In recent years, underwater acoustic sensor networks (UASNs) have attracted widespread attention in academia. Prolonging the network lifetime is a crucial issue for UASNs. Compared with traditional wireless sensor networks (WSNs), stringent energy becomes more critical in UASNs because the battery equipped at sensor nodes has the limited amount of energy and it is much more difficult to replace or recharge in underwater circumstance. This fact motivates us to pursue the solutions to reduce power consumption by using relay nodes and flow allocation mechanism in order to extend the network lifetime. In this paper, the issues of relay node placement and the flow allocation have been considered as a joint problem and are formulated into an integer nonlinear programming problem, which is node placement-hard in general. To solve the problem efficiently, this paper proposes a novel heuristic scheme for UASNs, which works based on a 3-D architecture. The proposed scheme consists of three algorithms, named as Alternative Flow and Relay-node Adjustment as a whole. Extensive simulation experiments demonstrate that the proposed scheme offers a simple yet attractive solution to the problem.

Recently, large scale vehicle ad hoc networks (VANETs)-based navigation systems have drawn much research attention. Although an enhanced secure and privacy VANET-based navigation (EVSPN) scheme has been proposed to prevent the replay and man-in-the- middle attacks, providing signature and verification on the public key infrastructure (PKI) based signatures of all messages relayed costs much computation resource and incurs a high authentication delay for not only the vehicles but also the roadside units (RSUs), especially when the navigation service is busy. In this paper, we propose a lightweight secure VANET-based navigation scheme (LSVN) that has a lower computation cost and a lower authentication delay. By the LSVN, a vehicle firstly initiates the navigation service with a RSU nearby to request a shared symmetric key for further communication with other RSUs in the VANET. Then, the best route will be calculated. The pseudo identity of the vehicle and the shared keying materials are sent to the RSUs on the route of the vehicle to its destination. At last, the vehicle will be led to the destination by these RSUs in series. We formally verify, by BAN Logic, that the LSVN scheme can provide the guarantee of the integrity of messages and mutual authentication. Performance analysis shows that the LSVN can minimize the use of cryptographic operations and reduce authentication delay significantly comparing with the VSPN scheme and the EVSPN scheme.

The most common approach adopted in the literatures to study the aggregated ICT (Inter-Contact Time) is focused on a certain mobile wireless network, and then characterizing the ICT in this type of network. Tip to now, it still lacks a general approach to model the aggregated ICT effectively in different type of networks. This paper proposes a new approach to characterize the aggregated ICT based on EVT (extreme value theory), which uses the GPD (generalized Pareto distribution) as the unique asymptotic model of the tail distribution. Parameter estimation methods are discussed and applied to real mobility traces collected on different opportunistic networks, such as social pocket switched networks and VANET (vehicular ad hoc network). By performing extensive experiments using EVT-based model, the statistical characteristics of aggregated ICT are found to generally have a power-law behavior in the tail distribution in social opportunistic networks, while an exponential behavior in VANETs. According to the KS (Kolmogorov-Smirnov) test, it illustrates that EVT-based model performs better than other models in characterizing the tail behavior of real mobility traces. Our results thus provide fundamental guidelines on design a new mobility models in opportunistic networks, new routing protocols and their performance analysis.

In this paper, we investigate reliable data transfer for multi-hop underwater acoustic networks. Motivated by experiences from real-world field tests, we propose a Practical Coding-based Multi-hop Reliable Data Transfer (PCMRDT) protocol. For the per-hop reliable data transfer, PCMRDT combines random linear coding and selective repeat to achieve high reliability and efficiency. We analyze the data recovery capability for random linear coding so that we can set an appropriate coding rate. In addition, PCMRDT utilizes a multi-hop coordination mechanism to eliminate collisions and decreases average end-to-end delay over multiple hops. Simulation results show that PCMRDT can significantly reduce the network delay with high energy efficiency.

It is important to protect power supply grid system against various damages for national economics. A high-voltage transmission line monitoring system is an effective way to protect the power supply system. This paper presents an energy-efficient data gathering mechanism for such a system. Our contributions are two-fold: (1) a detailed measurement of the energy consumption for wireless nodes, (2) the collaboration between backbone network nodes and subnets to implement the sleep-wakeup mechanism. To validate the proposed mechanism, we have established an indoor test bed consisting of 8 backbone network nodes. The energy consumption of each node with our mechanism is evaluated and compared to that without sleep. The results show that the energy consumption has decreased by 24% by our scheme.

When a node is not abiding by the rules of the protocol of a wireless network for its own benefit, it can cause severe degradation to network performance. Therefore it is important to detect such selfish behaviour. However, this is not an easy task. The main difficulty comes from the random operation of the carrier-sense multiple-access with collision avoidance (CSMA/CA) protocol, and is exacerbated by the nature of the wireless medium itself. The authors propose in this study a simple and quick algorithm, called sliding window non-parametric cumulative sum (SWN-CUSUM), to detect selfish nodes that deliberately modify its backoff window to gain unfair access to the network resources. SWN-CUSUM uses a sliding window to prevent unlimited build-up of the cumulating sum used in the protocol. The efficiency of this detection algorithm has been validated by extensive simulations using a Qualnet simulator. Comparative analysis of the proposed algorithm with a traditional CUSUM method demonstrates its superior performance with high detection accuracy and low false alarm rate. In addition, the authors compared SWN-CUSUM with other detection techniques, such as sequential probability ratio test and exponentially weighted moving average, the results show that our algorithm has a good performance in detection delay.

Admission and rate control are key components for providing QoS (Quality of Service) flows in multi- rate wireless ad hoc networks where transmission rate at the physical layer is adapted dynamically according to the channel condition. Key to these controls is the formulation of a rate constraint that can regulate the flow rate passing through each node. This paper formulates a cross-layer rate constraint to serve this purpose. Although node- based, the new rate constraint captures the interference level at the receiver side as well as the contention at the sender side, which is more accurate than that of existed work. Simulation results on DSR incorporated with such constraint show that the QoS routing algorithm can admit feasible flows and make full use of the bandwidth resource based on the rate constraint, moreover it outperforms the other algorithms in the scenarios we tested.

Intra- and Inter-flow interferences are the principal causes of network utilization degradation in MR-MC (Multi-Radio Multi-Channel) wireless mesh networks. To minimize these interferences, we propose in this paper a channel assignment algorithm and incorporate it in an on-demand routing protocol called the HCARP (Hybrid Channel Assignment Routing Protocol). In addition, HCARP uses load balancing in route discovery to avoid "hot-spots" with severe interference and to find a route satisfying QoS requirements of the incoming flows. Simulation results and test bed experiments demonstrate that intra- and interflow interferences can be mitigated significantly and the overall network throughput is improved considerably. In addition, our algorithm outperforms the one based on superimposed code if the strength of the superimposed code is less than the interferer number of a node. Our simulation results show that HCARP has the capability of circumventing congested areas in the network and enhancing the QoS support for bandwidth-intensive traffic.

Traditional medium access control (MAC) protocols utilize temporal mechanism to do contention resolution. This paper explores an alternative approach by adapting the space occupied by a transmission to resolve contention. Each successful transmission in a wireless network needs to occupy a certain part of space in which there are no other simultaneous transmissions. The size of the space occupied depends on the transmission rate and it consequently determines the level of spatial reuse. To optimize the aggregate network throughput needs to balance the transmission rate and the level of spatial reuse. This paper firstly derives the optimal transmission rate by analyzing the relationship between the transmission rate and the occupied space size, then a distributed algorithm is proposed to achieve the optimal spatial allocation approximately through tuning the carrier sense threshold and the transmission rate. Simulation results show that, the distributed algorithm works well in balancing the transmission rate and the level of spatial reuse, and the aggregate network throughput can approximate the theoretical one and is higher than that can be gained by other similar algorithms.

Selfish behavior at the MAC (medium access control) layer can have devastating side effects on the performance of wireless ad hoc networks. In this work, we consider the problem of detecting selfish behavior at the MAC layer in IEEE 802.11 wireless networks when a selfish node can manipulate the backoff operation. We propose a simple and robust mechanism based on CUSUM (cumulative sum) test by tracing the statistics characteristic in real time to detect the selfish behavior. This method can be used with any random access MAC protocols and it does not require any modification on the existing protocols. The efficacy of this detection mechanism has been validated by a Qualnet simulator. Our simulation results show that the detection mechanism has short detection time and high detection accuracy.

A key challenge in multihop wireless network is to provision for sufficient network capacity to meet user requirements. The contributions of this paper are two-fold: (a) we analyses wireless bandwidth, the ratio between the number of channels and the number of interfaces, the ratio between the number of gateways and the number of mesh routers, and the impact on the capacity of mesh backbone, and present the asymptotic upper bound of the average throughput of mesh routers (b) based on insights from capacity analysis, we built TJU MeshNet testbed and develop a multi-interface routing protocol (MIRP). We implement the proposed protocol in our testbed to demonstrate the feasibility in practice.

Security is a fundamental prerequisite for the survivability and reliability of wireless networks. In a network where limited wireless resources have to be shared, selfish nodes can manipulate relevant network parameters to gain more access to the resources, and hence obtain a higher performance than their fair share, while the performance of well-behaved nodes will be significantly degraded. This paper considers the environment of an IEEE802.11 WLAN, and proposes a solution from the prospective of a principal-agent system. Our solution uses an incentive and a constraint mechanism to encourage the selfish agent to perform normally. Our method does not modify the IEEE 802.11 protocol, but requires an additional principal node only. Simulation results show that our method can overcome the influence of selfish nodes improve the network fairness performance while maintaining the throughput performance.

Communication networks are traditionally assumed to be connected. However, in delay and disruption tolerant networks(DTN), there are many unconventional difficulties, such as intermittent connectivity, large delay and may never have an end-to-end contemporaneous path, a node has to store-and-carry messages for a long time, until a new forwarding opportunity arises. Because every node needs to store message, content storage becomes the core service of the DTNs, we can implement a content-based forwarding. This paper proposes a new data dissemination method, which classifies the forwarding messages by their content, every node only requests the message that it is interested in. So the messages transmitted in the network can be cut down largely. Of course, in order to improve delivery rate, nodes also request and store messages that requested by other nodes they have contacted with. Meanwhile, the paper adopts a buffer management scheme based on content popularity, a node manages its buffer depending on the times that messages are requested, when the buffer has no adequate capacity, firstly deletes the message that is requested the least. Simulation experiments illustrate that this method can provide low overhead while maintaining high delivery rate and low delivery latencies compared to epidemic routing.

In disruption tolerant networks, aggressive packet forwarding scheme like flooding has a major drawback in terms of network congestion. In this paper, we proposed a new routing algorithm, called adaptive randomized epidemic routing (ARER). ARER dynamically adjusts the forwarding probability for each message according to a new metric, replications density. Meanwhile, ARER arranges the forwarding sequence and the dropping priority based on their assigned weight. The weight is determined by the replication density, the delivery predictability, and TTL. An extensive simulation of ARER using various scenarios was carried out and its performance was compared to well known DTN routing protocols: epidemic routing, randomized routing and spray-and-wait routing. Our results show that ARER outperforms them in all scenarios in terms of packet delay and delivery.

Delay tolerant networks (DTNs) use a store-carry-forward communication model relying on the mobility of nodes because a persistent end-to-end path from source to destination generally does not exist. Epidemic routing is a typical protocol in which data can be replicated along multiple opportunistic paths. With the advent of network coding, it is intuitive that data can not only be replicated, but also coded, when the transmission opportunity arises. In this paper we have implemented the epidemic routing with network coding based on the qualnet platform to validate this theory. What's more, to obtain better performance we introduced adaptive scheduling mechanism. We analytically show that with network coding, the performances of the network including the delivery delay, throughput and the delivery rate have been improved, reflecting many realistic scenarios. And through the simulation result, the correctness of our analysis is confirmed. To sum up, our research will generate a significant impact on DTN, as one focus of future network.

In this paper, we propose a novel TCP congestion control algorithm, named TCP SPC, which improves upon the performance of TCP Reno in wireless networks. TCP SPC exploits statistic process control (SPC) methods that have been used effectively in a variety of monitoring and control applications other than TCP. A TCP SPC sender uses RTT statistics to judge the network status, whereby the congestion window can be adjusted more intelligently. Comparing with conventional TCP, TCP SPC is more robust to sporadic losses due to wireless channel errors. Such errors often cause conventional TCP to over react, leading to unnecessary congestion window reduction. TCP SPC controls the congestion window in a way that is completely transparent to intermediate nodes and the destination. Therefore, it is compatible with any TCP implementation at the destinations. In this paper, we introduce TCP SPC and its implementation in a simulation environment. The simulation results show that TCP SPC can significantly improve throughput and fairness, especially in wireless networks with high-error links.

Research on the effect of selfish node in wireless ad hoc networks has received considerable attention recently. However, most work concentrates on simulation study, but lacks an analytical study to accurately predict the throughput. This paper investigates the saturated and non-saturated load throughputs of IEEE 802.11 DCF (distributed coordinated function) in the presence of a selfish node. Using a modified Markov model, we have derived the throughput of a node under various traffic loads in the PHY (PHYsical) layer using DSSS (direct sequence spread spectrum) and the wireless MAC (medium access layer). The analytical model and throughput results have been validated by simulations.

This paper proposes a set of node-based rate constraints called NABE (node-based available bandwidth estimation) to model the interference relationship among nodes in a wireless ad hoc network and to provide rate constraints for its QoS flows. We evaluate the performance of NABE from three different perspectives: its capacity, its complexity to implement the MAC layer protocol and its efficiency. Our simulation results demonstrate that, NABE can always admit the feasible flows as well as make full use of the bandwidth resource when serving as an admission control scheme in the presence of both intra-flow and inter-flow interference.

It is important to study the traffic in the wireless network control and management. This paper proposes the use of the EVT (extreme value theory) for the analysis of wireless network traffic. The role of EVT is to allow the development of procedures that are scientifically and statistically rational to estimate the extreme behavior of random processes. We have performed extensive simulation experiments by taking traffic data that is greater than a given threshold value. The results of our experiments and analysis show the wireless network traffic model obtained through the EVT fits well with the empirical distribution of traffic. Meanwhile, we can obtain EVT model has the lowest "average deviation" compared with other popular distribution model such as exponential, lognormal, gamma, Weibull. Thus illustrates EVT is more suitable than other distributions to model the traffic and it has a good application foreground in the analysis of wireless network traffic.

A significant issue in mesh networks is to support multimedia transmissions while providing quality of service (QoS) guarantees to mobile users. For real-time multimedia streaming, unstable throughput or insufficient bandwidth will incur unexpected delay or jitter, and it remains difficult to provide comprehensive service guarantees for wireless mesh environment. In this paper, we target the problem of providing multimedia QoS in wireless mesh networks. We have designed and implemented a campus wireless mesh network testbed, and propose an available bandwidth estimation algorithm plus a QoS backup route mechanism to accommodate multimedia traffic flows in mobile wireless mesh networks. Moreover, to validate the correctness of our proposed algorithm, we have implemented the algorithm on the campus wireless mesh network testbed. Our implementation and experiments show that our mechanisms can improve the network stability, throughput, and delivery ratio effectively, while decreasing the number of route failures.

A novel type of learning machine called support vector machine (SVM) has been receiving increasing interests in the areas ranging from its original application in pattern recognition to other applications such as regression estimation due to its remarkable generalization performance. In this paper, we employ the SVM to forecast traffic in WLANs. We study the issues of one-step-ahead prediction and multi-step-ahead prediction without any assumption on the statistical property of actual WLAN traffic. We also evaluate the performance of different prediction models using four real WLAN traffic traces. The simulation results will show that among these methods, SVM outperforms other prediction models in WLAN traffic forecasting for both one-step-ahead and multi-step-ahead prediction.

In a typical installation of an 802.11 based WLAN (Wireless Local Area Network), mobile hosts would access the network through Access Points, even when two mobile stations can communicate within the same WLAN. Effectively, all the packets in a WLAN are required to forward through the AP (Access Point) according to the MAC (Medium Access Control) layer protocol. Since the AP has the same priority as the other mobile stations to access the channel, the AP usually becomes a bottleneck in WLANs and the network performance degrades significantly. In this paper, we propose a new MAC layer protocol for WLANs in order to improve the throughput performance. Theoretical analysis and simulation results show that our new protocol works much better in WLAN than the standard DCF.

This paper presents AODV-DFR, a hybrid routing scheme that gracefully integrates the characteristics of on-demand and proactive routings. AODV-DFR shows great scalability for mobility and traffic load. We have demonstrated that AODV-DFR outperforms on-demand routing protocols (such as AODV), georoutings (such as GPSR) and adaptive hybrid routing protocols (such as ADV) in high mobility and traffic load. The improvement is more significant with higher mobility and traffic load. AODV-DFR sustains high packet delivery rates far beyond the saturating points for other routing protocols

Energy efficient routings and power control techniques in wireless networks have drawn considerable research interests recently. In this paper, we address the problem of energy efficient reliable routing in wireless networks in the presence of unreliable communication links or devices or lossy wireless link layers by integrating the power control techniques into the energy efficient routing. We study both the case when the link layer implements a perfect reliability and the case when the reliability is implemented through the transport layer, e.g., TCP. We study the energy efficient unicast when the links are unreliable. Subsequently, we study how to perform power control (thus, controlling the reliability of each communication link) such that the unicast routings use the least power when the communication links are unreliable. We presented both centralized algorithms and distributed algorithms for all the questions we studied. We conducted extensive simulations to study the power consumption, the end-to-end delay, and the network throughput of our protocols compared with existing protocols

The 802.11 standard supports multiple data transmission rates. To achieve a high performance under varying conditions, wireless stations need to adapt their transmission rate dynamically. Typically, stations with 802.11b products would reduce their bit rate from 11 Mbps to 5.5, 2, or 1 Mbps if they are far away from an access point (AP) and subject to significant signal fading and interference. This leads to considerable rate diversity, particularly when the network is congested. Under such conditions, aggregate throughput of WLANs will be degraded drastically (M. Heusse et al., 2003) because the basic CSMA/CA channel access method would guarantee an equal long term CAP (channel access probability) to all hosts. The main contribution of this paper is the proposal of an algorithm that can be implemented at both the AP and the wireless stations (WSs) with the purpose of guaranteeing fairness and improving the aggregate throughput of 802.11b multi-rate WLANs, We use COT (channel occupancy time) as fairness index instead of the CAP to analyze the fairness of WLANs. With our algorithm, the AP and wireless stations in the WLAN can achieve COT-based fairness by adjusting their packet length, sending the multiple back-to-back packets at one time, or giving up an opportunity to access the channel. Through exclusive simulations, we show that our algorithm leads to significant improvements in aggregate throughput and provides COT-fairness under multi-rate condition

In this paper, we propose a novel on-demand routing protocol called backup source routing (BSR) to establish and maintain backup routes that can be utilized after the primary path breaks. The key advantage of BSR is the reduction of the frequency of route discovery flooding, which is recognized as a major overhead in on-demand protocols. We define a new routing metric, called the route reliability, and use it to provide the basis for the backup path selection. We use a heuristic cost function to develop an analytical model and an approximation method to measure this metric. Various algorithms for our BSR protocol in the route discovery phase and route maintenance phase have been designed based on this cost function. Extensive simulations demonstrated that our routing strategy has two interesting features: 1) in less stressful situations of lower mobility, BSR has similar performance to DSR, 2) in more challenging situations of high mobility, BSR can improve the performance significantly.

The packet-level traffic characteristics in the Internet are so complex that it is natural to do traffic engineering (TE) and control at the flow level. The emerging multi-protocol label switching (MPLS) has introduced an attractive solution to TE in IP networks. The main objective of this paper is to balance traffic at the flow level among the parallel label switched paths (LSPs) in MPLS networks. We first introduce a multipath load-balancing model at the flow level. In this model, each LSP is modeled as an M/G/1 processor-sharing queue. Based on the analysis of the model, we propose a heuristic but efficient mechanism that is implemented only at the ingress label switched routers (LSRs) and egress LSRs in the network. Extensive simulations using NS2 are performed with MPLS modules. The simulation results show that the load through the network is well balanced so that the network throughput is improved and the delay is decreased significantly.

Seasonal ARIMA model is a good traffic model capable of capturing the behavior of a network traffic stream. In this paper, we give a general expression of seasonal ARIMA models with two periodicities and provide procedures to model and to predict traffic using seasonal ARIMA models. Our feasibility study experiments showed that seasonal ARIMA models could be used to model and predict actual wireless traffic such as GSM traffic in China.

Significant TCP unfairness in ad hoc wireless networks has been reported during the past several years. This unfairness results from the nature of the shared wireless medium and location dependency. If we view a node and its interfering nodes to form a "neighborhood", the aggregate of local queues at these nodes represents the distributed queue for this neighborhood. However, this queue is not a FIFO queue. Flows sharing the queue have different, dynamically changing priorities determined by the topology and traffic patterns. Thus, they get different feedback in terms of packet loss rate and packet delay when congestion occurs. In wired networks, the Randomly Early Detection (RED) scheme was found to improve TCP fairness. In this paper, we show that the RED scheme does not work when running on individual queues in wireless nodes. We then propose a Neighborhood RED (NRED) scheme, which extends the RED concept to the distributed neighborhood queue. Simulation studies confirm that the NRED scheme can improve TCP unfairness substantially in ad hoc networks. Moreover, the NRED scheme acts at the network level, without MAC protocol modifications. This considerably simplifies its deployment.

This paper proposes a novel bandwidth reservation mechanism called the multipath bandwidth splitting reservation (MBSR) for ad hoc networks. In MBSR, an overall bandwidth B-quest is split into several smaller bandwidth requests, and these requests will be reserved on multiple disjoint paths respectively. Both theoretical analysis and simulation results prove that the probability of successful reservation of MBSR is higher than that of single-path reservation, In addition, simulation results show that the MBSR can improve the reserved packet ratio of QoS traffic, the packet delivery ratio and the end-to-end delay of both best-effort traffic and QoS traffic.

With the rising popularity of delay-sensitive real-time multimedia applications (video, voice, data) in wireless local area networks (WLANs), it is becoming important to study the delay performance of WLANs. When the medium access control (MAC) protocol is taken into consideration, the access contention delay is a key problem. In this paper, based on a Markov model, we analyze delay performance of the IEEE 802.11 distributed coordination function (DCF). In addition, through extensive simulations, we calculate the delay performance of both basic access and RTS/CTS access mechanism of the 802.11 protocol.

In this paper, we propose a new adaptive load balancing mechanism for MPLS networks in that core LSRs are not required to perform traffic engineering. Based on measurements, we obtain the average one-way delay between a pair of label switched routers (LSR), and dynamically distribute traffic load among multiple label switched paths (LSP) according to this average. Simulation results indicate that our approach improves end-to-end throughput and decreases packet loss probability. Our work demonstrates that our algorithm is robust and simple to use.

A load-balancing scheme has a significant effect on the performance of the multipath routing protocol, especially in an ad hoc network environment. In order to analyze the effect on the distribution of input traffic among multiple paths in MSR (multipath source routing), we first established a network queuing model that would incorporate the cross-traffic among these paths. We then considered the load balancing as an optimization problem. The solution to the optimization problem is interestingly in accordance with the heuristic equation proposed by Wang ICC'2001 (2001). Our simulation results show that MSR with load balancing is so effective that the end-to-end delay is decreased significantly while the network resource can be utilized more efficiently than that in DSR (dynamic source routing).

In this paper, we propose a new multipath routing protocol for ad hoc wireless networks-multipath source routing (MSR), which is an extension of DSR (dynamic source routing). Based on the measurement of RTT, we propose a scheme to distribute load among multiple paths. The simulation results show that our approach improves the packet delivery ratio and the throughput of TCP and UDP, and reduces the end-to-end delay and the average queue size, while adding little overhead. As a result, MSR decreases the network congestion and increases the path fault tolerance quite well.

The FARIMA (p,d,q) model is a good traffic model capable of capturing both the long-range and short-range behavior of a network traffic stream in time. In this paper, we propose a prediction-based admission control algorithm for an integrated service packet network. We suggest a method to simplify the FARIMA model fitting procedure and hence to reduce the time of traffic modeling and prediction. Our feasibility-study experiments showed that FARIMA models which have number of parameters could be used to model and predict actual traffic on quite a large time scale.

Previous traffic measurements have found the coexistence of both long-range and short-range dependence in network traffic. Therefore, models are required to predict traffic that has both long-range and short-range dependence. This paper provides a procedure to model and predict traffic using FARIMA (p,d,q) models. Our experiments illustrate that the FARIMA model is a good model and is capable of capturing the property of actual traffic. We provide guidelines to simplify the FARIMA model fitting procedure and thus to reduce the time of traffic modeling and prediction.