Besides Frequency Planning, the Handover Planning is also a most important planning step. When a mobile station in connected mode changes from one cell to the other, it must be ensured, that all boundary condition as described below are fullfilled. The task of the radio planner is to assign for each cell all necessary handover neighbours to ensure a continuous connection. The maximum number of handover neigbours should not be greater then 12 (ideal 6). Neighborhood relations should be in principle symmetrical.
The overall handover process is implemented in the MS, BS and MSC. Measurement of radio subsystem downlink performance and signal strengths received from surrounding cells, is made in the MS. These measurements are signalled to the BS for assessment. The BS measures the uplink performance for the MS being served and also assesses the signal strength of interference on its idle traffic channels. Initial assessment of the measurements in conjunction with defined thresholds and handover strategy may be performed in the BS.
Basic Handover Causes
The handover causes should have the following priority:
- quality (RXQUAL)
- level (RXLEV)
- distance (DISTANCE)
- better cell (PBGT)
Recommendation:
The network must also be optimised according the above ranking. An ideal network performes only handover based on the cause case “better cell”.
