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Demystifying Wireless Communications

by Jason Block | 7月 27, 2020

 

 

Why Consider Wireless

Currently, wireless technologies are used in a relatively small (6%) but continuously growing share of industrial communication applications based on 2019 data, as shown in Figure 1.

 

industrial network report 2020

Image 1: Industrial Networks Report 2020 HMS Networks

 

One of the key drivers is the increasing use of automated mobile equipment in manufacturing facilities. Where workers on forklifts once delivered components to production cells or fixed position conveyors moved product through the assembly process, these tasks are increasingly being performed by Automated Guided Vehicles (AGVs) controlled by software applications connected over wireless networks, most commonly based on 802.11 standards, but likely to be impacted in the future by 5G cellular communications. The flexibility of wireless communications allows for much faster redeployment of vehicles versus those on fixed-track systems.

 

Additionally, there is an increasing need to move machine visualization beyond the traditional fixed machine HMI. Implementing on-machine wireless connectivity allows mobile platforms such as tablets and smartphones to be used to visualize machine data from almost anywhere. This also enables safe service of equipment by maintenance personnel, who can now update controller and HMI programs comfortably outside of the control cabinet and beyond the safety guarding.

 

There are additional use cases where wireless technology makes sense, but it is important to consider several factors before implementing. Depending on technology, the performances of these networks in specific environments may vary.

 

 

Understanding Short-Range Wireless Technology and Usage Considerations

For factory automation, wireless technologies are typically deployed on shorter range networks below 500 meters of effective range. This is a result of the smaller physical footprint of the factory itself and easier access to the Ethernet backhaul that links machines to software applications.

 

The most commonly used technology for wireless connectivity in factory automation is based on the IEEE 802.11x set of standards commonly known as Wi-Fi™. These networks transmit at publicly available frequencies within either the 2.4 GHz or 5 GHz space and are sliced into channels usually 20 MHz or 40 MHz wide (adjacent channels bonded). These channels are essentially the pipes that data can pass through and the width of these channels significantly impacts throughput in the system. Over time, the IEEE 802.11x specification has evolved to incorporate changes in areas such as radio modulation, wider spatial streams (up to 160 MHz) and antenna structure (MIMO) to improve overall system throughput and reliability. Updated standards such as 802.11n and 802.11ac can realize typical networks speeds of several hundred bits per second. With 802.11 wireless, once you move above the radio as the physical layer, the lower protocol layers used are the same as 802.3 Ethernet which makes integration of the networks simple.

 

Other common technologies in the short-range space include Bluetooth, Bluetooth Low Energy and 802.15.4-based standards, such as Zigbee. These technologies exist within the same 2.4 GHz spectrum as 802.11 standards but use narrower channels resulting in slower data rates than 802.11. The benefit with many of these lower data rate standards is that they require less power which makes them optimal for battery-powered devices such as wireless sensors and mobile computing platforms. Since the lower layers of these protocols are not based on the TCP/IP stack, protocols need to be built into the higher layers to make them adaptable to Ethernet networks (ex. Bluetooth Network Encapsulation Protocol).

 

There are a several factors that affect the performance of wireless networks. Regarding 802.11, the theoretical limitation of a single IP-based subnetwork segment is 255 devices, but the practical limitation is significantly fewer devices. This is due to there being a limited number of channels available and those channel resources can be consumed by multiple networks. As the number of devices increase, smaller slices of bandwidth are available for each device to pass data through which can impact performance of the overall system. Additionally, the 2.4 GHz spectrum is shared by a lot of different transmitting devices (ex. microwave ovens, cordless handsets) creating significant noise that can lead to retries and lost packets. Bluetooth mitigates this some by using Adaptive Frequency Hopping where the network re-calibrates its channel hopping sequence when interference is detected.

 

With wireless communications, there will always be free-space loss of energy, but obstructions can compound this loss and reduce the effective range of these networks. All these factors need to be accounted for when deploying short range wireless networks.

 

 

Understanding Long-Range Wireless Technology and Usage Considerations

There are numerous automation applications where short-range networks cannot meet the need. This is particularly true for remote assets such as oil and gas wellheads, pumping stations for potable water and lift stations for wastewater where wireless is the only possible means for communication. In these cases, the assets are located several kilometers away from the point of data collection, so long-range wireless networks are needed.

 

Long-range networks normally function at lower frequencies within the wireless spectrum as lower frequency signals experience free-space loss at a lower rate than higher frequency signals. The most common non-cellular frequency used for remote wireless applications is 900 MHz which given enough runway to propagate and enough radio power can travel several kilometers before repeaters are needed. 900 MHz signals are also capable of transmitting more easily through structures, such as trees, which makes this good for outdoor applications, though the limits are not infinite. Line of sight still needs to be maintained between transceivers so repeaters will need to be placed more frequently in areas with hilly terrain. New technologies in the 900 MHz spectrum, such as LoRa and SigFox, have evolved to address the need for long-range low bandwidth, low payload and low energy consumption communications for wireless sensors. The greatest challenge with these technologies involves correct site planning and deployment of infrastructure as public infrastructure is not readily available.

 

Cellular networks can also be used for long-range communication, though they are not intrinsically long-range since many support frequencies significantly higher than 900 MHz. For example, the evolving 5G standard for cellular communications will use short-range millimeter-wave frequencies as part of its supported spectrum, which is about 100 times higher than 900 MHz. The benefit to these higher frequencies is significantly improved throughput for high data payload applications. Cellular networks accomplish long-range communications through a network of overlapping cells that can transmit data to each other before eventually connecting to a network backhaul. For wireless sensor communications, cellular networks have begun supporting Low-Power WAN (LPWAN) standards such as NB IoT and CAT M1 on 4G LTE networks and eventually mMTC (Massive Machine-Type Communications) on 5G. Like 900 MHZ, these technologies use sub 1 GHz frequencies for transmission of data. The benefits to using cellular are significant with the main challenges being existence of public infrastructure in some very remote installations and interference from structures when using the higher frequencies.

 

 

Best Practices When Using Wireless

Effectively using wireless communications comes down to understanding the use case and limitations for the technology. In cases where one is looking to deploy private networks either inside a facility or for remote applications, conducting a site survey is a highly recommended practice and can help understand potential challenges before installation and help determine where radios need to be installed to ensure success.

 

For troubleshooting wireless applications, spectrum analyzers can be a very useful tool to determine the presence of secondary networks in the same spectrum space and the presence of noise from other wireless transmitters.

 

In summary, there is a lot to be gained from using wireless but planning for and being aware of the challenges will be key. Learn more about HMS Networks Wireless offerings in the link below and contact us for more information:

 

 

Learn more here

 

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