Les xarxes WLANs possibiliten un accés de banda ampla a Internet des d'un terminal mòbil, essent una possible solució alternativa a les xarxes cel·lulars. Tanmateix, aquest tipus de tecnologia presenta certes limitacions, com és la difícil coexistència entre fluxos de tràfic rígids (VoIP) i fluxos de tràfic elàstic (TCP), degut al propi protocol d'accés al medi. En aquesta tesi es proposa la utilització d'un nou mecanisme de control d'admissió que utilitzant el nou estàndard de qualitat de servei en xarxes WLAN (EDCA). La utilització del mecanisme de control d'admissió millora notablement les prestacions que es poden obtenir de la xarxa, solucionant les diferents limitacions de la tecnologia. Per a l'avaluació i optimització del mecanisme de control d'admissió s'ha desenvolupat un conjunt d'eines matemàtiques que permeten capturar tant la dinàmica del protocol d'accés com el comportament dels diferents fluxos de tràfic multimèdia que s'han consideren (VoIP i tràfic elàstic, TCP). / WLANs provide a broadband access to Internet from a mobile terminal, which can be a possible alternative solution to cellular networks. However, this technology presents several limitations, as it is the difficult coexistence between rigid traffic flows (VoIP) and elastic traffic flows (TCP), due to the medium access protocol itself. In this thesis a new admission control mechanism is proposed. It uses the set of QoS mechanisms provided by the new EDCA standard. The use of the proposed admission control mechanism improves the overall WLAN performance, solving the different technology limitations. In order to be able to evaluate and optimize the admission control mechanism, several mathematical tools have been developed in order to capture the dynamics of both, the access protocol and of the different multimedia traffic flows that have been considered.

L’objectif de ce travail est l’amélioration de la qualité de service (QdS) dans les réseaux sans fil ad-hoc avec équité. La QdS dans les réseaux sans fil ad-hoc est actuellement définie par la norme IEEE802.11e (EDCA). Elle permet de garantir l’accès prioritaire aux ressources pour le trafic de priorité élevé (trafic temps réel et trafic multimédia). Elle est mise en œuvre dans chaque station par la classification des paquets dans différentes file d'attente caractérisant chacune une classe de trafic à laquelle est associée une priorité de traitement. Toutefois, EDCA n’est pas un protocole équitable. En effet, lorsque un nœud participe au routage du trafic des ces voisins, son trafic propre se trouve réduit. Pour résoudre ce problème, nous proposons un nouveau modèle appelé F-EDCA. Ce modèle permet à un nœud routeur d’accéder plus régulièrement au réseau en fonction de son taux d’occupation. Une autre forme de non équité résulte de la position d’un nœud source par rapport au nœud destination. Plus le nœud source est éloigné, moins il a de bande passante. Pour résoudre ce problème, nous proposons FQ-EDCA. Il améliore la QdS en distinguant dans chaque classe de trafic, une file d’attente par source de trafic. Le modèle met alors en œuvre des techniques d’ordonnancement équitable en se basant sur la technique du temps virtuel. Ainsi, les ressources sont allouées équitablement entre tous les nœuds. F-EDCA et FQ-EDCA sont mis en œuvre et évaluées de manière comparative avec EDCA. Ce travail montre que chacun d'eux améliore EDCA et pourrait allouer équitablement les ressources dans des conditions différentes et augmenter la garantie de la QdS / This thesis aims to enhance the quality of service (QoS) in wireless ad-hoc networks with fairness. The QoS in wireless ad-hoc networks is referred to the standard IEEE802.11e (EDCA) to guarantee the high priority traffic (i.e. Multimedia and Real-time traffics). Further, the QoS is managed in each station by differentiating the packets in categories to be queued depending on their priorities. Then, these packets will access the channel in different waiting time. However, EDCA cannot control the heavy traffic caused by the ill-behaved users. So, if the traffic is regulated with fairness, it could resolve some of networks’ problems like the congestion and starvation. These problems degrade the QoS guarantee, because the ill-behaved sources consume the majority of the allocated resources. That leads to some of source nodes suffer from the lack of bandwidth and unfairness. So, without a proper control mechanism, it could decrease the QoS guarantees. Therefore, we propose (FQ-EDCA) that is a Fairness Queuing model for EDCA. It enhances the QoS by implementing scheduling techniques and improving the architecture of EDCA. Thereby, the traffic is regulated between the source nodes by separating the ill-behaved sources. Thus, the resources are allocated fairly between all the source nodes. Further, a fairness model (F-EDCA) is proposed to differentiate between two source nodes. One of them is routing packets of its neighbors and the other is only sending its packets. Both of these models are implemented and evaluated with EDCA. As a consequence, each of them enhances EDCA, could allocate the resources with fairness in different conditions and increase the QoS guarantee

Doctor of Philosopy (PhD) / Wireless communication always attracts extensive research interest, as it is a core part of modern communication technology. During my PhD study, I have focused on two research areas of wireless communication: IEEE 802.11 network performance analysis, and wireless cooperative retransmission. The first part of this thesis focuses on IEEE 802.11 network performance analysis. Since IEEE 802.11 technology is the most popular wireless access technology, IEEE 802.11 network performance analysis is always an important research area. In this area, my work includes the development of three analytical models for various aspects of IEEE 802.11 network performance analysis. First, a two-dimensional Markov chain model is proposed for analysing the performance of IEEE 802.11e EDCA (Enhanced Distributed Channel Access). With this analytical model, the saturated throughput is obtained. Compared with the existing analytical models of EDCA, the proposed model includes more correct details of EDCA, and accordingly its results are more accurate. This better accuracy is also proved by the simulation study. Second, another two-dimensional Markov chain model is proposed for analysing the coexistence performance of IEEE 802.11 DCF (Distributed Coordination Function) and IEEE 802.11e EDCA wireless devices. The saturated throughput is obtained with the proposed analytical model. The simulation study verifies the proposed analytical model, and it shows that the channel access priority of DCF is similar to that of the best effort access category in EDCA in the coexistence environment. The final work in this area is a hierarchical Markov chain model for investigating the impact of data-rate switching on the performance of IEEE 802.11 DCF. With this analytical model，the saturated throughput can be obtained. The simulation study verifies the accuracy of the model and shows the impact of the data-rate switching under different network conditions. A series of threshold values for the channel condition as well as the number of stations are obtained to decide whether the data-rate switching should be active or not. The second part of this thesis focuses on wireless cooperative retransmission. In this thesis, two uncoordinated distributed wireless cooperative retransmission strategies for single-hop connection are presented. In the proposed strategies, each uncoordinated cooperative neighbour randomly decide whether it should transmit to help the frame delivery depending on some pre-calculated optimal transmission probabilities. In Strategy 1, the source only transmits once in the first slot, and only the neighbours are involved in the retransmission attempts in the subsequent slots. In Strategy 2, both the source and the neighbours participate in the retransmission attempts. Both strategies are first analysed with a simple memoryless channel model, and the results show the superior performance of Strategy 2. With the elementary results for the memoryless channel model, a more realistic two-state Markov fading channel model is used to investigate the performance of Strategy 2. The simulation study verifies the accuracy of our analysis and indicates the superior performance of Strategy 2 compared with the simple retransmission strategy and the traditional two-hop strategy.

L'objectif de ce travail est l'amélioration de la qualité de service (QdS) dans les réseaux sans fil ad-hoc avec équité. La QdS dans les réseaux sans fil ad-hoc est actuellement définie par la norme IEEE802.11e (EDCA). Elle permet de garantir l'accès prioritaire aux ressources pour le trafic de priorité élevé (trafic temps réel et trafic multimédia). Elle est mise en œuvre dans chaque station par la classification des paquets dans différentes file d'attente caractérisant chacune une classe de trafic à laquelle est associée une priorité de traitement. Toutefois, EDCA n'est pas un protocole équitable. En effet, lorsque un nœud participe au routage du trafic des ces voisins, son trafic propre se trouve réduit. Pour résoudre ce problème, nous proposons un nouveau modèle appelé F-EDCA. Ce modèle permet à un nœud routeur d'accéder plus régulièrement au réseau en fonction de son taux d'occupation. Une autre forme de non équité résulte de la position d'un nœud source par rapport au nœud destination. Plus le nœud source est éloigné, moins il a de bande passante. Pour résoudre ce problème, nous proposons FQ-EDCA. Il améliore la QdS en distinguant dans chaque classe de trafic, une file d'attente par source de trafic. Le modèle met alors en œuvre des techniques d'ordonnancement équitable en se basant sur la technique du temps virtuel. Ainsi, les ressources sont allouées équitablement entre tous les nœuds. F-EDCA et FQ-EDCA sont mis en œuvre et évaluées de manière comparative avec EDCA. Ce travail montre que chacun d'eux améliore EDCA et pourrait allouer équitablement les ressources dans des conditions différentes et augmenter la garantie de la QdS

As users become more comfortable using IEEE 802.11 Wireless Local Area Networks, the need for quality of service is becoming more important because of the lack of support in current standards and the increase of multimedia traffic over the Internet. The IEEE 802.11 working group has recognized this fact proposing the Enhanced Distributed Channel Access (EDCA), a priority-based distributed scheme meant to provide service differentiation. EDCA relies on either different Arbitrary Interframe Space (AIFS), or Contention Window (CW) parameters, or both to provide service differentiation. In this thesis, a performance evaluation of the EDCA using five different combinations of the above mentioned parameters is included and compared to the current DCF (Distributed Coordination Function) standard, which is used as the base case. Simulation results show that simpler schemes based on one parameter alone can provide good average service differentiation. However, only multiparameter schemes provide the average and instantaneous high throughput and low delay values needed to support streaming applications. Starvation is a problem spanning all these schemes. It is especially more pronounced in schemes using combinations of parameters. In this thesis, a measurement-based admission control mechanism is proposed to overcome the above stated problems. The admission control mechanism uses an algorithm that admits a flow depending on the jitter values for high priority traffic and the throughput of the low priority traffic. It also allows the administrator to set the bandwidth sharing policy between the high priority traffic and low priority traffic. Results show that the admission control mechanism not only protects existing high priority flows from jitter and low priority flows from starvation, but also improves upon the network utilization.

隨著行動通訊日漸普及，愈來愈多使用者希望能夠在任何時間、任何地點，不受限制地使用他們所需的服務。但是由於IEEE 802.11通訊協定的限制，導致使用者無法獲得適當的服務品質保障，特別是使用者在享受即時性的服務，例如：網路電話、視訊會議、線上即時影音等。雖然在2001年IEEE提出802.11e草案，提供具有服務品質的無線通訊協定，但是在服務品質的效能方面表現並非完美，特別是在隨時變化的真實網路中。我們提出一個隨時根據網路狀況動態調整系統參數且容易實作並相容於IEEE 802.11e網路下的新機制。根據實驗模擬結果中，我們可以看到我們所提出的方法提供比EDCA更好的服務品質，就語音方面的延遲而言，我們減少約80%，就視訊方面的延遲，我們改善約25%，而輸出量方面約增加45%的效能，並且提高系統約6% - 40%最大的容納數。而我們也導入了允入控管，根據事先模擬的結果及設定的系統參數門檻，達到允入控管的目地，確保系統所提供的服務品質能夠滿足使用者的需求。 / Wireless LANs (WLANs) based on the IEEE 802.11 family have recently become popular for allowing high data rates at relatively low cost. However, due to the limitation of 802.11 DCF, they are not suitable for real-time service and do not support service differentiation. To expand providing applications with quality of service (QoS) requirements in WLANs, the IEEE 802.11E Task Group was formed to enhance the current 802.11 medium access control (MAC) protocol. In real networks, the network condition is dynamic. The 802.11e cannot reach high performance of QoS. Besides, design of efficient MAC protocols with both high-throughput and low-jitter performance is the major focus in distributed contention-based MAC protocol research. In view of this, we propose a new and applicable approach, called Dynamic-EDCA (D-EDCA), adjusts the parameters of system based on the network condition. The result of　simulation shows that in comparison with EDCA, our proposed algorithm improves total throughput more than 45%, and the maximum of connection more than 40%. It also reduces voice delay about 80%, and video delay about 25%. Thus, the proposed D-EDCA utilizes bandwidth more efficiently and improves performance for service differentiation.

Doctor of Philosopy (PhD) / Wireless communication always attracts extensive research interest, as it is a core part of modern communication technology. During my PhD study, I have focused on two research areas of wireless communication: IEEE 802.11 network performance analysis, and wireless cooperative retransmission. The first part of this thesis focuses on IEEE 802.11 network performance analysis. Since IEEE 802.11 technology is the most popular wireless access technology, IEEE 802.11 network performance analysis is always an important research area. In this area, my work includes the development of three analytical models for various aspects of IEEE 802.11 network performance analysis. First, a two-dimensional Markov chain model is proposed for analysing the performance of IEEE 802.11e EDCA (Enhanced Distributed Channel Access). With this analytical model, the saturated throughput is obtained. Compared with the existing analytical models of EDCA, the proposed model includes more correct details of EDCA, and accordingly its results are more accurate. This better accuracy is also proved by the simulation study. Second, another two-dimensional Markov chain model is proposed for analysing the coexistence performance of IEEE 802.11 DCF (Distributed Coordination Function) and IEEE 802.11e EDCA wireless devices. The saturated throughput is obtained with the proposed analytical model. The simulation study verifies the proposed analytical model, and it shows that the channel access priority of DCF is similar to that of the best effort access category in EDCA in the coexistence environment. The final work in this area is a hierarchical Markov chain model for investigating the impact of data-rate switching on the performance of IEEE 802.11 DCF. With this analytical model，the saturated throughput can be obtained. The simulation study verifies the accuracy of the model and shows the impact of the data-rate switching under different network conditions. A series of threshold values for the channel condition as well as the number of stations are obtained to decide whether the data-rate switching should be active or not. The second part of this thesis focuses on wireless cooperative retransmission. In this thesis, two uncoordinated distributed wireless cooperative retransmission strategies for single-hop connection are presented. In the proposed strategies, each uncoordinated cooperative neighbour randomly decide whether it should transmit to help the frame delivery depending on some pre-calculated optimal transmission probabilities. In Strategy 1, the source only transmits once in the first slot, and only the neighbours are involved in the retransmission attempts in the subsequent slots. In Strategy 2, both the source and the neighbours participate in the retransmission attempts. Both strategies are first analysed with a simple memoryless channel model, and the results show the superior performance of Strategy 2. With the elementary results for the memoryless channel model, a more realistic two-state Markov fading channel model is used to investigate the performance of Strategy 2. The simulation study verifies the accuracy of our analysis and indicates the superior performance of Strategy 2 compared with the simple retransmission strategy and the traditional two-hop strategy.

This master thesis includes a short review of the structure of WLAN (Wireless Local Area Network) technologies 802.11a/b/g, the description of their physical interface and the description of the basic medium access control mechanisms implementing the PCF (Point Coordination Function) and DCF (Distributed Coordination Function) methods. I mainly focused on the detailed evaluation the new 802.11e standard which was designed to efficiently support real-time services in wireless environment. To provide QoS (Quality of Service) support, this standard specifies the EDCA (Ehanced Distributed Channel Access) and HCF (Hybrid Coordination Function) medium access control methods for the shared wireless environment. The next chapter of my work is devoted to the verification of the theoretical results in OPNET Modeler simulation environment. I studied in details the WLAN model available in OPNET Modeler, the effect of data-flow classification into separate categories and the configuration of several access method parameters. Next, I created my own WLAN model according to the 802.11e standard. This model contains four applications two of them with real-time requirements. The model is divided into several scenarios, each focusing on different aspects of wireless network technologies like QoS support and it´s dependency on the number of clients, mobility of wireless terminals and comparison of the 802.11a/b/g and the 802.11e technology.

This master thesis deals with creating laboratory exercises for students in simulator NS-3, where the IPv4 and IPv6 protocols, unicast and multicast transmission types, quality of services in wireless networks, furthermore protocols TCP and UDP are analyzed. The first section describes the NS-3 network simulator, the Eclipse development environment and the method how to connect them. In the next section protocols IPv4 and IPv6 are presented, the structure of the headers and the technique of fragmentation are described in detail. Based on this a laboratory exercise is created which deals with comparison of protocols IPv4 and IPv6. In the next section the types of transmissions are described, furthermore the multicast transmission type is explained more in detail. In the next practical section the second laboratory exercise is created, which deals with comparison of unicast and multicast transmission types. The subject of the following section is ensuring quality of services in data networks, the EDCA access method is discussed more in detail. In the next section the EDCA access method is implemented in a simulation as a laboratory exercise, in which the impact of the access category of EDCA to different transmission parameters is investigated. The next section deals with protocols TCP and UDP, furthermore with the structure of their headers. In the last section a laboratory exercise is created, in which the properties of the protocols TCP and UDP are compared.

Aquesta tesi suggereix usar un compte enrere determinista després de les transmissions exitoses en les xarxes d'àrea local sense fils. Com que les estacions que han transmès amb èxit en el seu darrer intent no poden col·lisionar entre elles en el seu proper intent, el nombre de col·lisions es redueix. Per tant, anomenem el protocol accés múltiple per detecció de portadora amb evitament de col·lisions millorat. El protocol es modela i es simula en diversos escenaris per a la seva avaluació. S'arriba a la conclusió de que el protocol proposat ofereix un rendiment igual o major que l'existent. / This thesis suggests the use of a deterministic backoff after successful transmissions in the MAC protocol of WLANs. Since those stations that successfully transmitted in their last collision attempt cannot collide among them in their next transmission attempt, the number of collisions is reduced. Hence, the protocol is called Carrier Sense Multiple Access with Enhanced Collision Avoidance. The protocol is modelled and simulations are used to assess its performance in a variety of scenarios. It is concluded that the proposed protocol performs always equal or better than the legacy one.