In multi-hop cellular networks, data packets have to be relayed hop by hop from a given mobile station to a base station and vice-versa. This means that the mobile stations must accept to forward information for the benefit of other stations. In this paper, we propose an incentive mechanism that is based on a charging/rewarding scheme and that makes collaboration rational for selfish nodes. We base our solution on symmetric cryptography to cope with the limited resources of the mobile stations. We provide a set of protocols and study their robustness with respect to various attacks. By leveraging on the relative stability of the routes, our solution leads to a very moderate overhead.

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We present a scheme for secure and privacy-preserving communication in hybrid ad hoc networks. Our scheme enables users to secure communication and to protect their anonymity and location privacy. Our approach is based on frequently changing node pseudonyms and cryptographic keys, which enable users to avoid being identified by the locations they visit, or by the type of tra#c they generate. We show how our scheme can be e#ectively used for secure and private routing in hybrid ad hoc networks. We study the robustness of the proposed solution with respect to various attacks. We further show that the proposed solution introduces a very moderate overhead to the network operation.

Ever increasing data traffic and limited capacity are major causes for congestion in current cellular systems. This paper presents a new architecture for the next generation wireless systems based on the integration of the cellular infrastructure and modern Ad-hoc relaying technologies. The new architecture can efficiently balance traffic loads between cells by using Ad-hoc relay stations (ARS) to relay traffic from one cell to another cell dynamically. This can not only increase a system's capacity cost-effectively, but also reduce transmission power for mobile hosts, and provide services for shadow areas. In this paper, we present the architectural concept including its basic operations and principle benefits. We also propose a seed-growing approach for ARS placement, and discuss the upper boundon the number of seed ARS's needed in the system. We evaluate the performance improvement of the new architecture through analysis and simulations. 1 Introduction Ever increasing data traffi...

Abstract — A mobile ad hoc network is a collection of wireless terminals that can be deployed rapidly. Its deficiencies include limited wireless bandwidth efficiency, low throughput, large delays, and weak security. Integrating it with a wellestablished cellular network can improve communication and security in ad hoc networks, as well as enrich the cellular services. This research proposes a cellular-aided mobile ad hoc network (CAMA) architecture, in which a CAMA agent in the cellular network manages the control information, while the data is delivered through the mobile terminals (MTs). The routing and security information is exchanged between MTs and the agent through cellular radio channels. A position-based routing protocol, the multi-selection greedy positioning routing (MSGPR) protocol, is proposed. At times due to the complicated radio environment, the position information is not precise. Even in these cases, the MT can still find its reachable neighbors (the association) by exchanging ”hello ” messages. This association is used in complement with the position information to make more accurate routing decisions. Simulation results show that the delivery ratio in the ad hoc network is greatly improved with very low cellular overhead. The security issues in the proposed architecture and the corresponding solutions are addressed. The experimental study shows that CAMA is much less vulnerable than a pure ad hoc network. Index Terms — heterogeneous networks, ad hoc networks, cellular networks, quality of service, security I.

Abstract—In this paper, we study the effect of multihop relaying on the throughput of the downstream channel in cellular networks. In particular, we compare the throughput of the multihop system with that of the conventional cellular system, demonstrating the achievable throughput improvement by the multihop relaying. We also propose a hybrid control strategy for the multihop relaying, in which we advocate the use of both, the direct transmission and the multihop relaying. Our study shows that most of the throughput gain can be obtained with the use of a two- and three-hop relaying scheme. Substantial throughput improvement could be additionally obtained by operating the concurrent relaying transmission in conjunction with the nonconcurrent transmission. We also argue here that the multihop relaying technology can be utilized for mitigating unfairness in quality-of-service (QoS), which comes about due to the location-dependent signal quality. Our results show that the multihop system can provide more even QoS over the cell area. The multihop cellular network architecture can also be utilized as a self-configuring network mechanism that efficiently accommodates variability of traffic distribution. We have studied the throughput improvement for the uniform, as well as for the nonuniform traffic distribution, and we conclude that the use of multihop relaying in cellular networks would be relatively robust to changes in the actual traffic distribution. Index Terms—Ad hoc network, cellular network, code-division multiple access (CDMA), concurrent transmission, downstream channel, fairness, multihop relaying, self-configuring network, throughput. I.

Abstract—A hybrid ad hoc network is a structure-based network that is extended using multihop communications. Indeed, in this kind of network, the existence of a communication link between the mobile station and the base station is not required: A mobile station that has no direct connection with a base station can use other mobile stations as relays. Compared with conventional (single-hop) structure-based networks, this new generation can lead to a better use of the available spectrum and to a reduction of infrastructure costs. However, these benefits would vanish if the mobile nodes did not properly cooperate and forward packets for other nodes. In this paper, we propose a charging and rewarding scheme to encourage the most fundamental operation, namely packet forwarding. We use “MAC layering ” to reduce the space overhead in the packets and a stream cipher encryption mechanism to provide “implicit authentication ” of the nodes involved in the communication. We analyze the robustness of our protocols against rational and malicious attacks. We show that—using our solution—collaboration is rational for selfish nodes. We also show that our protocols thwart rational attacks and detect malicious attacks. Index Terms—Network-level security and protection, wireless communication, authentication security, payment schemes. 1

Abstract—We consider usage of campus wireless LANs (WLANs) consisting of access points (AP) with potentially noncontiguous coverage. Through surveys on mobility patterns and wireless network usage on the University of Southern California (USC) campus, we find that mobility and usage patterns exhibit significant differences across various types of locations on campus. Using the collected data we build a realistic mobility model that we call Weighted-Way Point (WWP), to better simulate wireless network user behavior in a university campus environment. Using WWP, we show that unbalanced wireless network usage and hotspots are likely to occur on campus. We further propose a mechanism to alleviate the local hotspot congestion by using multi-hop ad hoc networks. When a MN determines the local AP is unable to provide satisfactory bandwidth to an on-going flow, it requests the flow to be switched to a neighboring access point (NAP). Our mechanism differs from other schemes by allowing MNs to make the decision of initiating the flow-switching procedure and using bi-directional route-discovery from both the switching MN and NAP to reduce the route discovery delay. We use simulations to show that with this flow-switching mechanism, flows are more evenly distributed across APs. We also show that our mechanism reduces congestion time for popular APs and improves the user-perceived quality. Keywords-Ad hoc network, wireless LAN, congestion alleviation I.

In this paper, we propose a link layer design for mobile hotspots. We design a novel system architecture that enables high-speed Internet access in railway systems. The proposed design uses a number of repeaters placed along the track, and multiple antennas installed on roof of vehicle. Each packet is decomposed into smaller fragments and relayed to the vehicle via adjacent repeaters. We also use erasure coding to add parity fragments to original data. This approach is called information raining since fragments are rained upon the vehicle from adjacent repeaters. We investigate two instances of information raining. In blind information raining, all repeaters awaken when they sense the presence of the vehicle. The fragments are then blindly transmitted via awakened repeaters. A vehicle station installed inside the train is responsible to aggregate enough number of fragments. In the throughput-optimized information raining, the vehicle station selects a bipartite matching between repeaters and roof-top antennas, and activates only a subset of the repeaters. It also dictates the amount of transmission power of each activated repeater. Both the bipartite matching and power allocations are individually shown to be NP-complete. Matching heuristics based on Hungarian algorithm and Gale-Shapley algorithm are proposed. A simplex-type algorithm is proposed as the power allocation heuristics.

Fixed infrastructured networks naturally support centralized approaches for group management and information provisioning. Contrary to infrastructured networks, in multi-hop ad-hoc networks each node acts as a router as well as sender and receiver. Some applications, however, requires hierarchical arrangements that—for practical reasons—has to be done locally and selforganized. An additional challenge is to deal with mobility that causes permanent network partitioning and re-organizations. Technically, these problems can be tackled by providing additional uplinks to a backbone network, which can be used to access resources in the Internet as well as to inter-link multiple ad-hoc network partitions, creating a hybrid wireless network. In this paper, we present a prototypically implemented hybrid wireless network system optimized for multimedia content distribution. To efficiently manage the ad-hoc communicating devices a weighted clustering algorithm is introduced. The proposed localized algorithm deals with mobility, but does not require geographical information or distances. Categories and Subject Descriptors C.2.1 [Network Architecture and Design]: Distributed networks, network communications, network topology, wireless