3G Network Performance Drive Test

White Paper

3G Radio Network Performance Measurement and Analysis Basics

Network Performance data can be collected from a variety of points in the 3G radio network and only by utilizing data from a combination of these sources can a full picture of the performance of the network be obtained. Each point offers different strengths and weaknesses in areas such as: § § § § §

Type of information (e.g. radio link information, circuit call information, or packet data information). Availability of data collection devices (delays in handset availability could limit the usefulness of this data source). Granularity of data (ability to use data to solve specific problems) Ease / cost of data collection. Volume of data that can be collected.

Once collected, the data must be filtered and reduced before it can be used to make decisions on improving network performance. In addition, collecting and analyzing various sources of data at the same time allows efficient utilization of resources. Although based primarily on the harmonized 3GPP standard for WCDMA (UTRA-FDD), much of this document is also applicable to the TDD mode (UTRA-TDD), which is still in the process of being harmonized with the TD-SCDMA contribution from the CWTS standards group of China.

Sources of Network Performance Data Performance data on the wireless transmission network can be gathered from many sources, but these are the most common: § § § § § §

Uu: Air-interface Iub: RNC-Node B interface Iu CS: RNC-MSC interface Iu PS: RNC-SGSN interface OMC: Performance Counters OMC: Measurement Programs

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Drive Test Notebook

Figure 1 - Components of the wireless transmission network, including interface points for gathering critical data Open standards are available for most of these interfaces; however, OMC performance counters and measurement programs almost always utilize proprietary interfaces and output data formats. In addition, infrastructure vendors do not always implement all available open interfaces, particularly in the case of the Iub interface.

Overview of Data Collection Techniques Drive Test Equipment Using equipment available from a variety of vendors, operators can drive around their network measuring performance from the perspective of the subscriber. Equipment typically consists of a special test mobile phone and wideband scanner, connected directly to a laptop, or indirectly through an intermediate hardware device. Scanners passively measure desired and interfering RF signals from base stations faster and with better accuracy than test mobiles, thereby complimenting the measurements available from the phone. In many cases, scanners can detect the underlying RF causes of the performance problems detected by test mobiles. Some vendors also offer drive test equipment that can be operated by remote control, allowing equipment to be placed in technicians' vehicles or fleet vehicles (such as taxi cabs), for automatic data collection.

White Paper Drive Test – Strengths § Good source of RF data with detailed position information that can be used to identify and resolve RF problems. § Scanner data is already available for multiple vendors. Drive Test – Weaknesses § Can be time-consuming and expensive to perform measurements. Many operators look to minimize drive testing for this reason. § Measurements do not accurately represent the experience of pedestrian and inbuilding users. § Measurements do not give performance information on all subscribers, only on an individual call. As a result, performance is only measured for the network components serving that specific call. § There are many vendors with many different formats, which are usually proprietary. § Large-scale production of handsets for testing may not happen until optimization is well underway.

OMC Measurement Program Using proprietary measurement programs which run on the switch or RNC, operators can collect performance data for specified mobile phone numbers. The log files are often used to collect uplink performance metrics to complement the downlink performance measured during drive tests. Log files may be synchronized to drive test data or used independently. Measurement Program – Strengths § Good source of low-resolution RF data for both uplink performance metrics, and downlink transmit parameters for a single call. § Ability to supervise uplink performance is key, since relative performance on uplink and downlink in WCDMA varies according to traffic loading. § Cost to perform measurements is low and no additional hardware is necessary. § Testing can be performed for any handset or user equipment. Measurement Program – Weaknesses § Often not available for initial infrastructure release of a new technology. § Specialized knowledge required to run the application and retrieve the results, however, the task itself is relatively straightforward. § No positioning information, however OMC data can be synchronized to drive test data with position information. § Limited capability to monitor multiple calls at the same time (due to system performance issues). § Many vendors with many different formats, which are almost always proprietary.

Protocol Analyzer Using protocol analyzers available from a number of vendors, operators can collect performance data directly from key infrastructure interface points including the Iu CS, Iu

White Paper PS, and Iub interfaces. Because these interfaces are based on open standards, the development of collection equipment and analysis software can be completed during infrastructure development. It is then available for use during the planning and lab/field trial phases prior to system launch. Protocol analyzers can collect a wide range of data: from performance data on the packet and circuit interfaces down to RF data as reported by the User Equipment. Protocol Analyzer – Strengths § Good source of low resolution RF data for both links as well as packet and circuit-link performance data. § Typically available in early stage trials before system launch, even for new technologies. § Easy to compare and combine data across multiple vendors, since collected data is typically based on open standards. § Very useful for analyzing detailed RF usage of packet and circuit connections. § Since data is based on actual subscribers, it accurately reflects indoor and pedestrian performance issues. § The cost to perform measurements, excluding hardware costs, is relatively low and a large quantity of data can be collected very quickly for many network elements. § The only limitation to how much data can be collected is the hardware configuration. Data for all subscribers can be collected, reduced and analyzed. Protocol Analyzer – Weaknesses § Equipment can be expensive, although less expensive alternatives are increasingly available. § If there is no traffic on the network, no data is generated. § Specialized knowledge is required for connecting and operating equipment, although the task itself is quite simple and fast once learned. § No position information; however, location may be estimated using propagation delay information. § Specific vendors may wrap open-interface protocol data into a proprietary interface, which must be decoded before accessing the open interface data.

OMC Performance Counters Performance counters are vendor-specific, proprietary statistical counts of key network events at a sector level of resolution. Operators have traditionally relied on performance counters to monitor the high-level performance of their networks, either using collection software provided by the vendor, third party software, or building in-house systems. Performance Counter – Strengths § Good source of sector-level resolution performance metrics. § Very large amounts of data can be collected quickly for all network elements. Performance Counter – Weaknesses § For the initial infrastructure release of a new technology, generally only very basic functionality (if any) is available and systems by third-party vendors are rarely available at all.

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Compilation of overall system performance can be very difficult when using different vendors for various network elements, due to lack of integration between elements, and differences in definitions of individual counters. Very limited ability to drill-down into lower-level causes of problems: counters typically only record what happened in a 5-15 minute block with no detailed data for troubleshooting. No position information for data (other than sector level). Many vendors with many different formats, which are usually proprietary.

Data Analysis Basics Once data has been collected, it must be processed, analyzed and archived. Processing the data can be challenging for a number of reasons: § §

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Operators typically have a number of vendors for different types of drive test and protocol analyzer equipment, each with a unique interface format. Operators often use measurement programs from different technology networks (e.g. GSM and WCDMA) and/or different infrastructure vendors, each with a unique interface format. Data sets collected at different interface points may need to be synchronized so that they can be merged for troubleshooting across network elements. Data sets may be extremely large (many gigabytes). Key information must be filtered and reduced before it can be used to make decisions. Formats are constantly being updated. The technology of the air-interface is constantly changing (e.g. 3G rolling out on the back of 2.5G technology). Many engineers have limited training and experience with newer technologies.

Key features of a data analysis platform are the ability to: § §

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Support interfaces to a variety of vendors of drive test equipment, protocol analyzers, and measurement programs. Provide support for open interfaces, which can typically be used to collect performance data well in advance of proprietary data sources, like test mobile and peg counter data. Support multiple technologies on one platform simultaneously (e.g. GSM/GPRS and WCDMA). Reduce data through binning and standard database type querying and filtering capabilities. Synchronize data collected from different network elements and sources to remove timing discrepancies. Provide interfaces into databases for storing collected data statistics and provide web-enabled reporting interfaces for extracting data. Support the latest technologies and vendor formats. Provide a user interface that allows less experienced engineers to become effective quickly. Embed engineering expertise into the software to automate the process of analyzing large amounts of data.

White Paper The system shown below in Figure 2 is designed to collect data from all available links from the air-interface through to the switch / SGSN. Data may be collected in discrete log files and processed through a desktop application for manual, on-the-spot analysis. Data may also be collected from any source and processed and loaded into a database system from which it may be served up through a web browser or other client.

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Server Desktop Analysis

Vendor performance comparison

Engineering users

Detailed RF performance optimization

Operations users

Performance Benchmarking Intranet Reports

Management users

Optimization engineers

Figure 2 - Key components of a data analysis system designed to address all feature requirements

White Paper Applications Based on Performance Data Once the data have been collected, operators can use the data to perform a variety of critical applications including: § § § § §

Network planning validation Infrastructure trial verification Accelerated network rollout Advance performance metrics Growth phase network optimization

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