Question is as simple as the title: How to measure GPS signal strength?
Are you sure you mean signal strength vs. accuracy? What good is the signal strength? Since the GPS position is determined via many satellites, you don't have "one" signal strength.
So assuming that you really mean signal strength, you can get the GpsStatus via LocationManager.getGpsStatus(), and that gives you a list of satellites via getSatellites()', and each one of those has a signal-to-noise ratio (getSnr()).
Assuming you mean accuracy, try Location.getAccuracy().
You can read signal strength in MNEA message GSV in SNR-Signal to Noise Ratio.
Signal strength is VERY important. Too weak of a signal and the receiver can't track them. You need several 'strong' satellites to get position, not just one.
Older receivers couldn't track in trees or inside buildings. Modern receivers are much more sensitive.
It is very difficult to measure the signal level of a gps satellite without very expensive test gear (spectrum analyzer or specialized gps receiver). There are no commercially available tools to do this.
Why would you want to do this, anyway? The signal level is actually quite irrelevant in determining position.
Related
I am building an application that collects the RSSI levels of APs around me and do some calculations based on that.
The problem is that the readings are unstable even if the device is still. For example, signals from an access point fluctuates between -71, -68,-75 and so on....
Is there a way to stabilize the signals?
In telecommunications, received signal strength indicator (RSSI) is a measurement of the power present in a received radio signal.
I think the best you can do is count them al together and devide them after a x amount of measssure time. (since you would never get an 100% accurate acces point because of al kinds of components).
source:
http://en.wikipedia.org/wiki/Received_signal_strength_indication
"The problem is that the readings are unstable even if the device is still. For example, signals from an access point fluctuates between -71, -68,-75 and so on...."
This is the nature of the wireless signal. Even if the device is still, the environment is "moving", so, the signal is suffering from small scale fading mostly due to the environment scatterers. So, it is normal to obtain these fluctuations in the device measurements.
The accurancy of each Android device Wi-Fi measurement is another story.
Moreover, keep in mind that the values returned are in dBm which means that is in mWatt but expressed in the log scale. So, as Thealon proposed the averaging, you have to be careful because you cannot devide dBm values.
one solution would be to convert the dBm values back to mWatt and then perform the averaging. like below
Convert dBm to mWatt: mWatt = 10^(dBm/10)
When getting the RSSI, Google recommends to:
Use calculateSignalLevel(int, int) to convert this number into an absolute signal level which can be displayed to a user.
Official Docs
I was wondering if you can set signal strength parameters. In andriod.telephony class I only see methods which get you the values, however, is it possible to set values too ?
No. Signal strength is a measurement of a physical thing- the ratio of signal to noise of the cellular signal. You can't set that- it is whatever it is. You can set its variable to 1 billion, it won't effect the physical reality. The only use of it would be to lie to other apps about what the real signal strength is. And no, there is no way to do that.
Even if I set requestLocationUpdates to 0 seconds and 0 meters, the GPS sensor data updates only about every second. I need the satellites SNR data more fequently; 10/s would be nice. Is there any possibility?
If you have direct access to the GPS chip, you can set the message interval for each message. On a smartphone you cannot set that message interval.
However for consumer GPS devices the maxmimum GPS message frequency is either 1/s or 2 messages per second.
So probably, as long as you don't use an specialized GPS chip with e.g 10/s msg frequency,
it does not make much sense, to raise from 1/s to 2/s.
No, the update frequency of the device is limited by the GPS hardware itself, usually to about 1hz. Android hardware seems to be mostly concerned with battery life being one reason. Also, most GPS hardware that produces an output frequency that is greater than 1hz is cheating somewhere in the background and interpolating points, which you can do in code if you want more points. This is because, in general, producing a higher output frequency means a sample of fewer points which means reduced accuracy. There are really no "easy" solutions around this problem. If you need more data and more accuracy you are looking at sensor fusions and and probably some sort of Bayesian filtering.
You set that when you start listening to the GPS. You pass it as a parameter.
requestLocationUpdates(Provider, TIME_INTERVAL, DISTANCE_INTERVAL, LISTENER)
TIME_INTERVAL is in milliseconds.
How would I verify/ track device location within a 5' accuracy? I've heard of people using cell towers/ gps combinations.
As far as I know, the only way to get a 5 feet accuracy figure is to use GPS, then it still isn't always that accurate depending on how good a fix of the satellites (clear view to the sky) you have.
Cell tower / Wifi triangulation methods only serve to speed up positioning and will seldom (if ever) be more accurate than satellite positioning methods.
GPS is the way to go. Cell towers won't cut it. In Android (and I believe iOS) the system will provide you with an accuracy reading in addition to the actual location. You could use this value to determine whether the value you've received should be uploaded to your server. Keep in mind using the GPS is very battery intensive and there's no guarantee of how good the accuracy will be. Depending on conditions you may not be able to achieve 5' precision.
As #CommonsWare points out, 5' is really unrealistic anyway although you can get close.
As CommonsWare says you will not get much better that 10 metters accuracy in a consummer-grade device. Even in open sky, the atmosphere characteristcs change minute by minute and thats enough to change the GPS readings.
However, it's teoreticaly possible to increase accuracy if you could get all of the following:
1-There are some stationary GPS receiver stations with fixed known locations which measure the current GPS signals deviation. You would need to have one of those close to you and have access to the data in real time.
2-You would need to have low level access to your phone GPS receiver to read the unprocessed data received from sattelites. This would be different from device to device, and as far as I know, no supplier is providing this access.
3-Finnaly, you would need to do all the calculations required to determine your location applying the deviations got from point 1 above.
good luck.
The only way you can get this type of accuracy is with WAAS. As far as I know, there are no Android handsets that can receive WAAS corrections. If this is for a specific controlled situation, you could use a bluetooth gps receiver with WAAS, and only in WAAS supported locations. However, if this was for a wider deployment, then I think you are out of luck.
I'm trying to have three bars that act as a notification to how strong your gps signal is. Three bars for good connection, one bar for weak etc. How do I check the gps signal strength and show the corresponding bars? Thanks
I think there is no such thing as strength, but I think you mean accuracy, the bars you see are "blinking"(on the notification bar on the phone) while device is retrieving the coordinates and other data related to your position.
You can measure the accuracy with using getAccuracy() method, but the accuracy depends on how much satellites cover your area and other factors (Google around), you can collect this information with getSatellites().
For your purpose you can measure the accuracy and display custom number of bars for your custom GPS indicator.
Satellites send raw data package known as NMEA which contains wide range of information (strings). You can read more here:
http://aprs.gids.nl/nmea/