PHAN TV H VA DANH GIA CAC MO HINH DIEU KHIEN THAM NHAP CUOC GOI SU DUNG L O G I C M O TRONG MANG TE BAO CDMA DA LOP LUU LUONG
ThS. NCS. VO TRUONG SON PGS. TS. LE HUNG LAN TS. NGUYEN THANH HAI Khoa Dien - Dien lu
Tnr&ng Dili hoc Giao thong Van ldi
Tdm tdt gaj i,ao ndy phdn tich cdc nghien ciru dd cd trong nhung ndm gdn ddy vi cdc mo hinh CAC cho cdc mgng te bdo CDMA da Idp dich vu trin ca sa logic md. Viic ddnh gid cac mo hinh ndy ciing dugc thuc hiin dudi cdc gdc do khde nhau. Cdc nhdn xet vi ini diim vd nhugc diim cua tirng md hinh cUng dugc Ir'inh bdy kem theo cdc phdn tich vd ddnh gid ndi tren.
Summary: ^his paper analyses the previous work on CAC schemes using Fuzzy Logic (ECAC) in CDMA Network with Multi Class Traffic. The estimation of the schemes is also made in differeiU aspects. The advantages and disadvantages of each scheme are also described in the paper.
I. GIOI THIEU
Quan ly tai nguyen la mdt trong nhiing van dl ky thuat quan trpng nhat trong cac he thdng 3G, noi dap irng dupe nhilu ldp luu lupng ma trong dd mdi ldp dugc dac trung bdi ciic tham sd chat lupng djch vu (QoS) yeu cau ciia rieng nd. Dilu khien tham nhap cudc gpi (CAC) la mdt trong nhung chirc nang quan ly tai nguyen, nd quy djnh viec tham nhap mang phai dam bao QoS. CAC dup-c sir dung dl quylt djnh chap nhan hay khdng mdt yeu cau dich vu mdi va muc tieu cua nd la cho phep mot so lugng toi da cac yeu cau djch vu trong khi van dam bao dugc QoS yeu cau ciia tat ca cac kit ndi dang boat ddng. CAC trong cac he thdng CDMA kinh dien deu dua vao viec danh gia nhilu hoac ty sd tin hieu tren nhieu va so sanh vdi ngudng. Theo truyln thong, mdt md hinh CAC phai xem xet mdt tap hgp cac tham sd do dugc tir trang thai mang nhu cdng suSt tin hieu thu dugc, cac gia trj QoS thuc te v.v... de quyet djnh chap nhan hay tir choi mdt yeu c^u kit noi. Dang md hinh nay khdng cho phep hoac cho phep mdt each rat ban chi sir thilu chinh xac cua cac ket qua do ndi tren. Tuy nhien, trong cac he thdng khdng day, do su di chuyin ciia cac thue bao, cac yeu cau QoS ddng, va dieu kien kenh thay ddi nen cac kit qua do nay ndi chung la thieu chinh xac. Han niia. rat khd de cd dupe mcit thdng ke day dil luu lupng dau vao. Do dd, cac quyet dinh tham nhap phai dua tren cac ket qua do mo- hd va thieu chinh xac.
Dk^ giai quylt van de nay, logic md cung cap mdt phuong phap thuc hien xap xi nhung hieu
qua cho md hinh CAC, theo dd neu sir dung cdng cu toan hpc thi rat phirc tap va khdng de thuc hien. Vdi kha nang cd the giai quyet cac van de mang tinh ma hd va thieu chinh xac, logic md dupe hy vpng se cung cap mpt giai phap tdt de phat triln cac md hinh CAC [16].
Bai bao nay phan tich cac nghien ciiu da cd trong nhtrng nam gan day ve cacjnd hinh CAC _ cho cac mang te bao CDMA da ldp dich vu tren ca sd logic md. Viec danh gia cac md hinh nay cung dugc thuc hien dudi cac gdc do dam bao QoS cung nhu sir tan dung tai nguyen. Cac nhan xet ve uu diem va nhugc diem ciia tirng md hinh cung dugc trinh bay kem theo cac phan tich ndi tren. Phan cdn lai cua bai bao nay bao gdm cac muc sau: phan 2 gidi thieu khai quat ve md hinh he thdng CDMA te bao. Phan 3 phan tich cac md hinh CAC cho cac mang te bao CDMA da ldp djch vu tren ca sd logic md. Phan 4 danh gia va nhan xet cac md hinh ndi tren. Cudi cimg, ket luan dugc cho d phan 5.
II. MO HINH HE THONG VA LU^U LlTOTVG
Gia thiet mdt he thdng te bao CDMA bang rdng vdi cac te bao luc giac cd kich thude bang nhau. Mdi te bao cd mdt BS tai tam ciia nd vdi mdt anten dang hudng (omni). Phd tan sd vd tuyen nhu nhau dugc tai sii- dung d tat ca cac te bao. Cac thue bao di ddng (Mobile Station, MS) lien lac vdi cac tram gdc (Base Station, BS) ciia te bao hien tai qua giao tiep vd tuyen va mdt vai BS dugc ket ndi tdi trung tam chuyen mach di ddng (Mobile Switching Center, MSC) va MSC nay dugc ket ndi tdi mdt mang true. Cac bang tan khac nhau dugc sii- dung cho cac hudng len va xudng, vi vay mdi mdt BS chi bj nhieu tir cac MS.
Hinh 1. Cdc te bdo luc gidc
Hinh 1 bieu dien cac te bao luc giac, d dd, MS xem xet dat tai diem M. Dl don gian trong trinh bay, chiing ta se chi tap trung tdi thdng tin di chuyen va bang thdng hieu dung ciia MS cd lien quan tdi BS phuc vu (ky hieu la BSo) va sau BS lan can vdi nd thupc ldp dau tien (ky hieu la BS|. BS: BS„). Gpi d|(t). 1 = 0, 1, ..., 6 la ky hieu khoang each giua MS va BS, tai thdi diem t. Gia thiet may thu phat dupe thiet ke tich hpp, tap am ciia kenh chii yeu la do hien tugng che khuat va sii\- hao dudng truyen. Gia trj trung binh ciia cdng suat tin hieu Pilot tii- BS| thu dugc tai MS cd the dugc md ta nhu [4]:
Tdp chi KHOA HQC GIAO HIONG yAN TAI So 29 - 03/2010 45
a (t) = Y d ( t ) / D 10
q,(t)/10^
Vj(t) (1)
a (t) = Y 1 0 ^ t ) / L
WfiC 1 iL 1 0
Trong do Yi la hang so ty le vdi cdng suat tin hieu dugc phat di, r la sd mu ciia suy hao
•Ig truyln. Do la la khoang each tham khao. va tM theo dB tai bat ky thdi diem t nao la m(?t J! ngau nhien Gaussian (vdi gia tri trung binh bang 0 va do lech chuan bang as) dac trung cho
;en tugng bdng md. Vdi 1 f k, £,i(t) va ^k(t) la cac qua trinh nglu nhien ddc lap. N I U cac mire dng suat phat ciia cac tin hieu Pilot la giong nhau thi YI = Y vdi 1 = 0, 1 6. V|(t) bieu dien cdng suat tap am nen va nhieu da tham nhap (MAI) tir cac tin hieu mang tin cua tuyen xudng tdi tat ca MS. Khi cd mpt so lugng Idn cac user trong he thong, MAI cd the dupe md hinh hoa xap xi bang mdt qua trinh ngau nhien Gaussian.
Trong bai bao nay, cudc gpi dupe hilu cd the la bat ky loai dich vu nao. Cac loai cupc gpi khac nhau dugc phan biet bang cac yeu cau nhu luu lupng. QoS. dp uu tien khac nhau. Cd hai tham sd chinh la ty le chan va ty le ngit, dugc sir dung de danh gia QoS trong cac mang khdng day. Ty le chan chi ra ty le tir chdi cac cupc gpi mdi. trong khi ty le ngat chi ra ty le hiiy bo cac cudc gpi chuyen giao. • ; -,
III. CAC MO HINH DIEU K H I E N THAM NHAP CUOC GOI M O
Do tinh chat quan trpng ciia thii tuc dilu khiln tham nhap cudc ggi trong cac mang te bao CDMA nen da cd nhilu nghien ciru tap trung vao cac md hinh CAC trong nhiing nam gan day.
Cd thi phan cac md hinh nay thanh ba nhdm ca ban, dugc trinh bay cu the dudi day.
3.1. Mo hinh C,\C tren co so danh gia miic do chiem dung tiii nguyen (loai md hinh 1) Loai md hinh nay da dugc gidi thieu trong cac nghien ciru [1], [2], [7], [8], [9] va [18].
Loai md hinh nay bao gdm mdt bd xir ly tham nhap cudc gpi md. mdt bd danh gia tai nguyen san dimg ciia mang va mdt bd danh gia mii-c dp chiem dung tai nguyen cua yeu cau cudc gpi mdi. Sa do tdng quat ciia loai md hinh 1 dugc bieu dien d hinh 2.
Bp danh gia nuic dp chilm dung tai nguyen ciia yeu cau cudc gpi mdi cd nhiem vu danh gia lugng tai nguyen ma cudc gpi mdi se chiem dung trong te bao se phuc vu nd (tai nguyen chilm dung trong tl bao) va cac tl bao lan can (tai nguyen chiem dung lien te bao). Lupng tai nguyen yeu cSu nay phu thupc vao yeu cau ve luu lugng (tdc dp bit R) va yeu cau ve QoS (ty sd mat dp nang lugng bit tren tap am (Eb/Io)). [2] de xuat each tinh lupng tai nguyen yeu cau ciia cudc goi theo R \ a (Eb/lo) bang each sir dung cac phep tinh gidi ban. Ket qua la cd hai gia trj yeu cau tai nguyen dupe tinh: mdt cue tieu va mdt cue dai. Hon nua. tham sd tham gia vao each tinh nay la gia trj cdng suat tin hieu phat di tir cac MS thu dirpc tai cac BS. ma gia trj nay trong thuc tl lai hoan toan khdng chinh xac do chju sir tac ddng cua cac hien tugng ngau nhien khdng the dir bao la fading va che khuat. Ket qua la gia tri tai nguyen yeu cau dugc tinh ra tir [2] la khdng chinh xac.
Yeu cau cugc gpi mai
^ Cac tham sd do dugc tir mang
^
QoS yeu cau
Danh gia mire chiem dung
tai nguyen Danh gia lugng tai nguyen
san diing
- • ' - Chap nhan/til-chdi
•
Bd xir ly tham nhap cudc ggi
li. A
/
i Mang te bac
Danh gia 1
Q o S \* ' • ' " - ••'
Thuc te
' • >
• - ' !
id o '
Hinh 2. So' do cdu true tdng qudt ciia logi md hinh 1 (Phdn nil dut Id kiin nghi bd sung trong phdn 4 ciia bdi bdo ndy)
De giai quyet van de nay, [1, 7, 8, 9, 18] da de xuat cac phuong phap sir dung he md de danh gia lugng tai nguyen chiem dung lien te bao ma mdi cudc ggi mdi yeu cau. Cach u'ng xir ciia cac phuong phap nay la dua vao viec md phdng cac cudc ggi tren may tinh, tao ra cac cap dir lieu huan luyen dau va dau ra. tii- dd xay dung nen cac luat suy dien md. Ket qua md phdng trang [1, 18] da chi ra rang, phuong phap sir diing he md cho ket qua danh gia chinh xac ban cac phuong phap khdng sii- dung he md.
Bd danh gia tai nguyen san dimg ciia mang thudng sir dung ly thuyet logic md hoac mang Neural de danh gia lugng tai nguyen cdn lai ciia he thdng sau khi da trir di lugng tai nguyen bj chiem dung bdi cac cudc gpi dang tdn tai trong te bao phuc vu va cac te bao lan can [1, 2, 7, 8, 9, 18] va cd the trir di ca lupng tai nguyen du trir cho cac cupc gpi chuyen giao [1, 8, 9, 18].
Mdt sd md hinh cu the su dung mang Neural de du bao chinh xac gia trj trung binh cua lugng lai nguyen bj chiem dung d budc tiep theo tir cac cudc ggi dang tdn tai [7, 8, 9] tir lugng tai nguyen bj chiem dung hien tai, trong khi mdt sd md hinh khac dua tren cac gia trj do QoS do dirge de thuc hien cdng viec nay [1, 18], Trong cac tinh toan nay, viec xac djnh lugng tai nguyen chiem dung lien te bao ciia cac cudc gpi dang tdn tai tien hanh tuang tu nhu vdi cudc gpi mdi da dugc trinh bay d phan tren. Tire la se chinh xac hon neu sir dung he md cho cdng viec nay. Ben canh dd. viec xac djnh lugng tai nguyen du tru cho cac cudc gpi chuyen giao thudng dua tren thdng tin di chu\en ciia cac MS (tiic la xac suat chuyen giao [1, 18]), ma thdng tin nay cd dupe la tir cdng suat tin hieu Pilot phat di tii- cac BS thu dupe tai cac MS. Muc cdng suat thu dirge nay trong thuc te cung hoan toan khdng chinh xac do chju sir tac ddng ciia cac hien tugng ngau nhien khdng the dir bao la fading va che khuat. Ket qua la thdng tin di chuyen dugc danh gia khdng chinh xac, va vi vay lugng tai nguyen dugc sir dung de du tru- cho cac cudc ggi chuyen giao ciing khdng chinh xac. De giai quyet van de nay, [1, 18] dl xuat phuang phap su dung he md de danh gia thdng tin di chuyen ciia cac MS thay cho each tinh truyln ihdng.
Bd xu ly tham nhiip cugc ggi md sir dung he suy dien md de quyet djnh chap nhan hay khdng mdt cudc gpi mdi dua tren mire dp chiem dung tai nguyen va QoS ciia yeu cau cudc gpi
. 9P chi KHOA HQC GIAO THONG V^LN TAI So 29 - 03/2010 .47
mdi da dugc danh gia va lugng tai nguyen cdn lai cua he thdng. Trong mdt sd md hinh, bd xii' ly nay cdn dua tren cac gia trj do QoS ciia tat ca cac loai luu lugng nhu mdt dirdng hdi tiep [7, 8, 9]. Mdi khi QoS da dugc gan bang vdi QoS yeu cau, cac yeu cau ve cudc gpi mdi vao he thdng se bj til- choi. Vi vay, cac yeu cau ve QoS khac nhau cd the dugc thda man. Viec xac djnh gia trj QoS thuc te ciia mang dugc dua vao cdng suat thu tin hieu tai cac BS tir cac MS. Theo cac phan tich tren, cac muc cdng suat thu nay deu chju anh hudng ciia cac hien tugng fading va che khuat dan den ket qua QoS do dupe la khdng chinh xac tac dpng xau den quyet djnh ciia bd xir ly tham nhap. Cac md hinh thugc loai nay deu sir dung logic md cho bg xii' ly tham nhap cugc ggi.
Bd luat md cd dugc bang each md phdng nhieu cudc gpi tham nhap vao mang vdi cac tan suat khac nhau va do cac thdng sd QoS ciia he thdng, tii- dd tien hanh dieu chinh luat cho den khi dat dupe ket qua tdt nhat. Cac ket qua md phdng trong phan ldn cac md hinh cu the deu chiing td dupe rang, phuong phap ap dung he md cd hieu qua ve sir dung tai nguyen hon va cac gia trj QoS cua he thdng tdt ban khi so sanh vdi cac phuong phap khdng diing he md.
3.2. Md hinh CAC tren c c sd suy giam lirong tai nguyen cap phat (loai md hinh 2)
Loai md hinh nay da dugc gidi thieu trong cac nghien ciru [6] va [16]. Cac md hinh CAC nay xem .xet den cac yeu cau ngudn tai nguyen mdt each thich nghi de nang cao hieu qua su dimg kenh trong cac mang khdng day. Khi mdt cudc ggi mdi dang tdi, md hinh CAC nay se danh gia xem bang thdng san diing cd the thda man yeu cau cudc gpi tdi hay khdng. Trong trudng hgp bang thdng san dimg khdng dii de dap irng yeu, md hinh CAC nay dira tren logic md se chpn mdt sd cudc gpi dang tdn tai cd dp uu tien thap, theo dd bang thdng danh cho nd se bj giam xudng de danh mdt lugng bang thdng cho cudc ggi tdi mdi (tire la tai cap phat tai nguyen).
Bang each nay, nhieu cudc ggi hon cd the dugc chap nhan tham nhap vao mang khdng day, trong khi cac cudc gpi dang tdn tai chi bj giam mdt it bang thdng d miic cd the chap nhan dugc [6]. Sa do cau tnic tdng quat ciia loai md hinh 2 dugc bieu dien d hinh 3.
Yeu cau cuoc goi mdi
• — ' • •
Danh gia miic chiem dung
tai nguyen
Cac cuoc goi dan" ket noi
Danh gia tai nguyen mang
va tai cap phat tai nguven
Bo xii- ly tham nhap
cuoc "oi
Chap nhan/
tii- choi ..-
^'
Mang te bao
Danh gia QoS Thuc te Hinh 3. Sa do cdu true Idng qudt cua logi md hinh 2.
(Phdn nil dut Id kien nghi bd sung trong phdn 4 cua bdi bdo ndy)
Trong [6], mdi cudc gpi cd it nhat hai loai yeu cau bang thdng, theo do, Bmin chi ra yeu cau bang thdng cue tieu va Binax chi ra yeu cau bang thdng cue dai. Khi mot cudc gpi mdi hay mdt cudc gpi chuyen giao tdi, CAC dugc kich hoat bdi yeu cau ciia dau cudi MS. Nlu bang
thdng san cd la dii nhieu va ldn hon yeu cau cue dai ciia cudc gpi tdi, bang thdng cue dai se d u p e cap phat cho cudc gpi mdi nay. Tuy nhien, khi te bao bj day tai, mdt hay mdt vai cudc gpi se bj suy giam ve c u e tieu. Thuat toan quyet dinh m d se chpn cac cupc gpi irng cir, ma cac cudc gpi nay cho phep danh mdt phan bang thdng cho cudc gpi tdi. T r o n g [16], khi mdt ngudi diing mdi tham nhap vao be thdng, bd C A C trudc het kiem tra xem ket ndi nay yeu cau thdi gian thuc hay khdng thdi gian t h u c . Neu la yeu cau djch vu thdi gian thuc, nd se kiem tra ngudn tai nguyen san cd trong te bao phuc vu va ca trong cac te bao ke can sau khi da du tru dii ngudn tai
nguyen cho cac cudc gpi chuyen giao. •%
Viec dir tru d u p e cap nhat djnh ky ddng thdi tai cac thdi diem cd cudc gpi mdi tdi. Neu he thdng cd dil ngudn tai nguyen, cudc gpi se dugc chap nhan. ngugc lai. tdc do du lieu ciia cac cudc gpi djch vu khdng thdi gian thuc se bj giam xudng mdt mire dp cd the nao dd de cung cap cho cudc gpi mdi. Neu la yeu cau djch vu khdng thdi gian t h u c , bd C A C se chap nhan tham nhap vdi tdc dp day dii (toan tdc) khi he thdng cd dii tai nguyen, Neu he thdng khdng cd dii tai nguyen, bp C A C se chap nhan tham nhap vdi mdt nira toan tdc (ban tdc) hoac tham chi % toan tdc. Cudc gpi khdng thdi gian thuc se chi bj chan khi he thdng khdng the cung cap djch vu ngay ca khi tdc dp da bj giam. Dieu nay chi xay ra khi he thdng cd tai ldn vdi nhieu cudc gpi thdi gian thuc.
Trong loai so- dd nay, cac thdng tin d u g c sir dung cho bd CAC t h u d n g la lugng tai nguyen cdn lai ciia he thdng, tai nguyen va Q o S yeu cau ciia cudc ggi, thdng tin di chuyen ciia MS v.v... Trong do, lugng tai nguyen cdn lai ciia he thdng phu thude vao tinh trang tai luu lugng ciia mang, ma tai luu lugng thay ddi mdt each manh me theo thdi gian va khdng gian [6]. Do viiy, vice tinh loan (hdng sd nay tai cac tluii diem CAC hoat dpng la hoan toan khdng do-n gian, va ket qua la khdng chinh xac. Ben canh dd, tai nguyen va Q o S yeu cau ciia cac cudc gpi, thdng tin dl chuyen ciia MS cimg bien ddng theo ca thdi gian lan khdng gian do anh hudng ciia mdi Iriiiing vd tuyen, nhu can ciia djch vu, tinh di chuyen ciia thue bao v.v... Vi vay, tim ra dugc thuat toan tuiing minh dc lira chon cac cudc ggi thich hgp nhat dang tdn tai cd the chap nhan suy giam cliiu lugng djch vu nham dimh tin nguyen cho cudc gpi mdi la mdt cdng viec het sire khd khan. [6] vii [16[ da chpn he suy dien m d cho md hinh nay. Ket qua md phdng trong cac md hinh ndi tren ciing chirng td rang, CAC sir dung he m d cho hieu suat sir dimg tai nguyen hieu qua hon va chat lugng djch vu dam bao hon. Cac bd luat suy dien m d cho cac md hinh nay thudng dugc xay d u n g dua tren y kien cua cac chuyen gia.
3.3. .Mo hinh C.\C t r e n co sd him tha> ddi t h a m sd n g u o n g chuyen giao m e m (lovii md hinh 3) Loai md hinh luiy da d u g c gidi thieu trong cac nghien ciru [10], [1 1], [12], [13] va [14].
Mdt he thdng te bao C D M A bao gdm tich hgp cac cudc gpi voice va data d u g c xem xet trong cac nghien ciru nay. Md hinh dugc phat trien dua tren viec du trd uu tien cho cac cudc gpi voice Vii data chuyen giao cimg vdi md hinh hiing chd cudc gpi ddi vdi cac cudc gpi data chuyen giao.
Sir ban che cac kenh bac cao dueic ap dat cho cac cac cudc gpi voice cung nhu cac cudc gpi data de danh uu tien cho cac cudc gpi chuyen giao. Nham quan ly tai nguyen tdt ban va tham nhap cudc gpi bieu qua vdi cac cudc gpi chii)'en giao va nguyen thiiy. mdt C A C Neural - Fuzzy d u g c
i9P chi KHOA HQC GIAO
T H 6 N G VANTAI So 29 - 03/2010 49
thilt kl. Bd dieu khien nay su' dung cac dac tinh cd the thich nghi ciia cac tham sd ngudng chuyin giao mim de duy tri cac cudc gpi voice va data quan trpng bang each giam sat kiem tra xac suat chan cudc gpi voice mdi hien tai, xac suat ngat cudc gpi data chuyen giao va tdc dp ciia cac thue bao voice chuyen giao. So- do phan tich ciia loai md hinh 3 dirge bieu dien d hinh 4.
Cuoc goi moi Voice
Cuoc ggi chuyen giao Voice
Cuoc go chuyen giao
Data
Cuoc goi moi Data
T Ngat cugc ggi
chuyen giao Data Cac kenh ma I Kich thirac hane dgi
Thay doi tham so nguong chuyen giao
Hinh 4. So' do phdn lich cua logi md hinh 3
Khac vdi hai loai md hinh tren, trong loai md hinh nay, ngudn tai nguyen dugc xem xet la cac kenh ma hda. Vdi mang te bao CDMA, cd mdt sd lugng ' M ' kenh ma hda san cd trong quy kenh. Toan bd cac kenh san cd nay deu dupe danh cho cac cudc gpi chuyen giao voice va data.
Sd lugng kenh san cd danh cho cac cudc ggi mdi voive va data dugc gidi ban chan tren cho mdi loai. Khi mdt cudc ggi mdi voice hay data yeu cau kenh va neu sd kenh dang sir dung cho cho cac loai djch vij nay hien tai bang vdi gidi ban tren ciia chiing thi yeu cau cudc ggi mdi se bj chan. Vdi qua trinh cudc ggi chuyen giao data, tire la djch vu khdng thdi gian thuc cd dp uu tien thap, md hinh hang chd dupe sii- dung. Md hinh hang chd cho cudc gpi chuyen giao data cd the dupe md ta tir tinh tu nhien cua vimg chdng lan chuyen giao mem. Dung lupng hang chd dirpc quyet djnh bang viec thiet lap hai thdng sd ngudng chuyen giao mem la T_ADD va T_DROP.
Vdi viec thay ddi cac thdng sd nay, dung lugng hang chd chuyen giao cho djch vu data se thay ddi dan den se cd mgt sd cudc ggi data bj ngat khi giam dung luo-ng hang chd, muc dich la dl danh kenh ma hda cho cac cudc gpi chuyen giao voice cd dp uu tien cao ban. Cac dau vao ciia bd CAC la xac suat chan cudc gpi voice mdi, xac suat ngat cudc ggi data chuyen giao va tinh di chuyen ciia cudc gpi voice chuyen giao. Ba gia trj nay deu dugc tinh tir cac thdng sd do, va cac thdng sd nay khdng hoan toan chinh xac do anh hudng ciia mdi trudng truyen dan. Do vay, khd
\
cd the xay dung dugc cac thuat toan tudng minh de quyet djnh rang, vdi mdt tap gia trj cu the cua cac dau vao thi T_ADD va T_DROP se bang bao nhieu. Cac md hinh cu the ciia loai nay da xay dung thuat toan CAC tren ca sd ket hgp Neural - Fuzzy. Tiiy thugc vao ca sd luat va dung lugng hang dgi cudc gpi data chuyen giao va ngudng cudc gpi voice mdi dupe xac djnh. Bd Neural - Fuzzy CAC cung tra ve cac gia trj da biet ciia cac tap dir lieu vao - ra. Phuong phap lan truyen nguac, dira tren co- sd hpc cd giam sat, dugc sii- dung de huan luyen bd dieu khien nay.
Cac ket qua md phdng deu cho thay chat lugng djch vu va hieu suat sir dung tai nguyen ciia cac md hinh dupe gidi thieu deu tdt ho-n so vdi cac md hinh khdng su dung ket hgp Neural - Fuzzy.
IV. DANH GIA VA NHAN XET
Tir viec phan tich ba loai md hinh ndi tren ket hgp vdi ket qua tinh toan md phdng ciia tii-ng nghien ciru, ta cd the nit ra dugc mdt sd danh gia va nhan xet sau:
(i) Trong loai md hinh 1, hau bet cac yeu td dac trung ciia mang te bao CDMA cd lien quan den tai nguyen vd tuyen da dugc xem xet va tinh den nhu nhieu lien te bao, anh hudng ciia hien tugng fading va che khuat, tinh di chuyen ciia cac MS... Tuy nhien vdi tirng md hinh cu the thi phan ldn khdng xem xet day dii cac yeu td nay. Tat ca cac md hinh cu the trong loai md hinh 1 deu khdng tinh den mire dp uu tien ciia cac loai djch vu khac nhau trong qua trinh CAC.
Mdt sd md hinh trong loai nay la dang he hd.
Trong sd cac md hinh cu the thupc loai nay, [1] va [18] la hoan thien ho-n ca vi da xet den day dil cac yeu td nhu tai nguyen trong te bao, lien te bao, tinb di chuyen ciia MS, cac anh hudng ciia hien tupng fading, che khuat. Cac md hinh cdn lai deu khdng xem xet day dii cac yeu td nhu hai md hinh nay. Tuy nhien, ba thieu sdt co- ban cira md hinh [1] va [18] la khdng tinh den mire dp uu tien ciia cac loai djch vii, la md hinh dang he hd va ban che sd lugng tai nguyen dir trii- cho cudc gpi chuyen giao.
Do Vciy, de loai md hinh nay hoan thien hon, can cd cac bd sung va dieu chinh nhu sau:
mdt la xay dung bp xir ly cudc gpi md' theo birdng cd cac mire uu tien tham nhap khac nhau cho cac loai djch vu khac nhau. Trong djnh nghia QoS ciia 3GPP, cd bdn ldp uu tien bao gdm P|, P,, Pi va P4 dai dien cho cac djch vu [6]. Vi vay cac muc uu tien nay can dugc ap dung cho each img xir ciia he md, tire la xay dung bd luat md chung cho tat ca cac djch vu cd tinh den do uu tiC-n ciia tirng loai djch vu, hoac mdi loai djch vu dugc ap dung mdt bd luat md rieng cung theo hudng uu tien khac nhau. Hai la sir dung cac tham sd QoS do dupe ciia he thdng quay trd lai tham gia \-ao boat ddng cua bd xir ly cudc gpi md vdi vai trd la cac bien dau vao va tao thanh mdi he kin. Khi dd neu hieu suat sir dicing tai nguyen cua mang dang cao, xac suat chan cudc gpi mdi thap trong khi xac suat ngat cudc gpi chuyen giao cao thi he md cd the dieu chinh de giam bdi cupc gpi mdi tham nhap, danh tai nguyen cho cudc gpi chuyen giao hoac ngugc lai. Ba la khdng gidi ban tren lugng tai nguyen du triT chuyen giao ciia tirng te bao, nham lam giam xac suat ngat cudc gpi chuyen giao.
Vdi cac dieu chmh \-a bd sung ndi tren, md hinh mdi se ke thira dupe cac uu diem sSn cd ciia cac md hinh cti nhu su dung he md de danh gia tai nguyen yeu cau trong te bao va lien tl
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bao ciia cudc gpi mdi, danh gia thdng tin di chuyin cua cac MS, danh gia kha nang dap irng tai nguyen ciia he thong va ca xu ly tham nhap cudc gpi. Ddng thdi, md hinh mdi ciing se khac phuc dugc cac nhupc dilm ciia cac md hinh cu nhu da la mdt he kin, tinh den yeu td uu tien ciia djch vu trong thuat toan xir ly tham nhap cudc ggi. Md hinh mdi nay phii hgp vdi viec ap dung cho cac mang t l bao CDMA da djch vu bang rdng ma d do mdi mdt cudc ggi cd mdt yeu cau tdi thilu vl luu lugng cimg vdi mdt yeu cau ve uu tien dich vu.
(il) Trong Loai md hinh 2, cac nghien ciru tap trung vao muc dp uu tien ciia cac loai djch vu. DAU vao ciia cac md hinh nay thudng la yeu cau ve bang thdng, QoS yeu cau va muc dp uu tien djch vu ciia tii-ng cudc gpi. Tuy nhien cac md hinh cu the lai khdng dua ra each tinh toan de cd dugc cac gia trj bang thdng yeu cau ciia cac cudc gpi nay, ma viec tinh toan nay la phirc tap do cd nhilu ylu td ngoai canh tac ddng vao. Mdt cudc gpi khi tham nhap vao he thdng khdng nhung chilm dung tai nguyen fren t l bao phuc vu nd ma cdn chiem dung ca bang thdng ciia cac tl bao lan can. Y I U to nay cung khdng dupe tinh den trong loai md hinh 2 nay. Cu the la, mdt yeu cau cudc ggi mdi thudng chi cd yeu cau ve luu lupng dudi dang tdc do bit yeu can va QoS.
He thong can phai tinh ra bang thdng yeu cSu ciia cudc ggi nay trong te bao va lien te bao. Day la cdng viec phirc tap vdi nhilu ylu td ngoai canh tac ddng nhu da chi ra d muc 3.2 ciia tai lieu nay. Tuy nhien cac md hinh da dugc dl xu^t thugc loai nay chi gia thilt cd gia trj bang thdng yeu cau trong tl bao ma khdng neu len each tinh toan cu the va ciing khdng d l cap tdi bang thdng hen tl bao. Trong trudng hgp cac cudc ggi trong te bao phuc vu da chap nhan suy giam bang thdng va t l bao nay da cd dii tai nguyen cho cudc ggi mdi thi cudc gpi dugc phep tham nhap. Tuy nhien, khi tham nhap vao, cudc ggi nay se chilm dung tai nguyen ciia ca cac cac te bao lan can, va chi cSn lupng tai nguyen cua mdt trong cac te bao nay da bj chiem dung het thi chat lupng djch vu ciia tat ca cac cudc gpi dang tdn tai trong t l bao nay deu bj giam xudng dudi yeu cau. Ngoai ra, loai md hinh 2 nay cung la dang he hd. '
D I loai md hinh nay hoan thien hon, can cd cac bd sung va dieu chinh nhu sau: mdt la bd sung them khoi tinh bang thdng hieu dung dl tinh lupng tai nguyen yeu cau ciia cudc gpi mdi se chilm dung trong t l bao va lien tl bao nhu trong [1, 18], Hai la cac thuat toan cap phat tai nguyen va CAC phai dugc thuc hien cho tl bao phuc vu va cac te bao ke can. Cudc gpi chi dugc phep tham nhap nlu lugng tai nguyen ciia tl bao phuc vu va cac te bao lan can, sau khi cap phat lai. dil dl dap img yeu cSu ciia cudc gpi mdi. Ba la sii' dung gia tri QoS do dupe ciia he thdng lam thdng tin hdi tilp vl bd xir ly tham nhap cudc gpi, tao thanh he kin nhu da de xuat trong muc (i) ciia phan 4 nay.
Vdi cac dilu chinh va bd sung nay, md hinh mdi se khac phuc dugc day dii cac nhugc diem ciia cac md hinh cu nhu da la mdt he kin, cd khdi chirc nang de tinh lugng tai nguyen yeu cau ciia cudc ggi mdi se chilm dung trong te bao va lien te bao, viec danh gia tai nguyen san diing ciia mang va tai cap phat tai nguyen cho cac cudc gpi dang tdn tai dugc thuc hien cho ca te bao phuc VII va cac te bao ke can. Ngoai ra, toan bd cac uu diem ciia loai md hinh cu van dugc ke thira kl. Md hinh mdi nay phii hgp vdi viec ap dung cho cac mang khdng day the he sau (NGWN), ma d dd mdi mdt cudc gpi cd nhieu yeu cau ve luu lugng (it nhat la hai yeu cau), trong do cd mdt danh cho che dp suy giam.
(iii) Trirdc bet, da> la mdt he kin vi cac gia trj QoS ciia mang la xac suat chan cudc gpi voice mdi, xac suat ngat cudc gpi data chuyen giao dugc hdi tiep lam dau vao cua tiep ve bd xir ly tham nhap cudc ggi. Trong khi cac loai md hinh 1 va 2 tap trung nghien ciru cac thuat toan CAC cho cac ngudn tai nguyen vd tuyen thi loai md hinh 3 lai nghien ciru cho ngudn tai nguyen la cac kenh ma hda. Ddi tugng nghien ciru cho hai tinh hudng nay la khac nhau. Do dd cac tham sd tham gia vao he thdng dieu khien cung khac nhau. Trong dd, loai md hinh 3 khdng tinh tdi dugc cac anh hudng ciia cac yeu td mdi trudng ciing nhu dac tinh bien thien khd du doan trudc cua tai luu lugng va mdt sd yeu td quan trgng khac len dung lugng ciia he thdng, tuc la tac ddng cua cac yeu td nay len tai nguyen ciia mang. Mdt nhugc diem ntra ciia loai md hinh nay la cac ngudng chuyen giao mem dugc thiet lap nhd bd suy dien md tren ca sd thdng sd mang. Tuy nhien, dac diem luu lugng tren mang la thay ddi theo khdng gian dan den cac thdng sd chuyen giao cd dugc cd the phii hgp vdi te bao nay nhung khdng phii hgp vdi cac te bao khac.
De giai quyet cac van de neu tren, ta cd the md rdng viec ap dung md hinh nay cho cac kenh truyen dan, noi van de tai nguyen vd tuyen la "ndng" hon. Trong md hinh mdi nay, tdng lugng bang thdng ciia te bao tuong img vdi sd lugng kenh "M" trong md hinh cii. Sd lugng tai nguyen ciia mdi te bao danh cho cudc ggi mdi voice va data la bj chan tren. Toan bg bang thdng ciia te bao cd the dugc danh cho cac cudc gpi chuyen giao. Cac cudc gpi chuyen giao voice cd dp uu tien cao dugc chuyen giao ngay khi cd yeu cau, trong khi cac cudc gpi chuyen giao data se dupe dua vao hang chd nhu trong md hinh cu. Tiiy thude vao tinh trang mang va tinh di chuyen ciia cudc gpi voice chuyen giao, bd xir ly tham nhap cudc ggi se quyet djnh cac gia trj ngudng chuyeii giao. Cac gia trj ngudng chuyen giao nay phai dugc thiet lap cho tirng te bao de tliich img vdi yeu cau luu lugng khac nhau ciia mang. Trong md hinh mdi nay, uu diem ciia viec sir dung logic md de dieu chinh tham sd ngudng chuyen giao nham dieu chinh tai nguyen he thdng, tac ddng true tiep den sir tham nhap ciia cac cudc gpi voice mdi dupe ke thira. Tuy nhien sir ke thira la khdng hoan toan khi tai nguyen dugc dieu chinh trong md hinh mdi la cac kenh vd tuyen, trong khi trong md binh cii la cac kenh ma bda. Yeu td 'kin" trong md hinh cu Cling dugc su dung lai trong md hinh mdi.
Md hinh nay pliii hgp cho thuat toan dieu khien tham nhap cudc ggi kenh vd tuyen trong cac mang te bao CDMA da djch vu, ma d do cd it nhat hai Idp djch vu, mdt ldp thdi gian thuc va ldp khdng thcri gian thuc.
V. KET LUAN
Dac tinh co ban ciia he thdng CAC la thdng tin ve ddi tupng khdng rd rang, nd thay ddi va chju nhiing tac ddng ngau nhien (vi du nhu dac tinh luu lupng ngau nhien theo khdng gian va thdi gian, kenh truyen chin tac ddng ciia hien tugng fading va che khuat, su di chuyen ciia cac MS v.v...). Cac thdng tin khdng rd rang nay cd ban chat khac cac qua trinh ngau nhien thudng dugc xir ly bang toan hgc xac suat va thdng ke kinh dien. Tuy cac thdng tin dd khdng biet trudc, cii the va chae chan nhung qua md phdng cd the riit ra nhtrng quy luat logic ve mire dp tdn tai trong he thdng. Dd chinh la ca sd ciia viec ap dung logic md trong CAC - mdt xu hudng mdi
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trong nghien ciru thdng tin di ddng thdi gian gan day.
Cac md hinh da dupe nghien ciiu tap trung nang cao chat lupng CAC cha mdt sd trudng hgp cu thi. Tuy nhien, chiing van cdn thilu tinh toan dien va chua hoan chinh. Bai bao sau khi xem xet, phan tich tirng md hinh da cd dua ra mdt sd kien nghj nham hoan thien ban cac md hinh nghien ciru cd trudc.
Tai lieu tham khao
[1]. Jiin Ye, Xiiemin (Sherman) Shen and Jon W.Mark, "Call Admission Control m Wideband CDMA Cellular Networks by Using Fuzzy Logic", IEEE Transactions on Mobile Computing, Vol. 4, No. 2, Marcli/Apnl2005.
[2]. Jamie S.Evans arid David Everitt, "Effective Bandwidth Based Admission Control for Multi-Service CDMA Cellular Networks " , IEEE Vehicular Technology Conference, 1996.
[3]. Nilesh Dixit. Ahliav Karandikar, "Effective Bandwidth in CDMA Cellular Networks with Soft Handoff" 2006.
[4]. Xuemin (Sherman) Shen. Jon W.Mark and Jun Ye, "User mobility profile prediction: An adaptive fuzzy inference approach". Wireless Networks, 2000.
[5]. TS. Rappaport, Wireless Communications: Principles and Practice, 2nd Edition, Prentice Hall, 1996.
[6]. Jmg-Long Wang and Shu-Yin Chiang, "Fuzzy-Based Call Admission Control Scheme for Mobile Networks", KES 2008, Part II, LNAI 5178, pp.958-965, 2008.
[7], Chimg-Ju Chang, Scon Shen, Jiiin-Hsiung Lin. and Fang Ching Ren, "Intelligent Call Admission Control for Differendated QoS Provisioning in Wideband CDMA Cellular System", IEEE, 2000.
[8]. Scott Shen. Chung-Ju Chang. ChingYao Huang, and Oi Bi, "Intelligent Call Admission Control for Wideband CDMA Cellular Systems", IEEE Transaction on Wireless Communications, Vol. 3, No. 5, September 2004.
[9]. Daipeng Zhang, Gang Zhu, "Distributed Intelligent call Admission Control", IEEE, 2005.
[10]. Ravi Sindal and Sanjiv Tokekar, "A Neuro-Fuzzy Call Admision Control Algorithm for Voice/Data traffic in CDMA Cellular Network", 2009 IEEE International Advance Commputing Conference (lACC 2009), Patiala, India, 6-7 March 2009.
[11]. Ravi Sindal and Sanjiv Tokekar, "Analysis of Queuing based Call Admision Control Scheme in CDMA Cellular Network for Variation m Mobility and Soft Handoff Threshold", 2008 IEEE Region 10 CoUoquim and the Third ICIIS, Kharagpur, India, 8-10 December 2008.
[12]. Ravi Sindal and Sanjiv Tokekar, "Modeling and Analysis of Voice -Data CAC Scheme in CDMA Cellular Networks for Variation in Soft Handoff Threshold Parameter", IEEE, 2008.
[13]. Ravi Sindal and Sanjiv Tokekar, "Analysis of Bi-Class Call Admission Control Scheme in CDMA Cellular Network for Variation in Soft Handoff Threshold Paramaters", IEEE, 2008.
[14]. Waqas Ahmad. Irfan Awan. and Makoto Takizawa, "An Adaptive Call Admission Control Approach for Multimedia 3 0 Network", Spnnger-Cerlag Berlin Heidelberg, 2007.
[15]. Y. Park and F. Adachi (eds.), "Enhanced Radio Access Technologies for Next Generation Mobile Communication", E 2007 Springer.
[16]. S.Malarkkanl, V.CRavichandran. "Performance Analysis of Call Admission Control in WCDMA Systems with Adaptive Multi Class Traffic based on Fuzzy Logic", IJCSNS - International Journal of Computer Science and Network Security, VOL.6 No.l 1, November 2006
[17]. Steve Dennett, The cdma2000 ITU-R RTT Candidate Submission (0.18).
[18], Jun Ye. Xuemin Shen and Jon W.Mark, "Call Admission Control in Wideband CDMA Cellular Networks by Using Fuzzy Logic", Canadian Institute for Telecommunications (CITR), 2003.
[19]. website: www.dieukhien.net4
