Index terms: RF Optimization, Handover, Agilent Drive test tool, Actix Post processing tool.

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1 Reducing Handover Failure Rate by RF Optimization Syed Imran Basha, Idrish Shaik Department of Electronics and Communication Engineering, Abstract: RF Optimization is a very critical set of activities in the life cycle of any GSM wireless network. The primary tool used by most service providers to solve network problems is a Drive-test tool system, with the goal of collecting measurement data as a function of location. Once the data has been collected, engineers can use the collection and postprocessing software tools to identify the causes of problems and determine how these problems can be solved effectively and efficiently. In this project, RF performance parameters such as the received signal strength, receive voice quality, carrier to interference ratio, etc., are defined for the efficient and effective functioning of the RF network. Also we will measure short-call and long-call control tests from the drive testing process. And this project requires us to work on various tools such as Agilent 15.2 Drive test tool, ACTIX Post processing tool. By analyzing the drive test results, the main motive is to identify the causes of handover failures in a BSNL service test area and necessitate steps to reduce the handover failure rate. How to optimize the BTS coverage area successfully is the real challenge. If the optimization is successfully performed, then the QOS, reliability and availability of RF Coverage area will be highly improved resulting in more customers and more profits to the mobile telecom service providers. Index terms: RF Optimization, Handover, Agilent Drive test tool, Actix Post processing tool. I. INTRODUCTION The Indian telecommunication industry is the second largest telecommunication network in the world. The main drivers for this extraordinary growth are because of Government s Telecom reforms and the stupendous success of GSM standard. In this environment, high quality of service is a competitive advantage for a service provider. Service providers must continually strive to improve their quality of service if they want to keep customers. If too much time is spent simply reacting to customer complaints, there may not be enough time to improve overall service quality. Therefore, Service providers need the ability to fix complaint-producing problems quickly. Hence RF Optimization is a very important process in any service provider s operating lifecycle. By gathering and analyzing network data and revising network parameters Cellular communication achieved by using proper RF Planning and Optimization. As we move further ahead the need for better technologies and reliability of services, integration and cost effective solutions have become a necessity for service providers. If the optimization is successfully performed means you achieve the QoS, reliability, Bapatla Engineering College, Bapatla availability, more profit and more customers. The main motive is to reduce the Handover failure rate through RF optimization. In this project, RF performance parameters are considered for the efficient and effective functioning of the RF network. This project requires us to work on various tools such as Drive test tool and Post processing tool. II. RF OPTIMIZATION Every a live Network needs to be under continues control to maintain/improve the Performance. Optimization is basically the only way to keep track of the network by looking deep into statistics and collecting/analyzing drive test data. It is keeping an eye on its growth and modifying it for the future capacity enhancements. It also helps operation and maintenance for troubleshooting purposes. Successful Optimization requires: Recognition and understanding of common reasons for call failure Capture of RF and digital parameters of the call prior to drop Analysis of call flow, checking messages on both forward and reverse links to establish what happened, where, and why. Optimization will be more effective and successful if you are aware of what you are doing. The point is that you should now where to start, what to do and how to do. Optimization is an important step in the life cycle of a wireless network. Fig 1: The Optimization Process. Drive-Testing is Performed to Verify that the Action Steps Taken to Solve Problems Were Effective 29

2 The optimization process is illustrated in below figure. Drive-testing is the first step in the process, with the goal of collecting measurement data as a function of location. Once the data has been collected over the desired RF coverage area, it is output to post-processing software. Engineers can use the collection and post-processing software to identify the causes of RF coverage or interference problems and determine how these problems can be solved. When the problems, causes and solutions have been identified, steps are performed to solve the problems. Figure 1 show that optimization is an ongoing process. The goals are to improve quality of service, retain existing subscribers and attract new ones while continually expanding the network. III. DRIVE TEST The quality of the network is ultimately determined by the satisfaction of the users of the network, the subscribers. Drive tests give the 'feel' of the designed network as it is experienced in the field. The testing process starts with selection of the 'live' region of the network where the tests need to be performed, and the drive testing path. Before starting the tests the engineer should have the appropriate kits that include mobile equipment (usually three mobiles), drive testing software (on a laptop), and a GPS (global positioning system) unit. When the drive testing starts, two mobiles are used to generate calls with a gap of few seconds (usually s). The third mobile is usually used for testing the coverage. It makes one continuous call, and if this call drops it will attempt another call. The purpose of this testing to collect enough samples at a reasonable speed and in a reasonable time. If there are lots of dropped calls, the problem is analyzed to find a solution for it and to propose changes. A. DRIVE TEST TOOL: JDSU E6474A v15.2 Agilent technologies have introduced the industry s first integrated test solution that in a single protocol analysis tool, seamlessly combines mobile device data captured from a RF interface and from a mobile terrestrial network. Troubleshooting and optimizing today s networks requires a broad understanding of the network performance over multiple interfaces. Rapid growth in the number of subscribers and in-data network usage has challenged the radio access network in both RF capacity and data throughput performance measuring across the last hop from the base station to the mobile device is essential for troubleshooting and optimization and without visibility to the air interface, network operators must manually correlate data from independent drive test and protocol analysis tools. Agilent s E6474A drive test tool has revolutionized and simplified end to end troubleshooting. The software allows users to correlate signaling procedures from the air interface and radio access network interfaces in a single view to detect and troubleshoot problems from the mobile phone to the network. 30 B. DRIVE TEST PROCEDURE After collecting the required information form the BTS and the OMC-R, the drive test is started. The equipment is set up in a vehicle and long calls as well as short calls are generated. A long call is a call which is generated as well as terminated by the user himself. A short call is a pre programmed call generated by the system for a very small duration, say 10 seconds or more. A long call is used to measure the handover success rate as well as the Rx quality, while CSR and Rx level are measured on a short call. The drive test is done over a distance of 3 km or more from the starting point. Various parameters are observed and recorded during the drive test. The following shots have been taken while conducting the drive test: Fig 2: Drive Test route map The drive test procedure is as follows: Tool may be setup for two mobiles One for Long call and another for short calls (2 minutes). In the route map following are to be enabled for Analysis. 1. Rx Level 2. RX Quality 3. Survey Markers (like H/O, DCR & H/O symbols) 4. Cell site Database. statistics for the s in the Point -1 to be enabled. Conduct the Drive Test covering all sectors by observing the following Parameters: 1. Rx Level 2. Rx Quality 3. Interference on BCCH & Hopping Frequencies. 4. Handovers & Drop s 5. Observe whether the nearest sector is serving or not. The data, as per the requirements are observed and recorded. The data is analyzed for performance.

3 IV. POST PROCESSING A. Introducing Actix Analyzer Actix Analyzer is a software application running under Microsoft Windows on a PC that provides a series of analysis tools for post-processing cellular network data. The tools are designed to address applications such as: Network performance optimization Feature testing Service validation Problem diagnosis and analysis Network bench-marking Competitive analysis2 The platform for Actix Solutions, Analyzer, can load network performance data from many different sources: Short : B. ANALYSIS GSM DT DESIGN VALIDATION AND QUICK ANLYSIS The set of reports contained in this application gives a summary of voice traffic performance and allows a verification of the radio network design. 1 details Drive Test Details report: This report provides a complete overview of the content of the drive test in terms of performed calls, call duration, performance indicators (call setup success rate, call completion rate, handover success rate and location update success rate) and a detailed list of the procedural messages. Various attributes of the file decoded from specific messages or sequences of messages can be counted or combined to give general indications, such as number of call setup procedures, call setup success rate and call completion success rate, or Update. Table 1: Drive Test calls details Short Long Fig 3: Handover Failure during Short Drive These data sources could include field-test equipment and switch call traces, and could be from a one-off test, or part of a planned series of samples to build up an image of overall network performance. Once the data is loaded, a variety of analysis tools and displays provide a clear view of network performance for engineers, technicians or operations management staff. Long : Handover Command Handover complete Handover Failure 1 1 Updating Request Updating Accept Updating Reject Outgoing Starts Outgoing Setup Ok Outgoing Setup Failure Incoming Starts Incoming Setup Ok Incoming call Setup Failure Completed Fig 4: Handover Failure during Long Drive 31

4 Dropped 3 2 Setup Success Rate % Drop Rate 1.595% TCH Blocking Rate 0.981% SDCCH Blocking Rate 0.326% Rx Quality(0-5) % Handover Success Rate % Update rate 100% Table 2: Drive Test analysis Report for TRAI V. HANDOVER ANALYSIS Reasons for handover failure could be unavailable time slots because of high traffic, congestion, low signal strength or bad quality on target cell. Handover can be failed because of hardware problems in target cells more likely TRX or time slot problems. If handover attempt fails, MS tries to return to old channel. If it cannot, call drops. Handover attempt is repeated after a penalty time. Short : Issues Observed: Problem occurred due to abnormal case, Unspecified. Problem Description: Here Handover failure causes due to the interference of same frequencies of two different BSICs. Same frequencies serving in same direction. Here the problem can be seen clearly as follows. Table 3: Handover failure at two different BSICs Cell ID BCCH BSIC So, here 21 and 36 BSICs serving same frequencies then the interference occurred and thereby Handover failure happened. Action Steps: Re-orient the sectors. Change the frequency planning. Long : Issues Observed: Problem occurred due to abnormal case, Timer expired. Problem Description: MS is lost after Timer T3103 expired. MS didn t answer the Base station within 2 seconds. T3103, Handover timer is the time the network waits after transmitting a HANDOVER COMMAND message until receiving HANDOVER COMPLETE or HANDOVERFAILURE or the MS re-establishes the call before the old channels are released (maximum 2 seconds). If the timer expires, then the channels are released from the old cell. Here the timer expires and thereby having low coverage in the old cell. Moreover, the network has not received the MS, and then the newly allocated channels are released. Hence it can t able to take place the Handover to the target cell. Action steps: Tilt the antenna direction. Increase the signal Level. Place the new tower. Handover Failures occurred in overall drive are two, and they are as follows. Table 4: Handover failure occurrence at different parameters Event Handover Handover Failure 1 Failure 2 Cell ID Time 17:16:45 17:00:51 Latitude Longitude VI. CONCLUSION The overall objectives of any RF design depend on a number of factors that are determined by the needs and expectations of the customer and the resources made available to the customer. Due to the mobility of subscribers and complexity of the radio wave propagation, most of the network problems are caused by increasing subscribers and the changing environment. Radio Network Optimization is a continuous process that is required as the network evolves. Radio network optimization is carried out in order to improve the network performance with the existing resources. The main purpose is to increase the utilization of the network resources, solve the existing and potential problems on the network and identify the probable solutions for future network planning. Through Radio Network Optimization, the service quality and resources usage of the network are greatly improved and the balance among coverage, capacity and quality is achieved. VII. FUTURE SCOPE At present Drive Testing in GSM RF Optimization is being performing manually for the improvement of performance of the network. Instead of doing drive testing manually, there may be a scope of ANMS (Automatic Network Management System) process. In this system, Drive Testing equipment can be attached to moving vehicle to serve in BSNL test area and it can be monitored by the server or clients. By using the internet, all the drive data can be simultaneously collected up to date to the server. 32

5 REFERENCES [1] Halonen T., Romero J., melero J.: GSM, GPRS and EDGE performance. John Wiley & Sons Ltd, [2] ITU-T recommendation G (2001), Communication quality of service: A framework and definition. [3] Jens Zander. Radio Resource Management for Wireless Networks. Artech House Inc., [4] Bilal Haider, M Zafrullah Khan, M.K.Islam: Radio Frequency Optimization and QOS in operational GSM network. [5] S. Kyriazakos, G. Karetsos, E. Gkroustiotis, C. Kechagias, P. Fournogerakis Congestion Study and Resource Management in Cellular Networks of present and Future Generation, IST Mobile summit 2001, Barcelona, Spain, 9-12 september [6] Wireless Communications, Principles and Practice, 2 nd edition, Theodore S. Rappaport, Pearson publications. [7] Kechagias, S.Papaoulakis, N.Nikitopoulos, D. Karambalis: A Comprehensive Study on performance Evaluation of Operational GSM and GPRS Systems under Varying Traffic Conditions. IST Mobile and Wireless telecommunications Summit, 2002, Greece. 33