In this paper we are concerned with the problem of data forwarding from a wireless body area network (WBAN) to a gateway when body shadowing affects the ability of WBAN nodes to communicate with the gateway. To solve this problem we present a new WBAN architecture that uses two communication technologies. One network is formed between on-body nodes, and is realized with capacitive body-coupled communication (BCC), while an IEEE 802.15.4 radio frequency (RF) network is used for forwarding data to the gateway. WBAN nodes that have blocked RF links due to body shadowing forward their data through the BCC link to a node that acts as a relay and has an active RF connection. For this architecture we design a network layer protocol that manages the two communication technologies and is responsible for relay selection and data forwarding. Next, we develop analytical performance models of the medium access control (MAC) protocols of the two independent communication links in order to be used for driving the decisions of the previous algorithms. Finally, the analytical models are used for further optimizing energy and delay efficiency. We test our system under different configurations first by performing simulations and next by using real RF traces.

We consider the problem of modeling the transmission of real-time data from a single node of a wireless sensor network to the next hop or access point. Generated packets are placed in a single position buffer and are transmitted over the wireless medium to the next hop, or they are discarded and replaced when a new data packet is generated from the sensor. To increase the percentage of packets delivered on-time to the next hop, we introduce a thresholding policy that is supported by an analytical model and it is responsible for deciding whether to transmit a data packet or drop it and transmit the next one. Our model considers the behavior at single sensor where data are generated with a Poisson process and have a fixed deadline associated to them while the impact of the other sensors is modeled through their effect on the MAC service time. However, we also evaluate the performance of the packet dropping scheme in a multi-hop sensor chain. The proposed policy leads to a higher percentage of on-time delivered packets in both scenarios.

In a number of application domains, the volatility of the environment where Wireless Sensor Networks (WSNs) should operate engenders time constraints on the generation, processing, and communication of sensory data. In this paper, we investigate the use of network coding and service reneging for the timely delivery of messages between wireless sensor nodes that utilize the IEEE 802.15.4 MAC/PHY standard. More specifically, we study the real-time performance of algebraic coding and traffic regulation under different traffic loads and for different timeliness requirements. Our simulation results indicate that both techniques can be on their own effective measures to improve on-time delivery of messages in overload conditions. An additional gain in performance is obtained when coding is carefully coupled with a traffic regulation based on proactive cleaning of transmission queues.

The paper investigates the scheduling of packets under overload in the context of wireless building control networks. We focus on the transmission specification of the IEEE 802.15.4 standard to provide actual transmission estimates. The paper analyses the optimal conditions for sending periodic packets with 1 or 2 transmission times and fixed deadlines. Simulations provide the transceiver usage values under the calculated optimal scheduling conditions. The simulations extend the results by looking at 8 transmission times and an exponential distribution of packet release times. A counterintuitive result is the occurrence of a performance decrease with increasing deadline, other conditions remaining constant.

This paper outlines an efficient variation of the Flooding Time Synchronization Protocol (FTSP) on real hardware with an IEEE 802.15.4 MAC layer. The paper compares the performance of two clock drift estimation techniques: Least Squares Linear Regression and the Kalman filter. In assessing the viability of time synchronization in an industrial setting, our reliance on real hardware gives confidence for the deployment in future products. The concrete result is a high time synchronization accuracy, with an achievable average error of 0.4 μs, and a repetition interval of a few seconds, while using a star network topology.