SiPhotonics/GaAs 28-GHz Transceiver With Reflective EAM for Laser-Less mmWave-Over-Fiber

Abstract

Exploring mmWave frequencies and adopting smallcell architectures are two key enablers for increased wireless data rates. To make these evolutions economically viable, centralized architectures based on radio-over-fiber (RoF) are devised. To reduce the complexity of the cellular network even further, RF-over-Fiber transmission schemes are adopted in combination with reflective uplink operation. This paper relies on a very low complexity narrowband GaAs electronics / Si photonics transceiver for scalable RFoF architectures with which we demonstrate a fiber-wireless link capable of transmitting over 7 Gb/s in down-and uplink for a 2 km fiber and 5 m wireless link in the 28 GHz band. Furthermore, it is shown that Rayleigh degradation caused by reflective uplink operation can be avoided by using a coherent detection scheme.

Beyond 5G Without Obstacles: mmWave-over-Fiber Distributed Antenna Systems

“…Shifting up-and down-conversion from RAU to CO both eliminates power-hungry mixers at the RAU and tightly synchronizes all RAUs, enabling distributed mMIMO and LIS implementations. Still, this requires high-speed opto-electronic devices and entails chromatic dispersion fading in the fiber [8]. To realize a highly efficient transceiver for mmWave-over-fiber communication, a high-speed ISIPP50G silicon-photonic photodetector and electroabsorption modulator were co-optimized and compactly integrated with dedicated GaAs amplifiers to maximize power transfer within the targeted mmWave frequency band [8].…”

“…Still, this requires high-speed opto-electronic devices and entails chromatic dispersion fading in the fiber [8]. To realize a highly efficient transceiver for mmWave-over-fiber communication, a high-speed ISIPP50G silicon-photonic photodetector and electroabsorption modulator were co-optimized and compactly integrated with dedicated GaAs amplifiers to maximize power transfer within the targeted mmWave frequency band [8]. Yet, even faster opto-electric transducers are actively researched, currently reporting devices with sub-THz bandwidths [9].…”

“…Yet, even faster opto-electric transducers are actively researched, currently reporting devices with sub-THz bandwidths [9]. Here, we leverage the link in [8] together with low-complexity and cost-effective RAUs to realize a scalable mmWave DAS. To increase the number of RAUs, while providing every RAU with a dedicated signal, required for next generation mMIMO or LIS systems to serve a large number of users, one may adopt a star configuration, with a dedicated point-to-point fiber link from the CO to each RAU, or a ring configuration, with wavelength division multiplexing (WDM) and optical filtering.…”

“…At lower mmWave frequencies and with standard fibers, chromatic dispersion fading only becomes problematic after kilometers of fiber, which is typically not encountered in indoor environments. Yet, if longer fiber connections are needed, as in large factories of the future, or operation at higher mmWave frequencies is targeted, this problem can be countered by optical single sideband architectures [8]. Figure 2 shows that such a bi-directional time-division-duplex (TDD) mmWave-over-fiber link yields a distributed mmWave antenna system that overcomes LoS-blocking, as required to meet the very challenging specifications of future-generation applications in realistic environments.…”

A 5-bit, 1.6ps resolution true time delay optical beamforming network for 4-element antenna arrays

“…To mitigate the problem of increased wireless losses, beamforming techniques can be implemented in these antenna arrays [4]. Two main architectural trade-offs are to be made for the beamformer in the context of a mmWave-over-Fiber link [5]. First, the location of the beamforming network, since it can be centralized at the CO or distributed at the RAUs.…”