CASE STUDY

ENGINEERING SERVICESGROUP

www.qualcomm.com/esg

Delivering services and technical evaluations for network operators worldwide

Qualcomm Engineering Services Group (ESG)

accelerates the adoption of mobile technologies

through initiatives, professional services

and technical education. By analyzing and

recommending technology evolution solutions,

optimizing network design and deployments,

educating via technical training and customized

workshops, and collaborating with key industry groups, Qualcomm

ESG enables operators to efficiently migrate to next-gen

technologies. The following case study shows how Qualcomm ESG

helped a Tier 1 operator develop a comprehensive, cost-and resource-

efficient inter-RAT (Radio Access Technology) optimization process.

AT ISSUE

Optimization of the WCDMA/HSPA network overlay Throughout the world, WCDMA (UMTS) or HSPA networks overlay many existing GSM networks. GSM is traditionally a stronger network than WCDMA/HSPA, a newer, less contiguous technology, deployed at higher frequency bands (1900/2100 MHz).

Successful inter-RAT HOs (Radio Access Technology handovers) from WCDMA/HSPA to GSM are critical to ensuring a positive end-user experience. However, in several networks, sub-optimal inter-RAT design degrades network capacity and negatively impacts end-user experience.

THE CHALLENGE

Solving inter-RAT related capacity and performance issues A Tier 1 operator in the Americas faced inter-RAT related performance issues in one of its large metropolitan areas. Their network was over utilized, and subscriber complaints were on the rise. The operator’s optimization process, based on drive testing, was inefficient and inaccurately captured inter-RAT failures. In addition, the operator was unable to identify the root cause of failures.

SITUATION

uHighinter-RAThandoverfailurerates

u3G-2Ghandoverproblemsandnetworkcapacitydegradation

uPoorenduserexperiencecausedbydroppedcalls

uFieldtestingsolutionsrequiredextensivetimeandresources

SOLUTION

uPrioritizedproblemareasandisolatedrootcausesbyevaluatingoperator’snetwork

uDevelopedprocessbasedonperformancecountersandnetworkprobes

uAnalyzedandidentifiedrootcauses-withnetworkprobes,RF,andneighborlistanalysis-onhighprioritysites

uDesignedspecializedreportstoregularlymonitorperformance

RESULTS

uRecommendedthattheoperatorreduceitsdrivetestingandisolate,andthenrepair,itsinter-RATproblems

uEliminatedapproximately3%ofinter-RATfailuresinoneparticularmetropolitanarea

INTER-RAT OPTIMIZATION IN OVERLAYS

COMPANY

- Tier 1 operator

- Nationwide deployment of HSPA

- Solution benefits all markets

ENGINEERING SERVICESGROUP

www.qualcomm.com/esg

THE SOLUTION

Applying best practices from Qualcomm experts The execution of this project required access to performance data on the operator’s network and close coordination with the operator’s engineering team. To ensure smooth communication and efficient data collection and analysis, ESG subject matter experts (SME) worked onsite with the operator.

To isolate the root causes, the Qualcomm ESG team drew upon internal best practices and past experiences to design

a “top-down” process, which used Performance Management (PM) counters, network probe traces and field testing (see Figure 1).

First, PM counters were identified to detect inter-RAT HO failures. Specialized reports were generated to locate the worst performing cells and assess the major failure causes for each cell. These specialized reports and analyses were used to create a list of high-priority cells, the largest contributors to inter-RAT HO failures. This step helped minimize the operator’s exposure to future inter-RAT HO issues.

The PM counter reports specified that many failures were attributed to GSM channel setup. To confirm and further analyze the operator’s inter-RAT failures, Qualcomm ESG evaluated network probe traces for worst performing cells. This investigation verified that those particular cells were experiencing GSM channel setup failure. Performing this assessment helped narrow down the GSM network coverage analysis and better identify neighbor lists for cells with high GSM channel setup failure.

As a final step, drive test logs were collected the around worst performing HSPA cells. An RF analysis showed that the target GSM cell had fragmented coverage and was overshooting, preventing other GSM cells from inter-RAT HOs. As a result, inter-RAT HOs were attempted from the incorrect GSM cell, increasing the risk of failure. Qualcomm ESG recommended that the operator remove its GSM cell from the worst performing HSPA (UMTS) cell neighbor list (see Figure 2).

RESULTS

Qualcomm ESG delivered specialized PM counter reports and decision flow charts, suggesting network improvements.

The process developed by Qualcomm ESG enabled the operator to reduce its OPEX. This was achieved by eliminating extensive drive testing requirements and reducing the amount of time to isolate and fix inter-RAT performance issues.

The optimization process eliminated approximately 3% of inter-RAT failures in this particular metropolitan area.

INTER-RAT OPTIMIZATION IN OVERLAYS | CASE STUDY

2010.05.V02

Figure1:High-levelinter-RATOptimizationProcess

Figure2:Inter-RATOptimizationResults(example)

No

PERFORMANCEMANAGEMENTCOUNTERS PROBES FIELD TESTING

No

Yes

Yes

Analyze inter-RAT handover performance

counters

Analyze message flow between network

elements

Collect drive test data in target inter-RAT area

Prioritize problem areasIdentify remaining call

drop reasons

Analyze inter-RAT failures

Determine the cause of failures

Success?

Success?

Look for RF issues, NL issues, and other

possible inter-RAT handover failure causes

Recommend CorrectiveAction

The recommended action deleted GSM Cell C from inter-RAT neighbor list of HSPA Cell A

LEGEND:

HSPA cells GSM cells