Performance evaluation of 1 tbps qpsk dwdm system over isowc

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 04 Issue: 11 | Nov -2015, Available @ http://www.ijret.org 22
PERFORMANCE EVALUATION OF 1 TBPS QPSK DWDM SYSTEM
OVER ISOWC
Amandeep Singh1
, Guneet Mander Uppal2
1
Student, Department Of Electronics & Communication Engineering, Chandigarh University, India
2
Asst Prof, Department Of Electronics & Communication Engineering, Chandigarh University, India
Scholaramandeep@Gmail.Com
Abstract
Optical wireless communications has been in latest trends of high speed communications. They enable the use of optical wireless
channel in applications like inter satellite links and underwater communications etc. In this paper, we communicate an ultra high
bit rate i.e. 1 Tbps (10 x 100 Gbps) QPSK WDM System over optical Wireless communication Link. The system is a Line of Sight
optical wireless link incorporating Coherent QPSK modulation Scheme for10 channels each at 100 Gbps The performance is
evaluated in terms of Q-Factor and Minimum Bit Error Rate which are noticed to be in acceptable standards. The Link is
analyzed under various parameters such as Power, Distance etc and maximum achievable distance is noticed to be 50,000 km at
power values ranging from 0 dBm to 40 dBm.
Key Words- WDM, CO-QPSK, OWC
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1. INTRODUCTION
Over the last two decades, wireless communications have
undergone massive alterations and contributing remarkable
alternatives for numerous high bandwidth and speed
processing applications [1]. The next major step on stair
towards these applications is realization of a network of
optical wireless satellites. This optical satellite network can
help in altering the complete scenario of space architecture
as the optical wireless communications went through a huge
expansion for its rewards over another competing techniques
like RF. Firstly, the cost of deployment in case of optical
communication systems decrements upto 10% as compared.
Secondly, unlike millimeter-wave systems optical links can
cover more distance in kilometers for which coventional
systems required repeaters. Finally, an unlicensed spectrum
of THz range can be used providing greater bandwidth and
no additional inferences [3]. Verifications of command and
control over pointing, acquisition ,tracking and telemetry
have been made in literature [4]. These links offer higher
bandwidth, tiny size, lesser weight, lower transmission
power and low cost substitute to at hand microwave
satellite systems [5] along with several benefits in weight
diminution directly concerning to launch costs and fuel
requirements [6].
In past, vast researches have been done and reported in
which Inter Satellite Optical Wireless Communication
Systems have been modelled [7] and the work includes
various parameters that needs to be taken care of while
designing optical wireless communication systems [8] such
as effects of vibration[8] transmitted power [9], size of
aperture of telescope [10]. Very high bit rate for OWC link
have been achieved by B. Patnaik et al in [11] and A
Penchala Bindushree in [12] by selecting Quadrature Phase
shift Keying (QPSK) as an optimum modulation scheme and
maximum achievable distance is reported up to
approximately 40,000 km at 5.6 Gbps and 5,000 km at 438
Gbps.
In this paper we present a 10 x 100 Gbps QPSK modulated
WDM system over Optical wireless communication Link
and the system is analyzed for different Powers at different
distances and aperture diameters of telescope measuring the
performance in terms of Quality Factor and Bit Error Rate.
The reported simulation is performed in Optiwave
Optisystem Software which is a design suite for Optical
Communication system design and analysis.
2. SIMULATION SETUP
The simulation setup of 10 channel QPSK WDM system
over OWC link is described below in Figure 1. The bit rate
at each channel is 100 Gbps and system architecture is made
by utilizing wavelength division multiplexing which is a
promising technology in optical systems for capacity
enhancement. The system comprises of three basic entities
of a communication system i.e. Transmitter, Communication
medium or channel and Receiver. These three have been
discussed in detail in subsections.

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Figure 1- Block diagram of 10*100 Gbps QPSK WDM
system over OW channel
2.1 Transmitter
The transmitter is a Coherent QPSK transmitter which
generates the QPSK signal by using two Mach Zehnder
modulators to encode QPSK symbols onto an optical carrier
[12]. Each modulator modulates the in-phase (I) and
Quadrature component (Q) of a carrier [11]. Number of bits
per symbol is 2. The PSK Sequence generator, which
generates the in-phase (I ) and quadrature signals (Q) as
given in (1) and (2), respectively [11]. The output of the
PSK sequence generator is given to the M-array pulse
generator, where M ¼ 4. Using a coupler the optical signal
is fed to the Mach–Zehnder (MZ) modulator and at the end
both I and Q signals is combined using an optical power
combiner as shown in Figure 2. The I and Q signals are
given
Ii = cos(fi) (1)
Qi= cos(fi) (2)
Where wi ¼ 2p(i 2 1)/M, i ¼ 1, 2, 3, 4 and M ¼ 4 [11]
The two symmetrical arms in transmitter each consists of a
Li-Nb Mach Zehnder dual arm modulator which is fed with
electrical inputs after gain and biasing of an M-ary Pulse
which gets its feed from a PSK Sequence generator. One of
the modulated arms’ phase is shifted and are collectively fed
into a coupler which at output port provides Optical QPSK
Signal.
Figure 2- Coherent optical QPSK Transmitter
2.2 Optical Wireless Channel
The optical wireless channel characterized by following
mathematical equation. The optical power at reception is
given by
PR = PT
η T
η R
4


 
 
   GT GR LT LR
Where PT is optical power transmitted by transmitter;
η R
and
η T are the optics efficiency of the receiver and
transmitter respectively; λ is the transmitted wavelength; Z
is the distance of optical wireless link; GT is the telescope
gain of transmitter; GR is the receiver telescope gain; and LT,
LR are the pointing loss factor of transmitter and the
receiver, respectively.
2.3 Coherent QPSK Receiver
The coherent QPSK receiver consists of a photodetector
which performs the optical to electrical conversion after
which adequate DSP operations on signal as shown in figure
are to be performed. The DSP for QPSK Block is shown in
figure and it explains how signal processing operations such
as DC blocking, Filtering, Resampling, time recovery,
Adaptive equalizing etc are performed at signal. After this
signal is fed into decision component which processes the I
and Q signals from DSP block. The thresholds are now
decided and I and Q signals are put into PSK Sequence
decoder at which we visualize the output signal using BER
test set in terms of Q factor and Bit error Rate.
Figure 3- DSP in Receiver for QPSK [13]
3. RESULTS AND DISCUSSION
The system is simulated at1 Tbps (10 channels with 100
Gbps at each channel). The output is visualized by using
BER Test Set in terms of Quality factor of received signal
and bit error rate and is found to be in acceptable limits.
Table 1 shows the Q factor and minimum BER obtained at
distance varying from 10,000 km to 50,000 km.
Table 1- Q-factor and Min BER at varied range of OW channel
Distance in Km Q-factor BER
10,000 8.12 0.432e-15
20,000 7.94 1.83e-15
30,000 7.60 28e-15
40,000 7.27 0.33e-12
50,000 6.87 6.11e-12

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Figure 4 shows graph of Distance vs. Q-factor from which it
can be concluded that Q factor goes on decreasing as we
move forward in terms of distance.
Figure 4- Graph showing Distance vs. Q Factor Trends
Figure 5 shows graph of Distance vs. log BER and shows
that error rate increases as the range of optical wireless
channel is increased.
Figure5- Graph showing Range vs. BER
The Constellation diagrams of received signals at various
distances are shown in Figure 6 and 7 and it becomes clear
from visualization geometry that constellation gets distorted
which shows the addition of noise with distance.
Figure 6- Electrical constellation diagram at 10000km
Figure 7- Electrical constellation Diagram at 50,000 km
The Constellation diagrams of received signals at minimum
and max power iterations are shown in figure are shown in
Figure 8 and 9 and it can be derived that the signal improves
as the transmitted Power of system is increased but in case
of power it is the non-linear effects and other issues like
inter channel crosstalk that are to be taken into account
while designing high power systems.

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Figure 8- Electrical constellation diagram at 0dBm Power
Figure 7- Electrical constellation Diagram at 40 dBm Power
Similarly Figure 10 and 11 shows the Input Power vs. Q-
factor and BER respectively and it can be seen that Q-factor
increases and Bit Error rate decreases as the transmitted
power is increased. Power is varied from 0dBm to 40 dBm
Figure 10- Trends in Q –Factor when power is varied from
0 to 40 dBm
Figure 11- Plot of Power vs. log BER
CONCLUSION
From the reported work on CO-QPSK-WDM-OWC system
on 1 Tbps the findings on Q-Factor and BER are under
acceptable limits and system is found to travel up to 50,000
Km at 100 Gbps data rate on each channel. The power of
system is varied from 0 dBm to 40 dBm and an ascending
trend in Q factor has been observed. Similarly the Distance
is iterated for various values and respective electrical
constellations have been seen proving that noise distorts the
signal as the link distance is increased up to 50000 km.
REFERENCES
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[3]. Juan-de-Dios, Arturo Arvizu M, Francisco J. Mendieta
and et al ,”Trends of the Optical Wireless

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Performance evaluation of 1 tbps qpsk dwdm system over isowc

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