## 3 Related Work
The minimum distance between the source node and the receiver used by the MS in [23], in order to initiate the handover process, is defined in Equation (1) [26]:  
\[d=R-(n-w)\bigg{(}\frac{N_{data}}{R_{t}}+\frac{N_{b}}{R_{t}}+2T_{SIFS}\bigg{)}v \tag{1}\]  
where \(R\) is the radio range, \(n\) is the number of data packets to be transmitted. Among these data, \(w\) is the first acknowledged packets. \((n-w)\) data packets are left for transmission. \(N_{data}\), \(N_{b}\), \(R_{t}\) and \(T_{SIFS}\) represent respectively the data packet size, the ACK beacon size, the transmission rate and the time necessary to switch from transmitting to receiving mode. Finally, \(v\) represents the velocity of movements. The authors in [24] propose the mobility aware MAC (MA-MAC) protocol in classical wireless sensor networks. MA-MAC is an extending implementation of any energy efficiency protocols such as BMAC and XMAC. This proposed protocol is implemented in all mobile nodes in the network, and it evaluates the acknowledgments packets in order to determine the quality of transmission using the RSSI values. If the case of a deterioration of RSSI value, the handover initiates by switching the transmission of packets from unicast mode to broadcast mode. A neighboring discovery is launched while broadcasting data packets. Once a neighbor node replies the neighboring discovery, the mobile node establishes a link with this node and switches again to unicast mode then this node starts sending the handover data. The mobility model used to study MA-MAC protocol is based on the human activities and movements with taking into consideration the slow speed of movements of people, which is 1.5 m/s. In [27], the authors propose a handover mechanism based on SMAC protocol for cluster-based wireless sensor networks. Each cluster in the wireless sensor network shares a schedule for transmitting data which is similar to SMAC protocol. The paper applies a small modification in the scheduling process, which is the Node-Type flag. By the end of this process, each cluster is divided into three types: cluster head, border node, and stationary node. The detection of the deterioration of links in the proposed handover mechanism is based on the RSSI value and link quality. In the case of degradation of link quality, a stationary node changes its flag to a mobile node. While the mobile node is moving, it receives a synchronization packet from the border node. When it receives this packet, it sets a handover-bit in its synchronization packet and broadcasts it to process the handover. The border node also broadcasts the synchronization packet, and it includes the schedule of the neighbor cluster in this packet. Thus, the mobile node can receive a copy of the neighbor cluster schedule and adopts its schedule and the schedule of the neighbor cluster as well. In this case, the mobile node acts like a border node, which allows handover process to another cluster. The mobile nodes use a random walk mobility model varying their speed from 0.5 m/s to 20 m/s. A zone-based routing mobile sensor network (Zoro MSN) is proposed in [28]. The network is composed of zones, and each zone has a zone head, and any node can be a mobile node. Routingdata using the proposed protocol is based on the discovery process of zone heads to find nodes in its vicinity in order to route data collected to other zones till data arrive at the base station (sink) which is considered as static. The mobility model used in this protocol is a random model with a random variation in the speed of the mobile nodes. There are also some research works that propose mobility support protocols with a handover mechanism based on 6 LoWPAN technology [4; 29]. The main idea of 6 LoWPAN technology is proposing an adaptation layer between the link layer and the network Layer to address the problem of IPv6 packets size compared to IEEE 802.15.4 frame size used in wireless sensor network with taking into consideration the characteristics of wireless sensor network.