The curse of dimensionality, due to lots of network-traffic attributes, has a negative impact on machine learning algorithms in detecting distributed denial of service (DDoS) attacks. This study investigated whether adding the filter and wrapper methods, preceded by combined clustering algorithms using the Vote classifier method, was effective in lowering the false-positive rates of DDoS-attack detection methods. We examined this process to address the curse of dimensionality of machine learning algorithms in detecting DDoS attacks. The results of this study, using ANOVA statistical analyses, showed that incorporating the wrapper method had superior performance in comparison with the filter and clustering methods. IT professionals aim at incorporating effective DDoS-attack detection methods to detect attacks. Therefore, the contribution of this study is that incorporating the wrapper method is the most suitable option for organizations to detect attacks as illustrated in this study. Subsequently, IT professionals could incorporate the DDoS-attack detection methods that, in this study, produced the lowest false-positive rate (0.012) in comparison with all the other mentioned studies.
Orthogonal frequency division multiplexing (OFDM) system has been proposed as a technique for broadcasting digital signals and for wireless communication. The bit-error-rate (BER) performance of the OFDM system is severely affected by the nonlinearity of the high power amplifier and by the Doppler effect impairments. In this paper, we analyze the effects induced on the OFDM signal by the amplifier nonlinearity and by the Doppler effect over multi-hop relaying channels. Moreover, simulation results are presented to validate the analysis. It is shown that the resulting inter-carrier interference (ICI) due to the cumulative effects of the phase noise generated by these impairments per hop becomes very significant in a multi-hop relaying communication system, and severely degrades the BER performance of the system. Theoretical results show perfect agreement with those obtained by simulation.
The bit-error-rate (BER) performance of orthogonal frequency division multiplexing (OFDM) systems in mobile multihop relaying (MMR) system is severely degraded by the effect of Doppler shift and the severity of this degradation increases with the number of hops traversed by the OFDM signal. In this study, the authors propose a method to mitigate the effect of Doppler shift in MMR system (such as the IEEE 802.16j system) using directional antennas. It is shown that the effect of the resulting inter-carrier interference (ICI) because of the phase noise generated by the Doppler shift over multi-hop relaying channels, can be reduced by employing directional antennas at both the mobile and relay stations. Consequently, the BER performance of MMR system is significantly enhanced. Analysis and simulation results show that the BER enhancements using the proposed approach are strongly related to the orientation and beamwidth of the directional antenna employed. As the antenna beamwidth is reduced, the BER enhancement increases for both the perpendicular and parallel antenna orientations, and comparing these two orientations, the parallel orientation case provides slightly better BER enhancements.
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