Despite years of research and the introduction of advanced features in 5G systems, no commercially available 5G device has yet met the stringent latency and reliability requirements defined for ultra-reliable and low-latency communication (URLLC). This raises fundamental questions about whether and how URLLC can be practically implemented under current technological constraints. To answer this question, in this work, we explore the combination of several features defined by the 3GPP standardization, including link adaptation, retransmission schemes, and scheduling algorithms. We evaluate the performance of these techniques to investigate the extent to which the requirements of URLLC can be achieved by using the NS-3 5G LENA simulator. Our results demonstrate that the shortest latency at which a reliability level of 99.999% can be achieved is 4 milliseconds, provided that the wireless channel is of exceptionally high quality. This level of performance is enabled by combining a retransmission scheme with an effective scheduling algorithm. However, in the presence of poor channel quality, it becomes necessary to relax the reliability constraint and/or provide more resources to the transmission to maintain system feasibility.

To fulfill the exponential growth of mobile traffic demands, 3GPP has standardized the use of LTE in the 5 GHz unlicensed band in the Release 13 dedicated to LTE Licensed-Assisted Access (LTE-LAA). Simulations and field trials have shown that incumbent WiFi (802.11ac) in the 5 GHz unlicensed band will be the victim in such co-channel deployment with LTE-LAA. Hence a concern is being raised about fair co-existence. In this work, we investigate the limits of Successive Interference Cancellation (SIC) to recover the WiFi packets corrupted by LTE-LAA in the event of a collision. For an indoor deployment, which is the most probable battleground for WiFi and LTE-LAA, we propose a method to perform SIC by using stored clean channel estimates of stronger signals obtained during an interference-free period. Our approach leverages the slow fading channel and hence high coherence time of the indoor channel. For an experimental proof of this phenomenon, we simulated a scenario with interference between 20 MHz 802.11ac and 20 MHz LTE-LAA at different inter-frame-intervals (IFI) of LTE-LAA frames. Our results show that for an LTE-LAA IFI up to 2 milliseconds, the proposed method of using stored channel estimates to perform SIC can achieve significant transmit power gain (TPG) compared to the conventional way of using instantaneous channel estimates. Our method complements the conventional approach to ensure improved WiFi Frame Detection and Decoding while applying SIC. Moreover, our method does not require any coordination between WiFi and LTE-LAA transceivers and hence can be deployed within existing infrastructure with minimal modifications.

The rapid increase in wireless devices and inherent limitation of RF spectrum is causing Co-Channel Interference (CCI). Effects of CCI are prevalent in Industrial Scientific Medical (ISM) bands which lack centralized control over devices operating on heterogeneous standards, a situation entirely different from cellular networks. In this study, we propose physical layer signal processing techniques for multi-antenna OFDM receivers in ISM band for mitigating narrowband CCI. Our work focuses only on receiver side modifications for interoperability with the existing infrastructure. We first analyze two such prominent multi-antenna interference mitigation methods: Optimal Combiner (OC) and Technology-Independent MIMO (TIMO). Optimal Combiner, although theoretically optimal, requires statistics of interferer which is difficult to obtain in practice. TIMO does not benefit from diversity gain despite having two antennas. We propose MLSC (Maximal Ratio Combiner with LLR Scaling) for multi-antenna OFDM receivers which mitigates CCI caused by narrowband interferers as well as benefits from diversity gain. For a given Packet Error Rate (PER), MLSC achieves comparable Transmit Power Gain (TPG) to OC without needing the statistics of the interferer. In addition, MLSC achieves significant TPG compared to TIMO. Further, we propose an improvement to TIMO: DC-TIMO (Diversity Combiner TIMO) which enables it to perform joint interference nulling and diversity combining.

Cooperative safety applications require dedicated short-range communications (DSRC) to provide position-awareness of neighboring vehicles at a specific level of reliability, i.e., awareness-quality, up to a given distance, i.e., awareness-range. However, heavy communication loads negatively impact such awareness requirements due to communication impairments, ranging from strict capacity limitations of DSRC channels to correlated packet collisions due to periodic communication patterns. Transmission control strategies may adapt power or rate to control such impairments but risk missing the requirements of cooperative safety applications. In this paper, we design a new awareness control strategy by implementing a spatial awareness framework. Specifically, we adapt the distribution of the awareness-quality as a function of the awareness-range. Therefore, we first propose random transmit power control (RTPC), which manages to provide different levels of awareness-quality at different ranges, while mitigating correlated packet collisions by randomizing them in space. As RTPC is able to reduce the channel load, we secondly propose to combine RTPC with transmit rate control (TRC) and to benefit from the gained channel resources by subsequently increasing the update-rate and by implication, the quality of position-awareness. The spatial awareness control capability of RTPC+TRC has been evaluated through simulations. We discuss the influence of RTPC+TRC on cooperative safety applications exemplarily for the forward collision warning (FCW) application.

Information dissemination in pure Vehicular Ad Hoc NETworks (VANETs) such as ITS-G5 becomes problematic when the network is sparse. In situations where the number of vehicles, that can act as a communication node, is insufficiently low, e.g. in rural areas, during nighttime or because of a low market penetration of the technology in the early years of market introduction, certain range limits (unavailability of forwarding nodes) or timing limits (store-and-forward techniques) are stressed. Due to the limited communication range, VANETs start to build separated clusters, if the density of equipped vehicles is too low. Consequently, information dissemination without delay-massive store-and-forwarding is only possible within one cluster, but not beyond. This paper investigates the integration of Car-to-Car (C2C) with an additional satellite communication technology, referred to as Car-to-Satellite (C2S). A realistic sparse vehicular network scenario has been simulated and evaluated with respect to the in-time reception of safety-related information. The results show that information dissemination can be significantly improved through a limited number of vehicles which are additionally equipped with satellite terminals. In fact, even the market introduction of VANET-based ITS can be significantly accelerated with just a few vehicles equipped with non-VANET communication technology.

ETSI ITS-G5 is the current vehicle-to-vehicle communication technology in Europe, which will be standardized by ETSI TC ITS. It is based on IEEE 802.11p and therefore uses a CSMA/CA scheme for Media Access Control (MAC). In this paper we analyze the performance of Cooperative Awareness Message (CAM) based safety applications using the ETSI ITS-G5 MAC technology in a challenging scenario with respect to MAC issues: A suitable freeway segment with 6 lanes in each direction. The freeway scenario is thoroughly modeled and implemented in the well known ns-3 simulation environment. Based on this model, the paper shows the performance of CAM based safety applications under MAC challenging conditions. We provide a set of simulation results resting upon a particular performance metric which incorporates the key requirements of safety applications. Finally we analyze two concrete example scenarios to determine how reliable CAM based safety applications are in high dense traffic scenarios with respect to MAC issues.

Modern cars comprise tens of electronic control units, serving for various purposes like entertainment, driver's comfort or occupant protection. To connect these networked embedded systems inside the car, widespread bus systems like CAN or FlexRay are used, each one offering projecting abilities and specific limitations for certain application areas. In order to point out the suitability of a certain in-car network topology for the transmission of highly timeand safety-critical data content, we investigated effects of routing by a central gateway on the communication delay. In cooperation with the German car manufacturer Audi, we installed a prototype measurement infrastructure and collected meaningful communication data samples for up-to-date and future in-car networks. The results we obtained from the data samples allow for a sophisticated evaluation of the in-car communication network with respect to the demands of time- and safety-critical functions at an early stage of system development.