Browsing by Subject "Radio transmission"

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    Error rate analysis of cognitive radio transmissions with imperfect channel sensing
    (Institute of Electrical and Electronics Engineers Inc., 2014) Ozcan, G.; Gursoy, M. C.; Gezici, Sinan
    This paper studies the symbol error rate performance of cognitive radio transmissions in the presence of imperfect sensing decisions. Two different transmission schemes, namely sensing-based spectrum sharing (SSS) and opportunistic spectrum access (OSA), are considered. In both schemes, secondary users first perform channel sensing, albeit with possible errors. In SSS, depending on the sensing decisions, they adapt the transmission power level and coexist with primary users in the channel. On the other hand, in OSA, secondary users are allowed to transmit only when the primary user activity is not detected. Initially, for both transmission schemes, general formulations for the optimal decision rule and error probabilities are provided for arbitrary modulation schemes under the assumptions that the receiver is equipped with the sensing decision and perfect knowledge of the channel fading, and the primary user's received faded signals at the secondary receiver has a Gaussian mixture distribution. Subsequently, the general approach is specialized to rectangular quadrature amplitude modulation (QAM). More specifically, the optimal decision rule is characterized for rectangular QAM, and closed-form expressions for the average symbol error probability attained with the optimal detector are derived under both transmit power and interference constraints. The effects of imperfect channel sensing decisions, interference from the primary user and its Gaussian mixture model, and the transmit power and interference constraints on the error rate performance of cognitive transmissions are analyzed.
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    Error rate analysis of cognitive radio transmissions with imperfect channel sensing
    (IEEE, 2013) Ozcan G.; Gursoy, M. C.; Gezici, Sinan
    In this paper, error rate performance of cognitive radio transmissions is studied in the presence of imperfect channel sensing decisions. It is assumed that cognitive users first perform channel sensing, albeit with possible errors. Then, depending on the sensing decisions, they select the transmission energy level and employ MI × MQ rectangular quadrature amplitude modulation (QAM) for data transmission over a fading channel. In this setting, the optimal decision rule is formulated under the assumptions that the receiver is equipped with the sensing decision and perfect knowledge of the channel fading. It is shown that the thresholds for optimal detection at the receiver are the midpoints between the signals under any sensing decision. Subsequently, minimum average error probability expressions for M-ary pulse amplitude modulation (M-PAM) and MI×MQ rectangular QAM transmissions attained with the optimal detector are derived. The effects of imperfect channel sensing decisions on the average symbol error probability are analyzed. Copyright © 2013 by the Institute of Electrical and Electronic Engineers, Inc.
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    Metamaterial-based wireless strain sensors
    (American Institute of Physics, 2009-07-07) Melik, R.; Unal, E.; Perkgoz, N. K.; Puttlitz, C.; Demir, Hilmi Volkan
    We proposed and demonstrated metamaterial-based strain sensors that are highly sensitive to mechanical deformation. Their resonance frequency shift is correlated with the surface strain of our test material and the strain data are reported telemetrically. These metamaterial sensors are better than traditional radio-frequency (rf) structures in sensing for providing resonances with high quality factors and large transmission dips. Using split ring resonators (SRRs), we achieve lower resonance frequencies per unit area compared to other rf structures, allowing for bioimplant sensing in soft tissue (e.g., fracture healing). In 5×5 SRR architecture, our wireless sensors yield high sensitivity (109 kHz/kgf, or 5.148 kHz/microstrain) with low nonlinearity error (<200 microstrain).
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    On the interplay between channel sensing and estimation in cognitive radio systems
    (IEEE, 2011) Gursoy, M.C.; Gezici, Sinan
    Cognitive radio transmissions in the presence of channel uncertainty are considered. In practical scenarios, cognitive secondary users need to perform both channel sensing in order to identify whether the channel is being occupied by the primary users or not, and also channel estimation in order to learn the channel fading coefficients. Generally, errors occur in both channel sensing and estimation, and this leads to a coupling between the two. More specifically, imperfect sensing affects both the structure and the performance of channel estimation schemes. With this motivation, the interactions between channel sensing and estimation are studied in this paper. In particular, different channel estimation schemes including minimum mean-square error (MMSE), linear MMSE, and mismatched MMSE estimations are analyzed, and their dependence on sensing decisions and their performances are investigated. © 2011 IEEE.
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    Sabit karasal mikrodalga LOS/NLOS radyo linklerin enterferans analizi
    (IEEE, 2015-05) Göktaş, Polat; Topcu, Satılmış; Karaşan, Ezhan; Altıntaş, Ayhan
    Bu çalışmada, NATO Band 3+ (1350-2690 MHz) ve NATO Band 4 (4400-5000 MHz) frekans bantlarında çalışan sabit karasal mikrodalga LOS (karasal görüş çizgisi)/ NLOS (ufuk ötesi) radyo linkleri için enterferans modellenmesi ele alınmıştır. Sabit karasal noktadan-noktaya haberleşme sistemlerinde enterferansa maruz kalan istasyonlardaki hem açık havadaki hem de yağmurdaki saçılmadan kaynaklanan enterferansın hesaplanması yapılmıştır. Ayrıca, ITU-R P.452 Tavsiyesinde bahsedilen açık havadaki enterferans kaybının hesabındaki enterferans yayılım mekanizmaları incelenmiştir. Enterferansa neden olan verici ve enterferansa maruz kalan alıcı istasyonların koordinat bilgileri, enterferansa neden olan verici ve enterferansa maruz kalan alıcı istasyonların antenlerinin yerden yükseklikleri, anten ayrımcılıgı, ˘ polarizasyon tipi, radyo kırılma indeksi, deniz seviyesinden ortalama kırıcılık, zaman yüzdesi, yığın kategorisi, sayısal arazi yükseklik haritası ve iklimsel veriler gibi enterferans yayılım parametreleri kullanılarak çeşitli mikrodalga radyo linkler için enterferans analizleri yapılmıştır.