Bluetooth 5: Mesh Networking
Greater Range, and Ability to Coexist Offer Potential for IoT and IIoT Applications
When the 2,822-page standard for Bluetooth 5 was released by the Bluetooth Special Interest Group (SIG) last December, it was obvious that the SIG’s intentions were to make the technology better suited for IoT applications. True to that goal, the SIG formally added mesh networking capability to the spec in July 2017, which has the potential to make Bluetooth 5 a strong contender for long-range wireless communications, particular in IoT and IIoT. To see why mesh capability is so important, it’s necessary to view it in context with the other improvements — greater range, faster data transfer, and ability to coexist with other technologies — that Bluetooth 5 provides.
Understanding Mesh Networking
Bluetooth is a star-type topology (Figure 1a) in which all devices are connected to a central hub. As the devices cannot themselves act as hubs, the only way to extend the network is to connect more devices to the central hub. While this can be accomplished in a wired network (although requiring lots of cable), the range of a wireless star-type network is limited, so its maximum distance is determined by the furthest connected device. A much better solution is the mesh network (Figure 1b) in which all devices communicate with each other, which makes the size and area covered by the network almost unlimited.
The absence of mesh networking in Bluetooth became a severe drawback as IoT began to evolve from an acronym to actual systems. For example, on a production floor there can be hundreds of wireless-enabled sensors, all of which must share information that is later communicated to the outside world and the Internet via wired or wireless means. Bluetooth couldn’t do that.
In fact, the need for mesh networking capability in Bluetooth was so important that companies such as Cambridge Silicon Radio (CSR), acquired by Qualcomm in 2015, created ways to allow Bluetooth low energy devices to form a mesh network even though mesh wasn’t yet included in the standard. These companies as well as Nordic Semiconductor and others worked with the Bluetooth SIG to speed mesh capability into Bluetooth 5.
Now that mesh networking is standardized in Bluetooth 5, it’s arguable that this factor alone makes the technology a major contender for any IoT application. Unlike most competing technologies, Bluetooth is incorporated in every smartphone, tablet, and laptop computer, so a Bluetooth 5 network can be configured and reconfigured on the fly from an app whose user could be in the same room or thousands of miles away. This reduces both cost and complexity of controlling a Bluetooth 5 network. In a IoT system, this is a major benefit.
Mesh networking capability also complements one of Bluetooth 5’s other enhancements — increased range — which, with a theoretical limit of 200 meters, is twice that of Bluetooth 4.0. Bluetooth 5 accomplishes this by increasing maximum output power from 10dBm (10mW) to 20dBm (100mW).
The Role of Range, Speed, and Coexistence
Increased range is desirable in any communication application, but it’s particularly important in home automation environments. Bluetooth 5 can now support this application, thanks to its greater range and mesh networking capability. Together, they allow Blueooth-5-enabled devices to be connected throughout a residence of any size and even outdoors and between buildings. As this wasn’t possible before, competing technologies like Wi-Fi and Zigbee began to take advantage of this shortcoming.
Increased range and mesh networking should also have an impact on Bluetooth beaconing, an application that, although available since 2013, hasn’t exactly taken the world by storm. This is true even though the attributes of beacon technology are compelling in many applications.
Beacons Defined
At a basic level, beaconing is a way to deliver very short messages to and track Bluetooth-enabled devices over a short distance, without the need for pairing between the beacon and the device. The only requirement is that the device, typically an Apple or Android smartphone or tablet, has an installed app dedicated to beaconing. The retail industry is currently the primary user of beaconing, so let’s use this is an application example.
In a mall, a retailer has installed beacons through its store in locations such as at the store entrance, display counters, and checkout lanes (Figure 2). These devices, which are tiny (as small as 1x5x0.75in.) broadcast signals at a specific interval, each containing small amounts of data. As data is minimal, RF output power is very low, and power consumption is miniscule, beacons can operate for years on a coin cell. They’re also inexpensive, so a retailer can install them in many places.
The process begins when a shopper passes by the store and receives a notification from the beacon that pops up in the display showing a URL or some other bit of information. This is typically a coupon, loyalty reward, or some other form of promotion. The user then taps the notification and is sent to somewhere on the retailer’s website, where more information is provided.
It doesn’t take much imagination to see how valuable this can be for retailers and other organizations like museums that could send out notifications with a link to details about what piece of art, dinosaur, or whatever the visitor is looking at. They can also be used for positioning and navigation, tracking of virtually anything (including people), and automatically registering trade show attendees, among many other applications. As beacons transmit only, they do not gather personal information, which minimizes security issues.
The usefulness of beacons depends entirely on what the retailer or other organization chooses to do with the information they provide. For example, a retailer can determine what products shoppers seemed most interested in, where they go in a store, and if they buy something (Figure 3).
Unfortunately, until Bluetooth 5, the maximum message length that could be transmitted by a beacon was limited to 31 bytes–too small to even contain all the characters in most URLs or provide a text message long enough to convey any useful information. Bluetooth 5 solves this by increasing message length to 255 bytes so much more information can be accommodated. Bluetooth 5 also provides higher data rates that should benefit not only beaconing but many other applications as well.
Faster Data Transfer
Bluetooth 5 increases its maximum data rate from 1Mb/s in Bluetooth 4.0 to 2Mb/s. While not a massive increase, it will still allow more data to be communicated in a shorter time. One of the greatest benefactors of this increase is likely to be IoT applications that require near-instantaneous round-trip communications, such as controlling robotic surgical devices in medicine and machines on a production floor. It can also let an IoT device store data for days and send it all at once in seconds rather than periodically in pieces. This will reduce power consumption in IoT devices, which is essential for long battery life.
Another benefit for IoT provided by Bluetooth 5’s increased speed is the ability to allow sensors to be updated much faster and much more frequently, which is important for ensuring that every device in the network has the latest security features and most current firmware. The security benefit will be essential as miscreants have already found ways to infect IoT devices and networks and will undoubtedly increase their activity as more IoT systems are in place.
Ability to Coexist
In addition to the benefits we’ve discussed, Bluetooth 5 has other enhancements that will increase its already formidable capabilities, one of the most important of which is its ability to coexist with other services in the 2.4 GHz Industrial Scientific and Medical (ISM) band.
Bluetooth is far from alone at the frequency and which it operates, and only through features incorporated within it and other services such as Wi-Fi can they operate without interfering with each other. For example, in developing Bluetooth 5, the SIG took into consideration that in many places, including those where IoT is employed, Bluetooth will not be the only service in operation.
To ensure that interference is minimal in these cases, the standard builds on existing capabilities such as avoiding channels used by Wi-Fi, while adding “slot availability masks” that detect and automatically prevent interference to cellular networks. This will be increasingly important in the future as cellular networks continue expanding to include frequencies very close to those used by Bluetooth.
The Bluetooth SIG is not alone in realizing that in some cases more than one connectivity solution will be used, and silicon vendors are addressing this by incorporating multiple connectivity protocols within their System on Chip (SoC) devices.
Simplifying the Solution
While many systems will use a single connectivity solution, others will use several. From a designer’s perspective, this would require a separate SoC for each one, driving up costs and complexity, and probably increasing time to market. It didn’t take long for silicon vendors to address this, and an increasing number of SoCs accommodate multiple protocols.
The first device manufacturer to do so was Nordic Semiconductor, which introduced the nRF52840 and the (nRF52840-PDK) preview development kit in December (Figure 4) even before the full standard was released. The single-board development tool for Bluetooth 5 and its low energy predecessors also has ANT, the IEEE 802.15.4m Low Power Wireless Area Network (LPWAN) standard, and proprietary 2.4-GHz applications.
The Arduino Uno Revision 3-compatible nRF52840 SoC employs a 64-MHz, 32-b ARM Cortex M4F processor, a new radio architecture, RF power amplifier, 1Mbyte of flash memory, 256Kbytes of RAM, a USB 2.0 controller, and many other features. It can operate from power supplies above 5 VDC, and addresses security with the ARM CryptoCell-310 cryptographic accelerator.
Another example is Skyworks Solutions’ SKY66112–11 front-end module (Figure 5) that serves Bluetooth 5, Thread, and ZigBee and produces up to five times the RF output power (100 mW, +20 dBm) of the radio in an SoC alone. This eliminates the need for further amplification and can increase receive sensitivity by 7 dB, more than doubling receive range.
Texas Instruments’ CC26xx SimpleLink wireless microcontrollers are also designed with this in mind, as they accommodate Bluetooth, ZigBee, and 6loWPAN. The family of devices combine an ARM Cortex-M 3 processor, prodigious amounts of memory, and a controller that connects to external sensors for autonomously collecting data while the rest of the system is in sleep mode. It consumes very little power, and incorporates a broad array of functions and interfaces along with AES-128 encryption.
Conclusion
The features of Bluetooth 5 described in this article are the major ones but there are many more “tweaks” to the standard contained within each one, along with other features that collectively make the low energy version of Bluetooth equal to or better than its competitors for IoT applications. Mesh networking is the most broadly useful as it makes the standard more than a short-range personal area network for the first time. However, its greater range, improved beacon support, higher data rate, and greater message length and dozens of other enhancements combined with frugal use of power, low implementation cost, and massive market penetration, ensure it will continue to be a highly competitive connectivity solution for years to come.
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