Design and Analysis the Performance of Long-Haul Inter ...

Design and Analysis the Performance of Long-Haul Inter-

Satellite Optical Wireless Communication System at 7.2

Gbps by Using Lithium-Niobate MZM.

Ahmed Refaat Elhelw

Electronics and Electrical Communication Engineering Department

Faculty of Electronic Engineering, Menouf university

Menofia ,Egypt

[email protected]

Hamdy A. SharSher



Menofia ,Egypt

[email protected]

Abd El–Naser A. Mohamed


Faculty of Electronic Engineering,Menouf university

Menofia ,Egypt

[email protected]

Ahmed Nabih Zaki Rashed



Menofia ,Egypt

[email protected]

Abstract—Inter-satellite optical wireless communication

systems (Is-OWC) is a technique that used to connect between

two satellites. One of them is the transmitter and the other is

the receiver. The medium between them is a free space. Is-OWC

using at the ultra-high bit rate. In this paper, the proposed

system using optical sub-carrier multiplexing (SCM) with four

frequencies channel 3.5, 7.2, 10.8, 14.4 GHz respectively. This

system is designed at distance 5000 Km, bit rate 4x1.8 Gbps,

wavelength 1550 nm and input power 3 dB. The proposed

system utilized electrical Phase Shift Keying (PSK) modulation

technique for the design of Is-OWC system due to it widely used

for the wireless communication system. PSK is a type of

modification that changes the phase angle by 180° at each

change of digital information from zero to one or via verse with

the installation of the capacitance and frequency value. This

type of frequency is less susceptible to transmission errors from

interferences, noise, and dispersion of signal compared to other

types. The quality factor (Q-Factor) and bit error rate (BER)

are measured by using the eye diagram analyzer. The

oscilloscope visualizer allows the user to calculate and display

electrical signals in the time domain and it can display the signal

amplitude and autocorrelation. Radio frequency (RF) spectrum

analyzer allows the user to calculate and display electrical

signals in the frequency domain and it can display the signal

intensity, power spectral density, and phase. The results show

that the output for the signal-to-noise ratio (SNR), the Q-factor

and BER are improved more than the system before modelled

which are shown at the eye diagram analyzers. The commercial

optical system software called Opti-system is used to simulate

and model The Is-OWC system.

Keywords— Is-OWC, SCM, PSK, Q-Factor, BER, SNR

I. INTRODUCTION

The next generations of the systems that using light waves are require large information rate to carry it for a high amount of utilizers and cover large distances. For these reasons, researchers and developers have thought a process of hybrid optical communication with radio waves. This process lead to the emergence of a new technology called optical wireless communications (OWC). The using of radio frequencies over fiber- optics (ROF) performs the ability to transmit information at an elevated velocity through long-haul distances because RF wavelength is much longer compared to lasers. Optical wireless communications link result in lower

loss compared to RF and this leading to use small size payload. Thus the reducing in the size of the payload lead to the mass and the cost of the satellite will also be decreases [1-7].

OWC systems consist of three basic part the transmitter, wireless channel, and the receiver. There are two free-space optics channel. The first channel called free space optic (FSO) channel and it’s using when the connection become from the ground to satellite or via verse. The other channel called optical wireless communication channel (OWCC) and it is using when the connection become between two satellites. In our system, the channel type that used is OWCC. This channel used to transmit the optical information signal from transmitter to the receiver through free-space. OWCC has been chosen because of connecting two satellites with each other. One of the major usages of free space optical techniques is IS-OWC because of it having high performance and features. IS-OWC has some benefits such as the bandwidth is wide which leads to large data capacity , swift weight, low power, low cost, and small dimensions. Is-OWC system utilizes the same fundamental form as for fiber-optic communication system but the variance between them is using the free space as a channel instead of optical fiber. [ 8-11]

In Is-OWC technology, the satellite can make connections with another satellite in the same orbit or with satellite in another orbit. Satellites spin around Earth in orbits. There are three main orbits for satellites. The first orbit called Low Earth Orbit (LEO) and this is used when the orbital distance for the satellite at 1000 km or less with a time range from 2 to 4 hours to rotate around the earth. The second orbit called Medium Earth Orbit (MEO) and this is used when the orbital distance for the satellite in the range of 5000 km to about 25,000 km with a time range from 4 to12 hours. The third orbit called Geosynchronous Earth Orbit (GEO) and this is used when the orbital distance for the satellite at 35,786 km and an orbital period of 24 h. In GEO, there are three satellites, every satellite placed 120◦ over the equator to cover all the world [12].

In OWC, many multiplexing techniques have been used in achieving high data rates with lower data loss. One of them is SCM that is a technique where combine multiple signals onto a single signal at radio frequency with a single wavelength. So, SCM using microwave devices due to they are more

Table1.Simulation parameters of SCM system [1].

mature than optical devices. The filter that used is a microwave filter due to it is more constancy than the optical filter [13].

The optical amplifier used to amplify the optical signal at long–distance transmission due to it happens to her decaying [14,15].

The rest of this paper is regulated as follow: Section II is the fundamental model simulation architecture, section III clarifies the obtained results and a general discussion and finally, section IV summarizes the conclusions.

II. DESIGN OF SIMULATION MODEL AND ANALYSIS

In this paper, there are two systems as shown in Figs. (1, 2). first system is the system before modified (previous model) which consists of the four-bit sequence generator, four PSK modulator, four bandpass rectangular filter at the transmitter and receiver, combiner, Mach-Zehnder Modulator, CW laser, OWC channel, an avalanche photodiode and splitter [1].

The second system is the system with enhancement (proposed model) and the difference between it and the first system is using a type of optical modulator called Lithium-Niobate (LiNbO3) Mach-Zehnder Modulator Instead of ordinary MZM in the transmitter, LiNbO3 MZM requires to work a FORK and electrical gain because it has two electrical inputs. In this system also adding a new devices control loop and optical attenuator in the wireless channel. The simulation is used to simulate the two model systems is "OPTISYSTEM V.7" and the simulation parameters for SCM system that used in the analysis for the two model systems are listed in table 1.

It's knowing that optical wireless communication systems consist of three main parts transmitter, wireless channel, and receiver. In our proposed system as shown in Fig.2, the transmitter formed of Bit sequence generator, electrical signal modulator, electrical filter, combiner and optical modulator, Fork, electrical gain and the optical source. The output from transmitter then transmits to the receiver within (through) the wireless channel. The receiver form of Detector, splitter, and Filter.

Bit sequence generator that utilizes is a Pseudo-Random Bit Sequence (PRBS) generator which creates a PRBS data according to the different operation modes. This bit sequence is encoded with different coding/modulation format so that, the output from PRBS is fed to the PSK.

The Electrical PSK Encodes and modulates a binary signal to an electrical signal. The output from Electrical PSK is then filtering by Band pass rectangular filter (BPRF).

The BPRF is an RF filter used to take band limited from the radio frequency signal. The multiplexer that using is SCM with four frequencies channel 3.5, 7.2, 10.8, 14.4 GHz thus after the filtering is done, the output from every filter is fed to the Nx1 combiner. This combiner combines evenly N input signals into a single output port. The output signal from the combiner enters to the input of 1x2 Fork that Copies the input signal into two output signals. One of them go to the optical modulator but the other goes to the electrical gain. Electrical gain is an Ideal gain element is used to amplify the input that entered it. The output signal from it applied to the other port of the optical modulator. The type of optical source that used in our proposed system is CW laser diode that generates a continuous wave (CW) optical signal where the output light emitted by the CW laser diode is monochromatic, coherent and has high radiance, which makes it suitable for long distance free space transmission. The electrical signal and optical signal are modulated by the optical modulator. Optical modulator varies the intensity or amplitude of the input light signal from CW laser according to the electrical signal.

The type of optical modulator used in our proposed system is LiNbO3 MZM. it is used to modulate the signal from the combined with optical signals from the continuous wave (CW) laser with an input power of 3 dB and wavelength of 193.1 THz. The output light pulses from the optical modulator are transmitted in the transmission medium to the receiver satellite.

The output from the transmitter connected with the Loop Control network. Loop control network consists of Loop control device, optical attenuator, OWC Channel and traveling wave semiconductor optical amplifier (SOA). The loop control device used for increasing the range of optical communication systems. The number of loops decides the distance travelled by the optical signal from the transmitter to receiver. The optical attenuator is a device used to reduce the power level of an optical signal, either in a free space or in an optical fiber. OWC Channel (OWCC) is an optical wireless communication (OWC) channel. It is a subsystem of two telescopes and the wireless communication channel between them. Traveling wave SOA Performs lumped amplification with traveling wave semiconductor optical amplifiers (SOA). The output from the Loop Control network connected with the receiver.

At the receiver side, the type of optical detector used in our proposed system is Avalanche photodiode (APD) due to its better performance characteristics than PIN photodiode. APD can measure even lower level light and due to its high sensitivity, high speed, and internal gain mechanism, thus widely used in long distance transmissions. The output from APD applied to the 1xN splitter. This splitter splits evenly the signal input power to N output ports. Every signal from the splitter is then filtering by Band pass rectangular filter (BPRF). The RF spectrum analyzer and BER analyzer both using to analyze the output of the system when the input characteristics of the system varying.

Units Values Parameters

Gbps 1.8 Bit Rate

dBm 3 Transmitted optical power

THz 193.1 CW laser frequency

nm 1064 OWCC Wavelength

Km 5000 Length

Cm 35 Transmitter aperture diameter

Cm 35 Receiver aperture diameter

A/W 1 Responsivity of APD

nA 10 Dark current of APD

GHz 1*bit rate and

1.5*bit rate

BPF cut-off frequency

Fig.2. The system simulation of proposed model.

Fig.1.The system simulation of previous model [1].

III. RESULTS AND DISCUSSIONS

The analysis in this paper is going to be performed by observing two cases, Case (A) the comparison between the proposed model and previous model at receiver filter bandwidth at 1*bit rate and Case (B) when the proposed model gave us improved again at receiver filter bandwidth at a 1.5*bit rate.

A. The comparison between the proposed / previous systems In this case, the band pass rectangular filter at the receiver

using bandwidth at a 1*bit rate for the proposed and previous system. The analysis of the results showed us that the proposed model had an improvement over the previous model because the MZM device was replaced in the previous model and also adding a new device.

The eye diagram analyzer figures show the Q-factor when channels frequency changes in the two model systems.

Figs. (3, 4) shows the eye diagram output of Q-factor in the two systems at channel frequencies 3.5, 7.2, 10.8, 14.4 GHz. At channel 1 for 3.5 GHz, the comparison between Figs. (3-a) and (4-a) shows the Q-factor is improving from 7.5 to 7.9 . At channel 2 for 7.2 GHz, the comparison between Figs. (3-b) and (4-b) shows the Q-factor is improving from 6.5 to 7.1 . At channel 3 for 10.8 GHz, the comparison between Figs. (3-c) and (4-c) shows the Q-factor is improving from 6.3 to 7.3 . At channel 4 for 14.4 GHz, the comparison between Figs. (3-d) and (4-d) shows the Q-factor is improving from 6.8 to 7.5 . Where, the OWC length, every channel bit rate, OWC wavelength, CW laser frequency (THz) and SCM optical frequency (THz) in these figures are constants.

Fig. 3. Eye pattern of SCM for previous model at (a) channel 1, (b) channel 2, (c) channel 3, (d) channel 4 [1].

Fig.4. Eye pattern of SCM for proposed model at (a) channel 1, (b) channel 2, (c) channel 3, (d) channel 4.

Figs. (5, 6) shows the RF spectrum at the output of a BPF 1, BPF 2, BPF 3, BPF 4 at SCM receiver at channel frequencies 3.5, 7.2, 10.8, 14.4 GHz respectively in the two systems (previous/proposed) model. The comparison between

them shows us that the outputs from the RF spectrum analyzer at four channel frequencies for the proposed model are enhanced over the outputs from RF spectrum analyzer for the previous model at the frequency of the same channel.

Fig. 5. RF spectrum at output of (a) BPF 1,( b) BPF 2, (c ) BPF 3,

(d) BPF 4 at SCM receiver for previous model [1].


(d) BPF 4 at SCM receiver for proposed model.

6

6.2

6.4

6.6

6.8

7

7.2

7.4

7.6

7.8

8

0 2 4 6 8 10 12 14 16

Q-F

acto

r

Channel Frequency (GHz)

previous[1] proposed

Fig.7. The relation between channel frequency (GHz) and Q-factor for proposed and previous systems.

Table2 shows the improvements in Q-factor between the previous model and the proposed model at PSK channel CH1, CH2, CH3 and CH4 at frequencies 3.5, 7.2, 10.8, 14.4 GHz respectively and Fig. (7) Shows the relation between channel frequency GHz and the Q-factor at the system before enhancement and the system after enhancement and it also comparing the Q-factor results at the two systems.

As shown in this figure, the proposed curve is better than the previous curve because of the improving occurred in Q- factor by using LiNbO3 MZM, optical attenuator, and electrical gain.

Table 2.Q-factor with channel frequency at previous / proposed models.

channel frequency (GHz) Q-factor at previous model[1] Q-factor at proposed model

CH1 3.5 7.5 7.9

CH2 7.2 6.5 7.1

CH3 10.8 6.3 6.9

CH4 14.4 6.8 7.5

7.5

7.7

7.9

8.1

8.3

8.5

8.7

8.9

9.1

9.3

9.5

0 2 4 6 8 10 12 14 16

SNR

(dB

)



Fig.8. The relation between channel frequency (GHz) and the SNR (dB) for proposed and previous systems.

Fig.9. The relation between channel frequency (GHz) and BER (dB) for proposed and previous systems.

-16

-15

-14

-13

-12

-11

-10

-9

0 2 4 6 8 10 12 14 16

BER

(d

B)



Table 4. BER with channel frequency at previous/ proposed model.

Table 3.SNR with channel frequency at previous / proposed model.

Tables (3,4) shows the improvement in both SNR and BER respectively between the previous model and the proposed model at PSK channel CH1, CH2, CH3 and CH4 at frequencies 3.5, 7.2, 10.8, 14.4 GHz respectively .

Figs. (8,9) Shows the relation between channel frequency GHz with both the SNR and the BER respectively at the system before enhancement and the system after enhancement and also, they are comparing both separately the results of SNR and BER respectively at the two systems.

As shown in figure(8) ,the proposed curve is better than the previous curve because of the improving occurred in the

Q-factor lead to improve in SNR. SNR improved by using LiNB3 MZM, optical attenuator, and electrical gain.

In figure(9) , a logarithm of the BER values produced at the output was done. As shown in this figure ,the proposed curve is better than the previous curve because of the decreasing in the values of BER at the proposed model and this lead to the outputs are enhanced and it becomes better and also due to the improving occurred in Q-factor and SNR.

channel frequency

(GHz)

SNR at

previous

model (dB)

SNR at

proposed

model (dB)

CH1 3.5 8.8 9

CH2 7.2 8.1 8.5

CH3 10.8 8 8.4

CH4 14.4 8.3 8.8

channel frequency

(GHz)

BER at

previous

model

BER at

proposed

model

CH1 3.5 2.7E-14 1.7E-15

CH2 7.2 2.7E-11 4.6E-13

CH3 10.8 1.1E-11 3.02E-12

CH4 14.4 2.9E-12 2.6E-14

Fig. 10. Eye pattern of SCM for second proposed model at (a) channel 1, (b) channel 2, (c) channel 3, (d) channel 4 .


(d) BPF 4 at SCM receiver for second proposed model.

Table 5. Q-factor with channel frequency at first/second proposed

model.

B. When the proposed model gave us improved again:

In this case, the band pass rectangular filter at the receiver using bandwidth at a 1.5*bit rate for the proposed system. The analysis of the results showed us that when the proposed model using a filter at the receiver with bandwidth at a 1.5*bit rate (second proposed model) had an improvement over the proposed model using a filter at the receiver with bandwidth at a 1*bit rate (first proposed model).

Figs. (10,11) shows the improvement in both Q-Factor from eye diagram analyzer and the outputs of RF spectrum analyzer respectively at four channel frequencies when the receiver filter at bandwidth 1.5*bit rate.

Table (5) shows the improvement in Q-Factor between the first and second proposed models.

Fig (12) shows the comparing between the first proposed model and the second proposed model for Q-factor. As shown in this figure, the second proposed curve is better than the first proposed curve because of using a filter at the receiver with bandwidth at a 1.5*bit rate.

channel frequency

(GHz)

Q-factor at

first proposed

model

Q-factor at

second proposed

model

CH1 3.5 7.9 8.2

CH2 7.2 7.1 7.5

CH3 10.8 6.9 7.3

CH4 14.4 7.5 7.8

Fig.12. The relation between channel frequency (GHz) and Q-factor for first and second proposed models.

7.5

7.7

7.9

8.1

8.3

8.5

8.7

8.9

9.1

9.3

9.5

0 2 4 6 8 10 12 14 16

SNR

(d

B)


first proposed model

second proposed model

Table 6. SNR with channel frequency at first/second proposed model.

Table 7. BER with channel frequency at first/second proposed model.

Tables (6,7) shows the improvement in both the SNR and BER respectively between the first and second proposed models.

Figs. (13,14) Shows the comparing between the first proposed model and the second proposed model for both SNR and BER respectively .

As shown in Fig.(13), the second proposed curve is better than the first proposed curve because of the improving occurred in the Q-factor lead to improve in SNR.

In Fig.(14), a logarithm of the BER values produced at the output was done. As shown in this figure, the second proposed curve is better than the first proposed curve because of using a filter at the receiver with bandwidth at a 1.5*bit rate.

channel frequency

(GHz)

SNR at first

proposed model

(dB)

SNR at second

proposed model

(dB)

CH1 3.5 9 9.1

CH2 7.2 8.5 8.8

CH3 10.8 8.4 8.6

CH4 14.4 8.8 8.9

channel frequency

(GHz)

BER at first

proposed model

BER at second

proposed model

CH1 3.5 1.7E-15 1.6E-16

CH2 7.2 4.6E-13 3.3E-14

CH3 10.8 3.02E-12 1.2E-13

CH4 14.4 2.6E-14 3.7E-15

Fig. 13. The relation between channel frequency (GHz) and the SNR (dB) for first and second proposed models.

6.5

6.7

6.9

7.1

7.3

7.5

7.7

7.9

8.1

8.3

8.5

0 2 4 6 8 10 12 14 16

Q-F

acto

r




-17

-16

-15

-14

-13

-12

-11

-10

0 2 4 6 8 10 12 14 16

BER

(d

B)




Fig. 14. The relation between channel frequency (GHz) and BER (dB) for first and second proposed models.

IV. CONCLUSION

In this paper, there are two cases where work has been done. The first case in it the comparison between the proposed model and previous model at receiver filter bandwidth at a 1*bit rate in PSK channels frequency 3.5, 7.2 10.8 and 14.4 GHz. The proposed model, in this case, is used optical modulator called Lithium-Niobate (LiNbO3) Mach-Zehnder Modulator Instead of ordinary MZM in the transmitter and adding a new devices control loop and optical attenuator in the wireless channel. The second case in it the proposed model gave us improved again because of using a filter at the receiver with bandwidth at a 1.5*bit rate with the same frequencies. In the first case, the comparison between the two models shows us that the results from the proposed model are better than the results from the previous model in the Q-factor, SNR and BER parameter. For examples, the Q- factor at channel frequency 3.5GHz is equal to 7.5 before modified but become 7.9 after modified and at channel frequency, 14.4 GHz is equal to 6.8 before modified but become 7.5 after enhancement. Because of the improvement in q-factor values, SNR values will also improve. The BER decreased due to the improvement in both Q-factor and SNR. In the second case, the proposed model that compared to the previous model improved again because of using a filter at the receiver with bandwidth at a 1.5*bit rate so that, the results values of Q-factor, SNR and BER are improved. Thus when the proposed model using a filter at the receiver with bandwidth at a 1.5*bit rate, the results values become better than when it using a filter at the receiver with bandwidth at a 1*bit rate.

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