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An Efficient TDMA Scheduling Scheme for Wireless Sensor and Actor Networks
Abstract
This paper presents an efficient time slot assignment algorithm for a wireless sensor and actor network (WSAN), which consists of stationary sensors for detecting events and mobile actors for performing tasks. TDMA protocols are suitable for WSAN due to time-critical tasks, which are assigned to actors. In order to improve the performance of TDMA protocol, a time slot assignment algorithm should generate not only efficient TDMA scheduling but also reduce periodic run-time overhead. The proposed algorithm offers O(delta2) run-time in the worst case, where delta is the maximum number of one-hop and two-hop neighbors in the network. The average run-time in simulation results is far less than O(delta2), however, while the maximum number of assigned slots is bounded by O(delta). In order to reduce the run-time further, we introduce two fundamental processes in the distributed slot assignment and design the algorithm to optimize these processes. We also present an analysis and verify it using ns-2 simulations. Although the algorithm requires time synchronization and prior knowledge of two-hop neighbors, simulation results show that it reduces the run-time significantly and has good scalability in dense networks.
... Some of these MAC protocols are contention-based protocols such as Sensor MAC (S-MAC) [14], T-MAC [18], and DSMAC [17]. Some of the MAC protocols are scheduled-based protocols such as BMA [3], (ALPR MAC) [5], IFCT [9] , TLTS [8], Chung et al. [6]; Lee et al. [8], and TFMAC [7]. Another TDMA protocol is proposed by Younis and Bushra [11] in which they implement HEEDS [12] to build clusters such that each cluster has one node acting as the Cluster Head (CH); CHs are selected according to the probability of being a cluster head (parameter of the protocol) and residual energy of the node. ...
In Wireless Sensor Networks (WSN), the energy of the sensor nodes is a very scarce resource and it is desired to decrease the energy consumption in sensor nodes. The sensor node consumes energy when it is in transmitting, receiving, or idle listening state. In this paper, we discuss the design of an Energy-Efficient Distributed Schedule-Based (EEDS) Communication Protocol for Wireless Sensor Networks. We decrease the energy consumed by decreasing the amount of time a sensor node is in idle listening state. EEDS is intended for applications with periodic data traffic where event reporting is initiated every specific time interval from the sensing node. In EEDS, the time is divided into rounds. Each round is composed of three phases: building the tree, building the schedule, and data transmission. In building the tree phase, an energy-aware tree is built. A TDMA schedule is constructed in a distributed manner during the building the schedule phase. This schedule will be used for data transmission in the data transmission phase. To ensure a reliable communication tree for the whole sensor network, at the beginning of each round the tree is rebuilt, and a new TDMA schedule is reconstructed. We evaluate EEDS in the context of network lifetime, aggregate throughput, and energy consumption. The simulation results show how EEDS can provide signification improvements when compared with Energy Aware Data centric routing protocol (EAD) and the well-known LEACH protocol for different network configurations.
The flexibility of wireless communication makes it more and more widely used in industrial scenarios. To satisfy the strict real-time requirements of industry, various wireless methods especially based on the time division multiple access protocol have been introduced. In this work, we first conduct a mathematical analysis of the network model and the problem of minimum packet loss. Then, an optimal Real-time Scheduling algorithm based on Backtracking method (RSBT) for industrial wireless sensor networks is proposed; this yields a scheduling scheme that can achieve the lowest network packet loss rate. We also propose a suboptimal Real-time Scheduling algorithm based on Urgency and Concurrency (RSUC). Simulation results show that the proposed algorithms effectively reduce the rate of the network packet loss and the average response time of data flows. The real-time performance of the RSUC algorithm is close to optimal, which confirms the computation efficiency of the algorithm.
A success of any sensor based application is determined by the overall performance of the network. The performance of any such network is heavily depends on how good the network formation is achieved. The key phase of the network formation is cluster head selection. All the nodes are transferring their data to base station as well as to other nodes through cluster head. In Wireless Sensor Network, dynamic cluster based routing approach is widely used. Such practiced approach, quickly depletes the energy of cluster heads and induces the execution of frequent re-election algorithm. This repeated cluster head reelection algorithm increases the number of advertisement messages which in turn depletes the energy of overall sensor network. Here, we proposed the Time Constrained Bee's Mating Approach (TCBMA) that reduces the cluster set up communication overhead and elects the stand by node in advance for current cluster head which has the capability to withstand for many rounds. Our proposed TCBMA method uses the Honey bee mating behaviour in electing the stand by node for current cluster head. This approach really outperforms the other methods in achieving reduced number of re election and also achieves excellence in improving the network performance measures such as data delivery ratio and latency.
To increase network lifetime, and reduce energy consumption of a WSN, this paper proposes a Generalised Energy-Efficient Time-Based Communication Protocol (GET). GET is a distributed approach that jointly optimises the routing tree and the medium access schedule for data transmissions. GET works in rounds, each round is composed of four phases, namely: selecting gateways, building a routing tree, establishing a TDMA schedule, and data transmission. GET is compared with EAD and LEACH via extensive simulation experiments. Simulation results show that our proposal can provide significant improvement in terms of network lifetime, aggregate throughput, and energy consumption.
In wireless sensor network, dynamic cluster-based routing approach is widely used. Such practiced approach, quickly depletes the energy of cluster heads and induces the execution of frequent re-election algorithm. This repeated cluster head re-election algorithm increases the number of advertisement messages, which in turn depletes the energy of overall sensor network. Here, we proposed the Advertisement Timeout Driven Bee's Mating Approach (ATDBMA) that reduces the cluster set-up communication overhead and elects the standby node in advance for current cluster head, which has the capability to withstand for many rounds.Our proposed ATDBMA method uses the honeybee mating behaviour in electing the standby node for current cluster head. This approach really outperforms the other methods in achieving reduced number of re-election and maintaining fair energy nodes between the rounds.
A new single channel, time division multiple access (TDMA) scheduling protocol, termed "Evolutionary- TDMA", is presented for mobile ad hoc networks. The protocol allows nodes in an ad hoc network to reserve conflict-free TDMA slots for transmission to their neighbors. Two topology-dependent schedules are generated and main- tained by the protocol: a broadcast schedule suitable for net- work control traffic and a mixed schedule which combines unicast, multicast and broadcast transmissions for user data traffic. The schedules are frequently updated in an evolu- tionary manner to maintain conflict-free transmissions. The protocol executes across the entire network simultaneously in a fully-distributed and parallel fashion. Traffic prioriti- zation and Quality of Service (QoS) can be supported. Sim- ulations have shown that the performance of the E-TDMA protocol is close to that of centralized algorithms, while be- ing insensitive to network size in terms of scheduling quality and scheduling overhead. It is a scalable protocol suitable for very large networks, and networks of varying size.
This paper describes the concept of sensor networks which has been made viable by the convergence of micro-electro-mechanical systems technology, wireless communications and digital electronics. First, the sensing tasks and the potential sensor networks applications are explored, and a review of factors influencing the design of sensor networks is provided. Then, the communication architecture for sensor networks is outlined, and the algorithms and protocols developed for each layer in the literature are explored. Open research issues for the realization of sensor networks are also discussed.
We propose B-MAC , a carrier sense media access protocol for wireless sensor networks that provides a flexible interface to obtain ultra low power operation, effective collision avoidance, and high channel utilization. To achieve low power operation, B-MAC employs an adaptive preamble sampling scheme to reduce duty cycle and minimize idle listening. B-MAC supports on-the-fly reconfiguration and provides bidirectional interfaces for system services to optimize performance, whether it be for throughput, latency, or power conservation. We build an analytical model of a class of sensor network applications. We use the model to show the effect of changing B-MAC 's parameters and predict the behavior of sensor network applications. By comparing B-MAC to conventional 802.11-inspired protocols, specifically SMAC, we develop an experimental characterization of B-MAC over a wide range of network conditions. We show that B-MAC 's flexibility results in better packet delivery rates, throughput, latency, and energy consumption than S-MAC. By deploying a real world monitoring application with multihop networking, we validate our protocol design and model. Our results illustrate the need for flexible protocols to effectively realize energy efficient sensor network applications.
Hybrid Medium Access Control (MAC) protocols combine the strength of random and schedule based MAC schemes. From random MAC schemes, Hybrid MAC protocols borrow flexibility and ease of operation while also incorpor ating the scalability and high capacity performance of schedule based schemes. A number of hybrid approaches exist. The most effective of those, as shown in (1), can dynamically adapt to the contention level in the medium. They achieve this adaptability by combining TDMA (schedule-based) and CSMA (random-based). Whereas the combination of TDMA and CSMA enhance contentions res- olution, the existing solutions do not allocate slots in pro portion to the bandwidth requirements of the individual nodes. This affects the performance adversely. In this paper we propose an algorithm to optimize slot allocations during the schedule-based phase of the Hybrid MAC protocol. Through simulations, we evaluate the performance of our algorithm in both single-hop and multihop networks. Our results show an improvement of upto 40% in some cases.
Three types of collision-free channel access protocols for ad hoc networks are presented. These protocols are derived from a novel approach to contention resolution that allows each node to elect deterministically one or multiple winners for channel access in a given contention context (e.g., a time slot), given the identifiers of its neighbors one and two hops away. The new protocols are shown to be fair and capable of achieving maximum utilization of the channel bandwidth. The delay and throughput characteristics of the contention resolution algorithms are analyzed, and the performance of the three types of channel access protocols is studied by simulations.
We present the hybrid activation multiple access (HAMA) protocol for ad hoc networks. Unlike previous channel access scheduling protocols that activate either nodes or links only, HAMA is a node-activation channel access protocol that also maximizes the chance of link activations using time- and code-division schemes. HAMA only requires identifiers for the neighbors within two hops from each node to schedule channel access. Using this neighborhood information, each node determines whether to transmit in the current time slot on a dynamically assigned spreading code. A neighbor protocol supplements HAMA with up-to-date two-hop neighborhood information by reliably propagating the one-hop neighbor updates through a novel random access technique. The throughput and delay characteristics of HAMA in randomly-generated multihop wireless networks are studied by analyses and simulations. The results of the analyses show that HAMA achieves higher channel utilization in ad hoc networks than a distributed scheduling scheme based on node activation, similar throughput as a well-known scheduling algorithm based on complete topology information, and much higher throughput than the ideal CSMA and CSMA/CA protocols.
A new single channel, time division multiple access (TDMA) based
broadcast, scheduling protocol, termed the five-phase reservation
protocol (FPRP), is presented for mobile ad hoc networks. The protocol
jointly and simultaneously performs the tasks of channel access and node
broadcast scheduling. The protocol allows nodes to make reservations
within TDMA broadcast schedules. It employs a contention-based mechanism
with which nodes compete with each other to acquire TDMA slots. The FPRP
is free of the “hidden terminal” problem, and is designed
such that reservations can be made quickly and efficiently with
negligible probability of conflict. It is fully-distributed and parallel
(a reservation is made through a localized conversation between nodes in
a 2-hop neighborhood), and is thus arbitrarily scalable. A
“multihop ALOHA” policy is developed to support the FPRP.
This policy uses a multihop, pseudo-Bayesian algorithm to calculate
contention probabilities and enable faster convergence of the
reservation procedure. The performance of the protocol is studied via
simulation, and the node coloring process is seen to be as effective as
an existing centralized approach. Some future work and applications are
also discussed
The traffic-adaptive medium access protocol (TRAMA) is introduced for energyefficient collision-free channel access in wireless sensor networks. TRAMA reduces energy consumption by ensuring that unicast and broadcast transmissions incur no collisions, and by allowing nodes to assume a low-power, idle state whenever they are not transmitting or receiving. TRAMA assumes that time is slotted and uses a distributed election scheme based on information about traffic at each node to determine which node can transmit at a particular time slot. Using traffic information, TRAMA avoids assigning time slots to nodes with no traffic to send, and also allows nodes to determine when they can switch off to idle mode and not listen to the channel. TRAMA is shown to be fair and correct, in that no idle node is an intended receiver and no receiver suffers collisions. An analytical model to quantify the performance of TRAMA is presented and the results are verified by simulation. The performance of TRAMA is evaluated through extensive simulations using both synthetic- as well as sensor-network scenarios. The results indicate that TRAMA outperforms contention-based protocols (CSMA, 802.11 and S-MAC) and also static scheduled-access protocols (NAMA) with significant energy savings.
Wireless sensor and actor networks (WSANs) refer to a group of sensors and actors linked by wireless medium to perform distributed sensing and acting tasks. The realization of wireless sensor and actor networks (WSANs) needs to satisfy the requirements introduced by the coexistence of sensors and actors. In WSANs, sensors gather information about the physical world, while actors take decisions and then perform appropriate actions upon the environment, which allows a user to effectively sense and act from a distance. In order to provide effective sensing and acting, coordination mechanisms are required among sensors and actors. Moreover, to perform right and timely actions, sensor data must be valid at the time of acting. This paper explores sensor-actor and actor-actor coordination and describes research challenges for coordination and communication problems.
This paper presents the design, implementation and performance evaluation of a hybrid MAC protocol, called Z-MAC, for wireless sensor networks that combines the strengths of TDMA and CSMA while offsetting their weaknesses. Like CSMA, Z-MAC achieves high channel utilization and low-latency under low contention and like TDMA, achieves high channel utilization under high contention and reduces collision among two-hop neighbors at a low cost. A distinctive feature of Z-MAC is that its performance is robust to synchronization errors, slot assignment failures and time-varying channel conditions; in the worst case, its performance always falls back to that of CSMA. Z-MAC is implemented in TinyOS.
This paper presents a distributed implementation of RAND, a randomized time slot scheduling algorithm, called DRAND. DRAND runs in O(δ) time and message complexity where δ is the maximum size of a two-hop neighborhood in a wire- less network while message complexity remains O(δ), assum- ing that message delays can be bounded by an unknown constant. DRAND is the first fully distributed version of RAND. The algorithm is suitable for a wireless network where most nodes do not move, such as wireless mesh net- works and wireless sensor networks. We implement the algo- rithm in TinyOS and demonstrate its performance in a real testbed of Mica2 nodes. The algorithm does not require any time synchronization and is shown to be effective in adapting to local topology changes without incurring global overhead in the scheduling. Because of these features, it can also be used even for other scheduling problems such as frequency or code scheduling (for FDMA or CDMA) or local identifier assignment for wireless networks where time synchronization is not enforced.
Channel assignment problems in the time, frequency and code domains have thus far been studied separately. Exploiting the similarity of constraints that characterize assignments within and across these domains, we introduce the first unified framework for the study of assignment problems. Our framework identifies eleven atomic constraints underlying most current and potential assignment problems, and characterizes a problem as a combination of these constraints. Based on this framework, we present a unified algorithm for efficient (T/F/C)DMA channel assignments to network nodes or to inter-nodal links in a (multihop) wireless network. The algorithm is parametrized to allow for tradeoff-selectable use as three different variants called RAND, MNF, and PMNF. We provide comprehensive theoretical analysis characterizing the worst-case performance of our algorithm for several classes of problems. In particular, we show that the assignments produced by the PMNF variant are proportional to the thickness of the network. For most typical multihop networks, the thickness can be bounded by a small constant, and hence this represents a significant theoretical result. We also experimentally study the relative performance of the variants for one node and one link assignment problem. We observe that the PMNF variant performs the best, and that a large percentage of unidirectional links is detrimental to the performance in general.
We present fast distributed algorithms for coloring and (connected) dominating set construction in wireless ad hoc networks. We present our algorithms in the context of Unit Disk Graphs which are known to realistically model wireless networks. Our distributed algorithms take into account the loss of messages due to contention from simultaneous interfering transmissions in the wireless medium.
We present randomized distributed algorithms for (conflict-free) Distance-2 coloring, dominating set construction, and connected dominating set construction in Unit Disk Graphs. The coloring algorithm has a time complexity of O(Δ log2n) and is guaranteed to use at most O(1) times the number of colors required by the optimal algorithm. We present two distributed algorithms for constructing the (connected) dominating set; the former runs in time O(Δ log 2n) and the latter runs in time O(log 2n). The two algorithms differ in the amount of local topology information available to the network nodes.
Our algorithms are geared at constructing Well Connected Dominating Sets (WCDS) which have certain powerful and useful structural properties such as low size, low stretch and low degree. In this work, we also explore the rich connections between WCDS and routing in ad hoc networks. Specifically, we combine the properties of WCDS with other ideas to obtain the following interesting applications:
An online distributed algorithm for collision-free, low latency, low redundancy and high throughput broadcasting.
Distributed capacity preserving backbones for unicast routing and scheduling.
In this paper we propose an on-line TDMA slot assignment/graph coloring algorithm for wireless sensor networks with the help of a mobile agent. It is known that graph coloring problem is NP-complete and several heuristics have been developed. Many of them are centralized algorithms and assume global knowledge of the network. We developed a mobile agent based slot assignment (MASA) algorithm in which a mobile agent moves from node to node and assigns a slot to nodes using two-hop neighborhood information. MASA is close to degree based lower bound (d + 1). It requires d + 1 number of colors or slightly more than d + 1 number of colors depending upon the topology, where d is the maximum nodal degree of the graph.
A distributed algorithm is presented for obtaining an efficient and conflict-free broadcasting schedule in a multi-hop packet radio network. The inherent broadcast nature of the radio channel enables a node's transmission to be received by all other nodes within range. Multiple transmissions can be scheduled simultaneously because of the multi-hop nature of the network. It is first shown that the construction of a broadcasting schedule of minimum length is NP-complete, and then a centralized algorithm based on a sequential graph-coloring heuristic is presented to construct minimal-length schedules. A distributed implementation of this algorithm is then proposed, which is based on circulating a token through the nodes in the network.< >
A transmission control strategy is described for slotted-ALOHA-type broadcast channels with ternary feedback. At each time slot, each station estimates the probability that n stations are ready to transmit a packet for each n , using Bayes' rule and the observed history of collisions, successful transmissions, and holes (empty slots). A station transmits a packet in a probabilistic manner based on these estimates. This strategy is called Bayesian broadcast. An elegant and very practical strategy--pseudo-Bayesian broadcast--is then derived by approximating the probability estimates with a Poisson distribution with mean nu and further simplifying. Each station keeps a copy of nu , transmits a packet with probability 1/nu , and then updates nu in two steps: For collisions, increment nu by (e-2)^{-l}=1.39221 cdots . For successes and holes, decrement nu by 1 . Set nu to max (nu + hat{lambda}, 1) , where hat{lambda} is an estimate of the arrival rate lambda of new packets into the system. Simulation results are presented showing that pseudo-Bayesian broadcast performs well in practice, and methods that can be used to prove that certain versions of pseudo-Bayesian broadcast are stable for lambda < e^{-1} are discussed.
Wireless ad-hoc sensor networks have emerged as an interesting and important research area in the last few years. The applications envisioned for such networks require collaborative execution of a distributed task amongst a large set of sensor nodes. This is realized by exchanging messages that are timestamped using the local clocks on the nodes. Therefore, time synchronization becomes an indispensable piece of infrastructure in such systems. For years, protocols such as NTP have kept the clocks of networked systems in perfect synchrony. However, this new class of networks has a large density of nodes and very limited energy resource at every node; this leads to scalability requirements while limiting the resources that can be used to achieve them. A new approach to time synchronization is needed for sensor networks.
Channel assignment problems in the time, frequency and code domains have hitherto been studied separately. Exploiting the similarity of constraints that characterize assignments within and across these domains, we introduce the first unified framework for the study of assignment problems. Our framework identifies eleven atomic constraints underlying most current and potential assignment problems, and characterizes a problem as a combination of these constraints. Based on this framework, we present a unified algorithm for efficient (T/F/C)DMA channel assignments to network nodes or to inter-nodal links in a (multihop) wireless network. The algorithm is parametrized to allow for use as three different variants - RAND, MNF, and PMNF. We provide comprehensive theoretical analysis characterizing the worst-case performance of our algorithm for several classes of problems. In particular, we show that the assignments produced by the PMNF variant are proportional to the thickness of the networ...
Motivated by the poor experimental scaling reported in a study of the performance of ad hoc networks in [15], we propose a new protocol for media access control in ad hoc networks. Our protocol seeks to avoid collisions without making explicit reservations for each and every packet. The key idea is to employ a random schedule which is driven by a pseudo-random number generator. By exchanging the seeds of their pseudo-random number generators within a two-hop neighborhood, the nodes effectively publish their schedules to all hidden as well as exposed nodes. This allows each node to opportunistically choose transmission slots. This scheme can also be employed during the reservation phase of a protocol such as IEEE 802.11. Throughput calculations and simulation results are presented.