Thomas Janson

Self-localization application for iPhone using only ambient sound signals

We present a smartphone application to localize a group of networking devices in a mobile environment without the need of any further infrastructure. Ambient sound signals are the only information source. Time marks are assigned to the recorded audio stream for distinctive audio events, out of which we evaluate the time differences of arrival (TDOA) between the devices. In contrast to common multilateration approaches we do not need any positional anchor points - neither any predefined smartphone positions nor the positions of the environmental sounds. As an application scenario we can localize arbitrary devices using only the random environmental noise peaks, e.g. in crowded areas like market places or concerts with the usual soundscape, or for thunderstorm tracking. Especially, our solution becomes useful when established positioning systems (e.g. GPS) are too imprecise or fail, as during indoor self-localization. We use a Wi-Fi connection to synchronize the clocks of the devices and to exchange time marks. In our experiments we evaluated the audio information and synchronized the devices up to an order of 0.1 ms. This results in a positioning precision in the order of 10 cm.

Self-Localization based on Ambient Signals

We present an approach for the localization of passive nodes in a communication network using ambient radio or sound signals. In our settings, the communication nodes have unknown positions. They do not emit signals for localization and exchange only the time points when environmental signals are received: the time differences of arrival (TDOA). The signals occur at distant but unknown positions and they can be distinguished. Since no anchors are available, the goal is to determine the relative positions of all communication nodes and the environmental signals. Our novel approach, the Ellipsoid TDOA method, introduces a closed form solution assuming that the signals originate from remote distances. The TDOA measurements characterize an ellipse from which the distances and angles between three network nodes can be inferred. In contrast to existing approaches, we do not require the receiver nodes to be synchronized. Furthermore, we can calculate the time offsets of the receiver clocks as a result of our calculations and synchronize the receivers in this way. The approach is tested in numerous simulations and in indoor and outdoor settings, where the relative positions of mobile devices are determined using only the sounds produced by assistants with noisemakers.

A Self-Stabilizing Locality-Aware Peer-to-Peer Network Combining Random Networks, Search Trees, and DHTs

We present 3nuts, a self-stabilizing peer-to-peer (p2p) network supporting range queries and adapting the overlay structure to the underlying physical network. 3nuts combines concepts of structured and unstructured p2p networks to over-come their individual shortcomings while keeping their strengths. This is achieved by combining self maintaining random networks for robustness, a search tree to allow range queries, and DHTs for load balancing. Simple handshake operations with provable guarantees are used for maintenance and self-stabilization. Efficiency of load balancing, fast data access, and robustness are proven by rigorous analysis.

Self-localization based on ambient signals

We present an approach for the localization of passive nodes in a communication network using ambient radio or sound signals. In our settings the communication nodes have unknown positions. They are synchronized but do not emit signals for localization and exchange only the time points when environmental signals are received, the time differences of arrival (TDOA). The signals occur at unknown positions and times, but can be distinguished. Since no anchors are available, the goal is to determine the relative positions of all communication nodes and the environmental signals. The Ellipsoid TDOA method introduces a closed form solution assuming the signals originate from far distances. The TDOA characterize an ellipse from which the distances and angles between three network nodes can be inferred. The approach is tested in numerous simulations and in indoor and outdoor settings where the relative positions of mobile devices are determined utilizing only the sound produced by assistants with noisemakers.

3rdf: Storing and Querying RDF Data on Top of the 3nuts Overlay Network

In current research Peer-to-Peer (p2p) based Semantic Web systems mainly use distributed hash table (DHT) based networks. These networks provide good load balancing by applying uniform hash functions with the drawback that they destroy possible semantic relations between data elements. But mapping the data semantics on the network structure could improve the routing time in the network and consequently the RDF query latency on application layer. In this paper, we present 3rdf, a distributed RDF system for storing and querying RDF data. The 3rdf system has been built on top of the 3nuts p2p network. The 3nuts network improves on reducing the query response time and bandwidth usage in our system by adapting the network structure to the semantics of the RDF data. In addition, we study how the evaluation of SPARQL BASIC graph patterns in existing distributed RDF repositories can be extended for other graph patterns such as OPTIONAL and UNION in our 3rdf system.

Broadcasting in logarithmic time for ad hoc network nodes on a line using mimo

We consider n wireless ad hoc network nodes with one antenna each and equidistantly placed on a line. The transmission power of each node is just large enough to reach its next neighbor. For this setting we show that a message can be broadcasted to all nodes in time O(log n) without increasing each nodes transmission power. Our algorithm needs O(log n) messages and consumes a total energy which is only a constant factor larger than the standard approach where nodes sequentially transmit the broadcast message to their next neighbors. We obtain this by synchronizing the nodes on the fly and using MIMO (multiple input multiple output) techniques. To achieve this goal we analyze the communication capacity of multiple antennas positioned on a line and use a communication model which is based on electromagnetic fields in free space. We extend existing communication models which either reflect only the sender power or neglect the locations by concentrating only on the channel matrix. Here, we compute the scalar channel matrix from the locations of the antennas and thereby only consider line-of-sight-communication without obstacles, reflections, diffractions or scattering. First, we show that this communication model reduces to the SINR power model if the antennas are uncoordinated. We show that n coordinated antennas can send a signal which is n times more powerful than the sum of their transmission powers. Alternatively, the power can be reduced to an arbitrarily small polynomial with respect to the distance. For coordinated antennas we show how the well-known power gain for MISO (multiple input single output) and SIMO (single input multiple output) can be described in this model. Furthermore, we analyze the channel matrix and prove that in the free space model no diversity gain can be expected for MIMO. Finally, we present the logarithmic time broadcast algorithm which takes advantage of the MISO power gain by self-coordinating wireless nodes.

Analyzing randomly placed multiple antennas for MIMO wireless communication

We present an analytical approach for determining the signal-to-noise-ratio (SNR) of m multiple antennas in the line-of-sight case. The antennas are placed at random positions within a disc of given diameter d. We characterize the angular signal strength with three sectors: the main beam, the side beams and an area of white Gaussian noise. The SNR and the sector angles depend on d, m, and the wavelength λ. It turns out that for randomized antenna positions the analysis can be reduced to the analysis of a random geometric walk in two dimensions. The angle of the main beam is approximately λ/d with a SNR proportional to √m. For the side beams the SNR is proportional to sinc(2αd=λ) where α denotes the angle deviating from the target. The range of the side beams is limited to an approximate angle of λ/d√m. Beyond this angle we observe average white Gaussian noise.

Effects of Network Structure Improvement on Distributed RDF Querying

In this paper, we analyze the performance of distributed RDF systems in a peer-to-peer (P2P) environment. We compare the performance of P2P networks based on Distributed Hash Tables (DHTs) and search-tree based networks. Our simulations show a performance boost of factor 2 when using search-tree based networks. This is achieved by grouping related data in branches of the tree, which tend to be accessed combined in a query, e.g. data of a university domain is in one branch. We observe a strongly unbalanced data distribution when indexing the RDF triples by subject, predicate, and object, which raises the question of scalability for huge data sets, e.g. peer responsible for predicate ’type’ is overloaded. However, we show how to exploit this unbalanced data distribution, and how we can speed up the evaluation of queries dramatically with only a few additional routing links, so-called shortcuts, to these frequently occurring triples components. These routing shortcuts can be established with only a constant increase of the peer’s routing tables. To cope with hotspots of unfair load balancing, we propose a novel indexing scheme where triples are indexed ’six instead of three times’ with only 23% data overhead in experiments and the possibility of more parallelism in query processing. For experiments, we use the LUBM data set and benchmark queries.

Turning interferences into noise in ad hoc networks

Ad hoc networks present a challenging network paradigm because of energy-limited mobile devices and the lack of a reliable backbone infrastructure. If users have a choice, they might not be willing to share battery lifetime to support the ad hoc infrastructure. Irregular distributions of devices also limit connectivity of devices in dense areas and require long distant communication. Furthermore, jammers may disturb the communication and compromise connectivity. We present a modulation scheme addressing all three problems by establishing communication without increasing transmission power while reducing the data rate. Our key method is to repeat symbols using additional pseudo-random phase shift keying. So, we increase the signal-to-noise ratio of the wireless channel above the reception threshold and remove the constraint of correlated interferences of parallel communication. We show a constant factor overhead for negotiating the initial data rate and establishing the connections.

Self-synchronized Cooperative Beamforming in Ad-Hoc Networks

We investigate the unicast problem for ad-hoc networks in the plane using MIMO techniques. In particular, we use the multi-node beamforming gain and present a self-synchronizing algorithm for the necessary carrier phase synchronization. First, we consider n nodes in a grid where the transmission power per node is restricted to reach the neighboring node. We extend the idea of multi-hop routing and relay the message by multiple nodes attaining joint beamforming gain with higher reception range. In each round, the message is repeated by relay nodes at dedicated positions after a fixed waiting period. Such simple algorithms can send a message from any node to any other node in time \(\mathcal{O}(\log \log n - \log \lambda)\) and with asymptotical energy \(\mathcal{O}(\sqrt{n})\), the same energy an optimal multi-hop routing strategy needs using short hops between source and target. Here, λ denotes the wavelength of the carrier. For λ ∈ Θ(1) we prove a tight lower time bound of Ω(loglogn).