ESA advanced coding and modulation performance under realistic channel conditions Massimo Bertinelli – ESA/Estec Paolo Burzigotti – ESA/Estec Guido Montorsi - PoliTo Enrico Vassallo – ESA/Esoc 27 October 2009 1
Outline • Introduction • Channel impairments • Simulation approach • Performance assessment • Conclusions • References 27 October 2009 2
Introduction • ESA Red/Orange book specifies a new coding and modulation scheme – SCCC – QPSK, 8PSK, 16-,32- and 64-APSK, with BICM • Action on ESA to investigate SCCC performance under realistic channel impairments – As agreed with CCSDS agencies 27 October 2009 3
Channel impairments (1) • Non-linear distortion – AM/AM and AM/PM characteristics of European (non-linearized) TWTA 26GHz technology 0 0 -2 -10 -4 -20 Phase[deg] -6 OBO[dB] -30 -8 -40 -10 -50 -12 -14 -60 -20 -15 -10 -5 0 5 10 -20 -15 -10 -5 0 5 10 IBO[dB] IBO[dB] 27 October 2009 4
Channel impairments (2) • Phase Noise – Same mask as the one applicable for 8PSK TCM at 8GHz 27 October 2009 5
Channel impairments (3) • I/Q imbalance – 0.5dB amplitude imbalance – 3 deg phase imbalance (with spot checks at 5 deg) • Group delay distortion – From on-board RF filter – Group delay variation (in band) up to 10% symbol duration 27 October 2009 6
Simulation approach (1) • Simulation chain developed by Politecnico di Torino (IT) • Transmission scheme compliant to ESA Orange/Red book Implemented 27 October 2009 7
Simulation approach (2) • Full simulator description (C++) – Receiver with optional centroids tuning i.e. alignment of the reference constellation to the averaged constellation points received during training TX Data Source BER Meter RX TX CCSDS SCCC RX_CCSDS_SCCC SCCC Decoder SRRC Demodulator Channel TWT PLL OMUX Centroids tuning Phase Jitter Sampler AWGN Channel I/Q Imbalance Filter 27 October 2009 8
RF filter specifics • Elliptic filter order 5 – Passband B p =1.5*R s =150MHz 10 3.5E ‐ 08 OMUX amplitude and group delay (R s =100Msps) Elliptic, 5th order 0 3.0E ‐ 08 Ripple=0.1 dB – Stopband Bp=75 MHz Bs=93.75 MHz ‐ 10 2.5E ‐ 08 B s =1.25*B p =187.5MHz Signal Band – In-band ripple up to 0.1dB ‐ 20 2.0E ‐ 08 Amplitude [dB] Group delay – Out-of-band rejection above ‐ 30 1.5E ‐ 08 30dB ‐ 40 1.0E ‐ 08 • 2.5-8ns group delay variation at the edge of the signal band ‐ 50 5.0E ‐ 09 – Roll-off 0.35 ‐ 60 0.0E+00 0.00E+00 2.50E+07 5.00E+07 7.50E+07 1.00E+08 1.25E+08 1.50E+08 1.75E+08 2.00E+08 Frequency – 25-80% symbol duration, with 100Msps 27 October 2009 9
RF filter spectrum – 32APSK -80 "spectrumRX.txt" "spectrumTX.txt" "spectrumRXwo.txt" -90 -100 -110 -120 -130 -140 -150 -2e+008 -1.5e+008 -1e+008 -5e+007 0 5e+007 1e+008 1.5e+008 2e+008 27 October 2009 10
Performance assessment – group delay • 100Msps, roll-off 0.35, 16APSK (mode 15) and 32APSK (mode 20) • 0.1-0.2dB loss due to RF filter alone – A simple equalizer can recover the loss and compensate for more severe linear distortion Group delay impact 16APSK (rate 0.73, ACM15) - 32APSK (rate 0.76, ACM20) 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 8 9 10 11 12 13 14 SNR (dB) 16APSK AWGN 16APSK, OMUX 32APSK AWGN 32APSK OMUX 27 October 2009 11
Performance assessment – phase noise • CCSDS phase noise mask • First-order PLL used for phase recovery – More elaborate yet feasible recovery algorithm can reduce the losses further Phase noise impact 32APSK (rate 0.76, ACM20) 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 12.6 12.8 13 13.2 13.4 13.6 13.8 SNR (dB) AWGN Phase noise, CCSDS mask 27 October 2009 12
Performance assessment – phase noise • CCSDS phase noise mask +3dB • First-order PLL used for phase recovery – More elaborate yet feasible recovery algorithm can reduce the losses further Phase noise impact 32APSK (rate 0.76, ACM20) 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 12.6 12.8 13 13.2 13.4 13.6 13.8 SNR (dB) AWGN Phase noise, CCSDS mask Phase noise, CCSDS mask+3dB 27 October 2009 13
Performance assessment – IQ imbalance • Amplitude imbalance 0.5dB, phase imbalance 3 deg • No specific recovery implemented I/Q imbalance impact 32APSK (rate 0.76, ACM20) 1.00E+00 1.00E-01 FER 1.00E-02 1.00E-03 1.00E-04 12.6 12.8 13 13.2 13.4 13.6 13.8 SNR (dB) AWGN I/Q imb (0.5dB, 3deg) 27 October 2009 14
Performance assessment – IQ imbalance • Amplitude imbalance 0.5dB, phase imbalance 5 deg • No specific recovery implemented I/Q imbalance impact 32APSK (rate 0.76, ACM20) 1.00E+00 1.00E-01 FER 1.00E-02 1.00E-03 1.00E-04 12.6 12.8 13 13.2 13.4 13.6 13.8 SNR (dB) AWGN I/Q imb (0.5dB, 3deg) I/Q imb (0.5dB, 5 deg) 27 October 2009 15
E2E performance in non-linear channel • All previous impairments considered, with TWT model • Chosen OBO minimized total degradation NL AWGN ⎛ ⎞ ⎛ ⎞ E E = − + ⎜ ⎟ ⎜ ⎟ D T OBO S S ⎝ ⎠ ⎝ ⎠ N N dB dB 0 0 req req • E s /N 0 metric includes TD • Optional centroids tuning (Rx end) and predistortion (Tx end) considered 27 October 2009 16
E2E performance assessment - QPSK • QPSK, code rate 0.36 (ESA mode 1) QPSK rate 0.36 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 1.00E-06 -1.5 -1 -0.5 0 0.5 1 Es/N0 (dB) AWGN TWT OBO=0dB Centroids tuning OBO=0dB 27 October 2009 17
E2E performance assessment - 8PSK • 8PSK, code rate 0.47 (ESA mode 7) 8PSK rate 0.47 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 Es/N0 (dB) AWGN TWT OBO=0dB Centroids tuning, OBO=0dB 27 October 2009 18
Fractional predistortion • Sensible performance improvement possible using predistortion with higher order modulations • Fractional pre-distortion used by PoliTo – Dynamic (with memory) pre-distortion would improve performance Gain based LUT fractional Gain based LUT fractional x x predistorter predistorter m m HPA HPA Pulse Pulse shaping shaping Amplitude Amplitude Phase Phase g LUT LUT m |.| 2 |.| 2 (F) (F) 27 October 2009 19
E2E performance assessment - 16PSK • 16PSK, code rate 0.73 (ESA mode 15) 16APSK rate 0.73 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 9 10 11 12 13 14 15 Es/N0 (dB) AWGN TWT OBO=1.42dB Centroids tuning,OBO=1.28dB Optimal predistortion,OBO=1.6dB 27 October 2009 20
E2E performance assessment - 32PSK • 32PSK, code rate 0.76 (ESA mode 20) 32APSK rate 0.76 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 12 13 14 15 16 17 18 19 20 21 Es/N0 (dB) AWGN TWT OBO=3.66dB Centroids tuning,OBO=2.8dB Optimal predistortion,OBO=1.67dB 27 October 2009 21
E2E performance assessment - 64PSK • 64PSK, code rate 0.79 (ESA mode 25) 64APSK rate 0.79 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 16 18 20 22 24 26 Es/N0 (dB) AWGN TWT OBO=5.62dB Centroids tuning,OBO=3.36dB Optimal predistortion,OBO=1.45dB 27 October 2009 22
E2E performance – Roll-off impact • 100Msps with roll-off 0.35 considered • Roll-off 0.2 as a worst case spot-check (TWT, no compensation) – Dynamic pre-distortion would likely have a positive impact 32APSK rate 0.76 TWT OBO=3.66dB 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 19 19.2 19.4 19.6 19.8 20 20.2 20.4 20.6 20.8 21 Es/N0 (dB) Roll-off 0.35 Roll-off 0.20 27 October 2009 23
Alternative SW implementation • ESA internal C++ simulator, fully compliant with Red/Orange book – Optional pilots included in the transmitted frame • Same channel impairments as in PoliTo’s implementation • Phase recovery based on open-loop DA estimation and interpolation • Optional static symbol predistortion at the Tx side 27 October 2009 24
ESA internal E2E assessment - 16PSK • 16PSK, code rate 0.73 (ESA mode 15) 16APSK rate 0.73 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 1.00E-06 9 10 11 12 13 14 15 16 Es/N0 (dB) AWGN TWT OBO=1.42dB Static predist,OBO=1.1dB 27 October 2009 25
ESA internal E2E assessment - 32PSK • 32PSK, code rate 0.76 (ESA mode 20) 32APSK rate 0.76 1.00E+00 1.00E-01 1.00E-02 FER 1.00E-03 1.00E-04 1.00E-05 12 14 16 18 20 22 24 Es/N0 (dB) AWGN TWT OBO=3.67dB Static predist,OBO=2.21dB 27 October 2009 26
Conclusions • Assessment of SCCC-based ESA scheme with channel impairments as agreed with CCSDS agencies • Two different and independent simulators used for the assessment – PoliTo: PLL at receiver, centroids tuning, fractional predistortion – ESA/Estec: DA phase and amplitude recovery, symbol predistortion • Sensible impact on performance from TWT – Predistortion (Tx) and centroids tuning (Rx) improve performance considerably at negligible costs – Other techniques such as dynamic predistortion (Tx) and equalization (Rx) would further reduce the total degradation • Results confirm feasibility and applicability of SCCC-based ESA transmission scheme 27 October 2009 27
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