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Abstract— In this paper, we introduce a full fiber-to-the-home
system architecture. The introduced system is used to obtain a
system bit rate of 10 Gbps and 20 Gbps downstream and 5 Gbps
and 10 Gbps upstream. Wavelength division multiplexing passive
optical network technique is used to share the overall bandwidth
between 32 users with 0.8 nm spacing between each user. To
reduce the overall cost of the proposed system, the bidirectional
subcarrier multiplexed technique is used at the optical network
unit to avoid using any optical laser sources at the receiver side
for upstream data transmission. Quality factor, bit error rate, and
eye diagrams are derived for different pulse shapes then used to
compare the results in order to select the best pulse shape that
gives the best performance. The pulse shapes used in this paper
are non-return to zero, return to zero, saw-up, triangle, raised
cosine, and hyperbolic-secant pulses. The results demonstrates
that the non-return to zero pulse shape at bit rate of 20 Gbps at
both downstream and upstream data transmission leads a high
quality factor. Furthermore, at 10 Gbps return to zero is selected
at the transmission side and hyperbolic-secant at the optical
network unit.
Index Terms—Fiber-to-the-home, WDM-PON, SCM, RSOA,
Bit error rate, Quality factor, Eye diagram, Central office,
Optical network unit, RZ, NRZ, Raised cosine, Hyperbolic-
secant, Triangle, and Saw-up pulse shape.
Manuscript received February 07, 2014.
1A. Elrashidi is with the Department of Electronics and Communications
Engineering, College of Engineering and Information Technology, University
of Business and Technology, Jeddah 21432, Saudi Arabia (phone: +966-561-
127894; e-mail: a.elrashidi@ubt.edu.sa).
2I. Ashry is with the Department of Electronics and Communications
Engineering, College of Engineering and Information Technology, University
of Business and Technology, Jeddah 21432, Saudi Arabia (e-mail:
i.ashry@ubt.edu.sa).
3A. Mahros is with the Department of Physics, King Abdulaziz University,
Jeddah 21432, Saudi Arabia (amr.mahros@mena.vt.edu)
4Department of Engineering Mathematics and Physics, Alexandria
University, Alexandria 21544, Egypt.
M. Alhaddad is with the Department of Electrical Engineering, College of
Engineering and Information Technology, University of Business and
Technology, Jeddah 21432, Saudi Arabia (e-mail: mmhaddad@cba.edu.sa).
K. Elleithy is with the Department of Computer and Electrical
Engineering, Faculty of Engineering, University of Bridgeport, CT 06604,
USA (e-mail: elleithy@bridgeport.edu).
I. INTRODUCTION
The explosive growth of the Internet is the main reason to
introduce a broadband access network based on Fiber-to-the-
Home (FTTH). Some applications such as streaming Internet
video, video-on-demand, and cloud-based storage require high
bandwidth [1]. Traditional single wavelength passive optical
network (PON) using time division multiplexing (TDM)
suffers from some problems such as [2];
1. The optical carrier is shared by means of passive splitter
among all users.
2. The number of optical network units (ONUs) is limited
which leads to power-splitter losses values in the range 16-
17 dB for 1×32 splitter.
3. Bandwidth sharing (10G-EPON).
4. Bit rate transparency is about 10 Gbps.
5. High-speed TDM-PON requires high-rate burst-mode
circuits.
So, the wavelength division multiplexed WDM-PONs are
expected to provide more capacity and flexibility to meet the
needs of higher bit rate delivered to each user (1 Gbps for
downstream and 0.5 Gbps for upstream). WDM-PON has
many advantages over TDM/TDMA-PON such as [3];
1. Bandwidth is available for all users (bit rate transparency is
unlimited).
2. Splitting loss is 3-5 dB (WDM filter loss).
3. There is no burst mode.
4. It is easy to implement fault localization (optical time
domain reflectometer).
5. It is scalable which implies that you can expand the installed
equipment for additional demand as needed.
6. It is possible to upgrade the capacity of the existing fiber
networks (without adding fibers).
For these reasons WDM-PON is considered as a primary
solution for NG-PONs with 40 Gbps downstream and 10 Gbps
upstream and 32 users for 15-20 km distance. On the other
hand, some design issues should be considered when WDM is
used in PONs system. The compatibility of WDM-PON with
existing TDM-PON is a major requirement for NG-PON to be
economically viable [4]. Single feeder architecture should be
maintained in the system and arrayed waveguide grating
(AWGs) would replace the passive power splitters at the
remote node (RN). Also, colorless optical network unit is very
urgent to eliminate redundancy for the network operator [5]. In
designing WDM-PON system, three parameters should be
Performance Analysis of WDM-PON FTTH
Using Different Pulse Shapes at
10 Gbps and 20 Gbps
A. Elrashidi1,4, I. Ashry2,4, A. Mahros3,4, M. Alhaddad, and K. Elleithy
considered which are bit rate, fiber length, and the transmitted
power.
In this paper, we introduce a full design of a WDM-PON
system using 32 channels for 20 km length using different
pulse shapes. The used pulses are non-return to zero, return to
zero, saw-up, triangle, raised cosine, and hyperbolic-secant
pulse shapes instead of on-off kenning (OOK). The
bidirectional subcarrier multiplexed (SCM) WDM-PON
technique is used to reduce the expenses of using a large
numbers of laser sources at OMUs [6]. Bit error rate, quality
factor, and Eye diagram at 10 and 20 Gbps for transmission
and receiving modes are presented using an Optiwave system
7.0 Software.
The paper is organized as follow; in the section II we
discuss the technical issues for WDM-PON network system. In
section III, we introduce our proposed structure for central
office (CO) for downstream and upstream data transmission
and receiving, and optical network unit (ONU). In section IV,
results and discussion are presented. Section V offers
conclusions.
II. TECHNICAL ISSUES IN WDM-PON NETWORK SYSTEM
WDM-PON is considered as an ultimate solution for access
network due to its upgradeability, capacity, and its security.
Figure 1 shows the transmission bit rate of access networks as
a function of time [7].
Although WDM-PON has many advantages, extra costs in
the installation of wavelength selected lasers needed in WDM-
PON structure represents a fault problem [8]. Some efforts to
solve this problem such as using spectrum sliced incoherent
light sources or ASE injected Fabry-Peroy lasers are reported
in [9]-[10]. The main issue of such solution would be the use
of identical light source at every subscriber’s site. In this case
the use of bidirectional subcarrier multiplexed technique is
very efficient to decrease the overall cost of the system. This
type of laser source suffers from long tuning time, up to a few
seconds [11].
Distributed feedback laser diode (DFB-LD) is a most
common tunable laser source using a Bragg gratings technique
which etched inside the laser cavity [12]. A thermoelectric
cooler (TEC) is required for stable operation for a wavelength
shift due to temperature change on the grating.
Figure 1. Bit rate of access network as a function of time [7].
Digital signal processing (DSP) is a very efficient solution
for increasing bit rate of each user in FTTH. Q. Guo and et. al.
introduced a 40 Gbps FTTH using modified duobinary coding
in the downlink and OOK code in the uplink to improve the
tolerance and reduce the crosstalk between uplink and
downlink. The authors demonstrated a system with 25 km
length, 40 Gbps for the uplink and 10 Gbps for downlink [6].
A DSP based on TDM-OFDM-PON architecture is introduced
and experimentally demonstrated as a NG-PON solution by H.
Yang and et. al. [13].
The architecture performancewhen OFDM symbols is
transmitted in different time slots, is compared to the
architecture used an OOK. The proposed system shows high
performance over distance of 26.7 km and low bit error rate.
SCM WDM-PON is experimentally demonstrated by J. Buset
and et. al. [2]. Square root raised cosine pulse shape is used to
generate an M-ary quadrature amplitude modulation for up and
down links using 10 GHz transceiver bandwidth over 20 km
single feeder. 2.2 GHz reflective semiconductor optical
amplifier on ONU is included with offset optical filter. A.
Lebreton and B. Charbonnier introduced an experimental
system of 20 Gbps using FDM PON architecture [14]. The
authors demonstrate a simulation system of 40 Gbps with RF
bandwidth of 12 GHz and roll-off filter of 10 GHz.
III. FTTH PROPOSED SYSTEM ARCHITECTURE
The overall system architecture for CO and ONU is given in
this section. Figure 2 illustrates the CO as a transmitter.
Distributed feedback laser diode source with 1 mW
transmitted power is used. The channel capacity is 32 starting
from 1550.12 nm to 1575.37 nm with spacing of 0.8 nm,
according to ITU standard [15].
Pulse generator generates different pulses shape such as
return to zero (RZ), non-return to zero (NRZ), and triangular
shape, and then modulated by Mach-Zehnder (MZM)
modulator with extinction ratio of 10 dB. The modulated data
is connected to an arrayed waveguide grating (AWG), then to
multiplexer and to EDFA amplifier with 5 m length.
CO (Tx)
EDFA (5 m)
Pulse Gen.
DFB
MZM
MUX
AWG
Figure 2. Central office as a transmitter structure.
The transmitted signal goes through 20 km fiber optics cable
before being received by the ONU. Demultiplexer is used
before band path filter with bandwidth 0.8 nm for each channel
as shown in Figure 3. Power splitter is then used to split the
received power to the photodetector, downstream receiver, and
to RSOA to demodulate the carrier signal with the upstream
data. Input and output coupling loss for RSOA is 1 dB each,
and the input and output facet reflectivity is 5×10-5 and 0.9
respectively. The output signals are multiplexed and then sent
to the US transmitter. The upstream signal transmits through
the 20 km fiber and then is received by the CO again as shown
in Figure 4. A band path filter is used after AWG with a
bandwidth of 0.8 nm, then an EDFA amplifier with length of 5
m is connected to the amplifier’s the received signal.
IV. RESULTS AND DISCUSSION
In this section we discuss the quality factor, bit error rate,
and the eye diagram for a fiber-to-the-home system at bit rate
10 Gbps and 20 Gbps at CO and ONU using different shapes
of pulse modulation techniques. Non-return to zero, return to
zero, saw-up, triangle, raised cosine, and hyperbolic-secant
pulses modulation techniques are used to compare the results
and to select the pulse shape that introduces the best
performance for downstream and upstream.
Figure 5 shows the quality factor for different pulse shapes
as a function of the bit period at the CO for bit rate 10 Gbps.
Return to zero pulse shape gives a quality factor of 691 at low
bit period, which is very efficient at the CO.
The quality factors at the transmitter side are shown in
Figure 6 for different shapes and at 20 Gbps. Non-return to
zero pulse shape gives a maximum quality factor, around 368,
and an acceptable bit period.
Figure 5. Quality factor for different pulse shapes at 10 Gbps at the
transmission side.
Figure 6. Quality factor for different pulse shapes at 20 Gbps at the
transmission side.
At OUNs, the quality factors for different pulse shapes at 10
and 20 Gbps bit rates are illustrated in Table 1. Hyperbolic-
secant pulse shape gives the best value for the quality factor,
860, while the non-return to zero gives the best quality factor
at 20 Gbps, 121.
Eye diagrams give illustrates the performance of any
downstream or upstream rates. Figure 7 shows the eye diagram
of return to zero pulse shape at the CO at bit rate of 10 Gbps.
The difference between the maximum and the minimum is 7
ma.u. and is of uniform shape, which gives a good indication
of bit rate and quality factor.
ONU
BPF
RSOA
DS Rx
DMUX
×
MUX
US Tx
Figure 3. Optical network unit structure.
CO (Rx)
EDFA (5 m)
US Rx
BPF
DMUX
AWG
Figure 4. Central office as an upstream receiver structure.
TABLE 1
QUALITY FACTOR FOR DIFFERENT PULSE SHAPES AT 10 AND 20 GBPS
AT THE ONU SIDE.
Pulse shape
Quality Factor
US (10 Gbps)
US (20 Gbps)
NRZ
206
121
RZ
680
112
Saw-up
755
102.8
Triangle
783
105.6
Raised Cosine
776
111.7
Hyperbolic-
Secant
860
118.6
Figure 7. Eye diagram of return to zero at the transmission side at 10 Gbps.
Figure 8. Eye diagram of non-return to zero at the transmission side
at 20 Gbps.
The eye diagram of non-return to zero pulse shape at the CO
at bit rate of 20 Gbps is shown in Figure 8. The difference
between the maximum and the minimum is 6 ma.u. At the
ONUs, the eye diagram for hyperbolic-secant pulse shape is
illustrated in Figure 9. Figure 10 shows the eye diagram for
non-return to zero pulse shape at the ONU and 20 Gbps.
The bit error rate for different pulse shapes at both CO and
ONU for 10 and 20 Gbps bit rate are illustrated in Table 2.
The minimum bit error rate at the CO at 10 Gbps is 0.97×10-5
for non-return zero and is 1.05×10-5 for non-return to zero
pulse also at the ONUs. At bit rate 20 Gbps, the bit error rate
at the CO is 1.01×10-3 for return to zero pulse and 2.00×10-3
for saw-up pulse shape at the ONU.
Figure 9. Eye diagram of hyperbolic-secant at the receiver side at 10 Gbps.
Figure 10. Eye diagram of non-return to zero at the receiver side at 20 Gbps.
TABLE 2
BIT ERROR RATE FOR DIFFERENT PULSE SHAPES AT 10 AND 20 GBPS
AT THE CO AND ONU SIDES.
Pulse shape
BER at 10 Gbps (10-5)
BER at 20 Gbps (10-3)
DS
US
DS
US
NRZ
0.97
1.05
5.60
3.07
RZ
1.34
1.40
1.01
2.07
Saw-up
1.20
1.34
1.07
2.00
Triangle
1.24
1.33
1.10
2.03
Raised
Cosine
1.33
1.45
1.09
2.09
Hyperbolic-
Secant
2.35
1.69
1.55
2.77
V. CONCLUSION
A complete Fiber-to-the-Home (FTTH) structure is
introduced in this paper. The structure includes CO as
transmitter for downstream and receiver for upstream and
ONU. The given structure used has a bit rate of 10 Gbps and
20 Gbps for downstream data transmission using a WDM-
PON to share the wavelength between 32 users, from 1537.4
nm to 1562.23 nm. Bidirectional SCM technique is used at
ONU for data upstream, so there is no need for optical laser
sources at the user side for upstream data transmission. Q-
factor, BER, and eye diagram are illustrated for different pulse
shapes and the results are compared to get the best pulse shape
that provides the best Q-factor. Non-return to zero, return to
zero, saw-up, triangle, raised cosine, and hyperbolic-secant
pulses are used in modulation technique at the CO using MZM
and at the ONU side using RSOA. Non-return to zero pulse
shape is selected for high Q-factor at bit rate 20 Gbps at both
downstream and upstream data transmission. Return to zero is
selected for downstream and hyperbolic-secant at the ONU at
10 Gbps.
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Ali M. Elrashidi received the B.Sc. degree in electric engineering from
Alexandria University in 2001, the MS Degree in fiber optics from the same
university in 2007, and he received Ph.D. degree in Computer Science and
Engineering in the University of Bridgeport from 2008-2012. From 2002 to
2008, he was with Physics and Electric Department, Alexandria University,
Egypt, as an assistant professor from October 2012 to August 2013 and in
University of Business and Technology from August 2013 till now.
Dr. Elrashidi is involved in many research projects in USA, Egypt and Saudi
Arabia related to antenna and wave propagations, Fiber-to-the-home, and
remote patient monitoring system.
Dr. Elrashidi has research interests are in the areas of electromagnetics and
wave propagation, mobile communications, optical fiber communication, and
hardware design in a nanoscale. He has more than eleven years of teaching
experience. From 2002-2013 he has taught solid state physics, physics, fiber
optics, solid state electronics, modern physics, fiber optics, solid state
electronics, electrical measurements, introduction to communications,
electronics II, and antenna systems courses.
Khaled M. Elleithy received the B.Sc. degree in computer science and
automatic control from Alexandria University in 1983, the MS Degree in
computer networks from the same university in 1986, and the MS and Ph.D.
degrees in computer science from The Center for Advanced Computer Studies
at the University of Louisiana at Lafayette in 1988 and 1990, respectively
Currently, Dr. Khaled Elleithy is the Associate Dean for Graduate Studies in
the School of Engineering at the University of Bridgeport. He has research
interests are in the areas of network security, mobile communications, and
formal approaches for design and verification. He has published more than
two hundreds research papers in international journals and conferences in his
areas of expertise.
Dr. Elleithy is the co-chair of the International Joint Conferences on
Computer, Information, and Systems Sciences, and Engineering (CISSE).
CISSE is the first Engineering/Computing and Systems Research E-
Conference in the world to be completely conducted online in real-time via
the internet and was successfully running for six years. Dr. Elleithy is the
editor or co-editor of 12 books published by Springer for advances on
Innovations and Advanced Techniques in Systems, Computing Sciences and
Software.
