Modeling and Performance Analysis of 10 Gbps Inter-Satellite-Link (ISL) In Inter-Satellite Optical-Wireless Communication (IsOWC) System between LEO and GEO Satellites

Modeling and Performance Analysis of 10 Gbps Inter-Satellite-Link (ISL) In Inter-Satellite Optical- Wireless Communication (IsOWC) System between LEO and GEO Satellites Tayy ab Mehmoood NUST, School of Electrical E ngineering and Computer Science Islamabad, P akistan tayyabjatoibaloch@g mail.com Nauman Ham eed Dept. of Telecommunication University of Engineeri ng & Technology Taxila, Pakistan Nauman112te@gmail.co m Abstract — Free space optical communication has merged the aspects of fiber optics and the wireless communication which are the most conqu ered and controlled telec ommunication technologies. M ost of the fea tures of fre e s pace optics (FSO) are interrelated to fiber op tics but the difference betw een the m is transmission medium , w hich is g lass in case of fi ber-optics and air/vacuum in c ase of FSO. In the near future, co mm unication between LEO & GEO satellites with each other which are orbiting the Earth will b e done by using inter-satellite op tical wireless co mm unication (IsOW C) systems. IsOWC syste ms is the most significant application of the FSO and it will be installed in the space in the near future because of its low input pow er, no licensing by ITU, low cost, light w eight, s ma ll size of the telescopes and very high data rates as compared to the radio fr equency (RF) satellite systems. In this research article, IsOWC system is designed between L EO and G EO sa tellites by using OPTI-System simulator w hich is not stat ed in past examined research works. Inter-s atellite link is established b etween satellites which a re separated by the distance of 40,000 Km at the bit rate of 10 Gbps. Index Terms — Free sp ace op tics, optical wireless communication, inter-satellite link, inter-satellite optical wireless communication system. I. I NTRODU CTION Since t he birth of human rac e, there has bee n a necessity of delivering messa ges from point A to remote po int B with reliability, security a nd speed of transferring m essage is of extreme impor tance. Later on, it was acknowledged that the fastest way o f communication was not a fastest horse but li ght. Hence, a net w ork o f lig ht towers was cr eated on the top of mountains i n ancient Gree ce. I nnovations and advancements in the field o f science and t echnology h ave fabricated tiny semiconductor devices e.g. laser dio de w hich p roduces a narrow beam of light in invisible b ands (1280 -1620 nm) or visible spectrum (400 -700 n m ). Optical wireless communication OWC is one of the most i mportant applications of communicati on based on laser. Free space optics (FSO) is t he only wireless tec hnology having data rat es in Gbps but v ulnerable to weath er conditions. FSO can be implemented in deep space due to un availability o f air in that atmosphere. Unlike Earth atm ospheric conditions, there is no such attenuation factor present in space. [1] Discuss the require ments to establi sh the optical i nter - satellite link ISL for satellite constellations. [2] suggest many schemes to establish the i nter-satellite li nk becau se high accuracy o f laser bea m positioning is essential to p rocess las er ISL, it also discuss t he di fferent method s and architectures o f free space optical co mmunications. Wo rld first truly deep space la sercom (laser co mmunication) was demonstrated by NASA and MIT Lincoln Laborato ry in 2003. Their mission is to demonstrate optical w ireless link of 3 -50 Mbps between Mars telecom orbiter and NASA satellite. This laser communication duplex lin k has a round trip time of 40 minutes. In this mission space terminal, telescope receive array and ground ter minal is developed by MIT Lincoln Laboratory. I n deep space optical w ireless co mmunication systems ca n be used to communicate with the space shuttles and the satellites to get the better performance than t he RF systems in terms of lo w co st, less p ower consumption of optical transmitter, low weight and with the sma ll antenna aperture size. LLCD (Lunar Laser Communications Demonstration) is the pro ject started b y the NASA and MIT Lincoln Laboratory in 200 9. T he main goal of LLCD p rogram is to de m onstrate high perfor man ce optical wireless duplex link of 622 Mb ps optical Do wnlink and 20 Mbps optical Uplink from a small ante nna terminal [3 -5]. Researchers and Engineers use amplified optical fiber transmitters, secure and p ower e fficient encoding and decoding methods, optical MZ mod ulators, coherent receivers, FEC( forward erro r correction) techniques and optical preamplifier at the receiver end in order to extend the link range of lasercom [6 ]. Today the highest cap acity communication satellite ViaS at -1has a data rate of 13 4 Gb ps. ViaSat-1 is launched from K azakhstan and it i s in GEO o rbit above No rth America [7]. At present 6967 satellites are in t he orbit and out of 6 967 s atellites o nly 1 328 activ e sa tellites a re orbiting th e earth [8]. Because of the co mmunication requirements of observatio n satellite s the numbers are increasing exponentially year by year. [9] Mod el the IsOWC link at d ifferent wavelengths, data rates and ranges between satellites at LEO and concl uded that performance o f the IsOW C link is badly affected b y increasing the data r ate and distance betwee n th e links. [ 10] investigated and m odeled the IsOWC systems bet ween to LEO satellite s at the data rate of 2.5 Gbps at the of 1000 Km. they compare 850 n m wavelength with 1550 nm wavelength and concluded that 850 nm w avelength gave better results in terms of S NR, Q factor and To tal Power at lo w transmitting power. Fig. 1: model of inter -satellite optical w ireless co mmuniation link between GEO & LEO satellites [11] modeled t he I sOWC syste ms and investigated t he syste m performance with a nd without square root module at the receiver end and co ncluded that accep table BER and improved SNR can be ac hieved by using Square root module. Thi s paper is p resented the model simulatio n and performance analysis of inter-satellite op tical wireless co mmunication IsOWC s ystem between GEO and LEO orbit satellites at the data rate of 1 0 Gbps over a space range of 4 0,000 Km. earlier research wo rk did not exceed the data rate abo ve 1 Gbps for GEO & L EO inter-satellite link (ISL). This research article is divided in to three sections. Section 2 covers the s ystem d escription and parametric configuration o f inter-satell ite link. Section 3 covers the results o f IsOWC syste m and section 4 concludes the research work. II. I NTER - SAT ELLITE MODEL DESCRI PTION The IsOW C system is modeled in thi s p aper which co mprises of three basic co mmunication co mponents wh ich ar e optical transmitter, pro pagation model an d the op tical receiver which is presented in figure 2. Inter -satellite link IS L is established between GEO and LEO satellite whic h is shown in f igure 1. IsOWC system is u sed to communicate with each other in full - duplex mode and t his s ystem is designed and simulate in OPTI-SYSTEM simulator. This full-duple x sys tem co nsists o f two si m plex s ystems; i n order to investigate the IsOW C system performance single simplex system is studied. Wher e optical tr ansmitter is in GEO satellite and o ptical recei ver is in LEO satellite a nd optical light at infrared wavelength is used to communicate bet ween i nter-satellite links ISL. IsOWC i s a kind of free space optics in which propagation medium is assumed a s vac uum and all the attenuation factors d ue to atmosphere ar e considered as zero. OW C is a little d issim ilar from optical fiber communication O FC in terms of propagation channel. Fre e space op tics FSO is also abbreviated as laserco m (laser communication). Tele metry, tracking and control TT&C system offer funda mental communication path to and from the sate llite a nd it is the only way to examine and control the satellite f unctions. TT&C subsystem of a sate llite offer a link bet ween the facilities on the Earth a nd the satel lite itself a nd the main goal of TT&C function i s to guarantee that the satellite i s workin g proper ly. Irrespective o f the applicati on of the TT&C s ubsystem is essential for all sate llites bec ause i t is a fundamental part of the spacecraft b us. Telemetry p erforms the operation o f Health monitoring of t he satellite and it collect, process and transmit the data from many satelli tes subsystems. Tracking and ranging is respo nsible for the satellite’s pr ecise location by transmitting, processing and receiving the ranging signals. Many of the satellite functions ar e automated and do not need ground station involvement. Pro per control of a spacec raft via receiving the commands, processing a nd then i mplementat ion of the commands fro m the satellite or from the ground statio n are the majo r operations which are done b y the control TT &C system. Tran smitter o f the optical signal receives the electrical data sequence from t he TT &C system o f satellite. N RZ pulse ge nerator is used alo ng with MZ -modulator w hich g ets the input from the CW laser . E DFA optical a mplifier is used to amplify the optical signal b efore the IsOWC link and then transmit the signal in space. In our proposed model we suppose that there is n o meteorite or any other space dust particles in the p ath of o ptical signal. CW laser of power of 15 dBm and li newidth of 10 MHz is used in our su ggested optical system. Op tical anten nas of tran smitter and r eceiver has an aperture d iameter of 20 c m and the gains of optical transmitter and receiver are zero. Optics efficiency o f optical transmitter and receiver is equal to one. Optical transmitter and receiv er antennas are supposed to be ideal and p ointing error of both antennas is 0 urad . Propagation delay and ot her additional losses d ue to mispointing ar e also supposed as zero . Simulation Parameters of the IsOWC system i s g ivern belo w in table 1. Fig. 1: Block diagram of IsOW C System: PBRS -Pseudo bit random sequence generator, NRZ- non return to zero, CW-Continuous wav e laser, MZM-Mach zander modulator, TT&C-telemetry tracking and communication, APD-Avalanche Photo-detector. TABLE 1 : SI MULATION PA RAMETERS OF ISOWC SY STEM Frequency 860 nm Range 40,000 Km Data rate 10 Gbps Sequence length 32 bits Samples per bit 64 Number of Samples 2048 Extension Ratio of MZM 30 dB Dark current 10 nA III. RESULT S AND DI SCUSSI ON In reference si mulation, wavelength of 8 60 nm is used in CW laser with t he input po wer of 15 d Bm . Line width o f 10 MHz is used in Optical transmitter of reference simulation. Data sequence from the TT&C subsyste m is passes through the NRZ pulse g enerator. MZ-modulator is used to externall y modulate the o ptical signal. Optical a m plifier is used befo re the OWC channel to amplify the optical trans m itting sig nal with the g ain of 3 0 dB and the noise f igure of 4 dB. OWC is considered as attenuatio n free channel because of vac uum. Range of t he OWC cha nnel is of 40,000 Km with the a ntenna diameter of op tical transmitter and rec eiver terminal is of 20 cm. On the op tical recei ver sid e, Avalanche photo d etector is used to detec t the lig ht with the ionization ratio of 0 .9. Lo w pass Bessel filter with t he cu t-off frequency of 0.7 5*bit rate with the order 4 is used to f ilter the electrical signal. After filtering, the electr ical signal is fed into the TT &C subsyst em of LEO satellite to anal y ze the signal quality, signal po wer, BER an d jitter in the signal. Figure 3 sho ws the eye d iagram of the reference simulation, it has the Q factor of 30 and t he BER of 2.933e -201. Eye diagra m has the height of 7.133e - 005 . Fig. 3: Eye diagram of refere nce simulati on o f IsOWC system at the wav eleng th of 860 nm . Fig. 4: (a ) shows t he eye diagram of IsOWC sy stem at wa veleng th of 1340 nm, (b ) show s the eye diagram of IsOWC sy stem at wave length of 145 0 nm, (c) sh ows the eye diagram o f IsOWC syste m at wavele ngth of 1550 nm, (d) show s the eye diag ram of IsOWC system at w avele ngth of 16 50 nm. By keeping all the para m eters constant, we c hange the wavelength of r eference simulation from 860 nm to 14 50 nm, 1340 nm, 1 550 nm and 165 0 nm. It is s een from f igure 4 that with the increase i n optical signal wavele ngth the signal quality factor a nd total signal po wer decreases. BE R and jitter of the IsOWC syste m increases graduall y as shown in figure 4. At w avelength of 134 0 nm, the Q -factor of the s ystem decreased to 14 .2005 and BER o f the IsOWC increased to 1.746e -52. Where signal p ower is also decreased to -64.9 dBm as shown in figure 4(a). At wa velength of 14 50 nm, t he Q - factor of the system dec reased to 13.265 and BER of the IsOWC increased to 1.84e -040. Where signal po w er is a lso decreased to -66.2 7 d Bm as sho wn in figure 4(b). At wavelength of 1550 nm, the Q -factor of the syste m decreased to 11.75 and BER of the IsOWC incre ased to 3 .26e-032. Where signal po wer is also de creased to 67 .43 dBm as shown in figure 4 (c). At w avelength of 1 650 nm, the Q -factor o f the system decreased to 10.464 and BER of the IsOWC increa sed to 6.31e-02 6. Where signal power is also decreased to - 68. 5201 dBm as shown in figure 4 (d). Fig. 5: (a) sh ows th e e ye di agram of IsOWC s yste m with the aperture diameter of ant enna is 15 cm, (b) shows the ey e diagram of IsOWC system with the aper ture diameter o f antenna is 30 cm . Antenna aperture diameter of transmitter and recei ver of both satellites has the si gnificant i m pact on the s atellite speed and drag. Because b y in creasing the aperture diameter of antenna the mass, drag a nd size of the satellite payload increases. In this pap er, excep t antenna aperture dia meter all the par am eter s are kept constant. By decreasing t he antenna ap erture dia meter from 20 cm to 15 cm, a s a res ult the mass, size a nd drag of the satellite decreases which is a good sign but by d ecreasing the aperture d iam eter t he Q-facto r and the signal po wer is also decreased to 12 .05 and -67.19 d Bm as sho wn in figure 5 ( a). Figure 5 (b) sho ws the ey e diagram of the IsOW C system simulation i n which antenna aperture diameter is 30 c m. b y increasing the aperture dia meter although the Q -factor and t he signal po wer is i ncreased as shown in figure 5 (b) but size, mass and drag of the pa yload is also increased. Fig. 6: (a) shows the eye diagram of the IsOW C system at the distance of 50,000 Km. (b) shows the eye di agram of t he IsOWC system a t th e distance of 60,000 K m. By keeping all the par ameters, range of the ISL is changed to see the effect o f d istance on the IsOW C system. To see the effect of distance, syste m is simulated at 50,00 0 km and at 60,000 Km. it is noticed t hat b y increasing the dist ance of ISL the q uality and total signal po w er o f the optical signal is decreased. By increasing the distance from 40,000 Km to 50,000 Km t he si gnal p ower is dec reased to -61.08 dBm a nd the Q -f actor is decreased to 21 .80 as sho wn i n figure 6 (a). When the dista nce is further increase to 60 ,000 Km the Q - factor is dec eased 1 6.23 and the total signal power is decreased to -64.24 dBm. C ONCLU SION I n this resear ch article, IsOWC s ystem is establis hed between LEO and GEO satellite over the distance of 40,0 00 Km and at the data rate of 10 Gbps. From this si mulation it is co ncluded that sys tem has the better Q-f actor and the total signal po wer in case o f 860 n m rather than 1450 nm , 1550 nm or 1650 nm . I t is also co ncluded t hat aperture diameter of the telescope and the ra nge o f the ISL link has a significant effect on the q uality of the optical signal. R EFERENCES [1] Baister, G. C., and P. V. Gatenb y. "Why optical communication links are needed for future satellite constellations." (1996): 6- 6. [2] Mulholland, John E., and Sean Anthony Cadogan. "Intersatellite laser crosslinks." Aerospace and Electronic Systems, IEEE Transactions on 32.3 (1996): 1011-1020. [3] Boroson, Don M., et al. "Overview and status of the lunar laser communications demonstration." SPIE LAS E . International Society for Optics and Photonics, 2012. [4] Robinson, Bryan S. , et al. "The lunar laser co mmunications demonstration." Space Op tical Systems and Applications (ICSOS), 2011 International Conference on . IEEE, 2011. [5] Boroson, Don M., et al. "T he lun ar laser comm unications demonstration (LLCD)." Space Mission Challenges for Information Technology, 2009. SMC-IT 2 009. 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