Field survey
After the preliminary planning work a group of engineer visits the location of the cell sites to investigate the followings.
Land procurement: The land should be purchased at the exact location of the base station or very adjacent to it. If land is cheap the guy mast tower is considered otherwise self supported tower should be installed.
Availability of commercial power supply: If high tension (HT) power line is available adjacent to the cell site then own transformer and switchgear is preferable (reliability of power supply) otherwise direct connection from low tension (LT) line can be taken. The detailed planning is altered based on the report of field survey.
Link budget calculations give the loss in the signal strength on the path between the mobile station antenna and base station antenna. These calculations help in defining the cell ranges along with the coverage thresholds. Coverage threshold is a downlink power budget that gives the signal strength at the cell edge (border of the cell) for a given location probability. As the link budget calculations basically include the power transmission between the base station (including the RF antenna) and the mobile station antenna, we shall look into the characteristics of these two pieces of equipment from the link budget perspective. Link budget calculations are done for both the uplink and downlink.
First step of capacity planning is to predict the behavior of users from filed survey. Next the expected offered traffic/user ‘a’ is evaluated from survey report. For a particular GoS and number of channel ‘n’ and the total offered traffic ‘A’ is evaluated from Erlang’s table. Now the number of users under a cell is evaluated from the relation, N=A/a. If this number is less than the expected number of users from survey report then the number channel has to be increased for recalculation of N. The same job is done by reducing the number of channels if the calculated N is greater than that of survey report.
Planning tools have frequency planning algorithms for automatic frequency planning. These require parameter setting and prioritization for the parameters as an input for the iteration. The planning tool can also be utilized in manual frequency planning. The tool uses interference calculation algorithms and the target is to minimize firstly the co-channel interference and also to find as low an adjacent channel interference as possible. Frequency planning is a critical phase in network planning. The number of frequencies that can be used is always limited and therefore the task here is to find the best possible solution.
In the parameter planning phase a recommended parameter setting is allocated for each network element. For radio planning the responsibility is to allocate parameters such as handover control and power control and define the location areas and set the parameters accordingly.
EmoticonEmoticon