Equipment sharing in a UMTS roll-out

What will be the financial impact of different levels of equipment sharing and the renting of space on towers for a mobile operator planning to migrate from a GSM to a UMTS network?

This model runs over a ten-year period, starting in 2000 and running through to 2010. This allows the use of current data as the baseline inputs for 2000-2001 while giving enough scope to see the introduction and maturation of GPRS services, the roll-out of the UMTS network and the introduction of UMTS services, as well as the rolling-off of GSM services.

The structure of the network as modelled is illustrated below.

The STEM model is presented in a series of views illustrating various aspects of its structure. These views are considered in turn below.

Voice and data services

The Service structure view describes the services offered by the network, as follows:

The demand for the data services is defined as a penetration into the corresponding voice subscribers (with GPRS data services taking GSM voice as their market). This is because all those who take the data services will have the corresponding voice service, regardless of whether that was their original motivation for taking the service.

All the services feed into transformations which specify the bandwidth required by each service. These transformations are then used in other parts of the model to drive the required resources.

Structure of the access network

The access network bridges the gap between users and the core network. The model contains three views presenting the structure of the access network.

The Base station equipment view splits the required bandwidth into urban, suburban and hotspot regions (hotspots are defined as areas where micro-cells are required). These allow the results for the network to be interrogated by region type to show areas of redundant capacity.

The Base station sites view incorporates options for the ownership of base stations, which may be owned, rented from another operator, or shared. Depending on which scenario is followed, the UMTS network will be rolled out by first upgrading the operator's existing GSM sites where possible, then renting space on other operators' sites, and finally building new UMTS base station sites (either wholly owned or shared, depending on which scenario is selected).

The Backhaul view calculates how many E3 lines are required as transport from the base stations to the Radio Network Controller. It is assumed that dedicated lines will be deployed for urban sites and UMTS hotspots, with all the other types of site being chained together on lines of appropriate size (i.e. E1 for GSM and E3 for UMTS).

Transport between RNCs and MSC

The Transport view is concerned with the transport from the RNCs to the Mobile service Switching Centres (MSCs). It also contains the calculations of the number of connections that are required between MSCs, and the number of connections between the Serving GPRS Support Nodes (SGSNs) and the Gateway GPRS Support Nodes (GGSNs).

A number of simplifying assumptions have been made. In particular, a number of network components are not listed as separate Resources, but are instead costed as part of the MSC. In addition, the RNC is assumed to include the costs for both the controller for the UMTS radio network and the controller for the GSM radio network.

The core network

The Core network view contains the network elements between the access network and the backbone network, namely the RNCs, SGSNs, GGSNs and the Home Location Register (HLR).

Interconnection and Internet connection

Calculations for the charges for interconnection and Internet connection are contained in the Interconnect view. Voice interconnect charges are levied on a per-minute basis and the proportion of calls that are incoming or outgoing are defined by parameters held in an Excel input sheet. The Internet connection charge is quite simply determined by the total packet-switched bandwidth required, and is charged per Mbit/s.

Scenarios

The model contains two sets of scenarios, as shown in the Scenarios view. Each set contains four variants, resulting in a total of sixteen different scenarios for the model as a whole. The first set of scenarios models different levels of equipment sharing for newly built UMTS base-station sites. The second set is concerned with the different options for the sharing of space for UMTS equipment on existing GSM base stations. These scenarios and their variants are detailed below.

Note that it is assumed that any sharing is done with only one other operator, thus dividing the costs by two. The capital expenditure with no sharing and with full sharing of sites is illustrated here (with neither leasing option in operation).

Excel input sheets

The model uses the Analysys STEM modelling platform to perform all the modelling calculations, whilst all the input variables are available to the user in a linked Microsoft Excel spreadsheet, which must accompany the STEM model. The Services input sheet is illustrated below.

The spreadsheet contains six worksheets containing data for Services (illustrated above), Assumptions, Resources, Locations, Transformations and finally Market & Services. The Market & Services sheet is a more complete version of the Services sheet: inputs on the Services sheet are used to calculate the values on the Market & Services sheet and thus the latter only needs to be accessed if the Services inputs do not offer enough flexibility to describe the situation adequately.

A run-time copy of this model can be downloaded on request to run on your desktop, complete with comprehensive documentation. This model can be viewed in conjunction with our standard demonstration package. Outputs can be regenerated for a limited range of inputs; prices are available on request for a fully functional model.