3G Faces Network Interference from Future Wideband Devices
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.
The report, by Mason Communications on behalf of the RA is available for download from here."
Posted to the site on 19th March 2003
