1. Comparison of RFI Mitigation of Aerospace SEW CDM with CCSDS CDM for Links to and from the Space Vehicle SLS-RFM_17-06
Donald P. Olsen
19 April 2017

2. Contents RFI Incidents and Capabilities Aerospace Approach to SEW
SEW Spread Spectrum Uplink Throughput
CCSDS CDM Spread Spectrum Uplink Throughput
SEW and CCSDS CDM Downlink Throughput
Conclusions and Recommendations

3. RFI Capabilities and Incidents
Google Search of Potential Nations that have repurposable transmitters
China
Ethiopia
Iran
Iraq
Jordan
Libya
North Korea
Russia
South Korea
Syria
Known Events Affecting Nations/Satellites
Multiple Middle East Jamming incidents
USA NASA Landsat-7 12 minutes in October 2007 also November 2008
USA Terra AM-1 nine minutes October 22, 2008

4. RFI Mitigation Approaches
Mitigation means to greatly reduce effectiveness of the source of RFI in real time
in contrast to monitoring, which may try to fix problems after the fact
Methods of mitigation
Spread spectrum for processing gain against RFI
Antenna steering or nulling against sources of RFI
Two approaches to spread spectrum
Frequency hopping
Broadband with high chip rate secure direct sequence spread spectrum (DSSS)
Comparison
Antenna nulling is a multiplicative factor on processing gain for RFI on downlinks
Omni Satellite antenna cannot null uplink RFI sources
DSSS is more effective:
Protects link of user from other band occupants as well as user RFI on others
Effective against frequency follower jammers
Frequency hopping:
Is easy to build and less critical of RF phase distortion
Protects itself against frequency followers
Does not protect other co-band signals from user signal degradation

5. Aerospace Approach to SEW
SEW based on two COTS waveforms
DVB-S2 subset1 for streaming data and WiMAX2 for short blocks
Several companies produce hardware and hardware definition language (HDL) supporting these waveform sets
Plus DSSS CDM, which doubles for ranging (20 Mchip G3 cell phones)
Effective way ahead for RFI mitigation
Square root raised cosine (SRRC) pulse shaping for spectrum control
Some of these modes (e.g., QPSK) exist in commercial DVB-S2 and other direct-on-the-carrier modulations usually contain their own Sync
Required for both up and downlinks
Aerospace report shows bit error rate simulations curves for DVB-S2
Following chart shows SEW for 10-6 BER at Eb/No = 0.6 dB
1 Specification is ETSI EN V1.1.2 ( )
2 IEEE Standard for Local and Metropolitan Area Networks, Part 16, Amendment 2 and Corrigendum 1, IEEE Std Feb 2006

6. Full DVB-S2 BER through Linearized Traveling Wave Tube Amplifier (LTWTA) SRRC (B = 0.35, K = 6)/QPSK (Rldpc = 2/5)

7. Spectrally Efficient Waveforms
Unspread Power/Bandwidth Efficiency Tradeoff Including LDPC Coding
Eb/No for BER = 1e-6, dB
Bandwidth Efficiency, bps/Hz
0.1 1 10
0.0001
0.001
0.01 -2 -1 2 3 4 5 6 7 8 9 11 12 13 14 15
Shannon/
Hartley
Capacity
SRRC/QPSK
SRRC/8PSK
SRRC/16APSK
SRRC/32APSK
Spectrally Efficient Waveforms 16 17 18 19 20 21
Increased Bandwidth Efficiency
Does not include implementation losses from 2 to 7.5 dB
Bandwidth efficiency includes SRRC bandwidth skirts
Increased Power Efficiency

8. SEW DSSS Processing Gain versus Data/Symbol Rates and Chipping Rates

9. SEW Spread Spectrum Uplink Throughput
GEO satellite used as a worst-case altitude
SEW waveform (DVB-S2 portion)
QPSK LDPC rate 0.4 block code
CCSDS CDM is based on TDRS waveform
Omnidirectional satellite antenna
The first graph shows theoretical uplink throughput versus RFI EIRP for selected ground terminal EIRP values with Kchips/sec DSSS
Second graph shows theoretical uplink throughput versus RFI EIRP for selected ground terminal EIRP values with CCSDS 3 Mchip/sec CDM

10. Spread Uplink SEW Throughput to GEO Satellite versus Interference EIRP for Selected Ground Terminal EIRPs (dBm) 65 Michps/sec DSSS

11. CCSDS Waveform Uplink Throughput with 3 Mchips/Sec CDM Spread with LDPC Coding

12. SEW Spread Spectrum Downlink Throughput
GEO satellite used as a worst-case altitude
Ground terminal within horizontal line of sight of 55 dBm RFI source
Assumed free space RFI propagation loss
The concave downward cups correspond to the peaks in the ground terminal theoretical antenna pattern
The upward peaks correspond to the nulls in the ground terminal antenna pattern
The dips at 7 and12 degrees off-boresite angle may be an artifact of the angle quantization steps
The next graph shows downlink throughput to a ground terminal versus off-boresite angle for selected standoff distances with 65 Mchips/sec DSSS
The last graph shows downlink throughput to a ground terminal versus off-boresite angle for selected DSSS chip rates with 32 Km standoff distance

13. Downlink SEW Spread Throughput versus Off- Boresite Angle for GEO Satellite for Selected Standoff Distances (Km) with 65 Mchip DSSS

14. Downlink SEW and CCSDS Spread Throughput versus Off-Boresite Angle for GEO satellite Selected DSSS Chip Rates (kchips/sec) with 32 Km Standoff Distance

15. Conclusions and Recommendations
Throughput under RFI for both uplinks and downlinks is greatly increased by spreading the signal spectrum with SEW over full band versus CCSDS CDM
NTIA frequency management is open to CDM SEW proposal approach for wide band RFI mitigation
With adequate spreading, the maximum throughput of the thermal noise limited link is approachable for certain geometry scenarios
The use of DSSS ranging on command and telemetry data modulation symbols can provide:
Mitigation of mutual RFI
High-precision ranging code
Recommendations:
CCSDS RF/Mod group review Aerospace SEW for the next step
What is Aerospace's next step?

16. Acronyms CCSDS Consultative Committee for Space Data Systems
CDM code division multiplex
dB decibel (a logarithmic representation of ratio)
dBm decibels referenced to one milliwatt
DSSS Direct Sequence Spread Spectrum
DVB-S2 Digital Video Broadcast System 2
Eb/No energy per bit to noise density ratio
EIRP effective isotropic radiated power
GEO altitude for earth-synchronous satellites
HDL hardware definition language
Kchip Kilo Chips (per second)
Km Kilo meter
LDPC low density parity check (codes)
LTWTA linearized traveling wave tube amplifier
Mchip Mega Chips (per second)
NASA National Aeronautics and Space Administration
NTIA National Telecommunications & Information Administration
QPSK quadrature phase shift keying (modulation)
RFI radio frequency interference
SEW spectrally efficient waveform
SRRC square root raised cosine (pulse shaping)
SV space vehicle
TDRS Tracking and Data Relay Satellite