Point to point licensed & unlicensed microwave equipment
Real time Vehicle Tracking equipment
GPS/CDMA/GSM Specifications & Technology Information TECHNOLOGY
CGVT-03 uses three primary technologies – GPS (Global Positioning System) data for location and the extensive & cost effective GSM and or CDMA Mobile Phone Network for communications.
Accurate to within approximately 10 meters (32ft), GPS position co-ordinates are provided by 24 Satellites that continually orbit our planet. These co-ordinates are collected by the GPS receiver incorporated within the CGVT-03 module to provide real-time location information.
Communication is made possible, cost effectively and extensively, by use of the GSM and or CDMA mobile phone networks. The GSM and or CDMA networks are available in most countries in the world, including the USA & Canada and are growing each year. A mobile phone module is incorporated into the electronics of CGVT-03. The GSM and or CDMA networks are accessed by obtaining and placing a GSM SIM card and or a CDMA UIM card into our module to make and received calls, text and data.
SIGNAL STRENGTH & AVAILABILITY
The best results are achieved in areas where both good GSM and or CDMA mobile phone service and GPS Satellite broadcast signals can be received.
Wide, open outdoor areas are ideal for the GPS satellite receivers. GPS will suffer interference from other transmitting devices which can corrupt GPS data. An obstructed view of the sky in large commercial centers, known as urban canyons, may also cause data drop outs. The CGVT-003 has an internal black box recorder to log the last known position to memory, should position drop outs occur.
GSM mobile and or CDMA networks coverage are provided by your local carrier. Poor coverage and signal strength will affect the good & effective operation of your CGVT-03 just like a mobile phone. Without GSM and or CDMA mobile phone coverage, the CGVT-03 cannot communicate; it will continue a number of re-tries to make a call out in the event of an alarm. It is highly recommended that you select a carrier that has the best service in the areas you may live or frequent. It is important that you assure that your GSM SIM card and or CDMA UIM card also carries sufficient credit to also allow it to make the calls.
WHAT IS GPS?
GPS stands for “Global Positioning System”. It is based on a constellation of typically 24 Satellites orbiting the earth at a very high altitude.
Developed by the US Defense Department, these satellites are tracked & controlled from strategic military bases that monitor each satellites exact position to ensure they provide accurate position information, anywhere in the world, 24 hours a day. Using a good quality commercial GPS receiver, within your navigation or tracking systems you can also identify your position with great accuracy on Earth, within meters, your height (Altitude), your speed & direction of travel and the times with a good view of the sky.
How does GPS Work?
Fundamentally, GPS location is calculated by using triangulation, essentially measuring your distance from a known reference point, in this case GPS Satellites high above the Earth. A GPS receiver needs to acquire a minimum of three good, clear satellite signals to enable the calculation providing the longitude and latitude coordinates for a location fix. Commercial receivers such as navigation systems, hand held devices & tracking systems will only provide position information to within a few meters of your actual location. Military receivers have much greater accuracy. GPS does have limitations; it cannot be used inside structures such as buildings, underground car parks, and it will have difficulties under heavy foliage. Ideally the receiver’s antenna requires a good clear view of the sky to receive the signal and give you the best possible location calculation.
What is a GPS Satellite?
GPS Satellites are effectively orbiting radio stations; they are solar powered and the satellites antenna sends and receives radio signals.
A highly accurate Atomic clock is the heart of the GPS Satellite. It is used to generate Morse code like signals; two are in code for the military and the third is for civilian use known as C/A-code all broadcast simultaneously.
Remarkably these satellites travel around our planet at over 20 Kilometers above the Earth’s surface and travel at amazing speed, about 4 Kilometers per second. GPS satellites orbit the Earth twice a day; they are not geo-stationary, meaning they rise and set like stars & planets.
What affects GPS accuracy?
While GPS is undoubtedly incredible technology available freely to everyday users, there are number of conditions (beyond anyone’s control) that may affect the accuracy of your system.
Multipath effects are caused by the satellite signal reflecting on objects. Typically, this occurs within cities; narrow streets around buildings and large structures will obscure or reflect the GPS signal. The signal is therefore delayed reaching the receiver resulting in a Multipath error of up to a few meters.
While radio signals travel at the speed of light in outer space, their propagation in the ionosphere & troposphere is slower. These layers refract electromagnetic waves from the satellites resulting in an elongated runtime of the signal. Ionosphere errors are mostly corrected by your receiver although commercial receivers are not capable of correcting unforeseen runtime changes from events such as strong solar winds that may result in an error of up to +/- 5 meters. Troposphere effects are caused by concentrations of water vapor from different weather conditions; while the error is smaller, +/- 1 meter, it cannot be eliminated by calculations.
Gravitational forces and to a lesser extent the sun & moon can influence orbits. While GPS satellites are in very precise orbits, orbit data is controlled & corrected regularly. This data is sent to receivers in packages of ephemeris data resulting in the error not being more than typically 2 meters.
This is the position of the Satellites to each other based on the view from the receiver. If a receiver sees four (4) satellites arranged for example in the north-west, this could be determined as “bad” geometry. It is possible that no position can be determined or extreme errors of up to 150 meters could be reported until the next “good” fix is established.
The theory of relativity is well-known. While we are mostly unaware of its effect, it does have an influence on many processes including the proper functioning of GPS Systems. As time is an important factor in GPS navigation, the fast movement of the satellite must also be considered.
The theory of relativity knows that time runs slower during very fast movement. For satellites moving at a speed of 3874 meters per second, clocks will run slower viewed from Earth. This relativistic time dilation induces inaccuracy of time of approximately 7.2 microseconds per day.
The theory of relativity also indicates that time moves slower the stronger the field of gravitation is. Observing a clock on board a satellite from the earth, it will be running fast due to the much weaker field of gravitation. This effect is six times stronger than time dilation.
Together, the clocks of the satellites seem to run a little faster. The shift of time to an earth observer would be about 38 milliseconds per day that would make a total error of approximately 10 km per day. To compensate for the relativistic error satellite clocks are set slightly off frequency 10.229999995453 MHz instead of 10.23 MHz to overcome constant correction.
There is a further relativistic effect called Sagnac effect, caused by the movement of the observer on the earth’s surface; this is based on movement at the speed of 500m/s due to the rotation of the globe. This effect is very small and too complicated to calculate as it depends on the direction of the movement so it is not often considered unless used for highly critical applications.