WiFi’s evolving role in IoT
This vendor-written tech primer has been edited by Network World to eliminate product promotion, but readers should note it will likely favor the submitter’s approach.
Internet of Things applications have diverse connectivity requirements in terms of range, data throughput, energy efficiency and device cost. WiFi is often an obvious choice because in-building WiFi coverage is almost ubiquitous, but it is not always the appropriate choice. This article examines the role WiFi can play and two emerging IEEE standards, 802.11ah and 802.11ax.
Data transfer requirements for IoT vary from small, intermittent payloads like utility meters to large amounts of continuous data such as real-time video surveillance. Range requirements can span from very short distances for wearables to several kilometers for weather and agriculture applications.
One thing that is common is power constraint. IoT devices require constant connectivity, but they may not always have continuous access to a power source. IoT devices are expected to be power thrifty, sometimes to the extent of running on button cells for years at a stretch.
The following diagrams show the relation of throughput and power conservation requirements as compared to the range requirements.
Other dimensions that influence the use of IoT connectivity technologies include:
1. Cost of devices and supporting infrastructure
2. Ease of deployment, commissioning and management
3. Reliability and security.
IoT connectivity technologies
A number of standards based and proprietary last mile connectivity options have evolved to service IoT, and each has advantages and limitations. Below is a reference table of technologies available for IoT connectivity:
IoT connection options
Role of WiFi in IoT
WiFi, or 802.11, is a wireless protocol that was built with the intent of replacing Ethernet using wireless communication over unlicensed bands. Its goal was to provide off-the-shelf, easy to implement, easy to use short-range wireless connectivity with cross-vendor interoperability. With zero spectrum cost, there was little focus on spectral efficiency and with expected use by desktop devices, power efficiency was not critical.
WiFi is an obvious choice for IoT connectivity because in-building WiFi coverage is now almost ubiquitous, however it is not always the appropriate choice.
Pros and Cons of using standard 802.11a/b/g/n/ac for IoT
3. Spectrum congestion
Standard WiFi, while being the obvious choice for IoT, has limitations in both range and energy efficiency. The IEEE addressed these shortcomings by publishing specifications for 802.11ah and 802.11ax:
* WiFi HaLow (802.11ah): WiFi HaLow technology is based on the IEEE802.11ah standard ratified in October 2016. It was introduced specifically to address the range and power concerns of IoT. 802.11ah uses the 900 MHz ISM license-exempt band to provide extended range with low power requirements. Power use is further optimized by using predefined wake/doze periods and provides a reach of over a radius of one kilometer. It allows for station grouping to minimize contention and relay to extend the reach.
However, 802.11ah will require specialized wireless access points (or radios inside the APs) and client hardware. Even though the protocol was ratified in October 2016, there has been very little enthusiasm for WiFi HaLow from chip vendors.
* HEW (802.11ax). The upcoming High Efficiency Wireless (IEEE802.11ax) standard also adds a number of IoT friendly features. It retains the targeted wake time and station grouping features from 802.11ah to allow the clients to be power thrifty and avoid collisions. In addition, the uplink multi-user MIMO capabilities, coupled with the smaller (78.125 kHz) subcarrier spacing, allows up to 18 clients to send data simultaneously within a 40 MHz channel.
The adoption of 802.11ax in IoT will depend on the cost of the 802.11ax clients and how fast the clients and the APs hit the market.
Standard WiFi (based on 802.11a/b/g/n/ac) is often not the best technology for IoT, but certain IoT applications can leverage installed standard WiFi, especially for in-building or campus environments. Obvious cases include building and home automation and in-house energy management, where installed WiFi can be leveraged as the communication channel and the devices can be connected to electric outlets.
WiFi HaLow, based on 802.11ah, is designed specifically for IoT, however it requires separate (as compared to standard WiFi) infrastructure and specialized clients. High Efficiency Wireless (802.11ax) standard holds a lot of promise, but we have to wait until Fall of 2017 to see how the adoption of 802.11ax takes off.
WiFi vendors continue to make improvements for IoT and some are beginning to provision enterprise Access Points with IoT technologies (ZigBee, Bluetooth and/or Thread) built into the box.
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