Every good RF design, after its implantation should be evaluated. There are few ways to do this, for example through analysis of KPI (Key Performance Indicator) or through prediction tools and signal interference. Other very common and efficient way to evaluate the network is conducting a Drive Test. But what is it?
The name is intuitive: take a drive test. The Drive Test is a test performed in cellular networks regardless of technology (GSM, CDMA, UMTS, LTE, etc. ...). Means collecting data on vehicle movement. Its variation has also intutive: Walk Test, ie, collect data by walking areas of interest.
The analysis of drive test are fundamental for the work of any professional in the field of IT and Telecom comprising two phases: data collection and data analysis.
Although through the analysis of KPI's we can identify problems such as dropped calls, among others, the drive tests allow a deeper analysis in field. Identifying areas of each sector of coverage, interference, evaluation of network changes and various other parameters.
Then let's know more about this technique, and know what we can do with it?
What is a Drive Test?
Drive Test, as already mentioned, is the procedure to perform a test while driving. The vehicle does not really matter, you can do a drive test using a motorcycle or bicycle. What matters is the hardware and software used in the test.
A notebook - or other similar device (1)
with collecting Software installed (2),
a Security Key - Dongle - common to these types of software (3),
at least one Mobile Phone (4),
one GPS (5),
and a Scanner – optional (6).
Also is common the use of adapters and / or hubs that allow the correct interconnection of all equipment.
The following is a schematic of the standard connections.
The main goal is to collect test data, but they can be viewed / analyzed in real time (Live) during the test, allowing a view of network performance on the field. Data from all units are grouped by collection software and stored in one or more output files (1).
GPS: collecting the data of latitude and longitude of each point / measurement data, time, speed, etc.. It is also useful as a guide for following the correct routes.
MS: mobile data collection, such as signal strength, best server, etc ...
SCANNER: collecting data throughout the network, since the mobile radio is a limited and does not handle all the necessary data for a more complete analysis.
The minimum required to conduct a drive test, simplifying, is a mobile device with a software to coleect data and a GPS. Currently, there are already cell phones that do everything. They have a GPS, as well as a collection of specific software. They are very practical, but are still quite expensive.
Drive Test Routes
Drive Test routes are the first step to be set, and indicate where testing will occur. This area is defined based on several factors, mainly related to the purpose of the test.
The routes are predefined in the office.
A program of a lot of help in this area is Google Earth. A good practice is to trace the route on the same using the easy paths or polygons. The final image can then be brought to the driver.
Some software allows the image to be loaded as the software background (geo-referenced). This makes it much easier to direct routes to be followed.
It is advisable to check traffic conditions by tracing out the exact pathways through which the driver must pass. It is clear that the movement of vehicles is always subject to unforeseen events, such as congestion, interdicted roads, etc.. Therefore, one should always have on hand - know - alternate routes to be taken on these occasions.
Avoid running the same roads multiple times during a Drive Test (use the Pause if needed). A route with several passages in the same way is more difficult to interpret.
Drive Test Schedule
Again depending on the purpose, the test can be performed at different times - day or night.
A Drive Test during the day shows the actual condition of the network - especially in relation to loading aspect of it. Moreover, a drive test conducted at night allows you to make, for example, tests on transmitters without affecting most users.
Typically takes place nightly Drive Test in activities such System Design, for example with the integration of new sites. And Daytime Drive Test apply to Performance Analysis and also Maintenance.
Important: regardless of the time, always check with the responsible area which sites are with alarms or even out of service. Otherwise, your job may be in vain.
Types of Calls
The Drive Test is performed according to the need, and the types of test calls are the same that the network supports - calls can be voice, data, video, etc.. Everything depends on the technology (GSM, CDMA, UMTS, etc. ...), and the purpose of the test, as always.
A typical Drive Test uses two phones. A mobile performing calls (CALL) for a specific number from time to time, configured in the Collecting Software. And the other, in free or IDLE mode, ie connected, but not on call. With this, we collect specific data in IDLE and CALL modes for the network.
The calls test (CALL) can be of two types: long or short duration.
Short calls should last the average of a user call - a good reference value is 180 seconds. Serve to check whether the calls are being established and successfully completed (being a good way to also check the network setup time).
Long calls serve to verify if the handovers (continuity between the cells) of the network are working, ie calls must not drop.
Types of Drive Test
The main types of Drive Test are :
Tests for Analysis Performance is the most common, and usually made into clusters (grouping of cells), ie, an area with some sites of interest. They can also be performed in specific situations, as to answer a customer complaint.
In integration testing of new sites, it is recommended to perform two tests: one with the site without handover permission - not being able to handover to another site - thus obtaining a total visualization of the coverage area. The other, later, with normal handover, which is the final state of the site.
Depending on the type of alteration of the site (if any change in EIRP) both tests are also recommended. Otherwise, just perform the normal test.
Marketing tests are usually requested by the marketing area of the company, for example showing the coverage along a highway, or at a specific region/location.
Benchmarking tests aims to compare the competing networks. If the result is better, can be used as an argument for new sales. If worse, it shows the points where the network should be improved.
Data Collecting (almost) Flawless
Who has done a Drive Test before already knows this: It looks as Murphy's sits in the back seat. That's because a lot of problems - but preventable - always end up happening.
To avoid, or at least minimize, the occurrence of these problems, always make a checklist before starting the Drive Test.
It is very frustrating to run a route, and only in order to realize that the data were not collected properly.
So before you start, check all connections, always! Mainly, make sure that all equipment is properly energized. You will not want to see a low battery warning on a busy road, will you?
When we say check, include making sure that the connections are tight and will not drop with vehicle movements.
Also make sure the equipment is tied, or you will see a flying laptop in case you need to give a halt.
When assembling the equipment, maintain a distance of at least a foot between each antenna, thereby ensuring that we have no electromagnetic interference or distortion of the radiation pattern of antenna that can affect measurements.
Making sure that all equipment involved are tied and connected to the power source, verify now that all were identified by the collection software. This must be done using the program interface, which displays each element on which port is connected properly.
Now with the equipment identified, make sure the GPS has acquired satellites it needs to determine its position. You must be an open area with sight to the satellites. It is advisable to configure the software to do the collection in Degrees, Minutes and Seconds. Familiarize yourself with the concept.
Another fact that should be taken into account in relation to its GPS antenna. It should generally stay in one place on the vehicle roof, where you can see the sky. If it is not waterproof, it is necessary to protect it with plastic if it rain.
If everything is OK with GPS, start a test collection to verify that all data being written.
In the program main window, make it an indicator that tells if the data are being recorded. Also note that the parameters of the network are visible on the window of each device - mobile, gps, scanner, etc.. Some software also offers the facility to visualize this data without saving. It is very important to make sure everything is OK before you start.
And now, finally, but certainly most important, remember that: first, you're driving!
It is recommended whenever possible to have one vehicle driver and one equipments operator. If this is not possible, always start, stop or make changes to a collectionat a secure point of the road.
And of course: always check the conditions of the vehicle, and always wear your seat belt!
Most software offer the facility to add notes (Marker) during the Drive Test. Whether through it, or using a piece of paper, always make notes.
Information related to the test should be recorded for future aid in the analysis. For example, how is the weather (rain), if there is some very big obstacle in the area, possible sources of noise, etc ...
And what is collected?
Okay, but what is actually collected?
Well, before that, we must ensure that data is able to be recorded. Remember that we are using a notebook, which arguably is subject to freeze the screen lock.
And if so, what to do? Unfortunately, there is much besides restarting the equipment.
But some practices can also minimize these errors.
A typical file size of Drive Test is from 30 minutes to an hour. Of course everything will depend on the size of the file, which in turn depends on information being recorded.
Very large files suffer more risk of being corrupted - especially in case of malfunction of the notebook - and are more difficult to move, load, and even to analyze.
Always leave a few GB free on your HD (Hard Drive) before beginning any data collection. And use the least amount of RAM specified - required - the software collection.
Another important thing: do not open or use other programs when you are collecting data only when strictly necessary.
Drive Test files are always big, and you're always moving them. So keep a daily basis - weekly is appropriate - to perform a defragmentation of hard drive and a scan for errors.
Whenever you finish the collection, stop the ongoing calls, and only then stop collecting. Otherwise, these calls may be interpreted erroneously as falls.
Now, yes. If the data were collected, we can talk about them. And to vary, depending on the equipment used and the purpose of Drive Test.
In the case of mobiles, there are collected all the messages exchanged between the sites and it, with all layers of information - even if you don't know much of it. It's because in most critical cases, such data can be sent to better prepared laboratories for deep analysis.
If using a scanner, we also have information from sites that were not "seen" by the mobiles.
Of course, everything is configurable, but it's always good to use the default setting, and record everything that is possible.
All information is stored with their respective data Date and Time as well as its geographical position.
Typical example of data output is shown below.
Equipment and Collection Software
We have spoken enough of them. And what are the equipment and collection software recommended?
Well, that question is not easy. Let's make an analogy: What is the car that you will buy next year?
Got it? You'll have to check what your need, availability in the market, and the best cost benefit. You may even continue by walking.
And with the equipment and software to collect and post-processing of Drive Test is the same.
You should verify if it is compatible with your network, what are the differential costs and benefits, not least, support!
Remember that new tools and features are constantly emerging. Keep up to date on this subject.
Note: we could have listed here some equipment and software, for example, the one we use. But we prefer not to quote any of them, to avoid the risk of eventually being somewhat unfair.
But anyway, whatever the equipment, software and procedures used, the end result is always the same: reports and output files.
The vast majority of collection (or processing) software have in common some software which also makes analysis. These are called post-processing software. Each post-processing software has its specific analysis, and as data (measures) collected is huge, they can be of great help to solve very specific problems. These tools present the data in tables, maps and comparison charts that help in making decisions.
Regardless of what the post-processing software, all have the functionality to export data in tabular form, in text format or CSV.
This may be an attractive option, especially if you have own tools, developed specifically for your needs.
The following are examples of drive test data processed by Hunter GE Drive Test tool, created entirely in VBA.
One advantage of working with the data this way is that no matter how they were collected, but its content. So for example we can, even if a team has run half the route with a type of software, and another team of drive test shot the rest with another software, we can plot the data from our network on a single desktop. That's where for example the generic geo-referenced analyzing softwares enters, such as Mapinfo and Google Earth.
Another advantage is that the analysis available in Mapinfo and Google Earth has often a better use, since they are more familiar to most professionals, not just those who specific do/analyse Drive Test. This can be understood as not having to purchase multiple software licenses for post-processing: only one for cases of deeper analysis.
Today we had an overview of Drive Test, a common and efficient technique for evaluating the network.
Analyses made through the information of data collected in the field represent a true picture of network conditions, and can be used in decision making in several areas, from planning and design through optimization and maintenance of the system, always with the goal of maximizing Quality, Capacity and Coverage in the Network.