# Mitigation of Nonlinear Distortions for a 100 Gb/s Radio-Over-Fiber-Based WDM Network
## 1 Introduction  
Utilizing optical fiber transmission links (OFTL) for long distance communication with a huge amount of data is mostly affected by the nonlinear impairments (NLIs) due to the channel and linear distortions (LDs) due to the system components [1; 2]. Apart from limiting the maximum data rate that can be transmitted through the system, such effects are bottleneck to the long-haul transmission distances. Although fronthaul networks are limited to transmission distances up to 20 km, the use of high bandwidth signals or intermediate frequency (IF) is still a question in the presence of such impairments [3]. Due to the capacity issues with the current CPRI transport, RoF can provide a promising solution for the integration of radio signals and OFTL as a significant procedure for high capacity and cost effective transmissions [4; 5; 6]. This transport scheme is a worthy suspension for huge capacity wireless transmission by virtue of low cost, due to its uncomplicated model and anti interference huge bandwidth, low medium distortion and low power consumption [7]. Furthermore, mobile communication adaptability and flexibility to associate with the growth of the overall network [8]. The mobile network industry has been ruled by the digital transmission of data over the optical fiber network for a long time in fourth generation (4G) long term evolution (LTE) systems due to its robustness to the nonlinear impairments and resistance towards the chromatic dispersion effects. The transportation of baseband data in CPRI to the remote antenna unit (RAU) requires the use of a digital to analog converter (DAC) to generate an analog waveform, which is further upconverted to the desired radio frequency (RF). The use of RoF transport not only lowers the cost of the RAU by avoiding the use of DACs, but it also requires low sampling rates to transport huge bandwidth signals. For example, the release 15 of third generation project partnership (3 GPP) for the 5G networks suggest that the bit rate transport requirement for CPRI is around 159 Gb/s for a 40 MHz bandwidth signal with 8 MIMO layers and 32 antenna elements at the RAU with three sectors. The same amount of transportation using RoF technology requires much lower data rates and thus can be considered as a potential candidate for the future 5G networks. Developing RoF systems with wavelength division multiplexing (WDM) technology has the potential to increase the fidelity by many folds with addition of advance modulation formats such as 64-quadrature amplitude modulation (QAM) using orthogonal frequency division multiplexing (OFDM) signals, thus intending to enhance the propagation path and data rate capacity [9; 10]. This paper investigates a WDM-based RoF transport system with an aim to suppress the NLIs and LDS.  
The improved long range and high capacity RoF network depends upon how best the LDs and NLIs are managed. In this model, single model fiber (SMF) is used as a backbone to transmit the RF wave, includes LDs like group velocity dispersion (GVD), polarization mode dispersion (PMD) and amplified spontaneous emission (ASE). The shape of the pulse is distorted due to these LDs. In this paper, LDs are addressed, narrowing the pulse width with the help of employing advance modulation schemes and installing filters and amplifiers.