Modeling and performance analysis of ad hoc broadcasting schemes

Broadcasting is a technique widely used for distributing control packets in ad hoc networks. The traditional flooding scheme has been proven to unnecessarily consume network capacity and may lead to severe packet collisions in high-density networks. New schemes have been proposed for alleviating this so-called broadcast storm problem and their efficiencies are usually analyzed and compared by ns-2 simulations. However, little work has been done on mathematical modeling and rigorous analysis. In this paper, we focus on two popular ad hoc broadcasting schemes and provide their detailed analysis in one-dimensional and two-dimensional ideal networks. The statistical results obtained have revealed new relationships between network parameters and the performance metrics. These results are useful for optimally setting network parameters in designing protocols. It is also expected that the analytical methods developed will lay a solid foundation for the development of mathematical models for other ad hoc broadcast and multicast schemes.     

Improving hybrid ad hoc networks: The election of gateways

The selection of an appropriate and stable route that enables suitable load balancing of Internet gateways is an important issue in hybrid mobile ad hoc networks. The variables employed to perform routing must ensure that no harm is caused that might degrade other network performance metrics such as delay and packet loss. Moreover, the effect of such routing must remain affordable, such as low losses or extra signaling messages. This paper proposes a new method, Steady Load Balancing Gateway Election, based on a fuzzy logic system to achieve this objective. The fuzzy system infers a new routing metric named cost that considers several networks performance variables to select the best gateway. To solve the problem of defining the fuzzy sets, they are optimized by a genetic algorithm whose fitness function also employs fuzzy logic and is designed with four network performance metrics. The promising results confirm that ad hoc networks are characterized by great uncertainty, so that the use of Computational Intelligence methods such as fuzzy logic or genetic algorithms is highly recommended.     

POPEYE: providing collaborative services for ad hoc and spontaneous communities

Next generation collaborative systems will offer mobile users seamless and natural collaboration amongst a diversity of agents, within distributed, knowledge-rich and virtualized working environments. This ambitious goal faces numerous challenges from the underlying communication infrastructure to the high level application services, with the aim to provide services with the appropriate quality (such as persistence, synchronization, and security). Most currently available tools supporting collaboration address either rather traditional and rigid intra-organizational collaboration scenarios or, at the opposite, completely free and unstructured open communities’s interactions. Emerging dynamic, flexible and ad hoc collaboration schemes are hardly or not supported at all. The POPEYE framework offers collaborative services for applications that aim to enable spontaneous collaboration over P2P wireless ad hoc groups, where fixed infrastructure is not a prerequisite, where virtual communities can emerge spontaneously and share data with the appropriate quality of service for business applications (persistence, synchronization, security, etc.).     

Dynamic frame length channel assignment in wireless multihop ad hoc networks

A good channel assignment scheme in a multihop ad hoc network should not only guarantee successful data transmissions without collisions but also enhance the channel spatial reuse to maximize the system throughput. From the channel assignment schemes in time division multiple access (TDMA) slot assignment protocols developed in previous studies, we have found that these protocols do not have a convenient frame length shrink scheme after the expansion of the frame length. As the network size grows, the frame length expands quickly, particularly when we set the frame length as a power of two. A very long frame may result in poor channel utilization when it contains many unused slots. In this paper, we propose a dynamic frame length expansion and recovery method called dynamic frame length channel assignment (DFLCA). This strategy is designed to make better use of the available channels by taking advantage of the spatial reuse concept. In DFLCA, the increase in the spatial reuse is achieved by adding certain amount of control overhead. We show that the bandwidth saved due to the channel spatial reuse is larger than the additional bandwidth spent on the control overhead.     

Guided interaction: A mechanism to enable ad hoc service interaction

Ad hoc interaction between web services and their clients is a worthwhile but seemingly distant goal. At present, most of the interest in web services is focused on pre-planned B2B interaction. Clients interact with services using advance knowledge of the data and sequence requirements of the service and pre-programmed calls to their interfaces. This type of interaction cannot be used for ad hoc interaction between services and their clients such as mobile devices moving in and around rich dynamic environments because clients may not have the necessary knowledge in advance. For unplanned ad hoc interaction an interaction mechanism is required that does not require clients to have advance knowledge of programmatic service interfaces and interaction sequences. The mechanism must ensure clients with different resources and diverse competencies can successfully interact with newly discovered services by providing assistance such as disambiguation of terminology, alternative types of inputs, and context sensitive error reporting when necessary. This paper introduces a service interaction mechanism called guided interaction. Guided interaction is designed to enable clients without prior knowledge of programmatic interfaces to be assisted to a successful outcome. The mechanism is grounded in core computing primitives and based on a dialogue model. Guided interaction has two parts; the first part is a language for the exchange of information between services and their clients. The second part is a language for services to create interaction plans that allow them to gather the data they require from clients in a flexible way with the provision of assistance when necessary. An interpreter uses the plan to generate and interpret messages in the exchange language and to manage the path of the dialogue.

Energy efficient multicast routing in ad hoc wireless networks

In this paper, we discuss the energy efficient multicast problem in ad hoc wireless networks. Each node in the network is assumed to have a fixed level of transmission power. The problem of our concern is: given an ad hoc wireless network and a multicast request, how to find a multicast tree such that the total energy cost of the multicast tree is minimized. We first prove this problem is NP-hard and it is unlikely to have an approximation algorithm with a constant performance ratio of the number of nodes in the network. We then propose an algorithm based on the directed Steiner tree method that has a theoretically guaranteed approximation performance ratio. We also propose two efficient heuristics, node-join-tree (NJT) and tree-join-tree (TJT) algorithms. The NJT algorithm can be easily implemented in a distributed fashion. Extensive simulations have been conducted to compare with other methods and the results have shown significant improvement on energy efficiency of the proposed algorithms.     

Understanding the real behavior of Mote and 802.11 ad hoc networks: an experimental approach

IEEE 802.11 and Mote devices are today two of the most interesting wireless technologies for ad hoc and sensor networks respectively, and many efforts are currently devoted to understanding their potentialities. Unfortunately, few works adopt an experimental approach, though several papers highlight that popular simulation and analytical approximations may lead to very inaccurate results. In this paper we discuss outcomes from an extensive measurement study focused on these technologies. We analyze the dependence of the communication range on several parameters, such as node distance from the ground, transmission data rate, environment humidity. Then, we study the extent of the physical carrier sensing zone around a sending node. On the basis of these elements, we provide a unified wireless link model for both technologies. Finally, by using this model we analyze well-known scenarios (such as the hidden node problem), and we modify the traditional formulations according to our experimental results.     

Scalability of routing methods in ad hoc networks

In an ad hoc network each host (node) participates in routing packets. Ad hoc networks based on 802.11 WLAN technology have been the focus of several prior studies. These investigations were mainly based on simulations of scenarios involving up to 100 nodes (usually 50 nodes) and relaxed (too unrealistic) data traffic conditions. Many routing protocols in such setting offer the same performance, and many potential problems stay undetected. At the same time, an ad hoc network may not want (or be able) to limit the number of hosts involved in the network. As more nodes join an ad hoc network or the data traffic grows, the potential for collisions and contention increases, and protocols face the challenging task to route data packets without creating high administrative load. The investigation of protocol behavior in large scenarios exposes many hidden problems. The understanding of these problems helps not only in improving protocol scalability to large scenarios but also in increasing the throughput and other QoS metrics in small ones. This paper studies on the example of AODV and DSR protocols the influence of the network size (up to 550 nodes), nodes mobility, nodes density, suggested data traffic on protocols performance. In this paper we identify and analyze the reasons for poor absolute performance that both protocols demonstrate in the majority of studied scenarios. We also propose and evaluate restructured protocol stack that helps to improve the performance and scalability of any routing protocol in wireless ad hoc networks.     

Contention-aware data caching in wireless multi-hop ad hoc networks

This paper studies a challenging problem of cache placement in wireless multi-hop ad hoc networks. More specifically, we study how to achieve an optimal tradeoff between total access delay and caching overheads, by properly selecting a subset of wireless nodes as cache nodes when the network topology changes. We assume a data source updates a data item to be accessed by other client nodes. Most of the existing cache placement algorithms use hop counts to measure the total cost of a caching system, but hop delay in wireless networks varies much due to the contentions among these nodes and the traffic load on each link. Therefore, we evaluate the per-hop delay for each link according to the contentions detected by a wireless node from the MAC layer. We propose two heuristic cache placement algorithms, named Centralized Contention-aware Caching Algorithm (CCCA) and Distributed Contention-aware Caching Algorithm (DCCA), both of which detect the variation of contentions and the change of the traffic flows, in order to evaluate the benefit of selecting a node as a cache node. We also apply a TTL-based cache consistency strategy to maintain the delta consistency among all the cache nodes. Simulation results show that the proposed algorithms achieve better performance than other alternative ones in terms of average query delay, caching overheads, and query success ratio.     

GeoQuorums: implementing atomic memory in mobile ad hoc networks

We present a new approach, the GeoQuorums approach, for implementing atomic read/write shared memory in mobile ad hoc networks. Our approach is based on associating abstract atomic objects with certain geographic locations. We assume the existence of focal points, geographic areas that are normally “populated” by mobile nodes. For example, a focal point may be a road junction, a scenic observation point, or a water resource in the desert. Mobile nodes that happen to populate a focal point participate in implementing a shared atomic object, using a replicated state machine approach. These objects, which we call focal point objects, are prone to occasional failures when the corresponding geographic areas are depopulated. The GeoQuorums algorithm uses the fault-prone focal point objects to implement atomic read/write operations on a fault-tolerant virtual shared object. The GeoQuorums algorithm uses a quorum-based strategy in which each quorum consists of a set of focal point objects. The quorums are used to maintain the consistency of the shared memory and to tolerate limited failures of the focal point objects, which may be caused by depopulation of the corresponding geographic areas. We present a mechanism for changing the set of quorums on the fly, thus improving efficiency. Overall, the new GeoQuorums algorithm efficiently implements read and write operations in a highly dynamic, mobile network.     

Modelling incentives for collaboration in mobile ad hoc networks

This paper explores a model for the operation of an ad hoc mobile network. The model incorporates incentives for users to act as transit nodes on multi-hop paths and to be rewarded with their own ability to send traffic. The paper explores consequences of the model by means of fluid-level simulations of a network and illustrates the way in which network resources are allocated to users according to their geographical position.     

Virtual node based adaptive routing in wireless ad hoc networks

It is a challenge to make the routes quickly adapt to the changed network topology when nodes fail in a wireless ad hoc network. In this paper, we propose an adaptive routing protocol, which groups the network nodes into virtual nodes according to their data transfer capabilities and creates virtual-node-based routes. The protocol can accommodate the routes to node failures by adaptively pdating the virtual nodes and just-in-time using available nodes during data transmission. The simulations indicate that the proposed protocol can keep the routes failed-node-freewhen the available virtual node members cover the failed nodes scattering area.     

Enhancing data security in ad hoc networks based on multipath routing

An ad hoc network is a self-organizing network of wireless links connecting mobile nodes. The mobile nodes can communicate without an infrastructure. They form an arbitrary topology, where the nodes play the role of routers and are free to move randomly.     

GRAP: Grey risk assessment based on projection in ad hoc networks

In this paper, we discuss the risk assessment of ad hoc networks, which have highly dynamic topology, open access of wireless channels, and vulnerable data communication. Conventional risk assessment methods are subjective and unreliable as some nodes reveal little information, and the quantity of samples is limited in ad hoc networks. To solve this problem, we propose a GRAP method, which includes grey relational projection (GRP), grey prediction, and grey decision making. Our scheme is designed to assess nodes’ risk under limited circumstances such as small number of samples, incomplete information and lack of experience. Compared with principal component analysis, GRAP has demonstrated better performance and more flexible characteristics. To further the practicability of this method, we utilize a dynamic grey prediction, which shows high accuracy for decision making. In our scheme, four major nodes’ attributes are selected, and the experiment results suggest that our model is more effective and efficient for risk assessment than principal component analysis in ad hoc networks.     

用于Ad hoc网络的鉴别路由协议及性能分析

剖析了多跳Ad hoc网络AODV与DSR路由协议的安全漏洞,并指出安全路由协议的设计需求。本文详细介绍了一种Ad hoc的鉴别路由协议ARAN,该协议采用公钥密码技术,利用节点对路由消息的签名,有效地抵制了各种恶意攻击,虽然在某种程度上增加了计算复杂度,提高了节点存储量,但仍不失为一种有效的按需安全路由协议,可以满足无线多跳Ad hoc网络在各种应用领域对路由的安全需求。     

Distributed power control in cooperative cognitive ad hoc networks

In this paper, a relay selection strategy and distributed power control algorithm are proposed for the underlay spectrum sharing mode based cooperative cognitive ad hoc network with energy-limited users. The study aims to minimize the total power consumption of cooperative cognitive ad hoc network while ensuring the quality of service (QoS) requirement of cognitive user and keeping the interference to primary user below interference tolerance. The power control problem is transformed into a convex optimization problem. Based on Lagrange dual decomposition theory, a gradient iterative algorithm is constructed to search for the optimal solution and complete distributed power optimization. Simulation results show that the algorithm converges fast and reduces transmit power of cognitive users effectively while guaranteeing the QoS requirement.     

Distributed cooperative spectrum sensing in cognitive radio for ad hoc networks

Cognitive radio refers to an intelligent radio with the capability of sensing the radio environment and dynamically reconfiguring the operating parameters. Recent research has focused on using cognitive radios in ad hoc environments. Spectrum sensing is the most important aspect of successful cognitive radio ad hoc network deployment to overcome spectrum scarcity. Multiple cognitive radio users can cooperate to sense the primary user and improve sensing performance. Cognitive radio ad hoc networks are dynamic in nature and have no central point for data fusion. In this paper, gradient-based fully distributed cooperative spectrum sensing in cognitive radio is proposed for ad hoc networks. The licensed band used for TV transmission is considered the primary user. The gradient field changes with the energy sensed by cognitive radios, and the gradient is calculated based on the components, which include energy sensed by secondary users and received from neighbors. The proposed scheme was evaluated from the perspective of reliable sensing, convergence time, and energy consumption. Simulation results demonstrated the effectiveness of the proposed scheme.     

RBC-OLSR: Reputation-based clustering OLSR protocol for wireless ad hoc networks

We consider the problem of assuring the trustworthiness (i.e. reliability and robustness) and prolonging the lifetime of wireless ad hoc networks, using the OLSR routing protocol, in the presence of selfish nodes. Assuring the trustworthiness of these networks can be achieved by selecting the most trusted paths, while prolonging the lifetime can be achieved by (1) reducing the number of relay nodes (MPR) propagating the topology control (TC) messages and (2) considering the residual energy levels of these relay nodes in the selection process. In this paper, we propose a novel clustering algorithm and a relay node selection algorithm based on the residual energy level and connectivity index of the nodes. This hybrid model is referred to as H-OLSR. The OLSR messages are adapted to handle the cluster heads election and the MPR nodes selection algorithms. These algorithms are designed to cope with selfish nodes that are getting benefits from others without cooperating with them. Hence, we propose an incentive compatible mechanism that motivates nodes to behave truthfully during the selection and election processes. Incentive retributions increase the reputation of the nodes. Since network services are granted according to nodes’ accumulated reputation, the nodes should cooperate. Finally, based on nodes’ reputation, the most trusted forwarding paths are determined. This reputation-based hybrid model is referred to as RH-OLSR. Simulation results show that the novel H-OLSR model based on energy and connectivity can efficiently prolong the network lifetime, while the RH-OLSR model improves the trustworthiness of the network through the selection of the most trusted paths based on nodes’ reputations. These are the two different processes used to define the reputation-based clustering OLSR (RBC-OLSR) routing protocol.     

闭合平面模型下CDMA自组织网络容量分析

为了更好的对直扩和跳频这两种方式下的CDMA自组织网络的容量进行分析和比较,本文采用了闭合平面模型对自组织网络节点情况进行建模,给出了在此模型下直扩和跳频两种方式网络容量公式并利用MonteCarlo方法进行了仿真。结果显示,链路数较大时跳频系统的容量首先随跳频点数增加而上升,在达到最大值后会持续下降并最终低于直扩系统的容量。跳频容量最大值以及达到跳频容量最大值时的跳频点数都随着链路数的增加而上升。因此跳频模式在容量上优于直扩模式是有条件的。本文的结论为跳频CDMA自组织网络系统的跳频点数选取提供了依据。     

Topology-transparent reservation time division multiple access in multihop ad hoc networks

In this paper, an optimal topology-transparent reservation time division multiple access (OTTR-TDMA) protocol is proposed for multihop ad hoc networks. Our MAC protocol is based on a slotted TDMA architecture in which every slot is divided into reservation phase and data transmission phase. Every node not only transmits data in its assigned slots that are computed by Chlamtac’s algorithm, but it also utilizes free slots among its non-assigned slots through reservation. Through theoretical analysis, we derive the proper parameter for the best performance. We compare our protocol with other TDMA protocols and find that it gives better performance. Simulation results show that they are consistent with our analytical results.