JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 32, NO. 16, AUGUST 15, 2014 2849 Integrated Microwave Photonics for Radio Access Networks Jos´ e Capmany,Fellow, IEEE, Fellow, OSA, and Pascual Mu ˜ noz, Senior Member, IEEE, Member, OSA (Invited Paper) Abstract—We explore the advantages that integrated microwave photonics (IMWP) can bring to access networks. We first of all review the most common architectures of radio access networks (RANs) to identify the segments where microwave photonic com- ponents and radio over fiber links are located. Then, we provide a short description of the basic principles of IMWP with the aim of illustrating the current state of the art of this technology and its potentials. We discuss the possibilities of incorporating IMWP technology into the RAN front-haul. In particular, we first of all identify the required MWP functionalities and then discuss the feasibility of implementing these in light of the current and near future state of the art. Index Terms—Access networks, integrated optics, microwave photonics. I. INTRODUCTION M ICROWAVE photonics (MWP) [1]–[3], a discipline that brings together the worlds of radiofrequency (RF) en- gineering and optoelectronics, has attracted great interest from both the research community and the commercial sector over the past 30 years. The added value that this area of research brings stems from the fact that, on the one hand, it enables the realization of key functionalities in microwave systems that ei- ther are complex or even not directly possible in the RF domain and, on the another hand, that it creates new opportunities for information and communication (ICT) systems and networks. While initially the research activity in this field was focused towards defense applications, MWP has expanded to address a considerable number of civil applications [3]–[5], including cellular, wireless, and satellite communications, cable televi- sion, distributed antenna systems, optical signal processing and medical imaging systems using terahertz (THz) waves. Many of these novel application areas demand ever-increasing values for speed, bandwidth and dynamic range while, at the same time, require devices that are small, lightweight and low-power, ex- hibiting large tunability and strong immunity to electromagnetic interference. Despite the fact that digital electronics is widely Manuscript received February 3, 2014; revised May 2, 2014 and May 26, 2014; accepted June 23, 2014. Date of publication June 26, 2014; date of current version July 25, 2014. This work was supported by the Generalitat Valenciana through the PROMETEO 2013/012 Research Excellency Award. This work was also supported by the Research Excellency Award Program GVA PROMETEO 2013/012. The authors are with the Optical and Quantum Communications Group, Institute of Telecommunications and Multimedia, Universitat Polit´ ecnica de Valencia, 46021 Valencia, Spain (e-mail: jcapmany@iteam.upv.es; pmunoz@ iteam.upv.es). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2014.2333369 Fig. 1. Concept of analog signal processing engine in the context of informa- tion and communications systems. used nowadays in these applications, the speed of digital sig- nal processors (DSPs) is normally less than several gigahertz (a limit established primarily by the electronic sampling rate) so, in order to preserve the flexibility brought by these devices and their limit constraints there is a need for equally flexible front-end analog solutions to precede the DSP. This situation is schematically depicted in Fig. 1, where the block that constitutes the analog signal processor engine is shown. One of the main driving forces for MWP in the middle term future is expected to come from converged broadband fiber- wireless access networks [3], where radio services are delivered as an overlay over existing passive optical network (PON) and local ring infrastructures. Fig. 2 shows a schematic configuration of this solution [6]. In this context wireless services can be efficiently delivered to a variety of end-users, including: shopping malls, airports, hospitals, stadiums, power plants and other large buildings. For instance, the IEEE standard WiMAX (the Worldwide Interoper- ability for Microwave Access) has recently upgraded to handle data rates of 1 Gbit/s, and it is envisaged that many small, WiMAX-based stations or pico-cells will soon start to spring up. To cope with this growth scenario, future networks will be expected to support wireless communications at data rates reach- ing multiple gigabits per second. In addition, the extremely low power consumption of an access network comprised of pico- or 0733-8724 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.