After introducing fronthaul requirements in Centralized Radio Access Network architecture, different fronthaul solutions are presented. Perspectives for medium term evolution including fronthaul supervision are hinted as well as challenges for future mobile evolution towards 5G.

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Abstract-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.Index Terms-Beat length, birefringence correlation length, fiber birefringence, polarization-mode dispersion (PMD), spun fibers.

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Spinning is one of the most effective and well-known ways to reduce polarization mode dispersion of optical fibers. In spite of the popularity of spinning, a detailed theory of spin effects is still lacking. We report an analytical expression for the mean differential group delay of a randomly birefringent spun fiber. The result holds for any periodic spin function with a period shorter than the fiber's beat length.

We present beat length and polarization mode dispersion (PMD) measurements performed on installed fibers. Results regard three different kinds of fibers: standard step index, dispersion shifted and nonzero dispersion (NZD). After a historical comparison with standard differential group delay measurement collected four years ago on the same fibers, we perform a spatial-resolved measurement of the beat length by analyzing the state of polarization of the backscattered field. We compare PMD properties of different fibers and calculate the statistical distribution of the beat length. The differential group delay (DGD) and the beat length statistics depend strongly on fiber type and on fiber position along the link. The influence of the beat length on the DGD is also discussed

We experimentally demonstrate the use of AMOOFDM format for remote modulation of low-bandwidth RSOA as a cost effective solution for 10 Gbit/s upstream transmission in 20 km single fiber WDM-PON architecture.

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