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 practical systems, channel correlation is more likely to be non-negligible. In this study, we investigate the dependence of the system performance of cooperative systems with single relay selection in correlated channel environments. A very tight upper bound of the system outage probability is given as a function of the channel correlation coefficient. We show that even though the system performance is considerably degraded in the high signal-to-noise ratio (SNR) region when the channel correlation approaches 1, the system still achieves a diversity order equal to the number of available relays. This implies that the system diversity order does not depend on the channel correlation. Next, we derive an asymptotic SNR loss of the system outage probability in the case of correlated channels compared with that derived in the case of independent channels. Finally, we derive a threshold value of the channel correlation because of which the system outage probability becomes twice that in the case of no correlation. Click to Close

This letter studies multicast dynamic resource allocation (MDRA) for single rate multicast group transmission in OFDMA-based cellular systems where the base station (BS) simultaneously serves multiple multicast groups. Due to the undesirable complexity of the optimal resource allocation solution, we reformulated the problem into convex optimization to obtain bounds on the original problem. We then propose a sequential variable fixing technique (SVFT) based on convexification and linearization of the original problem. Simulation results confirm that SVFT can achieve near-optimal spectral efficiency and reduce overall computation time. Click to Close

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. Click to Close

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. Click to Close

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. Click to Close

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. Click to Close

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. Click to Close

The radio spectrum is becoming increasingly congested everyday with emerging technologies and with increasing number of wireless devices. Considering the limited bandwidth availability, accommodating the demand for higher capacity and data rates is a challenging task requiring innovative technologies that can offer new ways of ex- ploiting the available radio spectrum. The idea of Cognitive Radios arises to be an aggressive solution to increasing spectrum utilization by introducing the notion of opportunistic spectrum access. The new approaches to spectrum usage make use of the advances in technology to implement new wireless systems that can share previously allocated spectra in such a way that the incumbents of these spectra are not affected. Additionally, the allowed use of this band by CR devices is permitted on an unlicensed basis. Read more ... » Click to Close