The number of PoP and sectors were estimated according to the requirements of a dimensioning project. The final step is to combine these results into the optimum BS configuration. Clearly the estimated PoP and sectors are the absolute minimum according the needs of coverage and capacity, respectively. At this stage joint consideration may suggest that more PoP or sectors may be necessary. There are three possible conditions:
- Balanced network: The number of PoP approaches 1/x of the number of sectors, which means that in each PoP roughly x sectors will be deployed. The number of sectors for blanket coverage should be 3 < x < 6, where x = 3 for Mobile WiMAX. This condition ensures both the integrity of the footprint and satisfies the capacity requirement.
- Coverage-limited network: The number of PoP is quite higher than 1/3 of sectors. The network is coverage limited and in this case the number of sectors should be increased until the previous condition is met. The fact that the original business plan leads to a coverage-limited network should be stated in the dimensioning study. CapEX is driven by coverage performance indicators, while the additional sectors will further increase the air-interface capacity. Operators may want to revise the size of the service area, or exploit the additional capacity.
- Capacity-limited network: The number of PoP is quite lower than 1/3 of sectors, which indicates either additional PoP or higher sectorization (sectors/PoP). Increasing the number of PoP will trigger additional CapEX and OpEX in terms of site acquisition and preparation. Therefore, if a higher sectorization scheme is possible, such as when the terminals are fixed-outdoor, fixed-indoor, or nomadic where handover is not necessary, it should be preferred as a cost-optimum solution. When the network needs to accommodate mobile terminals and provide handover capability, the sectors should be 3 < x < 4 and more PoP may be needed. An alternative approach would be to deploy a dual layer cell where 6 sectors of 120° are used, however each pair of sectors (i.e., 1 and 4) is assigned the same azimuth. For a dual layer cell at least 6 channels are necessary for the frequency reuse of 1.3.3.
The selected number of sectors per PoP defines the BS configuration in terms of frequency reuse/channel assignment, and antenna beamwidth/azimuth/tilt, while other air-interface parameters are not related to dimensioning. Capacity or coverage dimensioning should be revised based on the above-mentioned conditions, for coverage or capacity limited cases, respectively. A comparison between initial requirement and actual achievement should be included in the dimensioning study.
