Location techniques that satisfy the requirements of advanced Location-Based Services (LBS) in environments where GPS fails are needed, therefore accurate indoor positioning is becoming increasingly important. This PhD Thesis is devoted to the research on location of mobile devices employing WLAN (IEEE 802.11). The use of this kind of wireless networks infrastructures for positioning enables a powerful synergy between communications and location and allows solutions with good performances at moderated costs. However the adopted WLAN location methods suffer from important limitations that prevents from applying them to some fields that need more flexible and robust solutions. The main objective of this PhD is exploring precise WLAN location methods that allow overcoming these limitations. The researched methods here are based on measuring the Time Of Arrival (TOA), which is the time that takes the signal propagating from the transmitter to the receiver. TOA-based location works in two stages: ranging and positioning. The ranging consists of estimating the distances between the targeted terminal and several WLAN access points, each distance obtained measuring the TOA and then multiplying it by the speed of the WLAN signal. After that, the positioning takes as inputs the estimated distances and the known coordinates of the involved access points and calculates the position of the terminal by means of a trilateration or tracking algorithm. The key problem is that the characteristics of the IEEE 802.11 protocols difficult to perform accurate TOA measurements. The main challenge that faces the research work reported here is demonstrating the feasibility of achieving this while keeping the modifications over standard WLAN consumer equipment at minimum. The objective of this work can be understood as exploring the current limits of TOA-based methods over WLAN, making contributions that form a complete TOA-based location method that goes a step forward with respect to the other existing proposals. First, research on TOA-based ranging -the key component of TOA-based location methods- is reported. The general adopted approach consists of performing Round Trip Time (RTT) measurements employing IEEE 802.11 MAC frames, taking the maximum advantage of the combination of IEEE 802.11 protocol and WLAN consumer devices mechanisms. After that, the performed research on trilateration/tracking -the second stage of TOA-based location methods- is explained. Finally some performed studies about the achieved location method are presented. Lloc i data Signatura / Actualment existeix la necessitat de disposar de tècniques de localització que satisfacin els requeriments de serveis avançats basats en localització en entorns on GPS no està disponible, de manera que el posicionament precís en interiors d’edificis és cada vegada més important. Aquesta tesi doctoral està dedicada a la investigació sobre la localització de dispositius mòbils que utilitzen WLAN (IEEE 802.11). L'ús d'aquest tipus de xarxes sense fils per al posicionament permet una profitosa sinèrgia entre les comunicacions i la localització i permet solucions amb un bon rendiment a un cost moderat. No obstant això, els mètodes basats WLAN proposats fins el moment pateixen de limitacions importants que impedeix la seva aplicació a alguns camps que requereixen solucions més flexibles i robustes. L'objectiu principal d'aquesta tesi és explorar mètodes de localització precisa WLAN que permetin superar aquestes limitacions. Els mètodes que s’han investigat durant la tesi es basen en la mesura del time of arrival (TOA), que és el temps que tarda el senyal en propagar-se des del transmissor fins al receptor. En les tècniques de posicionament basades en TOA s’hi poden diferenciar dues fases: ranging i posicionament. El ranging consisteix en l’estimació de distàncies entre el terminal a localitzar i diversos punts d'accés WLAN; cada estimació de distància s’obté mesurant el TOA i multiplicant-lo després per la velocitat de propagació del senyal IEEE 802.11. Un cop fet això, el posicionament pren com a inputs les distàncies estimades per a, conegudes les coordenades dels punts d'accés involucrats, calcular la posició del terminal per mitjà d'un algoritme de tracking o trilateració. El problema clau és que les característiques dels protocols IEEE 802.11 a dia d’avui fan difícil la realització de mesures precises de TOA d’una manera senzilla. El principal repte que afronta el present treball de recerca és demostrar la viabilitat d’això darrer, minimitzant en la major mesura possible les modificacions sobre els equips WLAN comercials. L'objectiu d'aquest treball pot ser entesa com l'exploració dels límits actuals dels mètodes de posicionament basats en TOA sobre WLAN, realitzant contribucions que conformen un mètode complet de localització basat en TOA que pretén anar un pas endavant respecte a les propostes existents. En primer lloc, la investigació sobre ranging basat en TOA -el component clau dels mètode de localització TOA- és explicada en detall. El mètode general adoptat per a calcular el TOA consisteix en la mesura del temps d'anada i tornada del senyal, round trip time (RTT), utilitzant trames MAC IEEE 802.11 per tal de treure el màxim profit de la combinació del protocol IEEE 802.11 i els mecanismes dels dispositius WLAN comercials. Després d'això, es detalla la investigació realitzada sobre trilateració i tracking, la segona etapa dels mètodes de localització basats en TOA. Finalment es descriuen alguns estudis realitzats sobre les prestacions, possibles millores i encaix en futurs estàndars del mètode de localització explorat.

This thesis contributes toward the design of a quality-of-service (QoS) aware network layer for wireless ad hoc networks. With the lack of an infrastructure in ad hoc networks, the role of the network layer is not only to perform multihop routing between a source node and a destination node, but also to establish an end-to-end connection between communicating peers that satisfies the service level requirements of multimedia applications running on those peers. Wireless ad hoc networks represent autonomous distributed systems that are infrastructure-less, fully distributed, and multi-hop in nature. Over the last few years, wireless ad hoc networks have attracted significant attention from researchers. This has been fueled by recent technological advances in the development of multifunction and low-cost wireless communication gadgets. Wireless ad hoc networks have diverse applications spanning several domains, including military, commercial, medical, and home networks. Projections indicate that these self-organizing wireless ad hoc networks will eventually become the dominant form of the architecture of telecommunications networks in the near future. Recently, due to increasing popularity of multimedia applications, QoS support in wireless ad hoc networks has become an important yet challenging objective. The challenge lies in the need to support the heterogeneous QoS requirements (e.g., data rate, packet loss probability, and delay constraints) for multimedia applications and, at the same time, to achieve efficient radio resource utilization, taking into account user mobility and dynamics of multimedia traffic. In terms of research contributions, we first present a position-based QoS routing framework for wireless ad-hoc networks. The scheme provides QoS guarantee in terms of packet loss ratio and average end-to-end delay (or throughput) to ad hoc networks loaded with constant rate traffic. Via cross-layer design, we apply call admission control and temporary bandwidth reservation on discovered routes, taking into consideration the physical layer multi-rate capability and the medium access control (MAC) interactions such as simultaneous transmission and self interference from route members. Next, we address the network-layer resource allocation where a single-hop ad hoc network is loaded with random traffic. As a starting point, we study the behavior of the service process of the widely deployed IEEE 802.11 DCF MAC when the network is under different traffic load conditions. Our study investigates the near-memoryless behavior of the service time for IEEE 802.11 saturated single-hop ad hoc networks. We show that the number of packets successfully transmitted by any node over a time interval follows a general distribution, which is close to a Poisson distribution with an upper bounded distribution distance. We also show that the service time distribution can be approximated by the geometric distribution and illustrate that a simplified queuing system can be used efficiently as a resource allocation tool for single hop IEEE 802.11 ad hoc networks near saturation. After that, we shift our focus to providing probabilistic packet delay guarantee to multimedia users in non-saturated IEEE 802.11 single hop ad hoc networks. We propose a novel stochastic link-layer channel model to characterize the variations of the IEEE 802.11 channel service process. We use the model to calculate the effective capacity of the IEEE 802.11 channel. The channel effective capacity concept is the dual of the effective bandwidth theory. Our approach offers a tool for distributed statistical resource allocation in single hop ad hoc networks, which combines both efficient resource utilization and QoS provisioning to a certain probabilistic limit. Finally, we propose a statistical QoS routing scheme for multihop IEEE 802.11 ad hoc networks. Unlike most of QoS routing schemes in literature, the proposed scheme provides stochastic end-to-end delay guarantee, instead of average delay guarantee, to delay-sensitive bursty traffic sources. Via a cross-layer design approach, the scheme selects the routes based on a geographical on-demand ad hoc routing protocol and checks the availability of network resources by using traffic source and link-layer channel models, incorporating the IEEE 802.11 characteristics and interaction. Our scheme extends the well developed effective bandwidth theory and its dual effective capacity concept to multihop IEEE 802.11 ad hoc networks in order to achieve an efficient utilization of the shared radio channel while satisfying the end-to-end delay bound.

The focus of this thesis work is to evaluate the RSS (Received Signal Strength) Performance of the University of Gävle (HiG) based on IEEE 802.11 standards both indoor and outdoor. Authors investigated the issues of deploying access points for wireless local area networks in the library-2nd floor, building 99-4th floor and outdoor university campus. By using the program VisiWave Site Survey, Global Position System (GPS) and RSS sensor to analysis the received signal strength, throughput and radio map. The influence of the building material and distance for the signal strength and the throughput are done by investigating indoor environment. The results of investigation suggest that most parts of library-2nd floor and building 99-4th floor possess at least a good RSS performance. However, minority parts of these places have a poor RSS performance, and the new resolution of Access Points’ (AP) deployment for these poor-RSS-performance parts is provided. For the outdoor campus part, the RSS in the area which near the walls of building is satisfactory (Received Signal Strength Indication (RSSI) between -79.8 dBm and -57 dBm), however in the centre of outdoor campus the RSS is poor. Thus, the evaluation of APs deployment in HiG is achieved.

This thesis contributes toward the design of a quality-of-service (QoS) aware network layer for wireless ad hoc networks. With the lack of an infrastructure in ad hoc networks, the role of the network layer is not only to perform multihop routing between a source node and a destination node, but also to establish an end-to-end connection between communicating peers that satisfies the service level requirements of multimedia applications running on those peers. Wireless ad hoc networks represent autonomous distributed systems that are infrastructure-less, fully distributed, and multi-hop in nature. Over the last few years, wireless ad hoc networks have attracted significant attention from researchers. This has been fueled by recent technological advances in the development of multifunction and low-cost wireless communication gadgets. Wireless ad hoc networks have diverse applications spanning several domains, including military, commercial, medical, and home networks. Projections indicate that these self-organizing wireless ad hoc networks will eventually become the dominant form of the architecture of telecommunications networks in the near future. Recently, due to increasing popularity of multimedia applications, QoS support in wireless ad hoc networks has become an important yet challenging objective. The challenge lies in the need to support the heterogeneous QoS requirements (e.g., data rate, packet loss probability, and delay constraints) for multimedia applications and, at the same time, to achieve efficient radio resource utilization, taking into account user mobility and dynamics of multimedia traffic. In terms of research contributions, we first present a position-based QoS routing framework for wireless ad-hoc networks. The scheme provides QoS guarantee in terms of packet loss ratio and average end-to-end delay (or throughput) to ad hoc networks loaded with constant rate traffic. Via cross-layer design, we apply call admission control and temporary bandwidth reservation on discovered routes, taking into consideration the physical layer multi-rate capability and the medium access control (MAC) interactions such as simultaneous transmission and self interference from route members. Next, we address the network-layer resource allocation where a single-hop ad hoc network is loaded with random traffic. As a starting point, we study the behavior of the service process of the widely deployed IEEE 802.11 DCF MAC when the network is under different traffic load conditions. Our study investigates the near-memoryless behavior of the service time for IEEE 802.11 saturated single-hop ad hoc networks. We show that the number of packets successfully transmitted by any node over a time interval follows a general distribution, which is close to a Poisson distribution with an upper bounded distribution distance. We also show that the service time distribution can be approximated by the geometric distribution and illustrate that a simplified queuing system can be used efficiently as a resource allocation tool for single hop IEEE 802.11 ad hoc networks near saturation. After that, we shift our focus to providing probabilistic packet delay guarantee to multimedia users in non-saturated IEEE 802.11 single hop ad hoc networks. We propose a novel stochastic link-layer channel model to characterize the variations of the IEEE 802.11 channel service process. We use the model to calculate the effective capacity of the IEEE 802.11 channel. The channel effective capacity concept is the dual of the effective bandwidth theory. Our approach offers a tool for distributed statistical resource allocation in single hop ad hoc networks, which combines both efficient resource utilization and QoS provisioning to a certain probabilistic limit. Finally, we propose a statistical QoS routing scheme for multihop IEEE 802.11 ad hoc networks. Unlike most of QoS routing schemes in literature, the proposed scheme provides stochastic end-to-end delay guarantee, instead of average delay guarantee, to delay-sensitive bursty traffic sources. Via a cross-layer design approach, the scheme selects the routes based on a geographical on-demand ad hoc routing protocol and checks the availability of network resources by using traffic source and link-layer channel models, incorporating the IEEE 802.11 characteristics and interaction. Our scheme extends the well developed effective bandwidth theory and its dual effective capacity concept to multihop IEEE 802.11 ad hoc networks in order to achieve an efficient utilization of the shared radio channel while satisfying the end-to-end delay bound.

Characteristics of wireless home and office services and the corresponding networking issues are discussed. Local Area Networking (LAN) and Personal Area Networking (PAN) technologies such as IEEE 802.11 and Ultra Wideband (UWB) are introduced. IEEE 802.11a and UWB systems are susceptible to interference from each other due to their overlapping frequencies. The major contribution of this work is to provide a framework for coexistence of the two systems. The interference between the two systems is evaluated theoretically by developing analytical models, and by simulations. It is shown that the interference from UWB on IEEE 802.11a systems is generally insignificant. IEEE 802.11a interference on UWB systems, however, is very critical and can significantly increase the bit error rate (BER) and degrade the throughput of the UWB system. A novel idea in the MAC layer is presented to mitigate this interference by means of temporal separation. Simulation results validate our technique. Implications to wireless home services such as high definition television (HDTV) are provided. Future research directions are discussed.

It is a future trend to include the function of wireless networking in portable electronic devices, such as notebooks, tablet PC, PDA, mobile phone, and other information applicants. IEEE 802.11 is the most popular wireless LAN protocol that defines the functions in the medium access control (MAC) layer and physical layer. In this thesis, we design and implement a flexible and reusable soft IP (Intellectual Property) for wireless MAC that is compatible with AMBA system and can be used in SOC applications. The wireless MAC supports buffer descriptors, interrupt and DMA. The IP provides an AMBA-compatible interface for the host system bus, and provides a communication interface for the baseband processor in the physical layer.

Ad hoc network is a new tendency of data transmission in the future. Because of the convenience and necessity of mobile phone and/or portable computer coupled with wireless data services, TCP/IP has become an important topic for the study in wireless networks. However, there were a few difficulties in data transmission that must be overcome due to ad hoc environments and the characteristics of the IEEE 802.11 protocols. In these protocols, MAC layer is our primary research topic. Based on the RTS/CTS signal of dynamic retransmission [4], this study presented an improvement to solve the problems: (1) media resources was easily robbed due to the RTS/CTS signal competition, (2) data frame would be dropped by the IEEE 802.11 protocol due to too many times collisions. In addition, this study modifies the CWND in TCP layer in accordance with congestion conditions. Sender can transmit data packets to the network, in which resources can be completely utilized without any waste or loss. We also use the related parameters from the IP and TCP header to calculate flow numbers. The calculated parameters are recorded in IP and TCP header, and then instantly forwarded to the receiver via routers. The receiver can forward these parameters back to the sender by using back transmission method. The simulation result shows that the proposed methods can effectively improve TCP performance, such as packet loss rate, and fastly increase the CWND, the buffer utilization, and so forth. Thus, the network can perform more effectively while using the MAC-layer RTS/CTS signal.

Les réseaux sans fil constituent de plus en plus une technologie émergente permettant à ses utilisateurs<br />un accès à l'information et aux services électroniques indépendamment de leurs positions<br />géographiques. Le succès de ce type de réseaux est suscité par un grand intérêt de la part des particuliers,<br />des entreprises et du milieu industriel. Les débits atteints actuellement avec les réseaux<br />sans fil rendent possible le transfert de flux multimédia soumis à de fortes contraintes. Ainsi, le<br />respect de certaines contraintes telles que la bande passante, le délai ou encore le taux de pertes<br />de paquets devient primordial. Cependant, les solutions qui ont été introduites dans le monde des<br />réseaux filaires deviennent inadaptées pour des réseaux utilisant un médium radio partagé sans aucune<br />administration centralisée.<br />Dans ce cadre, plusieurs travaux concernant l'étude de la qualité de service (QoS) dans les réseaux<br />sans fil et notamment les réseaux ad hoc ont été réalisés afin de définir des modèle de QoS, des protocoles<br />d'accès au médium, des protocoles de routage avec QoS et des protocoles de signalisation. Pour<br />cela, notre premier objectif a été l'étude des différents mécanismes de QoS. Ce travail se place donc,<br />dans le cadre de la QoS et la proposition de mécanismes permettant d'offrir des solutions optimales<br />à des applications sensibles à certains facteurs de QoS. L'autre contribution de ce travail se situe<br />dans l'intégration du concept de l'ingénierie du trafic dans les réseaux ad hoc. En effet, ce concept<br />nous a permis de proposer des mécanismes offrant des services différenciés afin d'assurer la QoS dans<br />ces réseaux. De même, nous avons proposé de nouveaux mécanismes d'ordonnancement dans le but<br />de gérer les différents types de flux passant par la couche MAC du standard IEEE 802.11. Enfin, la<br />dernière contribution a été la proposition de solutions d'équilibrage de charge, d'ingénierie de trafic<br />et la validation des différents résultats par le biais de simulations et de preuves mathématiques.

Das Ziel dieser Arbeit ist es, ein Handover-Verfahren für ein Siemens Handset zu entwickeln. Die Entwicklungsumgebung beruht auf den Wireless-LAN Standards 802.11 der IEEE (Institute of Electrical and Electronics Engineers). Dabei liegen die Schwerpunkte auf den Standardisierungen 802.11f und 802.11i, wobei sich eine neue Arbeitsgruppe (IEEE 802.11r) direkt mit dem Thema "Handover" beschäftigen wird. Das Handset soll selbständig die Verwaltung und Einleitung des Handovers übernehmen und lediglich insofern vom Access Point unterstützt werden, dass dieser als Informationssammler dient und somit Entscheidungshilfen geben kann.

Thesis (M.S. in Computer Science and M.S. in Electrical Engineering)--Naval Postgraduate School, March 2004. / Thesis advisor(s): Gilbert M. Lundy, Roberto Cristi. Includes bibliographical references (p. 95-97). Also available online.