Monday, July 30, 2012
Electrical engineers keep you connected
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From the RoundTable blog
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The Roanoke Times published an article on July 15 headlined "Indoor guidance systems for phones go beyond GPS." The article contained serious errors in its description of how GPS works.
The article claims that "GPS ... works by beaming a signal from your phone to a satellite in space. The satellite uses the signal to pinpoint your position then sends your location to your phone." Later, the article continues, "GPS [is] a notorious [power] hog that requires bouncing signals from the Earth to a satellite." This is complete nonsense.
GPS position-location systems require only a radio receiver, and the receiver's location is calculated by a microprocessor (computer) in a cellphone. A cellphone does not transmit to GPS satellites, and the GPS receiver in a cellphone requires little power. Cellphones use most of their power when transmitting, so the more calls you make the faster the battery will run down.
Because GPS is a broadcast system, everyone in the world can use a GPS receiver for navigation at the same time. There are 24 operational GPS satellites in orbit at an altitude of 20,000 kilometers. Four satellites are required to find the location of the GPS receiver. GPS was designed during the Cold War era to enable missiles to reach their targets with great accuracy.
Part of the GPS system was released for commercial use in the 1980s, but included selective availability, a system that reduced the location accuracy. That system was removed in May 2000, allowing commercial GPS receivers to achieve typical accuracy of 10 to 20 meters. With five GPS satellites and a system created by the Federal Aviation Administration called the wide area augmentation system, location accuracy of 2 meters is obtainable. WAAS is used by aircraft to land at any airport in bad weather and eventually will be used to land aircraft automatically in zero visibility.
GPS is one example of the many contributions made by electrical engineers to modern society, along with radio, television, radar, computers, the Internet, satellite television broadcasting, audio and video recordings and many other systems that most people take for granted. Journalists frequently ascribe these new systems to "scientists"; however, they are the inventions of electrical engineers working with a new generation of radio systems, commonly referred to as wireless. There has been explosive growth in wireless devices in the last 20 years with the introduction of cellphones, wireless connection to the Internet and GPS navigation systems.
Traditionally, each new radio system that included a transmitter was allocated a license to use a specific frequency band by the Federal Communications Commission. This led to poor utilization of the radio frequency spectrum, a limited resource that must be shared by all wireless users. Cellphones, Wi-Fi devices and most other modern wireless devices use a microprocessor to decide which frequency to use and when to transmit, allowing many users to share a single frequency band.
The 100 million cellphones in the United States share a frequency band that previously had only a small number of licensed users.
The next challenge for wireless engineers is to find more ways to share the radio spectrum so that Wi-Fi speed can be increased and new wireless systems developed. This is an active area of research in the Wireless@VT group at Virginia Tech and many other universities throughout the world, along with indoor position location to supplement GPS.
Electrical engineering is regarded by many students entering university as one of the most difficult subjects, as it demands an ability to apply mathematics to the analysis of complex systems, creativity in the design of electrical circuits and software and good communication skills. Students who are successful and graduate with a BSEE degree have excellent job prospects and some of the highest starting salaries, and can look forward to an exciting career designing and developing new wireless devices. So next time you meet an electrical or computer engineer, remember to say thank you for all of the electronic devices you use every day.