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In the context of the Internet-of-Things (IoT), wireless connectivity of wide spread sensor networks for infrastructure and environment monitoring is one of the essential factors for implementation. Low-power wide-area networks (LPWAN) are cost-effective solutions for such applications. Their high maximum coupling loss makes them also appealing for deep indoor-to-outdoor applications. However, no suitable channel models for these scenarios are available, especially taking the long-term effects of stationary transmitters and receivers into account. Such long-term effects are e.g. generated by the opening or closing of doors. The consideration of these long-term effects are important for LPWAN as many use-cases only require a single successful transmission per day. To develop a suitable channel model we performed extensive long-term measurements in a suburban, a commercial and an industrial area. For these we used up to 50 special transmitters that enabled us to measure the channel characteristics over a period of several weeks with a temporal resolution of five minutes. Using thousands of measurement data we developed a generic indoor-to-outdoor channel model for LPWANs operated in license-exempt frequency bands based on statistical analyses of the obtained data.

Reliable wireless data links, which use the license free ISM/SRD frequency bands below 1 GHz are a key component for machine-to-machine communications in the environment of smart metering and smart grid. In contrast to mobile communication devices, the mounting position of such sensor, actor or metering devices is static over a long period. To design such specific low power wide area networks (LPWAN), knowledge about propagation channel and its temporal evolution is essential. Here, path loss and the multipath propagation conditions are the main aspects. To analyse the temporal evolution of typical sub-GHz ISM/SRD transmission channels, we performed two measurement field trials in the commercial area of Erlangen, Germany, in 2014 and 2016. Based on the measurement results for the 868 MHz ISM/SRD band, in this study the temporal evolution of the channel characteristic is adressed. Therefore we propose a two path channel model which describes the multipath propagation conditions. With reference to this model, a classification of the measured radio channels is done. Model parameters, like the amplitude of the first received signal path, are extracted from the measurement data and afterwards analysed with respect to the correlation between the two measurement field trials. The results show the unchanged characteristic of the majority of the measured radio channels after two years. Therefor, channels which indicate multipath propagation in 2014 are also observable in 2016. Furthermore, our correlation analysis of the model parameter show that besides the channel characteristic the temporal evolution of consecutive days in 2014 and 2016 is approximately constant. This indicates that the multipath propagation conditions are static over several years, and so our previous assumption of multipath effects of reflections on static structures, e.g. adjacent buildings, is plausible.

Antenna Diversity is a method to improve the reliability of DAB reception in mobile environment leading to less spots with undesired audio interruptions and increased coverage areas.

In Peer-to-Peer (P2P) networks, computers with equal rights form a logical (overlay) network in order to provide a common service that lies beyond the capacity of each single participant. Among other applications, fielded P2P networks have shown their viability for the distribution and exchange of large amounts of data. Current research on retrieval in P2P systems focuses largely on keyword-based retrieval and other weakly in- teractive query paradigms. Within this paper, we present a Bayesian image browser that helps the user in finding images in dis- tributed collections. Bayesian image browsers operate by presenting sequences of thumbnail-based collections to the user, at each step collecting user feedback that is used to update a Bayesian model. In contrast to query by example (QBE) no initial query image is needed in order to start the query process. Our approach is scalable in that the state of the Bayesian model is maintained locally in the browsing peer and only a small number of thumbnails is requested from the network at each step. Each query step is thus done in a short time frame. In this paper we present the method, as well as first experiments done using a JXTA-based implementation.

Hunt the Cluster (HTC) is an interactive image browser for small to medium-sized P2P networks that uses methods that are likely to scale also to larger net- works. In Peer-to-Peer (P2P) networks, computers with equal rights form a logical (overlay) network in order to provide a common service that lies beyond the capac- ity of each single participant. Current research on re- trieval in P2P systems focuses largely on keyword-based retrieval and other weakly interactive query paradigms. In contrast, interaction is at the center of our contri- bution. We demo a Bayesian, PicHunter-like image browser that helps the user in finding images in distributed col- lections. Such browsers operate by presenting sequences of thumbnail-based collection overviews to the user, at each step collecting user feedback that is used to update a Bayesian model. Our approach is scalable in that the state of the Bayesian model is maintained locally in the browsing peer and only a few thumbnails are requested from the network at each step. Each query step is thus done in a short timeframe. At the conference we will present one peer that is connected to a P2P network consisting of 50 peers, let- ting visitors try the browsing functionality of our sys- tem.