The st UTS-VNU Research School Advanced Technologies for IoT Applications Title All-Optical Two-Way Relaying Space Laser Communications for HAP-based Broadband Backhaul Networks Author Names and Affiliations Abstract Minh Q Vu1, Hien T T Pham1, Ngoc T Dang1,2 of Telecommunications, Posts and Telecommunications Institute of Technology 2Computer Communications Lab, The University of Aizu, Aizuwakamatsu, Japan High-altitude platforms (HAPs), which are innovative systems for next-generation wireless communication systems, are being researched and developed rapidly The HAPs combine the advantages of both satellite communication systems and terrestrial free space optical (FSO) link In this research, we propose an all-optical two-way relaying space laser communication system for HAP-based broadband backhaul networks to increase the coverage area and to cope with unexpected disasters which occur between two terminals We also applied network coding scheme for our proposed system by using an optical XOR gate at HAP to increase security and have the faster speed of processing than an electrical one The numerical results of our proposed system’s performance are exhibited to prove the feasibility of ours Problem Statement Contributions We consider the transmission in the broadband backhaul networks of the mobile communications which are between base transceiver station (BTS) and core network (CN) Normally, we can use the optical fiber or the copper to connect BTS to CN Nevertheless, if it has disasters, e.g earthquakes, floods, etc., the fiber can be broken and the communications will be interrupted It is difficult for us to repair this fiber when many obstructions will appear from collapsed buildings, trees, etc Hence, we propose a solution to deal with these difficult situations by using HAP-based backhaul networks using all-optical two-way relaying space laser communications, where HAPs are aircraft or airships situated above the clouds at typical heights of 17 to 25 km [1], as shown in Fig We assume that our proposed dual-hop system is symmetrical Two Free-space Optical Ground Stations (GSs) which are connected to BTS and to CN, respectively HAP, which has a role as a relay, is also equipped with two FSO transceivers to APD APD Optical signal communicate with GSs When Ground Laser Electrical signal Laser Ground drive drive Decision Decision Station the data from two GSs to HAP, Station Circuit Circuit B A they will be transmitted through (GSA) OOK OOK (GSB) Modulator Modulator XOR XOR two several optical hard-limiter (OHL) to detect bit “1” or bit “0” d1 d2 d1 d2 using the threshold power Pth [2] Instead of applying a full-duplex two-way relaying system and being experienced optical/electrical/optical conversion, we will apply a half-duplex two-way relaying system and alloptical relaying techniques for HAP to reduce its weight and complexity The number of time slots in data transmission between GSA-HAP-GSB can be reduced by using network coding scheme which is carried out by an optical XOR gate on HAP and electrical XOR gates in GSs At last, we investigate the performance of our proposed system over atmospheric turbulence channel by deriving the formula of bit-error-rate (BER) of this system and simulating the last results 1Faculty ζ H L ζ Core Network Earthquake MS BTS Optical fiber Optical fiber High Altitude Platform (HAP) Fig All-optical Twoway Relaying Space Laser Communications for HAP System Model XOR Fig Overview of All-optical Two-way Relaying Space Laser Communications for HAP Results Channel Model Performance Analysis -The free space channel state - Pc is the probability that d1 is transmitted at hc hl GSA and d1 is received correctly at GSB L h exp -The path loss l P P P (0 | 0) P (0 | 0) P (0 | 0) P P (0 | 0) P (1|1) P (1|1) -The atmospheric turbulence P P (1|1) P (0 | 0) P (1|1) P P (1|1) P (1|1) P (0 | 0) 00 A HAP 10 A HAP 1 2( ) f (ha ) (ha ) ( )( ) 0.49 exp 1 (1 1.11 ) R 12/5 7/6 R 1 K , 0.51 exp 1 (1 0.69 ) R 12/5 5/6 R 1 - The Rytov variance for slant path optical communications H R2 2.25k 7/6 sec11/6 ( ) Cn2 (h)(h h0 )5/6 dh h0 - The altitude-dependent refractive index structure coefficient 10 w h C (h) 0.00594 105 h exp 27 1000 h h 14 2.7 1016 exp 1.7 10 exp 1500 100 n B HAP B HAP HAP B HAP B 01 A HAP 11 A HAP B HAP B HAP HAP B HAP B - We assume that our proposed system is symmetrical and so we have 1 Pc [1 PA HAP (1| 0)]2 [1 PHAP B (1| 0)] [1 PA HAP (1| 0)][1 PB HAP (0 |1)][1 PHAP B (0 |1)] 4 1 [1 PA HAP (0 |1)][1 PB HAP (1| 0)][1 PHAP B (0 |1)] [1 PA HAP (0 |1)]2[1 PHAP B (1| 0)] 4 Where P h h P th PA HAP (0 |1) PB HAP (0 |1) f ( )erfc t GS a l 20 2 b2 P PA HAP (1| 0) PB HAP (1| 0) erfc th 2 2 b Fig BER versus the threshold level (Pth) of OHL for the different transmitted powers from HAP to GSs with the transmitted power from GSs to HAP is 30 dBm Fig BER versus the threshold level (Pth) of OHL for the different transmitted powers from GSs to HAP with the transmitted power from HAP to GSs is 18 dBm dha 1 0 PHAP B (0 |1) PHAP B (1| 0) f (ha )erfc dha 20 ( ) 1 M Pt HAP hl 12 2qM 2 x ( Ph t a hl Pb ) f - Bit error rate: 0 k BT f RL 02 2qM 2 xPb f k BT f RL BER Pc Future work In the future, we are going to focus on studying the impact of laser beam on BER of our proposed system We also will consider the pointing error in our channel model to expand all of the cases which can cause bit errors Instead of using a HAP to transmit data between two terminal, we can deploy multi-hop HAP architecture to extend the transmission distance Fig BER versus the altitude of the HAP for the different transmitted powers from HAP to GSs with the transmitted power from GSs to HAP is 30 dBm TABLE I SYSTEM PARAMETERS c Fig BER versus the attenuation coefficient for the Fig BER versus the zenith angle for the different different transmitted powers from HAP to GSs with transmitted powers from HAP to GSs with the the transmitted power from GSs to HAP is 30 dBm transmitted power from GSs to HAP is 30 dBm Parameter Wind speed, w HAP altitude, H Wavelength, Zenith angle, Transmitter height, h0 Attenuation coefficient, Background noise power spectral density, N APD’s Parameters Avalanche Multiplication Factor, M Responsivity of APD, x (To calculate the excess noise factor F ( M ) M x) Bit-rate, B Load resistor, RL Optical bandwidth, B0 Temperature, T Value 21 m/s 20 km 1550 nm π/6 0.4 km-1 2.89x10-25 W/Hz 10 1.1 A/W 0.8 10 Gbps 50 Ω 125 GHz 298oK References [1] F Fidler, M Knapek, J Horwath and W R Leeb, "Optical Communications for High-Altitude Platforms," in IEEE Journal of Selected Topics in Quantum Electronics, vol 16, no 5, pp 1058-1070, Sept.-Oct 2010 [2] P V Trinh, N T Dang and A T Pham “All-optical relaying FSO systems using EDFA combined with optical hard-limiter over atmospheric turbulence channels,” IEEE/OSA J Lightw Technol., vol 33, no 19, pp 4132–4144, Oct 2015