The task of radio planning is to define a set of site locations and respective BTS (Base Transceiver Station) configurations with addressing the coverage and capacity figures derived from dimensioning. Dimensioning a new network/service is to determine the minimum capacity requirements that will still allow the GoS (Grade of Service) to be met. Site densities in each clutter type are one of the outputs. The site count, i.e., number of sites in a considered service area, derived in radio planning often differ from the site count derived from dimensioning since the actual site coverage may differ significantly from the assumed empirical model(s). There is always a risk that the planned site count may exceed the estimated site count from dimensioning. As a result several planning iterations are needed to reach a reliable figure.
One problem with radio planning deals with site density. Firstly, higher site density poses more difficulty in finding suitable candidates. This is true in all clutter types. In dense areas, most suitable sites are already overcrowded with 2G and 3G antennas. This will likely put the WiMAX antennas in less ideal positions. Secondly, there is a tendency that the candidate sites are not having comparable heights. This is a major drawback in radio planning because large differences in heights can distort the site dominance areas and cell ranges. The third problem is the bandwidth constraint which may require tighter frequency reuse. In this case, the radio plan must be as close as the ideal case.
Radio network planning normally follows the dimensioning exercise. Sometimes the dimensioning process includes a rough plan to justify the site count and coverage level using some commonly accepted propagation model and generic WiMAX system modules in the planning tool. In the actual planning phase, a number of inputs are needed to improve the quality and accuracy of the radio plan. Depending on the selected planning tool to use, a number of inputs maybe required to be fully utilized by the tool. For example, it is assumed that following items are already well considered:
- Propagation characteristics of various areas (propagation models tuned)
- Required inputs defined (clutter maps, terrain maps, building data, etc.)
- Traffic and demographic information, i.e., per clutter type
- WiMAX RF equipment parameters are defined (antennas, RF [radio frequency] features, etc.)
- Options for BTS configuration (sectorized, omni, PUSC [partial usage of subchannels], FUSC [full usage of subchannels])
- CPE (customer premises equipment) types and parameters defined (antenna types, mounting, diversity)
Two important decisions with regards to radio planning have to be considered prior to the actual planning exercise. Firstly, the level of accuracy when it comes to coverage and capacity needs to be considered and this highly depends on the accuracy of the propagation model in the planning tool. Secondly, the planner needs to decide how much RF optimization will be undertaken during the planning phase. This is only possible if the planning tool together with the planning parameters and equipments models are accurate enough. It is often the case where optimization is neglected during the planning process. Postplanning optimization exercise is often costly and produces only minor improvements. It is often limited to antenna adjustments (tilting and azimuth changes).
There are a number of features that are useful when selecting a planning tool such as
- Automatic frequency selection
- Optimal site selection—when existing or candidate sites are provided
- Support of mixed and multiple propagation models
- Support of model tuning and user defined models
- Support of OFDMA system including channel impairments
- Optimal downtilting
- Propagation parameters (or constants) for 2.5 and 3.5 GHz
A number of commercial planning tools are available in the market. The major factor that determines the usability of the tool is the accuracy of the RF modeling such as propagation, BTS and CPE antenna models, interference prediction, frequency allocation, and channel models. Planning tools with OFDMA models for capacity planning are advantageous but not necessary since the capacity figures for each site of cluster can be estimated based on the signal quality outputs.
