5G NSA Accessibility KPI Optimization

Accessibility KPI

As 5G Networks is growing and maturing, Now operators are focusing on improving the the main key performance indicators (KPIs).

The Accessibility KPI is considered one of the most important KPI. Network Service Accessibility defines the probability that the user after a request to a network is successful and based on a certain threshold which is almost close to 100%. Some operators fix a threshold at 99.8%. The KPI measurement need to be evaluated daily and on the busy hour.

5G accessibility have two following two parts.

  • Session Setup Success Rate
  • Session Setup Time

5G NSA Accessibility Procedure 

To identify the main reason of KPI degradation first we need to understand the different accessibility procedures using NSA Call Flow messages. Then it is easy to classify the parameters related to each procedure and after that require to identify in which step the failure is contributing to KPI degradation. In Last, we can troubleshoot the problem and give the optimum solution for parameters tuning and recommendations.

The NSA accessibility contains following eight procedures starting from UE sends the first transmission on a LTE Master eNB (MeNB) cell until the 5G RACH procedure is completed on the 5G secondary gNB (SgNB) cell.

  1. EN-DC capable UEs will camp to LTE Cell
  2. RRC connection is completed on LTE Cell
  3. SRB and DRB setup on LTE Cell
  4. UE measures 5G Signal and report to eNB
  5. SgNB addition and 5G radio admission control
  6. 5G RRC reconfiguration
  7. 5G status transfer by switching user plane to gNB
  8. Successful 5G RACH procedure

5G NSA Accessibility Success Rate

The Success rate of NSA Accessibility is a product of SgNB addition success Rate, RRC Reconfiguration Success Rate and RACH Success Rate.

NSA Accessibility SR = SgNB addition SR * RRCreconfiguration SR * RACH SR

The Sub KPIs for NSA availability can be calculated as

  • SgNB addition SR =SgNB Addition Ack/ SgNb Addition Request
  • RRC reconfiguration SR= RRC Reconfiguration Complete/ RRC Reconfiguration
  • RACH SR = MSG#3 Contention Based RACH / RACH Attempt (MSG#1)

5G NSA Accessibility KPI at different Level of Call Flow

5G NSA Accessibility Optimization

RRC Reconfiguration Success 

The 5G RRC reconfiguration procedure is used for NSA mode after eNB has received the SgNB
Addition Request Acknowledge message on X2 (containing information to UE about the 5G radio configuration), the eNB forwards this information to UE (in RRC Connection Reconfiguration message), waits for Complete and then forwards the complete to the SgNB.

There are two timers which handle this procedure from both sides 4G and 5G. RRC Guard timer
(rrcGuardTimer) is running in 4G and timer dual connectivity over all (tDCoverall) is controlling 5G side. By using the optimum value of both timer we can get maximum Success Rate.

RACH Success

The Success Rate of RACH procedure depends Planning parameters and Configuration parameters. Planning parameters includes Root Sequence Index, Msg1 Frequency Start and RACH Configuration Index.

The Configuration Parameters includes  Initialpreamblepower, PowerRampingStep, PreambleTransMax, RandomResponseWindow, maxHarqMsg3Tx and raContResolutionTmr


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