Hongwu Lv

A Survey of MAC Protocols Design Strategies and Techniques in Wireless Ad Hoc Networks

Medium access control (MAC) protocols provide a means to nodes to access the wireless medium efficiently and collision free to the best of their ability. In this paper we provide a survey of MAC protocols developed for mobile ad hoc (MANETs) in the past based on certain methods and techniques such as multiple radios, multiple channels and specialized beamforming antennas. We discuss some of the MAC protocols designed for wireless sensor networks (WSNs) and their applicability in a MANET environment. There are some similarities between MANETs and WSNs in general but there is also critical differences between the two that affect the design of MAC protocols for both these networks. Traditionally, MAC protocols have been classified on the basis of two broad categories of contention free and contention based MAC protocols but a number of new algorithms proposed in the recent past merge the two schemes together in a single MAC solution and thus there is a need for a new classification approach. MANETs have their unique constraints and characteristics. In this classification, we will discuss various MAC solutions proposed in the past in the light of these constraints and characteristics. We do not intend to explain each and every protocol since the number of MAC solutions proposed in the past decade or so is very large. The purpose of this article is to give the readers a general idea on the various techniques and methods used in literature to develop MAC protocols for MANETs. The techniques range from algorithmic changes such as cross-layer design to enhancement in hardware such as directional antennas.

Analyzing the service availability of mobile cloud computing systems by fluid-flow approximation

Mobile cloud computing (MCC) has become a promising technique to deal with computation- or data-intensive tasks. It overcomes the limited processing power, poor storage capacity, and short battery life of mobile devices. Providing continuous and on-demand services, MCC argues that the service must be available for users at anytime and anywhere. However, at present, the service availability of MCC is usually measured by some certain metrics of a real-world system, and the results do not have broad representation since different systems have different load levels, different deployments, and many other random factors. Meanwhile, for large-scale and complex types of services in MCC systems, simulation-based methods (such as Monte-Carlo simulation) may be costly and the traditional state-based methods always suffer from the problem of state-space explosion. In this paper, to overcome these shortcomings, fluid-flow approximation, a breakthrough to avoid state-space explosion, is adopted to analyze the service availability of MCC. Four critical metrics, including response time of service, minimum sensing time of devices, minimum number of nodes chosen, and action throughput, are defined to estimate the availability by solving a group of ordinary differential equations even before the MCC system is fully deployed. Experimental results show that our method costs less time in analyzing the service availability of MCC than the Markov- or simulation-based methods.

A Self-Reflection Model for Autonomic Computing Systems Based on p-Calculus

Autonomic computing has emerged as a paradigm for distributed computing systems to stem the tide of rapidly increasing complexity and evolution problem. In this paper, a two-layer self-reflection model for Autonomic Computing systems(ACs) based on π-calculus is proposed from a theoretical point of view, which integrates self-awareness and context–awareness into a single model and provides a formal, verifiable basis for the development and further studies of ACs. According to the hierarchical structure, it does not only reduce the latency time of self-awareness in local domain but also gives consideration to the overall objectives of the system. In addition, the model is checked by MWB.

A Hybrid Reliable Heuristic Mapping Method Based on Survivable Virtual Networks for Network Virtualization

The reliable mapping of virtual networks is one of the hot issues in network virtualization researches. Unlike the traditional protection mechanisms based on redundancy and recovery mechanisms, we take the solution of the survivable virtual topology routing problem for reference to ensure that the rest of the mapped virtual networks keeps connected under a single node failure condition in the substrate network, which guarantees the completeness of the virtual network and continuity of services. In order to reduce the cost of the substrate network, a hybrid reliable heuristic mapping method based on survivable virtual networks (Hybrid-RHM-SVN) is proposed. In Hybrid-RHM-SVN, we formulate the reliable mapping problem as an integer linear program. Firstly, we calculate the primary-cut set of the virtual network subgraph where the failed node has been removed. Then, we use the ant colony optimization algorithm to achieve the approximate optimal mapping. The links in primary-cut set should select a substrate path that does not pass through the substrate node corresponding to the virtual node that has been removed first. The simulation results show that the acceptance rate of virtual networks, the average revenue of mapping, and the recovery rate of virtual networks are increased compared with the existing reliable mapping algorithms, respectively.

NWBBMP: a novel weight-based buffer management policy for DTN routing protocols

A delay-tolerant network (DTN) is a network with dynamic topology changes, network partitions and node mobility. Multi-copy routing protocols are usually adopted to overcome these characteristics. Although multi-copy routing protocols can improve the message delivery ratio and reduce the message propagation delay, they also easily exhaust the limited storage space of nodes, resulting in buffer overflows. The major task of buffer management is to determine which message will be discarded when buffer overflows happen. Determining the order of discarding messages will directly affect the performance of the network. In this paper, we propose a novel weight-based buffer management policy (NWBBMP) that divides messages in the node into a priority message queue, a high-weight message queue and a low-weight message queue. When a node receives a new message that causes a buffer overflow, the algorithm determines which queue’s messages will be discarded according to whether the current node is the destination node of the new message. Simulation results show that our algorithm outperforms traditional buffer management algorithms in terms of delivery ratio, average delay and network overhead.

A Fuzzy Ranking Based Buffer Replacement Strategy for Opportunistic Networks

In opportunistic networks, it always suffers from the problems that the topology of the network changes dramatically, the disconnection between nodes are prevalen. A store-carry-forward protocol is utilized to deal with those problems in which messages need to be stored in buffers and carried for a long time. Allowing for the limited buffer space, it likely brings buffer overflows and network congestion. A buffer replacement strategy based on fuzzy ranking is proposed to ease congestion and improve efficiency for opportunistic networks in this paper. In the strategy priority, timeliness and size of messages are taken into account, and fuzzy theory is employed to make multi-attribute evaluation and rank replacement sequence. Through simulation results, it can be observed that the proposed strategy can improve the effect of routing in opportunistic networks in terms of delivery ratio and packet loss rate.

An Adaptive Channel Sensing Approach Based on Sequential Order in Distributed Cognitive Radio Networks

We design an efficient sensing order selection strategy for distributed Cognitive Radio Networks (CRNs), where multiple CRs sense the channels sequentially for spectrum opportunities according to a channel Latin Square. We are particularly interested in the case that CRs’ quantity is more than the available channels’, where traditional approaches will have high probabilities of collision. We first introduce a system model and an adaptive sensing threshold for available channels which is estimated according to the sensing probability of the specific sequential order. Then, we propose a channel sensing and access strategy that can adjust its sensing and access probabilities based on the crowded degree of sequential order. Last, we conduct extensive simulations to compare the performance of our approach with other typical ones. Simulation results show that the proposed scheme achieves an outstanding performance on channel utilization in the case of heavy channel workload.

Modeling and Analysis of Apoptosis-Inspired Software Self-destruction

The advantages in intelligence computing and networking has been greatly enhanced the strength and means of malicious attacks, even in some extent, the existing simple encryption or authentication has not been enough to protect the security and privacy. As a feature of life, the mechanism of self-destruction existing in various biological systems is used to kill cells to avoid them out of control while at the risk of dropped or damaged. An apoptosis-inspired self-destruction model is proposed in this paper, which can be treated as an ultimate protection for privacy against the increasingly serious environment. Firstly, with respect to the mechanism of apoptosis, a self-destruction architecture is set up to implement irrecoverable destruction by itself. Then, the process of self-destruction is modeled by Markov Regeneration Stochastic Petri Net (MRSPN) to provide a capability of quantification analysis. Finally, the key parameters of the model are analyzed to study their impacts on self-destruction, and experimental results demonstrate the significance for enhancing self-destruction to set a proper period of heartbeat and keep the heartbeat from failing. Our method is independent of specific platforms and programming language, and can be widely used to protect privacy in mission-critical systems and network business.

ABSR: An Agent Based Self-Recovery Model for Wireless Sensor Network

Wireless sensor networks (WSN) have become increasingly one of the most promising and interesting areas over the past few years. But the character of constrained resources makes it vulnerable to Denial of Service (DoS) attacks, resulting in a large number of compromised nodes. Until now, it is unrealistic to prevent DoS attacks, but compromised nodes may be designed to self-recover to reduce the harm of DoS attacks. In this paper, an agent based self-recovery model (ABSR) was presented on the use of autonomic computing, which can recover itself in the approach of anomaly monitoring, anomaly deciding and node recovery. Finally, the model is analyzed and verified with the Eclipse Plug-in PEPA Tool, which suggests that compromised nodes can self-recover effectively using ABSR.

A Cooperative Indoor Localization Method Based on Spatial Analysis

We study the cooperative localization in indoor multipath environments considering the larger localization error and insufficient LOS (LOS) localization signals. Using the surrounding nodes as reference points, some existing localization schemes can cooperatively localize the candidate terminals when there are insufficient LOS localization signals. But the localization error arising from the reference points is unavoidable. We first propose a space-partitioning method based on ray tracing technology, in which the indoor area is divided into a direct localization area with LOS conditions (DLA) and a cooperative localization area with NLOS (NLOS) conditions (CLA). In a DLA, there are sufficient LOS localization signals that can be used for localization, while in a CLA, the number of LOS localization signals is insufficient. Then, we develop a cooperative localization scheme based on the space partitioning, in which the reference points can assist the candidate terminals to accomplish their localization. Finally, extensive experiments verify the effectiveness of the proposed cooperative localization scheme.