Browsing by Author "Koufos, Konstantinos"

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    An algorithm for dynamic spectrum allocation in shadowing environment and with communication constraints
    (2007) Koufos, Konstantinos; Ruttik, Kalle; Sähkö- ja tietoliikennetekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Jäntti, Riku
    The increasing demands in spectrum are not questionable. Instead of opening new spectrum bands we could utilize the spectrum that is currently in use more efficiently. Dynamic spectrum allocation access is a potential way to increase the spectrum utilization. According to the new access scheme, users that do not possess any dedicated frequency band could reuse some of the spectrum that belongs to licensed users. The main requirement for dynamic spectrum allocation is interference control. In the Thesis an algorithm for dynamic spectrum allocation is proposed. The algorithm is based on power detection, interference estimation and uses the principles of distributed decision with data fusion. The effects of shadow fading are considered to make the system model realistic. The algorithm performance is tested with and without capacity constraints for the communicated decisions and useful performance bounds are provided.
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    Performance Evaluation of H.264/AVC encoded Video over TETRA Enhanced Data Service (TEDS)
    (Helsinki University of Technology, 2009) Hussain, Sunbul Zahid; Koufos, Konstantinos; Mutafungwa, Edward; Elektroniikan, tietoliikenteen ja automaation tiedekunta; Jäntti, Riku
    Public Safety Systems (PSS) are communication networks oriented towards supporting activities of public safety actors (police, medical, fire-fighters, etc.). TErrestrial Trunked RAdio (TETRA) is a Professional Mobile Radio (PMR) standard designed to meet PSS requirements with specialized voice communication features and reliable, secure communication links. TETRA Release 2 introduces TETRA Enhanced Data Service (TEDS), to support emerging data-intensive applications such as online navigation and tele-medicine by providing higher, scalable data rates. This thesis studies the feasibility of streaming video over a wideband TEDS link using the H.264/AVC codec, a video compression standard that manages to retain high decoded video quality while dramatically reducing streaming bit rate. A bandwidth limiter is used to emulate a link that supports data rates equivalent to those specified in the TEDS standard. Effects of video streaming parameters such as codec rate and play-out buffer size coupled with link-induced delay variation on decoded video quality are investigated. Visual quality is rated using objective quality metrics to quantify results with some measure of reliability. The overall aim is to identify the technical requirements needed to support an acceptable quality of video transmission over TEDS. To this end, we measure decoded video quality in different channel loss conditions, varying video streaming parameters and at different channel bandwidths, plus enhancements such as data traffic prioritisation as defined in the TEDS specification.
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    Repeated Games For Inter-operator Spectrum Sharing
    (2014-08-25) Singh, Bikramjit; Koufos, Konstantinos; Sähkötekniikan korkeakoulu; Tirkkonen, Olav
    As wireless communication becomes an ever-more evolving and pervasive part of the existing world, system capacity and Quality of Service (QoS) provisioning are becoming more critically evident. In order to improve system capacity and QoS, it is mandatory that we pay closer attention to operational bandwidth efficiency issues. We address this issue for two operators' spectrum sharing in the same geographical area. We model and analyze interactions between the competitive operators coexisting in the same frequency band as a strategic noncooperative game, where the operators simultaneously share the spectrum dynamically as per their relative requirement. If resources are allocated in a conventional way (static orthogonal allocation), spectrum utilization becomes inefficient when there is load asymmetry between the operators and low inter-operator interference. Theoretically, operators can share resources in a cooperative manner, but pragmatically they are reluctant to reveal their network information to competitors. By using game theory, we design a distributed implementation, in which self-interested operators play strategies and contend for the spectrum resources in a noncooperative manner. We have proposed two game theoretic approaches in the thesis, one using a virtual carrier price; and the other based on a mutual history of favors. The former approach takes into account a penalty proportional to spectrum usage in its utility function, whereas in the latter, operators play strategies based on their history of interactions, i.e., how well the other behaved in the past. Finally, based on the simulations, we assess the performance of the proposed game theoretic approaches in comparison to existing conventional allocations.
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    Spectrum access in white spaces using spectrum sensing and geolocation databases
    (Aalto University, 2013) Koufos, Konstantinos; Ruttik, Kalle, Dr., Aalto University, Department of Communications and Networking, Finland; Tietoliikenne- ja tietoverkkotekniikan laitos; Department of Communications and Networking; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Jäntti, Riku, Prof., Aalto University, Department of Communications and Networking, Finland
    A spectrum license grants users the right to transmit on a particular piece of spectrum. Historically, a spectrum license has been allocated for a particular technology. While this strategy facilitates interference control, it also results in spectrum scarcity as more spectrum-efficient technologies are invented. In order to meet the increasing data traffic demands in a timely manner, a shared use of the spectrum seems to be the only viable solution. According to this line of thinking, different technologies with possibly different deployment densities can share the same spectrum under certain conditions. While shared spectrum access improves spectral efficiency, it also increases the risk for harmful interference among the different systems. This calls for a change in the traditional way of issuing spectrum licenses: instead of specifying transmit power levels, the spectrum usage rights specify the generated interference that is permitted. Spectrum access to white spaces would enhance spectrum utilisation, while also testing the approach of controlling the interference between different systems directly rather than through the transmission power. The amount of interference generated to the license holder can be controlled by spectrum sensing and/or geolocation database access. Interference control using spectrum sensing usually boils down to a signal detection problem. In this thesis, we show that the traditional signal detection framework is not appropriate for recovering transmission opportunities in the spatial domain and propose an alternative model. Also, sensing strategies for energy efficient wideband spectrum sensing and trade-off analysis between the service requirement and the demand in the measured spectrum are demonstrated. At this moment, spectrum access to white spaces is mostly possible via geolocation databases. The database is responsible for handling spectrum access requests while complying with certain regulatory conditions. In this thesis, we suggest some interference control and power allocation algorithms that may govern the operation of the database. The algorithms have a low complexity to enable a real-time operation in the database. They involve simple models to capture the impact of the non-uniform demand density, terrain-based propagation and fading correlations on the generated interference. Also, we propose a joint rate and power allocation algorithm that protects the license holder in all cases.
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    Spectrum avaílability assessment tool for TV white space
    (2012) Alemu, Tizazu Bayileyegn; Kerttula, Jussi; Koufos, Konstantinos; Tietoliikenne- ja tietoverkkotekniikan laitos; Sähkötekniikan korkeakoulu; Jäntti, Riku
    The growth of wireless communication relies on the availability of radio frequency for new services. More efficient spectrum allocations are required to serve the increasing data per user. The major regulatory bodies are formulating new spectrum management techniques to forge the growing spectrum scarcity. Exclusive use of spectrum is proved to be inefficient in many spectrum occupancy measurement campaigns. As a result, spectrum sharing methods are being considered. TV broadcasting is not using the allocated frequency in some geographic areas, creating coverage holes known as TV white spaces. Both the industry and the regulators are investigating the capability of TVWS, as a potential source of spectrum for emerging wireless services. The FCC, in the US, has already released the requirements for opportunistic access to the TV whites paces. In a similar fashion, ECC, the pan-European regulator is finalizing the work on the technical and operational requirements for the possible use of cognitive radio in this spectrum. In this thesis work, an integrated web-based spectrum availability assessment tool is developed for Finland. The tool is a front-end visualization of a time intensive computational process to answer key technical questions related to TVWS - what secondary data rate can be supported in the available white space spectrum? The assessment involves estimation of the available TVWS and its capacity for cellular-type secondary systems. The relative effects of the secondary system parameters on the TV system are compared using appropriate signal to noise and interference ratio plots. The tool uses dynamic web technologies for a seamless and user-friendly visualization of the assessment.