9 things to consider before deploying sensors

Defining application requirements for IoT networking standards.

This article is part of a series exploring the role of networking in the Internet of Things.

Each networking technology has very different attributes and capabilities. When evaluating protocols and standards for your IoT project, you’ll need to understand all of the technical and financial requirements underlying your application in order to effectively choose a technology to implement. Let’s take a look at the typical networking requirements in designing solutions for the Internet of Things.

To provide a concrete illustration of the requirements analysis, I will describe a hypothetical building energy management application and outline a comprehensive list of its wireless network requirements. This list of requirements will form a framework for future discussion of the networking technology standards currently on the market.

Here’s our hypothetical application: a building owner wishes to analyze, monitor, and optimize energy usage throughout their portfolio of medium-sized commercial buildings. To accomplish this, many more monitoring and control points need to be deployed throughout each building, including occupancy and temperature sensors. Sensor data will be aggregated back to a central building automation “panel” located in each building. A continuous collection of such data will provide a higher resolution of temperature and occupancy information, rendering better insight into HVAC performance and building utilization patterns. It will also allow for the comparison of each building’s energy utilization throughout the portfolio, allowing lower performing buildings to be flagged.

I have designed and implemented networked systems similar to the application described above. This example was chosen to show a degree of network complexity that goes beyond a short-range, point-to-point device connection, such as a Bluetooth-enabled earpiece linked to a mobile phone. Broad-range, low-data-rate applications sit on the opposite end of the application spectrum from the bandwidth-hungry audio and video-streaming applications that are so common today. In device (“thing”) networking, attributes such as data rates measured in bytes instead of megabytes will be important to understand and increasingly common as IoT networks are increasingly deployed.

To select an appropriate networking technology, the following networking requirements are considered.

The wireless network needs to span the building layout in buildings up to 200,000 square feet in size. This is the maximum size of the building within the portfolio. Given this size, the range from the farthest sensor to the building’s panel could be up to 1,000 feet. The technology selected for the application needs to support the transmission of sensor data and return control data to a distance of at least 1,000 feet.
Power consumption
One of the primary design goals of this network is the ability to operate with very low power consumption. Wireless products such as sensors, thermostats, and repeaters will be required to run off battery power for a minimum of one year without battery replacement. Two-month low-battery signal should be transmitted to the panel.
Because the sensor network will be used for control purposes (building control), the networking architecture and the RF technology should be designed for very high, mission-critical reliability and network uptime. Redundancy and resiliency should be integral to the networking architecture and/or built into the networking system where possible, so as to maximize network uptime and minimize single points of failure.
The wireless network will be deployed, in many cases, throughout an entire building. In larger facilities, the network will need to scale to hundreds of points (nodes) consisting of temperature and occupancy sensors, and thermostats.
Bandwidth/data rate
Each thermostat is polled two to three times per minute. Message size is 5-8 bytes. Combining these requirements reveals that the wireless sensor network needs to support a data rate of 20 Kbps; there are no streaming data or bulk data transfer requirements. Network latency, or overhead, should be minimal. Message latency from sensor/thermostat to controller, or controller to thermostat, should be less than one second.
The building portfolio is made up of a variety of building sizes and types, constructed with different materials, and containing a high degree of variation in the building’s interior space. The wireless network may be required to transmit data packets through, or route data packets around, potential RF obstacles, such as thick concrete walls. In some cases, interior layout of the buildings may have been modified in a variety of ways, resulting in the need for a wireless network to have a high degree of flexibility and adaptability to existing or changing building environments.

Once installed, the interior space may, in some cases, be reconfigured or remodeled with impacts on the RF environment. In these cases, the technology chosen should be able to be rapidly reconfigured to the new building layout and RF environment.

The networking technology and protocol should be based on an open standard to enable future interoperability with third-party devices. The open standard should be controlled by an outside, independent, open governing body.
Component/technology availability
The networking technology selected should be proven in the market, have a well-established installed base, and be clearly positioned to grow in the building-control market. This will also help ensure multi-vendor interoperability, as a broad range of solution providers utilize what may be developing as a de facto wireless standard for the building industry.
Selected networking technology needs to be available at a reasonably low cost, relative to other networking options on the market. The technology selected should be in production use in high volume to drive economies of scale, yielding the lowest possible run-rate production component cost.

A broader IoT solution may encompass a mix of networking technologies, each chosen to best address the specific device-to-device communication challenge at hand. Sensor data may aggregate to a gateway and then be analyzed in the cloud, transmitted to a cell phone, and communicated through an earpiece. In this case, three different network topologies would be utilized, each with very different bandwidth, range, scalability, and power requirements.

Isolating and correctly characterizing the network requirements for each link in this solution chain may, in the end, be the difference between enhancing value and future growth of your solution, or limiting its utility in the market.

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