In this article, we’ll find out how GPS systems, like GPS Socket Receiver, pull off this amazing trick. As we’ll see, the Global Positioning System is vast, expensive and involves a lot of technical ingenuity, but the fundamental concepts at work are quite simple and intuitive. The Global Positioning System (GPS) is actually a constellation of 27 Earth-orbiting satellites (24 in operation and three extras, in case one fails).

A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the Earth. Each satellite continually transmits messages which include

* the time the message was sent
* precise orbital information
* the general system health and rough orbits of all GPS satellite

The receiver measures the transit time of each message and computes the distance to each satellite. Geometric trilateration is used to combine these distances with the satellites’ locations to obtain the position of the receiver. This position is then displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included. Many GPS units also show derived information such as direction and speed, calculated from position changes.

Three satellites might seem enough to solve for position, since space has three dimensions. However, even a very small clock error multiplied by the very large speed of light[15]—the speed at which satellite signals propagate—results in a large positional error. Therefore receivers use four or more satellites to solve for the receiver’s location and time. The very accurately computed time is effectively hidden by most GPS applications, which use only the location. A few specialized GPS applications do however use the time; these include time transfer, traffic signal timing, and synchronization of cell phone base stations.

Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. (For example, a ship or plane may have known elevation.) Some GPS receivers may use additional clues or assumptions (such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer) to give a degraded position when fewer than four satellites are visible.

Today we post here a short explanation of how to work with a bluetooth gps receiver.

Before we get into trip planning on your Pocket PC, let’s look at how the Bluetooth GPS receiver works. You must first charge the Bluetooth GPS Receiver using the included in-vehicle power adapter. Socket does offer an AC power adapter for an additional cost. Make sure that you fully charge the receiver before using it for the first time. On top of the GPS receiver, you will find three LEDs, the power jack and the on/off switch. The LEDs indicate Bluetooth status, GPS status and Battery status, marked with little icons. There is also an external antenna port on the right hand side of the receiver where you can plug in an external antenna for maximum signal strength.

Turn on the Bluetooth GPS receiver to get a fix before connecting to your Pocket PC. The cold start takes about 25-30 seconds and warm start only a few second. I usually can track 5-6 satellites in full signal strength with 7-8 satellites in-sight. Once you have a fix, you can pair up your Pocket PC with your GPS by performing a Bluetooth device discovery on your Pocket PC. You’ll bond the two devices, making sure that you use “0183” as the Passkey.

The Bluetooth connection was very easy to create and the process is fairly simple. You don’t need to be Bluetooth savvy to use the Bluetooth GPS. The only small issue I’ve encountered with this Bluetooth receiver is the LEDs were a bit hard to see in strong sunlight.

The Socket Bluetooth GPS Receiver is very small, almost the size of a matchbox, with a rechargeable lithium ion battery. A full battery charge lasts approximately 6 hours.

When you open the box you’ll find a leather pouch for your receiver and a car charger, with a bonus: a Y (splitter) cable that recharges the GPS receiver and an adapter to charge your iPAQ!

The accuracy according to the specs is 10m, RMS, 25m CEP without SA. Velocity: 0.1 m/sec without SA and time 1 microsecond synchronized to GPS time. The antenna is built in but there’s a plug for an external antenna. The unit has 12 Channels all-in-view tracking, and the maximum dynamic conditions are altitude < 18,000 m, velocity < 515 m/sec and acceleration < 4 g.

The unit has three LEDs: a yellow one to indicate low battery, a green one to indicate fix (blinking) and a blue one to indicate Bluetooth activity.

I was surprised with the time to get a fix. The Socket Bluetooth GPS Receiver got its first fix in less than two minutes! After this, I could turn it off and on again and a fix in around 30 seconds. I’m not very technical on GPS things, but I like these times!

The Socket Bluetooth GPS Receiver comes in two flavours: the Receiver only package (product code GP0804-405) and the Nav Kit (product code GP0805-406). The difference is that MyNavigator CD Rom comes with the Nav Kit. The MyNavigator software for Pocket PC is available in American and British versions. It includes things like destinations, points of interest, speed alert, recording and GPS Info.

According to Socket website, this is a standard NMEA GPS unit, so it should work fine with softwares like Destinator, Mapopolis and Pharos.

First surprise: no need to pair the Bluetooth devices. I just had to change my TDK Bluetooth configuration to allow any device to connect, and after my first serial connection I was up and running. That was very promissing. But, still, not very mobile. I’m not carrying my desktop computer around.

First I had to add the Socket Bluetooth GPS Receiver to the iPAQ H3970 Bluetooth Manager list. That was easy in took me less than 20 seconds, just the time to search for new devices. Then, armed with my Pocket PC and with the Socket Bluetooth GPS Receiver I was ready to go out and explore.

In summary I am very impressed with the Socket Bluetooth GPS Receiver. It’s a small product, you can easily attach to the dashboard, or have it on a bike trip. The leather pouch is great for tramping. And being a Bluetooth device you can leave the cables behind.