CUSTOMIZED NETWORK DESIGN | WiMAX Networks Dimensioning

Customized network dimensioning provides a major advantage to vendors/integrators by highlighting their expertise and by indicating a cost-optimum solution. In many RFPs or project cases the developed business plan has extensive details which can be exploited in a very positive manner. A common occasion is that the overall service area is broken down into subareas with distinct characteristics, such as common type of customers and terminal profiles, common terrain, or service requirements. Such distinction allows a customized treatment of each subarea, where its characteristics are matched with an optimum solution, thus avoiding an overall rough approximation. The main customizations that can be applied in dimensioning, provided that the necessary information is available, are described below:

• Nonuniform sectorization: The use of different sectorization schemes, depending on the coverage type may result in reducing the required PoP. In some subareas there might be only SMEs, where a fixed-outdoor unit would be utilized. Therefore, in this case there is no restriction to use trisector cells. If the available spectrum is sufficient, up to eight sectors can be deployed in a PoP, depending on the capacity requirements.
• Dual layer coverage: In many occasions the subscribers will use both fixed-outdoor and mobile units hence in this case a more efficient approach is necessary. If extreme capacity is required, a high number of sectors can be used, building a trisector layer for the mobiles and overlapping layer for the fixed, provided that frequency reuse can be applied. The neighboring list for mobile handovers will include only a sector in the first layer, while the demanding fixed links will be isolated in the second layer. This approach is very cost effective in cases where an extreme capacity demand would require a PoP every 0.2–0.5 km, if plain trisector cell layout was considered.
• Nonuniform channel bandwidth: Assuming that extreme capacity is still the performance indicator, by using higher channel bandwidth the capacity per PoP is increased and therefore the number of PoP is maintained at a reasonable level. While the overall network may be implemented with trisector cells, 5 MHz channel bandwidth and 1.3.3 reuse scheme (using 3 out of 4 available channels), a specific subarea with SMEs may be served by quad-sector cells, with 10 MHz bandwidth. In this case, the 10 MHz in the upper band will be assigned in sectors 1 and 3, while the 10 MHz in the lower band in sectors 2 and 4. This arrangement provides a 260 percent increase in capacity for the same footprint. It should be noted that the use of nonuniform channel bandwidth requires specialized sector configuration (transmit power, UL receive target level, and antenna arrangement) and extensive interference studies, applying the interference rejection filter methodology that takes into account the impact from trasmissions in all channels.
• Hybrid coverage: When both fixed-outdoor and nomadic/mobile coverage is required, the design approach is to select the operating range for the worst case condition. This usually leads to a huge upfront network size and investment. An alternative approach would be to consider that only a portion of the service area will be covered with the worst case terminal, hence the cell range can be selected higher. As the network evolves and additional PoP will be deployed for capacity upgrade, the percentage of the mobile coverage in the service area will also increase. This approach is particularly efficient for networks that extend to a large area, however with low subscriber density. The dimensioning is based on fixed-outdoor coverage that can reach higher ranges, however close to a BS there will be opportunity to use fixed-indoor/nomadic/mobile terminals also. 
• Divide and conquer principle: To apply the previous customizations, the service area can be processed in pieces, where each subarea has a specific characteristic. If the segmentation of the service area is not available in the business plan, the designers can perform such action, by requesting or collecting more information (i.e., from site survey). This principle usually drives the network size up, and it is most useful for the actual design phase. The equipment quantities are increased in an exact manner because greater detail is taken into account during the actual design. This method approaches an optimum wireless network design.

It should be mentioned that the advances of the WiMAX air-interface allows greater flexibility and customizations during the wireless network design and hence balances the complexity of accommodating terminals with different profiles.