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During the past decades, technology in general and electronics in particular revolutionized our everyday life: starting with home computers, soon connected through the Internet and miniaturized into mobile portable devices, it brought us ubiquitous connectivity and distributed intelligence.
This tendency will not slow down, and the next step in this revolution is aiming at connecting together not only human interacted devices, but also every single intelligent device in order to provide an even better interaction with all these objects through new services that are still to be invented.
IoT : the Internet of Things
However, the Internet of Things is a big challenge: as the “Internet” word in its definitions implies it, all participating objects will have to be connected to a common inter-operable network. This clearly rules out all attempts to lock in users through the use of proprietary hardware, software or even service and promotes the use of open standards.
Moreover, given the mobility freedom that people have got using their mobile phone, it is difficult to imagine today a network of things which is not wireless, even if most of the connected devices will be intrinsically static.
The “Things” word in “Internet of Things” also implies that IoT will need to address every possible object, including the smallest, least significant and cheapest ones, and thus require the added connectivity to be equally small and affordable.
WiFi for IoT
Wireless connectivity of objects is almost a prerequisite, as today depending on a wire is considered as a major disadvantage.
In this regard, a lot of wireless network protocols already exist today, and more are yet to be defined to address particular needs. But it can be expected that existing widespread protocols that cover the required needs will get a faster adoption than emerging ones, and among these, the ones already present in our smartphones will be in a good position to be adopted for IoT.
Existing smartphones all feature 802.11 WiFi wireless connectivity, and the newest ones also bring in BlueToothTM Low-Energy (BLE). While the latter is targeting ultra-low power operation with low or medium data rates and volumes, WiFi is more appropriate for higher data rates or larger data volumes as its power consumption per bit ratio is significantly better in this situation.
Only the future will tell us the truth, but it is highly probable that both networks will coexist in the near future.
WiFi modules for IoT
WiFi is a complex protocol, requiring both state-of-the-art RF and digital electronic hardware, and proven software protocol stack to offer the required amount of security.
WiFi modules from mobile devices
The WiFi connectivity embedded into high-volume portable devices such as smartphones, tablets, laptops and camera is achieved using dedicated WiFi modules based on high-volume-only chips tailored for this market.
Being small, cheap and low-power, they would provide an ideal solution for the IoT, but unfortunately, given the exclusive high-volume production model of these mobile devices, it is extremely difficult to obtain these modules reliably in quantities less than a few millions. Their specification is accordingly very difficult to get, and most of the time, these modules rely on host-based closed-source drivers that are not suitable for embedding in a potentially large number of different host processors, such as required by the IoT.
Thus, despite the fact that the IoT market will eventually address more units than the current mobile phone market, the higher diversity of devices will not allow to use the existing mobile-dedicated WiFi modules as-is, and favor Open-Source friendly, off-the-shelf retail component solutions.
WiFi peripheral modules
The next existing solution consists in the low-cost WiFi peripheral chips and modules developed by semiconductor manufacturers for WiFi USB dongles, WiFi SDIO Cards, WiFi/UART bridges, M2M interfaces, etc. They have all in common to use only low pin count interfaces (SPI, UART, SDIO, USB) and not allow internal customization, thus requiring an external CPU to host the application code anyway, with more or less complex software stacks.
Sometimes, semiconductor manufacturers themselves directly develop their own WiFi module solution like TI’s CC3000, but most of the time, they rely on third-party module manufacturers, and it is possible to find cheap modules from unreliable origin for less than 1 USD!
However, these chip/module manufacturers are too focused on the hardware and unaware of software security implications, and often proposed crippled, limited or flawed designs that should only be considered with care, even among the biggest players.
WiFi AP SoC
The next most integrated existing solution to consider consists in the dedicated WiFi System-on-Chip (WiSoC), such as the ones sold under license by Mediatek/Ralink or Qualcomm/Atheros. Out of all the available WiSoC chips, the ones used in pocket WiFi AP/routers are the most appropriate, as they feature the smallest overall board area, cheapest Bill-Of-Material (BOM) and lowest power consumption. The most widespread chips in this category are the Qualcomm / Atheros AR9331 and the Mediatek / Ralink RT5350, with newer chips already existing or announced. However, from all these chips, the AR9331 stands out of the crowd because of its unrivaled low-power consumption. The RT5350 on the other hand provides more hardware peripherals for a lower price, and the MT7620 brings in even more high-end peripherals such as SDCard and PCIe support, along with 802.11ac (300 MBPS) WiFi.
Usually, these chips are also not available on the retail market and require signing an expensive license with these manufacturers to get hardware/software reference designs, required test suites and of course hardware chip provisioning, only for quantities in the million of devices range. But despite this fact and because of the wild semiconductor industry in China, it is easy to find modules featuring these chips in quantities down to a few hundreds of pieces at a price less than 10 USD, although the compliance to CE/FCC/IC/RoHS regulations and RF individual calibration needs to be checked with caution.
WiFi module firmware
On the software side, the LinuxTM operating system has proven its compactness and robustness by being used in many embedded devices, its TCP/IP stack has become a reference, and its not surprising to see that most of available WiSoCs use it as the base for their WiFi software stack.
Fortunately, because Linux is being licensed under the GPL v2 license, the vendors should in theory provide their modifications in source form to their user. Even if this obligation is difficult to enforce, this results in more and more code from vendors to be given back to the Community and integrated into other Linux distributions.
And among all Linux-flavored distributions, OpenWrt has become the reference Open Source distribution for all WiFi-oriented devices, based on its clean modular design, package management and small resource requirements. Offering full customization, most of the time it is able to bring better functionalities than the original stock vendor firmware.
Thus, designing a WiFi module based on an existing WiSoC and running OpenWrt seems like a natural choice for an efficient IoT WiFi solution.
WiFi IoT for DIY / Hackers / Makers
IoT is a fast-growing market, and it is difficult to envision what it will become even in the near future.
This is why addressing individual DIY / Hackers / Makers as well as larger entities is of utmost importance, as only agile users will be able to keep on with the fast-moving IoT technologies and test unexplored ways that would otherwise would not even be considered.
The success of the Arduino and Raspberry Pi Open-Source and / or Open-Hardware platforms demonstrates that even if this market is not the largest in terms of volume, it acts as a prescriber for industrial developments, as evening / week-end hackers are often passionate professional daytime engineers / software developers.
However, all these projects being developed with only a small hobby budget, reaching an affordable small quantity user price is important in order to unleash the usage possibilities, and a 10 USD target price is attractive.
Unfortunately, almost no existing WiFi IoT module is reaching this low price, all being at least 2 or 3 times more expensive, or having some sort of drawbacks.
One typical restriction often present in the existing WiFi modules is the requirement for fine-pitch or reflow-oven semi-professional soldering: one must remember that not all hobbyists are experienced electronics engineers, and providing an easy hand-solderable module is extremely important to reach the broadest audience.
Even further, providing a board compatible with 2.54 mm pitch through-hole breadboards is a desirable feature, as it allows easy prototyping with just jumper wires instead of soldering.
Using the same considerations, if several functional blocks requiring fine-pitch component soldering can be defined, it is interesting to provide them as separate breadboard-friendly modules that can be assembled together using only pin/header assembly or jumper wires, rather than a big monolithic board containing everything but that is both large and expensive.