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Going the Distance: How Range Affects IoT Design

Mike Justice, Founder and President
Grid Connect

When it comes to designing products for the burgeoning Internet of Things (IoT) market, there are many development options. Designers must consider choices for hardware and software, Internet connection method and device power, to name a few. When making these decisions, there is one factor that will influence all these choices: distance.

The network range required for IoT devices plays a surprisingly important role even in the smallest design decisions. After all, the transmission of data is at the core of IoT devices. Transmission range depends on the type of network used, the environment it will be used in, and the types of data being communicated.

Consider the following questions:

  • Will the device be used inside one building or between buildings?
  • Will the device need to transmit data through walls or floors?
  • Is transmission impacted by buildings or trees?
  • Will the device connect to a nearby existing network or to a cellular network miles away?
  • Will the device send short bursts of information, such as text messages, or longer information, such as video or files?

Grid Connect-MNetwork
Once you understand your transmission range and communication needs, determine which network technology works best. There are a number of network connection standards being used to connect devices to the Internet, each with its own pros and cons. These can be grouped into higher frequency and lower frequency networks.

Generally, higher frequency network technologies are higher performing, but may not be able to handle difficult environments, such as thick walls or communicating between buildings. Their range of network is limited to about 100 meters. Examples of higher frequency network technologies include Wi-Fi, Bluetooth, ZigBee and Thread.

Wi-Fi is a local area wireless technology that is great for sending large amounts of data wirelessly between devices. Bluetooth operates over shorter distances than Wi-Fi and allows you to pair devices like phones and computers together. ZigBee and Thread are designed for mesh networks, allowing devices to send data along a network, with each device capable of relaying the data toward its destination. Thread is an evolution of ZigBee, and can support a network of up to 250 connected devices.

Lower frequency networks, such as cellular and 900 MHz, can transmit data over greater distances (miles) and are capable of penetrating walls, but performance is diminished.
The easiest devices to connect will use Wi-Fi, Ethernet, cellular or Bluetooth. Wi-Fi and Ethernet are ubiquitous in most homes and businesses and Bluetooth taps into the existing cellular network via smart phones and tablets. Unlike ZigBee and Z-Wave, none require the addition of hardware or gateways to convert the network to either Ethernet or Wi-Fi, which adds cost and one more potential point of failure.

Grid Connect-BTopology
There are three topologies used in IoT networking: point-to-point, star and mesh networks. Network distance plays a role in each of these.

Just like it sounds, a point-to-point network establishes a direct connection between two network nodes, and communication takes place only between the two devices making the connection. Point-to-point networks are easy to use, but the range is limited by this single connection. Bluetooth is an example of this type of connection.

A star network consists of one hub or gateway, which acts as a common connection for other nodes on the network. Devices can communicate with each other by transmitting through the gateway. Star networks deliver fast and consistent transmission, but the transmission range is limited to the distance between a device and the gateway. Wi-Fi is an example of a star network.

A mesh network combines a gateway with sensors and router nodes, which can relay and transmit data to other nodes. Data can pass through multiple sensors/routers to reach the gateway node. Mesh networks can cover a larger area and can scale to thousands of nodes. The network is reliable and self-healing, reducing the chance that the network will fail. By nature, mesh networks are more complex than point-to-point and star networks. ZigBee, Z-Wave and Thread are examples of mesh networks.

Power
Finally, distance will determine the power requirements of devices. Generally, the higher the frequency, the more power is required.

Using a wall outlet (AC) is the most convenient and reliable method of powering IoT devices. Using AC power, designers of IoT devices have their choice of network and topography without restriction. However, one of the benefits of IoT devices is the ability to untether them. If the device cannot be powered by AC, the application, power needs, battery type and network power demands must be factored into the selection.

Consider the application of the device. If the device needs to be “on” constantly, a traditional battery won’t work because it will drain quickly. However, many connected products, such as motion or water sensors, are able to sleep and wake, reducing power consumption and enabling the device to be battery powered.

Some networks are more power efficient than others. Mesh network technologies are designed to conserve power by hibernating and quickly waking only when data needs to be transmitted. Star and point-to-point networks, on the other hand, generally have higher power demands.

Once a designer understands how long and how often a device will be connected and which wireless network is chosen, a proper size and type of battery can be selected. Among the batteries to consider is alkaline, lithium (rechargeable) and coin. There also are a variety of battery sizes from which to choose.

Another source of power for Ethernet-based devices is Power-over-Ethernet (PoE). This technology is popular for low-wattage IP phones and security cameras. Recent advancements and new switching technology are pushing the wattage available through PoE to new levels, thus opening up new possibilities for more power-hungry applications and devices.

Four Guiding Principles
For all of these design decisions, there are four guiding principles to ensure an IoT product that works:

  • Understand your application. Knowing how the IoT device will be used is core to making good design decisions. The application will drive decisions about the type of network and power that’s required.
  • Keep it simple. Networks can become complicated and there may be hidden requirements. For example, most designers feel that using cellular as a communications network will be the simplest; however, certifications are needed for each provider. This complicates the design process. On the other hand, Wi-Fi is ubiquitous and most consumers understand how to use it.
  • Look for points of failure. These points include using the wrong network or power source for the device application. Also, adding gateways and hubs to the network creates additional possible points of failure.
  • Finally, distance does matter. The range of the network impacts everything from which transmission technology you choose to how you will power your IOT device. Select the network that best meets the needs of your product application.

Mike Justice is founder and president of Grid Connect, a rapidly-growing manufacturer and distributor of networking products and wireless sensors. Grid Connect Inc. is an ISO 9001:2008 company and has been a leader in the embedded and networking marketplace for more than 20 years. For more information please visit www.gridconnect.com.

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