Spectrum Utilization and Congestion of IEEE 802.11 Networks in the 2.4 GHz ISM Band

Wi-Fi technology, plays a major role in society thanks to its widespread availability, ease of use and low cost. To assure its long term viability in terms of capacity and ability to share the spectrum efficiently, it is of paramount to study the spectrum utilization and congestion mechanisms in live environments. In this paper the service level in the 2.4 GHz ISM band is investigated with focus on todays IEEE 802.11 WLAN systems with support for the 802.11e extension. Here service level means the overall Quality of Service (QoS), i.e. can all devices fulfill their communication needs? A crosslayer approach is used, since the service level can be measured at several levels of the protocol stack. The focus is on monitoring at both the Physical (PHY) and the Medium Access Control (MAC) link layer simultaneously by performing respectively power measurements with a spectrum analyzer to assess spectrum utilization and packet sniffing to measure the congestion. Compared to traditional QoS analysis in 802.11 networks, packet sniffing allows to study the occurring congestion mechanisms more thoroughly. The monitoring is applied for the following two cases. First the influence of interference between WLAN networks sharing the same radio channel is investigated in a controlled environment. It turns out that retry rate, Clear-ToSend (CTS), Request-To-Send (RTS) and (Block) Acknowledgment (ACK) frames can be used to identify congestion, whereas the spectrum analyzer is employed to identify the source of interference. Secondly, live measurements are performed at three locations to identify this type of interference in real-live situations. Results show inefficient use of the wireless medium in certain scenarios, due to a large portion of management and control frames compared to data content frames (i.e. only 21% of the frames is identified as data frames)

A Markov Chain Approach to IEEE 802.11WLAN Performance Analysis

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

Supporting Real-Time Communication in CSMA-Based Networks : the VTP-CSMA Virtual Token Passing Approach

Tese de doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 200

Analysis of Impact in the Wi-Fi QoS of the EDCA Parameters

With the continuing development of the wireless technologies (Wi-Fi, 3G, 4G, WiMax and Bluethooth), the study of wireless multimedia transmissions has gained lately more attention. For example, the expectations of the company leaders on the growth of Wi-Fi video traffic has updated the lines of research on the standard IEEE 802.11e introduced to provide QoS (Quality of Service) to WLAN (Wireless LAN ) networks. In this paper we updated with greater accuracy, using other resources and the experience gained since the emergence of the standard, the work carried out previously on the quantitative impact of each EDCA (Enhanced Distributed Channel Access) parameter on the overall performance of the mechanisms MAC. A quantitative analysis of the optimizations that can be achieved has been performed by simulation. We use a node model EDCA 802.11e with the tool Möbius of the University of Illinois, which supports an extension of SPN (Stochastic Petri Networks), known as HSAN (Hierarchical Stochastic Activity Networks), what favors the contrast with other tools or mathematical resources. We use a realistic scenario formed by Wi-Fi stations with the capacity to transmit voice, video and best effort traffic. The results show that the default setting of EDCA parameters is not optimal, and that with an appropriate selection, very significant improvements can be obtained. Keywords: QoS, WLAN, EDCA 802.11e, MAC Parameters, Analysis of traffi

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

Survey of Spectrum Sharing for Inter-Technology Coexistence

Increasing capacity demands in emerging wireless technologies are expected to be met by network densification and spectrum bands open to multiple technologies. These will, in turn, increase the level of interference and also result in more complex inter-technology interactions, which will need to be managed through spectrum sharing mechanisms. Consequently, novel spectrum sharing mechanisms should be designed to allow spectrum access for multiple technologies, while efficiently utilizing the spectrum resources overall. Importantly, it is not trivial to design such efficient mechanisms, not only due to technical aspects, but also due to regulatory and business model constraints. In this survey we address spectrum sharing mechanisms for wireless inter-technology coexistence by means of a technology circle that incorporates in a unified, system-level view the technical and non-technical aspects. We thus systematically explore the spectrum sharing design space consisting of parameters at different layers. Using this framework, we present a literature review on inter-technology coexistence with a focus on wireless technologies with equal spectrum access rights, i.e. (i) primary/primary, (ii) secondary/secondary, and (iii) technologies operating in a spectrum commons. Moreover, we reflect on our literature review to identify possible spectrum sharing design solutions and performance evaluation approaches useful for future coexistence cases. Finally, we discuss spectrum sharing design challenges and suggest future research directions

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