How cellular technology will transform remote monitoring systems

Conventionally, remote unmanned facility monitoring systems were constrained by the limitations of the long-range communication interfaces available to the system integrators. The advent of advanced cellular communications technology has freed system integrators from these limitations and unleashed new potential in remote monitoring systems.

Traditional long-haul communications interfaces were traditionally serial-based and used a polling architecture. Simply receiving I/O data over the air was a formidable challenge, because wireless communications imposes a long response time. When the system covers a wide area, polling these remote stations takes even longer and data will often be lost.

The limited amount of bandwidth, or data throughput, available using older technology also imposed significant limitations on remote monitoring systems. Often, throughput is so low that the application can only deliver alarm point data acquisition. Instead of transmitting all the serial and analog data from the remote site, on-site intelligence was used to process this data and condense it into simple alarm points that are sent to the central monitoring site.

Figure 1: A system with too many data acquisition layers is costly and time-consuming to deploy and maintain.

The advent of advanced cellular communications technology has freed system integrators from these limitations and unleashed new potential in remote monitoring systems. This white paper explores how system integrators can close the performance gap between cellular and wired communications even further so that cellular networks can deliver advanced, bandwidth-heavy features such as live video at the central monitoring station.

IP-based cellular technology grows up

The beauty of cellular technology is that it is an IP-based technology. The vast majority of field monitoring devices are now IP-enabled, so it is possible to get all the data from field devices over a cellular network. But simply using IP-based communication media alone is not enough to create an ideal remote monitoring system. Bandwidth and latency are also important.

Fortunately, cellular technology has seen dramatic recent advances in performance. The transition from 2.5G GPRS technology to 3.5G HSDPA technology has unlocked substantial improvements in bandwidth and network latency (see the breakout box for definitions of current cellular data technology). Now, cellular uplink bandwidth can reach 384 kbps and downlink bandwidth can reach as high as 7.2 Mbps. Cellular latency has also been improved dramatically, now reaching as low as 100 ms. The bottom line is that cellular performance now exceeds most of the other long-range communications technologies available today.

Active data transmission optimises bandwidth usage and avoids communication time-outs

Cellular technology is clearly at the head of the pack when it comes to long-range wireless communications, but it obviously still cannot compare to hard-wired LAN or WAN communications technologies. Most ethernet devices are designed to communicate over LAN or high-speed WAN networks with more bandwidth and response times well under 100 ms. This disparity creates some potential problems when deploying ethernet devices on cellular networks. One such problem is data communication time-outs.

Field devices, ethernet-based and serial-based alike, often use remote polling to acquire data. Polling, however, needs to take communication time-outs into account. A device with a communication time-out value that is set to accommodate LAN communication speeds will face communication time-out issues when it is deployed in a cellular network. Repeated communication time-outs will simply crash the system and often incur additional fees for each reconnection attempt.

Active data reports are the solution to this problem. By replacing constant data polling with active reports, the system can overcome communications time-outs. With active reporting, the central monitoring server does not need to constantly interrogate field devices for data. Instead, the central server can just wait for incoming data. This not only reduces bandwidth usage, but also makes real-time alarms possible. Most importantly, with active reporting it is possible to dynamically adjust communications margins to accommodate the network’s time-out tolerance and prevent time-outs from occurring at all.

Streamlined data acquisition layers reduce maintenance costs

Traditional polling data acquisition and alarm systems often require multiple data acquisition layers. This multilayer architecture is designed to spread the system load and shorten the polling cycle. However, multilayer systems also need a lot of equipment on each layer, making them difficult to manage. In such a large system, a problem that occurs at one node will be time-consuming to locate and troubleshoot. Also, a large multilayer system is often cobbled together by different system integrators, each using different equipment and different protocols. Protocol unification alone can cause enough problems to cripple the entire system.

The development of cellular data acquisition and alarm systems that use active reporting technology has made it possible to eliminate data acquisition layers. Because cellular networks are IP-based, they have essentially no distance limitations compared to traditional radio or microwave communication interfaces. This reduces the number of communication relay nodes required. Since the system uses the communication infrastructure already built by the cellular provider, there are almost no infrastructure costs. What’s more, the cellular network’s bandwidth is significantly wider than RF and less vulnerable to outside interference, so fewer data acquisition relay points are required.

Adding video to the remote monitoring system

Long-distance video surveillance has long been an elusive goal for remote monitoring systems. With limited bandwidth, conventional remote monitoring systems could only rely on I/O data to get alarms from the field sites. Now, cellular communications has made it possible to transmit live images from a remote location to the central monitoring station.

Sufficient uplink bandwidth is key for video monitoring systems. In terms of uplink bandwidth, HSUPA is a cellular technology that exceeds even HSDPA with up to 5.8 Mbps of uplink bandwidth. But despite its technical merits, HSUPA applications are still uncommon and the cost of using HSUPA is high. In addition, the HSUPA service is still unavailable in many countries due to a lack of public demand, which makes it a less attractive choice for remote monitoring systems.

In order to use the more modest uplink bandwidth of HSDPA for video monitoring, system integrators need more expertise in optimising video technology and data communications. Bandwidth usage can be a real challenge, especially when video is combined with I/O alarms.

Figure 2: Remote video surveillance is a challenge for cellular networks, but can be achieved by using the right tools.

Moxa is developing a new technology that will optimise video remote monitoring in HSDPA. The idea is that by automatically detecting cellular bandwidth availability, the video device can dynamically adjust its frame rate to meet the current bandwidth restrictions. By sacrificing the video frame rate, the network can avoid the problems of network congestion, such as:

1. Video communication time-outs and time wasted on reconnecting to the host (which is also likely to result in a much lower frame rate and lower image quality).
2. Loss of UDP image packets causing no images to be received at all.
3. Traffic congestion preventing I/O data from getting through.

These developments when combined with existing technology that supports more efficient use of video will give SCADA users better options for their remote monitoring system.

One of these existing technologies is an OPC-based middleware layer that can overcome the problem of dynamic IP addresses used in cellular communications versus traditional LAN-based IP surveillance systems that cannot use them. Applications such as Moxa’s Active OPC Server provide a workaround for this problem by rerouting video streaming to the central host, and allowing users to use any type of IP-enabled SIM card.

Software is now also available that allows video images to be pushed from the OPC middleware server directly to, and integrated with, the SCADA system. Rather than having the video surveillance system separate from the SCADA system, with the accompanying need to maintain two separate systems, software such as Moxa’s Video Gadget video data can be used to display video images directly in the SCADA system.

Conclusion

With the advent of cellular communications, remote monitoring systems are changing. Simply put, remote monitoring systems can do more and cost less than before thanks to IP-based cellular technology. Their system complexity can be reduced by eliminating data acquisition layers, which reduces management and maintenance costs. Video functionality can be added. Even greater advances will be possible as 4G cellular technology is rolled out and more and more devices migrate to IP-based solutions. The future is bright for remote monitoring systems.

Definitions GSM - Global System for Mobile communications (GSM) is a digital technology used for mobile voice and data services up to 9.6 kbps. GPRS - General Packet Radio Service (GPRS) is an enhancement of GSM that provides a wireless data service with throughput rates of up to 40 kbps. It is also referred to (retrospectively) as ‘2G’. 2.5G/EDGE - Enhanced Data rates for GSM Evolution (EDGE) provides up to three times the data capacity of GPRS and can be overlaid on existing GSM networks. It is also known as ‘2.5G’. 3G/WCDMA/UMTS - Third Generation/Wideband Code Division Multiple Access (WCDMA) is also known as the Universal Mobile Telecommunication System (UMTS) and is a newer technology not backward compatible with previous 2G and 2.5G technologies - in other words, providers needed to deploy new infrastructure to provide it. It was developed by the 3rd Generation Partnership Project (3GPP) and provides voice and data services up to 384 kbps. 3.5G/HSPA - High-Speed Packet Access (HSPA) is a family of protocols that allows networks based on UMTS to have higher data transfer speeds and capacity, and can often be achieved by software upgrades to an existing 3G UMTS network. HSDPA - High-Speed Downlink Packet Access (HSDPA) is part of the HSPA family of protocols that provides theoretical downlink speeds of up to 14 Mbps. HSUPA - High-Speed Uplink Packet Access (HSUPA) (3GPP Release 6) is part of the HSPA family of protocols that provides theoretical uplink speeds of up to 5.8 Mbps. HSPA+ - Evolved HSPA (HSPA+), otherwise known as 3GPP Release 7 and 8, uses multiple input, multiple output (MIMO) technologies and higher order modulation to achieve possible downlink speeds of up to 84 Mbps and uplink speeds of up to 22 Mbps. Please note: For all of the above technologies, the data rates quoted are theoretical maximums and the actual data rates that can be practically achieved depend on a number of factors, not least of which are the design of the end device (your modem/phone/router) and the capacity of the network you are using. For example, currently the fastest HSDPA-compatible devices that are available can manage only up to 7.2 Mbps downlink (rather than 14 Mbps), and then only provided the carrier supports it in your area of deployment.

By Daniel Liu, Business Development Manager, Moxa Inc