Modeling and Performance Analysis of DWDM Based 100 Gbps Low Power Inter-satellite Optical Wireless Communication (LP-IsOWC) System

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1 ISSN(Print): ISSN(Online): DOI: /STSP Volume 2, Number 1, January 2015 SOP TRANSACTIONS ON SIGNAL PROCESSING Modeling and Performance Analysis of DWDM Based 100 Gbps Low Power Inter-satellite Optical Wireless Communication (LP-IsOWC) System Shekhar Saini, Amit Gupta* Chandigarh University, Punjab, India *Corresponding author: Abstract: Optical wireless communication (OWC) could be an influential communication method in near future for inter-satellite communication with high data rate. In this paper, a high capacity dense wavelength division multiplexing (DWDM) technique based LP-IsOWC System is proposed and its performance analysis has been done for various parameters. Role of EDFA is also analyzed on the proposed system for its acceptability in the given system. It is found that EDFA helps in reducing BER and improving Q-factor. Keywords: BER, DWDM, EDFA, IsOWC, OWC 1. INTRODUCTION In todays world, the longing for high speed and secure inter-satellite communication is increasing day by day. OWC emerged as an innovative substitute to the present radio communication for inter-satellite communication. High speed and secure communication makes OWC a promising technology for inter-satellite communication [1]. The IsOWC takes place at a very low wavelength, which results in achieving much narrower beam width. Line of sight and synchronization between optical transmitter and receiver terminal is the basic need for efficient IsOWC. Optical terminals are smaller, lighter in weight and consume less power as compared to the radio terminals [2]. In order to transmit information at high data rate with low BER over a longer transmission range in IsOWC, the amplification of the optical carrier signal or high input laser power is recommended [3]. In case of amplification, EDFA plays a vital role in space laser communication. EDFA introduce small noises to the communication system, which are unresponsive to the polarization of the optical signal [4]. On the other side, with the increase in input laser power many design issue arises like complexity, cost, large weight, energy consumption and increase in size of the system [5]. In previous work, comparison of NRZ and RZ modulation schemes is presented for IsOWC and RZ is recommended for longer IsOWC [6]. RZ modulation scheme is best for long distance communication while NRZ modulation scheme is suitable for short distance communication and it is cheaper and less complex in comparison to RZ [7]. A LP-IsOWC system is proposed and optimal modulation format is investigated [8]. Ultra high capacity DWDM system is designed and simulated for 3 dbm input laser power for 50 km 200 km [9]. In the proposed 20-channel DWDM based LP-IsOWC model the distance is increased to 1,000 km and the input laser power is 1

2 decreased to 0 dbm as the increase in number of channel will cause four wave mixing (FWM) effect. The EDFA is employed as booster amplifier and NRZ modulation format is used. The model wavelength is set from 1541 nm nm for 20 DWDM channels with 0 dbm input laser power. The model description is reported in Section 2 followed by the simulation results discussion in Section 3. The paper is concluded in Section MODEL DESCRIPTION In this paper, inter-satellite link (ISL) is modeled using Optiwave Optisystem TM 11.0 simulator. The IsOWC system receives information data from Telemetry, Tracking and Communication (TT&C) system that then modulated with an optical signal generated by a CW laser diode. The output light generated by laser diode is coherent, monochromatic and has high radiance, which makes it suitable for IsOWC. The output of 20 channels multiplexed with a DWDM multiplexer. The multiplexed signal further amplified with EDFA. The amplified signal transmits through optical wireless channel and then de-multiplexed at the receiver satellite with DWDM de-multiplexer. The optical wireless channel is free space, which considered as vacuum, free from atmospheric losses. The receiving satellite end consists of avalanche photo detector (APD) and a low pass filter (LPF) for each channel. The performance of an IsOWC is analyzed by observing BER and Q-factor value. The forward error correction (FEC) threshold is BER of less than or equal to for efficient communication system corresponding to Q value of 6.8 or greater for communication purpose [9]. The received power is given by Equation 1 [10], ( ) λ 2 P R = P T η T η R G T G R L T L R (1) 4πZ P R : Received Power, P T : Transmitted Power, η T : Optics efficiency of the transmitter, η R : Optics efficiency of the receiver, G T : Transmitter Gain, G R : Receiver Gain, L T : Transmitter pointing loss factor, L R : Receiver pointing loss factor, λ: Operating wavelength, Z: Distance between transmitter and receiver. The system model is as shown in Figure 1. Figure 1. DWDM-IsOWC system. 2

3 Modeling and Performance Analysis of DWDM Based 100 Gbps Low Power Inter-satellite Optical Wireless Communication (LP-IsOWC) System This paper focuses on studying the system performance due to EDFA with low input laser power. Some simulation parameters are in Table 1. Table 1. Simulation Parameters CW laser power (single channel) 0 dbm Laser Linewidth 5 MHz Extinction ratio 30 db WDM Channel Wavelength 1541 nm-1560 nm EDFA Forward Pump Power 0.8 W EDFA Backward Pump Power 0.2 W Dark Current 10 na Ionization ratio 0.9 Cutoff frequency of LPF 7.5 GHz Optical Receiver Antenna Diameter 15 mm Optical Transmitter Antenna Diameter 15 mm Sequence length 128 Samples per bit 64 Transmitter optics efficiency 0.8 Receiver optics efficiency 0.8 Transmitter pointing error 1.1 µrad Receiver pointing error 1.1 µrad Additional losses considered 1dB 3. RESULTS AND DISCUSSIONS An IsOWC system proposed with the help of OPTI-SYSTEM TM simulator. The distance between two satellites is 1,000 km. 20 DWDM channels each transmitting optical data at 5 Gbps will leads to multiplication of capacity of the system. By employing EDFA between the two communicating satellites the value of BER and Q-factor is obtained. Figure 2. Evaluation of BER at different WDM channels. 3

4 Figure 2 depicts impact of EDFA on all channels of the presented DWDM based 100 Gbps IsOWC system. The log of BER is used instead of BER for simplification. The BER tells about the number of error bits received on the receiver side. It can be observed that BER reduces with the implementation of EDFA. The min BER achieved is Figure 3. Evaluation of Q-factor at different WDM channels. Figure 3 depict impact of EDFA on Q-factor of the presented system. Q-factor tells about the quality of the signal received. It can be observed that the Q-factor improves due to EDFA. It means that EDFA plays a vital role in IsOWC and deserve employment in space laser communication. The max Q factor achieved is at channel having 1559 nm wavelength. The eye diagram of channel 1, 7, 14, 20 are as shown in Figure 4 which acknowledge that signal with considerable Q-factor has good eye diagram with higher eye-heights. Eye diagram tells about the inter symbol interference and the FWM effect. Wide eye opening is obtained at every channel. 4. CONCLUSION In this paper, a DWDM based IsOWC system is presented. A low power optical link of 1,000 km between two satellites is established for performance analysis. The data rate achieved is 100 Gbps. It can be concluded from the proposed system that EDFA proves beneficial in reducing BER and increasing Q factor. With laser power of 0 dbm min BER could be achieved. In future scope of this work, advanced modulation formats could be employed for optimization of the system and data carrying capacity could be enhanced by increasing the number of channels. In future a DWDM based Optical Burst Switching (OBS) can be used as with IsOWC for next generation transport network [11 13]. 4

5 Modeling and Performance Analysis of DWDM Based 100 Gbps Low Power Inter-satellite Optical Wireless Communication (LP-IsOWC) System Figure 4. Eye diagram of channel 1, 7, 14, 20. References [1] O. Wilfert, H. Henniger, and Z. Kolka, Optical communication in free space, in 16th Polish-Slovak-Czech Optical Conference on Wave and Quantum Aspects of Contemporary Optics, pp , International Society for Optics and Photonics, [2] J. Kaufmann, Free Space Optical Communications: An Overview of Applications and Technologies, [3] A. H. Hashim, F. D. Mahad, S. M. Idrus, and A. S. M. Supa at, Modeling and performance study of intersatellite optical wireless communication system, in Photonics (ICP), 2010 International Conference on, pp. 1 4, IEEE, [4] M. Pfennigbauer and W. R. Leeb, Optical satellite communications with erbium doped fiber amplifiers, Space Communications, vol. 19, no. 1, pp , [5] V. Sharma and A. Kaur, Modeling and simulation of long reach high speed inter-satellite link (ISL), OptikInternational Journal for Light and Electron Optics, vol. 125, no. 2, pp , [6] N. Liu, W. Zhong, Y. He, K. Heng, and T. Cheng, Comparison of NRZ and RZ modulations in laser intersatellite communication systems, in Proceedings of the 2008 International Conference on Advanced Infocomm Technology, p. 55, ACM, [7] J. Singh and N. Kumar, Performance analysis of different modulation format on free space optical communication system, Optik-International Journal for Light and Electron Optics, vol. 124, no. 20, pp ,

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