Conference papers

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Browsing Conference papers by Author "Alexandropoulos, George C."

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    Energy Efficient Switching between Data Transmission and Energy Harvesting for Cooperative Cognitive Relaying Systems
    (2016) Miridakis, Nikolaos I.; Tsiftsis, Theodoros A.; Alexandropoulos, George C.; Debbah, M´erouane
    A dual-hop cognitive (secondary) relaying system incorporating collaborative spectrum sensing to opportunistically switch between data transmission and energy harvesting is introduced. The secondary relays, first scan the wireless channel for a primary network activity, and then convey their reports to a secondary base station (SBS). Afterwards, the SBS, based on these reports and its own estimation, decides cooperatively the presence of primary transmission or not. In the former scenario, all secondary relays start to harvest energy from the transmission of one or more primary nodes. In the latter scenario, the system initiates secondary communication via a best relay selection policy. The performance of the proposed scheme is thoroughly investigated by assuming realistic channel conditions, i.e., non-identical link-distances and outdated channel estimation, while its overall energy consumption is evaluated, indicating the efficiency of the switching approach.
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    Simultaneous Spectrum Sensing and Data Transmission for Multi-User MIMO Cognitive Radio Systems
    (2016) Miridakis, Nikolaos I.; Tsiftsis, Theodoros A.; Alexandropoulos, George C.; Debbah, M´erouane
    We present a multi-user multiple-input multipleoutput (MIMO) cognitive radio system consisting of a secondary receiver that deploys spatial multiplexing to decode signals from multiple secondary transmitters, under the presence of primary transmissions. The secondary receiver carries out minimum mean-squared error detection to decode the secondary data streams, while it performs spectrum sensing at the remaining signal to capture the potential presence of primary activity. Assuming Rayleigh fading as well as the realistic cases of channel fading time variation and channel estimation errors, we present novel closed-form expressions for important system measures, namely, the detection and false-alarm probabilities as well as the transmission power of the secondary nodes. The enclosed numerical results verify the accuracy of the presented analysis.