Wireless personal-area networks (WPANs) are exceptionally useful for sensing, monitoring, and control applications. Cost-effective WPANs have the unique potential to implement wireless connectivity in many end products where this functionality wasn’t considered previously. A thorough, fact-based, logical, and organized evaluation of key WPAN design factors can closely manage system financial objectives, increasing end product value with a positive rate of return, while still achieving key wireless design objectives.
Sensing, monitoring, and control solutions drive specific consideration factors for WPAN implementation. Ranges for low-cost wireless networks in sensing, monitoring, and control applications encompass those distances of 300 m or less and data rates of 250 kbits/s or less. In WPAN end node designs, it’s often necessary to extend battery life to the optimum to meet product needs.
By proactively analyzing several key factors before design work begins, the embedded engineer can enhance the results of the final wireless network implementation. Developing and examining these key factors in a matrix format will aid the design engineer in the component and solution selection analysis process.
Reference design schematics, bills of materials, and other application information may also be gathered as a baseline for design initiation. An example wireless UART (universal asynchronous receiver/transmitter) reference design is included with this article.
It’s recommended that the embedded engineer consider review of the following areas in relation to WPAN design requirements: integration, wireless networking topologies, radio (RF modem or transceiver), performance, operating voltage, data rates, range, channel flexibility, output power, sensitivity, power management, peripherals, clocking, multitier software, ease of hardware and software design, antenna design, and packaging.
Also, when considering an integrated solution or a discrete solution, the microcontroller (MCU) should be evaluated with the following factors in mind: CPU features, performance, memory options, power management, clock source options, analog-to-digital conversion, peripherals, packaging, in-circuit debug and programming capabilities, and ease of software and hardware design. Such analysis will provide an organized perspective for engineering decisions, an avenue toward design success, a fast time-tomarket, and an easier implementation of cost-effective wireless networking.
INTEGRATION
A variety of implementation alternatives for low-cost wireless networking can offer the engineer a high level of flexibility in the design process. As one alternative, consider solutions from one-stop-shopping providers that offer various configurations of standalone transceivers to be used with a wide selection of microcontrollers (Fig. 1). As a second and equally effective alternative, consider the newest solutions that offer integrated transceiver/MCU products. Reusing design components and engineering investment may be important as designers work on multiple, yet similar, end products. Therefore, a structured evaluation of solution options can be both cost- and resource-efficient. Well-thought-out research can mold a basis for several end products to be designed from a single foundation (Fig. 2).
WIRELESS NETWORKING TECHNOLOGIES
The 2.4-GHz ISM band supports multiple short-range wireless networking technologies. Each alternative has been developed to optimally serve specific applications or functions. The networking topologies most commonly associated to the 2.4-GHz frequency range are Bluetooth, Wi-Fi, and ZigBee, as well as other proprietary solutions (see the table).
Each solution is suitable for WPANs. However, some offer extended capabilities that align best with sensing, monitoring, and control application needs. Non-standards-based proprietary solutions may be considered, too. But such solutions may pose some risk to the designer since they’re vendor-dependent and could be subject to change.
ZigBee, an IEEE 802.15.4 standardsbased solution as defined by the ZigBee Alliance (www.zigbee.org), was created to address networks that require low power consumption, low data rates, reliability, and security. The ZigBee solution accommodates network-specific support mesh networking, network recovery and healing, device interoperability, and vendor independence. The ZigBee solution frequencies are typically in the 868/915-MHz or 2.4-GHz spectrums.
ZigBee technology solutions have a 250-kbit/s data rate. Power consumption must be extremely low to optimize battery life for months or even years of operation (often equivalent to the shelf life of the battery) using alkaline or lithium cells. ZigBee technology theoretically supports up to 65,000 nodes. Common applications in sensing, monitoring, and control that are best supported by a ZigBee technology solution include personal and medical monitoring; asset management, status, and tracking; security, access control, and safety monitoring; fitness monitoring; process sensing and control; energy management; home automation; heating, ventilation, and air-conditioning sensing and control; building automation; industrial automation; and many others.
Some WPANs may be as simple as single point-to-point or star configurations. Depending on the application, other proprietary wireless solutions similar to ZigBee may offer the best match of ease of design versus system capability.
One low-complexity example is the simple media access controller, or SMAC. Look for solutions in this space where the vendor offers easy-to-use source code to speed time-to-market for simple networks. The IEEE802.15.4 standard-compliant media-access-controller (MAC) solution supports more complex configurations with packet and streaming data modes, beaconed and non-beaconed networks, and 128 AES data encryption.
Providers that offer multiple levels of stack capability give embedded engineers the opportunity to reuse their design software for a variety of WPANs, including those with varying levels of complexity. Multiple stack solutions act as the foundation on which the embedded engineer can easily set up the radio and focus most of the design effort on the application software.
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