HTS (Terabit Capacity) Systems: Will Interference be a Limiting Factor? Ifiok Otung Scope Mobile and Satellite Communications at University of South Wales (USW) Key Strategies and Trade offs in HTS Cross Polarisation Interference Co Channel Interference Role of Operational Experience and Data 1
MSc in Mobile & Satellite Communications at USW Six taught modules and a major project Satellite Communication Satellite Networking Digital Communication systems Applied DSP Mobile communication technologies Product innovation and entrepreneurship Our main driver in scholarship: Complexity is always a combination of simplicity. The art of solving a complex problem is to break it into its simple parts. Caveat: Simplism ignores underlying complexity. So don t be remiss or slipshod 2
You ask, what s remiss? 12 9 3 6 Apart from 6 o clock, at what time instants will the minute and hour hands of a clock be exactly 180 apart? If you answered, 5 past 7 of course!, that s remiss! Tx Message MSc Skill Example 1: Digital Communications FEC Coding APSK Mod AWGN + FEC Decoding APSK Demod Rx Message Tx message BER Measure BER 3
MSc Skill Example 2: Satellite Communication VSAT Network Design 3 4 N 2 System dimensioning Links availabilities Links bit rates Number of VSATs Access methods Protocol selection etc. 1 Hub Research in Mobile & Satellite Communications at USW Design of satellite communication systems for resilience, and spectrum & energy efficiency Interference mitigation in HTS systems Spatio temporal signal processing Mobility enhancement Ka/V band link measurements Channel modelling and short term fade prediction Adaptive modulation & coding Ka band Earth observation & surveillance 4
Main Facilities Satellite earth stations Weather stations Anechoic chamber Simulation platforms (STK, MATLAB/SIMULINK, FEKO, OPNET, etc.) Wireless and Digital Communications Labs. Earth Stations: Outdoor Units USW Campus Chilbolton Observatory 5
Avenues for collaboration with industry Internship 16 week major project Industrial Lecture Series Joint R&D projects Research Example: Employing time diversity (TD) to avert total link outage in live satellite broadcast during intense rain 6
26/06/2015 IRG 2015 Eutelsat Workshop, 25 26 June, Eutelsat HQ, Paris, France Time diversity solution being developed in our Group IRG 2015 Eutelsat Workshop, 25 26 June, Eutelsat HQ, Paris, France 7
TD Protocol Scope Mobile and Satellite Communications at University of South Wales (USW) Key Strategies and Trade offs in HTS Cross Polarisation Interference Co Channel Interference Role of Operational Experience and Data 8
Information Transmission: Fundamental Trade off We can transmit digital information at bit rate R b using a bandwidth B (Hz): R b rlog 2 M B 1 But we must provide: E N b o bits per second 1 4 1 1 10log10 M 1 db log2 M Impossible is a lie peddled on the back of a wrong method. Terabit capacity at Ka band means achieving R b = 1000 Gb/s in a bandwidth of 2.5 GHz That would require operating at bandwidth efficiency 500 b/s/hz with received power requirement of E b /N o 1400 db????? Impractical!!!! 9
To do HTS we must find ways to eat our cake and have it too HTS System: Strategies Allocated bandwidth B sliced into K sub bands (or colours) and a colour assigned to each of the N b beams that totalise coverage Thus multi beam coverage, i.e. multiple reuse of same frequency, with reuse factor = N b /K Illustrated below for K = 3 Dual polarisation further doubles reuse factor and hence capacity 10
HTS System: Cluster Combinations K = 3 K = 4 K = 7 Decreasing Capacity Increasing Interference HTS System: User link bandwidth requirement for N b = 200, K = 3, M = 32, r = ¾ (diamond), 4/5 (circle) and 9/10 (square), and = 0.1 (solid) and 0.2 (dashed) 3 2.5 Bandwidth (GHz) 2 1.5 1 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Maximum Data Rate (Tbps) 11
HTS System: User link bandwidth requirement for N b = 200, K = 3, M = 64, r = ¾ (diamond), 4/5 (circle) and 9/10 (square), and = 0.1 (solid) and 0.2 (dashed) 2.5 2 Bandwidth (GHz) 1.5 1 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Maximum Data Rate (Tbps) HTS System: User Link Transmit Power Requirement (Sat. Ant = 4.5 m; UT Ant. = 0.6 m; f = 20 GHz) Transmit Power (dbw) 42 41.5 41 40.5 40 39.5 32APSK (3/4) 32APSK (4/5) 32APSK (5/6) 32APSK (9/10) 64APSK (3/4) 64APSK (4/5) 64APSK (5/6) 64APSK (9/10) 39 38.5 38 12 13 14 15 16 17 18 Es/No (db) 12
Operational Plesio-HTS System Examples Hylas-2* Ka-Sat** ViaSat*** Number of spot beams 24 82 72 Data capacity (Gbps) 50 90 140 EIRP (dbw) 62??? 60.7 Number of gateways??? 10 17 *www.avantiplc.com/hylas2/# ** http://www.eutelsat.com/files/contributed/news/media_library/brochures/ka-sat-professional-services.pdf ***www.viasat.com Cross Polarisation Interference H & V polarisations transmitted b a Anisotropic medium a c a x b c b x Received XPI = 20log a b db; XPI = 20log b a db v c x h c x How clean is the receive channel? How clean is the XPDv = 20log ac ax db; XPDh = 20log bc bx db transmit system? Depolarisation induced interference depends on Inherent antenna isolation Co polar attenuation Path elevation angle Frequency of operation and tilt angle 13
XPD on 19.7 GHz link with 29.3 elevation and 7.6 tilt angle 45 Atmosphere only 40 35 XPD (db) 30 25 20 Atmosphere + Antenna effect 15 10-2 10-1 10 0 Percentage of time, % Link Parameters Employed in Computations Frequency 19.7 GHz Satellite EIRP 61.5 dbw Antenna diameter 2m Modulation QPSK (CNR = 13.6 db for BER of 10-6 ) Minimum E-S antenna XPD ES 25 db Minimum Satellite antenna XPD SAT 30 db Location 51.59 o N, 3.33 o E, 86m Elevation angle 29.30 o Polarisation Tilt angle 7.59 o 14
Link CNIR of single polarised (solid line) and dual polarised (dashed line) systems for various antenna sizes 35 30 25 20 CNIR (db) 15 10 5 4m 2m 0 0.6m -5 10-2 10-1 10 0 Percentage of time, p (%) Co channel Interference (CCI) Interference from other channels using the same frequency eliminates the possibility to increase frequency re use factor indefinitely K 3 CCI sets a limit on the capacity of multi beam satellites 15
CCI: Computation Parameters 30 GHz Uplink parameters Values 1 P t, Earth Station Output Power 23.01 dbw 2 G t E S Antenna Gain 54.00 dbi 3 G r, Satellite Antenna Gain 35.76 db 4 L s,freespaceloss 213.87 db 5 L ant,edgeofbeamloss 3.0dB 6 L a,clearairloss 0.8 db 7 L m, Miscellaneous Losses 0.5 db 8 B, Noise Bandwidth (27MHz) 74.31dBHz 9 T sys, Transponder Noise Temperature (500K) 26.99 dbk 20 GHz Downlink parameters Values 1 EIRP, Satellite 61.5 dbw 2 G r,e SAntenna Gain 54.00 dbi 3 L s,freespaceloss 210.34 db 4 L ant,edgeofbeamloss 3.0dB 5 L a,clearairloss 0.5 db 6 L m, Miscellaneous Losses 0.5 db 7 T sys, System Noise Temperature (150K) 21.76 dbk 8 B, Noise Bandwidth (27MHz) 74.31dBHz CCI: Computed Impact 16
Our Interference Research: Immediate Objectives To reliably compute interference in terabit capacity HTS due to cross polarisation and cochannels To develop effective interference mitigation techniques that enable realisation of terabit capacity HTS. Operational Experience and Data How do we validate computational models and results? How do we test and fine tune new interference mitigation algorithms? Is there operational experience with this type of interference in current plesio HTS systems? Do data exist from which this type of interference can be directly extracted? Can we define signal processing steps which we can employ to deduce this type of interference from existing operational data? 17
Final Words Interference does cost. Let s use historical operational data to take the guesswork out of this cost estimate. Again using operational data, let s analyse interfering signal characteristics in order to extract salient features leading to possible auto classification and hence more userfriendly operational tools. Acknowledgement Two of our researchers Leshan Uggalla and Abdulkareem Karasuwa contributed to some of the slides used in this presentation 18
Thank you Live in hope for the best, design in fear of the worst. 19