DIMENSIONING PROCESS

The process of dimensioning involves a sequence of steps, which serve different requirements such as capacity or coverage estimations, to conclude to a final outcome as shown in Figure 1. The input consists of the business plan, the assets, and the key performance indicators (KPIs). The first action is then to verify that all necessary information is available and clarified, alternatively an interactive “questions and answers” session is necessary. During the input analysis, the designers utilize their theoretical and technological expertise to define the dimensioning strategy. In somecases this analysis identifies that potential business plan assumptions could affect the network design process, and a discussion is likely to be initiated with the customer. Such an approach is more appropriate after the award of a contract. The following step is the processing of service characteristics such as the Internet rates and Voice-over-Internet Protocol (VoIP) codecs. In most cases the services are provided in the business plan with their marketing description and it is necessary to identify the impact of each service on the WiMAX air-interface. In the next step, the coverage analysis is performed: the provided service areas are identified and the required number of points of presence (PoP) is estimated. A PoP refers to a WiMAX site, with at least three sectors, which is capable of providing a 360° footprint.

 

Figure 1: Network dimensioning process.

Further to the coverage analysis, the service areas should be also offered sufficient capacity as dictated by customer numbers and services profiles. Therefore the next step is to estimate the required number of sectors to achieve this capacity. The estimates of PoP and sectors are then used to determine the configuration of the BS in the final joint analysis step. It is common after the joint analysis for designers to evaluate the results and proceed with customizations to further improve the solution. In this case, coverage, capacity, and joint analysis may be revised several times before providing the final output. A description of the strategy, the final bill of material (BoM), and a discussion of the assumptions and methodology are mainly the outcome of a dimensioning study.

1 BUSINESS PLAN, ASSETS, AND KEY PERFORMANCE INDICATORS

A well-defined business plan can be the most significant driver behind a successful investment on WiMAX technology. From a cost point of view, a very ambitious plan in terms of subscribers/services will certainly impact CapEX and OpEX, whereas from a design point of view, the impact comes when the requirements are not extensively defined or they contradict the technology capabilities. A revision of the business plan during or after the network design may compromise the network performance or create additional design costs but most importantly it will result in implementation delays. A list with the most common information provided with a business plan is presented as follows:

1. Service area(s): defined with geocoded polygons, including the size in km², and the terrain profile details (i.e., urban, suburban, rural, average building height, etc.).
2. Coverage type: such as fixed-outdoor, on rooftop, or on outer walls, fixed-indoor, nomadic outdoor/indoor, mobile outdoor or any combination thereof.
3. Subscriber profile(s): such as residential, small business, corporate. Subscriber profiles may relate to a specific type of coverage and service.
4. Subscriber distribution: subscriber numbers per profile, per service area, and per deployment year, according to the scalability plan.
5. Service profile(s): such as VoIP, broadband Internet, VPN along with their distinct characteristics (i.e., VoIP codecs, peak information rates, contention factors, etc.). Service profiles may relate to specific subscriber profiles and coverage types.
6. Available spectrum: defined as paired, along with local regulations concerning the allowed channelization and duplex schemes.
7. Existing infrastructure: such as sites that can be reused, available backhauling equipment with Ethernet interface, and core network PoPs.
8. Cartographic data: such as high-resolution digital maps with buildings.
9. Key performance indicators: such as coverage objective in terms of percentage of the service area, differentiated per terminal type, where a stable QPSK link can be achieved.
10. Customer requirement: such as duplex scheme, number of sectors/BS, channel bandwidth, reuse scheme, type of sites, deployment strategy.

2 STRATEGY

During request for information (RFI)/RFP stages, a dimensioning exercise may be requested by a customer, mainly for two reasons: either to acquire know-how by differentiated proposals or to identify the more cost-efficient solution. In the first case, the requirements are usually relaxed so that the participant vendors/integrators can design with flexibility, while the provided information (i.e., business plan, assets, service areas) is hypothetical. The submitted studies will probably be presented in various formats and most certainly based on diverse assumptions. In such case a direct comparison among the studies is complicated, and usually a more defined exercise is the next step. In the second approach, the case study is well defined so that the design assumptions are either implied or directly mentioned. The results are now directly comparable, hence a clear ranking list can be obtained. From RF network designer point of view a different strategy should be followed: showing flexibility in the network design and perhaps providing several alternatives for the first approach, while a more strict, cost-optimum solution is more appropriate for the second approach.