25 research outputs found
Hydrologic response of an alpine watershed: Application of a meteorological wireless sensor network to understand streamflow generation
No full textA field measurement campaign was conducted from June to October 2009 in a 20 km2 catchment of the Swiss Alps with a wireless network of 12 weather stations and river discharge monitoring. The objective was to investigate the spatial variability of meteorological forcing and to assess its impact on streamflow generation. The analysis of the runoff dynamics highlighted the important contribution of snowmelt from spring to early summer. During the entire experimental period, the streamflow discharge was dominated by base flow contributions with temporal variations due to occasional rainfall-runoff events and a regular contribution from glacier melt. Given the importance of snow and ice melt runoff in this catchment, patterns of near-surface air temperatures were studied in detail. Statistical data analyses revealed that meteorological variables inside the watershed exhibit spatial variability. Air temperatures were influenced by topographic effects such as slope, aspect, and elevation. Rainfall was found to be spatially variable inside the catchment. The impact of this variability on streamflow generation was assessed using a lumped degree-day model. Despite the variability within the watershed, the streamflow discharge could be described using the lumped model. The novelty of this work mainly consists in quantifying spatial variability for a small watershed and showing to which extent this is important. When the focus is on aggregated outputs, such as streamflow discharge, average values of meteorological forcing can be adequately used. On the contrary, when the focus is on distributed fields such as evaporation or soil moisture, their estimate can benefit from distributed measurements.EFLUMLCA
Target Transmission Radius over LMST for Energy-Efficient Broadcast Protocol in Ad Hoc Networks.
No full textWe investigate minimum energy broadcasting problem where mobile nodes have the capability to adjust their transmission range. Two formulas are generally used when considering this problem. The first, E = r^alpha, depends only on the transmitting range r of a node, while the second, E = r^alpha + c, considers some constant costs independent of the range, like signal processing. The latter seems to be more realistic and is widely used in literature. In this paper, we show that with this second energy consumption model, it is not always optimal to minimize the transmission range. Furthermore, we demonstrate that there exists an optimal radius, computed with an hexagonal tiling of the network area, that minimizes the power consumption. We propose also a localized broadcast algorithm which takes this optimal radius into account. This protocol is shown to be efficient in our comparison with other protocols like LBOP or BIP
Smaller Connected Dominating Sets in Ad Hoc and Sensor Networks based on Coverage by Two-Hop Neighbors
No full textInternational audienceIn this paper, we focus on the construction of an efficient dominating set in ad hoc and sensor networks. A set of nodes is said to be dominating if each node is either itself dominant or neighbor of a dominant node. Application of such a set may for example be broadcasting, where the size of the set greatly impacts on energy consumption. Obtaining small sets is thus of prime importance. As a basis for our work, we use a heuristic given by Dai and Wu for constructing such a set. Their approach, in conjunction with the elimination of message overhead by Stojmenovic, has been recently shown to be an excellent compromise with respect to a wide range of metrics. In this paper, we present an enhanced definition to obtain smaller sets in the specific case where 2-hop information is considered. In our new definition, a node u is not dominant if there exists in its 2-hop neighborhood a connected set of nodes with higher priorities that covers u and its 1-hop neighbors. This new rule requires the same level of knowledge used by the original heuristic: only neighbors of nodes and neighbors of neighbors must be known to apply it. However, it takes advantage of some topological knowledge originally not taken into account, that may be used to deduce communication links between 1-hop and 2-hop neighbors. We provide the proof that the new set is a subset of the one obtained with the original heuristic. We also give the proof that our set is always dominating for any graph, and connected for any connected graph. Two versions are considered: with topological and positional information, which differ in whether or not nodes are aware of links between their 2-hop neighbors that are not 1-hop neighbors. An algorithm for locally applying the concept at each node is described. We finally provide experimental data that demonstrates the superiority of our rule in obtaining smaller dominating sets. A centralized algorithm is used as a benchmark in the comparisons. The overhead of the size of connected dominating set is reduced by about 15% with the topological variant and by about 30% with the positional variant of our new definition
A dominating sets and target radius based activity scheduling and minimum energy broadcast protocol for ad hoc and sensor networks
No full text
A Turnover based Adaptive HELLO Protocol for Mobile Ad Hoc and Sensor Networks
No full textInternational audienceWe present a turnover based adaptive HELLO protocol (TAP), which enables nodes in mobile networks to dynamically adjust their HELLO messages frequency depending on the current speed of nodes. To the best of our knowledge, all existing solutions are based on specific assumptions (\eg{} slotted networks) and/or require specific hardware (\eg{} GPS) for speed evaluation. One of the key aspects of our solution is that no additional hardware is required since it does not need this speed information. TAP may be used in any kind of mobile networks that rely on HELLO messages to maintain neighborhood tables and is thus highly relevant in the context of ad hoc and sensor networks. In our solution, each node has to monitor its neighborhood table to count new neighbors whenever a HELLO is sent. This \emph{turnover} is then used to adjust HELLO frequency. To evaluate our solution, we propose a theoretical analysis based on some given assumptions that provides the optimal turnover when these assumptions hold. Our experimental results demonstrate that when this optimal value is used as the targeted turnover in TAP, the HELLO frequency is correctly adjusted and provides a good accuracy with regards to the neighborhood tables
Optimal Transmission Radius for Energy Efficient Broadcasting Protocols in Ad Hoc and Sensor Networks
No full textInternational audienceWe investigate the problem of minimum energy broadcasting in ad hoc networks where nodes have capability to adjust their transmission range. The minimal transmission energy needed for correct reception by neighbor at distance r is proportional to r^alpha + c_e, alpha and c_e being two environment-dependent constants. We demonstrate the existence of an optimal transmission radius, computed with a hexagonal tiling of the network area, that minimizes the total power consumption for a broadcasting task. This theoretically computed value is experimentally confirmed. The existing localized protocols are inferior to existing centralized protocols for dense networks. We present two localized broadcasting protocols, based on derived 'target' radius, that remain competitive for all network densities. The first one, TR-LBOP, computes the minimal radius needed for connectivity and increases it up to the target one after having applied a neighbor elimination scheme on a reduced subset of direct neighbors. In the second one, TR-DS, each node first considers only neighbors whose distance is no greater than the target radius (which depends on the power consumption model used), and neighbors in a localized connected topological structure such as RNG or LMST. Then, a connected dominating set is constructed using this subgraph. Nodes not selected for the set may be sent to sleep mode. Nodes in selected dominating set apply TR-LBOP. This protocol is the first one to consider both activity scheduling and minimum energy consumption as one combined problem. Finally, some experimental results for both protocols are given, as well as comparisons with other existing protocols. Our analysis and protocols remain valid if energy needed for packet receptions is charged
