Abstract—Wireless sensor networks, WSNs, are an efficient way to deal with low-rate communications in confined environments such as mines or nuclear power plants because of their simplicity of deployment and low cost. In these application domains, WSNs are used to gather data from sensor nodes towards a sink in a multi-hop convergecast structure. In this paper, we focus on a traffic-aware time slot assignment minimizing the schedule length for tree topologies and for two special deployments (i.e. linear and multi-linear) representative of unusual environments. We formalize the problem as a linear program and provide results on the optimal number of slots. We then propose a delay optimized algorithm with two heuristics that minimize on the one hand the energy consumption and on the other hand the storage capacity as secondary criteria. I. CONTEXT AND MOTIVATIONS The spectacular progress in miniaturization of radio and sensor technologies contributes to the development of wireless sensor networks, in short WSNs. WSNs are made of wireless sensor nodes, each of them being equipped with sensing devices, a processing unit and a radio module. Sensor nodes are generally deployed to monitor the physical conditions of their environment. Therefore, WSNs have been frequently put into use for data gathering applications, where sensed data are routed over a tree. Such a communication scheme is also called convergecast. We can cite many examples of automated data convergecast applications like environment monitoring, building automation, military field monitoring, industrial process control, precision agriculture, ehealth, to name a few. In these applications we speak about raw-data convergecast if every packet is forwarded individually. In such a case, intermediate nodes in a data gathering tree simply apply the store and forward strategy, without processing the received packets. Most of these applications share the requirement of deterministic delay bounds and a guarantee on packet delivery. Medium access protocols that are contention-based protocols are clearly inadequate as they suffer from collision and non deterministic delays especially under heavy traffic conditions.

Abstract: Rapid advances in Wireless Sensor Networks (WSNs) indicate that they are becoming increasingly complex. Consequently users and applications are becoming more demanding. Due to unique characteristics of WSNs, like small dimensions and limited resources and capabilities, Quality of Service (QoS) is imposed as one of the key factors of WSNs. In this paper, we surveyed two main approaches for QoS provisioning in WSNs: layered and cross-layer approach. QoS provisioning with layered approach is surveyed in three WSN layers: MAC, network and transport layer. Current de-velopments show that they can be efficiently used for QoS provisioning. However, they consider QoS only as layer spe-cific isolated set of problems and they are highly dependent on the performance of other layers. Cross-layer approach does not have the restrictions as layered approach and hence can dispose with information from all layers of the communication protocol stack. Although it has huge potential to become the most efficient solution for QoS provisioning in WSNs, cur-rent development indicate that there are still many issues and challenges that need to be overcome. Since the concept of the QoS is relatively new in WSNs, there are not a large number of patents currently dealing with this issue, however but in coming years a large increase in the number of such patents is expected. Available patents in this domain are described in the paper.