Primary cell selection: refers to the process of selecting a suitable cell to camp on when the mobile phone does not have a cell to camp on.
In the primary election of a community, similar to finding a job while graduating from university or being unemployed, the basic idea is to find a job as soon as possible.
Therefore, the basic idea of cell selection is to select the cell with the best signal quality as soon as possible.
Other conditions for selecting a cell include: selecting a cell with a high priority, selecting a cell of the home operator, selecting a cell allowed to access, and providing the lowest signal level C1 allowed for wireless access.
The basic process is as follows:
(1) RF channel scanning (for GSM, it is actually 125 carrier frequency scanning)
If you have camped in a cell before starting up, scan the average signal strength of all frequency points in the list first.
If there is no cell that has been camped on before starting up, scan the average signal strength of all frequency points on the frequency band.
(2) RF channel selection:
Choose a carrier with the strongest signal from the scanned channels, similar to when choosing a job, choosing the company with the highest salary.
(3) Obtain cell information: frequency correction channel (FCCH), synchronization channel, broadcast control channel (BCCH)
Frequency synchronization, time slot synchronization, TDMA frame synchronization, access to cell information
(4) Whether the community is allowed to access (is there any recruitment quota for the community)
(5) Whether the current signal strength meets the minimum conditions for cell access.
Just like looking for a job, the salary offered by each company must reach its own minimum psychological threshold, or give up.
(6) If the conditions of the current carrier frequency are not met, select the next carrier frequency and repeat steps 2-5.