Rainee N. Simons and Edwin G. Wintucky

Glenn Research Center, Cleveland, Ohio

David G. Landon, Jun Y. Sun, James S. Winn, Stephen Laraway, William K. McIntire,

John L. Metz, and Francis J. Smith

L-3 Communication Systems-West, Salt Lake City, Utah

Demonstration of Multi-Gbps Data Rates at

Ka-Band Using Software-Defi ned Modem

and Broadband High Power Amplifi er for

Space Communications

NASA/TM—2011-217035

April 2011
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Rainee N. Simons and Edwin G. Wintucky

Glenn Research Center, Cleveland, Ohio

David G. Landon, Jun Y. Sun, James S. Winn, Stephen Laraway, William K. McIntire,

John L. Metz, and Francis J. Smith

L-3 Communication Systems-West, Salt Lake City, Utah

Demonstration of Multi-Gbps Data Rates at

Ka-Band Using Software-Defi ned Modem

and Broadband High Power Amplifi er for

Space Communications

NASA/TM—2011-217035

April 2011

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

International Microwave Symposium for 2011 (IMS2011)

sponsored by the Institute of Electrical and Electronics Engineers, Microwave Theory and

Techniques Society (MTT-S)

Baltimore, Maryland, June 5–10, 2011
Acknowledgments

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NASA/TM—2011-217035 1 

Demonstration of Multi-Gbps Data Rates at Ka-Band Using SoftwareDefined Modem and Broadband High Power Amplifier for 

Space Communications 

Rainee N. Simons and Edwin G. Wintucky 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135

David G. Landon, Jun Y. Sun, James S. Winn, Stephen Laraway, 

William K. McIntire, John L. Metz, and Francis J. Smith

L-3 Communication Systems-West 

Salt Lake City, Utah 84116 

Abstract 

The paper presents the first ever research and experimental 

results regarding the combination of a software-defined multiGbps modem and a broadband high power space amplifier 

when tested with an extended form of the industry standard 

DVB-S2 and LDPC rate 9/10 FEC codec. The modem 

supports waveforms including QPSK, 8-PSK, 16-APSK, 

32-APSK, 64-APSK, and 128-QAM. The broadband high 

power amplifier is a space qualified traveling-wave tube 

(TWT), which has a passband greater than 3 GHz at 33 GHz, 

output power of 200 W and efficiency greater than 60 percent. 

The modem and the TWTA together enabled an 

unprecedented data rate at 20 Gbps with low BER of 10–9. The 

presented results include a plot of the received waveform 

constellation, BER vs. Eb/N0 and implementation loss for each 

of the modulation types tested. The above results when 

included in an RF link budget analysis show that NASA’s 

payload data rate can be increased by at least an order of 

magnitude (10X) over current state-of-practice, limited only 

by the spacecraft EIRP, ground receiver G/T, range, and 

available spectrum or bandwidth. 

I. Introduction 

NASA is in need of a versatile, higher data rate integrated 

space communications network to provide services to space 

flight missions located throughout the solar system (Ref. 1). 

The driving requirements for the network are quite broad, 

covering space based navigation and communications for 

manned and robotic missions from near-Earth to deep space, 

all with emphasis on higher data rates in the Gbps range. The 

justification for Gbps data rates is closely linked to the 

capabilities of remote spacecraft sensors, which are quickly 

outstripping the ability of current data links to rapidly move 

the sensor information back to Earth (Ref. 2). Four data links 

that are potential elements of NASA’s integrated space 

communications network are: satellites in low Earth orbit 

(LEO), lunar relay satellites (LRS), spacecrafts stationed at the 

second Lagrangian point (L2), and spacecrafts in deep space 

(DS). In addition, Gbps data rate technology is useful for 

fixed, mobile, broadcast, broadband and commercial Earth 

imaging satellite services (Ref. 3). 

In this paper, we present experimental results, which can 

enhance the RF communications capability of NASA’s 

spacecraft-to-Earth data links identified above. We 

demonstrated in a laboratory setting very high data rates on 

the order of multi-Gbps (20 Gbps) at Ka-band frequencies 

using software-defined modems (SDMs), bandwidth efficient 

modulation (BEM) techniques (PSK, APSK, and QAM) and a 

broadband high efficiency high power space amplifier. To the 

best of our knowledge this is the first ever demonstration of 

such high data rates through a high power space amplifier at 

Ka-band frequency. The presented results include a plot of the 

received waveform constellation, BER vs. Eb/N0, and 

implementation loss for each of the modulation types 

investigated. These results, when included in an RF link 

budget analysis, show that the data rate of the above links can 

be enhanced by an order of magnitude (10X) over current 

state-of-practice. By simultaneously using RHCP and LHCP 

for transmission, the data rate can be doubled (~20X). If a 

dual-polarization/dual-beam system is used, the data rate can 

be quadrupled (~40X). 

II. Enabling Technologies 

The two technologies, high-speed software-defined 

modems and Ka-band broadband high efficiency high power 

space amplifiers, are critical components in meeting the above 

goals of increasing user data rates. 
NASA/TM—2011-217035 2 

A. Software-Defined Modem (SDM) 

State-of-the-art mixed signal, fully software-defined 

modem (SDM) based on the latest field programmable gate 

array (FPGA) technology (Fig. 1) have been implemented, 

which currently support lower-order modulations (QPSK and 

8-PSK) and are programmable for higher-order modulations 

(Ref. 4). In addition, an advanced modem breadboard 

consisting of laboratory test equipment and in-house 

developed software has also been implemented, which can 

support 16-APSK, 32-APSK, 64-APSK, and 128-QAM 

waveforms operating in real time while transmitting standard 

pseudo random bit stream (PRBS) test patterns (Ref. 4). 

B. Traveling-Wave Tube Amplifier (TWTA) 

Space TWTAs for near-Earth and deep space missions at 

K-band and Ka-band frequencies are currently flying in space. 

Efficiencies of these amplifiers are in the range of 50 to 

60 percent and the corresponding RF output power level is in 

the range of 35 to 200 W. In References 5 and 6, examples of 

NASA space TWTAs and their RF performance 

characteristics including size and mass are presented. The 

typical design bandwidth has been 500 MHz, but these 

amplifiers perform well with bandwidths in excess of 3 GHz. 

The TWTA provides very high efficiency, high power, wide 

bandwidth, and good linearity. These characteristics, 

combined with pre-compensation in the SDM and in the 

advanced modem breadboard, allow dense higher-order 

waveform constellations to be supported with small 

implementation losses. 

III. Waveform Design and 

Implementation 

The waveforms investigated include the digital video 

broadcasting-satellite, second-generation (DVB-S2), family. 

Details of the modulation, constellation mapping, interleaving, 

and encoding for QPSK, 8-PSK, 16-APSK, and 32-APSK 

modes are available in Reference 7. We extend the DVB-S2 

modulation suite to higher-order modulation types and use the 

64-APSK constellation given in Reference 8 and the 128-QAM 

cross II constellation from Reference 9. The forward error 

correction (FEC) employed in our work is the low-density 

parity-check (LDPC) rate 9/10 code described by the European 

Telecommunications Standard Institute (ETSI) (Ref. 7). 

A. Using Software-Defined Modem 

The waveforms are implemented in the FPGA-based SDM 

shown in Figure 1. The modem has a transmit and a receive 

module. The transmit module has an I/Q-sampler and a twostage X-band/Ka-band up-converter and the receive module 

has a two-stage X-band/Ka-band down-converter as analog 

interfaces. The SDM supports QPSK and 8-PSK waveforms. 

Each also supports continuously configurable data rates (and 

bandwidth) via digitally interpolated symbol timing and a 

fixed sample clock. 

B. Using Advanced Modem Breadboard 

The advanced modem breadboard consists of laboratory test 

equipment and in-house developed software that provides the 

capability to test waveforms over actual channels. The 

advanced modem breadboard uses the same digital algorithms 

as used in the SDM at the same symbol rate and bandwidth at 

any data rate and modulation up to 20 Gbps. The advanced 

modem is used to test 16-APSK, 32-APSK, 64-APSK, and 

128-QAM waveforms. 

C. Distortion Mitigation 

To achieve high data rates, the advanced modem 

breadboard includes non-linear pre-compensation for the 

TWTA AM/AM and AM/PM, as well as compensation for the 

I/Q modulator distortions. Figure 2 shows the output spectrum 

of the TWTA, given a frequency-flat 3 GHz input signal, 

without and with pre-compensation. Notice that with precompensation the signal is flatter. 
NASA/TM—2011-217035 3 

IV. Experimental Setup 

The TWTA output power and phase as a function of the input 

drive power was measured across the 31 to 35 GHz band. For 

these measurements, the TWTA voltages and currents were set 

so that the saturated output power (PSAT) was 125 W. Figure 3 

shows the measured normalized output power and phase of the 

TWTA as a function of the input drive power at f0 = 33 GHz. 

Supporting hardware was set up around the TWTA to match the 

IF of the modem to the Ka-band test channel. A system level 

block diagram of the experimental setup is shown in Figure 4. 

The advanced modem breadboard modulator is comprised of a 

personal computer (PC) hosting software that emulates a 

software-defined modulator, a Tektronix Arbitrary Waveform 

Generator and a Hittite Microwave I/Q Mixer. The advanced 

modem breadboard demodulator consists of a PC hosting 

software that emulates a software-defined demodulator and a 

Tektronix digital oscilloscope. 

V. Advanced Modem Performance 

Results 

Transmitting a modulated waveform through the TWTA 

and then demodulating the received waveform enabled an 

assessment of the waveform performance through the test 

channel at 33 GHz. In order to induce bit errors for the 

purpose of a BER measurement, the advanced modem 

breadboard demodulator digitally added generated pseudo 

noise at precisely controlled levels to the received A/D output 

samples. The implementation of the digital noise generator is 

based on the work of Marsaglia and Tsang (Ref. 10) on the 

Ziggurat method for generating random variables. Modulation 

schemes of QPSK, 8-PSK, 16-PSK, 32-APSK, 64-APSK, and 

128-QAM were tested in conjunction with the DVB-S2 LDPC 

9/10 FEC codec. 
NASA/TM—2011-217035 4 

For each modulation type, the bit rate was selected such 

that a constant channel symbol rate of 3.2 Gsps was achieved. 

This led to an information bit rate of 5.7 Gbps for the lowestorder modulation tested, QPSK, and up to 20 Gbps for the 

highest-order modulation tested, 128-QAM. For each 

waveform under test, the input power to the TWTA was set 

such that its average output power back-off (OBO) from 

saturation was approximately equal to the peak-to-average 

power of the waveform in an ideal undistorted state. Figure 5 

plots BER vs. Eb/N0 for each of the modulation types tested 

with the DVB-S2 LDPC 9/10 codec. The recovered signal 

constellation diagrams for the six waveforms, when precompensation as well as adaptive equalization are applied, are 

shown in Figure 6. Notice that the symbols are distinct, which 

indicates excellent compensation for system non-linearity. 
NASA/TM—2011-217035 5 

VI. Space-To-Earth RF Link Budget 

Analysis 

The above results are included in a RF link budget analysis, 

which besides other parameters takes into account the TWTA 

output power, spacecraft antenna diameter, available spectrum 

or bandwidth, atmospheric attenuation, range, ground antenna 

diameter and G/T ratio. The analysis generates the achievable 

data rates for NASA’s four data links discussed in Section I. 

Table I compares the achievable data rates with the current 

state-of-practice. The data rate improvement factor in all cases 

is an order of magnitude or greater (10X). Commercial Earth 

imaging satellites transmit 800 Mbps from LEO, using two 

orthogonally polarized 400 Mbps channels, at X-band. If the 

next generation Earth imaging satellites migrated to Ka-band, 

the achievable data rate and improvement factor per 

polarization would be as high as 2.8 Gbps and 7X, 

respectively, using our advanced modem technology. 

TABLE I.—CURRENT STATE-OF-PRACTICE, ACHIEVABLE 

DATA RATE AND IMPROVEMENT FACTOR FOR 

NASA’S FOUR DATA LINKS IN SECTION I 

Current state-of-practice 

Type of link and 

distance 

Center frequency, 

GHz 

TWTA PSAT, 

W 

Data rate, 

Mbps 

LEO, 

700 km 

X-band, 8.45 20 150 

LRS, 

384000 km 

K-band, 25.65 40 100 

L2, 

1.5 million km 

K-band, 25.9 58 28 

DS, 

1 AU 

X- and Ka-band, 

8.45 and 32.05 

100 (X-band) and 

35 (Ka-band) 

6 

Achievable data rate at Ka-band and improvement factor 

TWTA PSAT = 40 W, Spacecraft ant dia. = 1 m, Bandwidth = 500 MHz 

Type of link and 

distance 

Ground antenna dia. 

(m) and elevation 

angle 

Achievable 

data rate, 

Gbps 

Improvement 

factor 

LEO, 

700 km 

2, 5 2.8 19X 

LRS, 

384000 km 

18.3, 10 

(G/T46.5 dB/K) 

0.95 10X 

TWTA PSAT = 100 W, Spacecraft ant dia. = 4 - 5 m, 

Bandwidth = 300 MHz

L2, 

1.5 million km 

18.3, 10

(G/T46.5 dB/K) 

0.95 34X 

DS, 

1 AU 

34, 10

(G/T60 dB/K) 

0.08 13X 

VII. Conclusions and Discussions 

The paper presents the first ever research and experimental 

results regarding the combination of a software-defined multiGbps modem and a broadband high power space amplifier 

when tested with the extended industry standard DVB-S2 and 

LDPC rate 9/10 FEC codec. The modem and the TWTA 

together enabled an unprecedented data throughput of 20 Gbps 

with low BER of 10–9. The presented results include a plot of 

the received waveform constellation, BER vs. Eb/N0 and 

implementation loss for each of the modulation types tested. 

The above results when included in a RF link budget analysis 

show that NASA’s payload data rate can be increased by at 

least an order of magnitude (10X) over current state-ofpractice. Finally, the above demonstration shows that a Kaband transmitter with data rate at 20 Gbps is achievable and 

the link capacity is limited only by the spacecraft antenna 

EIRP, ground receiver G/T, range, and available spectrum or 

bandwidth. 

References 

1. J. Schier, Space Communications and Navigation 

Integrated Network Architecture Definition Document 

Volume 1: Executive Summary, Jan 2010, NASA 

Headquarters, Washington, D.C. 

2. Earth Science and Applications from Space: National 

Imperatives for the Next Decade and Beyond, p. 96, p. 

113, p. 356, The National Academies Press, Washington, 

D.C., 2007. 

3. 2010 IEEE MTT-S IMS Workshop (WMF) notes entitled 

“High Efficiency, High Power Microwave Amplifiers for 

High Data Rate Space Communications,” Anaheim, CA, 

May 24, 2010. 

4. D.G. Landon, J.Y. Sun, J.S. Winn, S. Laraway, W.K. 

McIntire, J.L. Metz, F.J. Smith, R.N. Simons, and E.G. 

Wintucky, “Demonstration of Software-Defined MultiGbps Modem Technology for Ka-Band Satellite 

Communications,” GOMACTech-11, Orlando, FL, March 

21–24, 2011. 

5. R.N. Simons, J.D. Wilson and D.A. Force, “High Power 

and Efficiency Space Traveling-Wave Tube Amplifiers 

With Reduced Size and Mass for NASA Missions,” 2008 

IEEE MTT-S IMS Digest, pp. 319–322, Atlanta, GA, June 

15–20, 2008. 
NASA/TM—2011-217035 6 

6. R.N. Simons, D.A. Force, P.C. Spitsen, W.L. Menninger, 

N.R. Robbins, D.R. Dibb, and P.C. Todd, “High-Efficiency 

K-Band Space Traveling-Wave Tube Amplifier for NearEarth High Data Rate Communications,” 2010 IEEE MTTS IMS Digest, pp. 1400–1403, Anaheim, CA, May 23–28, 

2010. 

7. Digital Video Broadcasting (DVB); Second generation 

framing structure, channel coding and modulation systems 

for Broadcasting, Interactive Services, News Gathering and 

other broadband satellite applications, ETSI EN 302 307 

V1.1.1 (2005-03), 650 Route des Lucioles F-06921 Sophia 

Antipolis Cedex, France. 

8. L. Giugno, M. Luise, and V. Lottici, “Adaptive Pre- and 

Post-compensation of Nonlinear Distortions for High-level 

Data Modulations,” IEEE Trans. Wireless Commun., 

vol. 3, no. 5, pp. 1490–1495, Sept 2004. 

9. S. ten Brink, R. Mahadevappa, “Implementation Aspects 

of High-Speed Wireless LAN Systems,” Signals, Systems 

and Computers, 2004. Thirty-Eighth Asilomar Conf., 

vol. 1, pp. 789–793, Nov 7–10, 2004. 

10. G. Marsaglia; W. Tsang, “The Ziggurat Method for 

Generating Random Variables,” Journal of Statistical 

Software, vol. 5, issue 8, Oct 2000. 
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14. ABSTRACT

The paper presents the first ever research and experimental results regarding the combination of a software-defined multi-Gbps modem and 

a broadband high power space amplifier when tested with an extended form of the industry standard DVB-S2 and LDPC rate 9/10 FEC

codec. The modem supports waveforms including QPSK, 8-PSK, 16-APSK, 32-APSK, 64-APSK, and 128-QAM. The broadband high 

power amplifier is a space qualified traveling-wave tube (TWT), which has a passband greater than 3 GHz at 33 GHz, output power of 200 

W and efficiency greater than 60 percent. The modem and the TWTA together enabled an unprecedented data rate at 20 Gbps with low BER 

of 10-

9. The presented results include a plot of the received waveform constellation, BER vs. Eb/N0 and implementation loss for each of the 

modulation types tested. The above results when included in an RF link budget analysis show that NASA’s payload data rate can be 

increased by at least an order of magnitude (>10X) over current state-of-practice, limited only by the spacecraft EIRP, ground receiver G/T, 

range, and available spectrum or bandwidth. 

15. SUBJECT TERMS

Telecommunications; Transmitters; Deep Space Network; Space communication; Satellite communications; Microwave transmission; 

Microwave amplifiers; Microwave tubes; Power amplifiers; Power conditioning; Power efficiency; Traveling wave tubes 

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