Wireless Communication Options: Part 2

[Joel_Weder]

License-Free Solutions
Wireless products in the ISM bands (Industrial, Scientific and Medical) at 915 MHz, 2.45 GHz and 5.8 GHz do not require the acquisition of a government license for operation. Configuration of these units has generally been kept relatively straightforward, for quicker commissioning, and for wireless customers who may not have a strong technical support team available.

Most manufacturers of license-free radios have over time added greater data rates, up to 1 Mbps or even more in some cases. This has been accomplished primarily through the use of wider channels, though also through development of some new technologies. Innovation in modulation types does not seem to have had the same impact here as in the licensed space. This may be due, at least in part, to a perceived saturation of spectrum in RF-dense areas. However, this type of radio remains very popular today as a result of lower hardware and installation costs, as well as the avoidance of licensing fees.

The focus on improvements in license-free wireless for SCADA and telemetry instead has been on the addition of "value-added features." Among the most popular features are built-in (or add-on) I/O and increased processor capability. A more powerful microprocessor allows high-level applications to be loaded into some radio models. These will be discussed further in a later blog post.

Significant activity, however, is happening in the wider license-free bands. These include 5.8 GHz, 24 GHz and others even higher in the microwave spectrum, where bandwidth is plentiful. Channel data rates commonly far exceed 1 Mbps in these regions, rising to as much as 1 Gbps. Concerns do arise, however, about the ability of devices operating in these frequency bands to overcome distance and obstructions. Also, many such devices are not intended for Point to Multipoint operations, which is commonly required in the SCADA market.

Some very low-cost wireless models are being made available, which are basically consumer grade devices. It may be difficult for some end users to choose another option when such cheap devices exist. Some opt for the very lowest cost hardware possible, as long as the provided data rate is acceptable. They may however not have much understanding of the trade-offs which exist. These include reduced hardware reliability, reduced range and inability to handle interference or the presence of obstructions.

With the ever-increasing number of wireless spectrum users, and the growing demand for bandwidth, manufacturers continue to grow their product offerings to include new features, as well as moving ever upwards in frequency. There are multiple bands, both licensed and license-free, available in the spectrum above 1 GHz, though this varies somewhat by country and region.

The use of higher frequencies introduces challenges caused by greater free space and obstruction losses, and so in some cases (eg long range and/or heavily obstructed paths) options must be explored in the VHF and UHF ranges as well. The narrow-band licensed options, as discussed in Part 1 of this series, should always be considered where possible.

High Data Rate Solutions
There is much demand for wireless transport of very high data rate network traffic, and this will only increase over time. This may include traffic such as provision of connectivity to a large data concentrator site, synchronization between primary and backup servers, security camera video from vulnerable critical sites, very data-intensive or latency-sensitive industrial applications, Voice-over-Internet (VoIP), and provision of network access at remote locations.

Licensed narrow-band radios and even the faster frequency-hopping devices are not able to transport full-bandwidth video, though some of the fastest radios may carry one or two streams of highly-compressed low frame-rate video along with normal SCADA traffic. However, when using the higher frequency bands, such as 2.4 or 5.8 GHz, there is much more spectrum available. Some wireless devices take advantage of this, by using much wider channels than is usual for SCADA and telemetry purposes. Depending on channel width and the technology used, it may be possible to transport multiple full HD video streams simultaneously, at the same time as other types of traffic.

While transport of video is one commonly-requested application, there is also significant demand for general network connectivity over significant distances. This may be offered either within license-free ISM bands, or in licensed bands above 1 GHz. Several manufacturers offer point-to-point and multipoint systems which can carry any mix of network traffic at high data rates. Data rates on point-to-multipoint systems may reach 80 Mbps or more, while dedicated point-to-point microwave links may reach 1 Gbps or more. These systems require tall towers to avoid obstructions on longer paths, and typically require some sort of tower on even short paths. 

Schneider Electric partners with Redline Communications for applications which require these very high data rates over medium-to-long distances. Redline provides both wireless hardware and engineering/installation/maintenance services. Their products primarily operate in licensed and license-free bands above 1 GHz, and can operate at speeds of 80 Mbps or more.

Some vendors offer solutions for data rates approaching the speeds made available with hard-wired LAN connections. These wireless models tend to be much more expensive, however, and require very tall towers and dish antennas to cover significant distances.