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.