Performances of a UWB OFDM system over fiber based on laser direct modulation are found to be mainly limited by nonlinearities in the laser response. The OFDM signal quasi Gaussian level distribution leads to a redefinition of the optical modulation index.There is an increasing interest in ultra wideband (UWB) systems for indoor networks. UWB systems operate in the frequency range from 3.1 to 10.6GHz according to the U.S. Federal Communication Commission (FCC) [1] and are limited to distances of a few meters, with a negligible integration with the existing wired or wireless local area network. As a consequence, UWB-over-fiber technology may provide an effective solution to offer service availability across different networks and to achieve high-rate data access at any time and from any place [2]. Whereas recent papers have dealt with impulse based UWB [2], here we focus on the MB-OFDM over fiber technique [3] using laser direct modulation. We analyze the different parameters that come into play in order to reach the system optimum operating point keeping in mind the need for simplicity and economical solutions required by home networks. OFDM transmission over fiber may be critical because OFDM signals are characterized by a very large peak to average power ratio causing high sensitivity to nonlinearities in the electro-optic (e/o) conversion [4]. These distortions may be evaluated by the optical modulation index (OMI) of the signal [5], but this measure is somewhat approximate as will be demonstrated in this paper. Our goal is to define an easily measurable parameter capable of quantifying the distortions induced in the e/o conversion stage by taking into account the signal level distribution in order to exploit the advantages of OFDM modulation (e.g. high spectral efficiency and robustness to dispersion). The MB-OFDM parameters are described in the Standard ECMA-368 [3]. The maximum effective isotropic radiated power allowed by the FCC is equal to -41.3dBm/MHz corresponding to a power of -14dBm for a single OFDM bandwidth of 528MHz. Additionally, considering a directly modulated DFB laser with η Tx =0.102W/A, a single mode fiber of 1km, and a PIN photodiode with η Rx =0.8A/W, the corresponding gain of the optical link is found to be:out dB opt Rx Tx optRF 2 . 22 50 50 log 10 2 . 0 2 8 . 0 102 . 0 log 20 log 10 2 log 20 ,Given the low UWB power level and the amount of optical link loss, it is reasonable to realize the UWB transmission over fiber by means of the scheme represented in figure 1, i.e. by inserting a low noise RF amplifier before the laser. Thus, the parameters that come into play are the RF power corresponding to the modulation current, P RFin , the laser point of polarization, I bias , and the number of transmitted OFDM bands. We perform numerical simulations to explore the dependence of the error vector magnitude (EVM) [6] on these parameters. For each OFDM band, we generate a pseudo random bit sequence at 640Mb/s, we apply a QPSK modulation and obtain the OFDM signal according to [3] with Matlab™....
Combining Gigabit Passive Optical Network (GPON) architecture with Radio over Fibre (RoF) technology could be a cost-efficient and attractive solution for operators for the distribution of 3G Base Stations (BS). We have implemented a PON delivering 2 BS with WDM lasers at Remote Base Station (RBS) and a single photodiode at the Central Office (CO). An experimental study of this architecture for two BS has been performed and successful transmission has been shown for both uplink and downlink transmission. These results have been used to demonstrate the feasibility of distributing 12 3G BS over a 20km link on a GPON architecture. Index Terms -Radio over Fibre (RoF), Passive Optical Network (PON), 3G.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.