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This paper focuses on ultra-reliable low-latency Vehicle-to-Anything (V2X) communications able to meet the extreme requirements of high Levels of Automation (LoA) use cases. We introduce a system architecture and processing algorithms for the alignment of highly collimated V2X beams based either on millimeter-Wave (mmW) or Free-Space Optics (FSO). Beam-based V2X communications mainly suffer from blockage and pointing misalignment issues. This work focuses on the latter case, which is addressed by proposing a V2X architecture that enables a sensor-aided beam-tracking strategy to counteract the detrimental effect of vibrations and tilting dynamics. A parallel low-rate, low-latency, and reliable control link, in fact, is used to exchange data on vehicle kinematics (i.e., position and orientation) that assists the beam-pointing along the line-of-sight between V2X transceivers (i.e., the dominant multipath component for mmW, or the direct link for FSO). This link can be based on sub-6 GHz V2X communication, as in 5G frequency range 1 (FR1). Performance assessments are carried out to validate the robustness of the proposed methodology in coping with misalignment induced by vehicle dynamics. Numerical results show that highly directional mmW and/or FSO communications are promising candidates for massive data-rate vehicular communications even in high mobility scenarios.

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In this paper we consider a centralized radio access network (C-RAN) architecture with a fully analog fronthaul link between remote radio heads (RRHs) and baseband units (BBUs) based on the radio over fiber (RoF) paradigm. Mode division multiplexing (MDM) and frequency division multiplexing (FDM) are employed to provide an additional multiplexing signal dimension to meet the huge bandwidth requirements of next generation (5G) wireless mobile systems. The main contribution of the paper is to prove that a smart resource assignment between the radio antennas and the mode/frequency dimensions allows the communication over the RRH-BBU link at rates that are comparable to those achieved by an ideal fronthauling where BBU and RRH are assumed to be co-located, even without any complex and costly optical equalization technique. Validation is on the radio-link capabilities employing multiple antennas to meet the demand for massive MIMO technology.

Future (5G) mobile networks aim to pervasivity (cell size <; 1 km) and high data-rate (>20-50 Mb/s), centralized radio access network (CRAN) is the most promising paradigm that aggregates the baseband processing to comply with dense antennas deployment. Even if optical networks are the most promising solution for CRAN front-hauling, there is the need to investigate alternative and/or complementary solutions to digital front-hauling (e.g., CPRI protocol) that can make a parsimonious usage of the optical bandwidth and related electronics. In this framework, here we propose a new waveform coding for the transport of analog RAN signals by employing the pulse width modulation (PWM) for optical front-hauling. At the transmitter, the radio-signal is sampled and mapped onto the duration of an on/off optical signal, at the fiber receiving-end each PW optical modulated sample is digitized so that the overall communication is transparent. Conceptually, the front- hauling PW waveform is equivalent to split sampling (at transmitter) and quantization (at receiver) so as to avoid the bandwidth expansion of CPRI digitalization. Pros and cons of PW waveforms for CRAN front-hauling are evaluated by investigating the outcomes of an in-lab experiment transmitting 100-MHz RF signals with 16QAM modulation up to 20-km standard single mode fiber. Experimental results provide some room for discussion on this novel front-hauling technique