The MAC layer is the core layer in the network protocol stack that determines the reliability and efficiency of data transmission among the sensor nodes [17]. It has direct control of a sensor node's radio transceiver, hence is responsible for determining the access method of the communication medium. Existing MAC protocols for WSNs can be broadly categorized into two distinct groups: random access, that uses a scheme similar to the Carrier Sense Multiple Access (CSMA), or schedule driven, that uses a scheme similar to the Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA). In random access MAC protocols [37,34,6,7,1,20,22], sensor nodes contend for the communication medium to transmit data, hence data collision is possible. In schedule driven MAC protocols [27,25,21,2,5,35,9,15,36,30,28,3,29], the communication medium is divided into time or frequency slots and two sensor nodes communicate with each other in a uniquely selected slot. Since each communication slot is unique such that no two or more pairs of sensor nodes within communication range are communicating in the same slot, data collision is not likely. At the expense of possibly acceptable end-to-end latency delay, clearly a schedule driven MAC protocol is more suitable in manufacturing environments as it provides a collision-free environment.
Keeping in mind that all existing schedule driven MAC protocols for WSNs are designed for general frameworks, they do not specifically account for signal fading, interference, and obstruction (we term this signal disintegration) once the slot schedules are assigned. As a result, they will degrade in network performance in the presence of signal disintegration. Specifically, signal obstructions cause a transmitted signal to be reflected from the obstructing object and not reach the receiver, resulting in packet loss. If the periodicity and regularity of the signal obstruction is high, then the protocol will suffer massive packet losses. In addition, the battery power of both sending and receiving sensor nodes are also wasted because no successful communication has taken place although their radio transceivers are switched on to transmit and receive data respectively.
Ci et. al [7] proposed a random access MAC protocol for WSNs that estimates the ideal frame size for a data transmission using a stochastic closed-loop control process to optimize network performance and conserve energy. The Kalman Filter and extended Kalman Filter [33] is used in their protocol to predict the state of the communication medium quality based on past history, and approximate the ideal frame size for data transmission at any given time. Although similar approach can be applied to predict the state of the communication medium quality and approximate if the medium is clear enough for data transmission during an assigned slot, such systems are not efficient in WSNs. This is because, such complex stochastic equations require extensive computation before each data transmission and depends heavily on buffered data, hence not memory efficient.