Advances and current changes in cellular telemetry
Recent advances in cellular technology are offering more efficient and reliable wireless transmission of data between remote locations and the central collection points.
Wireless telephone technology has been around in various forms since the 1940’s. Stevens was the first company to introduce telephone telemetry technology for remote water monitoring with the Telemark in 1939. In 1969, Bell Systems demonstrated the first automatic cellular switching system. Bell installed a computer-switched 450 MHz cellular radiotelephone system along the tracks for the Metroliner train that ran between Boston and Washington, DC. All the payphones on the train used the system. Full time commercial cellular service began in 1983 in Chicago.
Today, most of the world uses GSM (Global System for Mobile communications) and/or one variant or another of CDMA (Code Division Multiple Access) technology, both digital cell phone standards. In recent years, the main drive in cellular technology advancement has been in the area of increased bandwidth for data services. The latest EVDO (EVolution Data Optimized) enabled systems are capable of data rates near 3.8 Mb/s, which rivals some hardwired cable and DSL installation.
As current technology advances, older technologies are now being phased out. On February 18, 2008, the US Federal Communications Commission will no longer require US cellular carriers to support Advance Mobile Phone Systems (AMPS). AMPS is the analog cellular system standard developed and introduced by Bell Labs in 1983. While the change in rules does not require cellular carriers to end AMPS support, it is expected that most, if not all, carriers will shut it off shortly after the rules change. This means that any system still using AMPS analog technology may very soon become inoperable.
In environmental monitoring applications, modern digital cellular data modems have been developed that allow quick and easy installation and ease of use. It is very common now for cellular modems to be assigned with individual TCP/IP addresses so that they can be access over the Internet. This capability allows tremendous flexibility in the design and implementation of monitoring and SCADA applications.
For instance, the Airlink Raven cell modem provided by Stevens is capable of operation on all global cellular systems, operates securely with static or dynamic TCP/IP addressing, and is capable of sending SMS messages and e-mail automatically in the event of an alarm. Interface to other equipment is through a simple serial cable.
When deciding whether cellular data communications should be part of a data collection system, knowing some of the advantages and disadvantages of such a system is helpful.
Some advantages of cellular data modems are easy integration into new and existing systems, including SCADA and robust support for machine protocols such as ModBus. Cellular modems also draw less power than many other telemetry solutions. However, a monthly data plan from a cellular carrier must be purchased to use the system and some very rural areas may not be properly covered.