27-12-2012, 03:02 PM
Performance Analysis of Different Modulation Schemes for Coherent
Optical OFDM System
[attachment=45433]
Abstract
Without optical dispersion compensation, the
performances of different modulation schemes are analyzed
and comparison of their transmission distance, transmission
capacity, band width efficiency and their resistance to BER
are made in Coherent optical orthogonal frequency division
multiplexing (CO-OFDM) system in this paper. Then some
simulation results are given using Matlab software. Simulation
results show that: in the same conditions, the relationship of
transmission capacity, transmission distance and bit error rate
of the system is contradictory. The anti-BER ability of 2PSK is
best, but its bandwidth efficiency is lower than other
modulation methods. The bandwidth efficiency of 4QAM is as
twice as the 2PSK, and the BER of the system is smaller than
10-3 and the required OSNR is about 9dB. When the OSNR is
12dB, the transmission distance is up to 1600km. Although the
bandwidth efficiency of 8QAM is higher than other two kinds
of modulation methods, its performance of anti-BER is
relatively poor. Therefore, we should choose the specific
scheme modulation depending on the actual needs of the
system when we design communication.
INTRODUCTION
With the development of optical communication, people
expect to enter the era of all-optical communication. And
high speed, ultra-large flow of data transmission will no
longer be a dream. At present, there are already many
scholars generating interests which are about studying the
OFDM applied to optical communications, that is, COOFDM
[1]. And it makes significant progress through
theoretical analysis and experiments, especially in terms of
large-capacity and distance. Because OFDM has better
tolerance to fiber dispersion and polarization mode
dispersion (PMD) [2-3], it has shown great potential in the
field of fiber communication. In the design of
communication systems, the choice of digital modulation
methods is very important and worthy of exploration. The
choice of digital modulation methods must be taken into
account a number of factors, such as: bandwidth efficiency,
BER, signal to noise ratio (SNR) and equipment
implementation complexity.
THE BASIC PRINCIPLES OF CO-OFDM
The block diagram of optical fiber communication
system is shown in Fig.1 [8], which mainly includes five
parts, namely: RF OFDM transmitter, RTO (RF-To-
Optical) up-converter, optical transmission links, OTR
(Optical-To-RF) down-converter, and RF OFDM receiver.
In this system, RF OFDM transmitter input digital signal
that is first converted from serial to parallel into a series of
information symbols, each may comprise multiple bits for
M-ary coding. These information symbols will be mapped
onto the two-dimensional complex signal cki, here, the
modulation is mentioned in the previous section. The timedomain
sequence is obtained through inverse discrete
Fourier transform (IDFT) of cki, and a guard interval is
inserted to avoid the channel dispersion [9].
THE EXPERIMENT SIMULATION RESULTS
AND THEORETICAL ANALYSIS
The binary digital modulation system is the most basic
way of a digital modulation system, but its bandwidth
efficiency is low. So in order to improve the bandwidth
efficiency, the digital system with M-ary is commonly
used. For MPSK and MQAM modulation, if the vector is
used, an important parameter can not be ignored, that is, the
minimum distance between the endpoints of these vectors.
The minimum distance shows the strength of anti-BER.
CONCLUSIONS
According to the simulation and comparison of the
several different modulations in the CO-OFDM system, the
anti-error rate and transmission distance of 2PSK are better
than 4QAM and 8QAM, but the bandwidth efficiency and
the anti-BER performance of 4QAM are relatively better.
And the bandwidth efficiency of 8QAM is higher than other
modulation methods, but its anti-BER is worse. Thus, in
terms of the design of the communication system, the
transmission capacity, transmission distance, BER and
implementation complexity of the equipment must be
comprehensively considered. Then, the concrete modulation
can be selected according to the requirements of the system,
such a system designed is more reasonable.
Optical OFDM System
[attachment=45433]
Abstract
Without optical dispersion compensation, the
performances of different modulation schemes are analyzed
and comparison of their transmission distance, transmission
capacity, band width efficiency and their resistance to BER
are made in Coherent optical orthogonal frequency division
multiplexing (CO-OFDM) system in this paper. Then some
simulation results are given using Matlab software. Simulation
results show that: in the same conditions, the relationship of
transmission capacity, transmission distance and bit error rate
of the system is contradictory. The anti-BER ability of 2PSK is
best, but its bandwidth efficiency is lower than other
modulation methods. The bandwidth efficiency of 4QAM is as
twice as the 2PSK, and the BER of the system is smaller than
10-3 and the required OSNR is about 9dB. When the OSNR is
12dB, the transmission distance is up to 1600km. Although the
bandwidth efficiency of 8QAM is higher than other two kinds
of modulation methods, its performance of anti-BER is
relatively poor. Therefore, we should choose the specific
scheme modulation depending on the actual needs of the
system when we design communication.
INTRODUCTION
With the development of optical communication, people
expect to enter the era of all-optical communication. And
high speed, ultra-large flow of data transmission will no
longer be a dream. At present, there are already many
scholars generating interests which are about studying the
OFDM applied to optical communications, that is, COOFDM
[1]. And it makes significant progress through
theoretical analysis and experiments, especially in terms of
large-capacity and distance. Because OFDM has better
tolerance to fiber dispersion and polarization mode
dispersion (PMD) [2-3], it has shown great potential in the
field of fiber communication. In the design of
communication systems, the choice of digital modulation
methods is very important and worthy of exploration. The
choice of digital modulation methods must be taken into
account a number of factors, such as: bandwidth efficiency,
BER, signal to noise ratio (SNR) and equipment
implementation complexity.
THE BASIC PRINCIPLES OF CO-OFDM
The block diagram of optical fiber communication
system is shown in Fig.1 [8], which mainly includes five
parts, namely: RF OFDM transmitter, RTO (RF-To-
Optical) up-converter, optical transmission links, OTR
(Optical-To-RF) down-converter, and RF OFDM receiver.
In this system, RF OFDM transmitter input digital signal
that is first converted from serial to parallel into a series of
information symbols, each may comprise multiple bits for
M-ary coding. These information symbols will be mapped
onto the two-dimensional complex signal cki, here, the
modulation is mentioned in the previous section. The timedomain
sequence is obtained through inverse discrete
Fourier transform (IDFT) of cki, and a guard interval is
inserted to avoid the channel dispersion [9].
THE EXPERIMENT SIMULATION RESULTS
AND THEORETICAL ANALYSIS
The binary digital modulation system is the most basic
way of a digital modulation system, but its bandwidth
efficiency is low. So in order to improve the bandwidth
efficiency, the digital system with M-ary is commonly
used. For MPSK and MQAM modulation, if the vector is
used, an important parameter can not be ignored, that is, the
minimum distance between the endpoints of these vectors.
The minimum distance shows the strength of anti-BER.
CONCLUSIONS
According to the simulation and comparison of the
several different modulations in the CO-OFDM system, the
anti-error rate and transmission distance of 2PSK are better
than 4QAM and 8QAM, but the bandwidth efficiency and
the anti-BER performance of 4QAM are relatively better.
And the bandwidth efficiency of 8QAM is higher than other
modulation methods, but its anti-BER is worse. Thus, in
terms of the design of the communication system, the
transmission capacity, transmission distance, BER and
implementation complexity of the equipment must be
comprehensively considered. Then, the concrete modulation
can be selected according to the requirements of the system,
such a system designed is more reasonable.