Wireless Connectivity for Mobile Devices
Using Wi-Fi to Connect Embedded Systems with Mobile Devices
Wi-Fi modules are enabling a new generation of wireless embedded systems through Internet connectivity and the increased processing power of microcontrollers. Future module improvements will enable innumerable intelligent devices all over the world to communicate with each other and be controlled from smartphones.
BY MITCH DALE, MICROCHIP TECHNOLOGY
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Embedded systems are not limited to simple 8-bit controllers; many are sophisticated and self-contained computer systems. These advanced embedded systems can support color LED displays, vast data storage, significant computing power and myriad interfaces. One growing trend in these systems is to add wireless connectivity. The use of proprietary or standards-based radios to add wireless requires RF and protocol expertise. Unfortunately, most companies do not have the RF expertise or tools to develop their own wireless interface.
Computers, smartphones and tablets comprise the majority of wirelessly connected devices. However, there is huge potential for the emerging market of embedded wirelessly connected clients, which is often called the “Internet of Things” or the “Wireless Connectivity of Things.” Some examples include temperature sensors, automotive diagnostics, blood-pressure monitors and many more. There are hundreds of applications within the smart home, energy grid, personal healthcare, medical and asset-tracking markets ready for the taking.
While many wireless options exist, Wi-Fi has quickly become the de facto standard for wireless embedded systems because of its global acceptance and interoperability. Additionally, with the availability of low-power, self-contained, industry-certified solutions, Wi-Fi fits into many markets; including those with mobile and battery-powered requirements (Figure 1).
Adding Wi-Fi to embedded systems enables them to tap into the vast installed wireless infrastructure.
There are many forms of wireless communication, based on different frequencies, modulation techniques and protocols. However, Wi-Fi has several advantages over the rest by directly interfacing to the World Wide Web. In this aspect, Wi-Fi leverages the Internet infrastructure, global connectivity and the interoperability of cloud services by exchanging data with computers or smartphones.
Wi-Fi is a truly worldwide standard. Wi-Fi is ubiquitous anywhere you travel. There is an enormous established Wi-Fi infrastructure in place. According to the market research group Informa Telecoms and Media, the number of access points worldwide continues to grow by over 300% annually; and by 2015, there will be 5.8 million public hotspots worldwide.
Another advantage of Wi-Fi is that people understand how to configure and use it. Unlike ZigBee or proprietary wireless protocols, the average user understands how to associate their mobile or embedded device clients onto a Wi-Fi network. Going forward, Wi-Fi should become even easier, as the Wi-Fi Alliance and smartphone manufacturers implement Hotspot 2.0 and mDNS. These extensions to the existing standards simplify the discovery, authentication and provisioning of devices on the Internet.
Wi-Fi has achieved critical mass. The market for Wi-Fi devices is driven by the ever-expanding Internet and the proliferation of smartphones and tablet connectivity. With Wi-Fi, devices can be connected anywhere, anytime. For example, a Wi-Fi-enabled thermostat can be accessed anywhere from a cell phone or computer. The challenge for embedded designers is how to take advantage of the Internet infrastructure, Wi-Fi hotspots and cloud applications. Since each embedded Wi-Fi device can function independently, nodes anywhere on a corporate network or anywhere in the world can be accessed from a central server, via a URL.
Alternative wireless options may have the advantages of range or power consumption, but they require a gateway to access the Internet. A gateway is an additional device that needs to be developed and supported. In addition to the added cost, it may also be a single point of failure in the network. Nevertheless, some applications, such as sensor networks, may use other wireless networks to configure, collect and forward data to the Internet. Even in these cases, gateways would likely include Wi-Fi, since it does not require the user to install additional Ethernet cables.
While many wireless options exist, autonomous Wi-Fi embedded systems create new opportunities for innovation and expanded business models (Figure 2). For example, combining everyday products such as washing machines and air conditioners with wireless Internet connectivity creates easy-to-install, long-term servicing options for installers. Another example is the management of large trucking fleets using embedded Wi-Fi monitors. In this case, Wi-Fi allows reporting to happen whenever a truck enters the fleet parking lot or a distribution facility. Route, driving statistics and engine data are sent to a centralized server that manages scheduling, monitors driver safety and predicts maintenance problems. Previous fleet-management systems were implemented with cellular radios, but they are being switched to Wi-Fi because it has no ongoing data charges.
A comparison of the wireless options for embedded systems.
Modules Make Embedded Wi-Fi Practical
Only a few years back, it was impractical for embedded system designers to implement Wi-Fi in small, power-sensitive devices. However, this all changed with the introduction of low-power, complete Wi-Fi system on chip components in 2010. This new generation of Wi-Fi silicon quickly became the building blocks for complete Wi-Fi solutions, in the form of certified modules that have antenna, RF, baseband and protocol stacks (Figure 3).
Microchip’s RN-171 is an example of a pre-certified Wi-Fi module with onboard TCP/IP stack and services.
Wireless connectivity requires both a hardware radio and a software protocol stack. In other words, the Wi-Fi alone is not sufficient for Internet connectivity. Modules come in two flavors, stack-on-board and stack-off-board. Stack-on-board modules include the processor on the module, or may have the processor integrated in the radio chip. These modules have a simple ASCII command interface for configuration, and natively support the majority of Wi-Fi networking protocols, such as UDP, TCP/IP, DHCP, DNS, TELNET, FTP, HTTP, XML, SSL, etc. Additionally, stack-on-board modules are the quickest approach to adding Wi-Fi, since they are simply a data interface to the embedded system. In other words, to send data over Wi-Fi to a server in the cloud, you only need to configure the IP address or URL to write the data to the module. The module takes care of the connection, packets and underlying Wi-Fi transport.
On the other hand, stack-off-board modules contain the radio components and provide drivers for running the protocol stack on an external processor. Typically vendors will provide a protocol stack library. However, this approach requires more software integration, while allowing more flexibility. Stack-off-board modules typically support more types of peripherals and provide for additional Wi-Fi security and services.