Looking for Trouble

The complexities of 2G and 3G wireless networks require a paradigm shift to drive testing methods.

Although aggressive pricing plans attract new customers, it's typically the quality of the network that retains them. One of the best ways to identify network problems that affect the quality of the customers' calls is to duplicate the problem and collect enough technical data to identify the root cause. One of the best methods for duplicating the customer problem is to perform a drive test.

Drive testing is conducted to understand the network performance from the subscribers' points of view. The equipment used consists of one or more cellular phones connected to either a PC or an embedded processor. The device also may have scanning receivers for identifying coverage and interference problems as well as a GPS receiver for logging the position of the collected data. An engineer or technician drives the area with the equipment and attempts to identify and troubleshoot the problem on the spot in real time or collects the data and troubleshoots the problem in the office with software-analysis tools such as mapping, reporting and spreadsheets.

This type of data gathering is expensive, due to personnel and vehicle costs, relative to test data gathered from the cellular switch and/or cell sites. However, the customers reside in the space between the cell sites, so drive testing must be performed in these locations.

As cellular systems evolve, wireless-network engineers and technicians are driven to improve their productivity. For example:

Network problems are increasing exponentially due to increasing density and number of cells, and the conversion from analog to digital and 2G to 3G.

Capital and personnel expenditures for engineering and operations are decreasing as a percentage of revenue due to increasing competition and lower airtime prices.

Recruiting qualified engineers and technicians is becoming increasingly difficult due to increasing competition and job-market demand.

The cycle time from when a network problem is reported to solving the problem can take days or weeks and needs to be reduced. Pressure to reduce this cycle time is due to increasing competition, the customer's increasing perception of quality and the need to reduce churn.

As air-interface technologies change and additional data tests are required, more testing will be needed to ensure quality.

Two general strategies or methods of drive testing and analysis are compared in Figure 1.

The current classic method is manual. It requires people to drive to the problem area and collect data and interpret it on the spot or manually bring the data back to the office for analysis. Back in the office the engineer will use software tools installed on his PC for mapping reporting and spreadsheet analysis.

The new enhanced method combines manual drive testing and analysis with automatic drive testing and analysis. In the automatic mode, data always is being collected and stored on a centralized file server. In addition, server-software tools are available to automated output reports, maps and analysis.

With the preferred system-architecture solution, data transfer between the remote units and the server is performed through a wireless modem. The server stores the data in a relational database with an open-architecture format and has mapping- and reporting-analysis utilities. The user interface into the server is through a standard Web browser, allowing access from any computer with an Internet connection and providing scaleability to regional or nationwide systems.

Solution Attributes A successful implementation of an automated data collection and analysis solution should have the following attributes:

Simple setup and reliable operation particularly for remote units in extreme environmental conditions

Open-architecture database to allow third-party software-data access

Mapping-, graphing- and reporting-analysis tools with interactive and automated analysis

Ability to be alerted upon an alarm event such as multiple dropped calls or continuous audio-quality degradation

Compare performance of multiple networks simultaneously

Ability to access data from any computer without having to install software applications.

As systems become more complex, the standardized functions of the test engineer must be offloaded to automated systems. In addition, the demands of the marketplace of increased quality, increased capacity at a lower cost, with more competition, are driving the need to solve problems and improve systems performance much faster than before. Automated systems are designed to fill this need and to provide continuous information to the system engineer.