Abdelmalik Bachir

MAC Essentials for Wireless Sensor Networks

The wireless medium being inherently broadcast in nature and hence prone to interferences requires highly optimized medium access control (MAC) protocols. This holds particularly true for wireless sensor networks (WSNs) consisting of a large amount of miniaturized battery-powered wireless networked sensors required to operate for years with no human intervention. There has hence been a growing interest on understanding and optimizing WSN MAC protocols in recent years, where the limited and constrained resources have driven research towards primarily reducing energy consumption of MAC functionalities. In this paper, we provide a comprehensive state-of-the-art study in which we thoroughly expose the prime focus of WSN MAC protocols, design guidelines that inspired these protocols, as well as drawbacks and shortcomings of the existing solutions and how existing and emerging technology will influence future solutions. In contrast to previous surveys that focused on classifying MAC protocols according to the technique being used, we provide a thematic taxonomy in which protocols are classified according to the problems dealt with. We also show that a key element in selecting a suitable solution for a particular situation is mainly driven by the statistical properties of the generated traffic.

Neighbor Discovery with Activity Monitoring in Multichannel Wireless Mesh Networks

One way of improving performance of wireless mesh networks is to use multiple non-overlapping channels. At the same time, the mesh network must continuously self-adapt to varying radio conditions and topology changes. Thus, we propose a neighbor discovery protocol that fits the requirements of multichannel networks while dealing at the same time with the deafness problem. The proposed scheme also takes advantage of neighbor discovery to continually monitor channel activity. We provide a theoretical analysis of the average discovery time. Our simulations show that the solution integrated within Molecular MAC, a multichannel MAC, results in efficient discovery and channel assignment.

Preamble sampling MAC protocols with persistent receivers in wireless sensor networks

We provide an analytical framework for preamble sampling techniques for MAC protocols in wireless sensor networks, from which we derive closed-form formulas for lifetime and reliability calculations. In addition to take into account transmitter behavior that controls the form and the content of the transmitted preamble, our model also considers receiver behavior that controls the duration of preamble reception in case of successful and failed reception. Along with both transmitter and receiver behavior, our model considers a non-perfect channel and thus takes into account the impacts of transmission errors and retransmissions on lifetime and reliability of preamble sampling protocols. Numerical results show that no protocol is universally optimal; that is, each protocol has its own optimal operation point that depends on the given channel and load conditions.

Joint Connectivity-Coverage Temperature-Aware Algorithms for Wireless Sensor Networks

Temperature variations have a significant effect on low power wireless sensor networks as wireless communication links drastically deteriorate when temperature increases. A reliable deployment should take temperature into account to avoid network connectivity problems resulting from poor wireless links when temperature increases. A good deployment needs also to adapt its operation and save resources when temperature decreases and wireless links improve. Taking into account the probabilistic nature of the wireless communication channel, we develop a mathematical model that provides the most energy efficient deployment in function of temperature without compromising the correct operation of the network by preserving both connectivity and coverage. We use our model to design three temperature-aware algorithms that seek to save energy (i) by putting some nodes in hibernate mode as in the Stop-Operate (SO) algorithm, or (ii) by using transmission power control as in Power-Control (PC), or (iii) by doing both techniques as in Stop-Operate Power-Control (SOPC). All proposed algorithms are fully distributed and solely rely on temperature readings without any information exchange between neighbors, which makes them low overhead and robust. Our results identify the optimal operation of each algorithm and show that a significant amount of energy can be saved by taking temperature into account.

Energy-Efficient Broadcasts in Wireless Sensor Networks with Multiple Virtual Channels

Multichannel solutions are increasingly used to cope with the problem of low capacity in sensor networks resulting from high contention during wake-up periods of nodes. We can consider wake-up schedules as virtual channels, because nodes using different schedules cannot communicate with each other. In this paper, we show that multiple virtual channel solutions come at the cost of an increased energy consumption in broadcasts. We analyze the problem of broadcasting over multiple virtual channels under different classes of MAC methods and propose Clustered Virtual Channels (CVC), a new network structure that limits the number of frames needed for maintaining multiple virtual channels synchronized. Our simulation results show that CVC reduces the cost of maintaining synchronization and increases capacity while making all types of broadcasts possible.

Energy Efficient Network Structure for Synchronous Preamble Sampling in Wireless Sensor Networks

We propose a new energy efficient network structure for maintaining synchronization in access methods based on Synchronous Preamble Sampling. Our scheme limits the number of synchronization messages and increases network capacity through the use of multiple non-interfering virtual channels. It consists in constructing independent clusters based on the Weakly Connected Dominating Set (WCDS) so that they can use different virtual channels and only need to maintain internal synchronization, while still offering global connectivity. We define a distributed and self-stabilizing algorithm for constructing and maintaining the clusters. Our simulation results show that the proposed scheme has comparable energy consumption to Scheduled Channel Polling, but results in better network capacity. Moreover, it achieves better energy savings and network capacity than recently proposed Crankshaft access method.

Block design multichannel MAC protocol for WSNs

In this paper, we aim at reducing the problems related to the use of a single channel by designing a multichannel protocol that allows interference mitigation, delay and collision reduction, as well as throughput improvement while still reducing idle listening through a receiver-based scheduling of communication slots. We design our protocol in a fully distributed way so that failure of nodes or links could be recovered by local message exchange. To achieve these features, we make use of combinatorial block design theory. Block Design is a system of subsets of a finite set which satisfies certain conditions related to the frequency of appearance of pairs of elements of the set in the subsets of the system. Our proposed solution increases the throughput, and completely eliminates the deafness problem without causing a large overhead. To validate our solution on large scale networks, we developed our proposal on ns3, which has improved features over traditional simulators. Simulation results show that our Latin Square based channel assignment significantly reduces collisions and end to end delay thereby making it suitable for most sensor network applications.

Temperature-Aware Density Optimization for Low Power Wireless Sensor Networks

High temperatures negatively affect the quality of radio communication links both at transmission and reception sides. In this paper, we investigate the effect of temperature on connectivity and show that more energy can be saved by allowing some nodes to go to deep sleep mode when temperature decreases and links improve. We propose a simple and fully distributed temperature-aware algorithm that dynamically adapts the network effective density to allow further energy savings while maintaining network connectivity.

Preamble MAC protocols with non-persistent receivers in wireless sensor networks

In preamble sampling MAC protocols, nodes keep their radios off most of the time to reduce idle listening and periodically wake up for a short time to check whether there is an ongoing transmission on the channel. Such access methods result in substantial energy savings in low traffic conditions. In this paper, we compare several representative preamble sampling MAC protocols in which receivers are non-persistent. Our analysis takes into account bit error rate and traffic load to compute energy consumption and link reliability. Our results show that two access methods obtain the longest normalized lifetime for a wide range of bit error rates: MFP (Micro Frame Preamble) and DFP (Data Frame Preamble).

Distributed cell scheduling for multichannel IoT MAC protocols

We provide a distributed solution to the scheduling of slots over multiple channels in low power wireless sensor networks organized in data gathering tree which are the topologies that are expected to be deployed in the Internet of Things (IoT). Our solution generates a dynamic and distributed schedule that achieves high throughput, low packet errors and collisions, as well as low energy consumption by avoiding deafness and reducing both overhead and overhearing. In our solution, nodes do not communicate large numbers of control message as local topology construction is only based on local link exchange to construct 2-hop neighborhood. To reach our goal, we chose to make use of Combinatorial Design theory, particularly Block Design. Within Block Design, we particularly focused on Latin Squares/Latin Rectangles (LS/LR), and Balanced Incomplete Block Design (BIBD). We evaluate the performance of our solution by comparing it with DiSCA (Distributed Scheduling for Convergecast in Multichannel WSN) and show that we obtain better results in terms of throughput, packet delivery rate, and energy consumption. Our results are based on our implementation of both protocols on NS-3.26.