JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 32, NO. 20, OCTOBER 15, 2014 3721 Radio-Over-Fiber Optical Polarization-Multiplexed Networks for 3GPP Wireless Carrier-Aggregated MIMO Provision Maria Morant, Member, IEEE, Josep Prat, Member, IEEE, and Roberto Llorente, Member, IEEE Abstract—This paper proposes and demonstrates experimen- tally the application of optical polarization-multiplexed radio- over-fiber wireless backhauling of fully standard 3GPP carrier- aggregated multiple-input multiple-output (MIMO) signals. The experimental work demonstrates successful long-reach optical transmission of 3GPP carrier-aggregated LTE-Advanced (LTE-A) signals using 2×2 MIMO spatial diversity. The suitability of MIMO provision using radio-over-fiber optical links is demon- strated over different E-UTRA frequency division duplex fre- quency bands. The performance of electrical carrier aggregation is evaluated in different configurations comprising one, three and five LTE-A component carriers of 10 and 20 MHz bandwidth each. The experimental results demonstrate successful 2×2 MIMO radio- over-fiber polarization-multiplexed transmission of five LTE-A carriers over 25 km, three LTE-A carriers over 75 km and an LTE-A carrier over 100 km of standard single mode fiber to pro- vide pervasive MIMO wireless service to a large number of users. Index Terms—Carrier aggregation, microwave-photonics, multiple-input multiple-output (MIMO), optical communications, polarization multiplexing, radio-over-fiber (RoF). I. INTRODUCTION N EXT-GENERATION communication systems target to significantly increase the wireless transmission capacity, i.e., bitrate per user by number of users, in cellular networks compared with current 4G communication systems. One of the key enabling factors to increase the user capacity is the inclusion of pervasive multiple-input multiple-output (MIMO) wireless connectivity in the coverage area [1]. With this implementation, a large number of radio-heads are scattered around the coverage area providing connectivity to a large number of moving users. This scenario requires that optical backhaul links connect the large number of radio-heads supporting MIMO wireless com- munications [2]. Recent advances in microwave photonic tech- nology including optical polarization multiplexing and MIMO transmission have made broadband millimeter-wave radio-over- fiber (RoF) systems feasible [3]. Manuscript received January 15, 2014; revised March 11, 2014; accepted April 7, 2014. Date of publication April 15, 2014; date of current version September 1, 2014. This work was supported in part by Spain the National Plan Project TEC2012-38558-C02-01 MODAL. The work of M. Morant was supported by the Generalitat Valenciana VALi+D Postdoc Program. M. Morant and R. Llorente are with the Nanophotonics Technology Cen- tre, Universitat Polit` ecnica de Val` encia, 46022, Valencia, Spain, (e-mail: mmorant@ntc.upv.es; rllorent@ntc.upv.es). J. Prat is with the Department of Signal Theory and Commu- nication, Technical University of Catalonia, 08034, Barcelona, Spain, (e-mail:jprat@tsc.upc.edu). 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.2014.2317591 Fig. 1. Optical backhaul connectivity using RoF links to provide MIMO communication service. Fig. 1 depicts the application scenario of optical backhaul connectivity using RoF transmission to provide MIMO wire- less services. MIMO multiple antenna transmission and recep- tion has been studied extensively in the literature [4] and is mandatory in the proposed scenario due to the limited band- width available in current cellular networks where a licensed spectrum band is subject to strict regulation. Using spatial mul- tiplexing diversity, multiple antennas at both the base station (eNB) and at the user terminals are employed to provide si- multaneous transmission of different data streams over a single radio link at the same frequency and time, which increases significantly the peak data rates that can be provided to the final user and the overall cell capacity [5]. Moreover, coordi- nated transmission from multiple base stations, requires a good backhaul connection [6] and, for this reason, the performance of next-generation wireless communication networks can take advantage of high-bandwidth optical links to obtain wireless backhauling connectivity as shown in Fig. 1. Next-generation wireless network architectures will evolve to support network MIMO coordination such as distributed antenna systems and cloud radio access networks [6]. Wireless backhauling using RoF transmission is a cost- efficient solution in pervasive MIMO scenarios, providing proper support for the transmission of MIMO signals included in the optical interconnection. Different solutions for MIMO provision in optical RoF systems have been reported in the literature: RoF enables using digital equalizers for the estimation 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.