319 research outputs found
Optimal Control of Transmission Power Management in Wireless Backbone Mesh Networks
International audienceno abstrac
Performance Optimization in Wireless Local Area Networks
Wireless Local Area Networks (WLAN) are becoming more and more important
for providing wireless broadband access. Applications and networking
scenarios evolve continuously and in an unpredictable way, attracting the
attention of academic institutions, research centers and industry. For designing
an e cient WLAN is necessary to carefully plan coverage and to
optimize the network design parameters, such as AP locations, channel assignment,
power allocation, MAC protocol, routing algorithm, etc... In this
thesis we approach performance optimization in WLAN at di erent layer
of the OSI model. Our rst approach is at Network layer. Starting from
a Hybrid System modeling the
ow of tra c in the network, we propose a
Hybrid Linear Varying Parameter algorithm for identifying the link quality
that could be used as metric in routing algorithms. Go down to Data Link,
it is well known that CSMA (Carrier Sense Multiple Access) protocols exhibit
very poor performance in case of multi-hop transmissions, because of
inter-link interference due to imperfect carrier sensing. We propose two novel
algorithms, that are combining Time Division Multiple Access for grouping
contending nodes in non-interfering sets with Carrier Sense Multiple Access
for managing the channel access behind a set. In the rst solution, a game
theoretical study of intra slot contention is introduced, in the second solution
we apply an optimization algorithm to nd the optimal degree between
contention and scheduling. Both the presented solutions improve the network
performance with respect to CSMA and TDMA algorithms. Finally we
analyze the network performance at Physical Layer. In case of WLAN, we
can only use three orthogonal channels in an unlicensed spectrum, so the frequency
assignments should be subject to frequent adjustments, according to
the time-varying amount of interference which is not under the control of the
provider. This problem make necessary the introduction of an automatic network
planning solution, since a network administrator cannot continuously
monitor and correct the interference conditions su ered in the network. We
propose a novel protocol based on a distributed machine learning mechanism
in which the nodes choose, automatically and autonomously in each time
slot, the optimal channel for transmitting through a weighted combination
of protocols
Distributed Control for Cyber-Physical Systems
Networked Cyber-Physical Systems (CPS) are fundamentally constrained by the tight coupling and closed-loop control and actuation of physical processes. To address actuation in such closed-loop wireless control systems there is a strong need to re-think the communication architectures and protocols for maintaining stability and performance in the presence of disturbances to the network, environment and overall system objectives. We review the current state of network control efforts for CPS and present two complementary approaches for robust, optimal and composable control over networks. We first introduce a computer systems approach with Embedded Virtual Machines (EVM), a programming abstraction where controller tasks, with their control and timing properties, are maintained across physical node boundaries. Controller functionality is decoupled from the physical substrate and is capable of runtime migration to the most competent set of physical controllers to maintain stability in the presence of changes to nodes, links and network topology.
We then view the problem from a control theoretic perspective to deliver fully distributed control over networks with Wireless Control Networks (WCN). As opposed to traditional networked control schemes where the nodes simply route information to and from a dedicated controller, our approach treats the network itself as the controller. In other words, the computation of the control law is done in a fully distributed way inside the network. In this approach, at each time-step, each node updates its internal state to be a linear combination of the states of the nodes in its neighborhood. This causes the entire network to behave as a linear dynamical system, with sparsity constraints imposed by the network topology. This eliminates the need for routing between “sensor → channel → dedicated controller/estimator → channel → actuator”, allows for simple transmission scheduling, is operational on resource constrained low-power nodes and allows for composition of additional control loops and plants. We demonstrate the potential of such distributed controllers to be robust to a high degree of link failures and to maintain stability even in cases of node failures
Economy of Spectrum Access in Timy Varying Multichannel Networks
We consider a wireless network consisting of two classes of potentially mobile users: primary users and secondary users. Primary users license frequency channels and transmit in their respective bands as required. Secondary users resort to unlicensed access of channels that are not used by their primary users. Primaries impose access fees on the secondaries which depend on access durations and may be different for different primary channels and different available communication rates in the channels. The available rates to the secondaries change with time depending on the usage status of the primaries and the random access quality of channels. Secondary users seek to minimize their total access cost subject to stabilizing their queues whenever possible. Our first contribution is to present a dynamic link scheduling policy that attains this objective. The computation time of this policy, however, increases exponentially with the size of the network. We next present an approximate scheduling scheme based on graph partitioning that is distributed and attains arbitrary trade-offs between aggregate access cost and computation times of the schedules, irrespective of the size of the network. Our performance guarantees hold for general arrival and primary usage statistics and multihop networks. Each secondary user is, however, primarily interested in minimizing the cost it incurs, rather than in minimizing the aggregate cost. Thus, it will schedule its transmissions so as to minimize the aggregate cost only if it perceives that the aggregate cost is shared among the users as per a fair cost sharing scheme. Using concepts from cooperative game theory, we develop a rational basis for sharing the aggregate cost among secondary sessions and present a cost sharing mechanism that conforms to the above basis
A Critical Review on Energy-Efficient Medium Access Control for Wireless and Mobile Sensor Networks
Wireless sensor network (WSN) has garnered remarkable attention due to its wide supports for plenty of applications such as, health systems; military based applications, environmental monitoring, and tactical system. In ContentionBased Medium Access Control (MAC) protocols related to the energy consumption. In this paper, a combative review of energy consumption in Contention-Based MAC protocols was provided. Furthermore, a general comparison that stated the strengths and drawbacks with every utilized technique was offered. The main aim of this paper is to assist the researcher to choose the right protocol for developing purpose or further investigation regarding the performance
Optimal Control for Generalized Network-Flow Problems
We consider the problem of throughput-optimal packet dissemination, in the presence of an arbitrary mix of unicast, broadcast, multicast, and anycast traffic, in an arbitrary wireless network. We propose an online dynamic policy, called Universal Max-Weight (UMW), which solves the problem efficiently. To the best of our knowledge, UMW is the first known throughput-optimal policy of such versatility in the context of generalized network flow problems. Conceptually, the UMW policy is derived by relaxing the precedence constraints associated with multi-hop routing and then solving a min-cost routing and max-weight scheduling problem on a virtual network of queues. When specialized to the unicast setting, the UMW policy yields a throughput-optimal cycle-free routing and link scheduling policy. This is in contrast with the well-known throughput-optimal back-pressure (BP) policy which allows for packet cycling, resulting in excessive latency. Extensive simulation results show that the proposed UMW policy incurs a substantially smaller delay as compared with the BP policy. The proof of throughput-optimality of the UMW policy combines ideas from the stochastic Lyapunov theory with a sample path argument from adversarial queueing theory and may be of independent theoretical interest
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