Effective Strategies for Satellite Communications RFI Mitigation Daniel L Oltrogge, SDC Program Manager Haroon Rashid, Sr Advisory Software Dev & Sr. Member, IEEE ESTEL Conference, Roma, Italy, 4 Oct 2012
Introduction Radio Frequency Interference (RFI) of Great Importance CSSI: Center for Space Standards & Innovation Goal of space standards is to help facilitate cooperative, sustainable and commercially-viable use of space Many of CSSI s innovations focused on detection and mitigation of collision & RFI threats RF Interference is current topic in Space News RFI has a large impact on the business of commercial SatCom ($Millions) due to lost bandwidth and transmission delays 2 of 30
Effective Strategies for Satellite RFI Mitigation Describe coupling of authoritative satellite operator data & capable analysis framework Provide space operators timely, actionable RFI mitigation Facilitate pre-emptive avoidance of anticipated RFI events while proactively identifying and quickly mitigating others Discuss RFI geolocation testing and simulation activities using satellite operator data Suggest Figures-of-Merit for pre-computed RFI solution sets 3 of 30
Most Problematic RFI Paths: 2 RFI types difficult to mitigate: Satellites-to/from-Ground Inter-Satellite vs GEO-to-Ground RFIs are either unintentional Bad Equipment, mistaken schedules or polarities, or Fly-By (LEOP or drifting) satellites or intentional (jamming/dos) Occurrence of intentional jamming varies by operator and satellite location, but is typically rare (<< 1%) Source: ITU Recommendation ITU-R S.1526-1 4 of 30
Typical Operator Workflow for RFI Mitigation Triggered by carrier monitoring or customer report Interference detected or reported Level 2 team investigates L2 specialists for persistent, complex RFI - Dedicated effort on RFI cases - Mitigation expertise (tools, carrier monitoring, DSP, geolocation, industry databases) - Liaise with all parties - Customer(s), Sales Engr., Suspected Source L1 Ops Center Priority: Restore service - Degraded but still operating? - Outage, can service be relocated? After restoring service: - Identify RFI - Remove RFI Trouble Ticket created 24x7 Level 1 Operations Center investigates Interference resolved? Escalate to Level 2 No Interference resolved? Yes 15% of tickets escalated to L2 Staff Inform 24x7 Ops Centers for restoration of affected services No Further actions: - Continue to investigate w/other orgs. - Seek corrective actions w/rfi source - ASI Operator actions - Legal/regulatory Yes Trouble Ticket closed Trouble Ticket closed 5 of 30
Typical RFI Incidents for Large GEO Operators Intermodulation 9% CW 7% Number of Tickets Sweeper 4% Unknown 1% Re-Transmit/ Re-Broadcast 4% ASI 19% Compression 1% RFI data based on number of tickets for each interference type 368 events, covering 30 satellites Better Metric: Weight incidents based upon affected bandwidth and time to resolve Cross-Pol 24% Source of data: Satellite Operator tickets, Dec 2010-May 2011 Major problems are Co-pol and Cross-pol (from Operator s own customers), followed by ASI Co-Pol 31% Level 1 Team fixes Co-pol, Cross-pol Bandwidth*Time to Resolve Sweeper Unknown Re-Transmit/Re- 6% 0% Broadcast 2% ASI Intermodulation 37% 6% CW 1% Cross-Pol 29% Adjacent Satellite Interference (ASI) is single largest RFI problem (37%) due to extensive ASI mitigation time Co-Pol 18% Source of data: Satellite Operator tickets Dec 2010-May 2011 Compression 1% 6 of 30
Adjacent Satellite Interference (ASI) ASI caused by [unintentional] multi-path of interfering signal thru interfered comm. satellite 7 of 30
Analytical Indication of Interference: ASI characterization: Crudely approximated by boresight off-axis angle [ Carrier ] [ Noise Interference] Occurs when < Receiver Sensitivity Limit 8 of 30
ASI Mitigation Via RFI Geolocation COTS capabilities already exist to perform highly accurate RFI geolocation Time and Frequency Difference of Arrival Interferometrics, Glowlink, RT Logic, Siemans Utilized by large space operators We re often tempted by new technical solutions www.interferometrics.com But existing COTS solutions very good if not data-starved Process improvement = biggest RFI mitigation gain AGI investigated benefit of injecting most current/actionable data into geolocation process Initial finding: 30x improvement in FDOA location 9 of 30
Multiple RFI Geolocation Approaches Exist: RFI geolocation determines interferer location Geolocation one of principal RFI mitigation tools today At least 5 geolocation technique broad categories: TDOA, FDOA or combined TDOA/FDOA-based methods Received signal power amplitude (RSPA) analysis based on a single pre-determined antenna pattern RSPA methods using an array of two or more antennas with pre-determined antenna patterns Angle of Arrival (AOA) using two simultaneous measurements of azimuth/elevation Line-of-Bearing, using two simultaneous measurements on two platforms or measurements at 2 separate times 10 of 30
TDOA/FDOA Typical Results Combining TDOA & FDOA measurements of two adjacent satellites yields a geolocation solution: 11 of 30
Space Data Association Overview SDA Executive Members: Chief Technology Adviser / SDC Operator: Commercial enterprise (NCAGE Code: U0HJ4) Space Data Center Verified, normalized data Automated analysis/reporting Open to all satellite operators in all orbital regimes Additional participants: Arabsat, Avanti, EchoStar, GeoEye, GE Satellite, NASA, NOAA, Optus, Paradigm, Space Systems/Loral, StarOne, Telesat Canada Strong legal agreements protect member information from disclosure/misuse 12 of 30
Motivations for SDA s Creation Enhance Safety of flight Definition: The condition where satellites are positioned and operated in a manner that preserves their long-term operational viability, the long-term operational viability of any other satellites, and the preservation of the orbital regime(s) involved EMI/RFI Geolocation and Resolution Support More rapidly find and address interference sources Efficient, timely, accurate conjunction assessments Consolidate and use best available data from operators, including planned maneuvers Reduce false alarms, missed events Minimize member time and resources devoted to CA SSA / Format Conversions / Information Repository Minimize confusion, potential for conflicting decisions Encourage evolution of best practices for Members SDA Enhances Satellite Operations & Lowers Operational Costs13 of 30
Space Data Center as Key RFI Mitigation Tool Collision Avoidance monitoring, maneuver planning & flight safety Radio Frequency Interference mitigation & geo-location support Authoritative contact info (ops center POCs) for SDA member satellites Space Data Center (SDC) currently supporting 231 satellites from 15 GEO operators and 110 satellites from 7 LEO operators 341 Sats 14 of 30
SDA RFI Planned Process Flow Members contribute and dynamically maintain proprietary RF data: Freq plan; polarization; translation freqs; antenna patterns, Rx & Tx chars, beam coverage Members contribute data on Reference Emitters/Calibrators Satellite ephemerides are automatically updated by all SDA members Members detect an RFI event and report the details to the SDC SDC Data stored in common format Frequency bands and beam coverages searched for suitable adjacent satellites for geolocation measurements Database queried for most likely region, satellite(s), and contact information to investigate potential interference source Get reliable contacts for other Operators, to investigate RFI Search RFI case studies from RFI database, to help find similar events Geolocation solution sets generated and sent to Member in format for geolocation system Optional information provided to third parties for geolocation or other services Flyby notification to warn of possible interference RFI Alert notification sent to Members System allows faster investigation of RFI events, improving service quality and creating more efficient operations 16 of 30
Summary of SDA s Technical Approach SDA striving to aggregate largest set of authoritative & normalized ephemeris, RF parameters & POCs into analysis Space Data Center to facilitate preemptive, proactive RFI mitigation Dynamically populate SDC s Radio Frequency (RF) database with current and actionable RF data may constitute biggest and most daunting task Once accomplished, however, RF analysts will be able to generate actionable forensic and predictive RF and RFI assessments Pre-generate RFI solution sets 17 of 30
RFI Mitigation #1: Pre-emptive Fly-By Analysis Fly-By events include: Satellite relocation to new GEO orbital slot Sea Launch & Arianne Equatorial or 5.3- inclined orbits yield LEOP drift phase with high RFI potential Satellite technicians can de-conflict anticipated RFIs if known in advance Requires sufficient detail is available on all pertinent satellite RF parameters, antenna patterns/orientation and orbital positions 18 of 30
Typical Fly-By Preemptive Analysis Product RFI avoidable by orbit maneuver or Tx coordination [Carrier]/[Noise] (db) Interfered Span Time (Seconds) [Carrier]/[Noise] (db) [Carrier]/[Noise + Interference] (db) 19 of 30
RFI Mitigation Analysis Cases #2 & #3: Case 1: Fly-By analysis was one example of the preemptive RFI mitigation figures-of-merit that can be generated given sufficient RF data We now examine figures of merit that can be precomputed if satellite operator RF parameters (incl. detailed, well-known antenna pattern) Case 2: RFI from transiting LEO satellite into GEO downlink to ship-based receiving antenna Case 3: RFI from a well-quantified interfering uplink signal impacting an adjacent satellite s communications Case 4: RFI from a well-quantified interfering downlink signal impacting an Earth station 20 of 30
RFI Preemptive Analysis Case #2: LEO satellite transits thru GEO downlink to ship-based receiving antenna; can evaluate transit impact Pre-interference nominal Received Signal Predicted Received Signal Including LEO Interference 21 of 30
RFI Preemptive Analysis Case #3 Description For this case: Earth station A is transmitting into satellite A Interfering Earth station B (at unknown location but w/known antenna pattern) transmitting into satellite B (2 from A in GEO belt) Assuming: Earth station B and GEO satellite A antenna pointing well-known Satellites A & B positionally well known Then: Can generate contours of [Interference : Noise] at all possible earth station B Tx locations 22 of 30
RFI Preemptive Analysis Case #3: Well-quantified uplink RFI into adjacent satellite Such contours + measured received normalized interference level yields a location area of admissibility e.g., Rx interference signal w/normalized power level 3 db above noise likely originates from green region 23 of 30
RFI Preemptive Analysis Case #4: Well-quantified downlink from adjacent satellite Identifies admissible interfering satellite antenna pointing e.g., if interfered comm. system withstands 3 db above noise, collaborating operator must avoid orange region 24 of 30
Sources of RFI Geolocation Degradation Many factors degrade RFI geolocation accuracy: Ephemeris uncertainty Undersampled orbit observations and time of day variations Selection of satellite pair w/non-synch movement Accumulation of multiple measurements over time ASI relative geometry (incl. Ref in line w/satellites & target) Adjacent satellite RF Compatibility & frequency bandwidth overlap Collector clock synchronization Uncertainty in center frequency and phase noise Geoid and terrain model uncertainties Processing and TDOA measurement errors Ionosphere-induced TDOA and FDOA errors Troposphere-induced path length errors 25 of 30
RFI geolocation sensitivity to orbit sampling/quality Gov t-sponsored RFI mitigation test conducted using three adjacent GEOs Jan 2012 Goal is to determine sensitivities to data Results of first test: SDA data 30x improvement in TDOA dimension But also noted distinct nightfavoring accuracy trend in TLEs May stem from systemic undersampling for optical obs 26 of 30
RFI geolocation sensitivity to OD w/o Ref. Emitters 27 of 30
Figures-of-Merit for Precomputed Sol n Sets Currently evaluating time-varying RFI geolocation degradation errors we can control or quantify FOM GeolocSolnSet = Aσ epha t + Bσ ephb t + C f Geom t + D f RF_Antennas_EIRP_etc + E f(freq_bw_overlap) + Next step: further definition of f(t) alternatives, implementation, simulation and test evaluation 28 of 30
Summary: Improving RFI Mitigation Timelines Customer Identifies Interference Issue Exhausted Level 1 Suuport Mitigation Options Schedule & Conduct Geoloc Search for Suitable Adj S/C Define & Exchange RF Search Adj Sats Search Adj Sats,POCs Post- Process, Identify Define & Exchange Ephem Notify Interferer; Resolve Schedule & Conduct Geoloc Search for Suitable Adj S/C Define & Exchange Ephem Post- Process, Identify Schedule & Conduct Geoloc Rectify Ephem Format/ Frame Notify Interferer; Resolve Rectify Ephem Format/ Frame Post- Process, Identify Define & Exchange RF Define & Exchange RF Notify Interferer; Resolve Search for Suitable Adj S/C Search for Suitable Adj S/C Schedule & Conduct Geoloc Schedule & Conduct Geoloc SDC Phonebk, Ephem, RF Alerts, RF Params, Ref Emitters, Precomputed Geoloc Sets Post- Process, Identify Post- Process, Identify SDC Phonebk, Ephem, RF Alerts, RF Params, Ref Emitters Notify Interferer; Resolve SDC Phonebk, Ephem, RF Alerts Notify Interferer; Resolve SDC Phonebk & RFI Alerts None 0 1 2 3 4 Time from Initial RFI Report (days) 5 29 of 30
Questions? 30 of 30
Cross-Organizational Data Fusion Radar/Optical sensor shortcoming is inability to predict or account for operators maneuvers SDA implemented workable data fusion concept Multi-source data sharing, orthogonal data and trustbut-verify independent data quality checks Few objects (e.g., <100): Share ephemeris Catalog (>100 RSOs): Adopt AIAA standards approach Astrodynamics Propagation Specifications, Test Cases, and Recommended Practices (ANSI S-131-2010) USG focus on improving algorithms; let users implement based on USG-provided governing equations, approach & test cases 31 of 30
Important Elements of Data Fusion Quantified uncertainty of inputs Data Alignment Reference Frames Coordinate Systems Time Scales Fundamental Measures of time, distance, and mass Input sequencing and synchronization 32 of 30