Hybrid MAC

Hybrid MAC is a combination of different protocols such as contention-based MAC and scheduled-based MAC to optimize the performance of wireless sensor networks. For example, contention-based MAC protocols, such as CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), allow nodes to access the medium based on a random backoff interval, which reduces collisions but may result in inefficient utilization of the medium. On the other hand, scheduled-based MAC protocols, such as TDMA (Time Division Multiple Access), divide the medium into time slots and assign them to different nodes, which can achieve high utilization but may not be flexible enough to adapt to changing network conditions. Hybrid MAC solved the issue by using other MAC protocols, During transmission of data if the channel is idle or the channel has low traffic then Hybrid MAC switches to contention-based MAC. If the traffic in the channel increases then it is switched to scheduled-based MAC such as TDMA.

Hybrid MAC Used in Wireless Sensor Networks

The IEEE developed 802.15.4 as a standard for low-rate WPANs, which outlines the PHY and MAC layers for low-power wireless communication in the 2.4 GHz ISM band. It was specifically created for applications that require low data rates, low power consumption, and cost-effectivenesses, such as sensor networks, home automation, and industrial automation. 

The physical layer employs DSSS modulation with a data rate of 250 kbps and works in the 2.4 GHz ISM band that has 16 channels with 5 MHz bandwidth. Additionally, it uses FHSS to prevent interference from other wireless devices. 

On the other hand, the media access control layer implements a CSMA-CA protocol to avoid device collisions. It supports different data packet sizes, ranging from 9 to 127 bytes, and also offers error detection and correction mechanisms.

Cross-Layer MAC

Cross-layer MAC allows the different layers in the protocol stack, typically including physical, MAC, and network layers, to interact and share information with one another. Firstly MAC layers gather information about the state of the channel whether the channel is busy or not. This information will be further used to control the other parameters such as data transmission rate, packet loss rate, and delay.

Once the parameters have been determined, the MAC layer sends the data packets to the PHY layer for transmission over the wireless channel. After the data transmission, the PHY layer sends feedback to the MAC layer about the success or failure of the transmission. If the transmission was unsuccessful. Based on the feedback MAC layer repeats the transmission

Overall, the working of Cross-Layer MAC involves the interaction between the MAC and PHY layers to improve the efficiency of data transmission and energy consumption in WSNs. By optimizing the transmission parameters

Cross-Layer MAC Used in Wireless Sensor Networks

The IEEE 802.11e standard expands on the existing IEEE 802.11 WLAN standard by incorporating Quality of Service (QoS) support. It utilizes a cross-layer approach, allowing the MAC layer to collaborate with higher layers such as the network and application layers, to provide specific services based on the application’s needs.

On the other hand, IEEE 802.16, or WiMAX, is intended for broadband wireless access and utilizes a cross-layer design as well. This design allows the MAC layer to communicate with the physical layer to adjust to the changing channel conditions, such as interference, noise, and fading.

Pre-requisites: Classification of MAC Protocols

In Wireless Sensor Networks (WSNs), the Medium Access Control (MAC) protocol is a set of guidelines that dictate how each node should transmit data over the shared wireless medium. The primary objective of the MAC protocol is to minimize the occurrence of idle listening, over-hearing, and collisions of data packets. By efficiently managing access to the wireless medium, the MAC protocol helps to reduce energy consumption and optimize the use of network resources.