1,721,033 research outputs found
Design and Evaluation of Protocol Stacks for Underwater Communications
No full textThe project revolves around three themes: (i) understanding the physics of acoustic propagation and its impact on the design of communication algorithms and network protocols, (ii) design of network protocols that are theoretically sound and suited to the needs of underwater applications, and (iii) experimental demonstration. The latter activity will benefit from Prof. Basagni collaborations with Woods Hole Oceanograhic Institute and with La Spezia NURC (Nato Underwater Research Center). Such collaborations will allow us to test our ideas in real settings, using equipments whose cost (in the million of Euros) would otherwise be not affordable, having impact on cutting edge ocean engineering
A logarithmic lower bound for time-spread multiple access protocols
No full textTime-Spread Multiple-Access (TSMA) protocols are scheduled access protocols for mobile multi-hop radio networks that guarantee deterministic access to the shared channel regardless of the possibility of radio interference. In scheduled access methods, time is considered to be slotted and time slots are cyclically organized into frames. In general, the shorter the frame, the more efficient the protocol. An Ω(log log n) lower bound is known on the minimum length of the frame of TSMA protocols in networks with n nodes. In this note we improve that lower bound by characterizing the multiple access to the radio channel as a combinatorial problem. The proposed characterization allows us to prove that no TSMA protocols can successfully schedule the transmissions of the nodes of a multi-hop radio network in frames with less than log n time slots
A mobility-transparent deterministic broadcast mechanism for Ad Hoc networks
No full textBroadcast (distributing a message from a source node to all other nodes) is a fundamental problem in distributed
computing. Several solutions for solving this problem in mobile wireless networks are available, in which mobility is dealt with either by the use of randomized retransmissions or, in the case of deterministic delivery protocols, by using conflict-free transmission schedules. Randomized solutions can be used only when unbounded delays can be tolerated. Deterministic conflictfree solutions require schedule recomputation when topology changes, thus becoming unstable when the topology rate of
change exceeds the schedule recomputation rate. The deterministic broadcast protocols we introduce in this paper overcome the above limitations by using a novel mobility-transparent schedule,
thus providing a delivery (time) guarantee without the need to
recompute the schedules when topology changes. We show that the proposed protocol is simple and easy to implement, and that it is optimal in networks in which assumptions on the maximum
number of the neighbors of a node can be made
Bluetooth Scatternet Formation and Scheduling: An Integrated Solution
No full textBuilding and deploying multi-hop networks of Bluetooth devices (aka scatternets) concerns devising methods for forming piconets, connecting them through shared gateways, and scheduling the presence of these gateways among the piconets they interconnect (inter-piconet scheduling). There are several types of gateways, and their efficient scheduling is affected by the gateway type. Scatternet formation and scheduling have been dealt with separately in the past. This leads to network performance degradation because of the missed opportunity of designing scatternet formation protocols that best address scheduling requirements and vice-versa. In this paper we propose SS-Blue, an integrated mechanism for the joint design of scatternet formation and scheduling. Specifically, we enhance an efficient scatternet formation protocol by adopting methods for piconets interconnection that favor types of gateways which will result in a better performing inter-piconet scheduling. At the same time, a fair and traffic adaptive mechanism is proposed to schedule all types of gateways (inter-piconet scheduling), and for managing intra-piconet scheduling, i.e., for scheduling traffic transmission within a piconet. Our solution is evaluated through extensive simulations. Our results show that SS-Blue succeeds in producing scatternets whose gateways are efficiently scheduled. The combination of the proposed intra- and inter-piconet scheduling is shown to be remarkably effective in favoring packet forwarding with very low end-to-end latency
Optimized Packet Size Selection in Underwater WSN Communications
No full textIn this paper, we investigate the effect of packet size selection on the performance of media access control (MAC) protocols for underwater wireless sensor networks, namely, carrier sense multiple access (CSMA) and the distance-aware collision avoidance protocol (DACAP). Our comparative analysis, conducted via ns-2 simulations, considers scenarios with varying, nonzero bit error rate (BER) and interference. We investigate metrics such as throughput efficiency (the ratio between the delivered bit rate and the offered bit rate), end-to-end packet latency, measured “per meter” to allow for different sizes of deployment areas, and the energy consumed to correctly deliver an information bit to the network collection point. Our results show the dependence of these metrics on the packet size, indicating the existence of an optimum. The optimum packet size is found to depend on the protocol characteristics, the bit rate, and the BER. For each protocol and scenario considered, we determine the packet size that optimizes throughput performance, and we show its effect on the normalized packet latency and on energy consumption
Localized protocols for ad hoc clustering and backbone formation: A performance comparison
No full textThis paper concerns the comparative performance evaluation of protocols for clustering and backbone formation in ad hoc networks characterized by a large number of resource-constrained nodes. Our aim is twofold: We provide the first simulation-based detailed investigation of techniques for clustering and backbone formation that are among the most representative of this area of ad hoc research. Second, we delve into the nature of the selected protocols to assess the effects of the "degree of localization" on their operations, i.e., how being able to execute the protocol based only on local information affects the overall protocol performance. Extensive ns2-based simulation results show that highly localized protocols are rewarded with good performance with respect to all metrics of interest which include protocol duration, energy consumption, message overhead, route length, and backbone size
Limiting the propagation of localization errors in multi-hop wireless networks
No full textThis paper concerns a study of the process of localizing the nodes of a multi-hop wireless networks, i.e., of having the node computing their coordinates with respect to a suitable reference system. We consider networks where the nodes perform measurements of distance and angle of arrival from nodes within their transmission radius. We describe a simple localization protocol, termed Range-Based Centroid (RBC), that starting from a single node (the beacon) with given coordinates localizes all the network nodes with reasonable accuracy. We then propose a new localization protocol that achieves greater accuracy by containing the propagation of the localization error as the process progresses away from the beacon. We quantify the improvements of the proposed protocol, termed MEC 2 (for Minimum Enclosing Circle Containment) by simulations. In the considered scenarios, MEC 2 keeps the localization error within 21% of the nodes' transmission radius, with 20-30% improvements over RBC. © 2006 IEEE
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