The sixth generation (6G) mobile communication networks are expected to intelligently integrate into various aspects of modern digital society, including smart cities, homes, health-care, transportation, and factories. While offering a multitude of services, it is likely that societies become increasingly reliant on 6G infrastructure. Any disruption to these digital services, whether due to human or technical failures, natural disasters, or terrorism, would significantly impact citizens’ daily lives. Hence, 6G networks need not only to provide high-performance services but also to be resilient in maintaining essential services in the face of potentially unknown challenges. This paper provides a general review of the state of the art on resilient systems, definitions, concepts, and approaches. Moreover, it introduces a comprehensive concept, i.e., resilience-by-design (RBD), in three different levels for designing resilient 6G communication networks, summarizing our initial studies within the German Open6GHub project. First, we outline the general RBD enabling principles and discuss their related sub-categories. Next, adopting an interdisciplinary approach, we propose to embed these principles across all 6G layers/perspectives including electronics, physical channel, network components and functions, networks, services, and cross-layer and cross-infrastructure considerations and discuss their challenges. We further elaborate the RBD principles and their realizations along with several 6G use-cases. The paper is concluded by presenting a comprehensive list of open problems for future research on 6G resilience.

Joint communications and radar sensing (JCRS) applications are currently being hailed as the innovation of the next generation of mobile communications. The combination of communications and sensor technology on one hardware platform offers various advantages, such as significant savings in space and costs. The two technologies are no longer being optimized and developed side by side, as has been the case in the past, but jointly. The physical channel is used by both simultaneously, including the transmitter and receiver structures, which must be optimized for the combined application. This inevitably leads to an influence on the performance of both systems. In this work, this influence is considered and analyzed with respect to the effects of the radio frequency components. For this purpose, our previously published code-division multiple access (CDMA)-based and vehicle-to-vehicle-focused model is extended to a JCRS model and evaluated according to the achieved bit error rate as well as the mean deviation of the detected distance and velocity in Simulink. The influence of the non-ideal hardware components (mixers, power amplifier, low noise amplifier, filter, antenna) and characteristics (S-parameters, non-linearity of the amplifiers and the noise) on the sensing and communications are analyzed and compared in this automotive context. The results reveal that the noise of the low noise amplifier at the receiver side has the most decisive influence. In contrast, the noise generated by the power amplifier at the transmitter has no effect due to the relatively high signal power. The non-linearity of amplifiers at the transmitter also significantly impacts the available sensing range by limiting and compressing signal power. Besides, the phase noise with a frequency offset higher than 10MHz can increase the communications and sensing error rate. In contrast, the influence of S-parameters is negligible, as the performance of communications and sensing is almost unchanged with different S-parameters. In the future, the proposed single-target scene will be further extended to a multi-target one.

Joint communications and sensing (JCAS) is regarded as a major technology building block in 6G networks. The combination of communications and radar sensing systems benefits from saved hardware costs, reduced energy consumption, and less spectrum occupation. phase-modulated continuous waveform (PMCW) is regarded as an attractive candidate waveform for future automotive JCAS systems due to its perfect anti-interference properties and radar sensing performance. However, PMCW-based JCAS systems usually suffer from extremely low data rates and undesirable communications reliability in dynamic environments, limiting their applicability in traffic scenarios, where the propagation channel may suffer from a high Doppler shift and spread and a large data throughput is expected. To overcome the shortcomings, in this work, a novel PMCW approach with simultaneously transmitted pilot and data sequences, named code-orthogonal PMCW (CO-PMCW), is introduced. The presented CO-PMCW approach benefits from significantly improved data rate and robustness in dynamic environments. Regarding the differences in system architecture between PMCW and CO-PMCW, the authors verified the advantages and investigated the potential side effects of the CO-PMCW system. The properties including the interference between the pilot and data, influence on transmission power, behavior in multipath fading channels, etc. are measured. The result shows that the presented CO-PMCW approach significantly improves the communications performance with slightly influenced radar properties. Based on the simulation result, the application feasibility and scenarios of the CO-PMCW-based JCAS system are analyzed.

Joint communications and sensing (JCAS) is regarded as a key technology of 6G communications since it allows the integration of sensing functions into communications networks with lower hardware costs, less energy consumption, and saved spectrum. As distributed sensing benefits from increased spatial diversity and accuracy, the combination of coordinated multipoint (CoMP) transmission technology and JCAS has become an attractive research direction. CoMP transmission has been applied in 4G and 5G communications networks due to its attractive capability in suppressing inter-cell interference and improving channel capacity, while CoMP sensing and CoMP JCAS have been widely discussed in recent years. However, relevant researches mainly focus on waveform design and optimization issues in the processes of CoMP signal transception and processing, while their system architecture and operation modes are less discussed. To fill the blank in these areas and discuss the benefits provided by CoMP JCAS, in this work, based on the modern CoMP transmission technologies in state-of-the-art mobile network architecture, we analyze the network architecture and required enabler technologies of CoMP JCAS in future mobile networks, focusing on the sensing aspect. In addition, we propose the potential sensing operation and clustering types and discuss their respective advantages and shortcomings. In the simulation, the sensing coverage and accuracy of different CoMP sensing types and conventional standalone sensing are compared. The simulation results show that CoMP sensing outperforms conventional single-radar sensing in accuracy, and the difference between them increases with the distance between the sensors. In addition, it is described that the coordinated passive sensing scheme extends the service area, while the active sensing scheme benefits from higher accuracy with the same bandwidth.

Vehicular communication systems get more and more attention with the upcoming fifth and sixth generation. Hereby, the focus lies on the development of the co-design or co-existence of communications and sensing. So called joints communications and radar sensing systems are seen as one key technology of 6G. As joint systems will have shared waveforms and hardware platforms, there is a huge benefit in cost and space which is one essential argument for the automotive industry. However, to design such a system for new applications like platooning or intersection assistance a physical layer has to be set up to represent the real physical layer properly. The proposed system design closes the lack of such a simulation tool and allows for full physical layer simulations, including e.g. the hardware non-idealities and the channel model for 77GHz. The whole signal processing chain of the physical layer is built up and will be integrated in the higher layer state-of-the-art simulation frameworks like Veins or Artery in the next step. The communications design is developed in Simulink, whereas the sensing part is discussed. The proposed communications architecture covers several transmission approaches (serial, parallel), a CDMA based spreading, a radio frequency representation, the channel (simulated in a 3D-Ray-Tracing-tool) and the receiver structure (e.g. the synchronisation or the channel estimation). Several design criteria are discussed, like the serial or parallel design architecture, the maximum ratio combining or the phase and frequency compensation method. The whole system architecture is freely available ( https://doi.org/10.5281/zenodo.6482565 ) and in consequence, the different signal blocks and parameters can be enabled or disabled for evaluations according to future design criteria requirements.

The sixth generation (6G) of wireless networks is envisioned to achieve far beyond the capabilities of fifth generation (5G), necessitating significant innovations at the physical layer (PHY). These include exploration of several fundamental trade-offs between spectral efficiency, reliability, and energy consumption, and enhancing the performance of key enablers for 6G PHY. This paper synthesizes key insights from the 6G-ANNA research initiative on emerging PHY technologies for 6G to provide a holistic exploration of the ongoing trends in the 6G research. The investigations span novel waveform and channel coding techniques for improved energy efficiency, the “Gearbox PHY" concept for adaptive transceiver operations, and optimized radio transceiver designs that balance complexity and power consumption. The study also examines advanced multiple access schemes and cell-free massive massive multiple-input multipleoutput (MIMO) architectures to enhance spectral efficiency and uniform coverage. Integrated artificial intelligence solutionsat the PHY layer and insights to security and trustworthiness challenges in 6G networks are also provided. The findings offer insights into the fundamental trade-offs and provide several key PHY innovations that address sustainability, capacity, and resiliency challenges of future 6G wireless systems.