Werner Haselmayr

Energy-efficient and reliable wireless sensor networks - an extension to IEEE 802.15.4e

Collecting sensor data in industrial environments from up to some tenth of battery-powered sensor nodes with sampling rates up to 100 Hz requires energy-aware protocols, which avoid collisions and long listening phases. The IEEE 802.15.4 standard focuses on energy-aware wireless sensor networks (WSNs) and the Task Group 4e has published an amendment to fulfill up to 100 sensor value transmissions per second per sensor node (low latency deterministic network (LLDN) mode) to satisfy demands of factory automation. To improve the reliability of the data collection in the star topology of the LLDN mode, we propose a relay strategy, which can be performed within the LLDN schedule. Furthermore, we propose an extension of the star topology to collect data from two-hop sensor nodes. The proposed retransmission mode enables power savings in the sensor node of more than 33%, while reducing the packet loss by up to 40%. To reach this performance, an optimum spatial distribution is necessary, which is discussed in detail.

Iterative channel estimation and turbo equalization for time-varying channels in a coded OFDM-LTE system for 16-QAM and 64-QAM

The main targets for the next generation of mobile communication systems, with LTE as a main candidate, are increased data rates and improved spectrum efficiency. The transmission scheme for the LTE downlink is OFDM which enables the design of low complexity and high performance receivers, if the channel is time-invariant. However in high-mobility scenarios, where the channel is time-variant, the receiver design is more challenging. Therefore in this paper the turbo equalizer presented in [1] is extended to 16-QAM and 64-QAM to compensate the effect of the time-varying channel. Furthermore an iterative pilot-assisted channel estimator based on DPS-BEM is presented. BER performance of the LTE downlink for the ITU Vehicular A channel shows that the improvement due to iterative processing is substantial.

Time variant channel estimation using a modified complex exponential basis expansion model in LTE-OFDM systems

In future wireless communication systems like LTE, wide bandwidths for the transmission of high data rates result in frequency selective mobile radio channels. If data transmission takes place at high mobile speeds the mobile radio channel becomes also time selective. In this paper we propose for the estimation of such double selective channels a modification to the well known complex exponential basis expansion model, which is based on the assumed knowledge of the maximum Doppler frequency at the mobile user. We are able to reduce the estimation error by an order of magnitude up to very high mobile speeds for the OFDMA-based LTE downlink.

Factor-Graph-Based Soft-Input Soft-Output Detection for Frequency-Selective MIMO Channels

In this letter we consider a MIMO communication system with iterative detection over a frequency-selective MIMO channel. We present a soft-input soft-output MIMO detector based on a cyclic factor graph representation and the sum-product algorithm with two different message schedules (serial and parallel). Computer simulations show that both schedules provide near-optimum performance in terms of bit error rate, while achieving a remarkable reduction in complexity compared to the optimal MAP detector.

Transposition Errors in Diffusion-Based Mobile Molecular Communication

In this letter, we investigate diffusion-based molecular communication between two mobile nano-machines. We derive a closed-form expression for the first hitting time distribution by characterizing the motion of the information particles and the nano-machines via Brownian motion. We validate the derived expression through a particle-based simulation. For the information transfer we consider single particles of different types, where transposition errors are the dominant source of errors. We derive an analytical expression for the expected bit error probability and evaluate the error performance for the static and the mobile case by means of computer simulations.

Equalization Algorithms for MIMO Communication Systems Based on Factor Graphs

In this paper, we consider a bit-interleaved coded spatial multiplexing MIMO communication system over a frequency-selective MIMO channel. We present a factor-graph-based derivation of two different equalization algorithms. To this end, we propose a cycle-free factor graph representation of the equalizer, to which we apply the sum-product algorithm (SPA). By using different message representations in the SPA, it is shown that the resulting equalization algorithms correspond to the optimal MAP equalizer and the low-complexity LMMSE equalizer, respectively. Both algorithms can be used in turbo processing and we demonstrate that after 3 iterations the BER performance of the LMMSE equalizer is similar to that of the MAP equalizer.

Mean field message passing for cooperative simultaneous ranging and synchronization

Many emerging technologies for wireless networks (WNs) require decentralized synchronization and ranging, i.e., distance estimation between neighboring pairs of nodes. Both tasks are related to each other when they are based on time measurements between nodes. Revealing this connection, we present a mean field (MF) message passing algorithm for cooperative simultaneous ranging and synchronization (CoSRAS), which jointly estimates the internode distances and clock parameters in a fully distributed way. It is shown that the use of the MF method reduces the computation and communication efforts compared to other message passing methods. For MF message exchange between nodes, only broadcast communication is required. Our simulation results demonstrate the equivalence in performance with centralized state-of-the-art joint ranging and synchronization algorithms.

Improving time variant channel estimation for 3GPP LTE-downlink

Accurate estimation of the doubly selective mobile radio channels is essential to achieve satisfactory performance in wideband wireless communication systems like 3GPP LTE. Pilot Assisted Channel Estimation (PACE) techniques like Linear Minimum Mean Squared Error (LMMSE), Least Square (LS) etc. are used to estimate the channel states at a certain time-frequency grid specified by the pilot symbols. A model like Basis Expansion Model (BEM) is used to track the doubly selective channel in time between the pilot symbols. BEM performance is sensitive to the PACE results. Imperfections in the PACE results are inevitable due to Inter Carrier Interference (ICI) at high speeds, changing signal to noise ratio (SNR) of the system and mismatch in the parameter values used in PACE calculations. We are able to reduce the effect of such imperfections by shaping the noise at the high frequencies in extended Fixed CE-BEM. Simulations show a decrease in MSE by a factor of ≈2 when the LMMSE results, obtained at 0dB SNR, are used to track the doubly selective channel at 350 km/h.

Addressing multiple nodes in networked labs-on-chips without payload re-injection

On a droplet-based Labs-on-Chip (LoC) device, tiny volumes of fluids, so-called droplets, flow in channels of micrometer scale. The droplets contain chemical/biological samples that are processed by different modules on the LoC. In current solutions, an LoC is a single-purpose device that is designed for a specific application, which limits its flexibility. In order to realize a multi-purpose system, different modules are interconnected in a microfluidic network — yielding so-called Networked LoCs (NLoCs). In NLoCs, the droplets are routed to the desired modules by exploiting hydrodynamic forces. A well established topology for NLoCs are ring networks. However, the addressing schemes provided so far in the literature only allow to address multiple modules by re-injecting the droplet at the source every time, which is a very complex task and increases the risk of ruining the sample. In this work, we address this issue by revising the design of the network nodes, which include the modules. A novel configuration allows the droplet to undergo processing several times in cascade by different modules with a single injection. Simulating the trajectory of the droplets across the network confirmed the validity of our approach.

Verification of networked Labs-on-Chip architectures

Labs-on-Chips (LoCs) revolutionize conventional biochemical processes and may even replace laboratories by integrating and minimizing their functionalities on a single chip. In a promising and emerging realization of LoCs, small volumes of reagents, so-called droplets, transport the biological sample and flow in closed channels of sub-millimeter diameters. This realization is called Networked Labs-on-Chips (NLoCs). The architecture of an NLoC defines different paths through which the droplets can flow. These paths are realized by splitting channels into multiple successor channels — so-called bifurcations. However, whether the architecture indeed allows to route droplets along the desired paths and, hence, correctly executes the intended experiment is not guaranteed. In this work, we present the first automatic solution for verifying whether an NLoC architecture allows to correctly route the droplets. Our evaluations demonstrate the applicability and importance of the proposed solution on a set of NLoC architectures.