Drive testing or RF (Radio Frequency) drive testing is one of the most traditional ways of measuring the quality and performance of a mobile radio network. The radio network is the air interface that includes the cell towers that our mobile phones connect with to establish a cellular connection.
RF drive testing is a test that allows a mobile operator to monitor, troubleshoot, tune and optimise the radio network to improve mobile network coverage and capacity. It requires RF engineers to take field measurements while driving within the cells on vehicles equipped with specialised RF tools.
RF engineers use drive tests to improve network performance
RF drive testing aims to improve the quality and performance of a mobile network to offer enhanced Quality of Service (QoS) and Quality of Experience to customers (QoE). Drive tests measure the network performance of the air interface, which is the connection between a mobile phone and the cell towers.
Cell towers, technically known as base stations, are called BTS in 2G GSM, Node B in 3G UMTS, eNodeB or eNB in 4G LTE and gNodeB or gNB in 5G NR networks. Base Stations are an essential part of the radio access network (RAN) within a mobile network; therefore, any work that deals with base stations is dealt with by the radio network teams.
It is worth distinguishing between a mobile network operator (MNO) and a mobile virtual network operator (MVNO) from a radio network perspective. MVNOs do not own a radio network and partner with MNOs to “rent” the radio network capacity to connect their customers to the network.
Within a mobile network operator (MNO), generally, there are dedicated engineering teams that look after various parts of a mobile network, including radio and core networks. The radio network is one of the largest parts of a mobile network and requires teams of RF engineers to plan, tune, monitor, and optimise it.
Drive tests allow the radio network teams to perform field measurements to record network quality from a mobile phone user’s perspective. The role of the drive test engineers is to perform a set of network tests by driving within a specific cell or a cluster of cells to monitor and troubleshoot cell sites.
While a mobile network gathers performance measurements in multiple ways, drive testing has been one of the key methods. Drive test engineers use specialised hardware and software to carry out drive testing. The simplified diagram above shows what the setup for a drive test looks like.
Depending on the RF tool vendor, drive test equipment involves mobile terminals (phones), RF scanners, Digital Signal Processors (DSPs), laptops or other mini-computers with specialised software to record the network logs and a vehicle (e.g. a car) carrying all the necessary equipment.
Just to give you an idea, some of the popular RF drive testing tools include TEMS Investigation, Nemo, and Genex, but there are many others also.
Field measurements vs network measurements
While drive testing has benefits, it is not the only way to measure network performance. In mobile networks, there are two types of performance measurements: field measurements and network measurements.
The field measurements are device-level measurements captured through drive testing or MDT (Minimization of Drive Tests). On the other hand, network or system-based measurements are captured by Operations & Maintenance systems like OSS – Operations Support Systems.
Drive testing is more laborious because it requires dedicated teams with specialised equipment to drive around various geographical locations to perform field measurements. As a result, it is time-consuming and costly, but it can provide a user-centric view of network health.
Network or system-generated measurements are easier to manage and can be performed directly by the network regularly. With OSS, mobile operators can get performance reports for both radio and core networks.
However, getting an in-depth understanding of radio network performance in specific geolocations using specific devices is more reliably achieved through field measurements. Field measurements provide a service-centric view of the network performance from a phone user’s perspective at a particular time in a specific location.
Generally, a balance between network and field measurements can be found by using drive tests to complement network or system-based measurements. Network measurements can be performed for the overall quality of the network, and drive testing can help dig deeper into specific issues.
Are drive tests still needed by 4G LTE and 5G NR networks?
An RF drive test is not limited to which network technology enables the cellular service and can be performed on any GSM or CDMA-based mobile network. Therefore, all cellular technologies, including GSM, UMTS, IS-95, CDMA2000, 4G LTE and 5G NR, can benefit from drive testing.
Automated measurements through network nodes like OSS have always been considered an essential source for minimising the dependency on drive tests. However, there are situations that demand an on-site test which can be achieved through drive tests or walk tests.
For example, in a 4G LTE network, if for any reason an LTE cell is not enabling Voice over LTE (VoLTE) calls, an RF test within the cell can allow an engineer to test the call flow and see what happens when the call is initiated. In situations like these, a field test can help determine the root cause by troubleshooting the issue at a local level.
For field testing, a feature MDT (Minimization of Drive Tests) was introduced in 3GPP Release 10 to reduce the dependency on drive tests in 3G and 4G networks. MDT can enable a regular 3G, 4G or 5G mobile phone (UE – User Equipment) to send performance logs directly to the mobile network. 3GPP Release 11 adds further updates to allow the UE to send a complete view of network performance.
There are two parts to MDT – Immediate MDT and Logged MDT. Immediate MDT sends network logs (e.g. Radio link failure) when a mobile phone (UE) is in the connected state. The Logged MDT performs measurements when the phone is in an idle state (inactive) and sends the report later on.
MDT can report network information at the physical (layer 1), data link (layer 2) and network (layer 3) layers. It sends radio network information for downlink and uplink communication along with the exact geolocation of the device using GPS.
MDT can report network parameters like RSCP (Received Signal Code Power), RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality), CQI (Call Quality Indicator), RTT (Roundtrip Time), and Tx power, among many others.
The primary advantage of MDT over traditional drive tests is that it can utilise existing user devices without having to install any specialised tools or send dedicated teams to perform the drive tests. However, MDT has a few dependencies, meaning its practicality is yet to be seen.
For MDT to work, the UE – User Equipment (mobile phone) must support the MDT capability. It is also dependent on user consent which means MDT requires permission from a mobile phone user to allow their phone to send measurements to their network operator. As a result, MDT is used by a small fraction of the overall mobile users.
5G New Radio (NR) mobile networks use various frequency bands, including millimetre waves, and they employ advanced antenna technologies like Massive MIMO at the network and device level for three-dimensional (3D) beamforming. Therefore, the device-level measurements are expected to continue playing a crucial role in mobile network performance.
Dedicated drive testing is not limited to mobile terminals only, and it also uses RF scanners to simultaneously measure radio network parameters for multiple channels from various mobile networks in any given location. It, therefore, adds value to all cellular networks, including 2G, 3G, 4G and 5G networks.
What does the drive testing process look like?
RF (Radio Frequency) drive testing has been a fundamental part of network testing to monitor and improve the quality of a mobile radio network. Over the years, mobile operators worldwide have spent a lot of money buying purpose-built RF network testing tools from market-leading vendors.
The RF network testing tools can provide a snapshot of the mobile network performance by identifying any problem areas and allowing mobile operators to address these issues to improve service quality.
The setup involved in drive testing follows the process used by consulting services, where you first gather information and then provide analysis-based recommendations to fix the identified issues. The key steps in drive testing are data collection, processing and analysis of data, and recommendations.
Drive testing requires the radio network engineering teams to monitor the existing performance of a mobile network, troubleshoot any coverage or capacity issues, and provide recommendations to improve the key network parameters for Quality of Service (QoS) and Quality of Experience (QoE).
When mobile operators perform drive tests, they measure the performance of the mobile network through a user device (test mobile phone). They connect purpose-built mobile terminals to specific software applications and use cellular services like voice calls and data sessions while driving within the different coverage zones.
Once the services are initiated, all the network data, including signalling, is recorded in log files that can be examined later by the same or other engineering teams for an in-depth analysis. The captured data is assembled, processed and analysed to identify potential issues so that network recommendations can be made to fix the problems.
How to conduct an RF drive test in mobile networks?
Drive testing can be performed for many reasons, and the planning may differ depending on your ambition level. For example, you may be drive testing to troubleshoot a specific network issue, in which case your drive test project can be a quick exercise.
But on the other hand, if you are performing a nationwide radio network quality audit, your drive test project can take a bit longer. The key activities in any drive test project are data gathering, data processing, analysis and recommendations.
1 – Data collection or data capture to perform network tests
The first step in any RF drive test is to make a plan so that you can perform the data collection activity without any issues. Some of the potential problems include the laptops or phones running out of power, laptop screens getting frozen, having to restart the laptop during the tests, forgetting the cables for the phones or scanners, having to write any new automated commands during the testing, issues with saving the test logs, not having a detailed drive test route, getting stuck in a traffic jam, and so on.
It is important to be mindful of the issues when creating your plan and setting up all the necessary equipment before embarking on your drive test journey. Depending on the purpose and ambition level, the drive tests can take time, so it is crucial to plan for all the logistics, including meals and comfort breaks.
Make sure that all the necessary equipment, including mobile terminals (with SIMs), RF scanners, laptops, GPS units and any external antennas, are connected neatly and plugged into the power sockets safely in your vehicle. It is vital to make all the checks by following the necessary hardware and software guidelines from your tool vendor. Once everything is connected and all powered up, you are ready to make a start.
You need a pre-defined route for your drive test based on the cell sites you plan to test. For example, you may choose to drive within specific cells or clusters of cells. A cluster in mobile networks is a group of cells that are adjacent to each other and share network resources to minimise interference.
The services you test can include voice calls using 2G/3G networks, IP-based calls using VoLTE or VoNR, web browsing, video streaming and so on. Ideally, you want to have automated commands already written down so that all the calls and data sessions take place automatically and you don’t miss any cells on your drive test route.
The voice calls can be short or long, where the former tests the call initiation and establishment parameters, whereas the latter checks for any drop calls. Usually, mobile operators have a test phone number that they dial so that you don’t require someone else to answer the calls on the other end manually.
Having one person driving the car and other colleagues managing all the equipment and test activities is a good idea. Once you have completed your drive test route, you should have recorded enough data to perform the analysis later. The recorded files that contain all the network measurements are called log files.
The log files can be recorded locally on the laptop or sent to an online network drive. Irrespective of where you store the log files, it is vital to ensure they can be easily accessed by those who will carry out the analysis.
2 – Processing and analysis of the collected data
When you finish the drive tests and get back into the office, it is easier to recall any network issues that you may have encountered during the drive test. It is, therefore, worth making notes so you can keep a record for when you start analysing the log files.
It may be that you and other colleagues encountered a whole bunch of problems in different locations, so it is important to be selective in your log files so that you can prioritise what you want to analyse first.
Sometimes during the recording, the phone or laptop can freeze, which means you cannot record correctly, leading to “corrupt” log files. Therefore, it is essential to first select which files you want to analyse and in what order. Once you have sorted all the files, you can start your analysis.
RF performance tools usually have different options for data collection and analysis. Many tools can provide a good-enough level of analysis that RF engineers can dive deeper into. However, analysing log files requires you to have specific skills and an understanding of how mobile radio networks communicate and how signalling works.
For example, if you were analysing a voice call on a 2G GSM mobile network, you would need an understanding of the call flow for GSM networks. That knowledge allows you to detect any issues or risks by analysing the communication flow through the different layers, including layer 2 (data link layer) and layer 3 (network layer).
3 – Using the analysis outcome to provide recommendations
Once the analysis has been carried out either by yourself or other teams, you will likely have a list of issues and risks that were captured in your log files. The analysis results can be used to dig deeper into the details of the problem areas and provide recommendations on what can be done to fix the issues.
Some post-processing and analysis tools also have the reporting capability to help you create detailed reports by simply importing all the log files. You can use that and possibly combine that with your own analysis to create summarised reports on all the identified issues. The recommendations for network changes can then be sent to the relevant network teams within your organisation.
Here are some helpful downloads
Thank you for reading this post. I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need extra support, especially when preparing for a new job, studying a new topic, or buying a new phone. Whatever you are trying to do, here are some downloads that can help you:
Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy, which explains the network nodes, e.g., BTS, MSC, GGSN etc.
Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience, which is why I’ve carefully put together a few slides to get you started in no time. So if you work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on the product overview and product roadmap.