Ridha Soua

A survey on energy efficient techniques in wireless sensor networks

The 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.

MODESA: An optimized multichannel slot assignment for raw data convergecast in wireless sensor networks

In aerospace applications, wireless sensor networks (WSNs) collect data from sensor nodes towards a sink in a multi-hop convergecast structure. The throughput requirement of these applications is difficult to meet with a single wireless channel. That is why, in this paper, we focus on a multichannel time slot assignment that minimizes the data gathering cycle. We first formalize the problem as a linear program and compute the optimal time needed for a raw data convergecast in various multichannel topologies. These optimal times apply to sinks equipped with one or several radio interfaces. We then propose our algorithm called MODESA and prove its optimality in various multichannel topologies. We evaluate its performances in terms of number of slots, maximum buffer size and number of active/sleep switches per node. Furthermore, we present variants of MODESA achieving a load balancing between the channels used.

Multichannel assignment protocols in wireless sensor networks

With the spectacular development in radio and MEMS technologies, having sensor nodes capable of efficiently tuning their frequency over different channels is becoming more and more straightforward. For instance, TelosB motes can communicate on multiple frequencies as specified in the 802.15.4 standard. This reality has given birth to the multichannel communication paradigm in Wireless Sensor Networks (WSNs). While, multichannel communication obviously mitigates interferences, jamming and congestion, it also raises a number of challenging issues. In this paper, we set out to present a picture of multichannel assignment protocols in WSNs. After identifying the reasons of resorting to multichannel communication paradigm in WSNs and the specific issues that should be tackled, we propose a classification of multichannel assignment protocols, pointing out different channel selection policies, channel assignment categories and channel assignment methods. We conclude by a recapitulative table presenting many examples of existing multichannel protocols designed for WSNs and highlight promising research directions.

Sensors Deployment Enhancement by a Mobile Robot in Wireless Sensor Networks

An inherent concern for a wireless sensor network(WSN)is the coverage problem. Sensors are usually deployed in the wild to create a network of sensors intended to monitor or control a target area: Sensor networks are assumed unattended in various environments such as disaster areas, hazard fields, or battle fields. However, random node deployment often makes initial sensing holes inside the deployed area inevitable even in an extremely high density network. Furthermore, enhancing coverage is important for sensor networks to provide continuous sensing services. The most challenging aspects of the studies conducted on this topic have been supporting autonomous system with self maintenance capability where sensors and robots work together. This paper proposes to use a mobile robot to assist the initial sensors deployment and to improve sensing coverage and connectivity of monitored area. Given a set of points of interest on the surface, we study how to guide the robot to effectively eliminate coverage holes and collect redundant sensors. We propose a set of heuristics for this problem and we will verify the performance through simulation. The superior coverage and connectivity efficiency of the proposed approach is demonstrated by conducting a comparative analysis and simulation with a greedy approach.

Wave: a distributed scheduling algorithm for convergecast in IEEE 802.15.4e TSCH networks

The IEEE 802.15.4e MAC amendment has been proposed to meet the requirements of industrial applications. Using slotted medium access with channel hopping, the MAC layer orchestrates the medium accesses of nodes according to a given schedule. Nevertheless, this amendment does not specify how this schedule is computed. The purpose of this paper is to propose a distributed joint time slot and channel assignment, called Wave, for data gathering in low-power lossy networks. This schedule targets minimised data convergecast delays by reducing the total number of slots in the schedule. Moreover, Wave ensures the absence of conflicting transmissions in the schedule provided. In such a schedule, a node is awake only during its transmission slots and those of its children in the convergecast routing graph. Thus, energy efficiency is ensured. In this paper, we present Wave with its properties e.g. support of heterogeneous traffic, support of a sink equipped with multiple interfaces, worst case delays and buffer size and compare it with a centralised scheduling algorithm like TMCP and a distributed one like DeTAS. Simulation results show the good performance of Wave compared with TMCP. Because in an industrial environment, several routing graphs can coexist, we study how Wave supports this coexistence. Copyright

A survey on multichannel assignment protocols in Wireless Sensor Networks

Micaz motes can communicate on multiple frequencies as specified in the 802.15.4 standard. This reality has given birth to multichannel communication paradigm in Wireless Sensor Networks (WSNs). Obviously, multichannel communication mitigates interferences, jamming and congestion, whereas it brings also challenging issues. Thus, in this paper, we are motivated to draw a picture of multichannel assignment protocols in WSNs. After having identified the reasons of resorting to multichannel communication paradigm in WSNs and the specific issues that should be tackled, we propose a classification of multichannel assignment protocols, pointing out different channel selection policies, channel assignment methods and channel coordination techniques. We conclude by a recapitulative table including many examples of existing multichannel protocols designed for WSNs.

A Distributed Joint Channel and Slot Assignment for Convergecast in Wireless Sensor Networks

In this work, we study raw convergecast in multichannel wireless sensor networks (WSNs) where the sink may be equipped with multiple radio interfaces. We propose Wave, a simple and efficient distributed joint channel and time slot assignment. We evaluate the number of slots needed to complete the convergecast by simulation and compare it to the optimal schedule and to a centralized solution.

An Adaptive Strategy for an Optimized Collision-Free Slot Assignment in Multichannel Wireless Sensor Networks

Convergecast is the transmission paradigm used by data gathering applications in wireless sensor networks (WSNs). For efficiency reasons, a collision-free slotted medium access is typically used: time slots are assigned to non-conflicting transmitters. Furthermore, in any slot, only the transmitters and the corresponding receivers are awake, the other nodes sleeping in order to save energy. Since a multichannel network increases the throughput available to the application and reduces interference, multichannel slot assignment is an emerging research domain in WSNs. First, we focus on a multichannel time slot assignment that minimizes the data gathering delays. We compute the optimal time needed for a raw data convergecast in various multichannel topologies. Then, we focus on how to adapt such an assignment to dynamic demands of transmissions (e.g., alarms, temporary additional application needs and retransmissions). We formalize the problem using linear programming, and we propose an incremental technique that operates on an optimized primary schedule to provide bonus slots to meet new transmission needs. We propose AMSA, an Adaptive Multichannel Slot Assignment algorithm, which takes advantage of bandwidth spatial reuse, and we evaluate its performances in terms of the number of slots required, slot reuse, throughput and the number of radio state switches.

DiSCA: A distributed scheduling for convergecast in multichannel wireless sensor networks

The new IEEE 802.15.4e standard does not specify how the schedule of medium accesses followed by wireless sensors is built. That is why, we propose a distributed interference-aware joint channel and time slot assignment, called DiSCA, for a traffic-aware convergecast in multichannel wireless sensor networks (WSNs). Unlike most previous studies, we consider two cases of transmissions: without acknowledgment and with immediate acknowledgment. We provide the minimum bound on the number of time slots needed for a convergecast with a sink equipped with multiple radio interfaces. Simulations results show that DiSCA is close to the optimal in terms of the number of slots and outperforms TMCP.

MUSIKA: A multichannel multi-sink data gathering algorithm in wireless sensor networks

A typical task in wireless sensor networks (WSNs) is to collect data from sensor nodes towards one or many sinks in a multi-hop convergecast structure. In this paper, we focus on the data gathering problem with differentiated traffic, each addressed to a specific sink in multichannel WSNs. In order to find a collision-free optimized multichannel time slot assignment that minimizes the data gathering cycle, we propose a centralized traffic-aware algorithm called MUSIKA. We formulate the problem as a linear program and compute the optimal time needed for a raw data convergecast in an illustrative example. More generally, we run simulations on various network topologies to evaluate the performance of MUSIKA in terms of cycle length, maximum buffer size and slot reuse ratio for different use cases: redundant functional processing chains, different application functionalities per sink.