This document may differ from the final, published version of the research and has been made available online in accordance with publisher policies. To read and/or cite from the published version of the research, please visit the publisher's website (a subscription may be required.)IEEE/OSA Journal of Lightwave Technology 1 Abstract-In this paper, we investigate a nonlinear compensation technique with two different architectures using direct modulation (DM) and external modulation (EM) techniques, termed as DM based frequency dithering (DMFD) and EM based frequency dithering (EMFD). We show that DMFD and EMFD methods operate substantially different in radio-over-fiber (RoF) system by optimizing the dithering technique relative to the LTE technology. The proposed techniques is only applicable if the condition of {f L < f d < f RF } is met, where f L represents the dithering boundary limit of 14 MHz, f d is DMFD signal frequency and f RF is the RoF carrier frequency. Analysis of the optical launch power for DMFD and EMFD methods reveal that the stimulated Brillouin scattering (SBS) threshold is above ~6 dBm for the LTE-RoF system. In addition, we also unveil that DMFD and EMFD methods do not introduce additional distortion for the linear and optimum optical launch power regions, which are frequency chirp driven regions. If the given condition is met, the proposed method improves the LTERoF system without any shortcoming. Finally, at 10 dBm launch power, DMFD and EMFD methods exhibits an average signal-tonoise ratio (SNR) gain of ~5.95 dB and ~7.71 dB, respectively.
Index Terms-Long Term Evolution (LTE); Radio-over-fiber (RoF); Nonlinear Compensation; Optical OFDM (OOFDM)
I. INTRODUCTIONThe actively growing end user subscriptions with bandwidth hungry, high specification, real-time, and delay-sensitive applications have been driving the mobile communications technology to continuously progress forward. The 3 rd generation partnership program (3GPP) established a standard known as the LTE to support the rapidly evolving mobile communication requirements [1].In the radio access network of LTE, eNodeB (eNB) functions as the base station (BS) similar to the global system Manuscript received April 29, 2013 for mobile communications (GSM) and universal mobile telecommunication system (UMTS) BSs. However, the eNB provides the real-time operation via a 2-node architecture, without an external central controller. The 2-node architecture is achievable because the eNB architecture is designed with built-in central controller with a radio access network, and such evolution leads to costly infrastructure expansion. In addition, the vastly allocated spectrums for LTE in urban locations throughout the world are either 2.6 GHz or 1.8 GHz [2] where the drawback is the excessive loss on the wireless propagation. As a result the eNB cell radius is limited to 1 km in urban operating conditions [3]. The throughput for the user equipment (UE) at the cell edge is <20 Mb/s from the maximum of 100 Mb/s owing to the deteriorating SNR, thu...