- IEEE 802.15.4a
IEEE 802.15.4a (formally called IEEE 802.15.4a-2007) is an amendment to
IEEE 802.15.4(formally called IEEE 802.15.4-20060 specifying that additional physical layers (PHYs) be added to the original standard.
IEEE 802.15.4-2006 specified four different PHYs, three of which utilized
Direct-Sequence Spread Spectrum(DSSS), and one which used Parallel Sequence Spread Spectrum (PSSS). [IEEE Computer Society, (September 8, 2006). IEEE Standard 802.15.4-2006. New York, NY: IEEE.] IEEE 802.15.4a specifies two additional PHYs using Ultra-wideband(UWB) and Chirp Spread Spectrum(CSS). The UWB PHY is designated frequencies in three ranges: below 1 GHz, between 3 and 5 GHz, and between 6 and 10 GHz. The CSS PHY is designated to the 2450 MHz ISM band. [IEEE Computer Society, (August 31, 2007). IEEE Standard 802.15.4a-2007. New York, NY: IEEE.]
The IEEE 802.15 Low Rate Alternative PHY Task Group (TG4a) for Wireless Personal Area Networks (WPANs), as its name implies, was tasked with amending the 802.15 standard to provide alternate PHY standards that would allow for high aggregate throughput (lots of throughput over time) communications with a precision ranging capability (within 1 meter accuracy) and low power usage within the scope of the WPAN. TG4a was one of two groups tasked to standardize UWB - the other being TG3a. However, TG3a fell apart because of a deadlock between proponents of two competing UWB technologies: Direct Sequence UWB and Multi-Band Orthogonal Frequency Division Multiplexing (OFDM) UWB. Direct Sequence UWB, which was promoted by the
ZigBee Alliance, found its home with TG4a, while Multi-Band OFDM UWB was adopted by the WiMedia Alliancewhich published ECMA-368 (ECMA is another telecommunications standardization body that is similar to the IEEE). [ [http://www.podnova.com/channel/122071/episode/14/ Part 5: Ultra Wideband Update: IEEE 802.15.4a and Ecma-368 Podcast] ]
As was mentioned above, the Direct Sequence UWB PHY was the one that ended up being added into the IEEE 802.15.4a standard. Direct Sequence UWB is spectrally efficient, can support precision ranging, and is very robust even at low transmit powers. The Chirp Spread Spectrum PHY was added to the standard because CSS supports communications to devices moving at high speeds and at longer ranges than any of the other PHYs in the IEEE 802.15.4 standard. [IEEE Computer Society, (August 31, 2007). IEEE Standard 802.15.4a-2007. New York, NY: IEEE.] Basically, both new PHYs added scalability to data rates, longer ranges, and lower power consumption into the standard - thus meeting the intent of the IEEE 802.15 standard to emphasize very low cost communications.
Although Nanotron Technologies of Germany led the way for getting Chirp Spread Spectrum added as an alternate PHY to the IEEE 802.15.4a standard [Davis, J. (October 2006). IEEE confirms new wireless spec. "www.edn.com". Retrieved 5 May, 2008 from http://www.edn.com/index.asp?layout=article&articleid=CA6379599] , there are still no products being sold using CSS technology that are IEEE 802.15.4a compliant. However, [http://www.imec.be/ovinter/static_general/start_en_flash.shtml IMEC] did make the first UWB transmitter that is compliant to the new standard [ [http://imec.be/wwwinter/mediacenter/en/UWB_ISSCC2007.shtml IMEC makes UWB transmitter] , IMEC news release] which they plan to use in wireless autonomous transducer systems used in healthcare, lifestyle and process automation applications.
* [http://standards.ieee.org/getieee802/802.15.html Download the 802.15 standards from IEEE]
* [http://www.ieee802.org/15/pub/TG4a.html IEEE 802.15 WPAN Low Rate Alternative PHY Task Group 4a (TG4a)]
* [http://www.ieee802.org/19/arc/stds-802-19list/doc00057.doc about coexistence of IEEE 802.15.4aCSS with
IEEE 802.11b/g (2.45GHz WLAN)]
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