Scenario:
Just imagine a big hall, let's say 20 meters x 30 meters. In this hall there are people walking. Imagine that each person has a mobile phone. We would like to determine the position of each mobile with an accuracy of 1 meter.
Question:
The question I've been asked is if this is possible by using local GSM antennas. I mean, if it is possible to allocate antennas inside the hall so that each phone is registered at the cells. Each cell should track every X amount of seconds the distance from the cell to the phone and send this info to a local server.
Has anybody experience on this?
Is this possible?
Thanks in advance
Related
We are trying to set in place a system of indoor localization based on BLE Beacons. The precize location of the client does not really matter, the valuable information is the room he is in.
The building to be equipped has large concrete walls. We thought that using one beacon per room, we could detect the closer beacon to the guest.
Are concrete wall able to stop most of the BLE signal? We tried some tests, but we are searching for serious studies.
Any wall will reduce BLE signals by some amount. A signal of -50 dBm on one side might be -60 dBm on the other side, a reduction of 10 dB. Because decibels are logarithmic, every 10 dB reduction in the signal level represents a loss of 90 percent of the power in the signal. So while it is typically true that a concrete wall will "stop most of the BLE signal", it doesn't really matter because there may still be enough signal on the other side of the wall to detect the beacon.
How much of a reduction in signal level there is depends on thickness of the wall and other materials in it (metal will increase the attenuation.) Of course, windows, doors and other breaks in walls provide other paths for the signals to travel and complicate the issue.
Since you are unlikely to create a system where signals from beacons in one room will never be detected in an adjacent room, your best bet is to use other algorithms. For example, you may detect all visible beacons in a time interval, determine which has the highest signal strength, and if above a certain threshold, use this as an indicator of which room you are in.
I have two questions regarding GPS sampling on iPhone:
1.Is it possible to use CLLocationManager (or any other method) for location readings based on GPS alone without WiFi or Cellular network affecting it?
2.Given a stationary device, is it possible to control the sampling rate? Can I use CLLocationManager to get nonstop location readings from GPS in nanoseconds resolution? If not, what's the best resolution I can get?
regarding number 1, apparently, you cannot directly control gps data. having said that: if you have speed > 0 AND high accuracy, then you can infer that your data has a high probability of having come from a gps reading.
as far as i know, gps fixing is not measured in nanoseconds, but rather in seconds. what you mean exactly by resolution (reading frequency?) is a bit unclear. but, if it is frequency, most navigational software (google, for example) refreshes location every second or so.
hi frequency position updating is very costly in terms of storage cost (server side), query times (server side), battery use (iphone) and heats the phone up bigtime. i would be going in the opposite direction, especially for stationary devices (sending a heartbeat every 5 minutes or so is usually more than enough).
reference on CLLocationManager
I am just looking iphone apps at apple store, and i have found this app g8, http://www.dynolicious.com/, but can you give some ideas or logic that how this app works, i mean how it is possible to measure car performance without using or communicating with any external hardware ...??? By using just hardware built into iphone, ie. accelerometer.
It works as follows. The data provided as results are actually estimates, not absolutely correct values measured attaching external hardware to the car. The estimates come from the GPS unit and the accelerometer embedded within the iPhone. Using the GPS you can estimate from the positions detected in different temporal instants the distance travelled and therefore the velocity. Then you can also estimate the acceleration using the accelerometer.
This is just a guess, but I would expect that you tell it your car make and model which will give the manufacturer's performance and fuel consumption figures. Then using the accelerometer and positional information in the phone you can calculate the speed of the car. A relatively simple equation can then be used to calculate the expected performance.
I would guess it uses the GPS to measure the 0-60 acceleration (start a stopwatch and stop when GPS says you're moving at 60 mph) and the built-in accelerometer to detect G-force. The horsepower estimate is just that - an estimate. They may have a performance table of various known cars and their 0-60 performance and horsepower. Based on that, they can give an estimate for yours.
What's the deal with iPhone's GPS? I never get a good reading when i'm in my office building, or in my room. What really ticks it! and what doesn't? Please help me understand the assisted GPS science.
If I'm not mistaken, the gps tries to pinpoint your position using three methods:
1. Satellite
2. Mobile network
3. Wi-fi networks
So if you don't have a good reading, then probably one or more of these methods cannot be used properly in your area. For instance, satellite will not always work that well in buildings with thick walls and ceilings.
Assisted GPS means that it may have it's location from different sources than GPS satellites, for instance known wifi hotspots, or GSM masts. However these sources are less accurate the true GPS.
Claus
For the actual GPS in your iphone to get a good position, it has to be in direct sight of the GPS satellites. It cannot do that inside a building. So if you are inside you are not going to get the best position from the iphone. It can give you a position using other methods such as the cell phone network and public wi-fi networks, but these positions aren't as accurate as the real GPS position.
Here is an article that explains the GPS system:
http://en.wikipedia.org/wiki/Gps
Depends on whose definition of Assisted GPS.
True 'assisted GPS' means the GPS receiver uses a known initial position, from the cell tower location, to bootstrap the GPS position calculations. If you know where you are it's much quicker for the position solution to lock to the signal - that's why GPS take so long to find first fix compared to updating.
Some APIs use assisted GPS as shorthand for alternate location services where if GPS is not available, is disabled, or would use too much battery power it will supply a lower grade position based on cell tower triangulation or other methods.
There are many answers I found in WWDC 2010 – Session 115 - Using Core Location in iOS 4.
Very advised.
Does anyone have any experience with the triangulated GPS used by the non-3G iPhone? How does it compare with 3G positioning? Does the iPhone 3G use triangulation in the event that there is no GPS signal available? Is there anyway to determine the accuracy of the non 3G coordinates? Thanks.
I have done a lot of mobile software with a bunch of different devices including 3G iphones and 3G blackberry's and here is what I have found.
The blackberry and iPhone GPS is really good when you have clear line of sight and at least 9 satellites present. In some dense residential or urban areas you might only get 5-6 satellites which can take a while to converge.
If you do not have a signal, GSM phones like the iPhone will try and find your position using cell tower signal strength but it is NOT as accurate as GPS... not by a long shot.
I have heard, though this has not been confirmed that the iPhone also uses some server side machine learning when it can't find a GPS lock meaning that it takes the average all of the cell towers, plus the average of all the users who have used GPS in your area to try and find your best position. This is sometimes called AGPS or assisted GPS where the GPS information and cell tower strength are used together.
Also, the only thing I can think of for finding the accuracy of the non 3G coordinates would be to programmaticly switch providers in your code, or simply go into preferences and turn off 3G and write an application that does some tests.
The Pragmatic Programmers have a great iPhone SDK book that just added a chapter on using the Location API, so that might be a great place to start.
Hope this helps.
The CLLocation class has the properties 'horizontalAccuracy' (for latitude/longitude) and 'verticalAccuracy' (for elevation).
In addition to cell towers and GPS, locations may also determined by Skyhook Wireless, which has a database of Wi-Fi base station MAC addresses and locations.
When using only GSM towers, it's +/- 500m (it varies greatly, sometimes it's more precise).
If it finds known Wi-Fi network, then it's down to +/- 50m.