Jelena Vlaovic

On the topic of RTT and delivery ratio in query driven Wireless Sensor Networks

Emerging new applications of Wireless Sensor Networks (WSNs) place new and complex requirements on existing systems and continuously propel new research topics. With the proliferation of WSNs in domains such as process control, automation and related domains, the need to establish reliable communication with low latency is becoming intensely expressed. Taking into account WSNs as low power, low cost and low reliability infrastructures, the process of establishing Quality of Service (QoS) support for WSNs is a non-trivial task. Furthermore, the majority of the scientific work focuses on simulations so there is a need to perform experimental measurements on contemporary hardware solutions used in WSNs for comparison. This paper evaluates WSN application for access control system where sensor nodes are query driven and the network follows star topology configuration. Considering specific network configurations, this paper investigates reliability and delay for round-trip communication - RTT. The emphasis is placed on the analysis of network performance from the sensor node point of view. Analysis is performed through simulation and experimental validation of a WSN deployed within the proposed testbed. The investigation of influence of network parameters on the proposed metrics for critical network conditions using simulation results in higher losses, reduced reliability and high values of RTT that needs to be avoided for real network deployment. Finally, comparison of simulated and experimental results yields a conclusion that the simulation does not accurately represent experimental data, and more accurate simulation model of WSN nodes should be proposed in order to mitigate the observed discrepancies.

Evaluation of Quality of Service Provisioning in Large-Scale Pervasive and Smart Collaborative Wireless Sensor and Actor Networks

Abstract With the production of low cost sensors, classical concept of Wireless Sensor Networks (WSNs) evolved into large-scale concept hosting thousands of nodes within a network and generating abundant quantities of data. As these networks are being continuously developed a new class of WSNs are proposed: Wireless Sensor and Actor Networks (WSANs). These networks introduce the actuating component, alongside with the sensing component, where QoS is becoming a very significant factor. The authors of this paper approach the problem of QoS support in large-scale WSAN from a physical layer, where the deployment parameters effects on QoS metrics are demystified. The analysis is formulated on two scenarios: worst case scenario (all nodes transmit data towards the network sink) and best case scenario (a single node transmits a stream of data towards a network sink). For both scenarios two routing protocols were compared, a simple flooding algorithm and a simple distance vector protocol. Also, a new relation between hop count and latency based on transmission power is observed, not reported in the available literature, resulting in a new proposed empirical latency model.

Improving QoS in query-driven WSN using a cross-layered handover algorithm

Quality of Service (QoS) provisioning in Wireless Sensor Networks (WSNs) presents an open research issue within the scientific community because the rapid development of microelectronics proliferates new applications for WSNs. These applications often require a connection of end-to-end delay and high reliability for various communication models. Within this scope, a special class of WSNs are query driven WSNs where each node sends a query to the network sink, which expects a response to the query. As the application of query driven WSNs becomes versatile, the need to establish QoS support becomes intensely expressed, particularly for medium and high traffic loads. An experimental validation for query-based communication in a star configuration topology for various numbers of nodes and packet generation interval is performed within this paper. In existing WSNs, the QoS deteriorates upon increased traffic load due to congestion and the shared medium. This paper proposes a cross-layered handover algorithm in order to improve deteriorated performance and the QoS by means of multi-channel redundancy. Measurement results show that the proposed algorithm improves the delivery ratio by 25% and the RTT by 40% in the worst-case scenario. However, it underperforms upon the heavy traffic load where the trade-off is shown accordingly.

Impact of propagation medium on link quality for underwater and underground sensors

With the rapid development of wireless networks new application domains are continuously proposed. One of these applications includes an underwater and underground sensor which relies on the properties of diminished RF performance to send the gathered information to a base station. Although many researchers deal with the theoretical background of the channel and propagation models, very few experimental studies regarding the link quality were conducted. Due to the fact that new and more powerful sensor nodes are continuously being developed, the question that arises is how these new and more powerful classes of wireless sensors can handle the harsh environment in underwater and underground networks. Therefore, in this paper the authors analyze the impact of soil, water, moisture and other parameters on the link quality between two sensor nodes in various scenarios. The obtained results present a basis for designing and planning an underground/underwater sensor network.

Overview of OFDM channel estimation techniques for DVB-T2 systems

Systems that are modeled according to DVB-T and DVB-T2 standards use Orthogonal Frequency Division Multiplexing (OFDM) as a modulation scheme. OFDM uses N parallel streams to ensure high-rate data transmission. Distinct carriers are used to transmit data streams. In OFDM subcarriers are orthogonal in order to ensure that receiver can distinguish separate signals carried by different subcarriers. Generally there are three approaches in estimating channel transfer function in systems that use OFDM, pilot symbols, scattered pilot tones and eigenvalue-decomposition-based methods. Pilot symbols are mainly used for initial channel estimation. Scattered pilot tones are used to help track changes in channels over time. The complexity of the first two methods can be reduced with the eigenvalue-decomposition-based methods. In recent studies multiple channel estimation techniques, mostly based on pilot patterns stemmed from initial estimation techniques. This paper gives an overview of the standard channel estimation methods used in OFDM and recently developed improved channel estimation methods.