Hassan Halabian

Trust establishment in cooperative wireless networks

In cooperative wireless networks, relay nodes are used to improve the channel capacity of the system. However, the presence of malicious relays in the network may severely degrade the performance of the system. More specifically, there exists a possibility that a node refuses to cooperate when it is selected for cooperation or deliberately drop the received packets. Trust establishment is a mechanism to detect misbehaving nodes in a network. In this paper, we propose a trust establishment method for cooperative wireless networks using Bayesian framework. In contrast with previous schemes, this approach takes the channel state information and relay selection policy into account to derive a pure trust value for each relay node. The proposed method can be applied to any system with a general relay selection policy whose decisions in each cooperative transmission are independent of the previous ones. Moreover, it does not impose additional communication overhead on the system as it uses the available information in relay selection procedure.

Network capacity region of multi-queue multi-server queueing system with time varying connectivities

Network capacity region of multi-queue multi-server queueing system with random connectivities and stationary arrival processes is studied in this paper. Specifically, the necessary and sufficient conditions for the stability of the system are derived under general arrival processes with finite first and second moments. In the case of stationary arrival processes, these conditions establish the network capacity region of the system. It is also shown that AS/LCQ (Any Server/Longest Connected Queue) policy stabilizes the system when it is stabilizable. Furthermore, an upper bound for the average queue occupancy is derived for this policy.

Throughput-optimal relay selection in multiuser cooperative relaying networks

The optimal relay selection problem in multiuser cooperative wireless networks is considered in this paper. A general discrete time model for such networks is introduced which takes into account the dynamic variations of the channel state as well as stochastic arrival of data packets into the system. The model consists of a set of mobile users, one destination node and R relay nodes which may be either mobile or fixed. The system uses the benefit of cooperative diversity by relaying in decode and forward or amplify and forward mode. We assume that each user either transmits its packets directly to the destination or selects a relay node to cooperatively transmit its packets. It is not however trivial whether a user at each time slot has to cooperate with any relay node or not and if so, which relay node should be selected for cooperation. We will propose a throughput optimal relay selection policy that can stabilize the system for all the arrival rate vectors strictly inside the stability region. Then, we show that the optimal policy is equivalent to finding the maximum weighted matching in a weighted bipartite graph at each time slot. We also use simulations to compare the performance of the throughput optimal relay selection strategy with an instantaneous throughput optimal policy as well as a non-cooperative policy in terms of average queue occupancy (or equivalently, queueing delay).

Trust Management in Wireless Mobile Networks with Cooperative Communications

Cooperative communication makes use of the broadcast nature of the wireless medium where adjacent nodes overhear the message transmitted by the source and assist in the transmission by relaying the overheard message to the destination. Although cooperative communication brings in significant benefits, it also raises serious security issues to wireless mobile networks. For example, there exists a possibility that a node refuses to cooperate when it is selected for cooperation or deliberately drop the received packets. In wireless mobile networks with cooperative communication, trust management is an important mechanism to monitor such networks for violations of security. In this paper, we propose a trust management method for wireless mobile networks with cooperative communications. Conventional Bayesian methodology is insufficient for the cooperative communication paradigm, as it is biased by the channel conditions and relay selection decision processes. Therefore, we modify the conventional trust management method by incorporating not only the relay selection policy but also the dynamic wireless channel conditions among the source, relays and destination. Simulation results are presented to show the effectiveness of the proposed scheme.

Optimal Joint Resource Allocation and Power Control in Bidirectional Relaying Networks

Cooperative relaying (CoR) and network coding (NC) are two promising techniques for improving the performance of next-generation mobile networks. In this paper, a dynamic joint resource allocation and power control scheme is proposed for bidirectional relaying in wireless mobile networks. We consider a bidirectional relaying network consisting of three nodes: user equipment (UE), base station or eNodeB (eNB), and an intermediate relay station (RS). We model the network by a two-way relay channel (TWRC) in which UE and eNB can choose between different transmission schemes: direct transmission, pure CoR (CoR scheme), or via the combination of NC and CoR (NC/CoR scheme). We first study the achievable rate regions for direct transmission, CoR, and NC/CoR and characterize them by a set of linear inequalities. We show that NC/CoR does not always achieve better performance than CoR or direct transmission in terms of achievable throughput. Therefore, we propose a hybrid transmission scheme with adaptive resource allocation to dynamically choose the best transmission strategy and the optimal resource allocation at each bidirectional transmission time frame. This is done on the basis of the system channel state information and the buffer occupancy of UE and eNB. The hybrid approach achieves the convex hull of the union of the rate regions of the direct, CoR, and NC/CoR schemes. Finally, we extend our hybrid approach by considering power control at the RS, and we use simulations to study the effect of power control in the hybrid scheme. It is shown that in both single-input-single-output and multiple-input-multiple-output systems, the hybrid scheme with joint power control and resource allocation improves the throughput and delay performance of the system considerably.

Trust establishment in cooperative wireless relayingnetworks

In cooperative wireless networks, relay nodes are employed to improve the performance of the network in terms of throughput and reliability. However, the presence of malicious relay nodes in the network may severely degrade the performance of the system. When a relay node behaves maliciously, there exists a possibility that such a node refuses to cooperate when it is selected for cooperation or deliberately drops the received packets. Trust establishment is a mechanism to detect misbehaving nodes in a network. In this paper, we propose a trust establishment method for cooperative wireless networks by using Bayesian framework. In contrast with the previous schemes proposed in wireless networks, this approach takes the channel state information and the relay selection decisions into account to derive a pure trust value for each relay node. The proposed method can be applied to any cooperative system with a general relay selection policy whose decisions in each cooperative transmission are independent of the previous ones. Moreover, it does not impose additional communication overhead on the system as it uses the available information in relay selection procedure. Copyright

Evaluating a modified PCA approach on network anomaly detection

As the number, complexity and diversity of cyber threats continues to increase, anomaly detection techniques have proven to be a powerful technique to augment existing methods of security threat detection. Research has shown that Principal Component Analysis (PCA) is an anomaly detection method known to be viable for pinpointing the existence of anomalies in network traffic. Despite its recognized utility in detecting cyber threats, previous relevant research work has highlighted certain inconsistencies when the classical PCA method is used to detect anomalies in network traffic, resulting in false positives and false negatives. Specifically, it has been shown that the efficiency of the results are highly dependent on the nature of the input data and the calibration of its parameters. In classical PCA, the parameters have to be carefully selected in order to correctly define the normal and abnormal space. By obtaining real network traffic traces from a small enterprise and artificially injecting anomalies, we experiment with a modified PCA method to address the above shortcomings. The results of our experimentation are encouraging. The results indicate our modified PCA method may possess promising capabilities to efficiently detect network anomalies while addressing some of the limitations of the classic PCA approach.

Optimal resource allocation in LTE-Advanced network using hybrid Cooperative Relaying and network coding

Cooperative relaying (CoR) and network coding (NC) are two promising techniques for improving the performance of next generation LTE-Advanced networks. In this paper, a dynamic resource allocation scheme is proposed in relay-assisted LTE-Advanced networks which consists of three nodes: User Equipment (UE), Base Station or eNodeB (eNB) and an intermediate Relay Station (RS). In such a network, LTE UEs and eNB can choose between different transmission schemes: direct transmission, pure CoR (CoR scheme) using an intermediate relay station, or via the combination of Network Coding and Cooperative Relaying (NC/CoR scheme). We study the achievable rate regions for direct transmission, CoR and NC/CoR and it is noticed that NC/CoR does not always achieve better performance than CoR or direct transmission. Therefore, a hybrid transmission scheme with adaptive resource allocation is proposed to dynamically choose the best transmission scheme among NC/CoR, CoR or direct transmission. The proposed hybrid scheme determines the best transmission strategy and the optimal resource allocation decision at each bidirectional transmission time-frame based on the system channel information as well as the queue length information. The simulation results show that the hybrid algorithm significantly outperforms conventional schemes for both SISO and MIMO systems.

Explicit Characterization of Stability Region for Stationary Multi-Queue Multi-Server Systems

We derive an explicit characterization of the stability region of stationary multi-queue multi-server (MQMS) queueing system by means of a finite set of linear inequalities. More specifically, we explicitly determine the coefficients of the linear inequalities describing the facet-defining hyperplanes of the stability region polytope. Such a characterization is useful for performance evaluation of certain scheduling algorithms such as maximum weight (MW) policy. Our results can be used for studying the asymptotic behavior of the MW policy and computing bounds for the average queueing delay, as well as limiting moments of the queue sizes in heavy-traffic regime. Furthermore, it may be directly applied as the constraint set of network stochastic optimization problems to provide an offline computational solution for such problems. Finally, we use our methodology to characterize the stability region of a fluid model MQMS system which is described by an infinite number of linear inequalities. For such a model, we present an example and show that depending on the channel distribution, the stability region can be instead characterized by a finite set of non-linear inequalities.

Optimal reliable relay selection in multiuser cooperative relaying networks

In this paper, we investigate the problem of optimal reliable relay selection in multiuser cooperative wireless networks in the presence of malicious relay nodes. A general discrete time queueing model for such networks is introduced which takes into account the dynamic variations of the channel state, the dynamic malicious behaviour of relay nodes as well as stochastic arrival of data packets into the system. The model consists of a set of mobile users, one destination node and a set of relay nodes which may be either mobile or fixed. The system uses the benefit of cooperative diversity by relaying in the decode and forward mode. We assume that each user either transmits its packets directly to the destination (direct mode) or transmits them with the cooperation of a selected relay node (cooperative mode). It is assumed that a centralized network controller manages the relay selection process in the system. At each time slot, a malicious relay node in the system may behave spitefully and refuse to cooperate with a user deliberately when it is selected to cooperate with that user. A malicious relay node usually acts stochastically to hide its malicious behaviour for longer time. In such a system, at each time slot the network controller should decide whether a user has to cooperate with any relay node or not and if so, which relay node must be selected for cooperation. First, we show that the malicious behaviour of relay nodes makes the stable throughput region shrink. Then, we propose a throughput optimal secure relay selection policy that can stabilize the system for all the arrival rate vectors strictly inside the network stability region. We show that the optimal policy is equivalent to finding the maximum weighted matching in a weighted bipartite graph at each time slot. Finally, we use simulations to compare the performance of the proposed policy with that of four other sub-optimal policies in terms of average queue occupancy (or queueing delay).