Joint Routing and STDMA-based Scheduling to Minimize Delays in Grid Wireless Sensor Networks

In this report, we study the issue of delay optimization and energy efficiency in grid wireless sensor networks (WSNs). We focus on STDMA (Spatial Reuse TDMA)) scheduling, where a predefined cycle is repeated, and where each node has fixed transmission opportunities during specific slots (defined by colors). We assume a STDMA algorithm that takes advantage of the regularity of grid topology to also provide a spatially periodic coloring ("tiling" of the same color pattern). In this setting, the key challenges are: 1) minimizing the average routing delay by ordering the slots in the cycle 2) being energy efficient. Our work follows two directions: first, the baseline performance is evaluated when nothing specific is done and the colors are randomly ordered in the STDMA cycle. Then, we propose a solution, ORCHID that deliberately constructs an efficient STDMA schedule. It proceeds in two steps. In the first step, ORCHID starts form a colored grid and builds a hierarchical routing based on these colors. In the second step, ORCHID builds a color ordering, by considering jointly both routing and scheduling so as to ensure that any node will reach a sink in a single STDMA cycle. We study the performance of these solutions by means of simulations and modeling. Results show the excellent performance of ORCHID in terms of delays and energy compared to a shortest path routing that uses the delay as a heuristic. We also present the adaptation of ORCHID to general networks under the SINR interference model

A comparative study of energy efficient routing strategies based on OLSR

Energy efficiency is a key issue in wireless ad hoc and sensor networks. In order to maximize network lifetime, several directions have been explored, among them energy efficient routing. In this report, we show how to extend the standardized OLSR routing protocol, in order to make it energy efficient. To take into account residual node energy, the native selection of multipoint relays of OLSR is changed. Three selection algorithms based on the minimum residual energy are evaluated and the best one is chosen. The OLSR extension we propose, selects the path minimizing the energy consumed in the end-to-end transmission of a flow packet and avoids nodes with low residual energy. As it has been shown that two-path routing is energy efficient, we compare this extension with a two-path source routing strategy (with different links or different nodes). An extensive performance evaluation allows us to conclude that our proposal maximizes both network lifetime and the amount of data delivered

Worst case end-to-end response times for non-preemptive FP/DP* scheduling

In this paper, we are interested in real-time flows requiring quantitative and deterministic Quality of Service (QoS) guarantees. We focus more particularly on two QoS parameters: the worst case end-to-end response time and jitter. We consider a non-preemptive scheduling of flows, called FP/DP*, combining fixed priority and dynamic priority, where the dynamic priority of a flow packet is assigned on the first node visited by the packet in the network. Examples of such a scheduling are FP/FIFO* and FP/EDF*. With any flow is associated a fixed priority denoting the importance of the flow from the user point of view. The arbritation between packets having the same fixed priority is done according to their dynamic priority. A packet can be transmitted only if (i) there is no packet having a higher fixed priority and (ii) there is no packet having a higher dynamic priority. A classical approach used to compute the worst case end-to-end response time is the holistic one, but it leads to pessimistic upper bounds. We propose the trajectory approach to improve the accuracy of the results. Indeed, the trajectory approach only considers worst case scenarios experienced by a flow along its trajectory. It then eliminates scenarios that cannot occur in the network

TRASA: TRaffic Aware Slot Assignment Algorithm in Wireless Sensor Networks

International audienceIn data gathering applications which is a typical application paradigm in wireless sensor networks, sensor nodes may have different traffic demands. Assigning equal channel access to each node may lead to congestion, inefficient use of the bandwidth and decrease of the application performance. In this paper, we prove that the time slot assignment problem is NP-complete when p-hop nodes are not assigned the same slot, with 1 <= p <= h for any strictly positive integer h. We propose TRASA, a TRaffic Aware time Slot Assignment algorithm able to allocate slots to sensors proportionally to their demand. We evaluate the performance of TRASA for different heuristics and prove that it provides an optimized spatial reuse and a minimized cycle length

SERENA: an energy-efficient strategy to schedule nodes activity in wireless ad hoc and sensor networks

In wireless ad hoc and sensor networks, an analysis of the node energy consumption distribution shows that the largest part is due to the time spent in the idle state. This result is at the origin of SERENA, an algorithm to SchEdule RoutEr Nodes Activity. SERENA allows router nodes to sleep, while ensuring end-to-end communication in the wireless network. It is a localized and decentralized algorithm assigning time slots to nodes. Any node stays awake only during its slots and the slots assigned to its neighbors, it sleeps the remaining time. SERENA is based on distributed and localized two-hop coloring. The node's color is then mapped in time slot. Thus, each node is ensured to get at least one time slot, it also gets additional time slots proportionally to its traffic rate. Such a solution adapts to varying traffic rates and supports late node arrivals. A performance evaluation allows us to compare SERENA coloring algorithm with existing ones such as DLF, both in terms of number of colors and complexity. Simulation results show that SERENA enables us to maximize network lifetime while increasing the number of user messages delivered. We quantify the slot reuse and evaluate the impact of the frame size on network performance. We then study how to dimension buffers at the router nodes. Finally, we show how SERENA improves the node energy consumption distribution and maximizes the energy efficiency of wireless ad hoc and sensor networks

A survey on energy efficient techniques in wireless sensor networks

International audienceThe myriad of potential applications supported by wireless sensor networks (WSNs) has generated much interest from the research community. Various applications range from small size low industrial monitoring to large scale energy constrained environmental monitoring. In all cases, an operational network is required to fulfill the application missions. In addition, energy consumption of nodes is a great challenge in order to maximize network lifetime. Unlike other networks, it can be hazardous, very expensive or even impossible to charge or replace exhausted batteries due to the hostile nature of environment. Researchers are invited to design energy efficient protocols while achieving the desired network operations. This paper focuses on different techniques to reduce the consumption of the limited energy budget of sensor nodes. After having identified the reasons of energy waste in WSNs, we classify energy efficient techniques into five classes, namely data reduction, control reduction, energy efficient routing, duty cycling and topology control. We then detail each of them, presenting subdivisions and giving many examples. We conclude by a recapitulative table

Optimal Number of Message Transmissions for Probabilistic Guarantee in the IoT

International audienceThe Internet of Things (IoT) is now experiencing its first phase of industrialization. Industrial companies are completing proofs of concept and many of them plan to invest in automation, flexibility and quality of production in their plants. Their use of a wireless network is conditioned upon its ability to meet three Key Performance Indicators (KPIs), namely a maximum acceptable end-to-end latency L, a targeted end-to-end reliability R and a minimum network lifetime T. The IoT network has to guarantee that at least R% of messages generated by sensor nodes are delivered to the sink with a latency ≤ L, whereas the network lifetime is at least equal to T. In this paper, we show how to provide the targeted end-to-end reliability R by means of retransmissions to cope with the unreliability of wireless links. We present two methods to compute the maximum number of transmissions per message required to achieve R. M F air is very easy to compute, whereas M Opt minimizes the total number of transmissions necessary for a message to reach the sink. M F air and M Opt are then integrated into a TSCH network with a load-based scheduler to evaluate the three KPIs on a generic data-gathering application. We first consider a toy example with eight nodes where the maximum number of transmissions M axT rans is tuned per link and per flow. Finally, a network of 50 nodes, representative of real network deployments, is evaluated assuming M axT rans is fixed. For both TSCH networks, we show that M Opt provides a better reliability and a longer lifetime than M F air, which provides a shorter average end-to-end latency. M Opt provides more predictable end-to-end performances than Kausa, a KPI-aware, state-of-the-art scheduler

Evaluation of the Bandwidth Needed at the MAC 802.11b Level

Mobile ad-hoc networks (MANETs) have many advantages, self-adaptivity for instance, that make them attractive for multiple applications. Most of these networks use the MAC 802.11b protocol for the medium access control. As all nodes use the same transmission frequency, interferences can occur compromising the quality of service (QoS) provided to flows. In this report, we show how to evaluate the bandwidth required at the MAC level for a flow whose characteristics are known at the application level. The bandwidth evaluation on a node accounts for the interferences due to the flow itself and the other flows. This evaluation has been validated by confrontation with results obtained by NS-2 simulations. We then propose an efficient admission control based on this evaluation. An example illustrates the proposed solution and highlights the accuracy of the evaluation

Analysis of Multipoint Relays Selection in the OLSR Routing Protocol with and without QoS Support

Mobile ad hoc networks have very attractive intrinsic qualities. However they will be adopted only if they are able to support applications with QoS requirements. They must provide a route providing the QoS requested by a flow. The OLSR routing protocol can be extended for that purpose. OLSR relies on multipoint relay (MPR) selection that has an important effect on the routing protocol's performances. Indeed, the overhead generated by the OLSR protocol and more particularly the flooding efficiency depend on MPR selection. Moreover, MPRs are used as intermediate nodes in the routes. The analysis of MPR selection presented in this report gives quantitative results and also takes into consideration QoS support. Simulations on large and dense networks show that our analysis is highly accurate

Introducing QoS support in Bluetooth Piconetwith a Class-Based EDF Scheduling

In this paper, we focus on the Bluetooth wireless network, analyzing its ability to support Quality of Service (QoS) requirements defined by the application. In particular, we are interested in two QoS parameters: (i) an application constraint denoting the importance degree of a message, and (ii) its delivery deadline. The QoS perceived by the application depends on the efficiency of the scheduling schemes chosen at the medium access layer. We define the minimal knowledge level required by a scheduling scheme to support these QoS constraints. As an example of classical scheduling schemes, we analyze performances of One-Round Robin (1-RR) and show that it does not provide a sufficient service differentiation. To achieve better service differentiation, we first present enhancements accounting locally for the two QoS parameters. These enhancements are applied to 1-RR scheduling scheme and we then give a comparison between the two versions. These comparisons are done by evaluating in each class, the average message response time and the percentage of messages missing their deadline. We then introduce enhancements in the intra-piconet scheduling. So, we define a new Bluetooth global scheduling, called Class-Based Earliest Deadline First (CB-EDF) that takes into account both locally and globally these two QoS parameters. Simulation results show that CB-EDF achieves a good service differentiation and allows the coexistence of messages with different application constraints on the same ACL link. Moreover, CB-EDF is a flexible solution that adapts itself to the provided knowledge level