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: