Top Eight Frequently Asked Questions about RF Drive Testing

What is RF drive testing?

Drive testing is the process of collecting samples of RF signals while driving in a certain geographical area. As you're driving and collecting these samples, the samples are geo-tagged or geo-located, so each sample is associated with a specific location.

To conduct a drive test, you need some equipment that can identify your geographical location, like GPS. Then you need equipment that can collect wireless signal data that you are testing which can be a spectrum analyzer or a technology scanner. The idea is that as you drive through your drive test route, the equipment continuously collects samples or readings from the RF spectrum. For example, at each location, you could be collecting signal strengths of the frequency band of 700 MHz. So, as you drive along, for each coordinate, you will plot or collect for this particular coordinate. You will measure signal strengths of varying levels from one location to the next. So, as you drive, it collects and stores all that information into a file which becomes your drive test. In summary, that’s what a drive test is.

What is RF drive testing used for? What are the different types of RF drive tests?

RF drive test has multiple purposes. Before a telecom operator deploys a network, they could do a spectrum clearing drive test. For example, they just purchased a frequency band or were granted a frequency to use and before they deploy their network, they want to make sure nobody else is using that frequency. So, they do a pre-deployment drive test. They're basically going to tune their equipment to the frequency that they want to check and drive around and hope that they don't find anything. For this test, they use an omnidirectional antenna on the receiver to capture signals from all directions. If they detect that the spectrum is in use or interference, then they're going to try to find the source of the signal and then try to understand why it's there and if it should be there. This activity is called “interference hunting”. Once a transmitting signal is detected, they will use a directional antenna to determine the exact location of the interference or transmitting signal. This may require walking around with the directional antenna to accurately pinpoint the location.

Another alternative for interference hunting is to perform geo-location through triangulation or TDOA (time-difference of Arrival) techniques. In addition to RF drive tests, spectrum monitoring equipment can be placed at specific locations around that area and use triangulation techniques to locate the source of interference or signal in question.

Interference hunting could also be required on a network that's already deployed. So, for example, in a certain area, you're experiencing interference on your network, you know, there's interference there, you know, it's not you, because you've already tried everything you can and couldn’t solve the problem. In this case, you can perform geo-location with triangulation if your spectrum monitoring system is set up to do so otherwise you will need to send a technician with a directional antenna to detect the source of the interference. For example, depending on the frequency band of cordless phones or streetlamps sometimes interfere with the cellular band in the 700 MHz spectrum.

The other types of RF drive tests are performed to ensure proper deployment of a network. In this case, you're going to use a test transmitter. This drive test is called a propagation model calibration drive test. In this test, you will place the test transmitter somewhere in a known location, with known power and configuration of the transmitter and then you will drive around the area of interest and transmit a test signal in continuous wave mode. For this test, you will be continuously transmitting on the frequency bands you’re checking. As you drive around, this test will determine how the signal level propagates and that information can then be used to calibrate the propagation model. So, when you’re designing your network, you're going to use a calibration model to predict the propagation of the transmitters that you're going to place in your design. And this propagation model can be calibrated based on real drive test data.

An important component of both pre-deployment tests mentioned above is a spectrum analyzer. A spectrum analyzer is a device that performs over-the-air measurements of the given frequency band. More precisely, a spectrum analyzer measures how strong the signal is in each part of the spectrum that you're interested in.

There's another type of drive test to assess the network performance. In this drive test, you try to assess the general performance of the network or try to locate the areas where you have performance issues during low and high traffic periods. For this type of drive test, we use another analyzer that not only provides the signal level of the spectrum but also decodes information from that part of the spectrum to get more insights into your system. For example, if you're doing a drive test for a 4G network, based on the frequency bands that you're measuring, you would use a spectrum analyzer to locate the center of the frequency channel. Once you detect the center frequency, you can start decoding additional information within the 4G protocol itself. This information will provide you with knowledge about the signal strength at that location. We use this information to understand the real performance of the network at that time and location.

Those are the three main types of tests; spectrum clearing, model calibration and then network performance.

For post-deployment, there is another type of test. When we talk about the performance of the network, you could also do a drive test for benchmarking. For example, you want to drive around a city and compare the performance of the three main telecom operators in that city. And that's a benchmarking drive test. So, in that situation, you would not be drive-testing just your network, but you would be drive-testing other networks as well. Another post-deployment drive test is, let's say you are creating a service or offering a product, for example, autonomous vehicles, drones, or even some IoT applications, and you require wireless coverage for this application. So, you may want to drive test a certain area, not to specifically test a network, but just to make sure you have coverage on that area for this application. Because if you don't have coverage in that area under investigation, you might have to deploy an additional 4G / 5G or cellular base station. Companies like power, hydro, transport or oil and gas need coverage for their applications across the areas they serve, therefore these companies may do drive tests to make sure they have coverage in the places where they plan to put a new extension to their network e.g. pipeline or new substation so that when their dispatch goes to that new location, they have cellular coverage. Currently, in several states in the US, buildings are required to insure first responders have cellular coverage everywhere in the building, therefore, indoor walk tests for cellular performances are required.

What kind of demodulation schemes does RF drive testing usually cover?

The most prevalent radio service today is 4G where the majority of the countries are gradually phasing out 2G and 3G while ramping up 5G quickly. Therefore, the demodulation schemes should be covered 4G to 5G since each service requires a different demodulation technique. Below is the list:

• 2G: BSIC, RSSI, C/I, BER
• 3G: RSSI, RSCP, EcI0
• 4G: PCI, RSRP, RSSI, RSRQ, SNR
• 5G: PCI, RSRP, RSSI, RSRQ, SNR

What types of customers need/use RF drive testing?

There is a variety of customers across several market segments. Telecom operators that serve both public and private networks make up a large portion of cellular deployments. The other customer type is private network deployments across many different industries including utility companies, large enterprises, marinas, transportation/transit, mines, etc. For example, because utility companies have their substations in remote locations, and have all their dispatches wireless on their own wireless smart grid, they have wireless surveillance systems for their substations. Another customer type is oil and gas with their oil platforms and pipelines. Most of their assets are not covered by current telecom operators because these assets are mostly in the middle of nowhere. So, most of the time, oil and gas companies have to build their own networks. Another customer type is transportation/transit e.g., trains, metro/subway, autonomous vehicles, drones, etc. There's a variety of other customers that rely on good operating wireless networks for them to carry their own data traffic, voice and all their wireless needs. There are also more consumer-focused networks that are getting more and more common now, for example, the hospitality industry. For example, generally, ski resorts don’t have LTE coverage on the mountain, and telecom operators have very little desire to build a network because it's not cost-effective for them. But with all the new CBRS frequencies and with all the small cells now, resort operators themselves can put small cells to provide wireless service for their customers and generate extra revenue from that.

So, there are a lot of new use cases that didn't necessarily exist five years ago that are now coming into play. After the pandemic and the remote learning, a lot of cities in the US decided to have common areas in the city that have either LTE small cells or free Wi-Fi, so kids that don't have good internet access at home can go to these common areas like a park or a library.

There are also customers like public safety, utilities, and transportation that heavily rely on mission-critical wireless communications for surveillance cameras, dispatch, etc. Firefighters and the coverage for their systems in buildings were already mentioned as an example. Mission-critical wireless services require very specific performance of the network. So those companies have to install their own networks that have those characteristics. Many times, companies looking for mission-critical wireless services are forced to deploy their own network because telecom operator networks are mostly built to work in populated areas. They're not built to provide guaranteed service or data rates, but mission-critical companies do require a consistent wireless network performance to ensure their network is operational in emergency situations.

What applications require RF drive testing?

Telecom operators are the obvious ones. In the previous sections, we also mentioned private network operators and mission-critical applications as part of it. The IoT industry opened a whole new universe for different forms of drive tests e.g., walk test, drone test, etc. When there is a network out there, it needs to be tested to ensure that the spectrum is available, and it works as intended.

We as consumers are focused on devices that we use like tablets, laptops, phones, etc. and don't think about the critical infrastructure that supports our daily life. For example, utility companies e.g., hydro, gas, power as well as our food supply and transportation systems. If you think about our food supply, farming, and livestock sectors; there are several wireless IoT applications in use today. In agriculture, soil moisture is tested remotely via wireless sensors to ensure irrigation and plant growth are optimized. In livestock breeding, for example, there are IoT devices for livestock to measure their general health like how much livestock is walking, standing, moving/not moving, and heart rate etc., so you can diagnose livestock’s health and act accordingly.

Another wireless IoT application is metro/subway transportation. Telecom operators lack coverage in those areas where transportation companies need to monitor parameters from trains so, they need to install their own networks to be able to get this information. Having a network will improve their service and maintenance quality. Instead of a drive test with a car, a train test will be performed, because they need to make sure they have service availability in their train network.

There are also drive test applications on planes where you need to do a plane test because airlines provide wireless connectivity on the plane. When we say drive test we think of cars, but really could be a walk test, a train test, or a plane test. It's basically a moving test where a sample is associated with a location.

What is crucial in an RF drive test for it to be successful?

I would say the first one is defining the route to ensure that you will cover the area that you're trying to measure, but also that will meet the purpose of what you're trying to measure. So, if you're conducting a performance drive test, you want to make sure you're driving your whole service area because you want to know that your network is good everywhere. But if you're driving for a model calibration drive test, you don't necessarily need to drive the whole service area, but you need to drive to characterize enough clutter types to calibrate your model. So, the route definition has to be number one and then ensure the route is covering the area of concern.

You also need to account for practical considerations. For example, am I going to be able to drive to this location? Many times, there are private areas such as private condominiums that don't allow cars to drive in that area. Am I able to drive at a reasonable speed for drive testing along the selected route? So, for example, you don't want to drive at 100 miles/hr but also you don't want to drive at 20 miles/hr. If you are on a highway that has a minimum speed limit and you should be driving at 40 miles an hour for the drive test, maybe it's not going to be possible or if there's a rush hour, you have to accommodate for the hour that you're going to be doing this drive test. It's all very related to this route definition. In summary, it’s all about routes and coverage areas and the purpose of the test has to be defined as the first step.

The second step, I would say it's probably in terms of the equipment. Do I have the correct equipment and set up my equipment correctly? So, for example, you need to ensure that the antenna, cable and mounting systems can support the frequency bands you are measuring. You have to ensure your equipment is set up properly when it's time to perform the drive test. What am I measuring with this equipment? What frequency band am I measuring? Are the cables, okay? Is the antenna mag mount okay? Is the antenna okay and grounded properly as well as VSWR so all those going considerations? Is this equipment set up correctly for measuring?

Another important step is to document the test setup. So, that when you do the drive test on the same route on a later date, you will ensure to collect the new data under the same test setup as the old data to have a proper comparison e.g., in the first drive test you may have used a van instead of a car or the antenna type, etc.

What kind of information is provided in a drive test and how is this information used?

What we do with any information depends on the purpose of the drive test. For example, a company bought a new spectrum and is going to deploy a 5G system. In that case, you would use an RF drive test to look if there is any interference or anyone else transmitting on this spectrum. The other thing you can do is propagation model calibration. You could have a CW transmitter and now you are collecting data on the signal level from the transmitter at different locations and then you would use that information as an input for a planning tool to adjust the propagation model. When you do the calibration for the propagation model, you will look at all the drive test data and would say, using the prediction that I have for all the same coordinates, I get these values for the drive test. I use the drive test values to fine-tune my model. The values collected during the propagation drive test will improve the predicted values.

The last use of drive test data could be used to improve the performance of networks, but just in terms of signal level for technologies that either don't follow a standard or don't transmit a lot of information that has to be decoded. For example, LMR - Land Mobile Radio Systems, like Tetra or P25 it’s very common to do a drive test, just with a spectrum analyzer. So, you can see the signal level at the bands that are being used. So that's one set. The other set would be technology scanner measurements. Now, you are not only reading something from the air or capturing something from the air, but you actually are interpreting what you're reading based on 2G, 3G, 4G, or 5G. So, this is much more performance, quality assessment, benchmark type of drive test because now really what you're doing is not only you’re driving and seeing do I have a signal here, but you're driving and seeing yes, I have a signal and it's a 3G signal and it has these characteristics or it's a 4G signal and I see this PCI at this location, this PCI at that location, the qualities like this, so it gives you a lot more details related to how the system is working besides just signal level. And that is important for network assessment to see the network quality. But it's also important for you. If you're not the owner of the network, you may be trying to decide whether you can rely on 4G coverage on that network.

Those are the most two common ways to use the data. What kind of information is provided basically depends on the devices you use to collect data during a drive test. When you use a spectrum analyzer, you get the signal strength and signal level. And then you make an analysis based on that signal level, the other method uses a technology scanner, where you get the technical information aside from signal level or signal strength, depending on the technology e.g., 2G, 3G, 4G or 5G.

What are the emerging application areas and use cases for drive tests?

We mainly talk about private networks and private network applications. So, I think different private network applications like the hospitality industry, transportation, unmanned vehicles, mission-critical and mining are going to be reliant on wireless services. All these applications along with utilities and smart grids will need the extra reliability of a wireless network.

This article has been written by thinkRF. They provide real-time, networkable and software-defined RF spectrum analyzers & downconverter / tuners. The R5750 from thinkRF is a Real-Time Spectrum Analyzer that can be used to conduct drive tests. It has a frequency range from 9 kHz to 27 GHz with real-time bandwidth up to 100 MHz. The analyzer has an integrated GPS chipset that makes it possible to know the location and time of measurements. The analyzer is able to provide positional and temporal information with signal information that can generate a complete map of the signal environment. Click here to learn more about this product from thinkRF.