A Tale of Two SONs: Unraveling D-SON and C-SON

Centralized SON (C-SON) is now being deployed for Automated Neighbor Recognition (ANR), cell configuration, power control, interference and load management at the network operations center. This is OSS Level SON emerged first for 3G networks as 3GPP introduced a number of Self Organizing Networks (SON) standards starting with Release 8 in 2008 and expanded them in Release 9 with use cases in 2010/11. C-SON provides a centralized architecture where the optimization algorithms reside in the network management system or a central SON server that manages all edge radio nodes. It can potentially orchestrate the behavior of radio network equipment across an entire network of multi-vendor and multi-technology environments. C-SON can take into consideration data from all nodes in the network to identify and address network-wide issues. And since the control of all SON functions is done centrally, these interactions can easily be coordinated and managed using a variety of resolution techniques.

C-SON solutions generally recommend optimization alternatives that network operations can accept or ignore. Once accepted, these ‘Open-loop’ solutions can be implemented in minutes and kept in place for hours or days. As operators gain confidence, these may become automated ‘Closed Loop’ solutions. Although ’Closed Loop‘ C-SON systems – where the system automatically completes tasks without human intervention – have proven to be successful in many instances, operators often prefer to include some level of human supervision of SON recommendations, particularly in the early days of an implementation. This is known as ‘supervised mode‘ and is a useful step to building confidence and trust of Network Operations Control Center (NOCC) personnel in the deployment of a fully automated SON system. When operators see for themselves the impact of C-SON and become confident of its reliability, stability and capabilities, they can move quickly to the fully closed-loop, automatic mode, ensuring that the economic and customer experience benefits of SON are captured as rapidly as possible.

Three Vendors that are leaders in developing C-SON solutions are: Celcite (acquired by AMDOCS), Ingenia Telecom and Intucell (acquired by Cisco). Arieso (acquired by JDSU) focuses on customer centric ‘location aware’ SON and Reverb is best known for its Antenna optimization capabilities.

C-SON solutions can be more robust against network instabilities caused by the concurrent operation of SON functions with conflicting objectives because control is centralized. However, centralized systems may respond too slowly in the emerging world of small cells that experience very transitory traffic loads.

Distributed SON (D-SON) offers another approach to SON with real time automation and ‘embedded’ RF control at the edge. This is Element Level SON whose functions are distributed among elements at the edge of the network, typically the ENodeB’s to rapidly configure the physical cell identity, transmission frequency and power. D-SON functionality is therefore designed for near real-time response in seconds or milliseconds and therefore supports more frequent and more localized changes than C-SON.

D-SON algorithms run in individual network edge nodes and exchange information directly with one another locally. Each node can initiate SON processes and provide optimization decisions independently or in co-ordination with other nodes. This architecture makes the SON functions highly dynamic and enables the network to adapt to local changes more rapidly.

Initially this decentralized architecture was very vendor-specific and did not allow for easy coordination among equipment from different infrastructure vendors - so a supervisory layer - like a C-SON - was still needed to coordinate the different instances of D-SON across a much broader scope and scale.

Two vendors are now, however, bringing D-SON into the SON mainstream as small cells and HetNets require the millisecond response times of D-SON.

Qualcomm has long focused on small cell technologies to allow simple plug-and-play deployment and increase network capacity by over 1000x of today’s macro networks - now referred to as ‘Neighborhood Small Cells’ (NSC). Based on earlier work for femtocell automation, Qualcomm has proposed a suite of self-organizing network features for NSC called UltraSON Open™. This currently enables 3G dense small cell deployments to automatically provide indoor and outdoor coverage. In parallel UltraSON Private™ “helps traditional restricted access small cell operate robustly with the existing macro-small cell network.” UltraSON Private is now being commercialized on Qualcomm FSM chipsets.