Medium access control protocol design for wireless communications and networks review

Medium access control (MAC) protocol design plays a crucial role to increase the performance of wireless communications and networks. The channel access mechanism is provided by MAC layer to share the medium by multiple stations. Different types of wireless networks have different design requirements such as throughput, delay, power consumption, fairness, reliability, and network density, therefore, MAC protocol for these networks must satisfy their requirements. In this work, we proposed two multiplexing methods for modern wireless networks: Massive multiple-input-multiple-output (MIMO) and power domain non-orthogonal multiple access (PD-NOMA). The first research method namely Massive MIMO uses a massive number of antenna elements to improve both spectral efficiency and energy efficiency. On the other hand, the second research method (PD-NOMA) allows multiple non-orthogonal signals to share the same orthogonal resources by allocating different power level for each station. PD-NOMA has a better spectral efficiency over the orthogonal multiple access methods. A review of previous works regarding the MAC design for different wireless networks is classified based on different categories. The main contribution of this research work is to show the importance of the MAC design with added optimal functionalities to improve the spectral and energy efficiencies of the wireless networks

Channel Allocation and post-CCA based Bandwidth Adaptation in Wireless Local Area Networks with Heterogeneous Bandwidths

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 박세웅.The new prominent 802.11ac standard aims at achieving Gbps data throughput for individual users while at the same time guaranteeing backward compatibility. The approaches to achieving this goal use enhanced physical-layer features, such as higher modulation levels, MIMO (Multiple Input Multiple Output), and wider bandwidth. As for the bandwidth, the channel bonding technique that makes use of multiple 20MHz channels in 5GHz band is adopted. However, the heterogeneity of bandwidth in a network can cause asymmetric interferences in which some transmissions are not sensed by some nodes. As a result, the conventional CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) may not work well in 802.11ac networks and the Gbps throughput, which is attainable for a single link, is not achievable network-widely, which we call the Hidden Channel (HC) problem. In this dissertation, we illustrate the HC problem with a 802.11ac network as a reference system. Then we analyze the problem using Markov chain technique and show how the contention parameters and transmission time affect collision probability and fairness in some deployment scenarios. The validity of the analysis is verified through simulation in the same chapter. As a solution to the HC problem, a centralized and heuristic channel allocation algorithm, PCA (Primary Channel Allocation), in an enterprise local area network is proposed in the next part of this dissertation. The PCA algorithm, an extended version of well known ``University Timetabling'' algorithm for incorporating multi-channel purpose, is designed to avoid HC problem effectively. Through simulations, we demonstrate that our proposed channel allocation algorithm lowers the packet error rate (PER) compared to uncoordinated and RSSI (Received Signal Strength Indicator) based allocation schemes and increases the network-wide throughput as well as the throughput of a station that experiences poor performance. This implies improved fairness performance among transmission pairs with various channel bandwidths. Then, simple experiments are conducted with USRP and WARP boards to show that the problem is real and to prove that the validity of our next solution. Based on that, we argue for the need of bandwidth adaptation based on post-CCA, which is another clear channel assessment (CCA) procedure after finishing a transmission. The post-CCA helps mimic the CSMA/CD (CSMA with Collision Detection) mechanism in the wired Ethernet, thus enhancing channel assessment capability. Then, we propose PoBA (Post-CCA based Bandwidth Adaptation) that alters bandwidth and channel configuration dynamically. Using simulation, we confirm that the PoBA increases network-wide throughput, channel utilization and fairness, and decreases packet error probability.1 Introduction 1 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Contributions and Outline . . . . . . . . . . . . . . . . 6 2 The HC (Hidden Channel) Problem 11 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2 Problem Description . . . . . . . . . . . . . . . . . . . 15 2.3 Numerical Analysis . . . . . . . . . . . . . . . . . . . . 20 2.4 Simulation Results . . . . . . . . . . . . . . . . . . . . 27 2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 31 3 PCA (Primary Channel Allocation) 33 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 33 3.2 Channel Allocation for Alleviating HC . . . . . . . . . 39 3.2.1 Problem Formulation . . . . . . . . . . . . . . 43 3.2.2 A Heuristic Primary Channel Assignment Algo- rithm . . . . . . . . . . . . . . . . . . . . . . . 51 iv 3.3 Simulation Results . . . . . . . . . . . . . . . . . . . . 57 3.3.1 Case for a Network with Two APs . . . . . . . 58 3.3.2 Case for a Chain Topology with Six APs . . . . 60 3.3.3 Case for Various Sized Random Networks . . . 62 3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 68 4 PoBA (Post-CCA based Bandwidth Adaptation) 69 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 69 4.2 Experimental Results . . . . . . . . . . . . . . . . . . . 72 4.3 Post-CCA & PoBA . . . . . . . . . . . . . . . . . . . . 78 4.3.1 Post-CCA Operation . . . . . . . . . . . . . . . 78 4.3.2 PoBA Algorithm . . . . . . . . . . . . . . . . . 81 4.4 Simulation Results . . . . . . . . . . . . . . . . . . . . 89 4.4.1 Case for a Chain Topology with Six APs . . . . 90 4.4.2 Case for Various Sized Random Networks . . . 92 4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . 96 5 Conclusion 97 5.1 Research Contributions . . . . . . . . . . . . . . . . . 97 5.2 Future Research Directions . . . . . . . . . . . . . . . 99Docto

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

Developing a Systematic Process for Mobile Surveying and Analysis of WLAN security

Wireless Local Area Network (WLAN), familiarly known as Wi-Fi, is one of the most used wireless networking technologies. WLANs have rapidly grown in popularity since the release of the original IEEE 802.11 WLAN standard in 1997. We are using our beloved wireless internet connection for everything and are connecting more and more devices into our wireless networks in every form imaginable. As the number of wireless network devices keeps increasing, so does the importance of wireless network security. During its now over twenty-year life cycle, a multitude of various security measures and protocols have been introduced into WLAN connections to keep our wireless communication secure. The most notable security measures presented in the 802.11 standard have been the encryption protocols Wired Equivalent Privacy (WEP) and Wi-Fi Protected Access (WPA). Both encryption protocols have had their share of flaws and vulnerabilities, some of them so severe that the use of WEP and the first generation of the WPA protocol have been deemed irredeemably broken and unfit to be used for WLAN encryption. Even though the aforementioned encryption protocols have been long since deemed fatally broken and insecure, research shows that both can still be found in use today. The purpose of this Master’s Thesis is to develop a process for surveying wireless local area networks and to survey the current state of WLAN security in Finland. The goal has been to develop a WLAN surveying process that would at the same time be efficient, scalable, and easily replicable. The purpose of the survey is to determine to what extent are the deprecated encryption protocols used in Finland. Furthermore, we want to find out in what state is WLAN security currently in Finland by observing the use of other WLAN security practices. The survey process presented in this work is based on a WLAN scanning method called Wardriving. Despite its intimidating name, wardriving is simply a form of passive wireless network scanning. Passive wireless network scanning is used for collecting information about the surrounding wireless networks by listening to the messages broadcasted by wireless network devices. To collect our research data, we conducted wardriving surveys on three separate occasions between the spring of 2019 and early spring of 2020, in a typical medium-sized Finnish city. Our survey results show that 2.2% out of the located networks used insecure encryption protocols and 9.2% of the located networks did not use any encryption protocol. While the percentage of insecure networks is moderately low, we observed during our study that private consumers are reluctant to change the factory-set default settings of their wireless network devices, possibly exposing them to other security threats