Saturation Throughput Analysis of IEEE 802.11 in Presence of Non Ideal Transmission Channel and Capture Effects

In this paper, we provide a saturation throughput analysis of the IEEE 802.11 protocol at the data link layer by including the impact of both transmission channel and capture effects in Rayleigh fading environment. Impacts of both non-ideal channel and capture effects, specially in an environment of high interference, become important in terms of the actual observed throughput. As far as the 4-way handshaking mechanism is concerned, we extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel. This way, any channel model characterizing the physical transmission medium can be accommodated, including AWGN and fading channels. We also extend the Markov model in order to consider the behavior of the contention window when employing the basic 2-way handshaking mechanism. Under the usual assumptions regarding the traffic generated per node and independence of packet collisions, we solve for the stationary probabilities of the Markov chain and develop expressions for the saturation throughput as a function of the number of terminals, packet sizes, raw channel error rates, capture probability, and other key system parameters. The theoretical derivations are then compared to simulation results confirming the effectiveness of the proposed models.Comment: To appear on IEEE Transactions on Communications, 200

Unsaturated Throughput Analysis of IEEE 802.11 in Presence of Non Ideal Transmission Channel and Capture Effects

In this paper, we provide a throughput analysis of the IEEE 802.11 protocol at the data link layer in non-saturated traffic conditions taking into account the impact of both transmission channel and capture effects in Rayleigh fading environment. The impact of both non-ideal channel and capture become important in terms of the actual observed throughput in typical network conditions whereby traffic is mainly unsaturated, especially in an environment of high interference. We extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel, along with a state characterizing the system when there are no packets to be transmitted in the buffer of a station. Finally, we derive a linear model of the throughput along with its interval of validity. Simulation results closely match the theoretical derivations confirming the effectiveness of the proposed model.Comment: To appear on IEEE Transactions on Wireless Communications, 200

Final report on the evaluation of RRM/CRRM algorithms

Deliverable public del projecte EVERESTThis deliverable provides a definition and a complete evaluation of the RRM/CRRM algorithms selected in D11 and D15, and evolved and refined on an iterative process. The evaluation will be carried out by means of simulations using the simulators provided at D07, and D14.Preprin

Advanced Wireless LAN

The past two decades have witnessed starling advances in wireless LAN technologies that were stimulated by its increasing popularity in the home due to ease of installation, and in commercial complexes offering wireless access to their customers. This book presents some of the latest development status of wireless LAN, covering the topics on physical layer, MAC layer, QoS and systems. It provides an opportunity for both practitioners and researchers to explore the problems that arise in the rapidly developed technologies in wireless LAN

Internet Access and QoS in Ad Hoc Networks

It is likely that the increased popularity of wireless local area networks (WLANs) together with the continuous technological advances in wireless communication, also increase the interest for ad hoc networks. An ad hoc network is a wireless, autonomous, infrastructure-less network composed of stations that communicate with each other directly in a peer-to-peer fashion. When discussing mobile ad hoc networks (MANETs), we often refer to an ad hoc network where the stations cooperate in forwarding packets on behalf of each other to allow communication beyond their transmission range over multi-hop paths. In order to realize the practical benefits of ad hoc networks, two challenges (among others) need to be considered: distributed quality of service (QoS) guarantees and multi-hop Internet access. This thesis presents conceivable solutions to both of these problems. The first two papers focus on the network layer and consider the provisioning of Internet access to ad hoc networks whereas the last two papers focus on the data link layer and investigate the provisioning of QoS to ad hoc networks. The first paper studies the interconnection between a MANET and the Internet. In addition, it evaluates three approaches for gateway discovery, which can be initiated by the gateway (proactive method), by the mobile station (reactive method) or by mixing these two approaches (hybrid method). The second paper also studies Internet access for MANETs, but with focus on micro mobility, i.e. mobile stations moving from one gateway to another. In particular, it evaluates a solution that allows mobile stations to access the Internet and roam from gateway to gateway. The third paper, gives an overview of the medium access mechanisms in IEEE 802.11 and their QoS limitations. Moreover, it proposes an enhancement to the contention-free medium access mechanism of IEEE 802.11e to provide QoS guarantees in WLANs operating in ad hoc network configuration. The fourth paper continues the work from the third paper by enhancing the scheme and dealing with the problems that occur due to hidden stations. Furthermore, it discusses how to deal with the problems that occur when moving from single-hop ad hoc networks (i.e. WLANs in ad hoc network configuration) to multi-hop ad hoc networks

Optimization of the interoperability and dynamic spectrum management in mobile communications systems beyond 3G

The future wireless ecosystem will heterogeneously integrate a number of overlapped Radio Access Technologies (RATs) through a common platform. A major challenge arising from the heterogeneous network is the Radio Resource Management (RRM) strategy. A Common RRM (CRRM) module is needed in order to provide a step toward network convergence. This work aims at implementing HSDPA and IEEE 802.11e CRRM evaluation tools. Innovative enhancements to IEEE 802.11e have been pursued on the application of cross-layer signaling to improve Quality of Service (QoS) delivery, and provide more efficient usage of radio resources by adapting such parameters as arbitrary interframe spacing, a differentiated backoff procedure and transmission opportunities, as well as acknowledgment policies (where the most advised block size was found to be 12). Besides, the proposed cross-layer algorithm dynamically changes the size of the Arbitration Interframe Space (AIFS) and the Contention Window (CW) duration according to a periodically obtained fairness measure based on the Signal to Interference-plus-Noise Ratio (SINR) and transmission time, a delay constraint and the collision rate of a given machine. The throughput was increased in 2 Mb/s for all the values of the load that have been tested whilst satisfying more users than with the original standard. For the ad hoc mode an analytical model was proposed that allows for investigating collision free communications in a distributed environment. The addition of extra frequency spectrum bands and an integrated CRRM that enables spectrum aggregation was also addressed. RAT selection algorithms allow for determining the gains obtained by using WiFi as a backup network for HSDPA. The proposed RAT selection algorithm is based on the load of each system, without the need for a complex management system. Simulation results show that, in such scenario, for high system loads, exploiting localization while applying load suitability optimization based algorithm, can provide a marginal gain of up to 450 kb/s in the goodput. HSDPA was also studied in the context of cognitive radio, by considering two co-located BSs operating at different frequencies (in the 2 and 5 GHz bands) in the same cell. The system automatically chooses the frequency to serve each user with an optimal General Multi-Band Scheduling (GMBS) algorithm. It was shown that enabling the access to a secondary band, by using the proposed Integrated CRRM (iCRRM), an almost constant gain near 30 % was obtained in the throughput with the proposed optimal solution, compared to a system where users are first allocated in one of the two bands and later not able to handover between the bands. In this context, future cognitive radio scenarios where IEEE 802.11e ad hoc modes will be essential for giving access to the mobile users have been proposed

TDMAとDCFの組み合わせによるアドホックネットワーク上でのQoS通信の実現方式

　An ad hoc network does not rely on the fixed network infrastructure; it uses a distributed network management method. With the popularity of the smart devices, ad hoc network has received more and more attention, supporting QoS in ad hoc network has become inevitable. Many researches have been done for provision of QoS in ad hoc networks. These researches can be divided into three types.　The first type is contention-based approach which is the most widely used. IEEE 802.11e MAC (media access control) protocol belongs to this type which is an extension of IEEE 802.11 DCF(Distributed Coordination Function). It specifies a procedure to guarantee QoS by providing more transmission opportunities for high priority data. However, since IEEE 802.11eis designed based on the premise that access points are used, when the number of QoS flows increases, packet collisions could occur in multi-hop ad hoc network.　The second type is using TDMA-based approach. The TDMA approach can provide contention-free access for QoS traffics through the appropriate time slot reservation. The current TDMA approaches reserve time slots for both QoS traffics and best-effort traffics. However, it is difficult for TDMA as the only approach to allocating channel access time for best-effort traffics sincet he required bandwidth of the best-effort traffics changes frequently.　We propose a QoS scheme, which takes advantage of both contention-based approach and TDMA-based approach. In the proposed scheme, contention-based approach DCF provides easy and fair channel time for best-effort traffics, and TDMA approach serves the QoS traffics. A time frame structure is designed to manage the bandwidth allocation. A time frame is divided into two periods, specifically the TDMA periods and the DCF periods. The proportion of two periods is decided by QoS traffics. Therefore the QoS traffics are given absolutely higher priority than best-effort traffics. In order to guarantee the transmission of each QoS packet in TDMA period, a time slot assignment algorithm based on QoS data rate has been proposed. The proposed scheme also employs an admission control scheme, which rejects the new QoS user when the channel capacity is reached. In addition, we provide the configuration of the proposed scheme in the mobile environment. The procedures are designed for route changes and new-adding users. 　The proposed scheme is simulated in the QualNet simulator. In the static environment, the performance of the proposed scheme is evaluated in the case of a gradual increase in the number TCP flows and in the case of gradual increase in QoS data rate. Simulation results show that in the static environment the proposed scheme can not only provide effective QoS performance, but also can provide good support for best-effort flows. In the mobile environment, we simulated the performance of the proposed scheme at different moving speed (maximum is 5 Km/h) when the ARF (Auto Rate Fallback) is available. From the simulation results, in a specific mobile environment, the proposed scheme can support the QoS transmission well.電気通信大学201

Analysis and design of efficient techniques for video transmission in IEEE 802.11 wireless ad hoc networks

[EN] Wireless mobile ad ho networks, also known as MANETs, are omposed by independent mobile stations that ommuni ate without requiring any sort of infrastru ture for support. These networks are hara terized by variable bandwidth values and frequent path breaks, whi h are due to hannel noise, interferen e between stations and mobility. Su h fa tors require significant adaptation apabilites at different levels of the proto ol suites employed, enabling stations to qui kly respond to fast- hanging network onditions. Resear h on the most adequate proto- ols for the physi al, MAC and routing layers is still on-going, though some basi onsensus has already been rea hed and several testbeds have been setup around the world. To deploy real-time multimedia servi es, namely voi e and video, on top of su h an unreliable network environment is a very hallenging task. In this thesis we propose to a hieve that goal starting from urrently available Wi-Fi te hnology, and gradually finding the most adequate enhan ements to ea h proto ol layer of interest; we then ombine these enhan ements until we a hieve a omplete QoS framework for ad ho networks. By using urrently available te hnology we assure that the proposal of this thesis has an inherent high-level of appli ability on real life environments. Sin e our working field fo uses on video transmission over wireless ad ho networks, we will show how it is possible to support several QoS- onstrained video streams in MANET environments hara terized by moderate to high mobility levels, and by a significant amount of best efort traffic[ES] Las redes inalámbricas ad hoc, también conocidas como redes MANET, están compuestas por un conjunto de estaciones móviles independientes capaces de omunicarse entre sí sin necesidad de ningún tipo de infraestructura común de comunicaciones. Estas redes se caracterizan por tener un ancho de banda variable y pérdidas frecuentes de ruta que se pueden atribuir al ruido del anal inalámbrico, a la interferencia entre las estaciones móviles o bien a la movilidad de las estaciones. Dichos factores requieren una gran capacidad de adaptación en las diferentes capas de la arquitectura de protocolos, permitiendo a una estación responder rápidamente a posibles cambios bruscos en las condiciones de la red. A pesar de que aún se están realizando trabajos de investigación en bus a de los protocolos más adecuados para las capas físicas, a eso al medio (MAC) y encaminamiento, ha sido posible llegar a un nivel básico de consenso, lo cual ha permitido el despliegue de plataformas y entornos aplicados que utilizan tecnología de red MANET. Ofrecer servicios multimedia, como voz y vídeo, en redes con tan poca habilidad es un desafío importante. En esta tesis nos proponemos alcanzar este objetivo partiendo de la tecnología Wi-Fi actualmente disponible, encontrando de forma paulatina las mejoras más importantes en las diferentes capas de la arquitectura de red, para llegar, finalmente, a una solución integrada capaz de ofrecer calidad de servicio (QoS) en las redes MANET. Al utilizar la tecnología que disponemos actualmente nos aseguramos que las propuestas de esta tesis tengan un alto grado de aplicabilidad en entornos reales. Ya que la línea de trabajo de la tesis está aplicada a la transmisión de vídeo en redes MANET, demostraremos que es posible ofrecer calidad de servicio a varios flujos de vídeo en una red MANET caracterizada por altos grados de movilidad en sus nodos y un nivel significativo de tráfico o de tipo best effortTavares De Araujo Cesariny Calafate, CM. (2006). Analysis and design of efficient techniques for video transmission in IEEE 802.11 wireless ad hoc networks [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/135282TESI