Industrial Wireless Technologies and their Applications for Protection Automation & Monitoring

Authors: Palak Parikh, Justin Smith, and Michael Pilon, GE Grid Solutions

Licensed Spectrum

This type of wireless technology requires a license from the government to operate in a given geographic area. In the United States, the government entity that grants licenses is the FCC (Federal Communications Commission). Different countries have different frequency bands available for licensed wireless operation. In North America, traditionally, there are frequency channels in portions of the 200, 400, and 900 MHz spectrum. Since these channels are spaced quite close together, this spectrum is often referred to as “licensed narrowband.” In the US, a commonly used narrowband frequency band is the 900 MHz Multiple Address Systems Band.

 Licensed Narrowband Channels are typically 12.5 kHz, 25.0 kHz, or 50.0 kHz wide, which offers data throughputs based on the modulation technique used (e.g. QPSK/QAM offer data throughput 2 to 6 times greater than FSK), in addition to advanced networking and security features.

The benefits of operating an industrial wireless network on a licensed wireless channel are:

  • No interference from other systems. Since permission to operate requires a license, no one else is operating equipment on the same frequency. This means that all bandwidth on the channel can be utilized privately
  • Greater transmit power. Since governments typically permit one licensed operator in a geographic area, the transmitter rules often allow for relatively high transmitter power. For example, 5-10 Watts is common. This is larger than for unlicensed bands, (Wi-Fi, Bluetooth, etc.) and means that the radio signals can propagate further

The high transmit power and good receiver sensitivities that accompany narrowband signals results in narrowband wireless signals that can propagate long distances and penetrate obstructions well. Because of that, licensed narrowband networks have typically been constructed in a point-to-multipoint fashion (hub-and-spoke) with the Master Station (Access Point) installed with its antenna at a great height, allowing these networks to be very large geographically.

For example, remote radios located 50 miles in all directions communicating with one master station is a common network model. In these types of systems, with remote locations that are hard to reach and located at a distance, it is important for the radio equipment to be rugged, reliable, and offer advanced diagnostics. Licensed wireless systems are often deployed with the remote devices communicating solely with the master station. Since the remote devices are at fixed locations, directional antennas can further improve the signal quality and allow for even more distant radio connections.

These directional antennas (which offer more signal gain than omnidirectional antennas) are typically mounted on poles and aimed at the master station. Geographically large wireless networks can be very economical solutions for monitoring remote power substations or industrial facilities. A network with a 50-mile radius, for example, covers 7800 total square miles. Contrast that to a typical 0.5 miles radius cellular system with a coverage area of 0.78 square miles - the licensed narrowband system is 10,000 times larger in this example. Now assume 400 to 500 remote devices can be monitored from this single master station. Since licensed wireless solutions are interference-free, the wireless channel can be dedicated to delivering data packets. Licensed narrowband systems, therefore, can provide very low latency even though their data throughput is also very low. For example, small-packet one-way latencies of under 15 ms are common. Figure 3 shows how a wireless network that supports different data speeds for different signal conditions (automatically), can more effectively use the radio spectrum and allow the network to support multiple applicatio

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