An Experimental Assessment of the BSOFDM-PON Architecture Reginaldo B. Nunes, Diogo Coelho, Jair A. L. Silva and Marcelo E. V. Segatto Abstract—In this paper, we present experimental investigations of a 6 Gbps passive optical networks (PON) based on bandwidth scalable orthogonal frequency division multiplexing (BSOFDM- PON). The BSOFDM-PON architecture is composed by an optical line terminal (OLT) and three optical network units (ONUs) located at distances ranging from 25 to 65 km of standard single- mode fibers (SSMF). The influence of the frequency guard band designed to accommodate intermodulation distortions (IMD) inherit of direct-detection optical OFDM (DDO-OFDM) systems is experimentally evaluated. Our results show that this guard band strongly depends on the received optical power (fiber length) and the subcarrier modulation format. An error free transmission in 65 km of SSMF for a scalable bandwidth of 3 GHz occupying 4096 subcarriers mapped in 4QAM is achieved without the frequency gap of the guard band. Index Terms—Bandwidth scalable, passive optical networks, orthogonal frequency division multiplexing, intemodulation dis- tortion. I. I NTRODUCTION T HE intensive use of information technology grows the need for a flexible and reliable transmission of data services. Among the several systems available, passive optical network (PON) has been considered as a promising option [1], [2], [3]. The attractiveness of PON access networks stems from its main characteristics. Firstly, a passive network simplifies management issues as there are no active elements to monitor apart from the terminal equipment. Secondly, a transparent network is easily upgradable by replacing only the terminal equipment. The transparency means that other signals can be in principle easily overlaid. Finally, its point to multipoint physical topology makes it a relatively economic alternative for deliver services to a large number of customers from a central point [1]. Orthogonal frequency division multiple access (OFDMA) has emerged as promising resource sharing mechanism for next generation PON networks [4]. However, for optical ac- cess techniques composed by multiple subbands, a bandwidth control is necessary. Optical access networks based on a bandwidth scalable orthogonal frequency division multiplex- ing (BSOFDM-PON) architecture proposed in [5] provides a bandwidth management. R.B. Nunes, J. A. L. Silva and M. E. V. Segatto are with the Department of Electrical Engineering, Federal University of Espirito Santo, Brazil. e-mail: segatto@ele.ufes.br. R. B. Nunes is also with the Department of Electrical Engineering, Federal Institute of Espirito Santo. D. Coelho is with INESC TEC and also Faculty of Engineering, University of Porto, Portugal. In this paper, we will present the first experimental results for the BSOFDM-PON architecture proposed in [5]. Our experimental setup consists of a passive optical network with three optcal network units (ONU), fiber spans of 25 km, 45 km, and 65 km, 4096 OFDM subcarriers carring 4 QAM or 16 QAM signals. Our goal is to garantee at least 1 Gb/s of raw data transmission per ONU while studiyng performance of the network. The paper is organized as follows: in section II we review the fundamentals of BSOFDM-PON architecture, in section III describes the experimental setup used for performance evaluation, experimental results are presented and discussed in section IV and finally section V draws the conclusions. II. BSOFDM-PON ARCHITECTURE The BSOFDM-PON architecture was first proposed by D. Coura et al. in [5], as shown in Fig.1. It considers a tree based topology with optical passive splitter/combiner (PSC) and uses one wavelength for downlink (λ down ) and another one for uplink (λ up ). The main characteristic of this architecture is the possibility of allocating and multiplexing independent channels to each optical network unit (ONU) in a bandwidth scalable way. For this purpose, BSOFDM- PON divides the total OFDM bandwidth in N subbands, each containing the quantity of subcarriers required by each ONU. In the downstream link, each user receives a copy of the OFDM symbol and extracts only the subcarriers targeting itself. In the uplink communication, each subscriber generates an OFDM signal with a given number of subcarriers of the transmitted signal. The signals from each optical network unit are optically combined at the PSC to generate an optical OFDM signal to be transmitted back to the OLT. A. OLT, PSC and ONU Structures The OLT, PSC and ONU structures are fully described in [5] and presented in Fig. 1. It is important to notice that the OLT consists of four main elements: Transmitter, Receiver, Optical Mux and Controller. At the Transmitter, the optical carrier at the wavelength (λ down ) is modulated by an electrical-to- optical converter (E/O) according to the OFDM signal to be transmitted. In addition, another continuous wave (CW) is generated at the wavelength (λ up ). The Optical Mux is responsible for combining both signals and send them in downlink direction to the PSC using the downlink fiber. The CW signal is used for uplink carrier remodulation. At the Receiver, the modulated OFDM signal is recovered by an 2014 copyright by IFIP ONDM 2014, 19-22 May, Stockholm, Sweden 228