@fibresystemsmag | www.fibre-systems.com


FEATURE MOBILE FRONTHAUL


ADVANTAGES OF A C-RAN ARCHITECTURE


A C-RAN architecture, where remote radio heads (RRHs) are sited at cell towers and baseband units (BBUs) are centralised and connected via predominantly radio over fibre links, promises several benefits over traditional approaches. One of the biggest


anticipated advantages is in


energy efficiency. Centralised processing enables the number of BS sites to be reduced, which brings savings on support equipment such as air conditioning. Centralised processing


should also help traffic to be allocated more efficiently between cells and reduce interference between RRHs.


This should simplify load balancing and traffic sharing between sites because all the BBUs are in one place and, in some implementations, shared across all the RRHs using virtualisation. This is a particular benefit for new LTE networks where rapid communication between BSs is an important part of


the standard. Optimising the use of each BBU and use of virtualisation also lowers power consumption because at times of lower use idle virtual BSs could be selectively turned off without disrupting the service. In addition to power


savings, the C-RAN architecture promises other savings in both capital


expenses and operating costs. Aggregating BBUs and site support equipment in a few central locations simplifies management and operation. In the C-RAN architecture the equipment located at cell sites is simpler and lighter so requires less maintenance and support and is quicker to install.


Ethernet signals over the same 10G wavelength,’ he said. According to the company’s latest quarterly


report: ‘Transmode’s Mobile Fronthaul solution was successfully tested in the quarter, securing type approval by France Telecom/Orange Labs in Lannion, France. Tis equipment has been verified against 3GPP standards for LTE and interoperability against Ericsson and Alcatel Lucent radio equipment.’ ‘We’re very proud of this development. It’s a


real testament to the capabilities of this product,’ said Baldry, who added that a second operator has also run successful field trials with the company’s fronthaul solution. ‘It’s early days for fronthaul over WDM. We’re pleased to be pushing it with equipment we’ve had for many years.’


New standards


Israel-based startup IP Light, which develops OTN processors for WDM communication, is also excited about the potential of fronthaul for mobile networks and is working hard to address the challenges. Markus explained: ‘Optical mobile fronthaul is unlike classical optical networks. It has unique features, so you can’t just repackage what’s done for other things. In order to carry CPRI signals, there are very strict requirements with delay, latency, and jitter and you need to transmit digitally.’ He continued: ‘In looking at effective ways to


integrate CPRI signals, operators are faced with two choices: proprietary or OTN.’ He noted that the barrier to using OTN is that


the current OTN standards have a binary structure. Tis is a challenge because cellular operators use directional antennas, each covering either 180 degrees or 60 degrees. Te signals from the latter – six antennas – do not divide neatly or efficiently into a binary transmission system. ‘At IP Light, we’ve come up with an idea of how to address the electrical parameters and we are


proposing modifications to the OTN standard that will be optimised for CPRI signals,’ he said. Tis solution, which he says ‘takes advantage of


different features of fronthaul’, will be presented to the ITU. ‘Our proposal will offer significant advantages,’


he said. ‘It’s a new type of signal so it would not only offer a much better solution for CPRI Option 3 but there is a natural evolution to other CPRI signals. Te benefits are tangible whichever rate of transmission operator goes for,’ he said. ‘We realised early on that we were catching


what would be an enormous market at very early stages and that there is an opportunity to help shape its course. Tis is very exciting for a young


At the start of 2013 not many people had heard of fronthaul; 2014 will be key


company,’ he continued. ‘We’ve also incorporated some capabilities to enable to operate in various scenarios, using greenfield new fibre or existing infrastructure, including relatively low-quality fibre, where operators still want to ensure very high-quality transport of, for example, real-time video.’


Weighing up the options


With any new approach there will be a range of options, and Baldry of Transmode anticipates that this will continue. ‘Operators have tens of thousands of cell sites, all in different conditions. Ultimately you’re competing against dark fibre. If that fibre is deemed to be virtually free, that can be challenging. Tat’s why we’ll probably end up


with a mixture of solutions, passive at short distance, active at longer maybe. Having a range of options will be an advantage.’ And this includes alternatives to fibre. ‘We


would love to have fibre everywhere but we are realistic that not all cell sites are fibred up and that for some it doesn’t make business sense,’ he said. ‘Because CPRI is digitised RF it is less spectrally efficient and so you need much more bandwidth for fronthaul than backhaul. If fibre exists you’d use fibre, if no fibre then you’d use other solutions, although some of these still have some challenges to address due to the bandwidth requirements and demanding technical requirements.’ Real networks could also be an interesting


mixture of approaches too. ‘One of the nice things with WDM is you can build a network carrying different types of traffic, including both fronthaul and backhaul, over the same fibre. You could draw a nice, neat diagram for these networks but that’s not the reality of networks as they totally overlap each other in practice.’ Baldry noted that, so far, conversations with


operators have been about macrocells but that some of the ideas could be extended to small cells in the future. ‘At the start of 2013 not many people had heard


of fronthaul; 2014 will be key for taking it forward.’ Markus agreed: ‘We have crossed the line of


the question mark. Te market that will be created with fronthaul could be enormous. To call it snowballing would be an understatement.’l


Further information


C-RAN The Road Towards Green RAN, White Paper Version 2.5 (Oct, 2011), China Mobile Research Institute labs.chinamobile.com/cran/wp-content/uploads/ CRAN_white_paper_v2_5_EN.pdf


CPRI www.cpri.info


Issue 3 • Spring 2014 FIBRE SYSTEMS 29


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36