Spectrum Sensing and Multiple Access Schemes for Cognitive Radio Networks

Increasing demands on the radio spectrum have driven wireless engineers to rethink approaches by which devices should access this natural, and arguably scarce, re- source. Cognitive Radio (CR) has arisen as a new wireless communication paradigm aimed at solving the spectrum underutilization problem. In this thesis, we explore a novel variety of techniques aimed at spectrum sensing which serves as a fundamental mechanism to find unused portions of the electromagnetic spectrum. We present several spectrum sensing methods based on multiple antennas and evaluate their receiving operating characteristics. We study a cyclostationary feature detection technique by means of multiple cyclic frequencies. We make use of a spec- trum sensing method called sequential analysis that allows us to significantly decrease the time needed for detecting the presence of a licensed user. We extend this scheme allowing each CR user to perform the sequential analysis algorithm and send their local decision to a fusion centre. This enables for an average faster and more accurate detection. We present an original technique for accounting for spatial and temporal cor- relation influence in spectrum sensing. This reflects on the impact of the scattering environment on detection methods using multiple antennas. The approach is based on the scattering geometry and resulting correlation properties of the received signal at each CR device. Finally, the problem of spectrum sharing for CR networks is addressed in or- der to take advantage of the detected unused frequency bands. We proposed a new multiple access scheme based on the Game Theory. We examine the scenario where a random number of CR users (considered as players) compete to access the radio spec- trum. We calculate the optimal probability of transmission which maximizes the CR throughput along with the minimum harm caused to the licensed users’ performance

Maximum likelihood detection of precoded SFBC in frequency-selective fading channels

In this paper, we derive the maximum likeli-hood detector (MLD) for precoded space-frequency block coded (SFBC) systems where orthogonal frequency divi-sion multiplexing (OFDM) is incorporated. The obtained results reveal that the precoding process can be exploited to construct low complexity MLD even when the channel frequency response is not equal across each SFBC block. The derived MLD structure is similar to the conventional Alamouti linear decoder except that the decoding matrix has to be selected from four possible matrices. However, the decoding matrix selection and symbols' detection can be performed jointly, which minimizes the additional computational complexity of the derived MLD as com-pared to the conventional Alamouti decoder. Monte Carlo simulation results show that the MLD outperforms the suboptimal detector reported in [1] by about 5 dB at bit error rate (BER) of 10-4 under various channel conditions. 2017 IEEE.Scopu