One of the most stringent FCC regulations is UWB’s low transmit power level. The maximum output transmit power is –41.3 dB/Hz when averaged over a 1-ms period. The instantaneous peak power cannot exceed 0 dBm. The average power level also depends on whether the radio is using a single band or is hopping over a three-band range.
Such a low power level puts the UWB signal down in the noise in some cases. But it is so low, it typically won’t interfere with any other signal in that range, mainly radar, wireless local-area networks (802.11a), and other wireless services. This low power means short range but also an attendant high level of security. Add encryption, and you have one of the most secure wireless technologies around.
The data transmission rates for UWB span 53.3 to 480 Mbits/s. That rate depends primarily upon environmental conditions and range. The maximum range is about 10 m, where the lower rate will prevail. The maximum rate can generally only occur over a 3- to 4-m range assuming few if any obstructions.
A key characteristic of the WiMedia standard is the WiMedia Common Radio Platform (Fig. 3). It consists of the basic UWB physical layer (PHY) and media access controller (MAC) layers, which can readily support higher-level protocol stacks and their protocol adoption layers (PALs).
The WiMedia architecture provides mechanisms for device discovery, wireless personal-area network (WPAN) management and medium access arbitration, and device power management, as well as two independent data transfer mechanisms for the secure exchange of data. Quality of service (QoS) provisions support latency-sensitive applications. Already, several other special interest groups (SIGs) and companies have taken advantage of this feature.
The Wireless USB Implementer’s Forum defines a wireless version of its USB 2.0 interface, which is used by virtually every PC, laptop, and peripheral device. The Bluetooth SIG recently chose WiMedia UWB as an “alternate MAC PHY” or “AMP” for higher speeds in the near future. And, some companies have developed proprietary protocols for special applications. For greater detail on WiMedia, go to www.wimedia.org.
THE FUTURE
Designers are still discovering many possible applications for UWB’s unique capabilities. The Bluetooth application of UWB will open some new possibilities. The movement to a Bluetooth version also is causing UWB chip vendors to make new versions of their chips to operate in the higher band groups. The Bluetooth SIG requires UWB chips to operate above 6 GHz specifically in band group 6. A faster version will eventually emerge to provide that magical 1-Gbit/s data rate.
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