OPTICAL DOMAIN MULTIUSER INTERFERENCE ESTIMATION
FOR SPECTRAL PHASE ENCODING OPTICAL FIBRE
CDMA SYSTEMS
Arash Yazdani
1,4
, Morteza Noshad
2
, Hojat Jaliloghli
3
,
Amirhossein Jaliloghli
3
and Mohammad Noshad
5
1
Islamic Azad University of Noor, Noor, Iran
2
Electrical and Computer Engineering Department, University of Tabriz, Tabriz, Iran
3
Islamic Azad University of Tabriz, Tabriz, Iran
4
Telematics Department, Universidad Politecnica de Catalunya, Barcelona, Spain
5
Electrical Engineering Department, University of Virginia, Charlottesville, U.S.A.
Keywords:
Optical fiber code division multiple access, Spectral phase encoding, Optical domain multiuser interference
detection, Temporal multiuser interference estimation, Nonlinear multiuser interference estimation.
Abstract:
In this paper, an effective technique for reducing the multi-user interference (MUI) in spectrally-phase-
encoded optical code division multiple access (SPE-OCDMA) systems has been proposed. In this method
the effect of MUI signal on the main user’s signal has been decreased using multiuser interference detection
(MID). Two structures have been introduced for accomplishing MID and degrading its destructive effect on
the decoded ultra-short light pulse; temporal multiuser interference estimation (TMIE) and nonlinear mul-
tiuser interference estimation (NMIE). Both of these methods utilize two photo-detectors for estimating the
MUI signal. In spite of simple structure of these two receivers, their performance analysis shows an improved
performances comparing to other receivers.
1 INTRODUCTION
A spectrally-phase-encoding optical fibre code divi-
sion multiple access (SPE-OFCDMA) system is a
system in which a phase encoding has been applied
on a coherent ultra-short light pulse with a rectangu-
lar spectral pattern (Salehi et al., 1990). Similar to
the other kind of optical fibre CDMA systems, the
MUI is the main limiting factor on the performance of
the SPE-OFCDMA systems (Salehi et al., 1990). The
MUI effect in these systems appear as an noise-like
signal distributed in the bit period in the vicinity of the
ultra-short optical pulse of main user. But because of
the slow response time of photo-detectors comparing
to the ultra-short pulse duration, a part of the noise-
like signals of other users is also gathered by the de-
tector and degrade the performance of the receiver.
Some solutions such as using time gating (Lee et al.,
2002), second harmonic generation (SHG) (Ni et al.,
2007), self phase modulation (SPM) (Ni et al., 2007),
and two photon absorption (TPA) detectors (Jamshidi
and Salehi, 2007), have been proposed for the fibre
OCMDA systems to alleviate the MUI problem.
Multi-user interference estimation has been pro-
posed for decreasing the undesired interference ef-
fect of the users in multiple access networks (Brandt-
Pearce and Aazhang, 1994). But because all of these
methods was in electrical domain, the estimation pro-
cess takes much time and limits the bit-rate of the sys-
tem. Also it needs to the information of the other
users. In this manuscript we investigate a novel
method for declining the MUI effect on the signal of
the desired user in SPE-OFCDMA systems. In this
approach a interference estimation in optical domain
has been used for this purpose. Actually two photo-
detectors with different integration times are used to
estimate and reduce the MUI destructive effect on de-
sired signal. In the both of the proposed structures for
MID the effect of interference is reduced after making
an estimation of it. In the TMIE structure, an estima-
tion of the interference is made using the temporal
distribution of the MUI signal. Then an estimation
of the interfering signal is made using the output of
second detector and subtracted from the output of the
146
Yazdani A., Noshad M., Jaliloghli H., Jaliloghli A. and Noshad M..
OPTICAL DOMAIN MULTIUSER INTERFERENCE ESTIMATION FOR SPECTRAL PHASE ENCODING OPTICAL FIBRE CDMA SYSTEMS.
DOI: 10.5220/0003526701460149
In Proceedings of the International Conference on Data Communication Networking and Optical Communication System (OPTICS-2011), pages
146-149
ISBN: 978-989-8425-69-0
Copyright
c
2011 SCITEPRESS (Science and Technology Publications, Lda.)