Fifth-generation mobile networks (5G) are the solution for the demanding mobile traffic requirements, providing technologies that fulfill the requisites of different type of services. The utilization of the millimeter-wave (mm-wave) band is the straightforward technique to achieve high bit rates. Moreover, analog radio-over-fiber (ARoF) brings outstanding benefits such as low cost, low power consumption, and high spectral efficiency, among others. Thereby, mm-wave ARoF is a strong candidate to pave the way for common public radio interface (CPRI) in the fronthaul for the future 5G architecture. As orthogonal frequency-division multiplexing (OFDM) is the adopted waveform in the 5G standard, it should be also utilized in mm-wave ARoF systems for 5G. However, phase noise is one of the most degrading factors in mm-wave OFDM ARoF systems. Therefore, in this work, an analysis of the phase noise is carried out through an experimental setup up. The configuration of this setup enables to gradually modify the final phase noise level of the system. Furthermore, an original and novel algorithm to compensate the phase noise in OFDM receivers is proposed. The performance of this algorithm is experimentally evaluated through the setup for different phase noise levels and different subcarrier spacings. The obtained results show the effectiveness of the proposed algorithm under those conditions, highlighting the viability of mm-wave OFDM ARoF for 5G and beyond.

5G mobile networks aim to support a large variety of services with different and demanding requirements. To achieve this, analog radio over fiber (ARoF) fronthaul along with millimeter-wave (mmWave) cells is a strong candidate to be part of the 5G architecture. Very high throughput can be achieved by using mmWave signals due to the large available bandwidths, which combines well with the advantages of employing ARoF technology. Nevertheless, combined mmWave and ARoF systems face a particular challenge as the impacts of both channels—such as high free-space path loss, phase noise, chromatic dispersion, and other degrading effects—affect the signal without the possibility for intermediate restoration. The selection of the signal waveforms plays an important role in reducing these defects. In addition, waveforms are one of the keys in the physical layer available towards satisfying the requirements for 5G and beyond. In this manuscript, several key requirements are presented to determine the merit of candidate waveform formats to fulfill the 5G requirements in the mmWave ARoF architecture. An overview of the different suitable waveforms for this architecture is provided, discussing their advantages and disadvantages. Moreover, a comprehensive comparison in terms of different requirements is also presented in this paper.

Light detection and ranging (LiDAR) sensors bring remarkable features to the automotive industry, enabling the development of autonomous vehicles. More concretely, frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) sensors offer several advantages over their time-of-flight (ToF) counterparts in terms of maximum achievable distance, interference immunity, and velocity detection. Nonetheless, FMCW LiDAR systems are inevitably affected by phase noise, limiting the sensor performance. One evident solution consists in using narrow linewidth lasers, at the expense of overall sensor cost. Therefore, in this work, a thorough analysis of the phase noise is conducted for FMCW LiDAR sensors. Moreover, a novel and low-complex phase noise compensation algorithm based on pre-estimation and feedforward correction (PNC-PEFC) is proposed. The PNC-PEFC algorithm is extensively evaluated in an experimental setup under different target distances and additive white Gaussian noise (AWGN) conditions. The experimental results show excellent performance when applying the proposed PNC-PEFC algorithm, proving its robustness across all evaluated conditions.

Analog beamforming is a key technology to enable millimeter-wave (mm-wave) mobile communications. Nonetheless, the most widespread beamforming solutions are based on electrical implementation, which is inefficient in terms of power consumption, signal bandwidth, and losses. Optical beamforming is a promising alternative for future mm-wave mobile communications due to its inherent benefits, such as large bandwidth, low cross-talk, and low losses. Optical beamforming networks (OBFN) are an outstanding technique to simultaneously generate and radiate multiple beams in an effective manner. True time delays (TTDs) based on optical waveguides are an attractive solution since they offer constant delay in the spectrum to avoid beam squint and allow highly scalable OBFN implementation. In this work, for the first time to the best of the authors' knowledge, an incoherent 4x4 OBFN based on optical waveguides and capable of simultaneously generating four beams is presented, including a thorough explanation of its operating principles and providing a detailed characterization. The presented OBFN is fabricated on Si $_{3}$ N $_{4}$ photonic integrated circuit (PIC), and designed for transmission at 27.5 GHz, within the n257 5 G band. Furthermore, the building blocks forming the OBFN PIC are deeply explained, providing their corresponding theoretical formulation and key design parameters. The fabricated PIC is exhaustively characterized through all its building blocks, showing in detail the realized measurement procedure. The experimental measures match the design parameters with minimal error, showing the feasibility of fabricating future OBFNs with the same technology and topology for larger antenna arrays. The experimental results corroborate the viability of the presented OBFN architecture as an excellent technology to consider in future mm-wave 5 G/6 G networks. The contribution of this work paves the road to turn optical beamforming into a mature, scalable, and efficient technology.