Experiment of 348 Mbps downlink from 50-kg class satellite

10th IAA Symposium on Small Satellites for Earth Observation

April 20 - 24, 2015 Berlin, Germany

Tomoya Fukami, The University of Tokyo

fukami.tomoya at ac.jaxa.jp

Hiromi Watanabe, Hirobumi Saito , Atsushi Tomiki

Takahide Mizuno, Naohiko Iwakiri, Osamu Shigeta

Hitoshi Nunomura, Kaname Kojima and Takahiro Shinke

IAA-B10-1302

Background

Recent small satellite is equipped with a high-resolution camera.

Skybox Imaging, Inc.

GSD < 1m

Planet Labs, Inc.

GSD ~ 5m

2 These satellites require high-speed downlink system to transmit the observed data.

Background

We can get the link budgets of these satellite on the Web.

3

Downlink system of existing satellite

SkySat-1 Flock 1

Operator Skybox Imaging Planet Labs

Launch date 21 November 2013 9 January 2014

Mass ~100 kg ~5 kg

Spatial resolution ~1 m 3-5 m

Downlink system

Number of channels 3 1

Frequency 8 GHz 8 GHz

Transmitter Power 1.0 W × 3 ch. 3.2 W

Modulation 8-PSK QPSK, 8-PSK

Maximum data rate 101 Mbps × 3 ch. 120 Mbps

How to increase the data rate? 4

For faster downlink communication

Increasing the channels

Many transmission modules is required.

Using the higher frequency bands (e.g. Ku-band or Ka-band)

Influence of rain attenuation becomes more serious.

Using optical communications

Ground station will be expensive.

Using higher order modulation schemes (e.g. 16APSK)

Amplitude-phase modulation requires high linearity of RF amplifier.

Therefore, power efficiency of RF power amplifier degrades.

5

The purpose of our research

High-Speed Downlink System

using Amplitude-Phase Modulation for Small Satellite

Goal

50 kg-class satellite @ 600 km orbit

Power consumption < 25 W

Small ground antenna < 4m

Data rate > 300 Mbps

Low total system cost

348 Mbps

6

16QAM Downlink with Nonlinear Amplifier

Why the amplitude-phase modulation is difficult?

Ref. SSC13-I-8 7

16QAM Downlink with Nonlinear Amplifier

Why the amplitude-phase modulation is difficult?

Ref. SSC13-I-8 8

16QAM Downlink with Nonlinear Amplifier

Why the amplitude-phase modulation is difficult?

The nonlinearity of RF power amplifier increases bit error rate.

Input [dBm]

AM-PM

Phas

e Sh

ift

[degr

ee]

Outp

ut

[dB

m]

Input [dBm]

AM-AM

IQ constellation

9

X Band Power Amplifiers

We developed a new GaN-HEMT amplifier.

Newly Developed 2W GaN HEMT AB Class

3cm

Amplifier GaAs AB GaN AB GaN F

Maximum Power 38dBm 37dBm 36dBm

Maximum Gain 10dB 11dB 12dB

Maximum PAE 37% 46% 60%

PAE at 3dB OBO 23% 36% 38%

Maximum Phase Shift 10° -2° -34°

10

11

AM/AM AM/PM IQ Constellation

GaAs

(AB)

GaN

(AB)

GaN

(F)

Phas

e Sh

ift

[degr

ee]

Outp

ut

[dB

m]

Input [dBm]

Input [dBm]

Phas

e Sh

ift

[degr

ee]

Outp

ut

[dB

m]

Input [dBm]

Input [dBm]

Phas

e Sh

ift

[degr

ee]

Outp

ut

[dB

m]

Input [dBm] Input [dBm]

Effect of AM-AM will be corrected by error correction code.

Onboard Transmitter Specifications of onboard transmitter

Frequency band 8160 ± 60 MHz

RF output power 2 W

Symbol rate 100 Msps

Modulation schemes QPSK, 16QAM,

8PSK, 16APSK, 32APSK,

64APSK, 64QAM

Data rate (user) 72 to 540 Mbps

Error correction

code

SCCC based on CCSDS

131.2-B-1

Data input interface LVDS

DC power 28 V, 22 W

Volume 12 × 10 × 7.3 cm

Weight 1330 g

Operating

temperature

-20 to +50 °C

Radiation test 20 kRad

Flight model

RF block

Baseband block

12

Error Correction and Modulations

CCSDS 131.2-B-1

Blue book was published in 2012.

QPSK to 64APSK

DVB-S2 supports up to 32APSK.

Turbo code

Serial Concatenated

Convolutional Code (SCCC)

13

Simulation Results of Frame Error Rate

Es/N0 [dB]

Fra

me E

rror

Rat

e

Ref. ESA 14 The data rate can be changed based on link condition.

Simulation Results of Bit Error Rate

Simulation results of bit error rate.

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Onboard small Antenna

Body-Fixed Medium Gain Antenna

Feed

point

Active

element

Passive

element

Satellite

3.8m

Ground

Station

14 dBi, 68g, 7x7cm

For high bit rate mode,

Satellite points ground

station.

16

Onboard small Antenna

Body-Fixed Iso-flux Antenna

5 dBi,150g

For Earth-Pointing Satellite,

Antenna pattern compensates

range variation.

17

3.8m Ground Antenna for S / X Band

S band : Telemetry & Command

X band : Mission Data Down Link

Ring-Focus

Cassegrain 36 dBi (S), 47.5 dBi (X)

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Ground Receiver

There are some commercial ground receivers which

support high data rate and SCCC error correction.

Since these receivers were developed for large satellites,

they are too expensive.

Zodiac ViaSat 19

Ground Receiver

In general, real time demodulation is not necessarily required

for mission data downlink. ->Software receiver

20

Link calculation

This system can transmit up to 32.5 GBytes per pass from 600 km

orbit with a 3.8 m ground antenna. (BER<10−6, 1 dB margin)

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Launch

Japanese Hodoyoshi #4 satellite equipped with our downlink

system was launched at June 2014.

Hodoyoshi #3

Dnepr Launch Vehicle

Yasny, Russia

37 small satellites were launched

Hodoyoshi #4

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Hodoyoshi #4

Hodoyoshi #4

Launch 20 June 2014

Mass 64 kg

Volume 50 × 50 × 80 cm

6 m GSD camera

Ion Propulsion

X-band transmitter

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Experiment of 348 Mbps downlink

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Results

Elevation = 84.5 degrees Distance = 622 km C/N0 = 96 dBHz Es/N0 = 16 dB Raw(400 Mbps) BER ≈ 1.2 × 10−3 Decoded(348 Mbps) BER < 1.7 × 10−9

Recent result

26

We began the challenge to 64APSK, for over the 500 Mbps.

Elevation = 83.3 degrees Distance = 658 km C/N0 = 100 dBHz Es/N0 = 20 dB Raw(600 Mbps) BER ≈ 2.7 × 10−2 Decoded(504 Mbps) BER < 7.6 × 10−7

Recent result of 64APSK

Received signal

Ground receiver for 64APSK is now developing. Current version of demodulation software requires the tuning of parameter by human.

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Conclusion

We developed the high speed transmitter for 50-kg class satellite

and demonstrated the downlink of 348 Mbps on orbit.

We began the challenge to 64APSK modulation, for over the 500

Mbps.

By combining the two transmitters and high gain antenna (HGA,

25.5 dBi, 1.2 kg), the downlink of over the 1 Gbps from 50-kg

class satellite can be achieved.

High Gain Antenna

for 50-kg class satellite

(PROCYON Spacecraft) Photo by Mynavi

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The End

Thank you for your attention!

Manufacturer of Transmitter Manufacturer of Power Amplifier

Manufacturer of Onboard Antenna Manufacturer of Ground Receiver

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