Exploring Trends in Technology and Testing in Satellite Communications Aerospace Defense Symposium Giuseppe Savoia Keysight Technologies
Agenda Page 2 Evolving military and commercial satellite communications Satellite basics & background Key technology shifts and resulting challenges Wider bandwidths for higher data rates and more channels Complex modulation formats to increase spectral efficiency Spectrum reuse with narrow spot beams Measurement solutions Satellite PA test Digital modulation troubleshooting Satellite signal monitoring Multi-channel antenna array calibration Summary, Q&A
Satellite Communications Technology and Test Paper Objective Give the audience a basic understanding of the test challenges found in the satellite communications industry and an introduction to modular test and measurement solutions to address them. Page 3
Satellite Basics and Background Page 4
Military & Commercial Communications Satellites Key applications Satellite TV, radio and broadband Coverage for legacy frequency bands: C Band (3.7 6.4 GHz) and Ku Band (11.5 14.5 GHz) Ever-increasing capacity for high-definition video and broad-band service Growing use of spot-beams and Ka band (18-31 GHz) Global Navigation L-Band (1.2 1.8 GHz) Military and public safety High availability links Secure communications High frequency and wide bandwidth (up to 40+ GHz) GPS satellite Page 5
Satellite Network Elements Space Segment Inter-satellite link Broadcast Two-way: Reverse Forward Ground Segment Telemetry, tracking & command (TT&C) Gateway stations Hub stations User terminals Gateways & hubs User Terminals (Fixed, mobile, handheld) Terrestrial Network Page 6
Satellite Components Payload 1 Payload 2 Payload Payload X Payloads Antennas Telemetry, Tracking & Control Attitude Control & Propulsion Command Processor & Data Handling Thermal Bus & Structure Solar Array(s) Power Regulation Battery System Page 7
Modern Satellite Payload Architecture Simplified block diagrams Bent pipe Signal amplified and frequency shifted. Less expensive, less complex Uplink signal demodulated to data packets, routed as needed, then modulated onto downlink carrier. Improved SNR, spectral efficiency Digitally regenerative payloads Demod DSP Mod Page 8
Key Technology Shifts Bring Challenges Page 9
Wider Bandwidths and Frequency Multiplexing Challenges Maintaining signal performance when many channels share 1 transponder Nonlinear distortion will result in interference between channels, reducing C/N and potentially decreasing throughput Tradeoff between intermodulation distortion and satellite mass (# of transponders) Optimizing between efficiency and throughput with potential for high peak-to-average power ratio (PAPR) Signals may add constructively resulting in much higher PAPR than any single channel Tradeoff between biasing power amplifier to avoid compression and power efficiency Power voltage Composite signal Page 10
Digital Modulation Formats Considerations and background Why round constellations? APSK constellation points lie on concentric rings Lower peaks than QAM lower PAPR more efficient for PA Compression has less effect on spacing, relative to QAM Higher order modulation requires higher SNR for equivalent link performance (bit error rate) Constellation points closer together, less tolerant of impairments 16 APSK 16 QAM 32 APSK Page 11
Spectrum Reuse with Narrow Spot Beams Challenges Single satellite can have dozens to hundreds of spot beams Example: Inmarsat GEO I-4 satellites each have ~200 narrow spot beams Greatly increased complexity for design & test Antennas require complex calibration KA-SAT spot beam coverage Trade-off of smaller coverage service may not be available everywhere all the time Smaller spot beams increase antenna size Easier to achieve at higher frequencies (Ka-band) Page 12
Measurement Solutions Page 13
SF Dynamic Range @ max BW Addressing Wideband Needs The analysis choices UXA signal analyzer 510 MHz @ >75 dbc PXA signal analyzer 160 MHz @75 dbc M9703 >600 MHz @<75 dbc Wideband VSA (PXA + Infiniium) ~1.0 GHz @ ~60 db* X93204A Infiniium oscilloscope 62 GHz @ ~50 db bandwidth Page 14
Emulating Real-World Satellite Traffic Conditions for Satellite PA Test Page 15
Challenges of Design and Test of Satellite PAs Characterizing nonlinear distortion Engineers working on satellites with wideband power amplifiers face a trade off between: Efficiency: minimize power consumption, increase reliability Linearity: minimize distortion, interference between channels Intermodulation distortion Page 16
Generating Stimulus for Satellite PA Test Multitone test method for IMD and NPR One vector source generates thousands of tones across bandwidth of DUT More efficient, accurate characterization of wider bandwidth of devices Stress device with higher peak-to-average ratio similar to real-world operation Simple, precise control of number of tones, magnitude and phase, and more Multitone test setup Page 17
Generating Stimulus for Satellite PA Test (continued) Multitone test method for IMD and NPR One vector source generates thousands of tones across bandwidth of DUT More efficient, accurate characterization of wider bandwidth of devices Stress device with higher peak-to-average ratio similar to real-world operation Simple, precise control of number of tones, magnitude and phase, and more Multitone test setup Page 18
Generating Stimulus for Satellite PA Test Correcting multitone signals for better results Magnitude & phase corrections enable suppression of distortion from source and other components in test system Remove DUT from test setup and measure system distortion, extracting corrections data Tone pre-correction setup Before corrections After corrections Page 19
Generating Stimulus for Satellite PA Test Available solutions for multitone N7621B Signal Studio for Multitone Distortion Sources include PSG, MXG, M8190A, M9330A X-Series signal analyzer for corrections M9099 Waveform Creator Sources M9381A, M9330A, M8190A M9391A, M9703A, or any 89600 supported analyzer for corrections Page 20
Response Analyzing PA Distortion Complex stimulus-response measurements Stimulus PA Response Stimulus Types of distortion measurements: AM/AM = mag(resp(t)) vs. mag(stim(t)) AM/PM = phase(resp(t)) vs. mag(stim(t)) Gain Compression = resp(t)/stim(t) vs. mag(stim(t)) Differential (, additive) EVM = mag(stim(t) resp(t)) With modulated signal Page 21
Analyzing PA Distortion Available solutions Stimulus PA Response Measurement Hardware Hardware Config. Stimulus Meas. Response Meas. Multi-channel instrument Channel 1 Channel 2 1 single channel instrument Channel 1 (saved) Channel 1 live (or saved) 2-channel M9393A PXIe performance VSA Page 22
Digital Modulation Techniques and Troubleshooting Page 23
Digitally Modulated Test Signals Challenges More closely space constellation points less tolerant of impairments Common impairments in SATCOM include: - Phase noise, gain imbalance, I/Q skew, gain compression, AM/AM, AM/PM - EVM (error vector magnitude) metric For higher order modulation need better SNR for given BER Page 24
Digitally Modulated Test Signals Identifying Common Signal Impairments Impairments degrade signal quality, potentially impacting data throughput Contribute to overall signal EVM Gain Imbalance Due to I/Q imbalance (amplitude & phase) in analog tuner in front-end filtering & D/C Skew Phase Noise AM/AM AM/PM Due to frequency conversion components (LO s) and amplifiers Due to non-linear distortion in amplifier Page 25 25
Digitally Modulated Test Signals Signal Analysis Solutions 89600 VSA software Modulation analysis Standards-based DVB signals Generic digital signals Custom digital signals In-depth troubleshooting tools Benchtop HW: X-Series Analyzers, Scopes Modular HW: M9393A, M9703A Signal Generation Solutions Signal Studio and Waveform Creator Signal generation Generic digital signals Custom digital signals Benchtop HW: N5182B, E8267D Modular HW: M9381A, M8190A SystemVue Signal generation Standards-based DVB signals Generic digital signals Custom digital signals Design and optimize link-level architecture & algorithms BER measurements Page 26
Digitally Modulated Test Signals Customizing APSK signals Optimize transmission for particular link parameters Define # of rings, # of states per ring, amplitudes & phases Pre-distort signal by varying space between rings before transmission Adjust ring spacing, coding, filtering for power efficiency (PAPR) and distortion (throughput) Page 27
Keysight Reference Solutions Page 28
What is a Reference Solution? A combination of hardware and software enabling users to more rapidly evaluate a test configuration for a specific test application Complete test system Keysight AEO / Partners / Internal test groups Additional hardware Test fixture HW integration SW integration Keysight Reference Solution Test expertise (Example program and block diagram) Standard application SW & HW (Solution brochure & configuration guide) Page 29
In-Orbit Satellite Signal Monitoring: Satellite Signal Monitoring Reference Solution Page 30
In-Orbit Satellite Signal Monitoring Overview & challenges Each band may contain several carriers each with different modulation and symbol rate Several bands may need to be monitored at once Interfering carriers need to be detected and identified Page 31
Sequential Scanning Model Shared VSA, multi-band, power spectrum scanning and digital demodulation Low power and weight Cost efficient Easy to scale # of scanned bands Page 32
Parallel Model Dedicated VSA for each band Supports parallel acquisitions for all bands and provides fast display updates (not gap-free) Supports cross band timing measurement to 1nS for up-link to down-link timing Required when spectrums overlap (example: block down-convert all to L band) Page 33
Satellite Signal Monitoring Power spectrum & digital demodulation measurements Multiple simultaneous measurements Wideband spectrum measurement - Broad band power monitoring Occupied bandwidth - Monitoring carrier power Digital demodulation - Analyzing signal quality Supports both sequential and parallel M9393A & 89600 configurations Page 34
Sequential Scanning Model 89600-SSA + digital demodulation for multiple satellite bands Page 35
Satellite Signal Monitoring Fast, effective solution for monitoring large blocks of spectrum (power spectrum analysis) combined with precise digital modulation analysis to validate satellite signal integrity while providing reduced size and cost Optimized to support fast display refresh rates and multi-band scanning Zoom-in on signals of interest within the IF bandwidth using digital vector analysis Physical size/weight improves transportability and deployment for WW applications up to four VSAs in a single PXI chassis Page 36
Reference Solution Example Logging Program Cycles between power and demodulation measurements Compares power measurements to limits Logs results to a file Page 37
Calibrating AESA Arrays for Spot Beams: Multi-channel Antenna Calibration Reference Solution Page 38
AESA Antennas for Spot Beams Calibration challenges Large phase arrays require phase synchronous sampling across all input channels Array element counts increasing, leading to long calibration times Measurements require high resolution sampling of IF signals and fast frequency switching Need to test and calibrate multiple types of antenna require flexible, multifunctional measurement system Page 39
Configuring a Test System for an AESA Antenna Page 40
Calibrating Phased Arrays for Spot Beams Multi-channel antenna calibration reference solution Ka-band frequency coverage DC to 40 GHz Reduce calibration time Typical 8x 10x throughput improvement Up to 40+ channels measured in parallel Improved beam-forming accuracy Ch-Ch phase coherence < 1, nom Extendable to wideband for future needs (up to 600 MHz bandwidth) Page 41
Receiver Calibration Block Diagram Page 42
Wrap Up & Questions Page 43
Satellite Communications Technology & Test Key takeaways Key technology shifts to meet growing demand for data - Wider bandwidths for higher data rates and more channels - Complex modulation formats to increase spectral efficiency - Spectrum reuse with narrow spot beams Many test challenges associated with these new technologies and increasing complexity New tools and test solutions are available to help Page 44
Questions?