China has always been the biggest driving force behind Cloud-RAN. China Mobile mooted the concept initially, and while its ideas have been adapted to suit all kinds of scenarios, Chinese carriers remain the most ambitious deployers. China Telecom is building a fronthaul network which it says will lay the foundations for a 4G/5G Cloud-RAN, enabling it to improve urban density and expand LTE coverage.
The fronthaul network, in north-east Liaoning province, is based on Huawei’s Blade OTN (optical transport network) solution. It will support long-range links between cell sites and virtualized, centralized basebands, but will also provide high speed fronthaul for clusters of small cells.
These will be essential for China Telecom’s local affiliate, Liaoning Telecom, to support dense urban deployments while also improving the reach of the existing LTE network. Deploying virtualized central base stations, serving multiple low-footprint, low-power radio/antenna units, helps address the issues of finding large numbers of sites and fiber links, since only the central equipment needs significant space or backhaul. Liaoning Telecom has been gradually adopting C-RAN architecture to cope with these difficulties in site acquisition and energy consumption.
Huawei says Blade OTN– which is part of its broader X-Haul architecture –uses its Turbo WDM Technology to achieve 100G bandwidth using 10G optical components. It supports up to of 15 channels of CPRI (Common Public Radio Interface) access and can aggregate multiple service channels. Huawei believes that the resulting lower TCO (total cost of ownership) will enable Liaoning Telecom to reduce core fiber requirements by over 90%.
The vendor also claims that its solution eliminates wavelength planning, automatically provisions services at power-on, and remotely locates faults, which all helps to fulfil the C-RAN fronthaul requirements for rapid network deployment and automatic operations and management. In addition, cascading is designed to enable smooth evolution towards 5G fronthaul.
Of course, many believe the key to unlocking the C-RAN market will be finding an alternative to CPRI, which has various downsides – each vendor’s implementation is proprietary; it is inefficient (it uses data even when there is no traffic); and it increases as additional antennas are added.
The guardians of the CPRI interface, Ericsson, Huawei, NEC and Nokia, have been extending the technology’s reach with projects focused on wireless CPRI, and a 5G-oriented new flavor, eCPRI. This is based on new functional partitioning of the base station functions, positioning the split point inside the physical layer.
The aim is to deliver several benefits:
- The new split point enables tenfold reduction of the required bandwidth, say the companies
- Required bandwidth can scale flexibly according to the user plane traffic
- Use of mainstream transport technologies like Ethernet will be enabled
- The new interface is a real time traffic interface enabling use of sophisticated coordination algorithms guaranteeing best possible radio performance
- The interface is future proof allowing new feature introductions by software updates in the radio network
However, some players believe eCPRI will still not be unified, since it remains dominated by the same vendors, and that it may be more efficient to look at other options such as millimeter wave, G.fast copper, or other Ethernet implementations. All of these are being trialled or even deployed, but have not yet displayed performance to match the likely demands of 5G. Other attention is focusing on potentially more cost-effective fiber approaches such as PLS (Physical Layer Split) and ARoF (Analog Radio over Fiber).