Presentation on theme: "Frank Box, Alexe Leu, and Leo Globus 22 September 2014"— Presentation transcript:
1 Frank Box, Alexe Leu, and Leo Globus 22 September 2014 ACP WG-F/31 WP08Unmanned Aircraft System (UAS) Terrestrial C2 Frequency-Planning Activities in RTCA SC-228Frank Box, Alexe Leu, and Leo Globus22 September 2014
2 C-Band Terrestrial Frequency Planning Characteristics of Strawman C2 SystemCoexistence Rules for Terrestrial C2 LinksChannelization PlanningVery-High-Altitude UASCoexistence with UAS C2 SATCOMAppendix: Sample Link Budgets
3 System Design Constraints Available frequency bands:L-band (960–1164 MHz)C-band (5030–5091 MHz)Maximum UA transmitter power per band for basic service: 10 wattsRequired availability (per band) = 99.8%Maximum UA groundspeed = 850 knotsFrequency instability: 1.0 ppm or betterTransmitter mask: GMSK (BT = 0.2) or comparableTime-division duplexingSynchronized among all users
4 Link Throughput Requirements Service Class1234Services Provided:Basic Telecommand and TelemetryATC voice and ATS data relayNavaid and Detect-and-Avoid DataVideo* and Airborne Wx Radar DataRequired Throughput (kbps):Uplink (automatic UA operation)1.2426.0916.230Downlink (automatic UA operation)1.2726.13111.163Uplink (manual UA operation)4.5939.44210.108Downlink (manual UA operation)7.59512.45418.391* These video links (for takeoff, landing, taxiing) would each carry 217 kbps plus overhead.A need for a single nationwide emergency video channel that would use 435 kbps (plus overhead) has also recently been identified but is not considered in the above table.
5 Strawman System Configurations Information Rate (kbps)Symbol Rate (kbaud)Standalone telecommand uplink or basic telemetry downlink14.8087.5Medium-throughput downlink35.28150Networked TDMA uplink with 4 slots28.48200Networked TDMA uplink with 8 slots56.96400Networked TDMA uplink with 12 slots85.44600High-throughput (video-capable) downlink237.52750Networked TDMA uplink with 16 slots113.92800Networked TDMA uplink with 20 slots142.401000System design is under review to improve spectral efficiency by:Providing additional configurations with smaller information ratesFinding ways to reduce symbol rates for all configurations
6 3-D Cellular Frequency Plan Highest altitude tier (50 kft)1/12 frequency reuse1/3 frequency reuse (better)Lowest altitude tier (surface)INTERMEDIATE TIERS NOT SHOWN“Cells” are airspace volumesFrequency list for each cell, assignable as needed when UA in cellNationwide plan to be developedGround stations (standalone/gapfiller) can be anywhere in a cell
7 Low-Altitude Coverage and Gapfillers CENTRAL 100’ TOWERCoverage down to 4000’Down to 1000’Down to groundCELL BOUNDARYGapfiller69 NAUTICAL MILESLikely cell radius 69 nmiCentral ground station (GS) cannot provide coverage down to ground throughout cellIn most of cell, low-altitude UA need “gapfiller” GSsWhen gapfillers are far enough apart, they may be able to share frequencies in same cell7
8 POTENTIALLY INTERFERING GS POTENTIALLY INTERFERING UA Examples of Potential Adjacent-Channel Interference (ACI) between CellsDESIRED GSPOTENTIALLY INTERFERING GSDESIRED UPLINKVICTIM UADESIRED DOWNLINKVICTIM GSPOTENTIALLY INTERFERING UAUplink-to-uplink ACI scenarioDesired GS and interferer on (first) adjacent channelsVictim UA at edge of its cellBoth UA have omni antennasPotential interferer must limit power radiated toward cell boundaryAdequate adjacent-channel rejection (ACR) also needed to prevent ACIDownlink-to-downlink ACI worst caseDesired UA and interferer are:On first adjacent channelsRoughly equidistant from victim GSBoth in victim GS’s main beamBoth UA have omni antennasHere, ACR may be victim GS’s only protection against ACI
9 Intersite Coexistence Rules (1 of 2) Interference prevention between cellsPower flux density (PFD) limits, in dBm/m2, at cell boundariesInterference prevention within cellsSingle-transmitter radiation limitsEIRP limitsFrequency-sharing rules for “gapfiller” and standalone ground stationsPFD, radiated-power, and EIRP limits will:Be different for uplinks and downlinksDepend on channel symbol rate (kbaud)
10 Intersite Coexistence Rules (2 of 2) Free-space PFD at cell edge shouldn’t exceed what the potentially interfering link would need for good availability if its own receiver were thereIn some scenarios, only protection against ACI is to ensure that ACR is large enough to provide link margin needed to allow for multipath, etc.Ground-antenna diversity (if affordable) would reduce ACR requirementsC2 channel spacings must be set large enough to ensure adequate ACRAlthough ACR is main threat, cochannel PFD limits also needed for very-high-altitude UA with very long radio lines of sight
11 Channelization Planning Decision Tree Channels Needed per Cell (20?)Max. Radio-Horizon Distance (261 nmi?)Max. Cell Altitude (45,000 feet?)ARequired ThroughputNecessary OverheadMin. Acceptable Freq. Reuse, 1/K (1/12?)Cell Radius (69 nmi?)Symbol Rate (e.g., 87.5 kbaud)Max. UA Ground Speed (850 kn)Required Availability(99.8%)Max. GS Distance from Cell Edge (69 nmi?)Min. UA Altitude at Cell Edge (4000 feet?)Modulation (GMSK,BT = 0.2?)Necessary Multipath/ Rain/Airframe Loss MarginTransmitter MaskReceiver MaskFreq. Stability (1 ppm)Diversity AssumptionsFrequency-Dependent Rejection CurveNecessary Adjacent-Channel Rejection (ACR)Max. UA Transmitter Power (40 dBm)UA SWAP ConstraintsChannel Spacing for Given Symbol RateNecessary Ground-Antenna Gain(L-band: 19 dBi? C-band: 38 dBi?)Number of Channels AvailableNecessary Ground-Antenna Aperture(L-band: 1 m2? C:-band: 3 m2?)A
12 How Much ACR Is Necessary? Ensure, through GS power/pointing/location restrictions, that at cell boundaries (the worst case) free-space interference power flux density (PFD) will not exceed free-space signal PFDDesign link budgets to allow received interference power (after filtering) to equal receiver noise power (INR = 0 dB)Sample C-band link budgets shown in Appendix AThen the minimum ACR sufficient to allow 99.8% availability in the presence of potential ACI from an adjoining cell can be calculated as:ParameterL-bandC-bandWorst-case 99.8%-availability link margin (dB) needed for multipath/rain/airframe losses29.6*33.6*Required Eb/N0 (dB)2.5Implementation margin (dB)1.0Allowance (dB) for interference = noise3.0Total (minimum required ACR in dB)36*40** Assumes dual airborne-antenna diversity but no ground diversity. Using dual or triple ground diversity could reduce necessary link margins and ACR values by 9–14 dB.
13 Offset from Channel Center Frequency (kHz) Strawman C-Band Masks39.570160.3122.521.980Attenuation (dB)Offset from Channel Center Frequency (kHz)Design assumptions:GMSK (BT = 0.2)87.5 kbaud850-knot Doppler shift1.0-ppm frequency instabilityReceiverTrans-mitter
14 Frequency-Dependent Rejection (FDR) of 87 Frequency-Dependent Rejection (FDR) of 87.5-kbaud C-band Transmitter and ReceiverRed curve allows for Doppler shift and frequency instability
15 Channelization Goals Spectral efficiency ACI prevention Simplicity Small channel spacings ( large number of channels)ACI preventionSpacings large enough to provide adequate ACRSimplicityEvery channel spacing should be integer multiple of smallest spacing in bandRound numbers preferredHarmonizationConsistency with channel spacings of other systems in bandMLS (300 kHz)UAS C2 SATCOM (300 kHz?)Not feasible to achieve every goal in same planTradeoffs necessary; no perfect plan
16 Channelization Principles FlexibilityEach C-band C2 radio may have full repertoire of channel spacings throughout its tuning rangeNo part of tuning range to be permanently tied to a single channel spacingChannels of same size should be grouped togetherHelps protect wide channels against ACI from narrow onesPartitions between channel groups should be movableSince relative utilization of symbol rates is unpredictable and will evolve over timeC-band needs wider channel spacings than L-bandGreater Doppler shifts and frequency instability
17 Possible C-band Channelization Plans Info Rate (kbps)Symbol Rate (kbaud)Simple Plan (Harmonized with MLS Channelization Plan)More Spectrally-Efficient Plan(Would Support More UAS)Spacing (kHz)ACR (dB)Channels in 60 MHz14.8087.51504440035.28300692002505824028.48553956.96600631005004812085.44900667505180237.521200685010005760113.928006752142.40150040125053NOTE: One or more smaller channel spacings (TBD) are also needed for narrowband signals.
18 “Footprint” of highest-altitude tier of cells Potential Cochannel Interference to and from Very-High-Altitude UA (VUA)Scenario:VUA stays 65 kft above its GS (above highest C2 cell)VUAS uses frequencies allocated to highest-tier cell beneath it“Not-very-high-altitude UA” (NUA) uses same frequency as VUASince VUA > 50 kft AGL, K=12 cell plan allows ground/air RLOS to 6 “cochannel” cells (only one shown in picture)Cochannel RFI (CCI) threatens VUAS uplink & NUAS downlink (VUAS downlink & NUAS uplink protected by earth curvature)VUAPotential Interference Path65kftNUA“Footprint” of highest-altitude tier of cells1210787VUAS GSNUAS GS35300 nmi ( 4.35 cell radii)
19 Key Findings of VUAS Analysis CCI to and from very-high-altitude UAS (VUAS) can be prevented by:– Assigning to each VUAS a frequency that has beenallocated to the highest-tier cell beneath it– Appropriately reducing VUAS uplinkand downlink transmitter powers– Using highly directional VUAS GS antennasTo protect VUAS against downlink ACI, operational procedures may be needed to keep not-very-high-altitude UA (NUA) from staying too close to VUAS GS in its main beam for too long
20 Coexistence between Terrestrial and SATCOM UAS C2 Links (1 of 2) Note: This slide and the next summarize ACP WGF28/WP13(rev1), “5-GHz Band-Planning Considerations for UAS CNPC Links,” March 2013WRC-12 decided 5030–5091 MHz band can be shared by AMS(R)S and AM(R)S C2 linksUnless AM(R)S or AMS(R)S is absent in a given region, putting AM(R)S in center of band and AMS(R)S at high and low ends would have these advantages:If AMS(R)S uses frequency-division duplexing, it needs to maximize frequency separation between Earth space and space Earth segments, because of filter-design constraintsRadio Regulations footnote 5.443C limits AM(R)S EIRP density to –75 dBW/MHz in the 5010–5030 MHz band, so large separation between that band and the AM(R)S segment would be useful
21 Coexistence between Terrestrial and SATCOM UAS C2 Links (2 of 2) If band is partitioned between AM(R)S and AMS(R)S, boundaries between segments should be movableProtects against having to make premature, binding decisions on relative terrestrial and SATCOM allocationsBoundary adjustments would be made infrequently based on capacity demand patternsAllows for the possibility that some regions might use only one of the two types of 5-GHz link (terrestrial or SATCOM, but not both)Allows common wideband RF filter (over the entire 5030–5091 MHz band) that would be:Simpler to implement than narrowband filtersUsable by hybrid terrestrial/SATCOM terminals
22 Next Steps Refine terrestrial C2 system design Firm up necessary data and symbol ratesRedesign masks and recompute FDR curvesDevelop firm list of channel spacings for each bandRecommend specific channel placementsDevelop nationwide channel planDevelop dynamic frequency-assignment procedures
24 Sample C-Band Uplink Budgets ParameterSymbolUnitsValuesNotesFrequencyfMHz5060Pex = Pt + Gt - LctAircraft altitude, AGLHaft180004000Pe = Pex - LptGround-antenna heightHt100Dpf = Pe - 20 log d - 10 log (4p*1852^2) = Pe - 20 log dPath distancednmi71Lf = 20 log f + 20 log dSymbol rateRskbaud87.5Prm = Pe - Lf + Gr - LcrTransmitter powerPtdBm40.0Eb/N0 = 2.5 dB for GMSK with BT = 0.2Maximum transmitting-antenna gainGtdBi38.0Bn assumed equal to RsTransmitter cable lossLctdB1.0N = Nt + 10 log Bn + FnMaximum EIRPPex77.0Dual airborne-antenna diversity assumed, but not ground diversityTransmitting-antenna pointing lossLpt2.0La obtained from SC203-CC016 data for 2.4-GHz signalEIRP toward receiverPe75.0Va estimated by assuming airframe loss increases from S- to C-bandFree-space value of received signal PFDDpfdBm/m2-38.4Lx based on ITU-R Recs. P , P , P.838, P.676-6, and P.840-3Free-space path lossLf148.9Mc = sqrt ((La + Va)^2 + Lx^2 + Mb^2) -- approximation in lieu of convolutionMean receiving-antenna gainGrM = Mm + Mc + Mi + MaReceiver cable lossLcrPrq = Eb/N0 + N + MMean received signal powerPrm-73.9Mx = Prm - PrqRequired signal-to-noise ratio per bitEb/N02.5Thermal-noise spectral power densityNtdBm/kHz-144.0Noise bandwidth of receiverBnkHzReceiver noise figureFn4.0Total receiver noiseN-120.6Implementation marginMmAirframe loss value for CDF = 0.002La20.0Est. variation from 2.4-GHz airframe lossVaExcess path-loss value for CDF = 0.002Lx16.424.7RFI multipath boost for CDF = 0.002Mb6.0Combined airframe/path/RFI marginMc28.133.6Allowance for interference = noiseMi3.0Aviation safety marginMaTotal required margin for 99.8% avail.M38.143.6Required signal powerPrq-80.0-74.5Excess marginMx6.10.624