For critical services, such as traffic safety and traffic efficiency, it is advisable to design systems with robustness as the main criteria, possibly at the price of reduced peak performance and efficiency.Ensuring robust communications in case of embedded or hidden antennas is a challenging task due to nonisotropic radiation patterns of these antennas. The challenges due to the nonisotropic radiation patterns can be overcome with the use of multiple antennas. In this paper, we describe a simple, low-cost method for combining the output of multiple nonisotropic antennas to guarantee robustness, i.e., support reliable communications in worst-case scenarios. The combining method is designed to minimize the burst error probability, i.e., the probability of consecutive decoding errors of status messages arriving periodically at a receiver from an arbitrary angle of arrival. The proposed method does not require the knowledge of instantaneous signal-to-noise ratios or the complex-valued channel gains at the antenna outputs. The proposed method is applied to measured and theoretical antenna radiation patterns, and it is shown that the method supports robust communications from an arbitrary angle of arrival.

The recent and upcoming releases of the 3rd Generation Partnership Project's 5G New Radio (NR) specifications include features that are motivated by providing connectivity services to a broad set of verticals, including the automotive, rail, and air transport industries. Currently, several radio access network features are being further enhanced or newly introduced in NR to improve 5G's capability to provide fast, reliable, and non-limiting connectivity for transport applications. In this article, we review the most important characteristics and requirements of a wide range of services that are driven by the desire to help the transport sector to become more sustainable, economically viable, safe, and secure. These requirements will be supported by the evolving and entirely new features of 5G NR systems, including accurate positioning, reference signal design to enable multi-transmission and reception points, service-specific scheduling configuration, and service quality prediction.

IEEE Transactions on Vehicular Technology (ISSN: 0018-9545)Citation for the published paper: Nagalapur, K. ; Brännström, F. ; Ström, E. et al. (2016) "An 802.11p Cross-Layered Pilot Scheme for Time-and Frequency-Varying Channels and Its Hardware Implementation".Abstract-Robust channel estimation in IEEE 802.11p systems in highly time-and frequency-varying vehicular channels in combination with long data packets is a challenging task due to the ill-suited pilot pattern. Solutions of increased receiver complexity that use decision feedback and iterative decoding have been proposed to overcome the difficulty in robust channel estimation. In this work, a cross-layered method to introduce complementary training symbols into an 802.11p frame is proposed. In the proposed approach, known bits are multiplexed with the data in higher layers and a modified receiver can utilize these bits as training data for improved channel estimation. A standard receiver treats these bits as data and passes them to the higher layers where they can be removed, making the method compatible with the standard 802.11p transceivers. A software/firmware update of the higher layers is needed in a standard receiver to remove the multiplexed bits. A modified receiver with low complexity channel estimation schemes that utilizes the complementary training symbols is implemented in a field programmable gate array platform. Frame error rate measurements have been performed by interfacing the hardware implementation with a channel emulator. The measurement results follow the computer simulation results validating the hardware implementation. Moreover, measurement results show that the modified receiver follows the performance of an ideal receiver that has full knowledge of the channel (with only an offset in signal-to-noise ratio) and significantly outperforms the commercial 802.11p transceiver we tested.

Abstract-Vehicular wireless channels are highly time-varying and the pilot pattern in the 802.11p orthogonal frequency-division multiplexing frame has been shown to be ill suited for long data packets. The high frame error rate in off-the-shelf chipsets with noniterative receiver configurations is mostly due to the use of outdated channel estimates for equalization. This paper deals with improving the channel estimation in 802.11p systems using a cross layered approach, where known data bits are inserted in the higher layers and a modified receiver makes use of these bits as training data for improved channel estimation. We also describe a noniterative receiver configuration for utilizing the additional training bits and show through simulations that frame error rates close to the case with perfect channel knowledge can be achieved.

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