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FEATURE MOBILE FRONTHAUL


networks to transmit the same amount of data. In addition, in order to maintain the speed of


response, people are used to with traditional RAN setups, fronthaul must deliver very low latency and latency jitter, over many kilometres. ‘How to achieve a low-cost, high-bandwidth


and low-latency wireless signal optical fibre transmission will become a key challenge for realisation of the future LTE and LTE network deployment by C-RAN,’ wrote China Mobile in the company’s white paper. Tere are several approaches for delivering


fibre fronthaul for C-RAN. First, there is the use of dark fibre, which can be a good option where there is already plenty of fibre available. Tis has benefits for speed of deployment, but network extensibility could be a challenge. An alternative is to use a solution based on


wavelength-division multiplexing (WDM) and optical transport network (OTN). Tis improves the bandwidth for transporting RF over fibre using standards such as the common public radio interface (CPRI) protocol and enables a large number of cascading RRHs on one pair of optical fibres. CPRI is a digitised RF signal that can be carried over an optical


network. It supports a number of line rates from roughly 600 Mbits/s to 10 Gbits/s. China Mobile conducted its first C-RAN trial


with partners in 2010 in Zhuhai city, Guangdong province, China and has since carried out several further trials with a range of cellular technologies and in a range of locations. Te operator reported the results as promising. ‘By using new technologies, we can change the network construction and deployment ways, fundamentally change the cost structure of mobile operators, and provide more flexible and efficient services to end-users.’


Optical options


‘Fronthaul is quite challenging to do. Fundamentally it’s quite simple, but the reality is that the synchronisation and low-latency requirements are really quite hard to achieve,’ observed Jon Baldry, technical marketing director for Sweden-based optical systems manufacturer Transmode. ‘Early developments in fronthaul have been in Asia, but have been almost exclusively throwing fibre at the problem rather than building an optical network. OTN multiplexing today can’t meet the


Jon Baldry Issue 3 • Spring 2014 FIBRE SYSTEMS 27


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