Enhancing Performance Of Multiple Ieee 802.11 Network Environment By Employing Cognitive Dynamic Channel Assignment

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2010Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2010Günümüzde pek çok kablosuz ağ, resmi birimler tarafından yapılan düzenlemeler ile kontrol edilen lisans sahiplerine ve servislere sabit spektrum dağıtım sözlesmeleri dikkate alınarak kullanılmaktadır. Bu dağıtılan spektrumun büyük bir kısmı düzensiz bir sekilde kullanıldığından spektrum bantları verimsiz kullanılmaktadır. Bilissel radyolar dinamik spektrum erisim teknikleri ile bu sorunları çözmek için önerilmis bir teknolojidir. Bilissel radyonun amacı daha iyi performans elde etmek için mümkün olan en iyi kanalda hizmet vermeye çalısmaktır. Spektrum algılama ve spektrum karar verme bilissel radyo ağlarında yerine getirilmesi gereken iki ana islevdir. Bilissel radyoların çalısma alanlarından biri de IEEE 802.11 tabanlı kablosuz ağlardır. Yapısal IEEE 802.11 tabanlı kablosuz ağlar, kendi ağlarındaki birimlerle haberlesmek için belirli bir kanalda çalısan erisim kontrol üniteleri kullanımını gerektirmektedir. Bu tezde, tasarlanmıs ve uygulanmıs bilissel erisim kontrol ünitesi için üzerinde en az trafik yükü olan ve kanallar arası parazitten en az etkilenen en iyi veri iletim kanalının seçilmesi üzerine odaklanılmıstır. Ayrıca kablosuz ağların ortak olarak kullandığı kablosuz ortamda kanallar arası parazitin önemli bir sorun olduğu gösterilmistir. Bunun yanında kanal seçim sisteminde daha da iyilesme yapılarak, sadece bizim bilissel erisim kontrol ünitemizin performansını arttırarak değil, komsu ağlarla birlikte tüm sistemin performansını arttıracak sekilde komsu ağlara da kanallar atayan bir sistem tasarlanmıstır. Kanal atamaları yapılırken ortamdaki kanalların kullanım oranı karakteristikleri, ağların trafik yükleri ve kanallar arasındaki parazit gerçeği göz önünde bulundurulmustur. Gerçek test ortamında yapılan test uygulamalarıyla tüm sistemin performansının arttırıldığı gösterilmistir. Test sonuçları ayrıca önerilen kanal atama uygulamasının, veri gonderim hızını arttırdığı gibi, bunu ağlar arasında dengelendirdiğini de göstermistir. Bunların yanında paketlerin gecikme zamanlarının istatistiksel değisiminde azalma sağladığı gibi paket kaybında da azalma sağlamıstır.Many wireless networks are controlled by governmental agencies through a fixed spectrum assignment policy today. By this policy the governmental agencies regulate the spectrum and assign to license holders or services. A large part of the assigned spectrum is being used in an irregular manner which results in low utilization of the spectrum bands. Cognitive radio is a technology which is proposed to solve this problem with dynamic spectrum access techniques. The aim of cognitive radio is to operate in the best available channel to achieve a better performance. Spectrum sensing and spectrum decision are the main challenging functions of cognitive radio (CR). One of the research fields related to CR solutions is IEEE 802.11 based wireless networks. Infrastructured IEEE 802.11 based wireless networks require the use of a wireless access point (AP) that works on a certain channel to communicate with the nodes in the network. In this thesis, we focused on selecting the best transmission channel for multiple AP environment by using the cognitive radio approach. The best transmission channel has the least activity on it. It is also the channel that is least affected by the interference. It is shown that interference is an important challenge for the neighboring wireless networks. A contribution to the channel selection system is made by selecting a channel not only to improve the performance of single AP (network), but also the performance of the neighboring networks forming the system. The channel utilization characteristic of the environment, the traffic load of the networks, and the interference are considered when deciding on the channel assignments. By using the test bed environment, the improvement of the system performance is shown. The test results also show that the proposed channel assignment scheme accomplishes performance improvement in throughput while balancing it among the networks. It also decreases jitter and packet loss.Yüksek LisansM.Sc

A novel MAC Protocol for Cognitive Radio Networks

In Partial Fulfilment of the Requirements for the Degree Doctor of Philosophy from the University of BedfordshireThe scarcity of bandwidth in the radio spectrum has become more vital since the demand for wireless applications has increased. Most of the spectrum bands have been allocated although many studies have shown that these bands are significantly underutilized most of the time. The problem of unavailability of spectrum bands and the inefficiency in their utilization have been smartly addressed by the cognitive radio (CR) technology which is an opportunistic network that senses the environment, observes the network changes, and then uses knowledge gained from the prior interaction with the network to make intelligent decisions by dynamically adapting transmission characteristics. In this thesis, recent research and survey about the advances in theory and applications of cognitive radio technology has been reviewed. The thesis starts with the essential background on cognitive radio techniques and systems and discusses those characteristics of CR technology, such as standards, applications and challenges that all can help make software radio more personal. It then presents advanced level material by extensively reviewing the work done so far in the area of cognitive radio networks and more specifically in medium access control (MAC) protocol of CR. The list of references will be useful to both researchers and practitioners in this area. Also, it can be adopted as a graduate-level textbook for an advanced course on wireless communication networks. The development of new technologies such as Wi-Fi, cellular phones, Bluetooth, TV broadcasts and satellite has created immense demand for radio spectrum which is a limited natural resource ranging from 30KHz to 300GHz. For every wireless application, some portion of the radio spectrum needs to be purchased, and the Federal Communication Commission (FCC) allocates the spectrum for some fee for such services. This static allocation of the radio spectrum has led to various problems such as saturation in some bands, scarcity, and lack of radio resources to new wireless applications. Most of the frequencies in the radio spectrum have been allocated although many studies have shown that the allocated bands are not being used efficiently. The CR technology is one of the effective solutions to the shortage of spectrum and the inefficiency of its utilization. In this thesis, a detailed investigation on issues related to the protocol design for cognitive radio networks with particular emphasis on the MAC layer is presented. A novel Dynamic and Decentralized and Hybrid MAC (DDH-MAC) protocol that lies between the CR MAC protocol families of globally available common control channel (GCCC) and local control channel (non-GCCC). First, a multi-access channel MAC protocol, which integrates the best features of both GCCC and non-GCCC, is proposed. Second, an enhancement to the protocol is proposed by enabling it to access more than one control channel at the same time. The cognitive users/secondary users (SUs) always have access to one control channel and they can identify and exploit the vacant channels by dynamically switching across the different control channels. Third, rapid and efficient exchange of CR control information has been proposed to reduce delays due to the opportunistic nature of CR. We have calculated the pre-transmission time for CR and investigate how this time can have a significant effect on nodes holding a delay sensitive data. Fourth, an analytical model, including a Markov chain model, has been proposed. This analytical model will rigorously analyse the performance of our proposed DDH-MAC protocol in terms of aggregate throughput, access delay, and spectrum opportunities in both the saturated and non-saturated networks. Fifth, we develop a simulation model for the DDH-MAC protocol using OPNET Modeler and investigate its performance for queuing delays, bit error rates, backoff slots and throughput. It could be observed from both the numerical and simulation results that when compared with existing CR MAC protocols our proposed MAC protocol can significantly improve the spectrum utilization efficiency of wireless networks. Finally, we optimize the performance of our proposed MAC protocol by incorporating multi-level security and making it energy efficient

Design and Analysis of Opportunistic MAC Protocols for Cognitive Radio Wireless Networks

As more and more wireless applications/services emerge in the market, the already heavily crowded radio spectrum becomes much scarcer. Meanwhile, however,as it is reported in the recent literature, there is a large amount of radio spectrum that is under-utilized. This motivates the concept of cognitive radio wireless networks that allow the unlicensed secondary-users (SUs) to dynamically use the vacant radio spectrum which is not being used by the licensed primary-users (PUs). In this dissertation, we investigate protocol design for both the synchronous and asynchronous cognitive radio networks with emphasis on the medium access control (MAC) layer. We propose various spectrum sharing schemes, opportunistic packet scheduling schemes, and spectrum sensing schemes in the MAC and physical (PHY) layers for different types of cognitive radio networks, allowing the SUs to opportunistically utilize the licensed spectrum while confining the level of interference to the range the PUs can tolerate. First, we propose the cross-layer based multi-channel MAC protocol, which integrates the cooperative spectrum sensing at PHY layer and the interweave-based spectrum access at MAC layer, for the synchronous cognitive radio networks. Second, we propose the channel-hopping based single-transceiver MAC protocol for the hardware-constrained synchronous cognitive radio networks, under which the SUs can identify and exploit the vacant channels by dynamically switching across the licensed channels with their distinct channel-hopping sequences. Third, we propose the opportunistic multi-channel MAC protocol with the two-threshold sequential spectrum sensing algorithm for asynchronous cognitive radio networks. Fourth, by combining the interweave and underlay spectrum sharing modes, we propose the adaptive spectrum sharing scheme for code division multiple access (CDMA) based cognitive MAC in the uplink communications over the asynchronous cognitive radio networks, where the PUs may have different types of channel usage patterns. Finally, we develop a packet scheduling scheme for the PU MAC protocol in the context of time division multiple access (TDMA)-based cognitive radio wireless networks, which is designed to operate friendly towards the SUs in terms of the vacant-channel probability. We also develop various analytical models, including the Markov chain models, M=GY =1 queuing models, cross-layer optimization models, etc., to rigorously analyze the performance of our proposed MAC protocols in terms of aggregate throughput, access delay, and packet drop rate for both the saturation network case and non-saturation network case. In addition, we conducted extensive simulations to validate our analytical models and evaluate our proposed MAC protocols/schemes. Both the numerical and simulation results show that our proposed MAC protocols/schemes can significantly improve the spectrum utilization efficiency of wireless networks