1 Mobility and Radio Resource Management in Future Aeronautical Mobile Networks Mobilität und Radio Resource Management in zukünftigen aeronautischen Kommunikationsnetzen Der Technischen Fakultät der Universität Erlangen-Nürnberg zur Erlangung des Grades D O K T O R - I N G E N I E U R vorgelegt von Serkan Ayaz Erlangen 2013
2 Als Dissertation genehmigt von der Technischen Fakultät der Universität Erlangen-Nürnberg Tag der Einreichung: Tag der Promotion: Dekan: Prof. Dr.-Ing. habil. Marion Merklein Berichterstatter: Prof. Dr.-Ing. Reinhard German Prof. Dr.-Ing. habil. Falko Dressler Prof. Dr.-Ing. Wolfgang Gerstacker
3 Abstract The aviation community is currently working on the standardization of data communication systems for the future air traffic management (ATM). The standardization effort has two main streams, namely, standardization of future radio access technologies in the L-band (i.e., LDACS) and standardization of a future IPv6-based aeronautical telecommunications network (ATN/IPS). In this thesis, different handover and radio resource management algorithms are developed for the most promising future radio access technology for the aviation, L-band digital aeronautical communications system option 1 (LDACS1) in conjunction with realistic IPv6-based network layer functionality (ATN/IPS). In the first part of this work, handover performance of network mobility (NEMO) is investigated and different cross-layer approaches are proposed in order to improve handover latency and signaling overhead. These improvements mainly use media independent handover functionality proposed by the IEEE standard and are important due to the following reasons: One of the main system requirements of LDACS is to deliver certain ATS messages in a timely manner (i.e., low latency) with minimum service disruption (i.e., high service availability). In parallel, future services like VoIP and transmission of sensor data for the aircraft health management also require real-time and near-real-time transmission of certain information with low latency and high availability. According to STATFOR statistics, number of flights in Europe will be around 17 million in 2030 annually, which is 1.8 times more than in Since LDACS is planned for the time frame of , it should be capable of handling the data traffic demands of the future ATM. From this perspective, reducing the signaling overhead over the wireless link should be one of the design criterion for future radio access technologies that will be used in the ATM domain. With our proposals, total handover latency (i.e., layer 2 and layer 3) is reduced from 3 s to around 0.4 s and signaling overhead due to router advertisement messages is reduced from 17 kbit/s to around 0.1 kbit/s. In the second part, the effect of handover event on transmission control protocol (TCP) performance is analyzed. In the first step, different TCP handover optimizations related to iii
4 iv Mobile IPv6 protocol are presented. In the next step, the applicability of these proposals to different handover scenarios is investigated and the most promising proposal (home agent buffering method) is integrated with LDACS1 handover functionality. Finally, the performance of home agent buffering method is analyzed in terms of TCP transmission completion time. With the help of this method, total transmission completion time of a session is reduced by at least 10% for a download of 110 kb of information. In the third part, different radio resource management (RRM) algorithms are analyzed for the LDACS1 since the resources should be distributed evenly among different users. This is not only important from fairness perspective but also from expiration time and latency requirements of ATS/AOS messages. Here, we analyzed different RRM algorithms in terms of bandwidth and end-to-end delay fairness. We also proposed a new modified deficit round robin algorithm which could be used for both links (i.e., forward and return link) and satisfies almost perfect fairness among different number of users. In the last part, different NEMO route optimization (RO) techniques are analyzed due to triangular routing problem of NEMO. With the help of NEMO RO, packets follow shorter paths (in terms of number of hops) between the end nodes so that the measured end-to-end delay is reduced. Most of these NEMO RO methods are published as Internet Engineering Task Force (IETF) drafts. Among those proposals, we have realized that some of them require mobility related functionalities to the end nodes and some others do not. In addition, some proposals try to solve nested NEMO problem without working on the main route optimization problem. In addition, since most of those protocols are published as IETF draft, some proposals lack protocol design and maturity in terms of implementation. Considering these issues, we mainly analyzed infrastructure based NEMO RO techniques; namely global home agent to home agent (global HAHA) and correspondent router (CR) protocols from ATN/IPS perspective in the first part. Later on, we proposed two new approaches for the global HAHA protocol in order to decrease end-to-end delay and mobility signaling overhead.
5 Kurzfassung Die Luftfahrt Community arbeitet derzeit an der Standardisierung von Kommunikationssystemen für die Zukunft des Flugverkehrsmanagements. Diese Standardisierungsaktivitäten haben zwei wesentliche Ziele. Zum einen sollen künftige Funktechnologien definiert werden (d.h. LDACS), zum anderen wird ein IPv6 basiertes aeronautisches Telekommunikationsnetz (ATN/IPS) spezifiziert. In dieser Arbeit werden verschiedene Handover und Radio Resource Management Algorithmen für das aussichtsreichste potentielle künftiges Funksystem für die Luftfahrt, L-band Aeronautical Communications System Option 1 (LDACS1), in Verbindung mit der Funktionalität von IPv6 auf der Netzwerkschicht untersucht. IPv6 wird von dem IP-basierten aeronautischen Telekommunikationsnetz ATN/IPS vorgesehen. Im ersten Teil dieser Arbeit wird das Handover Verhalten des Network Mobility (NEMO) Protokolls untersucht und verschiedene Cross-Layer Ansätze vorgeschlagen, um die Handover Latenz zu verringern und der Signalisierungs Overhead zu reduzieren. Diese Vorschläge nutzen vor allem die Media Independent Handover Funktionalität, die im IEEE Standard spezifiziert ist. Diese Verbesserungen sind aus mehreren Gründen von großer Bedeutung: Eine der wichtigsten Anforderungen an das LDACS System ist es, Nachrichten für die Flugverkehrskontrolle innerhalb der vorgegebenen Latenzzeiten und mit ausreichender Verfügbarkeit zu übertragen. Außerdem verlangen einige Dienste wie VoIP oder die laufende Überwachung des Zustands des Flugzeugs durch Sensoren nach einer Datenübertragung in Echtzeit oder nahezu in Echtzeit, d.h. mit minimaler Latenz und ebenfalls mit hoher Verfügbarkeit. Laut STATFOR, dem Statistikdienst der europäischen Flugsicherungsbehörde, wird die jährliche Zahl der Flüge in Europa bis 2030 auf rund 17 Millionen steigen, was einem Faktor von 1,8 gegenüber dem Jahr 2009 entspricht. Da LDACS in dem Zeitraum von eingesetzt werden soll, muss es in der Lage sein, die künftigen Anforderungen an das Flugverkehrsmanagement zu bewältigen. Daher sollte es ein Hauptziel bei der Entwicklung künftiger Funktechnologien für die Luftfahrt sein, den Signalisierungs Overhead zu minimieren, damit Kapazität nicht unnötig verschenkt wird. Mit unseren Vorschlägen kann die gesamte Latenzzeit eines Handovers (d.h. Layer 2 und Layer 3) von rund 3 s auf rund 0.4 s reduziert werden, und der Signalisierungs-Overhead durch IP Router Advertisements wird von rund 17 kbit/s auf nur 0.1 kbit/s reduziert. v
6 vi Im zweiten Teil dieser Arbeit werden die Auswirkungen eines Handovers auf das Transmission Control Protocol (TCP) untersucht. Zunächst werden verschiedene TCP Handover Optimierungen im Zusammenhang mit dem Mobile IPv6 Protokoll vorgestellt. Im zweiten Schritt wird die Eignung dieser Verfahren für verschiedene Handover Szenarien untersucht, und der vielversprechendste Vorschlag (die sog. Home Agent Buffering Methode) wird mit der Handover- Funktionalität von LDACS1 integriert. Schließlich wird die Leistungsfähigkeit der Home Agent Buffering Methode näher untersucht. Diese wird gemessen an der Zeit, die für eine vollständige Dateiübertragung über eine TCP Verbindung benötigten wird. Durch diese Methode wird die erforderliche Zeit für die Übertragung einer Datei von 110 kb um mindestens 10% reduziert. Im dritten Teil werden verschiedene Radio Resource Management (RRM) Algorithmen für LDACS1 analysiert, da die Ressourcen möglichst gleichmäßig auf die verschiedenen Nutzer verteilt werden sollen. Dies ist nicht nur aus Gründen der Fairness wichtig, sondern auch für die Einhaltung der Anforderungen der ATS/AOS Nachrichten bzgl. Expiration Time und Latenzzeit. Hierzu untersuchen wir verschiedene RRM Algorithmen in Bezug auf Bandbreite und Fairness der end-to-end Verzögerung. Wir schlagen außerdem einen neuen, modifizierten Deficit Round Robin Algorithmus vor, der für die Übertragung in beide Richtungen (d.h. Forward und Return Link) verwendet werden kann und nahezu perfekte Fairness zwischen den verschiedenen Nutzern garantiert. Im letzten Teil der Arbeit werden verschiedene Verfahren zur NEMO Routenoptimierung (RO) analysiert, die das Problem des Dreieck-Routings bei NEMO lösen sollen. Durch NEMO RO wählen die Datenpakete einen kürzeren Pfad zwischen den Endpunkten einer Verbindung, so dass die gemessene end-to-end Verzögerung und die Länge des Pfades reduziert werden. Die meisten dieser NEMO RO Methoden wurden als Internet Engineering Task Force (IETF) drafts veröffentlicht. Wir stellen fest, dass manche dieser Vorschläge zusätzliche Funktionalität für die Lösung des Mobilitätsproblems den Endknoten erfordern, andere hingegen nicht. Darüber hinaus versuchen einige Vorschläge, das Nested NEMO Problem zu lösen, ohne dabei das Problem der Routenoptimierung anzugehen. Außerdem mangelt es einigen der vorgeschlagenen Protokolle, da sie in der Regel nur als IETF drafts veröffentlicht werden, an der erforderlichen Reife und Erfahrungen mit praktischen Implementierungen. Angesichts dieser Probleme untersuchen wir vor allem infrastrukturbasierte NEMO RO Lösungen, nämlich die Home Agent to Home Agent (global HAHA) und Correspondent Router (CR) Protokolle, aus der Perspektive des ATN/IPS, das im ersten Teil der Arbeit vorgestellt wurde. Danach schlagen wir zwei neue Ansätze für das globale HAHA Protokoll vor, um die end-to-end Verzögerung und den Signalisierungs Overhead durch die Lösung für das Mobilitätsproblem zu verringern.
7 Contents Abstract Kurzfassung iii v 1 Introduction Main Challenges in the ATM Services in the ATM Airspace Domains in the ATM Stake Holders in the ATM Air/Ground Communications Service Provider Air Navigation Service Provider Airlines Future Communication Infrastructure Aeronautical Telecommunications Network New Radio Access Technologies Goal of the Thesis Structure of Thesis and Main Contributions Fundamentals LDACS LDACS LDACS Detailed Explanation of LDACS Message Abbreviations Frame Structure Resource Allocation ARQ Mechanism Handover Types Handling of Control Message Losses Mobile IPv Modes of Operation Dynamic Home Agent Address Discovery Network Mobility (NEMO) vii
8 Contents viii 2.5 Neighbor Discovery Address Autoconfiguration Duplicate Address Detection Neighbor Unreachability Detection IEEE Specification Reliable Transport with TCP TCP Reno TCP NewReno Simulation Platform LDACS1 Module Network Layer Module Handover Optimizations Related Work Performance Assessment Considered Topology Handover Performance with ARQ Mechanism High BER Scenario Low BER Scenario Reducing Router Advertisement Overhead Proposal 1 - Using IEEE Event Services Proposal 2 - Transmission of Stored Router Advertisement Message Discussion Overhead Analysis Proposal 3 - Removing Duplicate Address Detection Proposal 4 - Speeding Up Handovers in Congested Cells Conclusion TCP Analysis with LDACS TCP Optimizations for Mobile IPv6 Handovers Access Router Buffering Base Station Buffering Home Agent Bi-casting Analysis of Proposals Home Agent Buffering for Inter Access Network Handovers Performance Assessment Received Power and Wireless Channel Errors Network Layer Considerations Transport and Application Layer Considerations Further Assumptions Simulation Results and Analysis Unlimited LDACS1 Buffer Size
9 Contents ix Limited LDACS1 Buffer Size Relation Between Handover Completion Time and TCP RTO Expiry Time Mobility Signaling Message Loss Conditions in Home Agent Buffering Method Impact of Signaling Message Losses on the Handover Performance Home Agent Buffering Load Considerations Conclusion Radio Resource Management Scheduling Architecture QoS Mapping Time Complexity Analysis Modified Deficit Round Robin with Fragmentation Fair-Share Scheduling Randomized User Selection Scheduling Performance Evaluation Assumptions Considered Topology and Simulation Parameters File Transfer Analysis Modified Deficit Round Robin Scheduling Fair-Share Scheduling Randomized User Selection Scheduling Real-time Service Analysis Underloaded Case Overloaded Case Conclusion NEMO Route Optimization Analysis NEMO Route Optimization Classification Global HAHA Protocol New Mobility Header Messages Inter HAHA Operation Multihoming Support Multiple CoA Registration Flow Binding Correspondent Router Protocol New Mobility Header Messages New ICMPv6 Messages Analysis of Infrastructure Based NEMO RO Methods Network Attachment Scenarios and NEMO RO Usage Global HAHA Configurations Correspondent Router Configurations
10 Contents x 6.6 Home Agent Selection Methods in Global HAHA Networks Scenarios Proposals Static Method Dynamic Method Example Comparison Multiple Home Agent Usage in Global HAHA Networks Context Transfer in Global HAHA Networks Internet Key Exchange Context Transfer Protocol Proposals Node Initiated Proposal Network Initiated Proposal Overhead and Delay Comparisons Further Discussions SPI Collision Problem Authorization Token Generation Number of Home Agent Switches Conclusion Conclusions 90 A Mobile IPv6 Overhead Analysis 92 B LDACS1 Physical Layer Configurations 94 List of Acronyms 96 Bibliography 105
11 Chapter 1 Introduction Air Traffic Management (ATM) can be defined as the process, procedures and resources that are used to make sure that aircraft are safely guided in the skies and on the ground 1. It is composed of different systems such as airspace management, air traffic flow, capacity management and air traffic control. In 2003, EUROCONTROL and the Federal Aviation Administration agreed to undertake a joint study called Future Communications Study in order to investigate possible radio access technologies that will be used for ATM operations in the time frame of The study consists of mainly two activities: Identification of future communication requirements to support the future ATM concepts. The results are published in the Communication Operating Concept Requirements (COCR) document  in May Assessment of different radio access technologies based on the requirements in COCR. The results are published in the technology assessment document  in October Following the technology assessment report, an action plan  is published in November Main Challenges in the ATM The COCR document considers two phases of communications to support the ATM as shown in Fig In phase 1, voice communication is the primary means of communication for the provision of ATM, whereas in phase 2, data communication is the primary means of communication and voice is only used for exceptional circumstances. The document provides two sets of requirements for phase 1 and phase 2 for different ATM services. These requirements are mainly latency, expiration time, integrity, continuity, availability of provision and availability of use that will be used as a basis for selecting the Future Communications Infrastructure (FCI) including the future radio access technologies. Furthermore, some new future services like Voice over IP (VoIP) and sensor data transmission for the aircraft health management also add additional requirements since these services require 1 see 1
12 The FRS should, at a minimum, support the required air-ground and air-air data communications. The data communications may be broadcast, multicast, and/or addressed. Voice communication may be supported provided the FRS meets the 1.1 voice Main requirements Challenges in in the the ATM document. 2 Phase 1 Phase Figure 1.1 Phase 1 and Phase 2 concept evolution over time . Figure 1-1: Phase and Phase Concept Evolution Over Time real-time In some and regions near-real-time of the world, transmission Phase 1 data of communications certain information services withare low already latency being and high introduced through trials or implementation programmes. Other regions may begin availability. Phase 1 implementation at any time, or not at all, based on their ATM needs. In Similarly, addition to the themore low latency advanced and high services availability described requirements, in Phase there 2 may is another never important be requirement implemented in terms in some of data regions capacity. for various As mentioned reasons such above, as lower whentraffic the data density communication or lack is used of an asadequate a primarybusiness means of case. communication This is depicted in phase in Figure 2, there 1-1 will by be the strong dashed demand lines for high showing capacity continued radio access use technologies of Phase 1 since concepts the state in some of the regions art technologies while others like have VHF Data implemented those defined under Phase 2. Link Mode 2 (VDLm2) will go to saturation. In parallel, according to STATFOR statistics, the number The of performance flights in Europe requirements will be around provided 17in million this document in 2030 annually, are a snapshot which is 1.8 of times what more thandemands in 2009 a . full For set these of Phase reasons, 1 services new radio anticipated access to technologies be in place (such in some as L-Band regions Digital around 2020 would place on the communications system. The performance Aeronautical Communications System Option 1 (LDACS1)) that are developed for the time frame requirements for Phase 2 represent the same for a fully matured set of services of anticipated should to be in beplace capable in some of handling regions the in the data 2030 traffic timeframe. demands of the future ATM. A particular aircraft or ground system is not required to implement any of the services 1.2contained Services in this indocument. the ATMCoordination between the regional stakeholders will determine the operational services that benefit the local environment as part of a In today s global infrastructure. ATM, there are mainly two communication services available, namely Air Traffic Services (ATSs) and Airline Operations Services (AOSs) . ATS is used to provide navigation, control, 1.2 and Scope situational awareness services to the aircraft and AOS is used for business operations of airline companies. Currently, these services are primarily performed by using analogue voice The scope of the COCR document is to identify concepts, requirements, and trends communication that will be technologies. the basis for However, selecting itthe is already FRS. known Air Navigation that digital Service data communication Providers utilizes (ANSPs) the bandwidth industry moreare efficiently in the formative and overall stages is much of determining less error-prone many than of analogue the voice communication. In addition, only with data communications new ATM concepts like 4Dtrajectory exchange and graphical weather information 16 transmission is possible. Furthermore, two new services are also under discussion which are VoIP traffic  and transmission of sensor data for the aircraft health management  for the future ATM. 1.3 Airspace Domains in the ATM As defined in the COCR document , different ATS and AOS communication services are used by an aircraft depending on its position. According to the COCR  airspace is divided into four separate domains, namely, Airport (APT), Terminal Manoeuvring Area (TMA), En-Route (ENR) and Oceanic, Remote, Polar (ORP) as shown in Table 1.1.
13 1.4 Stake Holders in the ATM 3 Airspace Domain COCR Definition  APT TMA ENR ORP Consists of an airspace of 10 miles in diameter and up to 5000 feet. It also includes airport surface and immediate vicinity of the airport. Consists of an airspace surrounding an airport, starting at 5000 feet up to Flight Level 245. The TMA domain radiates out 50 Nautical Mile (NM) from the center of an airport. Consists of an airspace that surrounds TMA domain starting at Flight Level 245 to Flight Level 600. It is the continental or domestic airspace. COCR assumes ENR has a horizontal limit extending 300 NM by 500 NM. This is the same as ENR domain, except it is associated with geographical areas outside of domestic airspace. COCR assumes ORP have a horizontal limit extending 1000 NM by 2000 NM. Table 1.1 Airspace domain definitions . 1.4 Stake Holders in the ATM This section provides a general description about main stake holders in the ATM that are relevant for this thesis Air/Ground Communications Service Provider An Air/Ground Communications Service Provider (ACSP) operates an access network that includes different radio access technologies. Global ACSPs utilize terrestrial and satellite link technologies to provide ATS/AOS services that have a world-wide network and they are comparable to the tier 1 service providers in the Internet. Each global ACSP operates VDLm2 as the state of the art radio access technology for TMA and ENR stages of flight. The VDLm2 provides a nominal throughput of 31.5 kbit/s for all aircraft within a single cell. In addition global ACSPs utilizes different satellite technologies for ORP regions. In the future, it is also foreseen that there will be local ACSPs that operate in the local domains such as only in airport domain Air Navigation Service Provider An Air Navigation Service Provider (ANSP) manages the air traffic within a country or geographic region. Generally each ANSP has its own sub-network. An ANSP might also be a local ACSP within that geographical region by operating its own radio access technology, which might be due to security or cost motivations. Although International Civil Aviation Organization (ICAO) has an influence on ANSPs, these organizations also have their own network policies.
14 1.4 Stake Holders in the ATM Airlines Airline Operations (AOs) is used for managing the business operations of the aircraft that belong to a certain airline. Generally each AO has its own sub-network on the ground. 1.5 Future Communication Infrastructure Fig. 1.2 shows the Future Communications Infrastructure (FCI) of the ATM which is composed of different components from end-to-end communication perspective. This infrastructure is used by ANSPs and airlines in order to communicate with the aircraft Aeronautical Telecommunications Network The Aeronautical Telecommunications Network (ATN) is one of the main components of the FCI which is composed of different networking elements. The existing ATN standard is published by ICAO as Standards and Recommended Practices (SARPS)  document that defines the ATN based on the International Organization for Standardization (ISO) Open Systems Interconnection (OSI) reference model. The standard covers the definition of the protocol stack from layer 3 to layer 7. The specification adapts the Inter Domain Routing Protocol (IDRP) at the network layer not only for routing on the ground network but also to support mobility of aircraft. This version of the ATN is only partially deployed COCR at the Version present 2.0 time. ICAO recently produced a new ATN standard based on IPv6 protocol suite called Aeronautical Telecommunications processors, applications, Network using and networks) Internet needed Protocol for the Suite ANSP, (ATN/IPS) AOC, and  aircraft as shown to in Fig communicate with each other. 1.4 Approach Figure Figure 1-2: Scope 1.2 of Future the Future communications Radio System (FRS) infrastructure part of the FCI . To determine the overall context for future communications, numerous concepts of operations, vision statements, and plans being developed and circulated by ANSPs around the world were reviewed. These are identified in the document reference list in Section 1.6.
15 1.5 Future Communication Infrastructure 5 ATN/IPS mandates Mobile IPv6 (MIPv6) protocol as the main mobility management protocol and mentions Network Mobility (NEMO) as an optional protocol for air-ground communications. Network Components in ATN/IPS There are different networking components inside the ATN/IPS. Here, four main components that are relevant for this thesis are defined. Mobile Network Nodes Mobile Network Node (MNN) is a node located within a mobile network, either permanently or temporarily. An MNN might be either a Local Fixed Node (LFN) or a Local Mobile Node (LMN) . ATS and AOS domains have MNNs that are primarily LFNs, though potentially there could be some LMNs . They are operated by and are under control of the airline, although ICAO regulations and standards affect ATS MNNs. Mobile Router Mobile Router (MR) is a router onboard which is also called airborne router in the aviation environment. It is reasonable to assume that in the future there will be one IPv6-based MR on each aircraft that handles both ATS and AOS traffic, as the radio access technologies provide support for both services. Additional MRs may be on board for fault tolerance reasons or for passenger communication services. Home Agent A Home Agent (HA) is a router in mobile node s home network that maintains reachability information about the current point of attachment of mobile node in the network . We assume each HA serves both ATS and AOS domains. Application Layer Application Layer Transport Layer (TCP, UDP) Transport Layer (TCP, UDP) Network Layer (IPv6) Network Layer (IPv6, BGP-4) Network Layer (IPv6, BGP-4) Network Layer (IPv6) Link Layer Link Layer Link Layer Link Layer Local or intradomain subnetwork Inter-domain subnetwork Local or intradomain subnetwork Figure 1.3 ATN/IPS protocol architecture .
16 1.5 Future Communication Infrastructure 6 Correspondent Nodes ATS Correspondent Nodes (CNs) are ATS units that refer to air traffic controllers managing a certain air space, along with some non-controlling CNs that may provide weather or airtraffic flow-control information. These nodes are located within ANSP networks and generally dynamic; as the aircraft traverses different regions of the world, the responsible ATS unit changes. Generally ATS CNs are geographically close to the aircraft, whereas AOS CNs are located in an AO network that might be distant from the aircraft. Within the AO network, AOS CNs could be at airline headquarters/operations center or at the arrival or destination airport. These nodes are relatively static throughout a flight  New Radio Access Technologies Another main component of the FCI is the radio access technologies. The main motivation for considering new radio access technologies in the ATM is due to more data capacity need since with the usage of data communication links as a primary means of communication, the state of the art technologies will reach to saturation. For this purpose, EUROCONTROL and the Federal Aviation Administration concluded a study with selected radio access technologies  for different airspace domains as shown in Table 1.2. Chapter 2 will provide further details related to the LDACS1 technology which this thesis considers as a baseline radio access technology. Airspace Domain APT Surface APT, TMA, ENR ORP Air/Air Applicable Technology IEEE e, LDACS may be possible in some areas LDACS, Satellite-based may be possible in some areas Satellite-based LDACS Table 1.2 Airspace domains with selected technologies. 1.6 Goal of the Thesis There are two main goals of the thesis considering the requirements mentioned in Section 1.1. The first goal is to design novel mobility and handover management algorithms that improve the performance of state-of-art mechanisms so that aircraft perform layer 2 and layer 3 handovers as fast as possible in order not to affect any service which requires low-latency and high service availability. In addition, these methods should minimize packet drops during handover by some means (e.g., packet buffering) so that packets can be delivered to the end systems before their expiration times are exceeded . Another part of improvements is to reduce signaling overhead in the wireless link since it is the main bottleneck between communicating end nodes and as mentioned in Section 1.1, future radio access technologies should be capable of handling the data traffic demands of future ATM considering air traffic growth mentioned by the STATFOR .
17 1.6 Goal of the Thesis 7 The second goal is to design a radio resource management architecture including design of different algorithms for LDACS1 in order to distribute available resources evenly among different number of users (especially in case LDACS1 is highly loaded with many users). This is also important to comply with the expiration time and latency requirements of ATS/AOS messages . 1.7 Structure of Thesis and Main Contributions In the second chapter, we will present some important aspects of LDACS1 and IPv6-based mobile networking principles that are required for understanding and analyzing the contributions of the thesis. In chapter 3, different handover optimization techniques are explained in order to reduce handover delay and handover signaling overhead in LDACS1. The main contributions of this work are published in: Ayaz, Serkan; Hoffmann, Felix; Sommer, Christoph; German, Reinhard; Dressler, Falko Performance Evaluation of Network Mobility Handover over Future Aeronautical Data Link. GLOBECOM 2010, Miami, Florida USA, December, 2010 . Bauer, Christian; Ayaz, Serkan A Thorough Investigation of Mobile IPv6 for the Aeronautical Environment. VTC Fall 2008, IEEE Vehicular Technology Conference, Calgary, Canada, 2008 . In chapter 4, different TCP handover optimizations related to Mobile IPv6 protocol are investigated and the most promising approach (home agent buffering) is integrated with LDACS1. This technique is mainly used for reducing the transmission completion time of on-going Transmission Control Protocol (TCP) sessions during the handover process. The main contribution of this work is published in: Ayaz, Serkan; Hoffmann, Felix; Epple, Ulrich; German, Reinhard; Dressler, Falko Performance Evaluation of Network Mobility Handover over Future Aeronautical Data Link. Computer Communications (Elsevier), February, 2012 . Chapter 5 considers Radio Resource Management (RRM) topic for LDACS1. Three different RRM algorithms are analyzed and a new Deficit Round Robin (DRR) with fragmentation algorithm is developed. The new algorithm can be used not only in forward link but also in the return link. The main contribution of this work is published in: Ayaz, Serkan; Hoffmann, Felix; German, Reinhard; Dressler, Falko Analysis of Deficit Round Robin Scheduling for Future Aeronautical Data Link. PIMRC 2011, Toronto, Canada, September, 2011 . In chapter 6, different NEMO route optimization protocols are investigated. Two new approaches are proposed which optimize the global Home Agent to Home Agent (HAHA) protocol in terms of end-to-end delay performance and mobility signaling overhead. The main contributions of this work are published in:
18 1.7 Structure of Thesis and Main Contributions 8 Ayaz, Serkan; Bauer, Christian; Ehammer, Max. Applying IKE/IPsec Context Transfer to Aeronautical Networks. Mobiwac 2009, Teneriffe, Spain, October, 2009 . Ayaz, Serkan; Bauer, Christian; Arnal, Fabrice. Minimizing End-to-End Delay in Global HAHA Networks Considering Aeronautical Scenarios. Mobiwac 2009, Teneriffe, Spain, October, 2009 . Ayaz, Serkan; Bauer, Christian; Eddy, Wesley M.; Arnal, Fabrice. NEMO Route Optimization Solution Space Analysis and Evaluation Criteria for Aviation. 8th Conference on Intelligent Transport System Telecommunications (ITST), Phuket, Thailand, October 2008 . Ayaz, Serkan; Bauer, Christian; Ehammer, Max; Gräupl, Thomas; Arnal, Fabrice. Mobility Options in the IP-based Aeronautical Telecommunication Network. ICT MobileSummit 2008, Stockholm, Sweden, 2008 .
19 Chapter 2 Fundamentals This chapter provides some important aspects of future aeronautical mobile networks that are required for understanding and analyzing the main contributions of this thesis in the following chapters. These aspects are mainly L-Band Digital Aeronautical Communications System (LDACS), mobility management based on MIPv6, IEEE specification and TCP. The last section also provides information about our simulation platform. 2.1 LDACS EUROCONTROL and the Federal Aviation Administration are currently considering two candidate radio access technologies for the future provision of ATS and AOS services in the L-band 2. These technologies are referred to as LDACS option 1  and option 2 . Initial specifications for both technologies have been published by EUROCONTROL, and it is planned that one of these two systems will become operational in the time frame of As mentioned in , one of the main system requirements of LDACS is to deliver certain ATS and AOS information in a timely manner with minimized service disruption. Furthermore, it shall also support multiple QoS offerings, such as priority and preemption capabilities. As mentioned in chapter 1, some new future services like VoIP and sensor data transmission for the aircraft health management requires real-time and near-real-time transmission of certain information with low latency and high availability. For these reasons, it is important for LDACS has not only advanced RRM techniques for different Class of Service (CoS) applications but also advanced handover mechanisms for seamless mobility across different access networks LDACS1 LDACS1 has originated from the Broadband-Aeronautical Multi-Carrier Communications (B-AMC) system and the Project 34 standard of the Association of Public Safety Communications Officials. It is designed for the transmission of both digital voice and data. In LDACS1, Return Link (RL) and Forward Link (FL) are separated by means of Frequency Division Duplex (FDD). In the RL, a combination of Orthogonal Frequency-Division Multiple-Access (OFDMA) and Time-Division 2 see 9
20 2.1 LDACS 10 Multiple-Access (TDMA) is used, whereas in the FL, Orthogonal Frequency-Division Multiplexing (OFDM) is applied. The TDMA component in the RL is selected in order to minimize the possibility of interference with legacy systems which are operating on board on aircraft in the L-band, e.g. the distance measuring equipment. This is important since an LDACS1 transmitter operates close to other receivers on board, so it should only be active for a short time, reducing these receivers exposure to interference. The modulation and coding scheme of LDACS1 can be adapted to the channel state and, thus, implements adaptive coding and modulation. With that, the throughput varies between 291 kbit/s kbit/s in the FL (assuming 24 data channel physical layer Protocol Datagram Units (PDUs) and 3 common control channel physical layer PDUs per multiframe (MF)) and kbit/s kbit/s in the RL (assuming average dedicated control channel duration of ms per MF) . Section 2.2 will provide detailed information about LDACS1 features LDACS2 L-Band Digital Aeronautical Communications System Option 2 (LDACS2) has originated from the L-Band Digital Link and All purpose Multi-channel Aviation Communication System technologies. It is designed for transmission of digital data only. RL and FL are separated by means of Time-Division Duplex (TDD) and Gaussian minimum shift keying is the only supported modulation type. The available spectrum is in the range of 960 MHz MHz and is partitioned into a number of channels of 200 khz bandwidth each. A gross data rate of 270 kbit/s is offered by LDACS2. It is a TDMA system applying a 1 s of frame length as shown in Fig The forward link sub-frames (UP1 & UP2) are used by the base station to send messages to aircraft. These messages contain user data, acknowledgements, Clear-To-Send and framing messages. UP1 also contains a broadcast region which notifies the aircraft about the transmit and receive opportunities. The return link sub-frames (CoS1 & CoS2) carry information about user data, Request-To-Send, acknowledgements and Keep-Alive messages and login sub-frame is used to transmit the login request. UP1 UP2 Forward Link Return Link Login (Return Link) Forward Link Return Link Figure 2.1 LDACS2 frame structure. 2.2 Detailed Explanation of LDACS1 This section provides the main features of LDACS1 considering frame structure, resource allocation procedures, Automatic Repeat Request (ARQ) mechanism and handover types.