By Chris Larmour*, CMO, Celcite
Self-organizing networks (SON) address the challenges posed by increasingly complex mobile networks by automating the provisioning, configuration and reconfiguration of the radio access network (RAN) for optimal capacity and performance. The benefits are clear. Operators who have installed it have seen more than a 15 per cent improvement in capacity utilization and greater than 20 per cent improvement in the dropped call rate. However, like any powerful technology, it needs to be put in the right hands.
To explain the implications, we need to start at the beginning. There are two main types of SON, decentralized and centralized. Decentralized SON (D-SON) only applies to a single node and does not allow for any coordination between different infrastructure vendors' equipment. With D-SON, because the SON process happens at a distributed level, its effects are very localized. Nonetheless, that can set up conflicts with other instances of SON elsewhere on the network. From experience, most operators that have installed some level of D-SON on their network soon realize that they need some level of centralized organization layer. Because of those limitations and scope for conflict, there is even some concern that D-SON may already be a redundant technology.
Centralized SON (C-SON), on the other hand, allows the whole network to be self-optimized because it is a conglomeration of multiple, smaller use cases that focus on solving a single problem across the whole network. But even with C-SON, the vendor absolutely needs experience of live, in-network installations of SON or risk setting up conflicts in the operator network, which could potentially lead to making the network worse, not better.
There are two key functions required to prevent conflict in C-SON. These are the trigger function, which determines which use case to initiate based on specific symptoms, and the coordination function, which manages any conflicts on the outbound command path to the network. The coordination function plays a pivotal role in deciding which command should take precedence over another, and in which order they should be transmitted.
Without the coordination function in place, a worse-case scenario of “Runaway SON” could occur. It would come about if a command gets into a never-ending loop between two cells, setting in motion a chain of events which can ultimately lead to network outages. For example, one bad command may create a condition on one cell that the SON system senses, and corrects it on that and subsequent cells. Then, the first SON system catches the “bad” condition on the “corrected” cells, amplifying a single mistake and catalyzing a chain reaction of errors. While this is currently only a theoretical scenario, for SON vendors without in-network SON experience and years of network management experience, it is a potential reality.
Mobile operators are sometimes wary of autonomous systems because of the risk of such outages occurring without human involvement. But humans do not have to be completely left out of the picture, particularly at the early stages of an installation. Operators can start by incorporating some human involvement into the command loop. This “open-loop” method allows for greater control of the SON system since live personnel can decide if a particular change to a cell should be pushed to the network or not, minimizing the risk of a command being incorrectly prioritized and causing network outages. Once the foundation of trust is built, human intervention can slowly be removed from the equation to enable a completely autonomous SON system, once real people have seen how effective the system is.
Operators that have installed an “open-loop” system have made the switch to fully autonomous in as little as four weeks in our experience. This shows just how quickly operators can be convinced of the real-world benefits of SON when they see it in action. If operators keep a skeptical eye on D-SON and do not rush to engage partners without live SON experience, there is no need for conflicts to ever become an issue. Then finally, the positive impact of SON, and C-SON in particular, of improved customer experience and reduction in CAPEX and OPEX can be felt universally.