Navigating the Wireless World
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 Global Positioning System (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 toward 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 (Ultra High Frequency);
- 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 (Ultra High Frequency) 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 WirelessConsidered 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 wide-area GPS reference station networks.
Tuning In to RadioRadio started as a wireless telegraph at the turn of the 20th century for point-to-point links where regular telegraph lines couldn't be used. Radio use exploded with the ability to broadcast messages simultaneously to multiple locations, first using telegraphic code, later in full audio.
Today, surveyors commonly use both UHF and spread spectrum radios for wireless communication. UHF radios with frequency assignments in the 400-800 MHz RF band offer higher power and increased range than spread-spectrum radios. In most countries including the United States, UHF radio users must obtain a license for the frequency they use in their area.
Spread spectrum radios operate in three RF bands: 902-928 MHz, 2.4 GHz and 5.7 GHz. Spread spectrum radios using these frequency bands don't require licensing. They also offer lower power consumption and higher communication rates but shorter range than UHF radios. Rather than using a fixed channel, spread spectrum signals 'hop' over a wide range of frequencies. The sending and receiving radios change frequencies in unison, creating reliable communications over a spread of frequencies.
And Then Came CellularAlthough a relative newcomer to the wireless world, cell phone technology has already gone through four generations, each with increasing speeds and capabilities. And there's more to come. The first generation, known as 1G, was analog cellular or Advanced Mobile Phone System (AMPS) technology deployed in the 1980s.
The next phase was 2G, which brought digital technology for voice communication to the mobile phone system in the 1990s and continues to be used today. Both analog and digital networks can use one of several standards: GSM (Global System for Mobile Communication), CDMA (Code-Division Multiple Access) and TDMA (Time-Division Multiple Access).
Following 2G came 2.5G technology, which surfaced in the late 1990s and enabled users to transfer data via a wireless network, using packet-switched technology (see sidebar). The 2.5G iteration of GSM is General Packet Radio Service (GPRS) and of CDMA is CDMA2000 1xRTT. This 2.5G technology makes it possible for users to access the Internet via cell phones. The upcoming 3G technology, which is currently in test markets and slowly being mainstreamed, offers even higher data rates; 3G is expected to make larger office datasets more accessible to the field through the wireless Internet.
Wireless Meets BluetoothIn the last two years Bluetooth technology has gained popularity, enabling automatic short-range wireless connections between digital components. A cutting-edge open standard, Bluetooth uses the ISM RF band for worldwide compatibility, enabling wireless data transfer between devices within a 10 m (33 ft) range.
Bluetooth devices are miniature, short-range radio transceivers. More than just a radio solution, Bluetooth enables devices to find each other and communicate without user intervention. When two Bluetooth devices come within range, they automatically detect each other and "converse" to find out if they are configured to communicate with each other. If they are, they establish a 'piconet' or PAN (personal area network). Within seconds they are able to transfer data at high speed using a network protocol--without a cable. The PAN can include only two devices; it can also be a network similar to a local area network (LAN) of office computers but on a smaller, "personal" scale. And because Bluetooth uses spread spectrum frequency hopping technology, it is possible for a variety of Bluetooth devices with different piconets to be within range of each other and not interfere.
All this is good news for surveyors. Surveyors can choose from a variety of wireless communication methods, depending on the applications and area. Whether using optical or GPS equipment, surveyors can make use of the benefits of radio, cellular and Bluetooth technology, making data transfer quicker, easier, more cost-effective--and potentially cable-free. Let's look at how surveying equipment got there.
Surveying Goes WirelessIn the 1990s, optical surveying equipment began utilizing wireless radio technology to enable different components of a surveying system to communicate with each other. The world's first one-person surveying system, introduced in 1990, included a real-time wireless data communication link between the robotic surveying instrument and the rod. This first data communication link used a radio modem, which enabled the surveyor to control both the instrument and data collection from the rod.
In 1993, the marriage of GPS and a radio data communication link took place in the development of the world's first Real-Time Kinematic (RTK) GPS surveying system. RTK ushered in an enormous leap in surveying productivity, enabling surveyors to achieve centimeter accuracy in the field and eliminating the need for post-processing the GPS data. RTK uses a real-time data communications link for sending GPS data corrections; data from a base station can be accessed by the rover through a wireless radio data link. While revolutionary at the time, the initial systems still required up to six cables to connect the components that comprised the GPS rover.
By 1997, cables required for RTK GPS solutions were reduced to one. The first all-on-the-pole RTK solution included an integrated GPS receiver, GPS antenna and UHF radio modem; one cable linked the instrument and the data collector. With advances in wireless and surveying technology, equipment moved closer to becoming completely cable-free.
As cellular infrastructure has expanded worldwide and costs have decreased, cell phones are replacing conventional radio as the wireless mode of choice for many surveyors. Smaller in size and weight than radio modems, cell phones are able to transmit data over longer distances, as long as the user is within the cellular network area. Cellular technology also enables surveyors to use cell phones to connect to the Internet. And cell phones don't have the licensing and channel requirements of conventional radio.
Bluetooth technology was introduced for surveying components in 2002, enabling surveyors to operate an all-on-the-pole solution to receive RTK corrections using cellular technology--and with literally no cables. These advanced RTK rovers include an integrated GPS receiver, antenna, battery and Bluetooth wireless technology. Not only is cable snagging in the field eliminated, but users can also remotely control an instrument from up to 30 ft away. Bluetooth also allows users to share data in the field with other surveyors while carrying on their surveying tasks from the GPS receiver. And because Bluetooth can wirelessly connect users to cell phones, surveyors are able to wirelessly connect with the Internet to send and receive data files from the office or access surveying data websites.
Creating a Networked Surveying WorldThe benefits of wireless technology for the surveyor can best be seen in the growing GPS infrastructure being built throughout the world. These reference station networks can access the capabilities of every wireless mode, including GPS, radio, cellular and Bluetooth, to provide surveyors with a wide array of surveying options. GPS reference station networks allow surveyors using RTK GPS rovers to access RTK corrections without investing in a base station, which decreases their GPS equipment investment. With the addition of advanced software, the networking capabilities expand even further.
With conventional RTK, the farther users get from a base station the more susceptible they become to reduced accuracy and performance due to ionospheric and tropospheric factors (commonly called the PPM error). With a network of GPS reference stations and software that provides a fully modeled solution, users connect into the system using a wireless connection. The software acknowledges the users' field positions, allowing them to operate as though there is a reference station--a virtual reference station--right next to their rover. As a result, the PPM error is eliminated or significantly reduced, enabling surveyors to work at long distances from the physical reference stations. Trimble's name for this solution is VRS (Virtual Reference Station), which enables users to achieve RTK accuracies over much greater distances with fewer reference stations. Users can also retrieve stored GPS correction data from a control center via the Internet for post-processing.
Some GPS reference station networks use cellular packet-switched technology, which enables GPS network administrators to provide RTK corrections through the Internet as well as supply built-in access, authentication and accounting to know and manage who is accessing their system and how often. Users then access RTK correction data in the field via a cell phone connected to a GPS rover. And Internet protocol means users don't need to be in radio broadcast range like they do with a conventional RTK radio transmitter.
In the future, wide-area GPS reference station networks could become like cellular networks as the infrastructure for providing RTK surveying capabilities wherever a surveyor is. Imagine a time when surveyors could pick up their all-in-one rover enabled with Bluetooth technology, go anywhere and connect to an RTK reference network and the Internet through a cell phone: no cables, no extra base station. Set up and go, anywhere they are.
Today's wireless world differs significantly from that surveyors knew even a few decades ago. Yet the capabilities available through wireless communication provide surveyors with solid benefits: increased efficiency, enhanced productivity and increased profitability. For the surveyor the new wireless world opens new avenues of unlimited possibilities and, potentially, uninterrupted surveying. What's not to like?