# A 100 Gbps OFDM-Based 28 GHz Millimeter-Wave Radio over Fiber Fronthaul System for 5G
## 1 Introduction
In [13], the authors demonstrated the transmission of five bands of universal filtered (UF)-OFDM on a 28 GHz Vivaldi antenna wireless link for an aggregated total data rate of 4.56 Gbits/s, using 64-QAM modulation, 312 subcarriers and bandwidth of 152 MHz over a 25 km single mode fiber (SMF). Considering a threshold of an acceptable bit error rate (BER) of forward error correction (FEC) with 7% overhead, system performance below the FEC limit for all five bands is achieved. Figure 1: (**a**) Cloud-Radio Access Network (C-RAN) architecture; (**b**) Mm-wave Radio over Fiber Based Fronthaul system architecture. The authors in [14] have experimentally demonstrated in 60 GHz mm-wave a spectrally efficient frequency division multiplexing (FDM) RoF system to transmit a data rate of 3.75 Gbits/s over a bandwidth of 1.125 GHz and 250 m multi-mode fiber (MMF) as opposed to OFDM which supported 2.25 Gbits/s over the same bandwidth and fiber length. In [15], the authors investigated the effect of fiber transmission link parameters for data rates of (10.24, 20.48 and 30.72 Gbits/s) and (9.6, 51.2 and 76.8 Gbits/s) over bandwidths of 16 \(\times\) 200 MHz and 8 \(\times\) 1 GHz respectively, and reported for three modulation formats (QPSK, 16-QAM, and 64-QAM) for different fiber length. A 60 GHz mm-wave RoF link using QAM-OFDM modulation and optical coherent detection (OCD) for transmitting 40 Gbits/s data rate over 150 km SMF have been proposed in [16]. Also, the authors in [17] proposed and investigated the performance of 40 Gbits/s data rate using 64-QAM OFDM modulation for different number of OFDM subcarriers over 100 km SMF. Although the authors of these papers and several others have successfully investigated and demonstrated by simulation or experiments the realization of high-speed optical links in multi-Gbits/s, the purpose of this paper is to demonstrate by simulation in Optisystem 16 the transmission of 100 Gbits/s data rate over a 2 GHz bandwidth. In this paper, a 28 GHz mm-wave RoF fronthaul system based on OFDM modulation generated by external intensity modulation through the use of Mach-Zehnder (MZM) is proposed. This proposed OFDM-based fronthaul system is investigated for three modulation schemes (16-PSK, 16-QAM, and 64-QAM) for a fiber length of up to 35 km and comparing their performances each for two detection systems; OCD and direct detection (DD). In this paper, the performance of the proposed RoF system is enhanced through a digital signal processing (DSP) compensation scheme based on algorithms to compensate for chromatic dispersion and to correct in-phase and quadrature-phase (IQ-phase) imbalances. However, the chromatic dispersion and fiber non-linearity effects are compensated for through digital filtering and a digital backpropagation algorithm which are based on a Gram-Schmidt orthogonalization procedure and the inverse non-linear Schrodinger equation, respectively. The throughput performance of the system is evaluated and analyzed in terms of BER and quality factor (QF). Figure 2. Illustrates the block diagram of the proposed OFDM-RoF based fronthaul system. In this system, a 100 Gbits/s input- data signal is generated and modulated at a 28 GHz carrier frequency. The resulting bandpass signal is modulated over an optical carrier using external intensity modulation by utilizing a LiNbO\({}_{3}\) MZM. Filtering and amplification are used to improve the signal quality and transmitted over an optical fiber. OCD or DD are used to detect the signal in the receiver system. A DSP unit is used to compensate for chromatic dispersion, IQ-phase imbalances and fiber non-linearities. The resulting signal is demodulated and the output signal is analysed. The overall system architecture of the proposed system is illustrated in Figure 3.  
Figure 2: Proposed block diagram of the OFDM-RoF based fronthaul system.