Communication Technology Laboratory

Research programme:

The emphasis of the research activities within the Communication Technology Laboratory is given to the areas of: radio propagation, access architectures for heterogeneous wireless networks, management of radio and network resources and cognitive communications. We are also involved in the education of young researchers and in the transfer of knowledge and new technologies in the industrial environment.

In the field of radio transmission, we consider the properties of radio signal propagation, radio interface, adaptive modulation and coding schemes, interference mitigation and interference alignment methods, synchronization and equalization techniques, and procedures to assess the radio channel quality.

The investigation of the radio-signal propagation is currently focused on two main topics. The first topic concerns the research on radio-signal propagation in special environments, such as caves, long road and railway tunnels. The emphasis was on radio-wave propagation characteristics in curved tunnels for designing reliable communications in subway tunnels. The extensive propagation measurements conducted in subway tunnels provide an insight into the large-scale fading characteristics in real curved subway tunnels at various frequencies (920 MHz, 2400 MHz, in 5705 MHz). The qualitative analysis and corresponding findings are useful for realizing the intelligent transportation system in subway and railway systems as well the provision of wireless communications in caves in the case of emergency. We published the research results in the paper “A survey of radio propagation modelling for tunnels”, issued in the journal IEEE Communications Surveys and Tutorials. The second topic concerns the development, implementation and testing of a software tool for radio-wave propagation modelling in mobile communication systems and the optimization of wireless communication systems. The tool is integrated into an open-source geographical information system (GIS) and incorporates statistical models, channel models based on ray tracing and optimization procedures. We studied computationally efficient radio ray-tracing techniques in the context of physical channel models.

FIG: Radio signal reflections and refractions are recursively traversed using graphic primitives. The illustration shows three snapshots of a framebuffer object at increasing tree depth with black-and-white rendering of scene objects and visible reception points superimposed as red dots.

In collaboration with Xlab and Alanta on advanced ray-tracing techniques in radio environment characterization and radio localization, we are working on applied project investigating adapting algorithmic concepts known from ray tracing in computer graphics to radio environment modelling. We have already proposed the efficient use of the massively parallel hardware of graphical processors. Our approach to divergence handling in the single instruction multiple thread (SIMT) architectures is applicable to a wider set of problems that can be solved on graphical processors.

In wireless network optimization research topics we focused on using a multi-objective evolutionary algorithm, which determines for a given set of criteria functions the optimal network parameters. The aim of the proposed solution is to maximize the network efficiency, reduce the needed resources and consequently reduce the operational costs. Based on the terrain profile maps and construction locations, the tool calculates the path loss by applying state-of-the-art statistical models and determines the optimal base-station locations and their parameters by maximizing defined criteria functions. The implemented solution is generic and it could be used for planning any heterogeneous wireless network by appropriately adjusted criteria functions. The optimization algorithms have been included in the GRASS RaPlaT framework and applied for the optimization of frequency channel allocation in the digital wireless system for the Public protection and relief forces of the Republic of Slovenia that is operating in the VHF frequency band.

In cooperation with Telekom Slovenije we developed an open-source radio coverage calculation tool RaPlaT based on models such as Okumura-Hata, Walfish-Ikegami and Okumura-Hata considering terrain profile as well as on ray-tracing algorithms. The tool is suitable for radio network planning in various mobile and wireless networks including GSM, UMTS, WiFi, WiMAX and LTE. The tool is based on a fully modular approach and enables upgrading, it is independent of any particular technology and suitable for parallel, multiprocessor execution. The tool is integrated as a separate module in the software package for monitoring radio networks and in daily use by the largest mobile operator in Slovenia. We developed also a module for calculating signal coverage for broadcasting services and speed up the calculation of ray tracing method by parallel implementation on graphics processing unit. We have also prepared a user-friendly version of GRASS-RaPlaT tool, which is openly accessible from the JSI website.

FIG. Radio signal coverage calculation using in-house developed radio coverage tool GRASS RaPlaT

In collaboration with European partners within the H2020 project eWine “elastic WIreless Networking Experimentation” we investigate the wireless elastic networks that can scale to the needs of users and services through the use of intelligent software and flexible hardware. Within the project, we are focusing on problems related to retrieving and processing the location of a user as a context of communications applicable for the optimization of wireless communication systems. In an outdoor environment we succeeded to bring the location error close to 1 metre by using radio environment properties and measured received signal level. In the indoor environment we increased the localization precision by using an ultra-wide band (UWB) radio signal by not considering non-line-of-sight connections in triangulation of the user.

In the area of wireless networks we investigated optimal network topologies and procedures to ensure the mobility management. We studied new procedures for the effective integration of ad-hoc wireless networks in the backbone network and explored advanced concepts and technologies to increase the capacity of wireless mesh networks using network coding techniques, focusing on the development of advanced adaptive network coding algorithms and their adapted routing procedures. In addition, the design aspects for network-coding-enabled wireless mesh networks and applications were investigated and analysed. We showed that opportunistic network coding can improve the performance of different networks and supported applications in terms of throughput, delay and jitter; however, these benefits are more prominent if the usage of opportunistic network coding is considered upfront in the wireless-network design phase.

We successfully concluded the SatProSi-Alpha project, carried out for the European Space Agency (ESA). The purpose of the project was to investigate the atmosphere impacts on radio-wave propagation. Up to now, these effects were rather unexplored, especially at Q-band (39.4 GHz). The experience and measurement results obtained in the project with a newly developed 4-channel Alphasat beacon receiver on the rooftop of JSI will enable engineers to develop an efficient communication technology at high-frequency bands and hence enable high satellite communication throughputs of the order of terabits/s. The measurement results were analysed in collaboration with and contributed to the international European group ASAPE (Group of the AlphaSat Aldo Paraboni propagation Experimenters).

FIG: Alphasat receiving station with tracking mechanism for measuring high-frequency satellite signals.

We are also active in COST actions, and have already participated to more than 10 COST actions. In 2016 we started with active participation in the COST Action 15104 IRACON “Inclusive radio communication networks for 5G and beyond”, where we are contributing to several disciplinary working groups, manly DWG-1 radio channel, DWG-2 physical layer and DWG-3 network layer, as well in some experimental working groups: EWG-LT localization and tracking and EWG-IoT Internet of things.

In the scope of the FP7 SUNSEED project “Sustainable and robust networking for smart electricity distribution”, which aims at the efficient use of the communications infrastructure in smart grids, we applied our research expertise in the field of optimization and management of communication networks also to the field of smart grids. In the last period we were focused on the development of software modules and algorithms for a three-phase estimator in the distribution network. We investigated the optimal placement of synchronized phasor measurement units in the distribution network for the most efficient state estimation and developed software modules for the analysis and visualisation of the state of the distribution network. We also implemented an algorithm for the synchronized phasor measurement unit and optimised it for running in a low-cost device with restricted capabilities.

FIG: Distribution network state (Kromberk).

In the ABSOLUTE project we considered innovative robust architectures of telecommunication networks, suitable for the provision of secure broadband services over larger geographical areas. We performed optimization of the geographical layout and the number of ad-hoc ground and air base stations. We participated in the design and validation of an innovative rapidly deployable future network architecture. The network architecture should be resilient and capable of providing broadband multi-service, secure and dependable connectivity for large coverage areas affected by large-scale unexpected events or disasters leading to the partial or complete unavailability of the terrestrial communication infrastructure, or for temporary events requiring very high throughput and augmented network capacity. We focused on the development of new advanced techniques for radio spectrum management, on the development of new network solutions and on the integration of wireless sensor networks into the emergency architecture.