GPSS (Global Positioning Satellite System)

2 What is GPSS 24 satellites operating in a low-earth orbit, each transmitting a direct-sequence signal with a center frequency of 1575 MHz. A person, using a handheld receiver, can determine his/her position (x,y,z) to an accuracy of 25 meters or less, if he/she can track at least 4 satellites (receiving their data satisfactorily). He/she can also determine the speed and direction of the movement.

3 How does GPSS work The receiver measures the differences of the transmission times of the data of various satellites to the receiver. Those time differences are then converted into differences of distances between satellites and the receiver. If four satellites can be tracked by the receiver, it can calculate three differential distances (delays). The receiver can then estimate its position (see example below). If more than four satellites can be tracked, the additional information can be used to improve the estimate.

4 All satellites broadcast data regarding their position and the time at a rate of 50 bps. Each bit is 20 ms. The messages are sent in frames, each taking 30 seconds to transmit 1500 bits. The first 6 seconds of every frame contains data describing the satellite clock and its relationship to GPS time. The next 12 seconds contain the ephemeris data, giving the satellite's own precise orbit. The time needed to acquire the ephemeris is becoming a significant element of the delay to first position fix, because, as the hardware becomes more capable, the time to lock onto the satellite signals shrinks, but the ephemeris data requires 30 seconds (worst case) before it is received, due to the low data transmission rate.

5 Two precision modes Depending on the accuracy, two modes are available:  Standard Positioning Service (SPS)  Precise Positioning Service (PPS) SPS uses a coarse acquisition (C/A) code of 1023 chips at a rate of Megachips/s to spread the data. Each sequence (1023 chips) takes 1 ms. PPS uses Megachips/s to achieve higher precision. Each satellite uses its own code, which is known to the receiver. the PPS code (used by the military) is encrypted by the Y-code to produce the P(Y) code, which can only be decrypted by units with a valid decryption key.

6 Example Assume receiver’s location is The two satellites’ locations are The differences of times for radio signals to travel from the two satellites to the receiver is related to the locations (c is the speed of light):

7 Calculate the position Since there are three coordinates, x, y, and z for a position, we need three such equations to determine the position of the receiver. Therefore four satellites have to be tracked by the receiver to obtain three equations and to calculate its position.

8 Other systems in the world Galileo (EU joined by China, Israel, India, Morocco, Saudi Arabia, South Korea, and Ukraine): 30 satellites will be launched. Services of different qualities (the lowest being free) will be provided. Fully operational in 2012 (?). GLONASS (Russia) joined by India. Sixteen satellites are in operation (eventually a total of 24 is needed). Beidou Navigation System (China): four satellites launched. Eventually 35 satellites will be launched. Free service has an accuracy of 10 meters. India and Japan are also developing their own systems.

9 Telematics—Tracking Trucks Times are tough in trucking. Operating margins are low, driver turnover is high, and fuel costs are through the roof. The expenses associated with truck idling are high. As long-haul drivers rest in their cabs or operate onboard appliances such as microwave ovens and TVs, often they leave the engine running. According to a 2002 study by the Environmental Protection Agency, long-duration truck idling consumes about 960 million gallons of diesel fuel annually.

10 Introducing Telematics To rein in expenses, a growing number of trucking companies is investing in so-called telematics, a combination of computing, wireless data, and global positioning system (GPS). The idea behind telematics is to help fleet operators run their businesses more efficiently. The U.S. market for commercial vehicle telematics was $942 million in 2005, and is expected to rise to $2.13 billion by the end of 2010, growing annually at almost 20%.

11 Benefits of Telematics Increase driver productivity, Give dispatchers better information on driver location and helping them better assign routes Improve security Advance customer service Generate reports automatically

12 Improve Driver’s Productivity Save time and fuel: Telematics continuously monitors the truck's location, mileage, and speed, as well as other performance and diagnostic data, which businesses can access through a Web portal. One report says the system saves customers on average one hour per driver each day and that it reduces fuel costs by about 10% to 15%.

13 Increase Security Dow Chemical integrates radio frequency identification (RFID) and GPS tracking technology on trucks and rail cars Installs "smart boxes" that contain sensors for light, humidity, temperature, and shock Identifies whether shipments were tampered with or dropped

14 Generate Automatic Reports Helps compliance with state and federal reporting requirements Interstate drivers have to follow strict rules for so-called fuel tax reconciliation. These require them to keep tabs on where they purchased fuel, how much they spent, and how many miles they drove in each state Truckers also need to record the number of hours they work to comply with federal regulations.

15 Critics Critics among drivers and union representatives who consider it invasive