Adding location to a non GPS phone : using OpenCellID

1) Introduction

In this two parts article, we will introduce mobile positioning with CellID, and the open source database of CellIDs: OpenCellID. We will see how to use it through a simple sample. The second part will demonstrate how to use OpenCellID with OpenStreeMap and the 8Motion library to create a full interactive mobile mapping experience in JavaME, each of these examples being less than 100 lines of code.

2) What is CellID

We all know that GPS will be deployed in the vast majority of phones in the future. But now, only a few high end handsets are GPS enabled.
An alternative, available since a long time, but gaining momentum recently is CellID based location. What is CellID? A CellID is the number given to a specific cell (the radio tower to which your handset is connected) . In most of the case, it’s the closest tower to your location. So by knowing this tower, you know where the user is. But a tower can cover a huge area: from a few hundred meters, in high density area, to several kilometers in lower density area. That’s why CellID accuracy is lower than GPS accuracy, but this present a very good alternative.

CellID has become recently more popular, mainly thanks to his nice integration into GoogleMap mobile.

3) OpenCellID

So this sounds great, let’s just get the phone cellID, so we will have his location. The issue is that the location of cells is not a public information. Operators keep this private, for many reasons:

• They don’t want to give tower location to their competitors
• They use this as an extra revenue income, as they provide paying services to retrieve cell location.

That’s why we have set up a service called “OpenCellID”. OpenCellID.org is an open source database of CellID, serving two purposes:

• Everybody can create an application gathering information about cell locations, and send these information to the OpenCellID server, improving the coverage
• The database can be used by other applications to get the location of a cell, according to his cell id.

How to use OpenCellID (http://www.opencellid.org/api )

The API is a simple REST api. There are only two relevant calls: measure/add and get/cell

measure/add to add a measure of cell. This is used to by application which wants to add information to the database. These application produce content for the OpenCellID database. To use it, you need to require a key to OpenCellID.org. The key is used to track applications providers, and ensure that no fake data are inserted into the system.

Examples:

http://www.opencellid.org/measure/add?key=myapikey&mnc=1&mcc=2&lac=200&cellid=234&lat=3.42&lon=3.12

Replace myKey with the key that you received while registering at OpenCellID. This will tell the serveur that a client found a cell of id 234, for mcc=1, mcc=2 and the position 3.42,3.12 …Be careful: all informations are in decimal, while some handsets (sonyericsson for instance) provides lac and cellid in hexa, so you will need to convert them before calling the API.

Cell/get is used to get the position associated with a cell. You just need to give mcc,mnc,cellid and optionnaly lac.

http://www.opencellid.org/cell/get?mcc=250&mnc=99&cellid=29513&lac=0

You need to provide at least mcc, mnc (mobile country code, and mobile network code of the operator), and cell id. Lac (location area code) is an optional parameter, and will help to find an alternate position if cell is not found.
In return, the API will return a simple XML, like this one:

<rsp stat="ok">
<cell lat="57.8240013122559" lac="0" lon="28.00119972229" mcc="250" nbsamples="38" range="0" cellid="29513" mnc="99">
</cell></rsp>
Lat and lon are the coordinate of the cell, based on 38 samples…

If needed, you can use the optional parameter “fmt” to specify an output format,:

http://www.opencellid.org/cell/get?mcc=250&mnc=99&cellid=29513&lac=0&fmt=txt

will return something like this:

57.8240013122559,28.00119972229,250,99,0,29513,100,38

Same informations than before, but in a much compact form (see the API description for a complete description).

Others API are under development, to retrieve operators from mcc/mnc for instance.

4) Sample program:

So let’s use OpenCellID to create a small program, written in JavaME, which will just get the CellID of the phone , do a request to the OpenCellID server and display the results.

First, let’s get the CellID:

We use SonyEricsson specific properties. There properties are non standard, and only available on some devices.

// These properties are implemented on latest SonyEricsson phone
// This does not work on others (Nokia, etc...)
String cellid=System.getProperty("com.sonyericsson.net.cellid");
String mcc  = System.getProperty("com.sonyericsson.net.cmcc");
String mnc  = System.getProperty("com.sonyericsson.net.cmnc");
String lac  = System.getProperty("com.sonyericsson.net.lac");

Cellid is of course the cell id, mcc is mobile country code, mnc is mobile network code and identify the operator and the country (cmcc stands for current mcc). That’s all we need to find our location.

Then, verify if theses properties are supported:

String info="This phone does not support CellID";
if(cellid!=null){
   info="Cell:"+cellid+" mcc:"+mcc+" mnc:"+mnc+" lac:"+lac;
   url="http://www.opencellid.org/cell/get?cellid="+Integer.parseInt(cellid,16)+
 "&mcc="+mcc+"&mnc="+mnc+"&lac="+Integer.parseInt(lac,16)+"&fmt=txt";
   cellInfo.setString(info);       
   Thread t=new Thread(this);
   t.start();
   posInfo.setString("Requesting position...");
}

In this part, we have created the URL to request information on the server, and start the fetch of the information in a separate thread:

public void run(){
 try {
   HttpConnection cnx = (HttpConnection)Connector.open(url);
   InputStream is=cnx.openInputStream();
   StringBuffer b=new StringBuffer();
   int car;
   while( (car=is.read())!= -1){
      b.append((char)car);
   }
   is.close();
   cnx.close();
   String res=b.toString();
   if(res.startsWith("err")){
      posInfo.setString("Cell not found!");
   }else{
      int pos=res.indexOf(',');
      String lat=res.substring(0,pos);
      int pos2=res.indexOf(',',pos+1);
      String lon=res.substring(pos+1,pos2);
      posInfo.setString(lat+" "+lon);
   }
 } catch (IOException ex) {
   ex.printStackTrace();
   posInfo.setString(ex.toString());
 }
}

If the API call return something starting with err, we are probably in error. Otherwise, we will have our current cell id positioning.

And that’s done. The complete source code is available here.The compiled program is available here, with jad and jar.

So, what happens if the CellID is not in the database? Then the program will display an error. You can improve the accuracy of OpenCellID by discovering more cells. Check OpenCellID to know how to do it.

Next part will improve this first version, by creating an interactive program displaying the location on a map, using J2memap free component…

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