Mckay Williams ECE 5320 Mechatronics Assignment #1

 References  Motivation  Major Applications  Basic Working Principles  Reliability  Limitations

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 In the last decade, global positioning systems have gone from being the pinnacle of technology, with military only privileges, to common consumer owned electronics.  The incredible ability to pinpoint an object’s location within mere meters anywhere on the earths surface has profound effects on everything from warfare, to road trips, to a Saturday morning hike.

 Directional devices for consumer automobiles.  Hand held units for hiking, boating, etc.  GPS guided munitions.  Military command/control.

 Turn by turn directions from point A to B.  Mapping software determines level of functionality of turn by turn. Most modern software includes all highways and interstates, most residential paved roads, and even some dirt roads.  Newer WAAS enabled systems allow user to pinpoint location within 3 meters.  Battery powered, rechargeable through the cigarette lighter in the car.

 Include functions to guide user from waypoint to waypoint along a trail, or other pre- determined route.  Utility of systems depend on the mapping software which range from showing large rivers and lakes only, to high detail topographical maps.  Pinpoint location within 3 meters with WAAS enabled systems.  Generally powered by several AA batteries, that last hours in continual use.

 GPS guided munitions, know commonly as JDAMs(Joint Direct Attack Munitions) have made a huge impact in modern warfare.  JDAM munitions hit their targets within 13 meters. They are not limited by weather and sight like laser guided munitions.  It is possible to jam a JDAM, but they have built in back up guidance systems that are rated to 30 meter accuracy.

 The ability for commanders to know exactly where each of their units are has huge impact.  When friendly units know where each other are, friendly fire accidents are greatly decreased, and confidence soars.  This technology allows Air, Ground, and Naval forces to integrate, and pin point each other’s locations to work together synergistically.

 Global Positioning Systems communicate with 24 satellites that surround the earth in fixed orbits.  The GPS satellites emit time signals that are received by ground based GPS sensors. These times are then used to tell how far away each satellite is from the location.  The ground unit must receive the signals from 3 satellites to determine position, and 4 satellites to determine position and elevation.

 Once a GPS sensor has acquired the signals from 4 satellites, the microcomputer and software can then figure out position, elevation, speed, distance to target, time of arrival, etc.  Modern GPS sensors can communicate with satellites though dense forests, clouds, storms, and even inside some buildings.

 “GPS satellites transmit two low power radio signals, designated L1 and L2. Civilian GPS uses the L1 frequency of MHz in the UHF band. The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains.”

 “A GPS signal contains three different bits of information — a pseudorandom code, ephemeris data and almanac data. The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information. You can view this number on your Garmin GPS unit's satellite page, as it identifies which satellites it's receiving.”

 “Ephemeris data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits ephemeris data showing the orbital information for that satellite and for every other satellite in the system.”  “Almanac data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position.”

 Modern GPS systems provide reliable location estimates provided they can communicate effectively with at least 3 satellites.  The signals of these units can however be jammed in military applications.  Battery failure is the leading cause of unreliability among consumers.  The shooting down of GPS satellites in war to limit an enemy’s ability to command and control has been a hot issue lately.

 The quality of mapping software is still the biggest limitation to GPS navigation.  The accuracy of these devices is still limited to 3 meters in even the most advanced consumer versions.  A margin of error of 3 meters can severely effect the ability to use GPS to precisely calculate speed, direction, etc.  Electromagnetic interference (jamming) can make the technology obsolete.