Network optimisation
How can operators meet the challenge of optmising 2G and 3G networks to work effectively in combination? Here Gur Lavie explains the problems and solutions.
With more than 60 installations around the world and 33 million subscribers, the migration from 2G to 3G networks has become a functional reality. Typically, the transition period is facilitated by layering the new UMTS based 3G network over the incumbent 2G network, creating the operational challenge of managing the two co-existing network layers. Operators must take into account any adverse impact this co-existence may have on overall network quality, user experience and the service provider’s average revenue per unit (ARPU) in both the 2G and 3G network layers.
Two main considerations exist for operators managing the network layering. The first involves synchronising the planning and deployment of 3G over the existing 2G layer to achieve better coverage and increase ROI. The second consideration involves optimising the interaction between the two layers (e.g. handovers, timing, and power thresholds) to achieve greater capacity and a better user experience.
Synchronise planning
To maximise network performance, the 2G and 3G layers should be approached as a unified system rather than two distinct networks. Although operators often realise significant network efficiencies by site co-location and sharing the fixed and backhauling resources, the respective back office configuration databases are usually separate, especially when the 3G network is delivered by a different vendor than the 2G layer.
From a database maintenance standpoint, this means that information such as site locations and antenna profiles are duplicated, increasing the possibility of data inconsistency. From a planning standpoint, the existence of two separately defined systems limits the ability to analyze the two layers as a functional whole.
Moreover, lack of a unified view of both the 2G and 3G layers may result in non-optimal handover behavior, since the task of effective ‘Neighbor List’ planning (neighboring cell sites for implementing handovers) becomes very challenging to perform in a precise, repeatable manner. As a result, services can be adversely impacted. For example, it may not be possible to restore full bandwidth service when a mobile moves from 2G back into 3G coverage, thus resulting in degradation of the quality of data services. Similarly, real-time traffic (e.g. streaming video) might be delivered with degraded quality. Finally, users may experience increased dropped calls when leaving the 3G coverage area.
Over time, network performance problems of this type may lead to user dissatisfaction, resulting in increased churn.
Layer interaction
Parameter optimisation is crucial to network effectiveness, as is seen in the analysis of network statistics on deployed networks. Conversely, the absence of parameter optimisation can cause bad timing in 3G/2G handovers. Erring on the side of late handover timing causes the drop rate to increase as much as two fold; erring on the side of early handover timing risks losing precious traffic potential. Bad timing in 3G/2G reselection can yield a “ping pong” effect in terminals’ “idle” mode. Revenue loss is almost guaranteed in these situations as the user will appear to be ‘unavailable’.
Most of these issues will not appear on day one of a network launch, as their impact tends to increase with traffic load. While operators may be able to overcome some of these problems by investing in better 3G coverage, recent experience shows that proactive, continuous optimisation is a better solution. This is particularly true as 3G networks are only expected to be stable after three to four years of deployments.
Unified Network Modelling
Unified Modelling of the 2G and 3G layers of the Radio Access Network (RAN) is key to achieving optimisation of a layered network. Unified 2G and 3G RAN Modelling should incorporate multiple coverage and quality data sources, such as signal strength predictions, drive tests, frequency plans and operational measurements from RNCs, BSCs and MSCs. Further efficiencies can be achieved by using special algorithms and statistical methods that enable leveraging the same data for 2G layer planning and optimisation to 3G and vice versa.
In turn, this Modelling enables identification of traffic loads per sector and service type. Thus, sector and RNC parameters can be tuned to allocate the relevant traffic to the appropriate 2G or 3G sector. Unified Modelling can also play an important role in minimising 2G investments. By taking customer migration to the 3G network into consideration, 2G sites can be adjusted to accommodate the new traffic patterns thus freeing resources for other heavily loaded cells.
Finally, unified Modelling facilitates optimisation of inter-RAT (Radio Access Technology) handover strategy on the basis of traffic per site, taking both layers into consideration. This provides the best solution to questions like where, when, and what type of traffic should be handed over in each situation. For example, voice traffic can be handed over to the 2G layer, freeing 3G resources for uniquely 3G data services, maximising the 3G experience. optimisation characteristics must be set for 3G border sites to support short distance handover, so as to keep reasonable 2G radio conditions.
Summary
The complex challenge of successfully deploying and maintaining revenue-yielding 3G networks in conjunction with 2G networks can be greatly simplified by using automated planning and optimisation products.
As users migrate from 2G to the new 3G network, overall traffic levels increase and traffic patterns of the legacy 2G network also change. In this very dynamic environment, keeping the network synchronised and optimised is an ongoing challenge. Using automatic integrated optimisation products for 2G and 3G enables the carrier to sharpen the focus on the layered network as a whole. Products such as Schema’s UMTS OptiPlanner and GSM Forté integrate all relevant data sources to optimise the delicate balance between the GSM and UMTS layers and resolve key interaction problems between the network layers.
Network engineers use these types of products as a means to increase the overall network utilisation and effectiveness.
Using real-time integrated Modelling of the 2G and 3G environments, which takes continuously updated network data as input, can be an invaluable tool for achieving optimum, up to date handover configuration, parameter tuning and deployment planning. This approach paves the way for a smooth and controlled transition period.