Wireless plant and backhaul in the industrial environment

Invensys technical paper highlights the potential of the emerging WiMAX  standard in applications requiring greater performance across longer distances, and improved security:

London - Wireless technology makes it possible to incorporate new strategic measurements and other data within solutions that simply were either not practical or even possible to implement in a wired communications environment This includes solutions for process optimization, device management, real-time equipment condition monitoring, energy management, personnel tracking, asset tracking, security, and enterprise asset management that can all work in unison to address both industrial asset utilization and availability.

Many plants have existing applications that use either fibre or copper cables as the communication medium. There are some limitations to a wired infrastructure such as this, especially in the plant environment. New applications many times require upgraded cabling, and expansion to existing applications may require additional cabling.

Along with the cabling itself, there are many associated costs with this kind of infrastructure. In order to expand a cable plant, costly engineering studies need to be performed so that wiring locations and paths can be determined. Depending on the age and condition of the existing environment, there may be some issues that need to be remediated with the addition of cabling.

Asbestos, for example, may exist behind walls which are to house cabling. Also, trenching may be required to run new cabling. The environment inherently has some issues that need to be taken into consideration, such as excessive heat, magnetic fields, and other characteristics of a plant environment.

To alleviate these concerns, wireless networking has been investigated in the plant environment. Wireless networks provide the connectivity required by the existing and new applications, but also allow for some additional benefits. Deploying a wireless network for a particular application allows access even in places where it is impossible to run cables.

Wireless networks can be designed to be self-healing, and redundant so that single points of failure in the network are virtually eliminated. Roaming can be configured so that a mobile worker can traverse the entire plant and never lose connectivity to a centrally managed application. As in the case of wired networking deployments, an engineering, or site survey, study will need to be performed in order to determine the most efficient placement of wireless networking devices, but these studies are usually considerably less expensive than those of the wired variety.

The advantages of wireless networking are many, and include the following:

- More mobile workforce

- More efficient and less expensive asset tracking

- Eliminating wires leads to cost savings

- New applications are easily deployed and result in bottom line improvements

Types of Wireless Networking

There are many wireless protocols and technologies to choose from. In order to take full advantage of the wireless network, a site survey is recommended determine the best technologies to use and the placement of the related devices. A properly designed and deployed wireless network is fully expandable and has a ROI of a very short term. The next few sections describe the existing wireless technologies.

Wi-Fi (802.11a/b/g)

The catchall term “Wi-Fi” refers to the protocols contained in the 802.11a, b, and g standards, which are wireless technologies typically deployed in the home, office, and plant environment.

802.11b and 802.11g utilize the same wireless frequency range (2.4GHz), but offer different speeds. 802.11g is significantly faster, provides data rate of 54 Mbps, while 802.11b provides 11 Mbps. From a distance perspective, wi-fi can be classified into indoor and fixed outdoor wireless.

We can achive distances up to 25Kms with fixed outdoor wireless using either 2.4 or 5Ghz frequency by choosing a high gain antenna (provided there is line of sight), In indoor applications it offers a distance up to 300 feet, however the interior building materials provide enough of a signal reduction to lower the distance to 100 to 150 feet between devices.

The major drawback for these protocols is that there are a number of other devices, such as cordless telephones and microwave ovens that also utilize the 2.4 GHz band. That said, a properly conducted site survey will determine these points of contention and make sure that they are alleviated in the final design and deployment.

802.11a, on the other hand, utilizes the 5 GHz band and provides speeds up to 54 Mbps. The advantage of using this protocol is that there are so few devices utilizing the 5 GHz band, interference or signal contention is virtually eliminated. Also, whereas 802.11b and 802.11g are compatible with each other 802.11a is not compatible with either, so once again, there are few devices competing for this frequency.

Security within Wi-Fi

One of the concerns of administrators related to wireless networking is the issue of security. There are many security options (like WEP, WPA, WPA2, Radius Authentication) to address these issues. Encryption can be used to secure links so that the communications cannot be eavesdropped. Furthermore, access technologies can be implemented so that rogue users cannot connect to the network.

In addition to Wi-Fi networking, other application-specific wireless technologies can be deployed. These include wireless sensor networking (WSN) and radio frequency identification (RFID). The following sections illustrate these technologies.

WSN

Wireless sensor networking utilizes a technology designed from the IEEE 802.15.4 standard. This standard depicts a self-sensing, self-healing network of devices that can report sensor information back to a centralized management station. These devices can be deployed in a number of topologies, however the most efficient method is to deploy these devices in a mesh. The following diagram illustrates a mesh wireless sensor network reporting back to a central management station.

The devices on the left portion of the diagram represent the sensors enabled with wireless. These devices are configured in a mesh topology. Each device can route traffic back to the gateway, so that even if one device is not directly connected to the gateway, it can still send its information back. Furthermore, the network is self-healing. In short, if one of the wireless sensor devices fails, the network will correct itself to bypass the faulty device.

RFID

RFID can be used for asset tracking, for personnel tracking, and for information storage. The technology revolves around tags that are placed on devices and used for the purpose of tracking. A simple example is shown below:

The RFID tag is scanned by a wireless device and information about the inventory can be uploaded to a data base and used to track the piece. This is an example of a passive RFID tag. On the contrary, an active RFID tag has a small power source and can provide more services, have the ability to store information in the tag itself, and provide a greater distance from which the tags can be read (60 meters indoor/200 meters outdoors). An example of an active RFID tag is below:

Active RFID tags provide real time location services. This example is equipped with a battery which last over 4 years, is ATEX certified, intrinsically safe and features a call button for emergency services. This device is well suited for safety applications and asset tracking of expensive or critical equipment and products.

The Plant /Site Communications Environment

The challenges for developing and maintaining a wireless infrastructure in a plant are numerous. As noted above WiFi can provide a high speed wireless infrastructure to enable various plant applications. However, an emerging standard called WiMAX (Worldwide Interoperability for Microwave Access) provides greater performance across longer distances, and improved security.

IEEE 802.16a standardization focused on fixed broadband access. IEEE 802.16-2004 enhanced the standard by providing support for indoor CPE. The IEEE 802.16e standard is an extension to the approved IEEE 802.16-2004 standard. The purpose of 802.16e (also known as IEEE 802.16e-2005) is to add data mobility to the current standard, which is designed mainly for fixed operation

The most significant benefits of WiMAX in an industrial environment include:

Near-Line-of-Sight - WiMAX uses highly efficient frequency-multiplexing techniques to obtain a clear signal through multi-path reflection. This allows a subscriber unit (receiving station), obstructed from line-of-sight of a base station, to maintain a connection by “reassembling” the reflections and echoes from surrounding structures.

The ubiquity of radio frequency-reflective surfaces in an industrial environment can make wireless signal acquisition and tuning extremely challenging. WiMAX provides relief by being very forgiving in such conditions while allowing subscribers in places where other backhaul technologies would be unable to reach, or prohibitively expensive to implement.

Frequency-agile – WiMAX generally uses higher frequency bands for transmission. These frequency band is much wider than the 2.4GHz band used by WiFi. This provides a wider selection of sub-frequencies, or channels, to choose from when configuring access points.

The WiMAX Forum has begun the process of certifying initial fixed and stationary equipment in the 3.5 and 5.8 GHz bands. The WiMAX Forum is working with service providers and equipment manufacturers to expand the frequency allocation to cover all the key spectrum bands. For mobile applications, initial profiles have been developed for 2.3, 2.5, and 3.5 GHz.

As wireless networking technologies see increased use in industry, commerce and consumer applications, the risks of unwanted interference increases. WiMAX provides the ability to widely separate channels for different subscribers, and allows a “wide berth” for reconfiguration when external interference is detected.

Furthermore, WiMAX allows channel width to be user-selectable, allowing multiple subscribers near each other to function efficiently without interference, or for multiple channels to be dedicated to specific users or applications at one remote location.

Integral Quality-of-Service (QoS) – Quality-of-Service is built-in to the WiMAX standard. With multiple applications sharing the same bandwidth, it becomes important to prioritize traffic according to business needs. Although QoS is available as a vendor-added layer in WiFi, the out-of-the-box QoS in WiMAX can be configured based on application, packet characteristics or subscriber identity.

When control data, safety- or environmentally-critical monitoring, and delay-sensitive applications such as video or voice traffic share a transmission path, smooth and efficient sharing of the network path is essential. Unlike WiFi’s multiple-access access design, in which subscribers contend with each other for access, WiMAX uses a grant-request scheme that reduces re-transmissions and the overhead associated with sorting out and backing off competing subscribers.

Security - Security has been built into the product set for WiMAX. WiMAX security supports two quality encryptions standards, that of the DES3 and AES, which is considered leading edge. The standard defines a dedicated security processor onboard the base station.. There are also minimum encryption requirements for the traffic and for end to end authentication. Advanced Encryption Standard (AES), a block cipher that was ratified as a standard by National Institute of Standards and Technology of the United States (NIST),

For offshore-onshore communications WiMAX provides a rich set of features that offer better coverage, security, and aggregate speed compared to today’s WiFi technology.

A WiMAX “bubble” can be used to aggregate the various wireless applications that are feasible in a plant facility. This high speed wireless network can provide increased speed, security and reliability far greater than WiFi mesh networks can achieve.

Offshore Platform Communication

For a number of years oil and gas industries have faced the dilemma of identifying the best medium to facilitate communications from an offshore platform to shore and from shore to offshore platform.

Industry has, throughout the evolution of technology struggled to find a generic solution to this conundrum, a solution that fits all. It is unlikely they will succeed as there are a number of variables that have to be taken into consideration and when planning or designing a communications infrastructure for this type of connectivity.

Those variables include: geographic location of the platform, signal reflection, humidity, temperature and barometric pressure, changes in sea levels and ionospheric conditions.

Historically offshore platforms, academic bodies, defence consortiums and many others have tested a number of technologies in an effort to find the most ideal communications link between off-shore assets and onshore stations. The following is an overview of current communications mediums/spectrums.

Very Low Frequency (VLF) – this is not considered a practical solution due to the required antenna length and power. This is an ideal spectrum from communications with submersibles and is in fact used for communicating with submarines.

High Frequency (HF) – This is a feasible option and ideal for long distances but there are issues such as arcing, power requirements and it is not possible to achieve sustained communications on one frequency. A suitable frequency will depend on weather, time of day and ionospheric conditions to name but a few. HF signals rely on the ionosphere to bounce back to earth. As the ionosphere is not a constant, frequencies have to be changed to meet the changes in the ionosphere, usually high frequencies in the day-time and low frequencies at night.

Very High Frequency (VHF) and Ultra High Frequency (UHF) are used extensively by offshore platforms for communicating with seaborne vessels, helicopters and indeed between neighbouring platforms. Again, though it might be possible to achieve reliable communications in these spectrums, between the platform and shore, the distance between the two would have to be line-of-sight (LOS) and again weather will play its part in reliability.

VHF & UHF signals are easily blocked by obstructions such as high buildings, hills, mechanical structures and even trees. Ducting can also occur causing signals to travel great distances, this is where the signal gets caught in a type of thermal and bounces along its length or occasionally the E-layer of the ionosphere cause the signals to bounce back.

Microwave – a more expensive solution but a reliable one in the right conditions. If the distance between the transmitting platform and the receiver is suitable, then microwave offers a wide bandwidth, low latency and is generally reliable.

Troposcatter – a popular choice for communications in areas where climate is unpredictable and temperatures extreme. Communication is achieved by bouncing a signal off the troposphere. As long as there is reasonably accurate receiving station location information, the angle of transmission is easily calculated. The signal bounces off the troposphere and spreads thereby covering a wide area. Troposcatter is not the ultimate answer either as it suffers from echo which can have detrimental effects on reception.

Satellite and Very Small Aperture Terminals (VSAT) – Many parts of the industry has turned to this type of equipment in order to achieve a reliable communications link, but these tend to be more expensive, the latter less so. These solutions tend to be used to achieve communications over great distances. Reliability cannot be sustained as retention of a channel can be intermittent and still suffer from climatic conditions and subsequent latency.

Optical Fibre – Many offshore platforms have utilised Optical Fibre for connectivity to shore. This is an expensive option and utilisation is based on distance, however it is reliable and provides almost unlimited bandwidth.

With the advent of 802.x wireless technologies, industry is enthusiastic and very keen to adopt them, in the hope that it will put to rest the problems experienced for many years. These technologies offer security, reliability and very low cost in comparison to traditional communication methods. However, the same problems exist with the new technology: climate; obstructions; power limitations etc.

A number of offshore platforms have been able to exploit 802.x technologies to a significant gain.

IEEE 802.11 WIFI (Wireless Fidelity) – this is probably the most popular of the 802 technologies and widely adopted worldwide. WiFi is an inexpensive solution for the creation of local networks. WiFi offers scalability at very little cost, bandwidth similar to cable and connectivity to mobile units. WiFi is ideal for asset tracking as the network can be extended to cover all points of egress easily and at very low cost.

WiFi is not a feasible solution for the offshore-shore environment.

IEEE 802.16 WiMAX (Worldwide Interoperability for Microwave Access), officially known as WirelessMAN.

WiMAX is suitable for the following potential applications: [1]

• Connecting WiFi hotspots with each other and to other parts of the Internet.
• Providing a wireless alternative to cable and DSL for last mile (last km) broadband access.
• Providing high-speed mobile data and telecommunications services.
• Providing a diverse source of Internet connectivity as part of a business continuity plan. That is, if a business has a fixed and a wireless internet connection, especially from unrelated providers, they are less likely to be affected by the same service outage.
• Providing Nomadic connectivity.

Depending on installation and environment WiMAX offers either high bandwidth or long distance, but not both simultaneously. Distances of 50km and speeds of 75Mbps are feasible but not together. The number of active users will also reduce the bandwidth. WiMAX does not require the nodes to be in line of site of each other and is a feasible solution in the right conditions.

Scenario:

Lets imagine an offshore oil field that has five platforms within line-of-sight of each other. It would be feasible to use WiFi for on platform communication, asset tracking etc. WiMAX would be a suitable medium for communications between the platforms, thus allowing them to share data and reduce the number of backhaul facilities required. Instead of each platform requiring a microwave system, we could reduce this to just two platforms, one primary and the other secondary thereby providing resilience.

WiMAX in this environment would offer wide bandwidth at a low cost, with reliability and scalability. The backhaul element would still be dictated by geographical location of both the platform and ground station, as well as weather, ionospheric conditions etc.