This document presents a MATLAB Simulink model of a QPSK modulated reusable UWB-based optical network. Key aspects include: 1) The model simulates a WDM PON system using QPSK modulation to transmit data over single mode fiber, with and without wavelength reuse from downstream UWB signals. 2) System performance is evaluated by measuring BER and SNR over increasing fiber lengths. 3) Results show that wavelength reuse does not degrade performance, as SNR and BER values closely resemble the non-reuse method over transmission lengths up to 40,000km. 4) The study demonstrates an effective method for wavelength reuse in optical networks to reduce implementation costs without compromising performance.

1. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
INTERNATIONAL JOURNAL OF ELECTRONICS AND
6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 5, September – October (2013), © IAEME
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 4, Issue 5, September – October, 2013, pp. 66-72
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IJECET
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QPSK UWB BASED MODULATOR FOR REUSABLE SIMULINK
MODELED PON
M.S.V.Vara Prasad1, K.Kranthi2, K.Krishna Murthy3
1, 3
Department of Electronics, P.G. Center, P. B. Siddhartha College of Arts & Science, Vijayawada,
A.P., India.
2
Department of Electronic/Physics, S.R.R & C.V.R Govt. Degree College, Vijayawada, A.P., India.
ABSTRACT
This work presents the MATLAB SIMULINK 7.9 model of wavelength division multiplexed
communication system incorporating QPSK modulation format for simultaneously without and with
reusable UWB PON. To the best of our knowledge this simulator has been implemented for optically
amplified transmission through single mode fiber. In the other hand the wave length is reused from
the UWB down stream in optical network. Both the schemes are demonstrated with the Bernoulli
binary data transmission through WDM PON over the SMF. The performance is evaluated by
measuring the BER, SNR, eye diagram over fiber length increasing manner.
Keywords: Bit Error Rate (BER), Fiber Length, Micro Wave Photonics, Passive Optical Network
(PON), Quadrature Phase Shift Keying (QPSK), Single Mode Fiber (SMF), Signal To Noise
Ratio(SNR), Ultra Wide Band(UWB), Wavelength Division Multiplexing (WDM), Wave Length
Reuse.
I.
INTRODUCTION
A traditional UWB modulated optical PON network is proposed[1] below. In this method, the
data and UWB signals are QPSK modulated before reaching the optical modulator MZI. The
wavelength of the Laser diode is reused by modulating the optical signal generated by LASER diode
with the UWB carrier and transmitting via SMF as upstream signal. At the wired downstream side
the detected UWB waves can be further modulated with a (different frequency band) message data
and it can be used as an upstream for further transmission.
Simultaneously, the detected raw UWB signals can be up streamed to different wireless
systems for further modulation with (different frequency band) data. Thus the wavelength of one
time generated and UWB modulated centralized Light source is reused[1] for various applications.
Thus the data is included in the communication in the downstream side and the un modulated UWB
optical signal can be further used to other networks.
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2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 5, September – October (2013), © IAEME
II.
MODELING
The experimental [2] Implementation of the PON network with fixed data stream will be
implemented in a MATLAB SIMULINK Modeling environment, since the practical implementation
of the network costs beyond the scope of a student and SIMULINK is proven to be trustworthy for
accurate Modeling of Dynamic Systems. This simulator prototype was completed using MATLAB
7.9[3].
The first prototype that was designed in MATLAB SIMULINK was the Non-return to Zero
Transmitters from the experimental setup. The first stage of that design was signal modulation,
where the signal is modulated with two sources, a data generator and a random binary generator. The
next stage involved in designing the voltage bias function block.
Fig 1: Simulink Modelled Optical Network
Fig 2: Simulink model of QPSK modulated
reusable optical network
A optical modulated model consists of a QPSK modulated Binary, UWB, a 1500nm
wavelength LASER source, a configurable Single mode fiber in transmitter and a optical detector in
receiver side.
The only difference in the proposed system from the existing is the data modulation is done
in the downstream instead of upstream side. This completely changes the advantages of the system in
the application perspective, whereas the performance characteristics of the receiver sides are
untouched. Since previously used blocks are repeated with different combination we are directly
probing into the characteristic responses instead of the explanation. A random number generator
Data Block is included exclusively performance of the Random Data Characteristics.
2.1. QPSK UWB MODULATOR
Higher order modulation schemes, such as QPSK [4], are often used in preference to BPSK
when improved spectral efficiency is required. QPSK utilizes four constellation points, as shown in
figure below, each representing two bits of data. Again as with BPSK the use of trajectory. shaping
(raised cosine, root raised cosine etc) will yield an improved spectral efficiency, although one of the
principle disadvantages of QPSK, as with BPSK, is the potential to cross the origin, hence generating
100% AM.
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3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 5, September – October (2013), © IAEME
2.2. LASER SOURCE
A Laser source[5] is nothing but an ON and OFF high frequency state change. To simplify this
part of the simulation development, let us consider an ideal laser source (i.e. no frequency chirp
present) and implement this, in Simulink by selecting the “Signal Generator” block shown Fig.3.
Fig 3: Signal Generator DFB laser source 1550nm
This block models the desired sinusoidal optical carrier obtained from an ideal DFB laser
which takes the mathematical form(1),(2),(3).
c(t)=A cos ( W n + φ)
(1)
Where Wn and φ are the frequency and phase of the optical carrier respectively, with
Wn = 2 x π x 1.93 x 1014 rad/s
corresponding to the 1550 nm operating wavelength. A is the amplitude of the optical carrier
which has been normalized for simplicity and is thus set to unity.
f sampling ≥ 2B
(2)
T sampling ≤ 1 S = 2.59 X 10-15 S
2B
(3)
According to the Nyquist theorem, this sampling interval is at least twice the highest
frequency in the system. The Wave length Of the LASER block is reconfigurable just by double
clicking it.
2.3. OPTICAL MODULATOR
An (modulator) interferometer is an optical device which utilizes the effect of interference.
Typically, it starts with some input beam, splits it into two separate beams with some kind of beam
splitter (a partially transmissive mirror), and possibly exposes some of these beams to some external
influences (e.g. some length changes or refractive index changes in a transparent medium), and
recombines the beams on another beam splitter.
The Mach–Zehnder interferometer [6-7] was developed by the physicists Ludwig Mach and
Ludwig Zehnder. As shown in above Figure 6. It uses two separate beam splitters (BS) to split and
recombine the beams, having two outputs, which can be sent to photo detectors. The optical path
lengths in the two arms may be nearly identical, (or) may be different .The distribution of optical
powers at the two outputs depends on the precise difference in optical arm lengths and on the
wavelength (optical frequency).
If the interferometer is well aligned, the path length difference can be adjusted (by slightly
moving one of the mirrors) so that for a particular optical frequency the total power goes into one of
the outputs. For misaligned beams (e.g. with one mirror being slightly tilted), there will be some
fringe patterns in both outputs, and variations of the path length difference affecting mainly the
shapes of these interference patterns, whereas the distribution of total powers on the outputs may not
much change.
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4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 5, September – October (2013), © IAEME
2.4. DETECTOR
In order for the [8] receiver to receive the data that was transmitter by the receiver,
demodulation has to be done. In the demodulation block, the low pass filter excludes the high
frequency components and hence producing the demodulated signal by suppressing the carrier and
the QPSK symbols are detected again using a QPSK demodulator.
III.
RESULTS
Comparison of Eye diagrams with out and with resue
SMF distance of 5,000km
SMF distance of 10,000km
SMF distance of 15,000km
SMF distance of 20,000km
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5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 5, September – October (2013), © IAEME
SMF distance of 25,000km
SMF distance of 30,000km
SMF distance of 35,000km
SMF distance of 40,000km
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6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 5, September – October (2013), © IAEME
IV. COMPARISON OF GRAPHS
SNR (%)
BER (%)
SMF LENGTH (Km)
SMF LENGTH (Km)
Graph 1.SMF Length VS BER
(WITH OUT REUSE)
V.
Graph 2. SMF Length VS SNR
(WITH REUSE)
CONCLUSIONS
The concept of wavelength reuse over Single mode fiber and wireless channel is achieved
and tested using CAD design tools. The concern of the signal to noise ratio and the bit-error rate
parameters remain almost unchanged for both the methods of optical communication. The method of
reusing the wavelength for multiple applications is proved to be effective, since the SNR ratio of this
system resembles the previous method (without reuse).
This Bit error rate is varied from 0.0 to 0.0698, when the transmission of the single mode
fiber cable is shortened to below 5,000km. The bit error rate variation was found to be 0.1166, when
the transmission of the single mode fiber cable length is up to 40,000km. The variation in the SMF
cable length will also affect SNR variation from 50.49 to 15.0261 for length of the cable from
5,000km to 40,000km. This implies that as the SNR decreases the BER increases, as expected from
theory. This is depicted graphically by the eye diagram. A comparison of both the system is
represented graphically through curves. This shows that the method of reusing the wavelength, does
not degrade the performance of the system.
The aim of achieving wavelength reuse in the optical network is shown to compensate the
high implementation cost of the photonic systems. The performance characteristics of the system is
plotted. This indicates that noise is eliminated.
By analyzing the two performance curves, the proposed reuse scheme is proven to be
effective by completely resembling the performance of the old method without any degradation, at
the same time the frequency curve can be reused.
The studies carried out may further be extended beyond 40,000km and compared with the
experimental studies carried out by Dept. of Telecommunications, Govt. of India (or) Reliance
Communications.
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