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Definition:

Ration of failed SDCCH seizures due to busy SDCCH to the total requests of SDCCH.

Formula:

SDCCH congestion rate = Failed SDCCH seizures due to busy SDCCH/Total requests for the

SDCCH x 100%

Factor of SDCCH Blocking Rate in GSM

1. Congestion caused by Fault Equipment or Transmission

2. Congestion caused by insufficient Signaling Resource.

3. Congestion caused by improper Data Configuration.4. Congestion caused by Interference

# Congestion caused by Fault Equipment or Transmission

The faults on BTS, BSC, and Abis interface, such as broken LAPD link, cause the SDCCH congestion.

The alarm "Excessive Loss of E1/T1 Signals in an Hour" also causes the SDCCH congestion

# Congestion caused by insufficient Signaling Resource

The heavy traffic and burst traffic cause the SDCCH congestion. Proper setting of the number of

SDCCHs and TCHs, and the SDCCH dynamic conversion function can relieve the congestion.

# Congestion caused by Improper Data Configration

The SDCCH congestion relates to the relevant parameters of the BSCsuch as SDCCH Availability, LAC, Timer

Immediate assignment procedure and timer for update periodic.

# Congestion caused by Interference

Interference on the Um interface also causes congestion. For example, if the main BCCH in the serving

cell and the TCH in the neighboring cell share the same TRX frequency and BTS BSIC, the handover

access on this TCH may be mistaken as random access. As a result, the SDCCH is abnormally allocated

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and congestion occurs. The excessive receive sensibility can also make the interference signal mistaken

as access signal, which leads to congestion.

# Solution of SDCCH Blocking Rate

1. Checking Hardware

2. Checking Channels Configuration

3. Checking Data Configuration

4. Checking the Um Interface

Overview of SDCCH Call Drop Rate

Definition:

The SDCCH call drop rate indicates the probability of call drops when the MS occupies the SDCCH.

The SDCCH call drop rate is one of accessibility KPIs. This KPI reflects the seizure condition of

signaling channels. If the value of this KPI is high, user experience is adversely affected.

Formula:

Call Drop Rate on SDCCH = (Call Drops on SDCCH/Successful SDCCH Seizures + Successful

SDCCH Seizures in the signaling channel handover) x 100%

#Factor that affect SDCCH Call Drop Rate

1. Hardware Failure

2. Transmission

3. Version Upgrade

4. Parameter Setting5. Intra-Network and Inter-Network Interference

6. Coverage Antenna System and imbalance between UL/DL and Repeater

# Hardware Failure

When a TRX or a combiner is faulty, seizing the TCH becomes difficult, and thus the SDCCH call

drop rate increases.

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# Transmission

The SDCCH call drop rate increases in any of the following conditions: (1) The transmission quality

is poor on the A or Abis interface due to various reasons. (2) Transmission links are unstable.

# Version Upgrade

After the BTS version or BSC version is upgraded, the BTS version may be incompatible with the

BSC version, and the parameters and algorithms in the new version may be changed. In this case, the

SDCCH call drop rate increases.

# Parameter Setting

The settings of some parameters on the BSC and MSC sides may affect the SDCCH call drop rate.

If the following situations occur, the SDCCH call drop rate may increase:

# Intra-Network and Inter-Network Interference

If inter-network interference and repeater interference exist, or if severe intra-network interference

occurs because of tight frequency reuse, call drops may occur on SDCCHs due to poor QoS. This affects

the SDCCH call drop rate.

The following types of interference may occur:

Inter-network interference from scramblers or privately installed antennas

Interference from the CDMA network

Repeater interference

Intermodulation interference from BTSs

Intra-network co-channel and adjacent-channel interference

# Coverage

The following coverage problems may affect the SDCCH call drop rate.

Poor indoor coverage

Densely distributed buildings and thick walls cause great attenuation and low indoor signal level, which

causes call drops.

Coverage failure

If the signal from an antenna is blocked or the BCCH TRX is faulty, call drops may occur.

# Antenna System

The following antenna system problems may affect the SDCCH call drop rate

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If the transmit antennas of two cells are misconnected, the uplink signal level in each cell is much

lower than the downlink signal level in the cell. Therefore, call drops are likely to occur at a place far away

from the BTS.

If a directional cell has main and diversity antennas, the BCCH and SDCCH of the cell may be

transmitted from different antennas. If the two antennas have different pitch angles or azimuths, the

coverage areas of the two antennas are different. In this case, the following result may occur: An MS can

receive the BCCH signals from one antenna; when a call is made, the MS cannot seize the SDCCH

transmitted by the other antenna and thus a call drop occurs.

If the feeder is damaged, if water runs into the feeder, or if the feeder and the connector are not

securely connected, both the transmit power and receiver sensitivity of the antenna are reduced. Thus,

call drops probably occur.

# Imbalance between UL/DL

The difference between the uplink signal level and the downlink signal level may be great in the

following conditions: The transmit power of the BTS is high; the tower mounted amplifier (TMA) or BTS

amplifier does not work properly; the antenna and the connector are not securely connected. As a result,

call drops may occur at the edge of the BTS coverage area.

# Repeater

If a cell is installed with a repeater, BTS coverage problems may occur in the case that the

repeater is faulty or that the uplink and downlink gain is inappropriately set. Therefore, the call drop rate

increases.

If a wide-frequency repeater is used and the gain is set to a great value, strong interference may

be caused. As a result, the network quality is adversely affected and the call drop rate increases.

# Solution to reduce SDCCH Call Drop Rate1. Checking the Hardware (Alarm)

2. Checking the transmission (Alarm)

3. Checking the BSC and BTS version software4. Checking the parameter setting

5. Checking the Interference (Inter-Intra Network)

6. Checking the Antenna System, Coverage and Balance UL/DL

7. Checking the Repeater

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