NASA is presently in the planning stages for the next generation earth relay architecture which will transition to Ka-band services in a new, potentially commercially-driven architecture, by 2040. To assess the performance of various technologies and architectures, the Multiple Access Testbed for Research in Innovative Communications Systems (The MATRICS), is being developed to offer a flexible emulation platform for system-level architecture and technology assessments of candidate next generation Ka-band relay and user terminal solutions. In this paper, we describe the architecture and setup of the MATRICS, which is presently housed in GRCs 25-ft anechoic chamber

Downey, James M.

Nessel, James A.

Niederhaus, Charles E.

NASA Technical Reports Server

THE MULTIPLE ACCESS TESTBED FOR RESEARCH IN INNOVATIVE 
COMMUNICATIONS SYSTEMS (MATRICS) 
Dr. James Nessel(1), Dr. James Downey(2), Dr. Charles Niederhaus(3) 
(1)NASA Glenn Research Center, 21000 Brookpark Rd. Cleveland OH 44135 USA, Email:james.a.nessel@nasa.gov
(2)NASA Glenn Research Center, 21000 Brookpark Rd. Cleveland OH 44135 USA, Email:james.m.downey@nasa.gov
(3)NASA Glenn Research Center, 21000 Brookpark Rd. Cleveland OH 44135 USA, Email:charles.niederhaus@nasa.gov
Abstract – NASA is presently in the planning 
stages for the next generation earth relay 
architecture which will transition to Ka-band 
services in a new, potentially commercially-driven 
architecture, by 2040.  To assess the performance of 
various technologies and architectures, the Multiple 
Access Testbed for Research in Innovative 
Communications Systems (The MATRICS), is being 
developed to offer a flexible emulation platform for 
system-level architecture and technology assessments 
of candidate next generation Ka-band relay and user 
terminal solutions.  In this paper, we describe the 
architecture and setup of the MATRICS, which is 
presently housed in GRC’s 25-ft anechoic chamber. 
I. INTRODUCTION
TDRSS-M was launched in August 2017 and represents 
the final replenishment satellite of the TDRSS fleet. 
With a design life of 15 years, it is expected that as of 
2040, a new relay satellite architecture will be 
implemented to replace the TDRSS fleet to provide 
communications and navigation relay services for future 
NASA missions.  This next generation earth relay 
capability is presently in the planning stages and is 
expected to initiate optical communications services and 
herald NASA’s full utilization of the Ka-band spectrum. 
Over the past several years, NASA has funded studies, 
including the Space Based Relay (SBR) study, Earth 
Regimes Network Evolution Study (ERNEST), and the 
Pathfinder program, to look at how this new architecture 
could leverage existing and future commercial 
communications infrastructure to evolve concomitantly 
with commercial satellite communications (SATCOM) 
objectives [1-3]. 
As part of this effort, the Technology Assessment for 
Next Generation Architectures (TANGA) project was 
created to, as the name suggests, provide system-level 
performance assessments of potential technologies 
which may be implemented, either on the relay or user 
spacecraft, within the evolving design of the next 
generation relay system.  Some potential RF 
technologies being investigated include: Multibeam Ka-
band phased arrays (for both user and relay spacecraft), 
wideband or reconfigurable Ka-band systems capable of 
covering both commercial and government Ka-band 
frequencies, low cost commercial-off-the-shelf (COTS) 
phased array technologies, omni-directional Ka-band 
antennas, commercial spot beam technologies, digital 
beamforming technologies, and onboard processing 
technologies.  To support this research a testbed, dubbed 
the Multiple Access Testbed for Research in Innovative 
Communications Systems (The MATRICS), is being 
developed in order to assess these proposed 
technologies for potential insertion into the next 
generation communications architecture.  The 
MATRICS will provide NASA with the system level 
evaluation tools that address the knowledge trade space 
between simulation/component-level characterization 
and full flight payload demonstration for risk reduction 
and assessments of novel technologies that could play a 
role in the future NASA space network. 
II. OBJECTIVES/APPROACH OF THE MATRICS
The Multiple Access Testbed for Research in Innovative 
Communications Systems (MATRICS) was developed 
with the following goals in mind: 
• Provide a flexible, system-level architecture
assessment tool for candidate next generation Ka-
band relay and user terminal solutions.
– Develop unique capability within NASA to
support the demonstration and testing of
proposed technologies, architectures, and
CONOPS for an evolving next generation relay
platform in realistic link scenarios.
– Provide an opportunity to develop/demonstrate
novel approaches to next generation
architecture solutions.
– Validate NASA/Industry solutions for next
generation Ka-band architecture
• Mitigate pre-flight risk via enhanced testing in a
realistic emulation environment
• Provide NASA with a high fidelity assessment of
user terminal and multiple access technology
capabilities for the next generation relay.
The approach of the MATRICS is to create an accurate 
emulation environment within the confines of a 
(currently) 25 ft anechoic chamber at NASA Glenn 
1
https://ntrs.nasa.gov/search.jsp?R=20190000930 2019-08-30T10:26:57+00:00Z
 Research Center.  As such, the link requirements need 
to be effectively scaled from the roughly 40,000 km 
range distances down to the limited range distance 
available.  Configuration of the MATRICS takes into 
account Field of Regard (FOR) requirements for LEO-
GEO relay links (+/- 13), EIRP, G/T, and free space 
loss parameters that need to be scaled to realize 
commensurate link budgets, as depicted in Figure 1. To 
start, current TDRSS link performance parameters were 
used as a baseline configuration, and are summarized 
for the current Ka forward and return service in Table 1 
[4]. 
 
 
 
Figure 1: Depiction of user-relay links in the NASA 
Space Network (TDRSS). 
 
 
Table 1: Summary of Salient TDRSS Ka 
Forward/Return Link Parameters 
 
Parameter Ka (Forward) Ka (Return) 
EIRP 63 dBW -- 
G/T -- 26.5 dB/K 
Free Space Loss ~210 dB ~210 dB 
Bandwidth 50 MHz 225-650 MHz 
Modulation BPSK/UQPSK BPSK/UQPSK 
Data Rate 300kbps – 
25Mbps 
300 Mbps 
 
 
III. THE MATRICS ENVIRONMENT 
A depiction of the MATRICS concept is shown in 
Figure 2.  At its core, a dynamic testing platform 
involves a stationary mock relay positioned at one end 
of the anechoic chamber while a mobile mock low earth 
orbit (LEO) user is placed at the opposite end.  The 
LEO user is mounted to an approximately 6 ft boom 
affixed to a Moog QPT-500 pan and tilt positioner such 
that the user is physically gimbaled across the full field 
of regard of the relay.  In this way, dynamic link 
performance, as well as link establishment protocols and 
concepts of operation can be assessed as a LEO user 
traverses the relay.   
 
  
Figure 2: System diagram of the MATRICS setup in 
NASA GRC’s anechoic chamber. 
 
The first phase of the MATRICS development presently 
allows for direct error vector magnitude (EVM) 
measurements for return links (user transmitting to 
relay).  A Keysight M8190A Arbitrary Waveform 
Generator provides the source signal data at 1.2 GHz IF 
output which is upconverted via a single sideband mixer 
to the operational Ka-band frequency of interest.  The 
M8190A has the following performance specifications: 
 
 12-bit resolution up to 12 GSa/s 
 Variable sample rate from 125 MSa/s to 12 GSa/s 
 Up to 12.25 effective number of bits (ENOB) 
 Up to 2 GSa arbitrary waveform memory per 
channel 
 5 GHz analog bandwidth 
 Real-time DSP for digital up conversion to IF 
and changing waveform parameters on the fly 
 
The M8190A is coherent locked to a Keysight M9703B 
12-bit digitizer which is utilized for sampling the 
receive signal at the 1.2 GHz IF.  The M9703B is an 8-
channel high speed digitizer capable of simultaneous 
data captures of up to 3.2 GS/s.  In the first phase 
MATRICS setup, a single channel input is used for 
sampling the beamformed receive relay array.  
However, the M9703B can also be configured using the 
remaining channels to perform element sampling for 
digital beamforming demonstrations (planned for Phase 
2).  The combination M8190A/M9703B is used to 
perform the EVM measurements of the MATRICS.  
Doppler simulation is then imposed through the 
hardware by sweeping the up/downcoversion LOs via a 
Matlab script.  Presently, time delay and noise injection 
parameters are yet to be implemented. 
 
In the follow-on phase, flexible software defined radios 
will be integrated into the MATRICS to obtain direct 
bit-error-rate measurements of the various architectures 
and allow for investigation of DVB-S2 and adaptive 
coding and modulation schemes.  The flexibility of the 
setup will also allow for replacement of the relay and 
user antennas to demonstrate a wide variety of 
architectures and characterization of different user 
2
 terminals.  Of particular interest to NASA is the 
possibility of using current commercial spot-beam 
architectures to provide services to LEO spacecraft.  
Presently, this has been shown to work for airline 
services in flight, but the challenge of utilizing the same 
approach for much faster moving LEO satellites is one 
that still needs to be validated.  Also, assessments of 
various COTS phased arrays which could be 
implemented for LEO user terminals is of extreme 
interest for the development of low-cost Ka-band 
systems for future NASA missions. 
 
A. Mock Relay Hardware Setup 
The current setup of the MATRICS was implemented to 
perform initial validation of the concept.  For this setup, 
a linear array was developed to represent the relay 
receive system.  The linear array consists of an 8-
element scalar horn array, whose block diagram is 
shown in Figure 3.  Beamforming of the array occurs at 
the IF frequency of 1.2 GHz with a bandwidth of 650 
MHz to accommodate the maximum channel bandwidth 
of the current TDRSS return service.  Programmable 
Vaunix Lab Brick digital attenuators and phase shifters 
are implemented at IF to provide the amplitude and 
phase control with a resolution of 0.1 dB and 1 phase 
shift, respectively.  An IF beamforming system was 
chosen to allow for flexibility of the back end 
beamformer for testing across various channels within 
the full commercial and government Ka-band spectrum.  
A photograph of the MATRICS setup in the GRC 
anechoic chamber, as well as the relay receive array and 
beamformer electronics rack is shown in Figure 4. 
 
 
 
Figure 3: Block diagram of the mock relay receive 
array. 
 
Preliminary testing of the receive array with the IF 
beamforming network was performed and indicate good 
agreement with theory as the relay array is beamsteered 
across the full field of regard, as shown in Figure 5. 
 
  
Figure 4: Photograph of the MATRICS setup in NASA 
GRC’s anechoic chamber (left) and the relay receive 
array and beamforming rack (right). 
 
 
 
 
 
Figure 5: Beamsteering of the relay linear receive array 
from 0 deg to -9 deg using 4 of the 8 elements (top).  
Theoretical vs measured array pattern for a beemsteer 
of 4 deg (bottom). 
 
 
3
 IV. INITIAL TESTING 
First validation tests of the MATRICS were performed 
using an Anokiwave AWMF-0129 planar active 
antenna.  The operational parameters of the AWMF-
0129 are summarized in Table 2, below. 
 
Table 2: Anokiwave AWMF-0129 Phased Array 
 
Parameter Performance 
Frequency 27.5-30.0 GHz 
Number of Elements 64 
EIRP (at P1dB) 50 dBm 
G/T -7 dB/K (at boresight) 
Polarization Vertical Linear
Electronic Beam Scan +/- 60 deg 2D 
Number of Beams 1 
Beam Update Rate 13 us 
RF Interface Tx/Rx Half Duplex 
Average Power 18 W DC 
Size 11cm x 15cm x 4cm 
Weight 0.5 kg 
Supply Voltage 12 or 18 VDC 
Control Interface LVDS, Ethernet, USB 
 
The Anokiwave AWMF-0129 is a commercial off the 
shelf (COTS) phased array product intended for 5G 
wireless applications.  NASA’s interest, in general, is in 
identifying if COTS phased arrays like this one could 
potentially be leveraged for development of low-cost 
space applications.  However, being designed for 
commercial applications, testing was needed to identify 
performance limitations in operating outside the 
specified commercial Ka-band (27.5-30GHz) to 
NASA’s Ka-band allocation (25.5-27.5 GHz).  Figure 7 
shows the pattern measurements performed at various 
scan angles out to +/-30 deg at an in band operational 
frequency of 28 GHz and an out of band frequency of 
26.5 GHz.  From the plots, it is observed that the 
Anokiwave phased array does exhibit some efficiency 
losses operating outside its intended design frequency of 
approximately 3 dB and a nominally 1 dB scan loss out 
to 30 deg scan angle. 
 
 
A. First Link Test of the MATRICS 
The emulation link budget used was matched to the 
equivalent relay link parameters indicated in Table 3, 
which are arbitrarily chosen for this run.  The derived 
equivalent relay link parameters provided in Table 3 
were based on calculating the equivalent EIRP needed 
from a transmitting user terminal to match the same 
receive carrier-to-noise density (C/N0).   
 
The orbit simulated was that of a Ka-band payload 
attached to the International Space Station.  Orbit 
propagation simulations were conducted prior to the test 
to identify the necessary pointing angles (for both the 
relay and the user antennas) as a function of orbital 
position.  These pointing angles were then coordinated 
in time with the physical location of the mock LEO user 
in the MATRICS and program tracked for both ends of 
the link throughout the emulated orbital pass.  Pointing 
angles were directly sent to the Anokiwave system via 
the Ethernet interface and the calculated phasing 
weights were time synchronized for beam steering of 
the linear array representing the relay.   
 
As indicated in Table 3, a 100 Mbaud data rate was 
employed using QPSK modulation.  A screenshot of the 
resulting EVM performance characterized during the 
run is shown in Figure 8, where a maximum EVM of 
1.4% was achieved.  EVM was tracked throughout the 
orbital pass, demonstrating, as expected poorer 
performance at the look angles beyond ~50 deg, which 
represents the limit to which the Anokiwave phased 
array could steer with reliable array gain. 
 
 
 
Figure 7. Pattern measurements of the Anokiwave 
AWMF-0129 at 28 GHz (top) and 26.5 GHz (bottom) 
operational frequency. 
 
 
4
 Table 3: MATRICS Test Run Parameters 
 
 MATRICS Equivalent Relay 
Transmit Parameters 
Frequency 26 GHz 26 GHz 
EIRP -10 dBW 84 dBW 
Channel Loss Parameters 
Free Space Loss 77.64 dB 212.47 dB 
Polarization Loss 3 dB 3 dB 
Communications Parameters 
Bandwidth 100 MHz 100 MHz 
Modulation QPSK QPSK
Data Rate 100 Mbaud 100 Mbaud 
Receiver Parameters 
Noise Spectral 
Density -189.57 dB -198.59 dB 
G/T -14.49 dB/K 26.01 dB/K 
Receive Carrier 
Power -66.1 dBW -75.5 dBW 
C/N0 123.5 dBHz 123.5 dBHz 
 
 
 
 
Figure 8. Screenshot of the Keysight M8190A measured 
EVM performance of the link. 
 
 
V. FUTURE PLANS 
Beyond these initial demonstrations, the MATRICS still 
has some development effort needed to get the testbed 
to full functionality.  The following list details the 
planned upgrades to the MATRICS testbed in the 
coming year: 
 
• Addition of secondary rotation stage to include two 
user terminals for true multiple access emulation 
capability 
• Redesign of mock relay array from linear to 
hexagonal close-packed array, as is typical in most 
satellite configurations 
• Second analog beamformer hardware to support two 
simultaneous users in FDMA 
• Implementation of time delay and noise injection for 
accurate link emulation 
• Full utilization of the Keysight M9703B digitizer for 
digital beamforming demonstrations 
• Addition of a small transmit array for bi-directional 
communications. 
• Integration of SDRs into the system for direct bit 
error rate measurements and ACM and CONOPS 
demonstrations. 
 
 
VI. CONCLUSIONS 
The MATRICS is presently still in the build-up phase, 
but is showing to be a useful tool for NASA to assess 
realistic communications systems performance in a 
dynamic link environment.  As part of the technology 
assessment needed for NASA’s next generation relay 
architecture, Ka-band user terminal demonstrations will 
play an important role as NASA tries to entice future 
users into this underutilized NASA Ka-band spectrum.  
Furthermore, as the development of NASA next 
generation relay architecture continues to evolve, the 
flexibility of the MATRICS will allow for extensibility 
to changes until a final architecture is identified. 
 
VII. REFERENCES 
[1] NASA’s Space-Based Relay Study: Overview and 
Direction. Available at: https://www.nasa.gov/sites/ 
default/files/files/SBRSWhitePaper3-7-2013.pdf 
 
[2] D. Israel, G. Heckler, R. Menrad, Space Mobile 
Network: A Near Earth Communications and 
Navigation Architecture, NASA Technical Report, 
2016. Available at: https://ntrs.nasa.gov/archive/ 
nasa/casi.ntrs.nasa.gov/20160001698.pdf 
 
[3] Next Space Technologies for Exploration 
Partnerships 2 (NextSTEP-2) Omnibus Broad Agency 
Announcement (BAA) Appendix G Space Relay 
Partnership and Services Study, Available at: 
https://www.fbo.gov/  
 
[4] Space Network User’s Guide (SNUG) Rev. 10, 
August 2012 
5


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