Media Access Control (MAC) Protocols: An Overview

2007

This paper presents a distributed algorithm for efficient Time Division Multiple Access (TDMA) slot allocation in Wireless Sensor Networks, which is to be used in close association with a new TDMA-based MAC protocol called Latency-Energy Minimization Medium Access (LEMMA). Unlike most of the existent proposals, which try to guarantee interference-free allocation based on the n-hop criterion (which can only work with regular topologies), the presented algorithm bases its decisions on the received signal strength, allowing it to operate independently of the WSN topology. The performance of the proposed slot allocation algorithm was compared with centralized depth-first slot allocation using computer simulation. The results show that the proposed scheme is significantly faster, only paying the price of extra energy consumption during the initial network setup phase. Wireless Sensor Networks, MAC, TDMA, timeslot allocation I.

2012 IEEE/ACM 16th International Symposium on Distributed Simulation and Real Time Applications, 2012

Due to the fact that sensor nodes are untethered and unattended, energy management is a critical issue in communication mechanism of a wireless sensor network. In this paper, we address this problem and propose a novel solution based on media access control technique. Our protocol S-TDMA (for Sensor-Time Division Multiple Access) exploits the inherent features of TDMA to avoid the main sources of energy wastage. It assigns sensors with consecutive time slots to reduce the frequency of state transitions. S-TDMA is carefully designed to overcome the high latency of traditional TDMA protocols. It also conserves energy when a node may not be transmitting or receiving packets. Simulation results show that the S-TDMA protocol functions well.

2015

Conservation of energy is one of the main challenges in designing a wireless sensor network (WSN). The reason is that these large scaled networks cannot be arranged, configured, or maintained manually. Thus, automated deployment and configuration are required. One important factor determining the total energy consumption is the network topology. This article evaluates the relation between the maximum distance (link lengths) between the nodes in a WSN and the total energy consumed. The optimal topology for the two most commonly used medium access control (MAC) protocols were found. A WSN based on a Time Division Multiple Access (TDMA) protocol is limited by the maximum available or allowed emitted radio power. Thus, the criterion for optimal link lengths is related to the expected number of transmissions over the links. By including the retransmissions over the links we found an optimal internode distance. A Carrier Sense Multiple Access (CSMA) based WSN, on the other hand, is limite...

2012

All praise unto Allah for everything I have. I would like to thank the following persons who accompanied me during the time I was working for this degree. In preparing this thesis, I was in contact with many people, researchers, academicians, and practitioners. They have contributed towards my understanding and thoughts. In particular, I wish to express my sincere appreciation to my thesis supervisor, Assoc. Prof. Dr. Kamalrulnizam Abu Bakar, for encouragement, guidance, critics and advice till the end of glorious successful work. My fellow postgraduate students should also be recognized for their support. My sincere appreciation also extends to all my colleagues, En. Herman, Oon Erixno, Yoanda Alim Syahbana, M. Gary Shaffer, and others who have provided assistance at various occasions. Their views and tips are useful indeed. Unfortunately, it is not possible to list all of them in this limited space. I am grateful to all my family members, especially my mother 'Erlina', and my brother 'Aip' for their prayers and moral support. I also deeply thanks to my wife 'Asna Ningsih' for her prayer, advice and moral support.

In this paper, we present an efficient MAC layer scheme using Dynamic Slot Assignment (DSA) in TDMA-based MAC protocols for cluster-based wireless sensor networks. The DSA scheme is presented to analyze the energy efficiency and channel utilization in a bursty traffic environment under low traffic conditions with a large number of sensor nodes in a single cluster. The DSA scheme will allow the network to adapt to the changing traffic load. Based on the network activity, the connection is established between the cluster-head node and those sensor nodes which have data to send, and a TDMA slot is assigned to each of them dynamically. We present the complete system model and model the data traffic by a correlated stochastic process (i.e. Markov chain) for a network where the second and subsequent connection arrival rate is dependent on the first arrival rate. We numerically compare our DSA with a traditionally proposed static TDMA model, the BMA model, and a variant of the BMA model (E...

IEEE Wireless Communications and Networking Conference, 2005

The performance of Direct Sequence Code Division Multiple Access (DS-CDMA) sensor networks is limited by Multiple Access Interference (MAI). This paper proposes using frequency division to reduce the MAI in a DS-CDMA sensor network. We provide theoretical characterization of the mean MAI at a given node and show that a small number of frequency channels can reduce the MAI significantly. In addition, we provide a comparison of our proposed system to systems which do not use frequency division or which employ contention based protocols. Our study found that, by using only a small number of frequency channels, our system has less channel contention, lower packet latency, higher packet delivery ratio and lower energy consumption. We consider a wireless sensor network that consists of numerous sensor/actuator devices with integrated sensing, embedded microprocessors, low-power communication radios, on-board energy, with location awareness and organized in an ad hoc multi-hop network. Since sensor network applications are expected to utilize low data rate (e.g., 1-100Kbps), have small data packet size (e.g., 50 bytes), and sensors normally have limited energy, buffer space, and other resources, the contention based protocols may not be a suitable choice. Contention based protocols suffer from both low network throughput and long packet delays. Associating with each small data packet transmission, the RTS/CTS control packet exchange produces significant overheads. Woo and Culler [14] state that an RTS-CTS-DATA-ACK handshake sequence in transmitting a packet can constitute up to 40% overhead with small packet size in sensor networks. Although IEEE 802.11 standard specifies that RTS/CTS can be avoided with small data packet transmission, this may not be a suitable choice for sensor networks. Given the low data rate (e.g., 20Kbps) in sensor networks, a small data packet will take longer time to transmit than in an IEEE 802.11 network which has higher data rate (e.g., 2Mbps). As a result, the collision probability in sensor networks is much higher. Blough et al. [5] proved the crude lower bound that no contentions occur in a wireless channel with following lemma: Lemma 1 Lett be the time necessary to transmit a packet. For d = mt, the probability that no contention will occur in a wireless channel is strictly grater than exp(− 3h(h−1) 2m), where h denotes the number of nodes that are contending for the channel. An example was also given with 33 contending nodes, where d must be around 16000t to achieve a probabilistic guarantee of no contention of at least 0.9. Assume thatt represents the transmission time of a packet with 802.11 data rate (2Mbps) in above example. Now considering the same packet is transmitted with sensor network data rate (20Kbps). During the same period of time d, the probability of no collision will occur is 5.023 × 10 −5 , which is almost zero. In other word, collisions will always occur. The consequence is that control packet (RTS/CTS) exchange is inevitable to avoid collisions. Moreover, some energy efficient algorithms proposed for contention based protocols for sensor network require the information embedded in RTS/CTS packets. For example, SMAC [19] uses the transmission time embedded in RTS/CTS to turn off unintended receivers to avoid the energy consumption caused by overhearing. Furthermore, contention based protocols also suffer from the well documented hidden node and exposed node problems.

We compare centralized and distributed approaches for the coordination of transmission slots of wireless sensors for collision-free time division multiple access (TDMA) operation. For the centralized coordination, we focus on the guaranteed time slot (GTS) mechanism of the IEEE802.15.4 standard. For the distributed coordination, we present results with the DESYNC algorithm and its recent time-frequency extension. The results are derived via measurements with real TinyOS wireless sensor nodes using the CC2420 transceiver and reveal that both approaches obtain comparable throughput per node, with the GTS mechanism obtaining higher throughput only for the smaller permissible superframe duration. Moreover, distributed coordination is by nature more robust and scalable as it does not have a single point of failure and it can be scaled to multi-channel operation; however, it requires higher startup delay in order to converge to the steady state of operation.

2004

In the near future, some applications, such as information collection about almost anything (for example: a region, an organism, object tracking, chemical attacks, disaster relief operations, conference settings, and class room operations, etc.) will require forming dense wireless sensor networks and wireless ad hoc networks. In wireless ad hoc networks, the wireless medium is shared by all the users. Therefore, a Medium Access Control (MAC) protocol is required to provide an efficient mechanism to share limited spectrum resources fairly to serve all the users and still provide high throughput. The most popular wireless MAC protocol, CSMA/CA, has become the basis of the MAC protocol for the IEEE 802.11 standard [1]. However, when the number of users increases, the IEEE 802.11 MAC protocol encounters significant throughput degradation due to a high collision rate. Further, it is observed that the IEEE 802.11 MAC protocol results in short-term fairness among the users [2], which is desired by some applications such as information collection in sensor networks, real time traffic, and TCP applications.

This chapter provides a broad overview of the MAC protocols especially developed for sensor networks. These MAC protocols differ from typical WLAN access protocols in that they trade off performance (latency and throughput) for a reduction in energy consumption to maximize the lifetime of the network. This is in general achieved by duty cycling the radio, and it is the MAC layer that controls when the radio is switched on and off. An important consequence is that a MAC protocol needs to be aware of its neighbors' sleep/active schedules, since sending a message is only effective when the destination node is awake. An obvious solution is to have all nodes synchronize on one global schedule, so no separate neighbor state is required, which maps well onto the resource limitations of typical sensor nodes. However, grouping communication into small (active) periods increases the chance on collisions, hence, other forms of organization have been proposed. This chapter surveys, and details the historic development of, the three most common styles of medium access control for wireless sensor networks: random, slotted, and frame-based organization. and channel conditions at hand. In this chapter we will classify the major trends in MAC design for energy efficiency, and detail the historic advances within each class. We do not provide a thorough performance analysis, but include enough hints for end users to select an appropriate MAC for their (next) WSN deployment.

• Propose a multi-channel, cooperative MIMO MAC protocol for clustered WSNs.