In this thesis we investigate the performance of spatial reuse in wireless networks. More specifically, we investigate the performance of location-based spatial reuse built upon the identification of links in the network that form Collision-Free Sets (CFSs). We develop algorithms that efficiently find such CFSs. The main focus of this thesis is the application of our CFS-based algorithms to emerging WiMAX (Worldwide Interoperability for Microwave Access) networks. However, we will also apply our CFS-based algorithms to smaller scale networks, as well as to the issue of QoS routing. This thesis makes several contributions. We first show how CFSs can be found within polynomial time in small scale wireless networks. We then probe how CFSs can be used to enhance network efficiency when location is available. We also explore how CFS determination is affected by location error, determining what level of location error renders the use of CFSs ineffective. In this context, we discuss the density of access points required to ensure CFS-based spatial reuse remains effective. We then focus on the use of CFSs in emerging multihop WiMAX networks, showing in detail how enhanced spatial reuse is delivered. The spatial reuse gains are probed both in the presence of realistic channel conditions and realistic location errors. Within the context of the IEEE 802.16 standard we show how CFSs can enhance, by factors of two, the VoIP capacity of multihop WiMAX networks. We also discuss how our CFS algorithms can be applied to other ongoing efforts aimed at improving VoIP capacity in WiMAX networks. Finally, an application of our CFS algorithms in the context of QoS routing is studied. Specifically, we develop a two-hop QoS routing protocol that guarantees QoS specifications by securing higher bandwidth for the chosen routes.

In this thesis we investigate the performance of spatial reuse in wireless networks. More specifically, we investigate the performance of location-based spatial reuse built upon the identification of links in the network that form Collision-Free Sets (CFSs). We develop algorithms that efficiently find such CFSs. The main focus of this thesis is the application of our CFS-based algorithms to emerging WiMAX (Worldwide Interoperability for Microwave Access) networks. However, we will also apply our CFS-based algorithms to smaller scale networks, as well as to the issue of QoS routing. This thesis makes several contributions. We first show how CFSs can be found within polynomial time in small scale wireless networks. We then probe how CFSs can be used to enhance network efficiency when location is available. We also explore how CFS determination is affected by location error, determining what level of location error renders the use of CFSs ineffective. In this context, we discuss the density of access points required to ensure CFS-based spatial reuse remains effective. We then focus on the use of CFSs in emerging multihop WiMAX networks, showing in detail how enhanced spatial reuse is delivered. The spatial reuse gains are probed both in the presence of realistic channel conditions and realistic location errors. Within the context of the IEEE 802.16 standard we show how CFSs can enhance, by factors of two, the VoIP capacity of multihop WiMAX networks. We also discuss how our CFS algorithms can be applied to other ongoing efforts aimed at improving VoIP capacity in WiMAX networks. Finally, an application of our CFS algorithms in the context of QoS routing is studied. Specifically, we develop a two-hop QoS routing protocol that guarantees QoS specifications by securing higher bandwidth for the chosen routes.

<p>Examensarbetet som beskrivs i denna rapport handlar om en ny teknik för att förbättra säkerheten för flygplan i luften och i närheten av flygplatser. Denna teknik benämns ADS-B (Automatic Dependent Surveillance Broadcast), och är tänkt att göra det möjligt för piloter att själva få information om trafik i närområdet. Nuvarande system baserar sig i huvudsak på visuella observationer från flygledare i kontrolltorn samt radarspaning omkring flygplatserna. Med det nuvarande systemet kommer det att bli både dyrt och svårt att upprätthålla en acceptabel nivå på flygsäkerheten när trafiken ökar. </p><p>Arbetet har bedrivits i AerotechTelubs regi i Linköping samt med hjälp ifrån företaget Sectra Wireless Technologies AB. Huvuddelen av arbetet inriktar sig på implementerandet av C-funktioner för att hantera kommunikationen och sammankopplandet av ett tidigare skapat system, för grafikvisning, med en transponder som hanterar ADS-B (tillverkad av Sectra). Målet med detta var att göra förberedande arbete åt AerotechTelub som de förhoppningsvis kommer att kunna använda i ett eventuellt kommande projekt. Rapporten tar upp några standarder som hör till konceptet GP&C (Global Positioning & Communication), samt beskriver de delar som ligger till grund för programmets funktion. </p><p>Examensarbetet har resulterat i ett demonstrationsprogram för att visa hur en lösning av problemet kan se ut. Det har tyvärr inte gått att säkerställa om programmet fungerar till fullo, men genom simuleringar och andra tester har huvuddelen av programmets funktioner gått att verifiera.</p>

Examensarbetet som beskrivs i denna rapport handlar om en ny teknik för att förbättra säkerheten för flygplan i luften och i närheten av flygplatser. Denna teknik benämns ADS-B (Automatic Dependent Surveillance Broadcast), och är tänkt att göra det möjligt för piloter att själva få information om trafik i närområdet. Nuvarande system baserar sig i huvudsak på visuella observationer från flygledare i kontrolltorn samt radarspaning omkring flygplatserna. Med det nuvarande systemet kommer det att bli både dyrt och svårt att upprätthålla en acceptabel nivå på flygsäkerheten när trafiken ökar. Arbetet har bedrivits i AerotechTelubs regi i Linköping samt med hjälp ifrån företaget Sectra Wireless Technologies AB. Huvuddelen av arbetet inriktar sig på implementerandet av C-funktioner för att hantera kommunikationen och sammankopplandet av ett tidigare skapat system, för grafikvisning, med en transponder som hanterar ADS-B (tillverkad av Sectra). Målet med detta var att göra förberedande arbete åt AerotechTelub som de förhoppningsvis kommer att kunna använda i ett eventuellt kommande projekt. Rapporten tar upp några standarder som hör till konceptet GP&amp;C (Global Positioning &amp; Communication), samt beskriver de delar som ligger till grund för programmets funktion. Examensarbetet har resulterat i ett demonstrationsprogram för att visa hur en lösning av problemet kan se ut. Det har tyvärr inte gått att säkerställa om programmet fungerar till fullo, men genom simuleringar och andra tester har huvuddelen av programmets funktioner gått att verifiera.

<p>This report is a technical verification and validation of Traffic Information Service Broadcast (TIS-B) using the data link VDL Mode 4. </p><p>The main objective of the report is to examine the usefulness of TIS-B considering the results from tests performed in the Stockholm Terminal Area and for the Advanced Surface Movement Guidance and Control System (A-SMGCS) at Arlanda airport. The results are compared with the requirements that have been set by the standardisation organisations ICAO, RTCA, Eurocontrol and Eurocae. TIS-B is however such a new concept, so most of the operational requirements have not yet been defined.</p><p>The process for performing the evaluation of TIS-B involves three stages: </p><p>· Study the requirements on TIS-B, ADS-B, radar and A-SMGCS. </p><p>· Verify TIS-B by performing tests at Arlanda airport. </p><p>· Validate the test results through analysis. </p><p>A theoretical study of slot allocation optimisation is performed to decide how the slot allocation is to be implemented. </p><p>The report includes a Functional Hazard Analysis (FHA). The FHA is done to see if the applications for TIS-B are ready for implementation or if more hazard preventing actions has to be taken, before any operational actions can be performed. </p><p>The report also involves a theoretical introduction to Air Traffic Management (ATM), Surveillance techniques and TIS-B. </p><p>All parts included in the report results in conclusions and recommendations regarding the TIS-B service.</p>

<p>This licentiate thesis work investigates two medium access control (MAC) methods, when used in traffic safety applications over vehicular <em>ad hoc</em> networks (VANETs). The MAC methods are carrier sense multiple access (CSMA), as specified by the leading standard for VANETs IEEE 802.11p, and self-organizing time-division multiple access (STDMA) as used by the leading standard for transponders on ships. All vehicles in traffic safety applications periodically broadcast cooperative awareness messages (CAMs). The CAM based data traffic implies requirements on a predictable, fair and scalable medium access mechanism. The investigated performance measures are <em>channel access delay</em>, <em>number of consecutive packet drops</em> and the <em>distance between concurrently transmitting nodes</em>. Performance is evaluated by computer simulations of a highway scenario in which all vehicles broadcast CAMs with different update rates and packet lengths. The obtained results show that nodes in a CSMA system can experience <em>unbounded channel access delays</em> and further that there is a significant difference between the best case and worst case channel access delay that a node could experience. In addition, with CSMA there is a very high probability that several <em>concurrently transmitting nodes are located close to each other</em>. This occurs when nodes start their listening periods at the same time or when nodes choose the same backoff value, which results in nodes starting to transmit at the same time instant. The CSMA algorithm is therefore both <em>unpredictable</em> and <em>unfair</em> besides the fact that it <em>scales badly</em> for broadcasted CAMs. STDMA, on the other hand, will always grant channel access for all packets before a predetermined time, regardless of the number of competing nodes. Therefore, the STDMA algorithm is <em>predictable</em> and <em>fair</em>. STDMA, using parameter settings that have been adapted to the vehicular environment, is shown to outperform CSMA when considering the performance measure <em>distance between concurrently transmitting nodes</em>. In CSMA the distance between concurrent transmissions is random, whereas STDMA uses the side information from the CAMs to properly schedule concurrent transmissions in space. The price paid for the superior performance of STDMA is the required network synchronization through a global navigation satellite system, e.g., GPS. That aside since STDMA was shown to be scalable, predictable and fair; it is an excellent candidate for use in VANETs when complex communication requirements from traffic safety applications should be met.</p>

This report is a technical verification and validation of ADS-B (Automatic Dependent Surveillance – Broadcast) over VDL Mode 4 (Very High Frequency Data Link Mode 4) for the use in the surveillance element of an A-SMGCS (Advanced Surface Movement Guidance and Control System). The main objective of this report is to examine if ADS-B/VDL Mode 4 fulfils the technical requirements for an implementation at Arlanda airport, Stockholm Sweden. The report also includes a FMECA (Failure Mode, Effects and Criticality Analysis), a theoretical background and methods for monitoring. The process of making this report can be divided into three phases: 1. Preliminary Study. In this phase the requirements were examined and structured. 2. Verification. In this phase the system performance has been verified both theoretically and by several tests at Arlanda Airport. Simulation results have also been used. 3. Validation and documentation. The tests and verifications that were performed in phase 2 were validated in the third phase of the project. The final project document was also written in this phase. The main conclusion from this analysis is that ADS-B/VDL Mode 4 is well suited for surveillance. ADS-B/VDL Mode 4 has the possibility to fulfil all considered requirements, apart from detecting all obstacles. But if all the requirements are going to be fulfilled depends both on the implementation and the operational environment. The results from this verification and validation should be used as the technical subset in a future safety case, both in Sweden and internationally.

This report is a technical verification and validation of Traffic Information Service Broadcast (TIS-B) using the data link VDL Mode 4. The main objective of the report is to examine the usefulness of TIS-B considering the results from tests performed in the Stockholm Terminal Area and for the Advanced Surface Movement Guidance and Control System (A-SMGCS) at Arlanda airport. The results are compared with the requirements that have been set by the standardisation organisations ICAO, RTCA, Eurocontrol and Eurocae. TIS-B is however such a new concept, so most of the operational requirements have not yet been defined. The process for performing the evaluation of TIS-B involves three stages: · Study the requirements on TIS-B, ADS-B, radar and A-SMGCS. · Verify TIS-B by performing tests at Arlanda airport. · Validate the test results through analysis. A theoretical study of slot allocation optimisation is performed to decide how the slot allocation is to be implemented. The report includes a Functional Hazard Analysis (FHA). The FHA is done to see if the applications for TIS-B are ready for implementation or if more hazard preventing actions has to be taken, before any operational actions can be performed. The report also involves a theoretical introduction to Air Traffic Management (ATM), Surveillance techniques and TIS-B. All parts included in the report results in conclusions and recommendations regarding the TIS-B service.

<p>This report is a technical verification and validation of ADS-B (Automatic Dependent Surveillance – Broadcast) over VDL Mode 4 (Very High Frequency Data Link Mode 4) for the use in the surveillance element of an A-SMGCS (Advanced Surface Movement Guidance and Control System). </p><p>The main objective of this report is to examine if ADS-B/VDL Mode 4 fulfils the technical requirements for an implementation at Arlanda airport, Stockholm Sweden. The report also includes a FMECA (Failure Mode, Effects and Criticality Analysis), a theoretical background and methods for monitoring. </p><p>The process of making this report can be divided into three phases: </p><p>1. Preliminary Study. In this phase the requirements were examined and structured. </p><p>2. Verification. In this phase the system performance has been verified both theoretically and by several tests at Arlanda Airport. Simulation results have also been used. </p><p>3. Validation and documentation. The tests and verifications that were performed in phase 2 were validated in the third phase of the project. The final project document was also written in this phase. </p><p>The main conclusion from this analysis is that ADS-B/VDL Mode 4 is well suited for surveillance. ADS-B/VDL Mode 4 has the possibility to fulfil all considered requirements, apart from detecting all obstacles. But if all the requirements are going to be fulfilled depends both on the implementation and the operational environment. </p><p>The results from this verification and validation should be used as the technical subset in a future safety case, both in Sweden and internationally.</p>

This licentiate thesis work investigates two medium access control (MAC) methods, when used in traffic safety applications over vehicular ad hoc networks (VANETs). The MAC methods are carrier sense multiple access (CSMA), as specified by the leading standard for VANETs IEEE 802.11p, and self-organizing time-division multiple access (STDMA) as used by the leading standard for transponders on ships. All vehicles in traffic safety applications periodically broadcast cooperative awareness messages (CAMs). The CAM based data traffic implies requirements on a predictable, fair and scalable medium access mechanism. The investigated performance measures are channel access delay, number of consecutive packet drops and the distance between concurrently transmitting nodes. Performance is evaluated by computer simulations of a highway scenario in which all vehicles broadcast CAMs with different update rates and packet lengths. The obtained results show that nodes in a CSMA system can experience unbounded channel access delays and further that there is a significant difference between the best case and worst case channel access delay that a node could experience. In addition, with CSMA there is a very high probability that several concurrently transmitting nodes are located close to each other. This occurs when nodes start their listening periods at the same time or when nodes choose the same backoff value, which results in nodes starting to transmit at the same time instant. The CSMA algorithm is therefore both unpredictable and unfair besides the fact that it scales badly for broadcasted CAMs. STDMA, on the other hand, will always grant channel access for all packets before a predetermined time, regardless of the number of competing nodes. Therefore, the STDMA algorithm is predictable and fair. STDMA, using parameter settings that have been adapted to the vehicular environment, is shown to outperform CSMA when considering the performance measure distance between concurrently transmitting nodes. In CSMA the distance between concurrent transmissions is random, whereas STDMA uses the side information from the CAMs to properly schedule concurrent transmissions in space. The price paid for the superior performance of STDMA is the required network synchronization through a global navigation satellite system, e.g., GPS. That aside since STDMA was shown to be scalable, predictable and fair; it is an excellent candidate for use in VANETs when complex communication requirements from traffic safety applications should be met.