Multi-Band OFDM Networking Concepts Sofiene Blouza, Julie Karaki, Nicolas Brochier, Esther Le Rouzic, Erwan Pincemin Orange Labs 2 Av. Pierre Marzin 22300 Lannion Sofiene.blouza@orange-ftgroup.com Bernard Cousin University of Rennes 1, IRISA Campus de Beaulieu 35042 Rennes Bernard.Cousin@irisa.fr Abstract— In this paper, we present a novel networking technique based on optical Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM). We highlight the interesting features of the solution with respect to existing ones (fully opaque optical networks and transparent networks) for optical metro and core networks. We show that under certain traffic condition MB-OFDM may offer useful flexibility in the context of increasing wavelength bit rates. Keywords: multi-bands orthogonal frequency division multiplexing; optical networking; reconfigurable optical add and drop multiplexer I. INTRODUCTION In the last years, the overall traffic in core and metro networks has increased by 45% per year on average [1] partly driven by the increase of multimedia contents and peer to peer applications. To catch up with this increase, link capacity of core and metro optical networks have grown up to several terabit/s per fiber pair [2] mainly allowed by the improvement of transmission system performances. To benefit from the network transparency and thus reduce the overall cost and consumption of the networks [3], Reconfigurable Optical Add and Drop Multiplexers (ROADM) are now widely deployed. These all-optical transmission techniques allow managing and switching full WDM channels without requiring Optical to Electrical and Electrical to Optical interfaces (O-E-O). However the use of an electrical aggregation layer remains mandatory for finer granularity than the capacity of optical channels. After increasing the overall number of WDM channels up to more than one hundred per fiber, the race for capacity now goes through an increase of the capacity per channels and the 100 Gbit/s per WDM channel is becoming the next standard for optical transmission systems [4]. As a result, the minimum granularity managed by ROADMs is greatly increased, which may accentuate the needs for electrical switching leading to an important growth in power consumption. In this context, a new approach based on the multi-bands Orthogonal Frequency Division Multiplexing (MB-OFDM) modulation techniques can offer an interesting trade-off between capacity increase and electrical consumption. Indeed this technique allows to optically switch at the sub-band granularity [5]. In this paper, we present the concept of MB-OFDM networking and analyze its potential compared to trend-setting technologies. This paper is ordered as follows. The second section introduces the technological principles of MB-OFDM technique. In the third section the different types of flexibility offered by the MB-OFDM are described and modeled. Finally, in a fourth section, we compare three simple scenarios, purely opaque node, purely transparent node and MB-OFDM node in terms of optical WDM channels and electrical interfaces numbers. II. MB-OFDM A. Optical OFDM Basics The basic principle of orthogonal frequency division multiplexing (OFDM) technique is to split a high-rate data stream into a number of lower-rate data streams that are transmitted simultaneously over a number of subcarriers. The main feature of OFDM resides in the orthogonality of its subcarriers. It eliminates the inter-carrier interference and provides a high spectral efficiency by allowing spectral overlapping. To maintain this orthogonality and thus to eliminate the inter-symbol interference due to linear optical propagation impairments such as chromatic dispersion (CD) and polarization mode dispersion (PMD) a cyclic prefix is added to each OFDM symbol. This advantageously avoids external optical or electrical compensation components which otherwise would be required to overcome deleterious impact of CD and PMD. B. MB-OFDM Basics Compared to single band OFDM, MB-OFDM is based on the division of the WDM channel spectrum into several independent OFDM sub-bands [6]. Each sub-band b ij has its own optical frequency carriers IF ij as shown in fig. 1 where i, j are the sub-band and channel number respectively. MB-OFDM also overcomes Digital to Analog Converters (DAC) and Analog to Digital Converters (ADC) frequency limitations when bit rate increases (discussed in Section C). However the architecture of the MB-OFDM transponder remains complex because it requires several single band generation and reception. Figure 1. Optical spectra of MB-OFDM The work described in this paper was carried out with the support of the 100G FLEX project funded under the Ninth French FUI Framework.