Behrooz Razeghi

A novel multi-criteria relay selection scheme in cooperation communication networks

In this paper, we propose a new relay selection scheme for multi-user cooperation communications using a novel multiple criteria decision making optimization method. We consider jointly three criteria in our proposed relay selection method, two of which have been studied and employed for the process of relay selection in the literature, jointly and separately, and the next one has not been considered in relay selection schemes. In this paper we jointly consider these criteria as a new relay selection scheme. To best of our knowledge, no prior work has studied the process of relay selection from this point of view. Also, we propose a novel approach in the process of selecting the superior candidate relay, i.e., using an information theoretic measure (divergence) in conventional mathematical decision making methods.

Analysis of coverage region for MIMO relay network with multiple cooperative DF-relays

We study and analyze coverage region in MIMO communication systems for a multiple-relay network with decode-and-forward (DF) strategy at the relays. Assuming that there is a line-of-sight (LOS) propagation environment for source-relay channels and channel state information is available at receivers (CSIR), we consider the objective of maximizing coverage region for a given transmission rate and show numerically the significant effect of propagation environment on capacity bounds, optimal relay location and coverage region. Also, we study the situation in which two adjacent relays cooperate in transmission signals to the destination and show analytically that the coverage region is extended compared to noncooperative scenario.

Coverage region analysis for MIMO amplify-and-forward relay channel with the source to destination link

In this paper we study and analyze coverage region for half-duplex multiple-input multiple-output (MIMO) relay channel with amplify-and-forward (AF) strategy at the relay station. By assuming mixed Rayleigh and Rician fading channels with two different relay station situations, we consider the objective of maximizing coverage region for a given transmission rate and find the optimal relay location in the sense of maximizing coverage region. Using Monte Carlo simulations, the coverage region and capacity bounds are shown for different fading cases and different relay station locations. Finally, we compare our results with previous ones obtained for decode-and-forward (DF) MIMO relay channel.

A novel relay selection scheme for multi-user cooperation communications using fuzzy logic

In this paper we propose a novel relay selection method for cooperation communication networks using fuzzy logic. Many efforts have been made in the literature to select the superior relay based on relays SNR/SER and / or relays reputation (in cooperation stimulation methods). We jointly consider four criteria for the process of relay selection, relays SNR/SER, relays reputation, relaying strategy and relay location. We consider the condition in which network users employ different relaying strategies, i.e., some relay nodes employ decode-and-forward strategy, some nodes employ amplify-and-forward strategy, and the other ones employ compress-and-forward strategy. Also, we categorize the network users into LM clusters and take into account the relative distance of potential relay nodes from the source and destination nodes in the process of relay selection. This relative distance has significant impact on the average achievable rate in destination node. Finally, by using a fuzzy logic decision making method, we select the “best relay” based on these four criteria.

A novel approach to mathematical multiple criteria decision making methods based on information theoretic measures

In this paper, first we propose a new approach for mathematical multiple criteria decision making (MCDM) methods using information theoretic measures, entropy and divergence. Using the concept of entropy, we determine the impact of each criterion in decision making process. The Shannons entropy has been previously employed for this purpose. In this paper we use Renyis entropy and the concept of information potential of each criterion for weight assessment. Next, we introduce divergence as new separation measure for MCDM methods. The results indicate that the new measure outperforms the conventional Euclidean distance measure. These techniques employed in MCDM methods are new and may be of independent interest. Also, we introduce a new perspective for the decision making problems. We propose time as a new dimension for conventional mathematical MCDM methods. This dimension opens a new horizon for future MCDM methods which are based on given decision matrix. To the best of our knowledge, no prior work has studied the MCDM methods from this point of view. Using the criteria values for each candidate at different time instances, we estimate the probability distribution of each criterion in order to accommodation to the criteria value uncertainty. Finally, by utilizing the generalized correlation function, i.e. correntropy, we study the statistical dependencies of criteria in the same and different time instances.

C-trust: A trust management system to improve fairness on circular P2P networks

An important issue in Peer-to-Peer networks is to encourage users to share with others as they use the resources of the network. However, some nodes may only consume from users without giving anything in return. To fix this problem, we can incorporate trust management systems with network infrastructures. Current trust managements are usually made for unstructured overlays and have several shortcomings. They are made to be very similar to e-commerce scoring websites which may not be the best design for fairness in P2P networks. Several problems may arise with their designs such as difficulties to provide a complete history of freeloaders or lack of an autonomous removal mechanism in case of severe attacks. In this paper, we argue that such systems can be deployed more efficiently by using a structured paradigm. For this purpose, we propose C-Trust, a trust management system which is focused on fairness for P2P networks. This is done by getting help from current circular structured designs. This method is able to mark freeloaders, identify their severity of abusion and punish them accordingly. We are also able to effectively protect both Seeder-to-Leecher and Leecher-to-Leecher transactions. This feature is specially important for fairness which other trust systems have not considered so far.

On relay selection to maximize coverage region for cooperative cellular networks with multiple fixed and unfixed relays

The performance of a relay-based cooperative cellular network is affected by the relay location. Many efforts have been made in the literature for optimal relay placement from various perspectives and with different assumptions. A small group of research work focuses on maximizing coverage region of cooperative relaying networks by finding optimal relay location within network. In this paper, we propose a simple relay selection technique in a cooperative cellular network with the objective of maximizing coverage region of cellular network. We consider the condition in which we have two types of relays in the network, fixed and unfixed relays. The fixed relays are the relay stations which are installed at the optimal location to achieve maximum coverage region, and unfixed relays are network users which can act as relays, too. Our purpose is to select the superior relay node from these fixed and unfixed potential relay nodes. To this end, we consider three criteria in our relay selection scheme. These criteria are relay location, source-to-relay (S2R) channels gain and relaying strategy. We use two mathematical multiple criteria decision making methods to select the “best” relay node among available ones. The methods are verified by numerical results. Numerical results show that the proposed schemes effectively rank the potential relay nodes based on their superiority.

Counter attack to free-riders: Filling a security hole in BitTorrent protocol

Peer-to-Peer (P2P) networks are powerful distributed solutions which do not rely on external servers and gather required resources from their users. Therefore, fairness is an important feature for designers of these networks. Prevention of free-riding is a key aspect for fairness. One of the most important file-sharing protocols in P2P is BitTorrent. This protocol is distinguished from other P2P systems for its unique way of uploading process and its novel approach to fairness. For the first time by implementing eminent game theory strategy, “tit-for-tat” for its protocol, BitTorrent made a breakthrough on fairness for P2P networks. However, it did not take long for researchers to find security holes in its approach. It was proven several times that by making specific clients which do not follow BitTorrent algorithms, it is possible to achieve free-riding. In this paper, by making fairness a universal problem we make free-riding a much harder process. This is achieved by changing the role of Tracker from an indexing server to a more intelligent entity which makes the proper decisions based on different situations.

On the coverage region of MIMO two-hop amplify-and-forward relay network

We study and analyze coverage region for MIMO amplify-and-forward (AF) relay network. We consider the network geometry in which L relays are placed uniformly around the source, and assume that there is no direct link between source and destination. We analyze desired transmission rate with the purpose of maximizing coverage region. Using Monte Carlo simulations the impact of number of transceiver antennas and relay amplification factor on the coverage region is studied. Assuming that there is spatial correlation between transmit antennas and receive antennas we compare coverage region for two fading channels, i.i.d fading channel and spatially correlated fading channel. Assuming that channel state information is available at receivers (CSIR), we consider the objective of maximizing coverage region for a given rate and show numerically that spatial correlation decreases the coverage region.

A centralized evolutionary clustering protocol for wireless sensor networks

The energy of all sensor nodes in wireless sensor networks is limited. For this reason, providing a method of communication between nodes and network administrator to manage energy consumption is crucial. In this paper, a centralized evolutionary clustering protocol for wireless sensor networks is proposed. The proposed protocol selects the appropriate nodes as CHs according to three criteria that ultimately increases the network life time. This paper investigates the genetic algorithm (GA) as a dynamic technique to find optimum CHs. Furthermore, an innovative fitness function is proposed. Each chromosome which minimizes fitness function is selected by base station (BS) and its nodes are introduced to the whole network as proper CHs. Simulation results show that the implementation of the proposed method using GA, has done significant improvement in terms of the number of nodes alive and the network lifetime.