TRANSACTIONS ON EMERGING TELECOMMUNICATIONS TECHNOLOGIES Trans Emerging Tel Tech (2013) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/ett.2719 RESEARCH ARTICLE Exact outage analysis of underlay cooperative cognitive networks with maximum transmit-and-interference power constraints and erroneous channel information Khuong Ho-Van* HoChiMinh City University of Technology, 268 Ly Thuong Kiet street, District 10, HoChiMinh City, Vietnam ABSTRACT This paper presents exact analysis of interference probability and outage probability of underlay cooperative cognitive networks under quite general conditions such as imperfect channel information, maximum transmit-and-interference power constraints, correlation among received signal-to-noise ratios and non identically distributed fading channels In addition, asymptotic outage analysis at either large maximum transmit power or large maximum interference power is proposed to have useful insights into performance limits of underlay cooperative cognitive networks Analytical results reveal that underlay cooperative cognitive networks dramatically suffer outage saturation phenomenon, and saturation degree significantly depends on channel estimation quality Moreover, the performance of both licenced network in terms of interference probability and unlicenced network in terms of outage probability is considerably deteriorated by channel estimation error Furthermore, optimum relay position is dependent of several factors such as maximum transmit power, maximum interference power, licensee position and channel estimation quality Copyright © 2013 John Wiley & Sons, Ltd *Correspondence Khuong Ho-Van, HoChiMinh City University of Technology, 268 Ly Thuong Kiet street, District 10, HoChiMinh City, Vietnam E-mail: khuong.hovan@yahoo.ca Received 28 June 2013; Revised 11 August 2013; Accepted September 2013 INTRODUCTION Underlay decode-and-forward (DF* ) cooperative† cognitive network is a feasible-and-efficient solution to problems of spectrum scarcity, spectrum under-utilisation and coverage extension [1–4] For system design optimization such as power allocation optimization, channel information must be available However, it is almost impossibly expected to have full knowledge of channel information from existing channel estimation algorithms As such, the investigation on the impact of imperfect channel information on the system performance is necessary On the other hand, outage probability is a useful metric in providing insights into the information-theoretic * Popularly, the relay in most cooperative relaying schemes operates in either DF or amplify-and-forward type [33, 34] † Multi-hop communication (e.g [2], [6]) differs from cooperative relaying (e.g [7, 8]) in that the former bypasses the direct channel between the source and the destination while for enhanced space diversity, the latter does Copyright © 2013 John Wiley & Sons, Ltd performance limit [5] As a result, a general outage analysis framework for underlay DF cooperative cognitive networks, accounting for multiple practical operation conditions such as imperfect channel information on all channels, two maximum transmit-and-interference power constraints, non-identically distributed (i.d.) fading channels and the correlation among received signal-to-noise ratios (SNRs) is urgent and essential Nevertheless, current publications have not considered all these conditions concurrently For instances, the authors in [2–4, 6–8], [9–32] partially investigated them More specifically, the authors in [3, 7, 8], [16–20], [22–25] analysed the outage performance of underlay DF cooperative cognitive networks‡ in different aspects under the assumption of perfect channel information: (i) about ‡ This paper studies underlay DF cooperative cognitive networks, and hence, the works on other modes (e.g the interweave mode in [31]), error probability analysis (e.g [4], [27–30]), the amplify-and-forward type (e.g [14, 32]), and multi-hop communications (e.g [2, à s N v  à r F1 tF 2IT SL 2Pt 1C e I0 rF 1 ÁO SL ÁSL SL / Pt 0s N s C r/ N I T 4e A F2 D e Q@ 2Pt 0s s sF C rF / N0 v A tF @ sF rF / N0 v Q ; C rF 2Pt 2Pt  à s N v  à F2 tF IT p 2Pt 1C e I0 sN rN 2 rF 2Pt ˛SR ˇSR v (72) ˛SR N0 v Pt Trans Emerging Tel Tech (2013) © 2013 John Wiley & Sons, Ltd DOI: 10.1002/ett Ns r/ N IT ; 2Pt (73) s (74) K Ho-Van Meanwhile, with the aid of [45, Equation (24)], the F3 term is represented in closed form as F3 D 2Q uF ; vF / sF ˛SR N0 v sI N C 2PT Pt t e sF 2IT  I0 where IT sF D N0 v s Á (75) r SL / Pt ˛SR N0 v sN C IT Ã2 SL à ÁO SL ÁSL SL ÁO SL ÁSL / SL / (76) s uF D s vF D N0 v Pt N0 v Pt  à ˛SR C sN IT 2N0 v ˛SR C sN IT C sF 2N0 v  sF (77) à (78) By plugging Equations (60), (65) and (66) into Equation (59), one achieves the closed form of W ACKNOWLEDGEMENTS This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 102.04-2012.39 REFERENCES Goldsmith A, Jafar SA, Maric I, Srinivasa S Breaking spectrum gridlock with cognitive radios: an information theoretic perspective Proceedings of the IEEE 2009; 97(5): 894–914 Lee J, Wang H, Andrews JG, Hong D Outage probability of cognitive relay networks with interference constraints IEEE Transactions on Wireless Communications 2011; 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