Wireless connectivity protocols for embedded systems

When talking about wireless, the four primary networking protocols are Wi-Fi, Bluetooth, ZigBee and cellular. It's important to remember that each of these was originally created to meet the needs of varying applications.

Wi-Fi was created to replace the Ethernet cable, so that high data throughput was a priority at the expense of complexity and power consumption. Bluetooth was created to replace the serial cable and includes quality-of-service overhead to carry voice. Requiring much less power than Wi-Fi, Bluetooth has high pairing latency and is limited to a small network of seven slaves. ZigBee was created for large, robust sensor networks with low-cost, low-power nodes, but doesn't have nearly the throughput of Wi-Fi or Bluetooth.

The legacy of the original design trade-offs for these applications can become the baggage for using them in emerging applications like Home Area Networks (HAN) or Body Area Networks (BAN). One of the advantages of Wi-Fi, for example, is that the application does not need to know that the link is wireless. On the other hand, to build a Wi-Fi-connected smart light bulb means it needs enough processing power to run the TCP/IP stack.

It is also important to remember that while each of these popular protocols might be based on an industry radio standard, the network protocols themselves are not standards - but rather industry alliances. The alliances exist to promote the use of the protocol and guarantee interoperability. To market and sell products that use these protocols requires a membership in the alliance. This also helps to explain why new variants of these protocols seem to be targeting the application space traditionally dominated by others.

The new Wi-Fi Direct protocol, for example, attempts to simplify point-to-point ad-hoc connections between devices for syncing, file transfers, printing, etc. without the need to configure an access point (a function typically done using Bluetooth today). Another new variant of Wi-Fi, called Wi-Fi Display, allows for redirection of video and audio from a small screen (tablet or cell phone) to an HDTV.

In 2010, the Bluetooth SIG released version Bluetooth 4.0 which includes a new variant called Bluetooth Low Energy (now rebranded as Bluetooth Smart). This new version allows much larger networks, dramatically shortens latency, and reduces power consumption to ten percent that of classic Bluetooth, overcoming the previous limitations for using Bluetooth in sensor networks. However these changes came at the expense of backward compatibility – Bluetooth Smart can coexist, but isn't compatible with classic Bluetooth, and can't carry voice.