Is cellular encroaching on white space?
February 23, 2012The radio spectrum currently being considered for white space usage is the “TV bands” – the spectrum currently used for terrestrial TV broadcasting, increasingly in digital format. In many countries this spectrum previously extended from 470-862MHz – 392MHz of bandwidth. But most European countries have previously agreed that the band 790-862MHz would be made available for cellular usage making the default white space band 470-790MHz (320MHz). Recently, the World Radio Congress (WRC) decided that the band 694-790MHz – the so-called “700MHz band” should be harmonised for cellular usage by 2015 and made available in European and African countries on a voluntary basis. Does this pose any problem for white space usage?
The amount of white space is typically proportional to the total amount of TV spectrum – roughly halving the TV spectrum results in half the amount of white space. In some cases, the reduction may be slightly greater if a TV repacking process results in tighter use of TV frequencies and so less white space, but typically in Europe TV is already packed as tightly as engineers can manage. So any reduction in TV frequencies will reduce white space.
Current calculations of white space availability are generally based on the UK. Here, there has been an assumption that as well as the 800MHz part being used for cellular, the 600MHz part (from 550-614MHz) would also be auctioned and hence not available for white space. So the remaining UK spectrum for TV transmissions is 256MHz. Calculations suggest an average of around 100MHz of this is available as white space in any location.
If, instead, the UK decided to adopt the WRC plan then the TV transmissions would be 470-694MHz – 224MHz (perhaps less 8 or 16MHz for channels reserved for radio astronomy and wireless microphones). Scaling for the drop from 256MHz to 224MHz we might expect white space availability to fall from 100MHz to 88MHz. Such a small decrease is unlikely to make any material difference to white space usage.
Hence, an initial conclusion is that were countries to follow the WRC recommendation, the amount of white space left would not be materially different from that which most have been using in their calculations to date.
It is worth noting that the position may be better than this. Firstly, many European countries will find it very difficult to open up the 700MHz band without at best massive re-planning of TV transmission and at worst reducing the number of TV channels transmitted. This will likely mean that not all adopt the plan and many do not do so until well after 2015. Secondly, if 700MHz is replanned for cellular it is likely to be on the basis of frequency division duplex (FDD) with an uplink and downlink and central guard band. It is quite likely that this guard band would be available for white space usage and would form a set of national channels on which there was no licensed use, making them “superior” white space. Not only would this add back enough channels to bring the available white space back to around 100MHz it would actually increase the quality of the spectrum available. Thirdly, restricting the bandwidth of white space will allow more efficient antennas, increasing the efficiency of usage slightly.
So in summary, the WRC decision is not likely to have any impact for some time, at worse case results in a small reduction in white space availability, but may actually improve white space access.
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