Outgoing External Inter-Cell Handover Measurement per Cell

Description

Outgoing External Inter-Cell Handover Measurement per Cell can be classified into Outgoing External Inter-Cell Handover (Excluding Directed Retry) and Outgoing External Inter-Cell Handover (Directed Retry).

• Outgoing external inter-cell handover (excluding directed retry)

  As shown in Figure 1, after the BSC receives measurement reports from the MS, it uses the handover algorithm to decide whether a handover is required or not. If a handover is required and the source cell (the current cell where the MS is located) and the target cell (the cell where the MS is located after the handover) are controlled by two BSCs, an external inter-cell handover is initiated.

  The measurement of outgoing external inter-cell handover (excluding directed retry) is performed in the source cell.

  The procedure of the outgoing external inter-cell handover (excluding directed retry) is as follows:

  1. BSC1 initiates an external inter-cell handover based on the handover algorithm.

  2. BSC1 sends an HO RQD message to the MSC.

  3. Based on the HO RQD message and the relation between the cell and the BSC, the MSC finds BSC2 and sends an HO REQ message to BSC2.

  4. BSC2 requests for a traffic channel from the target cell. After the request succeeds, BSC2 sends a CHAN ACTIV message to the target cell. After receiving a CHAN ACTIV ACK message from the target cell, BSC2 requests for speech service resources. After the request succeeds, BSC2 sends the MSC an HO REQ ACK message to notify the MSC that the target cell is ready for the MS access.

  5. The MSC sends an HO CMD message to BSC1 and BSC1 forwards this message to the MS. This message is used to request the MS to access the target cell.

  6. The MS sends the target cell an HO ACC message to attempt to access the target cell. BTS2 sends an HO DETECT message to BSC2 and a PHY INFO message to the MS.

  7. The MS sends a FIRST SABM frame to BTS2. After receiving this frame, BTS2 sends an EST IND message to BSC2 and returns a UA frame to the MS.

  8. After the MS accesses the target cell, it sends an HO CMP message to BSC2 and BSC2 forwards this message to the MSC.

  9. The MSC sends a CLR CMD message to BSC1 and the BSC1 releases the terrestrial resources in the source cell.

  10. BSC1 sends a CLR CMP message to the MSC.

  Figure 1 Outgoing external inter-cell handover (excluding directed retry)
  
  

  A: Outgoing external inter-cell handover request(excluding directed retry)

  B: Outgoing external inter-cell handover response(excluding directed retry)

• Outgoing external inter-cell handover (directed retry)

  The procedure is as follows:

  1. As shown in Figure 2, the MS sends a CHAN RQD message to BTS1 and BTS1 forwards it to BSC1.

  2. BSC1 requests for a signaling channel from the source cell. If the request succeeds, BSC1 sends a CHAN ACTIV message to the source cell. After receiving a CHAN ACTIV ACK message from the source cell, BSC1 sends an IMM ASS CMD to the MS through the source cell.

  3. The MS sends a FIRST ASBM frame to BTS1 and BTS1 returns a UA frame. After receiving the FIRST ASBM frame, BTS1 sends an EST IND message to BSC1.

  4. BSC1 extracts the CM SERV REQ message carried in the EST IND message, encapsulates it into a connection request (CR) message, and sends the CR message to the MSC.

  5. The MSC returns a Connection Confirm (CC) message. The MM connection between the MS and the MSC is established.

  6. After the transmission of the CM SERV ACCEPT, SETUP, and CALL PROCEEDING messages, the MSC sends an ASSIGN REQ message to BSC1.

  7. BSC1 selects a kind of assignment procedure (normal assignment procedure, mode modify procedure, directed retry procedure) based on the load of the source cell.

  8. If the subsequent services are unavailable or the subsequent services affect the existing services because the cell load is too high, BSC1 selects the directed retry procedure. If the source cell and the target cell are controlled by two BSCs, the directed retry is performed through an external inter-cell handover procedure. If the measurement is performed in the source cell, the outgoing external inter-cell handover procedure is initiated.

  9. BSC1 sends an HO RQD message to the MSC to initiate an external inter-cell handover.

  10. Based on the HO RQD message and the relation between the cell and the BSC, the MSC finds BSC2 and sends an HO REQ message to BSC2.

  11. BSC2 requests for a channel from the target cell. After the request succeeds, BSC2 sends a CHAN ACTIV message to the target cell. After receiving a CHAN ACTIV ACK message from the target cell, BSC2 requests for speech service resources. After the request succeeds, BSC2 sends the MSC an HO REQ ACK message to notify the MSC that the target cell is ready for the MS access.

  12. The MSC sends an HO CMD message to BSC1 and BSC1 forwards this message to the MS. This message is used to request the MS to access the target cell.

  13. The MS sends the target cell an HO ACC message to attempt to access the target cell. BTS2 sends an HO DETECT message to BSC2 and a PHY INFO message to the MS.

  14. BSC2 sends an HO DETECT message to the MSC. The MS sends a FIRST SABM frame to BTS2. After receiving this frame, BTS2 returns a UA frame to the MS and sends an EST IND message to BSC2.

  15. The MS sends an HO CMP message to BSC2 and BSC2 forwards this message to the MSC.

  16. The MSC sends a CLR CMD message to BSC1 and the BSC1 releases the terrestrial resources in the source cell.

  17. BSC1 sends a CLR CMP message to the MSC.

  Figure 2 Outgoing external inter-cell handover (directed retry)
  
  

  A: Outgoing external inter-cell handover requests (Directed Retry)

  B: Outgoing external inter-cell handover responses (Directed Retry)

Measurement Object

Cells.

Measurement Counter

The following table lists the measurement counters related to Outgoing External Inter-Cell Handover Measurement per Cell.