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Recent improvements in affordable and efficient integrated electronic devices have a considerable impact on advancing the state of the art of wireless sensor networks (WSNs) (Sinopoli, Sharp, Schenato, & Sastry, 2003; Hill, Szewczyk, Woo, Hollar, Culler, & Pister, 2000). It constitute a platform of a broad range of applications related to security, surveillance, military, health care, environmental monitoring, inventory tracking and industrial controls (Szewczyk, Osterweil, Polastre, Hamilton, Mainwaring, & Estrin, 2004; Hanada, Hoshino, & Kudou, 2004; Lee & Hashimoto, 2001; Ray, Starobinski, Trachtenberg, & Ungrangsi, 2004). Handling such a diverse range of application will hardly be possible with any single realization.
The medium access control (MAC) protocol plays major role in determining the throughput, latency, bandwidth utilization and energy consumption of the network. Therefore it is of a paramount importance to design and choose the MAC protocol to provide the required quality of service QoS for a given application. There are several MAC protocols available for multihop wireless networks (Chlamtac & Lerner, 1987; Cidon & Sidi, 1989; Ephremides & Truong, 1990) which can be topology dependent or independent (Bao & Garcia, 2001; Chlamtac & Farago, 1994). These protocols are broadly classified as schedule and contention based MAC.
In Raviraj, Sharif, Hempel, & Ci (2005) MOB-MAC is presented for mobile wireless sensor network scenario. MOB-MAC uses an adaptive frame size predictor to significantly reduce the energy consumption. A smaller frame size is predicted when the signal characteristics becomes poor. However the protocol incurs heavy delays due to the variable size in the frame and is not suitable for mobile real time applications. AM-MAC is presented in Choi, Lee, and Kim (2008); it is the modification of S-MAC to make it more useful in mobile applications. In AM-MAC as the mobile node reaches the border node of the second cluster copies and hold the schedule of the approaching virtual cluster as well as the current virtual cluster. By adopting this phenomenon the protocol provides fast connection for the mobile node moving from one cluster and entering the other. The main drawback is the node has to wakeup according to both the schedule but cannot transmit neither receive data packet during the wakeup schedule other than the current cluster. This contributes to significant delay and loss of energy due to idle wakeup. In Pham and Jha (2004) another variation of S-MAC is presented by the name of MS-MAC. It uses signal strength mechanism to facilitate fast connection between the mobile node and new cluster. If the node experience change in received signal strength then it assumes that the transmitting node is mobile. In this case the sender node not only sends the schedule but also the mobility information in the synchronous message. This information is used by the neighboring node to form an active zone around the mobile node so that whenever the node reaches this active zone it may be able to update the schedule according to the new cluster. The down side of this protocol is idle listening and loss of energy. Moreover nodes in the so called active zone spend most of the time receiving synchronous messages rather than actual data packets thus resulting in low throughput and increase latency. In Lin, Qiao, and Wang (2004) another real time mobile sensor protocol DS-MAC is presented. In this protocol according to the energy consumption and latency requirement the duty cycle is doubled or half. If the value of energy consumption is lower the threshome ld value (Te) than the protocol double its wakeup duty cycle to transfer more data, thus increasing the throughput and decreasing the latency of the network. However the protocol requires overheads and during the process of doubling of wakeup duty cycle if the value crosses Te the protocol continues to transmit data using double duty cycle resulting in loss of energy. MD-MAC is proposed in (Hameed, Shaaban, Faheem & Ghoniemy, 2009) which is the extension of DS-MAC and MS-MAC. The protocol enforces Te value and during any time if the value of energy consumption is doubled then it halves the duty cycle. Moreover the mobile node only undergoes neighborhood discovery rather than other neighboring node which forms an active zone as in the case of MS-MAC. MD-MAC is complex and requires high overheads.