A mobile cellular network operator is already offering voice and data services – but should it enhance its existing network in particular hot-spot areas? And would this enhancement be best achieved by installing GPRS/UMTS micro-cells or by using a network of 802.11b access points which would also provide data services at a higher rate?
Context
The alternative technological structures for the network are illustrated below.
This model considers the incremental costs and revenues arising from these enhancements in a particular hot-spot. It is assumed that a macro-cell of the existing network already covers the hot-spot, so that the costs included in this model are simply those of the additional network hardware required in the hot-spots (i.e. no increase to indirect costs). Equally, the revenues gained are only those provided by the additional service over and above what the macro-cells can provide.
A number of scenarios are used to evaluate the business case for installing 802.11b equipment in hot-spot areas.
The model is presented in a series of views: (a) the Service structure view shows all the information about the demand and associated revenues; (b) the Services bandwidth view takes the demand and parameterises it in a way that can be used to dimension the network; (c) the Network hardware view illustrates all the costs; and finally, (d) the Scenarios view shows the various sets of scenarios. These are now considered in turn.
Market, voice and data services
The Service structure view defines the market, the users and their usage patterns, as well as tariff data. The total market is considered to be the number of visitors to the hotspot area over the course of a year. A penetration is then applied to this market to give the number of mobile Internet users, which is then divided according to the users' choice of technology – GPRS, 802.11b (if available), or UMTS (from 2005).
In order to calculate the requirement for GPRS and/or UMTS micro-cells it is necessary to know the demand for both data and voice services for these technologies. Consequently, in addition to the data services there are also two mobile voice services defined for GSM and UMTS.
Bandwidth calculations
The Services bandwidth view takes the busy-hour traffic from each of the services and puts them into a common form - namely, the bandwidth (Mbit/s) per service - which can be used to dimension the rest of the network. For the voice services (which have a busy-hour traffic in Erlangs) this requires an Erlang-B transformation to calculate the number of circuits required for a given probability of blocking (2% in this case). For the data services, the busy-hour traffic is already in the form of bandwidth, so the only requirement is that the voice and data traffic is summed separately for GSM/GPRS and UMTS so that the traffic above and beyond the capacity of the existing macro-cell can be established.
Network hardware
The Network hardware view shows the three sets of costs for the three access network alternatives (GPRS, UMTS and 802.11b), which work in combination to meet the specified demand for broadband Internet access. The 802.11b access points are installed to meet both the coverage requirements of the chosen hot-spot and the demand (in Mbit/s) per user. Equally, the GPRS and UMTS micro base stations are installed to meet the demand per user over and above that which can be accommodated by their respective macro-cells.
Scenarios
The Scenarios view defines four sets of scenarios, governing: (a) the scale and efficiency of the hotspot site, (b) whether or not 802.11b is installed at that site, (c) whether the user is charged per visit or per Mbyte, and (d) whether the 802.11b access points are configured for low coverage/high data rates or high coverage/low data rates. These are detailed in the table below.
| Scenarios |
Variants |
| Site details |
Airport; Mall; Park |
| 802.11b installed? |
Yes; No |
| 802.11b tariff option |
Charge per Mbyte; Flat fee per visit |
| 802.11b coverage type |
High coverage; Low coverage |
The resulting Network NPV with and without 802.11b is illustrated to the right (for a high-coverage airport scenario with per-Mbyte charging).
Excel input sheets
The model uses STEM to perform all the modelling calculations, but it can also be controlled entirely through a Microsoft Excel interface. A linked Excel spreadsheet (DATA.XLS) holds all the key input variables, allowing users to readily alter scenario inputs to run what-if analyses, and to change the costs of the network elements. The STEM model can be run via an add-in toolbar in Excel, and the results from the model are available to the workbook and can be comprehensively interrogated without leaving Excel.
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.
