ADMISSION CONTROL

Admission control function admits or denies new users. AD mechanism consists of two main step:

1. RAB Matching : This performs the mapping of the requested RAB onto a supported radio Bearer configuration. This step includes a RAB radio bearer mapping table which provides the means to admit a RAB at a rate lower than the requested Max bit rate according to the cell load. This function, which is called intelligent RAB mapping, only applies to a RAB with an interactive or background traffic class.
2. Call Admission control: THis is the function located in the CRNC responsible for deciding whether a request to establish a radio access bearer can be admitted in the UTRAN or not based on the available resources. Radio CAC is based on power and OVSF codes in the DL and on interference in the UL that other CAC function are performed at the transport. NodeB and RNC levels.

CAC is applied: 

• On initial admission
• On RB reconfiguration: Such as RB bit rate downgrading/upgrading, cell_Fach to Cell_Dch transition..
• On mobility: SHO, inter-frequency HHO and 2G to 3G HHO.

CHANNEL REQUEST

The MS initiates a call by sending a CR message, with an REF. The REF include and establishment cause and a RAND. It is transmitted on the RACH channel. The RACH channel is associated with the CCCH channel which the MS is monitoring while in idle mode. 
The establishment cause have 7 field of the REF specifies:

1. An emergency call
2. Call re-establishment
3. Response to paging
4. MS-originating speech call
5. MS-originating data call
6. Location update
7. Service call, like SMS.....

The MS note the random number and frame number associated with each CR message. These are used by the MS to recognize the response sent form the BSS. This response is sent on the AGCH, which can be monitored by many MS. The MS decodes all message sent on this AGCH, and only accepts a message with a random number and frame number matching one of the last three requests sent. The MS continuous to transmit Channel Request message until it receives a response. If no response is received before the MS has transmitted a predefined number or retries, the MS have two follow:

1. Displays a network error message for all calls except location update.
2. Performs automatic re-selection for location update calls, This means that the MS attempts random access on a different cell.

On receipt of the CR message from the MS, the  BST sends a CR message to the BSC. This message contains the random number sent by the MS, and the TA measured by the BTS.

Under peak load conditions, resource maybe over allocated due to this process.

Below will show how the Immediate Assignments Extended feature work to alleviate.

In order to establish a radio connection on a VGCH between a MS which is in group receive mode on that channel and the BTS, the MS sends an uplink access message with the Subsequent talker uplink request parameter on the voice group call channel. The uplink access message is similar to a CR message but is sent only on the group call channel uplink.

The MS sends and uplink access message when:

1. A subsequent talker uplink is required: The BTS performs any necessary contention resolution and grants the uplink to one MS by sending a VGCS  uplink grant message to the MS in unacknowledged mode on the main signaling link. The BSS send uplink busy message on the main signaling link in all cells of the group call area.
2. There is a replay to an uplink access request.

POWER CONTROL FOR BSC

PC: Power control is ensuring that any mobile is connected with cell in which the output powers from the mobile station and base station are as low as  possible while keeping a satisfactory link quality.
- Reduce emitted power to the minimum possible.
- Ensuring quality and received level of peer entity.
- For uplink PC: decrease uplink interference and save mobile station battery.
- Adapted in real-time.

   **** Based on a threshold comparison mechanism to decrease emitted power when received level and quality measured by peer entity are better than a given value. and for increase emitted power when the received level or quality is lower then a given value. And dose not decrease power if the resulting level is below the low level threshold.

MAJORS KPI

Here We can see much improvement after do optimize such as:

- Handover Success Rade
- Call Setup Success Rate
- Call Drop Rate

How to Solved Low Coverage Issue

Here are step how to solved low coverage complains:
- Check exactly Lat/Long
- Check QoS around location complains, make sure all cells point to complains are KPI normal.
- Check how far customer complains from our cells

      ** Solution:
- If cells have issue, like QoS degradation need to urgently to BSS team to fixed as soon as possible, and test with customer.
- We can up tilt or adjust azimuth antenna point to customer complains and tell with customer.
- Finally, if action above still not yet clear, need to propose new site to observe these area.

Drive Test Analysis

Here is step of the log file drive test after re-tune some frequency:

Radio Link Supervision

For each active radio channel, a counter “S” is

•decremented by 1 each time an SACCH frame cannot be decoded (BFI=1)

•Incremented by 2 each time a valid SACCH frame is received is received

The value of S gives a measure of the “quality” of uplink radio link

Initial value of S = BS_RADIO_LINK_TIMEOUT

•If S reaches N_BSTXPWR_M, a radio link recovery is triggered

•If S reaches 0, a radio link failure is detected

RADIOLINK_TIMEOUT_BS > RADIOLINK_TIMEOUT is important because the mobile must release the radio channel first.

Optimal setting for RLT parameters will give the call time for recovery in case of degraded call quality and not just regard it as radio link failure. Therefore this can reduced drop calls specially for radio link fault cases due to burst interference or blind areas owing to high rise buildings or shadowing.

After adjusting the Ho quality and interference parameter

Will be improvement such as:

• Handover incoming and outgoing efficiency improved.

• Handover incoming and outgoing  rate is degraded due to congestion (many site).

• It is not conclusive that radio and ho drop number  is  lessen due to high BSS drop  and rtch congestion was observed.

• Cannot determine the improvements in some isolated cell which is not affected by bss drops and congestion due to very low traffic.

RECOMMENDATION:

•BSS drops and high rcth congestion must be resolved first in order to see the impact of the changes. It is recommended that we keep the adjusted parameter at this time.

• If no improvements, ho parameter can be adjusted in lower value until we finalize the optimize value.

CELL RESELECT HYSTERESIS

• Level hysteresis for cell reselection applied when the new cells is in different location area.
• Alcatel default value 6dB; Value range 0dB to 14dB.
• Figure below is some example of border cells.  

 

 CELL RESELECTION

• If the mobile is moving in a border area between location areas, it might repeatedly change between location areas. Each change requires location updating and cause heavy signaling load and risk paging message being lost.  
• To prevent this, a cell reselect hysteresis parameter CRH is used. 
• The cell in a different location area will only be selected if the C1 of that cell is higher than the C1 of the current serving cell by the value of the Reselect Hysteresis. 

Since the Value of CRH maybe different for each cell, the CRH used for comparison will be the one broadcast by the serving cell. If the value is set very low then the mobile will Ping-Pong between location areas which will increase signaling load. If the value is set very high the mobile may camp in the wrong cell too long.

  

Parameter for change satlile to Microwave/Optic on cell

Please change these parameters following:
1.       BS_CV_MAX:     change from 15 to 9.
2.       T3168:                   change from 3 to 2 (x0.5 sec)
3.       T3192:                   change from 1500 to 500 m
4.       Round trip delay MFS-MS:           change from 70 to 16 (x 10 ms
5.       T_ul_assign_PCCCH:       change from 0.7 to 0.4 sec
6.       T_GCH_CORR:   change from 14 to 8 (x 0.1 sec)

T_GCH_ESTAB: from 10 to 4 (x 0.1 sec)

Parameter for change satlile to Microwave/Optic

Should be change following MFS parameters at MFS_Evo
1.       T_ACK_WAIT: change from 17 to 12 (x0.1 sec)
2.       T_One_Block: change from 5 to 4 (sec)
3.       T_GCH_release: change from 10 to 5 (x 0.1 sec)

-T_ACK_WAIT = tackwait
-T_One_Block = toneblock
-T_GCH_release = trelease