I. Amdouni - Academia.edu (original) (raw)

Papers by I. Amdouni

The goal of this research report is to present OSERENA "Optimized SchEduling RoutEr Node Activity... more The goal of this research report is to present OSERENA "Optimized SchEduling RoutEr Node Activity", a distributed coloring algorithm optimized for dense wireless networks. Network density has an extremely reduced impact on the size of the messages exchanged to color the network. Furthermore, the number of colors used to color the network is not impacted by this optimization. We describe in this research report the properties of the algorithm and prove its correctness and termination. Simulation results point out the considerable gains in bandwidth.

ABSTRACT Graph coloring is used in wireless ad hoc and sensor networks to optimize network resour... more ABSTRACT Graph coloring is used in wireless ad hoc and sensor networks to optimize network resources: bandwidth and energy. Nodes access the medium according to their color. It is the responsibility of the coloring algorithm to ensure that interfering nodes do not have the same color. In this paper, we focus on wireless ad hoc and sensor networks with grid topologies. How does a coloring algorithm take advantage of the regularity of grid topology to provide an optimal periodic coloring, that is a coloring with the minimum number of colors? We propose the Vector-Based Coloring Method, denoted VCM, a new method that is able to provide an optimal periodic coloring for any radio transmission range and for any h-hop coloring, he1. In h-hop coloring, no nodes that are p-hop away, with 1 d p d h use the same color. This method consists in determining where a color can be reproduced in the grid without creating interferences while minimizing the number of colors used. We compare the number of colors provided by VCM with the number of colors obtained by a distributed coloring algorithm with line and column priority assignments. Finally, we discuss the applicability of this method to a real wireless network.

ABSTRACT In this report, we study the issue of delay optimization and energy efficiency in grid w... more ABSTRACT In this report, we study the issue of delay optimization and energy efficiency in grid wireless sensor networks (WSNs). We focus on STDMA 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. 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.

Graph coloring is used in wireless networks to optimize network resources: bandwidth and energy. ... more Graph coloring is used in wireless networks to optimize network resources: bandwidth and energy. Nodes access the medium according to their color. It is the responsibility of the coloring algorithm to ensure that interfering nodes do not have the same color. In this research report, we focus on wireless sensor networks with grid topologies. How does a coloring algorithm take advantage of the regularity of grid topology to provide an optimal periodic coloring, that is a coloring with the minimum number of colors? We propose the Vector-Based Coloring Method, denoted VCM, a new method that is able to provide an optimal periodic coloring for any radio transmission range and for any h-hop coloring, h ≥ 1. This method consists in determining at which grid nodes a color can be reproduced without creating interferences between these nodes while minimizing the number of colors used. We compare the number of colors provided by VCM with the number of colors obtained by a distributed coloring algorithm with line and column priority assignments. We also provide bounds on the number of colors of optimal general colorings of the infinite grid, and show that periodic colorings (and thus VCM) are asymptotically optimal. Finally, we discuss the applicability of this method to a real wireless network.

Wireless sensor networks (WSNs) are prone to node/link failures, message losses, and dynamic node... more Wireless sensor networks (WSNs) are prone to node/link failures, message losses, and dynamic node joins and departures. For instance, in data gathering applications that constitute a common type of applications in WSNs, links between nodes and their parent in the data gathering tree may be broken. Protocols supporting such applications should adapt their behaviour to guarantee reliable wireless communications while keeping a low overhead. In particular, this paper focuses on the optimization of a known coloring algorithm called SERENA (‘SchEdule RoutEr Node Activity’). SERENA assigns colors to nodes such that no two interfering nodes share the same color. Each color is mapped to a time slot during which nodes having the associated color can transmit data. To ensure collision free communications, SERENA should be aware about the set of interfering nodes. However, in case of topology changes, this set may vary. Consequently, SERENA should adapt to this. Our solutions proactively select one or more parent backups and guarantee that the coloring remains valid if a parent is replaced by its backup. Simulation results show that reliability is obtained at the price of a small increase in the number of colors used to color the network.

Coloring is used in wireless networks to improve communication efficiency, mainly in terms of ban... more Coloring is used in wireless networks to improve communication efficiency, mainly in terms of bandwidth, energy and possibly end-to-end delays. In this research report, we define the h-hop node coloring problem, with h any positive integer. We prove that the associated decision problem is NP-complete. We then present a 3-hop distributed coloring algorithm that is optimized for dense networks: a node does not need to exchange the priorities and colors of its 2-hop neighbors. Through simulation results, we highlight the impact of priority assignment on the number of colors obtained for any network. We then focus on grids and identify a color pattern that can be reproduced to color the whole grid. We show how the coloring algorithm can use regularity properties to obtain a periodic color pattern with the optimal number of colors. We present the Vector Method that provides the otimal number of colors among all periodic h-hop colorings. We establish lower and upper bounds on the number of colors needed in a periodic h-hop coloring.

2010 17th International Conference on Telecommunications, 2010

... of the 14th ACM MOBICOM, September 2008. [16] V. Navda, A. Prabhu Subramanian, K.Dhanasekaran... more ... of the 14th ACM MOBICOM, September 2008. [16] V. Navda, A. Prabhu Subramanian, K.Dhanasekaran, A. Timm-Giel, SR Das, “MobiSteer: using steerable beam directional antenna for vehicular network access”, in Proc of MobiSys'2007, June 2007. ...

2011 4th Joint IFIP Wireless and Mobile Networking Conference (WMNC 2011), 2011

Coloring is used in wireless networks to improve communication efficiency, mainly in terms of ban... more Coloring is used in wireless networks to improve communication efficiency, mainly in terms of bandwidth, energy and possibly end-to-end delays. In this paper, we define the h-hop node coloring problem, with h any positive integer, adapted to two types of applications in wireless networks. We specify both general mode for general applications and strategic mode for data gathering applications. We prove that the associated decision problem is NP-complete. We then focus on grid topologies that constitute regular topologies for large or dense wireless networks. We consider various transmission ranges and identify a color pattern that can be reproduced to color the whole grid with the optimal number of colors. We obtain an optimal periodic coloring of the grid for the considered transmission range. We then present a 3-hop distributed coloring algorithm, called SERENA. Through simulation results, we highlight the impact of node priority assignment on the number of colors obtained for any network and grids in particular. We then compare these optimal results on grids with those obtained by SERENA and identify directions to improve SERENA.

2012 International Conference on Communications and Information Technology (ICCIT), 2012

In data gathering applications which is a typical application paradigm in wireless sensor network... more In 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.

2009 IEEE Vehicular Networking Conference (VNC), 2009

The low price of commodity wireless LAN cards and access points (APs) has resulted in the rich pr... more The low price of commodity wireless LAN cards and access points (APs) has resulted in the rich proliferation of high density WLANs in enterprises, academic environments, and public spaces. In such environments, wireless clients have a variety of affiliation options. The state of the art mechanism behind such a decision typically relies on received signal strength indicator (RSSI). This approach

International Journal of Networked and Distributed Computing, 2013

The goal of this paper is to present OSERENA, a distributed coloring algorithm optimized for dens... more The goal of this paper is to present OSERENA, a distributed coloring algorithm optimized for dense wireless sensor networks (WSNs). Network density has an extremely reduced impact on the size of the messages exchanged to color the WSN. Furthermore, the number of colors used to color the network is not impacted by this optimization. We describe in this paper the properties of the algorithm and prove its correctness and termination. Simulation results point out the considerable gains in bandwidth.

2014 IEEE 28th International Conference on Advanced Information Networking and Applications, 2014

Current Wireless Sensor Networks (WSNs) are deployed over unlicensed frequency bands that face an... more Current Wireless Sensor Networks (WSNs) are deployed over unlicensed frequency bands that face an increased level of interference from various wireless systems. Cognitive Radio Sensor Networks (CRSNs) overcome this problem by allowing sensor nodes to access new spectrum bands to minimize interferences. In this paper, we focus on the MultiChannel Time Slot Assignment problem (MC-TSA) in CRSN. Each sensor node is assigned the number of time slots it needs to transfer its own data as well as the data received from its children in the rooting tree rooted at the sink without interfering with other secondary users. Besides, sensor nodes cannot transmit on a channel occupied by a primary user. Our objective is to increase the network throughput offered to sensor nodes. We start by formulating the MC-TSA problem as an Integer Linear Program where the goal is to minimize the number of slots in the schedule. We then propose an Opportunistic centralized TIme slot assignment in COgnitive Radio sensor networks (OTICOR). We evaluate its performance in terms of number of slots and throughput.

2012 International Conference on Wireless Communications in Underground and Confined Areas, 2012

Wireless sensor networks, WSNs, are an efficient way to deal with low-rate communications in conf... more Wireless sensor networks, WSNs, are an efficient way to deal with low-rate communications in confined environments such as mines or nuclear power plants because of their simplicity of deployment and low cost. In these application domains, WSNs are used to gather data from sensor nodes towards a sink in a multi-hop convergecast structure. In this paper, we focus on a traffic-aware time slot assignment minimizing the schedule length for tree topologies and for two special deployments (i.e. linear and multi-linear) representative of unusual environments. We formalize the problem as a linear program and provide results on the optimal number of slots. We then propose a delay optimized algorithm with two heuristics that minimize on the one hand the energy consumption and on the other hand the storage capacity as secondary criteria.

Future Internet, 2010

In wireless sensor networks, energy efficiency is mainly achieved by making nodes sleep. In this ... more In wireless sensor networks, energy efficiency is mainly achieved by making nodes sleep. In this paper, we present the combination of SERENA, a new node activity scheduling algorithm based on node coloring, with TDMA/CA, a collision avoidance MAC protocol. We show that the combination of these two protocols enables substantial bandwidth and energy benefits for both general and data gathering applications. As a first contribution, we prove that the three-hop node coloring problem is NP-complete. As a second contribution, the overhead induced by SERENA during network coloring is reduced, making possible the use of these protocols even in dense networks with limited bandwidth. The third contribution of this paper is to show that applying any slot assignment algorithm with spatial reuse based on node neighborhood without taking into account link quality can lead to poor performances because of collisions. The use of good quality links will prevent this phenomenon. The fourth contribution consists of optimizing end-to-end delays for data gathering applications, by means of cross-layering with the application. However, color conflicts resulting from topology changes, mobility and late node arrivals can give rise to collisions. As a fifth contribution, we show how the MAC layer can detect color conflicts, and cope with them at the cost of a slightly reduced throughput. Then, we discuss the tradeoff between requesting SERENA to solve the color conflicts and dealing with them at the MAC layer, our third contribution. The combination of SERENA and TDMA/CA is evaluated through simulations on realistic topologies. Future Internet 2010, 2 470

Future Internet, 2010

Sensor nodes are characterized by a small size, a low cost, an advanced communication technology,... more Sensor nodes are characterized by a small size, a low cost, an advanced communication technology, but also a limited amount of energy. Energy efficient strategies are required in such networks to maximize network lifetime. In this paper, we focus on a solution integrating energy efficient routing and node activity scheduling. The energy efficient routing we propose, called EOLSR, selects the route and minimizes the energy consumed by an end-to-end transmission, while avoiding nodes with low residual energy. Simulation results show that EOLSR outperforms the solution selecting the route of minimum energy as well as the solution based on node residual energy. Cross-layering allows EOLSR to use information from the application layer or the MAC layer to reduce its overhead and increase network lifetime. Node activity scheduling is based on the following observation: the sleep state is the least power consuming state. So, to schedule node active and sleeping periods, we propose SERENA that colors all network nodes using a small number of colors, such that two nodes with the same color can transmit without interfering. The node color is mapped into a time slot during which the node can transmit. Consequently, each node is awake during its slot and the slots of its one-hop neighbors, and sleeps in the remaining time. We evaluate SERENA benefits obtained in terms of bandwidth, delay and energy. We also show how cross-layering with the application layer can improve the end-to-end delays for data gathering applications.

Advances in wireless communication technologies as well as the low cost of wireless equipments ha... more Advances in wireless communication technologies as well as the low cost of wireless equipments have increased the ubiquity of network connectivity, illustrated by the large deployment of IEEE 802.11 access points (APs). Anytime, anywhere, users are being connected to networks and desire consequently more services on their mobile devices.

The goal of this research report is to present OSERENA "Optimized SchEduling RoutEr Node Activity... more The goal of this research report is to present OSERENA "Optimized SchEduling RoutEr Node Activity", a distributed coloring algorithm optimized for dense wireless networks. Network density has an extremely reduced impact on the size of the messages exchanged to color the network. Furthermore, the number of colors used to color the network is not impacted by this optimization. We describe in this research report the properties of the algorithm and prove its correctness and termination. Simulation results point out the considerable gains in bandwidth.

ABSTRACT Graph coloring is used in wireless ad hoc and sensor networks to optimize network resour... more ABSTRACT Graph coloring is used in wireless ad hoc and sensor networks to optimize network resources: bandwidth and energy. Nodes access the medium according to their color. It is the responsibility of the coloring algorithm to ensure that interfering nodes do not have the same color. In this paper, we focus on wireless ad hoc and sensor networks with grid topologies. How does a coloring algorithm take advantage of the regularity of grid topology to provide an optimal periodic coloring, that is a coloring with the minimum number of colors? We propose the Vector-Based Coloring Method, denoted VCM, a new method that is able to provide an optimal periodic coloring for any radio transmission range and for any h-hop coloring, he1. In h-hop coloring, no nodes that are p-hop away, with 1 d p d h use the same color. This method consists in determining where a color can be reproduced in the grid without creating interferences while minimizing the number of colors used. We compare the number of colors provided by VCM with the number of colors obtained by a distributed coloring algorithm with line and column priority assignments. Finally, we discuss the applicability of this method to a real wireless network.

ABSTRACT In this report, we study the issue of delay optimization and energy efficiency in grid w... more ABSTRACT In this report, we study the issue of delay optimization and energy efficiency in grid wireless sensor networks (WSNs). We focus on STDMA 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. 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.

Graph coloring is used in wireless networks to optimize network resources: bandwidth and energy. ... more Graph coloring is used in wireless networks to optimize network resources: bandwidth and energy. Nodes access the medium according to their color. It is the responsibility of the coloring algorithm to ensure that interfering nodes do not have the same color. In this research report, we focus on wireless sensor networks with grid topologies. How does a coloring algorithm take advantage of the regularity of grid topology to provide an optimal periodic coloring, that is a coloring with the minimum number of colors? We propose the Vector-Based Coloring Method, denoted VCM, a new method that is able to provide an optimal periodic coloring for any radio transmission range and for any h-hop coloring, h ≥ 1. This method consists in determining at which grid nodes a color can be reproduced without creating interferences between these nodes while minimizing the number of colors used. We compare the number of colors provided by VCM with the number of colors obtained by a distributed coloring algorithm with line and column priority assignments. We also provide bounds on the number of colors of optimal general colorings of the infinite grid, and show that periodic colorings (and thus VCM) are asymptotically optimal. Finally, we discuss the applicability of this method to a real wireless network.

Wireless sensor networks (WSNs) are prone to node/link failures, message losses, and dynamic node... more Wireless sensor networks (WSNs) are prone to node/link failures, message losses, and dynamic node joins and departures. For instance, in data gathering applications that constitute a common type of applications in WSNs, links between nodes and their parent in the data gathering tree may be broken. Protocols supporting such applications should adapt their behaviour to guarantee reliable wireless communications while keeping a low overhead. In particular, this paper focuses on the optimization of a known coloring algorithm called SERENA (‘SchEdule RoutEr Node Activity’). SERENA assigns colors to nodes such that no two interfering nodes share the same color. Each color is mapped to a time slot during which nodes having the associated color can transmit data. To ensure collision free communications, SERENA should be aware about the set of interfering nodes. However, in case of topology changes, this set may vary. Consequently, SERENA should adapt to this. Our solutions proactively select one or more parent backups and guarantee that the coloring remains valid if a parent is replaced by its backup. Simulation results show that reliability is obtained at the price of a small increase in the number of colors used to color the network.

Coloring is used in wireless networks to improve communication efficiency, mainly in terms of ban... more Coloring is used in wireless networks to improve communication efficiency, mainly in terms of bandwidth, energy and possibly end-to-end delays. In this research report, we define the h-hop node coloring problem, with h any positive integer. We prove that the associated decision problem is NP-complete. We then present a 3-hop distributed coloring algorithm that is optimized for dense networks: a node does not need to exchange the priorities and colors of its 2-hop neighbors. Through simulation results, we highlight the impact of priority assignment on the number of colors obtained for any network. We then focus on grids and identify a color pattern that can be reproduced to color the whole grid. We show how the coloring algorithm can use regularity properties to obtain a periodic color pattern with the optimal number of colors. We present the Vector Method that provides the otimal number of colors among all periodic h-hop colorings. We establish lower and upper bounds on the number of colors needed in a periodic h-hop coloring.

2010 17th International Conference on Telecommunications, 2010

... of the 14th ACM MOBICOM, September 2008. [16] V. Navda, A. Prabhu Subramanian, K.Dhanasekaran... more ... of the 14th ACM MOBICOM, September 2008. [16] V. Navda, A. Prabhu Subramanian, K.Dhanasekaran, A. Timm-Giel, SR Das, “MobiSteer: using steerable beam directional antenna for vehicular network access”, in Proc of MobiSys'2007, June 2007. ...

2011 4th Joint IFIP Wireless and Mobile Networking Conference (WMNC 2011), 2011

Coloring is used in wireless networks to improve communication efficiency, mainly in terms of ban... more Coloring is used in wireless networks to improve communication efficiency, mainly in terms of bandwidth, energy and possibly end-to-end delays. In this paper, we define the h-hop node coloring problem, with h any positive integer, adapted to two types of applications in wireless networks. We specify both general mode for general applications and strategic mode for data gathering applications. We prove that the associated decision problem is NP-complete. We then focus on grid topologies that constitute regular topologies for large or dense wireless networks. We consider various transmission ranges and identify a color pattern that can be reproduced to color the whole grid with the optimal number of colors. We obtain an optimal periodic coloring of the grid for the considered transmission range. We then present a 3-hop distributed coloring algorithm, called SERENA. Through simulation results, we highlight the impact of node priority assignment on the number of colors obtained for any network and grids in particular. We then compare these optimal results on grids with those obtained by SERENA and identify directions to improve SERENA.

2012 International Conference on Communications and Information Technology (ICCIT), 2012

In data gathering applications which is a typical application paradigm in wireless sensor network... more In 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.

2009 IEEE Vehicular Networking Conference (VNC), 2009

The low price of commodity wireless LAN cards and access points (APs) has resulted in the rich pr... more The low price of commodity wireless LAN cards and access points (APs) has resulted in the rich proliferation of high density WLANs in enterprises, academic environments, and public spaces. In such environments, wireless clients have a variety of affiliation options. The state of the art mechanism behind such a decision typically relies on received signal strength indicator (RSSI). This approach

International Journal of Networked and Distributed Computing, 2013

The goal of this paper is to present OSERENA, a distributed coloring algorithm optimized for dens... more The goal of this paper is to present OSERENA, a distributed coloring algorithm optimized for dense wireless sensor networks (WSNs). Network density has an extremely reduced impact on the size of the messages exchanged to color the WSN. Furthermore, the number of colors used to color the network is not impacted by this optimization. We describe in this paper the properties of the algorithm and prove its correctness and termination. Simulation results point out the considerable gains in bandwidth.

2014 IEEE 28th International Conference on Advanced Information Networking and Applications, 2014

Current Wireless Sensor Networks (WSNs) are deployed over unlicensed frequency bands that face an... more Current Wireless Sensor Networks (WSNs) are deployed over unlicensed frequency bands that face an increased level of interference from various wireless systems. Cognitive Radio Sensor Networks (CRSNs) overcome this problem by allowing sensor nodes to access new spectrum bands to minimize interferences. In this paper, we focus on the MultiChannel Time Slot Assignment problem (MC-TSA) in CRSN. Each sensor node is assigned the number of time slots it needs to transfer its own data as well as the data received from its children in the rooting tree rooted at the sink without interfering with other secondary users. Besides, sensor nodes cannot transmit on a channel occupied by a primary user. Our objective is to increase the network throughput offered to sensor nodes. We start by formulating the MC-TSA problem as an Integer Linear Program where the goal is to minimize the number of slots in the schedule. We then propose an Opportunistic centralized TIme slot assignment in COgnitive Radio sensor networks (OTICOR). We evaluate its performance in terms of number of slots and throughput.

2012 International Conference on Wireless Communications in Underground and Confined Areas, 2012

Wireless sensor networks, WSNs, are an efficient way to deal with low-rate communications in conf... more Wireless sensor networks, WSNs, are an efficient way to deal with low-rate communications in confined environments such as mines or nuclear power plants because of their simplicity of deployment and low cost. In these application domains, WSNs are used to gather data from sensor nodes towards a sink in a multi-hop convergecast structure. In this paper, we focus on a traffic-aware time slot assignment minimizing the schedule length for tree topologies and for two special deployments (i.e. linear and multi-linear) representative of unusual environments. We formalize the problem as a linear program and provide results on the optimal number of slots. We then propose a delay optimized algorithm with two heuristics that minimize on the one hand the energy consumption and on the other hand the storage capacity as secondary criteria.

Future Internet, 2010

In wireless sensor networks, energy efficiency is mainly achieved by making nodes sleep. In this ... more In wireless sensor networks, energy efficiency is mainly achieved by making nodes sleep. In this paper, we present the combination of SERENA, a new node activity scheduling algorithm based on node coloring, with TDMA/CA, a collision avoidance MAC protocol. We show that the combination of these two protocols enables substantial bandwidth and energy benefits for both general and data gathering applications. As a first contribution, we prove that the three-hop node coloring problem is NP-complete. As a second contribution, the overhead induced by SERENA during network coloring is reduced, making possible the use of these protocols even in dense networks with limited bandwidth. The third contribution of this paper is to show that applying any slot assignment algorithm with spatial reuse based on node neighborhood without taking into account link quality can lead to poor performances because of collisions. The use of good quality links will prevent this phenomenon. The fourth contribution consists of optimizing end-to-end delays for data gathering applications, by means of cross-layering with the application. However, color conflicts resulting from topology changes, mobility and late node arrivals can give rise to collisions. As a fifth contribution, we show how the MAC layer can detect color conflicts, and cope with them at the cost of a slightly reduced throughput. Then, we discuss the tradeoff between requesting SERENA to solve the color conflicts and dealing with them at the MAC layer, our third contribution. The combination of SERENA and TDMA/CA is evaluated through simulations on realistic topologies. Future Internet 2010, 2 470

Future Internet, 2010

Sensor nodes are characterized by a small size, a low cost, an advanced communication technology,... more Sensor nodes are characterized by a small size, a low cost, an advanced communication technology, but also a limited amount of energy. Energy efficient strategies are required in such networks to maximize network lifetime. In this paper, we focus on a solution integrating energy efficient routing and node activity scheduling. The energy efficient routing we propose, called EOLSR, selects the route and minimizes the energy consumed by an end-to-end transmission, while avoiding nodes with low residual energy. Simulation results show that EOLSR outperforms the solution selecting the route of minimum energy as well as the solution based on node residual energy. Cross-layering allows EOLSR to use information from the application layer or the MAC layer to reduce its overhead and increase network lifetime. Node activity scheduling is based on the following observation: the sleep state is the least power consuming state. So, to schedule node active and sleeping periods, we propose SERENA that colors all network nodes using a small number of colors, such that two nodes with the same color can transmit without interfering. The node color is mapped into a time slot during which the node can transmit. Consequently, each node is awake during its slot and the slots of its one-hop neighbors, and sleeps in the remaining time. We evaluate SERENA benefits obtained in terms of bandwidth, delay and energy. We also show how cross-layering with the application layer can improve the end-to-end delays for data gathering applications.

Advances in wireless communication technologies as well as the low cost of wireless equipments ha... more Advances in wireless communication technologies as well as the low cost of wireless equipments have increased the ubiquity of network connectivity, illustrated by the large deployment of IEEE 802.11 access points (APs). Anytime, anywhere, users are being connected to networks and desire consequently more services on their mobile devices.