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A Frequency Assignment Strategy for Common Data Link (CDL) Users

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1 A Frequency Assignment Strategy for Common Data Link (CDL) Users
An Inspection of USCENTCOM Operations in Afghanistan Rob Moser, The MITRE Corporation Jeff Bench, L-3 Communications 16 March 2011

2 Purpose and Agenda (U) Provide a Frequency Allocation Strategy for CDL Links supporting ISR Operations in Afghan Theater Problem Statement USCENTCOM Study Guidance CDL Background Information Approach to Problem Study Limitations Options Availability Option 1: Limited Airspace Management Option 2: Managing Airspace, More CDL Links Further Study Summary Recommendations

3 Problem Statement (U) Demand for Ku-band CDL assignments exceeds allocation by 300% 700% in “hot spot” regions of Combined Joint Operations Area Afghanistan (CJOA-A) New Wide Area Surveillance (WAS) aircraft consume 75% of allocation by themselves Aircraft using overlapping frequency assignments will interfere with one another without a solid deconfliction plan Interference causes loss of data or loss of UAV control No pre-mission or real-time spectrum deconfliction tools are currently available for frequency managers or ISR planners in the CJOA-A Current approach to frequency assignment is best effort A frequency plan is needed that can mitigate interference and still support ISR operations Each operating location (e.g. Kandahar) has requests for 1 to 3 GHz worth of downlink spectrum. The frequency band only supports 0.43 GHz. Clever ways to re-use spectrum must be achieved. Most aircraft require 30MHz for a downlink. Half of the deployed aircraft require 2 downlinks, half require only one downlink. Some wide area surveillance systems (e.g. Blue Devil, Gorgon Stare, AAA) require extremely wideband links that consume 300MHz by themselves. Some operating locations have more than one of these wide area surveillance aircraft

4 USCENTCOM Study Guidance (U)
Many studies produce “academic” recommendations Current situation is a growing problem; need actionable results now Operational Guidance Use no formulas! Allow operators/planners to apply guidance within 5 seconds (from question to answer) Be based on situational data already available to the operators/planners Rely on tools, maps, software, etc. already available to the operators/planners CCJ6 described two distinct types of guidance required Guidance for mission planners to assign daily frequencies for CDL aircraft. This has been described as a “thoughtful exercise with meticulous care.” Guidance for J3 operations personnel to rapidly respond to ad hoc requests for coverage. The 5-second rule applies here. Examples: Can I move aircraft “A” from where it is now to where I need it to be without causing frequency interference/fratricide? We need to launch another aircraft. Can the coverage area handle another aircraft? Can I quickly determine what frequency to use?

5 Background (U) Common Data Link (CDL) operates in Ku-band
14.4 – GHz Air to Ground Downlink (430 MHz bandwidth) 15.15 – GHz Ground to Air Uplink (200 MHz bandwidth) OSD Policy & Public Law require CDL to be incorporated in all manned & unmanned ISR platforms (circa 2005) Affects the acquisition pipeline for every UAV Program of Record Influences QRC development activities OSD Waiver (Feb 2011) authorizes 15.7 – 17.3 GHz for CDL in AOR 14 unique models of CDL-enabled ISR aircraft were deployed to CJOA-A as of Jan 2011 Does not include Recce pods on fighter/bomber aircraft Data throughput requirements for aerial downlinks has steadily increased due to advances in sensor technology (i.e. WAS, HD FMV, etc.) Constant Hawk: 21Mbps Blue Devil / Gorgon Stare / Yellow Jacket / AAA: 274Mbps OASD Policy Memorandum, “Department of Defense Common Data Link Policy”, Dated 30 DEC 2005 mandates CDL for ISR Dissemination other than Tactical UAVs (under 30 lbs) OSD Policy Memorandum, “UAS Spectrum Regulatory Policy Guidance”, Dated 14 APR 2006 reinforces earlier 30 DEC 2005 policy and quotes Public Law Public Law , Dated 6 Jan 2006, withholds acquisition funding for UAS (other than tactical) that do not include CDL capability for ISR dissemination

6 Approaching the Problem (U)
USCENTCOM J2/J6 tasked MITRE to … Study the problem Propose frequency mgt/deconfliction guidance for specific geographic areas of interest in the CJOA-A MITRE collaborated with L-3 Communications Used “FlyPlan” Modeling & Simulation (M&S) software Created by L-3 specifically to solve CDL management problems Developed under contract to CDL PMO, Hanscom AFB (ESC) Analyzed CDL equipped platforms operating in CJOA-A Platform data provided by the Services via USCENTCOM data call Performed RF analysis of inputs/outputs/results Developed recommended operational guidelines Identified deconfliction procedures applicable across the CJOA-A Provided focused examples for Regional Command South (RC-S) All analysis for this USCENTCOM study performed collaboratively by Mr. Jeff Bench (L-3 Communications) and Mr. Rob Moser (MITRE) Platform data was provided by US Gov’t program offices within the Services in response to USCENTCOM data call (CCJ2/OR , 21 Oct 2010) Prime Integrators and/or datalink subcontractors provided additional engineering fidelity with approval from their respective Gov’t acquisition offices L-3 Communications developed an enhanced version of FlyPlan for this effort (funded out of pocket). Enhanced version addresses critical comments from the Joint Spectrum Center Platform data includes substantial amounts of proprietary vendor information; therefore, copies of the vendor-provided platform data will not be available for dissemination

7 Study Limitations (U) 90% solution delivered
Analysis is limited to aircraft in USCENTCOM data call Omits Ku-band microwave towers; ground-based interferers Data call is not complete Not all platform program offices responded PTDS / Canadian King Air New systems arriving since data call; Inbound systems not included : Yellow Jacket / Fire Scout Operating locations for inbound platforms are still TBD (AAA aircraft) Engineering data not available (platform not included in data call) The FlyPlan analysis tool can, and has, successfully modeled the aircraft in the data call and verifies the correctness of the Downlink & Uplink frequency plan proposals in this briefing. If the data call were 100% correct and inclusive, then guarantees could be offered. We know that not all contributors of RF interference were modeled (e.g. microwave towers, commercial Ku-band satellite terminals, Persistent Threat Detection System [PTDS] teathered blimps, etc.). We also know that additional platforms are projected to be in the theater this year (or may already be in place), but were not included in the data call (e.g. Yellow Jacket, Shadow WAAS, Fire Scout, MARSS, etc.). There is therefore some level of risk that interference may still occur even when the recommended frequency plans in this briefing are followed. One means of mitigating interference is to have USCENTCOM require that each platform, US and coalition, that operates CDL provide USCENTCOM/CCJ6 with the engineering data outlined in the data call template. Systems may then be modeled in FlyPlan on a continuing basis to help ensure that problems do not arise, or that problems may be anticipated and mitigated with changes to the frequency plan.

8 FlyPlan Software Analysis Key Findings (U)
Minimum frequency separation between 10Mbps channels is 15MHz for currently deployed aircraft Key factor is the spectral emission mask May be different for systems not included in the data call Minimum angular separation between 274Mbps aircraft 30 Degrees if using the same frequency assignment 15 Degrees if frequencies spaced as far apart as possible & GHz (30 MHz separation – no further separation is possible) Minimum angular separation between 10Mbps aircraft is 10 Degrees (if using the same frequency) 21Mbps users (e.g. Constant Hawk) consume equivalent of two 10Mbps channels These key findings will be applied to formulate frequency plans for varying scenarios, presented in the following slides. All determinations were made using FlyPlan software and data provided by the respective Program Managers

9 Minimum Frequency Separation Explained (U)
Signals are not “Lego Bricks”; they are complex functions FlyPlan assesses interference as signals overlap; finds the breaking point regardless of how bandwidth is defined (e.g. 3 dB, Necessary, etc) 10Mbps links require 15MHz frequency separation to share the same airspace without interference 3 dB BW (10.1MHz) 90% of the Power (11.5MHz) Necessary BW (18.2MHz) As used by: Vader MARSS Harvest Hawk Constant Hawk Hunter AAA A signal in space has energy dispersed across a nearly infinite bandwidth; therefore, the term “bandwidth” has no meaning without an associated qualifier. Typical qualifiers are bandwidths at 3 dB down from peak, some specified percentage of power (e.g. 90%), and Necessary Bandwidth The Joint Spectrum Center prefers to use 3 dB Bandwidth definitions when describing signals The SPECTRUM-XXI GMF database typically identifies Necessary Bandwidths BOTTOM LINE: FlyPlan software does not care how we choose to define bandwidth. FlyPlan uses the actual spectral response curve to find the breaking point on minimum frequency separation. LESSON LEARNED: This type of analysis clearly points to the continued need for USCENTCOM to request spectral emission plots for each aircraft heading into the theater. Without this detailed data, it is impossible for FlyPlan (or any other software) to make an accurate determination on interference assessments.

10 Minimum Angle Separation Explained (U)
All GCS antennas in the data call are highly directional (4 ft parabolic) Example: 5 Degrees offset has a 31 dB drop in antenna gain FlyPlan assesses interference at off-axis angles; finds breaking point Takes into account GCS pointing stability and A/C power outputs The high directionality of the CGS antennas identified in the data call is the key determinant in permitting frequency re-use in the airspace surrounding any given operating location. One may observe an alarming trend The original U-2 MIST ground antenna was 2 meters (78 Inches). Current antennas in the data call are 4 ft (48 Inches) There are antennas on the market that are only 3 feet (36 inches) As the ground antenna gets larger Peak gain increases Side lobes decrease Off-axis angle differences provide greater interference rejection Allow faster frequency re-use Future systems that arrive in theater may have large impacts on frequency reuse if their ground antennas are smaller than the 4 ft antennas analyzed for this current data call Investigating the operational impact of ground antenna sizes is one of the long term study areas recommended at the end of this briefing

11 Links vs. Aircraft (U) 10Mbps Narrowband Aircraft fall into one of two categories Narrowband aircraft using only Omni Antennas Narrowband aircraft using Directional Antennas Omni-Only Narrowband Aircraft Omni antennas broadcast everywhere, in all directions Broadcast reach GCS & Remote Video Terminals (RVT) simultaneously Directional Narrowband Aircraft Focuses a radio beam at the GCS with directional antenna Directional radio beam does not illuminate dismounted soldier RVT’s Most A/C in data call require support to dismounted soldiers; therefore Directional narrowband aircraft require a second CDL link RVT links typically use an omni so as to reach all soldiers on the ground The term “Links” is used throughout this briefing If referring to omni-only aircraft, then # Aircraft = # Links If referring to directional aircraft, then # Aircraft = Half the # Links

12 Data Call CDL-Platform Summary for Afghanistan (U)
The above table contains a summary of the platforms whose program offices responded to USCENTCOM Data Call Canadian King Air and PTDS did not respond Yellow Jacket and Fire Scout were not included in the Data Call because their deployments to Afghanistan were not certain at the time of the Data Call release (21 Oct 2010)

13 Two Frequency Mgt Option Approaches Available (U)
Develop frequency plans requiring little or no airspace management or tasking considerations Aircraft can fly anywhere without regard to frequency considerations Use airspace management to expand the number of CDL links Requires disciplined airspace management Airspace management tied directly to aircraft tasking in support of ISR collection requirements Aircraft cannot fly “anywhere” Coordination must occur before an A/C can change from one geographical sector to another Frequencies may need to be centrally or regionally assigned (perhaps daily) to manage channels USCENTCOM desires a frequency plan that will enable aircraft operating from a given location to fly anywhere within their line of sight range without changing frequencies or causing interference to other CDL users This is possible and is presented in this briefing; however, the quantity of CDL links that can be supported may be insufficient for large operating locations This presentation presents options to increase the number of CDL links, but the cost of doing this is disciplined airspace~frequency management Aircraft will not be able to fly “anywhere” Aircraft flight operations will have to be pre-planned and have frequencies assigned each day based on planned operating location This pre-planning with daily frequency assignments may have to be performed by a central authority that may or may not exist today.

14 Option 1: Little to No Airspace Management (U)
Max number of CDL links that fit into Ku-band (each base) 27 10Mbps (15 MHz separation) 1 274Mbps Mbps (15 MHz separation) Aircraft can fly anywhere within LOS range of base (200NM) Useful if you do not want to manage airspace & frequencies Two downlink frequency plans are shown: One for 100% 10Mbps platforms One to accommodate a wideband platform with 100% 10Mbps aircraft Not all aircraft use 10Mbps; a separate plan has been developed but not shown in this presentation for brevity Each downlink frequency plan requires an associated uplink frequency plan Uplink frequency plans are not shown in this presentation for brevity Many operating locations have 100% narrowband (10Mbps) aircraft 27 Links probably sounds pretty good Narrowband aircraft that employ directional antennas require a second, dedicated RVT broadcast to support dismounted soldiers If all of the aircraft operating of a given base were directional type systems, then 27 links translates to 13 aircraft This may not be enough to satisfy a given operating location

15 274Mbps Wideband Considerations (U)
There is not enough spectrum to separate two wideband A/C that share the same airspace Minimum angular separation between two wideband A/C measured from operating location is 30° A/C use same frequency Depending on orbit size, airspace can handle upwards of 9 wideband A/C Each separated by 30° Spread out around the base Twelve 10Mbps CDL links can operate simultaneously anywhere within range of base 12 10Mbps can fly anywhere This plan requires use of the CDL frequency downlink plan of the previous slide in which one wideband and twelve 10Mbps channels are defined Separating the wideband A/C by 30 degrees as measured from the runway allows the wideband frequency assignment to be re-used Key Point: The twelve additional 10Mbps links do not necessarily translate to twelve aircraft Each of wideband aircraft require a separate RVT broadcast which consumes one of the twelve channels. With two wideband A/C, that leaves only ten links. If each of the narrowband platforms use directional antennas (e.g. Grey Eagle), then they too will need two channels (one for the GCS link, and one for the RVT broadcast). This worst case scenario implies 5 narrowband aircraft operating from the same base as the two wideband aircraft. Co-located GCS on same base

16 Bringing Wideband A/C Closer Together (U)
There is insufficient spectrum available for use to separate two wideband A/C to share the same airspace; but, Spacing two wideband A/C channels as far as possible reduces the minimum angular separation From 30° to 15° Channel assignments of & GHz 30 MHz max separation possible Huge cost; Number of 10Mbps links drops from 12 to 4 The 4 10Mbps can be anywhere in the airspace The above scenario was fully tested in the FlyPlan M&S software. No additional 10Mbps narrowband platforms can radiate in close proximity to the wideband aircraft without causing mutual interference As with the previous slide, the four 10Mbps links does not translate to four narrowband aircraft Each of the two wideband aircraft require a dedicated 10Mbps link for RVT dissemination. That leaves two links left If narrowband platforms employing directional antennas are used, then they too require a separate, dedicated RVT broadcast link This worst case scenario implies only one narrowband aircraft can operate out of the same base as the two wideband aircraft

17 Overcoming Cost of 2 Wideband A/C Close Together (U)
Minimum separation angle between 10Mbps platforms is 10° Result Wedge containing wideband A/C can support 4 10Mbps (shown in green) Larger wedge (shown in red) can reuse frequencies with normal 10Mbps pattern (below) supporting 27 links 27 Links 4 Links The green wedge shows two wideband aircraft separated by 15 degrees with four additional 10Mbps CDL links These four links can operate anywhere within the green wedge without causing interference to anybody Since the minimum separation angle for narrowband aircraft is 10 degrees, we may leave 10 degrees of “no-man’s land” on either side of the green wedge, and then re-use the entire Ku-band spectrum! The frequency plan for the red wedge is the original plan shown under Option 1. This assumes that all 27 links are 10Mbps users.

18 Option 2: Managing Airspace to Increase CDL Links (U)
B Divide airspace into 4 sectors Alternate frequency patterns Results 13 Links (10Mbps) in “A” 14 Links (10Mbps) in “B” 54 10Mbps) Freedom of Movement: A/C in “B” can move into “A” & vice versa Provides 270° of freedom By staggering the original frequency of Option 1 into “A” and “B”, and assigning these two frequency patterns into alternating Sectors “A” and “B”, we can achieve 100% frequency re-use and double the number of CDL links Aircraft no longer can operate “anywhere within line of sight of their runway”, but they do have reasonable freedom of movement for ad hoc ISR coverage requests Any aircraft may operate in its assigned sector or either adjacent sector under proper coordination

19 Further Link Increases => More Sectors (U)
1 2 3 4 5 6 Dividing airspace into more sectors yields more links 4 Sectors: 54 10Mbps 6 Sectors: 81 10Mbps 8 Sectors: Mbps 12 Sectors: Mbps Alternate Even/Odd frequencies A/C have freedom to move into adjacent sector 1 2 3 4 5 6 8 7 10 9 11 12 1 2 3 4 5 6 8 7

20 Caution (U) Conclusions in this study based exclusively on data for aircraft currently operating in CJOA-A Future A/C may have different transmitter/receive characteristics Conclusions contained herein may not apply Urge all future deployments provide USCENTCOM with completed Data Call worksheet Can assess impact (if any) fairly quickly (two weeks) Importance is amplified for wide band assets or narrow band assets operating out of a FOB that supports a wide band asset

21 Recommended Further Study (U)
Due to operational urgency, this study focused exclusively on the here and now Mitigation steps for the long term are likely 9 Months estimated to complete a long term study Long term study areas: Waveform improvements Modulation, Coding, Tunability, Power Control Antenna improvements (Aircraft & Ground Stations) Diplexer improvements Cross-Polarization benefits Improvements to FlyPlan M&S software

22 Summary (U) Ku-band spectrum supports…
27 10Mbps, or 1 274Mbps Mbps 274Mbps A/C require 30° separation if using same channel 12 10Mbps can overlap same area of operations 274Mbps A/C can operate within 15° w/staggered frequencies 4 10Mbps can overlap same area of operations Spectrum reuse begins 10° later, provide 27 10Mbps Airspace can be divided into sectors to further increase # of Links Requires airspace management A/C are restricted to their assigned sector + adjacent sectors (each side)

23 COA #1: Assign Frequencies Independent of Airspace
Assign Blue Devil and Gorgon Stare a “shared” wideband channel ( GHz center frequency) and assign narrowband users remaining channel assignments per below IJC and RC-S CM&D need to be cognizant that tasking Blue Devil and Gorgon Stare within 30o of angular separation will result in signal interference (i.e. imagery degradation to PED cell) COA supports the minimum number of assets but requires the least day-to-day deconfliction measures by RC-S CM&D.

24 COA#2: Include two “Keep-Out” zones Around Wideband Aircraft
Same as COA#1, but with two pre-planned 10° keep out zones on either side of the wideband aircraft Enables 12 narrowband links as with COA#1 co-located with wideband aircraft 27 Links 12 Links 10° Keep-Out Zone Complete frequency re-use beyond the keep-out zones Enables 27 additional narrowband links to be assigned as needed IJC and RC-S CM&D need to be aware that … A/C in green zone are confined to green sector A/C in red zone are confined to red sector

25 COA#3: Operate Wideband A/C in Close Proximity
Same as COA #2, but change frequency plan for the Green Zone Enables IJC and RC-S CM&D to bring wideband A/C within 15° of each other Reduces narrowband assignments from 12 to 4 Red zone is unaffected Wideband center frequencies will be & GHz 10° Keep-Out Zone 4 Links 27 Links

26 COA#4: Assign Frequencies by Sector
Use a 4/6/8/10/12-sector approach to divide airspace around the designated RC-S FOB Permits the frequency re-use of both wideband and narrowband users Alternate Red/Blue channel assignments with sectors Minimizes and/or prevents “accidental” blue-on-blue frequency interference Aerial assets communicating with GCS at FOB locations other than the sectors radius but in the general Area of Operations may require dedicated channels COA supports the highest number of possible assets (and channel assignments) although requires the RC-S CM&D (or appropriate authority) to have an intimate hand in spectrum coordination based on aircraft tasking requirements

27 Backup BACKUP

28 Minimum Separation Angles for Frequency Reuse
This briefing (slide 8) showed that… Min separation angle = 30° for 274Mbps wideband links Min separation angle = 10° for 10Mbps narrowband links In reality, min separation angle is a function of range CCJ6 guidance (slide 4) was “no formulas”, “5 second decision time” Therefore, this briefing took worst case separation angle (max range) Planners probably need to know that they have options, particularly for the 274Mbps wideband aircraft See Slide 29 – 31 for examples

29 274Mbps (STD-CDL) Wideband Aircraft (Blue Devil & Gorgon Stare, both with Directional Antennas)
150NM 140NM 130NM 120NM 30 Deg Separation out to 140NM 10 Deg Separation out to 130NM 5 Deg Separation out to 120NM

30 30 Deg Separation out to 50NM 10 Deg Separation out to 40NM
274Mbps (STD-CDL) (Blue Devil [Omni Antenna] & Gorgon Stare [Directional Antenna]) 50NM 30 Deg Separation out to 50NM 40NM 10 Deg Separation out to 40NM

31 10 Mbps (STD-CDL) (25,000 Feet Altitude, Directional Antennas)
160NM 150NM 140NM 30 Deg Separation out to 160NM 10 Deg Separation out to 150NM 2.5 Deg Separation out to 140NM


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