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In cognitive radio networks, secondary users can be coordinated to perform cooperative spectrum sensing to achieve higher detection accuracy. However, when the number of cooperative users increases, more overhead traffic of decision transmission introduced to network and throughput of cognitive radio network decreases. Furthermore, the performance of cooperative spectrum sensing is limited by the...
Cognitive radio is a new technology that solves the problem of spectrum scarcity. In this technology, secondary users, users that do not have license to use the spectrum, can access the frequency bands that are idle in time or frequency whenever the primary users (PUs), users that have license to access the spectrum, are not using these bands. So, cognitive radio networks improve the spectrum utilization...
Cognitive radio has been proposed as a key solution for the problem of inefficient usage of spectrum bands. Spectrum sensing is one of the most important issues in each cognitive radio system. Classically-used spectrum sensing techniques require that the cognitive transmitter is not in operation while detecting the presence/absence of the primary signal during the sensing period. In this paper, we...
In this work, we consider a uni-directional (one way) relay network with a pair of primary transmitter and receiver which are relay-assisted by multiple cognitive radio (CR) terminals. A CR base station is deployed to sense the absence/presence of the primary user based on the received signal-to-noise ratio (SNR) at the fusion center. The primary network utilizes a two-step one-way amplify-and-forward...
A serious threat to cognitive radio networks which sense the spectrum in a cooperative manner is the transmission of false spectrum sensing data by malicious secondary nodes. This enforces the system to acquire authentication. Actually, the decision maker needs to determine the reliability or trustworthiness of the shared data. In this paper, the evaluation process is considered as an estimation dilemma...
We study myopic sensing policy for an opportunistic communication system in which the states of channels evolve as independent Markov chains. A Secondary User (SU) takes one channel to sense and access in each time slot by myopic sensing policy. In the myopic policy, SU ignores the impact of the current action on the future decisions and tries to maximize the expected immediate reward. We propose...
This paper considers a cognitive radio network, which has a two secondary users (SU) equipped with multiple antennas, one acting as transmitter (SU TX) and the other receives the signals transmitted by SU TX (SU RX) and coexists with a primary network users, each with only one antennas. Our objective is to maximize the achievable rates or symbol error rates of the SU subject to the interference constraints...
In this paper, a new algorithm is proposed for cooperative beamforming in the multiple input multiple output (MIMO) orthogonal frequency division multiple access (OFDMA) cognitive radio (CR) systems. The objective is to maximize the signal to interference plus noise ratio (SINR) of the selected secondary users subject to guarantee the primary user's quality of service over all subchannels. In each...
A physical layer security scheme based on joint antenna and timeslot randomization is proposed which is named Deliberate Symbol Convolution. In this scheme, consecutive phase modulated data symbols are convolved using random weights and the convolved symbols are sent simultaneously over a multi input - single output channel. The legitimate channel is estimated at the transmitter side using pilot symbols...
We analyze of the effects of carrier frequency offset (CFO) and timing offset in multiuser offset QAM (OQAM) filter bank multicarrier (FBMC) systems. These effects are quantified by signal-to-interference ratio (SIR) of a desired user. Expressions for SIRs are derived. Numerical results show that the multiuser OQAM multicarrier system is more robust to CFO than orthogonal frequency division multiple...
Up to now, various detection algorithms have been offered and investigated for DS-CDMA systems in multipath conditions. Here, We intend to implement sub-optimum receivers based on Maximum-Ratio-Combining (MRC) via neural network structures in Downlink systems. We will demonstrate that our design based on Radial Base function (RBF) and Multi Layer Perceptron (MLP) outperform in comparison of conventional...
This paper experimentally investigates and compares the performance of the free space optics system employing three different modulation schemes, on-off keying (OOK) with non-return-to-zero (NRZ) and return-to-zero (RZ) and the binary phase shift keying (BPSK) operating under the turbulent atmosphere. The received average signal is measured and used to characterize the strength of the turbulence....
This paper proposes a new method to solve the permutation problem in the frequency-domain source separation based on Independent Component Analysis (ICA). Traditionally, the correlation coefficient of separated signal envelopes is calculated to determine if the separated signals originate from the same source. Recently, a new measure has been proposed, which represents the dominance of the separated...
Smart antenna is one of the most efficient and useful innovations in achieving maximum capacity, improved quality as well as coverage. In this investigation, we try to run a systematic comparison of the performance of different modified blind adaptive beamforming algorithms based on constrained constant modulus (CCM). Two of them use adaptive step size mechanisms, in the stochastic Gradient (SG) algorithm...
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