subject: Global Compliance Is An Important Design Consideration For A Number Of Wireless Rf Applications [print this page] Both 2.4GHz and sub-GHz technologies are expanding in the consumer, industrial and automotive marketplaces. The 2008 2.4GHz TAM was 172 million units while the sub-GHz TAM was almost three times that number at 492 million.
Remote keyless entry (RKE) is a common sub-GHz application, where low-data-rate transmission at a fairly long range (100+ meters) and very long battery life are high priorities. The same is true for remote garage door openers (GDO) and tire pressure monitoring systems (TPMS).
There are several markets, such as toys, medical equipment, security systems and building automation, where both wireless options are used in the same system. For example, in building security, 2.4GHz radios are needed to serve high-data-rate video cameras while proximity, pressure and acceleration sensors are networked using a sub-GHz protocol.
Range, power consumption, antenna size and data rate are not the only design considerations for wireless applications. Worldwide deployment and software stack size and cost also have to be addressed.
Worldwide deployment
Global compliance is an important design consideration for a number of wireless applications. For instance, video game manufacturers who market their products worldwide can use 2.4GHz radios for all their consoles because it is a global ISM allocation. Similarly, wireless applications using the 433MHz band share a global sub-GHz ISM allocation, with Japan being the sole major market exception. In addition, 915MHz is used extensively in North America and Australia, 868MHz is deployed across all of Europe and 315MHz is available in North America, Asia and Japan.
Standard vs. proprietary solutions
A number of standard solutions for the radio PHY, MAC, and stack layers are available for 2.4GHz and sub-GHz applications. 802.15.4 (PHY/MAC), ZigBee, Bluetooth, 6LoWPAN, Wi-Fi and RF4CE are widely used 2.4GHz solutions. Sub-GHz standards-based solutions include ZigBee (currently the only protocol offering both 2.4GHz and sub-GHz versions in the 868MHz and 900MHz bands), EnOcean, io-homecontrol, ONE-NET, INSTEON and Z-Wave.
While standard solutions offer the advantage of vendor-independent interoperable nodes, they normally will increase each nodes cost and footprint. For example, a 2.4GHz ZigBee radio node will cost approximately $2.00 (USD) and the software stack will require about 128KB of embedded memory. Conversely, proprietary sub-GHz nodes generally target low-cost systems, with each node costing approximately 30-40% less and requiring 4KB memory for the stack (in this case, Silicon Labs EZMacPRO).
With specialized functions and small software stacks, proprietary solutions can achieve smaller die sizes and reduced memory footprints. Whats more, the less complex stacks simplify deployments and lower maintenance costs. Therefore, proprietary sub-GHz solutions can offer among the least expensive point-to-point localized networks, such as a garage door opener or home automation system.
The opportunities for more extensive long-range sub-GHz mesh networks, proprietary or standards-based, are growing by leaps and bounds with the emergence of smart grid technology.
by: Chris Bartik
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