Description
This measurement provides the counters based on the originating cell when an internal inter-cell handover is performed, that is, when a handover is performed between two cells under the same BSC. The outgoing internal inter-cell handover occurs in two scenarios: the BSC determines an internal inter-cell handover based on the measurement report, or the BSC determines a directed retry of internal inter-cell handover based on the channel usage, congestion conditions after the MSC sends an ASS REQ message to the BSC. The measurement in both scenarios are performed in the originating cell. These two scenarios are respectively described as follows:
- Handover triggered based on measurement report (excluding directed retry)
After seizing a dedicated channel, the MS periodically reports a measurement report to the BSC. The BSC processes the measurement report received from the MS and determines whether to initiate a handover based on the handover algorithm. The handover algorithm is performed based on the cell load, the concentric subcells, and signal interference level, and the signal quality and transmit/receive level reported in the MR. If the handover algorithm decides to trigger the handover, and the originating cell (serving cell) and the target cell are not in the same BSC, then an internal inter-cell handover is triggered.
The BSC sends a CHAN ACTIV message to the BTS to activate the channel specified by the handover algorithm in the target cell. After the BSC receives the CHAN ACTIV ACK message, it applies for the circuit resources. After the resources are obtained, the BSC sends an HO CMD message to the MS in the originating cell to notify it of the handover to the specified channel in the target cell.
The MS sends an HO ACC message to the target BTS to attempt to access a new cell. The target BTS forwards this message through an HO DETECT message to the BSC and sends a PHY INFO message to the MS. The MS sends a FIRST SABM frame to the target BTS and the target BTS sends an EST IND message to the BSC, indicating that the MS has successfully accessed the target cell. The MS also sends an HO CMP message to the BSC. The BSC sends an HO PERFORMED message to the MSC.
Outgoing internal inter-cell handover is part of the internal inter-cell handover procedure. It refers to the handover procedure performed in the originating cell (the cell where the MS is located before the handover) in the whole internal inter-cell handover procedure. The originating cell (the cell where the MS is located before the handover) and the target cell (the cell where the MS is located after the handover) can be two cells in the same BTS or two cells in two BTSs controlled by the same BSC.
Figure 1 Measurement of the counters related to outgoing internal inter-cell handover (excluding directed retry)
A
Measurement point of Outgoing Internal Inter-Cell Handover Requests (Excluding Directed Retry)
B
Measurement point of Outgoing Internal Inter-Cell Handover Commands (Excluding Directed Retry)
C
Measurement point of Outgoing Internal Inter-Cell Handover Detection Messages Received by BSC (Excluding Directed Retry)
D
Measurement point of Successful Outgoing Internal Inter-Cell Handovers (Excluding Directed Retry)
- Handover triggered after MSC sending an ASS REQ message (directed retry)
When an MS starts a call, it sends a CHAN RQD message to the BSC through the BTS. Then, the BSC allocates a signaling channel (SDCCH or TCH) based on the current condition of the serving cell, and sends a CHAN ACTIV message to the BTS to activate the channel. After receiving the CHAN ACTIV ACK from the BTS, the BSC sends an IMM ASS CMD message to the MS, indicating the MS to access the network through the allocated signaling channel.
Upon receipt of the EST IND message from the MS, the BSC retrieves the CM SERV REQ information from the message, and sends it in CR message to the MSC. Then the MSC returns a CC message to the BSC. Thus, the MM connection between the MS and the MSC is established. After a series of CM SERV ACCEPT, SETUP, and CALL PROCEEDING message, the MSC sends an ASS REQ message to the BSC. After receiving an ASSIGN REQ message from the MSC, the BSC decides the assignment mode based on the current conditions of the serving cell by analyzing the factors such as cell load and signal quality. There are three assignment procedures: normal assignment procedure, directed retry procedure, and mode modification procedure. If the load of the cell is so high that the cell cannot admit a new service or that a new admitted service will affect the current services, the BSC decides to perform a directed retry to allocate the service to another better cell.
- The BSC sends a CHAN ACTIV message to the target cell.
- After receiving the CHAN ACTIV ACK from the BTS, the BSC requests the circuit service resources. After the requested sources are allocated successfully, the BSC sends an HO CMD to the MS in the originating cell.
- The MS attempts to access the network through the HO ACC message in the target cell. The BTS sends the HO DETECT message to the BSC and sends the PHY INFO message to the MS.
- The MS sends the FIRST SABM frame to access the network. The BTS sends the EST IND message and sends the UA frame to the MS.
- The MS reports the HO CMP message to the BSC in the target cell. The BSC sends the ASS CMP message to the MSC, and proceeds with other signaling processing during the assignment procedure. Thus, the originating call procedure is completed.
The directed retry assignment is implemented by performing an inter-cell handover. If the originating cell and the target cell are under the same BSC, then an internal inter-cell handover is performed. Outgoing internal inter-cell handover is a part of the internal inter-cell handover procedure. It refers to the handover procedure performed in the originating cell (the cell where the MS is located before the handover) during the whole internal inter-cell handover procedure. The originating cell (the cell where the MS is located before the handover) and the target cell can be under the same BTS or two different BTSs controlled by the same BSC.
Figure 2 Measurement of the counters related to outgoing internal inter-cell handover (directed retry)
A
Measurement point of Outgoing Internal Inter-Cell Handover Requests (Directed Retry)
B
Measurement point of Outgoing Internal Inter-Cell Handover Commands (Directed Retry)
C
Measurement point of Outgoing Internal Inter-Cell Handover Detection Messages Received by BSC (Directed Retry)
D
Measurement point of Successful Outgoing Internal Inter-Cell Handovers (Directed Retry)
Measurement Object
Cells.
Measurement Counter
The following table lists the measurement counters related to the Outgoing Internal Inter-Cell Handover Measurement per Cell.