Simplify embedded Wi-Fi connectivity with Near-Field Communications
Security and other concerns: Wi-Fi beacon approach
As previously mentioned, the initial configuration for connecting Wi-Fi applications requires user input, and Wi-Fi protected setup is not widely deployed. One approach is to use a special probe request or “beacon” from a Wi-Fi enabled handset already connected to the router or network. This approach requires a specially crafted SSID and some form of user interaction. This method is relatively secure, but an attack can be made on a system using the beacon if the attacker knows the details of how the system works. Additionally, a hard-coded and completely automated process does not provide any control or allow the user to make any decisions. Customizability becomes difficult as both the hard-coded beaconing device and the Wi-Fi device being configured lack the user interface or flexibility when it comes to option selection.
An alternative to the beacon method is to use the NFC in peer-to-peer mode. In the implementation example shown below (Figures 6-12), an NFC-enabled handset already connected to the Wi-Fi network pushes the SSID and key/password to the headless Wi-Fi module through the ultra-low-power 16-bit MCU via the NFC transceiver link at close range. This eliminates security concerns like undesired users on the network “sniffing” a beacon.
Alternative security features and enhancements
Recent security feature enhancements developed for microcontrollers can also be employed to further improve the security of Wi-Fi and NFC operations. For example, memory and data security features in the MCU enable vendors to securely place a passphrase or unique key to authenticate the NFC transaction. Only when the initiating device, typically a handheld device, offers a valid key will the MCU application authenticate and proceed with the NFC handover. This is definitely useful for the application to accurately acquire new information from the handheld device. The reverse is also true when the handheld wants to retrieve sensitive data from the other device. These types of NFC-secured transactions use low-energy transmitting devices to transfer simple data, or they enable encryption on the data to heighten security beyond what the air interface itself can provide.
A real-world example of a Wi-NFC-Fi system, enabled by a 16-bit MCU with universal memory
Figure 6: This project combined various wireless, MCU and Android technologies to demonstrate a complete picture of wireless connectivity and the Internet of Things (IoT)
As an example, we will highlight a recent Wi-Fi + NFC + MCU project that combines various wireless, MCU and Android technologies to demonstrate a complete picture of wireless connectivity and the Internet of Things (IoT). This example used a SimpleLink CC3000 Wi-Fi radio and a TRF7970A NFC transceiver in the wireless sensor system controlled by the MSP430FR5739 ultra-low-power MCU with universal FRAM memory technology. Each described system acts as an autonomous wireless sensor node that, upon NFC handover transaction and subsequent Wi-Fi authentication, can join a secured Wi-Fi network and connect to a TCP/IP server. FRAM’s universal memory feature allows for flexible partitioning of code and data across two different wireless stacks as well as the user application. In order to demonstrate the flexibility of IP-based applications, the Internet of Things (IoT) and the ubiquity of the wireless connectivity, two different implementations of the servers were developed: one as a Windows-based application and another as an Android application.
In this case, we show a custom app here which acts as a “middle man” to gather enough information to push over to the node via NFC link.
Figure 7: The front screen of the Android app
Figure 8: The app’s initial launch screen (note SSID and IP data)
Figure 9: Presenting the handset’s NFC antenna to the TRF7970A NFC transceiver in NFC-F target mode
Figure 10: Sensor data comes back from the node via Wi-Fi, which means the NFC push was good and Wi-Fi connection handover has been completed.
Figure 11: Five Wi-NFC-Fi nodes have joined the network and are sending data back to the phone via TCP/I. The nodes are represented graphically as planets rotating around the center orb.
Figure 12: An IP address is entered for the data destination. In this case, we selected to send it to a PC on the same network we called “TP-Link”.
Figure 12 shows the result of re-presenting the handset to the NFC antenna zones for three Wi-Fi nodes, each represented by a ringed planet rotating around a star. Temperature data is expressed by the color of the planet, alongside the raw data, IP address of each node, battery voltage, and accelerometer data. More importantly, the SSID, network, and IP address reconfiguration for the server and individual Wi-Fi/NFC nodes can be applied quickly and effortlessly by using a single NFC tap.
Conclusion
Wi-Fi technology is a well-established and time-proven wireless connectivity infrastructure for a multitude of device types. The addition of NFC technology offers convenience and security features that significantly improve the usability and scalability of new and existing Wi-Fi infrastructure and networks, and will enable previously inconceivable embedded designs in applications for home and industrial automation, smart grid, medical, and consumer electronics.
Josh Wyatt is currently an Embedded RF Applications/Systems Engineer at Texas Instruments. While his early background was in airborne active and passive detection systems at various frequencies, he has been working with ground based LF, HF, and UHF short range RFID,
contactless payment, and NFC systems since 1997. He has been at Texas Instruments since 2002.
Dung Dang is an applications engineer for Texas Instruments' ultra-low-power MSP430 microcontroller (MCU) group. He joined Texas Instruments in 2007 and has since served in various roles in new product development. He works closely with MSP430 MCU silicon development in addition to supporting development tools and software solutions. His focus also includes realizing various ultra-low-power wireless solutions on MSP430 MCUs. Dung Dang holds an MSEE degree from St. Mary's University at San Antonio, concentrating on embedded systems and image processing.
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