Getting the Best Out of Cloud RAN in LTE

Operators considering a move to Cloud RAN architectures will need tools that can control inter-cell interference, co-ordinate super-cells, and provide advanced scheduling to manage constrained resources. Paul Mace explains how these elements can cost-effectively upgrade the network, and deliver enhanced user experience.

The early years of the twenty first century witnessed an intense scramble to capture customers with network operators offering mega deals to entice users. By the end of the decade, mobile subscription rates had risen to 128% in Europe. This left the operators with a new challenge – how to manage their networks in a way that provided the best end user experience without overloading their networks.

The arrival of smart terminals and the rising demand for mobile broadband has opened a new revenue stream for operators. However, it has also increased the load on networks. The insatiable appetite for data heavy services, whether it’s business applications, videos, using GPS location services or the ubiquitous gaming apps, have put even more stress on the already creaking networks.

LTE Delivers Capacity for Network Operators
The introduction of Long Term Evolution (LTE), the next generation of mobile network technology, represents a beacon of hope. It will equip network operators with advanced technology to deliver superfast connections, improved end user experience and increased return on investment. But LTE is not without its challenges.

LTE Challenges

Heterogeneous networks sharing the same frequency:
When 3G was first introduced in the late 2000s, the technology from both generations (2G and 3G) coexisted. There was no need to rip and replace existing network infrastructure. The same principle will apply to the deployment of LTE. Thus, three generations of technology will live side by side but heterogeneous networks sharing the same frequency leads to signal interference.

Densely situated base-stations:
LTE comprises of various layers of different-sized cells ranging from big (macrocells) to small (picocells and femtocells). In order to maximise the full bandwidth capacity of the radio spectrum, operators need to support traditional large macrocells with small cells. As a result there is a higher density of base stations when compared to 2G and 3G networks. This is a major contributor of inter-cell interference and limits the transmission capacity of wireless networks.

Network Congestion:
Adding to this explosive mix is the growing demand for mobile data. According to the GSMA, by 2015, Europeans will consume more mobile data than any other region in the world. This will have a direct impact on network congestion making signal interference a big hurdle for the operators.

The amalgamation of all these challenges is expected to result in an acute interference problem in LTE networks. Interference has a direct impact on the network performance, especially at the cell edge and will affect not only resource utilization but also end user experience.

To ensure the substantial sums being invested in updating to an LTE network deliver the best return-on-investment for operators and customers, mobile service providers need to plan ahead. The key is to find a resolution that effectively addresses the interference problem. A solution that will break through the limitations of existing collaboration technologies, improve network performance, especially at the cell edge, without another round of investment in bearer network.

CoMP only works if there are extensive backhaul assets in place. Despite the best intentions and planning, these assets are seldom available in real world environments.

Coordinated Multipoint Transmission/Reception (CoMP), an interference management technology that coordinates and combines signals from multiple cells’ antennas has been built into the LTE protocol. It works by turning the signal interference, common at the cell edge and when instigating handovers, into a useful signal and enables operators to optimise their network and deliver a more consistent user experience. It does this by incorporating a number of key technologies such as multi-antenna enhancement, MU-MIMO, and multi-point joint coordinated transmission. However, CoMP only works if there are extensive backhaul assets in place. Despite the best intentions and planning, these assets are seldom available in real world environments.

Software Based Radio Optimises Spectrum Efficiency
Network infrastructure providers such as ZTE are already working on a set of ground breaking network optimisation tools that will help to eliminate interference. Based on Software Defined Radio (SDR) technology such as IP-RANs (IP-Radio Access Networks), Microwave and Packet Transport Network (PTN), these tools will enable the operators to make the most out of the huge investments they’ve already made in fibre and backhaul assets without requiring another round of investment. These tools incorporate two key elements – Cloud Coordinator and Cloud Scheduler.

Cloud Coordinator:
Many operators, especially in Europe, do not have enough dark fibre and thus rely on IP fibre – a significantly slower alternative. ZTE therefore developed a new technology called cloud co-ordination that can be used for soft bit (after-process data) combining. This enables seamless and borderless coordination for the whole network and improves end user experience. The ground breaking technology creates a super cell by combining traditional physical cells into an umbrella cell. It helps reduce the number of cell edges and handover times and thereby improves user experience. The enhanced cell cluster or the super cell will actually follow the user as they move around the network, replacing the static clusters which often suffer from drops in service levels at the cell edge where there is most interference, or as the user is handing over to a new cell cluster.

Cloud Scheduler:
ZTE developed cloud scheduling in order to address the issue that many operators have, in that they still have very limited fibre and use microwave for backhaul. The Cloud Scheduler provides real time management of network resources. It utilises a central scheduler to allocate resources on a real-time basis according to user distribution, service type, traffic flow and cell interference. It drastically reduces interference between cells and improves cell throughput by creating a unified network scheduling.

Network operators are desperate for revenue growth and are moving from focusing on subscriber growth to customer retention. The secret behind customer loyalty is a great end user experience. Mobile network operators are depending on LTE technology to deliver this. Therefore, it is imperative to plan any network upgrade with care to ensure the best possible end user experience and return on investment. Interference has been identified as a major issue but there is a way out. SDR based technology has the potential to address this and thereby mitigate another round of investment further down the road.

Paul Mace is Infrastructure Director, ZTE UK.

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