Mobility in wireless sensor networks poses unique challenges to the medium access control (MAC) protocol design. Previous MAC protocols for sensor networks assume static sensor nodes and focus on energyeﬃciency. In this paper, we present a mobilityadaptive, collision-free medium access control protocol (MMAC) for mobile sensor networks. MMAC caters for both weak mobility (e.g., topology changes, node joins, and node failures) and strong mobility (e.g., concurrent node joins and failures, and physical mobility of nodes). MMAC is a scheduling-based protocol and thus it guarantees collision avoidance. MMAC allows nodes the transmission rights at particular timeslots based on the traﬃc information and mobility pattern of the nodes. Simulation results indicate that the performance of MMAC is equivalent to that of TRAMA  in static sensor network environments. In sensor networks with mobile nodes or high network dynamics, MMAC outperforms existing MAC protocols, like TRAMA and S-MAC , in terms of energyeﬃciency, delay, and packet delivery. sensor nodes are static. Researchers have, however, envisioned sensor networks with mobile sensor nodes . In this paper, we show that the current MAC protocols for wireless sensor networks are not suited for mobile sensor network environments, and present a mobility-adaptive, collision-free medium access control (MMAC) protocol for sensor networks. MMAC follows the design principles of TRAMA  a scheduling-based MAC protocol for static multi-hop wireless sensor networks. In mobile environments the ﬁxed frame time of current MAC protocols causes performance degradation in a number of ways: a) the mobile nodes, upon joining a new neighborhood, need to wait for a long time before they can send data, b) in contention-based MAC protocols, there is a considerable increase in packet collisions, c) in schedule-based MAC protocols, the two-hop neighborhood information at each node remains inconsistent for a long period which could effect the correctness of the protocol. A dynamic frame time, that is inversely proportional to level of mobility, is required to cope with these problems. MMAC introduces a mobility-adaptive frame time that enables the protocol to dynamically adapt to changes in mobility patterns, making it suitable for sensor environments with both high and low mobility. MMAC assumes that the sensor nodes are aware of their location. This location information is used to predict the mobility pattern of the nodes according to the AR-1 [11, 12] model. We present a novel mobilityadaptive distributed algorithm that dynamically adjusts the MAC frame time according to mobility. Experimental results indicate that the performance of MMAC is equivalent to that of TRAMA  in static sensor network environments. In sensor networks with mobile nodes or high network dynamics, MMAC outperforms existing MAC protocols, like TRAMA and SMAC, in terms of energy-eﬃciency, delay, and packet delivery. We discuss related work in section 2. Section 3 presents the MMAC protocol and section 4 presents
Wireless sensor networks have emerged as one of the ﬁrst real applications of ubiquitous computing. Sensor networks play a key role in bridging the gap between the physical and the computational world by providing reliable, scalable, fault tolerant, and accurate monitoring of physical phenomena. Sensor network environments, inherently diﬀerent from the Internet, pose some unique challenges to systems researchers. Energy eﬃciency has been considered as the single most important design challenge in sensor networks . Hence, the recent work on medium access control (MAC) protocol for sensor networks focused on energy eﬃciency instead of, traditional wireless MAC design...