diff --git a/tools/nmea2um.c b/tools/nmea2um.c
new file mode 100644
index 0000000..924c9d6
--- /dev/null
+++ b/tools/nmea2um.c
@@ -0,0 +1,139 @@
+// nmea2um:
+//   Convert NMEA GGA data generated by the free GPS NMEA simulation
+//   software from LabSat into the ECEF user motion data for gps-sdr-sim. 
+//   http://www.labsat.co.uk/index.php/jp/free-gps-nmea-simulator-software
+
+#define _CRT_SECURE_NO_DEPRECATE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <math.h>
+
+#define MAX_CHAR 256
+#define R2D 57.2957795131
+
+void llh2xyz(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 = 6378137.0;
+	e = 0.0818191908426;
+	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;
+}
+
+int main(int argc, char *argv[])
+{
+	FILE *inp,*outp;
+	char str[MAX_CHAR];
+	char *token;
+	double llh[3],xyz[3],t=0.0;
+	char tmp[8];
+
+	if (argc!=3)
+	{
+		printf("Usage: nmea2um <nmea_gga> <user_motion>\n");
+		exit(1);
+	}
+
+	if ((inp=fopen(argv[1],"rt"))==NULL)
+	{
+		printf("Failed to open NMEA file.\n");
+		exit(1);
+	}
+
+	if ((outp=fopen(argv[2],"wt"))==NULL)
+	{
+		printf("Failed to open user motion file.\n");
+		exit(1);
+	}
+
+	while (1)
+	{
+		if (fgets(str, MAX_CHAR, inp)==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, xyz);
+
+			// Print out
+			fprintf(outp, "%5.1f,%12.3f,%12.3f,%12.3f\n", t, xyz[0], xyz[1], xyz[2]);
+			
+			t += 0.1; // at 10Hz
+		}
+	}
+
+	fclose(inp);
+	fclose(outp);
+
+	return(0);
+}
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