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Scientific Contributions & Technical Publications

Journals

 Publication TitleIF & Links
1Richard O. Afolabi, Binh V. Nguyen, A. Mehrabi, Kiseon Kim, "QoS-Aware Multimedia Multicasting with Minimum Outage in Future Multicarrier Cellular Networks," in IEEE Trans. Broadcasting, Dec. 2014.

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Several innovative applications are emerging that require significant multimedia data transmissions, which unfortunately, current communication systems struggle to provide. In this work, we examine the high outage tendencies of conventional multimedia multicasting (CVM) due to the bottleneck imposed by the user with minimum signal-to-noise-ratio (minSNR) and we present a technique based on the statistical approximations of the amortized weighted averaging (AWG) of users’ SNR. For completeness, we propose a suboptimal multicast resource allocation algorithm using memoization with stochastic rounding (MSR). We compare the system performance of AWG scheme with the CVM scheme in multicarrier wireless network using our newly derived system outage probability and mean capacity as performance metrics. Numerical results not only show that the performance gap of our suboptimal algorithm is reasonably within 10% from the optimal solution, but also show that the AWG scheme admits more users and is more energy efficient than the CVM especially when low power is available to the system.
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2A. Dadlani, S. K. Muthukrishnan, Richard O. Afolabi, Kiseon Kim, "Opportunistic Spectrum Access with Retrial Phenomenon in Cognitive Radio Networks," in IEEE Communications Letter, Dec. 2014.

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Opportunistic spectrum access (OSA) is a promising reform paradigm envisioned to address the issue of spectrum scarcity in cognitive radio networks (CRNs). While current models consider various aspects of the OSA scheme, the impact of retrial phenomenon in multi-channel CRNs has not yet been analyzed. In this work, we present a continuous-time Markov chain (CTMC) model in which the blocked and preempted secondary users (SUs) enter a finite retrial group (or orbit) and re-attempt for service independently after exponentially distributed random time. Taking into account the retrial tendency of SUs, we numerically assess the performance of the proposed scheme in terms of dropping probability and throughput of SUs.
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3Binh V. Nguyen, Richard O. Afolabi, Kiseon Kim, "Outage Probability of DnF with Best Relay Selection in Inter-Path Correlated Environment," in IEEE Communications Letter, Dec. 2014.

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Most of the existing studies on cooperative communications using relay selection schemes assume that wireless channels are statistically independent. However, in reality, channel correlation is more likely to be non-negligible. In this study, we investigate performance of decode-and-forward relaying systems with best relay selection scheme in an inter-path correlated environment by deriving an upper bound on the system outage probability. We show that the considered correlation form has
great impact on the system performance. More specifically, as the channel correlation approaches 1: (i) the system outage probability is significantly degraded and (ii) the lower the system outage probability, the more quickly the system diversity order converges to 1. Simulation results are also provided to validate our analysis.
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4Richard O. Afolabi, Binh V. Nguyen, Kiseon Kim, "Amortized Weighted Averaging For Multimedia Broadcast and Multicast Systems," in IEEE Communications Letters, vol. 18, no. 5, pp. 837–840, May 2014.

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We consider the inefficiencies of conventional multimedia broadcast multicast systems (MBMS) limited by the user with worst signal-to-noise-ratio (SNR) and we present a novel technique based on amortized weighted averaging (AWG) of individual user’s SNR. We model the system using ordered statistics of exponential and uniform distribution and derive statistics for the probability distribution function.We then apply the modelling results to study the performance of wireless multicast systems over Rayleigh fading channels. More specifically, we obtain the outage probability and reliability function for broadcast and multicast systems. Finally we compare our proposed scheme with the conventional multicast scheme. Numerical results show that the proposed AWG scheme is more reliable and significantly reduces service outage than the conventional multicasting.
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5Richard O. Afolabi, A. Dadlani, Kiseon Kim, "Multicast Scheduling and Resource Allocation Algorithms for OFDMA-based Systems: a Survey" IEEE Communications Surveys & Tutorials, vol. 15, no. 1, pp. 240–254, 2013.

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Multicasting is emerging as an enabling technology for multimedia transmissions over wireless networks to support several groups of users with flexible quality of service (QoS) requirements. Although multicast has huge potential to push the limits of next generation communication systems; it is however one of the most challenging issues currently being addressed. In this survey, we explain multicast group formation and various forms of group rate determination approaches. We also provide a systematic review of recent channel-aware multicast scheduling and resource allocation (MSRA) techniques proposed for downlink multicast services in OFDMA based systems. We study these enabling algorithms, evaluate their core characteristics, limitations and classify them using multidimensional matrix. We cohesively review the algorithms in terms of their throughput maximization, fairness considerations, performance complexities, multi-antenna support, optimality and simplifying assumptions. We discuss existing standards employing multicasting and further highlight some potential research opportunities in multicast systems.
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6Binh V. Nguyen, Richard O. Afolabi, Kiseon Kim, "Dependence of Outage Probability of Cooperative Systems with Single Relay Selection on Channel Correlation," in IEEE Communications Letters, Vol. 17, No. 11, Nov. 2013.

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—The relay selection method is a promising technique for improving the performance of cooperative systems. Most of the existing studies assume that wireless channels are statistically independent. However, in reality, channel correlation is more likely to be non-negligible. In this study, we investigate the dependence of the performance of cooperative systems with single relay selection in equally correlated environments. A tight upper bound of the system outage probability is given as a function of the channel correlation coefficients. We show that even though the system performance is considerably degraded in the high signal-to-noise ratio (SNR) region when the channel correlations are sufficiently large, yet less than one, the system still achieves a diversity order equal to the number of available relays.
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7Richard O. Afolabi, Aftab Ahmad, Kiseon Kim, "Security assessments of IEEE 802.15. 4 standard based on X. 805 framework," in International Journal of Security and Networks, vol. 5, No. 2, pp. 118-197, March 2010.

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One such wireless technology used to deploy sensitive network services requiring low rate communication, short distance application with low power consumption is the IEEE802.15.4 Low-Rate Wireless Personal Area Networks (LR-WPAN). These network services have stringent security requirements and, irrespective of the scale of deployment, the network should be secure enough to protect users, infrastructure, network services and applications. In this paper, we focus on the security mechanisms defined in the standard; evaluating it in the light of the ITU-T recommendation X.805 security architecture for end-to-end communication. We identify and assess the security dimensions, planes and layers in IEEE802.15.4 LR-WPAN as defined in the X.805 framework.
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Conferences

 TitleDownload
1Richard O. Afolabi, and Kiseon Kim, "Adaptive Resource Allocation in Multicast OFDMA Transmissions Using Scalable Amortize Factor," in Proc. 4th IEEE International Conference on Ubiquitous and Future Networks, (ICUFN'12), Puket, Thailand, pp. 255-260, July 2012.

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WiMAX broadband technology can potentially provide extremely high data rates for immobile nodes but its performance drops off significantly as speed of mobile nodes increases. In this paper, we study the deployment of IEEE802.16j relays as vehicle-to-roadside (V2R) infrastructures for uplink transmission of emergency mobile video surveillance (EMVS) in WiMAX networks to mitigate the degradation effect. Simulation results in OPNET confirm that relay deployment in WiMAX vehicular network can offer almost 20% capacity gain and a possible linear increase in capacity gain especially when mobile users have low gain antenna in relay environment.
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2Richard O. Afolabi, Kiseon Kim, Aftab Ahmad "On Secure Spectrum Sensing in Cognitive Radio Networks Using Emitters Electromagnetic Signature," in Proc. 18th IEEE International Conference on Computer Communications and Networks, (ICCCN'09), IEEE Computer Society, San Francisco, CA, USA, pp. 255-260, Aug. 2009.

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As Cognitive Radio Network (CRN) emerges as an extremely promising next generation wireless technology that can ease the apparent spectrum scarcity and support novel wireless applications; they will become bigger targets for hackers. Moreover, they will also be exposed to diverse security threats especially at the physical layer (PHY) spectrum sensing module. Hence, security consideration is central in its development. Starting with overview of on-going research efforts in CR-based network security, this paper describes a PHY attacker model that exploits the adaptability and flexibility of CRN. In thwarting this attack, we propose a waveform pattern recognition scheme to identify emitters and detect camouflaging attackers by using the Electromagnetic Signature (EMS) of the transceiver. On the performance of the technique, our simulation results show that our approach is effective for spectrum monitoring, mitigating denial-of-service threats and facilitating spectral efficiency.
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Technical Reports

 TitleDownload
1Richard O. Afolabi "Spectrum and Power Efficient Multimedia Transmissions in OFDMA Wireless Networks,"Ph.D. Dissertation, School of Information and Communications, Gwangju Institute of Science and Technology, Winter 2015.Abstract
2Richard O. Afolabi "Electromagnetic Signature-Based Detection of Incumbent Emulation Attackers in Spectrum Sensing of Cognitive Radio Networks,"Masters Degree Thesis, School of Information and Communications, Gwangju Institute of Science and Technology, Fall, 2009.



Abstract
3Richard O. Afolabi "Emergency Mobile Video Surveillance Over Relay-Enhanced WiMAX Vehicular Networks"

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WiMAX broadband technology can potentially provide extremely high data rates for immobile nodes but its performance drops off significantly as speed of mobile nodes increases. In this paper, we study the deployment of IEEE802.16j relays as vehicle-to-roadside (V2R) infrastructures for uplink transmission of emergency mobile video surveillance (EMVS) in WiMAX networks to mitigate the degradation effect. Simulation results in OPNET confirm that relay deployment in WiMAX vehicular network can offer almost 20% capacity gain and a possible linear increase in capacity gain especially when mobile users have low gain antenna in relay environment.
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