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Unmanned Aircraft System (UAS) Terrestrial C2 Frequency-Planning Activities in RTCA SC-228 Frank Box, Alexe Leu, and Leo Globus 22 September 2014 1 ACP.

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Presentation on theme: "Unmanned Aircraft System (UAS) Terrestrial C2 Frequency-Planning Activities in RTCA SC-228 Frank Box, Alexe Leu, and Leo Globus 22 September 2014 1 ACP."— Presentation transcript:

1 Unmanned Aircraft System (UAS) Terrestrial C2 Frequency-Planning Activities in RTCA SC-228 Frank Box, Alexe Leu, and Leo Globus 22 September ACP WG-F/31 WP08

2 C-Band Terrestrial Frequency Planning Characteristics of Strawman C2 System Coexistence Rules for Terrestrial C2 Links Channelization Planning Very-High-Altitude UAS Coexistence with UAS C2 SATCOM Appendix: Sample Link Budgets 2

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 watts Required availability (per band) = 99.8% Maximum UA groundspeed = 850 knots Frequency instability: 1.0 ppm or better Transmitter mask: GMSK (BT = 0.2) or comparable Time-division duplexing –Synchronized among all users 3

4 Link Throughput Requirements Service Class 1234 Services Provided: Basic Telecommand and Telemetry  ATC voice and ATS data relay  Navaid and Detect-and-Avoid Data  Video* and Airborne Wx Radar Data  Required Throughput (kbps): Uplink (automatic UA operation) Downlink (automatic UA operation) Uplink (manual UA operation) Downlink (manual UA operation) * 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 5 Configuration Information Rate (kbps) Symbol Rate (kbaud) Standalone telecommand uplink or basic telemetry downlink Medium-throughput downlink Networked TDMA uplink with 4 slots Networked TDMA uplink with 8 slots Networked TDMA uplink with 12 slots High-throughput (video-capable) downlink Networked TDMA uplink with 16 slots Networked TDMA uplink with 20 slots System design is under review to improve spectral efficiency by: Providing additional configurations with smaller information rates Finding ways to reduce symbol rates for all configurations

6 3-D Cellular Frequency Plan 6 Highest altitude tier (50 kft) 1/12 frequency reuse 1/3 frequency reuse (better) Lowest altitude tier (surface) INTERMEDIATE TIERS NOT SHOWN “Cells” are airspace volumes Frequency list for each cell, assignable as needed when UA in cell –Nationwide plan to be developed Ground stations (standalone/gapfiller) can be anywhere in a cell

7 Low-Altitude Coverage and Gapfillers Likely cell radius  69 nmi Central ground station (GS) cannot provide coverage down to ground throughout cell In most of cell, low-altitude UA need “gapfiller” GSs When gapfillers are far enough apart, they may be able to share frequencies in same cell 7 CENTRAL 100’ TOWER Coverage down to 4000’ Down to 1000’ Down to ground CELL BOUNDARY Gapfiller 69 NAUTICAL MILES

8 Examples of Potential Adjacent-Channel Interference (ACI) between Cells 8 DESIRED GS POTENTIALLY INTERFERING GS DESIRED UPLINK VICTIM UA DESIRED DOWNLINK VICTIM GS POTENTIALLY INTERFERING UA Uplink-to-uplink ACI scenario Desired GS and interferer on (first) adjacent channels Victim UA at edge of its cell Both UA have omni antennas Potential interferer must limit power radiated toward cell boundary Adequate adjacent-channel rejection (ACR) also needed to prevent ACI Downlink-to-downlink ACI worst case Desired UA and interferer are: –On first adjacent channels –Roughly equidistant from victim GS –Both in victim GS’s main beam Both UA have omni antennas Here, ACR may be victim GS’s only protection against ACI

9 Intersite Coexistence Rules (1 of 2) Interference prevention between cells –Power flux density (PFD) limits, in dBm/m 2, at cell boundaries Interference prevention within cells –Single-transmitter radiation limits –EIRP limits –Frequency-sharing rules for “gapfiller” and standalone ground stations PFD, radiated-power, and EIRP limits will: –Be different for uplinks and downlinks –Depend on channel symbol rate (kbaud) 9

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 there In 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 requirements –C2 channel spacings must be set large enough to ensure adequate ACR Although ACR is main threat, cochannel PFD limits also needed for very-high-altitude UA with very long radio lines of sight 10

11 Channelization Planning Decision Tree Required Throughput Necessary Overhead Symbol Rate (e.g., 87.5 kbaud) Transmitter Mask Modulation (GMSK, BT = 0.2?) Max. UA Ground Speed (850 kn) Receiver Mask Frequency-Dependent Rejection Curve Channel Spacing for Given Symbol Rate Necessary Adjacent- Channel Rejection (ACR) Necessary Multipath/ Rain/Airframe Loss Margin Required Availability (99.8%) Max. GS Distance from Cell Edge (69 nmi?) Cell Radius (69 nmi?) Max. Radio-Horizon Distance (261 nmi?) Max. Cell Altitude (45,000 feet?) Min. Acceptable Freq. Reuse, 1/K (1/12?) UA SWAP Constraints Max. UA Transmitter Power (40 dBm) Necessary Ground-Antenna Gain (L-band: 19 dBi? C-band: 38 dBi?) Necessary Ground-Antenna Aperture (L-band: 1 m 2 ? C:-band: 3 m 2 ?) Min. UA Altitude at Cell Edge (4000 feet?) Number of Channels Available Channels Needed per Cell (20?) A A Freq. Stability (1 ppm) Diversity Assumptions 11

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 PFD Design 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 A Then the minimum ACR sufficient to allow 99.8% availability in the presence of potential ACI from an adjoining cell can be calculated as: 12 ParameterL-bandC-band Worst-case 99.8%-availability link margin (dB) needed for multipath/rain/airframe losses 29.6*33.6* Required E b /N 0 (dB) 2.5 Implementation margin (dB) 1.0 Allowance (dB) for interference = noise 3.0 Total (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 Strawman C-Band Masks Attenuation (dB) Offset from Channel Center Frequency (kHz) Receiver Trans- mitter Design assumptions: GMSK (BT = 0.2) 87.5 kbaud 850-knot Doppler shift 1.0-ppm frequency instability

14 Frequency-Dependent Rejection (FDR) of 87.5-kbaud C-band Transmitter and Receiver Red curve allows for Doppler shift and frequency instability 14

15 Channelization Goals Spectral efficiency –Small channel spacings (  large number of channels) ACI prevention –Spacings large enough to provide adequate ACR Simplicity –Every channel spacing should be integer multiple of smallest spacing in band –Round numbers preferred Harmonization –Consistency with channel spacings of other systems in band MLS (300 kHz) UAS C2 SATCOM (300 kHz?) Not feasible to achieve every goal in same plan –Tradeoffs necessary; no perfect plan 15

16 Channelization Principles Flexibility –Each C-band C2 radio may have full repertoire of channel spacings throughout its tuning range No part of tuning range to be permanently tied to a single channel spacing Channels of same size should be grouped together –Helps protect wide channels against ACI from narrow ones Partitions between channel groups should be movable –Since relative utilization of symbol rates is unpredictable and will evolve over time C-band needs wider channel spacings than L-band –Greater Doppler shifts and frequency instability 16

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 MHz Spacing (kHz) ACR (dB) Channels in 60 MHz NOTE: One or more smaller channel spacings (TBD) are also needed for narrowband signals.

18 Potential Cochannel Interference to and from Very-High-Altitude UA (VUA) 18 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 VUA Since 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) VUA 12 7 Potential Interference Path NUA 300 nmi (  4.35 cell radii) NUAS GS VUAS GS “Footprint” of highest-altitude tier of cells 65 kft

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 been allocated to the highest-tier cell beneath it – Appropriately reducing VUAS uplink and downlink transmitter powers – Using highly directional VUAS GS antennas To 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 19

20 Coexistence between Terrestrial and SATCOM UAS C2 Links (1 of 2) WRC-12 decided 5030–5091 MHz band can be shared by AMS(R)S and AM(R)S C2 links Unless 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 constraints –Radio 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 20 Note: This slide and the next summarize ACP WGF28/WP13(rev1), “5- GHz Band-Planning Considerations for UAS CNPC Links,” March 2013

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 movable –Protects against having to make premature, binding decisions on relative terrestrial and SATCOM allocations Boundary adjustments would be made infrequently based on capacity demand patterns –Allows 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 filters Usable by hybrid terrestrial/SATCOM terminals 21

22 Next Steps Refine terrestrial C2 system design Firm up necessary data and symbol rates Redesign masks and recompute FDR curves Develop firm list of channel spacings for each band Recommend specific channel placements Develop nationwide channel plan Develop dynamic frequency-assignment procedures 22

23 Appendix: Sample C-Band Uplink Budgets 23

24 24 ParameterSymbolUnitsValuesNotes FrequencyfMHz5060 P ex = P t + G t - L ct Aircraft altitude, AGLHaHa ft P e = P ex - L pt Ground-antenna heightHtHt ft100 D pf = P e - 20 log d - 10 log (4p*1852^2) = P e - 20 log d Path distancednmi71 L f = 20 log f + 20 log d Symbol rateRsRs kbaud87.5 P rm = P e - L f + G r - L cr Transmitter powerPtPt dBm40.0 E b /N 0 = 2.5 dB for GMSK with BT = 0.2 Maximum transmitting-antenna gainGtGt dBi38.0 B n assumed equal to R s Transmitter cable lossL ct dB1.0 N = N t + 10 log B n + F n Maximum EIRPP ex dBm77.0 Dual airborne-antenna diversity assumed, but not ground diversity Transmitting-antenna pointing lossL pt dB2.0 L a obtained from SC203-CC016 data for 2.4-GHz signal EIRP toward receiverPePe dBm75.0 V a estimated by assuming airframe loss increases from S- to C-band Free-space value of received signal PFDD pf dBm/m L x based on ITU-R Recs. P , P , P.838, P.676-6, and P Free-space path lossLfLf dB148.9 M c = sqrt ((L a + V a )^2 + L x ^2 + M b ^2) -- approximation in lieu of convolution Mean receiving-antenna gainGrGr dBi2.0 M = M m + M c + M i + M a Receiver cable lossL cr dB2.0 P rq = E b /N 0 + N + M Mean received signal powerP rm dBm-73.9 M x = P rm - P rq Required signal-to-noise ratio per bitE b /N 0 dB2.5 Thermal-noise spectral power densityNtNt dBm/kHz Noise bandwidth of receiverBnBn kHz87.5 Receiver noise figureFnFn dB4.0 Total receiver noiseNdBm Implementation marginMmMm dB1.0 Airframe loss value for CDF = 0.002LaLa dB20.0 Est. variation from 2.4-GHz airframe lossVaVa dB2.0 Excess path-loss value for CDF = 0.002LxLx dB RFI multipath boost for CDF = 0.002MbMb dB6.0 Combined airframe/path/RFI marginMcMc dB Allowance for interference = noiseMiMi dB3.0 Aviation safety marginMaMa dB6.0 Total required margin for 99.8% avail.MdB Required signal powerP rq dBm Excess marginMxMx dB Sample C-Band Uplink Budgets 24


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