On the PerfOrmance analysis Of cOOPerative cOmmunicatiOns with Practical cOnstraints

Blekinge Institute of Technology

Doctoral Dissertation Series No. 2012:08 School of Computing

On the PerfOrmance analysis Of

cOOPerative cOmmunicatiOns with Practical cOnstraints

the Perf O rmance a nal y sis O f era tive cO mmunica ti O ns with Pra ctical cO nstraints Quang Trung Duong

ISSN 1653-2090 ISBN 978-91-7295-235-5

With the rapid development of multimedia services, wireless communication engineers may face a ma- jor challenge to meet the demand of higher data-rate communication over error-prone mobile radio chan- nels. As a promising solution, the concept of coope- rative communication, where a so-called relay node is formed to assist the direct link, has recently been applied to alleviate the severe pathloss and shado- wing effects in wireless systems. In addition, wit- hout spending extra spectrum and power resources, multiple-input multiple-output (MIMO) antenna systems have been shown to provide an immense improvement in system performance compared to its single-antenna counterpart. As such, cooperative MIMO communication is essential for wireless and mobile networks because of its remarkable increase in spectral efficiency and reliability. Although the utilization of cooperative communication in MIMO systems has gained great attention in the literature, most of the research works have assumed perfect conditions. Inspired by the aforementioned discus- sion, this thesis takes a step further to investigate the performance of cooperative communications with practical constraints. The thesis provides a general framework for performance analysis of cooperative communications subject to several practical cons- traints such as antenna correlation, rank-deficiency of the channel matrix, co-channel interference, and interference-limited constraint of cognitive radio networks based on an underlay spectrum-sharing approach.

The thesis is divided into six parts. The first part investigates the performance of orthogonal space-

time block codes (OSTBCs) over MIMO relay networks in Nakagami-m fading channels under the antenna correlation effect. The second part ex- tends the full-rank MIMO channel to the case of the MIMO channel matrix being of rank-deficiency. Se- veral important findings on the impact of the sing- le-keyhole effect (SKE) and double-keyhole effect (DKE) are observed for two types of amplifying mechanism at the relay, namely, linear and squaring approaches. An important observation corroborated by our studies is that for offering a tradeoff bet- ween performance and complexity, we should use the linear approach for SKE and the squaring ap- proach for DKE. The third part generalizes the key- hole effect to multi-keyhole channels. The exact and asymptotic expressions for symbol error probability (SEP) are derived for some specific cases such as multi-keyhole MIMO/multiple-input single-output (MISO) channel. The fourth part proposes a distri- buted Alamouti space-time code for two-way fixed gain amplify-and-forward (AF) relaying. In parti- cular, closed-form expressions for approximated er- godic sum-rate and exact pairwise error probability (PWEP) are derived for Nakagami-m fading chan- nels. To reveal further insights into array and diver- sity gains, an asymptotic PWEP is also obtained.

The fifth part analyzes the outage performance of a two-way fixed gain AF relay system with beamfor- ming, arbitrary antenna correlation, and co-channel interference (CCI). Finally, the sixth part investiga- tes the impact of interference power constraint on the performance of cognitive relay networks based on the spectrum-sharing approach.

aBstract

2012:08

2012:08

Quang Trung Duong

Communications with Practical Constraints

Quang Trung Duong

On the Performance Analysis of Cooperative Communications with Practical Constraints

Quang Trung Duong

Doctoral Dissertation in Telecommunications Systems

School of Computing Blekinge Institute of Technology

SWEDEN

Publisher: Blekinge Institute of Technology, SE-371 79 Karlskrona, Sweden

Printed by Printfabriken, Karlskrona, Sweden 2012 ISBN: 978-91-7295-235-5

ISSN 1653-2090

urn:nbn:se:bth-00531

To my parents Ky and Thanh

Abstract

With the rapid development of multimedia services, wireless communication engineers may face a major challenge to meet the demand of higher data-rate communication over error-prone mobile radio channels. As a promising solu- tion, the concept of cooperative communication, where a so-called relay node is formed to assist the direct link, has recently been applied to alleviate the se- vere pathloss and shadowing effects in wireless systems. In addition, without spending extra spectrum and power resources, multiple-input multiple-output (MIMO) antenna systems have been shown to provide an immense improve- ment in system performance compared to its single-antenna counterpart. As such, cooperative MIMO communication is essential for wireless and mobile networks because of its remarkable increase in spectral efficiency and relia- bility. Although the utilization of cooperative communication in MIMO sys- tems has gained great attention in the literature, most of the research works have assumed perfect conditions. Inspired by the aforementioned discussion, this thesis takes a step further to investigate the performance of coopera- tive communications with practical constraints. The thesis provides a general framework for performance analysis of cooperative communications subject to several practical constraints such as antenna correlation, rank-deficiency of the channel matrix, co-channel interference, and interference-limited con- straint of cognitive radio networks based on an underlay spectrum-sharing approach.

The thesis is divided into six parts. The first part investigates the per- formance of orthogonal space-time block codes (OSTBCs) over MIMO relay networks in Nakagami-m fading channels under the antenna correlation ef- fect. The second part extends the full-rank MIMO channel to the case of the MIMO channel matrix being of rank-deficiency. Several important findings on the impact of the single-keyhole effect (SKE) and double-keyhole effect (DKE) are observed for two types of amplifying mechanism at the relay, namely, lin- ear and squaring approaches. An important observation corroborated by our studies is that for offering a tradeoff between performance and complexity, we should use the linear approach for SKE and the squaring approach for DKE. The third part generalizes the keyhole effect to multi-keyhole channels.

The exact and asymptotic expressions for symbol error probability (SEP) are

derived for some specific cases such as multi-keyhole MIMO/multiple-input

single-output (MISO) channel. The fourth part proposes a distributed Alam-

outi space-time code for two-way fixed gain amplify-and-forward (AF) relay-

ing. In particular, closed-form expressions for approximated ergodic sum-rate

and exact pairwise error probability (PWEP) are derived for Nakagami-m

fading channels. To reveal further insights into array and diversity gains, an

asymptotic PWEP is also obtained. The fifth part analyzes the outage perfor-

mance of a two-way fixed gain AF relay system with beamforming, arbitrary

antenna correlation, and co-channel interference (CCI). Finally, the sixth part

investigates the impact of interference power constraint on the performance

of cognitive relay networks based on the spectrum-sharing approach.

Preface

This thesis summarizes my work within the field of cooperative communica- tions. The work has been performed at the School of Engineering and School of Computing, Blekinge Institute of Technology, Karlskrona, Sweden. The thesis consists of six parts:

Part I

Orthogonal Space-Time Block Codes with CSI-Assisted Amplify-and- Forward Relaying in Correlated Nakagami-m Fading Channels

Part II

Keyhole Effect in MIMO AF Relay Transmission with Space-Time Block Codes

Part III

Multi-Keyhole Effect in MIMO AF Relay Downlink Transmission with Space-Time Block Codes

Part IV

Distributed Space-Time Coding in Two-Way Fixed Gain Relay Net- works over Nakagami-m Fading Networks

Part V

Beamforming in Two-Way Fixed Gain Amplify-and-Forward Relay Sys- tems with CCI

Part VI Cognitive Cooperative Communication with Amplify-and-Forward Relay and Spectrum-Sharing Approach

A Exact Outage Probability of Cognitive AF Relaying with Underlay Spectrum Sharing

B Cooperative Spectrum Sharing Networks with AF Relay and Se- lection Diversity

C Effect of Primary Networks on the Performance of Spectrum Shar-

ing AF Relaying

Acknowledgements

It is now time to write some final sentences for my Ph.D. study, which has been a joyful journey. When looking back to the last four and a half years, I am indebted to my principle advisor Prof. Hans-J¨ urgen Zepernick. This thesis would not have been completed without his guidance and support. I still remember the first time we met at IEEE VTC-Fall conference 2007 in Baltimore, USA. Afterwards, he offered me a Ph.D. fellowship to pursue my postgraduate study at Blekinge Institute of Technology (BTH), Sweden. I am lucky to have him as my supervisor. To me, he is the best advisor that a Ph.D.

student can ask for. I have learnt many useful things from him: patience and passion. His professional skills have lifted me to a level that I am now today.

Working with him is one of few privileges in my life.

During my Ph.D. study, I was lucky to meet many experts in the field.

One of them is my co-advisor, Prof. Markus Fiedler at BTH. I admire him for his deep knowledge and expertise in Quality-of-Experience, cross-layer design for mobile multimedia applications. From his guidance, I figured out that I can collaborate with other researchers whose interests are different from mine.

This thesis topic is cooperative communications and it is even more mean- ingful to have great cooperation from other scholars and friends: Prof. Aru- mugam Nallanathan (King’s College London, UK), Dr. Himal A. Suraweera (Singapore University of Technology and Design, Singapore), Prof. Theodoros A. Tsiftsis (Technological Educational Institute of Lamia, Greece), Dr. Vo Nguyen Quoc Bao (Posts and Telecommunications Institute of Technology, Vietnam), Prof. Kyeong Jin Kim (Inha University, Korea). A devout thank goes to Prof. Nallanathan for his support and guidance. The warmest thank to Himal for so many interesting daily talks, I have learnt a lot from his ma- turity and expertise. Many thanks to Theo, the first researcher that I have collaborated with, for showing me how to make international collaboration successful. Special thanks to Bao, I still recalled the first joint work, our EL paper, is a huge driving-force for my research, which gave me a lot of confi- dence to continue the challenging journey of my academic life. Many thanks Keyongjin for helpful discussions about cyclic-prefix single-carrier systems. I am thankful to all of you for both technical and non-technical issues, which bring to my life wonderful friends and colleagues.

Throughout these years, it has been an excellent opportunity to visit other

institutions. Deepest thanks go to Prof. Yao Wang, Prof. Elza Erkip, and

Prof. Chau Yuen for giving me an opportunity to join their research group

as a visiting scholar at Polytechnic Institute of New York University in 2009

and Singapore University of Technology and Design in 2011. I would also like to thank Prof. Yan Zhang (Simula Research Laboratory, Norway), Dr.

Yuexing Peng (Beijing University of Posts and Telecommunications, China), Dr. Lei Shu (Osaka University, Japan), Prof. Magnus Jonsson (Halmstad University, Sweden) for inviting me to present my works. Special thanks go to the Knowledge Foundation (KK-Stiftelsen) for funding this research.

I am also thankful to all of my co-authors for many fruitful discussion and collaboration over these years. My gratefulness goes to Dr. Maged Elkashlan (Queen Mary University of London, UK), Dr. George C. Alexandropoulos (Athens Information Technology, Greece), Dr. Phee Lep Yeoh (University of Melbourne, Australia), Dr. Nan Yang (University of New South Wales, Australia), Dr. Daniel Benevides da Costa (Federal University of Cear´a, Brazil), Dr. Fawaz S. Al-Qahtani (Texas A&M University at Qatar, Qatar), Dr. Nguyen-Son Vo (Huazhong University of Science and Technology, China), Mr. Hien Quoc Ngo (Linkoping University, Sweden), Dr. Xianfu Lei (South- west Jiaotong University, China). I would like to thank my other colleagues and friends at the Radio Communications Group, the School of Engineering, and the School of Computing at BTH for making my stay in Karlskrona and Ronneby more enjoyable.

Finally, I would like to thank my parents Ky and Thanh, my brother Huy, my aunt Melodie, my uncle Tom for always being there for me, for giving me their permanent love and support, which makes me the luckiest son and nephew. Last but certainly not least, I want to thank my wife Hien for her love and encouragement. Thank you for always believing in me.

Quang Trung Duong

Karlskrona, May 2012

Publication List

Part I is published as

T. Q. Duong, G. C. Alexandropoulos, T. A. Tsiftsis, and H.-J. Zepernick, “Or- thogonal Space-Time Block Codes with CSI-Assisted Amplify-and-Forward Relaying in Correlated Nakagami-m Fading Channels,” IEEE Trans. on Veh.

Techno., vol. 60, no. 3, pp. 882–889, Mar. 2011.

Based on

T. Q. Duong, H.-J. Zepernick, T. A. Tsiftsis, and V. N. Q. Bao, “Amplify-and- Forward MIMO Relaying with OSTBC over Nakagami-m Fading Channels,”

in Proc. IEEE International Communications Conference, Cape Town, South Africa, pp. 1–6, May 2010.

T. Q. Duong, G. C. Alexandropoulos, T. A. Tsiftsis, and H.-J. Zepernick,

“Outage Probability of MIMO AF Relay Networks over Nakagami-m Fading Channels,” Electron. Lett., vol. 46, no. 17, pp. 1229–1231, Sep. 2010.

Part II is published as

T. Q. Duong, H. A. Suraweera, T. A. Tsiftsis, H.-J. Zepernick, and A. Nal- lanathan, “Keyhole Effect in MIMO AF Relay Transmission with Space-Time Block Codes,” IEEE Trans. Commun., Feb. 2012, under revision.

Based on

T. Q. Duong, H. A. Suraweera, T. A. Tsiftsis, H.-J. Zepernick, and A. Nal- lanathan, “OSTBCs in MIMO AF Relay Systems with Keyhole and Corre- lation Effects,” in Proc. IEEE International Communications Conference, Kyoto, Japan, pp. 1–6, Jun. 2011.

Part III is published as

T. Q. Duong, H. A. Suraweera, C. Yuen, and H.-J. Zepernick, “Multi-Keyhole

Effect in MIMO AF Relay Downlink Transmission with Space-Time Block

Codes,” in Proc. IEEE Global Communications Conference, Houston, TX,

pp. 1–6, Dec. 2011.

Part IV is published as

T. Q. Duong, H. Q. Ngo, H.-J. Zepernick, A. Nallanathan, “Distributed Space- Time Coding in Two-Way Fixed Gain Relay Networks over Nakagami-m Fad- ing Networks,” in Proc. IEEE International Communications Conference, Ottawa, Canada, June 2012.

Based on

T. Q. Duong, C. Yuen, H.-J. Zepernick, X. Lei, “Average Sum-Rate of Dis- tributed Alamouti Space-Time Scheme in Two-Way Amplify-and-Forward Re- lay Networks,” in Proc. IEEE Global Communications Conference Workshop, Miami, FL, pp. 79–83, Dec. 2010.

Part V is published as

T. Q. Duong, H. A. Suraweera, H.-J. Zepernick, C. Yuen, “Beamforming in Two-Way Fixed Gain Amplify-and-Forward Relay Systems with CCI,”

in Proc. IEEE International Communications Conference, Ottawa, Canada, June 2012.

Part VI is published as

T. Q. Duong, V. N. Q. Bao, H. Tran, G. C. Alexandropoulos, and H.-J. Zeper- nick, “Effect of Primary Networks on the Performance of Spectrum Sharing AF Relaying,” Electron. Lett., vol. 48, no. 1, pp. 25–27, Jan. 2012.

T. Q. Duong, V. N. Q. Bao, G. C. Alexandropoulos, and H.-J. Zepernick,

“Cooperative Spectrum Sharing Networks with AF Relay and Selection Di- versity,” Electron. Lett., vol. 47, no. 20, pp. 1149–1151, Sep. 2011.

T. Q. Duong, V. N. Q. Bao, and H.-J. Zepernick, “Exact Outage Probability of Cognitive AF Relaying with Underlay Spectrum Sharing,” Electron. Lett., vol. 47, no. 47, pp. 1001-1002, Aug. 2011.

Publications in conjunction with this thesis but not included:

Book and Book Chapters

Quang Trung Duong, “On Cooperative Communications and Its Applications

to Mobile Multimedia,” Blekinge Institute of Technology, Karlskrona, Sweden,

Licentiate Thesis, Apr. 2010.

T. Q. Duong and H.-J. Zepernick, “Cross-Layer Design for Packet Data Trans- mission in Co-located MIMO Systems,” Chapter 16 in the book “Using Cross- Layer Techniques for Communication Systems Techniques and Applications”

IGI Publisher, 2012.

T. Q. Duong, N.-S. Vo, H.-J. Zepernick, et al., “Replication Strategies for Video On-Demand over Wireless Mesh Networks: A Cross-Layer Optimiza- tion Approach,” Chapter 15 in the book “Using Cross-Layer Techniques for Communication Systems Techniques and Applications” IGI Publisher, 2012.

Journals

T. Q. Duong and H.-J. Zepernick, “Cross-Layer Design for MRT Systems with Channel Estimation Error and Feedback Delay,” Wireless Personal Commu- nications, vol. 58, no. 4, pp. 681–694, 2010.

T. Q. Duong, H.-J. Zepernick, and V. N. Q. Bao, “Symbol Error Probability of Hop-by-Hop Beamforming in Nakagami-m Fading,” Electron. Lett., vol. 44, no. 20, pp. 1206–1207, Sep. 2009.

T. Q. Duong and H.-J. Zepernick, “On the Performance Gain of Hybrid Decode-Amplify-Forward Cooperative Communications,” EURASIP Journal on Wireless Communications and Networking, vol. 2009, article ID 479463, 10 pages, 2009. doi:10.1155/2009/479463.

T. Q. Duong, V. N. Q. Bao, and H.-J. Zepernick, “On the Performance of Se- lection Decode-and-Forward Relay Networks over Nakagami-m Fading Chan- nels,” IEEE Commun. Lett., vol. 13, no. 3, pp. 172–174, Mar. 2009.

Conferences

T. Q. Duong, O. Alay, E. Erkip, and H.-J. Zepernick, “End-to-End Perfor- mance of Randomized Distributed Space-Time Codes,” in Proc. IEEE Per- sonal, Indoor and Mobile Radio Communications, Istanbul, Turkey, pp. 988–

993, Sep. 2010.

T. Q. Duong, H.-J. Zepernick, T. A. Tsiftsis, and V. N. Q. Bao, “Performance

Analysis of Amplify-and-Forward MIMO Relay Networks with Transmit An-

tenna Selection over Nakagami-m Channels,” in Proc. IEEE Personal, Indoor

and Mobile Radio Communications, Istanbul, Turkey, pp. 368–372, Sep. 2010.

T. Q. Duong, U. Engelke, and H.-J. Zepernick, “Cooperative Wireless Com- munications with Unequal Error Protection and Fixed Decode-and-Forward Relays,” in Proc. International Conference on Communications and Electron- ics, Nha Trang, Vietnam, pp. 702–706, Aug. 2010.

T. Q. Duong, H.-J. Zepernick, and M. Fiedler, “Cross-Layer Design for In- tegrated Mobile Multimedia Network with Strict Priority Traffic,” in Proc.

IEEE Wireless Communications and Networking Conference, Sydney, Aus- tralia, pp. 1–6, Apr. 2010.

T. Q. Duong and H.-J. Zepernick, “Performance Analysis of Cooperative Spa- tial Multiplexing with Amplify-and-Forward Relays,” in Proc. IEEE Per- sonal, Indoor and Mobile Radio Communications, Tokyo, Japan, pp. 1963–

1967, Sep. 2009.

T. Q. Duong and H.-J. Zepernick, “Adaptive Transmission Scheme for Wire- less Cooperative Communications,” in Proc. IEEE Personal, Indoor and Mo- bile Radio Communications, Tokyo, Japan, pp. 1958–1962, Sep. 2009.

T. Q. Duong and H.-J. Zepernick, ‘Hybrid Decode-Amplify-Forward Cooper- ative Communications with Multiple Relays,” in Proc. IEEE Wireless Com- munications and Networking Conference, Budapest, Hungary, pp. 1–6, Apr.

2009.

T. Q. Duong and H.-J. Zepernick, “On the Ergodic Capacity of Cooperative Spatial Multiplexing Systems in Composite Channels,” in Proc. IEEE Radio and Wireless Symposium, San Diego, CA, pp. 175–178, Jan. 2009.

T. Q. Duong, U. Engelke, and H.-J. Zepernick, “Unequal Error Protection for Wireless Multimedia Transmission in Decode-and-Forward Relay Networks,”

in Proc. IEEE Radio and Wireless Symposium, San Diego, CA, pp. 703–706, Jan. 2009, (finalists for the Student’s Best Paper Competition).

T. Q. Duong and H.-J. Zepernick, “Average Symbol Error Rate of Cooper-

ative Spatial Multiplexing in Composite Channels,” in Proc. IEEE Interna-

tional Symposium on Wireless Communication Systems, Reykjavik, Iceland,

pp. 335–339, Oct. 2008.

T. Q. Duong and H.-J. Zepernick, “Robust EZW Image Transmission Scheme Using Distributed-Alamouti Codes in Relay Networks,” in Proc. International Conference on Signal Processing and Communication Systems, Gold Coast, Australia, pp. 1–6, Dec. 2008.

T. Q. Duong and H.-J. Zepernick, “On the Performance of ROI-Based Im- age Transmission Using Cooperative Diversity,” in Proc. IEEE International Symposium on Wireless Communication Systems, Reykjavik, Iceland, pp.

340–343, Oct. 2008.

Other publications:

Journals

K. J. Kim, T. Q. Duong, and H. V. Poor, “Performance Analysis of Adaptive Decode-and-Forward Cooperative Single-Carrier Systems,” IEEE Trans. on Veh. Technol., Apr. 2012 (accepted).

T. Q. Duong, D. B. da Costa, M. Elkashlan, and V. N. Q. Bao, “Cogni- tive Amplify-and-Forward Relay Networks over Nakagami-m Fading,” IEEE Trans. on Veh. Technol., 2012 (in press).

H. Phan, T. Q. Duong, and H.-J. Zepernick, “Performance Analysis of Decoup -le-and-Forward MIMO Relaying in Nakagami-m Fading,” IEICE Trans on Communications, May 2012, accepted.

H. Phan, T. Q. Duong, H.-J. Zepernick, and L. Shu, “Adaptive Transmission in MIMO AF Relay Networks with Orthogonal Space-Time Block Codes over Nakagami-m Fading,” EURASIP Journal on Wireless Communications and Networking, vol. 2012:11, 2012. doi:10.1186/1687-1499-2012-11.

H. Tran, T. Q. Duong, and H.-J. Zepernick, “Delay Performance of Cogni- tive Radio Networks for Point-to-Point and Point-to-Multipoint Communica- tions,” EURASIP Journal on Wireless Communications and Networking, vol.

2012:9, 15 pages, 2012. doi:10.1186/1687-1499-2012-9.

H. Phan, T. Q. Duong, M. Elkashlan, and H.-J. Zepernick, “Beamforming Amplify-and-Forward Relay Networks with Feedback Delay and Interference,”

IEEE Sig. Process. Lett., vol. 19, no. 1, pp. 16–19, Jan. 2012.

M. Yan, Q. Chen, X. Lei, T. Q. Duong, and P. Fan, “Outage Probability of Switch and Stay Combining in Two-way Amplify-and-Forward Relay Net- works,” IEEE Wireless Commun. Lett., Feb. 2012, (in press).

V. N. Q. Bao and T. Q. Duong, “Exact Outage Probability of Cognitive Underlay DF Relay Networks with Best Relay Selection,” IEICE Trans on Communications, vol. E95-B, no. 6, Jun. 2012.

M. Elkashlan, P. L. Yeoh, N. Yang, T. Q. Duong, and C. Leung, “A Com- parison of Two MIMO Relaying Protocols in Nakagami-m Fading Channels,”

IEEE Trans. on Veh. Technol., vol. 61, no. 3, Mar. 2012.

V. N. Q. Bao and T. Q. Duong, “Outage Analysis of Cognitive Multihop Net- works under Interference Constraints,” IEICE Trans. on Communications, vol. E95-B, no. 3, pp. 1019–1022, Mar. 2012.

F. S. Al-Qahtani, T. Q. Duong, C. Zhong, A. Qaraqe, and H. Alnuweiri,

“Performance Analysis of AF Dual-Hop Relaying Systems over Nakagami-m Fading Channels in the Presence of Interference at the Relay,” IEEE Sig.

Process. Lett., vol. 60, no. 3, pp. 882–889, Mar. 2011.

J. Yang, P. Fan, T. Q. Duong, and X. Lei, “Exact Performance of Two-Way AF Relaying in Nakagami-m Fading Environment,” IEEE Trans. on Wireless Commun., vol. 10, no. 3, pp. 980–987, Mar. 2011.

T. Q. Duong, L.-N. Hoang, and V. N. Q. Bao, “On the Performance of Two- Way Amplify-and-Forward Relay Networks,” IEICE Transactions on Com- munications, vol. Vol.E92-B, no. 12, pp. 3957–3959, Dec. 2009.

T. Q. Duong, N.-T. Nguyen, T. Hoang, and V.-K. Nguyen, “Pairwise Error Probability of Distributed Space-Time Coding Employing Alamouti Scheme in Wireless Relays Networks,” Springer Wireless Personal Communications, vol. 51, no. 2, pp. 231–244, Oct. 2009.

T. Q. Duong and V. N. Q. Bao, “Performance Analysis of Selection Decode- and-Forward Relay Networks,” Electron. Lett., vol. 44, no. 20, pp. 1206–1207, Sep. 2008.

T. Q. Duong, H. Shin, and E.-K. Hong, “Error Probability of Binary and M- ary Signals with Spatial Diversity in Nakagami-q (Hoyt) Fading Channels,”

EURASIP Journal on Wireless Communications and Networking, vol. 2007,

article ID 53742, 8 pages, 2007. doi:10.1155/2007/53742.

Conferences

C.-T.-M. Chinh, T. Q. Duong, and H.-J. Zepernick, “MRT/MRC for Cog- nitive AF Relay Networks Under Feedback Delay and Channel Estimation Error,” in Proc. IEEE Personal, Indoor and Mobile Radio Communications, Sydney, Australia, Sep. 2012.

N.-S. Vo, T. Q. Duong, and L. Shu, “Bit Allocation for Multi-Source Multi- Path P2P Video Streaming in VoD Systems over Wireless Mesh Networks,”

in Proc. IEEE International Communications Conference, Ottawa, Canada, June 2012.

M. V. Nguyen, C. S. Hong, and T. Q. Duong, “Joint Optimal Rate, Power, and Spectrum Allocation in Multi-hop Cognitive Radio Networks,” in Proc. IEEE International Communications Conference, Ottawa, Canada, June 2012.

H. Phan, T. Q. Duong, and H.-J. Zepernick, “MIMO Cooperative Multiple- Relay Networks with OSTBCs over Nakagami-m Fading Channels,” in Proc.

IEEE Wireless Communications and Networking Conference, Paris, France, Apr. 2012.

H. Tran, T. Q. Duong, and H.-J. Zepernick, “Performance Analysis of Cogni- tive Relay Networks Under Power Constraint of Multiple Primary Users,” in Proc. IEEE Global Communications Conference, Houston, TX, pp. 1–6, Dec.

2011.

H. Phan, T. Q. Duong, and H.-J. Zepernick, “MIMO AF Semi-Blind Re- lay Networks with OSTBC Transmission over Nakagami-m Fading,” in Proc.

IEEE International Conference Signal Processing and Communication Sys- tems, Honolulu, HI, pp. 1–5, Dec. 2011

H. Phan, T. Q. Duong, and H.-J. Zepernick, “Outage Performance for Op- portunistic Decode-and-Forward Relaying Coded Cooperation Networks over Nakagami-m Fading,” in Proc. IEEE International Symposium on Wireless Communications Systems, Aachen, Germany, pp. 417–421, Nov. 2011.

H. Tran, T. Q. Duong, and H.-J. Zepernick, “On the Performance of Spec-

trum Sharing Systems over Alpha-Mu Fading Channels for Non-identical Mu

Parameters,” in Proc. IEEE International Symposium on Wireless Commu-

nications Systems, Aachen, Germany, pp. 477–481, Nov. 2011.

H. Q. Ngo, T. Q. Duong, and E. G. Larsson, “Uplink Performance Analysis of Multicell MU-MIMO with Zero-Forcing Receivers and Perfect CSI,” in Proc.

IEEE Swedish Communications Technology Workshop, Stockholm, Sweden, pp. 40–45, Oct. 2011.

C.-T.-M. Chinh, T. Q. Duong, and H.-J. Zepernick, “Outage Probability and Ergodic Capacity for MIMO-MRT Systems under Co-Channel Interference and Imperfect CSI,” in Proc. IEEE Swedish Communications Technology Workshop, Stockholm, Sweden, pp. 46–51, Oct. 2011.

H. Phan, T. Q. Duong, and H.-J. Zepernick, “SER of Amplify-and-Forward Cooperative Networks with OSTBC Transmission in Nakagami-m Fading,” in Proc. IEEE Vehicular Technology Conference Fall, San Francisco, CA, pp. 1–

5, Sep. 2011.

S.-N. Vo, T. Q. Duong, H.-J. Zepernick, L. Shu and X. Du, “Cross-Layer Design for Video Replication Strategy over Multihop Wireless Networks,” in Proc. IEEE International Communications Conference, Kyoto, Japan, pp. 1–

6, Jun. 2011.

T. Q. Duong, T.-T. Le, and H.-J. Zepernick, “Performance of Cognitive Radio Networks with Maximal Ratio Combining over Correlated Rayleigh Fading,”

in Proc. International Conference on Communications and Electronics, Nha Trang, Vietnam, pp. 65–69, Aug. 2010.

H. Tran, T. Q. Duong, and H.-J. Zepernick, “Average Waiting Time of Pack- ets with Different Priorities in Cognitive Radio Networks,” in Proc. IEEE International Symposium on Wireless Pervasive Computing, Modena, Italy, pp. 122–127, May 2010.

H. Phan, T. Q. Duong, and H.-J. Zepernick, “Full-Rate Distributed Space–

Time Coding for Bi-Directional Cooperative Communications,” in Proc. IEEE International Symposium on Wireless Pervasive Computing, Modena, Italy, pp. 22–26, May 2010.

N.-N. Tran and T. Q. Duong, “Training Design Upon Mutual Information for

Spatially Correlated MIMO-OFDM,” in Proc. IEEE Wireless Communica-

tions and Networking Conference, Sydney, Australia, Apr. 2010.

F. Al-Qahatani and T. Q. Duong, “Selection Decode-and-Forward Relay Net- works with Rectangular QAM in Nakagami-m Fading Channels,” in Proc.

IEEE Wireless Communications and Networking Conference, Sydney, Aus- tralia, pp. 1–4, Apr. 2010.

V. N. Q. Bao, T. Q. Duong, and N.-N. Tran, “Ergodic Capacity of Cooper- ative Networks Using Adaptive Transmission and Selection Combining,” in Proc. International Conference Signal Processing and Communication Sys- tems, Nebraska, NE, pp. 1–6, Oct. 2009.

T. Q. Duong, “Exact Closed-Form Expression for Average Symbol Error Rate of MIMO-MRC Systems,” in Proc. International Conference on Advanced Technologies for Communication, Hanoi, Vietnam, pp. 20–23, Oct. 2008.

T. Q. Duong, D.-B. Ha, H.-A. Tran, and N.-S. Vo, “Symbol Error Probability of Distributed-Alamouti Scheme in Wireless Relay Networks,” in Proc. IEEE 67th Vehicular Technology Conference Spring, Singapore, pp. 648–652, May 2008.

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icable Orthogonal Designs,” in Proc. IEEE Radio and Wireless Symposium,

Orlando, FL, pp. 559–562, Jan. 2008.

Contents

Abstract . . . vii Preface . . . ix Acknowledgements . . . xi Publications list . . . xiii Contents . . . xxiii Abbreviations . . . xxv Introduction . . . 1 Part I

Orthogonal Space-Time Block Codes with CSI-Assisted Amplify-and- Forward Relaying in Correlated Nakagami-m Fading Channels . . . . 33 Part II

Keyhole Effect in MIMO AF Relay Transmission with Space-Time Block Codes . . . 57 Part III

Multi-Keyhole Effect in MIMO AF Relay Downlink Transmission with Space-Time Block Codes . . . 89 Part IV

Distributed Space-Time Coding in Two-Way Fixed Gain Relay Net- works over Nakagami-m Fading . . . 111 Part V

Beamforming in Two-Way Fixed Gain Amplify-and-Forward Relay Sys- tems with CCI . . . 131 Part VI

Cognitive Cooperative Communication with Amplify-and-Forward Re- lay and Spectrum-Sharing Approach

A Exact Outage Probability of Cognitive AF Relaying with Underlay

Spectrum Sharing . . . 153

B Cooperative Spectrum Sharing Networks with AF Relay and Se-

lection Diversity . . . 165

C Effect of Primary Networks on the Performance of Spectrum Shar-

ing AF Relaying . . . 177

Abbreviations

c.n.i.d. correlated but not necessarily identically distributed i.n.i.d. independent but not necessarily identically distributed i.i.d. independent and identically distributed

AF Amplify-and-Forward

AWGN Additive White Gaussian Noise

BER Bit Error Rate

BPSK Binary Phase-Shift Keying

BRS Best Relay Selection

CCI Co-Channel Interference

CDF Cumulative Distribution Function

CRN Cognitive Radio Networks

CSI Channel State Information

DASTC Distributed-Alamouti Space-Time Code

DF Decode-and-Forward

DKE Double Keyhole Effect

DSTC Distributed Space-Time Code

MGF Moment Generating Function

MIMO Multiple-Input Multiple-Output MISO Multiple-Input Single-Output

ML Maximum-Likelihood

MRC Maximal-Ratio Combining

OP Outage Probability

OSTBC Orthogonal Space-Time Block Code PDF Probability Density Function PRS Partial Relay Selection

PU Primary User

PWEP Pairwise Error Probability SEP Symbol Error Probability

SINR Signal-to-Interference Plus Noise Ratio SISO Single-Input Single-Output

SNR Signal-to-Noise Ratio

SKE Single Keyhole Effect

SU Secondary User

TAS Transmit Antenna Selection

1 Motivation

With the ever increasing demand of multimedia services, future wireless gen- erations aim to achieve higher data rates and more reliable communications for Quality of Service (QoS) provision. However, due to multipath fading, severe shadowing, pathloss, and co-channel interference (CCI), communica- tion in single-hop wireless networks has faced some fundamental limits [1].

In order to alleviate the impairment inflicted by wireless channels, multiple- input multiple-output (MIMO) systems have been proposed to exploit the rich-scattering nature of multiple-antenna channels [2–7]. By deploying mul- tiple antennas at the transceivers, the diversity and multiplexing gains have increased up to n S n D and min(n S , n D ), where n S and n D are the number of antennas at the source and destination, respectively. In comparison to its single-antenna counterpart, this enhancement of MIMO systems is remark- able as single-input single-output (SISO) systems are known to only achieve unit order of diversity and multiplexing gains. As a result, the MIMO tech- nology has been adopted to many commercial standards [8]. The concept of MIMO systems in single-hop has been intensively studied in many aspects, e.g., capacity [9,10], spatial diversity [11], space-time code design [12,13], and information theory [14]. However, due to the error-prone wireless channels, MIMO communication over a single-hop transmission may not be feasible.

As a result, an alternative communication technique for wireless networks, namely cooperative communication, is required, where the signals from the source should traverse through multiple intermediate terminals.

The basic concept of cooperative communication/relay networks is to uti- lize the assistance of relay nodes for conveying the source’s messages to the destination. In particular, the transmission between the source and desti- nation nodes is divided into two main phases: 1) Broadcasting phase: the source transmits its messages to both relay and destination, and 2) Multiple-

1

access phase: the relay manipulates its received messages from the source before forwarding them to the destination. With this transmission strategy, cooperative communications can overcome the severe pathloss and shadowing effects. As a result, the concept of cooperative communications has gained great attention, inspired by the pioneering works [15–17]. It has been shown that cooperative communications can achieve significant power savings for extending network life-time, expand the communication range, and keep the implementation complexity low [18–21].

Although extensive research has been made on cooperative communica- tions, most of the previous works have assumed perfect conditions. As a re- sult, the contribution of this thesis is to aim at investigating the performance of cooperative communications in realistic environments, e.g., the impact of antenna correlation at the transmit and received sides, the lack of scattering objects in MIMO relay channels (keyhole/multi-keyhole effects), the existence of co-channel interference from adjacent cells.

In addition, the inefficiency of spectrum utilization can be alleviated by using the cognitive radio concept, where secondary networks can co-occupy frequency bands which are licensed to a primary network. However, the cog- nitive network performance is decreased as the transmit power is limited so that the secondary signal does not cause any harmful interference on primary networks. As a result, utilizing relaying can significantly improve the cogni- tive network performance. Our main target in this thesis is to investigate the impact of peak interference power constraint imposed by the primary receivers and the interfering power from primary transmitters on the performance of cognitive relay networks.

2 An Overview on Cooperative Communica- tions

2.1 Background

The concept of cooperative communications was first introduced in [22], where

the capacity for the three-terminal communication shown in Fig. 1 was stud-

ied. Since 2000, this concept has gained great attention in the research com-

munity [15–21, 23–25]. Depending on the relaying operation, the relay can

be mainly categorized into two schemes: i) decode-and-forward (DF) and ii)

amplify-and-forward (AF), each of which has its own advantages and disad-

vantages. For the DF scheme, the relay is required to perform an extra opera-

tion by decoding the source signal before forwarding it to the destination [19].

In contrast, for the AF scheme, the relay simply amplifies the received mes- sage with a scalar gain without performing any signal regeneration, which may cause noise accumulation at the destination.

Relay

Source Destination

S

R

D

Figure 1: Basic relay network: A source S communicates with a destination D through the assistance of a relay R.

In AF relaying, depending on how the scalar gain is generated, the re- lay can be further classified as variable-gain, in which the full knowledge on channel state information (CSI) of the first hop is required, and fixed-gain, i.e., only the statistical distribution of the fading of the first hop is needed.

The performance of variable-gain AF relaying over Rayleigh and Nakagami-

m fading channels has been reported in [26, 27]. The work in [27] is limited

to the harmonic mean of two gamma random variables (RVs), which causes

the final expressions not to be an exact closed-form but lower bound. The

exact closed-form expressions of the outage probability (OP) and bit error

rate (BER) for fixed-gain AF relaying have been obtained for Rayleigh fading

channels in [28]. Tsiftsis et al. have derived exact closed-form expressions of

both variable-gain and fixed-gain AF relaying over Nakagami-m fading chan-

nels in [29]. Moreover, the impact of the direct link has been considered by

applying selection combining at the destination. It is important to note that

the works of Hasna and Alouini in [26,27,27] and of Tsiftsis et al. in [29] have

inspired a series of research papers which will be addressed in the sequel.

2.2 Cooperative Communications with Single-Antenna Terminals

2.2.1 Multi-hop Transmission

The use of relaying, previously mainly focusing on dual-hop, has been ex- tended to multi-hop communication by allowing the signal to traverse through the multiple intermediate nodes, as shown in Fig. 2. It has been shown in [26,27,30–33] that multi-hop relay networks significantly improve the com- munication coverage of cellular and ad hoc networks without spending extra network resources such as bandwith and power. The performance analysis for fixed-gain AF multi-hop relaying has been first proposed for Rayleigh fading in [34]. In [35], the authors have studied the performance bounds for multi- hop transmissions with fixed-gain AF relaying over several important fading models such as Nakagami-n (Rice), Nakagami-q (Hoyt), and Nakagami-m fad- ing channels. For Nakagami-m fading channels, the OP of variable-gain AF multi-hop relaying has been addressed in [36].

Source Destination

Hop 1 Hop 2 Hop N

R

S R

R

R

D

Figure 2: Cooperative communications system with multiple relays: Multi- hop transmission.

2.2.2 Dual-hop Transmission with Multiple Relays

It is important to note that one of the main challenges for multiple-relay

communications is the synchronization between different distributed termi-

nals, which requires a centralized controller. The best relay selection (BRS),

proposed by Bletsas et al. in [37], has been considered as the simplest relaying

combining strategy for achieving the full diversity, as shown in Fig. 3. As such,

the performance of the BRS scheme has been extensively studied [38–42]. It

has been shown in [43] that the opportunistic relaying with DF relays achieves

the global optimum in OP performance. The performance of BRS transmis-

sion has been derived for DF relays in [38, 39, 42]. The work in [43] has been

extended to opportunistic AF relaying, where an exact closed-form expression

for OP has been obtained [44]. For Nakagami-m fading channels, Duong et

al. have derived closed-form expressions for outage probability, symbol error probability (SEP), and ergodic capacity in [41]. Recently, the performance of multiple relays where the destination deploys the maximal-ratio combin- ing (MRC) technique has been derived in [45]. The aforementioned works on BRS require the full CSI knowledge of the dual-hop. A simpler version of BRS, namely partial relay selection (PRS), has been considered to reduce the complexity and signaling overhead for relay communication [46]. Although PRS reduces the performance compared with BRS, by assuming that only the CSI of the first hop is needed, its simple implementation has attracted increasing interest [47–53]. The performance of PRS fixed-gain AF relays for Rayleigh and Nakagami-m fading channels have been reported in [47] and [52], respectively. The asymptotic result for PRS variable-gain AF relays has been obtained in [48]. An important impact on the performance of PRS, namely feedback delay, has been investigated in [51].

Source Destination

R

S

R

R

R

D N Relays

Figure 3: Cooperative communications system with multiple relays: Best

relay selection (solid line: selected relay).

2.2.3 Two-Way Relaying

Transmission of cooperative communications has to take place over dual-hops or multi-hops, which significantly reduces the spectral efficiency of relay net- works compared to its single-hop counterpart. This loss can be recovered by utilizing two-way relay networks (e.g., see [54–56]), where the communication between multiple sources occurs in two-way or multi-way transmission, as shown in Fig. 4. Particularly, two source nodes simultaneously transmit their information to the relay node in the multiple-access phase (solid lines). Then, the relay node broadcasts the received signal to the two source nodes in the broadcast phase (dotted lines) [57]. Exact closed-form expressions for outage probability, SEP, and ergodic capacity for two-way AF relay networks over Rayleigh fading channels have been introduced in [58]. This work has been extended to Nakagami-m fading channels with the fading severity parameter m being integer or integer plus 0.5 [59]. The relay selection for two-way AF relaying has been considered in [60].

S

R S

Figure 4: Cooperative communications system with multiple sources: Two- way transmission (multiple-access phase: solid lines; broadcast phase: dotted lines).

2.2.4 Coded Cooperation and Distributed Space-Time Coding

Coded cooperation, a combination between channel coding and relay coop-

eration, is also promising to improve system performance [61–63]. Besides

channel coding, space-time codes can be also utilized for cooperative com-

munications. Here, each relay can act as a virtual antenna to form the

space-time code in a distributed fashion, namely distributed space-time code

(DSTC) [18, 64–68]. Specifically, a group of single-symbolwise maximum-

likelihood (ML) decoding DSTCs with full diversity order has been proposed

in [69]. However, these DSTCs contain a large number of zero entries in the DSTC design, which may yield a large peak power for non-linear amplifier at the transmitter. In [70], the existing orthogonal and quasi-orthogonal designs for co-located MIMO systems have been applied in AF relay networks. It has been demonstrated in [70] that these DSTCs can achieve full diversity order with single-symbolwise ML decoding complexity. However, double number of time-slots for the first-hop transmission is needed which leads to a decrease of data rate compared to the proposed scheme in [69].

3 MIMO Relay Networks

MIMO systems offer efficient solutions to increase the reliability and data rate of wireless networks by deploying multiple antennas at both ends. Re- lay/cooperative communication has been considered to provide the benefit of extending coverage of wireless networks when the direct link may not be applicable. As such, combining MIMO and relay concepts has drawn great attention in recent years (see, e.g., [25,71] and the references therein). Specif- ically, the potential application of MIMO relay systems shown in Fig. 5 has been presented and several bounds of the ergodic capacity over Rayleigh fad- ing channels have been provided in [25]. Several important MIMO AF re- lay schemes have been applied, for example: 1) transmit antenna selection (TAS) at the transmitter and MRC at the receiver, i.e., TAS/MRC sys- tems [72–79], 2) end-to-end best antenna selection in two-hop systems, i.e., TAS/TAS systems [80–85], and 3) hop-by-hop beamforming, i.e., MRC/MRC systems [86–90].

S R D

n

n

n

n

Figure 5: Basic MIMO cooperative communication system.

The performance of TAS/MRC over Rayleigh fading channels has been reported in [72–74]. The exact and asymptotic SEP of TAS/MRC over inde- pendent and identically distributed (i.i.d.) Nakagami-m fading with multiple antennas being deployed at all terminals have been derived for fixed-gain and variable-gain AF relaying in [77] and [78], respectively. The OP and SEP of TAS/MRC over independent but not necessarily identically distributed (i.n.i.d.) Nakagami-m fading with a single-antenna relay have been reported in [79].

By assuming that perfect CSI is available at both the transmitter and receiver, the TAS scheme has been utilized for both hops in MIMO relay systems. The performance of TAS/TAS over Rayleigh fading channels in dual-hop relay networks has been shown in [80–82]. Then, these works have been extended to the case of multi-hop Rayleigh fading channels in [83].

Later, closed-form expressions for the exact and asymptotic OP and SEP of TAS/TAS over the Nakagami-m have been derived in [84, 85]. The com- parison between TAS/MRC and TAS/TAS has been reported in [91]. It has been shown that the two schemes exhibit the same diversity order.

Another scheme to achieve the full diversity gain while keeping the com- plexity low is hop-by-hop beamforming, i.e., MRC/MRC systems. The per- formance of hop-by-hop beamforming over independent Rayleigh fading chan- nels is shown in [86]. The effect of antenna correlation on the performance of MRC/MRC system has been investigated for Rayleigh fading in [87]. These works [86,87] considered the variable-gain AF relay and Rayleigh fading chan- nels. For Nakagami-m fading channels, the variable-gain and fixed-gain AF relay have been taken into account in [88] and [89], respectively. Finally, a comparison between these two variable-gain and fixed-gain relaying schemes for MRC/MRC system has been conducted in [90].

One common aspect of the three mentioned MIMO AF relaying schemes, i.e., TAS/MRC, TAS/TAS, and MRC/MRC, is that the system requires full CSI knowledge of the two hops to obtain the full diversity gain. Recently, it has been shown that by using orthogonal space-time block codes (OST- BCs) [92, 93] over dual-hop relay networks, one may achieve the full diver- sity order without acquiring such large amount of CSI knowledge [94–102].

Specifically, the error rate performance of OSTBC transmission with fixed- gain AF relay over Rayleigh fading channels has been obtained in [95, 96].

These works have been extended to study the impact of line-of-sight (LOS)

in [94]. Here, the relay simply amplifies the received messages with a fixed

value and forwards the resulting signals to the destination without any ad-

ditional operation. This may cause noise accumulation at the destination.

Alternatively, the relay may decouple the source messages using the squaring approach [92] and then re-construct a new OSTBC before forwarding them to the destination. This relaying operation has been shown to provide full diversity gain without requiring the full CSI at the source as in the three above mentioned approaches, i.e., TAS/MRC, TAS/TAS, and MRC/MRC.

As such, it has attracted numerous scholars’ interest [97,100–102]. By consid- ering a single-antenna relay, the error rate for OSTBC transmission over AF relay networks with squaring approach has been derived for single-antenna and multiple-antenna destination in [98, 100], respectively. For Nakagami-m fading, the performance of OSTBCs transmission with squaring approach has been derived for independent and correlated channels in [101, 102], respec- tively.

3.1 Realistic MIMO Environment: Antenna Correlation and Rank-Deficiency

The benefit of multiple-antenna systems has been achieved by exploiting the rich scattering nature of MIMO channels together with the assumption of sufficient spacing between antenna elements so that the channels can undergo independent fading. However, due to the space-limit at mobile terminals, the closely co-located antennas will induce spatial correlation between the signals [103–106], which significantly degrades the diversity gain offered by the antenna arrays. In addition, the rank-deficiency effect of the channel matrix, namely, keyhole or pinhole as shown in Fig. 6, reduces the multiplexing gains of MIMO systems [103, 107–114]. As such, to precisely assess the potential of MIMO extension to cooperative communications for practical transmission environment, these two important channel impairments should be taken into account.

Recently, by considering a downlink communication with DF relay, the

authors in [115,116] have demonstrated that cooperative communications can

mitigate the loss in multiplexing gain inflicted by the deleterious keyhole ef-

fect. Motivated by these works, the diversity gain of MIMO AF relay has

been studied for keyhole and multi-keyhole in [117, 118], respectively. These

works are limited to the case where only the second hop is keyhole and the

relay performs linear operation (fixed-gain AF relaying). It has been shown

that when the first hop is keyhole-free, the diversity order of min(n ^R , n ^D ) can

be achieved, where n ^R and n ^D are the number of antennas at relay and desti-

nation, respectively. A more general model where single-hop/dual-hop suffers

keyhole together with linear/squaring approach at the relay has been inten-

T

R

Keyhole

Figure 6: Keyhole effect in multiple-antennas systems.

sively studied in [119], which reveals important insights into the behavior of system performance.

4 Cognitive Relay Networks

Frequency spectrum is one of the most important resources of wireless com-

munication. However, it has been shown by many recent measurements that

only a small portion of licensed radio spectrum is occupied at a certain time,

see e.g., [120–127]. Cognitive radio, invented by Mitola [128], is a promising

solution to alleviate the spectrum under-utilization, where the secondary user

(SU) may be allowed to use the spectrum which is assigned prior to the pri-

mary user (PU). Cognitive radio networks (CRNs) can be mainly classified

as overlay, interweave, and underlay networks. In overlay CRN, both SU and

PU occupy the spectrum at the same time and the SU utilizes the knowledge

of PU’s CSI to perform dirty paper coding so that the interference from PU

is mitigated [129]. In contrast, in interweave CRN, the SU is allowed to use

the spectrum only when it is not occupied by the PU [130]. As such, this

technique can be considered as opportunistic access. In an underlay network,

however, the SU simultaneously occupies the spectrum with the PU as long

as its interference on the primary network does not cause any harmful in-

terference on the PU [131]. In our work, we are interested in the underlay CRN, also known as spectrum-sharing as shown in Fig. 7, since it requires the least implementation complexity in comparison with overlay and interweave approaches.

PU SU

Power Power

Frequency Frequency

Figure 7: Cognitive radio networks: a) Interweave, and b) underlay.

However, the signal-to-interference plus noise ratio (SINR) at the sec- ondary receiver of an underlay CRN is usually low due to: i) The limitation of transmit powers of the secondary system, and ii) The interfering signals from the primary transmitter. Recently, cooperative communication has been ap- plied to underlay CRN to exploit the distributed spatial diversity gain under a limited transmit power condition. Generally, CRN with relaying has been considered for DF relays [132–140] and AF relays [141–145]. In particular, the OP of cognitive DF relay networks has been first reported in [132]. Then, the SEP performance has been derived in [139]. The best DF relaying selection has been considered for CRN under spectrum sharing approach in [133, 134].

In cognitive relay networks, due to the channel from the secondary source

to the primary receiver, the end-to-end signal-to-noise ratio (SNR) at the sec-

ondary destination is the combination of correlated RVs. This is because there

exists a common RV, i.e., channel gain of the link from secondary source to the

primary receiver, in each individual SNR corresponding to the transmission

over each relay. As a result, the end-to-end SNR is now given in the form of the

maximum of multiple correlated RVs although the fading under consideration

is independently distributed. This fact is also witnessed in previous works,

e.g., [132, Eq. (6)], [134, Eq. (3)], [141, Eq. (6)], and [133, Eq. (9)]. How-

ever, the statistical dependence among the RVs was not taken into account in

those works. As a result, the derivations presented in [132–134, 141] serve as

a bound. In particular, they are lower bounds for the OP [132, 133, 141] and

upper bounds for the ergodic capacity [134]. To overcome these drawbacks noticed in previous works, an exact analysis has been introduced in [138] for cognitive DF relay systems. In this work, the authors have derived exact closed-form expression for cognitive networks with best DF relay selection by taking into account the statistical dependence effect among the RVs. For cog- nitive AF relay networks, an exact closed-form expression given in elementary functions has been reported in [142]. Then, the spatial diversity technique is applied for cooperative cognitive networks, where the selection combining is used at the destination to maximize the SNR [143]. In this work, the depen- dence among two RVs has been clearly taken into account, which results in an exact closed-form expression of the OP for the considered system.

Besides BRS, other important relaying schemes, e.g., partial relay selec- tion, have been also included in cognitive relay networks [141, 146]. Most of the previous works have only focused on Rayleigh fading channel for cogni- tive relay networks based on spectrum sharing. An extension to Nakagami-m fading channels for DF and AF relaying has been given in [137] and [145], respectively. However, all of these works have assumed that the primary transmitter is located far away from secondary networks, and hence the ef- fect from primary transmitter can be neglected. Being one of the important aspects of cognitive relay networks, the signals from the primary network, in- flicted by the concurrence of the transmission from the primary transmitter, may severely interfere the secondary receiver. It has been shown in [144] that, when the interference power from primary transmitter is proportional to the secondary transmitter, it is useless to allow the secondary network to occupy the spectrum as the outage occurs for the whole considered SINR range.

5 Thesis Contribution

Although the performance of cooperative communications has been exten- sively studied in the research community, most of these works have assumed perfect conditions. Hence, this thesis has aimed at investigating coopera- tive communications with practical constraints such as antenna correlation, keyhole/multi-keyhole effects, CCI, and interference power constraint.

This thesis consists of six parts. Part I analyzes the performance of

MIMO dual-hop AF relay systems using OSTBCs over arbitrarily correlated

Nakagami-m fading channels. Part II investigates the impact of the keyhole

effect of the MIMO channel matrix, where the relay terminal can deploy linear

and squaring approaches. Part III extends the keyhole effect to a more gen-

eral case, namely, multi-keyhole, where the rank of the channel matrix can be varied from one to full-rank. In Part IV, we propose a DSTC for the two-way relay to compensate the loss in spectral efficiency of its one-way counterpart while keeping the full diversity gain. In Part V, the joint impact of CCI and antenna correlation is taken into account for a beamforming two-hop AF relay network. Finally, Part VI investigates the performance of spectrum sharing AF relay networks in an interference-limited environment, where the interfer- ence induced by the transmission of primary networks and the existence of a direct link are taken into account. In the following, the contribution of each part is summarized.

5.1 PART I: Orthogonal Space-Time Block Codes with CSI-Assisted Amplify-and-Forward Relaying in Cor- related Nakagami-m Fading Channels

In this part, the performance of MIMO dual-hop AF relay systems with OS- TBCs transmission over arbitrarily correlated Nakagami-m fading channels is analyzed. Below are important contributions of this part:

• Closed-form expressions for the end-to-end OP and the SEP with arbi- trary number of transceiver antennas and general correlation matrices are derived. Their mathematically tractable forms readily enable us to evaluate the performance of MIMO AF relay systems that utilizes OSTBCs.

• For sufficiently high signal-to-noise ratios, asymptotically tight approx- imations for the OP and SEP are also attained which reveal insights into the effects of fading parameters and antenna correlation on system performance.

• We prove that for a full-rank correlation matrix, the antenna correlation has no impact on the achievable diversity gain which is equal to the minimum of the sum of fading parameters between the two hops.

5.2 PART II: Keyhole Effect in Dual-Hop MIMO AF Relay Transmission with Space-Time Block Codes

This part extends the work in Part I, where the channel is assumed to be of

full-rank, to the case of rank-deficiency. In particular, we analyze the perfor-

mance of a downlink communication system where the amplifying processing

at the relay can be implemented by either the linear or squaring approach.

Our contributions in this part are summarized as follows:

• We derive tractable asymptotic SEP expressions, which enable us to obtain both diversity and array gains. An important observation cor- roborated by our studies is that for satisfying the tradeoff between per- formance and complexity, we should use the linear approach for single keyhole effect (SKE) and the squaring approach for double keyhole effect (DKE).

• Our finding reveals that for the downlink system, i.e., n ^S > min(n R , n D ), the linear approach can provide the full achievable diversity gain of min(n R , n D ) with SKE, where n S , n R , and n D are the number of antennas at source, relay, and destination, respectively. However, for the case that both the source-relay and relay-destination links experience the keyhole effect, i.e., DKE, the achievable diversity order is only one regardless of the number of antennas. In contrast, utilizing the squaring approach, the overall diversity gain can be achieved as min(n R , n D ) for both SKE and DKE.

5.3 PART III: Multi-Keyhole Effect in MIMO AF Re- lay Downlink Transmission with Space-Time Block Codes

This part generalizes the keyhole effect considered in Part II to the multi- keyhole scenario. Specifically, we study the impact of multi-keyhole, i.e., the bridge between single keyhole and full-scattering MIMO channels, on the performance of MIMO AF relay downlink transmission with OSTBCs. The contributions of this part are summarized as follows:

• We derive an analytical SEP expression for the considered system with arbitrary number of keyholes.

• Moreover, SEP approximations in the high SNR regime for several im- portant special scenarios of multi-keyhole channels are further derived.

These asymptotic results provide important insights into the impact of

system parameters on the SEP performance.

5.4 PART IV: Distributed Space-Time Coding in Two- Way Fixed Gain Relay Networks over Nakagami-m Fading

One-way relay networks have a loss in spectral efficiency due to the multi-hop transmission. In this part, to remedy this shortcoming, the fixed gain AF relaying has been applied to distributed-Alamouti space-time code (DASTC) two-way transmission. Below are the contributions of this part:

• Closed-form expressions for ergodic sum-rate and pairwise error prob- ability (PWEP) over Nakagami-m have been derived. The two-way system has been shown to surpass the commonly considered one-way counterpart by one nats/s/Hz, which is a remarkable improvement in spectral efficiency knowing that the contemporary wireless system can support up to 2-3 nats/s/Hz.

• The final results are given in the form of Fox-H function which readily enable us to evaluate the PWEP and capacity of the proposed scheme in some representative scenarios. Moreover, the asymptotic PWEP re- vealing the array and diversity gains are also derived.

5.5 PART V: Beamforming in Two-Way Fixed Gain Amplify-and-Forward Relay Systems with CCI

In this part, we analyze the outage performance of a two-way fixed gain AF relay system with beamforming, arbitrary antenna correlation, and CCI. Our contributions in this part are as follows:

• Assuming CCI at the relay, we derive the exact individual user OP in closed-form. Additionally, we also investigate the system OP of the considered network, which is declared if any of the two users is in trans- mission outage.

• Our results indicate that in this system, the position of the relay plays an important role in determining the user OP as well as the system OP via such parameters as signal-to-noise imbalance between the two hops, antenna configuration, spatial correlation, and CCI power.

• To render further insights into the effect of antenna correlation and CCI

on the diversity and array gains, an asymptotic expression which tightly

converges to exact results is also derived.

5.6 PART VI: Cognitive Cooperative Communication with Amplify-and-Forward Relay and Spectrum- Sharing Approach

Radio frequency spectrum is a scarce and expensive resource of wireless net- works. However, most of the licensed spectrum bands are not efficiently uti- lized. CRN has been proposed as a practical technique to improve spectrum utilization. The performance of CRN may be limited since the transmit power at the SU is strictly governed by the interference power constraint imposed by the PU. As a result, utilizing cooperative communication is essential to im- prove CRN performance. In this part, we investigate the advantage of using relaying in CRNs. Our contributions in this part are as follows:

• The exact closed-form expression for the OP of cognitive radio dual- hop AF relay networks is derived. The tractable expression of the OP, given in the form of elementary functions, readily enables us to evaluate the effect of the PU on the secondary system performance. It has been shown that the use of AF relaying significantly improves the performance of CRNs compared to the direct transmission.

• The spatial diversity for cognitive dual-hop relay networks is analyzed under interference power constraint imposed by the PU. The tractable closed-form OP expression readily enables us to evaluate the system performance, which indicates the significance of using diversity combin- ing in a distributed fashion in CRNs with underlay spectrum sharing approach.

• The effect of the primary network on spectrum sharing AF relaying is also taken into account. We show that under fixed interference from the primary network, the diversity order of the secondary network is not affected but only the array gain. However, when the interference power is dependent on the average SNR of the secondary network, it is infeasible to operate the secondary system as an irreducible error floor exists for the whole SNR regime.

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