This paper is primarily concerned with the performance of Medium Access Control (MAC) layer plans for Wireless Sensor Networks (WSNs) in the context of buffer management solutions. We propose a novel buffer management solution that improves the general performance of MAC layer plans, in particular those crafted for WSNs. An analytical model is introduced in order to evaluate the cost of different buffer management solutions. The proposed buffer management solution, Single Queue Multi Priority (SQMP), is compared with well-known Single Queue Single Priority (SQSP) and Multi Queue Multi Priority (MQMP) buffer management solutions. All buffer management solutions are investigated in terms of throughput performance, utilization of the buffer and prioritization capabilities. Despite the relatively good performance of the different buffer management solutions in uncongested networks, the characteristic features of WSNs cause a degradation in the performance. In bursty conditions, SQMP controls and manages this degradation more effectively in comparison with the other two solutions. Simulations based on Omnet++ and Castalia confirm the performance improvements of our buffer management solution.

Wireless Sensor Networks (WSNs) have been proposed for monitoring vital signs of patients at home. This scenario requires inter-cell mobility; however, WSNs are not designed to support this characteristic. In this paper we propose a cross-layer protocol to manage the handoff, called WSN-HaDaS (Handoff aware of Data Sending), which operates in the transport layer and medium access control (MAC) sub-layer based on an interaction between the layers (transport and MAC). This protocol interacts with a sending data mechanism (like TCP protocol) to notify the beginning or ending of the handoff process; therefore, the mechanism can stop or resume data sending, respectively. Therefore, WSN-HaDaS prevents packet loss during the handoff process. WSN-HaDaS comprises two main processes to manage mobility: Monitoring Handoff Trigger (MHT) and Handoff Execution Process (HEP); they are responsible for generating the handoff warning messages and executing the handoff process, respectively. Therefore, MHT delay and HEP delay are used as the key performance metrics. To evaluate the proposal, we use a physical test-bed in an indoor environment with the intention of obtaining practical results. The results demonstrate that the proposed protocol performs the handoff process with less delay than the selected reference work. They also show that WSN-HaDaS is an appropriate solution to provide inter-cell mobility in WSNs. Furthermore, we demonstrate the possibility of embedding the WSN-HaDaS in devices with limited resources using the IEEE 802.1.5.4 standard.

Optimizing lifetime of a wireless sensor network has received considerable attention in recent years. In this paper, using the feasibility and simplicity of grid-based clustering and routing schemes, we investigate optimizing lifetime of a two-dimensional wireless sensor network. Thus how to determine the optimal grid sizes in order to prolong network lifetime becomes an important problem. At first, we propose a model for lifetime of a grid in equal-grid model. We also consider that nodes can transfer packets to a grid which is two or more grids away in order to investigate the trade-off between traffic and transmission energy consumption. After developing the model for an adjustable-grid scenario, in order to optimize lifetime of the network, we derive the optimal values for dimensions of the grids. The results show that if radio ranges are adjusted appropriately, the network lifetime in adjustable-grid model is prolonged compared with the best case where an equal-grid model is used.