Peyman Teymoori

DT-MAC: An Efficient and Scalable Medium Access Control Protocol for Wireless Networks

Recent advancements in wireless protocols and technologies such as IEEE 802.11n enhances communication systems in terms of offering high physical rates that are well-suited for multimedia and bandwidth-hungry applications. Since efficiency at the medium access control (MAC) layer decreases with increasing the physical rate, few researches have used aggregation, as a compensatory method, to improve efficiency. They have, however, underscored scalability in terms of parameters such as physical rate or number of users. Thus, providing a more scalable MAC protocol has become as issue of paramount concern. In this paper, we propose the Dual-channel Token-based MAC (DT-MAC) protocol that can provide scalability and improve efficiency especially for a large number of users and high physical rates. Then, DT-MAC is analytically evaluated in saturated conditions, and a predictable and optimal bandwidth allocation scheme to sub-channels is proposed. Simulation results for various parameters show that DT-MAC can approximately improve throughput 68% and decrease transmission delay and jitter nearly 90% compared with IEEE 802.11n for a dense high-data-rate single-hop network and operates well under low load.

Local reconstruction of virtual backbone to support mobility in wireless ad hoc networks

Constructing a connected dominating set (CDS) has been widely used as a topology control method and a virtual backbone to reduce energy consumption and communication overhead. Previous works emphasize on constructing the minimum CDS (MCDS) and do not consider node mobility and CDS reconstruction where energy balancing is required. In this paper, we propose a CDS reconstruction algorithm which is able to reconfigure the CDS locally in the presence of mobility and energy balancing without the need for reconstructing the whole CDS. The algorithm does not increase the approximation factor of the algorithm which has constructed the CDS already and it has O(Delta log Delta) and O(Delta) time and message complexity, respectively, which is a great improvement in comparison with the other approaches, where Delta is the maximum degree of the network graph.

Analyzing delay limits of high-speed wireless ad hoc networks based on IEEE 802.11n

Recent advances in high-speed wireless LANs with physical layer (PHY) rates reaching 600Mbps make them ideal for multimedia applications. It has been shown that efficiency at medium access control (MAC) layer decreases with increasing the PHY rate. To achieve high efficiency, few researches have tried to use aggregation in which few packets are concatenated into a larger frame. The resultant frame is sent at once in order to reduce the media access protocol overhead. Unfortunately larger frames increase delays. Since demand for real-time data communication and delay-sensitive applications have become more critical, especially for high-speed networks, a thorough delay analysis is required to examine the effect of aggregation on delay in high-speed networks. In this paper, we propose an analytical model for examining packet delay in IEEE 802.11n networks in the saturation mode. To the best of our knowledge, this is the first work which focuses on packet delay analysis in the presence of aggregation. Analysis and simulation results show that packet delay increases in larger aggregation sizes, and IEEE 802.11n performs poorly in high rates in terms of packet delay. Moreover, based on two new metrics that we propose in the paper, it is shown that aggregation loses its effectiveness in higher rates.

An efficient medium access control protocol for WSN-UAV

Recent advances in Unmanned Aerial Vehicle (UAV) technologies have enhanced Wireless Sensor Networks (WSNs) by offering a UAV as a mobile data gathering node. These systems are called WSN-UAV that are well-suited for remote monitoring and emergency applications. Since previous Medium Access Control (MAC) protocols proposed in WSNs are not appropriate in the presence of a UAV, few researches have proposed new MAC protocols to meet WSN-UAV requirements. MAC protocols of WSN-UAV should be extremely efficient and fair due to the time-limited presence of the UAV in the neighborhood of each sensor. However, issues such as high throughput in dense networks, fairness among sensors, and efficiency have not been resolved yet in a satisfactory manner. Moreover, previous works lack analytical evaluation of their protocols. In this paper, we present a novel MAC protocol in WSN-UAV, called Advanced Prioritized MAC (AP-MAC), that can provide high throughput, fairness, and efficiency, especially in dense networks. We also analytically evaluate AP-MAC using a 3-dimensional Markov chain and validate its correctness using simulation. Simulation results under various scenarios confirm that AP-MAC can approximately improve throughput and fairness up to 20% and 25%, respectively, leading to higher efficiency compared with previous work in WSN-UAV systems such as Prioritized Frame Selection (PFS).

A Fair and Efficient Resource Allocation Scheme for Multi-Server Distributed Systems and Networks

Maintaining efficiency and fairness is a challenging problem in distributed systems and networks. In this paper, we focus on distributed multi-server systems and networks in which each user may be allocated resources by different servers. Reemphasizing polling systems as abstractions of resource sharing systems, in this paper, first we introduce a multi-server polling system in which each server (resource) can poll (be allocated to) only a subset of queues (users) in the system to model a wide range of multi-server systems such as multihomed networks and cloud computing. Then, to obtain a fair resource allocation vector to queues, a network utility maximization problem with a general utility function is defined. Depending on the type of the utility function, the presented scheme can attain different kinds of fairness such as weighted proportional and max-min fairness. Although maintaining fairness is important in many applications, providing efficiency is also crucial. Hence, we present an efficient algorithm to convert the obtained fair resource allocation vector into a Markovian routing matrix to determine the polling order of queues. This algorithm is capable of improving performance measures such as delay variance and mitigating short-term unfairness by minimizing the probability of consecutive polling of the same queue. Two distributed schemes are presented to obtain fairness and efficiency in even highly dynamic and distributed environments. The effectiveness of the presented schemes is also studied through simulation and numerical evaluation. Our results show their success in attaining fairness and efficiency in dynamic multi-server distributed systems and networks.

Delay-Constrained Optimized Packet Aggregation in High-Speed Wireless Networks

High-speed wireless networks such as IEEE 802.11n have been introduced based on IEEE 802.11 to meet the growing demand for high-throughput and multimedia applications. It is known that the medium access control (MAC) efficiency of IEEE 802.11 decreases with increasing the physical rate. To improve efficiency, few solutions have been proposed such as Aggregation to concatenate a number of packets into a larger frame and send it at once to reduce the protocol overhead. Since transmitting larger frames eventuates to dramatic delay and jitter increase in other nodes, bounding the maximum aggregated frame size is important to satisfy delay requirements of especially multimedia applications. In this paper, we propose a scheme called Optimized Packet Aggregation (OPA) which models the network by constrained convex optimization to obtain the optimal aggregation size of each node regarding to delay constraints of other nodes. OPA attains proportionally fair sharing of the channel while satisfying delay constrains. Furthermore, reaching the optimal point is guaranteed in OPA with low complexity. Simulation results show that OPA can successfully bound delay and meet the requirements of nodes with only an insignificant throughput penalty due to limiting the aggregation size even in dynamic conditions.

High throughput low power CCMP architecture for very high speed wireless LANs

Considering the pervasion of wireless portable devices and growing trends in the use of multimedia applications, access to a high speed and, especially, a high throughput wireless channel are of significant importance. In addition to security concerns in wireless devices, deficiency in throughput and also increase in power consumption are introduced to the system by applying security. Therefore, designing a secure, high-speed wireless device with low power consumption would be a suitable response to worldwide demands. In this paper, we propose a solution to reduce encryption overhead and we almost eliminate it. Furthermore, a customized hardware architecture for Counter Mode with Cipher Block Chaining Message Authentication Code Protocol (CCMP) is proposed. This protocol is the fundamental security architecture of IEEE 802.11i standard. To improve throughput and reduce overhead, encryption is accomplished in the spare time intervals, such as DCF Inter-Frame Spaces (DIFS) used in IEEE 802.11i standard. In order to overcome the restrictions in dealing with these time intervals, a multi-core structure is proposed. Moreover, to reduce power consumption, a particular scheduler is implemented for processing cores. In the proposed architecture, we achieve up to 2Gbps throughput in the single core mode for MPDU (MAC Protocol Data Unit) and A-MSDU (Aggregated MAC Service Data Unit) input frames, and 17Gbps throughput in multi core mode for A-MPDU (Aggregated MPDU) input frames.

Fair Flow Control and Fairness Evaluation in Computer Networks and Systems

Fairness is an important property of computer networks and systems. In a wide range of these systems such as distributed multi-hop wireless networks, multihomed networks, and cloud computing, each user may be allocated a number of system resources; this resembles a many-to-many relationship between the sets of users and resources, which raises the problem of system-wide fair resource allocation. In this paper, we assume that each user/node can be allocated a number of resources, which could be either in its neighborhood or far from it. As a key difference with previous works and through incorporating the concept of “flow”, we model near/far resources allocated to nodes. To attain fair flow control in such systems, first we model this situation by introducing a new multi-server system called multi-ring, in which a server that represents a resource, can serve only a subset of either neighboring or far nodes in the system. Then, we define a centralized optimization problem to attain weighted proportional fairness among all nodes meaning that the sum of allocated capacities from all servers to each node (while considering its flow) is fair. We evaluate fairness properties of multi-ring networks and provide conditions on system parameters under which a system can have a fair resource allocation. Moreover, we present a distributed method to attain fairness in distributed environments, and its stability/convergence is evaluated by non-linear discrete dynamical systems. We present conditions under which the system is stable, and through numerical analysis, we show how to obtain stable system parameters for large systems. The effectiveness of the presented method is studied through extensive numerical evaluation. Results show the success of our method in attaining fairness for various topologies and system parameters, and confirm our stability analysis. A number of systems with fairness issues are also studied as potential applications of our model.

Heterogeneous distributed clustering in sensor networks

Many clustering algorithms in various contexts have been proposed for wireless sensor networks but they usually assume that the environment is homogeneous, i.e. only specific and related data are transmitted. Furthermore, these approaches only consider a particular clustering parameter e.g. cluster diameter, load and spatial positions. As wireless sensor networks are widely extending in terms of broadness, heterogeneity, multitasking, and etc., single-purpose clustering seems not to be effective. Moreover, this is of more interest to form clusters based on various parameters and desires dynamically. In this paper, we propose a general network clustering approach which is able to operate in heterogeneous environments and clusters network nodes by considering multi-task and multi-parameter characteristics. The proposed solution takes some desired clustering parameters as its input and fuzzily decides how to form clusters of the network nodes. We formalize this solution and introduce a problem-unrelated distributed algorithm. This is also proved that in a very dynamic and noisy environment, the performance of the algorithm degrades at most by the factor of p where p is the probability of accessing a neighboring node.

Game-theoretic analysis of Markovian play order in wireless networks

Repeated games are a common tool for the analysis of communication networks; they consist of a number of consequent stage games. It is usually assumed that in each stage game, players play either simultaneously or in a predefined order. However, there can be found several situations, especially in wireless networks, in which the play order, e.g. the channel access order, is random. In this paper, we extend repeated games to address these new situations; we assume that the play order is determined using a positive recurrent Markovian transition matrix where the probability of selecting the next player/node depends on the current stage player. We call this kind of games repeated games with Markovian play order. After presenting a formal definition, we establish some necessary theorems leading to a Folk Theorem to show how and when cooperation is enforced in such games, and also present an extensive-form game. To better reflect applications of this model, we discuss its applications in some wireless networks in which the play order of nodes is Markovian; we evaluate a forwarding communication network and a token-based network as case studies and apply the obtained results to analyze the network against selfish nodes.