ort and limited spectral availability may constrain market adoption. 13.3 The Backhaul Mix So how will the backhaul mix between fibre, cable, copper and wireless change over time? Let's try and answer the question initially in terms of mobile broadband access backhaul economics. It seems likely that backhaul from femtocells will continue to be carried for at least part of the way over copper twisted pair with the caveat that fibre over utility poles may change this over time, a topic addressed in the next chapter. Microwave vendors argue that microwave transport will meet the foreseeable capacity needs for mobile backhaul for many years to come using a combination of licensed, lightly licensed or unlicensed spectrum. The argument is based on the assumption that a 10-MHz LTE radio channel will require a backhaul of the order of 150 Mbit/s. 2 Point-to-multipoint hardware examples, with thanks from Cambridge Broadband Networks. Making Telecoms Work The number of channels supported depends on the configuration of the base station on the site including the number of sectors and number of channels per sector, the channel spacing used (5, 10, 20 MHz or bonded channels up to 100 MHz) and cell geometry. Cell geometry is the term used to describe the distribution of users in a cell relative to the cell centre. The further away from the cell centre the weaker the link budget and therefore the lower the data throughput. The IP packet throughput is therefore likely to be significantly less than the headline physical layer throughput figures would imply. A counterargument is that if operators start sharing the radio access network or if neutral host networks become more prevalent and if legacy GSM voice channels and HSPA and LTE data channels and ultimately presumably LTE IP voice get aggregated together then this implies several hundred MHz of instantaneously available bandwidth. A 13-band base station, if such a beast existed would have access to more than 1100 MHz of radio bandwidth, potentially available on each of three o