7,980 research outputs found
Spectrum sensing by cognitive radios at very low SNR
Spectrum sensing is one of the enabling functionalities for cognitive radio
(CR) systems to operate in the spectrum white space. To protect the primary
incumbent users from interference, the CR is required to detect incumbent
signals at very low signal-to-noise ratio (SNR). In this paper, we present a
spectrum sensing technique based on correlating spectra for detection of
television (TV) broadcasting signals. The basic strategy is to correlate the
periodogram of the received signal with the a priori known spectral features of
the primary signal. We show that according to the Neyman-Pearson criterion,
this spectral correlation-based sensing technique is asymptotically optimal at
very low SNR and with a large sensing time. From the system design perspective,
we analyze the effect of the spectral features on the spectrum sensing
performance. Through the optimization analysis, we obtain useful insights on
how to choose effective spectral features to achieve reliable sensing.
Simulation results show that the proposed sensing technique can reliably detect
analog and digital TV signals at SNR as low as -20 dB.Comment: IEEE Global Communications Conference 200
Cooperative Access in Cognitive Radio Networks: Stable Throughput and Delay Tradeoffs
In this paper, we study and analyze fundamental throughput-delay tradeoffs in
cooperative multiple access for cognitive radio systems. We focus on the class
of randomized cooperative policies, whereby the secondary user (SU) serves
either the queue of its own data or the queue of the primary user (PU) relayed
data with certain service probabilities. The proposed policy opens room for
trading the PU delay for enhanced SU delay. Towards this objective, stability
conditions for the queues involved in the system are derived. Furthermore, a
moment generating function approach is employed to derive closed-form
expressions for the average delay encountered by the packets of both users.
Results reveal that cooperation expands the stable throughput region of the
system and significantly reduces the delay at both users. Moreover, we quantify
the gain obtained in terms of the SU delay under the proposed policy, over
conventional relaying that gives strict priority to the relay queue.Comment: accepted for publication in IEEE 12th Intl. Symposium on Modeling and
Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt), 201
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