UMTS Low CS/PS IRAT Handover Success Rate Analysis

Analysis of low CS/PS IRAT HOSR can be done using the below mentioned procedure:

1. Neighbor Audit - removal of illogical neighbors is equally important as adding Tier 1 cells
2. External neighbors configuration check - Often times, BCCH/NCC/BCC is modified and should be updated in external cells on the UMTS end
3. Parameter check
4. GSM State mode - can be modified in case of severe handover failures on one relation 

Apart from these steps, it should be checked whether the IRAT HOSR is low for both CS and PS or just one of these. If it is low for only one of the services, compressed mode parameters can be tuned to trigger early handover when the signal strength is high. Analysis should be followed from cluster to cell to relation level to pinpoint the issue.

Base Station Solution

Base station solution can be classified into two types:

Macro: where BBU and RFU are part of the cabinet of the base station
Distributed: where the cabinet comprises of BBU and RRU. RRU can be deployed close to the antenna which reduces antenna loss and can contribute to enhanced coverage.

RRU can be singe mode or multimode (GSM, UMTS, and/or LTE). A typical RRU contains sub systems such as Transciever (TRX), Power Amplifier (PA)/LNA, and Duplexer (DFL).

UMTS Reselection Parameters

General parameters with typical network values of the three types of reselection in UMTS is presented below:

3G to 3G

• qrxlevmin = -109 dBm     (min acceptable threshold of cell RSCP)
• qqualmin = -18 dB           (min acceptable threshold of cell quality EcNo)

• sintersearch =  10 dB   (f1,f2 case)
• sintrasearch =  14 dB    (same frequency)

3G to 2G

• ssearchrat = 2dB            (indicates when to trigger measurements on GSM cells, increasing this value quickens while decreasing it delays the process)
• treselect = 2s
• qoffset1sn = 7dB for gsmrelation; 0 dB for utranrelation                                                       (Source and target signal offset when reselection strategy is RSCP)
• qoffset2sn = 0 dB                 (Source and target signal offset when reselection strategy is EcNo)

2G to 3G

• FDDqRSCPmin = -102 dBm
• FDDqmin = -12 dB

Equation

The equations on which the decision is made using these parameters are:

For EcNo based reselection:

Squal <= sintrasearch     OR        sintersearch           OR            ssearchrat

where Squal = qmeasured  -    qqualmin

Thus the equation becomes:

qmeas - qqualmin <= sintrasearch

qmeas  <= qqualmin + sintrasearch

Similarly, EcNo values can be replaced with RSCP for the RSCP based reselection.

UMTS - Types of congestion

UMTS cells can have below congestion types:

1. CE (Channel Elements) Congestion:  This happens when resources on the hardware are fully utilized. One solution is to add extra cards/boards in the Node B to increase capacity. For example, ZTE has BPK1 and BPKd cards that comprises of 384 and 768 CE respectively. CE congestion is always monitored by observing UL CE (since UL CE consumption is always greater than that in the DL)
2. Code Congestion:  High number of users could result in code congestion. Parameters such as minHSDPA users can be decreased to make room for cell DCH users. Carrier expansion can be done to accommodate larger  number of users.
3. TCP Congestion:  This represents that Total Carrier Power limit has been reached. Addition of Power Amplifier, new nodes/sites, decreasing CPICH power, or increasing cell transmission power are some of the remedial steps for rectification. 
4. Iub Congestion:  Congestion results due to fully utilized transmission media which can be increased to resolve the issue. 

UMTS Drive Test Basic Analysis

A basic overview of UMTS drive test analysis comprises of two key KPIs which are RSCP and EcIo corresponding to coverage and quality. The common cases and their remedies are presented below:

1. Bad RSCP and bad EcIo (Coverage): This means weak coverage of the serving cell which should be improved to better the EcIo
2. Good RSCP and bad EcIo (Pilot Pollution/High Cell Load): If the issue is due to multiple servers (pilot pollution) having RSCP within 3dB, dominance of one cell should be formed. For high cell load problem, carrier expansion or traffic balancing are some ways of improving the EcIo.
3. Bad RSCP and good EcIo: Low cell load or no handover in the area represents this condition. 

An example of pilot pollution issue is shown below:

GSM TCH Channel Allocation Priorities - Zero Traffic Analysis

Zero traffic means the hardware is not carrying traffic even if there is blocking on the cell. Below are the steps to check for this issue:

1- Filter out TRXs having zero attempts/traffic
2- Check those cells TCH availability - if there is low TCH, then resolve low TCH first
3- Examine TCH blocking on these cells - if there is zero blocking, then the traffic is not high enough
4- Inspect the below TCH channel allocation priorities to finalize the zero traffic TRXs and recommend for health check

Note: TRXs can have zero or low assignments with normal ranges of availability if there is no blocking.

UMTS Paging Success Rate

Paging success rate is a KPI that can be checked if there are complaints involving user not responding messages or missed call notifications. If paging success rate is degraded, it is mainly due to poor coverage. In such case, below actions may be taken:

• increase minimum required received level (QRxLevmin) (eg:-111 to -105) and minimum required quality level (qqualmin) (eg: -18 to -15) of worst cells
• increase PICH power by a few dB (eg: -7 to -5) and increase downlink DCH AC threshold (eg: 85 to 95)
• reduce detected preamble threshold (dB) (eg: -21 to -24)
• increase PRACH initiation Tx power constant value (dB) (eg: -21 to -18)
• Reduce Location update timer both at the core and RNC (say from 3 hour to 1 hour)

Paging flow chart is given below for understanding.

Note:
Paging type 1 = Idle mode
Paging Type 2 = Dedicated mode