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Impact of UWB on Third-Generation Telecommunications
March 24, 2003 - source: Cellular
News
The UK's Radiocommunications Agency has commissioned a report that
has concluded that future ultra wideband (UWB) devices could have
a serious detrimental impact on 3G - UMTS mobile phones. While the
report studied both the network and the handsets that are expected
to be used, it found that handsets would be subjected to the highest
level of interference from UWB transmitters primarily due to the
probably locations of the UWB boxes. A handset would have to be
within about 5 meters of a UWB transmitter to suffer interference,
but that could result in 3G handsets not working in users own home.
While the handset will be subjected to the maximum interference,
due to the way W-CDMA works, this will in fact has a serious impact
on handsets in other nearby cell sites. This is due to the fact
that all the physical channels on a base station cell downlink are
scrambled by a scrambling code. This means that different cells
can be identified through the use of different scrambling codes
allocated to different cells on the same carrier frequency. Scrambling
codes are nearly orthogonal, but not perfectly orthogonal to one
another, so additional power from one base station leads to an increase
in Intercell Interference experienced in cell phones in adjacent
cells. Because of the increase of Intercell Interference in adjacent
cells, UMTS handsets connected in these adjacent cells will require
additional downlink power from their serving base station cells
to overcome this additional Intercell Interference. This in turn
causes additional Intercell Interference to their adjacent cells
(including the cell connecting the UMTS device being interfered
with by the UWB device), and so on. The effect becomes diminished
but could extend for many cells.
The spectrum from 3.1GHz to 10.6GHz has already been set aside
for UWB; however, its proximity to UMTS around 2GHz is of concern
to operators of those networks. UWB devices are widely expected
to used in domestic locations for wirelessly connecting home-entertainment
units together, due to their high bandwidth capabilities that make
them ideal for broadcasting video from a central box to several
receivers.
The report concludes that changes in dropped call rate are generally
very small. In most cases, the calls are dropped because the UWB
device causes the maximum load to be exceeded in the handset. Such
an occurrence is modelled as degrading the cell coverage. In reality,
it may well kill the pilot channel and so the call would be lost
altogether. Therefore, practically, no amount of extra power from
the basestation, or number of basestations, would recover the lost
call. In future handsets, it may well be that the power-control
algorithms allow the handset to reach higher loads and this may
offer extra mitigation against interference effects.
However, as changes to the base stations will not cure the problem,
there are no fears that the network operators would face demands
for even more towers as UWB devices start to proliferate. This will
reassure the network operators who are facing calls to lower their
infrastructure spending and would not look forward to a future technology
that would lead to an increase in CAPEX.
You can download the report at here:
http://www.radio.gov.uk/topics/research/topics/other/final3greport/3gfinalreport.zip
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