LoRa networks represent a promising technology for Internet of Things applications due to their long range, low cost, and energy efficiency. However, their ALOHA-based access method and duty cycle restrictions can limit their scalability and reliability in high-density networks. To address such a challenge, this article proposes the autonomous time-slotted LoRa (ATS-LoRa), protocol that allows LoRaWAN nodes to autonomously determine their optimal transmission parameters without extensive downlink transmissions from the gateway. ATS-LoRa utilizes the geographical coordinates of the nodes and their gateway in a novel way to allow them to determine their appropriate transmission parameters, such as the spreading factor, the channel frequency, and the slot ID. ATS-LoRa performance is evaluated through extensive simulations under different operating conditions showing an average throughput of around 47 times better than the adaptive data rate algorithm of LoRaWAN protocol.

Time-Slotted Medium Access Control protocols bring advantages to the scalability of LoRa networks as an alternative to the ALOHA access method. However, such Time-Slotted protocols require nodes synchronization and schedules dissemination under stringent duty cycles likely resulting in improper performance and limited scalability. One possible solution is to adopt decentralized approaches where nodes autonomously determine their schedules and other transmission parameters. Thus, this paper proposes a novel Time-Slotted MAC protocol, named Autonomous Adaptive Frame Size (AAFS-LoRa) protocol, that allows nodes to individually determine their transmission parameters without extensive downlink transmissions from the gateway. The proposed protocol can conFigure nodes by maintaining information, such as their location and the gateway location. The main contribution of the proposed protocol is the adoption of adaptive frame sizes that are large enough to accommodate nodes with common transmission parameters to mitigate collisions among them. The proposed protocol has been investigated under different operating conditions, and the experiments demonstrates that our protocol can effectively improve the network performance, in terms of latency as well as the capacity.

Long-Range (LoRa) has been a major avenue for deploying the Internet of Things (IoT) in large scale environments due to its long-scale connection, energy efficiency, and cost-effectiveness. LoRa networks provide multiple configurable transmission parameters that greatly affect the performance of the overall network. To the best of our knowledge, the optimal combination of these parameters that can allow orthogonal simultaneous transmissions to be successfully decoded by the gateway has not been reported in the literature. Exploiting all the transmission parameters in the physical layer to find optimal combinations between them will inevitably increase the throughput of LoRa without affecting the energy consumption. In this paper, authors propose annulus-based distribution algorithm of LoRa transmission parameters to mitigate well-known and challenging issues, namely the capture effect and the limited scalability. The performance of the proposed algorithm has been compared with the Adaptive Data Rate(ADR) algorithm of LoRaWAN and the simulation results show that the proposed algorithm significantly outperforms the ADR especially in large-scale dense networks. Specifically, the proposed algorithm has improved the network throughput by an average of 59% compared to the legacy LoRaWAN.

Deriving a mobility model that mimics the motion of freely floating underwater acoustic sensor networks is of great importance as it greatly impacts the networking protocols efficiency. In this paper, we further investigate the mobility model proposed in [31] for freely floating and randomly deployed underwater acoustic sensors, where each sensor will end up sinking at a given depth and then follow a given trajectory due to the waves currents in addition to the sensor gravitational weight along with the buoyant force and the water resistance. Indeed, in this work we study the impact of the water velocity on the network connectivity and coverage. Along with the work proposed in [31], our study aims at providing the underwater networking community with a clearer understanding of the mobility challenges of freely floating underwater sensor networks that can be exploited to conceive more realistic communication protocols.

Collisions in underwater acoustic networks can not be tolerated due to the fundamental differences between underwater acoustic propagation and terrestrial radio propagation. Thus, conceiving medium access protocols that avoid collision to the most possible extent is of paramount importance. In this paper, a multi-channel MAC protocol, MC-UWMAC, especially designed for underwater acoustic sensor networks, is proposed and evaluated. MC-UWMAC is an energy efficient MAC protocol that aims at achieving a collision free communication. MC-UWMAC operates on a single slotted control channel to avoid the missing receiver problem and multiple data channels to improve the network throughput. To guarantee to the most possible extent a collision free communication, MC-UWMAC uses two key newly designed procedures: i) a grid based slot assignment procedure on the common slotted control channel that approaches the 2-hop conflict free slot assignment and ii) a quorum based data channel allocation procedure. More precisely, according to MC-UWMAC, a sender uses its own dedicated slot on the common control channel for handshaking with an intended neighbor receiver. However, data transmission takes place in a unique data channel especially reserved for this pair of neighbor nodes. In fact, MC-UWMAC reserves for each pair of neighbor nodes a unique data channel that aims at being 2-hop conflict free. As such, the probability of collision is highly reduced and even completely mitigated in some scenarios. In addition, by using multiple channels, MC-UWMAC allows multiple data communications along with handshaking on the common control channel to take place at the same time and hence the network throughput as well as energy efficiency are improved. Simulation results show that MC-UWMAC can greatly improve the network performance especially in terms of energy consumption, throughput, and end-to-end delay.

Underwater mobile acoustic sensor networks (UW-ASNs) require the design of new networking protocols due to fundamental differences with terrestrial wireless sensor networks. The performance of these protocols is highly impacted by the mobility of sensors, especially when they are freely floating. In such mobile UW-ASNs, nodes move with the water currents but are constrained by the gravitational weight of the sensor along with the water resistance and the buoyant force. A realistic mobility model that can reflect the physical movement of randomly scattered and freely floating sensor nodes under ocean currents provides clearer understanding of the communication challenges and hence helps conceiving efficient communication protocols. In this paper, we first propose an exhaustive physically inspired mobility model which meticulously captures the dynamics of underwater environments. We, then, study the resulting time evolution of network coverage and connectivity. Our objective is to provide the underwater network research community with a realistic mobility model that could be exploited in conceiving networking communication protocols such as routing, localization, and medium access. Namely, we show that the network mobility effect on coverage and connectivity is more significant in intermediately dense UW-ASNs. Less effect is recorded on the coverage and connectivity for low- and high-density UW-ASNs.

UnderWater Acoustic Sensor Networks (UW-ASNs) require protocols that make judicious use of the limited energy budget of the underwater sensor nodes. In this paper, we tackle the problem of energy holes in UW-ASNs. We show that we can balance the energy consumption through the network provided that sensors can use multiple transmission ranges when they send or forward the periodically generated data. In particular, we suppose that sensors can adjust their communication ranges up to three possible levels and we determine the set of possible next hops with the associated load weights that lead to a fair energy consumption among all underwater sensors. Hence energy holes can be avoided and consequently the network lifetime is highly increased.

Fundamental differences between underwater acoustic propagation and terrestrial radio propagation impose the design of new networking protocols. In this paper, a multichannel MAC protocol, MC-UWMAC, especially designed for underwater acoustic sensor networks, is proposed and evaluated. MC-UWMAC is a low power MAC protocol operating on multichannel using a single slotted control channel and multiple data channels. To guarantee a collision free communication, MC-UWMAC uses a virtual grid based slot assignment linked with a quorum based data channel allocation. Specifically, control channel slots are dedicated for handshaking. Data transmission takes place in a unique data channel especially reserved for each communicating pair. Simulation results show that MC-UWMAC can greatly improve the network performance especially in terms of energy consumption, packet delivery ratio and end-to-end delay.

Interest in underwater acoustic sensor networks (UW-ASNs) has rapidly increased with the desire to control the large portion of the world covered by oceans. Fundamental differences between underwater acoustic propagation and terrestrial radio propagation may impose the design of new networking protocols and management schemes. In this paper, we focus on these fundamental differences in order to conceive a balanced routing strategy that overcomes the energy holes problem. Indeed, energy management is one of the major concerns in UW-ASNs due to the limited energy budget of the underwater sensor nodes. In this paper, we tackle the problem of energy holes in UW-ASNs while taking into consideration the unique characteristics of the underwater channel. The main contribution of this study is an in-depth analysis of the impact of these unique underwater characteristics on balancing the energy consumption among all underwater sensors. We prove that we can evenly distribute the transmission load among sensor nodes provided that sensors adjust their communication power when they send or forward the periodically generated data. In particular, we propose a balanced routing strategy along with the associated deployment pattern that meticulously determines the load weight for each possible next hop, that leads to fair energy consumption among all underwater sensors. Consequently, the energy holes problem is overcome and hence the network lifetime is improved.

Abstract Interest in underwater acoustic sensor networks (UW‐ASNs) has rapidly increased with the desire to control the large portion of the world covered by oceans. Energy efficiency is one of the major concerns in UW‐ASNs due to the limited energy budget of the underwater sensor nodes. In this paper, we tackle the problem of energy holes in UW‐ASNs while taking into consideration the unique characteristics of the underwater channel. We prove that we can evenly distribute the transmission load among sensor nodes provided that sensors adjust their communication range when they send or forward the periodically generated data. In particular, we propose a balanced routing strategy along with the associated deployment pattern that meticulously determines the load weight for each possible next hop that leads to fair energy consumption among all underwater sensors. Consequently, the energy holes problem is overcome, and hence, the network lifetime is improved. To the best of our knowledge, this is the first work that addresses the energy hole problem in UW‐ASNs. Copyright © 2016 John Wiley & Sons, Ltd.

In this paper, we propose UW-OFDMAC, a distributed Medium Access Control (MAC) protocol tuned for Under-Water Acoustic Sensor Networks (UW-ASNs). It is a transmitter based Orthogonal Frequency Division Multiple Access (OFDMA)scheme that integrates an original power and OFDMA parameters self-assignment algorithm to set the optimal transmit power, subcarrier spacing and guard interval duration. UW-OFDMAC aims at achieving two objectives, namely, guarantee high bandwidth efficiency and low energy consumption. Simulation results show that UW-OFDMAC outperforms the basic OFDMA protocol tuned for the underwater environment.

Wireless sensor networks (WSNs) require energy- efficient protocols to improve the network lifetime. In this work, we adopt a cross-layer strategy that considers routing and MAC layers jointly. At the routing layer, we propose balancing the traffic through the WSN. We show that sending the traffic generated by each sensor node through multiple paths instead of using a single path allows significant energy conservation. On the other hand, at the MAC layer, we propose to control the retry limit of retransmissions over each wireless link. We show that by efficiently adjusting the retry limit for each link, further energy conservation can be achieved, improving thus the network lifetime. A new analytical model for the joint optimization system is complemented by simulations in order to quantitatively evaluate the benefits of our proposal.

Energy conservation is a primary concern in wireless sensor networks due to the limited capacity of the sensor nodes' batteries. In this paper, we study the relationship between sensor networks performance, particularly its lifetime, and the number of reporting nodes N by using both analytical and simulation approaches. We first show that decreasing N increases considerably the network lifetime. Moreover, we demonstrate that the average time required to report an event is a convex function of N. Based on these results, and as a main contribution, we prove that the optimal number of reporting nodes enabling the shortest latency to report reliably an event does not really lead to the most efficient way of energy consumption. In this paper, we analyze the tradeoff between these two requirements. We provide a simple methodology to achieve this tradeoff which is specific to each sensor application, depending on its particular needs.

Wireless sensor networks (WSNs) require appropriate protocols that make judicious use of the finite energy resources of the sensor nodes. In this paper, we investigate the potential energy conservation achieved by balancing the traffic throughout the WSN. We show that distributing the traffic generated by each sensor node through multiple paths instead of using a single path allows significant energy savings. In order to quantitatively evaluate the benefits of the proposed load balancing technique, a new analytical model for load-balanced systems is elaborated and approved by simulations.

Energy-efficiency is one of the major concerns in wireless sensor networks since it impacts the network lifetime. In this paper, we investigate the relationship between sensor network performance, particularly its lifetime, and the number of active reporting nodes N by using both analytical and simulation approaches. We first demonstrate that decreasing the number of reporting nodes increases the number of reports that need to be sent to the sink, in order to achieve the desired information reliability regarding the detected event. On the other hand, we show that reducing the number of reporting nodes alleviates the energy wastage due to collisions. Based on this tradeoff, and as a main contribution, we derive the optimal number of reporting nodes Nopt.energythat minimizes the energy consumed to report reliably the occurrence of an event. In other words, we prove that limiting the reporting tasks of a detected event to a small subset of sensor nodes (i.e., Nopt.energy), instead of using all the sensor nodes in the event area, enables significant energy conservation.

Energy conservation is a primary concern in wireless sensor networks due to the limited capacity of the sensor nodes' batteries. In this paper, we study the relationship between sensor networks performance, particularly its lifetime, and the number of reporting nodes N by using both analytical and simulation approaches. We first show that decreasing N increases considerably the network lifetime. Moreover, we demonstrate that the average time required to report an event is a convex function of N. Based on these results, and as a main contribution, we prove that the optimal number of reporting nodes enabling the shortest latency to report reliably an event does not really lead to the most efficient way of energy consumption. In this paper, we analyze the tradeoff between these two requirements. We provide a simple methodology to achieve this tradeoff which is specific to each sensor application, depending on its particular needs.

Energy-efficiency is one of the major concerns in wireless sensor networks since it impacts the network lifetime. In this paper, we investigate the relationship between sensor network performance, particularly its lifetime, and the number of active reporting nodes N by using both analytical and simulation approaches. We first demonstrate that decreasing the number of reporting nodes increases the number of reports that need to be sent to the sink in order to achieve the desired information reliability regarding a detected event. On an other side, we show that reducing the number of reporting nodes reduces the probability of collision occurrence. Based on these results, and as a first main contribution, we derive the optimal number of reporting nodes Nopt_energy that minimizes the energy consumed to report reliably the occurrence of an event. In other words, we prove that limiting the reporting tasks of a detected event to a small subset of sensor nodes (i.e., Nopt_energy), instead of using all the sensor nodes in the event area, enables significant energy conservation.

Energy-efficiency is one of the major concerns in wireless sensor networks since it impacts the network lifetime. In this paper, we investigate the relationship between sensor networks performance, particularly its lifetime, and the number of reporting nodes N by using both analytical and simulation approaches. We first show that the network lifetime and the number of correctly received reports increase when N decreases. Moreover, we demonstrate that the average time required to report an event is a convex function of N. Based on these results, and as the main contribution, we prove that the optimal number of reporting nodes minimizing the energy consumption in the network does not correspond to the optimal number of reporting nodes allowing the fastest way to report an event. The tradeoff between these two requirements is therefore specific to each sensor application, depending on its particular needs. In this paper, we provide a simple methodology to achieve this tradeoff.