Search

This paper provides a review of the new fronthaul network segment that appears in centralized radio access network (C-RAN) architecture. C-RAN drivers are presented under an operational, economic, and radio point of view. The different fronthaul interfaces are briefly described as they have to be taken into account to build a fronthaul transport solution. Then, fronthaul requirements are detailed going from the technical ones to the business ones. Finally, different fronthaul solutions are presented. Perspectives for medium term evolution including fronthaul supervision are hinted as well as challenges for future mobile evolution toward 5G.

In this paper, we first identify the key requirements for the deployment of a 1-Gb/s ultra-broadband home area network (UBB-HAN). Second, we propose an architecture based on a transparent optical backbone feeding local access points. Third, we underline the role of the IEEE802.15.3c pre-standard to provide a suitable radio interface for the UBB-HAN and demonstrate the technical feasibility of the concept using radio over fiber (RoF). More than 1-Gb/s transmission is demonstrated for 50-m optical antenna remoting using radio-over-fiber plus 15-m radio transmission.

Spinning a fiber is the most viable and used technique to reduce polarization mode dispersion (PMD). Many papers have shown that by properly tuning the spin parameters, the differential group delay (DGD) of spun fibers can be greatly reduced. However, the precision with which these optimal profiles are practically implemented may be a problem. In this paper, we perform a statistical analysis of the effects that spin inaccuracy may have on fiber PMD, quantifying how the random uncertainty on spin parameters impairs the DGD. Some preliminary experimental results about spin-induced PMD reduction are also reported.

Polarization-mode dispersion (PMD) causes significant impairment for high bit-rate optical telecommunications systems. It is known that PMD can be strongly reduced by spinning the fiber as it is drawn. In this paper, we focus on the case of randomly birefringent fibers spun at a constant rate, providing analytical expressions for the asymptotic statistical properties of PMD. In particular, we investigate the behavior of the first- and second-order PMD, demonstrating that a constantly spun fiber behaves asymptotically as an unspun fiber. Conversely, we show that the distance at which the PMD reaches its asymptotic trend increases with the spin rate up to lengths of several kilometers.

Spun fibers are increasingly used in telecommunication systems because their polarization-mode dispersion (PMD) is lower than that in unspun fibers. In this paper, we investigate the effects of a periodic spin on the PMD of fibers with randomly varying birefringence. Numerical simulations show that when the spin period is of the same order as or larger than the beat length, the mean differential group delay of a spun fiber depends on the model used for the random birefringence. We then carry out a general theoretical analysis using the second Wai-Menyuk model, which is the only model of fiber birefringence to date that is consistent with polarization optical time domain reflectometry data. Finally, we consider some particular regimes by means of a perturbative approach.

Polarization-mode dispersion (PMD) is a serious impairment for high-bit-rate optical telecommunication systems. It is known that spinning the fiber during the drawing process drastically reduces the PMD. However, the analysis of pulse propagation through a randomly birefringent spun fiber is still at an early stage. In this paper, we derive an analytical formula for the mean differential group delay of a periodically spun fiber with random birefringence. We model the birefringence with fixed modulus and a random orientation under the condition that the spin period is shorter than the beat length. Finally, we numerically compare the analytical results with those given by the random-modulus model of birefringence, and we obtain good agreement as long as the short-period assumption is satisfied.

In the literature, two system solutions have been proposed to overcome high dispersion problems typical of G.652 fibers at high bit rates (40 Gb/s): they are periodic and all-at-the-end dispersion compensation. We carry out an exhaustive comparison between the two methods that, up to this moment, have been studied separately. In the first part, we introduce a simplified model on strong dispersion management (DM) with intrachannel four-waves mixing (IFWM) and intrachannel cross-phase modulation (IXPM). We then carry out extensive numerical simulations of a complete system in order to verify the results as a function of the input average power and of the input pulsewidth. Finally, we tackle a typical system aspect, i.e., the influence of nonlinear effects on dispersion compensating fibers (DCFs).

It is known that the differential group delay (DGD) due to polarization mode dispersion (PMD) can be effectively reduced by spinning the fiber during drawing. In this paper, we propose an analytical approach that allows optimization of the spinning design. The fundamental idea is that, in the absence of polarization coupling, an optimized spinning profile can balance the effects of the intrinsic linear birefringence so that the differential group delay can be forced to be periodic and, consequently, have a limited amplitude as a function of distance. Our approach Is independent of the spin profile. In other words, with a fixed set of parameters that characterize a particular spin function, we are able to find analytically the values corresponding to a periodic DGD in a deterministic regime. Numerical results based on waveplate model confirm the analytical prediction and show that PMD can be reduced by about two orders of magnitude with respect to the same fiber without spinning, even after the introduction of random polarization coupling.

When measuring very low differential group delay (DGD), standard techniques are affected by rather high uncertainties. This problem is usually solved by repeating many times the DGD measurements while randomly perturbing the fiber. Such an approach is founded on the basic assumption that polarization scrambling induces the DGD's decorrelation. Nevertheless, it has not been proved yet that the measured DGDs belong to an homogeneous statistical ensemble. We experimentally validate this approach by means of polarization-sensitive reflectometric measurements

The authors carry out a numerical and experimental comparison between three different techniques for chromatic dispersion compensation on a terrestrial 40-Gb/s system. They are: periodic dispersion compensation at the amplifier places; the same but with initial prechirp; and dispersion compensation all at the end of the system by means of highly dispersed pulses. Numerical results are consistent with experimental ones and suggest the most convenient compensation technique with respect to fiber type (G.652 or G.655) and pulsewidth (3-10 ps).