dio transmission. The broadcast and cellular industries have a strong engineering common interest. Generally, when a strong engineering common interest exists there is also a strong commercial common interest, though sometimes this is not immediately apparent to the parties and vested interests involved. The broadcasting industry also has extensive experience of implementing OFDM- based physical layer transmission networks. The consensus to emerge from WRC2007 was that mobile broadband would take three to five years to implement at the top end of the UHF band. This has proved overoptimistic, though commercial networks are now launched in parts of Europe including Germany and in the USA (AT and T and Verizon). Engineering issues include managing coexistence between very different radio network topologies working at very different powers. In the days of omnipresent analogue TV, a country the size of the UK could be covered from 50 large high-powered transmitter sites and 1100 lower-power relay sites. This provided the statutory required coverage of 98% of the population including all communities with more than 200 people. Getting 90% coverage for a 3G network at 1900 MHz takes over 7000 base stations. Major urban conurbations such as London were and still are covered substantially by one TV transmitter. For example, Crystal Palace in London broadcasts to a 'local' population of 8 million people. The analogue transmitter delivers one megawatt, cosharing mast space with DVB, DAB, FM and medium-wave transmissions. The station has a range of 60 miles for analogue TV and 30 miles for digital TV. HDTV broadcasts started from the site in May 2006. Digital TV transmitters typically have effective radiated power outputs (the power that is delivered as a result of the transmitter power plus antenna gain) ranging from 2 to 50 kW. Crystal Palace is 20 kW. These output powers though relatively modest compared to analogue TV are still substantial when compared to cellular base stations. There is also a height-gain effect that in