Earticle

In vehicular ad hoc network (VANET), nodes have to cooperate to forward each other’s packets through the networks. Every node, including source and intermediate nodes, has a fair opportunity to transmit a packet. Consequence, the hot spot may incur traffic congestion. The packet loss rate and the transmission delay are increased, but the throughput is decreased. On account of the contention for the shared channel, the throughput of each single node is limited not only by the channel capacity, but also by the transmissions in its neighborhood. Additionally, the network throughput still restrict by the channel capacity. Some other related works using multiple channels simultaneously to transmit packets without interfering each other increases the throughput. But if the traffic load is heavy, these schemes may trigger off more serious packet loss on the contrary because they do not consider the congestion problem especially in VANET environment. In this paper we use cross layer approach to design routing protocol for VANET with aim to restrict the number of packets of every flow passing by congested nodes. Firstly, we estimate congested probability at each node by using MAC overheads, quality of link, and data rate. Subsequently, we use congested probability assessment as route metric. This method enhances link stable and network throughputs. For building routing protocol operation we use hybrid model (inherit good characteristics from proactive and reactive routing protocols). It helps restrict route overheads and fast convergence of route discovery process. The simulation results illustrate our prominent proposed routing protocol.

Correct prediction of path loss is a pivotal step of WiMAX network planning to estimate external interference level and cell radius accurately. In this paper, different path loss models are compared depending on various parameters like frequency, height of receiver antenna, distance between transmitter and receiver etc. For comparative analysis, COST 231 Hata model, COST 231 Walfisch-Ikegami model, Stanford University Interim (SUI) model, Ericsson model, ECC-33 model and Free Space Path Loss models are used in three different environments (Urban, Suburban and Rural environments). After analyzing the results, it is found that no single model is suited or recommended for all types of propagation environments at 2.5 GHz frequency band.

A trust and reputation management framework for VANETs (Vehicular Ad Hoc Networks) is proposed. In the framework, a similarity mining technique is used for identifying similar messages or similar vehicles. And a reputation evaluation algorithm is proposed for evaluating a new vehicle’s reputation based on the similarity theory. Similarities from different recommenders are used as weights for computing a vehicle’s recommendation based reputation. An updating algorithm for reputations is proposed in the framework. The framework is applied to decide whether a message is trustworthy when a vehicle receives an event message.

Round-trip time (RTT) is defined as the round-trip delay of a data packet between a source and a destination node and is a very important metric for measuring the performance of network applications. The measurement and estimation of RTTs has received a great deal of attention in network measurement research over the years. An interesting question is how RTTs from different source nodes to a common destination node are correlated, which describes to what extent the RTTs exhibit the same changing trend. Such correlation is useful since it would make it feasible to only make some nodes perform RTT measurement while some others estimating RTTs based on the correlation, thus reducing the overhead incurred by RTT measurement. In this paper, we perform a quantitative analysis on the correlation of RTTs, in particular, how network topological properties can affect such correlation. Based on experiment data, our analysis shows that (1) correlations are not much different for path length combinations that only differ in the length of the shorter private path but will become the weakest in statistics when the lengths of the two private paths become the same; (2) correlations are not much different for path length combinations that have the same path length ratio (which is defined as the ratio of the length of the common path to that of the longer private path); and (3) correlation increases along with path length ratio with ratio 1/1 being the inflection point. The results from our analysis of RTT correlation can be applied not only to RTT measurement and estimation, but also to the deployment or selection of measurement nodes in a general network measurement infrastructure.

The 3GPP Long Term Evolution-Advanced (LTE-A) system extends the capabilities of 3rd Generation Partnership Project (3GPP) LTE Rel-8 with the support of carrier aggregation, where two or more component carriers are aggregated in order to support wider transmission bandwidths up to 100 MHz and for spectrum aggregation. A user terminal may simultaneously receive or transmit one or multiple component carriers depending on its capabilities. From the User Equipment (UE) perspective, the Layer 2 aspects of Hybrid automatic repeat request (HARQ) are similar to those of Rel-8. There is one transport block (in the absence of spatial multiplexing, or up to two transport blocks in the case of spatial multiplexing) and one independent HARQ entity per scheduled component carrier. Each transport block (TB) is mapped to a single component carrier on which all HARQ re-transmissions may take place. A UE may be scheduled over multiple component carriers simultaneously, but at most one random access procedure will be ongoing at any time. This paper presents the main types of carrier aggregation and focuses on intra band non-contiguous carrier aggregation. A simulation is designed to show the main performance of intra band non-contiguous carrier aggregation for different frequencies between 30 MHz – 100 MHz.

With the increasing scale of grid systems, reliability evaluation for both grid systems and applications become more and more challenging, especially when taking the heterogeneity and dynamical workload into consideration. In this work, a workload-aware reliability evaluation model is proposed, in which queuing system is applied to describe the dynamic workload and working of grid resources. To supporting deadline-sensitive applications, a new class of resource fault, namely Deadline-Miss fault, is introduced to evaluate the reliability of these applications. The validity of the proposed model and its approach to calculate deadline-sensitive job’s reliability are presented theoretically. Extensive experiments are conducted to verify its performance, and the results show that the proposed model can significantly improve the accuracy of reliability evaluation in presence of dynamic workload. Also, scheduling algorithm based on this model can reduce mean response time and the deadline-miss rate for deadline-sensitive grid applications.

Although MIMO (multiple input multiple output) represent a solution to increase the ca-pacity and the reliability of wireless channels, it is particularly challenging from a channel estimation perspective. There are many algorithms that can be applied in MIMO channel es-timator. Motivated by analysis of the autocorrelation matrix at the receiver, which is consid-ered as a important step in computation of channel parameter based on whitening-rotation (WR) channel estimation algorithm, this paper modify transmit signal frame by embedded its second order statistic data. This idea is described as solution resolved ill-condition of WR-based channel estimation approach. We show that considerable improvement in the perfor-mance of channel estimator can be obtained by using this modified algorithm, especially for larger number of transmit/receive antennas.

In the hierarchical wireless sensor network (WSN), cluster-based network architecture can enhance network self-control capability and resource efficiency, and prolong the whole network lifetime. Thus, clustering has also been a topic of interest in many different disciplines. Finding an energy-effective and efficient way to generate cluster is very important in WSN. We propose a distributed, energy-efficient and flexible clustering approach. Based on the hierarchical agglomerative clustering (HAC) method, the algorithm uses the qualitative connectivity data as input data, and tailor simple numerical method to generate a cluster tree. Simulation results demonstrate that this method is energy-effective and flexible, which can enhance network self-control capability and resource efficiency, and prolong the whole network lifetime.

In this paper we focus on physical attacks on sensor nodes in a wireless sensor networks. Node capture attacks is one of the most dangerous attacks applied to WSNs which aims to capture a node in the network and try to steal some secret information. To be more specific we first survey node capture attacks and then a novel security mechanism to deal with these types of attacks will be presented. For this purpose a key management protocol is proposed based on authentication and data encryption preventing from node capture attacks. The key of protocol is generated by embedded PUF on sensor nodes chip. This key is unique and all tasks in protocol performed by this key and its products. The proposed solution is resistant against node capture attacks and is efficient in points of the cost and memory size.

Welchia worms were launched to terminate the Blaster worms and patch the vulnerable hosts. They created complex worm interactions as well as detrimental impact on infrastructure. Worm propagation analysis, including exploring mechanisms of predator-prey worms’ propagation and formulating effects of network/worm parameters, has great importance for worm containment and host protection. In this paper, an integrated worm ecology model is given to study the propagation of such worms. The analytical results provide insights of the worm design and impact to network. The simulation results verify the correctness of our model and show the effectiveness of the worm model by applying it to the LiOn/Cheese and MSBlaster/Welchia.

At present the hash algorithm analysis is mostly confined to the randomness of the hash values. Researchers have not analyzed the effect of hash algorithm in the network equipment. We propose three evaluation measures of hash algorithm from the perspective of theory analysis and experimental evaluation: the output stream integrity by combining with the dictionary sorting and binary search method to verify, the flow distribution uniformity of hash algorithm, load balancing effect according to the group packet number variance and the max-min packet number ratio. In the experiments, we evaluate the hash algorithm of the current domestic well-known network equipment manufacturers with the backboneflow. The results show that the evaluation measure can effectively measure hash algorithm. It network is helpful for network equipment manufacturers to choose proper hash algorithm.

Nodes in wireless ad hoc networks depend on others for forwarding packets hop by hop. However, nodes may behave selfishly and do not forward packets for saving their limited resources. Approaches based on Vickrey, Clarke and Groves (VCG) pay to the intermediate nodes a premium over their actual costs to stimulate cooperation for their forwarding services and are truthful routing protocols in which nodes can maximize their utility only when the nodes declare truthful cost for forwarding packets. But the route overhead of the existing routing protocols based on VCG is at least O(n2) which is likely to become prohibitively large as the network size grows and leads to serious traffic congestion and packet dropping. In response to the problems, we proposed a truthful and low-overhead routing protocol (TLOR) based on VCG for ad hoc networks with selfish nodes which can achieve cost-efficient routing and truthfulness. TLOR incur the route with overhead of O(Ln), where L is an upper bound on the hop number of the path and n is the number of nodes in network. Analysis and simulation results verify that TLOR is truthful and can significantly reduce the route overhead.

This paper analyzes a web crawler for the Web 2.0 network, which presents new challenges. A comprehensive overview on various programs and strategies is presented, which includes the design and realization of Ajax reptiles. Experimental verification indicates that an Ajax Crawler can effectively obtain Ajax dynamic pages. The proposed Ajax Crawler is then compared with common Ajax reptiles in terms of their download speeds.

The frequency hopping technology is widely used in wireless sensor networks with the security becomes more and more important. Channel evaluation is important for adaptive frequency hopping system and we proposed a scheme of optimal channel selection with channel evaluation, which can get an accurate and comprehensive channel evaluation by analyzing the Signal-To-Noise Ratio (SNR), loss rate and delay.

In this paper, through analyzing the process of publishing resource files in DHT network and from the viewpoint of making full use of the information stored in values nodes, we propose two methods to improve the lookup efficiency of source nodes: values-node-based lookup algorithm and source nodes exchange algorithm. The former firstly sends find_node message to those found values nodes, then sends get_peers message to nodes in the returned nodes-list so that increase the number of source nodes in fewer iterations. The latter organizes source nodes into a connected graph taking advantage of the information stored in values nodes, and based on this, with additional interactive messages we can improve the performance of looking up source nodes.

As for the next generation of Internet, the Internet of things impacts people's lives profoundly, its application will be more broadly. There are many kinds of things network terminal, network topological structure is complex, the reset of network resource will drive the topological structure, changes, which have an important impact on network performance. By using the Simulative method, we study the relationship between the changes of topological structure and network performance before the network resource reset, which can improve the project of resource replacement, furthermore, improve the network performance.