An Adaptive Error Correction Scheme For Synchronous Digital Hierarchy-Based Wavelength Division Multiplexed Optical Network
In optical communications there are a variety of noise and distortion sources which can cause errors. These errors become essential and more intense in the high-capacity and long-haul wavelength-division multiplexing (WDM) systems. Therefore, the development of a forward error correction (FEC) te...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English English |
| Published: |
2007
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| Online Access: | http://psasir.upm.edu.my/id/eprint/5317/1/FK_2007_79.pdf http://psasir.upm.edu.my/id/eprint/5317/ |
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| Summary: | In optical communications there are a variety of noise and distortion sources which
can cause errors. These errors become essential and more intense in the high-capacity
and long-haul wavelength-division multiplexing (WDM) systems. Therefore, the
development of a forward error correction (FEC) technique to mitigate errors in
WDM optical networks is very relevant and important.
The existing FEC techniques for optical communications are based on fixed codes,
which consume unnecessary overhead bandwidth even when there are no errors. This
thesis proposes an adaptive forward error correction (AFEC) scheme for
synchronous digital hierarchy (SDH)-based WDM optical networks, referred to as
the SDH-AFEC. The scheme supports adaptive codes because it uses a dedicated
WDM channel for transmission of different sizes of FEC redundancy for the
payloads. Unlike most previous adaptive FEC techniques which change to a stronger
code after an error has occurred, the SDH-AFEC is able to do so before an error
occurs. This is achieved by using the combination of B2 error and corrected error count as the input parameters for the algorithm. Then the algorithm is designed in
such a way that it adaptively assigns a suitable value of error correction capability, t
for error correction, and the number of corrected errors is maintained not exceeding
t/2.
The SDH-AFEC adopts Bose–Chaudhuri–Hocquenghem (BCH) and Reed–Solomon
(RS) codes for correcting random and burst errors respectively. A new technique is
also proposed for estimation of the error pattern so that a suitable type of code can be
assigned accordingly. This technique is based on the analysis of the corrected error
locations, referred to as the error location analysis (ELA).
Simulation results show that the SDH-AFEC is able to use different values of t
adaptively for error correction. It assigns stronger t with increasing channel bit error
rate (BER) or average burst length (ABL) to maintain the output BER below the
target BER of 10-9, until the strongest value of t is assigned. The SDH-AFEC uses
the maximum FEC overhead for high BER or long ABL. However, the FEC
overhead requirement reduces with decreasing BER or ABL. Hence, in addition to
the adaptive BER performance, the SDH-AFEC also provides a way to use the FEC
overhead efficiently. Lastly, the results also show that by using ELA, the
performance of the SDH-AFEC is further improved that it is able to correct about
three times more random errors and three times longer burst length. Meanwhile, the
average FEC overhead reduction after ELA is about 38% and 36% for random and
burst errors respectively. |
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