- Email: [email protected]
Improved analysis of 2.5 Gbps-inter-satellite link (ISL) in inter-satellite optical-wireless communication (IsOWC) system
Optics Communications 286 (2013) 99–102
Contents lists available at SciVerse ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Improved analysis of 2.5 Gbps-inter-satellite link (ISL) in inter-satellite optical-wireless communication (IsOWC) system Vishal Sharma a,n, Naresh Kumar b a b
Department of Electronics and Communication Engineering, Shaheed Bhagat Singh College of Engineering and Technology, Ferozepur, Punjab, India National Institute of Technology, Hamirpur, Himachal Pradesh, India
a r t i c l e i n f o
abstract
Article history: Received 16 April 2012 Received in revised form 18 June 2012 Accepted 26 August 2012 Available online 24 September 2012
Inter-satellite optical-wireless communication systems (IsOWC), one of the important applications of FSO/WSO technology, will be deployed in space in the near future. The IsOWC systems provide a high bandwidth, small size, light weight, low power and low cost alternative to present microwave satellite systems. In this paper, we have reported the improved investigation through implementation of a TM square root module using OPTISYSTEM simulator to establish an inter-satellite link (ISL) between two satellites estranged by a distance of 1000 Km at data rate of 2.5 Gbps which is not reported in previous investigated work. & 2012 Elsevier B.V. All rights reserved.
Keywords: Optical-wireless communication (OWC) Signal to Noise Ratio (SNR) Inter-satellite link (ISL)
1. Introduction The application of laser technology to communications, particularly space communications, was envisioned in the very early days of laser development around 1962, described a method for secure communications between a satellite and a submarine. From the last 40 years to now, government agencies, companies, universities, and individuals in many countries have made tremendous technical progress in optical-space communication i.e. inter-satellite optical-wireless communication [1]. The present satellite communication system uses microwave technology for space-to-ground and geosynchronous satellite to low earth orbiting vehicles. In the future system, the satellite to ground links would remain in the microwave regime but satellite to satellite communication will be governed by optical-wireless links. The technology uses laser light of infrared wavelengths to transmit optical signals between two points via free space. This requires devices similar to those used for the transmission through fiberoptic cable, except that the signal is transmitted through free space and not via optical cable capable of transmitting data, voice or video. IsOWC can be used to connect one satellite to another, whether the satellite is in the same orbit or in different orbits. The data can be sent in IsOWC systems at the speed of light without much delay and with minimum attenuation since the space is considered to be a vacuum. The advantage of using optical link over radio frequency (RF) links is the ability to send high speed
n
Corresponding author. Tel.: þ91 8872544401. E-mail address: [email protected] (V. Sharma).
0030-4018/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optcom.2012.08.055
data to a distance of thousands of kilometers using small size payload [2]. By reducing the size of the payload, the mass and the cost of the satellite will also be decreased. Another reason of using OWC is the wavelength. RF wavelength is much longer compared to lasers; hence the beam width that can be achieved using lasers is narrower than that of the RF system [3]. Due to this reason, OWC link results in lower loss compared to RF, but it requires a highly accurate tracking system to make sure that the connecting satellites are aligned and have line of sight. However, the transmission of such transmissions is affected in different ways by the environment processes such as absorption, scattering and shimmering. All three conditions attenuate the transmitted energy, affecting reliability and the bit error levels. Satellites revolve around the earth at their own orbit, and there are three commonly used orbits for satellites. Satellite orbits with orbital height of approximately 1000 km or fewer are known as Low Earth Orbit (LEO). LEOs tend to be in general circular in shape. LEO satellites take from 2 to 4 hours to rotate around the earth. This orbit is commonly used for multi-satellite constellations where several satellites are launched up to space to perform a single mission. Satellite orbits with orbital heights typically in the range of 5000 km to about 25,000 km are known as Medium Earth Orbit (MEO)/Intermediate Circular orbit (ICO). MEO and ICO are often used synonymously, but MEO classification is not restricted to circular orbits. In Geosynchronous Earth Orbit (GEO), the satellite is in equatorial circular orbit with an altitude of 35,786 km and orbital period of 24 hours. Three satellites in GEO placed 1201 apart over equator cover most of the world for communications purposes [4]. At present, there are 6124 satellites orbiting the earth and this number increases year by year [5]. At the same
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V. Sharma, N. Kumar / Optics Communications 286 (2013) 99–102
From Satellite TT&C System
Data Source
CW Laser
NRZ
Modulator
Optical Wireless Channel
SATELLITE 1
APD + LPF
SM
To Satellite TT&C System
SATELLITE
Fig. 1. Design of inter satellite optical-wireless communication systems using Opti-System Simulator: CW—Continuous-wave laser diode, LPF—Low Pass filter, APD—Avalanche Photo-detector and TT&C—Telemetry, Tracking and Communication systems.
time, the optical-wireless communication (OWC) technology has grown and advanced throughout the year. Laser communication is now able to send information at data rates up to several Gbps and at a distance of thousands of kilometers apart. This has opened up the idea to adapt optical-wireless communication technology into space technology; hence inter-satellite opticalwireless communication is developed. In this work, we have presented the improved simulative investigation of Inter-satellite optical-wireless communication systems at high transmission rate of 2.5 Gbps over a spacing distance of 1000 Km by means of the square root module. The paper is organized as follows: section I contains the system description, section II discusses the results of inter-satellite optical-wireless communications system and finally, the section III summarizes and concludes this paper.
2. System description The IsOWC system consists of three main communication parts which are transmitter, propagation channel and receiver as shown in Fig. 1 where the transmitter is in the first satellite and the receiver is in the second satellite. Optical-wireless communication uses light at a near-infrared frequency to communicate. The IsOWC system is not much different from free space optics and fiber optic communication where the difference relies in the propagation medium. The free space between two connecting satellites is considered as OWC channel, which is the propagating medium for the transmitted light. In the OptiSystem software, the OWC channel is modeled between an optical transmitter and optical receiver with a 15 cm optical antenna at each end. The transmitter and receiver gains are 0 dB. The transmitter and receiver antennae are also assumed to be ideal where the optical efficiency is equal to 1, and there are no pointing errors. Additional losses from scintillation and mispointing are also assumed to be zero. The OWC channel is considered to be outer space where it is assumed to be a vacuum and free from atmospheric attenuation factors. The aperture Diameter of transmitting- and receiving- antenna is taken as 10 cm. The IsOWC transmitter receives data from the satellite’s Telemetry, Tracking and Communication (TT&C) system of the satellite works along with its counterparts located in the satellite control earth station. The telemetry system collects data from sensors on board the satellite and sends these data via telemetry link to the satellite control center which monitors the health of the satellite. Tracking and ranging system located in the earth station provides information related to the range and location of the satellite in its orbit. The command system is used for switching on/off of different subsystems in the satellite based on the telemetry and tracking data. As the output light emitted by the laser diode is monochromatic, coherent and has high radiance, which makes it suitable for long distance free space transmission [6], a CW laser diode of linewidth of 5 MHz is used in our proposed IsOWC system.
Fig. 2. Optical antenna.
The electrical signal from TT&C system and optical signal from the laser are modulated by an optical modulator before it is transmitted out to space. The output light-pulses from the optical modulator are transmitted in the transmission medium to the receiving satellite. There are a number of attenuation factors that degrade the performance of FSO systems such as atmospheric turbulence, thick fog, rain and atmospheric temperature [8]. A coherent fiber array consisting of densely packed multiple sub-apertures, with each sub-aperture interfaced to a SMF fiber, is reported for improving the performance of an atmospheric coherent FSO system in the presence of atmospheric turbulence [9]. Different from free space optics (FSO) that are subjected to many losses due to weather and atmospheric attenuation, the inter-satellite optical-wireless communication channel is considered as vacuum and free from atmospheric losses. Therefore, the free space loss is taken as 0 dB/Km of optical-wireless channel various in our proposed model. At an ideal case, the only cause of signal attenuation is the distance of the transmission. Optical antenna or optical lenses can be used at the transmitter and the receiver. The optical antenna allows wider light beam divergence and detection. An optical antenna, actually, is a lens or a telescope that is placed before and after the transmission medium to increase the signal divergence as shown in Fig. 2. The receiving end of the IsOWC system consists of an Avalanche photodiode and a low pass filter followed by a square root module. Amplification in APD photo detector occurs when charged electrons are introduced in such high electric field area and collide with neutral semiconductor atoms, thus generating other carriers. This process is then repeated, effectively, to amplify the limited number of carriers [7]. The simulation parameters of our proposed IsOWC system are listed in Table 1 as given below.
3. Result and discussion An inter-satellite optical-wireless system is designed with TM the help of OPTI-SYSTEM simulator consisting of two satellites with a space- difference of 1000 Km. The two satellites exchange
V. Sharma, N. Kumar / Optics Communications 286 (2013) 99–102
101
Table 1 Simulated parameters. Dark Current Quantum noise Quantum efficiency Laser line width Free space loss (Vacuum) Input power Optical antenna diameter Divergence angle Multification factor of APD Cutoff frequency of LPF Order of Bessel function MZM modulator chirp MZM biasing voltage MZM offset voltage
10 nA Off 0.799 5 MHz 0 dB/Km 10 dBm 20 cm 2 mrad 3 0.75nbit rate 4 Zero 8V 4V
Fig. 4. Evaluation of total power (dBm) w.r.t space-difference between the two Satellites with- and without- SM module at an operating wavelength of 1550 nm.
Fig. 3. Evaluation of SNR (dB) w.r.t space-difference between the two Satellites with- and without- SM module at an operating wavelength of 1550 nm.
externally-modulated optical-data at 2.5 Gbps through the freespace medium at an operating wavelength of 1550 nm. Fig. 3 depicts the measurement of SNR at satellite 2 at different spacedifferences between the two satellites and different transmitted powers at an operating wavelength of 1550 nm. It has been observed that SNR reduces from 44 dB to 4 dB in the range of space-difference of 100 Km–1000 Km between the two satellites without using the SM module. Alternatively, SNR varies in the range of 84 dB to 60 dB with SM module in the range of 100 Km to 1000 Km as shown in Fig. 3. It means that an efficient improvement in SNR ratio is achieved with SM module, which further helps in increasing the length of ISL link between the two satellites. Further, it has been also observed that the total power received of IsOWC system is also improved by using SM module as depited in Fig. 4 and revealed that an improvement of 52 dBm is achieved in total received power at satellite 2 after an ISL link of 1000 Km. The total power received at satellite 2 is computed as [ 14 dBm, 28 dBm and 34 dBm] and [ 48 dBm, 80 dBm and 86 dBm] after an ISL link of [100 Km, 500 Km and 1000 Km] with- and without- SM module respectively. Further, it has been also observed that the acceptable/improved SNR ratio of IsOWC system is achieved with less satellite transmitted power by using SM module as depicted in Fig. 5. The computed SNR is as [68 dB and 76 dB] and [16 dB and 36 dB] after an ISL link of 1000 Km for
Fig. 5. Evaluation of SNR ratio w.r.t transmitted Power (dBm) with- and withoutSM module after an ISL link of 1000 Km at an operating wavelength of 1550 nm.
satellite transmitted power of [10 dBm and 20 dBm] with- and without- SM module respectively. The SNR ratio and total power received is also improved at varied Responsivity with SM module as shown in Figs. 6–7. An mprovement of 40 dB in both the evaluated parameters such as SNR ratio and total power received, after an ISL link of 1000 Km, is computed for Responsivity of 10 A/W with the use of SM module. It means that less power is involved with the use of SM module in transmitting the optical data over an ISL link of 1000 Km. In Fig. 8, the Q-factor of the IsOWC system is also plotted against ISL link length. The Q-factor is computed approximately as 16 to 18 in the range of ISL link of 100 Km–1000 Km with SM module. Alternatively, the Q factor decreases continuously from 22 to 2 in the range of ISL link of 100 Km to 1000 Km without using SM module. It is quite evident from our simulated results that a stable and acceptable improvement in Q factor can be achieved with the use of SM module after an ISL link of 1000 Km at an operating wavelength of 1550 nm.
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V. Sharma, N. Kumar / Optics Communications 286 (2013) 99–102
Fig. 6. Evaluation of SNR ratio w.r.t Responsivity (A/W) with- and without- SM module after an ISL link of 1000 Km at an operating wavelength of 1550 nm.
Fig. 8. Evaluation of Q-factor w.r.t ISL link between the two satellites with- and without- SM module at an operating wavelength of 1550 nm.
satellites at data rate of 2.5 Gbps with- and without- SM module. It is concluded from our simulated IsOWC system that the ISL link of 1000 Km with improved SNR ratio in conjunction with acceptable BER can be achieved by using the SM module. Also, less transmitted-power is required to transmit the externallymodulated data of 2.5 Gbps over an ISL link of 1000 Km at an operating wavelength of 1550 nm.
References
Fig. 7. Evaluation of total power w.r.t Responsivity (A/W) with- and without- SM module after an ISL link of 1000 Km at an operating wavelength of 1550 nm.
4. Conclusion In this work, we have designed an inter-satellite OWC system to establish an inter-satellite link of 1000 Km length between two
[1] Gerhard A. Koepf, Robert G. Marshalek, David L. Begley, Space Laser Communications: A Review of Major Programs in the United States, International Journal of Electronics and Communications (AEU), 56, Elsevier, 2002 232–242. [2] Roy Szweda, III–Vs Review, the Advanced Semiconductor Magazine 14 (8) (2001) 46. [3] A. Jamalipour, Low Earth Orbital Satellites for Personal Communication Networks, Artech House Publishers, Norwood, Mass, 1998. [4] SATCAT Boxscore, /http://celestrak.com/satcat/boxscore.aspS, June 2012. [5] Zhili Sun, Satellite Networking—Principles and Protocols, University of Surrey, John Wiley & Sons, UK, 2005. [6] J.C. Palais, Fiber Optic Communications, 5th Edition, Prentice Hall, Upper Saddle River, New Jersey, 2005. [7] IBM: Optical Modulator, Retrieved April 29, 2009, from /http://www03.ibm. com/press/us/en/photo/22808.wssS. [8] W. Popoola, Z. Ghassemlooy, M.S. Awan, and E. Leitgeb, Atmospheric channel effects on terrestrial free space optical communication links, ECAI 2009, 3rd International Conference on Electronics, Computers and Artificial Intelligence, Pitesti, Omania, 3rd–5th July, 2009. [9] Aniceto Belmonte, Joseph M. Kahn, Journal of Optical Communication and Networking 3 (11) (2011).
Contents lists available at SciVerse ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Improved analysis of 2.5 Gbps-inter-satellite link (ISL) in inter-satellite optical-wireless communication (IsOWC) system Vishal Sharma a,n, Naresh Kumar b a b
Department of Electronics and Communication Engineering, Shaheed Bhagat Singh College of Engineering and Technology, Ferozepur, Punjab, India National Institute of Technology, Hamirpur, Himachal Pradesh, India
a r t i c l e i n f o
abstract
Article history: Received 16 April 2012 Received in revised form 18 June 2012 Accepted 26 August 2012 Available online 24 September 2012
Inter-satellite optical-wireless communication systems (IsOWC), one of the important applications of FSO/WSO technology, will be deployed in space in the near future. The IsOWC systems provide a high bandwidth, small size, light weight, low power and low cost alternative to present microwave satellite systems. In this paper, we have reported the improved investigation through implementation of a TM square root module using OPTISYSTEM simulator to establish an inter-satellite link (ISL) between two satellites estranged by a distance of 1000 Km at data rate of 2.5 Gbps which is not reported in previous investigated work. & 2012 Elsevier B.V. All rights reserved.
Keywords: Optical-wireless communication (OWC) Signal to Noise Ratio (SNR) Inter-satellite link (ISL)
1. Introduction The application of laser technology to communications, particularly space communications, was envisioned in the very early days of laser development around 1962, described a method for secure communications between a satellite and a submarine. From the last 40 years to now, government agencies, companies, universities, and individuals in many countries have made tremendous technical progress in optical-space communication i.e. inter-satellite optical-wireless communication [1]. The present satellite communication system uses microwave technology for space-to-ground and geosynchronous satellite to low earth orbiting vehicles. In the future system, the satellite to ground links would remain in the microwave regime but satellite to satellite communication will be governed by optical-wireless links. The technology uses laser light of infrared wavelengths to transmit optical signals between two points via free space. This requires devices similar to those used for the transmission through fiberoptic cable, except that the signal is transmitted through free space and not via optical cable capable of transmitting data, voice or video. IsOWC can be used to connect one satellite to another, whether the satellite is in the same orbit or in different orbits. The data can be sent in IsOWC systems at the speed of light without much delay and with minimum attenuation since the space is considered to be a vacuum. The advantage of using optical link over radio frequency (RF) links is the ability to send high speed
n
Corresponding author. Tel.: þ91 8872544401. E-mail address: [email protected] (V. Sharma).
0030-4018/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optcom.2012.08.055
data to a distance of thousands of kilometers using small size payload [2]. By reducing the size of the payload, the mass and the cost of the satellite will also be decreased. Another reason of using OWC is the wavelength. RF wavelength is much longer compared to lasers; hence the beam width that can be achieved using lasers is narrower than that of the RF system [3]. Due to this reason, OWC link results in lower loss compared to RF, but it requires a highly accurate tracking system to make sure that the connecting satellites are aligned and have line of sight. However, the transmission of such transmissions is affected in different ways by the environment processes such as absorption, scattering and shimmering. All three conditions attenuate the transmitted energy, affecting reliability and the bit error levels. Satellites revolve around the earth at their own orbit, and there are three commonly used orbits for satellites. Satellite orbits with orbital height of approximately 1000 km or fewer are known as Low Earth Orbit (LEO). LEOs tend to be in general circular in shape. LEO satellites take from 2 to 4 hours to rotate around the earth. This orbit is commonly used for multi-satellite constellations where several satellites are launched up to space to perform a single mission. Satellite orbits with orbital heights typically in the range of 5000 km to about 25,000 km are known as Medium Earth Orbit (MEO)/Intermediate Circular orbit (ICO). MEO and ICO are often used synonymously, but MEO classification is not restricted to circular orbits. In Geosynchronous Earth Orbit (GEO), the satellite is in equatorial circular orbit with an altitude of 35,786 km and orbital period of 24 hours. Three satellites in GEO placed 1201 apart over equator cover most of the world for communications purposes [4]. At present, there are 6124 satellites orbiting the earth and this number increases year by year [5]. At the same
100
V. Sharma, N. Kumar / Optics Communications 286 (2013) 99–102
From Satellite TT&C System
Data Source
CW Laser
NRZ
Modulator
Optical Wireless Channel
SATELLITE 1
APD + LPF
SM
To Satellite TT&C System
SATELLITE
Fig. 1. Design of inter satellite optical-wireless communication systems using Opti-System Simulator: CW—Continuous-wave laser diode, LPF—Low Pass filter, APD—Avalanche Photo-detector and TT&C—Telemetry, Tracking and Communication systems.
time, the optical-wireless communication (OWC) technology has grown and advanced throughout the year. Laser communication is now able to send information at data rates up to several Gbps and at a distance of thousands of kilometers apart. This has opened up the idea to adapt optical-wireless communication technology into space technology; hence inter-satellite opticalwireless communication is developed. In this work, we have presented the improved simulative investigation of Inter-satellite optical-wireless communication systems at high transmission rate of 2.5 Gbps over a spacing distance of 1000 Km by means of the square root module. The paper is organized as follows: section I contains the system description, section II discusses the results of inter-satellite optical-wireless communications system and finally, the section III summarizes and concludes this paper.
2. System description The IsOWC system consists of three main communication parts which are transmitter, propagation channel and receiver as shown in Fig. 1 where the transmitter is in the first satellite and the receiver is in the second satellite. Optical-wireless communication uses light at a near-infrared frequency to communicate. The IsOWC system is not much different from free space optics and fiber optic communication where the difference relies in the propagation medium. The free space between two connecting satellites is considered as OWC channel, which is the propagating medium for the transmitted light. In the OptiSystem software, the OWC channel is modeled between an optical transmitter and optical receiver with a 15 cm optical antenna at each end. The transmitter and receiver gains are 0 dB. The transmitter and receiver antennae are also assumed to be ideal where the optical efficiency is equal to 1, and there are no pointing errors. Additional losses from scintillation and mispointing are also assumed to be zero. The OWC channel is considered to be outer space where it is assumed to be a vacuum and free from atmospheric attenuation factors. The aperture Diameter of transmitting- and receiving- antenna is taken as 10 cm. The IsOWC transmitter receives data from the satellite’s Telemetry, Tracking and Communication (TT&C) system of the satellite works along with its counterparts located in the satellite control earth station. The telemetry system collects data from sensors on board the satellite and sends these data via telemetry link to the satellite control center which monitors the health of the satellite. Tracking and ranging system located in the earth station provides information related to the range and location of the satellite in its orbit. The command system is used for switching on/off of different subsystems in the satellite based on the telemetry and tracking data. As the output light emitted by the laser diode is monochromatic, coherent and has high radiance, which makes it suitable for long distance free space transmission [6], a CW laser diode of linewidth of 5 MHz is used in our proposed IsOWC system.
Fig. 2. Optical antenna.
The electrical signal from TT&C system and optical signal from the laser are modulated by an optical modulator before it is transmitted out to space. The output light-pulses from the optical modulator are transmitted in the transmission medium to the receiving satellite. There are a number of attenuation factors that degrade the performance of FSO systems such as atmospheric turbulence, thick fog, rain and atmospheric temperature [8]. A coherent fiber array consisting of densely packed multiple sub-apertures, with each sub-aperture interfaced to a SMF fiber, is reported for improving the performance of an atmospheric coherent FSO system in the presence of atmospheric turbulence [9]. Different from free space optics (FSO) that are subjected to many losses due to weather and atmospheric attenuation, the inter-satellite optical-wireless communication channel is considered as vacuum and free from atmospheric losses. Therefore, the free space loss is taken as 0 dB/Km of optical-wireless channel various in our proposed model. At an ideal case, the only cause of signal attenuation is the distance of the transmission. Optical antenna or optical lenses can be used at the transmitter and the receiver. The optical antenna allows wider light beam divergence and detection. An optical antenna, actually, is a lens or a telescope that is placed before and after the transmission medium to increase the signal divergence as shown in Fig. 2. The receiving end of the IsOWC system consists of an Avalanche photodiode and a low pass filter followed by a square root module. Amplification in APD photo detector occurs when charged electrons are introduced in such high electric field area and collide with neutral semiconductor atoms, thus generating other carriers. This process is then repeated, effectively, to amplify the limited number of carriers [7]. The simulation parameters of our proposed IsOWC system are listed in Table 1 as given below.
3. Result and discussion An inter-satellite optical-wireless system is designed with TM the help of OPTI-SYSTEM simulator consisting of two satellites with a space- difference of 1000 Km. The two satellites exchange
V. Sharma, N. Kumar / Optics Communications 286 (2013) 99–102
101
Table 1 Simulated parameters. Dark Current Quantum noise Quantum efficiency Laser line width Free space loss (Vacuum) Input power Optical antenna diameter Divergence angle Multification factor of APD Cutoff frequency of LPF Order of Bessel function MZM modulator chirp MZM biasing voltage MZM offset voltage
10 nA Off 0.799 5 MHz 0 dB/Km 10 dBm 20 cm 2 mrad 3 0.75nbit rate 4 Zero 8V 4V
Fig. 4. Evaluation of total power (dBm) w.r.t space-difference between the two Satellites with- and without- SM module at an operating wavelength of 1550 nm.
Fig. 3. Evaluation of SNR (dB) w.r.t space-difference between the two Satellites with- and without- SM module at an operating wavelength of 1550 nm.
externally-modulated optical-data at 2.5 Gbps through the freespace medium at an operating wavelength of 1550 nm. Fig. 3 depicts the measurement of SNR at satellite 2 at different spacedifferences between the two satellites and different transmitted powers at an operating wavelength of 1550 nm. It has been observed that SNR reduces from 44 dB to 4 dB in the range of space-difference of 100 Km–1000 Km between the two satellites without using the SM module. Alternatively, SNR varies in the range of 84 dB to 60 dB with SM module in the range of 100 Km to 1000 Km as shown in Fig. 3. It means that an efficient improvement in SNR ratio is achieved with SM module, which further helps in increasing the length of ISL link between the two satellites. Further, it has been also observed that the total power received of IsOWC system is also improved by using SM module as depited in Fig. 4 and revealed that an improvement of 52 dBm is achieved in total received power at satellite 2 after an ISL link of 1000 Km. The total power received at satellite 2 is computed as [ 14 dBm, 28 dBm and 34 dBm] and [ 48 dBm, 80 dBm and 86 dBm] after an ISL link of [100 Km, 500 Km and 1000 Km] with- and without- SM module respectively. Further, it has been also observed that the acceptable/improved SNR ratio of IsOWC system is achieved with less satellite transmitted power by using SM module as depicted in Fig. 5. The computed SNR is as [68 dB and 76 dB] and [16 dB and 36 dB] after an ISL link of 1000 Km for
Fig. 5. Evaluation of SNR ratio w.r.t transmitted Power (dBm) with- and withoutSM module after an ISL link of 1000 Km at an operating wavelength of 1550 nm.
satellite transmitted power of [10 dBm and 20 dBm] with- and without- SM module respectively. The SNR ratio and total power received is also improved at varied Responsivity with SM module as shown in Figs. 6–7. An mprovement of 40 dB in both the evaluated parameters such as SNR ratio and total power received, after an ISL link of 1000 Km, is computed for Responsivity of 10 A/W with the use of SM module. It means that less power is involved with the use of SM module in transmitting the optical data over an ISL link of 1000 Km. In Fig. 8, the Q-factor of the IsOWC system is also plotted against ISL link length. The Q-factor is computed approximately as 16 to 18 in the range of ISL link of 100 Km–1000 Km with SM module. Alternatively, the Q factor decreases continuously from 22 to 2 in the range of ISL link of 100 Km to 1000 Km without using SM module. It is quite evident from our simulated results that a stable and acceptable improvement in Q factor can be achieved with the use of SM module after an ISL link of 1000 Km at an operating wavelength of 1550 nm.
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V. Sharma, N. Kumar / Optics Communications 286 (2013) 99–102
Fig. 6. Evaluation of SNR ratio w.r.t Responsivity (A/W) with- and without- SM module after an ISL link of 1000 Km at an operating wavelength of 1550 nm.
Fig. 8. Evaluation of Q-factor w.r.t ISL link between the two satellites with- and without- SM module at an operating wavelength of 1550 nm.
satellites at data rate of 2.5 Gbps with- and without- SM module. It is concluded from our simulated IsOWC system that the ISL link of 1000 Km with improved SNR ratio in conjunction with acceptable BER can be achieved by using the SM module. Also, less transmitted-power is required to transmit the externallymodulated data of 2.5 Gbps over an ISL link of 1000 Km at an operating wavelength of 1550 nm.
References
Fig. 7. Evaluation of total power w.r.t Responsivity (A/W) with- and without- SM module after an ISL link of 1000 Km at an operating wavelength of 1550 nm.
4. Conclusion In this work, we have designed an inter-satellite OWC system to establish an inter-satellite link of 1000 Km length between two
[1] Gerhard A. Koepf, Robert G. Marshalek, David L. Begley, Space Laser Communications: A Review of Major Programs in the United States, International Journal of Electronics and Communications (AEU), 56, Elsevier, 2002 232–242. [2] Roy Szweda, III–Vs Review, the Advanced Semiconductor Magazine 14 (8) (2001) 46. [3] A. Jamalipour, Low Earth Orbital Satellites for Personal Communication Networks, Artech House Publishers, Norwood, Mass, 1998. [4] SATCAT Boxscore, /http://celestrak.com/satcat/boxscore.aspS, June 2012. [5] Zhili Sun, Satellite Networking—Principles and Protocols, University of Surrey, John Wiley & Sons, UK, 2005. [6] J.C. Palais, Fiber Optic Communications, 5th Edition, Prentice Hall, Upper Saddle River, New Jersey, 2005. [7] IBM: Optical Modulator, Retrieved April 29, 2009, from /http://www03.ibm. com/press/us/en/photo/22808.wssS. [8] W. Popoola, Z. Ghassemlooy, M.S. Awan, and E. Leitgeb, Atmospheric channel effects on terrestrial free space optical communication links, ECAI 2009, 3rd International Conference on Electronics, Computers and Artificial Intelligence, Pitesti, Omania, 3rd–5th July, 2009. [9] Aniceto Belmonte, Joseph M. Kahn, Journal of Optical Communication and Networking 3 (11) (2011).