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1 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. IEEE TRANSACTIONS ON COUNICATIONS, ACCEPTE FOR PUBLICATION Performance Comparion between Adaptive and Fixed Tranmit Power in Underlay Cognitive Radio Network Hela Hakim, Student ember, IEEE, Hatem Boujemaa, ember, IEEE, and Weam Ajib, ember, IEEE Abtract In thi paper, we compare the performance in term of ymbol error probability, data rate and power conumption of the ue of fixed tranmit power (FTP and adaptive tranmit power (ATP in underlay cognitive radio network. The ue of FTP alleviate the ignaling requirement of underlay cognitive radio network compared to the ATP. Neverthele, the ue of FTP influence the performance of the underlay cognitive radio network. To tudy thi influence, we conider three relay election cheme uing FTP: opportunitic decode and forward with FTP (O-F with FTP, opportunitic amplify and forward with FTP (O-AF with FTP and partial relay election with FTP (PR with FTP. We compare the performance of thee cheme in term of ymbol error probability, data rate and power conumption with three relay election cheme uing ATP: opportunitic decode and forward with ATP (O-F with ATP, opportunitic amplify and forward with ATP (O-AF with ATP and partial relay election with ATP (PR with ATP. We provide exact and/or lower bound expreion of the ymbol error probabilitie of O-F, O-AF and PR with FTP. The analytical tudy for the data rate and the power conumption i alo provided. Our comparion tudy how that FTP ha a poitive impact on the data rate and power conumption performance while it deteriorate the ymbol error probability performance. Index Term Cognitive radio, relaying, fixed tranmit power, adaptive tranmit power, ymbol error probability, data rate, power conumption. I. INTROUCTION EVER increaing demand for high data rate wirele ervice burden the available pectrum reource which become unable to atify thi demand and uffer from evere carcity. Cognitive radio ha emerged a a promiing technology to optimize pectrum reource exploitation by uing the licened pectrum in an opportunitic fahion []. In thi technology, any cognitive econdary uer may hare the pectrum with a licened primary uer a long a the latter fulfill it Quality of Service (QoS requirement. The protocol ettling the coexitence of primary and econdary uer are claified into three approache [2]: (i interweave approach where the econdary uer can operate a long a the anucript received Augut 7, 22; revied January 2 and June 8, 23. The editor coordinating the review of thi paper and approving it for publication wa L. Huheng H. Hakim i with the epartment of Applied athematic, Communication and Signal, Higher School of Communication of Tuni, Ariana 283, Tuniia, and with the epartment of Computer Science, Univerité de Québec à ontréal, ontreal, QC H2X 3Y7, Canada ( hela.hakim@com.tn. H. Boujemaa i with the epartment of Applied athematic, Communication and Signal, Higher School of Communication of Tuni, Ariana 283, Tuniia ( boujemaa.hatem@com.rnu.tn. W. Ajib i with the epartment of Computer Science, Univerité de Québec à ontréal, ontreal, QC H2X 3Y7, Canada ( ajib.weam@uqam.ca. igital Object Identifier.9/TCO /3$3. c 23 IEEE primary uer i idle and mut witch off whenever thi latter become active; (ii overlay approach where the econdary and primary uer hare imultaneouly the pectrum wherea the econdary node mut implement and perform ome technique in order to ait the primary communication; (iii finally, an underlay approach where econdary uer hare the pectrum with the primary one but have to adjut their tranmit power to keep the induced interference alway below a given allowable threhold. To fulfill the interference contraint, the econdary tranmitter ue generally low tranmit power which limit largely the performance of the cognitive radio network and hence thi network may uffer from low data rate and high ymbol error probability (SEP. A way to ameliorate the performance of the econdary network i the ue of relaying. Recently, everal work have focued on relaying technique in cognitive radio network [3]-[9]. In [3], Zou et al. have propoed to elect the relay with the larget ignal-to-noie ratio (SNR in relay-detination link under the contraint of atifying a required primary outage probability. In [4], Chen et al. have propoed a ditributed relay election cheme while conidering adaptive modulation and coding and energy tate of relay node. The ame author have propoed in [5] a relay election cheme that maximize the econdary data rate whilt enuring a minimum required primary data rate. In [6], a ditributed relay election concurrently conidering the channel tate of all related link and reidual energy tate of the relay node have been propoed. In [7], krihna et al. have propoed that relay ue beam teering capability to impoe a target ignal to interference plu noie ratio (SINR whilt fulfilling the primary requirement. In [8], Lin et al. have ued the pricing function in game theory to propoe a novel low-interference relay election derived from the conventional max-min relay election. In [9], amplify-and-forward relay election cheme i invetigated in the preence of interference from primary tranmitter. All previou work aume that econdary tranmitter can adjut their tranmit power. Recently, ome effort have focued on the ue of econdary tranmitter node uing fixed tranmit power (FTP []-[3]. In thee work, everal relaying cheme are invetigated where econdary tranmitter (ource and relay ue their maximum available power when the primary interference contraint i verified and remain ilent otherwie. Thi approach i olely propoed in []-[3] and i different from the approach where the relay remain ilent when the direct link i of high quality [4]. In thi paper, we conider a econdary network compoed by imple node tranmitting with FTP. The econdary network conit of a ource, a detination and everal available

2 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. 2 IEEE TRANSACTIONS ON COUNICATIONS, ACCEPTE FOR PUBLICATION relay. We invetigate the ue of FTP which require le ignaling than the ue of ATP. We invetigate and compare the performance of three relay election cheme: opportunitic F relaying with FTP (O-F with FTP, Opportunitic AF relaying with FTP (O-AF with FTP and partial relay election with FTP (PR with FTP. We tudy the performance of the conidered relay election cheme in term of SEP, data rate and power conumption. Uing FTP in underlay cognitive radio network alleviate the ignaling requirement compared to the ATP node. But, it influence the performance of the cognitive radio ytem. The target of our work i to tudy thi by comparing the performance of FTP and ATP in term of ymbol error probability, data rate and power conumption. Thi give inight to cognitive network architecture if uing ATP or FTP i worthy. The relaying cheme when ATP i ued are called: O-F with ATP, O-AF with ATP and PR with ATP. Our comparion tudy how that FTP ha a poitive impact on the data rate and power conumption performance while it deteriorate the ymbol error probability performance. In []-[3], author have conidered only the FTP and have not provided a performance comparion between FTP and ATP. Alo they have conidered only amplify and forward (AF relaying and have omitted the interference caued by the primary tranmitter to the econdary receiver. oreover, they have analyed only the SEP and the outage probability performance. In addition, in thee work, all relay are aumed to be equiditant from primary receiver. The contribution of our work compared to []-[3] conit in providing performance comparion between the FTP and ATP in term of SEP, data rate and power conumption. oreover, we have conidered both decode and forward (F and AF relaying mode. In addition, we have provided analytical tudy and imulation reult of SEP, data rate and power conumption of the econdary network in the preence and abence of interference from the primary tranmitter. The relay poition in our work are uniformly generated in a quare 3x3 and imulation and numerical reult are averaged over many topologie. The remainder of thi paper i organized a follow. In ection II, we decribe our ytem model. In ection III, we preent the new relaying cheme. Section IV i dedicated to preent the SEP analyi of each relaying cheme uing FTP. Section V i dedicated for the data rate and power conumption analyi. Section VI how and dicue with theoretical and imulation reult. Finally, ection VII draw ome concluding remark. II. SYSTE OEL We conider an underlay cognitive radio network operating near a primary network. The primary network conit of a primary tranmitter (PT communicating with a primary detination (P. The cognitive radio network conit of a ource S communicating with a detination imultaneouly with the primary communication. We aume that r relay are available to ait S. The ytem model i depicted in Fig.. We denote the et of the r available relay by R. We aume that each tranmiion i ubject to an additive white Gauian noie (AWGN with zero mean and variance N.The channel coefficient of the link X-Y i denoted by h X,Y and i aumed to conit of path lo and independent fading effect S Fig.. Primary tranmitter (PT Sytem model. R R i R Primary detination (P irect tranmiion Cooperative tranmiion Interference caued to P a h X,Y = X X,Y d α 2 X,Y,whered X,Y i the ditance between X and Y and α i the path lo exponent. X X,Y i the fading coefficient modeled a a circular ymmetric complex Gauian random variable with variance. We aume that the channel coefficient are invariant during two time lot and may change independently each two time lot. Node are aumed to be half dlex. The communication time i divided into two time lot. In the firt time lot, S end it ignal while the relay liten a hown by bold arrow in Fig.. The tranmitted ignal i alo perceived by P and hence caue ome interference. In underlay cognitive radio network, the interference level at P caued by the econdary tranmitter (ource and relay mut be below an interference threhold noted I th. The interference caued by a tranmitter X, noted I X uing a fixed tranmit power PX F i a follow I X = PX F h X,P 2 I th, ( where PX F denote the FTP ued by the tranmitter X. Ifthe econdary tranmitter X (S or R i find that the contraint ( i atified, then it tranmit with PX F. Hence, the SINR of the link X-Y i given by PX F Γ X,Y = h X,Y 2 P p h PT,Y 2. (2 + N If the econdary tranmitter i unable to atify the primary interference contraint, then it remain ilent. Thi implie that the tranmiion proce tart only if S atifie the interference contraint in (. S tranmit with a fixed power noted PS F and each relay R i R, tranmit with a fixed power noted PR F i. The value of PS F and P R F i are et at the activation of the cognitive radio network and remain fixed during all the tranmiion. The relay and receive ueful data from S and interference from PT a hown in Fig.. Thereby, the received ignal at during the firt time lot can be written a follow. y = PS F h S,x + P P h PT, x p + n, (3 where x i the econdary ymbol, x p and n are the primary tranmitted ymbol and the noie at during the firt time lot. Some relay, with the ue of their FTP, will fall hort of the interference contraint and thu they can not be elected to forward the econdary ignal. The et of relay atifying the interference contraint i denoted by U. In the econd time lot, one relay belonging to U i elected to forward the received ignal. Two relaying mode can be ued: F and AF.

3 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. HAKI et al.: PERFORANCE COPARISON BETWEEN AAPTIVE AN FIXE TRANSIT POWER IN UNERLAY COGNITIVE RAIO NETWORKS 3 If F relaying i ued, a ubet from U, denoted by C gathering decoding relay i formed, i.e., the relay that have correctly decoded the received ignal. The elected relay from C, denoted by R O-F, decode the received ignal then regenerate and forward it. The received ignal at during the econd time lot i given by y O-F,2 = P F R O-F h R O-F,x + P P h PT, x 2 p + n2. (4 where x 2 p and n2 are the primary tranmitted ymbol and the noie at during the econd time lot. If AF relaying i ued, the elected relay from U, denoted by R O-AF, amplifie the received ignal uing an amplification factor G = P F S h S,R O-AF P F R O-AF 2 +P p h PT,R O-AF. Then, the elected 2 +N relay forward the amplified ignal to. The received ignal at during the firt and econd time lot are repectively given by y O-AF,2 where y R O-AF = Gh R O-AF S, yr + P O-AF P h PT, x 2 p + n22, = P S h S,R O-AF x + P P h PT,R O-AF x p + n R O-AF, i the ignal received by the elected relay during the firt time lot. The tranmiion during the econd time lot i hown by a dahed arrow in Fig.. III. RELAYING SCHEES IN UNERLAY COGNITIVE RAIO NETWORK The relay election proce mut repect the end-to-end SINR a well a the interference contraint impoed by the primary ytem. In the following, we preent the three relaying cheme uing FTP: namely the O-F with FTP, O-AF with FTP and PR with FTP. Then, we preent the correponding relaying cheme uing ATP: namely O-F with ATP, O-AF with ATP and PR with ATP. A. Opportunitic F Relaying with FTP (O-F with FTP In underlay cognitive radio network operating in F mode, the elected relay mut repect the three following contraint: Interference contraint: the level of the interference caued by the elected relay hould be below the threhold allowed by the primary receiver. ecoding contraint: the elected relay hould correctly decode the econdary ignal. Finally, the elected relay hould maximize the SINR of the relay-detination link. To elect a relay, we firt determine the et U, then, the ubet C (C U. Finally, the elected relay i the one in C maximizing the SINR of the relay-detination link. Hence R O-F = argmax Γ Ri, whereγ Ri i defined in (2. R i C B. Opportunitic AF Relaying with FTP (O-AF with FTP When the network operate in AF mode, the elected relay mut repect two contraint: Interference contraint: the interference perceived by the primary receiver i lower than I th. The elected relay maximize the SINR of the ourcerelay-detination link. The SINR of the relaying link ource-relay-detination i given by Γ SRi Γ Ri Γ SRi = Γ SRi +Γ Ri +. (5 For the relay election, we firt determine the et U. Then, the elected relay for O-AF with FTP, denoted by R O-AF,i choen a R O-AF = argmax Γ SRi. C. Partial relay election with FTP (PR with FTP The propoed O-AF cheme require knowing the tate of ource-relay and relay-detination channel. When the number of available relay increae, the amount of required ignaling become important. Thi increae the complexity and may contitute an implementation bottleneck. An alternative olution i to rely only on the SINR of ource-relay link to moderate ignaling requirement. Thi idea wa firt propoed for non-cognitive radio network in [5]. The new cheme i called partial relay election. Conequently, the elected relay hould Satify the interference contraint impoed by the primary uer. aximize the SINR of the ource-relay link. Hence, the elected relay for PR with FTP, denoted by R PR, i choen a R PR = argmax Γ SRi.. Opportunitic F relaying with adjutable tranmit power (O-F with ATP In thi cheme, in order to maximize the ytem performance while repecting the interference contraint, each tranmitter adjut it power before each tranmiion a follow PX A = min( h X,P 2,Pmax X, (6 where PX A max denote the ATP ued by the tranmitter X, PX i the maximum available power for the tranmitter X. To elect a relay, the decoding et of relay C i firt formed. Then, each relay R i in C adjut it power a in (6. The elected relay, O-F, ATP denoted by R, i the one that maximize the SINR of O-F, ATP the relay-detination link uch a: R = argmax Γ Ri. R i C E. Opportunitic AF relaying with adjutable tranmit power (O-AF with ATP In thi cheme, each relay R i R, adjut it power a in (6. Then, the relay maximizing the SINR of the relaying link I th O-AF, ATP ource-relay-detination denoted by R i elected a O-AF, ATP follow R = argmax Γ SRi, whereγ SRi i defined in (5. F. Partial relay election with adjutable tranmit power (PR with ATP In thi cheme, each relay R i R, adjut it power a in (6. Then, the relay which maximize the SINR of the relaying link ource-relay i elected. The elected relay i denoted by PR, ATP PR, ATP R and i given by R = argmax Γ SRi. R i R

4 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. 4 IEEE TRANSACTIONS ON COUNICATIONS, ACCEPTE FOR PUBLICATION Relay node Id CSI of R i - link TABLE I REQUIRE CSI FOR THE IFFERENT RS SCHEES Fig. 2. Signaling overhead tructure ued by fixed tranmit power relay. Fixed tranmit Power node Identity of R i The CSI of R i -SR link Adaptive Tranmit Power node Identity of R i The CSI of R i - link The tranmit power PR A i Relay node Id CSI of R i - link value of P A R i Fig. 3. Signaling overhead tructure ued by adaptive tranmit power relay. where gpk =in 2 ( π. Similar expreion can be obtained for -QA modulation. G. Signaling requirement comparion We compare the ignaling requirement of FTP and ATP and we how that FTP require le ignaling than ATP. When the ignaling requirement increae, extra reource mut be provided to carry more ignaling information. Thi increae the practical implementation complexity of the deigned wirele ytem. We aume that S i the central cheduler that collect information and elect the relay. Fixed Tranmit Power: If FTP node are ued, each relay R i compare the amount PR F i h Ri,P 2 to the interference threhold I th.ifr i find that PR F i h Ri,P 2 <I th, then it end it identity and the value of h Ri, to S. The ignaling overhead tructure ued by FTP relay i hown in Fig. 2. S then collect the identitie of the relay verifying the interference contraint and ince it i aumed to have a prior knowledge about the value of PR F i, R i R, it can elect the bet relay. 2 Adaptive tranmit Power: If ATP node are ued, to elect the bet relay, each relay R i verifying PR A i h Ri,PR 2 <I th, ha to end it identity, the value of h Ri, and the value of it tranmit power PR A i to S. The ignaling overhead tructure of ATP i hown in Fig. 3. In Table., we compare the ignaling requirement of the ue of FTP and ATP. We can eaily ee that comparing to FTP, in ATP, relay have to further end the value of their adapted tranmit power to S. Obviouly, when the number of relay increae. the ignaling amount required to tranmit thi information become huge. IV. SEP ANALYSISOFTHERELAYING PROTOCOLS In thi ection, we derive the exact form expreion of the SEP of O-F with FTP and exact and lower bound form of the SEP of O-AF and PR with FTP in the abence of interference from PT. The exact SEP expreion of the O-F with FTP in the preence of interference from PT i alo derived while for O-AF and PR with FTP, only lower bound expreion are given, due to the intractability of the exact form expreion. To derive the SEP at a node X, we ue the moment generating function (GF of the SINR at X, Γ X,defined a follow ΓX ( = E(e ΓX, (7 where E(. i the expectation operator. For -PSK modulation, the SEP at X can be deduced from the GF of Γ X a follow [6] P,X = π π ( gpk ΓX in 2 dθ, (8 (θ A. SEP analyi of the O-F with FTP For the O-F, the SEP at can be written a P O-F, = P O-F, U=ΘP(U =Θ. (9 Θ R The probability P(U =Θi given by P(U =Θ = P(I Ri,P I th P(I Rj,P >I th, R i Θ where Θ=R\Θ and R j Θ P(I Ri,P I th = exp( I th I Ri,P (, ( where I Ri,P = P Ri E( h Ri,P 2.ToderiveP O-F, U=Θ,two cae arie. Cae : if U =, then the conditional probability P, U=Θ O-F i given by P O-F, U=Θ = π ( gpk ΓS, π in 2 dθ, (2 (θ where ΓS, ( can be obtained by uing the probability denity function (PF of the SINR Γ S, given in (38 in Appendix A and equation (7. In the abence of interference (i.e., the interference from PT i negligible and could be approximated by, ΓS, (, can imply be written a ΓS, ( = +λ 2 S,,whereλ2 XY = P F X d. α xy N Cae 2: if U, then given that in O-F with FTP, only relay belonging to U and having correctly decoded the ignal are retained a candidate relay, P O-F, U=Θ can be written a P O-F, U=Θ = P O-F, U=Θ,C=JP(C = J U =Θ. (3 J U Next, we derive each term of (3. P O-F, U=Θ,C=J, i given by (2, if C =. Otherwie,iti given by P O-F, U=Θ,C=J = π ( gpk ΓS, π in 2 (θ ( gpk ΓR O-F in 2 dθ, (4 (θ where the expreion of ΓR ( i derived in Appendix O-F A. In the abence of interference, ΓR ( i derived in O-F Appendix B.

5 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. HAKI et al.: PERFORANCE COPARISON BETWEEN AAPTIVE AN FIXE TRANSIT POWER IN UNERLAY COGNITIVE RAIO NETWORKS 5 P(C = J U =Θ,igivenby P(C = J U =Θ= ( P,Ri (P,Rj, (5 R i J R j J where J = U\J and P,X i the SEP at X given by (2 by replacing by node X. B. SEP Analyi of the O-AF with FTP In thi ubection, we provide an exact form and a lower bound expreion of the SEP for the O-AF with FTP in the abence of primary interference. The lower bound expreion i derived to provide which i impler than the exact one ince thi latter i given in the form of double integral. ue to the intractability of the exact form expreion of the SEP in the preence of interference from PT, only the lower bound expreion i derived. Exact form expreion: The SEP at can be written a P O-AF, = θ R P O-AF, U=θP(U = θ, (6 where P(U = θ i given by (. Next, we derive the exact form expreion of the firt term of (6. To derive P O-AF, U=θ, two cae arie. Cae : if U =, thenp O-AF, U=θ i given by (2, where ΓS, ( = +λ 2 S,. Cae 2: if U, thenwehave P O-AF, U=θ = π π ΓS, ( gpk in 2 (θ ΓSR O-AF ( gpk in 2 dθ, (θ (7 where ΓSR ( can be computed a in (7 uing the PF O-AF of Γ SR O-AF which can be written a [7] f (γ = ΓSR f O-AF ΓSRi (γ F ΓSRj (γ, (8 R j U R j R i where f ΓSRi (γ and F ΓSRi (γ are the PF and the cumulative ditribution function (CF of Γ SRi. f ΓSRi (γ and F ΓSRi (γ are given repectively by [8](9 and (2, where ν Ri = λ 2 SR i, μ Ri = λ 2 R i and K v (. i the v-th order modified Beel function of the econd kind. 2 Lower Bound expreion: Γ SRi can be per-bounded a follow Γ SRi < min(γ SRi, Γ Ri =Γ Ri. (2 Next, we derive the lower bound expreion in the abence and in the preence of interference from PT. a Abence of interference from PT: When the interference from PT i not conidered, we have Γ SRi and Γ Ri are two exponential random variable with mean λ 2 SR i and λ 2 R, i repectively. Thu, Γ Ri i an exponential random variable with mean λ2 SR λ 2 i R i λ 2 SR +λ 2 i R i. Let Γ Sel denote the maximum of ΓRi,R i U. Hence, the GF of Γ Sel can be deduced from (4 a follow Γ Sel ( = i U 2 U p= where ω Ri = λ2 SR i λ 2 R i λ 2 SR i +λ 2 R i ( ξ(p U ω ω Ri ++ Ri ξ p(k ω RlRi k=,k, (22 and {l Ri,k} U k= i the et of relay indice in U\{R i }. b Preence of interference from PT: In the preence of interference from PT, the CF of Γ Ri can be written a F R Γ i (γ = ( ( σ 2 S,R i σ 2 S,R i + σ 2 PT,R i γ exp( N γ σ 2 S,R i σr 2 i. σr 2 + i, σ2 PT, γ exp( N γ σr 2 i, where σx,y 2 can be found by deriving the CF of Γ Ri the PF of Γ Sel can be computed a, (23 = P X F d α X,Y.ThePFofΓRi denoted by f Γ R i given above. Finally, f Γ Sel (γ = f R Γ i (γ F Γ R j U R j R i R i (γ, (24 and the Γ Sel( can be deduced from (24 a in (7. Uing thee reult, a lower bound of P O-AF, U=Θ i given by Blow O-AF = π π ΓS, ( gpk in 2 (θ ( gpk γ Sel in 2 dθ. (θ (25 Subtituting the lower bound of P O-AF, U=Θ given in (25 and ( in (6, we obtain a lower bound for the SEP of O-AF with FTP. C. SEP Analyi of the PR with FTP We firt give the exact form expreion of the SEP of PR with FTP in the abence of interference from PT. Lower bound expreion are derived in the preence and in the abence of interference from PT. Exact form expreion: Conidering the PR with FTP cheme, the SEP at can be written a P PR, = P PR, U=ΘP(U =Θ, (26 Θ R where P(U =Θi given by (. To derive P PR, U=Θ,two cae arie. If U =, thenp PR, J=U U =, then, P PR, J=U P PR, J=U = π i given by (2. Otherwie, if i given by π ΓSR PR ( gpk ΓS, in 2 (θ ( gpk in 2 (θ where ΓSR PR ( i derived in appendix C. dθ, (27

6 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. 6 IEEE TRANSACTIONS ON COUNICATIONS, ACCEPTE FOR PUBLICATION [ f ΓSRi (γ = 2e (νr i +μr i γ ν Ri μ Ri (2γ +K (2 ν Ri μ Ri γ(γ + +(ν Ri + μ Ri ν Ri μ Ri γ(γ +K (2 ] ν Ri μ Ri γ(γ +, (9 F ΓSRi (γ = 2e (νr i +μr γ i ν Ri μ Ri γ(γ +K (2 ν Ri μ Ri γ(γ +, (2 2 Lower Bound expreion: Γ SRi can be per-bounded a (2. Let the per bound of Γ SRi be denoted by Γ Sel. The GF of Γ Sel, can be expreed a follow Γ Sel ( = R Γ i (P(R PR = R i, (28 where P (R PR of Γ Ri of Γ Ri = R i i given by (44 and R Γ i ( i the GF. In the preence of interference from PT, the expreion i computed imilar to the previou ection while in the abence of interference it i given by R Γ i ( = +ω Ri. Hence, a lower bound of P, J=U PR i given by B PR low = P(R PR = R i π π ( dθ. +ω gpk Ri in 2 (θ (29 Subtituting the lower bound of P, J=U PR given in (29 and ( in (26, we obtain a lower bound for the SEP of PR with FTP. V. ATA RATE AN POWER CONSUPTION ANALYSIS We derive the data rate and power conumption expreion for the three relaying protocol, O-F with FTP, O-AF with FTP and PR with FTP. A. ata rate Analyi The data rate i defined to be the amount of data uccefully delivered per time unit. For the direct tranmiion, the data rate can be written a th x = ρ( Px,, (3 E(T where ρ (bit//hz i the target tranmiion rate, x { O- F, O-AF, PR, d }, wherex = d tand for the direct tranmiion, P x, i the SEP of the relaying cheme x. The exact form expreion of P O-F, i derived in IV-A, in the preence and abence of primary interference. The exact form expreion of P O-AF, and PO-PR, in the abence of primary interference are derived in IV-B and IV-C, repectively. The per bound of the data rate expreion of O-AF and PR with FTP in the preence of interference are alo given in IV-B2 and IV-C2, repectively. P d, i given in (2. E(T i the expected number of time lot to tranmit one ymbol. According to our ytem et, E(T for O-F with FTP can be computed a follow E(T = P(I S,P >I th +P(I S,P I th [( P(C = (P(U = +2( P(U = +P(C = ]. (3 For O-AF and PR with FTP, E(T can be computed a follow E(T = P(I S,P >I th +P(I S,P I th [P(U = +2( P(U = ]. B. Power Conumption Analyi (32 The power conumption i the power conumed by the ource and the elected relay to tranmit one ymbol. For O- F with FTP, the power conumption can be computed a follow P O-F Conumed = P(I S,P I th P + P(U =Θ P(C = J U =Θ Θ R J U Θ J ( ]] P(R i = R x U =Θ,C = JP Ri, (33 R i C where P(R i = R O-F U =Θ,C = J i given by (34. For O- AF and PR with FTP, the power conumption can be computed a follow P x Conumed = P(I S,P I th P + P(U =Θ Θ R Θ [ ]] P(R i = R x U =Θ P R i, (35 where x { O-AF, PR }; P(R PR = R i i given in (44 in appendix C and the expreion of P(R i = R O-AF U =Θi given by P(R i = R O-AF U =Θ = ( F ΓSRi (γ R k C R k R i f ΓSRk (γdγ. (36 VI. NUERICAL RESULTS In thi ection, we preent theoretical and imulation reult carried out in order to compare the performance of relaying cheme uing FTP node with thoe uing ATP node. Simulation reult are averaged over many random topologie generated in a quare 3 3. The path lo exponent i et to 3. Without lo of generality, we have conidered a imple binary phae hift keying (BPSK modulation. The maximum

7 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. HAKI et al.: PERFORANCE COPARISON BETWEEN AAPTIVE AN FIXE TRANSIT POWER IN UNERLAY COGNITIVE RAIO NETWORKS 7 P(R i = R O-F U =Θ,C = J = [ R k C R k R i σ 2 R O-F σ 2 R O-F,, + σ2 PT, γ exp( N γ σr 2 O-F, N σr 2 k, + σ2 PT, γ exp( N γ σr 2 σr 2 + k, σ2 PT, k, (σr 2 k, + exp( N γ σ2 PT, γ2 σr 2 k, ] dγ. (34 tranmit power of the econdary ource i PS max =.5 watt. The ame value i ued for relay, PR max i =.5 watt, R i R. We aume that all relay ue the ame fixed tranmit power denoted P F. For each given primary tranmit power, we chooe the fixed tranmit power P S and P F at the beginning of imulation. To do o, we may find numerically the FTP value that minimize the econdary SEP or the one that maximize the econdary data rate. Without lo of generality, we chooe the one that minimize the econdary SEP auming that application require low error rate. The primary tranmit power P p i et to.5 watt. Our imulation are carried out to compare the SEP, the data rate and the power conumption of the invetigated relaying cheme uing FTP node over relaying cheme uing ATP node. For the direct tranmiion, the ource tranmit only when it i able to repect the interference contraint. The value of I th i et to.5 watt. In the Figure, we denote by I p the interference cauedbypt. In Fig. 4, Fig.5 and Fig.6, we compare the SEP, the data rate and the power conumed to tranmit one ymbol of the O- F with FTP and O-F with ATP, repectively for a number of relay r =2and r =4. In the preence of primary interference, the deterioration of SEP performance due to the ue of FTP node i by about.4 at 3 db. oreover, Fig. 6 how that O-F with ATP conume more power than O-F with FTP. Thi i becaue, in O-F with FTP the cooperation i not alway performed and hence the power that may be ued by the elected relay i aved. In the abence of interference, the difference between the SEPofO-FwithFTPandO-FwithATPbecomemore important. In high SNR, O-F with ATP ignificantly outperform the SEP of O-F with FTP. Thi i mainly becaue at high SNR, tranmitting with low power i more efficient mainly in the abence of primary interference. Beide, in O-F with FTP, cooperation i not performed when relay direpect the primary interference contraint while in O-F with ATP, the cooperation i alway performed. Hence, the SEP of O-F with ATP i ignificantly better than that of O-F with FTP. We oberve that the preence of primary interference largely deteriorate the SEP performance of the econdary network. For the ame conumed power, the performance of O-F with FTP are deteriorated by about.5 at 2 db. In term of data rate, Fig. 5 how that O-F with FTP lightly outperform O-F with ATP. Thi i due to the fact that in O-F with FTP, the cooperation i not alway performed. We oberve that when the number of relay increae the SEP performance of the econdary ytem improve. Thi i becaue, when the number of relay increae, the central chedular S may have better choice to elect the bet relay. SEP SEP 2 3 Theoretical curve irect Tranmiion O F with FTP (I P 4 O F with ATP (I P O F with FTP (I P O F with ATP (I P (a irect Tranmiion 4 O F with FTP (I p O F with ATP (I p O F with FTP (I p O F with ATP. (I p (b Fig. 4. SEP comparion of O-F with FTP and O-F with ATP (a r=4 relay, (b r=2 relay. oreover, when the number of relay increae the probability that all the relay do not repect the interference contraint decreae and hence cooperation will often be performed. In term of data rate, the performance decreae when the number of relay increae. Thi i becaue, a explained earlier when the number of relay increae, the cooperation i often performed which deteriorate the data rate. Obviouly, when the cooperation i alway performed, the econdary ytem will dipene more power (power allocated for the relay. Finally, we oberve that analytical and imulation curve are in perfect accordance which validate the preented performance analyi. In Fig. 7, Fig. 8 and Fig. 9, we compare the SEP, the data rate and the power conumed to tranmit one ymbol of the O- AF with FTP and O-AF with ATP, repectively for a number

8 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. 8 IEEE TRANSACTIONS ON COUNICATIONS, ACCEPTE FOR PUBLICATION.9.8 Theoretical curve irect Tranmiiom O F with FTP (I p O F with ATP (I p O F with FTP (I p O F with ATP (I p ata Rate.7 r =2 relay.6 r = 4 relay.5.4 =4 relay r =2 relay r SEP 2 irect Tranmiion O AF with FTP (I p O AF with ATP (I 3 p O AF with FTP (I p O AF with ATP (I p Theoretical exact curve Theoretical lower bound curve Fig. 5. ata rate comparion of O-F with FTP and O-F with ATP for r=4 relay and r=2 relay. Fig. 7. SEP comparion of O-AF with FTP and O-AF with ATP for r=4 relay Power conumption r = 4 relay r = 2 relay irect Tranmiion O F with FTP O F with ATP Theoretical curve ata Rate irect Tranmiion O AF with FTP (I p O AF with ATP (I p O AF with FTP (I p O AF with ATP (I p Theoretical exact curve Theoretical per bound curve (I p Fig. 6. Power conumption comparion of O-F with FTP and O-F with ATP for r=4 relay and r=2 relay. Fig. 8. ata rate comparion of O-AF with FTP and O-AF with ATP for r=4 relay. of relay r =4. In the preence of primary interference, we oberve that the deterioration in SEP of O-AF with FTP compared to O-AF with ATP i not ignificant. Fig. 9 indicate that O-AF with ATP require more power than O-AF with FTP. In the abence of interference, the deterioration in performance become a little important that in the preence of primary interference. Thi i expected ince the primary interference ha a great impact on the SEP performance of the econdary network. For data rate performance, Fig. 8 how that O-AF with FTP lightly outperform O-AF with ATP. Thi i becaue in O-AF with FTP, the cooperation i not alway performed contrarily to O-AF with ATP where cooperation i alway performed. Form Fig.7-Fig.9, we conclude that O-AF with FTP require le power than O-AF with ATP while preerving cloe SEP performance to thi latter and o, in thi cae it i more intereting for practical implementation than O-AF with ATP. The theoretical curve in Fig. 7-Fig. 9 match well with the imulation curve. oreover, the lower bound curve are very cloe to the exact curve. In Fig., Fig. and Fig. 2, we compare the SEP, data rate and the average power conumed to tranmit one ymbol of the PR with FTP and the PR with ATP, repectively for a number of relay r =4. Like other cheme, we note that the SEP performance of both PR with FTP and PR with ATP are cloe. eanwhile, a difference in power conumption i oberved in Fig. 2. In the abence of interference, the deterioration in SEP performance of PR with FTP compared to PR with ATP i more important due to the improvement of the channel qualitie. In term of data rate, Fig. how that the data rate of PR with FTP i a little higher than that of PR with ATP. The data rate of both cheme remain cloe in the abence of interference. We oberve that the exact curve matche well with the imulation one. oreover, the provided lower bound curve are cloe to the exact one. We conclude that in the preence of interference, which i a practical cae, the deterioration in performance due to the ue of FTP node i light. Thee reult can be exploited to have inight in deigning imple and efficient cognitive radio network. Alo, for O-F relaying, Figure how that the deterioration of SEP performance compared to O-F with ATP i more important than O-AF with FTP and PR with FTP relaying. Thi i due to the efficiency of cooperation in F relaying compared to AF relaying. Since in FTP the cooperation i not alway performed, thi influence the SEP performance when uing F relaying more that AF relaying.

9 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. HAKI et al.: PERFORANCE COPARISON BETWEEN AAPTIVE AN FIXE TRANSIT POWER IN UNERLAY COGNITIVE RAIO NETWORKS Power Conumption irect Tranmiion O AF with FTP O AF with ATP Theoretical curve ata Rate irect Tranmiion PR with FTP (I p PR with ATP (I p PR with FTP (I p PR with ATP (I p Theoretical exact curve Fig. 9. Power conumption comparion of O-AF with FTP and O-AF with ATP for r=4 relay. Fig.. ata rate comparion of PR with FTP and PR with ATP for r =4 relay SEP 2 irect tranmiion PR with FTP (I p 3 PR with ATP (I p PR with FTP (I p PR with ATP (I p Theoretical exact curve 4 Theoretical lower bound curve Fig.. SEP comparion of PR with FTP and PR with ATP for r ==4 relay. Power Conumption irect Tranmiion PR with FTP PR with ATP Theoretical curve E /N (db b Fig. 2. Power conumption comparion of PR with FTP and PR with ATP for r =4 relay. VII. CONCLUSION In thi paper, we have howed that FTP need le ignaling than the ATP and we have evaluated the performance degradation incurred by the FTP node compared to the ATP. We have invetigated three relaying cheme uing FTP for an underlay radio cognitive network operating near a primary receiver: O-F with FTP, O-AF with FTP and PR with FTP. Our propoed relaying cheme work by electing a relay that i able to atify the interference contraint impoed by primary receiver. The correponding relaying cheme with ATP are alo preented in order to compare the performance of relaying cheme with FTP: O-F with ATP, O-AF with ATP and PR with ATP. In thee cheme, relay adjut their tranmit power in order to repect the primary interference contraint. Exact form expreion in the abence and preence of primary interference of the SEP, the data rate and power conumption of O-F are preented in order to validate imulation reult. For implification reaon, exact form expreion for the SEP, the data rate and the power conumption of O-AF with FTP and PR with FTP are provided in the abence of primary interference. Bound of the performance of O-AF with FTP and PR with FTP are given in both the abence and the preence of primary interference. We proved that the ue of O-AF with FTP and PR with FTP conume le power than O-AF with ATP and PR with ATP, repectively. But, O-AF with FTP and PR with FTP incur a light deterioration in SEP performance compared to O-AF with FTP and PR with ATP. For O-F with FTP relaying, we found that the deterioration of SEP performance compared to O-F with ATP i more important than O-AF with FTP and PR with FTP relaying. APPENIX A EXPRESSION OF ΓS, ( AN ΓR ( IN THE O-F PRESENCE OF PRIARY INTERFERENCE To derive the expreion of ΓS (, we need to derive the PF and CF of Γ S. P We have Γ S = S h S, 2 P p h PT,Y 2 +N. Let Z = P S h S, 2 and Y = N + P p h PT, 2. h S, 2 and h PT, 2 are two exponential random variable with mean d and α S, d, α PT, repectively. The CF of Γ S = Z Y i given by ( F ΓS (γ = exp( z N σs, 2 σpt, 2 γ exp( t N σpt, 2 dt, for γ, (37 γ

10 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. IEEE TRANSACTIONS ON COUNICATIONS, ACCEPTE FOR PUBLICATION where σx,y 2 = PX d and σ α PT,Y 2 = X,Y yield to the following expreion F ΓS, (γ = Pp d α PT,Y. Solving thi integral σs, 2 σs, 2 + σ2 PT, γ exp( N γ σs, 2. The PF of Γ S, can be obtained by making the derivative of thi expreion with repect to γ. The obtained expreion i given by f ΓS, (γ = + σ 2 S, σ2 PT, N σs, 2 + σ2 PT, γ exp( N γ σs, 2 (σs, 2 + exp( N γ σ2 PT, γ2 σs, 2, for γ The expreion of ΓS, ( can be obtained by uing the expreion of f ΓS, (γ a in (7. For the derivation of (, we need the PF of Γ ΓR O-F R O-F. Thi i can be determined a follow f (γ = ΓR f O-F Γi, (γ F Γi, (γ. i U k U,k i Thi can be yet expreed a (38 [9], where {l Ri,k} C k= i the et of relay indice in C\{R i }, [ξ p (,...,ξ p ( C ] i the binary repreentation of p 2 C, ξ(p = C ξ p (k and k= Λ (γ = Λ 2 (γ = N σ 2 R i, + σ2 PT, γ and σ 2 R i, σ2 PT, (σr 2 +. (39 i, σ2 PT,γ2 Finally, the expreion of ΓR ( can be obtained by O-F uing the expreion of f ΓR (γ a in (7. O-F APPENIX B EXPRESSION OF ΓR ( IN THE ABSENCE OF O-F PRIARY INTERFERENCE If we ignore the interference from PT, then the PF of when C igivenby[9] Γ R O-F p (γ = ΓR O-F R i C exp γ λ 2 + R i C k= 2 C p= ξ p (k λ 2 R lri,k ( ξ(p λ 2 R i, (4 where {l Ri,k} C k= i the et of relay indice in C\{R i }, [ξ p (,...,ξ p ( C ] i the binary repreentation of p 2 C C and ξ(p = ξ p (n. n= Uing the PF of Γ R O-F in (38, we can deduce it GF, R i C ( = ΓR O-F 2 C p= ( ξ(p λ 2 C R ++ i k=. (4 λ 2 R i ξp(k APPENIX C EXPRESSION OF ( γsr PR WITH FTP The expreion of ΓSR ( can be written a PR with FTP ( = ΓSR PR with FTP ΓSR PR with FTP PR with FTP RPR with FTP =R i ( P(R = R i. (43 PR with FTP The probability P(R = R i i given by [2] R k U R k R i PR with FTP P(R = R i = 2 U 2 p= + λ2 SR k λ 2 SR i ( ξ(p + λ 2 SR k U 2 n= ξ p(n λ 2 SR lri,r k,n, (44 where {l Ri,R k,n} U 2 n= = U\{R i,r k } i the et of relay indice except R i and R k. The conditional GF R PR with FTP =R i = ΓS, ( ΓSRi (, where, the expreion of ΓSRi ( i given by (42 [8], where Ψ(a, b; z i the Tricomi confluent hypergeometric function [2] and ϕ ± ν,μ ( 2 [ + ν + μ ± ( + ν + μ 2 4νμ]. Uing (43 and (44, we obtain the GF of ( γsr PR with FTP when U. REFERENCES [] S. Haykin, Cognitive radio: brain-empowered wirele communication, IEEE J. Sel. Area Commun., vol. 23, no. 2, pp. 2 22, Feb. 25. [2] A. Goldmith, S. Jafar, I. aric, and S. Srinivaa, Breaking pectrum gridlock with cognitive radio: an information theoretic perpective, Proc. IEEE, vol. 97, no. 5, pp , ay 29. [3] Y. Zou, J. Zhu, B. Zheng, and Y. Yao, An adaptive cooperation diverity cheme with bet-relay election in cognitive radio network, IEEE Tran. Signal Proce., vol. 58, no., pp , Oct. 2. [4]. Chen, H. Ji, and X. Li, Optimal ditributed relay election in underlay cognitive radio network: an energy-efficient deign approach, in Proc. 2 IEEE Wirele Commun. Networking Conf., pp [5], itributed bet-relay node election in underlay cognitive radio network: A retle bandit approach, in Proc. 2 IEEE Wirele Commun. Networking Conf., pp [6] C. Luo, F. Yu, H. Ji, and V. Leung, itributed relay election and power control in cognitive radio network with cooperative tranmiion, in Proc. 2 IEEE Int. Conf. Commun., pp. 5. [7] R. Krihna, K. Cumanan, Z. Xiong, and S. Lambotharan, Cooperative relay for an underlay cognitive radio network, in Proc. 29 IEEE Int. Conf. Wirele Commun. Signal Proce., pp. 4. [8] P. Lin, S. Su et al., A low-interference relay election for decode-andforward cooperative network in underlay cognitive radio, in Proc. 2 IEEE Int. Conf. Cognitive Radio Oriented Wirele Netw. Commun., pp [9]. Seyfi, S. uhaidat, and J. Liang, Relay election in underlay cognitive radio network, in Proc. 22 IEEE Wirele Commun. Networking Conf., pp [] S. Huain,. Abdallah,. Alouini,. Hana, and K. Qaraqe, Performance analyi of elective cooperation in underlay cognitive network over rayleigh channel, in Proc. 2 IEEE Int. Workhop Signal Proce. Advance Wirele Commun., pp [] S. Huain,. Alouini,. Hana, and K. Qaraqe, Partial relay election in underlay cognitive network with fixed gain relay, in Proc. 22 IEEE Veh. Technol. Conf. Spring, pp. 5. [2] S. Huain,. Abdallah,. Alouini,. Hana, and K. Qaraqe, Bet relay election uing SNR and interference quotient for underlay cognitive network, in Proc. 22 IEEE Int. Conf. Commun., pp

11 Thi article ha been accepted for incluion in a future iue of thi journal. Content i final a preented, with the exception of pagination. HAKI et al.: PERFORANCE COPARISON BETWEEN AAPTIVE AN FIXE TRANSIT POWER IN UNERLAY COGNITIVE RAIO NETWORKS f (γ = ΓR O-F 2 R i C n= 2 C Λ n (γ p= C ( ξ(p k= σ 2 R lri,k σ 2 R lri,k +σ2 PT, γ ξ p(k exp γ( N σr 2 + i C k= N ξ p (k σr 2. lri,k, (38 ν Ri + μ Ri ΓSRi ( = ϕ + ν Ri,μ Ri ( ϕ ν Ri,μ Ri ( [Ψ(, ; ϕ ν Ri,μ Ri ( Ψ(, ; ϕ + ν Ri,μ Ri (] ( + ϕ+ ν Ri,μ Ri (+ϕ ν Ri,μ Ri ( ν Ri μ [ Ri [ϕ + ν Ri,μ Ri ( ϕ + ν Ri,μ Ri (] 2 ϕ + ν Ri,μ Ri ( ϕ Ψ(, ; ϕ ν ν Ri,μ Ri ( Ri,μ Ri ( ] ( Ψ(, ; ϕ + ν Ri,μ Ri ( + ϕ+ ν Ri,μ Ri (+ϕ ν Ri,μ Ri ( ν Ri + μ Ri 2 [ϕ+ ν Ri,μ Ri ( ϕ ν Ri,μ Ri (] 2 [ϕ + ν Ri,μ Ri ( ϕ ν Ri,μ Ri (] 2 [ ] ϕ ν Ri,μ Ri (Ψ(2, ; ϕ ν Ri,μ Ri ( + ϕ + ν Ri,μ Ri (Ψ(2, ; ϕ + ν Ri,μ Ri ( 2ν Ri μ Ri [ϕ + ν Ri,μ Ri ( ϕ ν Ri,μ Ri (] 2 [ ] ϕ ν Ri,μ Ri (Ψ(2, 2; ϕ ν Ri,μ Ri ( + ϕ + ν Ri,μ Ri (Ψ(2, 2; ϕ + ν Ri,μ Ri (. (42 [3] S. Huain,. Alouini, K. Qaraqe, and. Hana, Reactive relay election in underlay cognitive network with fixed gain relay, in Proc. 22 IEEE Int. Conf. Commun., pp [4] A. S. Ibrahim, A. K. Sadek, W. Su, and K. R. Liu, Cooperative communication with relay-election: when to cooperate and whom to cooperate with? IEEE Tran. Wirele Commun., vol. 7, no. 7, pp , 28. [5] I. Krikidi, J. Thompon, S. claughlin, and N. Goertz, Amplifyand-forward with partial relay election, IEEE Commun. Lett., vol. 2, no. 4, pp , Apr. 28. [6]. Alouini and. Simon, An QF-baed performance analyi of generalized election combining over Rayleigh fading channel, IEEE Tran. Commun., vol. 48, no. 3, pp. 4 45, ar. 2. [7] N. Kong and L. iltein, Average SNR of a generalized diverity election combining cheme, IEEE Commun. Lett., vol. 3, no. 3, pp , ar [8] B. Barua, H. Ngo, and H. Shin, On the SEP of cooperative diverity with opportunitic relaying, IEEE Commun. Lett., vol. 2, no., pp , Oct. 28. [9] H. Boujemâa, Exact and aymptotic NEP of cooperative S-CA ytem uing decode and forward relaying in the preence of multipath propagation, IEEE Tran. Wirele Commun., vol. 8, no. 9, pp , Sept. 29. [2], Exact ymbol error probability of cooperative ytem with partial relay election, European Tran. Telecommun., vol. 2, no., pp , Jan. 2. [2] I. Gradhteyen, I. Ryzhik, and A. Jeffrey, Table of Integral, Serie and Product. Academic Pre, 2. Hela Hakim (S wa born in Sfax, Tuniia in 985. She received the iplôme d ingénieur and the ater degree in telecommunication (both with honor from the higher chool of communication of Tuni (S Com in 29 and 2, repectively. Since September 2, he ha been a Ph.. tudent in information and communication technologie at the higher chool of communication of Tuni. She received everal Tuniian Government fellowhip for her academic excellence during her Sc and Ph.. tudie. She i alo a winner of the Travel Grant of IEEE Wiob Conference 23 and i preelected by the École polytechnique de ontréal a a candidate for the competition of the pretigiou erit Scholarhip program for Foreign Student offered by the initère de l Éducation, du Loiir et du Sport de Québec. Hela Hakim main reearch focu on the cooperative communication, performance analyi of wirele ytem and the pectrum haring in cognitive radio ytem. She act a a reviewer for the IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY journal. Hatem Boujemaa ( 9 wa born in Tuniia in 974. He received the Engineering degree from Ecole Polytechnique, Tuni, Tuniia, in 997 and the.sc. and Ph.. degree in electronic and communication from Ecole Nationale Sérieure de Télécommunication, Pari (Telecom Pari Tech, in 998 and 2, repectively. From October 998 to September 2, he prepared the Ph.. degree at France Télécom R& (Orange Lab. He participated in the National Network for Telecommunication Reearch (RNRT project New Baeband UTS Architecture (AUBE. Between 2 and 22, he wa with Ecole Serieure délectricite (SUPELEC, Gif-ur-Yvette Cedex, France, where he worked on mobile localization for the RNRT project emergency localization uing cellular phone (LUTECE. Since September 22, he ha been with the Higher School of Communication of Tuni, Ariana, Tuniia, where he i currently a Profeor. Hi reearch activitie include the field of digital communication, with pecial emphai on localization, direct-equence code diviion multiple acce (CA, multi-carrier CA, hybrid automatic repeat requet protocol, cognitive radio network and cooperative communication. Weam Ajib ( 5 received the Engineer iploma degree in phyical intrument from the Intitute National Polytechnique de Grenoble, Grenoble, France, in 996 and the iplome detude Approfondie degree in digital communication ytem and the Ph.. degree in computer cience and computer network from the cole Nationale Srieure de Tlcommunication, Pari, France, in 997 and 2, repectively. From October 2 to June 24, he wa an Architect and a Radio Network eigner with Nortel Network, Ottawa, ON, Canada, where he had conducted many project and introduced different innovative olution for the third generation of wirele cellular network. From June 24 to June 25, he wa a Potdoctoral Fellow with the epartment of Electrical Engineering, Ecole Polytechnique de ontral, ontreal, QC, Canada. Since June 25, he ha been with the epartment of Computer Science, Univerity of Quebec at ontreal, ontreal, where he i currently an Aitant Profeor of computer network. He i the author or coauthor of many journal and conference paper. Hi reearch interet include wirele communication and wirele network, multipleand medium-acce control deign, traffic cheduling, multiple-inputmultipleoutput ytem, and cooperative communication. All in-text reference underlined in blue are linked to publication on ReearchGate, letting you acce and read them immediately.