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.

We examined the complexity and power efficiency of wireless systems and the capacity of the radio channel. We were focused on finding adaptive processes for space-time coding in MIMO systems. We dealt with the prediction of the radio channel state and the procedures for adjusting the receiver to the predicted changes of the channel. We studied the models of the radio signal propagation in challenging environments such as road and rail tunnels and underground garages in typical frequency bands for voice communication systems (400 MHz), high-speed data communication systems (2.4 GHz and 3.5 GHz) and low-data-rate wireless sensor networks (868 MHz and 2.4 GHz). 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.

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. We built a simulation model for evaluation of arbitrary network coding algorithms and routing procedures in randomly generated wireless mesh network topologies.

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.

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

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

A significant part of our research was conducted within EU Framework Programme. At present we are involved in 3 FP7 projects.

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.

Aerial Base Stations with Opportunistic Links for Unexpected &Temporary Events

Aerial Base Stations with Opportunistic Links for Unexpected &Temporary Events

In the CREW project we contributed to the integration of LOG-a-TEC heterogeneous outdoor testbed for spectrum sensing in the ISM and TV frequency bands into existing CREW testbed. The aim of the project is to facilitate experimentally driven research on spectrum sensing, cognitive radio and cognitive networking strategies. Our research work in this area is focused on stand-alone and collaborative spectrum sensing in licensed and unlicensed frequency bands. We used our GRASS-RaPlaT simulation and development tool as a standalone GRASS mapset to enhance the testbed with additional GIS functionalities and with transmitter radio coverage calculation to support radio environment map estimation. We added to the GRASS-RaPlaT tool all the necessary layers for pathloss calculation including the digital elevation model (DEM) and clutter file containing the terrain usage.

In the SUNSEED project we proposed an evolutionary approach to exploitation of common, converged communication infrastructures for future smart energy grid services with the analysis of regional overlap of DSO and telecommunications operator infrastructures. We are developing an advanced platform for real-time management, analytics and forecasting services for energy distribution networks for small DSOs. We are considering information about network topology and devices, energy demand and consumption, and environmental data. Our research work is focused on the development of a platform for “Load balancing” and “Demand-response” scenarios, including the development of detailed DSO grid model and development of load management module.

In the ESA project SatProSi we developed a low cost ground station based on software-defined radio for receiving and processing satellite signals in the Ka band. We have also developed a software tool for statistical processing and evaluation of the received satellite signals.

Comparison of Hotbird 6 satellite signal attenuation with rainfall measurements

Comparison of Hotbird 6 satellite signal attenuation with rainfall measurements

We participate in the ESA PECS project SatProSi “Ka/Q-band Propagation Measurements and Modelling for the Design of Prediction and Impairment Mitigation Techniques” The main goal of the project is to establish a Ka-band band satellite-beacon measuring site in Ljubljana and to statistically analyse the received signals. We developed a low cost SDR based ground station for reception of the Ka-band satellite signals from EUTELSAT HotBird 6, SES ASTRA 3B and joint ESA and Inmarsat Alphasat satellite. We established one Ka-band receiver in collaboration with Joanneum Research at Hilmwarte in Graz. A network of three low-cost SDR-based Ka-band beacon receivers has been established for the purpose of site diversity experiment, one in Ljubljana and other two at the distance of 26 and 40 km from Ljubljana (Lisec, Krvavec). More than one year of measurements, collected in Ljubljana, has already been processed and statistics of in-excess attenuation and rainfall rate have been calculated.

Alphasat satellite receiver, developed at IJS and installed in collaboration with Joanneum Research institute on Hilmwarte tower in Graz, Austria.

Alphasat satellite receiver, developed at IJS and installed in collaboration with Joanneum Research institute on Hilmwarte tower in Graz, Austria.

We are actively participating in several COST actions. In the COST Action IC1101 “Optical Wireless Communications − An Emerging Technology” we investigated in cooperation with TU Graz the influence of weather conditions on the performance of wireless optical communication systems. In the COST Action IC1104 “Random Network Coding and Designs over GF(q)”, we are developing practical network coding procedures and evaluating them in a purpose-built simulation model. In COST action IC1004 “Cooperative Radio Communications for Green Smart Environments” we mainly participate in topics related to radio propagation aspects and problems of physical layer.

An important research achievement of the reporting period are two granted US patents at the USPTO. The first patent relates to a new iterative method which allows efficient determination of the position of the mobile station. The method is based on measuring the power of the received signal from at least two base stations. The second patent was granted for a method that supports automatic setup and optimization of the operating parameters of a new base station in a wireless telecommunication network. Both patents were originally developed in cooperation with the Slovenian company 4G Neuron and later taken over by the US company Accelera Mobile Broadband, Inc.