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Concept of Key Performance Indicators in GSM (KPIs):
RF Optimizer makes frequent use of statistical data for routine optimization activities. This raw data, which is actually based on counters, makes optimization tasks quite cumbersome as counters are in thousands. So, to make the tasks simpler, counters are appended into formulae, whereas, each formula reflects a specific performance indicator. All major performance indicators are categorized as Key Performance Indicators (KPIs). The KPIs are actually the statistical measure of network quality and encompass all the QoS parameters related to Network Accessibility, Service Accessibility, and Network Retainability. Telenor Pakistan Management defines yearly KPI targets in agreement with Regional RF Managers. Major KPIs include:
– Call Setup Success Rate (CSSR)
– Dropped Call Rate (DCR)
– Handover Success Rate (HSR)
– Minutes Per Drop (MPD)
– TCH Raw Blocking
– SDCCH Blocking
KPIs for Circuit Switched Traffic
The major KPIs for circuit switched traffic (voice) that need to be diligently monitored include:
Call Setup Success Rate (CSSR)
CSSR is a measure of successful call attempts over total number of call attempts. A call is affirmed to be successful if SDCCH is accessed, occupied and then TCH is accessed successfully. CSSR is majorly affected due to blocking (SDCCH/TCH) or due to operational issues.
Dropped Call Rate (DCR)
DCR is measure of dropped calls over total number of successfully set-up calls. A call is affirmed to be dropped if TCH is dropped after assignment. DCR is dependent on Radio Link Timeout (RLT), and Handover (HO) drops from RF point of view.
RLT is a counter for loss of SACCH frames (max value: 32 SACCH Frames for AMR cells; 20 SACCH Frames for non-AMR cells in TP Network). It decrements by value of 1 when one SACCH is lost and increments by value of 2 if one SACCH is received. RLT value is affected due to poor RF environment (Interference, low coverage).
Probability of increase in HO Drops is directly proportional to increase in HO failures. These drops can be due to RF as well as due to Operational issues. From RF point of view, neighbor plan should be optimal, frequency clashes need to be removed in all neighboring cells, and all HO Control & Adjacency Parameters need to be at optimal value. DCR can increase due to operational issues as well.
Handover Success Rate (HSR/HOSR)
HSR is measure of successful handover attempts over total number of handover attempts. HSR is categorized as Outgoing HSR (Out_HSR) and as Incoming HSR (IN_HSR).
Out_HSR means the success rate of handovers from Source cell to Target cells. IN_HSR means the success rate of handovers from Target cells to Source Cell.
Out_HSR is dependent on Adjacency and HO Control Parameters. It can also be affected due to TCH Blocking issues in the adjacent (neighboring) cells leading to Blocked Handovers. IN_HSR is also dependent on Adjacency and HO Control Parameters. It is affected by TCH blocking on Source cell as well.
Minutes Per Drop (MPD)
has an MPD of 60, it would imply that a call stays on that cell for 60 minutes on average, before getting dropped. MPD is calculated by dividing total minutes of voice traffic with the total number of TCH Drops.
TCH Raw Blocking
Handover attempts, or TCH Blocking due to Incoming Directed Retry TCH Seizure Attempts.
SDCCH Blocking is measure of attempts for SDCCH seizure that could not be facilitated due to non-availability of SDCCH.