Multiple Input Multiple Output (MIMO) systems are a key technology for next generation high speed wireless communication standards like 802.11n, WiMax etc. MIMO enables spatial multiplexing to increase channel bandwidth which requires the use of multiple antennas in the receiver and transmitter side. The increase in bandwidth comes at the cost of high silicon complexity of MIMO detectors which result, due to the intricate algorithms required for the separation of these spatially multiplexed streams. Previous implementations of MIMO detector have mainly dealt with the issue of complexity reduction, latency minimization and throughput enhancement. Although, these detectors have successfully mapped algorithms to relatively simpler circuits but still, latency and throughput of these systems need further improvements to meet standard requirements. Additionally, most of these implementations don’t deal with the requirements of reconfigurability of the detector to multiple modulation schemes and different antennae configurations. This necessary requirement provides another dimension to the implementation of MIMO detector and adds to the implementation complexity. This thesis focuses on the efficient VLSI implementation of the MIMO detector with an emphasis on performance and re-configurability to different modulation schemes. MIMO decoding in our detector is based on the fixed sphere decoding algorithm which has been simplified for an effective VLSI implementation without considerably degrading the near optimal bit error rate performance. The regularity of the architecture makes it suitable for a highly parallel and pipelined implementation. The decoder has intrinsic traits for dynamic re-configurability to different modulation and encoding schemes. This detector architecture can be easily tuned for high/low performance requirements with slight degradation/improvement in Bit Error Rate (BER) depending on needs of the overlying application. Additionally, various architectural optimizations like pipelining, parallel processing, hardware scheduling, dynamic voltage and frequency scaling have been explored to improve the performance, energy requirements and re-configurability of the design.

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This master's thesis compares wireless technologies which they are used at current time. The most of information in this thesis are obtained from my practical experiences with design and realization of wireless network during last four years. The thesis briefly describes standards and security of WiFi. More time is devoted to the description of new standard 802.11n and the E-Band. The use of E-Band is allowed in Czech Republic from a year 2008. The thesis describes a practical evaluation of wireless network 802.11a/b/g/n and E-Band. Examples of the use are described in case studies of high-speed point-to-point wireless bridge, coverage of a logistic warehouse and wireless network with location in a hospital.

This thesis deals with the investigation and assessment of communication standards LTE-Advance and WiFi (IEEE 802.11n/ac). The EVM error parameter is examined for each standard. To work with different standards a universal workplace have been proposed (testbed). This universal workplace serves for adjusting transmitting and receiving means and for processing signals transmitted and interpreted. Matlab was chosen for this work, through which only control devices such as generators and analyzers from Rohde & Schwarz. This workplace also measures the coexistence of these standards. At the conclusion of this thesis, different coexistence scenarios were designed and evaluated through testbed results.

Frame aggregation is one of the major MAC layer enhancements in the IEEE 802.11 family that boosts the network throughput performance. It aims to achieve higher throughput by transmitting huge amount of data in a single transmit oppor- tunity. With the increasing awareness of energy e ciency, it has become vital to rethink about the design of such frame aggregation protocol. Aggregation techniques help to reduce energy consumption over ideal channel conditions. However, in a noisy channel environment, a new energy-aware frame aggregation scheme is required. In this thesis, a novel Green Frame Aggregation (GFA) scheduling scheme has been proposed and evaluated. GFA optimizes the aggregate size based on channel quality in order to minimize the consumed energy. GFA selects the optimal sub-frame size that satisfies the loss constraint for real-time applications as well as the energy budget of the ideal channel situations. The design, the implementation, and evaluation of GFA using testbed deployment is done. The experimental analysis shows that GFA outperforms the conventional frame aggregation methodology in terms of energy e ciency by about 6⇥ in the presence of severe interference conditions. Moreover, GFA also outperforms the static frame sizing method in terms of network goodput and maintains almost the same end- to-end latency.

Orthogonal Frequency Division Multiplexing (OFDM) is fast gaining ground as a preferred modulation technique for short range wireless data application such as 802.11a/g, 802.15.3a and 802.16. Recently, use of multiple transmit and receive antenna for improving spectral efficiency in a wireless system has received much interest. IEEE 802.11 has set up the Work Group 802.11n to develop a standard for enhanced rate 802.11 based on OFDM using Multi Input/Multiple Output (MIMO) techniques. The most dominant proposal is the use of singular value decomposition based MIMO methods to achieve the high data rate. The selection of modulation and coding rates plays a significant role in the overall throughput of the system, more so in cases where the traffic between the transmitter and the receiver consists of short bursts and the user location is not fixed. The performance of a given modulation and coding technique depends on the channel condition. Closed form or bounding solutions exists for various modulation and coding techniques. But these techniques are not suitable for real time application where the channel is dynamic. The approach taken in this thesis is to decouple frequency selective MIMO OFDM channel into orthogonal spatial and frequency domains channels using Fast Fourier Transforms and Singular Value Decomposition. The channels can be viewed as parallel flat fading channels for which the expected BER rate can be computed. A SNR-BER table is used to efficiently compute the performance efficiently. An effective SNR is computed using the table and compared with rate threshold to select a suitable rate. Improvements of 15 dB and above are shown the link budget while using a four transmit four receive MIMO system. Proposed 802.11n TGn Sync physical layer standard is used to evaluate the performance. The performance in case of one of the systems being a legacy 802.11a/g nodes is also looked into. Gains up to 7 dB are shown in the link budget. / Master of Science

Après l'augmentation des capacités physiques des réseaux sans-fil, l'amélioration du faible rendement MAC permet aujourd'hui aux utilisateurs de bénéficier de bandes passantes inédites. Cette amélioration est notamment rendue possible par la création de systèmes d'agrégation. Or si ces systèmes permettent d'améliorer la bande passante offerte, plusieurs problématiques se posent quant à leur influence sur le comportement du système en particulier en cas de forte concurrence pour l'accès au medium. L'agrégation étudiée dans ce mémoire effectue une concaténation de plusieurs paquets dans une seule trame. Cette opération permet aux paquets de partager les en-têtes. Outre la perte de signification quant à la valeur d'un paquet, la configuration des paramètres d'un tel système reste aujourd'hui obscure pour le fournisseur d'accès. Comme les intérêts du fournisseur et de ses clients peuvent diverger, il est également nécessaire de tenir compte du compromis entre leurs exigences respectives. Afin d'adresser ces problématiques, ces travaux de thèse se concentrent sur une analyse approfondie du comportement et des implications d'un système d'agrégation de paquets (avec IEEE 802.11n pour cas d'étude). L'influence de l'agrégation sur la qualité de service offerte à une application est quantifiée au travers de plusieurs milliers de simulations effectuées avec Riverbed Modeler. Des recommandations sont ensuite proposées pour la bonne configuration du système d'agrégation dans l'optique d'optimiser les délais et l'arriéré de traitement. L'accent est mis sur les performances offertes à un flux particulier en concurrence pour le medium. Ceci dans le but de clarifier l'influence de l'agrégation sur chaque client. Cette thèse développe également un modèle analytique dudit système basé sur la théorie du calcul réseau. Les limites d'un tel modèle sont démontrées et son pessimisme est déterminé à l'aide d'une analyse fine du comportement de l'agrégation 802.11n. Cette étude démontre notamment une relative inadaptation de la théorie du calcul réseau au système d'agrégation considéré. Des ajustements de la théorie sont alors proposés, en particulier vis à vis du calcul du service rendu à un flux. Afin d'aider le fournisseur d'accès dans la configuration du système d'agrégation, cette thèse propose en dernier lieu un algorithme de configuration dynamique des paramètres d'agrégation. Cet algorithme est établi à partir des recommandations instructives établies précédemment. Son originalité repose sur la désactivation de l'agrégation en fonction de l'état des stations concurrentes. Implémenté dans Riverbed Modeler, cet algorithme montre son efficacité. De nouvelles problématiques se posent quant à son implémentation réelle (distribuée, centralisée, ...). / After the increase of the capacity of wireless networks, the improvement of the low efficiency allows users to benefit from higher bandwidths. This improvement is partly due to the creation of aggregation's systems. Now, if these systems allow to improve the offered bandwidth, several problems arise about their influence on the behavior of the system. In particular, the case of strong competition for the access to the medium remains unknown. The aggregation studied in this thesis makes a concatenation of several packets in a single frame. This operation allows the packets to share headers. Besides the loss of meaning about the value of a packet, the configuration of such a system remains today obscure for the access provider. As the interests of the provider and its customers may differ, it is also necessary to consider a compromise between their respective requirements. To address these issues, this thesis focuses on a thorough analysis of the behavior and the implications of a packet aggregation system (with IEEE 802.11n as case study). The impact of aggregation on the quality of service provided to an application is quantified through thousands of simulations with Riverbed Modeler. Recommendations are then proposed for the proper setup of the aggregation system to optimize delay and backlog. This thesis focuses on the performances offered to a particular flow in competition for the medium. Its aim is to show the influence of the aggregation on each customer. This thesis also develops an analytical model of the aggregation system using the network calculus theory. The limitations of such a model are demonstrated. Its pessimism is determined using a detailed analysis of the 802.11n aggregation. This study demonstrates a particular relative inadequacy of network calculus to the aggregation system considered. Adjustments of the theory are then proposed, particularly for the calculation of the residuel service offered to a customer. To help the access provider in the configuration of the aggregation system, this thesis lastly proposes an algorithm for a dynamic configuration of the aggregation. This algorithm is established from the recommendations previously established. Its originality is based on the deactivation of the aggregation according to the state of the competing stations. Implemented in Riverbed Modeler, this algorithm shows its efficiency. Then, new problems arise about its real implementation (distributed, centralized, ...).

Les communications sans fil sont essentielles pour les nouveaux systèmes des transports. Ainsi, ces communications sans fil doivent être capables d'opérer sans interruption quelque soit l'environnement électromagnétique (EM) dans lequel elles se trouvent. Pour cette raison, nous nous étudions comment certains environnements EM affectent les systèmes de communication. Dans cette thèse, nous nous sommes intéressés aux trains à grande vitesse. Dans ce secteur, on peut trouver des interférences EM intentionnelles (IEMI) et des interférences EM non intentionnelles (EMI). Nous avons considéré comme EMI les signaux interférences électromagnétiques transitoires produites par les pertes de contact entre la caténaire et le pantographe. Pour les IEMI, nous avons utilisé des signaux d'interférence générés par des brouilleurs. Nous avons étudié la vulnérabilité du réseau de communication IEEE 802.11n face à ces différents types d'interférences. Par la suite nous avons identifié le mécanisme d'accès au canal comme un point potentiellement vulnérable aux deux types d'interférences. En effet, une interférence de faible puissance peut faire croire que le canal est occupé, empêchant toute communication. Concernant les IEMI, nous avons remarqué que la période de balayage de la bande de fréquence du signal du brouillage est un paramètre important pour que celui-ci soit efficace. Pour les signaux EMI, nous avons identifié la période DIFS comme étant un autre paramètre vulnérable de la norme, car à partir d'un certain niveau de puissance d'interférence et dès que l'intervalle de répétition entre les transitoires est inférieur au DIFS, la communication est systématiquement interrompue. / Wireless communications are essential for new transportation systems. Thus, these wireless communications must be able to operate without interruption, regardless of the electromagnetic (EM) environment. For this reason, we study how some EM environments affect communication systems. In this thesis, we are particularly interested in the transportation sector, especially high speed trains. In this sector, both unintentional EM interferences (EMI) and intentional EM interferences (IEMI) can be found. We considered unintentional EM interferences (EMI), such as transient EM interference signals produced by contact losses between the catenary and the pantograph. For intentional EM interferences (IEMI) we used interference signals as those generated by low power commercial jammers. We have studied the vulnerability of the IEEE 802.11n communication network facing these different interference types. We identified the channel access mechanism as a vulnerable feature of IEEE 802.11n. As a matter of fact, in the presence of low power interferences, the channel can be considered busy by the channel access mechanism, preventing any communication. With regard to the IEMI, we have noticed that the sweep period of the frequency band of the jamming signal is an important parameter on the jamming performance. For transient EM interference signals, we identified the DIFS period as another vulnerable parameter of the standard. Indeed, when the repetition interval between transients is lower than DIFS period, with a certain interference power level, the communication is systematically interrupted.

<p>The wide spread use of IEEE Wireless LAN 802.11 in battery operated mobile devices introduced the need of power consumption optimization while meeting Quality-of-Service (QoS) requirements of applications connected through the wireless network. The IEEE 802.11 standard specifies a baseline power saving mechanism, hereafter referred to as standard Power Save Mode (PSM), and the IEEE 802.11e standard specifies the Automatic Power Save Delivery (APSD) enhancement which provides support for real-time applications with QoS requirements. The latest amendment to the WLAN 802.11 standard is the IEEE 802.11n standard which enables the use of much higher data rates by including enhancements in the Physical and MAC Layer. In this thesis, different 802.11n MAC power saving and QoS optimization possibilities are analyzed comparing against existing power saving mechanisms.</p><p>Initially, the performance of the existing power saving mechanisms PSM and Unscheduled-APSD (UAPSD) are evaluated using the 802.11n process model in the OPNET simulator and the impact of frame aggregation feature introduced in the MAC layer of 802.11n was analyzed on these power saving mechanisms. From the performance analysis it can be concluded that the frame aggregation will be efficient under congested network conditions. When the network congestion level increases, the signaling load in UAPSD saturates the channel capacity and hence results in poor performance compared to PSM. Since PSM cannot guarantee the minimum QoS requirements for delay sensitive applications, a better mechanism for performance enhancement of UAPSD under dynamic network conditions is proposed.</p><p>The functionality and performance of the proposed algorithm is evaluated under different network conditions and using different contention settings. From the performance results it can be concluded that, by using the proposed algorithm the congestion level in the network is reduced dynamically thereby providing a better power saving and QoS by utilizing the frame aggregation feature efficiently.</p>

The need for higher data rates in WLANs boosts drastically because tremendous consumer interest in emerging multimedia applications, such as HDTV, has been increased. Currently, the IEEE 802.11a/b/g WLANs provide a limited data rate for the current user application requirements. In order to overcome substantial limitations of the existing WLANs, the next generation of WLANs, IEEE 802.11n, is in the course of development and expected to support higher throughput, larger coverage area and better QoS. The high performance IEEE 802.11n WLAN can improve data rate significantly by using smart antenna systems in the physical layer to take advantage of multi-path fading of wireless channels. In this thesis, an analytical model is developed to study the MAC performance and the underlying smart antenna technologies used in multi-path fading channels. Multiple antennas employed in the AP arise two popular approaches to provide a significant performance improvement, diversity and multiplexing. Considering the diversity gain of multiple antennas at the AP in which the AP with multiple antennas serves one user at a time, the capacity and throughput can be obtained. In addition, the AP is possible to serve multiple users in the downlink, by exploiting the multiplexing gain of the wireless channel. We investigate the maximum network throughput when the traffic intensity of the AP approaches to one. Unlike most of previous research which focus on either the physical or the MAC layer performance, our analytical model jointly considers the MAC protocol and the smart antenna technology.