 241, 241, 240, 239, 238, 237, 236, 235, 234, 233, 232,
	 230, 229, 228, 227, 225, 224, 223, 221, 220, 218, 217, 215, 214, 212, 210, 209,
	 207, 205, 204, 202, 200, 198, 196, 194, 192, 190, 188, 186, 184, 182, 180, 178,
	 176, 173, 171, 169, 167, 164, 162, 160, 157, 155, 153, 150, 148, 145, 143, 140,
	 138, 135, 132, 130, 127, 125, 122, 119, 116, 114, 111, 108, 105, 103, 100,  97,
	  94,  91,  89,  86,  83,  80,  77,  74,  71,  68,  65,  62,  59,  56,  53,  50,
	  47,  44,  41,  38,  35,  32,  29,  26,  23,  20,  17,  14,  11,   8,   5,   2,
	  -2,  -5,  -8, -11, -14, -17, -20, -23, -26, -29, -32, -35, -38, -41, -44, -47,
	 -50, -53, -56, -59, -62, -65, -68, -71, -74, -77, -80, -83, -86, -89, -91, -94,
	 -97,-100,-103,-105,-108,-111,-114,-116,-119,-122,-125,-127,-130,-132,-135,-138,
	-140,-143,-145,-148,-150,-153,-155,-157,-160,-162,-164,-167,-169,-171,-173,-176,
	-178,-180,-182,-184,-186,-188,-190,-192,-194,-196,-198,-200,-202,-204,-205,-207,
	-209,-210,-212,-214,-215,-217,-218,-220,-221,-223,-224,-225,-227,-228,-229,-230,
	-232,-233,-234,-235,-236,-237,-238,-239,-240,-241,-241,-242,-243,-244,-244,-245,
	-245,-246,-247,-247,-248,-248,-248,-249,-249,-249,-249,-250,-250,-250,-250,-250,
	-250,-250,-250,-250,-250,-249,-249,-249,-249,-248,-248,-248,-247,-247,-246,-245,
	-245,-244,-244,-243,-242,-241,-241,-240,-239,-238,-237,-236,-235,-234,-233,-232,
	-230,-229,-228,-227,-225,-224,-223,-221,-220,-218,-217,-215,-214,-212,-210,-209,
	-207,-205,-204,-202,-200,-198,-196,-194,-192,-190,-188,-186,-184,-182,-180,-178,
	-176,-173,-171,-169,-167,-164,-162,-160,-157,-155,-153,-150,-148,-145,-143,-140,
	-138,-135,-132,-130,-127,-125,-122,-119,-116,-114,-111,-108,-105,-103,-100, -97,
	 -94, -91, -89, -86, -83, -80, -77, -74, -71, -68, -65, -62, -59, -56, -53, -50,
	 -47, -44, -41, -38, -35, -32, -29, -26, -23, -20, -17, -14, -11,  -8,  -5,  -2,
	   2,   5,   8,  11,  14,  17,  20,  23,  26,  29,  32,  35,  38,  41,  44,  47,
	  50,  53,  56,  59,  62,  65,  68,  71,  74,  77,  80,  83,  86,  89,  91,  94,
	  97, 100, 103, 105, 108, 111, 114, 116, 119, 122, 125, 127, 130, 132, 135, 138,
	 140, 143, 145, 148, 150, 153, 155, 157, 160, 162, 164, 167, 169, 171, 173, 176,
	 178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202, 204, 205, 207,
	 209, 210, 212, 214, 215, 217, 218, 220, 221, 223, 224, 225, 227, 228, 229, 230,
	 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 241, 242, 243, 244, 244, 245,
	 245, 246, 247, 247, 248, 248, 248, 249, 249, 249, 249, 250, 250, 250, 250, 250
};

/*! \file gpssim.c
 *  \brief GPS Satellite Simulator
 */

/*! \brief Structure representing GPS time */
typedef struct
{
	int week;	/*!< GPS week number (since January 1980) */
	double sec; 	/*!< second inside the GPS \a week */
} gpstime_t;

/*! \brief Structure repreenting UTC time */
typedef struct
{
	int y; 		/*!< Calendar year */
	int m;		/*!< Calendar month */
	int d;		/*!< Calendar day */
	int hh;		/*!< Calendar hour */
	int mm;		/*!< Calendar minutes */
	double sec;	/*!< Calendar seconds */
} datetime_t;

/*! \brief Structure representing ephemeris of a single satellite */
typedef struct
{
	int vflg;	/*!< Valid Flag */
	gpstime_t toc;	/*!< Time of Clock */
	gpstime_t toe;	/*!< Time of Ephemeris */
	int iodc;	/*!< Issue of Data, Clock */
	int iode;	/*!< Isuse of Data, Ephemeris */
	double deltan;	/*!< Delta-N (radians/sec) */
	double cuc;	/*!< Cuc (radians) */
	double cus;	/*!< Cus (radians) */
	double cic;	/*!< Correction to inclination cos (radians) */
	double cis;	/*!< Correction to inclination sin (radians) */
	double crc;	/*!< Correction to radius cos (meters) */
	double crs;	/*!< Correction to radius sin (meters) */
	double ecc;	/*!< e Eccentricity */
	double sqrta;	/*!< sqrt(A) (sqrt(m)) */
	double m0;	/*!< Mean anamoly (radians) */
	double omg0;	/*!< Longitude of the ascending node (radians) */
	double inc0;	/*!< Inclination (radians) */
	double aop;
	double omgdot;	/*!< Omega dot (radians/s) */
	double idot;	/*!< IDOT (radians/s) */
	double af0;	/*!< Clock offset (seconds) */
	double af1;	/*!< rate (sec/sec) */
	double af2;	/*!< acceleration (sec/sec^2) */
	double tgd;	/*!< Group delay L2 bias */

	// Working variables follow
	double n; 	/*!< Mean motion (Average angular velocity) */
	double sq1e2;	/*!< sqrt(1-e^2) */
	double A;	/*!< Semi-major axis */
	double omgkdot; /*!< OmegaDot-OmegaEdot */
} ephem_t;

typedef struct
{
	gpstime_t g;
	double range;
	double rate;
	double d;
} range_t;

/*! \brief Structure representing a Channel */
typedef struct
{
	int prn;	/*< PRN Number */
	int ca[CA_SEQ_LEN]; /*< C/A Sequence */
	double f_carr;	/*< Carrier frequency */
	double f_code;	/*< Code frequency */
	unsigned int carr_phase; /*< Carrier phase */
	int carr_phasestep;	/*< Carrier phasestep */
	double code_phase; /*< Code phase */
	gpstime_t g0;	/*!< GPS time at start */
	unsigned long dwrd[N_DWRD]; /*!< Data words of sub-frame */
	int iword;	/*!< initial word */
	int ibit;	/*!< initial bit */
	int icode;	/*!< initial code */
	int dataBit;	/*!< current data bit */
	int codeCA;	/*!< current C/A code */
} channel_t;

/* !\brief generate the C/A code sequence for a given Satellite Vehicle PRN
 *  \param[in] prn PRN nuber of the Satellite Vehicle
 *  \param[out] ca Caller-allocated integer array of 1023 bytes
 */
void codegen(int *ca, int prn)
{
	int delay[] = {
		  5,   6,   7,   8,  17,  18, 139, 140, 141, 251,
		252, 254, 255, 256, 257, 258, 469, 470, 471, 472,
		473, 474, 509, 512, 513, 514, 515, 516, 859, 860,
		861, 862};
	
	int g1[CA_SEQ_LEN], g2[CA_SEQ_LEN];
	int r1[N_DWRD_SBF], r2[N_DWRD_SBF];
	int c1, c2;
	int i,j;

	if (prn<1 || prn>32)
		return;

	for (i=0; i<N_DWRD_SBF; i++)
		r1[i] = r2[i] = -1;

	for (i=0; i<CA_SEQ_LEN; i++)
	{
		g1[i] = r1[9];
		g2[i] = r2[9];
		c1 = r1[2]*r1[9];
		c2 = r2[1]*r2[2]*r2[5]*r2[7]*r2[8]*r2[9];

		for (j=9; j>0; j--) 
		{
			r1[j] = r1[j-1];
			r2[j] = r2[j-1];
		}
		r1[0] = c1;
		r2[0] = c2;
	}

	for (i=0,j=CA_SEQ_LEN-delay[prn-1]; i<CA_SEQ_LEN; i++,j++)
		ca[i] = (1-g1[i]*g2[j%CA_SEQ_LEN])/2;
	
	return;
}

/*! \brief Convert a UTC date into a GPS date
 *  \param[in] t input date in UTC form
 *  \param[out] g output date in GPS form
 */
void date2gps(const datetime_t *t, gpstime_t *g)
{
	int doy[12] = {0,31,59,90,120,151,181,212,243,273,304,334};
	int ye;
	int de;
	int lpdays;

	ye = t->y - 1980;

	// Compute the number of leap days since Jan 5/Jan 6, 1980.
	lpdays = ye/4 + 1;
	if ((ye%4)==0 && t->m<=2)
		lpdays--;

	// Compute the number of days elapsed since Jan 5/Jan 6, 1980.
	de = ye*365 + doy[t->m-1] + t->d + lpdays - 6;

	// Convert time to GPS weeks and seconds.
	g->week = de / 7;
	g->sec = (double)(de%7)*SECONDS_IN_DAY + t->hh*SECONDS_IN_HOUR 
		+ t->mm*SECONDS_IN_MINUTE + t->sec;

	return;
}

/*! \brief Convert Earth-centered Earth-fixed (ECEF) into Lat/Long/Heighth
 *  \param[in] xyz Input Array of X, Y and Z ECEF coordinates
 *  \param[out] llh Output Array of Latitude, Longitude and Height
 */
void xyz2llh(const double *xyz, double *llh)
{
	double a,eps,e,e2;
	double x,y,z;
	double rho2,dz,zdz,nh,slat,n,dz_new;

	a = WGS84_RADIUS;
	e = WGS84_ECCENTRICITY;

	eps = 1.0e-3;
	e2 = e*e;

	x = xyz[0];
	y = xyz[1];
	z = xyz[2];

	rho2 = x*x + y*y;
	dz = e2*z;

	while (1)
	{
		zdz = z + dz;
		nh = sqrt(rho2 + zdz*zdz);
		slat = zdz / nh;
		n = a / sqrt(1.0-e2*slat*slat);
		dz_new = n*e2*slat;

		if (fabs(dz-dz_new) < eps)
			break;

		dz = dz_new;
	}

	llh[0] = atan2(zdz, sqrt(rho2));
	llh[1] = atan2(y, x);
	llh[2] = nh - n;

	return;
}

/*! \brief Convert Lat/Long/Height into Earth-centered Earth-fixed (ECEF)
 *  \param[in] llh Input Array of Latitude, Longitude and Height
 *  \param[out] xyz Output Array of X, Y and Z ECEF coordinates
 */
void llh2xyz(const double *llh, double *xyz)
{
	double n;
	double a;
	double e;
	double e2;
	double clat;
	double slat;
	double clon;
	double slon;
	double d,nph;
	double tmp;

	a = WGS84_RADIUS;
	e = WGS84_ECCENTRICITY;
	e2 = e*e;

	clat = cos(llh[0]);
	slat = sin(llh[0]);
	clon = cos(llh[1]);
	slon = sin(llh[1]);
	d = e*slat;

	n = a/sqrt(1.0-d*d);
	nph = n + llh[2];

	tmp = nph*clat;
	xyz[0] = tmp*clon;
	xyz[1] = tmp*slon;
	xyz[2] = ((1.0-e2)*n + llh[2])*slat;

	return;
}

/*! \brief Compute the intermediate matrix for LLH to ECEF
 *  \param[in] llh Input position in Latitude-Longitude-Height format
 *  \param[out] t Three-by-Three output matrix
 */
void ltcmat(const double *llh, double t[3][3])
{
	double slat, clat;
	double slon, clon;

	slat = sin(llh[0]);
	clat = cos(llh[0]);
	slon = sin(llh[1]);
	clon = cos(llh[1]);

	t[0][0] = -slat*clon;
	t[0][1] = -slat*slon;
	t[0][2] = clat;
	t[1][0] = -slon;
	t[1][1] = clon;
	t[1][2] = 0.0;
	t[2][0] = clat*clon;
	t[2][1] = clat*slon;
	t[2][2] = slat;

	return;
}

/*! \brief Convert Earth-centered Earth-Fixed to ?
 *  \param[in] xyz Input position as vector in ECEF format
 *  \param[in] t Intermediate matrix computed by \ref ltcmat
 *  \param[out] neu Output position as North-East-Up format
 */
void ecef2neu(const double *xyz, double t[3][3], double *neu)
{
	neu[0] = t[0][0]*xyz[0] + t[0][1]*xyz[1] + t[0][2]*xyz[2];
	neu[1] = t[1][0]*xyz[0] + t[1][1]*xyz[1] + t[1][2]*xyz[2];
	neu[2] = t[2][0]*xyz[0] + t[2][1]*xyz[1] + t[2][2]*xyz[2];

	return;
}

/*! \brief Convert North-Eeast-Up to Azimuth + Elevation
 *  \param[in] neu Input position in North-East-Up format
 *  \param[out] azel Output array of azimuth + elevation as double
 */
void neu2azel(double *azel, const double *neu)
{
	double ne;

	azel[0] = atan2(neu[1],neu[0]);
	if (azel[0]<0.0)
		azel[0] += (2.0*PI);

	ne = sqrt(neu[0]*neu[0] + neu[1]*neu[1]);
	azel[1] = atan2(neu[2], ne);

	return;
}

/*! \brief Compute Satellite position, velocity and clock at given time
 *  \param[in] eph Ephemeris data of the satellite
 *  \param[in] g GPS time at which position is to be computed
 *  \param[out] pos Computed position (vector)
 *  \param[out] vel Computed velociy (vector)
 *  \param[clk] clk Computed clock
 */
void satpos(ephem_t eph, gpstime_t g, double *pos, double *vel, double *clk)
{
	// Computing Satellite Velocity using the Broadcast Ephemeris
	// http://www.ngs.noaa.gov/gps-toolbox/bc_velo.htm

	double tk;
	double mk;
	double ek;
	double ekold;
	double ekdot;
	double cek,sek;
	double pk;
	double pkdot;
	double c2pk,s2pk;
	double uk;
	double ukdot;
	double cuk,suk;
	double ok;
	double sok,cok;
	double ik;
	double ikdot;
	double sik,cik;
	double rk;
	double rkdot;
	double xpk,ypk;
	double xpkdot,ypkdot;

	double relativistic, OneMinusecosE, tmp;

	tk = g.sec - eph.toe.sec;

	if(tk>SECONDS_IN_HALF_WEEK)
		tk -= SECONDS_IN_WEEK;
	else if(tk<-SECONDS_IN_HALF_WEEK)
		tk += SECONDS_IN_WEEK;

	mk = eph.m0 + eph.n*tk;
	ek = mk;
	ekold = ek + 1.0;
  
	OneMinusecosE = 0; // Suppress the uninitialized warning.
	while(fabs(ek-ekold)>1.0E-14)
	{
		ekold = ek;
		OneMinusecosE = 1.0-eph.ecc*cos(ekold);
		ek = ek + (mk-ekold+eph.ecc*sin(ekold))/OneMinusecosE;
	}

	sek = sin(ek);
	cek = cos(ek);

	ekdot = eph.n/OneMinusecosE;

	relativistic = -4.442807633E-10*eph.ecc*eph.sqrta*sek;

	pk = atan2(eph.sq1e2*sek,cek-eph.ecc) + eph.aop;
	pkdot = eph.sq1e2*ekdot/OneMinusecosE;

	s2pk = sin(2.0*pk);
	c2pk = cos(2.0*pk);

	uk = pk + eph.cus*s2pk + eph.cuc*c2pk;
	suk = sin(uk);
	cuk = cos(uk);
	ukdot = pkdot*(1.0 + 2.0*(eph.cus*c2pk - eph.cuc*s2pk));

	rk = eph.A*OneMinusecosE + eph.crc*c2pk + eph.crs*s2pk;
	rkdot = eph.A*eph.ecc*sek*ekdot + 2.0*pkdot*(eph.crs*c2pk - eph.crc*s2pk);

	ik = eph.inc0 + eph.idot*tk + eph.cic*c2pk + eph.cis*s2pk;
	sik = sin(ik);
	cik = cos(ik);
	ikdot = eph.idot + 2.0*pkdot*(eph.cis*c2pk - eph.cic*s2pk);

	xpk = rk*cuk;
	ypk = rk*suk;
	xpkdot = rkdot*cuk - ypk*ukdot;
	ypkdot = rkdot*suk + xpk*ukdot;

	ok = eph.omg0 + tk*eph.omgkdot - OMEGA_EARTH*eph.toe.sec;
	sok = sin(ok);
	cok = cos(ok);

	pos[0] = xpk*cok - ypk*cik*sok;
	pos[1] = xpk*sok + ypk*cik*cok;
	pos[2] = ypk*sik;

	tmp = ypkdot*cik - ypk*sik*ikdot;

	vel[0] = -eph.omgkdot*pos[1] + xpkdot*cok - tmp*sok;
	vel[1] = eph.omgkdot*pos[0] + xpkdot*sok + tmp*cok;
	vel[2] = ypk*cik*ikdot + ypkdot*sik;

	// Satellite clock correction
	tk = g.sec - eph.toc.sec;

	if(tk>SECONDS_IN_HALF_WEEK)
		tk -= SECONDS_IN_WEEK;
	else if(tk<-SECONDS_IN_HALF_WEEK)
		tk += SECONDS_IN_WEEK;

	clk[0] = eph.af0 + tk*(eph.af1 + tk*eph.af2) + relativistic - eph.tgd;  
	clk[1] = eph.af1 + 2.0*tk*eph.af2; 

	return;
}

/*! \brief Compute Subframe from Ephemeris
 *  \param[in] eph Ephemeris of given SV
 *  \param[out] sbf Array of five sub-frames, 10 long words each
 */
void eph2sbf(const ephem_t eph, unsigned long sbf[5][N_DWRD_SBF])
{
	unsigned long wn;
	unsigned long toe;
	unsigned long toc;
	unsigned long iode;
	unsigned long iodc;
	long deltan;
	long cuc;
	long cus;
	long cic;
	long cis;
	long crc;
	long crs;
	unsigned long ecc;
	unsigned long sqrta;
	long m0;
	long omg0;
	long inc0;
	long aop;
	long omgdot;
	long idot;
	long af0;
	long af1;
	long af2;
	long tgd;

	unsigned long ura = 2UL;
	unsigned long dataId = 1UL;
	unsigned long sbf4_page25_svId = 63UL;
	unsigned long sbf5_page25_svId = 51UL;

	unsigned long wna;
	unsigned long toa;

	wn = (unsigned long)(eph.toe.week%1024);
	toe = (unsigned long)(eph.toe.sec/16.0);
	toc = (unsigned long)(eph.toc.sec/16.0);
	iode = (unsigned long)(eph.iode);
	iodc = (unsigned long)(eph.iodc);
	deltan = (long)(eph.deltan/POW2_M43/PI);
	cuc = (long)(eph.cuc/POW2_M29);
	cus = (long)(eph.cus/POW2_M29);
	cic = (long)(eph.cic/POW2_M29);
	cis = (long)(eph.cis/POW2_M29);
	crc = (long)(eph.crc/POW2_M5);
	crs = (long)(eph.crs/POW2_M5);
	ecc = (unsigned long)(eph.ecc/POW2_M33);
	sqrta = (unsigned long)(eph.sqrta/POW2_M19);
	m0 = (long)(eph.m0/POW2_M31/PI);
	omg0 = (long)(eph.omg0/POW2_M31/PI);
	inc0 = (long)(eph.inc0/POW2_M31/PI);
	aop = (long)(eph.aop/POW2_M31/PI);
	omgdot = (long)(eph.omgdot/POW2_M43/PI);
	idot = (long)(eph.idot/POW2_M43/PI);
	af0 = (long)(eph.af0/POW2_M31);
	af1 = (long)(eph.af1/POW2_M43);
	af2 = (long)(eph.af2/POW2_M55);
	tgd = (long)(eph.tgd/POW2_M31);

	wna = (unsigned long)(eph.toe.week%256);
	toa = (unsigned long)(eph.toe.sec/4096.0);

	// Subframe 1
	sbf[0][0] = 0x8B0000UL<<6;
	sbf[0][1] = 0x1UL<<8;
	sbf[0][2] = ((wn&0x3FFUL)<<20) | (ura<<14) | (((iodc>>8)&0x3UL)<<6);
	sbf[0][3] = 0UL;
	sbf[0][4] = 0UL;
	sbf[0][5] = 0UL;
	sbf[0][6] = (tgd&0xFFUL)<<6;
	sbf[0][7] = ((iodc&0xFFUL)<<22) | ((toc&0xFFFFUL)<<6);
	sbf[0][8] = ((af2&0xFFUL)<<22) | ((af1&0xFFFFUL)<<6);
	sbf[0][9] = (af0&0x3FFFFFUL)<<8;

	// Subframe 2
	sbf[1][0] = 0x8B0000UL<<6;
	sbf[1][1] = 0x2UL<<8;
	sbf[1][2] = ((iode&0xFFUL)<<22) | ((crs&0xFFFFUL)<<6);
	sbf[1][3] = ((deltan&0xFFFFUL)<<14) | (((m0>>24)&0xFFUL)<<6);
	sbf[1][4] = (m0&0xFFFFFFUL)<<6;
	sbf[1][5] = ((cuc&0xFFFFUL)<<14) | (((ecc>>24)&0xFFUL)<<6);
	sbf[1][6] = (ecc&0xFFFFFFUL)<<6;
	sbf[1][7] = ((cus&0xFFFFUL)<<14) | (((sqrta>>24)&0xFFUL)<<6);
	sbf[1][8] = (sqrta&0xFFFFFFUL)<<6;
	sbf[1][9] = (toe&0xFFFFUL)<<14;

	// Subframe 3
	sbf[2][0] = 0x8B0000UL<<6;
	sbf[2][1] = 0x3UL<<8;
	sbf[2][2] = ((cic&0xFFFFUL)<<14) | (((omg0>>24)&0xFFUL)<<6);
	sbf[2][3] = (omg0&0xFFFFFFUL)<<6;
	sbf[2][4] = ((cis&0xFFFFUL)<<14) | (((inc0>>24)&0xFFUL)<<6);
	sbf[2][5] = (inc0&0xFFFFFFUL)<<6;
	sbf[2][6] = ((crc&0xFFFFUL)<<14) | (((aop>>24)&0xFFUL)<<6);
	sbf[2][7] = (aop&0xFFFFFFUL)<<6;
	sbf[2][8] = (omgdot&0xFFFFFFUL)<<6;
	sbf[2][9] = ((iode&0xFFUL)<<22) | ((idot&0x3FFFUL)<<8);

	// Subframe 4, page 25
	sbf[3][0] = 0x8B0000UL<<6;
	sbf[3][1] = 0x4UL<<8;
	sbf[3][2] = (dataId<<28) | (sbf4_page25_svId<<22);
	sbf[3][3] = 0UL;
	sbf[3][4] = 0UL;
	sbf[3][5] = 0UL;
	sbf[3][6] = 0UL;
	sbf[3][7] = 0UL;
	sbf[3][8] = 0UL;
	sbf[3][9] = 0UL;

	// Subframe 5, page 25
	sbf[4][0] = 0x8B0000UL<<6;
	sbf[4][1] = 0x5UL<<8;
	sbf[4][2] = (dataId<<28) | (sbf5_page25_svId<<22) | ((toa&0xFFUL)<<14) | ((wna&0xFFUL)<<6);
	sbf[4][3] = 0UL;
	sbf[4][4] = 0UL;
	sbf[4][5] = 0UL;
	sbf[4][6] = 0UL;
	sbf[4][7] = 0UL;
	sbf[4][8] = 0UL;
	sbf[4][9] = 0UL;

	return;
}

/*! \brief Count number of bits set to 1
 *  \param[in] v long word in whihc bits are counted
 *  \returns Count of bits set to 1
 */
unsigned long countBits(unsigned long v)
{
	unsigned long c;
	const int S[] = {1, 2, 4, 8, 16};
	const unsigned long B[] = {
		0x55555555, 0x33333333, 0x0F0F0F0F, 0x00FF00FF, 0x0000FFFF};

	c = v;
	c = ((c >> S[0]) & B[0]) + (c & B[0]);
	c = ((c >> S[1]) & B[1]) + (c & B[1]);
	c = ((c >> S[2]) & B[2]) + (c & B[2]);
	c = ((c >> S[3]) & B[3]) + (c & B[3]);
	c = ((c >> S[4]) & B[4]) + (c & B[4]);

	return(c);
}

/*! \brief Compute the Checksum for one given word of a subframe
 *  \param[in] source The input data
 *  \param[in] nib Does this word contain non-information-bearing bits?
 *  \returns Computed Checksum
 */
unsigned long computeChecksum(unsigned long source, int nib)
{
	/*
	Bits 31 to 30 = 2 LSBs of the previous transmitted word, D29* and D30*
	Bits 29 to  6 = Source data bits, d1, d2, ..., d24
	Bits  5 to  0 = Empty parity bits
	*/ 

	/*
	Bits 31 to 30 = 2 LSBs of the previous transmitted word, D29* and D30*
	Bits 29 to  6 = Data bits transmitted by the SV, D1, D2, ..., D24
	Bits  5 to  0 = Computed parity bits, D25, D26, ..., D30
	*/ 

	/*
	                  1            2           3
	bit    12 3456 7890 1234 5678 9012 3456 7890
	---    -------------------------------------
	D25    11 1011 0001 1111 0011 0100 1000 0000
	D26    01 1101 1000 1111 1001 1010 0100 0000
	D27    10 1110 1100 0111 1100 1101 0000 0000
	D28    01 0111 0110 0011 1110 0110 1000 0000
	D29    10 1011 1011 0001 1111 0011 0100 0000
	D30    00 1011 0111 1010 1000 1001 1100 0000
	*/

	unsigned long bmask[6] = { 
		0x3B1F3480UL, 0x1D8F9A40UL, 0x2EC7CD00UL,
		0x1763E680UL, 0x2BB1F340UL, 0x0B7A89C0UL };

	unsigned long D;
	unsigned long d = source & 0x3FFFFFC0UL;
	unsigned long D29 = (source>>31)&0x1UL;
	unsigned long D30 = (source>>30)&0x1UL;

	if (nib) // Non-information bearing bits for word 2 and 10
	{
		/*
		Solve bits 23 and 24 to presearve parity check
		with zeros in bits 29 and 30.
		*/

		if ((D30 + countBits(bmask[4] & d)) % 2)
			d ^= (0x1UL<<6);
		if ((D29 + countBits(bmask[5] & d)) % 2)
			d ^= (0x1UL<<7);
	}

	D = d;
	if (D30)
		D ^= 0x3FFFFFC0UL;

	D |= ((D29 + countBits(bmask[0] & d)) % 2) << 5;
	D |= ((D30 + countBits(bmask[1] & d)) % 2) << 4;
	D |= ((D29 + countBits(bmask[2] & d)) % 2) << 3;
	D |= ((D30 + countBits(bmask[3] & d)) % 2) << 2;
	D |= ((D30 + countBits(bmask[4] & d)) % 2) << 1;
	D |= ((D29 + countBits(bmask[5] & d)) % 2);
	
	D &= 0x3FFFFFFFUL;
	//D |= (source & 0xC0000000UL); // Add D29* and D30* from source data bits

	return(D);
}

/*! \brief Replace all 'E' exponential designators to 'D'
 *  \param str String in which all occurrences of 'E' are replaced with *  'D'
 *  \param len Length of input string in bytes
 *  \returns Number of characters replaced
 */
int replaceExpDesignator(char *str, int len)
{
	int i,n=0;

	for (i=0; i<len; i++)
	{
		if (str[i]=='D')
		{
			n++;
			str[i] = 'E';
		}
	}
	
	return(n);
}

/*! \brief Read Ephemersi data from the RINEX Navigation file */
/*  \param[out] eph Array of Output SV ephemeris data
 *  \param[in] fname File name of the RINEX file
 *  \returns Number of SV found in the file, -1 on error
 */
int readRinexNav(ephem_t eph[], const char *fname)
{
	FILE *fp;
	int nsat;
	int sv;
	char str[MAX_CHAR];
	char tmp[20];

	datetime_t t;
	gpstime_t g;
	gpstime_t g0;
	double dt;

	if (NULL==(fp=fopen(fname, "rt")))
		return(-1);

	for (sv=0; sv<MAX_SAT; sv++)
		eph[sv].vflg = 0; // Clear valid flag

	while (1)
	{
		if (NULL==fgets(str, MAX_CHAR, fp))
			break;

		if (0==strncmp(str+60, "END OF HEADER", 13))
			break;
	}

	nsat = 0;
	g0.week = -1;

	while (1)
	{
		// PRN / EPOCH / SV CLK
		if (NULL==fgets(str, MAX_CHAR, fp))
			break;

		strncpy(tmp, str+3, 2);
		tmp[2] = 0;
		t.y = atoi(tmp) + 2000;

		strncpy(tmp, str+6, 2);
		tmp[2] = 0;
		t.m = atoi(tmp);

		strncpy(tmp, str+9, 2);
		tmp[2] = 0;
		t.d = atoi(tmp);

		strncpy(tmp, str+12, 2);
		tmp[2] = 0;
		t.hh = atoi(tmp);

		strncpy(tmp, str+15, 2);
		tmp[2] = 0;
		t.mm = atoi(tmp);

		strncpy(tmp, str+18, 4);
		tmp[2] = 0;
		t.sec = atof(tmp);

		date2gps(&t, &g);
		
		if (g0.week==-1)
			g0 = g;

		dt = g.sec - g0.sec;

		if ((g.week==g0.week) && (dt>-SECONDS_IN_HOUR) && (dt<=SECONDS_IN_HOUR))
		{
			strncpy(tmp, str, 2);
			tmp[2] = 0;
			sv = atoi(tmp)-1;

			if (eph[sv].vflg==0)
			{
				eph[sv].toc = g;

				strncpy(tmp, str+22, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19); // tmp[15]='E';
				eph[sv].af0 = atof(tmp);

				strncpy(tmp, str+41, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].af1 = atof(tmp);

				strncpy(tmp, str+60, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].af2 = atof(tmp);

				// BROADCAST ORBIT - 1
				if (NULL==fgets(str, MAX_CHAR, fp))
					break;

				strncpy(tmp, str+3, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].iode = (int)atof(tmp);

				strncpy(tmp, str+22, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].crs = atof(tmp);

				strncpy(tmp, str+41, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].deltan = atof(tmp);

				strncpy(tmp, str+60, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].m0 = atof(tmp);

				// BROADCAST ORBIT - 2
				if (NULL==fgets(str, MAX_CHAR, fp))
					break;

				strncpy(tmp, str+3, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].cuc = atof(tmp);

				strncpy(tmp, str+22, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].ecc = atof(tmp);

				strncpy(tmp, str+41, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].cus = atof(tmp);

				strncpy(tmp, str+60, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].sqrta = atof(tmp);

				// BROADCAST ORBIT - 3
				if (NULL==fgets(str, MAX_CHAR, fp))
					break;

				strncpy(tmp, str+3, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].toe.sec = atof(tmp);

				strncpy(tmp, str+22, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].cic = atof(tmp);

				strncpy(tmp, str+41, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].omg0 = atof(tmp);

				strncpy(tmp, str+60, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].cis = atof(tmp);

				// BROADCAST ORBIT - 4
				if (NULL==fgets(str, MAX_CHAR, fp))
					break;

				strncpy(tmp, str+3, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].inc0 = atof(tmp);

				strncpy(tmp, str+22, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].crc = atof(tmp);

				strncpy(tmp, str+41, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].aop = atof(tmp);

				strncpy(tmp, str+60, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].omgdot = atof(tmp);

				// BROADCAST ORBIT - 5
				if (NULL==fgets(str, MAX_CHAR, fp))
					break;

				strncpy(tmp, str+3, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].idot = atof(tmp);

				strncpy(tmp, str+41, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].toe.week = (int)atof(tmp);

				// BROADCAST ORBIT - 6
				if (NULL==fgets(str, MAX_CHAR, fp))
					break;

				strncpy(tmp, str+41, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].tgd = atof(tmp);

				strncpy(tmp, str+60, 19);
				tmp[19] = 0;
				replaceExpDesignator(tmp, 19);
				eph[sv].iodc = (int)atof(tmp);

				// BROADCAST ORBIT - 7
				if (NULL==fgets(str, MAX_CHAR, fp))
					break;

				eph[sv].vflg = 1;
				
				nsat++;
			}
		}
		else
			break;

		// Update the working variables
		eph[sv].A = eph[sv].sqrta * eph[sv].sqrta;
		eph[sv].n = sqrt(GM_EARTH/(eph[sv].A*eph[sv].A*eph[sv].A)) + eph[sv].deltan;
		eph[sv].sq1e2 = sqrt(1.0 - eph[sv].ecc*eph[sv].ecc);
		eph[sv].omgkdot = eph[sv].omgdot - OMEGA_EARTH;
	}

	fclose(fp);

	return(nsat);
}

/*! \brief Subtract two vectors of double
 *  \param[out] y Result of subtraction
 *  \param[in] x1 Minuend of subtracion
 *  \param[in] x2 Subtrahend of subtracion
 */
void subVect(double *y, const double *x1, const double *x2)
{
	y[0] = x1[0]-x2[0];
	y[1] = x1[1]-x2[1];
	y[2] = x1[2]-x2[2];

	return;
}

/*! \brief Compute Norm of Vector
 *  \param[in] x Input vector
 *  \returns Length (Norm) of the input vector
 */
double normVect(const double *x)
{
	return(sqrt(x[0]*x[0]+x[1]*x[1]+x[2]*x[2]));
}

/*! \brief Compute dot-product of two vectors
 *  \param[in] x1 First multiplicand
 *  \param[in] x2 Second multiplicand
 *  \returns Dot-product of both multiplicands
 */
double dotProd(const double *x1, const double *x2)
{
	return(x1[0]*x2[0]+x1[1]*x2[1]+x1[2]*x2[2]);
}

/*! \brief Compute range between a satellite and the receiver
 *  \param[out] rho The computed range
 *  \param[in] eph Ephemeris data of the satellite
 *  \param[in] g GPS time at time of receiving the signal
 *  \param[in] xyz position of the receiver
 */
void computeRange(range_t *rho, ephem_t eph, gpstime_t g, double xyz[])
{
	double pos[3],vel[3],clk[2];
	double los[3];
	double tau;
	double range,rate;
	double xrot,yrot;
	
	// SV position at time of the pseudorange observation.
	satpos(eph, g, pos, vel, clk);

	// Receiver to satellite vector and light-time.
	subVect(los, pos, xyz);
	tau = normVect(los)/SPEED_OF_LIGHT;

	// Extrapolate the satellite position backwards to the transmission time.
	pos[0] -= vel[0]*tau;
	pos[1] -= vel[1]*tau;
	pos[2] -= vel[2]*tau;

	// Earth rotation correction. The change in velocity can be neglected.
	xrot = pos[0] + pos[1]*OMEGA_EARTH*tau;
	yrot = pos[1] - pos[0]*OMEGA_EARTH*tau;
	pos[0] = xrot;
	pos[1] = yrot;

	// New observer to satellite vector and satellite range.
	subVect(los, pos, xyz);
	range = normVect(los);
	rho->d = range;

	// Pseudorange.
	rho->range = range - SPEED_OF_LIGHT*clk[0];

	// Relative velocity of SV and receiver.
	rate = dotProd(vel, los)/range;

	// Pseudorange rate.
	rho->rate = rate; // - SPEED_OF_LIGHT*clk[1];

	// Time of application
	rho->g = g;

	return;
}

/*! \brief Compute the code phase for a given channel (satellite)
 *  \param chan Channel on which we operate (is updated)
 *  \param[in] rho0 Range at start of interval
 *  \param[in] rho1 Current range, after \a dt has expired
 *  \param[in dt delta-t (time difference) in seconds
 */
void computeCodePhase(channel_t *chan, range_t rho0, range_t rho1, double dt)
{
	double ms;
	int ims;
	double rhorate;
	
	// Pseudorange rate.
	rhorate = (rho1.range - rho0.range)/dt;

	// Carrier and code frequency.
	chan->f_carr = -rhorate/LAMBDA_L1;
	chan->f_code = CODE_FREQ + chan->f_carr*CARR_TO_CODE;

	// Initial code phase and data bit counters.
	ms = (((rho0.g.sec-chan->g0.sec)+6.0) - rho0.range/SPEED_OF_LIGHT)*1000.0;

	ims = (int)ms;
	chan->code_phase = (ms-(double)ims)*CA_SEQ_LEN; // in chip

	chan->iword = ims/600; // 1 word = 30 bits = 600 ms
	ims -= chan->iword*600;
			
	chan->ibit = ims/20; // 1 bit = 20 code = 20 ms
	ims -= chan->ibit*20;

	chan->icode = ims; // 1 code = 1 ms

	chan->codeCA = chan->ca[(int)chan->code_phase]*2-1;
	chan->dataBit = (int)((chan->dwrd[chan->iword]>>(29-chan->ibit)) & 0x1UL)*2-1;

	return;
}

/*! \brief Read the list of user motions from the input file
 *  \param[out] xyz Output array of ECEF vectors for user motion
 *  \param[[in] filename File name of the text input file
 *  \returns Number of user data motion records read, -1 on error
 */
int readUserMotion(double xyz[USER_MOTION_SIZE][3], const char *filename)
{
	FILE *fp;
	int numd;
	char str[MAX_CHAR];
	double t,x,y,z;

	if (NULL==(fp=fopen(filename,"rt")))
		return(-1);

	for (numd=0; numd<USER_MOTION_SIZE; numd++)
	{
		if (fgets(str, MAX_CHAR, fp)==NULL)
			break;

		if (EOF==sscanf(str, "%lf,%lf,%lf,%lf", &t, &x, &y, &z)) // Read CSV line
			break;

		xyz[numd][0] = x;
		xyz[numd][1] = y;
		xyz[numd][2] = z;
	}

	fclose(fp);

	return (numd);
}

int readNmeaGGA(double xyz[USER_MOTION_SIZE][3], const char *filename)
{
	FILE *fp;
	int numd = 0;
	char str[MAX_CHAR];
	char *token;
	double llh[3],pos[3];
	char tmp[8];

	if (NULL==(fp=fopen(filename,"rt")))
		return(-1);

	while (1)
	{
		if (fgets(str, MAX_CHAR, fp)==NULL)
			break;

		token = strtok(str, ",");

		if (strncmp(token+3, "GGA", 3)==0)
		{
			token = strtok(NULL, ","); // Date and time
			
			token = strtok(NULL, ","); // Latitude
			strncpy(tmp, token, 2);
			tmp[2] = 0;
			
			llh[0] = atof(tmp) + atof(token+2)/60.0;

			token = strtok(NULL, ","); // North or south
			if (token[0]=='S')
				llh[0] *= -1.0;

			llh[0] /= R2D; // in radian
			
			token = strtok(NULL, ","); // Longitude
			strncpy(tmp, token, 3);
			tmp[3] = 0;
			
			llh[1] = atof(tmp) + atof(token+3)/60.0;

			token = strtok(NULL, ","); // East or west
			if (token[0]=='W')
				llh[1] *= -1.0;

			llh[1] /= R2D; // in radian

			token = strtok(NULL, ","); // GPS fix
			token = strtok(NULL, ","); // Number of satellites
			token = strtok(NULL, ","); // HDOP

			token = strtok(NULL, ","); // Altitude above meas sea level
			
			llh[2] = atof(token);

			token = strtok(NULL, ","); // in meter

			token = strtok(NULL, ","); // Geoid height above WGS84 ellipsoid
			
			llh[2] += atof(token);

			// Convert geodetic position into ECEF coordinates
			llh2xyz(llh, pos);

			xyz[numd][0] = pos[0];
			xyz[numd][1] = pos[1];
			xyz[numd][2] = pos[2];
			
			// Update the number of track points
			numd++;

			if (numd>=USER_MOTION_SIZE)
				break;
		}
	}

	fclose(fp);

	return (numd);
}

void usage(void)
{
	printf("Usage: gps-sdr-sim [options]\n"
		"Options:\n"
		"  -e <gps_nav>     RINEX navigation file for GPS ephemerides (required)\n"
		"  -u <user_motion> User motion file (dynamic mode)\n"
		"  -g <nmea_gga>    NMEA GGA stream (dynamic mode)\n"
		"  -l <location>    Lat,Lon,Hgt (static mode) e.g. 30.286502,120.032669,100\n"
		"  -o <output>      I/Q sampling data file (default: gpssim.bin)\n"
		"  -s <frequency>   Sampling frequency [Hz] (default: 2600000)\n"
		"  -b <iq_bits>     I/Q data format [8/16] (default: 8)\n");

	return;
}

int main(int argc, char *argv[])
{
	clock_t tstart,tend;

	FILE *fp;

	int sv;
	int neph;
	ephem_t eph[MAX_SAT];
	gpstime_t g0;
	
	double llh[3];
	double pos[3],vel[3],clk[2];
	double tmat[3][3];
	double los[3];
	double neu[3];
	double azel[2];
	
	int i;
	int nsat;
	channel_t chan[MAX_CHAN];
	double elvmask = 0.0/R2D;

	int isbf,iwrd;
	unsigned long tow;
	unsigned long sbf[5][N_DWRD_SBF];
	unsigned long sbfwrd;
	unsigned long prevwrd;
	int nib;

	int ip,qp;
	int iTable;
	short *iq_buff = NULL;
	signed char *iq8_buff = NULL;

	gpstime_t grx;
	range_t rho0[MAX_SAT];

	double delt;
	int isamp;

	int iumd;
	int numd;
	char umfile[MAX_CHAR];
	double xyz[USER_MOTION_SIZE][3];

	bool staticLocationMode = false;
	bool nmeaGGA = false;

	char navfile[MAX_CHAR];
	char outfile[MAX_CHAR];

	double samp_freq;
	int iq_buff_size;
	int data_format;

	int result;

	int gain[MAX_CHAN];

	////////////////////////////////////////////////////////////
	// Read options
	////////////////////////////////////////////////////////////

	// Default options
	navfile[0] = 0;
	umfile[0] = 0;
	strcpy(outfile, "gpssim.bin");
	samp_freq = 2.6e6;
	data_format = SC08;

	if (argc<3)
	{
		usage();
		exit(1);
	}

	while ((result=getopt(argc,argv,"e:u:g:l:o:s:b:"))!=-1)
	{
		switch (result)
		{
		case 'e':
			strcpy(navfile, optarg);
			break;
		case 'u':
			strcpy(umfile, optarg);
			nmeaGGA = false;
			break;
		case 'g':
			strcpy(umfile, optarg);
			nmeaGGA = true;
			break;
		case 'l':
			// Static geodetic coordinates input mode
			// Added by scateu@gmail.com
			staticLocationMode = true;
			sscanf(optarg,"%lf,%lf,%lf",&llh[0],&llh[1],&llh[2]);
			llh[0] = llh[0] / R2D; // convert to RAD
			llh[1] = llh[1] / R2D; // convert to RAD
			break;
		case 'o':
			strcpy(outfile, optarg);
			break;
		case 's':
			samp_freq = atof(optarg);
			if (samp_freq<1.0e6)
			{
				printf("Invalid sampling frequency.\n");
				exit(1);
			}
			break;
		case 'b':
			data_format = atoi(optarg);
			if (data_format!=SC08 && data_format!=SC16)
			{
				printf("Invalid data format.\n");
				exit(1);
			}
			break;
		case ':':
		case '?':
			usage();
			exit(1);
		default:
			break;
		}
	}

	if (navfile[0]==0)
	{
		printf("GPS ephemeris file is not specified.\n");
		exit(1);
	}

	if (umfile[0]==0 && !staticLocationMode)
	{
		printf("User motion file / NMEA GGA stream is not specified.\n");
		printf("You may use -l to specify the static location directly.\n");
		exit(1);
	}

	// Buffer size	
	samp_freq = floor(samp_freq/10.0);
	iq_buff_size = (int)samp_freq; // samples per 0.1sec
	samp_freq *= 10.0;

	delt = 1.0/samp_freq;

	////////////////////////////////////////////////////////////
	// Receiver position
	////////////////////////////////////////////////////////////

	if (!staticLocationMode)
	{
		// Read user motion file
		if (nmeaGGA==true)
			numd = readNmeaGGA(xyz, umfile);
		else
			numd = readUserMotion(xyz, umfile);

		if (numd==-1)
		{
			printf("Failed to open user motion / NMEA GGA file.\n");
			exit(1);
		}
		else if (numd==0)
		{
			printf("Failed to read user motion / NMEA GGA data.\n");
			exit(1);
		}

		printf("Track points = %d\n", numd);

		// Initial location in Geodetic coordinate system
		xyz2llh(xyz[0], llh);
	} 
	else 
	{ 
		// Static geodetic coordinates input mode: "-l"
		// Added by scateu@gmail.com 
		printf("Using static location mode.\n");
		llh2xyz(llh,xyz[0]); // Convert llh to xyz

		numd = USER_MOTION_SIZE;
		
		for (iumd=1; iumd<numd; iumd++)
		{
			xyz[iumd][0] = xyz[0][0];
			xyz[iumd][1] = xyz[0][1];
			xyz[iumd][2] = xyz[0][2];
		}
	}

	printf("xyz = %11.1f, %11.1f, %11.1f\n", xyz[0][0], xyz[0][1], xyz[0][2]);
	printf("llh = %11.6f, %11.6f, %11.1f\n", llh[0]*R2D, llh[1]*R2D, llh[2]);

	////////////////////////////////////////////////////////////
	// Read ephemeris
	////////////////////////////////////////////////////////////

	neph = readRinexNav(eph, navfile);

	if (neph==-1)
	{
		printf("Failed to open ephemeris file.\n");
		exit(1);
	}

	g0.week = -1;

	if (neph>0)
	{
		for (sv=0; sv<MAX_SAT; sv++)
		{
			if (g0.week<0 && eph[sv].vflg==1)
			{
				g0 = eph[sv].toe; // Set simulation start time
				break;
			}
		}
	}

	g0.sec = (double)(((unsigned long)g0.sec)/30UL) * 30.0; // align with the full frame length = 30 sec

	printf("Start Time = %4d:%.1f\n", g0.week, g0.sec);

	////////////////////////////////////////////////////////////
	// Check visible satellites
	////////////////////////////////////////////////////////////

	for (i=0; i<MAX_CHAN; i++)
		chan[i].prn = 0;

	ltcmat(llh, tmat);

	nsat = 0;

	for (sv=0; sv<MAX_SAT; sv++)
	{
		if (eph[sv].vflg==1)
		{
			satpos(eph[sv], g0, pos, vel, clk);
			subVect(los, pos, xyz[0]);
			ecef2neu(los, tmat, neu);
			neu2azel(azel, neu);

			if (azel[1]>elvmask)
			{
				chan[nsat].prn = sv+1;
				nsat++;

				printf("%02d %6.1f %5.1f %10.1f\n", sv+1, azel[0]*R2D, azel[1]*R2D, normVect(los));
			}
		}
	}

	printf("Number of channels = %d\n", nsat);

	////////////////////////////////////////////////////////////
	// Baseband signal buffer and output file
	////////////////////////////////////////////////////////////

	// Allocate I/Q buffer
	iq_buff = calloc(2*iq_buff_size, 2);

	if (iq_buff==NULL)
	{
		printf("Faild to allocate IQ buffer.\n");
		exit(1);
	}

	if (data_format==SC08)
	{
		iq8_buff = calloc(2*iq_buff_size, 1);
		if (iq8_buff==NULL)
		{
			printf("Faild to allocate IQ buffer.\n");
			exit(1);
		}
	}

	// Open output file
	if (NULL==(fp=fopen(outfile,"wb")))
	{
		printf("Failed to open output file.\n");
		exit(1);
	}

	////////////////////////////////////////////////////////////
	// Initialize channels
	////////////////////////////////////////////////////////////

	// Initial reception time
	grx = g0;

	for (i=0; i<nsat; i++)
	{
		// C/A code generation
		codegen(chan[i].ca, chan[i].prn);
	}

	// Initialize carrier phase
	for (i=0; i<nsat; i++)
	{
		range_t tmp;
		double ref[3]={0.0};
		double r_ref,r_xyz;
		double phase_ini;

		sv = chan[i].prn-1;

		computeRange(&tmp, eph[sv], grx, ref);
		r_ref = tmp.range;

		computeRange(&tmp, eph[sv], grx, xyz[0]);
		r_xyz = tmp.range;

		phase_ini = (2.0*r_ref - r_xyz)/LAMBDA_L1;
		phase_ini -= floor(phase_ini);
		chan[i].carr_phase = (unsigned int)(512 * 65536.0 * phase_ini);
	}

	////////////////////////////////////////////////////////////
	// Generate subframes and data bits
	////////////////////////////////////////////////////////////

	for (i=0; i<nsat; i++)
	{
		sv = chan[i].prn-1;

		eph2sbf(eph[sv], sbf);

		chan[i].g0 = g0; // Data bit reference time

		tow = ((unsigned long)g0.sec)/6UL;

		prevwrd = 0UL;

		for (isbf=0; isbf<N_SBF; isbf++)
		{
			for (iwrd=0; iwrd<N_DWRD_SBF; iwrd++)
			{
				sbfwrd = sbf[(isbf+4)%5][iwrd]; // Start from subframe 5

				// Add TOW-count message into HOW
				if (iwrd==1)
					sbfwrd |= ((tow&0x1FFFFUL)<<13);

				// Compute checksum
				sbfwrd |= (prevwrd<<30) & 0xC0000000UL; // 2 LSBs of the previous transmitted word
				
				nib = ((iwrd==1)||(iwrd==9))?1:0; // Non-information bearing bits for word 2 and 10

				chan[i].dwrd[isbf*N_DWRD_SBF+iwrd] = computeChecksum(sbfwrd, nib);

				prevwrd = chan[i].dwrd[isbf*N_DWRD_SBF+iwrd];
			}

			tow++; // Next subframe
		}
	}

	////////////////////////////////////////////////////////////
	// Generate baseband signals
	////////////////////////////////////////////////////////////

	tstart = clock();

	printf("Generating baseband signals...\n");

	printf("\rTime = %4.1f", grx.sec-g0.sec);
	fflush(stdout);

	//
	// Generate I/Q samples for every user motion data
	//

	// Initial pseudorange
	for (i=0; i<nsat; i++)
	{
		sv = chan[i].prn-1;
		computeRange(&rho0[sv], eph[sv], grx, xyz[0]);
	}

	// Update receiver time
	grx.sec += 0.1;
	
	for (iumd=1; iumd<numd; iumd++)
	{
		for (i=0; i<nsat; i++)
		{
			// Refresh code phase and data bit counters
			int sv = chan[i].prn-1;
			range_t rho;

			// Current pseudorange
			computeRange(&rho, eph[sv], grx, xyz[iumd]);

			// Update code phase and data bit counters
			computeCodePhase(&chan[i], rho0[sv], rho, 0.1);
			chan[i].carr_phasestep = (int)(512 * 65536.0 * chan[i].f_carr * delt);

			// Save current pseudorange
			rho0[sv] = rho;

			// Path loss
			gain[i] = (int)(20200000.0*100.0/rho.d); // scaled by 100

			// Receiver antenna gain
		}

		for (isamp=0; isamp<iq_buff_size; isamp++)
		{
			int i_acc = 0;
			int q_acc = 0;

			for (i=0; i<nsat; i++)
			{
				iTable = (chan[i].carr_phase >> 16) & 511;

				ip = chan[i].dataBit * chan[i].codeCA * cosTable512[iTable] * gain[i];
				qp = chan[i].dataBit * chan[i].codeCA * sinTable512[iTable] * gain[i];

				i_acc += ip/100;
				q_acc += qp/100;

				// Update code phase
				chan[i].code_phase += chan[i].f_code * delt;

				if (chan[i].code_phase>=CA_SEQ_LEN)
				{
					chan[i].code_phase -= CA_SEQ_LEN;

					chan[i].icode++;
					
					if (chan[i].icode>=20) // 20 C/A codes = 1 navigation data bit
					{
						chan[i].icode = 0;
						chan[i].ibit++;
						
						if (chan[i].ibit>=30) // 30 navigation data bits = 1 word
						{
							chan[i].ibit = 0;
							chan[i].iword++;
						}

						// Set new navigation data bit
						chan[i].dataBit = (int)((chan[i].dwrd[chan[i].iword]>>(29-chan[i].ibit)) & 0x1UL)*2-1;
					}
				}

				// Set currnt code chip
				chan[i].codeCA = chan[i].ca[(int)chan[i].code_phase]*2-1;

				// Update carrier phase
				chan[i].carr_phase += chan[i].carr_phasestep;
			}

			// Store I/Q samples into buffer
			iq_buff[isamp*2] = (short)i_acc;
			iq_buff[isamp*2+1] = (short)q_acc;

		} // End of omp parallel for

		if (data_format==SC08)
		{
			for (isamp=0; isamp<2*iq_buff_size; isamp++)
				iq8_buff[isamp] = iq_buff[isamp]>>4; // 12-bit bladeRF -> 8-bit HackRF

			fwrite(iq8_buff, 1, 2*iq_buff_size, fp);
		} 
		else 
			fwrite(iq_buff, 2, 2*iq_buff_size, fp);

		// Update receiver time
		grx.sec += 0.1;

		// Update time counter
		printf("\rTime = %4.1f", grx.sec-g0.sec);
		fflush(stdout);
	}

	tend = clock();

	printf("\nDone!\n");

	// Free I/Q buffer
	free(iq_buff);

	// Close file
	fclose(fp);

	// Process time
	printf("Process time = %.3f[sec]\n", (double)(tend-tstart)/CLOCKS_PER_SEC);

	return(0);
}