Summary: MAC protocol classification for Wireless Sensor Networks

Wireless sensors have been described in detail in the previous article. As the focus of future technological development, wireless sensors are one of the two major technologies-Wireless Technology + micro-sensing technology. This article focuses on the MAC protocol classification of wireless sensor networks.

Classification Based on MAC protocol of wireless sensor networks using node Access Channels

Currently, for different sensors "> sensor network applications, researchers have proposed various MAC protocols from different aspects. However, there is still a lack of a unified classification method for the MAC protocol of WSN. The MAC classification method proposed in this section is based on the method of accessing the node: assigning a fixed wireless channel to the node or randomly competing access channel to the node. the MAC protocol of the sensor network is divided into four types: contention-based MAC protocol; Scheduling-based MAC protocol; non-Collision (Collision free) MAC protocol; Hybrid) MAC.

Classification of MAC protocol in wireless sensor networks-based on competitive MAC protocol

Most distributed MAC protocols use the carrier listening or conflict avoidance mechanism and use additional signaling control messages to handle node hiding and exposure issues. The MAC protocol based on competing random access means that wireless channels are used through competition when nodes need to send data. The MAC protocol of adopts Carrier SensorMultiple Access with Collision Avoidance (CSMA/CA), which is a typical competitive MAC protocol. Based on the IEEES02.11 MAC protocol, researchers have proposed many competitive MAC protocols for sensor networks. For example: s-MAC protocol, T-MAC protocol, ARC-MAC protocol, Sift-MAC protocol, Wise-MAC protocol and so on.

MAC protocol classification for wireless sensor networks-MAC protocol based on CSMA/CA

CSMA/CA is mainly used in the Protocol of IEEE802.11MAC protocol in the Distributed Collaborative Learning (DCF) mode. In DCF mode, when a node detects that the wireless channel is busy, it uses the CSMA/CA mechanism and random backoff algorithm to share the wireless channel.

Basically, 802.15.4 uses CSMA/CA communication similar to IEEF802.11. nodes listen to the channel regularly and receive Beacon frames. when no data is sent or received, it enters the sleep turntable. Coordinator caches the data sent to the sleep node and regularly sends Beacon frames. The frames carry the data to the destination node address, after the node discovers that the Coordinator caches the data sent to itself, it sends a POLL frame to it, indicating that it can receive the data. After receiving the POLL frame, the codecator first sends an ACK frame to the node, after receiving the cached data, the node sends an ACK frame to the Coordinator.

Wireless sensor network MAC protocol classification-S-MAC Protocol

S-MAC (Sensor-MAC) protocol is an earlier MAC protocol for Wireless Sensor Network (WSN). Based on 802.11MAC, it uses various mechanisms described below to reduce node energy consumption. Fixed periodic listening and sleep: to reduce energy consumption, the sensor "> sensor nodes should be in sleep state with low power consumption as much as possible. The S-MAC protocol uses low duty cycle for sleep/listening. In order to make the S-MAC Protocol have good scalability, many different virtual clusters are formed in the Coverage Network.

Message transmission technology: for wireless channels, the transmission error is proportional to the packet length. The probability of successful transmission of a short packet is greater than that of a long packet. In the S-MAC protocol, message passing technology divides long messages into several short packets, and uses the RTS/CTS handshake mechanism to send the entire long message at one time, which improves the sending success rate and reduces the control message. Adaptive Traffic listening mechanism: Sensor "> sensor nodes do not enter sleep immediately after communication with neighboring nodes, but keep listening for a period of time. The adaptive traffic listening mechanism is used, reduces the transmission latency in the network.

Compared with MAC, S-MAC protocol has greatly improved in energy saving. However, the introduction of the sleep mechanism increases network transmission latency and reduces throughput. In view of the shortcomings of S-MAC protocol, the researchers improved it and proposed a S-MAC protocol with adaptive sleep.

Wireless sensor network MAC protocol classification-T-MAC Protocol

T-MAC (Timeout-MAC) protocol and adaptive sleep S-MAC protocol basic idea is roughly the same. DATA transmission still uses the four handshaking mechanisms of RTS/CTS/DATA/ACK. The difference is that a TA (Time Active) Time slot is inserted in the Active Time slot of the node, if there is no time between the TA time slot, the activity ends and enters the sleep state. The value of TA is crucial to the performance of T-MAC protocol. The constraints are as follows: TA = m (C + R + T), m> 1, where C is the competitive channel time, R indicates the time when the RTS group is sent, and T indicates the time from the end of the RTS group to the start of the CTS group. During simulation, we usually select m = 1.5, that is, TA = 1.5.