Knut Grythe

Linking Acoustic Communications and Network Performance: Integration and Experimentation of an Underwater Acoustic Network

Underwater acoustic networks (UANs) are an emerging technology for a number of oceanic applications, ranging from oceanographic data collection to surveillance applications. However, their reliable usage in the field is still an open research problem, due to the challenges posed by the oceanic environment. The UAN project, a European-Union-funded initiative, moved along these lines, and it was one of the first cases of successful deployment of a mobile underwater sensor network integrated within a wide-area network, which included above water and underwater sensors. This contribution, together with a description of the underwater network, aims at evaluating the communication performance, and correlating the variation of the acoustic channel to the behavior of the entire network stack. Results are given based on the data collected during the UAN11 (May 2011, Trondheim Fjord area, Norway) sea trial. During the experimental activities, the network was in operation for five continuous days and was composed of up to four Fixed NOdes (FNOs), two autonomous underwater vehicles (AUVs), and one mobile node mounted on the supporting research vessel. Results from the experimentation at sea are reported in terms of channel impulse response (CIR) and signal-to-interference-plus-noise ratio (SINR) as measured by the acoustic modems during the sea tests. The performance of the upper network levels is measured in terms of round trip time (RTT) and probability of packet loss (PL). The analysis shows how the communication performance was dominated by variations in signal-to-noise ratio, and how this impacted the behavior of the whole network. Qualitative explanation of communication performance variations can be accounted, at least in the UAN11 experiment, by standard computation of the CIR and transmission loss estimate.

Underwater acoustic network performance: Results from the UAN11 sea trial

An underwater acoustic network (UAN) represents a communication infrastructure that can offer the necessary flexibility for continuous monitoring and surveillance of critical infrastructures located by the sea. Given the current limitation of acoustic-based communication methods, a robust implementation of UANs is still an open research field. The FP7 UAN project moved along these lines, and it was one of the first cases of successful deployment of a mobile underwater sensor network integrated within a wide-area network, which included above water and underwater sensors. This contribution gives details on the UAN network structure and equipment. It reports statistics on the performance of the system as collected during the project final sea trial, which was held in Trondheim, Norway, in May 2011. The UAN network was in operation for five continuous days and was composed of up to four fixed nodes, two autonomous underwater vehicles and one mobile node mounted on the supporting research vessel. Results from the experimentation at sea are reported in terms of channel impulse response and signal to noise plus interference ratio as measured by the acoustic modems during the sea tests. The performance of the upper network levels are measured in terms of round trip time and probability of packet loss. Finally, the experimental results have been compared with those obtained in simulation using the BELLHOP acoustic code, fed with the environmental data gathered during the sea trial.

Quality of Service, Adaptation, and Security Provisioning in Wireless Patient Monitoring Systems

Modern patient monitoring systems are designed to put the individual into the centre of the system architecture. In this paradigm, the patient is seen as a source of health-relevant data that are processed and transferred. Patient monitoring systems are used in health care enterprises as well as in paramedic, mobile, and home situations to foster ambient assisted living (AAL) scenarios. There are a multitude of standards and products available to support Quality of Service (QoS) and security goals in patient monitoring systems. Yet, an architecture that supports these goals from data aggregation to data transmission and visualisation for end user has not been developed. Medical data from patient monitoring systems includes sampled values from measurements, sound, images, and video. These data often have a time-aspect where several data streams need to be synchronised. Therefore, rendering data from patient monitoring systems can be considered an advanced form of multimedia data. We propose a framework that will fill this QoS and security gap and provide a solution that allows medical personnel better access to data and more mobility to the patients. The framework is based on MPEG-21 and wireless sensor networks. It allows for end-to-end optimisation and presentation of multimedia sensor data. The framework also addresses the QoS, adaptation and security concerns of handling this data. In Section 2 we present background on patient monitoring systems, their requirements and how we envision communication is handled. We present communication systems in Section 3 and how to treat QoS in Section 4. A short introduction to data streaming, binary XML and how they relate to patient monitoring systems is presented in Section 5. In Section 6we our proposed solution for the framework and present a security analysis of it in Section 7. Finally, we offer our conclusions in Section 8. 36

On the use of the MPEG-21 framework in medical wireless sensor networks

This paper proposes a system architecture for wireless sensor network (WSN) using the MPEG-21 multimedia framework in medical applications. It has been envisioned that future hospitals will have networks comprising WSNs for low rate medical sensors as well as other network nodes supporting high rate audiovisual content. The increasing collection and variety of media content (multimedia) in such a scenario, needs a framework for the interaction with the external users regarding data filtering, meta information tagging, authentication and data rights control. Furthermore due to different user terminals and network resources, media adaptation will become important to provide reliable and robust quality of services. The MPEG-21 standard seems to have potential to meet some of the mentioned requirements. In this paper, we argue for an extension of the MPEG-21 terminology for use in biomedical wireless sensor networks and incorporate the requirements needed for medical applications. We show the architecture of a demonstration prototype based on this extended MPEG-21 framework that is under development, capable of displaying selected biomedical sensor data. The deployment of such a system may become warranted in future healthcare enterprises.

Non-perfect channel estimation in OFDM-MIMO-based underwater communication

The main focus in this publication is on the mean square error of underwater acoustic channel estimators as function of the delay and Doppler spreads of the channel, and the effect this estimation error has on the bit error rate performance of the system both using conventional single antennas (SISO) and when using multiple antennas (MIMO). It is investigated at which delay and Doppler spreads the decoding of the signal in the receiver becomes erroneous. It is assumed that there is no non-uniform Doppler shift. The radio communication standard IEEE 802.16e is modified to match underwater communication conditions. The system parameters are taken from measurements conducted in the Trondheim harbour in Norway in 2007. The channel estimator used is not optimal in the Wiener interpolator sense. Hence, the estimator is sub-optimal, but shows good performance and has relatively low complexity. For the described communication system to perform well the results indicate that movements in the water should be less than 0.01–0.1 m/s, and delay spreads should be less than 0.05–0.5 ms. In systems where the main problem is large Doppler spread, the number of sub-carriers should be small. In systems where the main problem is large delay spread, the number of sub-carriers should be large. The use of MIMO makes the system more robust against estimation errors. The density of pilot symbols may be increased to reduce the channel estimation error somewhat, at the expense of reduced efficiency. Considering the Trondheim harbour channel measurement results and their variability throughout the year, we find that the tested system copes well with the summer conditions while the winter conditions seems to be more challenging.

Effects of Channel Estimation Errors in OFDM-MIMO-Based Underwater Communications

State-of-the-art radio communication systems are in a large extent based on multi-carrier communication (OFDM) and multiple antennas (MIMO). In this paper the performance of such systems adapted to an underwater acoustic communication channel is assessed. The effect of the channel characteristics on an OFDM-MIMO scheme similar to that used in WiMAX (IEEE802.16e) is analyzed, in particular related to channel estimation error. Simulation results illustrate the relation between estimation error and BER performance for single antenna systems (SISO) and when a MIMO technique is applied.

The Trondheim harbour: Acoustic propagation measurements and communication capacity

This paper presents results from a propagation measurement campaign carried out in the Trondheim harbour during the period from June to November 2007. Two vertically mounted transducers operating at a carrier frequency of 38 kHz permitted both single-input/single-output (SISO) and multiple-input/multiple-output (MIMO) channel measurements. The upper transducers at both sides were mounted around 2 meters from the sea surface. The sound velocity profile measurements showed large variations in the upper layers of the water column during the campaign period. Due to the fixed mechanical transducer constructions, the observed Doppler spread was low. The Delay spread however varied from 0.5 ms in the summer up to 9 ms in November. The calculated spatial multiplexing capacity within a 3 kHz bandwidth of the MIMO topology gave a factor in the order of 1.8 capacity improvement compared to derived SISO capabilities. The reference SISO propagation channels used in the calculations were one of the estimated elements of the corresponding MIMO channel matrices. Channel state information (CSI) at the transmitter maximises the capacity, particularly at low signal to noise (SNR) rations. Simulations comparing capacities achieved with and without transmitter CSI are shown. The results show that for the observed channels, spatial multiplexing MIMO capacity outperforms SISO and verified that CSI is beneficial at decreasing SNR values.

Interactive system design and end-to-end optimization in sensor networks

This paper proposes an application oriented four layered quality of service (QoS) stack for wireless sensor networks (WSN), including a supporting system architecture for interacting with WSNs using the MPEG-21 multimedia framework in an medical application setting. The application of the WSNs is signal processing algorithms reporting elaborated observed sensor data to external users. The QoS model supports the tradeoff between end-users expected QoS combined with optimized energy consumption. The MPEG-21 standard is chosen as the media resource framework due to the fact that future hospitals will have networks comprising WSNs supporting an always increasing amount of both low rate medical sensor data as well as high rate audiovisual content. Furthermore due to the heterogeneous set of user terminals and network resources, media adaptation will become important to provide reliable and robust quality of service. In this paper, we argue for an extension of the MPEG-21 terminology for use in biomedical wireless sensor networks and incorporate the requirements needed for medical applications.

SmartPipe: Self Diagnostic Pipelines and Risers

The principal objective with the SmartPipe R&D project is to develop a concept for online monitoring of the technical condition of offshore pipelines and risers, suitable for integration into E-field concepts and integrated process management approaches. This will be achieved by developing and linking different technologies into a system for condition monitoring to enable rapid detection of dangerous situations, optimal use of production facilities and improved safety control. Sub-goals include development of a distributed sensor network, local power supply, communication infrastructure, improve the models for materials degradation and to develop better numerical tools for structural integrity analyses. Parameters to be measured in order to establish a complete condition monitoring system for offshore pipelines have been identified. Based on this, the necessary sensor network and sensor principles are evaluated and adapted. Integration of sensors in the pipe structure, with emphasis on developing concept for packaging to withstand loads introduced during installation and operation is a major challenge. Adequate communication infrastructure and concepts for energy supply are also evaluated. Processing of data retrieved from the sensor network will be realized through a coupling of numerical analysis tools and improved models for materials degradation, reflecting the effects of local conditions and previous load history. The results will be presented through a graphical user interface, allowing for visualization and the possibilities to run simulations regarding future operation.© 2007 ASME

Some properties of the log-likelihood difference of mismatched maximum likelihood sequential estimation

Due to the consideration of additive white Gaussian noise, the performance evaluation of most communication receivers applying the maximum likelihood principle (MLSE) is based on the Euclidean distance, denoted by d/sup 2/0. The present authors consider another parameter, the log-likelihood difference for describing the performance of a MLSE receiver under uncoded modulation. This parameter proves to be simpler and exhibits some nice properties under the mismatched receiver situation. Some bounds on the tolerable mismatch are given. The performance of a blind channel estimator is illustrated.<<ETX>>