GSM - TRX Planning

ZTE Magic RRU consists of 6 ports to which 3 PA (power amplifiers) can be connected. Each PA supports 80 Watt linked with a sector/cell and the power is distributed uniformly among the TRXs connected to a PA. This means that with a minimum recommended power of 20 W per TRX, no more than 4 TRXs should be configured on one PA or sector. Thus, for a site having 3 sectors, 444 configuration is suitable.

Transmission requirement for TRX depends on multiple factors such as:

• TRX configuration
• Coding Scheme - Higher coding scheme (MCS-9) requires more transmission bandwidth
• Number of static and dynamic PDCH configuration
• Half Rate utilization

In general, a site with a 444 configuration, 2 static and 4 dynamic PDCHs per cell, 100% Half Rate utilization, and an average of MCS6 can be supported by 1 E1 (2.048 Mbps).

GSM - Paging Success Rate (PSR) Analysis

Paging success rate can be degraded due to increase in MOC/MTC attempts, low TCH availability of source and neighboring cells, high LAC/BSC utilization. Following steps should be taken to analyze the root cause:

• Check for MOC/MTC trend - increase may cause high PPS (Paging Per Second) causing paging discards, indicating paging capacity limitation. LAC splitting could be done to resolve the issue
• Examine TCH Availbility of sites in the affected BSC
• Inspect cell level paging stats from the core network to zero in on the problematic LACs
• Parameter discrepancy between BSC and MSC can cause degradation - check parameters such as Location Update Timer, paging retransmissions by MSC, paging times etc.
• Interference, low coverage due to large distance or dense areas, path balance issues contribute to PSR degradation

GSM - TCH Availablility

TCH Availability is the ratio available TCH (Full Rate, Half Rate, dynamic radio channels) to the total available and unavailable TCH (Full Rate, Half Rate, dynamic radio channels). Generally, TCHA follows the pattern of available TCH/F and dynamic radio channel.

TCHA is one of the first KPI that should be checked in environments where power outages are common. It degrades blocking, DCR, HOSR and other KPIs to a large extent. More often than not, low TCHA of neighboring cell causing severe KPI degradation in a particular cell. It is always safe to revive TCHA of the network before implementation of parametric or design changes for KPI improvement.

Major alarms causing low TCHA are STP link association broken (transmission), and GENSET on (power outage).

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.