Truyn thng thit b n thit b trong mng t bo 5G: Thch thc, Gii php v nh hng tng laiDevice-to-Device Communication in 5G Cellular Networks: Challenges, Solutions, and Future DirectionsNhm 4, TS. V Nguyn SnKhoa in in t vin thng, H GTVT TP.HCMEmail: dovanvo21@gmail.com

Tm tt - Trong mt h thng di ng thng thng, cc thit b khng c php trc tip giao tip vi nhau trong bng thng di ng c cp php v tt c vic truyn thng phi din ra thng qua cc trm c s. Trong bi vit ny, chng ti hnh dung mt mng di ng hai tng c lin quan n tng macrocell (v d, truyn thng gia BS v thit b) v tng thit b (v d, truyn thng gia thit b v thit b). Thit b chuyn tip u cui c th gip cho cc thit b trong mng hot ng nh trm chuyn tip n cc thit b khc v hot ng nh mt mng li khng dy rng ln. iu ny r rng l mt thay i ln t cc kin trc di ng thng thng v mang li nhng thch thc k thut c o. Chng hn, trong mt h thng di ng hai tng, khi m cc d liu ngi dng c nh tuyn thng qua cc thit b ca ngi dng khc, vn bo mt mt phi c m bo. m bo ti thiu nh hng n hiu sut ca trm macrocell BS hin ti, mng hai tng cn phi c thit k vi chin lc qun l can thip thng minh v phn b ngun lc ph hp cho n. Hn na, m hnh nh gi mi nn c thit k sao cho thu ht cc thit b tham gia trong loi hnh truyn thng ny. Bi vit ca chng ti cung cp mt ci nhn tng quan v nhng thch thc ln trong cc mng hai tng v xut mt s nh gi n vi nhiu loi khc nhau ca cc thit b chuyn tip.T kha - Mng t bo 5G, truyn thng thit b n thit b, thch thc, gii php, nh hng tng lai.Abtract - In a conventional cellular system, devices are not allowed to directly communicate with each other in the licensed cellular bandwidth and all communications take place through the base stations. In this article, we envision a two-tier cellular network that involves a macrocell tier (i.e., BS-to-device communications) and a device tier (i.e., device-to-device communications). Device terminal relaying makes it possible for devices in a network to function as transmission relays for each other and realize a massive ad hoc mesh network. This is obviously a dramatic departure from the conventional cellular architecture and brings unique technical challenges. In such a two-tier cellular system, since the user data is routed through other users devices, security must be maintained for privacy. To ensure minimal impact on the performance of existing macrocell BSs, the two-tier network needs to be designed with smart interference management strategies and appropriate resource allocation schemes. Furthermore, novel pricing models should be designed to tempt devices to participate in this type of communication. Our article provides an overview of these major challenges in two-tier networks and proposes some pricingschemes for different types of device relaying.Keywords 5G cellular networks, device to device communication, challenges, solution, futer directions.1. TNG QUANVi s ra i ca v s cc thit b cm tay thng minh, nhu cu s dng bng thng rng di ng ngy cng gia tng. S tng trng mnh m ca cc ng dng cn nhiu bng thng chng hn nh video streaming v chia s tp tin a phng tin ng n gii hn ca h thng di ng hin ti. Trong thp k ti, cc ng dng di ng phng tin ngy cng phong ph nh hi hp t xa v 3D holography s yu cu tc d liu n gin l khng th thc hin c mng th h th t (4G). Cc nhu cu ngy cng tng i vi d liu cao hn gi v nng lc i hi t duy c o cho cc th h h thng di ng tip theo (5G). Truyn thng hp tc x c li ha nh vy! Truyn thng hp tc x i din cho lp mi ca cc k thut thng tin lin lc khng dy trong cc nt mng gip cc nt mng khc trong vic chuyn tip thng tin s dng li th a dng khng gian. y l m hnh truyn mi ha hn s tng hiu sut ng k v lin kt tin cy, hiu qu quang ph, cng sut ca h thng v phm vi truyn dn. Truyn thng hp tc x nghin cu rng ri trong ti liu v thit b chuyn tip u cui c nh (trong bao gm vic trin khai cc trm gc cng sut thp h tr cc giao tip gia ngun v cc im n) p dng cng ngh 4G Long Term Evolution 4G (LTE) - Tiu chun tin tin [1].Thit b chuyn tip u cui c nh mang li nhng ci tin trong h thng di ng, nhng tim nng y ca hp tc ch c th c thc hin thng qua vic thc hin ca cc thit b chuyn tip. Cc thit b gii hn y c cp n mt in thoi di ng hoc bt k thit b khng dy cm tay khc vi kt ni di ng (tablet , my tnh xch tay,) ca ngi dng. Thit b chuyn tip gip cho cc thit b trong mt mng c hot ng nh rle truyn cho nhau v hot ng nh mt mng li khng dy. iu ny, tt nhin, l c th thc hin vi chc nng giao tip thit b n thit b, cho php hai thit b ln cn giao tip vi nhau trong bng thng di ng cp php m cnmt trm gc (BS) hoc hn ch s tham gia ca BS. iu ny r rng l mt thay i ln so vi cc kin trc di ng thng thng.Trong bn th h u tin ca mng di ng, chc nng giao tip D2D khng c cp. L do phn ln l v n ch yu c hnh dung nh l mt cng c gim chi ph cung cp dch v a phng, trong s dng phn on trong qu kh da trn thng k th trng khai thc di ng. Thi ca cc nh khai thc hng ti chc nng D2D c thay i v mt s xu hng trong th trng khng dy [2]. V d, s lng dch v nhn bit ng cnh v cc ng dng c pht trin nhanh chng. Cc ng dng ny yu cu v tr pht hin v giao tip vi thit b ln cn, v s sn c ca mt chc nng nh vy s gim c chi ph truyn thng gia cc thit b. Chc nng D2D cng c ng vai tr quan trng trong vic tnh ton m my di ng v to iu kin chia s hiu qu cc ngun lc (quang ph, sc mnh in ton, ng dng, ni dung x hi,) cho ngi dng n ngi dung khc trong khng gian gn. Cc nh cung cp dch v c th nng cp chc nng D2D p ng cho mng a phng nh mt sn vn ng hoc mt trung tm ln bng cch cho php truyn trc tip gia cc in thoi di ng v cc thit b khc. Hn na, truyn thng D2D c th c s dng cnh bo trong cc thm ha thin nhin.Trong mt trn ng t hoc bo, mt mng li thng tin lin lc khn cp c th c thit lp bng chc nng D2D trong mt thi gian ngn, thay th cc mng li giao thng b h hng v c s h tng Internet. Trn th trng hin nay, cc cng ngh nh WiFi hoc Bluetooth cung cp mt s chc nng truyn thng D2D. Tuy nhin, cc hot ng ny khng c giy php v s can thip l khng kim sot c. Ngoi ra, chng khng th cung cp bo mt v cht lng dch v (QoS) m bo nh trong mng di ng. Khng mun mt th trng D2D mi ni, cc nh khai thc di ng v nh cung cp ang tm ti cc kh nng a giao tip D2D vo mng di ng. Mt s cng trnh gn y v D2D trong h thng di ng a kt qu v vn qun l can thip v phn b ti nguyn v tuyn [4-6] cng nh thit lp phin truyn thng v quy trnh qun l [3].Trong bi vit ny, u tin chng ti cung cp mt loi ca truyn thng D2D da trn mc s tham gia ca cc nh iu hnh di ng. Sau chng ti tm tt mt s thch thc ln cn c gii quyt trc khi chc nng D2D c gii thiu. C th, chng ti tho lun v an ninh, qun l can thip, v phn b ngun lc vn v ch ra mt s nh hng cho nghin cu trong tng lai. Trong phn cn li ca bi vit, chng ti tp trung vo gi c, mt thch thc ln trong thc hin D2D trong thc tin v kin ngh mt s phng n gi hp dn cho c ngi dng v khai thc2. TNG QUAN V PHN LO TRUYN THNG D2D V NHNG THCH THC K THUTTrong bi vit ny, chng ti hnh dung mt mng di ng 5G hai tng c gi l tng macrocell v tng thit b. Tng macrocell lin quan n truyn thng gia trm gc v thit b nh trong mt h thng di ng thng thng. Tng thit b lin quan n truyn thng D2D. Nu mt thit b kt ni vi mng di ng thng qua mt BS, thit b ny c cho l hot ng trong cc tng macrocell. Nu mt thit b kt ni trc tip n thit b khc hoc nhn truyn thng tin qua s h tr ca cc thit b khc, cc thit b ny c gi l hot ng trong tng thit b. Trong mt h thng nh trn, BS s tip tc phc v cho cc thit b nh bnh thng. Tuy nhin, ti nhng thi im mng qu ti hoc ti vng b tc nghn, cc thit b s c php giao tip vi nhau, to ra mt mng li khng dy.Trong vic thc hin truyn thng trong tng thit b, cc nh iu hnh c th c mc iu khin khc nhau. Da trn m hnh kinh doanh, iu ny kim sot mt phn hoc ton b i vi ti nguyn phn b cc ngun, ch v chuyn tip thit b, hoc khng c bt k s kim sot no. Do , chng ta c th chia thnh bn loi chnh ca truyn thng ca tng thit b (Hnh 1-4).Thit b chuyn tip vi s iu khin thit lp lin kt ca nh iu hnh (DR-OC): Mt thit b nm trong vng qu ti hoc trong mt khu vc sng yu c th giao tip vi BS qua vic chuyn tip thng tin ca mnh thng qua cc thit b khc. iu ny cho php cc thit b t c cht lng dich v tt hn hoc tng tui th ca pin. Cc nh iu hnh giao tip vi cc thit b chuyn tip thit lp lin kt kim sot mt phn hay ton b.

Hnh 1. Minh ha thit b chuyn tip thng tin lin lc vi s iu khin lin kt ca nh iu khai thc (DR-OC). Mt thit b giao tip vi BS thng qua chuyn tip thng tin ca n thng qua cc thit b khc.Qun l truyn thng D2D vi s iu khin thit lp lin kt ca nh kai thc (DC-OC): Cc cc thit b ngun v thit b ch ni chuyn v trao i d liu vi nhau m khng cn thng qua trm gc, nhng chng vn c h tr bi cc nh iu hnh cho php thit lp lin kt.

Hnh 2. Minh ha qun l truyn thng D2D vi s iu khin thit lp lin kt ca nh kai thc (DC-OC). Cc thit b ngun v ch c th ni chuyn v trao i d liu vi nhau m khng cn BS, nhng h c h tr bi cc BS thng qua mt lin kt kim sot.

Thit b chuyn tip vi s iu khin thit lp lin kt ca thit b (DR-DC): Cc nh iu hnh khng phi l tham gia vo qu trnh hnh thnh lin kt. Do , cc thit b ngun v ch phi phi hp giao tip nh thit b chuyn tip.

Hnh 3. Thit b chuyn tip vi s iu khin thit lp lin kt ca thit b (DR-DC). Cc thit b ngun v ch trc tip ni chuyn vi nhau v khng s dng bt c lin kt iu khin t cc nh khai thc.Qun l truyn thng D2D s iu khin thit lp lin kt ca thit v (DC-DC): Thit b ngun v thit b ch c th giao tip trc tip vi nhau m khng c bt k s kim sot ca nh iu hnh. Do , thit b ngun v thit b ch nn s dng cc ngun ti nguyn ttheo mt cch no m bo hn ch s can thip vi cc thit b khc trong cng mt tng v tng macrocell.

Hnh 4. M t Qun l truyn thng D2D s iu khin thit lp lin kt ca thit v (DC-DC).Mt h thng di ng hai tng, nu c thit k cn thn, c th mang li nhng ci thin ng k trong kin trc h thng di ng c in. Trc khi gii thiu chc nng D2D, mt s thch thc k thut, c bit l trong cc vn bo mt v qun l can thip, nn c khc phc.Khi d liu ngi dng c nh tuyn thng qua cc thit b ca ngi s dng khc, bo mt phi c m bo. Mt gii php c th m bo bo mt l truy cp ni b cho php cc thit b mun hot ng trong tng thit b. Trong truy cp ni b, mt thit b c trong tay danh sch cc thit b "tin cy", v cc thit b khng co trong danh sch ny th phi s dng tng macrocell giao tip vi n. V d, ngi s dng trong mt khu ph hoc ni lm vic m bit nhau, hoc nhng ngi s dng c xc thc thng qua mt bn ng tin cy nh mt t chc, c th trc tip giao tip vi nhau. Cc thit b trong mt nhm c th thit lp mt m ha thch hp trnh tit l thng tin vi cc thit b khc. Trong trng hp truy cp m, mi thit b c th hot ng nh mt thit b chuyn tip cho cc thit b khc m khng c bt k hn ch no. V khng c bt k loi gim st no, bo mt trong trng hp ny m ra thch thc i vi vn nghin cu. Vn bo mt trong truyn thng D2D lin quan n vic xc nh cc kh nng ca cc cuc tn cng, e da, v d b tn thng ca h thng. Trc y, lm vic v cc vn bo mt ca truyn thng gia cc my mc [7-11] c th c khai thc gii quyt cc vn bo mt trong truy cp m D2D. V d, cc cng vic trong [7] xut mt mi trng tin cy thit lp mi quan h tin cy gia cc thit b M2M, trong khi bo mt da trn iu khin truy cp c tho lun trong [8]. Bo mt nh tuyn, phn mm da trn kha mt m cn i, v pht hin nguy c ca cc cuc tn cng ang tip tc c nghin cu trong [9-11].Mt mi quan tm ng k trong mt h thng hai cp l qun l can thip. Trong DR-OC v DC-OC, phn b ngun lc v thit lp cuc gi c thc hin bi BS. V vy, cc BS c th gim bt vn qun l can thip n mt mc no bng cch s dng cc phng php tp trung, mt khu vc nghin cu lu di trong truyn thng khng dy. Mt khc, trong DR-DC v DC-DC, khng c s tp trung thc th qun l phn b ngun lc gia cc thit b. Hot ng trong cng bng tn cp php, cc thit b chc chn s nh hng n ngi dng macrocell. m bo tc ng ti thiu v tc ng hin ti ca trm BS, mt mng hai tng cn phi c c thit k vi chin lc qun l can thip thng minh v phn b ngun lc ph hp vi n. Bn cnh s giao thoa gia cc tng macrocell v tng thit b, gy ra nhiu cho nhng ngi s dng trong tng thit b. gii quyt vn phn phi ti nguyn cho loi truyn thng ny, nhng phng php tip cn khc nhau nh tng hp ti nguyn [4], tr chi khng hp tc hoc tr chi thng lng [12], quyn kim sot v phn b nng lng [6], phn vng cluster, v la chn thit b chuyn tip [13] c th c s dng.Trong DR-OC, nh minh ha trong Hnh 1, trm BS l mt trong cc bn giao tip, mt s nhng thch thc ni trn c th c gii quyt bi s kim sot ca cc BS s dng cc phng php hin c [5]. Cc BS c th xc thc cc thit b chuyn tip v s dng m ha thch hp duy tr bao mt thng tin ca thit b. Cc BS cng c th qun l vic phn b ph tn gia cc thit b chuyn tip c th ngn chn s can thip t cc thit b khc.Trong DC-OC, minh ha trong Hnh 2, cc thit b giao tip trc tip vi nhau thng qua s iu khin thit lp lin kt ca nh iu hnh. C th, nh iu hnh xc thc truy cp, kim sot kt ni, phn b ngun lc, v s tng tc tin t gia cc thit b. N c y kim sot cc kt ni D2D, bao gm c chc nng iu khin my bay (v d, thit lp kt ni v bo tr), v chc nng d liu my bay (v d, phn b ngun lc). Cc kt ni D2D trong tng thit b phn c chia s bng tn cp php di ng vi cc kt ni di ng thng xuyn trong tng macrocell. H thng mng c th t ng phn b ngun lc cho mi kt ni D2D theo cng mt cch nh l mt kt ni di ng thng xuyn hoc ng k mt nhm ti nguyn dnh ring cho tt c cc kt ni D2D.Trong DR-DC v DC-DC, khng c BS hay my ch kim sot cc thng tin lin lc gia thit b. Nh th hin trong Hnh 3 v 4, nhiu thit b giao tip vi nhau bng cch s dng truyn thng hp tc hoc truyn thng khng hp tc, v mt hoc nhiu thit b c th ng vai tr thit b chuyn tip cho cc thit b khc. Loi hnh truyn thng ny t ta nhiu thch thc hn so vi cc loi truyn thng trc , v khng c s gim st tp trung ca trm chuyn tip. Thit lp kt ni, qun l giao thoa v phn b ngun lc cn c gii quyt bng cch s dng phng php phn phi. Trc giai on truyn d liu, hai thit b cn phi tm thy nhau v cnh nhau (v d, pht hin thit b tng thch v thit lp kt ni D2D). Cc thit b c th pht thng tin nh k nhn dng cc thit b khc c thc s tn ti v quyt nh xem cc thit b c kt ni D2D trc tip hoc l truyn thng chuyn tip hay khng [4].

3. VN V NH GIBn cnh nhng thch thc k thut tm tt trong phn trc, mt nh khai thc cn phi bit thc hin nh th no kim sot v chi ph cho dch v D2D. C th i vi mt s ngi dng, nu tnh ph cho cc dch v D2D, c th h s chuyn sang cng ngh D2D truyn thng, c min ph b li tc thp hn v bo mt km. Do , cc nh khai thc phi gii quyt c cu hi "chi tin vo vic g" trc khi h c th thc tin s kim sot - iu hnh cng ngh D2D, trong yu cu phn tch su cc loi hnh s dng v m hnh kinh doanh.Thit b chuyn tip cho nhng ngi dng khc s dng ngun lc nh vic lu tr pin, d liu, v bng thng. V vy, m hnh nh gi cng cn c thit k thu ht cc thit b tham gia vo loi hnh truyn thng ny. Hn na, trong truyn thng D2D trc tip, cc thit b cn phi c mt mi trng an ton cho qu trnh mua v bn ti nguyn vi nhau. Cc nh iu hnh c th kim sot v to ra mi trng an ton cho truyn thng loi ny. V vy, cc nh khai thc c th mong i thanh ton t thit b cho vic bo mt v QoS trong giao tip D2D.Sau y, chng ti tho lun v vn gi c cho mi loi truyn thng D2D v kin ngh mt s gii php s dng cng c t l thuyt tr chi v l thuyt u gi.3.1 NH GI CHO DR-OCThch thc chnh trong DR-OC l cung cp y tin ch cho thit b chuyn tip. H s dng cc ngun lc (v d, pin, bng thng) chuyn tip cc thng tin ca cc thit b khc, h cn thu ht v gi hoc cc u i cc thit b tham gia vo loi hnh truyn thng ny. Mt la chn khc l cc nh khai thc c th gim gi trn ha n hng thng da trn lu lng d liu m ngi dng s dng thng qua thit b. T quan im cu nh cung cp th gim gi nh vy c xem l phng php hp l, bi v li ch ca nh khai thc n t cc dch v cung cp cho thit b thiu bo v hoc i hi d liu mc gi cao hn th c sn trong tng macrocell.Cc u i khc cho cc chuyn tip thit b, thay v gim gi cho ha n hng thng, cc nh khai thc c th cung cp mt s dch v min ph i s lng d liu m h s dng. V d, gi s rng sau y tin ch c xc nh [12]:

Trong , l knh bng thng c s dng bi thit b th i, v "doanh thu" ca t vic s dng ny l . y, ki = 1.5/ln(0,2 / BERtar) biu th hiu sut ph [7], l tn s tn hiu trn nhiu trung bnh (SNR) biu th mc lin kt gia cc thit b th i v BS, BERtar l t l li bit, v M l s hops gia cc BS v cc thit b th i trong d liu truyn. Theo nh thit b trung k cho thy, thit b th i nn gi bipi cho nh nh khai thc, vi pi l n gi ca ph. Gi tr cui cng trong biu thc (1) l hoa li ca thit b thit b th i l bng thng c tng () l s khuyn khch a ra bi cc nh khai thc cho cc thit b chuyn tip. biu th gi tr SNR trung bnh cho lin kt gia thit b th i v BS trong sut qu trnh truyn ti trn nn d liu c tng. Gi s c N thit b , doanh thu cho cc nh khai thc c th c tnh nh sau:

Hnh 5. So snh doanh thu cu thit b v nh khai thc trong h thng di ng n tng thng thng v h thng xut hai tng vi DR-OC.Trong Hnh 5, chng ti minh ha cc ngun thu nhp ca nh khai thc v ca cc thit b trong DR-OC v so snh vi truyn thng truyn thng. Trong DR-OC, cc nh khai thc nh gi c nh ph tn v cung cp ph min ph cho cc thit b trong qu trnh trao i chuyn tip d liu. Chng ti gi nh bi = 5 MHz, ki = 0.2 v 5 25 dB, v M = 1 (tc l, giao tip qua hop n). S lng thit b phc v bi cc iu hnh c gi nh l 100 (N = 100). Bng thng cp pht cho cc thit b, chng ti gi nh = 2.5 MHz v 2.5 12.5 dB. iu ny cho thy bng thng c cp pht min ph th t. Trong truyn thng hp tc th cc thit b h tr QoS tt hn, n c th c d kin rng chng s c tch hp nhiu hn bi cc nh khai thc so vi h thng di ng tng n thng thng. Chng ti gi nh rng cc n gi ca ph l 1 (tc l, pi = 1) cho truyn thng thng thng (khng hp tc) v pi = 1.2 i vi trng hp DR-OC. Theo gi nh, ta quan st trong Hnh 5 rng doanh thu ca nh khai thc v cc thit b trong mt mng hai tng vi DR-OC tng so vi h thng di ng n tng. C th, i vi cc gi tr ca con s t c, nh khai thc doanh thu tng gp i vi SNR cao, trong khi doanh thu ca cc thit b tng khong 28 phn trm trong iu kin tt nht. Do , chng ta c th kt lun rng DR-OC l mang li nhiu li ch hn cho cc nh khai thc.

3.2 NH GI CHO DC-OCMt thch thc quan trng trong DC-OC l c phng n gi hp dn p ng nhu cu ngi dng vi dch v ny thay v s dng WiFi min ph hoc Bluetooth. Thit k mt m hnh nh gi c th c xem xt nh l mt vn giao dch ph. Trong kinh doanh ph, mc tiu ca mt ngi bn l ti a ha doanh thu/li nhun, trong khi mc ch ca ngi mua l ti a ha cc tin ch ca vic s dng ph tn. Tuy nhin, nhng mc tiu ny thng mu thun vi cc mc tiu khc. V vy, mt gii php ti u v n nh trong kinh doanh ph v nh gi v phn b ph s c t ra doanh thu v tin ch c ti a ha, trong khi c ngi bn v ngi mua u hi lng v khng mun lm lch hng vi cc gii php. L thuyt u gi cung cp mt khun kh hu ch ca cc cng c ton hc cho vic thit k cc m hnh nh gi. K t khi thit b khng bit cc b dn nhp gi tr (cc thit b khc) gn vi cc ngun ti nguyn, cung cp mt c ch u gi hiu qu cho cc thit b c c doanh thu cao hn l vic u gi thng qua gi c tnh. u gi cng c li cho cc nh u t, nhn chung chng s c n nh cho nh thu no tr gi cao nht. Mt bi cnh khc l cch tip cn thit k phng n hiu qu cho vic phn b ti nguyn chng hn l mt mi trng s hn ch s can thip c gi l l thuyt tr chi. L thuyt tr chi cung cp mt tp hp cc cng c ton hc mnh m gii thch cc mu thun v hp tc gia s quyt nh hp l v thng minh ca cc nh sn xut.Trong s cc loi u thu, mt c cu thu nh gi u tin, gi c c th c s dng nh mt chng trnh gi hp dn cho DC-OC trong mt th trng c quyn2 [12]. Trong kiu u thu ny, cc cp thit b, nhng ngi mun trao i vi nhau s np h s d thu n BS. BS chn gi cao nht v n nh cc knh truyn. BS c th thit lp mt mc gi dnh cho mt knh, nh thu no nh gi cao hn mc ngng th s ginh chin thng. Cc BS cng c th bn cng mt knh cho hn hai ngi dng, gi s khong cch khng b nhiu3, v t c doanh thu nhiu hn t mt knh trong so vi trng hp khng hp tc.i vi mt th trng c quyn, khi c nhiu ngi bn, ngi ta c th s dng m hnh Bertrand [12] cho vic thit k cc m hnh nh gi. Trong m hnh khng hp tc, c hai chc nng tin ch khc nhau, mt cho nhng ngi bn hng v mt cho ngi mua. Ngi bn v ngi mua c gng ti a ha doanh thu ca h thng qua vic ti a ha tin ch ca h. Trong m hnh ny, cc thit b mun bn ti nguyn c nh mt mc gi v thng bo cho cc thit b mun mua ngun lc. M hnh ny c th xem nh l nh l cn bng Nash m mc ch l tm mt im cn bng nh vy nu khng c ngi bn th c th ci thin c mc tiu ca n bng cch a ra cc chin lc c la chn bi cc ngi bn hng khc cng nh l t phn ng ca ngi mua.Ly mt v d minh chng doanh thu ca cc nh khai thc v cc thit b trong mt h thng di ng hai tng vi DC-OC, chng ta xem xt mt v d sau y. Gi s ch c mt nh khai thc trong th trng c 50 knh c sn, vi mi bng thng l 5 MHz, v s lng cc thit b bin thin khong t 100 n 800. Trong mt h thng di ng n tng thng thng, ti mt thi im ch c 100 thit b c th ni chuyn vi nhau theo cc gi nh 50 knh c sn. Hin nay gi s mt h thng di ng hai tng vi DC-OC v thit lp mt mc gi r dnh cho cc h s d thu. Do , cc thit b c th gi bt k gi cao hn so vi gi nh da trn nh gi ca h v ph tn. Cho pC = 1 biu th n gi ph trong mt h thng di ng mt tng. Chng ti tip tc gi nh rng nh thu a ra cho ph bi cc thit b trong mt h thng hai tng c gi tr trong khong [r, pmax], trong pmax l gi tr ti a ca h s d thu. Cc nh khai thc thu thp tt c cc h s d thu v phn b cc knh c sn cho nh thu a ra gi cao nht. Doanh thu ca nh khai thc l tng doanh thu t thit b trng thu, trong khi doanh thu ca cc thit b n t s chnh lch gia nh gi ca h v gi thanh ton cho cc nh khai thc [12].Trong Hnh 6, chng ti s dng k hiu ca n v tin t (CU) thay v cho cc loi ngoi t khc, gi s r = 0.1, pmax = 2, v minh ha cho doanh thu ca c nh khai thc v thit b. Theo quan st ta thy rng doanh thu ca cc nh iu hnh DC-OC tng vi s lng ca cc thit b ngy cng tng ln theo gi tr ca h s d thu tng. Mt khc, trong h thng di ng n tng, doanh thu ca cc nh khai thc vn khng i ngay c khi cc nh khai thc khai thc ti a ca mt mng li. Doanh thu ca cc nh khai thc trong mng hai tng vi DC-OC l hn 10 phn trm so vi h thng di ng n tng. Doanh thu ca cc thit b trong c hai trng hp th gim so vi s gia tng s lng thit b. Tuy nhin, s lng doanh thu m c th t c cho cc thit b trong mt mng hai tng hn 48 phn trm so vi mng n tng khi s lng thit b l 100. iu ny lm gim n 6 phn trm doanh thu khi s lng thit b tng ln 800. Do gi tr ca h s d thu tng cng vi s gia tng s lng thit b dn n doanh thu ca cc thit b gim. Cn lu thm rng trong DC-OC, v c rt nhiu knh c sn, thit b c th c hng lu lng nhiu hn so vi h thng di ng n tng.

Hnh 6. So snh doanh thu ca thit b v nh khai thc trong h thng di ng n tng v h thng hai tng vi DC-OC. Mt th trng c quyn c gi nh v c cu thu nh gi u tin c dng.3.3 NH GI CHO DR-DC v DC-DCKhi cc nh khai thc khng c bt k s kim sot no i vi cc thit b chuyn tip, v th s khng c bt k doanh thu no t cc thit b. Trong khun kh truy cp DR-DC, khi cc thit b bit nhau thng qua nhiu cch khc nhau chng hn thng qua mt mi lin h hoc l mt thnh vin ca mt nhm hoc hip hi, h c th thng lng v gi c hoc ch n gin l trao i thng tin m khng cn phi thanh ton bt k khong ph no cho cc thit b khc, tng t nh khi mt ngi dng gi mt tp tin bng cch s dng Bluetooth hoc WiFi cho bn b ca mnh. Trong truy cp m DR-DC, ngi dng c th p dng cc phng php nh gi khc nhau nh cn bng th trng, tr chi hp tc, m hnh hp tc, hoc u gi kp [12].i vi vic nh gi gia cc thit b trong DC-DC, chng ti c th gi nh rng ngi s dng ch ngh n li ch bn thn v c cc mi quan h x hi, v do s khng biu th cc thi ging nhau i vi tt c cc thit b khc. Cc thit b ny cng s cn phi gi tin nhn n cc thit b khc vo nhng thi im no , cc thit b cn li ch ca bn thn nn chng s khng yu cu bt k thanh ton no t cc thit b trong nhm hoc tp th m n lm vic chung. V d, mt phng php nh gi c xut trong [14], trong mi thit b ghi li cuc gp g vi khc thit b. Bt c khi no mt thit b ch k no nhn c tin nhn t mt thit b khc, n cp n nhng h s ny v tnh ton t l gp mt, v khong cch ca cc cuc gp hng ngy. Da v iu ny, cc thit b ny s hng ti thit b m h thng xuyn gp nhau, v n hiu rng cc thit b ny l tt hn so vi cc thit b ch bit v li ch c nhn.4. KT LUNTrong bi vit ny, chng ti hnh dung ra mt mng di ng 5G hai tng vi tng macrocell v tng thit b. Trong vic thc hin truyn thng ca tng thit b, cc nh khai thc c cc mc can thip khc nhau da trn cc m hnh kinh doanh. Chng ti a ra mt loi truyn thng D2D nh gi mc tham gia ca cc nh khai thc di ng. Sau , chng ti tho lun v mt s thch thc cng ngh ch yu cn gii quyt i vi tng loi, chng hn nh bo mt, qun l s giao thoa, v vn phn b ti nguyn. Trong phn cn li ca bi vit, chng ti tp trung vo vn nh gi v xut mt s phng n nh gi cho mng hai tng s dng cc cng c ca l thuyt tr chi v l thuyt u gi. Kt qu ca chng ti chng minh rng phng n nh gi c thit k mt cch sng sut cho mt mng di ng hai tng mang li doanh thu ng k cho c cc nh khai thc v ngi s dng so vi mt mng di ng n tng.TI LIU THAM KHO[1]C. Hoymann et al., Relaying Operation in 3GPP LTE: Challenges and Solutions, IEEE Commun. Mag., vol. 50, no. 2, Feb. 2012, pp. 15662.[2]D. Astely et al., LTE Release 12 and Beyond, IEEECommun. Mag., vol. 51, no. 7, 2013, pp. 15460.[3]K. Doppler et al., Device-to-Device Communication as an Underlay to LTE-Advanced Networks, IEEE Commun. Mag., vol. 47, no. 12, Dec. 2009, pp. 4249.[4] G. Fodor et al., Design Aspects of Network Assisted Device-to-Device Communications, IEEE Commun. Mag., vol. 50, no. 3, Mar. 2012, pp. 17077.[5] L. Lei et al., Operator Controlled Device-to-Device Communications in LTE-Advanced Networks, IEEE Wireless Commun., vol. 19, no. 3, June 2012, pp. 96104.[6] D. Feng et al., Device-to-Device Communications Underlaying Cellular Networks, IEEE Trans. Commun., vol. 61, no. 8, 2013, pp. 354151.[7] I. Cha et al., Trust in M2M Communication, IEEE Vehic. Tech. Mag., vol. 4, no. 3, Sept. 2009, pp. 6975.[8] J. Yue et al., Secrecy-Based Access Control for Deviceto - Device Communication Underlaying Cellular Networks, IEEE Commun. Letters, vol. 17, no. 11, 2013, pp. 206871.[9] A. Perrig, J. Stankovic, and D. Wagner, Security inWireless Sensor Networks, Commun. ACM, vol. 47, no. 6, June 2004, pp. 5357. [10] Y. Zhou, Y. Fang, and Y. Zhang, Securing Wireless Sensor Networks: A Survey, IEEE Commun. Surveys Tutorials, vol. 10, no. 3, 2008, pp. 628.[11] R. Muraleedharan and L. A. Osadciw, Jamming Attack Detection and Countermeasures in Wireless Sensor Network Using Ant System, Defense and Security Symp., May 2006, p. 62480G.[12] E. Hossain, D. Niyato, and Z. Han, Dynamic Spectrum Access and Management in Cognitive Radio Networks, 1st ed., Cambridge Univ. Press, 2009.[13] B. Zhou et al., Intracluster Device-to-Device Relay Algorithm with Optimal Resource Utilization, IEEE Trans. Vehic. Tech., vol. 62, no. 5, 2013, pp. 231526.[14] N. Fernando, S. W. Loke, and W. Rahayu, MobileCloud Computing: A Survey, Future Generation Computer Systems, vol. 29, no. 1, Jan. 2013, pp. 84106.