Archives June 2014

Signal strength and more: Virtual drive testing


The ICE high speed line Cologne – Frankfurt was one of the first tracks completely equipped with GSM-R technology

The Westerwald low mountain range on right banks of the river Rhine is not the obvious place to build a high-speed railway line. However, over steep climbs, through long tunnels, cutting through hills, and over viaducts arching across small valleys run the trains of the Cologne-Frankfurt high-speed railway with speeds up to 300 km/h. What is a master-piece of civil engineering is a nightmare for network operators. Signal strength is impeded by all sorts of disturbances and sufficient coverage hard to achieve, but still vital for some.

GSM-R is a very special wireless technology to control high speed trains and ensure communication between railway staff. The operator has to ensure that there is no communication loss along the entire line, because the communication is security relevant and a disconnected call may have fatal consequences.

Still, it was on the above described line through the Westerwald mountains where the operator of the German GSM-R network noted that the connection of a Voice Group Call was always interrupted in a certain area.  To detect what caused the interruption proved to be difficult. Test drives were nearly impossible, as test trains are only allowed to drive with very low speed and the whole track has to be closed for them. The solution to this problem was Qosmotec’s virtual drive test concept.

“Signal strength emulation is more than ramping attenuators up and down”

Qosmotec was in 2004 the first company to offer network operators a solution that enabled them to emulate drive tests in their test lab and achieve complete reproducibility of radio conditions. For this, we have helped ourselves with a technique that was anything else but new: The use of digital step attenuators to control the signal strengths received from several base stations. We enhanced it with a control software that is able to model real life like conditions and to calculate the correct settings, so that tests in the lab really reflect what subscribers experience in the field.

“Signal strength emulation is a very powerful method for reproducing radio conditions. The typical misconception is that it is only about ramping up one attenuator while ramping down another. It is much more than that”, explains Qosmotec’s managing director Mark Hakim. By means of controlling attenuators based on physical models, it is possible to simulate the most impacting radio conditions like signal degradation, shadowing, and even fast fading. Also 3D antenna pattern can be perfectly modeled in the lab – without making any change in the radio part. German news channel N24 took note of Qosmotec’s virtual drive test approach in September 2013.

This virtual drive test concept helped to reconstruct the GSM-R network operator’s problem. It was possible to extract the conditions, under which the call disruption occurred, from radio measurements taken in the problem area, and to replay the whole scenario on the attenuator hardware at the DB test center. With this reconstruction the reason could be found. A cell change after a hill, where a frequency had been reused, was not successful – a result that became only obvious in execution, not in network planning.

Funkschau_1Field studies with customers

Another example was a tunnel scenario that was re-created with a large European network operator in their test lab. In this case, all standardized channel emulation scenarios failed to reproduce a situation where data connections got lost in high speed trains, while they were stable in normal trains. But the situation described by the customer was almost trivial to re-create with the virtual drive test approach. We detected exactly under which radio conditions the problem occurred and how it could be solved. A detailed description of this use case has been published in the magazine “Funkschau” in 2010.

Prediction of signal propagation in cities

The real drive test through the city of Munich (red) brings almost identical result than the prediction for the route (green)

The real drive test through the city of Munich (red) brings almost identical result than the prediction for the route (green)

Together with the institute of theoretical information technology at Aachen University, Qosmotec also developed a mechanism to emulate drive tests through real cities. “Our propagation algorithms take into account radio wave reflections, deflection and diffractions on cities and can calculate signal strength and multipath effects in any location in a city”, explains Dr. Michael Reyer the research activities that contribute to our QPER feature for predicted drive tests. With these calculations, emulations can be done, based on building data of any city. Comparisons between a real drive test executed in the city of Munich and a virtual drive test show an impressive compliance of the completely theoretical approach with reality. Currently, Qosmotec runs a new project to adapt those algorithms for Car-to-Car and Car-to-Infrastructure communication. This joint research activity is funded by the German ministry for economics BMWi.

Versatility that goes beyond signal strength simulation

Over the years, the Qosmotec virtual drive test approach has become popular with mobile network operators – but infrastructure vendors have adopted the idea as well. Mark Hakim explains the success of Qosmotec’s methodology: “It is so simple to use and goes far beyond standard conformance test methodologies. With a few mouse clicks, it offers a high versatility in creating test scenarios that have already revealed a lot of problems which would have remained undetected otherwise”. Signal strength simulation is still the most important simulated propagation effect, but it is not restricted to that. With LTE and the MIMO technology coming up, Qosmotec has extended the approach to simulate phase differences of multiple antennas on sender and receiver side. Currently, we are developing a solution to emulate even multipath fading. “This will be an interesting solution, especially for wireless technologies restricted to short-distance communication like WiFi or Car-to-X communication technology”, says Mark Hakim. First results on this are expected for the first quarter of 2015. “We plan to introduce our solution at the Mobile World Congress in March 2015 in Barcelona”.


Dealing with data rates from UMTS to LTE

While automatic network testing today is focused on LTE, ten years ago Qosmotec had to deal with the introduction of the UMTS networks in Europe. The newly founded company had just received the order to supply a test system for Europe’s first UMTS network and had to integrate a new technology into its test systems, which was nowhere available in the field. One of the main challenges at this time was a very simple, but severe problem: “There were no UMTS phones available in Germany in 2004. Luckily, Aachen is just on the border to Belgium, where we got hold of a Nokia 6650, one of the first available UMTS mobiles, to develop our first UMTS test system with”, says Mark Hakim.

The Nokia 6650 from Belgium which was used by Qosmotec for the company’s first UMTS test system

The Nokia 6650 was used by Qosmotec for the development of the first UMTS test system

Working with handsets and mobile phones

Integrating new technologies into its test system is an issue Qosmotec has come to deal with almost on a daily basis. “Network operators use our test systems to run laboratory tests with bleeding edge technologies that have yet to be rolled out. We have to see, how we get access to the latest phone models – sometimes even in pre-commerical state – or to industrial modems with latest chipset to integrate them in our test system,” explains Mark Hakim. When Qosmotec supplied H3G with a test system to prepare the roll out of Europe’s first UMTS network in Italy, they were asked to test video calls. “That was the feature which was used to advertise 3G technology at the time. We solved this by using a Motorola A835 phone – a mobile with a really large display and an even bigger body. We integrated 16 of these phones in a rack and used them for integrated testing,” remembers Mark Hakim.

Testing high data rates and QoS

Qosmotec's LTS test automation system as a rack setup to control large numbers of UEs in parallel

Qosmotec’s LTS test automation system as a rack setup to control large numbers of UEs in parallel

Even though videos calls have yet to make their breakthrough, data rates became a huge challenge for Qosmotec, when High Speed Packet Access (HSPA) or 3.5G succeeded UMTS. It was the time, when data rates really mattered for the first time. HSPA provided higher data rates up to 21Mbit/s on the downlink, which brought laptop users into play: “The idea was to make laptop users more mobile, allowing them mobile access to the internet. The higher data rates were realized with data cards,” says Hakim. While a laptop used only one of these cards, Qosmotec had to find a solution to test with several of these cards simultaneously. “We developed a data card control server with 16 PCMCIA slots, so we could control 16 data cards at the same time to emulate laptop users within the network.”

Dealing with smartphones and LTE

Another important aspect of HSPA was quality of service. Network operators had started to promise certain data rates to their subscribers, meaning they had to ensure that these rates were constantly available. “We tackled this issue by developing a feature that made it possible to request a certain data rate from the network and the test system could verify whether this specific data rate was actually provided to a specific subscriber,” says Hakim. Since then, the issue of constantly available data rates has been intensified by LTE and LTE Advanced. The latter being promoted with 150 Mbit/s, and specified with a peak rate of 3 Gbit/s.

“First of all, a test system has to verify that the promised data rates can be constantly provided by the network. Therefore, a test system for these technologies has to measure how often this peak is actually achieved and for what time slot it is kept. This is what we are working on, analysis methods that show the use of the data rate,” explains Hakim, before he draws attention to  another topic: The changes in subscriber behaviour, caused by the introduction of smartphones. “The introduction of smartphones and the apps running on smartphones had massive impact on subscriber behaviour. Therefore, it became import to test the various protocols that are used by apps as well.” However, this challenge offered Qosmotec an opportunity to gain independence from the availability of mobile phones: “We addressed this by developing our own app, Qosdroid, that runs on the smartphone itself. This allows us to use smartphones to test networks. The app can be installed on any kind of Android phone. This means we no longer have to chase the latest available phones, as we can now use any phone running an Android OS.”

Voice tests come back

Looking ahead, Hakim believes the next challenge will be the combination of data rates with voice testing: “Voice testing is coming back. Not as we have known it in the past, which was relevant for GSM testing, but testing various facilities of voice, for example, high definition voice or voice over LTE, which is going to come soon. Our task is to provide easy and effective mechanisms to test these technologies. Regarding voice quality testing, we have to work with other mechanisms, like POLQA which is more suitable for VoIP transmissions than the PESQ standard. This is what we are working on at the moment.”

Qosmotec – Test Automation since 2004

Mark Hakim, Dr Dieter Kreuer and Axel C. Voigt (lefto right) present the first AIS handover test system in 2004

Mark Hakim, Axel C. Voigt, and Dr Dieter Kreuer present the first AIS handover test system in 2004

10 years Qosmotec – over the course of the next 10 weeks, we want to tell ten interesting stories about our company, our different fields of activity and our technological achievements.

How it all started

In January 2004 Dr. Dieter Kreuer, Mark Hakim and Axel Voigt founded Qosmotec. “We knew each other a while before Qosmotec: Dieter supervised my diploma thesis in 1998 and I did the same three years later for Axel, when he finished his studies”, remembers Mark Hakim. “All the three of us were convinced that it is possible to make end-to-end test automation equipment for wireless networks a commercial success. Up to that time, this kind of activity was – if enforced at all – still stuck in some self-made and prototype developments by the network operators.”

Aachen's local newspapers quickly took note of Qosmotec's business scheme

Aachen’s local newspapers quickly took note of Qosmotec’s business scheme

To be prepared as good as possible, the three founders participated in a business plan contest in Aachen, which was carried out for the first time that year. “Our ideas gained approval, and we ended up as one of three winners. By the way: Qosmotec was the only company of the rewarded ones that was actually founded,” lets Hakim know smiling.

Over the years, Qosmotec has established substantial reputation: Dr. Dieter Kreuer in his position as Qosmotec director was listed as one of the 500 most important people in the Rhineland region in 2012.

Successful co-operations

Dr Dieter Kreuer was recognised as one of the 500 most important people in the Rhineland region

Dr Dieter Kreuer was recognised as one of the 500 most important people in the Rhineland region

But even the best business concept would be worthless without engaged and convinced co-operation partners. Right after founding the company, we established sales partnerships with Delo Instruments in Italy, Artiza Networks in Japan and Teraquant Corporation in the US which all generated first business within a few months. Based on these experiences, Qosmotec maintains a network of local sales agents, who know and understand the customer needs, and who can help them in any kind of questions and problems. “It is very important for us to have these front-ends to most of our customers. The feedback of our sales partners has helped us a lot to improve our products over the time”, honors Mark Hakim the work of Qosmotec’s sales partners. Today, our most successful co-operation is with FSTC consulting from Vienna, who have taken over the responsibility for Austria, Germany, and several other European countries.

On the technological side, Qosmotec is not on its own. The most outstanding and closest co-operation with the electronic designer Manfred Kopp from Aachen persists already since 2004. “Manfred and his team have often helped us out with tiny and intelligent designed circuits that are custom made for our products”, says Mark Hakim.

Access to internationally renown research facilities

The big locational advantage of Aachen is the proximity to RWTH Aachen University that is known world-wide for its excellent research capabilities. The faculties of electronical engineering and computer sciences contain various institutes and chairs that deal with mobile communication. The institute for theoretical information technology under the direction of Prof. Rudolf Mathar has been working together with Qosmotec in various research projects. One of their biggest contributions to Qosmotec products was their development on ray tracing algorithms that enables to predict signal propagation in urban areas and enable us to emulate radio conditions in the test lab taking into account building environments of real cities. Mark Hakim speaks about the newest joint activities: “We have just set up a new project about radio signal propagation in Car to Car communication with our research partner. This is a very challenging area with very different requirements compared to public mobile networks. We expect a high demand on test systems there in the near future. ”

Qosmotec’s data card control server for PCMCIA cards

Qosmotec’s data card control server for PCMCIA cards

Broad customer basis

Qosmotec has a huge variety of customers with a broad range of application areas, and was involved in very interesting activities in the telecom world. In 2004, Qosmotec participated in testing the world wide first UMTS network that was established in Italy. One year later, we oversaw the roll-out of the first GSM-R network in Germany with our test systems. Whether it has been Toll Collection or Self-Organizing Networks – Qosmotec has dealt with all issues concerning wireless networks. Currently, we are working on supporting Car-to-Car and Car-to-Infrastructure communication with our test systems – quite a challenge, because it changes Qosmotec target market: “With this, we are more addressing the automotive industry than suppliers and operators of public networks.”

Some of our developments have meanwhile become out-of date again. Mark Hakim remembers: “We have been involved also in test systems for GSM-BOS, a special security standard that was never introduced. Instead, TETRA prevailed”. Other things were only of interest for a limited lifetime. For example our datacard control server – a system that was able to control up to 16 PCMCIA datacards in parallel which were soon replaced by USB sticks. Mark Hakim concludes: “These examples show how fast the telecom business moves. We have always been flexible enough to react on these quick changes. After ten years we are experienced enough to expect the unexpected and react adequately to challenges in front of us.”