What Role for Photonics in Xhaul Networks of 5G Systems? P. Castoldi * , L. Valcarenghi*, F. Cugini # , F. Cavaliere ° , P. Iovanna * Scuola Superiore Sant’Anna, Pisa, Italy, # CNIT, Pisa Italy, °Ericsson Research Author e-mail address: castoldi@sssup.it, luca.valcarenghi@sssup.it, filippo.cugini@cnit.it, fabio.cavaliere@ericsson.com, paola.iovanna@ericsson.com Abstract: This paper reviews key challenges in designing a transport network for 5G systems. Then it outlines how optics can contribute in solving some of them and which features the optical transport network shall be provided with. OCIS codes: (060.4256) Networks, network optimization; (060.2330) Fiber optics communications 1. Introduction Mobile networks are experiencing an exponential increase in the volume of data as a result not only of the increasing number of users and smart devices, but also of the enormous bandwidth required for novel applications. Smartphone subscriptions are set to more than double by 2020: by this time, 70 percent of the world´s population will have a smartphone [1]. Forecasts in [1] also indicate that there will be 26 billion connected devices by 2020. Along with the increase in capacity, users are expecting to count with real-time mobile applications with no delays and strong availability and reliability. The envisioned 5G cellular systems will need to provide very high data rates, as high as 10 Gbps per user and sub-ms latency, for time-critical applications as traffic safety and control of critical infrastructure and industry [2]. These objectives can be achieved by exploiting advanced Radio Access Technologies (RAT), such as Small Cells, Co-ordinated Multi Point (CoMP), massive Multiple-Input Multiple-Output (MIMO), and carrier aggregation Errore. L'origine riferimento non è stata trovata.. However advanced RAT technologies are not sufficient but shall be supported by novel reconfigurable optical transport networks interconnecting the Radio Access Network (RAN) nodes among themselves and with the 5G core network. In this paper first the main aspects of the 5G scenario that affect the transport network will be outlined. Then specific requirements of the optical transport network for supporting the 5G scenario will be discussed. 2. Transport relevant trends in 5G In contrast to earlier generations, 5G should not be seen as a specific radio access technology, targeting new radio spectrum, but as an overall access solution that will have an impact on the whole network architecture, including the fixed transport infrastructure interconnecting 5G architectural elements as depicted in Figure 1. RRU1 RRU2 RRU3 BBU1 BBU3 BBU2 X2 BBU pool EPC S1 Fronthaul + Midhaul + Backhaul SAE GW Figure 1 – Xhaul general architecture for 5G networks In the 5G scenario, heterogeneous networks [3] will exploit a mix of radio technologies and cell types working together to seamlessly deliver additional capacity, coverage and speed. This will require to improve and densify the macro cellular layer for enhancing coverage and capacity, and to add integrated small cells in strategic locations, to offer cost-effective connections in traffic hotspots, fix coverage holes and serve demanding areas, such as enterprises and airports. Improving the macro layer requires an increase of capacity of the backhaul network: