Link Adaptation and Carriers Detection Errors in Multibeam Satellite Systems with Linear Precoding Anxo Tato, Stefano Andrenacci, Symeon Chatzinotas, Carlos Mosquera atlanTTic Research Center, University of Vigo SnT, University of Luxembourg September 11, 2018 Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 1 / 18
Introduction High Throughput Satellite (HTS) at Ka-band • Multibeam satellite + Linear Precoding + Link Adaptation Full Frequency reuse, 245 beams Imperfect Channel State Information at the Transmitter (CSIT) • Carriers detection errors = Nullification Unicast Random interbeam scheduling Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 2 / 18
Introduction CSIT: Estimated channel Actual channel available at GW Actual Estimated precoded precoded SINR SINR Precoding matrix _ + LUT MODCOD Lookup Table SINR LUT SINR absolute error ¿Allows quasi-error-free Selected transmission with Modulation and MODCOD this MODCOD? Coding Scheme Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 3 / 18
System model Signal model: y = Hx + n = HWs + n Channel model: ESA’s 245 beams radiation pattern ˆ H : Imperfect CSIT due to... Nullification Gaussian estimation errors Linear Precoding: MMSE with Sum Power Constraint (SPC) � − 1 � H H + 1 W = η · ˆ H ˆ ˆ H H (1) snr I N Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 4 / 18
Nullification effect CSIT: Estimated channel Actual channel available at GW CSIT: Estimated channel available at GW Actual channel #1 #2 #3 Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 5 / 18
Nullification description Estimation of CSI coefficients: Asynchronous systems → I/C ≈ − 15 dB Synchronous systems : → I/N ≈ − 15 dB Real system : 30 25 Carrier is nulli fi ed 20 C/I (dB) 15 10 Carrier is estimated 5 0 -10 -5 0 5 10 15 20 C/N (dB) Architecture of the receiver CSI estimation performance for CSI detection and estimation Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 6 / 18
Example of nullification Carrier to Noise in a subset of 9 beams Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 7 / 18
Number of estimated channel coefficients Total number of coefficients per channel vector = 245 DVB-S2X standard allows to report up to 32 coefficients Number of estimated coefficients with nullification: 1-15 Estimated coefficients 200 14 180 160 12 140 10 120 100 8 80 6 60 4 40 20 2 50 100 150 200 250 300 Results with real nullification Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 8 / 18
SINR absolute error due to nullification SINR calculated by the GW CSIT: Estimated channel Actual channel available at GW | ˆ h ⊥ k w k | 2 ˆ sinr k = j � = k | ˆ k w j | 2 + N 0 h ⊥ � Actual Estimated precoded Actual user SINR precoded SINR SINR Precoding matrix _ | h ⊥ k w k | 2 + sinr k = k w j | 2 + N 0 j � = k | h ⊥ LUT � MODCOD Lookup Table SINR LUT SINR absolute error in dB SINR absolute error ¿Allows quasi-error-free Selected transmission with Modulation and MODCOD this MODCOD? Coding Scheme e k = 10 log 10 ˆ sinr k − 10 log 10 sinr k Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 9 / 18
System parameters Parameter Value Satellite orbit GEO Downlink frequency Ka-band (20 GHz) Number of beams 245 Color scheme Full frequency reuse Fading No fading Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 10 / 18
Interbeam scheduling Unicast : only one user served per beam in each frame Interbeam scheduling: Users selecting user randomly among... central positions of the beam within a radius of 2 / 6, 3 / 6 or 4 / 6 of the total beam radius all beam positions Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 11 / 18
Maximum of the SINR absolute error (global results) Comparison different Synchronous nullification nullifications Maximum error over the whole satellite coverage [SYNC] Maximum error over the whole satellite coverage 3 7 Users within a radius of 2/6 Users within a radius of 2/6 Users within a radius of 3/6 Users within a radius of 4/6 Users within a radius of 3/6 2.5 All beam positions 6 Users within a radius of 4/6 All beam positions 5 2 SINR absolute error (dB) SINR absolute error (dB) 4 1.5 3 1 2 0.5 1 0 -10 dB -15 dB -20 dB -25 dB I/N null. threshold (dB) 0 ASYNC I/C = -15 dB REAL SYNC I/N = -15 dB Nullification type Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 12 / 18
Complementary CDF of the error Margin required to guarantee a given Frame Error Rate (FER) in all the coverage Error over the whole satellite coverage 10 0 10 -1 10 -2 CCDF: P(error > x) 10 -3 10 -4 Users within a radius of 2/6 10 -5 Users within a radius of 3/6 Users within a radius of 4/6 All beam positions 10 -6 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 SINR absolute error (dB) High capacity losses due to the required large margins! Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 13 / 18
Geographical distribution of the error Maximum error per position when in the rest of the beams a random user is scheduled from the 3x3 central users Map of the SINR maximum error per beam over 1,000 realizations with MMSE-SPC precoder, real nullification and scheduling users from inner circle of radius 2 / 6 Best solution: independent margin per user to avoid performance loss of worst-case margin. Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 14 / 18
Countermeasure: link adaptation with adaptive margin CSIT: Estimated channel Actual channel available at GW Actual Estimated precoded precoded SINR SINR Precoding matrix _ + LUT MODCOD Lookup Table SINR LUT SINR absolute error ¿Allows quasi-error-free Selected transmission with Modulation and MODCOD this MODCOD? Coding Scheme Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 15 / 18
Countermeasure: link adaptation with adaptive margin Add to the SINR calculated by the gateway an adaptive margin, independent for each user, updated with its ACK/NAK exchange Note: these are not used for retransmission purposes Calculated by the gateway LUT Selected SINR DVB-S2X ModCod ModCods Updated with Margin ACK/NAK exchange ACK: Margin ✘ Margin + ∆ACK NAK: Margin ✘ Margin - ∆NAK ∆ACK p 0 = 1 − p 0 , p 0 = Target FER (Typically 1E-5) ∆NAK Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 16 / 18
Simulation results Scenario: Continuous transmission of frames to 10 users located in 10 non-neighbour beams scattered over all Europe. Target FER : p 0 = 10 − 3 , 10 − 4 , 10 − 5 Results: Without adaptive margin FER ≫ Target value p 0 With adaptive marging Experimental FER of users is within 90 − 110% of the target FER Avoiding the performance loss of a global fixed margin. Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 17 / 18
Thanks for your attention! The research was done during a stay at the Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, supported by the project SatNEx-IV, co-funded by the European Space Agency (ESA). Anxo Tato (atlanTTic, UVigo) ASMS/SPSC 2018 Berlin September 11, 2018 18 / 18
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