Belaidžio ryšio tinklų terpės prieigos valdymo tyrimas

Over the years, consumer requirements for Quality of Service (QoS) has been growing exponentially. Recently, the ratification process of newly IEEE 802.11ad amendment to IEEE 802.11 was finished. The IEEE 802.11ad is the newly con-sumer wireless communication approach, which will gain high spot on the 5G evolution. Major players in wireless market, such as Qualcomm already are inte-grating solutions from unlicensed band, like IEEE 802.11ac, IEEE 802.11ad into their architecture of LTE PRO (the next evolutionary step for 5G networking) (Qualcomm 2013; Parker et al. 2015). As the demand is growing both in enter-prise wireless networking and home consumer markets. Consumers started to no-tice the performance degradation due to overcrowded unlicensed bands. The un-licensed bands such as 2.4 GHz, 5 GHz are widely used for up-to-date IEEE 802.11n/ac technologies with upcoming IEEE 802.11ax. However, overusage of the available frequency leads to severe interference issue and consequences in to-tal system performance degradation, currently existing wireless medium access method can not sustain the increasing intereference and thus wireless needs a new methods of wireless medium access. The main focal point of this dissertation is to improve wireless performance in dense wireless networks. In dissertation both the conceptual and multi-band wireless medium access methods are considered both from theoretical point of view and experimental usage. The introduction chapter presents the investigated problem and it’s objects of research as well as importance of dissertation and it’s scientific novelty in the unlicensed wireless field. Chapter 1 revises used literature. Existing and up-to-date state-of-the-art so-lution are reviewed, evaluated and key point advantages and disadvantages are analyzed. Conclusions are drawn at the end of the chapter. Chapter 2 describes theoretical analysis of wireless medium access protocols and the new wireless medium access method. During analysis theoretical simula-tions are performed. Conclusions are drawn at the end of the chapter. Chapter 3 is focused on the experimental components evaluation for multi-band system, which would be in line with theoretical concept investigations. The experimental results, showed that components of multi-band system can gain sig-nificant performance increase when compared to the existing IEEE 802.11n/ac wireless systems. General conclusions are drawn after analysis of measurement results

Cross-layer analysis for video transmission over COFDM-based wireless local area networks

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Distributed Cooperative Framework and Algorithms for wireless Network Performance Optimization

In Wireless Local Access Networks (WLANs), the Medium Access Control (MAC) protocol is the primary element that determines the efficiency of sharing the limited communication bandwidth of the wireless channel. IEEE 802.11 MAC uses the contention-based Distributed Coordination Function (DCF) as a fundamental medium access mechanism. However, the dynamic nature of the wireless environment creates mobility challenges of maintaining maximum channel capacity, of obtaining optimal throughput and latency, and of retaining good security in a distributed wireless network. This dissertation first introduces a set of parameters to characterize the medium status and radio environment, and a mechanism for mobile devices to exchange measurements in order to obtain broad and comprehensive knowledge of the wireless environment. Then the dissertation proposes a distributed cooperative wireless architecture and framework, and three cooperative algorithms to optimize wireless network performance. The cooperative algorithms allow wireless devices to cooperatively adjust configurations and optimize operations based on the characteristics of the environment. The first algorithm adaptively adjusts the contention window size to reduce the number of collisions as the number of mobile devices increases, in order to reach maximum channel utilization. However, if a channel reaches the saturated state, the throughput per user decreases significantly. Therefore, the second algorithm discussed in this dissertation is to select the best Access Point (AP) in overlapped AP coverage areas to balance network loads and maximally utilize the network capacity. When the mobile device transitions from one AP to another AP, it may take milliseconds to seconds due to required re-association and re-authentication with the new AP. Thus, the third cooperative algorithm optimizes the device transition to provide an acceptable balance of latency and security. The corresponding simulation or experiment results that demonstrate a significant improvement of wireless network performance are explained for each algorithm. Forgery and confidentiality are major concerns for distributed radio resource measurement and cooperation. Thus, this dissertation concludes with an analysis of security threats to radio resource measurement and cooperation, and proposes an action frame protection scheme to ensure secure distributed cooperative wireless networks