http://www.inf.ufes.br/~zegonc/material/Redes%20de%20Sensores%20sem%20Fio/MAC%20in%20WSN.pdf

Medium access control in wireless sensor networks

Techniques to improve the standby time of a station in a wireless network are described An access point may advertise or convey a maximum listen interval and/or an association timeout supported by that access point A station may operate in a power-save mode and may wake up every listen interval to receive a beacon and any potential traffic for the station The station may select a suitable listen interval based on the maximum listen interval The station may be dormant for a longer duration than the listen interval and may become active at least once in every association timeout in order to keep the association with the access point alive The access point may also send broadcast and multicast traffic that might be of interest to stations in the power-save mode less frequently and using a special indication message

Standby time improvements for stations in a wireless network

Broadcast or multicast traffic is classified into different types of traffic and different transmission schedules associated with each of the different types of traffic The different types of broadcast and multicast traffic may be implemented in an 80211-based system where an access point is configured to classify broadcast and multicast traffic into different types and assign different transmission schedules to each of the different traffic types An associated wireless station may thereby wake from a power save mode only at intervals corresponding to delivery times of the types of traffic that the wireless station has elected to receive In some aspects the different types of broadcast and multicast traffic may comprise user plane traffic and control plane traffic

Standby time improvements

Recent advances in wireless communications and sensor technologies have enabled the development of low-cost wireless sensor networks (WSNs) for a wide range of applications. Medium access control (MAC) protocols play a crucial role in WSNs by enabling the sharing of scarce wireless bandwidth efficiently and fairly. This article provides a survey of the literature on MAC protocols for WSNs. We first briefly describe the unique features of WSNs. We then review representative MAC protocols from the following four categories: contention-based protocols, contention-free (scheduled-based) protocols, hybrid protocols, and preamble sampling protocols. Our discussions focus on the background, main features, operation procedures, major design issues, and the advantages and disadvantages of these protocols. We also present an analysis of the inherent and desirable features of the protocols, and the key challenges of MAC technology for WSNs. Finally, we present our view on future research directions for WSN MAC protocols in a reader-friendly way using illustrative diagrams.

A survey and projection on medium access control protocols for wireless sensor networks

Recent developments in sensor technology, as seen in Berkeley's Mica2 Mote, Rockwell's WINS nodes and the IEEE 802.15.4 Zigbee, have enabled support for single-transceiver, multi-channel communication. The task of channel assignment with minimum interference, also named as the 2-hop coloring problem, allows repetition of colors occurs only if the nodes are separated by more than 2 hops. Being NP complete, development of efficient heuristics for this coloring problem is an open research area and this paper proposes the Dynamic Channel Allocation (DCA) algorithm as a novel solution. Once channels are assigned, a Medium Access Control protocol must be devised so that channel selection, arbitration and scheduling occur with maximum energy savings and reduced message overhead, both critical considerations for sensor networks. The contribution of this paper is twofold: (1) development and analysis of the DCA algorithm that assigns optimally minimum channels in a distributed manner in order to make subsequent communication free from both primary and secondary interference and (2) proposing CMAC, a fully desynchronized multi-channel MAC protocol with minimum hardware requirements. CMAC takes into account the fundamental energy constraint in sensor nodes by placing them in a default sleep mode as far as possible, enables spatial channel re-use and ensures nearly collision free communication. Simulation results reveal that the DCA consumes significantly less energy while giving a legal distributed coloring. CMAC, our MAC protocol that leverages this coloring, has been thoroughly evaluated with various modes in SMAC, a recent protocol that achieves energy savings through coordinated sleeping. Results show that CMAC obtains nearly 200% reduction in energy consumption, significantly improved throughput, and end-to-end delay values that are 50-150% better than SMAC for our simulated topologies.

Channel allocation and medium access control for wireless sensor networks

We have developed adaptive coordinated medium access control (AC-MAC), a contention-based medium access control protocol for wireless sensor networks. To handle the load variations in some real-time sensor applications, ACMAC introduces the adaptive duty cycle scheme within the framework of sensor-MAC (S-MAC). The novelty of our protocol is that it improves latency and throughput under a wide range of traffic loads while remaining as energy-efficient as S-MAC. We illustrate such optimized trade-offs of AC-MAC via extensive simulations performed over wireless sensor networks. Our simulation results show that AC-MAC is as energy-efficient as S-MAC while its latency and throughput are always trying to follow the classic IEEE 802.11 MAC (no duty cycle), which outperform the S-MAC (fixed duty cycle), specially under the heavy load.

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Jin Ai

Papers

An adaptive coordinated medium access control for wireless sensor networks