survey and infrastructure segment manager,
americas region, trimble, usa
GPS Infrastructure Applications Engineer
GPS Infrastructure Systems Manager
Wireless? Cable-free? Cellular? Bluetooth? What is all this? How does it impact the surveyor? And how can a surveyor be prepared for the wireless world? Travel with us to a world without cables and judge for yourself. You may never return to cables, cords and bulky equipment again
Today, cables attached to surveying (and other) equipment are fast becoming a thing of the past. Like other technological advances, cable-free capabilities offer benefits for surveyors including fewer complications, less fuss, and greater efficiency and productivity on the job. Now, a surveyor can take a GPS surveying unit in the field with virtually no cables connecting the receiver and data controller. GPS rovers can receive data from a GPS reference station over long distances using a cell phone and no cables. And leading infrastructure technology now allows surveyors to increase that distance while significantly reducing the RTK GPS surveyor’s classical worst enemy: the PPM (parts per million) error. It’s a new wireless world-and surveyors are embracing it.
How Did We Get Here?
From drums and smoke signals, to telegraph and telephone, to today’s Internet and wireless communication networks, humans have steadily developed ways to communicate over distances. Today, a growing number of wireless communication technologies add the advantages of mobility to the benefits of wired networks. Radio, walkie-talkie, cellular mobile telephony, Personal Communication Services (PCS) and the increasingly used wireless specification Bluetooth technology, all continue the march towards more efficient communication without the limitations of wires or cables. Wireless communication uses a variety of radio frequencies (RF): AM radios use the MF (Medium Frequency) band (530-1700 kHz); FM radios operate on the VHF (Very High Frequency) band (88-108 MHz); Most surveying radios are in the 400-800 MHz band of the UHF; Spread spectrum radios use three bands: the 902-928 MHz, 2.4 GHz – the globally available Industrial, Scientific and Medical Devices (ISM) band, and 5.7 GHz; Cellular phones operate in the 800 MHz and PCS in the 1900 MHz areas of the UHF band. Trade-offs exist between the benefits and limitations among frequency bands. Today, lower frequencies provide better range for effective data communication than do higher frequencies but may be more susceptible to interference due to higher user density. Higher frequency bands accommodate larger channel bandwidth, which supports higher data rates, but can only be used over a shorter range.
GPS is Wireless
Considered a broadcast radio-navigation satellite service, GPS gained strong support from surveyors early on. The first GPS satellites were launched in 1978; today’s constellation boasts 28 satellites. Each satellite sends out two radio signals, known as L1 and L2, that travel some 20,200 km (approximately 12,600 miles) through space to Earth. These signals contain pseudo-random codes enabling GPS receivers to simultaneously track several different signals and perform calculations that provide precise positioning information anywhere on Earth at any time.
Current GPS signals operate on the 1575.42 MHz (L1) and 1227.6 MHz (L2) RF bands. The Department of Defense’s (DOD’s) GPS Modernization Program will introduce two new civilian signals and frequencies in the near future. The L2C signal, scheduled to be available within the next 12 months, will broadcast at a higher power level than L2; the new L5, slated to be available in 2006, will use the 1176.45 MHz band and provide a higher power level than the other signals.
GPS is perhaps the ultimate wireless technology for surveyors, providing accuracy and application opportunities unimaginable even two decades ago. In fact, many of the more ‘earth-bound’ wireless technologies are used with the space-based GPS to offer surveying solutions that range from one-person surveying to area-wide GPS reference station networks.