Athanassios V. Adamis

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Spectrum pooling and unlicensed spectrum access by cognitive radios can compensate for spectrum scarcity, caused by static licensing policies, by utilizing spectrum opportunities. In this work we modify CSMA/CA MAC protocol for operation over a spectrum pooling environment and for secondary, overlay, distributed cognitive radio networks. New performance(More)
Cognitive Radios (CR) have recently appeared as a solution to the spectrum scarcity problem, caused by static licensing policies. CRs can utilize spectral opportunities when and where Licensed Systems (LS) remain idle, operating in an overlay mode under the major restriction of not causing harmful interference to them. In this Paper, first, we investigate(More)
Overlay access has recently appeared as a promising solution that improves licensed spectrum utilization, by allowing secondary networks to exploit portions of spectrum when they are not used by licensed networks. Moreover wireless local area networks, with the IEEE 802.11 standard as their major representative, have widely spread as a very successful(More)
Time and frequency offsets can cause severe degradation in the performance of any OFDM-based System. Therefore synchronization procedures are necessary for the proper function of a receiver. In OFDMA, where different users share the available subcarriers, synchronization becomes an arduous task. Synchronization errors as far as the uplink transmission is(More)