Majid Nabi

A robust protocol stack for multi-hop wireless body area networks with transmit power adaptation

Wireless Body Area Networks (WBANs) have characteristic properties that should be considered for designing a proper network architecture. Movement of on-body sensors, low quality and time-variant wireless links, and the demand for a reliable and fast data transmission at low energy cost are some challenging issues in WBANs. Using ultra low power wireless transceivers to reduce power consumption causes a limited transmission range. This implies that a multi-hop protocol is a promising design choice. This paper proposes a multi-hop protocol for human body health monitoring. The protocol is robust against frequent changes of the network topology due to posture changes, and variation of wireless link quality. A technique for adapting the transmit power of sensor nodes at run-time allows to optimize power consumption while ensuring a reliable outgoing link for every node in the network and avoiding network disconnection.

MCMAC: An Optimized Medium Access Control Protocol for Mobile Clusters in Wireless Sensor Networks

Wireless sensor networks (WSNs) are developing into a promising solution for many applications, for example in healthcare. In many scenarios, there is some form of node mobility. The medium access control (MAC) mechanisms should support the expected kind of mobility in the network. Mobility is particularly complicating for contention free MAC protocols like TDMA-based protocols, because they dedicate unique slots to every node in a neighborhood. In scenarios such as body-area networking, some clusters of nodes move together, creating further challenges and opportunities. This paper proposes MCMAC (Mobile Cluster MAC), a TDMA-based MAC protocol to support mobile clusters in WSNs. The proposed protocol does not need adaptation time after movement of clusters. Several optimization mechanisms are proposed to decrease power consumption. Simulation results show that the optimizations decrease power consumption of nodes around 70% without increasing latency of data transmission compared to the non-optimized version.

Dynamic data prioritization for quality-of-service differentiation in heterogeneous Wireless Sensor Networks

In many applications of Wireless Sensor Networks (WSNs), heterogeneity is a common property in terms of different sensor types and different circumstances like node location, link quality, and local node density. In many applications, there are several different sensor types with entirely different Quality-of-Service (QoS) requirements. The requirements may also vary over time according to the application scenario and also due to network dynamics. Different requirements appeal different approaches while forwarding sensed data through a multi-hop communication network. This paper proposes a dynamic priority assignment strategy to be used for data routing in heterogeneous WSNs aiming to fairly propagate information according to its importance and requirements. To cope with heterogeneity and dynamics, nodes in the routing path dynamically compute priorities for individual data items according to the attached QoS requirements. We apply the proposed strategy for a healthcare monitoring application scenario which consists of an ambient network and several mobile clusters of nodes in the form of Wireless Body Area Networks (WBANs). The nodes have very different requirements and WBANs show a high mobility in the network with more stringent demands. The results show a large improvement in the achieved QoS for more demanding information.

A Probabilistic Acknowledgment Mechanism for Wireless Sensor Networks

The inherently unreliable communication infrastructure compel WSN protocols to employ error control mechanisms. Traditionally, error control is achieved by a retransmission scheme using acknowledgment mechanisms. WSN architectures are severely resource constrained and the additional energy expense of transmitting error control messages can seriously degrade network lifetime. In this paper, we analyze performance of error control schemes for the case of point-to-multipoint communication. An explicit acknowledgment mechanism may provide for reliable communication, but has two major drawbacks: 1) the over head is significant for small data messages, and 2) in case of asymmetrical communication links, multi-hop dissemination of acknowledgments is required. As an alternative to such explicit acknowledgment schemes we propose the use of probabilistic acknowledgments. In this probabilistic scheme, a sender estimates the probability that a message has been successfully delivered, based on information about the quality of the radio channel. A message is then retransmitted until the probability of successful delivery reaches a defined threshold value. Network capacity available for error control can be distributed prudently among all information items to be disseminated, possibly taking into account different application requirements. We formulate are transmission control strategy which results in minimal latency and maximal message delivery ratio.

On-demand data forwarding for automatic adaptation of data propagation in WBANs

Practical experience reveals the characteristic properties of Wireless Body Area Networks (WBANs), signifying the need for a well-designed communication protocol. High mobility, stringent resource constraints, and low and time-variant quality of wireless links are some of the challenging issues in WBANs. Typical applications further have varying Quality-of-Service requirements and demand reliable and fast data transmission at low energy cost. This paper proposes a simple, robust, and optimized protocol for data propagation in WBANs. A hybrid design approach is proposed that automatically adapts the network topology according to the connectivity status of the network. An on-demand data forwarding mechanism combined with an epidemic data propagation strategy realize a proper data delivery and robustness while minimizing the idle listening and unnecessary data forwarding. Several experiments using wireless sensor nodes deployed on a body reveal how this protocol can automatically adapt the network in different situations. The results confirm the robustness and improved behavior of this protocol in comparison with existing fixed protocol architectures.

TIGeR: A Traffic-Aware Intersection-Based Geographical Routing Protocol for Urban VANETs

In recent years, vehicular ad-hoc networks (VANETs) have received increasing interests because of their promising solutions in many urban applications. VANETs are distinguished from other kinds of ad-hoc networks, such as Mobile Ad-hoc Networks (MANETs), by high mobility and reduced communications. The topology of the network is highly time-varying due to high mobility of wireless nodes, and also joining and leaving nodes. This makes it challenging to find and maintain efficient and reliable data forwarding routes between different nodes in the network. On the other hand, equipment such as positioning systems usually exist in current vehicles which can be used to improve the efficiency of packet dissemination. This paper proposes TIGeR, a new Traffic-aware Intersection-based Geographical Routing protocol. Nodes that are at intersections make routing decision to forward packets based on both the local vehicular traffic information of different roads and the roads angle with respect to the direct vector toward the destination. Local vehicular traffic information is considered as a sign of network connectivity in a road. Simulation results show that TIGeR improves the packet delivery ratio, especially in sparse networks.

Configuring multi-objective evolutionary algorithms for design-space exploration of wireless sensor networks

Wireless sensor networks (WSNs) consist of numerous sensor nodes with several possible configurations for each node. As there are a lot of nodes in a typical WSN, each with its own set of configurations, the number of configurations for the network as a whole is huge and the design space is extremely large. The configuration of a WSN has a strong effect on the quality of services of running applications and the performance of the WSN. Multi-objective evolutionary algorithms (EAs) are well suited to explore the trade-offs in a WSN design space. However, an EA has many configuration parameters in itself. This paper presents several guidelines for configuring a multi-objective EA for design space exploration, given a specification of the WSN to be configured and a time budget available for analysis. We demonstrate the effectiveness of these guidelines on a specific type of WSN that uses a gossip strategy for disseminating data over the network.

Enhanced Time-Slotted Channel Hopping in WSNs Using Non-intrusive Channel-Quality Estimation

Cross-technology interference on the license-free ISM bands has a major negative effect on the performance of Wireless Sensor Networks (WSNs). Channel hopping has been adopted in the Time-Slotted Channel Hopping (TSCH) mode of IEEE 802.15.4e to eliminate blocking of wireless links caused by external interference on some frequency channels. This paper proposes an Enhanced version of the TSCH protocol (ETSCH) which restricts the used channels for hopping to the channels that are measured to be of good quality. The quality of channels is extracted using a new Non-Intrusive Channel-quality Estimation (NICE) technique by performing energy detections in selected idle periods every timeslot. NICE enables ETSCH to follow dynamic interference well, while it does not reduce throughput of the network. It also does not change the protocol, and does not require non-standard hardware. ETSCH uses a small Enhanced Beacon hopping Sequence List (EBSL) to broadcast periodic Enhanced Beacons (EB) in the network to synchronize nodes at the start of timeslots. Experimental results show that ETSCH improves reliability of network communication, compared to basic TSCH and a more advanced mechanism ATSCH. It provides higher packet reception ratios and reduces the maximum length of burst packet losses.

Fast simulation methods to predict wireless sensor network performance

With the increasing capabilities of Wireless Sensor Networks (WSN), complexity and expectation of the WSN applications increase as well. In order to make design-space exploration possible, it is necessary to have fast models that provide adequate insight in system behavior. In this paper, we propose a highly abstracted, hierarchical, system-level modeling method for WSN. Based on the model properties, fast simulation techniques can be applied. First, an abstract discrete event simulation based on a Probabilistic Graph Model (PGM) is introduced. Then, a fast Monte Carlo simulation approach is proposed for speeding up the simulation process. This approach combines Stochastic-Variable Graph Models (SVGM), providing a high level of abstraction, with shortest path calculations. As a case study, a temperature mapping application in a gossip-based WSN is used, showing a good accuracy of the model predictions.

Efficient Cluster Mobility Support for TDMA-Based MAC Protocols in Wireless Sensor Networks

Node mobility is a key feature of using Wireless Sensor Networks (WSNs) in many sensory applications, such as healthcare. The Medium Access Control (MAC) protocol should properly support the mobility in the network. In particular, mobility is complicated for contention-free protocols like Time Division Multiple Access (TDMA). An efficient access to the shared medium is scheduled based on the nodes local neighborhood. This neighborhood may vary over time due to node movement or other dynamics. In scenarios including body-area networking, for instance, some clusters of nodes move together, creating further challenges but also opportunities. This article presents a MAC protocol, MCMAC, that provides efficient support for cluster mobility in TDMA-based MAC protocols in WSNs. The proposed protocol exploits a hybrid contention-free and contention-based communication approach to support cluster mobility. This relieves the protocol from rescheduling demand due to frequent node movements. Moreover, we propose a listening scheduling mechanism to avoid idle listening to mobile nodes that leads to a considerable energy saving for sensor nodes. The protocol is validated by performing several experiments in a real-world large-scale deployment including several mobile clusters. The protocol is also evaluated by extensive simulation of networks with various scales and configurations.