diff --git a/README.md b/README.md
index 42353f3..8a44333 100644
--- a/README.md
+++ b/README.md
@@ -37,13 +37,14 @@ Doppler for the GPS satellites in view. This simulated range data is
 then used to generate the digitized I/Q samples for the GPS signal.
 
 The bladeRF command line interface requires I/Q pairs stored as signed 
-16-bit integers, while the hackrf_transfere supports signed bytes.
+16-bit integers, while the hackrf_transfer supports signed bytes.
 
 ```
 Usage: gps-sdr-sim [options]
 Options:
   -e <gps_nav>     RINEX navigation file for GPS ephemerides (required)
-  -u <user_motion> User motion file (required)
+  -u <user_motion> User motion file
+  -l <location>    Latitude,Longitude,Height (static mode) eg: 30.286502,120.032669,100
   -o <output>      I/Q sampling data file (default: gpssim.bin)
   -s <frequency>   Sampling frequency [Hz] (default: 2600000)
   -b <iq_bits>     I/Q data format [8/16] (default: 8)
@@ -55,6 +56,10 @@ For example:
 > gps-sdr-sim -e brdc3540.14n -u circle.csv -b 16
 ```
 
+```
+> gps-sdr-sim -e brdc3540.14n -l 30.286502,120.032669,100 -b 16
+```
+
 ### Transmitting the samples
 
 The TX port of a particular SDR platform is connected to the GPS receiver 
diff --git a/gpssim.c b/gpssim.c
index ad3b0d0..c61ad1b 100644
--- a/gpssim.c
+++ b/gpssim.c
@@ -1076,7 +1076,7 @@ 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 (required)\n"
+		"  -u <user_motion> User motion file \n"
 		"  -l <location>    Latitude,Longitude,Height (static mode) eg: 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"
@@ -1213,9 +1213,10 @@ int main(int argc, char *argv[])
 		exit(1);
 	}
 
-	if (umfile[0]==0)
+	if (umfile[0]==0 && !staticLocationMode)
 	{
 		printf("User motion file is not specified.\n");
+		printf("Or you may use -l to specify llh coordinate directly.\n");
 		exit(1);
 	}