Autonomous driving relies on a variety of sensors, especially on radars, which have unique robustness under heavy rain/fog/snow and poor light conditions. With the rapid increase of the amount of radars used on modern vehicles, where most radars operate in the same frequency band, the risk of radar interference becomes a compelling issue. This article analyses automotive radar interference and proposes several new approaches, which combine industrial and academic expertise, toward the path of interference-free autonomous driving. INTRODUCTION AND MOTIVATION Radar is becoming the standard equipment in all modern cars, supporting, e.g., cruise control and collision avoidance in most weather conditions whilst providing high-resolution detections on the order of centimeters in the millimeter-wave (mmWave) band. The next generation of Advanced Driver Assistance (ADAS) and Autonomous Drive (AD) vehicles will have a multitude of radars covering multiple safety and comfort applications like crash-avoidance, self-parking, in-cabin monitoring, cooperative driving, collective situational awareness and more. Since automotive radar transmissions are uncoordinated, there is a non-negligible probability of interference among vehicles, as shown in Fig. 1. While current automotive radars are already impacted by interference to some extent, it is today unlikely to get issues noticeable to the customer as the state-of-the-art automotive radars are continuously updated and improved on multiple system levels. However, the mutual interference problem is expected to become more challenging, unless properly handled, as more vehicles are equipped with a larger number of radars providing 360 • situational awareness at various distances to enable more advanced future ADAS and AD functionalities.

An ultra-low power wake-up radio receiver using no oscillators is described. The radio utilizes an envelope detector followed by a baseband amplifier and is fabricated in a 130-nm complementary metal-oxide-semiconductor process. The receiver is preceded by a passive radio-frequency voltage transformer, also providing 50 antenna matching, fabricated as transmission lines on the FR4 chip carrier. A sensitivity of dBm with 200 kb/s on-off keying modulation is measured at a current consumption of 2.3 A from a 1 V supply. No trimming is used. The receiver accepts a dBm continuous wave blocking signal, or modulated blockers 6 dB below the sensitivity limit, with no loss of sensitivity. IndexTerms-Blocking signal, complementary metal-oxide-semiconductor (CMOS), envelope detector sensitivity, radio-frequency identification (RFID), ultra low power, wake-up radio, wireless sensor networks. I. INTRODUCTIONT HE RESEARCH on low-power radio technology is motivated by the needs from several application areas. Among these application areas are distributed wireless sensor networks, which may include chemical security monitoring [1], buried sensors for buildings and structure health [2], biotelemetry [3],[4], or surveillance in logistic chains [5]. These types of networks are sometimes referred to as Internet of Things (IoT), ubiquitous computing, or simply as radio-frequency identification (RFID). A common requirement is the need for ultra low power receiver solutions. The network node lifetime is determined by its power consumption and its battery capacity. Energy scavenging from mechanical vibrations, thermal gradients, or electromagnetic fields could increase the lifetime or eliminate the need for batteries. Exclusion of batteries may drastically change the service required to maintain the network, but with available radio technology this will also severely reduce the communication range for the nodes. A common accepted dc power consumption level where energy scavenging is feasible for a node is around 100 W [6].

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To generate performance predictions of borehole thermal energy storage (BTES) systems for both seasonal and short-term storage of industrial excess heat, e.g., from high to low production hours, models are needed that can handle the short-term effects. In this study, the first and largest industrial BTES in Sweden, applying intermittent heat injection and extraction down to half-day intervals, was modelled in the IDA ICE 4.8 environment and compared to three years of measured storage performance. The model was then used in a parametric study to investigate the change in performance of the storage from e.g., borehole spacing and storage supply flow characteristics at heat injection. For the three-year comparison, predicted and measured values for total injected and extracted energy differed by less than 1% and 3%, respectively and the mean relative difference for the storage temperatures was 4%, showing that the performance of large-scale BTES with intermittent heat injection and extraction can be predicted with high accuracy. At the actual temperature of the supply flow during heat injection, 40 °C, heat extraction would not exceed approximately 100 MWh/year for any investigated borehole spacing, 1–8 m. However, when the temperature of the supply flow was increased to 60–80 °C, 1400–3100 MWh/year, also dependent on the flow rate, could be extracted at the spacing yielding the highest heat extraction, which in all cases was 3–4 m.