Bluetooth Smart and ZigBee: If you can't beat them, join them
September 21, 2015
Combining Bluetooth Smart with ZigBee offers the classical 1 + 1 = 3. The trade media loves the standards war as competing technology narratives keep...
Combining Bluetooth Smart with ZigBee offers the classical 1 + 1 = 3.
The trade media loves the standards war as competing technology narratives keep the media users on their toes while providing the thrill and suspense of a soap opera. Take, for instance, the wireless networking tango between IEEE 802.11 (aka Wi-Fi) and Bluetooth during the late 1990s, when one industry group claimed that Bluetooth would wipe Wi-Fi from the face of the earth. Conversely, when Wi-Fi 802.11b arrived in 1999, its proponents said that it would kill Bluetooth.
Eventually, Wi-Fi settled for networking of computers in home and office environments, while Bluetooth became a popular connectivity tool between computers and peripherals. Bluetooth and Wi-Fi standards now peacefully co-exist, and the key take-away from the Wi-Fi vs. Bluetooth spat is that protocol wars slow down both the technology deployment and market acceptance. Moreover, each technology has its strengths, and it’s usually prudent to use those strengths in a coordinated manner.
Now there’s a sense of deja vu in the Internet of Things (IoT) realm where questions are being asked: Will Bluetooth Smart (aka Bluetooth Low Energy or BLE) will win over ZigBee? Will ZigBee decline? Can BLE and ZigBee co-exist? BLE is the low-power version of the short-range Bluetooth wireless technology. It addresses the battery-life shortcomings of the classic Bluetooth BR/EDR technology and is popular in wearable devices like smart watches and fitness bands.
When BLE arrived in 2010, its backers asserted that it would kill the IEEE 802.15.4 low-rate wireless personal area network (PAN) standard, which comes in various flavors: ZigBee, RF4CE, and Google’s Thread. The renewed confidence in the BLE camp comes from the 2013 introduction of Bluetooth 4.1 and the 2014 introduction of Bluetooth 4.2, which both brought significant improvements to enable IoT scenarios, thanks to new features such as longer packets, improved security and privacy, and the ability to do 6lowPAN/IPv6 over BLE, and be slave and master at the same time.
These functions are opening the door to mesh networking on top of Bluetooth, which is still implemented in proprietary ways by various vendors, but is soon to be standardized as the outcome of the Bluetooth Smart Mesh Working Group. It’s worth noting that mesh networking is a key strength of ZigBee and has served well in industrial and home automation environments.
BLE vs. ZigBee
The home automation industry is evolving into the “smart home” premise, and here, BLE is bucking the trend with its Bluetooth Smart credentials. The overall trend in home automation is to go smart, and one of the key leverages of BLE is that it can be controlled from a smartphone. ZigBee, on the other hand, is not present in smartphones.
So will smartphone makers add ZigBee wireless connectivity? Probably not. ZigBee’s key advantages are mesh and 6lowPAN, and BLE now offers both. Moreover, BLE solutions are extremely low power, even lower than ZigBee.
Not surprisingly, therefore, the BLE deployment has been brisk. It emerged in 2010, and is now everywhere. That’s in sharp contrast to ZigBee, which took ages to be deployed and has suffered from the lack of good interoperability. ZigBee – which has been around since the early 2000s – has accomplished relatively low volumes so far.
The notion that it’s the end of the road for ZigBee is a bit exaggerated. ZigBee is everywhere in home automation applications such as lighting, shutter, and HVAC control. While BLE can support applications similar to ZigBee, there’s resistance to switching due to a large installed base.
Smart-home OEMs acknowledge BLE as a clear trend, but, at the same time, they aren’t willing to abandon ZigBee, a mature technology that’s been available for more than 12 years. ZigBee was initiated in 1998, officially standardized in 2003 as 802.15.4, revised in 2006 as 802.15.4-2006, then consolidated in 2011 with new PHYs and amended in 2012 as 802.15.4e with MAC improvements. Now the release of ZigBee 3.0 in late 2015 is a clear attempt at streamlining the interoperability issues by uniting the previously disparate elements of ZigBee’s software stack.
Where do ZigBee solutions go from here? The BLE chips adding a ZigBee stack seem to be the clear way forward. Though BLE is adding ZigBee-like features like meshing and support for IP traffic, BLE and ZigBee can complement each other in a number of smart-home settings. Take a door lock, for instance, which can be opened through a smartphone via a Bluetooth link. The same door lock can be connected to the home router via ZigBee and controlled over an Internet connection. So when the owner approaches the door, his phone communicates with the router using cellular or Wi-Fi and automatically opens the door using the ZigBee stack inside the router. However, if the Internet connection is down, the owner can open the door lock using his smartphone via Bluetooth Smart.
That’s a clear trend in the IoT segments – a single platform open to several technologies. Moreover, BLE, and ZigBee have similar building blocks such as RF, modem, encryption, and 6LowPAN. The combination of two technologies will still be an inexpensive product, as it will use similar radio, modulation, and security schemes.
BLE uses the GMSK modulation technique while ZigBee employs an offset QPSK scheme that’s similar to GMSK without the Gaussian shaping filter; both BLE and ZigBee use AES-based encryption accelerators. TI’s SimpleLink CC2650 and Freescale’s KW40Z wireless MCUs are two examples of BLE and ZigBee combo chips, and there’s more on the way.
The trade media is keenly looking for standards wars in the next technological front – aka IoT – but the smart home market, one of the early success stories in the IoT space, is more inclined toward a prudent arrangement in which BLE and ZigBee work concurrently to create a win-win situation.