SATCOM Availability Analysis : SATCOM Availability Analysis ICAO Working Group M Iridium Subgroup August 23, 2006


Background: Background This briefing describes work supporting NASA, the FAA and EUROCONTROL to develop technology evaluation criteria for evaluation of new technologies for mobile aeronautical communications as part of the FCS The technology assessment team was charged to “investigate new terrestrial and satellite-based technologies” The technologies that are recommended must: Meet the needs of aviation (as identified in the COCR and ICAO consensus documents) Be technically proven Be consistent with the requirements for safety Be cost beneficial Promote global harmonization


SATCOM Task Activity Overview: SATCOM Task Activity Overview The purpose of this task was to assess the viability of using existing commercial satellite systems with AMS(R)S frequency allocations to provision the communications services that are detailed in the COCR Task Activities SATCOM Availability Analysis Provide a comparative analysis of the availability of identified commercial satellite architectures and a VHF terrestrial communication architecture for provision of aeronautical mobile services COCR Service Provisioning Using SATCOM & Hybrid Architectures Determines if SATCOM technology candidates can meet COCR requirements This briefing only covers COCR Service Provisioning Using SATCOM Architectures


Comparative Analysis: Comparative Analysis The following tasks were performed for this comparative availability analysis: Identify/describe architectures for analysis Define availability, assumptions and analysis approach Calculate and analyze availability contributors Compare/discuss analysis results


Identify/Describe Architectures for Analysis: Identify/Describe Architectures for Analysis


Identify Architectures for Analysis: Identify Architectures for Analysis Two satellite service architectures with AMS(R)S frequency allocations were identified for consideration in this analysis Inmarsat-4 SwiftBroadband (SBB) service Iridium communication service These architectures were contrasted with a generic VHF terrestrial communication architecture Data communications architecture based on existing infrastructure


Identify Architectures for Analysis: Inmarsat SBB (3): Identify Architectures for Analysis: Inmarsat SBB (3) Representative Inmarsat SBB NAS coverage area Example reference area is covered by three SBB spot beams within the Inmarsat I-4 satellite coverage area Spot beam coverage for this area is illustrated below


Identify Architectures for Analysis: Iridium (2): Identify Architectures for Analysis: Iridium (2) Representative Iridium coverage area Example Iridium reference area falls within 2 orbital planes Approximately 20% of this area falls within view of two orbital planes ORBITAL PLANE 1 ORBITAL PLANE 2


Identify Architectures for Analysis: Terrestrial (2): Identify Architectures for Analysis: Terrestrial (2) Representative coverage area The analyzed terrestrial architecture assumed a redundancy scheme loosely based on current RCAG/BUEC redundancy For portions of the reference area, BUEC sites providing RCAG/BUEC redundancy are shown Figure illustrates coverage density with significant overlap; for analyzed architecture, minimal overlap was assumed Credit for significant redundancy in current A/G voice architecture was not taken Assumed that a unique RCAG/BUEC redundant pair provides area coverage in the analyzed terrestrial architecture


Define Availability, Assumptions and Analysis Approach: Define Availability, Assumptions and Analysis Approach


Definitions, Assumptions and Approach: Definitions, Assumptions and Approach Availability Given that link interruptions and system component failures can lead to service outages, and each outage requires varying restoration times, availability characterizes the impact of interruptions, failures and service restoration times on the usability of a system Percentage of the time a system is available for use Generally described as the following ratio: To apply the ratio above, a definition of ‘Outage Time’ is needed Typically, an outage is defined as the time the service is not meeting a specified performance or Quality of Service For data service, this is often described as a service providing a certain bit error rate (BER) while meeting maximum latencies


Definitions, Assumptions and Approach (2): Definitions, Assumptions and Approach (2) RTCA DO-270, MASPS for the AMS(R)S as Used in Aeronautical Data Links, considers two categories of outages Multi-User Service Outage: A Service Outage simultaneously affecting multiple aircraft within a defined service volume Single-User Service Outage: A Service Outage affecting any single user aircraft within a defined service volume Focus for this analysis is service provisioning for multiple aircraft within a defined service volume Consideration of outages is ‘multi-user service outages’


Definitions, Assumptions and Approach (3): Definitions, Assumptions and Approach (3) Geographically Dependent Availability Ratio If a system covers a large region of airspace and if partial outages could occur, then a geographically dependent availability ratio should be used This was applied in some cases of the current analysis


Definitions, Assumptions and Approach (4): Definitions, Assumptions and Approach (4) Approach Utilized SATCOM availability analysis model described in RTCA DO-270 Defines availability fault-tree to permit individual characterization and evaluation of multiple availability elements Organized into two major categories System Component Failures Fault-Free Rare Events Model is useful for comparing architectures and was used for this study


Definitions, Assumptions and Approach (5): Definitions, Assumptions and Approach (5) Approach (cont’d) When a complex system consists of independent serial elements, the overall availability is equal to the product of the availability ratios for the individual elements: This can be applied to the availability tree model to characterize an architecture availability with a single number and is the approach presented in DO-270 However; this approach has its limitations The independence assumption is not always valid Reducing this complex model into a single number oversimplifies the issue “Tall poles in the tent” in a multiplicative relation dominate the entire product Operating Time (or Observation Time) periods may be different for different elements This approach is risky when one or more of the element availability calculations are based on incomplete or unavailable data, as in this case Due to these limitations, this approach was not used for this study AoSYS = Ao1 x Ao2 x Ao3 x … x AoN


Definitions, Assumptions and Approach (6): Definitions, Assumptions and Approach (6) Methodology used for this task First, availability was assessed for each availability element for each of the three architectures System component availability elements Fault-free event availability elements These findings were then compared and contrasted for each of the three architectures (SATCOM and terrestrial) Compared estimated availability performance (terrestrial vs. SATCOM) Identified outage impact for terrestrial vs. SATCOM systems


Definitions, Assumptions and Approach (7): Definitions, Assumptions and Approach (7) System Component Failure Availability Elements Ground Station Equipment Failure Event For Satellite Systems, failure events associated with the Ground Earth Station (GES) or stations and any terrestrial networking between the GESs (if there are more than one) For terrestrial VHF radio, failure events associated with the ground radios and radio control equipment at the radio sites Satellite Control Equipment Failure Event For Satellite Systems, failure events associated with the Network Operations Center (NOC) Not applicable to terrestrial architecture Aircraft Station Equipment Failure Event For both satellite and terrestrial VHF radio, failure events associated with aircraft radio equipment Satellite Equipment Failure Event For satellite systems, failure events associated with the satellite (for communication relay) Not applicable to terrestrial architecture


Definitions, Assumptions and Approach (8): Definitions, Assumptions and Approach (8) Fault-Free Event Availability Elements RF Link Event For both satellite and terrestrial communication systems, accounts for random radio frequency events (such as severe fading) for which defined system link budgets are not met and which could lead to service outage Capacity Overload Event For both satellite and terrestrial communication systems, accounts for conditions where available communications capacity is overloaded Interference Event Accounts for aggregated interference environmental effects from external sources that may lead to service outage For satellite systems, emissions from other SATCOM communication systems operating from other aircraft in the same operating space For terrestrial systems, emissions from aircraft in the same operating space Scintillation Event Accounts for ionospheric events involving the sun and the earth’s magnetic field, which produce random variations in electromagnetic waves traversing the ionosphere For this analysis, scintillation only applies to satellite communication systems (not relevant to VHF communications propagation effects)


Calculate and Analyze Availability Contributors: Calculate and Analyze Availability Contributors


Calculate and Analyze Availability: System Components: Calculate and Analyze Availability: System Components System component availability calculations were based on FRS component failure model elements: Ground Station Equipment Satellite Control Equipment Aircraft Station Equipment Satellite Equipment


Calculate and Analyze Availability: Modeling the FRS: Calculate and Analyze Availability: Modeling the FRS For the two SATCOM systems, the Future Radio System (FRS) includes system components encompassed by Points B through C, as shown in the standard Aeronautical Mobile Satellite System (AMSS) model Standard AMSS Model Block Diagram


Calculate and Analyze Availability: Inmarsat SBB: Calculate and Analyze Availability: Inmarsat SBB Modeled Inmarsat architecture General architecture assumptions NAS is serviced by a single I-4 satellite with ground spare available for backup in the case of unrecoverable spacecraft failure Users can be accommodated by either SAS Inmarsat offers a fully redundant Network Operations Center (NOC)


Calculate and Analyze Availability: Iridium: Calculate and Analyze Availability: Iridium Modeled Iridium architecture General architecture assumptions NAS is serviced by one or two Iridium orbital planes Iridium offers a fully redundant NOC Aeronautical Gateway User Control Site Equipment/Applications User Telecom User Telecom Iridium Satellite Constellation Modeled Iridium FRS Iridium OSN User Applications Aircraft Earth Station (AES)


Calculate and Analyze Availability: VHF Terrestrial: Calculate and Analyze Availability: VHF Terrestrial Modeled VHF Terrestrial Architecture Includes primary/backup radio redundancy General architecture assumptions Primary radios are configured with redundancy equivalent to current Remote Communication A/G (RCAG) sites Backup radios are configured with redundancy equivalent to current BackUp Emergency Communication (BUEC) A/G sites


Calculate and Analyze Availability: Ground Station: Calculate and Analyze Availability: Ground Station Ground Station components modeled for availability calculation Aeronautical Gateway Iridium Satellite Constellation Modeled Iridium FRS Iridium OSN Aircraft Earth Station (AES)


Calculate and Analyze Availability: Ground Station (2): Calculate and Analyze Availability: Ground Station (2) Ground Station Equipment Availability SATCOM: Specific ground system outage information was not available from Inmarsat or Iridium Instead, available GES outage information was used to derive ‘similar in kind’ assumptions applied to both Inmarsat and Iridium GES availability calculations Terrestrial: Availability values associated with individual components were calculated based on published MTBF/MTTR values for existing NAS radio equipment (e.g. for RCAGs/ BUECs) Reference NEXCOM SRD, Appendix E


Calculate and Analyze Availability: Ground Station (3): Calculate and Analyze Availability: Ground Station (3) Calculated availability values: Inmarsat Gnd Stn: Availability: essentially 1 for yearly observation for all coverage volumes Iridium Gnd Stn: Availability: 0.99997 for yearly observation for all coverage volumes VHF Terrestrial Gnd Stn Equip Availability: 0.99999 for yearly observation for all coverage volume Ground Station Equipment Inmarsat offers very high availability ground systems for the entire service volume Due to lack of ground station redundancy, Iridium ground station availability is not quite as high For VHF terrestrial ground systems, this result is the system component availability


Calculate and Analyze Availability: Ground Control Equipment: Calculate and Analyze Availability: Ground Control Equipment Satellite Ground Control Equipment modeled for availability calculation Primary Remote A/G Radios Aircraft Radio Modeled Terrestrial FRS Backup Remote A/G Radios This element is not applicable to the Terrestrial Architecture Iridium Satellite Constellation Modeled Iridium FRS Iridium OSN Aircraft Earth Station (AES) Aeronautical Gateway


Calculate and Analyze Availability: Ground Control Equipment (2): Calculate and Analyze Availability: Ground Control Equipment (2) Satellite Ground Control Equipment Availability Both Inmarsat and Iridium offer fully redundant NOCs For both Inmarsat SBB and Iridium, all users were assumed to be normally serviced by a single NOC Specific satellite ground control equipment outage information was not available from Inmarsat or Iridium Instead, review of available Ground Control outage information was used to derive ‘similar in kind’ assumptions applied to both Inmarsat and Iridium Ground Control availability calculations Upon investigation of ground control station outages, it was difficult to find much outage information; however trends point to highly reliable ground control stations


Calculate and Analyze Availability: Ground Control Equipment (3): Calculate and Analyze Availability: Ground Control Equipment (3) Calculated availability values: Inmarsat Ground Control: Availability: essentially 1 for yearly observation for all coverage volume Iridium Ground Control: Availability: essentially 1 for yearly observation for all coverage volume VHF Terrestrial Ground Control Not Applicable Satellite Ground Control Equipment Both Inmarsat and Iridium offer very high availability ground control systems for the entire service volume


Calculate and Analyze Availability: Aircraft Station: Calculate and Analyze Availability: Aircraft Station Aircraft Earth Station Equipment For both satellite system and terrestrial VHF communications, the aircraft station equipment is highly dependent on the installation For multi-user availability calculations, the focus is on service provisioning rather than on connectivity to an individual user For multi-user availability calculations, aircraft station equipment availability is considered to be one (1) This is consistent with the approach presented in DO-270 Failures in aircraft station equipment that are dependent on installation, local interference effects for the aircraft, etc. are not accounted for; rather focus is on whether the user population in an associated service volume is accommodated in general


Calculate and Analyze Availability: Spacecraft: Calculate and Analyze Availability: Spacecraft SATCOM Spacecraft Equipment SATCOM For SATCOM, the spacecraft equipment element includes the space segment components For the Inmarsat SBB architecture, this addresses the single I-4 satellite that would provide SBB service to the NAS For Iridium, this includes all satellites (including crosslinks) in the one or two orbital planes that would provide communication service to NAS coverage areas Terrestrial VHF Communications This component is not applicable to the terrestrial VHF architecture


Calculate and Analyze Availability: Spacecraft (2): Calculate and Analyze Availability: Spacecraft (2) SATCOM Spacecraft Equipment Availability Satellite failure information from Inmarsat and Iridium was not available for this study To derive outage rates and durations for individual satellite availability contributors, historical satellite failure anomaly/outage information was reviewed to apply “similar in kind” statistics Sources included: “Satellite G&C Anomaly Trends”, Brent Robertson & Eric Stoneking, NASA AAS 03-071 General satellite failure information from http://www.sat-index.com/failures/index.html?http://www.sat-index.com/failures/echo4.html NAVY GEOSAT Follow-On (GFO) detailed satellite event log “Historical and Recent Solar Activity and Geomagnetic Storms Affecting Spacecraft Operations”, Joe H Allen, SCOSTEP, GOMAC 2002 “Spacecraft Anomalies and Lifetime” by Charles Bloomquist of Planning Research Corporation Satellite Insurance Rates on the Rise: Market Correction or Overreaction, Futron Corporation, July 10, 2002 Informal Iridium tracking site: http://www.rod.sladen.org.uk/iridium.htm


Calculate and Analyze Availability: Spacecraft (3): Calculate and Analyze Availability: Spacecraft (3) SATCOM Spacecraft Equipment Considerations for SATCOM architectures Two categories of spacecraft components were considered to contribute to individual satellite outages Platform – comprises the following individual elements Electrical Power System Attitude Control System Mechanical Propulsion Command & Data Handling Communications Software Operations Payload - includes component failures and software anomalies associated with payload equipment Categories in red were the major Mean Time to Replace (MTTR) recoverable outage contributors


Calculate and Analyze Availability: Spacecraft (4): Calculate and Analyze Availability: Spacecraft (4) Inmarsat Spacecraft Equipment Availability Availability was calculated using historical satellite failure anomaly/outage information and the following relation : Where: TObs = Observation time = assumed mission life = 10 years Pk rec = Probability of recoverable failure for kth equipment element (Tout)k = Outage time associated with failure and recovery of kth equipment element PTot = Combined probability of total (unrecoverable) equipment failure (1%) based on industry bus failure statistics and reasonable assumptions TOut Tot = Outage due to total failure = time to replace (relaunch/orbit) spacecraft = estimated 3 months


Calculate and Analyze Availability: Spacecraft (5): Calculate and Analyze Availability: Spacecraft (5) Iridium Spacecraft Equipment Availability Iridium spacecraft availability was calculated based on the assumption that the constellation serving the area under analysis is composed of one or two orbital planes each comprised of 11 satellites Calculated using a geographic dependent availability formula Assumed a two region model: in one region the reference area is serviced by a single orbital plane, and in the second region the reference area is serviced by two orbital planes Because the Iridium architecture utilizes satellite crosslinks as part of the service chain, one crosslink was included in the service chain for the area under analysis It was assumed that a satellite outage affects only the spotbeam associated with the satellite experiencing the outage (e.g. any crosslinks it had accommodated would be routed through neighboring satellites)


Calculate and Analyze Availability: Spacecraft (6): Calculate and Analyze Availability: Spacecraft (6) Iridium Spacecraft Equipment Availability (cont’d) The availability observation period for Iridium was set to the median design lifetime, or 6.5 years The anomaly incident rate, approximately 12%, defined in the NASA study for LEO systems was assumed For total failure recovery time, the outage time (time to move in-orbit spare into place) was taken to be 10 days For orbital plane recoverable satellite failures, two approaches were employed Approach 1: Use a set of recoverable failures identified in the NASA study* Approach 2: Assume recoverable satellite anomalies are primarily due to weekly scheduled maintenance lasting up to 3 hours** and assumed to affect all satellites in an orbit simultaneously *Satellite G&C Anomaly Trends”, Brent Robertson & Eric Stoneking, NASA AAS 03-071 * *Described in the Iridium Implementation Manual, IRD-SWG03-WP06, 2-15-06, p. 46.


Calculate and Analyze Availability: Spacecraft (7): Calculate and Analyze Availability: Spacecraft (7) Satellite Equipment Inmarsat Satellite: Average Availability/ Mission Life: 0.9999 for all airspace Iridium Satellite: Average Availability/Mission Life: Approach 1: 0.9995 Approach 2: 0.99 Geographically dependent on one or two orbital plane coverage VHF Terrestrial: Not Applicable Calculated availability values: Spacecraft availability calculation issues Straight-forward availability calculation results are difficult to apply Spacecraft tend to be engineered for very high reliability due to inability to perform repairs Long MTTR are typically the drivers in the availability calculations


Calculate and Analyze Availability: Fault-Free Rare Events: Calculate and Analyze Availability: Fault-Free Rare Events Fault-Free Rare Events consist of communications outages due to statistically unlikely events not associated with any system failure mode Fault-Free Rare Event availability calculations include: RF Link Event Capacity Overload Event Interference Event Scintillation


Calculate and Analyze Availability: RF Link Events: Calculate and Analyze Availability: RF Link Events RF system link availability can be defined as: Where ∑(TOUT)k is the total interval of time within the observation interval when the RF system link is not available for use “Available for use" means that the RF link is capable of providing communications with the specified level of integrity while meeting the maximum transfer delay permitted by the operational application. Typically the integrity parameter for RF digital links is bit error rate (BER)


Calculate and Analyze Availability: RF Link Events (2): Calculate and Analyze Availability: RF Link Events (2) Satellite system design allows for outage events that: Have a very low probability Are not precluded by elements of the system design Will occasionally occur even when the system is operating within its specifications. In DO-270 Appendix B, RF link system performance is based on the parameter, , which is the probability that the RF link satisfies the link budget by providing the necessary C/N to meet the BER integrity requirement Thus, if the performance is observed by sampling the RF link, with each sample defined as an event, then some fraction, 1−, of all events will not satisfy the link budget Typically,  is a design parameter, not an inherent characterization of the satellite link performance The satellite service provider determines what level of availability it seeks to provide and then selects its hardware operating parameters to provide enough link margin to mitigate against random link and RF component degradations


Calculate and Analyze Availability: RF Link Events (3): Calculate and Analyze Availability: RF Link Events (3) In Appendix B of DO-270, the pro forma RF link budgets include margin MC necessary to meet the specified availability () while accommodating typical random losses associated with satellite links, including the following: Atmospheric Absorption Losses Degradation of G/T from the Sun Precipitation Loss Satellite Antenna Variations Satellite Hardware Variations LNA Noise Figure Variations Polarization Coupling Losses Satellite Modulation Imperfections Scintillation Loss Because aeronautical SATCOM links are typically modeled as Rician fading multipath channels, the DO-270 pro forma RF link budgets accommodate fading losses with a Rician fading margin value


Calculate and Analyze Availability: RF Link Events (4): Calculate and Analyze Availability: RF Link Events (4) As indicated in the previous slide, SATCOM link availability for a specific SATCOM system is highly dependent on numerous system-specific parameter values. For the most part, these parameter values are not readily available from Inmarsat and Iridium However, some link availability design goals for these two systems have been presented in technical studies According to the Eurocontrol AeroBGAN Study: A “95% link availability, under all worst-case link conditions is the link design criterion” for Inmarsat IV. This is based on a minimum 5 degree elevation angle. As yet, Iridium is “silent” on stated availability in the February 2006 draft of the Iridium Tech Manual for ICAO, though earlier studies state a link availability of 99.5% at the stated user data rate of 2400 bps, with a packet error rate of 10-6


Calculate and Analyze Availability: RF Link Events (5): Calculate and Analyze Availability: RF Link Events (5) Further observations of SATCOM service RF link availability As a point of comparison, DO-270 specifies multi-year availability of at least 0.993 over an Observation Time of one year Inmarsat SBB service has not been in operation long enough for the vendor to gather sufficient RF link availability statistics The broad range in operating parameters of SBB (e.g. data rate and transmit power) provides Inmarsat with significant latitude in providing specific levels of RF link availability RF link availability is driven more by business considerations than technical considerations (e.g., the relatively small percentage of Inmarsat business represented by aeronautical services) Iridium probably has less latitude in providing a broad range of RF link availabilities Relatively fixed system design based on original Motorola Iridium design and operating parameters (e.g., its limited data rate and data rate range)


Calculate and Analyze Availability: RF Link Events (6): Calculate and Analyze Availability: RF Link Events (6) Terrestrial VHF link availability DO-224B notes that [italics added]: “the service availability goal of the end-to-end communication system” for data service is 0.999 (Section 2.4.1) Observation Time is not specified


Calculate and Analyze Availability: RF Link Events (7): Calculate and Analyze Availability: RF Link Events (7) RF Link Event Inmarsat RF Link: Availability: 0.95 (design criterion) Observation Time is not specified Iridium RF Link: Availability: 0.995 (as advertised by 1st generation operator) Observation Time is not specified VHF Terrestrial RF Link Availability: 0.999 Observation Time is not specified Presumed availability values: As an operating parameter of a turnkey system, SATCOM system availability is predominantly under the control of the service provider and driven by business rather than technical considerations With no definitive SATCOM service availability specified by the vendors for aeronautical A/G ATC data communications, this parameter is very limited as a useful quantitative criteria for comparison


Calculate and Analyze Availability: Capacity Overload Event: Calculate and Analyze Availability: Capacity Overload Event This factor accounts for the probability that a system can be overloaded by aeronautical services This study implemented both a simple Erlang-B Model and a finite source Erlang-C model following DO-270 methodology and key assumptions Focus was on En Route domain Applicable domain for satellite service Highest data rate required per user Erlang-B (Blocked Calls Cleared) Services requests are processed immediately or dropped immediately No queuing More pessimistic estimate Erlang-C (Blocked Calls Delayed) Request for service is either served immediately or placed at the end of a first-in-first out service queue (possibly infinite)


Calculate and Analyze Availability: Capacity Overload Event (2): Calculate and Analyze Availability: Capacity Overload Event (2) Availability Estimates for Iridium & Inmarsat (ATS & AOC) For Iridium, a steady-state condition cannot be achieved for uplink traffic [SATCOM to AES] (average traffic intensity per server, r, is greater than 1) For Inmarsat, the Erlang-B model results show capacity for both uplink and downlink traffic can be met with availability of .997; using Erlang-C model, availability improves to approximately 1 Driver of availability values is uplink traffic (SATCOM to AES)


Calculate and Analyze Availability: Capacity Overload Event (3): Calculate and Analyze Availability: Capacity Overload Event (3) Availability Estimates for Iridium & Inmarsat (ATS only traffic) Again for Iridium, a steady-state condition cannot be achieved for uplink (SATCOM to AES) traffic (average traffic intensity per server, r, is greater than 1)


Calculate and Analyze Availability: Capacity Overload Event (4): Calculate and Analyze Availability: Capacity Overload Event (4) Availability Estimates - Capacity Overload Event Terrestrial VHF architecture results for ATS & AOC Traffic A low data rate VHF terrestrial architecture does not provide sufficient capacity to provide a steady-state system or reasonable availability for the combined ATS & AOC traffic load A higher data rate reference terrestrial architecture (e.g. value based on the reference architecture developed for L-band business case) provides sufficient capacity with availability of approximately 1 for the combined ATS & AOC traffic load when considering the Erlang C model


Calculate and Analyze Availability: Capacity Overload Event (5): Calculate and Analyze Availability: Capacity Overload Event (5) Availability Estimates - Capacity Overload Event Terrestrial VHF architecture results for ATS Traffic only As with the ATS&AOC combined traffic results, the low data rate VHF terrestrial architecture does not provide sufficient capacity to provide a steady-state system; the higher data rate reference terrestrial architecture, however, does provide sufficient capacity with high availability (approx. 1)


Calculate and Analyze Availability: Capacity Overload Event (6): Calculate and Analyze Availability: Capacity Overload Event (6) Capacity Overload Event Inmarsat Capacity Overload: Availability - ATS-only load: ~ 1 ATS & AOC load: ~ 1 Iridium Capacity Overload: Availability of downlink (AES to SATCOM) traffic is ~ 1 (for both ATS only and ATS & AOC); No steady-state can be achieved for uplink (SATCOM to AES) traffic VHF Terrestrial Capacity Overload Availability – No steady-state can be achieved Note that the values above represent results of calculations that employ the Erlang-C model. With assumed queue size of 100 data blocks and declared outage after queuing for 5 seconds, both inputs above represent fairly conservative approaches. Terrestrial Capacity Overload availability is for VHF-Band reference architecture business case; for L-Band Terrestrial Capacity Overload availability would be essentially one (1). Calculated availability values:


Calculate and Analyze Availability: Interference Event: Calculate and Analyze Availability: Interference Event This Fault-Free Rare Event element considers system unavailability due to outages caused by external interference DO-270 establishes the requirement that a SATCOM system shall provide adequate performance in the presence of aggregate interference from external sources equivalent to 25% of the total noise power in the received RF channel There are occasionally instances where substantially higher levels of interference are experienced, which exceed the system design requirement and thus cause service outages. A volumetric availability model based on DO-270 was used to calculate unavailability due to potential interference between SATCOM-equipped aircraft operating in the same airspace.


Calculate and Analyze Availability: Interference Event (2): Calculate and Analyze Availability: Interference Event (2) 1000 Ft. Potential Victim Interference Volumes AES Source Antenna Beamwidth Source Aircraft Potential Victim Aircraft The volumetric model determined the probability that “victim” aircraft using a different SATCOM system would be within an “interference volume” of the transmitting source aircraft RM = Interference radius, within which victim aircraft in the source aircraft beam width would receive interference power within its received pass band exceeding its allowed threshold RM


Calculate and Analyze Availability: Interference Event (3): Calculate and Analyze Availability: Interference Event (3) Interference Availability was computed as follows: Where LE = Average traffic load of source aircraft, based on traffic loading models developed for Capacity Overload availability calculations PV = Probability a victim aircraft is in an interference volume, based on a COCR uniform density assumption for Phase 2 Enroute airspace VK = Interference volume at flight level k Assumed airspace was composed of 50% Inmarsat and 50% Iridium aircraft Interference Volumes Interference volumes needed to be determined for victim aircraft both above and below the source aircraft. RM, the interference radius, is smaller below the source aircraft because of differences in antenna gain


Calculate and Analyze Availability: Interference Event (4): Calculate and Analyze Availability: Interference Event (4) VHF Terrestrial External Interference There was no directly analogous case with which to compare with the SATCOM cases, i.e. two SATCOM systems operating in the same airspace, but with adjacent frequency allocations Calculated potential interference availability for a slightly analogous case of aircraft in the same airspace, but using different VHF frequencies/channels (e.g. ATC and AOC channels) Used DO-186A (VHF radio MOPS) parameters and a volumetric model similar to that for the SATCOM systems Determined that interference radius RM was so low (well below the 1000 feet minimum vertical spacing separation standard for aircraft) as to result in no interference volumes, and thus make availability essentially one


Calculate and Analyze Availability: Interference Event (5): Calculate and Analyze Availability: Interference Event (5) Interference Event Inmarsat Satellite: Availability: approx. 1 For Enroute airspace Iridium Satellite: Availability: 0.996 For Enroute airspace VHF Terrestrial: Availability: approx. 1 For Enroute airspace Calculated availability values: Iridium interference availability may be an issue because of the robust Inmarsat I-4 SBB AES power levels and high gain antennas necessary to provide the high SBB data rates up to the GEO spacecraft The value calculated can be considered to bound the availability because it assumed Inmarsat source aircraft using all 16 available channels within a single spot beam and all 16 aircraft simultaneously transmitting


Calculate and Analyze Availability – Scintillation Event: Calculate and Analyze Availability – Scintillation Event Scintillation Event Inmarsat Scintillation: Availability: 1 for all airspace (assumes no scintillation effects in airspace of interest) Iridium Scintillation: Availability: 1 for all airspace (assumes no scintillation effects in airspace of interest) VHF Terrestrial Scintillation: Not Applicable Scintillation events can be attributed to ionospheric events that impact satellite communications This component is not a contributor to terrestrial VHF Communications Upon investigation of scintillation effects (reference Propagation Effects Handbook for Satellite System Design, Ippolito, 2000), significant impact on satellite communications occurs in the equatorial latitudes (+/- 20 deg latitude) and in the polar regions (above 65 deg latitude) For the middle latitudes that constitute our region of interest for the NAS, there are minimal scintillation effects Assumed availability values:


Compare/Discuss Analysis Results: Compare/Discuss Analysis Results


Compare/Discuss Analysis Results: Compare/Discuss Analysis Results Summary – Limiting factors for availability are as follows: SATCOM systems: Satellite equipment failures and RF link effects Capacity Overload (Iridium) Interference (Iridium) VHF Terrestrial communication systems: RF link events


Compare/Discuss Analysis Results (2): Compare/Discuss Analysis Results (2) Overall Comparison/Discussion Caution is needed for interpretation of availability results Because certain SATCOM availability data is unavailable, many of the availability contributors have been estimated by ‘similar in kind’ systems and will be influenced by specific system implementation and/or margins incorporated to improve performance Focus has been on availability alone, but other criteria to assure suitability of a communication channel must also be investigated For example, long and short term reliability (i.e. continuity of service) and restoral time Need to investigate impact of unlikely but significant outages that contribute to availability/reliability for satellite systems


Compare/Discuss Analysis Results (3): Compare/Discuss Analysis Results (3) Other considerations: unlikely but significant outages for satellite systems Impact of any single-point-of-communication-service-failure varies significantly between terrestrial and satellite systems Example shows availability impact of system failure outage of a major communication service component and associated impact Selected a satellite outage for satellite architectures and a ground radio outage (RCAG and associated BUEC) for terrestrial architecture Inmarsat SBB Availability = 0 for entire region during MTTR period ( several months for ground spare or time to re-allocate comm services to another satellite or comm system) Terrestrial VHF Availability = .997 in outage area (availability of backup radio equipment string) and .99999 in all other areas; MTTR is on the order of hours 0 .99999 Slightly below .999 Iridium 7 min outage per 100 minutes for majority of region during MTTR period (10 days for on-orbit spare) and reduced availability for region within redundant satellite coverage area


COCR Service Provisioning Using SATCOM : COCR Service Provisioning Using SATCOM


Outline: Outline Objective COCR Availability Requirements COCR Service Provisioning over SATCOM


Objective: Objective Examine the provisioning of COCR services over Inmarsat SBB and Iridium with respect to availability performance


COCR Availability Requirements: COCR Availability Requirements


COCR Availability Requirements: COCR Availability Requirements The COCR identifies the following types of performance requirements Data capacity Latency QoS Number of Users Security Availability Availability was not explicitly investigated as part of the FCS Phase II technology evaluation Availability is an architecture design factor, and the majority of the investigated technologies are not associated with a specific architecture During system design, appropriate performance/cost trade-offs would be performed The evaluated SATCOM technologies do have defined architectures Availability can be explicitly considered This is important as the SATCOM availability metric is a potential driver in determining applicability of the technology to COCR service provisioning


COCR Availability Requirements (2): COCR Availability Requirements (2) COCR version 1.0 indicates specified availability for the FRS is based on availability parameters (and associated definitions) provided in RTCA DO-290 Two parameters are specified Availability of Use (AU): Probability that the communication system between the two parties is in service when it is needed Availability of Provision (AP): Probability that communication with all aircraft in the area is in service


COCR Availability Requirements (3): COCR Availability Requirements (3) In the COCR, the AU is specified as two orders of magnitude less than AP when AP is greater than 10-7; otherwise AU is specified as one order of magnitude less than AP Au addresses connectivity to a user and includes user installations that are part of the communication link Appropriate for single user availability calculations that account for the aircraft station availability AP is a requirement on the air traffic service provider Appropriate for multi-user availability calculations that focus on service provision to an entire service volume (and do not account for individual aircraft station availability contributors) The focus of this analysis is multi-user availability, thus the focus is on AP requirements


COCR Availability Requirements (4): COCR Availability Requirements (4) COCR Service Availability Requirements: ATS AP requirements: Phase I: 0.9995 Phase II: With A-EXEC: Range from .9995 to .9999999995 [or (.9)95] Without A-EXEC: Range from .9995 to .99999995 [or (.9)75 for PAIRAPP, ACL, ACM] AOC AP requirements: Phase I & II: Range from .9995 to .999995 [or (.9)55] COCR Phase I Availability Requirement Examples COCR Phase II Availability Requirement Examples


COCR Service Provisioning over SATCOM: COCR Service Provisioning over SATCOM


SATCOM Availability Performance: SATCOM Availability Performance Earlier slides identify availability contributors and analysis results for Inmarsat SBB/Iridium architectures Availability estimates vary widely with availability contributors For Inmarsat, individual availability contributor values range from .95 to 1 For Iridium, calculated availability contributors range from .995 to 1 Inmarsat/Iridium may provide sufficient availability performance to meet a subset COCR service availability performance requirements in limited applications It is clear, however, that these SATCOM architectures will not provide sufficient availability to provision most if not all of the COCR services defined for Phase II operations


SATCOM Availability Performance (2): SATCOM Availability Performance (2) The described results are in line with other recent studies that have investigated Inmarsat/Iridium availability performance EUROCONTROL – Inmarsat SBB Services for Air Traffic Services No explicit calculation of availability, but indication that this service is not sufficient as a standalone solution for ATS Boeing Team - GCNSS – Phase I Availability analysis was undertaken for a proposed architecture for NAS ATS Individual calculation details not available However, to meet availability requirements, recommended architecture includes five satellite infrastructure


COCR Service Provisioning over SATCOM: COCR Service Provisioning over SATCOM Results indicate that Inmarsat SBB and Iridium will not provide sufficient availability to provide a stand alone solution for the future radio system These SATCOM systems may provide a meaningful role in specific domains (e.g. oceanic/remote) and/or specific, limited applications (e.g. disaster recovery) This does not preclude consideration of other SATCOM systems to provide a wider role in provisioning ATS services Proposed architectures, for example SDLS, may be designed specifically for ATS and with architectures specifically engineering to meet all COCR requirements


Backup Material: Backup Material


Background: Background ICAO ANC/11 noted: Aeronautical communication infrastructure has to evolve Various proposals to address this problem have been offered; none has achieved global endorsement There are universally recognized benefits of harmonization and global interoperability Consequently, ANC/11 recommended: Adopt an evolutionary approach for global interoperability Investigate new terrestrial and satellite-based technologies Undertake new standardization work only when system meets ATM requirements, is technically proven, consistent with the requirements for safety, cost beneficial and promotes global harmonization FAA and Eurocontrol embarked on a bi-lateral study (FCS) with the support of NASA; study is to provide input to the ICAO Aeronautical Communications Panel (ACP) FCS goals and process are outlined in Action Plan 17 (AP-17)


Background – Future Communications Study: Background – Future Communications Study FAA/Eurocontrol 3 year joint study* Objectives: Identification of requirements and operating concepts Investigation into new mobile communication technologies Investigation of a flexible avionics architecture Development of a Future Communications Roadmap Creation of industry buy-in Improvements to maximise utilisation of current spectrum * Federal Aviation Administration/EUROCONTROL , Cooperative Research and Development Action Plan 17: Future Communications Study (AP 17-04) CCOM FAA/EUROCONTROL Coordination Committee


Identify Architectures for Analysis: Inmarsat SBB: Identify Architectures for Analysis: Inmarsat SBB Inmarsat SwiftBroadband (SBB) is a service provided within the spot beams of I-4 satellites with the potential for providing FRS aeronautical services Circuit and packet switch connections Guaranteed ‘streaming’ service data rates between 32 and 256 kbps 630 channels of up to 200 kHz in bandwidth Note: F1 and F2 have been launched. Launch of F3 is to be determined; it may remain a ground spare.


Identify Architectures for Analysis: Inmarsat SBB (2): Identify Architectures for Analysis: Inmarsat SBB (2) Inmarsat SBB (cont’d) European based ground infrastructure to support I-4 F1 and F2 SBB Notes: From: “SwiftBroadband Capabilities to Support Aeronautical Safety Services”, TRS064/04, Eurocontrol, Nov 16, 05, pg 30 SAS – Satellite Access Station gateway; RAN – Radio Access Network; DCN – Data Communication Wide Area Network; NOC – Network Operations Center Inmarsat offers internal routing between its SAS sites via the DCN to accommodate re-routing of traffic in the event of a SAS gateway failure


Identify Architectures for Analysis: Iridium: Identify Architectures for Analysis: Iridium Iridium offers two-way global voice and data aeronautical communication services Iridium Aeronautical Service Details Satellite constellation 66 fully operational satellites and 11 in-orbit spares Global 24 hour real time coverage Full constellation life to mid-2014; plan to extend constellation beyond 2020 Satellites are in 6 planes in near-polar orbit and circle earth every 100 minutes Gateways A single aeronautical gateway provides this service Satellite Network Operations Center Main facility in Landsdown, VA Back-up facility in Chandler, AZ Processing Offers 2400 bps traffic channels using one uplink and one downlink time-slot in each TDMA frame


Identify Architectures for Analysis: Terrestrial: Identify Architectures for Analysis: Terrestrial VHF terrestrial architecture used for the study was a generic architecture based on current NAS VHF A/G radio infrastructure