This paper highlights the value of Digital Twins (DTs) in optimizing and maintaining Cyber-Physical Systems (CPSs) across domains like manufacturing and communication. It proposes the interaction between an industry DT and a 6G DT and identifies Situational Awareness (SA) as a key step toward supporting critical services. A use case involving 6G communication with mobile User Equipment (UE) in manufacturing is analyzed to identify critical operating scenarios and how SA can predict and mitigate the risk of failure in these scenarios. Based on this use case, relevant parameters for improving the SA of the entire CPS are identified in both DTs and an example of interaction is given for optimizing the joint task planning and execution. Additionally, the benefits of cross-domain SA are demonstrated through 5G testbed measurements. The use case illustrates the broader applicability of our proposal.

In this work we use an Orthogonal Time Frequency Space (OTFS) joint communication and sensing (JCAS) system to perform monostatic sensing. OTFS is discussed as a potential future waveform for 6G communications, due to the performance increase in high-mobility communication scenarios over other transmission schemes, like orthogonal frequency division multiplexing (OFDM). We apply OTFS in an otherwise 5G 3GPP compliant uplink to perform sensing at the user equipment (UE). For equalization, pilots are used to estimate the communication channel. These pilots are placed in the transmit resource grid, which, besides estimating the communication channel, also can be used for sensing purposes. In this work, we compare monostatic sensing performance of different pilot-aided techniques suggested for OTFS communications. These techniques are compared with the approach of using communication data for sensing. The radar channel is estimated by a matched-filter (MF), ensuring that all approaches require the same computational complexity for a fair comparison. In the simulation we compare the different approaches with various pilot-to-data power ratios. The results show that up to a certain level, it is suggested to use the data- driven approach for sensing. However, with increasing pilot power and the subsequent decrease in the root mean square error (RMSE) of the range and velocity estimation, it is more effective to use the pilot-aided approaches.

The Internet of Bio-Nano Things is a promising technology to reduce turnover and increase resolution of medical data collection. Therefore, tiny devices, so-called Nano Machines (NMs) are placed inside the human body, where the collect, process and transmit information to devices outside the human body. Interfaces between in-body and the external electrical domain are crucial to the realization of this technology. In this paper, we propose sweat glands, a pre-existing infrastructure, as a novel interface through which NMs can transmit information from the inside to the outside of the human body. We provide a detailed mathematical model of the envisioned communication system and evaluate its communication performance using different types of detectors (e.g., Neural Network based detector).

We demonstrate a private 5G network integration with precise ultra-wideband (UWB)-based localization for enabling a collaborative robots use case in an industrial environment. The results confirm 5G’s ability to provide high throughput, low latency, and reliable connectivity, even in complex industrial environments. UWB provides real-time decimeter-level wireless localization accuracy, critical for reliable and precise object localization. These combined capabilities are essential for real-time monitoring, automation, and operational efficiency. The developed demonstrator serves as proof of concept, showcasing how 5G, when coupled with advanced localization technologies, can optimize industrial processes and improve safety. This study offers a valuable system performance evaluation under real-world conditions for researchers and industry, underscoring the transformative potential of 5G in future industrial systems and its integration with precise wireless localization technology.

In wireless communications, trustworthiness computation has emerged as a crucial aspect of safeguarding modern systems against cybersecurity threats, ensuring reliable data transmission and upholding user trust. However, there is no unified definition of trustworthiness computation in the literature, and it is often presented as a specifically tailored adaptation of attack detection mechanisms. In contrast, this work introduces a general method for trustworthiness computation in wireless networks. It leverages key system characteristics, such as the channel, timing, and packet information to identify measurable Quality of Service (QoS) features with sufficient sensitivity across varying operational conditions. Building on these features, a novel three-step approach is applied. It employs changepoint detection to identify potential trustworthiness issues, calculates indicators based on the observed features, and finally combines them into a quantitative representation of trustworthiness. This systematic method effectively distinguishes between regular statistical variations in QoS features and actual trustworthiness issues. The applicability of the presented approach is demonstrated using a typical IEEE 802.11 wireless link, where different QoS features and scenarios are defined. These scenarios include network attacks, system malfunctions, and typical operational conditions. Our trustworthiness computation method correctly alerts the system to all trustworthiness issues that we challenge it with.

The Internet of Bio-Nano Things (IoBNT) is an envisioned extension of the Internet of Things (IoT), which aims to connect natural and synthetic biological systems and networks to the Internet. Due to the access to new domains (e.g., human body) this concept may help to enable transformative applications in healthcare and nanomedicine. However, it also faces several challenges, such as suitable interfaces and appropriate communication methods. Synthetic Molecular Communications (MC), a molecule-based bio-compatible communication concept, is among the most promising solution, which also defines the requirements for the respective interfaces. Typically, MC systems require a digital representation of the information to be transmitted and, thus, the development of devices for the conversion of analog biological signals to digital signals is crucial, but not well investigated. Thus, in this paper we propose a novel Molecular Analog-to-Digital converter (MADC). The MADC is based on a new neural network representation of the electronic flash ADC concept. This representation enables the implementation of the MADC using the recently proposed Molecular Nano Neural Networks (M3N). In particular, the proposed MADC consists of two matrix multiplication layers that are connected via a ReLU and threshold layer. We derive general design guidelines for the MADC and successfully validate it through computer simulations.

Intelligent behavior is an emergent phenomenon observed in biological organisms across all scales. It describes the cooperative behavior of low complexity entities to accomplish complex tasks, which exceed their individual capabilities. This property is particularly important for the Internet of Bio-Nano Things (IoBNT), which consists of Bio-Nano Things (BNTs) used in the human body, where they face many restrictions, such as bio-compatibility and size constraints. In this paper, we present a novel BNT-architecture, called Molecular Nano Neural Networks (M3N), which allows the implementation of intelligence on the micro-/nano-scale. The proposed structure consists of compartments (low complexity entities) that are connected to each other to form a network. Based on reaction and diffusion of molecules in and between connected compartments, this network mimics an artificial neural network, which is an important step towards artificial intelligence in the IoBNT. We provide design guidelines for the proposed M3N and successfully validate it by applying a regression and classification task.

6G networks will play a crucial role in Industry 4.0 advancing further smart manufacturing and trustworthy communication. This paper introduces a reinforcement learning scheduler that considers environmental knowledge designed to improve reliability and security aspects of trustworthiness by favoring to serve nodes when in line-of-sight. We evaluate the performance in a factory floor scenario for two different heights of remote-radio heads and various blockage densities. The results show that the proposed method outperforms traditional schedulers such as round robin and proportional fair in terms of reliability, availability and fairness enhancing thus reliability and security aspects of trustworthiness when the environment is prone to a mixture of line-of-sight and non-line-of-sight.

Wireless Sensor Networks (WSNs) play a pivotal role in diverse domains such as environmental sensing, industrial monitoring, and entertainment. This paper focuses on modeling the connectivity of the link considering the quality of service (QoS) criterion. This is a baseline for considering the probability density function (PDF) of the node’s distance from the base station (BS) to form a multi-hop wireless sensor networks (WSNs) structure. We delve into modeling the connectivity behavior in multi-hop networks, addressing scenarios involving non-homogeneous Poison Point Process (NHPPP) and homogeneous Poison Point Process (HPPP). Furthermore, we introduce closed-form expressions with reduced computational complexity. This contribution establishes a comprehensive framework for understanding and enhancing the performance of multi-hop wireless sensor networks.

The constraints imposed by the computational and energy capabilities of Internet of Things (IoT) devices are challenging for ensuring secure communication between these devices. One promising solution to address these security challenges is leveraging Physical Layer Security (PHYSEC) principles. This paper investigates in the area of PHYSEC, particularly focusing on the utilization of channel reciprocity for generating a secret key, commonly referred to as Physical Layer Secret Key Generation (PSKG), in Ultra-Wideband (UWB) technology. PSKG usually contain an Information Reconciliation (IR) stage to improve the probability for identical keys, which comes with substantial computational and communication cost. The primary objective of this paper is to eliminate this IR stage and its associated costs while still achieving a high probability for identical keys. To accomplish this goal, we propose a Pre-Processing (PP) stage involving a Discrete Fourier Transform (DFT)-based approach. This approach extracts reciprocal randomness from the Channel Impulse Response (CIR). By exploiting the CIR and our proposed PP stage, we were able to slightly improve the key generation rate while reducing the probability of successful attacks by a significant 87% in dynamic environments compared to the state-of-the-art. Notably, our approach does not require a training phase, making it more efficient for IoT devices.

The third generation partnership project (3GPP) has outlined ultra-reliable low latency communication (URLLC) essential to ensure enhanced network dependability under stringent latency constraints. A transmission scheme known as configured grant (CG) transmission, defined in 3GPP Release 15, allows devices to compete for resources and transmit their data without explicit permission in a specified time budget. In this study, we introduce an enhanced modeling approach for CG transmission that takes into account the repetition and retransmission, allowing a thorough evaluation of network performance. The numerical results shed light on configuring CG transmission settings to achieve a predetermined probability of success for successful packet decoding. Importantly, the system model in the paper closely follows 3GPP-based Transmission Time Interval (TTI) models, which helps to map the observed results to real system performance.

We present a trustworthiness score for double-sided two-way ranging on ultra-wideband devices. It serves as quantitative measure for assessing the reliability and security aspects of ranging. Leveraging the trustworthiness score, we propose two localization schemes that utilize the weighted non-linear least squares approach. The computation of the trustworthiness score relies on an autoencoder model trained on trustworthy data. To evaluate the performance of our trustworthiness score, we conduct indoor localization experiments that include channel manipulations such as line-of-sight obstructions and timestamp attacks resembling the well-known Cicada attack. The incorporation of trustworthiness led to an improvement in localization accuracy, reducing the root mean square error (RMSE) by up to 50% in the dynamic scenario.

The third generation partnership project (3GPP) has defined ultra-reliable low latency communication (URLLC) as one of the key 5G competencies to provide high network reliability and low latency. The configured grant (CG) transmission, defined in 3GPP Release-15, is a technique that automatically transmits a URLLC packet with a configured number of repetitions to increase reliability. In this paper, we propose enhanced modeling for CG transmission considering the communication channel state to evaluate the network performance. The results show how to configure CG transmission to reach a defined probability of success for decoding the packets.

Bluetooth Low Energy (BLE) is one of the key enablers for low-power and low-cost applications in consumer electronics and the Internet of Things. The latest features such as audio and direction finding will introduce more and more devices that rely on BLE for communication. However, like many other wireless standards, BLE relies on the unlicensed 2.4 GHz frequency band where the spectrum is already very crowded and a channel access without collisions with other devices is difficult to guarantee. For applications with high reliability requirements, it will be beneficial to actively consider channel access from other devices or standards. In this work, we present an approach to estimate the connection parameters of multiple BLE connections outside our control and knowledge by passively listening to the channel. With this, we are able to predict future channel access of these BLE connections which can be used by other wireless networks to avoid collisions. We show the applicability of our algorithm with measurements from which we can identify unknown BLE connections, reconstruct their specific connection parameters, and predict their future channel access.

5G, the latest generation of cellular technology, targets not only enhanced data rates but also new applications which require, e.g., ultra-reliable low latency communication. Verticals like industrial automation or automotive, which want to make use of this type of wireless services, need experimental deployments to test the performance of 5G in various modes and environments for their use cases. Due to the ongoing stan-dardization process, experimental 5G networks based on open-source frameworks are especially well suited, as they provide the possibility to easily implement new features introduced by the yearly 5G standard releases. We thus present an experimental 5G standalone deployment, based on the OpenAirInterface, which is an open-source framework, that is being used both, commercially and for academic purposes. We evaluate coverage parameters including reference signal received power, reference signal received quality, and signal to interference and noise ratio both for single user and multiple user scenarios. The measured downlink data rate reaches up to 390 Mbps at a bandwidth of 60 MHz, which is close to the achievable theoretical value. The average latency both for uplink and downlink was measured to be 19 ms for the round trip time, while the minimum latency value was 6 ms, which is acceptable for many application.

Nowadays Internet of Things and Industry 4.0 devices are often connected wirelessly. Current wireless sensor network (WSN) deployments are relying in most cases on the industrial, scientific, and medical (ISM) bands without centralized resource scheduling. Thus, each device is a potential source of interference to other devices, both within its own WSN but also to devices in other collocated WSNs. If the transmission behavior of devices from other WSNs is not random, we are able to find patterns in the time domain in their channel access. This is, for example, possible for periodic channel access, which is quite common for WSNs with demanding low-power and reliability requirements. The main goal of this work is to detect multiple sources of periodic interference in time slotted signal-level measurements and estimate the time windows of future transmissions. This gives a WSN a certain understanding of the radio surrounding and can be used to adapt the transmission behavior to thus avoid collisions. For this, the multihypothesis tracking algorithm is adapted and used together with timeslot-based interference measurements on low-cost sensor nodes. The applicability of the algorithm is shown with extensive simulations and the performance is demonstrated with measurements on a time-division multiple access-based WSN built upon the Bluetooth low-energy physical layer.

Long-range wide-area networks (LoRaWANs) are emerging technologies for the Internet of Things. They provide ultralong-range communication and low power consumption but have poor scalability due to the ALOHA media access method. In this article, we first present a novel medium access control (MAC) protocol which is time-slot-based and channel contention constrained to enhance the network performance in terms of throughput and energy consumption. We propose an analytical model which is based on three assumptions and Markov chains to analyze the performance. Various protocol and network scale settings are considered during the analysis of the performance of the network. We performed simulations in MATLAB to verify the validity of the assumptions and the accuracy of the model. We show that our new protocol enhances the throughput by approximately two times as compared to ALOHA in LoRaWAN networks, while the average energy consumption per packet is significantly reduced if the optimum protocol settings are used.

Functional safety protocols provide automatic protection against system failures. Safety will be of critical importance for future industrial systems since they are undergoing automation and digital transformation under the Industry 4.0 revolution. However, functional safety depends on the underlying communication system employed in the manufacturing area. An extensive evaluation of the communication system and the functional safety protocol is needed before deploying it to the production environment. To facilitate the evaluation process of a fail-safe communication protocol, we integrate openSAFETY in the OMNeT++ simulation framework. We validate its integration by comparing the simulation results with an existing experimental work where the results show similar trends. Furthermore, we simulate an industrial closed-loop control use case with IEEE 802.11n being the communication technology. The results obtained in terms of safe-state duration and packet error rate demonstrate that 802.11n with its default configuration is not suitable for a high demanding industrial application.

In this paper, we show that our recently proposed method to enhance distance bounding (DB) by time difference of arrival (TDOA) measurements improves the security of current DB protocols by reducing their uncertainty area (UA). DB protocols are employed such that a verifier node can authenticate a prover node and at the same time ensure that the prover is close enough to the verifier. TDOA-Enhanced DB increases the security of existing DB protocols by the use of passively listening verifiers, that are employed additionally to the DB primary verifier. We verify our proposed method with measurements in a laboratory setup with hardware that is equipped with Qorvo DW1000 Ultra-Wideband transceivers. We also derive the Crámer-Rae Lower Bound for TDOA with different noise sources and compare it with the measurements to calculate the TDOA-Enhanced UA. By performing a TDOA-Enhanced location verification, we show that an UA reduction is possible in 78% of positions in a 20m x 20m square. This significantly reduces the probability of a successful attack at the physical layer of DB protocols.

Functional safety has become a crucial part of industrial automation. With industry environments being connected more than ever, achieving required functional safety depends on establishing safety-critical communication. Numerous application layer safety protocols have been developed to ensure compliance with functional safety standards for wired communications. However, with all the benefits wireless communications entails, wireless communication is pushing for an important place in the future of industrial automation. It is important that safety protocols also follow this transition and are able to operate as intended using a wireless channel. By default, openSAFETY frames are exchanged using UDP broadcast, whereas TCP provides additional reliability features. Thus, the aim of this paper is to analyze if safety-critical communication using a wireless channel can benefit from the additional reliability features provided by TCP. To answer this, we experimentally analyze the performance of openSAFETY protocol providing functional safety over the IEEE 802.11 standard for three different test cases. We analyze the performance in terms of median end-to-end delay and time spent by a safety node in a safe state for both protocol stacks. Results show that UDP provides lower median end-to-end delay, whereas TCP is able to achieve less time spent in a safe state under bounded delay constraint.

In the current mobile communication standards there is a trend towards higher order modulation schemes in order to meet the rising demand for higher data rates. Higher order modulation schemes require a low error vector magnitude (EVM). The phase noise contained in the LO-signal generated by the all-digital phase-locked loop (ADPLL) of a cellular receiver has a big impact on the EVM. One way to reduce this impact and therefore improve the EVM-performance of the receiver is feed-forward phase noise cancellation (FFNC) applied in the digital baseband. Here the timing error measured by the time-to-digital converter (TDC) of the ADPLL is used to correct the phase error in the baseband. In this work we compare a phase-locked loop (PLL) with and without FFNC where both cases are optimized for a low integrated phase noise (IPN). We examine in simplified theoretical considerations how to choose the PLL- and FFNC-filter bandwidths to minimize the resulting IPN. Additionally we investigate how increased phase noise in the PLL affects the resulting IPN in the case with FFNC. The results from theoretical considerations have been confirmed by simulation using a time-domain MATLAB model of a type-II ADPLL.

Wireless embedded devices are key elements of Internet-of-Things (IoT) and industrial IoT (IIoT) applications. The complexity of these devices as well as the number of connected devices to networks increase steadily. The high intricacy of the overall system makes it error-prone and vulnerable to attacks and leads to the need to test individual parts or even the whole system. Therefore, this paper presents the concept of a flexible and distributed testbed to evaluate correct behavior in various operation or attack scenarios. It is based on the Robot Operating System (ROS) as communication framework to ensure modularity and expandability. The testbed integrates RF-jamming and measurement devices to evaluate remote attack scenarios and interference issues. An energy harvesting emulation cell is used to evaluate different real-world energy harvesting scenarios. A climatic test chamber allows to investigate the influence of temperature and humidity conditions on the system-under-test. As a testbed application scenario, the automated evaluation of an energy harvesting wireless sensor network designed to instrument automotive engine test benches is presented.

Digital-to-time converters (DTCs) are a promising technology for radio frequency (RF) transceivers but are prone to spur generation. A common approach to change the spurious emissions to a spur-free shape is a method called dithering. The power added due to dithering is an important aspect of this approach and gives raise to investigations on additive dither as well as methods for subtractive dithering. This work presents a mathematical model for dithering DTC-based local oscillator (LO) generators. It proposes concepts for the application of subtractive dither and it introduces a novel generalization of quantization-dither to allow for optimal dithering of nonlinear quantizers.

Due to its scalability, tuneability, low latency and high linearity, the radio frequency digital to analog converter (RFDAC) is shown to be an attractive choice for the transmitter architecture for the long term evolution (LTE) and new radio (NR) standards, especially for the sub 8 GHz frequency range. When placing several transmitters (TX) and receivers (RX) next to each other on a single die, it is necessary to understand any influence of the components to each other to enable undisturbed functionality and by that to fulfill the tough requirements that are defined by the 3rd Generation Partnership Project (3GPP). One of the unwanted effects generated by the RFDAC structure are harmonics. These harmonics can further lead to effects such as: Inphase Quadrature image generation, TX to TX crosstalk, TX to digitally controlled oscillator (DCO) crosstalk also known as pulling, TX to RX crosstalk etc. In this paper we conduct a thorough analysis of the harmonics that are generated by an RFDAC and show that the widening of the bandwidth does not depend on the harmonic order but rather on the RFDAC specific nonlinearities. Theoretical and mathematical observations are supported by a highly developed MATLAB simulation chain containing an RFDAC model whose behavior is aligned with a physical implementation.

We propose to add a monitoring system consisting of so-called path-and guard nodes to industrial wireless sensor networks (IWSNs), to increase the security level by using receive signal strength indicator (RSSI) measurements. Via these measurements, the monitoring system determines the presence of a mobile sensor node in a predefined area, which can be used to handle access rights and to increase automation capabilities in industrial applications. We add this monitoring system to an IWSN based on the EPhESOS protocol, which has a high degree of flexibility to meet industrial requirements in different applications throughout the lifetime of a sensor node while enabling energy-autonomous operation. Two practical machine learning algorithms for RSSI-based presence detection are presented, namely a support vector machine and a neural network algorithm. They are evaluated in an automotive example and tested for their robustness against malicious attacks. Additionally, a method to find the best node locations of the monitoring system is presented.

Secure wireless communication is essential for most industrial applications. The secure and reliable control of processes as well as the data integrity of measured values are key targets in these applications. The industrial Internet-of-Things (IIoT) tries to connect an increasing number of sensors wirelessly. The wireless sensors form wireless sensor networks (WSNs). However, wireless sensor nodes are exposed to various security threats ranging from physical modification on the device itself to remote attacks via the communication channel. It is important to secure the complete lifetime of the wireless sensor nodes and other system components. This includes the production phase, shipping, preparation phase and operational phase. This paper presents a lifetime security concept for a wireless sensor network applied in automotive test beds. In this application scenario, the wireless sensor nodes are used to capture various temperatures in an automotive unit under test. In order to indicate the current state of trustworthiness of the system, a trustworthiness indicator is implemented which is shown to the user. An evaluation of the impact of encrypted communication on power consumption shows that the increase is negligible, and can be expected to be provided by the wireless sensor node's power supply without reducing the node lifetime.

In this paper, a new method to secure non-ideal distance bounding techniques using time difference of arrival measurements is presented. Accurate and secure localization is crucial for many applications of real life wireless sensor networks, and extensive research has been dedicated to this topic in recent years. Distance bounding protocols are employed such that a verifier node can authenticate a prover node and at the same time ensure that the prover is close enough to the verifier. In order to increase the robustness of existing distance bounding protocols to attacks such as “early detect” or “late commit the use of passively listening verifiers that are employed additionally to the distance bounding primary verifier is studied. In such a way an extended set of measurements is obtained. The proposed approach is able to prevent those attacks. We study the presence of some vulnerabilities in our method and we show a way to prevent them.

The paper presents a sampling method that dramatically improves the measurement accuracy of the round trip time (RTT) measurement in digital communication systems. For state of the art methods, the accuracy of time measurements in discrete time systems and low noise scenarios is limited to the sampling period T. If the measurement is repeated m-times, the upper bound of the quantization mean square error (MSE) is ~1/m. The proposed sampling scheme reduces the upper bound of the MSE to ~1/m2. This exceptional feature is enabled by applying a prime relation between sampling rate and bit rate of the communication system.

In this work, we consider a bit-interleaved coded modulation unique word (UW) OFDM system with turbo equalization. For such a system, only a limited performance improvement over the turbo iterations was observed in a previous work. This is because interleaving was limited to one UW-OFDM symbol, which causes dependencies between the log-likelihood ratios exchanged between the equalizer and the decoder. To overcome this issue, we propose interleaving beyond one UW-OFDM symbol. Moreover, through bit error ratio simulations we determine the minimum number of UW-OFDM symbols across which interleaving should be performed to reach the matched filter bound (MFB).

The stringent requirements from 3rd Generation Partnership Project (3GPP) standards pose a big challenge for the design of cellular radio frequency transmitters. Architectural limitations and non-ideal effects of state-of-the art complementary metal-oxide-semiconductor (CMOS) devices need to be carefully addressed to achieve sufficient performance at low costs. In this work, the systematic problem of an IQ image in digital-intensive IQ transmitters is analyzed. The root cause is explained and an efficient cancellation method is presented. A proof of concept for long term evolution (LTE) signals is given via Matlab simulation results and measurements from a test chip implemented in 28 nm Complementary Metal-Oxide-Semiconductor (CMOS). The proposed concept improves the error vector magnitude up to 4% for wideband signals.

In this paper, we consider diffusion-based molecular communication with and without drift between two static nano-machines. We employ type-based information encoding, releasing a single molecule per information bit. At the receiver, we consider an asynchronous detection algorithm which exploits the arrival order of the molecules. In such systems, transposition errors fundamentally undermine reliability and capacity. Thus, in this paper, we study the impact of transpositions on the system performance. Toward this, we present an analytical expression for the exact bit error probability (BEP) caused by transpositions and derive computationally tractable approximations of the BEP for diffusion-based channels with and without drift. Based on these results, we analyze the BEP when background is not negligible and derive the optimal bit interval that minimizes the BEP. Simulation results confirm the theoretical results and show the error and goodput performance for different parameters such as block size or noise generation rate.

In this paper a state-space approach for modeling radio-frequency digital-to-analog-converters is presented. We explain the root cause of the sign-change error appearing in RF-DAC architectures with local oscillator (LO) switching and present its impact in time domain and on the spectrum of the output RF signal. The main contribution of this paper is a solution for the removal of the sign-change error. The solution is implemented in a linear state-space model, considering static nonlinearities of the switched-capacitor power amplifier cells. We demonstrate the feasibility of our approach by simulation results for LTE5, LTE10 and LTE20 signals and show that the out-of-band noise contribution of the sign-change error is completely removed. Additionally, the impact of static nonlinearities on the system is investigated.

Labs-on-Chips (LoCs) implement laboratory procedures on a single chip and are successfully used for chemical and biomedical applications. A promising and emerging realization of such chips are Networked LoCs (NLoCs) in which small volumes of fluids, so-called droplets, flow in closed channels of submillimeter diameters. NLoCs allow for an incubation and storage of assays over a long period of time and, hence, avoid evaporation and unwanted reactions. To increase the flexibility, effectiveness, and reusability, network functionalities allow to passively route droplets in channels and, hence, to dynamically select operations depending on the executed experiment. However, only manually designed architectures are considered for NLoCs thus far. They frequently suffer from large execution times and/or a high contamination of channels. To overcome these drawbacks, we propose the consideration of application-specific architectures for NLoCs. To this end, an automatic design method is proposed which, for a given set of experiments as well as constraints and objectives from the designer, is able to generate an optimized NLoC architecture realizing these experiments. Evaluations and case studies demonstrate the potential of the proposed solution for design exploration. Moreover, we are able to show that application-specific architectures are capable of realizing experiments in just a fraction of the time needed by architectures used thus far as well as with a substantially reduced contamination.

In this paper, we study the capacity and symbol error probability (SEP) of generalized spatial modulation (GSM) multiple-input multiple-output (MIMO) using measured channels that are obtained by channel sounding in an indoor office environment at 60GHz. Spatial modulation (SM) and GSM are emerging low-complexity MIMO schemes that have been extensively researched for low-GHz (below 6GHz) communications. Recently, they have been considered and shown to be promising also for (mmWave) communications. In the simplest possible case, they require only one RF chain both at the transmitter (TX) and receiver (RX), and thus, are especially attractive for mmWave communications, in which the number of RF chains needs to be as low as possible. Despite of some early works on the theoretical analysis of SM/GSM for mmWave communications, there have been no investigations using real-world channel data. We focus on the office line-of-sight (LOS) scenario and investigate three problems: 1) the performance of GSM using the extracted LOS component of measured channels; 2) the impact of non-LOS NLOS components on the performance of GSM; and 3) possible simple modulation and reception algorithms for GSM that rely only on the LOS component of the channel. The results being reported in this paper not only validate the main claims of previous studies based on ideal pure LOS channels, but also lead to novel findings. One major conclusion is that NLOS components are harmful to the SEP of GSM and should be avoided. As another important outcome, our results strongly motivate the use of precoding in GSM systems to simultaneously improve the channel capacity and reduce the physical size of MIMO arrays (thus eliminating one major issue of LOS GSM).

Spatial modulation (SM) and generalized spatial modulation (GSM) are emerging multiple input multiple output (MIMO) schemes that use transmitter (TX) antenna switching for data transmission. Their operating principle makes optimization of channel capacity and mutual information usually more difficult than for conventional MIMO schemes which are not based on antenna switching. We propose to use channel cut-off rate as a relevant and more tractable metric for performance optimization of spatial modulation (SM)/GSM systems, as it constitutes a practical lower-bound of channel capacity. In particular, we propose four TX precoding schemes for increasing the cut-off rate of SM/GSM systems. We show that those TX precoding schemes which are designed for increasing array gain provide the largest improvement of cut-off rate for low signal-to-noise ratio (SNR). On the other hand, the TX precoding schemes that are designed for increasing the minimum Euclidean distance of GSM symbols are more suitable for application to medium to high SNR setups and correlated channels. The proposed precoding schemes are shown to be able to enhance mutual information, and the gain is shown to be of the same order of magnitude as the gain of the corresponding channel cut-off rate.

Labs-on-Chip integrate and minimize the functionality of complete conventional laboratories on a single chip. An upcoming and especially biocompatible realization are Networked Labs-on-Chips (NLoCs). In NLoCs, small volumes of reagents, so-called droplets, flow in an immiscible fluid in closed channels. An external pump applies a force to this immiscible fluid driving the droplets through the channels of the NLoC. However, the exact flow behavior of droplets in NLoCs physically depends on many factors and interdependencies. This makes it cumbersome to manually determine the taken path of a droplet and the time it needs to pass the NLoC. For the same reason, also almost no automated design solutions exist for NLoCs yet. In this work, we present a discrete model enabling designers and design automation tools to efficiently determine the droplets' path and positions. The precision of the proposed model is evaluated by a systematic examination for basic building blocks of NLoCs as well as for a complete architecture. The resulting model can be used for manual inspections of the droplets' behavior in an NLoC and, additionally, provides the basis for automated design solutions.

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.

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.

A machine type communication (MTC) system for wireless transmission of sampled sensor data between two devices is considered. In order to reduce the latency between collecting the sample at the transmitting device and making it accessible at the receiving device, a novel cross-layer design is proposed and appropriate channel coding is discussed. The novel scheme deviates from traditional packet oriented communication in that the sampling is triggered by the physical layer of the transceiver once the packet transmission has started, instead of commanding a packet transmission at the application layer after the sample is available at the CPU. Thereby, delays from data buffering and packet generation are eliminated. Furthermore, in order to maintain guaranteed transmission latencies, appropriate channel codes are selected and their error correction performance is assessed in industrial environments.

In industrial applications synchronized sensor nodes are vital for many tasks like multi parameter sampling of complex machinery behavior. The wirelessly connected nodes are usually synchronized to a base station. Therefore, frequency or period estimation of the reference clock is a key issue for all connected tasks like sampling, localization or applying energy optimized communication protocols. In wireless systems and especially in harsh industrial environments, it is likely to miss one or more synchronization events. The available data for clock estimations is therefore sparse and periodogramm estimators, at a complexity of at least O(N log N), are commonly used for accurate clock estimation. We introduce a period estimator for sparse clock signals with O(N) complexity. Furthermore, we present an equation for the observation time necessary to estimate the clock period at a certain quality. Mostly due to temperature influences, the crystal frequency at the nodes are varying. Our iterative period estimator follows those changes with a given estimation accuracy. We analyze an equation, which allows to calculate the accuracy of the estimator given a certain change rate of time variant system clock. The work is concluded with simulations considering sparse and time varying processes, including a discussion of the application of the method.

In this letter, we investigate the extrinsic log-likelihood ratio (LLR) computation of a soft-input soft-output equalizer used in a turbo equalization system. The optimum LLRs are obtained by a maximum a posteriori -based equalizer, which may be computationally expensive. Thus, several reduced-complexity equalizers have been proposed. The most promising approach first applies linear minimum mean square error filtering to the channel output and then computes the LLRs based on a scalar Gaussian approximation of the filter output. The resulting LLRs can be viewed as an approximation of the optimum LLRs. In order to improve the approximation, we investigate the computation of the LLRs based on a vector Gaussian approximation of the filter output, which incorporates the correlation between the estimated symbols after filtering. Surprisingly, it turns out that both approaches, although their derivation is different, give the same LLRs. We verify this remarkable result through an analytical proof and bit error ratio simulations.

In this paper, we propose to use variable-Nugeneralized spatial modulation (VGSM), which is a specific type of generalized spatial modulation, in indoor line-of-sight (LOS) millimeter-wave (mmWave) communication. As compared with fixed-Nugeneralized spatial modulation, VGSM needs less number of transmitter (TX) antennas to achieve the same data rate. Reducing the number of antennas is especially important for LOS mmWave MIMO communication, since it means reduced array lengths and routing loss in the RF front-end. We first derive and analyze the channel capacity for LOS VGSM, and then propose a novel switching structure for implementation of the VGSM TX at mmWave frequencies and analyze its performance in terms of power added efficiency and capacity. Two optimizations of the system performance of VGSM are performed: 1) power allocation optimization for the proposed TX, and 2) antenna separation optimization in order to optimize the capacity in LOS. Our results show that VGSM is a feasible and promising scheme for indoor LOS mmWave communication. For example, we show that an 8 × 8 VGSM system with practical component values can achieve more than 20bpcu spectral efficiency within a distance of 1-5m and more than 17bpcu within 5-10m.

Timestamp free clock synchronization in a master-slave network, i.e., synchronization where no timestamps are exchanged between the nodes, is considered. For highly accurate synchronization, a novel discrete-valued clock model is introduced. It is based on the observation that clocks are discrete counters in digital wireless radios. Considering this model, it is shown that the round-trip time (RTT) measurements follow specific pulse or step shaped functions. The estimated parameters of these RTT functions are used to determine the clock parameters (clock skew and phase) and the propagation delay. Numerical analysis illustrate that when RTT measurements are collected using discrete-valued clocks, the proposed estimation schemes outperform estimators derived from the continuous clock model, which is used in the state-of-the-art methods. Moreover, the presented scheme performs similar to recently presented discrete-valued clock approaches with more stringent hardware assumption. The correctness of the proposed models is validated through hardware experiments.

The idea of Internet of Things has grown into multiple dimensions, encompassing also the industrial world leading to initiatives like Factories of the Future (FoF) or Industrial Internet. Wireless Sensor and Actuator Networks (WSAN) play an important role in this professional domain. Their successful deployment in real-world applications calls for advanced testing and debugging effort in advance. This poster presents the architecture of TWECIS, a Testbed targeting the investigation of Wireless Energy Constrained Industrial Sensor and Actuator Networks. The proposed architecture tries to unite scalability, maintainability and a cost-saving design of the testbed infrastructure with the special requirements of research in industrial wireless network design.

Cooperative communication uses spatial diversity to mitigate multipath fading. With an appropriate assignment of partners it also decreases the energy expenditure of the network. Together with optimum transmit power allocation, it is a useful technique to overcome the energy constraint problem in wireless sensor nodes. The calculation of optimum power in a Rician fading channel is a computationally complex process especially for nodes with limited resources. Approximate techniques like using the concept of coding gain yields a simple expression but the conditions for which the approximation is valid limit its use in many practical scenarios. Using a piecewise linear approximation for the power gain of the Rician channel, we propose a computationally simple method to calculate transmit power for amplify-and-forward relay links. The scheme is then used in an IEEE 802.15.4 compatible wireless sensor network where nodes cooperate with each other in an amplify-and-forward relaying scheme using partners assigned with the help of a worst-link-first partner selection algorithm. The outage probability and error rates which are computed with the proposed scheme are found in accordance with the theoretically predicted results, while keeping the computational effort such low that the optimum transmission power calculation can be performed on commercial low-cost sensor node hardware.

Wireless sensor networks (WSNs) currently see a strong increase in demand for various industrial applications like smart testing and production systems. Open frequency bands (e.g. 2.4 GHz) allow the use of commercial low-cost hardware, but need to be shared with other devices and systems, leading to interference and therefore transmission errors. Re-transmitting damaged packages might eventually succeed, but at the costs of increased latency and additional energy consumption of the node. As minimizing energy consumption is paramount for self-owered WSN nodes, interference avoidance is highly desired. In this work a channel management procedure for WSNs is proposed which can react to dynamically changing interference scenarios. A short monitoring period is used to sample received signal strength indication values of a set of candidate frequency bands. An extensive measurement campaign is performed and six analysis methods are compared, and effects of applying the resulting choice of “best” frequency bands to WSNs in an automotive testing environment are investigated. The best method allows a reduction of energy consumption of a node by about 15%.

In order to support very small cycle times, Profinet isochronous real-time (IRT) was improved by implementing the dynamic frame packing (DFP) mechanism. It turned out that DFP is relatively efficient, but it still has two crucial drawbacks. The complex scheduling has to be recalculated every time the network structure is modified. Furthermore, DFP only operates efficiently in line topology. This study presents a proposal for further improvements of Profinet IRT by implementing an automatic packing mechanism (APM). The main advantage of APM lies in the fact that a dedicated scheduling algorithm is not required. Furthermore, APM achieves approximately the same performance as DFP in line topology, but it has a distinctive advance in star or tree topologies. This paper also presents experimental validation results that prove the functionality of the approach. APM could be implemented with only minor modifications of the media access control (MAC) and physical layer (PHY) hardware to improve the flexibility of Profinet IRT.

In this paper, we propose to use spatial modulation (SM) and the generalized spatial modulation (GSM) MIMO schemes in indoor line-of-sight (LOS) millimeter-wave (mmWave) communication at 60GHz. SM/GSM are known but only at low-GHz frequencies where the channels are typically rich scattered and characterized by Rayleigh or Rician distribution. However, 60-GHz indoor channels are typically not rich but rather sparsely scattered and dominated by the LOS component, thus making them different from low-GHz fading channels and our work novel. We first seek to optimize SM in LOS by finding the channel conditions that minimize its symbol error probability (SEP). Then, we extend our studies to LOS GSM and derive its channel capacity and SEP. Furthermore, we present numerical studies on the behavior and performance of SM/GSM in LOS. LOS spatial multiplexing and beamforming MIMO schemes are used as benchmarks for comparison. At last, we propose novel TX and RX hardware architectures, both of which use only a single RF chain, for implementation of SM/GSM at mmWave frequencies. Both simplicity and good performance are exhibited by LOS SM/GSM thus making them very attractive techniques for short-range indoor mmWave communications at 60GHz.

In modern wireless communication devices, cost- and area-effective signal processing architectures are essential. Flexible and reconfigurable front-end solutions are necessary to achieve high-spectral efficiency. Direct conversion transceivers are suitable but have to deal with I/Q mismatch, for which large bandwidths become frequency selective. Blind I/Q mismatch compensation can be based on a statistical property called properness, which is fulfilled for a large class of digitally modulated communication signals and which is destroyed by I/Q mismatch. We propose a novel DSP-algorithm for blind adaptive I/Q mismatch compensators using only real-valued filters, which rebuilds this properness in two stages. Additionally, we add a simple compensation solution for dc offset which can be integrated in the I/Q mismatch compensator. In a detailed analysis, we prove that nonlinear even-order distortions resulting from finite mixer isolation have only negligible influence on properness under realistic impairment levels. A stability analysis exhibit conditions of those compensator parameter regions for which the optimal steady-state is asymptotically stable. For practical frequency-independent I/Q mismatch values, we show that the algorithm converges with a suitable initial value to the optimum steady state. The proposed algorithm outperforms other state-of-the-art algorithms while its computational complexity is reduced. Results from a 3GPP LTE downlink simulator support the analysis.

In this paper a novel synchronization method for wireless sensor networks with star topology is presented. We address timing synchronization using low frequency real-time clocks in all nodes. A beacon-driven TDMA-protocol for bidirectional node/base communication is used. Between the beacons, which are sent by the base station, lie the superframe time intervals to handle data transmission from node to base. We discuss the protocol and its energy saving advantages including the challenges of synchronization. We reduce the required communication for synchronization based on long term synchronicity of the node to save energy. Due to the individual node clock, the accurate superframe time interval usually will consist of a rational number of clock ticks. We propose to use a ΔΣ-converter to generate a sequence of superframes with different time durations, but each consisting of integer multiples of clock ticks, which - on average - achieve the accurate superframe duration for any rational number of clock ticks. We show by theory and measurements that our novel approach leads to a variance of the synchronization error which is constant at a value of 0.25 clock cycles. The variance is independent of the rate at which the nodes listen to the beacon of the base station.

We analyse the use of a ΔΣ-modulator in the nodes of a wireless sensor network, which is a new method to achieve long term synchronization. We consider star topology WSNs (Wireless Sensor Networks) with a central base station and address timing synchronization using low frequency realtime clocks. The WSN uses a beacon driven TDMA-protocol for bidirectional node/base communication. Between the beacons, which are sent by the base station, lie the superframe time intervals to handle data transmission from node to base. The ΔΣ-modulator is used to generate - at average - the accurate superframe duration for any rational number of clock ticks, by generating a sequence of superframes with different time durations, but each consisting of integer multiples of clock ticks. We discuss the synchronization accuracy based on the internal arithmetic of the ΔΣ-modulator and show by theory a relation between synchronization accuracy and word length of the internal arithmetic. Additionally the fractional part of a crystal clock module is responsible for variations in the synchronization quality. We present an equation that allows us to interpret measurements showing periodic variations of synchronization quality.

In this paper we investigate the hardware implementation of the subspace marginalization with interference suppression (SUMIS) detector using high-level synthesis (HLS). SUMIS is a promising detection approach for multiple-input multiple-output (MIMO) systems, due to its fixed computational complexity and well-defined tradeoff between complexity and performance. Based on a SystemC implementation, the Xilinx Vivado HLS tool is used to implement the SUMIS algorithm on a Virtex-7 field programmable gate array (FPGA). By defining different macro- and micro-architectures we propose three hardware designs of the SUMIS algorithm and compare them in terms of area, speed, and energy (design space exploration (DSE)). Our investigations reveal that hardware design using HLS is a viable approach for rapid prototyping and DSE.

In a wireless sensor network, the energy consumption of the nodes continues to impose a tight constraint. Researchers have therefore proposed several MAC protocols to decrease the energy consumption of the radio transceiver, which has increased the complexity of the firmware running on the nodes. In this paper, we show the consequences of ignoring runtimes of state-of-the-art MAC protocols, as proposed by some simulators. The quantitative discussion is based on a comparison between hardware measurements and simulations. We ported the Contiki operating system to STEAM-Sim, a recently developed simulator. With this setup it is possible to omit runtimes of firmware in a stepwise manner. We further used STEAM-Sim to accurately evaluate the X-MAC, Low Power Probing, and ContikiMAC radio duty-cycling protocols. The energy consumption profiles of hardware modules thus generated give interesting insights into the protocols. Scalability comparisons to the state-of-the-art simulator COOJA/MSPSim show that scalable and time-accurate simulation of WSNs in the nanosecond range is possible.

In this paper Minimum Mean Square Error (MMSE) precoding for the Preprocessing aided Spatial Modulation (PSM) transmission scheme is investigated. PSM is capable to transmit data both in the spatial domain and in the modulation domain. We derive the upper bound for the Average Bit Error Probability (ABEP) for MMSE precoded PSM data transmission and we show by means of simulations that the bound is tight for a large signal to noise ratio (SNR) range. Also, the influence of the number of transmit and receive antennas on the ABEP is analyzed. It is shown that the increase of the number of transmit antennas will improve the ABEP. We demonstrated that the analytical ABEP for MMSE precoded PSM is considerably lower than for Zero-Forcing (ZF) precoded PSM. We determined that for constant bit rate, the lowest Bit Error Rate (BER) is achieved with a balanced number of bits in the spatial and modulation domain. The correlation at the receive antennas has a dominant influence on the BER.

In this paper we consider Generalized Pre-coding aided Spatial Modulation (GPSM), which was recently proposed as a promising alternative to conventional Multiple Input Multiple Output (MIMO) transmission schemes. In GPSM only a part of the receive antennas is activated with the aid of pre- coding at the transmitter. Hence, information bits are mapped to a spatial symbol, corresponding to a particular activation pattern, and to modulation symbols. Optimal performance is achieved with a Maximum Likelihood (ML) detector, but its exhaustive search leads to an intractable complexity. In this paper we present a novel detector, referred to as Soft MMSE with Exhaustive Search (SOMES) detector, that computes soft information for each symbol by employing a soft- output Minimum Mean Square Error (MMSE) detector. The soft information is used to determine the activation pattern using a small exhaustive search and to obtain the symbols in the particular activation pattern. Link level simulations show that the proposed algorithm possesses the near- optimal Bit Error Rate (BER) performance while achieving a remarkable reduction in complexity.

Profinet IRT makes use of dynamic frame packing (DFP) in order to support very short cycle times. The applied packing order is highly dependent on the network topology, and thus the scheduling must be recalculated offline every time the network structure is changed. This study presents a proposal for an automatic packing mechanism (APM) that is based on subframes with delimiters using control characters. As a consequence the subframe positions can be recognized by each device, which makes a scheduling dispensable. Furthermore, APM achieves better performance than DFP, especially in star or tree topology. The paper also presents experimental validation results.

Many applications in factory and process automation require robust wireless sensor networks (WSNs) for collecting sensor data with sampling and transmission rates up to 100 Hz from battery powered sensor nodes. To establish real-time communication in a star network topology, the LLDN mode of IEEE 802.15.4e amendment was released. We present a demonstration system which applies a recently introduced relaying method compatible to the LLDN mode, which uses dedicated relay nodes, thus increasing the reliability of the network while reducing the energy consumption of the sensor nodes. Furthermore, packet combining schemes on packets received erroneously from both, sensor node and relay node, are proposed, applied, and analyzed. Measurements with the demonstration system have shown that 96.4% of these erroneous transmissions could be recovered correctly.

In this paper, we present a highly accurate but still cost-effective measurement solution for tracking the highly dynamic power consumption of wireless embedded systems. We extended the conventional measurement of a single shunt resistor's voltage drop by using a dual shunt resistor stage with an automatic switch-over between both stages, which leads to a large dynamic measurement range of 50 dB (1μA to 100 mA) with an average measurement error smaller than 1.2 %. Using two zero-drift current sense amplifiers for measuring the voltage drop over two different sized shunt resistors together with a 16 bit SAR ADC for each of both amplifiers leads to a far better thermal noise behaviour and a higher total measurement resolution compared to a single shunt solution, providing a minimum invasive measurement system with a maximum voltage drop of 100 mV. Using a state-of-the-art Ethernet connection allows our measurement system to forward the power samples with up to 250 kHz sampling rate to any remote networked computer.

Wireless sensor and actuator networks (WSAN) for industrial applications usually have tighter requirements on dependability, synchronization, and real-time capability as compared applications in environmental monitoring or health care. For WSAN research and development, testbeds are a valuable tool as they enable controlled operation under conditions close to reality. In this contribution we present TWECIS, a testbed targeting the investigation of Wireless Energy Constrained Industrial Sensor and Actuator networks. We describe the concept, its architecture and the used hardware. Unique feature of TWECIS is the use of an industrial Real Time Ethernet system which offers the evaluation of the timing behavior of the nodes with a jitter below 100 ns. In addition TWECIS offers synchronized network-wide current measurements on all testbed nodes in a range from 1 μA to 100 mA for accurate power consumption profiling, remote and parallelized programming of nodes, remote in-circuit debugging, monitoring of UART output, and centralized storage of all captured data.

Real-Time Ethernet networks increasingly gain importance for the employment in industrial applications. Certain Real-Time Ethernet networks were optimized to reach very small cycle times well below 100 μs by modifying the Ethernet hardware. Two important and wide-spread systems of this class are EtherCAT and Profinet IRT. VABS is a newer high-performance system which is still under development. This study presents an objective performance comparison of the three systems. It turns out that both Profinet IRT and the summation frame based systems EtherCAT and VABS exhibit distinctive strengths and weaknesses. Profinet IRT gains the advantage with asymmetric inbound and outbound data payloads, but it runs behind EtherCAT and VABS for very small data-payloads.

In this paper we consider a unique word OFDM (UW-OFDM) system with iterative detection, for which we explore two soft-input soft-output (SISO) detection algorithms: A LMMSE detector and a detector based on the generalized approximate message passing (GAMP) algorithm. For the GAMP based detector we propose additional simplifications suitable for UW-OFDM to further reduce the complexity while exhibiting only a small BER performance loss. As verified by computer simulations, both algorithms show a significant BER performance improvement over the iterations. Moreover, the GAMP based detector with the proposed simplifications outperforms the computational more complex LMMSE detector.

Clock synchronization and ranging are important topics in the field of wireless networks, where internode time measurement allows both tasks to be completed in one. Such networks are generally time-variant due to possible changes in environmental conditions and mobility of network nodes. We present a fully distributed filtering algorithm for combined clock synchronization and ranging based on message passing by belief propagation on a factor graph representation of a time-variant wireless network. The resulting message passing equations can be interpreted as a variant of Kalman filtering locally on each network node. Simulation results show that tracking estimation parameters improves estimation accuracy significantly without additional communication effort.

We propose a novel diversity combining method called local average gain combining (LAGC) that is based on the local average of channel gains. Compared with MRC, which requires the instantaneous complex channel coefficients, and EGC, which requires only the instantaneous channel phases, LAGC requires the instantaneous channel phases but the lo- cal average of the channel gains, implying an implementation complexity between those of MRC and EGC. The average bit error probability (ABEP) of LAGC is analyzed and derived in closed-form using a method that is based on the characteristic function (cf) and the Paserval's theorem, showing that LAGC approximates to MRC in slow fading and to EGC in balanced fast fading. Simulations are performed to validate the analysis. The channel phase estimation error is included in the simulation, and it turns out that LAGC and EGC significantly outperform MRC and SC. This is a distinct advantage of LAGC because in fast fading it is more difficult to track the channel coefficients and on average the channel phase error is larger.

Nowadays automation manufacturers focus increasingly on Real Time Ethernet (RTE) based networks. The RTE protocols are closely related to standard Ethernet, which has been developed originally for pure asynchronous, non-time-critical communication. Hence, conventional RTE networks are confined to certain performance limits. In this study we present VABS (Very High Performance Automation Bus System), a new RTE approach, which uses its own specified data link layer protocol but still deploys Ethernet physical components. We compare VABS with Profinet IRT and EtherCAT by the use of performance indicators, specified in IEC 61784. The presented analysis exhibits that VABS indeed achieves a performance advance concerning both, the real-time and the asynchronous communication. It turns out that the benefits in terms of the asynchronous channel are considerable.

Receive antenna diversity is a technique that uses multiple antennas at the receiver side to improve signal reception performance by exploiting spatial diversity. However, in a mobile diversity receiver, the diversity performance is degraded by mobile antenna mismatch created by, e.g., body and hand effects. In this paper, we first explain the mechanism of antenna mismatch and then derive analytic results on the distribution and mean value of the combined SNR in a general frequency-flat Rayleigh fading environment. Three combing techniques are considered: MRC (maximal ratio combing), EGC (equal gain combing) and SC (selection combing). We also present simulated results on BER performance showing that, in a mobile terminal with two receive antennas, single mobile antenna mismatch up to -7 dB causes considerable degradation in array gain, but only negligible reduction in diversity order such that the diversity system still exhibits significant improvement in BER performance compared to an ideal single receive antenna system. Even when both antennas have a mismatch up to -7 dB, the diversity system shows noticeable improvement in BER performance at high SNR.

The range of applications for wireless sensor networks (WSNs) is continuously growing and is expanding into new branches and markets rapidly. Largely different requirements regarding network structure, powering possibility, latency, data rates, and reliability, lead to the need of suitable systems and protocols. An approved way to implement an energy aware wireless network is the Time Division Multiple Access (TDMA) strategy. In this work we propose two different TDMA schedules for highly reliable sensor data collection with sample rates of 10 Hz and analyze and compare them regarding reliability and energy consumption. A standard coin cell can power a sensor node for more than 2 month with a sensor data loss smaller than 10-3percent at 3% PER in the radio channel.

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.

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.

Building compact and low-cost yet flexible and reconfigurable radios for future wireless systems is generally a challenging task. On one hand, the needs for flexibility and re-configurability prevent using dedicated hardware particularly designed and optimized for only a single application or part of the radio spectrum. And on the other hand, to keep the overall size and cost of the radio equipment feasible, especially in multi-antenna multi-radio scenarios, the cost and size of individual radios are strongly limited. As a result, various imperfections and impairments are expected to take place in the used radio transceivers, especially in the radio frequency (RF) analog electronics. Good examples of such imperfections are, e.g., mirror-frequency interference due to I/Q imbalance, non-linear distortion due to mixer and amplifier nonlinearities, timing jitter and non-linearities in sampling and analog-to-digital (A/D) converter circuits, and oscillator phase noise. These impairments, if not properly understood and taken into account, can easily become a limiting factor to the quality and performance of the radio device and thereon of the whole wireless link. This is even more so, when more complex and more sensitive high-order modulated wideband communications waveforms are being deployed in the future systems. This article gives an overview of the essential RF impairments in modern radio communication context. Furthermore, different conceptual alternatives for reducing the effects of RF impairments in radio transmitters and receivers utilizing digital signal processing are described.

In this paper, we present a methodology to establish an accurate and power-aware simulation of wireless sensor networks. As the design of software applications running on resource-constrained sensor nodes mainly influences both timing and power consumption in the network, it is crucial to include these components in the simulation. Besides considering the software aspect in the network, it is also important to obtain a detailed and accurate power consumption profile of every hardware module present in the network.

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.

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.

In this contribution we introduce a new digital signal processing (DSP)-oriented implementation of a feedforward linearizer. The intermodulation distortion (IMD) signal is regenerated entirely in the digital baseband which gives better control over the linearization process and also improves the efficiency of the overall amplifier. A new scheme to estimate the parameters of the proposed feedforward linearizer is presented which decouples the parameters of the signal and error cancellation loop. We have verified the new DSP oriented feedforward linearizer by means of simulations in the presence of component impairments like, e.g., IQ mismatch. Initial measurements results in a laboratory setup show a reduction of the adjacent channel power of approximately 15 to 20 dB.

Multi-mode operation of wireless transceivers has become a major issue due to the ongoing evolution of 2G to 3G and beyond mobile communication standards. As a result the cellular market is confronted with the challenge of a broad diversity of communication standards. This paper discusses the design of an adaptive wireless receiver for multi-mode operation and power efficiency by sharing digital signal processing stages for all operation modes and adapting them for minimum power consumption with respect to the channel selection requirements of the main cellular communication standards (GSM/EDGE, CDMA2000, and W-CDMA/HSDPA) and satellite navigation systems (Galileo). The proposed approach is verified by simulations exhibiting an error-vector-magnitude (EVM) of 2.9 % in W- CDMA while the estimated power consumption can be reduced by 62 % versus full featured mode.

In almost every wireless RF application, a phase locked loop (PLL) is required. Digital signal processing especially for PLLs in CMOS technology is increasingly used instead of conventional analog processing to improve reliability, to reduce power consumption, and to allow for re-configurability. This paper presents a simulative analysis of an all digital PLL (ADPLL) with a two bit frequency discriminator (FD) in the feedback path. Effects on the in-band noise performance due to the sampling rate are treated. Furthermore, a theoretical prediction and simulative analysis of spurious emission offset frequencies will be given.

The HSDPA extension of UMTS promises an improved cell capacity and throughput. This enhancement is mainly achieved by three newly introduced techniques, namely adaptive modulation and coding, hybrid automatic repeat request, and fast scheduling. The used coding and modulation scheme depends on the transmitted transport block size, which in turn is signalled via the channel quality indicator (CQI). The CQI values are calculated with the help of SINRs at each User Equipments and fed back to the base station. An appropriate CQI estimation is necessary to transmit data packets with transport block sizes that maximize the throughput. Therefore, in this work we propose a novel SINR-to-CQI mapping which achieves optimum throughput for selected ITU propagation channel models.

We investigate the update rate for channel estimation in time-varying channels for UMTS-HSDPA. Our channel estimator is based on correlation of the received chip stream and the known pilot stream. This results in an averaging of the estimated channel over a block. First, we investigate the influence of the update rate by averaging over the perfectly known channel at the receiver. This corresponds to the upper bound for block averaging. Second, we examine the throughput by averaging over correlation based channel estimation. We find specific update rates for the ITU-channel models PB3, VA30, and VA120 in combination with RAKE reception or LMMSE equalization for 16-QAM symbol constellation

This paper presents radio frequency (RF)-receiver investigations related to UMTS-HSDPA throughput performance (TP). The investigated concept is based on a direct conversion receiver (DCR) architecture enhanced with a digital-front-end (DFE). Due to the use of a DFE some analog requirements decrease on the expense of a tightened ADC specification and a more complex digital signal processing chain. To efficiently use the whole dynamic range of the ADC under all operating conditions requires a smart automatic gain control (AGC) strategy for the analog gain stages. The effects of different ADC levels on the TP performance are investigated in detail. Based on these results a smart leveling strategy is developed. TP results including the proposed AGC-method are presented for the ITU-channel models PA3, PB3, and VA120.

This paper introduces a combined UMTS/NAVSAT receiver architecture with one common reconfigurable radio frequency (RF) front-end. After a review of the state-of-the-art for UMTS and NAVSAT receivers, a configurable UMTS/-NAVSAT architecture is proposed. The investigated concept is based on a digital-front-end (DFE) to prevent duplication of hardware, which will result in considerably lower costs. The integration of digital signal processing block into the RFIC is further favored by the advent of RF-CMOS as mainstream technology for RFICs, due to the availability of high speed and low power digital logic blocks. The DFE includes highly reconfigurable filter structures, which enable channel selection for different signal bandwidths according to the configured mode. The analog to digital conversion is carried out with a high dynamic-range/low-power DeltaSigma-analog-to-digital-converter (ADC). This simplifies the design of the analog anti-aliasing filter considerably

This paper introduces a combined GNSS/UMTS receiver architecture. After a review of the state-of-the-art, a configurable GNSS/UMTS architecture is proposed. The investigated concept is based on a reconfigurable receive chain to prevent duplication of hardware, which will result in considerably lower costs. The biggest challenge in the design of Galileo receivers are the extremely right noise figure (NF) requirements. Another key issue of integrated GNSS/UMTS receivers is the maximum tolerable UMTS transmit leakage injected into the Galileo receiver

In this letter, we propose the concept of combined equalization for uplink multicarrier code-division multiple access (MC-CDMA) and perform a theoretical analysis which shows that better single-user bounds than the classical matched-filter bounds are achieved with this new concept. Moreover, we illustrate how to properly design an uplink MC-CDMA transmitter and receiver for combined equalization, and show by Monte Carlo simulations that the improved single-user bounds are closely approached, even in the case of a fully loaded system.

In this paper, uplink time division duplex (TDD) multi-carrier code-division multiple-access (MC-CDMA) systems applying pre-equalization to combat channel impairments are considered. Especially, the performance degradation caused by the Doppler induced frequency offsets among the different mobile users is analyzed in detail. Based on this analysis different frequency interleaving schemes are proposed and their potential to reduce the performance degradation is investigated. It turns out, that a frequency interleaver which is allowed to skip a few, well-defined subcarriers is capable of reducing the influence of Doppler induced frequency offsets significantly causing a very little loss in bandwidth efficiency.

In this work we investigate the meaning of decision feedback equalization for a single carrier system with frequency domain equalization (SC/FDE) in an overall system approach, based on the parameters of the IEEE 802.11a standard. The concept of SC/FDE allows an advantageous combination of feed forward frequency domain equalization and feed back equalization in the time domain, that combines low signal processing complexity and powerful equalization. Although the concept of decision feedback equalization (DFE) is a well known and developed theory, this nonlinear equalization is rarely investigated in an overall system approach. Based on that the possible performance gain will be characterized under the constraints of channel characteristics, error propagation, higher order modulation schemes and channel coding. It will be demonstrated that these elements have significant influence on the possible performance of DFE and may reduce the propagated high performance gain.

In this work we investigate the effect of convolutional coding, interleaving and Viterbi decoding, as they are used for OFDM (orthogonal frequency division multiplexing) in the IEEE 802.11a standard, for a single carrier system with frequency domain equalization (SC/FDE). We will characterize the effect of decision length (maximal length of the trellis) and code rate in terms of bit error behavior, reliability of soft decisions and implementation effort for the classical Viterbi algorithm as well as for the soft output Viterbi algorithm (SOVA). The (coding) parameters of the simulated system are adapted to the IEEE 802.1 Ia standard for WLAN applications. In detail we will elaborate on the advantages of pilot symbols, that are multiplexed into the data stream as a method to reduce the necessary decision length as well as to reduce the implementation effort and to improve the SOVA output. It will be demonstrated that the use of pilot symbols shows significant advantages that dominate the disadvantages.

Single carrier transmission with frequency domain equalization (SC/FDE) has been shown to be a promising alternative to orthogonal frequency division multiplexing (OFDM) systems for wireless LANs. In this work we add time domain turbo decision feedback equalization to conventional SC/FDE for block transmission with cyclic prefix. The proposed scheme achieves the potential of ideal decision feedback equalization. Simulation results show a considerable performance increase for highly frequency selective radio channels given in W-LAN environments.

We investigate the use of a known symbol sequence - a so-called unique word (UW) - instead of the well-known cyclic prefix (as it is used in OFDM, orthogonal frequency division multiplexing, systems) for a single carrier system with frequency domain equalization (SC/FDE). The considered SC/FDE system is similar to the one proposed in the IEEE 802.16.3c target group. It is shown that the UW fulfils the theorem of cyclic convolution required for efficient implementation of the SC/FDE structure. We elaborate on the advantages that result for equalization, channel estimation, and synchronisation. Compared to the advantages, the disadvantages in terms of BER behaviour and bandwidth efficiency are rather modest.

A high data-rate wideband chirp spread spectrum system for indoor communication is proposed. The use of chirp signals with the well known pulse compression technique makes the system extremely robust and therefore suitable for applications in an industrial environment. By using /spl pi//4 DQPSK modulation, overlapping chirp signals, and optimized chirp signal design we get data rates up to 70 Mbps. There is no need for sophisticated digital signal processing due to the use of surface acoustic wave (SAW) filters for the generation and filtering of the chirp signals. Production tolerances, temperature drift, and other system imperfections are shown to be either negligible or can easily be tracked. Simulation results reveal that the limiting factor for the data rate is intersymbol interference caused by multipath propagation.