Transmitters for Combined Radio Over a Fiber and Outdoor Millimeter-Wave System at 25 GHz

Abstract

In the modern wireless networks, millimeter-wave radio-frequency (RF) bands are becoming more attractive as they provide larger bandwidth and higher data rates than the today-used systems operating at frequencies below 6 GHz. In addition, according to the fact that coaxial cables exhibit extremely high attenuation for millimeter-wave RF signals, analog radio over fiber techniques (RoF) form a promising technology for delivering unaltered radio waveform to a remote antenna. This paper experimentally analyzes three types of RoF modulations, namely a directly modulated laser, an electro-absorption modulator, and a Mach-Zehnder Modulator. The primary focus is on the implementation of each RoF transmitter in an RoF system, such as those in 5G networks. The experimental study includes a detailed characterization of an RoF system with a 50-m long outdoor free-space RF channel operating in the frequency band of 25 GHz. Frequency response (S-parameters) and third-order nonlinear distortion are investigated in detail. Tests of EVM performance were conducted using an orthogonal frequency division multiplexing signal modulated with 16-quadrature amplitude modulation (16-QAM) with a long-term evolution signal. It is demonstrated that the transmitters studied can operate under a 13.5% EVM limit given for 16-QAM. Apart from the detailed system performance, the considerable power fluctuations in the 25 GHz free-space RF outdoor channel are reported.

Transmission of 10 Gbps C-band-signal-based Radio Over Fiber for Next Generation Communication Systems

“…Several techniques have been introduced to improve the RoF architecture. In [9], the researchers analyze three optical modulation types: electro-absorption modulator (EAM), directly modulated laser (DML), Mach-Zehnder modulator (MZM) or external modulator. They provide an outdoor free-space RF channel of 50 m with 16 QAM, demonstrating that transmitters can operate under the EVM limit of 13.5%.…”

Usability of a 5G Fronthaul Based on a DML and External Modulation for M-QAM Transmission Over Photonically Generated 40 GHz

“…Moreover, the use of linear externally modulated lasers at the BBU allowed a multiband operation up to 12 Gb/s over the MFH link in [20] and an electro-absorption modulated (EAM) laser, in spite of its inherent nonlinearities, was employed to transmit of 24 OFDM bands of 100-MHz-bandwidth as shown in [17]. The comparison between different transmitters at 25 GHz for RoF systems including DML, EAML and MZM has been recently published in [21]. Noteworthy, very recent work demonstrates the monolithic integration of multiple DMLs for 5G RoF systems [22], opening new opportunities for infrastructure sharing in 5G networks.…”