IEEE 802.15.4a standard (2007) is an amendment to the original 802.15.4 standard from 2006. It defines both the MAC (link) and PHY (physical) layers from the ISO/OSI reference model. The original standard introduced new ways for communications in small WPAN (Wireless Personal Area Networks) networks with short range and low data rates. These technologies, such as ZigBee for instance, are great for building up so-called Wireless Sensor Networks (WSN). The 802.15.4a amendment added two new PHYs into the standard: CSS and Ultra Wideband. These additions introduced new features that the original standard was lacking: higher data throughput and also the feature of very precise ranging gained by the UWB PHY.
In 2011 the IEEE 802.15.4–2011 revision was introduced and it serves as a revision of the original standards in order to roll them all into a single document. The standard specifies three frequency bands, the sub-gigahertz, the low and high band yielding 16 radio channels in total. Of course, it depends on each state’s regulatory office, which of these bands can or cannot be used geographically. It also specifies four data rates for the UWB PHY: 110 kbps, 850 kbps, 6.8 Mbps and 27 Mbps. The standard also shows clear support for ranging capabilities by the UWB PHY.