Steve Henriksen

ITT Corporation, Herndon, Virginia

Unmanned Aircraft System Control and ATC

Communications Bandwidth Requirements

NASA/CR—2008-214841

February 2008
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Prepared under Contract NNC05CA85C

Steve Henriksen

ITT Corporation, Herndon, Virginia

Unmanned Aircraft System Control and ATC

Communications Bandwidth Requirements

NASA/CR—2008-214841

February 2008
Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

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Available electronically at http://gltrs.grc.nasa.gov

This work was sponsored by the Fundamental Aeronautics Program

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by NASA technical management.
NASA/CR—2008-214841 iii

Executive Summary 

E.S.1 Introduction 

There are significant activities taking place to establish the procedures and requirements for safe and 

routine operation of unmanned aircraft systems (UAS) in the National Airspace System (NAS). Among 

the barriers to overcome in achieving this goal is the lack of sufficient frequency spectrum necessary for 

the UAS control and air traffic control (ATC) communications links. This shortcoming is compounded by 

the fact that the UAS control communications links will likely be required to operate in protected 

frequency spectrum, just as ATC communications links are, because they relate to “safety and regularity 

of flight.” To support future International Telecommunications Union (ITU) World Radio Conference 

(WRC) agenda items concerning new frequency allocations for UAS communications links, and to 

augment the Future Communications Study (FCS) Technology Evaluation Group efforts, NASA Glenn 

Research Center has sponsored a task to estimate the UAS control and ATC communications bandwidth 

requirements for safe, reliable, and routine operation of UAS in the NAS. This report describes the 

process and results of that task. The study focused on long-term bandwidth requirements for UAS 

approximately through 2030. 

E.S.2 Task Process and Analysis 

The task workflow diagram shown in Figure 1 provides an overview of the methodology used to 

perform this task. As shown in the figure, it roughly followed a parallel track of UAS control 

communications and ATC communications bandwidth analysis activities, with common processes during 

the initial and final stages of the task. 

Figure 1.—Task workflow diagram. 
NASA/CR—2008-214841 iv

Figure 2.—UAS line-of-sight communications architecture assumed for the task. 

This task was based on the concept that both control and ATC communications will be provided via a 

sectorized air/ground line-of-sight (LOS) communications architecture. This architecture is illustrated in 

Figure 2. 

The assumed architecture included up to seven separate links that may be required to provide control 

communications and both voice and data ATC communications, as follows: 

 Existing ATC radio facility to unmanned aircraft (UA) link: Channel for ATC communications 

shared with all aircraft in sector as shown in red (currently simplex very high frequency (VHF) 

double sideband amplitude modulation (DSB–AM)) (Not part of estimation) 

 New UAS radio facility to UA links 

− Dedicated voice and data channels for ATC communications (uplink and downlink) as shown 

in blue—up to four links 

− Dedicated channels for control communications (uplink and downlink) as shown in green—

up to two links 

E.S.3 Task Results, Conclusions, and Recommendations 

It was found that the total required UAS communications bandwidth requirements were quite sensitive 

to certain parameters and study assumptions, including the following: 

 UA peak counts 

− UA were assumed to be 10 percent of the total peak instantaneous aircraft count (PIAC); a 

different value based on emerging plans and future operational practice linearly scales the 

results. 

 UAS control communications link architecture configuration assumptions 
NASA/CR—2008-214841 v

− Required UAS control communications data capacity was estimated for two configurations 

defined by Standardization Agreement (STANAG) 4586 (ref. 1), corresponding to two 

alternative UAS ground control station to UA link architectures. One configuration 

(Configuration A) assumed a non-networked, native, or proprietary-type radiofrequency (RF) 

link with some security overhead, while the second configuration (Configuration B) implied 

an RF link that included overhead for standards-based security, STANAG 4586 data link 

interface (DLI) wrappers, and transport/network layer protocols. 

• Configuration B resulted in significant network and transport layer protocol overhead on 

the air/ground (A/G) links. 

• The Configuration A non-networked assumption significantly reduced required 

bandwidth. 

 Data rate requirements of the UAS Command and Status/Telemetry messages 

− These are highly dependent on update rates associated with varying degrees of autonomy. 

Conservative values were assumed to upper bound the aggregate rate, based on low to 

moderate autonomy UAS. 

− In addition, for the networked Configuration B, a conservative assumption was made that 

multiple command/status messages were not combined into internet protocol (IP) datagram 

payloads; that is, each IP data payload consisted of only one command/status message. 

 The channel modulation selected and amount of link forward error correction (FEC) coding 

necessary to increase link margin to accommodate excess path losses, directly impacted required 

channel bandwidth 

− A range of link FEC coding alternatives were used to provide a range of total required 

bandwidth. 

− Sector architecture, including sector size and “layering,” and the corresponding selection of 

reuse parameters to mitigate co-channel interference. 

Figure 3 illustrates required total UAS control and ATC communications bandwidth estimates for the 

notional architecture developed for this study for each link type considered and their sensitivity to 

overhead and link FEC coding assumptions. A box has been placed around the values that provide a 

reasonable range of bandwidth requirements, while still providing suitable performance. 

Figure 3.—Required total UAS communications bandwidth estimates and their sensitivity to 

overhead and link FEC coding assumptions. 
NASA/CR—2008-214841 vi

Given the fact that UAS civil and private aviation in the NAS1 is still in its earliest stages, the range of 

possibilities for implementing a broadbased means of providing both UAS control communications and 

ATC communications is fairly wide open. Because of its focus on the need to identify potential future 

UAS frequency spectrum needs in support of WRC activities, this study concentrated on just one of 

several possible means of providing these capabilities, that is, by way of UA relay as illustrated in Figure 

2. Other potential architectures are being considered by RTCA SC–203, if not by other organizations. 

Even within this one architectural approach there are still many practical variables and uncertainties in 

developing the assumptions and the notional architecture design decisions needed to make the UAS 

communications bandwidth estimates. The sensitivity of this estimation process to these design decision 

assumptions and selection of certain key parameters was discussed, and this demonstrated the 

inadvisability of trying to derive a single number to estimate total bandwidth requirements. Therefore for 

this study a range of estimated bandwidth requirements was developed to provide bounds, based on the 

stated configurations and assumptions. 

For the selected notional architecture, the findings based on modest FEC coding, such as provided by 

the two rate 3⁄4-cases provide the most reasonable compromise between performance and bandwidth 

within the range of results. In particular, the concatenated Reed Solomon (255, 223) block encoding and 

3⁄4 rate convolutional FEC coding case provided significant excess path margin for protection against 

interference sources and signal degradations, including protection against burst errors. These two cases 

resulted in the following bandwidth estimates: 

 Control communications bandwidth estimates on the order of 10 to 11.4 MHz for the networked 

configuration 

− 8.5 to 9.7 MHz for the UA to UAS radio control station downlink 

− 1.5 to 1.7 MHz for the UAS radio control station to UA uplink 

 Control communications bandwidth estimates on the order of 3.6 to 4.1 MHz for the nonnetworked configuration 

− 3.3 to 3.8 MHz for the UA to UAS radio control station downlink 

− About 0.3 MHz for the UAS radio control station to UA uplink 

 ATC voice communications bandwidth estimates on the order of 2.7 to 3.1 MHz, split equally 

between the uplink and downlink 

 ATC data communications bandwidth estimates on the order of 5.2 to 5.9 MHz 

− About 3.3 to 3.8 MHz for the downlink 

− About 1.9 to 2.1 MHz for the uplink 

The notional architecture used to estimate total bandwidth requirements allowed for significant link 

margin because of the modest sector radii. Other possible architectures may be more efficient. 

Some additional summarizing remarks and recommendations can be made. Because a detailed design 

was beyond the scope of this task, several relevant issues were not considered. These include the 

following: 

 Co-site interference issues, both on the UA and for the UAS ground radio facilities, not 

considered for this study, need to be explored. Assume that both the control communications and 

ATC communications use the aeronautical L-band allowed for straightforward analysis; however, 

simultaneous transmission on these links present serious design challenges, especially on the UA, 

to mitigate potential co-site interference. 

 

1

Military UAS were not considered in this task. 
NASA/CR—2008-214841 vii

 The potential impacts of sub-banding need to be addressed. Though in certain respects it might be 

easier to identify noncontiguous “chunks” or sub-bands of spectrum for the different control and 

ATC communications links than it would be to find 10 to 20 contiguous MHz of available 

bandwidth to manage, this spectrum management issue should be investigated. 

 The entire issue of whether or not a national UAS communications service could be implemented 

was beyond the scope of this study, and to a certain extent, it does not affect the analysis. 

However, this study was based on a uniform design, regardless of how and by whom it would be 

implemented and/or operated, and the study results are therefore dependent on this assumption. 

 Just as with the Communications Operating Concept and Requirements (COCR), for estimation 

purposes, this study nominally assumed a uniform density of aircraft throughout a sector and/or 

service volume. In reality, this often is not the case, as both manned and unmanned aircraft would 

be concentrated along particular corridors or “hot spots.” This could affect UAS bandwidth 

requirements and should be considered as a future topic of study. 

 For the purposes of link efficiency and interference mitigation, it might be advisable to combine 

the ATC voice and data links. Furthermore, each of the uplink/downlink pairs might be 

implemented via simplex or full duplex links, potentially reducing the number of UAS radio 

facility to UA links to as few as two. In the limit, control communications and ATC 

communications message traffic could be combined and implemented via a single link, though 

this potential single point of failure configuration might present too much risk. This issue needs 

further investigation. 

 Though the target 10-dB link margin was mostly exceeded over the range of link parameter 

values assumed for the link analyses, further work in the area of required link margin, including 

acceptable excess path loss, should be pursued. 

NASA/CR—2008-214841 ix

Contents 

Executive Summary .....................................................................................................................................iii

E.S.1 Introduction ..............................................................................................................................iii

E.S.2 Task Process and Analysis .......................................................................................................iii

E.S.3 Task Results, Conclusions, and Recommendations .................................................................iv

1.0 Background and Introduction............................................................................................................... 1

1.1 Background ...............................................................................................................................1

1.2 Task Objectives and Scope........................................................................................................1

1.3 Approach ...................................................................................................................................2

1.3.1 Identifying UAS Mission Types and Needs.................................................................3

1.3.2 Estimating UAS Peak Counts and Densities................................................................4

1.3.3 Calculating UAS Control Communications Data Capacity .........................................5

1.3.4 Calculating UAS ATC Communications Data Capacity..............................................5

1.3.5 Estimating UAS Control and ATC Communications Bandwidth................................5

1.4 Assumptions ..............................................................................................................................5

1.4.1 Task Modeling Assumptions........................................................................................5

1.4.2 Communications Architecture Assumptions................................................................6

2.0 Analysis................................................................................................................................................ 8

2.1 Introduction ...............................................................................................................................8

2.2 UAS Specific Mission Types and Needs...................................................................................8

2.3 UAS Aircraft Counts and Densities ..........................................................................................8

2.3.1 UAS Aircraft Counts....................................................................................................8

2.3.2 UAS Aircraft Densities ..............................................................................................10

2.4 UAS Message Statistics...........................................................................................................10

2.4.1 UAS ATC Communications Message Statistics ........................................................10

2.4.2 UAS Control Communications Message Statistics ....................................................11

2.5 UAS Control Message Quantities/Sizes..................................................................................12

2.5.1 Introduction ................................................................................................................12

2.5.2 Message Overhead Assumptions................................................................................13

2.5.3 UAS Control Configuration Messages (Configuration B) .........................................14

2.5.4 UAS Control Mission Upload Messages (Configuration B)......................................14

2.5.5 UAS Flight Vehicle Command and Status Message Capacities ................................14

2.6 Estimating UAS C&C Bandwidth Requirements....................................................................18

2.6.1 Channel Access Approach..........................................................................................19

2.6.2 Channel Bandwidth Requirements.............................................................................20

2.6.3 Sector Architecture.....................................................................................................24

2.6.4 Link Budget Results ...................................................................................................31

2.6.5 Calculating Total UAS C&C Communications Bandwidth.......................................32

3.0 Conclusions and Recommendations................................................................................................... 36

Appendix A—List of Acronyms and Abbreviations .................................................................................. 39

References................................................................................................................................................... 41

NASA/CR—2008-214841 1

1.0 Background and Introduction 

1.1 Background 

There are significant activities taking place to establish the procedures and requirements for safe and 

routine operation of unmanned aircraft systems (UAS) in the National Airspace System (NAS). Among 

the barriers to overcome in achieving this goal is the lack of sufficient frequency spectrum necessary for 

the UAS control and air traffic control (ATC) communications links. This shortcoming is compounded by 

the fact that the UAS control communications links will likely be required to operate in protected 

frequency spectrum, just as ATC communications links are, because they relate to “safety and regularity 

of flight.” Related to this spectrum issue and concurrent with the UAS standards development activities 

are the ongoing efforts within the international aviation community to develop requirements for next 

generation aeronautical communications systems. Several recent and current activities relevant to both 

UAS and aeronautical communications have included the following: 

 (2004 to 2006) The NASA Glenn Research Center team supporting NASA’s Access 5 Project 

defined functional communication requirements for UAS. 

 (2004 to present) The FAA/NASA/EUROCONTROL Future Communications Study (FCS) is 

identifying requirements and technologies for the future radio system. 

− The Communications Operating Concept and Requirements (COCR) (ref. 2) for the Future 

Radio System, which drives the technology evaluations, acknowledges the potential future 

impact of UAS, and implicitly includes UAS in its capacity analyses. 

 (2004 to present) The RTCA SC–203 UAS Control and Communications Working Group is 

addressing UAS communications spectrum requirements. 

 (2006 to present) International Telecommunications Unit (ITU) World Radio Conference (WRC) 

planning activities include the U.S seeking an agenda item for WRC–11 addressing UAS 

communications spectrum requirements. 

To support future ITU WRC agenda items concerning new frequency allocations for UAS 

communications links, and to augment the FCS Technology Evaluation Group efforts, Glenn has 

sponsored a task to estimate the UAS control and ATC communications bandwidth requirements for 

routine operation of UAS in the NAS. This report describes the process and results of that task. 

1.2 Task Objectives and Scope 

Figure 4 depicts the RTCA 203 UAS notional architecture, which includes the two principal types of 

UAS communications links (ref. 3): 

 Control link: The equipment and links used for receiving commands from pilots in the control 

segment (telecommand uplink) and for transmitting aircraft health, status, and situation awareness 

data to the control segment (telemetry downlink). Because the UAS may be operated in both LOS 

(line of sight) and BLOS (beyond line of sight) conditions, this functionality may be provided by 

more than one data link subsystem. 

 ATC communications links: Consist of equipment and links used for voice and data 

communications between the pilot in the control segment and an air traffic controller as well as 

other participants and users of the airspace. 

The objective of this task was to estimate future bandwidth requirements for these two UAS 

communications types needed for safe, reliable, and routine operation in the NAS, in support of U.S. 

WRC preparation activities. The study focused on long-term bandwidth requirements for UAS 

approximately through 2030. 
NASA/CR—2008-214841 2

Figure 4.—UAS notional architecture showing task focus. 

As seen in the figure, control communications is provided strictly between the UAS Control Segment 

and the Aircraft Segment (i.e., the unmanned aircraft or UA) by way of radiofrequency (RF) air/ground 

 (A/G) link. The figure also reveals that UAS to ATC communications connectivity can be provided 

through several alternatives in one or more combinations of A/G and terrestrial links. The multiplicity of 

alternative approaches is the subject of study efforts within the RTCA SC–203 UAS Control and ATC 

Communications (C&C) Working Group. 

Because of specific interest in supporting future ITU WRC RF spectrum activities, this task focused 

on a specific LOS A/G link architecture that features direct UAS control communications connectivity 

and ATC communications that relies on the UA to provide a relay function between the NAS ATC 

facilities and the UAS Control Segment. This link architecture is described in more detail in section 1.4.2. 

1.3 Approach 

The task workflow diagram shown in Figure 5 provides an overview of the methodology used to 

perform this task. As shown in the figure, it roughly followed a parallel track of UAS control 

communications and ATC communications bandwidth analysis activities, with common processes during 

the initial and final stages of the task. Each of the subtasks shown in the figure is described in the 

following sections. 

An important part of the task methodology was the presentation of three status briefings to key Federal 

Aviation Administration (FAA) and NASA representatives and some of their technical support 

contractors over the 7-month duration of the task. These provided the opportunity to solicit and receive 

insightful feedback and direction to help maintain the appropriate focus of the task. 
NASA/CR—2008-214841 3

Figure 5.—Task workflow diagram. 

1.3.1 Identifying UAS Mission Types and Needs 

The Future Communications Study COCR models for air traffic services are based primarily on a gate-to-gate 

operational scenario typified by traditional manned aircraft flights and necessarily feature homogenous service 

volumes, flight durations, peak instantaneous aircraft counts (PIACs), and other homogeneous operational statistics. 

However, some augmentation needs to be made to accommodate “new” UAS operating concepts. Thus, it is 

important to be able to define the UAS communications characteristics that are both common to and distinct from 

typical communications characteristics of manned aircraft. This was accomplished in this subtask by reviewing and 

evaluating over 60 UAS missions and operational scenarios descriptions developed in RTCA SC–203. In addition to 

providing useful operational information such as expected flight durations, altitudes of operation, and mission 

descriptions for specific UAS, these descriptions provided some high-level communications characteristics. Table I 

and Table II are examples of the UAS mission/scenario information provided by the RTCA SC–203 guidance 

material. 

Table I.—Example of UAS scenario description and flight characteristics (ref. 3) 

Scenario 7, Communication Repeater 

7b. Scenario Description: Multiple UAVs used together to create a continuous repeater/relay for UHF communications over remote 

areas. First vehicle is launched from airport and proceeds to the loiter fix. Second vehicle is launched halfway through first vehicle 

mission time to nonconflicting loiter fix. Once second vehicle is established at its respective fix, first vehicle returns to original launch 

airport via preprogrammed route. Vehicle is met upon return and towed to ramp. 

8. Define characteristics of scenario for each phase of flight 

a. Pre-flight: Normal airworthiness pre-flight and check of communication equipment for operation. 

b. Taxi operations: Manually controlled taxi with voice communications to obtain clearance and discrete beacon code 

c. Takeoff/departure: Manually controlled to departure gate 

d. En-route (outbound): Preprogrammed and autonomous operation to loiter fix 

e. Mission area: Racetrack loiter area, 10 miles in length 

f. En-route (inbound): Autonomous fix departure to arrival gate 

g. Approach/landing: Manually controlled and approach utilizing current approach procedures 

f. Post-flight: Exits runway and shuts down; manually towed to recovery area 
NASA/CR—2008-214841 4

Table II.—Example of UAS scenario description performance characteristics (ref. 3)

9. Define system performance characteristics—Aircraft 

a. Max. speed: 400 TAS 

b. Cruise speed: 350 TAS 

c. Min. speed: 90 KTS 

d. Climb rate: 3500 fpm 

e. Descent rate: 3500 fpm 

f. Max. altitude: >60 000 MSL 

g. Typical op alt: 51 000 MSL 

h. Turn rate: 3 deg/s 

i. Gross TO rate: 25 600 lb 

j. Payload capacity: 20 000 lb 

k. Endurance: 35 hr 

l. Range: >12,000 nm 

10. Define system performance characteristics—Airspace utilized 

a. × 

b. ×

c. ⊗

d. ⊗

e. ⊗

f. ⊗

11. Define system performance characteristics—Communications links 

a. Primary command/control link: INMARSAT or equivalent 

b. Secondary command/control link: UHF/HF 

c. Primary sensor data link: 

d. Secondary sensor data link: 

e. ATC voice communications: HF 

f. Other communications links: 

g. Security/information assurance methodology: 

12. Define system performance characteristics—Operations 

a. Taxi method: Human escort 

b. Launch method: Rolling 

c. Launch environment: Towered airport 

d. Recovery method: Rolling 

e. Man/machine control level: Autonomous route plan-man monitors 

f. Mission type: Loitering 

g. VFR/IFR: IFR 

h. Operation type: Scheduled 

i. Pilot/operator qualification: FAA certified manned aircraft pilot 

j. Navigation: GPS/INS 

13. Describe weather-related operational constraints 

None 

14. Describe contingency handling methodology 

Preprogrammed to return to home base if communications fail. 

For engine failure, preprogrammed to proceed to closest identified landing site. Manual control for attempted landing. 

1.3.2 Estimating UAS Peak Counts and Densities 

A critical parameter in estimating UAS communications bandwidth is the number of unmanned 

aircraft actually flying in the NAS for the time period of interest, that is, approximately through 2030. 

This subtask involved identification and review of future UAS projections to make a reasonable estimate 

of how many UA, as a percentage of the total number of flights in the NAS, might be flying in the NAS 

in the future.2

 

2

Just as with the COCR, for estimation purposes, this study nominally assumed a uniform density of aircraft throughout a 

sector and/or service volume. In reality, this often is not the case, as both manned and unmanned aircraft would be 

concentrated along particular corridors or “hot spots.” This could affect UAS bandwidth requirements and should be 

considered as a future topic of study. 
NASA/CR—2008-214841 5

1.3.3 Calculating UAS Control Communications Data Capacity 

This activity string included a series of subtasks to determine UAS control communications data 

requirements, including determining UAS control message statistics, such as instances (how often they 

occur), size, and quantities; defining a control communications sector architecture; and performing link 

analyses to determine suitable channel bandwidth. The sector architecture and channel bandwidth were 

then used to determine the total number of control communications channels, and hence the total required 

UAS control communications bandwidth. 

1.3.4 Calculating UAS ATC Communications Data Capacity 

The FCS COCR developed per aircraft A/G data capacity requirements for providing future air traffic 

services (ATS). This activity string included an effort to determine the applicability of these COCR 

requirements to the UAS case. COCR assumptions, analysis, and results were evaluated to make this 

determination and to identify any potential non-COCR-defined ATC communications traffic necessary 

for operating UAS in the NAS. The UAS ATC data capacity requirements resulting from this analysis 

were then used as inputs to link budget calculations that allowed the selection of suitable modulation and 

forward error correction (FEC) coding techniques, and hence appropriate channel bandwidth. Also 

determined was a suitable technical approach to providing ATC digitized/vocoded voice communications 

traffic and the associated data requirements and channel bandwidth needed to provide this traffic. 

1.3.5 Estimating UAS Control and ATC Communications Bandwidth 

The preceding steps estimated projected future UA PIACs and densities, and the UAS control and 

ATC communications data rates necessary to transfer messages between a UAS control station and a low 

to medium autonomy UA. This step converted the UA densities and data requirements into the required 

bandwidth necessary to provide for all the UA flying in the NAS. The process included selecting 

appropriate channel access approaches for the UAS control and ATC communications links; defining an 

appropriate sector architecture to determine A/G link slant ranges and the number of channels needed; 

identifying suitable modulation and FEC coding and other link parameters to determine the required 

channel bandwidth for each of the links; and then multiplying the number of required channels by the 

channel bandwidths of each of the required links to provide an aggregate required bandwidth. 

As it was determined that the UAS control and ATC communications bandwidth estimation process 

was highly sensitive to the selection of the above-mentioned input parameters and configurations, some 

high-level sensitivity analysis was performed to quantify the extent of this sensitivity and to provide some 

bounds on the range of values for these estimates. 

1.4 Assumptions 

As is usually the case, several modeling and architecture assumptions were made in the performance 

of this task. Some initial task assumptions were later changed or removed after it was determined that 

they resulted in unsatisfactory or incomplete results. The following sections list the assumptions that 

applied to this task. 

1.4.1 Task Modeling Assumptions 

The following assumptions were used to effectively limit the scope of the task analyses by allowing 

focus on the most significant task parameters. Some assumptions were based on FAA and/or NASA 

direction and feedback, particularly from FAA spectrum engineering and FAA communications 

representatives, including the FAA FCS COCR development team. Task modeling assumptions included 

the following: 

 UAS ATC communications services were assumed to be as defined in the COCR for A/G 

services. The task scope included both data and voice services. 

 The task estimated control and ATC communications (C&C) bandwidth requirements for new 

UAS radio facility to UA links only; it was assumed that COCR defined ATC communications 

capacity requirements already accommodate ATC to UA links. 
NASA/CR—2008-214841 6

 The task did not include UAS Sense and Avoid related communications links (e.g., radar, optical, 

video, etc.) or UAS payload-related communications. 

 The task focused on long term bandwidth requirements for UAS approximately through 2030. 

 Potential aircraft or ground co-site interference issues were not considered. 

1.4.2 Communications Architecture Assumptions 

As stated above, several alternative architectures are possible for providing both control and ATC 

communications connectivity. Some of these alternatives have been explored by the C&C Working Group of 

RTCA SC–203. Because of its focus on supporting WRC preparation activities, this task was based on the 

concept that both control and ATC communications will be provided via a sectorized A/G LOS 

communications architecture, although control and ATC sector sizes and boundaries are not necessarily the 

same. This architecture is illustrated in Figure 6. 

In this architecture UAS control sectors exist in parallel with existing ATC A/G radio sectors, as shown in 

the figure. In the figure the UAS sectors are shaded in color, while the ATC sectors are transparent. In each 

UAS control sector, a UAS radio control facility provides all communications connectivity between this 

facility and each UA within its sector. This connectivity is denoted by the blue arrows indicating ATC 

communications links, and by the green arrows for the control communications links. The light red arrows in 

the figure depict all the ATC radio facility to aircraft links, including both manned and unmanned aircraft. 

Each UA is controlled by a different pilot (i.e., pilot in charge—PIC), who may be remotely located from any 

of the UAS radio control facilities. Connectivity between UA pilots and UAS radio control stations is by 

terrestrial network connectivity, shown in light orange in the figure. 

Since this architecture works solely by LOS A/G radio link connectivity, as the UAs transit the 

airspace, they will need to be “handed off” from one UAS radio control sector to another. This implies 

that the UA will break the RF link from one UAS radio control facility and establish a new link to a 

different UAS radio control facility in the newly entered UAS control sector. This is analogous to the 

situation for ATC communications, where every manned and unmanned aircraft pilot is handed off from 

Figure 6.—UAS line-of-sight communications architecture assumed for the task. 
NASA/CR—2008-214841 7

the ATC controller in the sector being exited, to a new ATC controller in the new ATC sector being 

entered. Note that UAS control handoffs do not necessarily coincide with ATC controller handoffs. 

However, ATC controller handoffs for UAs should take place transparently to the ATC controllers, and it 

is probable that the ATC controllers will have information indicating the unmanned status of the aircraft. 

Though the UAS control facility to UA control communications links should be fairly straightforward in 

implementation, the UAS control facility to UA ATC communications links represent the second link (or 

“hop”) of the two-hop end-to-end connectivity necessary to connect ATC controllers to the PIC. This is 

sometimes referred to as a relay or “bent pipe” configuration, and usually relies on two radios connected 

“back-to-back” within the UA, shown as the blue and red boxes in Figure 7. The green box in the figure 

represents the transceiver required for the control communications link. 

Figure 7 shows that up to seven separate links may be required to provide control communications and 

both voice and data ATC communications, including the following: 

 One existing ATC radio facility to UA link: channel for ATC communications shared with all 

aircraft in sector shown in red (currently simplex very high frequency (VHF) DSB–AM) 

 New UAS radio facility to UA links 

− Dedicated voice and data channels for ATC communications (uplinks and downlinks) shown 

in blue—Up to four links, depending on whether these are simplex or duplex 

− Dedicated channels for control communications (uplink and downlink) shown in green—Up 

to two links, depending on whether these are simplex or duplex 

For the purposes of link efficiency and interference mitigation, it might be advisable to combine the 

ATC voice and data links. Furthermore, each of the uplink/downlink pairs might be implemented via 

simplex or full duplex links, potentially reducing the number of UAS radio facility to UA links to as few 

as two. This architecture decision is discussed further in section 2.6.1. In the limit, C&C message traffic 

could be combined and implemented via a single link, though this potential single point of failure 

configuration might present too much risk. For this task the control communications and ATC 

communications links were assumed to be implemented separately. 

Other architecture-related assumptions for the control communications links are presented in section 

2.4.2.1 

Figure 7.—UA communications relay links. 

.
NASA/CR—2008-214841 8

2.0 Analysis 

2.1 Introduction 

This section describes the specific processes and findings for the analyses performed for each of the 

methodology steps described in the previous section. 

2.2 UAS Specific Mission Types and Needs 

As mentioned above, numerous RTCA SC–203 UAS mission scenarios were examined to identify 

UAS specific needs that might affect UAS communications requirements. Evaluation of these mission 

scenarios identified two main differences from traditional manned aircraft flight scenarios. 

(1) A principal new paradigm typifying many proposed UAS missions is the need to “loiter” within 

particular airspace for periods from hours to months. 

a. Aside from the potential operational impact this has on ATC controller procedures, from the 

traffic modeling perspective it points to potentially heterogeneous flight durations and service 

instances (i.e., typical number of times a service is used within a service volume) for manned 

and unmanned aircraft. 

b. This impacts the COCR queuing model message arrival rate for ATC communications, which 

is inversely proportional to flight duration. 

(2) A second major difference is the fact that many UAS missions will not traverse airports or the 

terminal maneuvering area (TMA) domains. 

a. This affects ATC communications flight durations and service instances for these domains. 

b. This does not affect control communications channel capacities, because the associated 

service volumes are assumed to not be part of the NAS. In any case, certain preflight 

command/status messages are required regardless of where the aircraft takes off. 

An evaluation of the COCR traffic model led to the conclusion that the heterogeneous flight durations 

and message arrival statistics for manned and unmanned aircraft should not significantly affect the COCR 

ATS capacity requirements, which implicitly include UAS traffic. One reason for this assessment is that 

not all ATS service message types defined in the COCR have arrival statistics based on time; rather some 

only need to be sent under certain conditions, like entering or leaving a sector. Also, the fact that some 

UA will not traverse some NAS flight domains would probably have a second-order effect on the COCR 

flight statistics and data capacities because this would involve a small percentage of all UA in flight, 

which in turn would be a small percentage of all aircraft in flight. Thus, for this task, the COCR estimated 

per aircraft data capacities were used without modification. 

2.3 UAS Aircraft Counts and Densities 

2.3.1 UAS Aircraft Counts 

As explained previously, UAS bandwidth requirements are dependent on projected UAS traffic 

densities and thus depend on estimates of the associated PIACs. This stage in the analysis involved 

conducting a search and evaluation of future projections of UA flying in the NAS. In contrast with the 

considerable information available on projected UAS systems to be acquired for military purposes, 

projected UAS estimates for operation in the NAS are not readily available and are highly speculative, 

probably because 

 There are too many stakeholders, with broadly diverse potential uses and user categories, some of 

which have not yet been defined. 

 Some projected commercial applications are proprietary and/or competition sensitive and 

therefore not widely disclosed. 
NASA/CR—2008-214841 9

 There are well-documented barriers to NAS operation that make it difficult to predict when and to 

what extent UAS will be allowed to operate. These include 

− Certification and regulatory issues 

− Current lack of appropriate standards 

− Lack of sufficient frequency spectrum 

− Safety concerns 

− Uncertain business cases 

Despite the general dearth of UAS projections, two studies were located that provided some sense of 

the number of future UAS, based on the authors’ assessments of the industry. Figure 8 and Figure 9 

present two unmanned aircraft projections for several different time periods in the future. 

An assessment of Figure 8 indicates that for the endpoint of the timeframe of interest for this study, 

2030, the projected percentage of UA instrument flight rules (IFR) traffic would be greater than 3.9 

percent and less than 38 percent. Since the projected growth curve looks to be nonlinear, rough order 

curve fitting to these few points shows that somewhere in the range of 5 to 10 percent of IFR traffic in 

2030 could be unmanned. 

Examination of Figure 9 reveals that the study author(s) believe that the number of civil unmanned 

aircraft in the 2015 timeframe would be smaller, but of the same order of magnitude as the number of jet 

transports and regional/commuter aircraft (i.e., in the thousands, as compared to the hundred of thousands 

of general aviation aircraft). Now it is reasonable to expect that UA flight operations would be more 

typical of these “working” aircraft than that of the general aviation class of aircraft. In other words, it 

might be expected that a significant percentage of UA in operation in 2015, would actually contribute to 

the PIAC. Looking further at the numbers, if, in the 2015 timeframe, the NAS PIAC is about two times 

Figure 8.—Future projection of unmanned aircraft as a percentage of IFR traffic (ref. 5). 

Figure 9.—Future projection of unmanned 

aircraft as a percentage of manned 

aircraft (ref. 6). 
NASA/CR—2008-214841 10

the approximately 5000 PIAC in the NAS today, this would yield a total PIAC of around 10 000. If 25 

percent of the predicted 2700 operational civil UA were actually “working,” that is, in flight, this would 

indicate that these 675 flying UA would contribute about 7 percent to the PIAC. 

Based on these admittedly “back of the envelope” analyses, it was decided to select a range of 5 to 

10 percent as the assumed percentage of UA flying in the NAS by the 2030 timeframe. 

2.3.2 UAS Aircraft Densities 

The COCR calculates aircraft densities for each of the flight domain service volumes it defines. A 

related Eurocontrol FCS investigation (ref. 4) defined several test service volumes for European airspace 

and estimated aircraft densities for these service volumes. The COCR and Eurocontrol service volume 

PIACs, physical volumes, and resulting aircraft density values are provided in Table III. Added to this 

data in the table are the associated UA densities corresponding to the two PIAC percentage values derived 

in section 2.3.1, namely 5 and 10 percent. These UA density numbers were used in later stages of the 

analysis to determine the number of UA per sector for the sector architecture defined in section 2.6.3.3. 

Table III.—COCR and EUROCONTROL FCS service volumes 

UA density: 

Aircraft/nmi2

Service volume Total 

PIAC 

Volume, 

nmi3

Total 

aircraft/nmi2

5% 10% 

COCR—NAS Airport HD Phase 1 200 --------- -------- --------- -------- 

COCR—NAS Airport LD Phase 1 12 --------- -------- --------- -------- 

COCR—NAS Airport HD Phase 2 290 --------- -------- --------- -------- 

COCR—NAS Airport LD Phase 2 19 --------- -------- --------- -------- 

COCR—NAS TMA LD Phase 1 14 3039 0.0046 0.0002 0.0005 

COCR—NAS TMA HD Phase 1 16 2831 0.0057 0.0003 0.0006 

COCR—NAS en route LD Phase 1 24 20,782 0.0012 0.0001 0.0001 

COCR—NAS en route HD Phase 1 24 5119 0.0047 0.0002 0.0005 

COCR—NAS TMA LD Phase 2 39 9240 0.0042 0.0002 0.0004 

COCR—NAS TMA HD Phase 2 44 7691 0.0057 0.0003 0.0006 

COCR—NAS en route LD Phase 2 59 33,388 0.0018 0.0001 0.0002 

COCR—NAS en route HD Phase 2 45 10,132 0.0044 0.0002 0.0004 

COCR—NAS en route super sector 95 31,996 0.0030 0.0001 0.0003 

EUROCONTROL—TV1 Airport in flight 200 --------- -------- --------- -------- 

EUROCONTROL—TV1a Airport surface 264 --------- -------- --------- -------- 

EUROCONTROL—TV1 Airport in flight 26 259 0.1004 0.0050 0.0100 

EUROCONTROL—TV2.1—TMA small 44 7691 0.0057 0.0003 0.0006 

EUROCONTROL—TV2.2—TMA large 53 18,056 0.0029 0.0001 0.0003 

EUROCONTROL—TV3.1—ENR small 28 10,132 0.0028 0.0001 0.0003 

EUROCONTROL—TV3.2—ENR medium 62 33,739 0.0018 0.0001 0.0002 

EUROCONTROL—TV3.3 ENR large 204 134,957 0.0015 0.0001 0.0002 

EUROCONTROL—TV3.4 ENR super large 522 53,929 0.0010 0.00005 0.0001 

2.4 UAS Message Statistics 

2.4.1 UAS ATC Communications Message Statistics 

As noted in section 2.2, UAS ATC communications service statistics and associated data capacity 

requirements were assumed to be identical to the manned aircraft ATS service statistics defined in the 

COCR. Table IV provides the per aircraft COCR A/G data capacity requirements for ATS services for 

each of the COCR defined flight domains, assuming the use of a separate channel for each aircraft. These 

numbers where used in later stages of the investigation to determine UAS ATC data communications 

bandwidth requirements. 

Table IV.—COCR V1.0 A/G data capacity requirements, kpbs 

Phase 2 APT SV 

dep 

APT SV 

arr 

TMA 

SV dep 

TMA 

SV arr 

ENR 

SV 

OPR 

SV 

AOA 

UL 6.9 1.8 5.6 3.8 5.7 5.7 6.7 

DL 6.2 1.9 6.8 1.6 6.7 8.5 12.5 

Separate 

ATS 

UL & DL 6.9 1.9 6.9 3.8 6.7 8.5 12.5 
NASA/CR—2008-214841 11

2.4.2 UAS Control Communications Message Statistics 

During the review of the UAS scenarios developed by RTCA SC–203, it became apparent that the 

great diversity of UAS missions and variety of system and aircraft characteristics has resulted in many 

distinct and possibly proprietary communications link implementations. For this task, it was desirable to 

identify an accepted UAS standard that defines a standard architecture and specifies standard UAS 

message types, sizes, and quantities. Members of the UAS manufacturing community pointed to NATO 

STANAG 4586 (ref. 1) as an accepted generic standard for UAS message types and formats. Thus for this 

task, UAS message statistics for UAS control communications messages were based on implementation 

of STANAG 4586 compliant data link interface (DLI) messages.3

 

The following sections describe the development of the STANAG-4586-based UAS control 

communications messages statistics, including message instances, quantities, size, and calculated message 

data rates. 

2.4.2.1 UAS Architecture Task Assumption 

The STANAG 4586 standard architecture specifies that command and status messages must flow 

across the DLI between the vehicle-specific module (VSM) and the core UAV control system (CUCS), as 

shown in Figure 10. To allow STANAG 4586 compliant control stations to operate with legacy UA 

without STANAG 4586 compatibility built in, the standard accommodates the VSM residing either on the 

ground (for a legacy UA), as shown in the figure as Configuration A, or within a 4586-compliant UA, as 

shown as Configuration B. STANAG 4586 specifies that messages flowing across the DLI must include, 

in addition to a DLI “wrapper,” network layer, transport layer, and security layer overhead. Because a 

VSM located on the ground, as in Configuration A, could strip out undesired network-related overhead 

data before RF transmission, this means that this A/G link might be able to transport significantly fewer 

bits per second (and require less bandwidth) than the A/G link in Configuration B, which has to carry the 

DLI required overhead. That is, there may be advantages to providing network connectivity to the UA. 

For this study, both configurations were considered for the major data rate driver, that is, for the 

command and status messages. For the less data-intensive message types, only statistics for Configuration 

B were calculated. Configuration A assumes a non-networked, native, or proprietary-type RF link with 

Figure 10.—Alternative VSM and the CUCS configurations. 

 

3

Information presented in RTCA SC–203 indicates that a newer STANAG that may possibly supersede STANAG 

4586 is under development, but at the time of this study it is only in draft form. 
NASA/CR—2008-214841 12

some security overhead, while Configuration B implies an RF link that includes overhead for standardsbased security and transport and/or network layer protocols. 

2.5 UAS Control Message Quantities/Sizes 

2.5.1 Introduction 

In STANAG 4586, unmanned aircraft control and status messages fall into three general categories: 

 Initialization, configuration, and mission upload messages exchanged preflight 

− Configuration messages also can be exchanged infrequently during flight as necessary if the 

operating mode or configuration of the aircraft is changed. 

 Control messages sent to control the aircraft and its engines 

− The frequency of these messages is highly related to the level of autonomy characterizing the 

aircraft. 

 Status messages sent (pushed) by the aircraft 

− These report dynamic changes in aircraft movements, direction, orientation, engine operation, etc. 

− These messages can be sent very frequently. 

• Typical update rates range from 1 to 20 times per second for critical parameters 

according to UAS manufacturers, where 1/s would be appropriate for a fully autonomous 

aircraft, and 20/s would apply to a hand flown UA. 

• These update rates are the major drivers in determination of aggregate aircraft to ground 

data rate, and hence bandwidth. 

Specifically, this task included the following STANAG 4586 message types as part of its analysis: 

 System identification (ID) messages 

 Flight vehicle command and status messages 

 Data link messages 

− Data link command and status messages 

− Data link transition messages 

 Mission messages 

 Subsystem status messages 

 General configuration messages 

As stated in the assumptions in section 1.4.1, payload data and payload control data were not included 

in the analysis, with the exception of a payload configuration message needed by the control system 

because of the payload’s potential affect on flight dynamics. 

Table V provides an example of STANAG 4586 defined system ID messages and flight vehicle 

command and status messages, and shows message length, and an assessment of the message “Class of 

Service” (CoS) for each of the messages listed. CoS is defined as follows: STANAG 4586 specifies 

allowable maximum transport delay between the human computer interface (HCI) and the DLI (see 

Figure 10). This serves a human factors purpose by ensuring that “human in the loop” (low autonomy) 

control systems operate with the low latency flight control and status messages (e.g., flight dynamics or 

heading information) necessary for remote control of unmanned aircraft. 
NASA/CR—2008-214841 13

Table V.—Example of STANAG 4586 messages 

Message 

no. 

Description Push/pull Source Message length, 

bytesa

Class of 

service 

System ID Messages 

1 CUCS authorization request Push CUCS 31 4 

2–19 Reserved CUCS -- 

20 Vehicle ID Pull VSM 73 3 

21 VSM authorization response Push/pull VSM 31 4 

22–39 Reserved VSM -- 

40 Vehicle configuration command Push CUCS 20 5 

41 Loiter configuration Push CUCS 42 

42 Vehicle operating mode command Push CUCS 17 5 

43 Vehicle steering command Push CUCS 66 3 

44 Air vehicle lights Push CUCS 18 3 

45 Engine command Push CUCS 21 2 

46 Flight termination command Push CUCS 18 2 

47 Relative route/waypoint absolute reference message Push CUCS 61 2 

48–99 Reserved Push -- 3 

Flight vehicle command and status messages 

100 Vehicle configuration Pull VSM 53 5 

101 Inertial states Push VSM 84 3 

102 Air and ground relative states Push VSM 64 3 

103 Body-relative sensed states Push VSM 40 1 

104 Vehicle operating states Push/pull VSM 145 32 

105 Engine operating states Push/pull VSM 36 4 

106 Vehicle operating mode report Push/pull VSM 17 2 

107 Vehicle lights state Push VSM 18 4 

108 Flight termination mode report Push/pull VSM 18 

109–199 Reserved VSM -- 

a

Does not include network/transport layer nor message wrapper overhead. 

Though STANAG 4586 does not specify data link latencies, the HCI to DLI latency requirements 

indicate the relative criticality of the different messages. Therefore for this study, these latencies were 

translated into a CoS as shown in Table VI. The CoS help select relative message update rates for 

periodic messages, such as flight vehicle command and status messages. This is discussed in section 

2.5.5. 

Table VI.—STANAG 4586 HCI–DLI latency 

requirements mapped to a class of service 

STANAG 4586 specified maximum latency, ms Class of service 

200 1 

500 2 

1000 3 

2000 4 

10,000 5 

2.5.2 Message Overhead Assumptions 

As recommended by STANAG 4586, messages for Configuration B included the following overhead: 

 STANAG 4586 wrapper overhead: 34 bytes 

 Network/transport layer overhead 

− STANAG 4586 recommends using Space Communications Protocol Standards (SCPS) to solve 

potential TCP/IP performance issues over the A/G wireless data link. Studies have shown that 

SCPS over IP is much more efficient than TCP/IP for wireless links. SCPS–TP over SCPS–NP 

seems to provide a marginal improvement over SCPS–TP/IP, though it is less clear. 

− For this study SCPS–TP/IPv6 overhead was assumed. 
NASA/CR—2008-214841 14

• SCPS transport protocol (SCPS–TP) with user datagram protocol (UDP) messages: 8-

byte header 

• IPv6: 40-byte header 

 Security overhead 

− SCPS security protocol (SCPS–SP) with 14-byte overhead was assumed. 

• 2-byte header 

• 12-byte (96 bit) length integrity check value (ICV) 

• Key management overhead was not included 

Messages for Configuration A were assumed to include 10 percent security overhead, and not include 

DLI wrapper, or transport/network layer overhead. 

The following sections present the results of the analyses to determine appropriate UAS control 

configuration, mission upload, and flight vehicle command and status message statistics. 

2.5.3 UAS Control Configuration Messages (Configuration B) 

UAS control configuration messages are characterized by a two-way message exchange as the 

aircraft’s operating parameters are initially configured during the preflight period. It was determined that 

the total amount of data exchanged is modest (see Table VII). 

 Less than 15K bytes are sent from the control station to the UA 

 Less than 25K bytes are sent from the UA to the control station 

Several hundred bytes are also exchanged during each handoff from one UAS radio control station to 

another (not shown in table). 

2.5.4 UAS Control Mission Upload Messages (Configuration B) 

These are messages also exchanged during the preflight period, as the control station uploads mission 

information to the UA. During this time the UA periodically sends Upload Status messages. Typically, 

the UAS Control Mission Upload process requires relatively few bytes exchanged, as shown in Table 

VIII, which provides an example for a loitering-type mission. 

2.5.5 UAS Flight Vehicle Command and Status Message Capacities 

The exchange of UAS Flight Vehicle Command and Status messages includes the major driver of 

UAS data link capacities: UA status and telemetry messages. For the modeled UA to UAS control station 

downlink, a moderate level of autonomy was assumed, with critical parameter update rates ranging from 

1 to 10 times per second (Hz) and varying among message type according to an assigned CoS. The 

mapping of CoS to update rate used for this analysis is shown in Table IX. Exceptions to the adopted 

method of mapping latencies to update rates are noted in the table. 

Aggregated status/telemetry message data rate was found to be tens of thousands of bits per second—

almost 29 kbps was estimated for Configuration B, as shown in Table X. The table also shows that the 

Configuration A (non-networked link) UA status/telemetry data rate estimate was around 11 kbps. 

Control message traffic was modeled as being periodic with fairly low update rates that are assumed to 

vary according to aircraft autonomy. For the low to medium autonomy case assumed in the analysis, 

average aggregate the UAS control station uplink command data rate was estimated to be around 

5000 bps for Configuration B. 
Table VII.—Calculated UAS control configuration message statistics (Configuration B) 

CUCS originated VSM originated 

 STANAG 

4586 

msg no. 

No. of 

msg 

sent 

Msg 

length

Msg 

length 

w/DLI 

wrapper 

Msg length 

network/ transport 

layer 

overhead 

(bytes) 

Msg 

length 

with 

security 

overhead 

(bytes) 

Total 

DLI 

bytes 

 STANAG 

4586 

msg no. 

No. of 

msg 

sent 

Msg 

length 

Msg 

length 

w/DLI 

wrapper 

Msg length 

network/ transport 

layer 

overhead 

(bytes) 

Msg 

length 

with 

security 

overhead 

(bytes) 

Total 

DLI 

bytes 

Field configuration request Excludes payload related message types, except 300 1200 97 35 69 117 131 12707 Configuration complete 1203 1 28 62 110 124 124 

Field configuration integer response 1300 7 146 180 228 242 1694 Field configuration double response 

 Excludes payload related message types 1301 51 202 236 284 298 15198 

Field configuration enumerated response 

 Excludes payload related message types 1302 6 128 162 210 224 1344 

Field configuration command 

 Excludes payload related message types 1303 28 32 66 114 128 358 

Vehicle configuration 100 1 53 87 135 149 149 Vehicle ID 20 1 73 107 155 169 169 Data link configuration/assignment message 500 1 28 62 110 124 124Payload configuration 

 (Needed for vehicle assumes 2 payloads) 300 2 28 62 110 124 248 

Configuration complete 1203 1 28 62 110 124 124 

CUCS configures user interface Data link assignment request 404 1 25 59 107 121 121 

Data link configuration/assignment message 500 1 28 62 110 124 124 

Data link set up message 400 1 33 67 115 129 129 Pedestal configuration message 402 1 40 74 122 136 136 Data link control command 401 1 25 59 107 121 121 Pedestal control command 403 1 46 80 128 142 142 

Data link control command status 502 1 24 58 106 120 120 Data link status report 501 1 38 72 120 134 134 Pedestal status report 503 1 58 92 140 154 154 

Specified vehicle ID connection request CUCS authorization request CUCS requests control over a specific vehicle/vehicle type 

1 1 13 65 113 127 127 

VSM authorization response 

 VSM grants CUCS control over specified 

vehicle/vehicle type 

21 1 31 65 113 127 127 

CUCS configuration and command messages: CUCS controls the AV/payload at specified LOI Display unit request 1201 1 25 59 107 121 121 CUCS resource report 1202 1 34 68 116 130 130 Vehicle configuration command 40 1 20 54 102 116 116 Vehicle operating mode command 42 1 17 51 99 113 113 Loiter configuration 41 1 42 76 124 138 138 Vehicle steering command 43 1 66 100 148 162 162 Air vehicle lights 44 1 18 52 100 114 114 Relative route/waypoint absolute reference message 47 1 61 95 143 157 157 Configuration complete 1203 1 28 62 110 124 124 

 VSM status message/configuration updates  Vehicle operating mode report 106 1 7 51 99 113 113  Vehicle operating mode report configuration 

complete 

1203 1 28 62 110 124 124

Number of bytes associated with initial connection and configuration Total bytes from control station 14,782 Total bytes from aircraft 23,530 

NASA/CR—2008-214841 15
Table VIII.—Calculated UAS control mission upload message statistics (Configuration B) 

CUCS (control stations) originated VSM (aircraft) originated 

Functions STANAG 

4586 

msg no. 

No. of 

msg 

sent 

Msg 

length 

Msg length 

w/DLI 

wrapper 

Msg length 

network/ transport 

layer 

overhead 

(bytes) 

Msg 

length 

with 

security 

overhead 

(bytes) 

Total 

DLI 

bytes 

 STANAG 

4586 

msg no. 

No. of 

msg 

sent 

Msg 

length 

Msg 

length 

w/DLI 

wrapper 

Msg length 

network/ transport 

layer 

overhead 

(bytes) 

Msg 

length 

with 

security 

overhead 

(bytes) 

Total 

DLI 

bytes 

Point-to-point mission

Messages no. 800 to 900 ref. Vol 1: STANAG 4586 Implementation Guidelines 

Mission related 3.4.3.2.6 mission messages 

This sequence assumes ground VSM with message 800 to convert and transmit to AV in native format 

Mission plan upload Msg 802 to 806 sequence for each waypoint 

AV position waypoint 802 10 60 94 142 156 1560 AV loiter waypoint 803 0 38 72 120 134 0 Payload action waypoint 804 0 58 92 140 154 0 Airframe action waypoint 805 5 20 54 102 116 580 

 Vehicle specific waypoint 806 5 39 73 121 135 675  Assumed no. waypoints 10 

AV route 801 1 39 73 121 135 135 Mission upload command 800 10 39 73 121 135 1350 

 Mission upload/download status 900 2 18 52 100 114 228 

Assumed no. updates 2 

Total bytes from control station 4165 Total bytes from aircraft 228 

Table IX.—Update rate assignments for UA status/telemetry messages 

Message Message 

number 

STANAG 4586 

specified HCI–

DLI latency, 

ms 

Mapped 

class of 

service, 

CoS 

Assigned 

update rate, 

Hz 

Remarks 

Inertial states 101 1000 3 2 Air and ground relative states 

102 1000 3 2 

Body-relative sensed states 

103 200 1 10 

Vehicle 104 1000 3 2 

Operating states 

Engine operating states 105 500 2 5 Vehicle light states 107 500 2 1 Took exception to CoS assignment; did not agree vehicle light state should be a low latency item. Data link status report 501 1000 3 1 Took exception to CoS assignment; thought data link status was more critical.Pedestal status report 503 2000 4 0.2 Took exception to CoS assignment; did not agree pedestal status should be a low latency item. Do not believe that pedestals can 

move very fast. 

Subsystem status report 1101 1000 5 1 Took exception to CoS assignment; thought subsystem status was more critical. 

NASA/CR—2008-214841 

16
Table X.—Calculated UAS flight vehicle command and status message statistics 

CUCS (ground) originated VSM (aircraft) originated 

 STANAG 

4586 

msg no 

Aperiodic: 

no. of msg 

sent per 

phase of 

flight 

Periodic 

msg rate 

no./s 

Msg 

length 

(bytes) 

Msg length 

w/DLI 

wrapper 

(bytes) 

Msg length 

network/ 

transport 

layer 

overhead 

(bytes) 

Msg 

length 

with 

security 

overhead 

(bytes) 

Aperiodic: 

total bytes 

per phase of

flight 

Periodic 

bits/s 

Periodic 

bits/s 

w/o 

transport 

network 

overhead

 STANAG 

4586 

msg no. 

Aperiodic: 

no. of msg 

sent per 

phase of 

flight 

Periodic 

msg rate 

no. s 

Msg 

length, 

bytes 

Msg 

length 

w/DLI 

wrapper, 

bytes 

Msg length 

network/ 

transport 

layer 

overhead, 

bytes 

Msg length 

with 

security 

overhead, 

bytes 

Aperiodic: 

total bytes 

per phase 

of flight 

Periodic 

bits/s 

Periodic 

bits/s 

w/o 

transport 

network 

overhead 

Vehicle steering command 

43 -- 0.2 66 100 148 162 0 259.2 116.2 

Engine command 45 -- 0.1 21 55 103 117 0 93.6 18.5 Subsystem status request 1000 -- 5 20 54 102 116 0 4640 880.0 Subsystem status detail request 

1001 1 --- 20 54 102 116 116 0 0.0 

Inertial states 101 -- 2 84 118 166 180 0 2280 1478.4 Air and ground relative states 

102 -- 2 64 98 146 160 0 2560 1126.4 

Body-relative sensed states 

103 -- 10 40 74 422 136 0 10880 3520.0 

Vehicle operating states 104 -- 2 145 179 227 241 0 3856 2552.0 Engine operating states 105 -- 5 36 70 118 132 0 5280 1584.0 Vehicle light status 107 -- 1 36 70 118 132 0 1056 316.8 Data link status report 501 -- 1 38 72 120 134 0 1072 334.4 Pedestal status report 503 -- 0.2 58 92 140 154 0 246.4 102.1 Subsystem status report 1101 -- 1 22 56 104 118 0 944 193.6 Subsystem status alert message 

1100 1 --- 107 141 189 203 203 0 0.0 

 404 1 25 59 107 121 121 

Aggregate data rate from control station, bps B 4993 

networked 

1015 A 

non-networked 

Aggregate data rate from aircraft, bps B 28,774 

networked 

11,208 A 

non-networked 

NASA/CR—2008-214841 

1

7
NASA/CR—2008-214841 18

2.6 Estimating UAS C&C Bandwidth Requirements 

The preceding sections presented the methods and results of the analyses performed to estimate: (1) 

projected future UA PIACs and densities and (2) the UAS control and ATC communications data rates 

necessary to transfer messages between a UAS control station and a low to medium autonomy UA. The 

goal for this task was to determine the required channel bandwidth for the links shown in Figure 11 

necessary to provide the required data rates to all the UA flying in the NAS as characterized by the 

projected UA densities. The methodology used to accomplish this goal is shown in Figure 12. 

The process began by selecting appropriate channel access approaches for the control and ATC 

communications links to provide the desired link connectivity (see Figure 11). It should be noted that this 

step was taken only so far as to allow the desired estimation process be performed. In other words, this 

step made some reasonable “design” decisions; however, identifying the best or most efficient design or 

technology was beyond the scope of this task. Specific design decisions included determination of the 

need for simplex or duplex channels, which helped drive the sector architecture definition step; and 

whether dedicated or shared channel resources are needed. 

The next step was the definition of an appropriate sector architecture to help define certain important 

system parameters such as required slant range (to allow calculation of path loss in the link budgets), and 

to help to determine how many communications channels would be necessary per sector, based on the 

assumed UA densities. This step included exercise of certain constraints to ensure required sector 

coverage and to avoid co-channel interference. 

Figure 11.—UAS A/G radio links of interest for this task. 

Figure 12.—Methodology for developing UAS C&C bandwidth estimates. 
NASA/CR—2008-214841 19

The step of determining the channel bandwidth requirements involved making a design decision 

concerning suitable modulation types and determining how much FEC coding would be needed to 

provide the required link performance. The principal tool for this step was link budget analysis to evaluate 

bandwidth and power tradeoffs. The principal output of this step was the required channel bandwidth for 

each of the identified control and ATC communications links. 

Given the required channel bandwidth per link and the calculated number of links necessary to provide 

complete coverage, as determined by the sector architecture, the total aggregate required bandwidth for 

each of the defined links was estimated. During the course of this task it was clearly apparent that the total 

estimated aggregate required bandwidth was greatly influenced by a few specific modeling assumptions 

and design decisions. For this last step of the analysis, this sensitivity was briefly analyzed and 

graphically illustrated to show its effect. 

The following sections describe the methodology and results in more detail. 

2.6.1 Channel Access Approach 

2.6.1.1 UAS Control Communications 

As shown in section 2.5.5, UAS control communications message capacity estimates are driven by 

nominally constant rate command messages uplinked to the UA and status/telemetry messages 

downlinked from the UA. This high, continuous demand for the channel points to the need for dedicated 

full duplex channels for each ground station to UA link. Dedicated channels are needed because 

contention-based protocols could not efficiently provide sufficient quality of service (QoS) in terms of 

latency and availability. There is no queuing possible because the message arrival rates are constant and 

deterministic for each user. Full duplex channels are needed for the same reason. Dedicated bandwidth 

can be provided by frequency division multiple access (FDMA), time division multiple access (TDMA), 

or code division multiple access (CDMA) approaches; each has its advantages and disadvantages, some 

of which are listed in Table XI.4

 

Table XI.—UAS control communications access type high-level comparison 

Access type Complexity UA power and bandwidth 

demands 

FDMA Low Low 

TDMA Medium High 

CDMA High High 

Based on this high-level comparison, an FDMA system consisting of one set of asymmetrical 

dedicated full duplex channels per ground station to UA link was assumed to be best and most 

straightforward for bandwidth estimation purposes. Asymmetrical channels are needed because the 

downlink (status and/or telemetry) capacity requirements are greater than the uplink (command) capacity 

requirements. 

2.6.1.2 ATC Communications 

The UA to UAS control facility link is analogous to the hard wired circuit that connects a manned 

aircraft pilot with an aircraft radio. On a manned aircraft this is a dedicated high-availability, low-latency 

“link.” 

In the UAS case this link could be provided either by a shared link or a dedicated link, each with its 

own advantages and disadvantages. Table XII presents a simple comparison of these two approaches. As 

with the control communications link case, an FDMA system consisting of two dedicated fixed rate 

 

4

One factor not considered in the table has to do with propagation issues, specifically the bandwidth of the signal (or 

equivalently, the symbol duration) in relation to the frequency dependence of the propagation channel. Using low bit 

rate FDMA signals in the typical aeronautical A/G radio channel will tend to reduce the effects of delay spread and 

the associated intersymbol interference (i.e., ensure “flat fading” channel conditions). 
NASA/CR—2008-214841 20

duplex channel pairs per ground station to UA link (voice and data) was assumed for bandwidth 

estimation purposes. 

It should be noted that for implementation, voice and data traffic could be multiplexed, resulting in 

one duplex ATC communications uplink and downlink channel pair. This could have some advantages in 

cost and simplicity; reduction of interference issues (fewer links means fewer opportunities for 

interference); and even potentially provide some bandwidth efficiencies due to the statistical nature of 

ATC communications. Further consideration of this option was beyond the scope of this study. 

Table XII.—UAS ATC communications access type high-level comparison 

Access Advantages Disadvantages 

Dedicated • Minimum latency 

• Predictable availability 

• Simpler 

• Possible to use nonaviation standard technologies 

(P25) 

• Bandwidth intensive 

• No current ICAO standard 

Shared • Minimum potential bandwidth impact 

• Possible use of existing ICAO standard (VDL–M3) 

• More complex 

• Availability issue—channel contention for two links 

rather than for one link 

• Existing standards like VDL–M3 might not work without 

modifications, which should have to be standardized 

2.6.2 Channel Bandwidth Requirements 

2.6.2.1 UAS C&C Link Budgets 

Communications link budgets are typically used to perform power-bandwidth tradeoffs for links and 

were developed in this study to determine appropriate channel bandwidths. Key link budget parameters 

for this task included the following: 

 Range between the UA and the UAS ground station, which was determined by the sector 

architecture 

 Required received Eb/N0 performance, which is dependent on modulation type and FEC coding (if 

any) 

 Frequency band—aeronautical bands were considered 

 Receive system noise temperature, which is dependent on external noise, line losses, and front 

end (receiver or low noise amplifier) noise figure 

 Antenna gains—based on aeronautical standards 

Selected UAS control and ATC communications link parameters used for this task are discussed in the 

following sections. 

2.6.2.2 Selected UAS Control Communications Link Parameters 

The next few sections describe the specific link parameter design decisions made for the UAS control 

communications links, including modulation and FEC coding selection, frequency band, system noise 

temperature, and antenna gains. 

2.6.2.2.1 UAS Control Communications Modulation Types 

Existing UAS often use aeronautical telemetry standard constant envelope5

 modulations such as 

narrow band frequency modulation (FM), some type of continuous phase modulation (CPM), or other 

interoperable modulation types for LOS control/status/telemetry links, including 

 

5

Constant envelope modulations provide good performance with the less expensive and simpler, nonlinear 

amplifiers often used in transmitters for aeronautical and spacecraft applications. In particular, constant envelope 

modulations resist spectral spreading, which can cause adjacent channel interference typical of nonlinear amplifiers. 

Please note that the SRRC OQPSK modulation selected as the notional modulation for this study is not a constant 
NASA/CR—2008-214841 21

 Variants of shaped offset QPSK (SOQPSK) 

 Variants of Feher patented QPSK (FQPSK) 

The Consultative Committee for Space Data Systems (CCSDS) has standardized similar bandwidth 

efficient modulations for space telemetry applications, which include, in addition to the two modulations 

just listed: 

 Gaussian minimum shift keying (GMSK)—a type of CPM 

 Filtered OQPSK modulations (aside from SOQPSK), such as square root raised cosine (SRRC) 

OQPSK 

 4D–8PSK–Trellis coded modulation (TCM) 

The telemetry standard modulations are fairly bandwidth efficient and, when employed with suitable 

FEC coding, provide excellent Eb/N0 performance. A summary of the bandwidth efficiencies and 

performance of these modulation types is shown in Table XIII. 

Square root raised cosine (SRRC) filtered (α = 0.5) OQPSK was selected as the notional modulation 

used in the link budgets, as it combines good Eb/N0 performance with good interference susceptibility 

performance. Figure 13 illustrates the channel efficiency of this particular modulation. It should be noted 

that Rs used in the figure is the coded symbol rate, that is, it represents the bit rate after the FEC encoder, 

not the channel symbol rate after the modulator. 

Figure 13.—Spectrum of suitable modulation type for UAS control communications. 

 

envelope modulation; however, the effect of nonlinear amplifier spectral spreading has been included in the spectral 

efficiency value presented below. 
NASA/CR—2008-214841 22

Table XIII.—Performance of potential UAS control communications modulation types (ref. 6) 

Modulation 

type 

Two-sided –60 dB 

bandwidth 

Occupied 

bandwidth 

Unfiltered BPSKa 635 RS 20.56 RS

Baseband filtered OQPSK/PM 

Butterworth 6th order 2.70 RS 0.88 RS

SSRC α = 0.5 2.68 RS 0.88 RS

Bessel 6th order 3.69 RS 0.93 RS

Baseband filtered OQPSK I/Q 

Butterworth 6th order 4.06 RS 0.86 RS

SSRC α = 0.5 4.24 RS 0.88 RS

Bessel 6th order 4.95 RS 1.34 RS

Precoded GMSK BTs=0.25 2.14 RS 0.86 RS

SOQPSK 

Version A 1.94 RS 0.77 RS

Version B 2.06 RS 0.83 RS

FQPSK-B 2.18 RS 0.78 RS

Occupied bandwidth recommended efficient modulations after spectral regrowth due to saturated SSPA. Please note that RS is the coded 

symbol rate, that is, after the FEC encoder, not the channel symbol rate after the modulator. 

Modulation 

type

Receiver 

type

Eb/N0 for 10–6 BER CCSDS yellow 

book reference

Unfiltered BPSK (reference only) Integrate and dump 2.55 dB 1–06, 1–14 

Baseband filtered OQPSK/PM 

Butterworth 6th order 3.09 dB 

SRRC α = 0.5 Integrate and dump 3.16 dB N/A 

Baseband filtered OQPSK I/Q 

Butterworth 3rd order 2.91 dB 

Butterworth 6th order 3.04 dB

SRRC α = 0.5

Integrate and dump

3.06 dB

1–06, 1–14

Pulse-shaped SRRC α = 0.5 Matched filter 2.77 dB

Shaped offset QPSK 

Version A 3.74 dB

Version B Integrate and dump 3.46 dB N/A 

Precoded GMSK BTs = 0.25 Quasi-matched filter + 3 tap 

equalizer 2.73 dB 1–06, 1–14 

FQPSK-B Quasi-matched filter + 3 tap 

equalizer 2.88 dB 1–4 

Simulated BER of selected bandwidth-efficient modulations using the CCSDS standard rate, 1⁄2, k=7 convolutional inner code 

concatenated with a (225, 223) Reed-Solomon outer code. 

a

Constant envelope modulations provide good performance with the less expensive and simpler, nonlinear amplifiers often used in transmitters 

for aeronautical and spacecraft applications. In particular, constant envelope modulations resist spectral spreading, which can cause adjacent 

channel interference typical of nonlinear amplifiers. Please note that the SRRC OQPSK modulation selected as the notional modulation for this 

study is not a constant envelope modulation; however the effect of nonlinear amplifier spectral spreading has been included in the spectral 

efficiency value presented below. 

The link budget parameters relating to modulation performance and FEC coding selection included the 

following: 

 Spectral efficiency at 99 percent bandwidth (occupied bandwidth6

) = 70.88Rs 

 Required bit error rate (BER)8

 = 10–6

 

6

Occupied bandwidth is defined by article 1.153 of the ITU Radio Regulations (ITU RR) as the width of a frequency 

band such that, below and above the upper frequency limits, the mean powers emitted are each equal to a specified 

percentage β/2 of the total mean power of a given emission, where β is taken to be 1 percent. For β = 1 percent; this 

is often referred to as the 99 percent power containment bandwidth. 

7

This value includes the slight spectral spreading due to nonlinear amplification in the transmitter. 

8

Selection of this value is discussed in section 2.6.4. 
NASA/CR—2008-214841 23

Table XIV lists the range of FEC coding schemes and the associated required Eb/N0 performance for 

the selected modulation (SRRC OQPSK) used for the link analyses to determine the control and ATC 

communications channel bandwidths. 

Table XIV.—Theoretical performance of example modulation 

with different levels of FEC coding 

Link FEC coding Theoretical Eb/N0, dB 

Uncoded 11.5 

3⁄4 Conv. FEC only 6.5 

CC RS+3⁄4 Conv. FEC 4.5 

1⁄2 Conv. FEC only 5.0 

CC RS+1⁄2Conv. FEC 3.0 

2.6.2.2.2 Other Selected UAS Control Communications Link Parameters 

UAS control communications link budgets were based on an implementation in the aeronautical “Lband,” that is 960 to 1215 MHz.9

 This yields a 2-dB range in free space path loss across this band. A 

frequency of 1088 MHz (center of band) was used in the link budgets for path loss. 

For the determination of system noise temperature (see Figure 14), line loss values consistent with 

typical aeronautical application link budgets were assumed. These were 3-dB transmit line losses for the 

UA, and 2-dB receive line losses for the UAS radio control facility. In addition, system noise temperature 

was dependent on a conservative 100K external noise assumption, and an 8-dB receiver noise figure (also 

conservative) for the UAS radio control facility. 

Antenna gains assumed for the link budget analysis were as follows. The task assumed a 6-dBi gain 

for the ground system antenna consistent with typical aeronautical application link budgets, and a 0-dBi 

gain for the UA antenna consistent with antenna gains specified for aircraft antennas in the universal 

access transceiver (UAT) MOPS (ref. 7). The operational frequencies for the UAT antennas are similar to 

the frequency range (L-band) assumed for this study. 

The ATC voice communications channel was assumed to carry 4800 bps vocoded data; the same 

modulation and FEC coding parameters used for the control communications links were applied for the 

ATC voice communications link analysis. In addition, duplex (separate uplink and downlink) channels 

were assumed because they might be necessitated by the end-to-end latency issues with vocoded speech 

in two directions and the burden of two “hops.” 

For ATC data communications the same filtered SRRC OQPSK modulation and range of FEC coding 

was used as for the other links. Just as in the case with control communications and ATC voice 

communications, duplex (separate uplink and downlink) channels were assumed for ATC data channels. 

Table XVII indicates which data capacity values were used in the ATC data communications link 

analyses, based on the similarities to the associated components of the sector architecture defined for this 

task. In the case of the airport and TMA domains, the larger of the two data capacity values for each flight 

domain were selected for sizing the UA to UAS ground radio facility ATC data communications links. 

Please note that selecting the data capacity requirements associated with the autonomous operations area 

(AOA) provided a conservative upper bound for the larger, higher altitude service volumes. 

 

9

Please note that International Civil Aviation Organization (ICAO) is presently considering spectrum from 960 to 

1024 MHz for the Future Radio System. 
NASA/CR—2008-214841 24

Figure 14.—Calculating system noise temperature and noise figure. 

Table XV.—COCR V1.0 A/G data capacity requirements, kpbs 

Phase 2 APT SV 

Dep 

APT SV 

Arr 

TMA SV 

Dep 

TMA SV Arr ENR SV ORP SV AOA 

UL 6.9 1.8 5.6 3.8 5.7 5.7 6.7 

DL 6.2 1.9 6.8 1.6 6.7 8.5 12.5 

Separate 

ATS 

UL & DL 6.9 1.9 6.9 3.8 6.7 8.5 12.5 

2.6.3 Sector Architecture 

Consistent with standard telecommunications practice, the sector architecture for this task was defined 

using hexagonal tiling. In this approach, each hexagonal sector provides a given number of separate 

channels to serve the expected maximum number of users in that sector. All available frequencies are 

allocated and reused in repeating clusters of sectors of size N. N, the reuse factor, can only take on values 

according to the following relation: N = i2

 + ij + j2, where i and j are nonnegative integers (ref. 8). Figure 

15 provides some examples of different reuse patterns. In each example, the colored hexagons 

represent sectors with the same set of frequencies, that is, “co-channel” sectors. The normalized distance 

between co-channel sectors is found to be (ref. 8): 

Q D R (i ij j ) (3N) = 2 + + 2 =

where 

R = radius of the sector (cell) 

D = distance to the center of the nearest co-channel sector 

Figure 15.—Examples of different reuse patterns. 
NASA/CR—2008-214841 25

The selection of N is based in part on the co-channel protection required for the particular cellular 

telecommunications application. Increasing the value for N will increase the co-channel interference protection 

for the nearest co-channel sectors. The tradeoff in increasing N is the fact that, for a given number of 

frequencies required per sector, it increases the total number of frequencies required for the system. 

It should be noted that the co-channel interference discussion to follow is based on the full duplex channel 

design decisions stated section 2.6.1. In contrast with the typical aeronautical A/G radio interference scenario 

based on simplex channels (such as the VHF A/G ATC radio channel case), in the full duplex channel case, 

co-channel interference considerations do not include aircraft to aircraft interference issues that usually drive 

the derivation of required reuse distance. 

If it can be assumed that most of the co-channel interference into an individual sector comes from the six 

closest sectors (see Figure 17), and assuming (1) all the transmitting stations are equidistant from the victim 

sector and (2) each of the interfering transmitter transmits with the same power, then the signal to interference 

ratio (S/I) can be approximated as (ref. 8): 

= ∑ = [ ( )] − − S I R D 3N 6 n n

i n

where 

n = path loss exponent, typically around 2 for A/G radio channels 

Di = distance between the sector and the i interfering transmitters, assumed to be 6 in this case 

Table XVI provides the estimated S/I for several values of reuse factor for path loss exponent values 

n = 2, 3, and 4. As shown in the table, the values for n = 2 (assumed for the A/G channel) point to the 

need in many cases to choose a fairly high reuse factor, that is, fairly large spacing between co-channel 

sectors to provide reasonable co-channel interference protection. 

Table XVI.—S/I versus reuse factor for different path loss exponents 

N S/I (dB) 

n = 2 

S/I (dB) 

n = 3 

S/I (dB) 

n = 4 

1 –3.0 –0.6 1.8 

3 1.8 6.5 11.3 

4 3.0 8.4 13.8 

7 5.4 12.1 18.7 

9 6.5 13.7 20.8 

12 7.8 15.6 23.3 

13 8.1 16.1 24.0 

16 9.0 17.4 25.8 

19 9.8 18.6 27.3 

21 10.2 19.2 28.2 

25 11.0 20.3 29.7 

27 11.3 20.8 30.4 

28 11.5 21.1 30.7 

For the cell sizes and distances typically considered for cellular telecommunications, co-channel interference is 

not usually limited by the curvature of the Earth; however, for A/G communications interference can be 

mitigated by the curvature of the Earth. For aircraft communicating with a ground station, radio line of sight 

(RLOS) can be calculated as RLOS (nmi) = ( ) 23 h1 h 2 1. × + (ref. 9), where h1 is height in ft of the aircraft 

and h2 is the height in feet of the ground station antenna (4/3 Earth effective radius assumption), see Figure 16. 

What this means is that sector sizes can be selected so that co-channel sectors are beyond LOS from each other, 

in which case S/I becomes high enough to have negligible effect on system performance.10 

 

10Tropospheric ducting can be a source of interference that might impact UAS communications in some cases. It is not 

considered in this study, but should be investigated in the context of a detailed UAS communications design and 

development. 
NASA/CR—2008-214841 26

Figure 16.—Definition of radio line of sight. 

Figure 17.—Sector architecture example cluster size (Reuse) N = 3. 

Figure 17 provides an example of a sector architecture for N = 3. The figure illustrates the frequency reuse 

pattern, and illustrates the fact that if the RLOS at the sector lower boundary is approximately 

equal to the sector radius, then the RLOS at the upper boundary of the three dimensional sector necessarily 

exceeds the sector radius. This impacts selection of the sector dimensions, as explained in the next section. 

2.6.3.1 Sector Architecture Constraints 

In defining candidate sector architecture, and given the full duplex channel design decision adopted for this 

study, two constraints come into play (see also Figure 19): 

 To assure coverage R < RLOSLower, where 

− R is the sector radius, and 

− RLOSLower is the radio line of sight of the lower boundary of the sector. 

• For sectors with a lower boundary at ground level, this condition is satisfied through typical 

ground station antenna heights and take-off/landing aircraft altitudes; for example, at 1000 ft, 

RLOS = 39 mi. 

 To avoid co-channel interference (for duplex channels) RLOSUpper /R < (Q – 1), where 

− RLOSUpper is the radio line of sight of the upper boundary of the sector 

− Q is the co-channel reuse distance = (3 , as defined above N)
NASA/CR—2008-214841 27

Figure 18 shows the sector reuse factor as a function of RLOSUpper/R required to provide co-channel 

interference protection due to LOS coverage limitations. Please note that for values of RLOSUpper/R on the blue 

curve, the next highest value of N must be selected. For example, for RLOSUpper/R = 3, since the value on the 

curve is about 5.2, a value of N = 7 must be selected. Conversely, if a reuse factor of 3 was desired, then 

RLOSUpper/R must be less than 2 to avoid co-channel interference. 

The two constraints provided above were used to define suitable sector architectures to permit the 

estimation of total UAS control and ATC communications bandwidth requirements. Figure 19 illustrates the 

approach for a desired reuse factor of 3. 

2.6.3.2 Multilevel Sector Architecture 

An initial sector architecture was defined to roughly parallel the layered approach used for air traffic 

control. It features an N = 3 reuse factor for the top three levels, and N = 7 for the bottom level. This approach 

would require sub-banding of frequencies for each sector layer, as well as separate sub-bands for uplinks and 

Figure 18.—Required reuse factor based as a function of RLOSUpper/R. 

Figure 19.—Illustration of sector architecture constraints. 
NASA/CR—2008-214841 28

downlinks, to avoid co-channel interference between layers11 and between uplinks and downlinks. Figure 20 

illustrates this architecture and provides a table listing its physical parameters. Also, Figure 21 shows Medium 

Sector and Super High Sector coverage patterns overlaid a map of the United States. Figure 21 shows that by 

tiling with the hexagons, but “sectorizing” with circles means that about 21 percent of every sector is 

overlapped by adjacent sectors.12 This is to avoid coverage gaps. 

Figure 20.—Multilevel sector architecture parameters. 

 

11Please note that in any particular sector layer, the RLOS between aircraft in that sector and the associated ground radio 

facility pass right through any lower layer sector. Without sub-banding, that is, providing a separate band of frequencies 

for each of the sector layers, the co-channel interference problem is significantly more complicated. This tends to favor 

architectures with fewer layers. 

12Hexagonal sector volumes were used to determine UA PIACs to avoid double counting UA due to sector overlap. 
NASA/CR—2008-214841 29

Figure 21.—CONUS coverage examples for multilevel sector architecture; 

Reuse = 3. 

Please note that the architecture also includes an “Airport Surface” component shown in the figure for 

UA to UAS control facility communications on the ground. Also note that it is understood that this is an 

ideal sector tiling for the CONUS that does not take into consideration actual terrain effects on coverage. 

In a real implementation, sectors sizes and shapes would necessarily depart from the ideal uniform size 

cylindrical case depending on the area topography. 

It is important to understand that the reuse factor determines how many frequencies are required to 

provide complete area coverage. For example, as shown in Figure 17 and Figure 21, for N = 3, the three 
NASA/CR—2008-214841 30

sets of frequencies representing the three sector cluster are used over and over again across the entire area 

of desired coverage, in our example the CONUS. In other words, if X, Y, and Z represent the number of 

frequency channels in each of the three respective sectors in the cluster, then X + Y + Z frequencies will 

cover the entire CONUS. For a sectored architecture with reuse factor “R,” there would be R sets of 

frequencies used over and over again and “tiled” across the coverage area of interest. The right side of 

Figure 15 shows what this would look like for reuse factor = 7, where, as before, each color represents a 

different set of frequencies. 

2.6.3.3 Preferred Sector Architecture 

A simpler alternative two-layer sector architecture was defined to avoid multiple layers and the need 

for significant sub-banding (see Figure 22). It features high sector coverage from 5000 ft through 60 000 

ft, an 80-mi sector radius, and a reuse factor N = 9; and a low sector with coverage from ground level 

through 5000 ft, a 30-mi sector radius, and a reuse factor N = 7. Just as in the earlier example, this 

Figure 22.—Preferred sector architecture parameters. 
NASA/CR—2008-214841 31

architecture also includes an “Airport Surface” component not shown in the figure for UA to UAS control 

facility communications on the ground. It requires separate sub-bands for uplinks and downlinks to 

provide co-channel interference protection. 

2.6.4 Link Budget Results 

Link budgets were performed for both sector architectures to derive acceptable bandwidth and power 

parameters for each of the UAS control and ATC communications links. All link budgets were based on 

the following assumptions: 

 Required BER = 10–6

 At least 10 dB required link margin 

The selection of a BER of 10–6 was based on good engineering practice for similar links and on earlier 

work in Access 5, which recommended this value (ref. 10). The Access 5 reference also cited ongoing 

development of the STANAG Interoperable C2 Data Link standard, which in the draft version described 

in the Access 5 document specified a fairly stringent BER requirement of 10–8. Product literature from L–

3 Communications for the UA communications transceivers for Global Hawk and Predator also cites 

product BER performance of less than 10–8. Depending on the type and amount of FEC coding used, the 

increase in Eb/N0 needed for 10–8 versus 10–6 BER performance would range from about 0.5 to 2 dB for 

additive white gaussian noise (AWGN) channel, potentially more for a fading channel. Figure 23 

illustrates the bottom end of that range with a highly coded SRRC OQPSK example. 

The 10-dB required link margin was specified as a reasonable value to accommodate excess path 

losses due to multipath and fading, and is a typical target value used in aeronautical link budgets.13

Though this is simplification of an important performance issue, detailed discussion is beyond the scope 

of this study. 

The two architectures provided similar performance, except that the upper two layers in the 

multilayered architecture, because of their sector radii, necessarily offer higher free space path loss in 

their link budget performance than the two relatively small radius sector sizes in the two-layer 

architecture. Even then, all links are able to meet or exceed the 10-dB margin. 

 

13 Fading depth due to simple two-ray path loss calculations is highly dependent on ground antenna height, 

multipath incidence angles, and receive antenna beam pattern, but fade margins of 2 to 6 dB would not be 

unreasonable at the notional L-band frequencies assumed for this study. 
NASA/CR—2008-214841 32

Figure 23.—Measured BER versus Eb/N0 for SRRC-a OQPSK system with CC FEC 

coding (ref. 12). 

An example of the two-layer architecture link performance for the UAS control A/G downlink is 

provided in Table XIX. Aside from ensuring that the link performance provided adequate link margin, the 

principal outputs of this step were the channel bandwidths needed to calculate the total UAS control and 

ATC communications bandwidth. In the example shown in the figure, the channel bandwidth was 

calculated to be 60 800 Hz. 

Table XVII.—Example link budget resultsa

Link budget parameter High sector 

5000 to 60 000 ft 

Low sector 

0 to 5000 ft 

Airport surface 

Air-to-ground slant range, nmi 80 30 5 

Transmit power, dBm 41.8 41.8 41.8 

Transmit line losses, dB –3 –3 –3 

Transmit antenna gain, dBi 0 0 0 

Transmit EIRP, dBm 38.8 38.8 38.8 

Free space path loss, dB 136.6 128.1 112.5 

Receive antenna gain, dBi 6 6 6 

Receive line losses, dB –2 –2 –2 

Received power, dBm –93.8 –85.3 –69.8 

Receiver noise figure, dB 8 8 8 

External noise figure, dB 1.3 1.3 1.3 

System noise figure, dB 10.1 10.1 10.1 

Noise floor, kT0B, dBm –126.2 –126.2 –126.2 

Receiver noise power, dBm –116.0 –116.0 –116.0 

Theoretical Eb/N0 dB 3.0 3.0 3.0 

Theoretical C/N, dB 3.6 3.6 3.6 

Implementation losses, dB 2 2 2 

Required C/N, dB 5.6 5.6 5.6 

Received C/N, dB 22.2 30.7 46.3 

Margin, dB 16.6 25.1 40.7 

a

SRRC (α = 0.5) OQPSK with concatenated RS (255, 233) and rate 1⁄2, k = 7 convolutional FEC coding. 

2.6.5 Calculating Total UAS C&C Communications Bandwidth 

For this step it was necessary to select appropriate UA densities to determine the UA PIAC for the 

high sector and low sector service volumes in the sector architecture. For this, COCR and 

EUROCONTROL FCS test service volumes similar in size to the notional architecture sector volumes 

were used (see Table XVIII). The selected service volumes are bold in the table.14 Please note that for the 

airport surface case a PIAC without a density is listed because a volume estimate is not appropriate for the 

surface coverage. Thus, the UA PICA for the airport surface case is calculated directly as a percentage of 

the total PIAC. The UA densities/PIACs corresponding to the selected COCR/EUROCONTROL service 

volumes were applied to the sector architecture assumptions along with the individual channel 

bandwidths calculated from the link analysis, and the results were tabulated. Table XIX shows the 

resulting estimated total bandwidth (about 17.1 MHz) for the UAS control communications links, 

assuming Configuration B (networked links) and based on the concatenated RS (255, 233) and 1⁄2 rate 

convolution FEC coding case. Calculated total bandwidths for the other link cases are provided 

graphically in the next section. 

 

14As shown in the figure, the aircraft density value for the Lower Sector was based on the density value for the NAS 

TMA high density (HD) Phase 1, because of the similarity in sector volume. The argument might be made that a 

Phase 1 density might not be appropriate because of the time frame involved; however, the COCR NAS TMA HD 

Phase 2 density is the same as the Phase 1 density, which is the same as the EUROCONTROL TV2.1 TMA small 

service volume density. 
NASA/CR—2008-214841 33

Table XVIII.—FCS test service volumes used to provide suitable total UA PIAC densities 

UA density: aircraft, 

nmi2

Service 

volume 

Total 

PIAC 

Volume, 

nmi2

Total aircraft, 

nmi2

5% 10% 

COCR—NAS Airport HD Phase 1 200 -------- -------- --------- -------- 

COCR—NAS Airport LD Phase 1 12 -------- -------- --------- -------- 

COCR—NAS Airport HD Phase 2 290 -------- -------- --------- -------- 

COCR—NAS Airport LD Phase 2 19 -------- -------- --------- -------- 

 

COCR—NAS TMA LD Phase 1 14 3039 0.0046 0.0002 0.0005 

COCR—NAS TMA HD Phase 1 16 2831 0.0057 0.0003 0.0006 

COCR—NAS En Route LD Phase 1 24 20,782 0.0012 0.0001 0.0001 

COCR—NAS En Route HD Phase 1 24 5119 0.0047 0.0002 0.0005 

 

COCR—NAS TMA LD Phase 2 39 9240 0.0042 0.0002 0.0004 

COCR—NAS TMA HD Phase 2 44 7691 0.0057 0.0003 0.0006 

COCR—NAS En Route LD Phase 2 59 33,388 0.0018 0.0001 0.0002 

COCR—NAS En Route HD Phase 2 45 10,132 0.0044 0.0002 0.0004 

 

COCR—NAS En Route Super Sector 95 31,996 0.0030 0.0001 0.0003 

EUROCONTROL—TV1 Airport Total 200 -------- -------- --------- -------- 

EUROCONTROL—TV1a Airport Surface 264 -------- -------- --------- -------- 

EUROCONTROL—TV1 Airport in Flight 28 259 0.1004 0.0050 0.0100 

EUROCONTROL—TV2.1 TMA Small 44 7691 0.0057 0.0003 0.0006 

EUROCONTROL—TV2.2 TMA Large 53 18,056 0.0029 0.0001 0.0003 

EUROCONTROL—TV3.1 ENR Small 28 10,132 0.0028 0.0001 0.0003 

EUROCONTROL—TV3.2 ENR Medium 62 33,379 0.0019 0.0001 0.0002 

EUROCONTROL—TV3.3 ENR Large 204 134,957 0.0015 0.0001 0.0002 

EUROCONTROL—TV3.4 ENR Super Large 522 539,829 0.0010 0.00005 0.0001 

Table XIX.—Calculated total UAS control communications bandwidth result 

Sector architecture parameters High 

sector 

Low 

sector 

Airport 

surface 

Total 

Sector radius, nmi 80 30 ---------- ---------- 

Sector top, ft 60,000 5000 ---------- ---------- 

Sector bottom, ft 5000 0 ---------- ---------- 

Sector height, nmi 9.1 0.8 ---------- ---------- 

Circular sector area, nmi2 20,106 2827 ---------- ---------- 

Hexagonal sector area, nmi2 16,628 2338 ---------- ---------- 

Hexagonal sector volume, nmi3 150,511 1924 ---------- ---------- 

Cylindrical sector volume, nmi3 181,998 2327 ---------- ---------- 

Ratio, circular/hexagonal area 1.21 ---------- ---------- ---------- 

RLOS at top, nmi 301 87 ---------- ---------- 

RLOS at bottom, nmi 87 0 ---------- ---------- 

RLOStop/RLOSbottom 3.46 ---------- ---------- ---------- 

RLOStop/sector radius 3.77 2.90 ---------- ---------- 

Reuse factor 9 7 1 ---------- 

Reuse distance – 1 (Q – 1) 4.20 3.58 ---------- ---------- 

Total aircraft density (no. per nmi3) 0.00151 0.00565 ---------- ---------- 

Percentage of UA in the NAS 10 10 10 ---------- 

UAS aircraft density (no. per nmi3) 0.000151 0.000565 ---------- ---------- 

Computed peak UA count per sector 23 1 26 ---------- 

Control link—number of downlink/uplink channels 207 7 26 240 

Control link—downlink channel bandwidth, Hz 60,800 60,800 60,800 60,800 

Control link—uplink channel bandwidth, Hz 10,600 10,600 10,600 10,600 

Control link—total downlink bandwidth, Hz 12,585,600 425,600 1,580,800 14,592,000 

Control link—total uplink bandwidth, Hz 2,194,200 74,200 275,600 2,544,000 

Control link—total uplink + downlink BW, Hz 14,779,800 499,800 1,856,400 17,136,000 
NASA/CR—2008-214841 34

2.6.5.1 Required Bandwidth Estimation Sensitivity 

It is probably not surprising to note that the total required UAS communications bandwidth 

requirements were quite sensitive to certain parameters and study assumptions, including the following: 

 UA peak counts 

− UA were assumed to be 10 percent of the total PIAC; a different value based on emerging 

plans and future operational practice linearly scales the results. 

 UAS control communications link architecture configuration assumptions 

− Required UAS control communications data capacity was estimated for two configurations 

defined by STANAG 4586 (ref. 1), corresponding to two alternative UAS ground control 

station to UA link architectures. One configuration (Configuration A) assumed a nonnetworked, native or proprietary type RF link with some security overhead, while the second 

configuration (Configuration B) implied an RF link that included overhead for standardsbased security, STANAG 4586 DLI wrappers, and transport and/or network layer protocols. 

• Configuration B resulted in significant network and transport layer protocol overhead on 

the A/G links. 

• The Configuration A non-networked assumption significantly reduced required 

bandwidth. 

 Data rate requirements of the UAS Command and Status/Telemetry messages 

− These are highly dependent on update rates associated with varying degrees of autonomy. 

Conservative values were assumed to upper bound the aggregate rate, based on low to 

moderate autonomy UAS. 

− In addition, for the networked Configuration B, a conservative assumption was made that 

multiple command/status messages were not combined into IP datagram payloads, that is, 

each IP data payload consisted of only one command/status message. 

 The channel modulation selected and amount of link FEC coding necessary to increase link 

margin to accommodate excess path losses, directly impacted required channel bandwidth. 

− A range of link FEC coding alternatives were used to provide a range of total required 

bandwidth. 

 Sector architecture, including sector size and “layering,” and the corresponding selection of reuse 

parameters to mitigate co-channel interference. 

2.6.5.2 Required Bandwidth Results 

Figure 24 graphically illustrates required total UAS C&C bandwidth estimates for the two-layered 

architecture for each link type and their sensitivity to overhead and link FEC coding assumptions. A box 

has been placed around the values that provide a reasonable range of bandwidth requirements, while still 

providing suitable performance. It should be noted that the multilayer architecture provided slightly worse 

performance and resulted in slightly higher bandwidth estimates. 
NASA/CR—2008-214841 35

Figure 24.—Required total UAS communications bandwidth estimates and their sensitivity to 

overhead and link FEC coding assumptions. 
NASA/CR—2008-214841 36

3.0 Conclusions and Recommendations 

Given the fact that UAS civil and private aviation in the NAS is still in its earliest stages, the range of 

possibilities for implementing a broad-based means of providing both UAS control communications and 

ATC communications is fairly wide open. Because of its focus on the need to identify potential future 

UAS frequency spectrum needs in support of WRC activities, this study concentrated on just one of 

several possible means of providing these capabilities, that is, by way of UA relay. As mentioned earlier, 

other potential architectures are being considered by RTCA SC–203, if not by other organizations. Even 

within this one architectural approach there is still a lot of leeway in developing the assumptions and the 

notional architecture design decisions needed to make the UAS communications bandwidth estimates. 

The sensitivity of this estimation process to these design decision assumptions and selection of certain 

key parameters was discussed in the preceding section and this demonstrated the inadvisability of trying 

to derive a single number to estimate total bandwidth requirements. Therefore for this study a range of 

estimated bandwidth requirements was developed to provide bounds, based on the stated configurations 

and assumptions. 

For the selected notional architecture, the findings based on modest FEC coding, such as provided by 

the two rate 3⁄4 cases provide the most reasonable compromise between performance and bandwidth 

within the range of results. In particular, the concatenated (CC) Reed Solomon (255, 223) block encoding 

and 3⁄4 rate convolutional FEC coding case provided significant excess path margin for protection against 

interference and signal degradations, including protection against burst errors. These two cases resulted in 

the following bandwidth estimates: 

 Control communications bandwidth estimates on the order of 10 to 11.4 MHz for the networked 

configuration 

− 8.5 to 9.7 MHz for the UA to UAS radio control station downlink 

− 1.5 to 1.7 MHz for the UAS radio control station to UA uplink 

 Control communications bandwidth estimates on the order of 3.6 to 4.1 MHz for the nonnetworked configuration 

− 3.3 to 3.8 MHz for the UA to UAS radio control station downlink 

− About 0.3 MHz for the UAS radio control station to UA uplink 

 ATC voice communications bandwidth estimates on the order of 2.7 to 3.1 MHz, split equally 

between the uplink and downlink 

 ATC data communications bandwidth estimates on the order of 5.2 to 5.9 MHz 

− About 3.3 to 3.8 MHz for the downlink 

− About 1.9 to 2.1 MHz for the uplink 

 The notional architecture used to estimate total bandwidth requirements allowed for significant link 

margin because of the modest sector radii. Other possible architectures may be more efficient (though the 

initial architecture resulted in poorer performance in almost every respect). 

In closing, some additional concluding remarks and recommendations can be made. Because a detailed 

design was beyond the scope of this task, several relevant issues were not considered. These included the 

following: 

 Co-site interference issues, both on the UA and for the UAS ground radio facilities, not 

considered for this study, need to be explored. Assuming that both the control communications 

and ATC communications use the aeronautical L-band, for example, (and assuming sufficient 

available bandwidth could be identified) allowed for straightforward analysis; however, 
NASA/CR—2008-214841 37

simultaneous transmission on these links present serious design challenges, especially on the UA, 

to mitigate potential co-site interference. 

 The potential impacts of sub-banding need to be addressed. Though in certain respects it might be 

easier to identify noncontiguous “chunks” or sub-bands of spectrum for the different control and 

ATC communications links than it would be to find 10 to 20 contiguous MHz of available 

bandwidth to manage, this spectrum management issue should be investigated. 

 The entire issue of whether or not a national UAS communications service could be implemented 

was beyond the scope of this study, and to a certain extent, it does not affect the analysis. 

However, this study was based on a uniform design, regardless of how and by whom it would be 

implemented and/or operated, and the study results are therefore dependent on this assumption. 

 Just as with the COCR, for estimation purposes, this study nominally assumed a uniform density 

of aircraft throughout a sector/service volume. In reality, this often is not the case, as both 

manned and unmanned aircraft would be concentrated along particular corridors or “hot spots.” 

This could affect UAS bandwidth requirements and should be considered as a future topic of 

study. 

 As stated earlier, for the purposes of link efficiency and interference mitigation it might be 

advisable to combine the ATC voice and data links. Furthermore, each of the uplink/downlink 

pairs might be implemented via simplex or full duplex links, potentially reducing the number of 

UAS radio facility to UA links to as few as two. In the limit, control communications and ATC 

communications message traffic could be combined and implemented via a single link, though 

this potential single point of failure configuration might present too much risk. This issue needs 

further investigation. 

 Though the target 10-dB link margin was mostly exceeded over the range of link parameter 

values assumed for the link analyses; further work in the area of required link margin, including 

acceptable excess path loss, should be pursued. 

NASA/CR—2008-214841 39

Appendix A—List of Acronyms and Abbreviations 

The following list identifies acronyms and abbreviations used throughout this report. 

A/G air/ground 

AOA autonomous operations area 

ATC air traffic control 

ATS air traffic services 

AWGN additive white gaussian noise 

AV air vehicle 

BER bit error rate 

BLOS beyond line of sight 

BT bandwidth x symbol duration 

C4I command, control, communications, computers, and intelligence 

C&C Control and ATC Communications 

CC concatenated 

CCI command and control interface 

CCISM command and control interface specific module 

CCSDS Consultative Committee for Space Data Systems 

CDMA code division multiple access 

COCR communication operating concept and requirements 

CoS class of service 

CPM continuous phase modulation 

CUCS Core UAV Control System 

D distance 

DSB–AM double sideband amplitude modulation 

DL downlink 

DLI data link interface 

Eb/N0 energy per bit over noise power spectral density 

FAA Federal Aviation Administration 

FCS future communications study 

FDMA frequency division multiple access 

FEC forward error correction 

FM frequency modulation 

FQPSK Feher patented QPSK 

GMSK gaussian minimum shift keying 

HCI human computer interface 

HD high density 

Hz Hertz 

ICAO International Civil Aviation Organization 

ICV integrity check value 

ID identification 

IFR instrument flight rules 

IP internet protocol 

L&R launch and recovery 

ITU International Telecommunications Union 

LD low density 

LOS line of sight 

MHz Megahertz 

n Path loss exponent 

NAS National Airspace System 
NASA/CR—2008-214841 40

NASA National Aeronautics and Space Administration 

NATO North Atlantic Treaty Organization 

OQPSK offset quadrature phase shift keying 

P25 Project 25 

PIC pilot in charge 

PIAC peak instantaneous aircraft count 

PIC pilot in charge 

QoS quality of service 

QPSK quadrature phase shift keying 

R radius 

RF radiofrequency 

RLOS radio line of sight 

SCPS Space Communications Protocol Standard 

S/I signal to interference ratio 

SOQPSK shaped offset quadrature phase shift keying 

SRRC square root raised cosine 

SSPA solid state power amplifier 

TCM trellis coded modulation 

TCP transmission control protocol 

TCP/IP transmission control protocol/internet protocol 

TDMA time division multiple access 

TMA terminal maneuvering area 

UA unmanned aircraft 

UAS unmanned aircraft system 

UAT universal access transceiver 

UAV unmanned aerial vehicle 

UCS UAV control system 

UDP user datagram protocol 

UL uplink 

VDL very high frequency digital link 

VHF very high frequency 

VSM vehicle specific module 

WRC World Radiocommunications Conference 
NASA/CR—2008-214841 41

References 

1. STANAG 4586. Standard Interfaces of UAV Control System (UCS) for NATO UAV 

Interoperability, Edition 2, March 2005. 

2. Communications Operating Concept and Requirements (COCR) for the Future Radio System. 

Version 1.0, EUROCONTROL/FAA Future Communications Study Operational Concepts and 

Requirements Team, 2006. 

3. Draft RTCA SC 203. Guidance Material and Considerations for Unmanned Aircraft Systems, 

Document Number P1−001−A (Paper No. RTCA 224−06/SC203−016), Jan. 24, 2007. 

4. Nuke Newcome: Technologies for the 21st Century UAVs. SRA, NASA/DHS Homeland Security 

Workshop July 6−7 2005. http://www.nasa.gov/centers/dryden/research/civuav/dhs_docs.html 

Accessed July 17, 2007 

5. US UAV Market Forecast, 2006—2015. Moire Incorporated, Feb. 2005. 

6. EUROCONTROL Draft Study: Future Communications Infrastructure—Technology Investigations. 

Step 2: Evaluation Scenarios, version 0.d, Dec. 12, 2006. 

7. CCSDS 413.0−G−1. Bandwidth Efficient Modulations, Summary of Definition, Implementation, and 

Performance. Appendix B, April 2003. 

8. Minimum Operational Performance Standards for Universal Access Transceiver (UAT) Automatic 

Dependent Surveillance⎯Broadcast (ADS−B). Vol. 1, RTCA DO−282A, July 29, 2004, p. 16. 

9. Wireless Communications. Theodore Rappaport, Prentice Hall, 1996, p. 28. 

10. Spectrum Management Regulations and Procedures Manual. FAA Order 6050.32B, Appendix 2, 

Nov. 17, 2005, p. 6. 

11. HALE UAS Command and Control Communications Step 1 Functional Requirements Document. 

Version 4.0, Appendix F, Access 5 WP6 Team, Feb. 8, 2006, p. 40. 

12. Vassallo, E.; Povero, G.; and Visintin M.: End-to-End Losses of Selected BW-Efficient 

Modulations—Part.2: Coded Channel Performance. Proceedings of the CCSDS RF and Modulation 

Subpanel 1E Meeting of May 2001 Concerning Bandwidth-Efficient Modulation, CCSDS 

B20.0−Y−2, Yellow Book, June 2001, pp. 1−244. 
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14. ABSTRACT

There are significant activities taking place to establish the procedures and requirements for safe and routine operation of unmanned aircraft 

systems (UAS) in the National Airspace System (NAS). Among the barriers to overcome in achieving this goal is the lack of sufficient 

frequency spectrum necessary for the UAS control and air traffic control (ATC) communications links. This shortcoming is compounded by 

the fact that the UAS control communications links will likely be required to operate in protected frequency spectrum, just as ATC 

communications links are, because they relate to “safety and regularity of flight.” To support future International Telecommunications 

Union (ITU) World Radio Conference (WRC) agenda items concerning new frequency allocations for UAS communications links, and to

augment the Future Communications Study (FCS) Technology Evaluation Group efforts, NASA Glenn Research Center has sponsored a 

task to estimate the UAS control and ATC communications bandwidth requirements for safe, reliable, and routine operation of UAS in the 

NAS. This report describes the process and results of that task. The study focused on long-term bandwidth requirements for UAS 

approximately through 2030. 

15. SUBJECT TERMS

Pilotless aircraft; Command and control; Aircraft communication; Bandwidth; Spectrum 

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