The role of Wi-Fi in the Internet of Things

When to use a star network.

Photo: Robo56This article is part of a series exploring the role of networking in the Internet of Things.

In my previous post we evaluated a point-to-point networking technology, specifically Bluetooth, to determine its applicability to our building monitoring and energy application. In this post, we will evaluate the use of a star networking technology to meet our application needs.

A star network consists of one central hub that establishes a point-to-point network connection with all other nodes in the network (e.g. sensor nodes). This central hub acts as a common connection point for all nodes in the network. All peripheral nodes may therefore communicate with all others by transmitting to, and receiving from, the central hub only.

Today, Wi-Fi is by far the most commonly used wireless star topology. It is deployed widely throughout many environments, providing near ubiquitous internet access in facilities such as schools, campuses, office buildings, lodging, residential homes and so on. The term Wi-Fi is not a standard, but a term trademarked by The Wi-Fi Alliance and covering a number of IEEE 802.11 standards along with details of implementation.

As in past posts, let’s take a closer look at the technology and evaluate WI-Fi’s capabilities against the nine key application attributes that characterized our building monitoring and energy management application.

Range

Wi-Fi networks have limited range. A typical Wi-Fi access point will have an approximate range of 120 ft (32 m) indoors and 300 ft (95 m) outdoors. The range is limited to the point-to-point transmission range of the Wi-Fi router, also called the Wi-Fi access point. If wider Wi-Fi coverage is needed, more access points will need to be installed.

Power Consumption

Wi-Fi has fairly high power consumption compared to some other standards. Technologies such as Bluetooth (reviewed in my last post) provide a much shorter propagation range (up to 10m for Bluetooth) and so in general have lower power consumption.

Reliability

In general, Wi-Fi provides a high degree of interference immunity. In some cases, Wi-Fi connections can be disrupted or the Internet speed lowered by having numerous other devices in the same area. This type of interference would not be a problem for the low-data rates needed for our building energy management application.

Scalability and Flexibility

Theoretically, one Wi-Fi access point can handle up to 255 connected devices. Performance is a function of total network traffic. In practice, most deployed Wi-Fi access point will support up to 10-15 devices. More devices can be supported by deploying multiple access points through an environment.

Bandwidth

802.11a and 802.11g support bandwidths up to 54Mbps. 802.11n will support over 100Mbps. This bandwidth is ideal for data-intensive applications such as surfing the web, and streaming audio and video.

Interoperability

Wi-Fi is the most widely used wireless technology fueled by the universal interoperability of the technology. Over 5 billion Wi-Fi-enabled devices having now been shipped worldwide. The Wi-Fi Alliance manages the certification requirements to insure certain standards of interoperability.

Component Availability

WI-Fi chipsets and modules are widely available from dozens of vendors, such as Qualcomm, Broadcom, Marvell and Texas Instruments.

Cost

A good example of the financial effectiveness of Wi-Fi is the TI CC3000, described as a “self-contained Wi-Fi network processor”, a completely integrated solution with TCP/IP stack included. This chip costs about $10 in quantities of 1,000.

In the exploding Internet-of-Things, Wi-Fi is a fundamental, ubiquitous wireless technology that is utilized in a myriad of IoT applications and devices. Wi-Fi connectivity is shipped with almost all smart phones, tablets, laptops, and countless devices, making it a widely utilized link within the chain of connectivity—from thing-to-Internet and then Internet-to-mobile-device-to-person. From residential smart thermostats, to fitness devices, to health monitoring, to security applications, Wi-Fi’s ubiquity has been a fundamental enabling factor in fueling the rapid growth of the Internet-of-Things.

However, there are several characteristics of the technology which make it questionable for our building monitoring and energy management application. The technology is designed to support high-bandwidth applications, quite different from our low-bandwidth energy management application. Because of this, the technology has a relatively high power consumption, limiting the use of battery-powered devices over long periods of time. Note that in the applications mentioned earlier, where Wi-Fi shines, power can be wired to the device (e.g. a thermostat) or periodic battery recharging acceptable (e.g. a smart phone).

A second concern is the range limit of a Wi-Fi access point. The network is limited to the transmission range of the router, about 120ft indoors. For a wider range of coverage, multiple access points will need to be installed throughout the environment.

In my next post we will explore the attributes of mesh networks, including Zigbee and Z-Wave, and consider each technology’s applicability for our building monitoring and energy management application.

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