1,138 research outputs found
Cooperative Wideband Spectrum Sensing Based on Joint Sparsity
COOPERATIVE WIDEBAND SPECTRUM SENSING BASED ON JOINT SPARSITY
By Ghazaleh Jowkar, Master of Science
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science at Virginia Commonwealth University
Virginia Commonwealth University 2017
Major Director: Dr. Ruixin Niu, Associate Professor of Department of Electrical and Computer Engineering
In this thesis, the problem of wideband spectrum sensing in cognitive radio (CR) networks using sub-Nyquist sampling and sparse signal processing techniques is investigated. To mitigate multi-path fading, it is assumed that a group of spatially dispersed SUs collaborate for wideband spectrum sensing, to determine whether or not a channel is occupied by a primary user (PU). Due to the underutilization of the spectrum by the PUs, the spectrum matrix has only a small number of non-zero rows. In existing state-of-the-art approaches, the spectrum sensing problem was solved using the low-rank matrix completion technique involving matrix nuclear-norm minimization. Motivated by the fact that the spectrum matrix is not only low-rank, but also sparse, a spectrum sensing approach is proposed based on minimizing a mixed-norm of the spectrum matrix instead of low-rank matrix completion to promote the joint sparsity among the column vectors of the spectrum matrix. Simulation results are obtained, which demonstrate that the proposed mixed-norm minimization approach outperforms the low-rank matrix completion based approach, in terms of the PU detection performance. Further we used mixed-norm minimization model in multi time frame detection. Simulation results shows that increasing the number of time frames will increase the detection performance, however, by increasing the number of time frames after a number of times the performance decrease dramatically
Multiband Spectrum Access: Great Promises for Future Cognitive Radio Networks
Cognitive radio has been widely considered as one of the prominent solutions
to tackle the spectrum scarcity. While the majority of existing research has
focused on single-band cognitive radio, multiband cognitive radio represents
great promises towards implementing efficient cognitive networks compared to
single-based networks. Multiband cognitive radio networks (MB-CRNs) are
expected to significantly enhance the network's throughput and provide better
channel maintenance by reducing handoff frequency. Nevertheless, the wideband
front-end and the multiband spectrum access impose a number of challenges yet
to overcome. This paper provides an in-depth analysis on the recent
advancements in multiband spectrum sensing techniques, their limitations, and
possible future directions to improve them. We study cooperative communications
for MB-CRNs to tackle a fundamental limit on diversity and sampling. We also
investigate several limits and tradeoffs of various design parameters for
MB-CRNs. In addition, we explore the key MB-CRNs performance metrics that
differ from the conventional metrics used for single-band based networks.Comment: 22 pages, 13 figures; published in the Proceedings of the IEEE
Journal, Special Issue on Future Radio Spectrum Access, March 201
Analytical Studies of Fragmented-Spectrum Multi-Level OFDM-CDMA Technique in Cognitive Radio Networks
In this paper, we present a multi-user resource allocation framework using
fragmented-spectrum synchronous OFDM-CDMA modulation over a frequency-selective
fading channel. In particular, given pre-existing communications in the
spectrum where the system is operating, a channel sensing and estimation method
is used to obtain information of subcarrier availability. Given this
information, some real-valued multi-level orthogonal codes, which are
orthogonal codes with values of , are provided
for emerging new users, i.e., cognitive radio users. Additionally, we have
obtained a closed form expression for bit error rate of cognitive radio
receivers in terms of detection probability of primary users, CR users' sensing
time and CR users' signal to noise ratio. Moreover, simulation results obtained
in this paper indicate the precision with which the analytical results have
been obtained in modeling the aforementioned system.Comment: 6 pages and 3 figure
Spatial-Spectral Joint Detection for Wideband Spectrum Sensing in Cognitive Radio Networks
Spectrum sensing is an essential functionality that enables cognitive radios
to detect spectral holes and opportunistically use under-utilized frequency
bands without causing harmful interference to primary networks. Since
individual cognitive radios might not be able to reliably detect weak primary
signals due to channel fading/shadowing, this paper proposes a cooperative
wideband spectrum sensing scheme, referred to as spatial-spectral joint
detection, which is based on a linear combination of the local statistics from
spatially distributed multiple cognitive radios. The cooperative sensing
problem is formulated into an optimization problem, for which suboptimal but
efficient solutions can be obtained through mathematical transformation under
practical conditions.Comment: To appear in the Proceedings of the 2008 IEEE International
Conference on Acoustics, Speech and Signal Processing, Las Vegas, NV, March
30-April 4, 200
Wideband Spectrum Sensing in Cognitive Radio Networks
Spectrum sensing is an essential enabling functionality for cognitive radio
networks to detect spectrum holes and opportunistically use the under-utilized
frequency bands without causing harmful interference to legacy networks. This
paper introduces a novel wideband spectrum sensing technique, called multiband
joint detection, which jointly detects the signal energy levels over multiple
frequency bands rather than consider one band at a time. The proposed strategy
is efficient in improving the dynamic spectrum utilization and reducing
interference to the primary users. The spectrum sensing problem is formulated
as a class of optimization problems in interference limited cognitive radio
networks. By exploiting the hidden convexity in the seemingly non-convex
problem formulations, optimal solutions for multiband joint detection are
obtained under practical conditions. Simulation results show that the proposed
spectrum sensing schemes can considerably improve the system performance. This
paper establishes important principles for the design of wideband spectrum
sensing algorithms in cognitive radio networks
Peak to average power ratio based spatial spectrum sensing for cognitive radio systems
The recent convergence of wireless standards for incorporation of spatial dimension in wireless systems has made spatial spectrum sensing based on Peak to Average Power Ratio (PAPR) of the received signal, a promising approach. This added dimension is principally exploited for stream multiplexing, user multiplexing and spatial diversity. Considering such a wireless environment for primary users, we propose an algorithm for spectrum sensing by secondary users which are also equipped with multiple antennas. The proposed spatial spectrum sensing algorithm is based on the PAPR of the spatially received signals. Simulation results show the improved performance once the information regarding spatial diversity of the primary users is incorporated in the proposed algorithm. Moreover, through simulations a better performance is achieved by using different diversity schemes and different parameters like sensing time and scanning interval
Joint Spectrum Sensing and Resource Allocation for OFDM-based Transmission with a Cognitive Relay
In this paper, we investigate the joint spectrum sensing and resource
allocation problem to maximize throughput capacity of an OFDM-based cognitive
radio link with a cognitive relay. By applying a cognitive relay that uses
decode and forward (D&F), we achieve more reliable communications, generating
less interference (by needing less transmit power) and more diversity gain. In
order to account for imperfections in spectrum sensing, the proposed schemes
jointly modify energy detector thresholds and allocates transmit powers to all
cognitive radio (CR) subcarriers, while simultaneously assigning subcarrier
pairs for secondary users (SU) and the cognitive relay. This problem is cast as
a constrained optimization problem with constraints on (1) interference
introduced by the SU and the cognitive relay to the PUs; (2) miss-detection and
false alarm probabilities and (3) subcarrier pairing for transmission on the SU
transmitter and the cognitive relay and (4) minimum Quality of Service (QoS)
for each CR subcarrier. We propose one optimal and two sub-optimal schemes all
of which are compared to other schemes in the literature. Simulation results
show that the proposed schemes achieve significantly higher throughput than
other schemes in the literature for different relay situations.Comment: EAI Endorsed Transactions on Wireless Spectrum 14(1): e4 Published
13th Apr 201
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