Behnam Kamali

Mercer University, Macon, Georgia 

Jeffrey D. Wilson and Robert J. Kerczewski

Glenn Research Center, Cleveland, Ohio

Application of Multihop Relay for Performance 

Enhancement of AeroMACS Networks

NASA/TM—2012-217658

August 2012

G2
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Behnam Kamali

Mercer University, Macon, Georgia 

Jeffrey D. Wilson and Robert J. Kerczewski

Glenn Research Center, Cleveland, Ohio

Application of Multihop Relay for Performance 

Enhancement of AeroMACS Networks

NASA/TM—2012-217658

August 2012

G2

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Integrated Communications, Navigation and Surveillance (ICNS) 2012 Conference

sponsored by the Institute of Electrical and Electronics Engineers

Herndon, Virginia, April 24–26, 2012
Acknowledgments

The authors would like to thank Chad Jeffrey Wilson for preparation of Figures 2 to 7. The authors also gratefully acknowledge 

the Federal Aviation Administration’s support of AeroMACS research at the NASA Glenn Research Center.

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Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217658 1

Application of Multihop Relay for Performance 

Enhancement of AeroMACS Networks

Behnam Kamali

Mercer University

Macon, Georgia 31207

Jeffrey D. Wilson and Robert J. Kerczewski

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

A new transmission technology, based on IEEE 802.16-2009 

(WiMAX), is currently being developed for airport surface 

communications. A C-band spectrum allocation at 5091 to 

5150 MHz has been created by International 

Telecommunications Union (ITU) to carry this application.

The proposed technology, known as AeroMACS, will be used 

to support fixed and mobile ground to ground applications and 

services. This article proposes and demonstrates that IEEE 

802.16j-amendment-based WiMAX is most feasible for 

AeroMACS applications. This amendment introduces 

multihop relay as an optional deployment that may be used to 

provide additional coverage and/or enhance the capacity of the 

network. Particular airport surface radio coverage situations 

for which IEEE 802.16-2009-WiMAX provides resolutions 

that are inefficient, costly, or excessively power consuming are 

discussed. In all these cases, it is argued that 16j technology 

offers a much better alternative. A major concern about 

deployment of AeroMACS is interference to co-allocated 

applications such as the Mobile Satellite Service (MSS) feeder 

link. Our initial simulation results suggest that no additional 

interference to MSS feeder link is caused by deployment of 

IEEE 802.16j-based AeroMACS.

1.0 Introduction

In order to accommodate the large volume of data that is 

planned by Next Generation Air Transportation System 

(NextGen) for information exchange between different mobile 

units, such as between aircraft and other airport systems 

including air traffic management (ATM), airline operational 

control (AOC), weather and advisory information, and so on, 

wideband wireless communication technologies are required.

To this end the 2007 ITU World Radiocommunication 

Conference (WRC-2007) took an action that allowed the

development of a new international standard of aeronautical 

mobile route services (AM(R)S) to support airport surface 

communications in what is known as the microwave landing 

system (MLS) extension band. The authorized C-band 

spectrum covers 5091 to 5150 MHz and an additional band 

5000 to 5030 MHz may potentially become available in the 

future. The Future Communications Infrastructure study 

completed jointly by the US Federal Aviation Administration, 

NASA, and EUROCONTROL recommended that this new 

aviation specific communication technology should be based 

on the IEEE 802.16e standard (Ref. 1). The proposed standards 

will be used to support fixed and mobile ground-to-ground and 

ground-to-air data communications applications and services 

(Ref. 2). 

According to a document published by EUROCONTROL 

(Ref. 3); no technical obstacles have been found which would 

make it impossible to apply this technology for AeroMACS 

(Aeronautical Mobile Airport Communications System) 

(Ref. 4) over the MLS extension band. A major concern about 

development of AeroMACS over the MLS Extension band is 

interference to co-allocated applications. In particular, the

allocation of the 5091 to 5150 MHz band to the fixed-satellite 

service (FSS) (Earth-to-space), limited to feeder links of nongeostationary-satellite (non-GSO) systems in the mobilesatellite service (MSS) limits the power levels that are allowed 

for AeroMACS networks. With this power restriction, the 

developed AeroMACS network for an airport may leave 

certain severely shadowed areas with no coverage or very 

weak linkage. To afford robust communications throughout the 

airport surface, while limiting the power levels, as well as 

providing a host of other benefits, this article argues and 

demonstrates that WiMAX networks based on IEEE 802.16j, 

the multihop relay specification amendment for 802.16, is 

most suitable for AeroMACS application. 

Section 2.0 of this article provides some introductory 

remarks on the IEEE 802.16j amendment. In Section 3.0, the 

IEEE 802.16j based relay systems are defined and classified.

The benefits of employing multihop relays are listed. A list of 

key usage model applications for relay augmented cellular 

networks is provided. Section 4.0 of this paper briefly reviews 

the most recent AeroMACS profile to determine whether there 

are any technical obstacles or challenges in application of 

IEEE 802.16j-based WiMAX to AeroMACS. The potential 

benefits of multihop relay configuration for AeroMACS 

networks are discussed in Section 5.0. The case for IEEE 

802.16j based technology against IEEE 802.16-2009 is made 

in this section. Section 6.0 is devoted to discussion on IEEE802.16j-based AeroMACS interference to MSS feeder links.
NASA/TM—2012-217658 2

Visualyse Professional software (Ref. 5) is used to make 

estimations on the level of such interference. Finally, in 

Section 7.0 some concluding remarks are ventured. 

2.0 IEEE 802.16J Amendment: 

Multihop Relaying 

Owing to practical shortfalls arising from early 

implementation of IEEE 802.16e-based WiMAX networks, the 

need for some modification and amendment to the standard 

was recognized early on. In particular, initial field trials of 

mobile WiMAX products have shown that IEEE802.16e 

systems provide poor Quality-of-Service (QoS) around 

WiMAX cell boundaries for indoor users and in areas severely 

shadowed by manmade structures and natural obstacles. For 

instance, even with application of advanced signal processing 

techniques such as OFDM (Orthogonal Frequency Division 

Multiplexing), MIMO (Multiple Input Multiple Output), and 

AMC (Adaptive Modulation and Coding); the projected data 

rates requires SINR (Signal-to-Interference plus Noise-Ratio) 

levels at the front end of the receivers that are difficult to 

obtain at the WiMAX cell boundaries or in shadowed areas. To 

address this issue IEEE802.16j Multihop Relay (MR) Task 

Group has been working to define a new relay station (RS) that 

can be used as an extension to the base station (BS) and relay 

traffic between the BS and the subscriber station (SS). An RS 

communicates with the macro BSs through a wireless channel 

and can operate without additional carrier frequency. This 

eliminates the need for a wired or a dedicated wireless 

connection to the backhaul network and significantly reduces 

the installation and operation cost compared with using microBSs to cover these areas. By replacing the direct link between 

a BS and an SS in a poor coverage area with two links with 

better channel quality, the overall network capacity will 

increase dramatically (Ref. 6). 

The amendment introduces multihop relay (MR) as an 

optional deployment that may be used to provide additional 

coverage or provide improved performance/ enhanced capacity 

in an access network. In relay-augmented networks, the BS 

may be replaced by a multihop relay BS, MR-BS, and as many 

RSs as needed. Traffic and signaling between the SS and MRBS may be direct, or may be relayed by the RS thereby 

extending the coverage and enhancing performance of the 

system in areas where RSs are deployed. Each RS is under the 

supervision of an MR-BS. In a system with more than two 

hops, traffic and signaling between an access RS and MR-BS 

may also be relayed through intermediate RSs. The RS may be 

fixed in location, it may be nomadic, or in the case of an access 

RS, it may be mobile (Ref. 5). 

The allocation of bandwidth and other resources for RSs and 

SSs may be controlled using one of the two modes; centralized 

or non-centralized (distributed) scheduling. In centralized 

scheduling mode, the bandwidth allocation for an RS’s 

subordinate SSs is determined at the MR-BS; whereas in 

distributed scheduling mode, the bandwidth allocation of an 

RS’s subordinate SSs are determined by the RS in cooperation 

with the MR-BS. In other words RSs share resource allocation 

responsibilities with their superordinate MR-BSs. 

The IEEE 802.16j working group was responsible for 

generating a standard for WiMAX Mobile Multihop Relay 

(MMR) network. The standard specifies a set of technical 

issues in order to enhance the previous standards (IEEE 

802.16-2009) with the main objective of supporting relay 

concepts.

3.0 Relays: Definitions and

Classification 

First and foremost among the benefits of deployment of 

IEEE 802.16j-defined relay is the cost-effective, lowcomplexity, and easy-to-install-infrastructure alternative that it 

offers for wireless network radio outreach extension in a 

variety of situations. Secondly, the relays can provide capacity 

improvement and throughput enhancement in areas which are 

not sufficiently covered by the associated BSs. One other 

important result of deployment of the relay-fortified wireless 

infrastructure, compared to the all-BS architecture, is the 

reduction of aggregate output power of the cellular network.

For the AeroMACS application, this translates into less 

interference into co-allocated applications such as MSS feeder 

link. A partial list of major usage models and applications of 

relay augmented cellular networks is provided below.

• Extension of radio coverage into areas severely 

shadowed by buildings or natural obstacles.

• Enhancement of coverage and throughput on or beyond 

the WiMAX cell footprint boundary.

• Improvement in radio coverage inside a building or a 

high rise complex.

• Coverage in a dense urban area.

• Coverage in a rural area.

• Temporary coverage and temporary capacity upgrade.

• Network capacity improvement to support intense-usage 

areas; “hot spots”. 

• Special coverage challenges, e.g., “coverage hole 

filling”.

• Extension of radio access to moving vehicles such as 

buses, trains, aircraft.

• Radio coverage over roads and tunnels.

In short, the main aspects for present and future usage of 

relays are; coverage extension, capacity and throughput 

enhancement, support for mobility at all levels, cost efficiency, 

and improvement in frequency planning (Ref. 7).

In all RS-augmented standards, the main concept is to 

complement the BS with less complex, less costly, and easierto-install relay stations instead of adding new BSs in a 

broadband cellular network. MR-BS covers an extended area, 

beyond what the BS alone covers, which is denoted by
NASA/TM—2012-217658 3

Figure 1.—A simple relay network consisting of two relay stations.

multihop relay cell, MR-cell. MR-BS manages all 

communications resources within a MR-cell through a 

centralized or distributed procedure. Resource management of 

subscriber stations (SS) may be carried out directly by the BS 

or via radio links through relay stations. Traffic and signaling 

between BS and SS may be routed through “access RSs” or 

via a direct link between BS and the SS. Figure 1 shows a 

simple two-hop relay configuration. The physical channel 

between the MR-BS and a relay is called a relay link, and the 

channel between an access relay and a SS is termed as an 

access link as illustrated in Figure 1.

In more complex multihop relay networks for which more 

than two hops may occur, the signaling between the MR-BS 

and an access RS may be relayed through intermediate RSs. In 

those cases the link between BS and the access RS, which may 

include several consecutive relay links and intermediate RSs, 

is called relay path (Ref. 8). 

The IEEE 802.16j standard provides the following attributes 

for air interface between RS and BS-RS as minimum 

requirements. The 802.16j RS is fully backward compatible to 

the 802.16e, i.e., no changes are required in the legacy mobile 

stations. That implies that all SS-BS air interface protocols are

supported by an 802.16j relay network with no need for any 

upgrade in the SS. The RS devices need to support all the 

licensed bands allocated for IEEE 802-16j-based systems. The 

network topology that is supported by the RS is limited to 

point-to-point, i.e., mesh topology is not supported at this 

point. The IEEE 802.16j standard specifies two modes of 

scheduling for controlling the allocation of bandwidth for RSs 

and SSs: centralized scheduling and distributed scheduling.

Relays may be classified according to their Physical (PHY) 

layer and Medium Access Control (MAC) layer 

functionalities. In terms of PHY layer processing, relay 

stations may be classified as Transparent Relays (TRS); Type 

II relays in Long Term Evolution (LTE) terminology, and 

Non-Transparent Relays (NTRS), or Type I relays in LTE 

jargon.

• A TRS essentially functions as a repeater that is 

transparent to the SS and bears no logical connection to 

it. As such TRS does not transmit preamble, nor does it 

broadcast control messages such as DL-MAP (Media 

Access Protocol). The SS served by a TRS receives 

traffic data from the TRS but control data comes from 

the corresponding MR-BS.

• An NTRS operates as a “mini BS” and thus is physically 

and logically connected to the SSs that are connected to 

it. The NTRS transmits preamble and broadcasts control 

messages, therefore the MSs served by an NTRS receive 

both traffic and control data directly from the NTRS. 

In so far as MAC functionalities are concerned, RSs can be 

characterized on the basis of their scheduling arrangements

and security capabilities. In these respects the RS may operate 

in centralized or distributed modes. Distributed mode with 

respect to scheduling means that the RS is capable of 

scheduling network resources in coordination with MR-BS; 

otherwise the RS operates in centralized mode. RS in 

distributed scheduling mode creates DL-MAP and UL-MAP 

for allocation of bandwidth to its subordinate SS. The same 

can be said about security, i.e., the RS can be in distributed or 

centralized mode with respect to security arrangements. A

TRS always operates in centralized mode with respect to both 

scheduling and security. In this case bandwidth allocation and 

other scheduling procedures are carried out by the MR-BS. 

The main function of TRSs is network throughput 

enhancement. On the other hand a NTRS in distributed 

scheduling and security mode may provide radio outreach 

extension and higher bandwidth efficiency, as well as 

throughput enhancement in a WiMAX network. In centralized
NASA/TM—2012-217658 4

scheduling mode all information related to the access link 

(bandwidth request, channel measurement, etc.) is forwarded 

to the MS-BS for generation of proper DL-MAP and UL-MAP 

by the MR-BS on behalf of the RS. This incurs latency in the 

network. On the other hand a RS with distributed scheduling 

mode can process the information and generate proper 

DL/UL-MAPs by itself (Ref. 9).

4.0 AeroMACS Profile Draft; Are 

There Any Technical Obstacles?

The most recent version of the AeroMACS Profile draft 

published on December 15, 2010, documents the adaptations 

required for the IEEE 802.16-2009 standard to provide 

wireless data communication service to fixed and mobile 

platforms in AeroMACS (Ref. 10). The proposed standard 

would support ground-to-ground and air-to-ground data 

communication services, including but not limited to 

Collaborative Decision Making (CDM), Surveillance 

Broadcast Systems (SBS), and System Wide Information 

Management (SWIM). The transmission requirements for 

these applications demand data rates that range from a few 

hundred Kbits per second to hundreds of Mbits per second.

User applications for transport over AeroMACS have been 

classified into the following five categories:

• Air Traffic Management (ATM)/Air Traffic Control 

(ATC)

• Aeronautical Information Management and 

Meteorological Data (AIM/MET)

• Owner/ Operator

• Airport Authority

• Airport Infrastructure

It is noted that these applications may have different 

performance characteristics, security needs, and QoS 

requirements. Operational applications requiring access to 

AeroMACS will continue to emerge as the modernization of 

national and international airspace systems progresses. 

In order to minimize hardware development to implement 

the standard, while maximizing the utilization of 

“Commercial-Off-The-Shelf” (COTS) components, it was 

decided that AeroMACS should be developed based on 

WiMAX (IEEE 802.16) technology. However, it is required 

that WiMAX technology be extended over the aeronautical 

band of 5091 to 5150 MHz. This is one of the major required 

adjustments of WiMAX technology for AeroMACS 

applications, as WiMAX was originally developed for 

different bands of frequencies.

Other than those issues related to general application of 16j 

technology to any scenario, it appears that there are no 

additional technical challenges in application of IEEE 802.16jbased WiMAX to AeroMACS. Nevertheless, a more thorough 

study of this important subject is in order and is highly 

recommended. 

5.0 Multihop Relay Configuration for 

AeroMACS

This section is devoted to discussion of particular airport 

surface radio coverage situations for which the IEEE 802.16-

2009-WiMAX system either fails to offer a viable solution, or 

the resolution it provides is inefficient, costly, or excessively 

power consuming. In all these cases, it is argued that IEEE 

802.16j-based technology offers a much better alternative with 

the application of multihop relays. 

• When a portion of an airport is significantly shadowed 

by a new obstacle, such as a building constructed for a 

new terminal in an airport, a 16j-defined transparent or 

non-transparent relay can be added to the airport 

network to provide higher capacity and acceptable QoS 

to the shadowed area. Adding a relay to an already 

established network does not require network 

reconfiguration and radio resource reallocation. The 

alternatives that IEEE 802.16-2009 offers are; the 

addition of another BS to the system which requires 

network redesign and entails reallocation of resources, 

or an increase the output power of the other BSs, which 

may or may not resolve the problem while increasing the 

total airport system output power.

• Short-term coverage for areas temporarily blocked (e.g., 

by construction), or coverage for areas on a temporary 

basis because of special circumstances (e.g., special 

events) may be readily provided by a TRS or a NTRS.

This is where a mobile relay may be most suitable.

• If a station is outside of the airport area but needs 

connection to the AeroMACS network, an RS (as 

opposed to a BS) can be used to establish the 

connection.

• Coverage to single point assets on the airport surface 

that are outside of the BSs coverage area can readily be 

rendered by an RS. This may be particularly suitable for 

airport security equipment such as cameras.

• Relays may be also used to provide coverage to other

airport assets such as lighting systems, navigational aids, 

weather sensors, wake vortex sensors, etc.

• Relays may provide coverage to relatively small areas 

on the airport surface outside of the BS cell footprint, 

including permanently shadowed areas.

• Multihop relays may be used to provide coverage to 

airport surface locations outside of the base station 
NASA/TM—2012-217658 5

coverage area where there are relatively few users. The 

IEEE 802-2009 alternative would either add a new BS to 

the network for a few users, or increase the power of the 

current BS’s in the system.

• Multihop relays enable increased link physical layer 

security for single point connections through a narrow 

beam antenna, for example to assets at or beyond the 

airport perimeter.

• Spectrum efficiency and/or network capacity may be 

improved by application of spatial diversity. This is 

feasible with IEEE 802.16j with RS.

• Multihop relays may be applicable to large airports with 

dense/complex operations where localized spectrum 

saturation may occur. Additional capacity may be 

obtained in dense areas by deployment of TRSs as an 

alternative to adding more BSs and/ or smaller cells.

6.0 AeroMACS Interference to MSS

Feeder Links

A major concern about deployment of AeroMACS over the 

5091-5150 MHz band is interference to co-allocated 

applications, in particular to the feeder links of nongeostationary-satellite systems in the mobile-satellite service 

(MSS). The Globalstar Satellite Constellation is an example of 

an existing operational MSS system that operates feeder links 

in this band (Ref. 11). The potential for interference between 

AeroMACS and MSS feeder links limits the power levels that 

are allowed for AeroMACS networks (Ref. 8). Analytical 

methods and computer modeling have been employed to test 

and measure the level of interference posed by AeroMACS 

networks to co-allocated applications. At the NASA Glenn 

Research Center the software program Visualyse Professional 

(Ref. 5) has been utilized to estimate the limitations of 

AeroMACS transmitter output power levels in order to avoid 

unacceptable interference with MSS feeder link signals 

(Ref. 12). A similar approach was previously adopted by 

MITRE Corporation (Ref. 13). In both of these models a 

single BS per airport was assumed and an airport was viewed 

as a power emitting point on the contiguous United States 

global surface. The antenna directivity pattern for each of the 

497 towered airports was selected randomly in order to reflect 

a more realistic scenario.

To compare interference performance for IEEE 802.16-

2009-based AeroMACS with IEEE 802.16j-based 

AeroMACS, six model cases were created and simulated. Two 

of these cases (Cases 1 and 4) represent all-BS airport 

networks, while the other cases (Cases 2, 3, 5, and 6) represent 

mixed BS-RS networks. The output power of a BS antenna (or 

a sector of a BS antenna) is assumed to be 100 mW, and the 

output power of an RS antenna is assumed to be 3 dB lower, 

i.e., 50 mW. The relative directions of the BS and RS antenna 

beams are shown in Figure 2 to Figure 7 for each case.

Figure 2.—Case 1: An all-BS network with four BS antenna 

beams oriented at 0°, 90°, 180°, and -90°.

Figure 3.—Case 2: A mixed BS-RS network with three BS 

antenna beams oriented at 0°, 90°, and 180° and with two 

RS beams oriented at –45° and –135°.

Figure 4.—Case 3: A mixed BS-RS network with three BS 

antenna beams oriented at 0°, 90°, and 180° and with one 

RS beam oriented at –90°
NASA/TM—2012-217658 6

Figure 5.—Case 4: An all-BS network with three BS antenna 

beams oriented at 0°, 120°, and -120°.

Figure 6.—Case 5: A mixed BS-RS network with two BS 

antenna beams oriented at 0° and 180° and with two RS 

beams oriented at 90° and –90°.

Figure 7.—Case 6: A mixed BS-RS network with two BS 

antenna beams oriented at 0° and 180° and with one RS 

beam oriented at –90°.

For each of the six cases, all of the 497 towered airports in 

the contiguous United States were assumed to have the given 

antenna gain pattern, but the direction corresponding to 0° was 

randomized from airport to airport. Ten runs each with a 

different randomization were generated for each case. An 

example of the resulting interference power profile at low 

Earth orbit (LEO) is shown in Figure 8 for one of the runs 

with Case 1. For each run, the position (in Northern Canada) 

and value of the maximum aggregate interference power was 

recorded. Figure 9 illustrates the simulation results and Table I

shows the corresponding average maximum interference 

power and standard deviations. 

With four 100 mW beams spaced 90° apart, Case 1 has 

close to an omnidirectional gain pattern. Thus the different 

randomization runs have little variation in maximum 

interference power as shown in Figure 9 and reflected by the 

small standard deviation in Table I. In Case 2, one of the BS 

beams has been replaced by two RS beams, thus the total 

power radiated is the same at 400 mW. Figure 9 and Table I

show that the average maximum interference power is almost 

identical to that of Case 1, but there is a larger spread among 

the ten randomized runs due to the asymmetrical nature of the 

gain pattern.

Both Cases 1 and 2 generate interference power higher than 

the threshold of –157.3 dBW established so as to limit the 

increase in the MSS feeder link satellite receiver’s noise

temperature to less than 2 percent (Ref. 14). In Case 3, one of 

the BS beams is replaced with an RS beam, reducing the total 

radiated power from 400 to 350 mW. It is seen in Figure 9 and 

Table I that this is enough to reduce the maximum interference 

power below the threshold value.

The total radiated power is decreased further to 300 mW in 

both Cases 4 and 5. Case 4 has three BS beams, while Case 5 

has two BS beams and two RS beams. The maximum 

interference power decreases as expected and as in the 

comparison between Cases 1 and 2, there is not much 

difference between the results of Cases 3 and 4, although there 

is somewhat more variation among the randomized runs in 

Case 4.

Figure 8.—Aggregate interference power at LEO from 497 

airports each with a randomized orientation of the antenna 

gain pattern for Case 1, the scale is in dBW.
NASA/TM—2012-217658 7

Figure 9.—Simulated maximum interference power for 10 randomized runs for each of the six antenna 

configuration cases shown in Figure 2 to Figure 7.

TABLE I.—AGGREGATE INTERFERENCE POWER POSED BY ALL 497 CONTIGUOUS U.S. 

TOWERED AIRPORTS INTO MSS FEEDER LINK FOR VARIOUS AeroMACS CONFIGURATIONS

Case Configuration Output power,

mW

Average maximum 

interference power,

dBW

Standard 

deviation, 

dBW

1 Four BS beams at 0° , 90°, 180°, and –90° 400 –156.91 0.01

2 Three BS beams at 0° , 90°, and 180°and two RS beams at –45° and –135° 400 –156.92 0.05

3 Three BS beams at 0°, 90°, and 180° and one RS beam at –90° 350 –157.50 0.04

4 Three BS beams at 0°, 120°, and –120° 300 –158.16 0.09

5 Two BS beams at 0° and 180° and two RS beams at 90°and –90° 300 –158.17 0.05

6 Two BS beams at 0° and 180° and one RS beam at 90° 250 –158.96 0.15

Case 6 radiates 250 mW with just two BS beams and one 

RS beam. The maximum interference power decreases again 

as expected and the spread among the runs is higher than in 

any of the other cases because of the increased asymmetry. 

These results reveal that under equal output power 

transmission for each airport and each configuration, there is 

no additional interference into MSS feeder link from the 16jbased AeroMACS as compared to that of all-BS AeroMACS 

network. It is the total power that is radiated from each airport 

that is most important; the distribution is only of secondary 

importance.

In summary we make the following observations that are the 

key conclusions of this preliminary simulation study. 

• No additional interference to the MSS feeder link is 

caused by deployment of IEEE 802.16j-based 

AeroMACS.

• The total antenna output power level has the dominant 

effect on AeroMACS interference to co-allocated 

applications. Antenna orientation and directivity, and 

whether the network employs all-BS configuration or BSRS architecture, play an insignificant role in this regard.
NASA/TM—2012-217658 8

7.0 Summary and Future Work

This article makes a case for IEEE 802.16j WiMAX system 

as a feasible technology for AeroMACS. Practical shortfalls 

arising from early implementation of IEEE 802.16e-based 

WiMAX networks demanded a new amendment to the IEEE 

802.16e standard; the IEEE802.16j is such an amendment. 

This amendment allows for relay stations to be used as an 

extension to the BS and relay traffic through a wireless 

channel and can operate without backhaul connection. The 

usage of RSs significantly reduces network complexity, output 

power emission, and installation and operational costs. 

For AeroMACS, IEEE 802.16j-based technology provides 

feasible radio coverage at airport surface for situations in 

which the IEEE 802.16-2009-WiMAX system either fails to 

offer a viable solution, or the resolution it provides is 

inefficient, costly, or excessively power consuming. A rather 

long list of future studies can be envisioned at this point and 

many more will be added, should the IEEE 802.16j-based 

technology be adopted for AeroMACS. In this article we have

glanced at the most recent AeroMACS profile and have found 

no additional technical challenges for application of IEEE 

802.16j-based WiMAX to AeroMACS. However, there is a 

need for thorough examination of the present, as well as future 

drafts of the AeroMACS profile to ensure that there are no 

insurmountable technical challenges for application of 16j to 

AeroMACS. 

A critical future study relates to the type of relays that are 

appropriate for AeroMACS applications. TRSs and NTRSs 

may be used for capacity improvement and radio outreach 

extension, respectively. The selection of relay type has a 

number of implications related to the DL and UL frame 

structure, PHY layer and MAC layer protocols, latency, and 

interference level within the AeroMACS network and into coallocated applications.

Challenges and technical complications of applications of 

the IEEE 802.16j amendment need to be studied. In particular 

PHY and MAC layer difficulties that arise from inclusion of 

relays in the network, especially in MR-BS, must be 

exhaustively investigated. The MR-BS system ought to be 

modified to accommodate both SSs and RSs.

A more meaningful comparison is made between the 

interference effects of IEEE 802-2009 and IEEE 802.16j 

technologies if the airport size is taken into consideration 

(small, medium, large airports). Simulation runs with 

Visualyse Professional should be conducted for other relevant 

scenarios. These scenarios should be carefully identified and 

selected. Comparison between interference levels and other

key system parameters, such as the size and shape of coverage 

area, throughput/ capacity, and cost of the system, should be 

made between the two alternatives.

In our simulation effort we have focused on the network 

transmission side. An interesting future study is addressing the 

question of how to model the user transmission side and then 

investigate the interference effect to co-allocated applications.

References

1. Budinger, James, Edward Hall, 2011, “Aeronautical 

Mobile Airport Communications System (AeroMACS),” 

NASA Technical Memorandum. 

2. RTCA, 2009 “Terms of Reference August 7, 2009, SC 

223 Airport Surface Wireless Communications,” Paper 

No. 182-09/PMC-749.

3. EUROCONTROL Feb. 2010 “AeroMACS System 

Requirement Document.”

4. Hall, Edward, et al., 2010, “Aeronautical Mobile Airport 

Communications System Development Status,” 

Proceedings of ICNS.

5. Transfinite Systems Limited, www.transfinite.com.

6. Rewind Project document, 2009 “REWIND WP4-D4.2,”

http://rewind-project.eu/deliverables

7. IEEE Std. 802.16j TM-2009, Part 16: Interface for 

Broadband Wireless Access Systems, Amendment1: 

Multihop Relay Specification.

8. Kamali, Behnam, Robert J. Kerczewski, 2011, “On 

Selection of Proper IEEE 802.16-Based Standard for 

Aeronautical Mobile Airport Surface Communications 

(AeroMACS) Application,” Proceedings of IEEE ICNS 

2011.

9. Okuda, M. et al, 2008, “Multihop Relay Extension for 

WiMAX Networks-Overview and Benefits of IEEE 

802.16j Standard,” FUJITSU Sci. Tech. J.

10. RTCA, 2010 “Airport Surface Wireless Communications 

Profile Draft R1, RTCA SC-223.

11. http://www.globalstar.com/en/

12. Wilson, Jeffrey D. 2011, “Modeling C-Band Co-Channel 

Interference from AeroMACS Omni-Directional 

Antennas to Mobile Satellite Service Feeder Uplinks,” 

NASA/TM—2011-216938, NASA Glenn Research 

Center. 

13. Gheorghisor, Izabela L. et al., 2010, “Compatibility of 

Wireless Broadband Networks with Satellite Feeder 

Links in the 5091-5150 MHz Band,” Proceedings of

ICNS.

14. Gheorghisor, Izabela. L., et al., 2009, “Analysis of 

ANLE Compatibility with MSS Feeder Links,” MITRECAASD Report MTR090458.

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Application of Multihop Relay for Performance Enhancement of AeroMACS Networks 

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14. ABSTRACT

A new transmission technology, based on IEEE 802.16-2009 (WiMAX), is currently being developed for airport surface communications. A 

C-band spectrum allocation at 5091 to 5150 MHz has been created by International Telecommunications Union (ITU) to carry this 

application. The proposed technology, known as AeroMACS, will be used to support fixed and mobile ground to ground applications and 

services. This article proposes and demonstrates that IEEE 802.16j-amendment-based WiMAX is most feasible for AeroMACS 

applications. This amendment introduces multihop relay as an optional deployment that may be used to provide additional coverage and/or 

enhance the capacity of the network. Particular airport surface radio coverage situations for which IEEE 802.16-2009-WiMAX provides 

resolutions that are inefficient, costly, or excessively power consuming are discussed. In all these cases, it is argued that 16j technology 

offers a much better alternative. A major concern about deployment of AeroMACS is interference to co-allocated applications such as the 

Mobile Satellite Service (MSS) feeder link. Our initial simulation results suggest that no additional interference to MSS feeder link is caused 

by deployment of IEEE 802.16j-based AeroMACS. 

15. SUBJECT TERMS

Airports; Antenna radiation patterns; Communication networks; Microwave landing system 

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