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Hybrid Automatic Repeat Request Assisted Cognitive Radios UNIVERSITY OF SOUTHAMPTON FACULTY OF PHYSICAL SCIENCES AND ENGINEERING SCHOOL OF ELECTRONICS AND COMPUTER SCIENCE Hybrid Automatic Repeat Request Assisted Cognitive Radios by Ateeq Ur Rehman B.Eng A doctoral thesis submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy at the University of Southampton November 2016 SUPERVISOR: Prof. Lie-Liang Yang BEng, MEng, FIET, FIEEE and Prof. Lajos Hanzo FREng, FIEEE, FIET, EIC, EIC of IEEE Press, FEURASIP Chair of Southampton Wirelss Group School of Electronics and Computer Science University of Southampton Southampton SO17 1BJ United Kingdom c Ateeq Ur Rehman 2016 Dedicated to my Grandmother ii UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF PHYSICAL SCIENCES AND ENGINEERING SCHOOL OF ELECTRONICS AND COMPUTER SCIENCE Doctor of Philosophy Hybrid Automatic Repeat Request Assisted Cognitive Radios by Ateeq Ur Rehman It is widely known that the Cognitive Radio (CR) paradigm has the potential of improving the exploitation of the earmarked but momentarily unoccupied spectrum, which is exclusively allocated to the primary users (PUs) based on the conventional fixed spectrum allocation policy. The CR systems first have to sense, whether the PU’s band is unoccupied and then dynamically access it. Naturally, CR systems suffer from the same propagation impairments as the traditional wireless communication systems, such as interference, fading and noise, which affect both the reliability and the attainable data rate. In order for the CR system to achieve both reliable data transmission as well as a high throughput and low delay, we propose novel CR-aided Hybrid Automatic Repeat Request (HARQ) protocols, which intrinsically amalgamate the CR functions with HARQ protocols and study their performance. Both perfect and imperfect spectrum sensing are considered. Specifically, we propose the cognitive stop-and-wait-HARQ (CSW-HARQ), cognitive Go- Back-N-HARQ (CGBN-HARQ) as well as the cognitive selective-repeat (CSR-HARQ) schemes and study their throughput and delay both by analysis and simulation. To protect the PUs legal rights, we model their activity of occupying a primary radio (PR) channel as a two-state Markov chain consisting of ‘ON’ and ‘OFF’ states. In order to use the PR channel, the CR system first senses the presence of the PUs and once the PR channel is found to be free (i.e., in the OFF state), the CR system transmits its data packets relying on the principles of SW-HARQ, GBN-HARQ and SR-HARQ. Otherwise, the CR system continues sensing the channel until finding a free one. Naturally, the PR channel may be sensed erroneously, which results either in false alarm or in mis- detection. Therefore, the channel may be modelled by a two-state Markov chain, provided that sensing is ideal, or by a four-state Markov chain, if sensing is non-ideal. Here, the four states are determined by the actual state of the PR channel and the state sensed by the CR system. We analyse both the throughput and delay of CR systems relying on different HARQ schemes. We invoke a pair of analytical approaches, namely the probability based approach and the Discrete Time Markov Chain (DTMC) based approach. Closed-form expressions are derived for the throughput, average packet delay and the end-to-end packet delay. Furthermore, for the end-to-end packet delay, we derive both the probability distribution and the average end-to-end packet delay. In the DTMC- based approach, we propose a state generation algorithm for eliminating the illegitimate states, which helps reduce both the dimensionality of the related state transition matrices and the associ- ated computational complexity. All the equations obtained by analysis are validated by numerical simulations. Our performance results reveal that both the achievable throughput and delay of the CSW- HARQ, CGBN-HARQ and the CSR-HARQ schemes are substantially affected by the activity of the PUs, by the reliability of the PR channels, by the unreliable sensing decisions and by the number of packets transmitted per time-slot (TS). Specifically, when the probability of the PR channel being busy is high and/or its reliability is relatively low, the throughput attained by these HARQ schemes becomes relatively low and their packet delay increases. Furthermore, for the CGBN-HARQ and CSR-HARQ, our results show that when the propagation environment is time-variant, the number of packets transmitted within a TS should be adapted accordingly, in order to attain the highest throughput and the shortest average transmission delay. v Declaration of Authorship I, Ateeq Ur Rehman, declare that the thesis entitled Hybrid Automatic Repeat Request Assisted Cognitive Radios and the work presented in it are my own and has been generated by me as the result of my own original research. I confirm that: This work was done wholly or mainly while in candidature for a research degree at this • University; Where any part of this thesis has previously been submitted for a degree or any other quali- • fication at this University or any other institution, this has been clearly stated; Where I have consulted the published work of others, this is always clearly attributed; • Where I have quoted from the work of others, the source is always given. With the exception • of such quotations, this thesis is entirely my own work; I have acknowledged all main sources of help; • Where the thesis is based on work done by myself jointly with others, I have made clear • exactly what was done by others and what I have contributed myself; Parts of this work have been published. • Signed: ................................................ Date: ................................................ vii Acknowledgements First of all, I would like to give the greatest gratitude to both of my supervisors Professor Lie-Liang Yang and Professor Lajos Hanzo. I really appreciate their generous and insightful guidance as well as wise advice in the past four years of my PhD study, which encouraged me to build my own career that I am so passionate about. I appreciate that they shared with me their valuable experiences, not only in science, but also in life. Secondly, I am deeply grateful to Dr. Chen Dong, Dr. Varghese Antony Thomas, Dr. Rakshith Rajashekar, Dr. Jie Hu, Abbas Ahmed, Shruti Gupta and Dr. Halil Yetgin. Their presence has helped me endure the ups and downs of being a researcher. The support and kindness of many friends and colleagues whom I have made throughout these past few years have been invaluable to me. Although there are too many names to mention, I would like to express my gratitude to all those, who have been at least once with Southampton wireless, both past and present. I want to particularly thank Dr. Mohammed El-Hajjar, Dr. Soon Xin Ng, Dr. Rob Maunder, Dr. Rong Zhang, Ibrahim Hemadeh, Dimitrios Alanis, Dr. Zunaira Babar, Dr. Abdulah Jeza Aljohani, Dr. Liang Wei, Dr. Xuan Li, Dr. Li Li, and all other colleagues and staff, too numerous to mention here explicitly. Without the support, patience and guidance of the following people, this study would not have been completed, Hassan Younas, Faheem Tanoli, Brekhna Faheem, Kelsey Glass, Gao Quinn, Faheem Wali, Azmat Ali Shah, Arshad Khan, Uzair Khan, Palwasha Sajjad, Mouzzam Khattak, Gulaly Khan, Saad Balooch, Saad Rahoojo, Zia Noori, Muhammad Khan, Ziggrawer Muneir. Southampton has always been better with them. I owe my deepest gratitude to my father, Hidayat Ullah and my mother, my lovable uncles, brothers and sisters for their love, support and care for me, and Thank’s To ALLAH for every thing. The financial support of Abdul Wali Khan University Mardan, Pakistan is also gratefully ac- knowledged. viii List of First-Author Publications Journal Paper 1. A. U. Rehman, C. Dong, L. L. Yang and L. Hanzo, “Performance of Cognitive Stop-and- Wait Hybrid Automatic Repeat Request in the Face of Imperfect Sensing”, IEEE Access, vol.4, pp.5489-5508, July 2016. 2. A. U. Rehman, C. Dong, V. A. Thomas, L. L. Yang and L. Hanzo, “Throughput and Delay Analysis of Cognitive Go-Back-N Hybrid Automatic Repeat reQuest Using Discrete-Time Markov Modelling”, Accepted in IEEE Access, November 2016. 3. A. U. Rehman, V.A. Thomas, L. L. Yang and L. Hanzo, “Performance of Cognitive Selective- Repeat Hybrid Automatic Repeat Request”, Accepted in IEEE Access, November 2016. 4. A. U. Rehman, L. L. Yang and L. Hanzo, “Throughput and Delay Analysis of Cognitive Go-Back-N Hybrid Automatic Repeat reQuest Using Discrete-Time Markov Modelling in the Face of Imperfect Sensing”, Submitted to IEEE Access. Conference Paper 1. A. U. Rehman, L. L. Yang and L. Hanzo, “Performance of Cognitive Hybrid Automatic Repeat reQuest: Stop-and-Wait”, IEEE 81st Vehicular Technology Conference (VTC Spring), Glasgow, Uk, May 2015. 2. A. U. Rehman, L. L. Yang and L. Hanzo, “Performance of Cognitive Hybrid Automatic Repeat reQuest: Go-Back-N”, IEEE 83rd Vehicular Technology Conference (VTC Spring), Nanjing, China, May 2016. ix Contents Abstract iv Declaration of Authorship vii List of Symbols xv 1 Introduction 1 1.1 Motivation and Research Challenges . .1 1.2 Summary of Contributions . .3 2 Background Overview 7 2.1 Cognitive Radio Evolution . .7 2.1.1 Dynamic Spectrum Access . 11 2.1.2 The Concept of Cognitive Radio . 12 2.1.3 Design and Architecture of Cognitive Radio Systems . 13 2.1.3.1 Cognitive Radio Access Paradigms . 14 2.1.4 Cognitive Radio Functions . 15 2.1.4.1 Spectrum Sensing . 15 2.1.4.1.1 Spectrum Sensing Model . 15 2.1.4.2 Non-Cooperative Sensing . 16 2.1.4.3 Cooperative Sensing . 18 2.1.4.4 Interference Temperature . 19 2.1.5 Spectrum Decision . 19 x 2.1.6 Spectrum Mobility and Hand-off . 20 2.1.7 Spectrum Sharing .
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