For short range data transmission, Visible Light Communication (VLC), in which data is transmitted in the visible light spectrum, is a very interesting alternative to classical radio frequency transmission. Display-camera communication is one variant of such VLC systems, using displays as transmitters and cameras as receivers. The properties and possibilities of these channels are currently subject to research. In this paper, a model for the display-camera channel is presented. The model is then adapted to differential display-camera communication, which enables an imperceptible data transmission while still using the transmitting display for image content presentation. With this model, the available channel capacity is derived and determined for a selection of measured display-camera combinations. Knowledge of the available channel capacity will help designing and optimizing forward error correction procedures for the differential display-camera channel.

Parallel sequence spread spectrum (PSSS) is a novel physical layer (PHY) technique allowing a flexible resource allocation through code multiplexing. This broadband technique is designed for high data rates in industrial applications, as it offers benefits in fading environments at a relatively low hardware complexity. In this paper we compare different approaches for the equalization of wireless channels in a PSSS communication system. For this purpose we employ multiple baseband impulse responses representing diverse transmission conditions. We analyze the performance of the cyclic prefix based PSSS design from previous work and compare it with our more efficient equalization approaches.

Optical transmission of barcodes using handheld cameras offers a practical solution for transmitting small amounts of data without device pairing. In various application scenarios, 2D matrix codes such as QR Code and Data Matrix have become ubiquitous for broadcasting short information such as web links. In recent years, both the increasing demand for higher data throughput and the rapid development of on-board cameras in smartphones have driven research into high-capacity systems. While the reduction of 2D symbol size can quadratically increase the spatial data capacity, accurate localization of small symbols, each consisting of only a few pixels, is extremely difficult due to the non-idealities of the camera-based optical channel. As a result, the data throughput achieved by state-of-the-art systems employing pattern-based methods is still far from optimal. In this work, we propose, for the first time to the best of our knowledge, a novel patternless approach to symbol position recovery for high-density matrix codes. We adapt the even-law synchronizer to estimate the symbol positions in each spatial dimension separately, and compensate for the impact of lens distortion by a successive curve fitting process. Simulation and experimental results show that our method significantly outperforms pattern-based benchmark methods by providing excellent accuracy and reliability.

The published IEEE 802.11ax standard introduces spatial reuse to WLAN and the upcoming IEEE 802.11be standard expands spatial reuse to multiple operation modes under the topic of multi-access point coordination. Literature shows that there is potentially a high performance increase to WLAN by using spatial reuse in selected scenarios. However, there is little work about general evaluation of spatial reuse and its potential application. Using simple two-link network examples, this paper discusses power domain related different versions of spatial reuse from an operating point and performance perspective. The discussion may help to structure application scenarios of spatial reuse for potential yield of additional system performance and decreased latency. Finally, the derived conclusions allow optimizing spatial reuse algorithms from research and can be useful for manufacturers to implement decision points for spatial reuse in actual hardware.

Alongside classic Visible Light Communication using LEDs and photodiodes, Optical Display-Camera Communication offers another promising way of transmitting data through visible light wirelessly: A display serves as a multi-parallel transmitter array and a camera as the corresponding receiver. Due to the high number of pixels, high data rates in the range of several Mbit/s can be achieved despite comparatively low temporal rates. A major challenge that all high rate system realizations have to overcome is the lack of synchronization between display and camera. Along with varying playback and recording behavior of the devices, this typically results in mixed recordings of display frames in the receiver, which complicates frame decoding. In this paper, we fundamentally investigate the temporal sampling process in display-camera communication. Using our improved modeling we determine the minimum temporal oversampling factor required for lossless frame acquisition, in order to maximize system efficiency in the temporal domain. We propose a solution for the synchronization problem for invisible system approaches with differential modulation, in which the original display frames are recovered from asynchronous recordings in the receiver. Experimental results show that this method works robustly even with high motion background videos and without the need for embedded synchronization markers.

We propose a closed-loop industrial radio system with a star topology for factory automation using Parallel Sequence Spread Spectrum (PSSS) technology. This system implements all significant concepts for synchronization, duplex-communication, channel estimation/equalization based on an innovative transceiver concept. The industrial environment tends to have non-line of sight channels that lead to RMS delay spreads of less than 100 ns. Here, we propose a channel equalization scheme to compensate for these delay spreads. Another challenging aspect is the implementation of a code division duplexing (CDD) scheme. We propose a closed-loop system architecture that can achieve the targets set by Industry 4.0 bodies such as IWSAN. This paper gives an overview of the closed-loop systems concept.

Parallel sequence spread spectrum (PSSS) is a novel physical layer (PHY) broadband technique, that offers a flexible resource allocation and benefits against fading on wireless channels at a relatively low complexity. This spread spectrum method may especially be used in industrial radio and for high data rates in the THz range. In this paper, we first present the characteristics of the root-raised cosine (RRC) pulse shaped PSSS signal. We examine the amplitude distribution and the peak-to-average power ratio (PAPR) for different roll-off factors. Surprisingly, for large roll-off values high amplitudes become more likely. We then analyze the performance of PSSS under the influence of a memoryless nonlinearity introduced by a solid-state power amplifier (SSPA) using baseband simulation. This power amplifier (PA) is modeled using the well-established Rapp model. We compare the system to a basic orthogonal frequency-division multiplexing (OFDM) implementation.

Parallel Sequence Spread Spectrum (PSSS) is a spread spectrum physical layer (PHY) offering beneficial properties against the effects of fading as well as the possibility of a flexible resource allocation, while maintaining a low complexity. Additionally it is being investigated for high data rates in the THz range. In this paper, we give an overview on the current state of research on PSSS, its advantages, but also its challenges. We present simulations and measurements comparing the performance of PSSS with OFDM, showing its potential for future wireless communications.

Wireless extensions of time-critical industrial communication systems could provide many benefits including increased flexibility and mobility. Moreover, they might enable completely new manufacturing solutions. On the other hand, seamless integration to the existing infrastructure and high performance with minimal increase of latency and jitter are key requirements. A wireless network with these features is developed in the project ParSec. Here, especially the MAC layer design and the gateway concepts between the existing Industrial Ethernet solutions and the wireless ParSec system are improved. In this paper, we show the ParSec system's proof of concept using typical industrial components. In the experimental evaluation, low round-trip times and low jitter were measured that satisfy the majority of industrial requirements.

Wireless industrial communication requires high reliability and low latencies. In order to fulfill both requirements simultaneously, wireless approaches are being developed. One of these technologies is parallel sequence spread spectrum (PSSS). In comparison to direct sequence spread spectrum approaches, which employ a set of appropriate pseudonoise (PN) sequences, PSSS data symbols are spread based on a single cyclically shiftedm-sequence. Each cyclic shift of the chosenm-sequence is used as an individual PN-sequence. This enables a code division multiple access (CDMA) scheme with simple processing and thus, a fast hardware implementation. In order to investigate the impact of an inaccurate time synchronization, this paper presents a theoretical and simulative PSSS evaluation. Moreover, an iterative symbol detection is introduced, which neutralizes the impact of the nonorthogonalm-sequences and mitigates the degradation due to inaccurate synchronization. In addition, several reasonable resource allocation schemes are presented, which emphasize the PSSS systems flexibility.

Display-camera data links can be regarded as a massive MIMO visible light communication. They are a research topic since several years. Imperceptible data transmission while simultaneously presenting video sequences for human viewers on the display is an innovative approach allowing for many new applications. Several groups work on this concept. This paper describes a new approach with specific modulation schemes and proposes a system, which combines concepts from digital data transmission and real time video processing while carefully taking the characteristics of the human visual system into account. The modulation parameters are selected as a compromise between picture quality deterioration and decoding performance in terms of data rate and bit error probability. Characterizing a video representation by luminance Y and chrominance U and V as usual in electronic media distribution and video source coding, subjective tests show that data modulation of the chrominance signals is a promising option. An early experimental setup applying modulation of U and V video components already provided data rates of 4.5 Mbit/s at acceptable error rates without significant degradation of perceived video quality.

Novel wireless systems are often first evaluated by simulation, before prototypes are tested and the concepts are standardized. In order to ensure relevant simulation results, the wireless channel has to be modelled properly and application oriented. Currently, only few considerable industrial channel models are available. The IEEE 802.15.4a model is the most commonly used. CM 7 applies for LOS modelling and CM 8 for NLOS environments. Both are only applicable for distances up to 8m. In order to enhance the existing channel models, an extended wide band measurement campaign including seven scenarios at three different industrial locations was performed. From different LOS and NLOS measurement series in a warehouse, a manufacturing shop and a mechanical workshop, values for the path loss exponent, RMS delay spread, coherence bandwidth and fading statistics were obtained, valid for distances up to 40m. Setup, scenarios and the results of these measurements are presented in this paper. The abundance of metallic reflectors and scatterers leads to a dense multipath environment, which causes Rayleigh distributed small scale fading for both LOS and NLOS scenarios. The path loss exponent is smaller than 2 for LOS scenarios and the PDPs show very small power decay constants due to the rich scattering environment. Moreover, the RMS delay spread was found to increase proportionally to the distance. Corresponding to this, the coherence bandwidth decreases inversely proportional to the distance. The measurement results are compared to the related work and especially with the IEEE 802.15.4a channel model.

Many statistical wireless channel models for different standards and environments have been defined. However, a single stationary statistical model does not reproduce the long term characteristics of the wireless transmission channel sufficiently. When a wireless link is modeled over longer periods of time, changes of the environment must be considered. These changes can be characterized by different phases, which are alternatively experienced by the channel. On top of that, when a whole network is considered, there are interdependencies between the phases experienced by different links. In this paper, a two level hidden Markov wireless residential channel model is described. The global state reflects the presence of residents in the house. It affects all links. The local state of a single link depends on actual movement in the vicinity of that link. Based on the observation of channel measurements a reasonable parameterization is identified. The model can be used to analyze systems for residential control applications with 24/7 operation.

Communication in industrial applications like factory automation (FA) demands very low latency combined with high reliability. Since state of the art wireless technologies are not entirely fulfilling FA requirements, novel approaches are being developed. In this context Parallel Sequence Spread Spectrum (PSSS) is a promising technology, which enables shortest latencies, whereas its bit error performance has not yet been analyzed. Similar to Direct Sequence Spread Spectrum (DSSS), where data symbols are spread each with an appropriate sequence, PSSS spreading is performed based on a cyclically shifted m-sequence. Each cyclic shift of the base m-sequence is code, which enables a CDMA scheme. This paper deduces a theoretical and simulative approach determining the bit error performance for an ideal CDMA and for a time offset between several nodes in an AWGN channel. Based on this analysis, performance constraints and reliability limits such as requested synchronization accuracy are revealed.

Vehicular channels are among the most challenging wireless channels due to their high Doppler frequencies and multiple path delays. To meet these challenges, the IEEE standard 802.11p was developed. To improve performance, a vast variety of extended receiver concepts has been proposed and evaluated under different test conditions. In this paper, we study the two most promising standard-compliant receiver extensions with respect to their performance in demanding vehicular channels. First, there is maximum ratio combining (MRC), which exploits antenna diversity by using multiple antennas. The second approach is often referred to as decision feedback equalization (DFE), which allows tracking the channel's impulse response throughout the packet without requiring additional pilot data. Consequently, we also present the combination of both approaches to identify complementing effects.

The combination of low-density parity-check (LDPC) codes and higher-order modulation does usually neither require an interleaver in between nor elaborated signal mapping design rules. However, as the constellation size increases, a matching interleaver can be employed to compensate performance losses, especially in case of structured codes. This interleaver can be generally described by mapping distributions. In this paper, we discuss optimized mapping distributions for short LDPC codes, i.e. in the order of 102-103bits. We point out that mapping distributions optimized by means of density evolution may not be suited for short codes. An alternative framework is introduced that utilizes an extended version of extrinsic information transfer functions. Their visualization feature helps to identify good mapping distributions for short codes.

The interconnection of smart home devices plays a key role in future smart grid energy systems. It is reasonable to apply wireless technologies for smart home networks, as they can be easily retrofitted in existing homes. Due to multipath propagation in indoor environments, wireless technologies have to cope with frequency selective fading. Thus, this paper presents an enhanced frequency hopping mechanism for reliable interconnection of low power smart home devices. The evaluations are based on the Bluetooth Low Energy standard. Different options are compared by evaluating the indoor coverage range, the energy consumption, and the latency.

Car-to-car and car-to-infrastructure communications are currently under intense research as they enable a wide variety of applications. Besides security-driven applications which require only small amounts of individual data there are also applications which require medium to high amounts of uniform data delivered to an unknown number of nodes. For this kind of broadcast and multicast applications, the use of fountain codes is highly suitable. In this paper, we investigate the applicability of fountain codes in an infrastructure-based automotive communication system and introduce an expedient method to design a system deploying IEEE 802.11p and fountain codes. By means of simulation results obtained for three representative vehicular scenarios we compare the performance of our method to an alternative method also applied in this field, i.e. the data carousel. For specific configurations the system based on fountain codes outperforms the conservative approach by a factor of four in terms of the overall throughput and thus provides the potential to significantly increase the overall efficiency.

For ad-hoc home networks without central coordinator, IEEE 802.11 systems merely support service differentiation. In many usage scenarios of a typical home network with applications requiring a strict quality of service (QoS), this MAC functionality is not sufficient. In order to counteract this problem, we developed in previous works a modified MAC scheme based on the IEEE 802.11 enhanced distributed channel access (EDCA) function. This paper describes enhancements of the modified MAC scheme enforcing prioritized medium access for strict QoS applications. For the first time, the established concept is realized in a distributed way with in-band signaling. Our enhanced MAC is embedded into a comprehensive IEEE 802.11n reference application to demonstrate its effectiveness in combination with the latest amendments like frame aggregation. The reference application is modeled in SystemClick, a framework for describing and evaluating packet processing applications on resource constraint network nodes. This enables functional validation and provides a path to future, cost-efficient implementations on programmable devices. On this basis, the paper presents simulation results substantiating the significant improvement of QoS parameters like delay and throughput. Besides enforcing strict priorities, collisions can be reduced to zero and the average waiting time can be decreased by up to 33 % for typical usage scenarios.

In order to evaluate and to compare the performance of communication systems and the impact of improvement methods a suitable measure is essential. This paper describes an efficiency measure for the analysis and assessment of wireless home area networks. In contrast to existing definitions suitable for this specific application area, the proposed efficiency measure accounts for the resources spent to achieve the actual performance as well as for the severity of the transmission task. On the basis of this definition we assessed and compared wireless systems as well as specific optimization methods in different national and international research projects. Besides the definition, we will point out the significance of the measure and demonstrate its usage by means of typical examples.

Car communication acts as a base for advanced traffic and car services. There is a strong potential to utilize existing hardware to introduce first car communication applications and services. Potentially first car communication technologies should be seen as initial base to learn about car communic

This paper describes properties of a network management concept designed in the scope of the project ldquoHOMEPLANErdquo. Following to the projectpsilas vision, the future home network has a strong focus on multimedia applications. For the userspsila convenience, media transfers are realized based on IEEE 802.11 WLAN. To ensure high quality of service different enhancement concepts have been developed and evaluated in hardware. This paper gives an overview on the fundamental concepts of wireless resource managing as well as current implementation results.

This paper describes dynamic frequency selection (DFS) as a method to improve wireless local area network (wireless LAN or WLAN) capacity in home environments with focus on reliable media transmission. The gain obtained with this method is evaluated based on measurements of the dynamic behaviour of wireless channels. The application of DFS for each link between two nodes in ad-hoc mode can improve the performance of home media networks.