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DiY IoT: Let's talk WiFi

Posted: 16 Oct 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Internet of Things? IoT? microcontrollers? Texas Instruments? CC3200?

Welcome back! In today's post, we will talk about WiFia few general concepts about it, its relationship to the CC3200, some practical ways to use it, and lastly, a little step-by-step project.

WiFi (a.k.a wireless LAN) is a way to connect multiple clients in a wireless network. It is so common nowadays that we hardly even think about it anymore unless we are away from home and must go into "hunting" mode to find it wherever we can. Even though we take WiFi for granted, the internals of it are quite interesting and complicated. The set of protocols to describe the MAC (or media access control) and physical layers of this communication is specified by the IEEE 802.11 standard, which was first introduced in 1997 and has seen a magnificent amount of improvement since then. The standard covers multiple variations (and some that even account for future applications), but I will focus on the most relevant ones today. In consumer networking products, you will encounter these four common varieties of the IEEE 802.11 standard:
???801.11b: This operates in the microwave 2.4GHz frequency range and allows throughput of 11 Mbit/s.
???802.11g: This operates in same range (2.4GHz) and allows a rate of 54 Mbit/s.
???802.11n: This introduces MIMO (multiple input, multiple output) antenna technology and operates mainly in same 2.4GHz range but adds optional support for the 5GHz frequency range. This version supports data rates up to 600 Mbit/s.
???802.11ac: This improved version of 802.11n supports wider channels in the 5GHz range and adds a more advanced MIMO variation, allowing the increased maximal throughput of 1.3 Gbit/s.

As you have probably noticed, wireless operates on two main frequencies: 2.4GHz and 5GHz. The first one is mainly used because it does not require FCC licensing. The primary reason for the licensing waiver is that microwave ovens operate on this frequency. Early microwaves used to produce too much noise around 2.4GHz and because of this, the frequency band was considered useless for communications. Ironically, it is now one of the main household communication frequency bands, and is also used for Bluetooth, RF remote controls, etc.

The second one, 5GHz, is a fairly recent addition to common household devices. It brings interesting advantages including wider channels, less noise, higher throughput, and (since less effort is needed to get a good SNR) longer battery life, but it also comes at a price of reduced range and poor wall penetration because of its shorter wavelength.

Now that we all understand the concepts, let's get back to our development board.

In general, nearly all of the small MCU-class WiFi-enabled boards out there today are 2.4GHz, 802.11b/g/n variety only. There are early signs of 5GHz-enabled system-on-chips appearing, but these SoCs are still very expensive and very, very rare. Our CC3200 Launchpad is no exception; it only supports 2.4GHz networks, so if your router is set to exclusively operate in the 5GHz range (for whatever reason), you will not be able to connect. Keep that in mind.

When it comes to WiFi, the CC3200 board can operate in several different ways:

It can connect to an existing WiFi network as any normal device would do. (This is the simplest way to get started.)

It can connect to an existing WiFi network, but then go into low power mode and implement a communication scheme called beacon skipping* where the device sleeps and only rarely responds to access point packets, thus conserving precious energy.

It can work in AP mode making it an access point. This is very useful especially for initial setup if you want to provide your device with local WiFi credentials. The idea is to connect to the device's own network and provide the local WiFi name and password so the device can then drop the AP mode and switch to acting as a client.

It can work in WiFi direct modea mode meant for peer-to-peer communication between WiFi devices that support this mode.

*Somehow in my mind it becomes "bacon skipping" and the thoughts drift away...

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