A look at how wireless technology affects surveyors
Tuning In to Radio
Radio 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 US, 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 Cellular
Although 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.
Why Packet-Switched?
Until the late 1990s, all telecommunication networks primarily used circuit-switched technology. That means each call creates one path, or circuit, which reserves a channel between two parties for the call's duration. Today, packet-switching is becoming the standard for data communication, providing a more cost-effective method to send data using cellular technology. With packet-switching, each call sends its data 'packets' on any circuit available, reassembling them in order at the destination. Packets from other calls also use these circuits, maximizing the use of available bandwidth. CDPD (Cellular Digital Packet Data), GPRS, CDMA2000, Bluetooth (described below) and 3G technology all use packet-switching.