Impacts Of Nonlinear Stimulated Raman Scattering On The Performance Of Optical Codedivision Multiple-Access Transmission Systems
Code-division multiple access (CDMA) is a well-known scheme for multiplexing communication channels that is based on the method of directsequence spread spectrum. This concept was introduced into fiber optic communication systems in the middle of 1980’s as optical CDMA (OCDMA), where encoding an...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English English |
| Published: |
2008
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/5363/1/FK_2008_15.pdf |
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| Summary: | Code-division multiple access (CDMA) is a well-known scheme for
multiplexing communication channels that is based on the method of directsequence
spread spectrum. This concept was introduced into fiber optic
communication systems in the middle of 1980’s as optical CDMA (OCDMA),
where encoding and decoding operations are all performed in optical domain
using optical devices and large number of users with asynchronous access
capability. In addition to the good performance at high number of users and
asynchronous access to the network, OCDMA systems provide the users
with high security by coding the data before transmission and at the same
time using this code to recover the data at the receiver.
However, there are various nonlinear effects that limit the performance of
OCDMA systems. In particular, nonlinear stimulated Raman scattering (SRS)
causes the optical power from one mode to be transferred in the forward direction to the same, or other modes, at a different frequency. The process
of SRS can severely limit the performance of multi-channel communication
systems through the transfer of energy between the signals at different
wavelengths.
The main motivation behind this research is the need to understand signal
distortion due to SRS in OCDMA transmission systems. Specially, there is no
real attention paid to investigate this issue in OCDMA systems while most of
researches that study nonlinear effects are based on wavelength-division
multiplexing (WDM) systems. Therefore, this work is attempting to
understand SRS effects on the performance of OCDMA systems as a
function of system design parameters (i.e. power per chip, transmission
distance, and number of users), and hence, to determine the fundamental
transmission limits in OCDMA systems in the presence of SRS nonlinear
effects. The system performance is evaluated by measuring the bit-error-rate
(BER) and tilt ratio which indicates the power transfer between the chips at
different wavelength.
It is demonstrated through numerical simulations that the performance of
OCDMA systems, at high input powers, large number of users and/or long
transmission distances, is significantly degraded due to SRS effects.
Furthermore, the transmission limits to keep the performance of the system
under study within acceptable levels in the presence of SRS effects is
estimated according to the BER threshold of 10-9 and 10-12. |
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