FEATURE MOBILE FRONTHAUL
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Tackling the mobile data tsunami
Over the past couple of years a new buzzword has entered network discussions. Siân Harris finds out what mobile fronthaul is, and why mobile operators are so excited about it
L
ess than two decades ago, the idea of mobile communication was a novelty and the possibility of mobile data was not much more than a dream. But
within the past three or four years that dream has really become a reality, and checking email or Facebook, sending photos, and watching YouTube clips on smartphones are now normal parts of everyday life. Such a transformation has of course come
about as the result of phenomenal developments in mobile technology behind the scenes. But it’s not over yet. Data over mobile devices is slower than people are used to at home, and there is a limit to what people can do over 3G networks – or even over the new LTE networks. According to Ruben Markus, CEO of
Israel-based IP Light, ‘the objective of mobile operators beyond LTE is to deliver to portable devices bandwidth that is comparable to fibre to the home. In principle this means hundreds of Mbit/s per device.’ He continued: ‘In order to deliver this kind of
bandwidth, you need to increase the number of RF transmitters and receivers,’ adding that mobile operators usually address this with a combination of increasing the number of antenna sites and increasing the number of operating bands. However, this all comes at a price – and, in a
competitive environment, mobile revenues are not growing in line with costs. Tis is an issue that operators are very
concerned about. In a white paper first published in 2010, with subsequent updates, the operator China Mobile set out the challenges in detail, particularly in relation to the RAN (or radio access network). Traditional RAN architectures consist of
base stations (BSs) connected to a fixed number of antennas covering individual cells. Each BS needs to be able to cope with the peak traffic in
26 FIBRE SYSTEMS Issue 3 • Spring 2014
that cell, but traffic varies hugely depending on the location and time of day. For example, cells in residential areas see a traffic surge at breakfast time and in the evening but during the daytime much of that traffic shiſts to where people are working. Similarly, cells near sports or concert venues see traffic surges when there is a big game, or a popular band is performing. Having individual BSs for particular cells
limits the possibility of responding to changes in traffic demands. To date, cells have been required to be able to cater for their peak traffic, meaning that, in quiet times, processing capacity, and power, are wasted.
In a competitive environment, mobile revenues are not growing in line with costs
And, as mobile internet demands increase
and technology advances, the number of sites increases. For example, China Mobile said that, in the past five years, it has almost doubled its number of BSs, to provide better network coverage and capacity. As a result, the operator said, the total power consumption has also doubled. Tis all has major implications for operators
working in an increasingly competitive market. ‘Traditional RAN will become far too expensive for mobile operators to keep competitive in the future mobile internet world,’ reported the China Mobile white paper. In addition, there are capital costs involved in
installing BSs at each cell site. According to China Mobile: ‘In general, up to 80 per cent
CAPEX [capital expenditure] of a mobile operator is spent on the RAN.’ What’s more, as cellular telecoms technology
evolves, operators are required to support multiple standards and frequently update their equipment, and there are high maintenance costs every time engineers need to be sent to cell sites.
Centralising in the cloud
A proposed solution that has begun to receive much attention in the past couple of years is to separate the processing part of the system from the radio head and to centralise much of the BS technology. Tis creates a so-called C-RAN architecture,
where the ‘C’ stands for ‘centralised’ or ‘cloud’. In C-RANs, remote radio heads (RRHs) are positioned at the cell sites and the baseband units (BBUs) are located away from the cell towers in a central location, which might be anything from 10km to 40km away. With this set-up, each RRH is no longer tied
to a specific BBU, saving space and power at antenna sites and making it easier to allocate processing power to where it is needed. ‘Once you get rid of individual RANs you
simplify cost, power, maintenance and demands on technical staff. Basically it’s win, win, win, win,’ said Markus.
Glass pathways
A key component of this new approach is having a good link between the RRH and the BBU. Optical fibre is an obvious choice for this so-called ‘fronthaul’. However, there are stringent requirements for this fibre. Information is transmitted as unprocessed RF over fibre signals. As a result, significantly more bandwidth is required than would be aſter processing; fronthaul networks need around 20 or even 30 times the bandwidth of backhaul
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