External Cells and Neighbor Cells

External Cells

External cells are not controlled by the local BSC. External cells can be 2G external cells or 3G external cells. 2G external cells are the GSM/GPRS cells. 3G external cells are the WCDMA cells.

Neighbor Cells

Neighbor cells are adjacent to the serving cell. Neighbor cells can be the local BSC cells, 2G external cells, or 3G external cells.

The configuration principles of neighbor cells are as follows:

• One cell can be configured with up to sixty-four 2G neighbor cells and sixty-four 3G neighbor cells.
• Any two 2G neighbor cells of a cell should not have the same main BCCH frequencies or the same BSIC.
• Any two 3G external neighbor cells of a cell should not have the same frequencies, scrambling code, or diversity indication.
• The cell configured with the enhanced concentric cell function must be set as the neighbor cell of itself. Therefore, the cell configured with the enhanced concentric cell function (except for the cell itself) can be configured with up to sixty-three 2G neighbor cells and sixty-three 3G neighbor cells.

Configuration Principles of Neighbor Cells Adjacent to Cells from Different Frequency Bands

For cells from different frequency bands, the number of neighbor cells to be added is limited.

The BA1 table carrying the frequency information about neighbor cells is sent through the 2/2bis/2ter system information. The BA2 table is sent through the 5/5bis/5ter system information. In GSM specifications, cell channel descriptions in system messages have different bitmap descriptions and restrictions for the BA1 table and the BA2 table. The frequency coding principles are as follows:

NOTE:

The actual frequency coding principle needs to meet at least one of the following principles.

1. One ARFCN is more than 0 and less than or equal to 124.
2. The interval between the maximum ARFCN and the minimum ARFCN is smaller than or equal to 111.
3. The interval between any two adjacent ARFCNs is greater than or equal to 913.
4. The number of frequencies is smaller than or equal to 16.
5. The number of frequencies is equal to 17. In addition, the minimum ARFCN is 0.
6. The number of frequencies is smaller than or equal to 18, and the maximum interval between two ARFCNs (including "minimum frequency - maximum frequency + 1024) is greater than 512.
7. The number of frequencies is smaller than or equal to 22. In addition, the maximum interval between two ARFCNs (including "minimum frequency - maximum frequency + 1024) is more than 768.
8. The number of frequencies is smaller than or equal to 29, and the maximum interval between two AFRCNs (including "minimum ARFCN - maximum ARFCN + 1024) is greater than 896.

If the main BCCH ARFCN is in the range [0, 124] or [955, 1023], the frequency set comprising ARFCNs within the range 0, [128, 251], [512, 810], and [955, 1023] in the BA table must meet the previous coding principles.

If the main BCCH ARFCN is in the range [128, 251], the frequency set comprising ARFCNs within the range [0, 124], [512, 810], and [955, 1023] in the BA table must meet the previous coding principles.

If the main BCCH ARFCN is in the range [512, 810], the frequency set comprising ARFCNs within the range [0, 124], [128, 251], and [955, 1023] in the BA table must meet the previous coding principles.

Combined with the situation of network frequency resources (975 to 999 and 512 to 536), the restriction principles of neighbor cells are as follows:

• 900 MHz cells: Frequencies range from 975 to 999. All the 900 MHz cells on the network are on limited frequency bands. In addition, because the neighbor cells of these cells include both 900 MHz cells and 1800 MHz cells, the sixth principle is applicable, that is, the maximum number of main BCCH frequencies of all neighbor cells is 18.
• 1800 MHz cells: Frequencies range from 512 to 536. All the 1800 MHz cells on the network are on unlimited frequency bands. The number of neighbor cells of these cells are not limited. The frequencies from 975 to 999 of neighbor cells of 900 MHz cells should meet the eighth principle. The maximum number of main BCCH frequencies of neighbor cells on the 900 MHz frequency band is 29.