ABSTRACT

GPS and GSM is used to locate and track traffic vehicles as they transverse there route. By using satellites and towers the system is able to monitor the vehicles direction and location within a few feet. This paper will explore the problem of tracking vehicles, in real time, from one point to another. Improving latency and software calculations to be more precise with time accuracy. The paper will include hardware that utilize the technology and software that enables the system to work as designed. Function within the software will make allowance for any latency that is produce from the hardware.

INTRODUCTION

With the increase of wireless technology transportation companies are taking advantage of the possibilities to improve their efficiency of real timed supervision. Therefore the need to implement GPS and GSM has become an important part of their operation.
Before the system can be operational certain problems need to be addressed.
1) The system's data has to be in real time.
2) Interference has to be eliminated, such as mountains, tall buildings, other RFs, etc.
3) System alerts received when a vehicle is ahead of time or off route.
Global Positioning System satellites (GPS) and Global System for mobile (GSM) are used to determine precise location of a vehicle. GPS and GSM tracking are accomplished by a receiver collecting data from at least 4 satellites in order to determine precise position. The satellites reference the information from the tower closet to the GPS/GSM device attached to the vehicle.
Improvements in GSM software have allowed GPS/GSM to work together more efficiently. The software allows the transfer such as location, speed, engine idle, engine stop and start, and more (http://www.liveviewgps.com/gps+gsm+tracker+.html). Not only does the software handle the information stated it also gives alerts to different situations, such as speeding. Problem Statement
How do GPS/GSM over come latency and inference to accurately track vehicles in a timely manner. GPS/GSM use radio frequencies that propagate from satellites to towers on the earth's surface. As radio frequencies transverse their route they are subject to various obstacles, natural and manmade, that can weaken or block signals.
Depending on the region the communication is taking place fading or blocking of signals can be a big obstacle to overcome. To mitigate fading, uplinks and downlink transmitters are equipped with automatic power boosters to increase power as needed. To remove the issue of blockish, towers are erected in strategic locations, such as hills, mountains or tall buildings, to keep obstructions from blocking signals.
Fading and the blocking of signals correlate with timely accessing of vehicle's location/movements. If signals are not received in a timely manner then the receiving software cannot accurately report the time to supervision. Accurate timing is essential for operations of companies that rely on time for movement of stock and commuters.
To get more control of the movements of commercial or private vehicles businesses and people alike are turning to new technology. the technology is Global positioning system (GPS). With GPS a person can locate anything that has a monitor attached, whether it's a car, truck, bus, or a mobile phone. With the advent of GPS anything with a monitor can be located.
Companies who install this device are concern with the on time delivery of their deliverable. companies can keep their customers up to date, in real time, where their shipment are and how much time will lapse before they should arrive. GPS will enable them to be more competitive in their perspective field, because on time delivery is a requirement most customers appreciate.

In the public domain, GPS is used for personal reasons, such as, to keep track of loved ones, especially children. GPS is not meant to spy on children, just keep track of their whereabouts. People love their children, but they also love their property, such as automobiles. Let's say, If a car is stolen it would be easier to find because the GPS install would tell you exactly where the car is located.
GPS
Global Positioning System (GPS) and Global System for Mobile communication (GSM) are the systems that are used to keep track of equipped mobile products, such as cars, trucks, buses, PDA, phones, etc. Even though GPS and GSM sounds like a single system they are completely two separate systems and work quite differently. First let us take a look at what is involved in GPS.
Global Positioning System is a constellations of satellites that orbit the earth, controlled by the United States Air Force ("Control segment," 2009). The first launch took place in 1973, and since then more improved satellites have been sent into orbit. At the present time there are a total of 31 GPS satellites orbiting the earth. These satellites are monitored by control stations that are located around the world.
The GPS satellites orbit 11,000 nautical miles (12,656.8 miles or 20.373 km) above the earth and circles the earth at a speed of 3.9 km per second, as shown in Figure 1. The satellites have a circulation time of 12 h sidereal time, corresponding to 11 h 58 min earth time ("GPS Satellite", 2012). At any given time there are 4 satellites within signal range of any GPS receiver. Figure 1 GPS Satellites circling the Earth
GPS use two kinds of carrier signals, one is L1 with a frequencies 1575. 42 MHz with a wavelength of 19.05cm, and L2 with a frequencies 1227.60 MHz and a wavelength of 24.45cm. The radio signals travel at the speed of light (186,000 miles per second) and take approximately 6/100ths of a second to reach the earth (Cooksey). Frequency L1 is used for civil purpose, while L2 is used by Department of Defenses. The code that the satellite's carrier signals transmits is C/A code (coarse acquisition). This code is a 1023 “chip” long code, being transmitted with a frequency of 1.023 MHz. A “chip” is the same as a “bit”, and is described by the numbers “one” or “zero”(Transmitted GPS Signals) GSM
Global System of Mobile communication (GSM) is a wireless standard that was developed in Europe and used by 80 countries. GSM is Time Division Multiple Access (TDMA) digital system that transmits digital voice data in bursts during brief time slots allocated to multiple subscribers sharing a radio channel (Fitzgerald 524). GSM also use General Packet Radio Service (GPRS) to ensure guilty of service as the data travels through the network.

The GSM system has the following components, (Protocol tester)figure 2 shows these :
• Mobile Station (MS) - a handset or any enable device.
• Base Station (BS) - Controls the radio link to the MS.
• Base Station Transceiver (BST) - which is part of the BS.
• Base Station Controller (BSC) - also a part of the BS.
• Network Subsystem (NSS) - controls mobility management (MM) as a user moves as well as controlling connections to other fixed or mobile networks. (Massam,2010) Figure 2 Components of the GSM system

Now that GPS and GSM systems have been defined let understand how they work together. But before we show how they work together, it is important to understand how GPS gets a mobile's device location.

As mentioned above, at any given time there are 4 satellite in signal reach of a GPS mobile receiver. These satellites continuously send out signals in which a GPS receiver can locate the satellite's position. Knowing the location of satellites it can determine the distance, and with this information the GPS it can compute its location by using trilateration. With the satellite's signal the GPS receiver knows that its location is somewhere within the satellite's radius. Knowing just one location is not enough to know its exact position. To extract its exact location the GPS needs the other two satellite's signal. Once the signals are received, by three of the satellites, the intersection of all three spheres will result in a single point as shown in figure 3. Figure 3 Usually the receiver can discard one of the last two points because it is nowhere near the earth. So, we're left with one point which is the location of the GPS receiver (Cooksey). The fourth satellite signal is used for corrective measure.
Knowing the location doesn't explain how the system know the speed and time, on a continuous basis, of the mobile GPS device. A GPS satellite have on board an Atomic clock that keeps time and sends the with the signal the time the signal was transmitted.
The GPS receiver also has a clock, and once the signal is received the GPS receiver compares the time it sent a signal with the time of signal received. Once the GPS has the time and the distance travel then it can calculate the speed, the equation is distance/time = speed.
Now that the information needed has determine its has to be sent and displayed. To send data GPS receiver will relay on GSM. GSM modem sends continuous signals to the BTS. The signal that how the data transverse the GSM network until it reaches a data base in which time it will be stored until requested or the data will be displayed on a console or some other form of display device. To display a the data on a map there are downloads on the internet or you can use Google map.
ERRORS
Inference of signals can cause inaccuracy of location and time. Inaccuracy can be a structure in which the signal cannot pass through, such as tall buildings, mountains, and even a highway overpass, but is only none visible for a matter of seconds. GPS signals need a line of sight. Since this occurrence was foreseen GPS comes equipped with two methods of rectifying such incidences.
Errors can occur in the upper atmosphere due natural barriers. As the satellite's signal propagate through the ionosphere and the troposphere the velocity of the signal slows down. The sun can also have an effect on the signal, causing the signal to slow to half its speed. Again the GPS receiver compensate for these inaccuracies.

The methods are dead reckoning and map matching.
• Dead reckoning is a method of navigation, used commonly by ships and aircraft, in which the distance and direction traveled from a previous position are used to estimate the current position.
• Map matching compares the movement of the vehicle with the last known mapped position and maps of the area to determine the current position (What can inference).
These methods work well for a GPS receiver only going through these obstacles for a few seconds, but what about a device that transverses big cities, like New York City. It can take quite a few minute to pass all the tall building. To overcome this kind inference it will be advice, on the receiver side, to continue moving until the GPS can get a better reading. Because since satellite are constantly moving a better reading will appear.
Tall buildings present other inference than just blocking signals, multipath effect. Multipath effect happens when signals reflect off of objects and are delayed. This delay cause the GPS to be off a couple of meters, but just as in the city if your destination is further out it will not be problem, because the GPS will correct itself. GSM is a wireless system that propagates signal to a cell (tower). The data that is passed to the GSM modem by the GPS receiver is only as good if the Data reaches its intended target. If there is data lost (lost call) because of the cell does not accepting the subscriber transmit location will be lost and companies loss track of their vehicles. The three main issues, which cause lost calls for GSM, are
1. Coverage problems
2. Interference, both cochannel and adjacent channel.
3. Neighbor list problems (Smith,2003)
To solve these problem the engineer department responsible for the cells in the troubled area need to assess the situation. By analyzing reports, that are generated monthly, weekly or daily, the can pinpoint the cell that is causing the coverage problem.
The problem could be that the cell is not configured properly or their just may not be any coverage in the area. If the latter is the situation, this might be the opportunity to setup a new cell.
Conclusion
Tracking has become one of today's most sort after technology. Civilians and companies alike are placing GSP system on the vehicles, smart phones and other mobile devices. They are enjoying being able to pinpoint their items in real-time.
As GPS systems evolve to become every more accurate, despite the errors, people will continue to depend on the GPS system.