As a promising technology for broadband communication, passive optical network (PON) has been deployed to support the last-mile broadband access network. In particular, time-division-multiplexing PON (TDM-PON) has been widely used owing to its mature technology and low cost. To practically implement TDM-PONs, the combination of intensity modulation and direct detection is a very promising technique because it achieves cost reduction in system installation and maintenance. However, the current intensity-modulation and direct-detection TDM-PON still suffers from some problems, which mainly include a high-power penalty, detrimental Brillouin backscattering (BB), and so on. Thus, using directly modulated lasers (DMLs) and colorless optical network units (ONUs), respectively, two intensity-modulation and direct-detection TDM-PON architectures are proposed. Using VPI (an optical simulation software developed by VPIphotonics company) simulators, we first analyze the influences on DML-based intensity-modulation and direct-detection TDM-PON (system 1) performances, which mainly include bit error rate (BER) and power penalty. Next, the BB effect on the BER of the intensity-modulation and direct-detection TDM-PON that uses colorless ONUs (system 2) is also investigated. The simulation results show that: (1) a low-power penalty is achieved without degrading the BER of system 1, and (2) the BB can be effectively reduced using phase modulation of the optical carrier in system 2.
KEYWORDS: Orthogonal frequency division multiplexing, Modulation, Distortion, Optical engineering, Nonlinear optics, Receivers, Data communications, Interference (communication), Data conversion, Signal generators
High peak-to-average power ratio (PAPR) of the orthogonal frequency division multiplexing (OFDM) signal is one of the limitations to the transmission performance of an optical OFDM system. Many PAPR reduction techniques have been proposed in previous works. However, most of them only consider a single scheme while overlooking the complementary features of these techniques. We propose a twofold PAPR reduction technique called Hadamard transform combined with a partial transmit sequence (PTS) (HTCP). The proposed HTCP scheme combines the merits of two complementary techniques, i.e., Hadamard transform and PTS, to improve the performance of the optical OFDM system in terms of PAPR and bit error rate (BER). Furthermore, the side information generated in PTS is transmitted by pilot sequences which increase the utilization of subcarriers. Least square estimation is used to estimate the pilot signal’s phase to recover the side information. The HTCP scheme is theoretically analyzed in a direct-detection optical OFDM system. Simulation results show that the HTCP scheme has a better performance with regards to PAPR and BER compared with the case of applying only the Hadamard transform or PTS technique.
Through integrating advantages of optical and wireless communications, the Fiber-Wireless (FiWi) has become a promising solution for the “last-mile” broadband access. In particular, greening FiWi has attained extensive attention, because the access network is a main energy contributor in the whole infrastructure. However, prior solutions of greening FiWi shut down or sleep unused/minimally used optical network units for a single segment, where we deploy only one optical linear terminal. We propose a green mechanism referred to as energy-efficient ring (EER) for multisegment FiWi access networks. We utilize an integer linear programming model and a generic algorithm to generate clusters, each having the shortest distance of fully connected segments of its own. Leveraging the backtracking method for each cluster, we then connect segments through fiber links, and the shortest distance fiber ring is constructed. Finally, we sleep low load segments and forward affected traffic to other active segments on the same fiber ring by our sleeping scheme. Experimental results show that our EER mechanism significantly reduces the energy consumption at the slightly additional cost of deploying fiber links.
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