Multiuser centralized radio access networks (C-RANs) need to adapt to time-varying radio environments, and adaptation is advantageously split between remote antenna units (RAUs) and centralized baseband units (BBUs) to minimize the required fronthaul throughput. To this end, hybrid beamforming to spatially multiplex signals to/from a pool of users is split between RAU and BBU, and optical analog signal processing can be performed at the RAU. The goal here is to reduce the number of fronthaul channels and the corresponding number of analog/digital converters at the BBU in wideband (>100 MHz) millimeter wave (mmWave) radio communication. An algorithm for hybrid beamforming design is developed, and shown to approach the performance of ideal digital beamforming with a number of fronthaul channels comparable to the number of simultaneously served users rather than with the number of array elements. To cope with the radio-access of multiple users, optical analog processing is made adaptive by tuning delay lines built with optical ring resonators (ORRs). The tunability of analog beamforming by means of thermo-optic phase shifters is designed for time-varying configuration compliant to the 5G new radio specifications and the performance degradation of beamforming transients due to the tunability of optical components is assessed.

High accuracy pulse width modulation (PWM) is crucial for saturating devices such as optical communication systems, control and energy efficient amplification. In this paper we propose a closed-loop PWM architecture, called Sigma-Delta (ΣΔ) PWM, showing jitter robustness and compensation for some PWM inaccuracies arising from clock imprecision. The ΣΔ-PWM architecture trades oversampling and some increases in architectural complexity to gain in signal quality, leveraging on the noise shaping capability of the ΣΔ loop. Analytical results as well as numerical simulations assess the impact of timing jitter as key parameter in PW modulators.

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.

Centralized Radio Access Network (C-RAN) architecture is considered the only viable solution to handle the complex interference scenarios generated by massive antenna and small cell deployment foreseen for next generation (5G) mobile networks. The fronthaul links used to exchange the signal between Base Band Units (BBUs) and Remote Radio Heads (RRHs) are conventionally based on optical fiber, due to its huge bandwidth. In this paper we propose the radio over copper (RoC) as a complementary technology for the fronthaul architectures leveraging on the pre-existing LAN cables that are largely deployed in buildings and enterprises. To fully exploit the capabilities of LAN cable over the last 50–200m, a joint space and frequency division multiplexing is proposed. In particular, the main contribution of the paper is to prove that a smart mapping between the radio antennas/spectrum and the copper cable space/frequency dimensions allows an efficient communication over the RRH-BBU link with performances that are comparable to those achieved by an ideal fronthauling where BBU and RRH are assumed to be co-located. Validation is on the radio-link capabilities of RoC over Cat-6 cable to meet the demand for massive MIMO technology.

Centralized Radio Access Network (C-RAN) architecture is the only viable solution to handle the complex interference scenario generated by massive antennas and small cells deployment as required by next generation (5G) mobile networks. In conventional C- RAN, the fronthaul links used to exchange the signal between Base Band Units (BBUs) and Remote Antenna Units (RAUs) are based on digital baseband (BB) signals over optical fibers due to the huge bandwidth required. In this paper we evaluate the transport capability of copper-based all-analog fronthaul architecture called Radio over Copper (RoC) that leverages on the pre-existing LAN cables that are already deployed in buildings and enterprises. In particular, the main contribution of the paper is to evaluate the number of independent BB signals for multiple antennas system that can be transported over multi-pair Cat-5#x002F;6#x002F;7 cables under a predefined fronthauling transparency condition in terms of maximum BB signal degradation. The MIMO-RoC proves to be a complementary solution to optical fiber for the last 200m toward the RAUs, mostly to reuse the existing LAN cables and to power-supply the RAUs over the same cable.