It is foreseeable that the 100 Gb/s/$\lambda$ and beyond passive optical network (PON) will be required in future optical access networks to meet the explosive growth of data traffic. The coherent optical systems coul...
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It is foreseeable that the 100 Gb/s/$\lambda$ and beyond passive optical network (PON) will be required in future optical access networks to meet the explosive growth of data traffic. The coherent optical systems could be a promising solution for the future beyond 100 G PON. Coherent PON using digital subcarrier multiplexing (DSCM) can provide flexible bandwidth allocation to a large number of access subscribers by dividing subcarriers of the DSCM signal into time slots for time-and-frequency division multiple access. When the optical network unit is allocated a new subcarrier, digital signal processing (DSP) should converge fast in the allocated time slot to ensure a low handoff latency for real-time bandwidth allocation. However, the traditional coherent DSP is hard to realize fast convergence due to blind and complex algorithms. In this paper, we design a specific training sequence (TS) structure and propose data-aided DSP to achieve fast convergence for coherent PON. The feasibility of the proposed scheme is experimentally verified in an 8 Gbaud/SCx8 SCs 400 Gb/s-net-rate coherent PON using DSCM with 16 quadrature amplitude modulation. The experimental results show that fast convergence is jointly realized by the proposed TS structure and data-aided DSP using a 416-symbol TS with a 52 ns duration. The receiver sensitivity at the 20% soft-decision forward error correction limit is approximately $\mathbf{-27}$ dBm and an optical power budget of about 35.5 dB is achieved with a booster amplifier.
This paper presents a signal-to-noise ratio (SNR) estimation algorithm for advanced digital video broadcasting-return channel via satellite (DVB-RCS) systems using adaptive coding and modulation (ACM). Due to the abse...
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This paper presents a signal-to-noise ratio (SNR) estimation algorithm for advanced digital video broadcasting-return channel via satellite (DVB-RCS) systems using adaptive coding and modulation (ACM). Due to the absence of a repetitive pilot symbol structure, SNR estimation has to be performed using the fixed symbol preamble data. Moreover, sporadic nature of data traffic on the return link causes variation in interference level from slot to slot and, therefore, the estimation has to be done within one traffic slot duration. Hence, it becomes necessary to use a combination of data-aided and decision-directed (DD) algorithms so as to make use of traffic data. A non-data-aided estimator that was previously proposed by the authors for binary and quadrature phase shift keying schemes is extended to 8-PSK in a decision directed manner. The inherent bias of DD approach at low values of SNR is reduced by using a hybrid approach, that is, using the proposed estimator at moderate/high values of SNR and the moments-based estimator (M2M4) at low values of SNR. Overall improved performance of the proposed hybrid estimator, in terms of accuracy and complexity, makes it an attractive choice for implementing ACM in advanced DVB-RCS systems.
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