Multihop data delivery through vehicular ad hoc networks is complicated by the fact that vehicular networks are highly mobile and frequently disconnected. To address this issue, we adopt the idea of carry and forward, where a moving vehicle carries a packet until a new vehicle moves into its vicinity and forwards the packet. Being different from existing carry and forward solutions, we make use of predictable vehicle mobility, which is limited by traffic pattern and road layout. Based on the existing traffic pattern, a vehicle can find the next road to forward the packet to reduce the delay. We propose several vehicle-assisted data delivery (VADD) protocols to forward the packet to the best road with the lowest data-delivery delay. Experimental results show that the proposed VADD protocols outperform existing solutions in terms of packet-delivery ratio, data packet delay, and protocol overhead. Among the proposed VADD protocols, the Hybrid Probe (H-VADD) protocol has a much better performance.

Increasing need for people to be "connected"; while at the same time remain as mobile as ever poses several interesting issues in wireless networks. It is conceivable in the near-future that wireless "hotspots" experience flash crowds-like traffic arrival pattern. A common phenomena in the Internet today characterized by sudden and unpredicted increase in popularity of on-line content.

Abstract — Data caching can significantly improve the efficiency of information access in a wireless ad hoc network by reducing the access latency and bandwidth usage. However, designing efficient distributed caching algorithms is non-trivial when network nodes have limited memory. In this article, we consider the cache placement problem of minimizing total data access cost in ad hoc networks with multiple data items and nodes with limited memory capacity. The above optimization problem is known to be NPhard. Defining benefit as the reduction in total access cost, we present a polynomial-time centralized approximation algorithm that provably delivers a solution whose benefit is at least one-fourth (one-half for uniform-size data items) of the optimal benefit. The approximation algorithm is amenable to localized distributed implementation, which is shown via simulations to perform close to the approximation algorithm. Our distributed algorithm naturally extends to networks with mobile nodes. We simulate our distributed algorithm using a network simulator (ns2), and demonstrate that it significantly outperforms another existing caching technique (by Yin and Cao [31]) in all important performance metrics. The performance differential is particularly large in more challenging scenarios, such as higher access frequency and smaller memory. Index Terms- caching placement policy, ad hoc networks, algorithm/protocol design and analysis, simulations. I.

Abstract—Vehicular ad hoc networks (VANETs) have recently received considerable attention. To support VANET-based applications, it is important to disseminate data from an information source (data center) to many vehicles on the road. Although disseminating data from a server to a large number of clients has been studied in the database community and the network community, many unique characteristics of the VANET bring out new research challenges. In this paper, we propose a data pouring (DP) and buffering paradigm to address the data dissemination problem in a VANET. In DP, data are periodically broadcast to vehicles on the road. In DP with intersection buffering (DP-IB), data poured from the source are buffered and rebroadcast at the intersections. We provide analytical models to explore the dissemination capacity (DC) of the proposed schemes. The analytical models also provide guidelines on choosing the system parameters to maximize the DC under different delivery ratio requirements. Simulation results show that the proposed DP-IB scheme can significantly improve the data delivery ratio and reduce network traffic. Index Terms—Ad hoc networks, broadcasting, data dissemination, dissemination capacity, vehicular networks. I.

As vehicular networks become popular, more and more people want to access data from their vehicles. When many vehicles want to access data through a roadside unit, data scheduling becomes an important issue. In this paper, we identify some challenges in vehicle-roadside data access. As vehicles move pretty fast, the requests should be served quickly. Also, vehicles may upload data to the roadside unit, and hence the download and upload requests compete for the same bandwidth. To address these challenges, we propose several scheduling schemes. We first propose a basic scheduling scheme called D ∗ S to consider both service deadline and data size. We then enhance it by using a single broadcast to serve multiple requests. Finally, we identify the effects of upload requests on data quality, and propose a Two-Step scheduling scheme to provide a balance between serving download and update requests. Simulation results show that the Two-Step scheduling scheme outperforms other scheduling schemes.

Emerging multi-hop wireless mesh networks have much different characteristics than the Internet. They have low dimensionality and large diameters. Content and service replication can greatly improve their scalability. However, replication strategies in such networks have not been well studied. This paper studies the optimality of replication strategies and explores it in multi-hop wireless mesh networks for the first time. We start with the problem of determining the optimal numbers of replicas for a set of objects which have distinct probabilities of being requested in large 2-D mesh networks. We reveal the structure of the optimal replication strategy to minimize object access cost. To minimize average cost to access an object in 2-D mesh networks, the optimal strategy replicates an object such that the number of its replicas is proportional , where p is the access probability of the object. This result indicates the inefficiency of demand-driven content and service replication in 2-D mesh networks, where an object is replicated such that the number of its replicas is proportional to p. We further study practical, online algorithms to approximate the optimal strategy. Interestingly, the optimal replication can be approximated well by a localized replacement algorithm. The algorithm utilizes only handy information and incurs no communication overhead. The paper demonstrates a significant performance gain by the optimal strategy, and the effectiveness of the online replacement algorithm.

Nodes in wireless ad hoc networks are often limited in terms of resources, such as storage, power, and bandwidth. A downside of this is the fact that local storage at one node cannot accommodate the vast amount of data contained in the network. In this paper, we present Shared-State, a scheme for storage, replication, and distribution of common-interest data in wireless networks of resourceconstrained devices (e.g. sensor nodes or embedded devices). SharedState works under the assumption that individual nodes would greatly benefit from having access to the wealth of information in the network, but are unable to store it locally at once. SharedState strives to make data available to every node by providing local access to a subset of the whole collection of data items in the network at any moment in time and ensuring that this subset is updated periodically. This is accomplished by probabilistic propagation and replication of data items, ensuring the availability and persistence of information in the face of changing network conditions. We evaluate the performance of SharedState by studying the effectiveness with which nodes can gather information from the network. In addition, we optimize the bandwidth usage of our proposed solution by minimizing unnecessary communication based on feedback from the local neighborhood. 1.

Abstract — In this paper we focus on the problem of content distribution in wireless ad hoc networks. Our goal is to study the performance of a cooperative content distribution mechanism to distribute content from one source to a potentially large number of destinations. Despite the large literature on content distribution schemes available for wired settings we argue that the very nature of the underlying ad hoc network poses new challenges that cannot be addressed with current schemes. We propose a cooperative peer-to-peer scheme that allows parallel download of the content based on swarming protocols. Our scheme builds a distribution overlay network that takes into account traffic locality and allows peers to trade parts of the content while sustaining cooperation. We evaluate through simulations the performance of our scheme for different static scenarios using a variety of metrics to characterize the impact of our solution at different layers of the system stack. Our results highlight the great benefits of our solution in terms of system fairness, achievable throughput, and energy consumption. We also study the scalability properties of our solution under the extended network model. I.

Location-based spatial queries (LBSQs) refer to spatial queries whose answers rely on the location of the inquirer. Efficient processing of LBSQs is of critical importance with the ever-increasing deployment and use of mobile technologies. We show that LBSQs have certain unique characteristics that traditional spatial query processing in centralized databases does not address. For example, a significant challenge is presented by wireless broadcasting environments, which often exhibit high-latency database access. In this paper, we present a novel query processing technique that, while maintaining high scalability and accuracy, manages to reduce the latency considerably in answering location-based spatial queries. Our approach is based on peer-to-peer sharing, which enables us to process queries without delay at a mobile host by using query results cached in its neighboring mobile peers. We illustrate the appeal of our technique through extensive simulation results. 1.

In this paper, we address an optimization problem that arises in context of cache placement in sensor networks. In particular, we consider the cache placement problem where the goal is to determine a set of nodes in the network to cache/store the given data item, such that the overall communication cost incurred in accessing the item is minimized, under the constraint that the total communication cost in updating the selected caches is less than a given constant. In our network model, there is a single server (containing the original copy of the data item) and multiple client nodes (that wish to access the data item). For various settings of the problem, we design optimal, near-optimal, heuristic-based, and distributed algorithms, and evaluate their performance through simulations on randomly generated sensor networks. 1