DANH GIA HIEU NANG CUA MOT SO GIAI PHAP TRUYEN VIDEO TREN MANG CUC BO KHONG DAY
LETAN Trudng Dgi hgc Suphgm - Dgi hgc Hue Tom tat: Bai bao nay nham muc tieu danh gia mpt s6 giai phap tmySn video Uen mang cue bp khong day (WLAN). Cac giai phap 802.lie EDCA, Static mapping. Adaptive mapping duac thuc hien dua tren thuat toan quan Iy hang dpi kSt hpp vai viec ma hoa file video theo chuSn MPEG-4 [3], nhim dam bao viec truyen file video va tan dung khong gian hang doi mpt each hieu qua.
Thong qua cac giai phap tinygn file video (802.1 le EDCA, Static mapping.
Adaptive mapping), tac gia da phan tich, so sanh, danh gia hieu nang, bing each dua vao file video nhan dupc sau khi tmyin, ti le mat goi va chi s6 PSNR (Peak signal-to-noise ratio) dudi cac dieu kien tai mang khac nhau.
Tir khoa: MPEG-4, 802.1 le video, mang khong day I.DATVANDE
Trong nhiing nam gan day, WLAN da tra nen pho bien trong cac ca quan, doanh nghiep, truang hgc. Ben canh do do nhu cau cupc song ngay cang cao, nguai diing ngay cang su dung nhidu cac thiet bi tmy cap co h6 trg WLAN dl trao d6i thong tin cung nhu phuc vu nhu cau giai tri, trong do co viec su dung dir lieu video. Tuy nhien, vi6c truyen dir lieu video trong WLAN thuang bi anh huong bai nhieu yeu to nhu giai han bang thong, do tre, do nhieu va ti Ie mat goi Iam cho chat lugng video a phia nhan khong cao.
Do do nha quan Ii mang phai tim ra cac giai phap tmyen video nham nang cao chat lugng dich vu, dap iing nhu cau cho nguai su dung.
Ngay nay, cac chuan ma hoa video phat trien khong ngiing va da gop phan nang cao kha nSng va hieu qua trong viec truySn du lieu theo dang truyen thong da phuang tien.
De cho viec tmyen video dugc lmh d6ng va hieu qua han nguoi ta thuang dung k^ thuat ma hoa phan cap [1], [8].
Vai ma hoa phan cap, khi du lieu dugc tmyen tren duong tmyen co bang thong thap, cac goi tin co uu tien thap co the bi Ioai bo. Chinh nha ca che nay ma luong dii lieu kieu video hoac audio co miic uu tien cao hon se dugc tmyen di truac.
Ngoai viec su dung ma hoa file video tmac khi tmyen, trong WLAN sii dung chuan IEEE 802.1 Ie [5] de h6 trg chat lugng dich vu tmyen goi tin.
2. CAC Glkl PHAP TRUYT&^ VIDEO TREN WLAN
Thai gian vua qua da co nhieu nghien ciiu ve nhiing ca che nham cai tien kha nang tmyen video tren mang su dung chuan 802.1 le. Trong [6], [7], Takeuchi va Wang da de xu^t mpt giai phap de cai tien gia tri kich thuac ctia so xung dot nham tang thong lugng he thong. Trong [2], Hasegewa de xuat ca che lap lich de tmyen lai dua vao EDF Tap chi Khoa hoc va Giao due, Truang Bai hoc Su pham Hui
ISSN 1859-1612, 86 03(31)/2013:tr. 65-72
nhien, mac di tit ca nhung giai phap tren dSu thuc thi tot hon chuAn 802.11e nhtnig chiing khong xem xet dSn tam quan trong ciia du Heu (chSng han nhu ki6u dO lieu video can dugc dat miic uu tien cao hon) nen viec truyen du lieu nay khong dat hieu qua, chit luong rjt kem. Vi vay tac gia nghien cuu mpt s6 giai phap truyen video hieu qua t6t hon.
2.1. Giai phip cua 802.ne EDCA
Trong chuin 802.lie co sir dung co chS phan tranh kenh truyjn phan tan (Enhanced Distributed Channel Access (EDCA)), Co chj nay phan loai luu luong mang vao b6n cip dp truy cap khac nhau gpi la AC (Access Categories) gom AC_VO (voice), AC_V1 (video), AC_BE (best effort), va AC _BK (background). Trong nghien cilu nay, tac gia ki hieu AC_VO la AC3, AC_VI la AC2, A C B E la ACl, va AC_BK la ACO.
Doi vcfi giai phap tren cac luong dir lieu video co uu tien cao nhat se dupc chuyen vao hang dpi AC2, cac lu6ng dii lieu khac se dupc chuyen vao cac AC con lai, Su khac biet ve dp uu tien dupc su dung boi EDCA dam bao chat lupng dich vu tot hon trong khi van dam bao dich vu toi thieu cho cac luong dii lieu tren mang co dp uu tien thap. Mac dii giai phap nay da cai tien dupc chat lupng dich vu ciia luong dii lieu tren mang theo thai gian thuc nhung hieu suat truyen video dat dupc van chua dupc toi im. Ly do cho viec nay la trong dieu kien tai mang cao, dung lupng cac luong dii lieu video den qua Ion dan den se bi danh rot ngiu nhien. Do do, 6 phia nhan se nhan khong du so goi tin video de giai ma, vi vay chat lupng video rit kem.
2.2. Giai phap Static mapping [4]
Giai phap nay tan dung them khdng gian cua hai hang dpi ACl va ACO dS luu trii file video. DQ lieu video sau khi dupc ma hoa theo chuin MPGE-4, cac goi tin video se dupc anh xa vao cac hang dpi theo thii tu uu tien. Cu thj la khung I se dupc chuySn vao AC2, khung P dupc chuyen vao ACl va khung B se dupc chuySn vao ACO. Nho vao co che nay ma s6 goi tin se bi han chS bi danh rot. Tuy nhien, giai phap nay con han chS a cho khong toi uu trong cac tinh trang tai mang khac nhau. Thuc ti la khi tai mang cao, giai phap nay thuc hien rit tot vi cac lu6ng dii lieu video dupc phan b6 d6ng dSu vao cac hang dpi, tranh xayra trudng hop danh rot goi tin. Tuy nhien, khi tai mang tai thip, hang dpi AC2 co the rong, din dSn viec tri goi tin cho qua trinh fruySn goi tin d6i vcri cac hang dpi ACl va ACO, va tham chi niu nhu ACl va ACO diu diy tai cimg mpt thoi diem thi ti le mat goi se rit Ion.
2.3. Giai phip Adaptive mapping
Giai phap nay dua vao kich thudc hien thai cua hang dpi di nhan biit tinh trang tai raang khac nhau. Nho vao viec quan ly timg hang dpi cu thi ma giai phap da tan dung toi da khong gian hang dpi. Qua do, giai phap da han che viec danh rot cac goi tin, dac biet la goi tin co dp uu tien cao nhit. Trong giai phap nay, sau qua trinh ma hoa file
BANH GIA HIEU NANG CUA MOT SO GIAI PHAP TRUYEN VIDEO... 67
video theo chuan MPEG-4. Khung video cd u u tien cao nhit se dugc gan ProJType thap n h l t (Prob_B> ProbP > ProbJ). Giai phap Adaptive mapping dugc mo ta b i n g gia ma nhu sau:
Khori t a o : RN«—Randoin[0,l]
N ^ 2
K h i mQi g o i t i n v i d e o d i n ( * ) :
Kiem t r a c h i l u d a i h a n g d g i h i § n t a i c u a AC[N]
I f q l e n ( A C [ N ] ) < t h r e s h o l d _ l o w Cho g o i t i n v a o AC[N]
E l s e
I f q l e n ( A C [ N ] ) > t h r e s h o l d _ h i g h
G o i t i n d u g c c h u y S n d i n AC[N-1] v a g o t o (*) E l s e
T i n h t o a n x a c s u i t a n h xa PrDb_N
qlen(AC\N\) - threshold_low
?rob_N=?rob_t}pe*-
threshold_high - threshold_low I f ( P r o b _ N > RN)
Goi tin dugc chuyen din AC[N-l]va goto (*) Else
Cho goi tin vao AC[N]
Doi vcfi giai phap Adaptive mapping thi khi mpt goi video den, thuat toan kiem tra kich thuoc hang dgi hien thai AC2 va so sanh vai cac gia tri nguong cao thresholdJtigh va ngudng t h i p thresholdjov^'. Neu kich thuac hang dgi nho han gia tri thresholdjow (tai mang thip) t i t ca Iu6ng dxi lieu video se dugc dua vao AC2. Nhung neu kich thuac hang dgi lan hem threshold-high (tai mang cao) thi dii lieu video se dugc dua vao hang dgi CO dp uu tien t h i p han AC I hoac ACO. Truong hgp con lai thi quyet dinh dua vao AC nao dugc xac dinh dua vao xac suat anh xa (ProbType) va dieu kien kich thuac hang dpi hien tai dugc xac dinh theo cong thiic tinh xac suat. Vi v|iy, xac suat moi (Prob_N) dugc tinh b i n g each thay doi ti Ie ProbType tiiy theo lugng dii lieu hien tai.
Ket qua la goi du lieu video sg dugc dua vaoAC2, A C l hoac ACO tuy thupc vao gia tri xac suat dugc tinh lai. Bang each xet theo luge do im tien nhu tren cimg chien luge quan Ii kich thuac hang dcd, ti le danh rot ciia video dugc giam thieu dong thai tan dung hieu qua cac tai nguyen cua mang.
3. KET QUA NGHIEN ClTU VA KET LUAN
Di danh gia hieu suit cua cac giai phap, tac gia xay dung moi truang mo phong tren phan mim NS2 [9]. Trong kiin tnic m?ng gia lap, thuc hien gia lap truyen don diem (mot niit gui lam chiic nang server truyin din mpt mit nhan), toe dp truyen la 1Mbps.
Di tao su canh nanh ao, tac gia tao them cac luu lupng va cimg truyin dong thai la lim luong am thanh {64k), UDP, TCP. Thong qua mo phong, cac thong so vi viec truyen tti dii lieu cua ba giai phap 802.11 e EDCA, Static mapping va Adaptive mapping dupc lay va so sanh.
Moi khung video dupc phan doan thanh nhiing goi tin truac khi truyen va kich thuoc goi tin fruyin toi da qua mang gia lap la 1000 byte.
Mo hinh mang sii dung trong mo phong:
f i f f
Hinh 1. Md hinh md phdng 3.2. Quy trinh mo phong v^ phan tich ket qua
Moi tmang gia lap la tmang hgp mang tmyen mgt luong video tir ben gui den ben nh$n. Mo phong dugc thuc hien bai hai kich ban dugc trinh bay duai day.
3.2.L Kjch bdn 1
Trong kich ban 1, tac gia danh gia chat lugng video nhan dugc tii phia nhan dua vao so goi tin mat cua tiing loai khung video va trung binh PSNR. Miic dp sii dung khong gian hang dgi dugc danh gia thong qua su bien thien hang dgi cua moi AC.
Tir khia canh ve so khung hi mat dugc cho a bang 1, chiing ta co thS thay rang trong 802.Ue EDCA chua co ca che quan Ii hang dgi hieu qua, do do tit ca cac goi tin video deu dua vao AC2. Ket qua dugc din den la khi luu lugng video nhidu thi bp dem hang dpi se diy, cac goi tin tai se bi danh rot, trong do co khung I la khung co dp quan trpng cao va ket qua la chat lugng video tai phia nhan se thip. Trong Iiic do giai phdp Static mapping da sii dung them hai hang dgi la ACl va ACO nen ti Ie mit goi it hon 802.He EDCA. Tuy nhien, theo nhu kdt qua minh hga a hinh 2, hinh 3, hmh 4 \k muc d0 su dung khong gian hang dgi thi giai phap Static mapping khong khai thac dugc t6i da khong gian hang dgi uu tien AC2. Ngugc Igi, giai phap Adaptive mapping co hieu qua rat tot bai vi thuat toan nay da so sanh chidu dai cua timg hang dgi cu thd, qua do thuat toan da sii dung t6i da hang dgi co dp uu tien cao nhit la AC2. Nha co co chd quan ly hang dgi ma thuat toan da sii dung t6i da kich thuac ciia cac hang dgi con lai.
BANH GIA HIEU NANG CUA MOT SO GIAI PHAP TRUYEN VIDEO...
fVp—
Hinh 2. Sir dung chiiu ddi hdng dgi ciia 802. He EDCA
I
Hinh 3. Sir dgng chieu ddi hdng dgi cua Static mapping
THOI GIAN M O PI
Hinh 4. Sii- dung chieu ddi hdng dgi cua Adaptive mapping
Cac chi so hidu suat dugc su dung dd danh gia chat lugng tmyen video gom ti Id mat khung, ti Id mat goi, tmng binh PSNR, va video dugc cau tnic lai dugc danh gia qua hinh thu dugc.
Bang 1 thong kd gia tri PSNR va ti Id mat goi cua video. So lugng cac goi bi mat ciia nhiing loai khung khac nhau phu hgp vcri dp quan trgng cua khung video. Vi Ii do nay ma khung I se nhan do uu tidn cao nhat trong thuat toan Adaptive mapping va thuat toan
uu tien thip nhit, vi vay khung B co ti le m i t goi Ion h a n nhiing Ioai khung khac.
Bang I. So sdnh trung binh PSNR vd so khung bi mat cua limg logi khung Thuat toan
802.1 Ie EDCA Static mappine Adaptive mappins
Tmng binh PSNR 41.74 43.87 44.73
KhungI 1 0 0
Khung?
0 4 0
Khung B 19 4 10
T6ng 20 8 10 Dua vao chi s6 tmng binh PSNR trong bang 1, thuat toan Adaptive mapping co gia tri tmng binh PSNR cao hon so vai thuat toan con lai, thong qua Hinh 5 cho ta su so sanh true quan vd chit lugng truydn video cua 3 thuat toan dugc xet trong mo hinh gia lap.
No cho thiy ring, chit lugng tmyen video su dung thuat toan Adaptive mapping co hidu qua tot hon
Hinh 5. Hinh sau khi nhdn dirge cua 3 thugt todn 3.2.2. Kjch ban 2
Kdt qua mo phong cac thuat toan vai cac dieu kidn tai mang khac nhau qua timg tmang hgp: T H I , TH2, THS, TH4, THS dugc cho trong bang 2.
Bang 2. Sd ludng liru lugng mgng khdc nhau cua tung tnrdng hgp THI
TH2 TH3 TH4 THS
I audio 2 audio 3 audio 5 audio 10 audio
1 best effort 2 best effort 3 best effort 5 best effort 10 best effort
1 backgound trafic 2 backgound trafic 3 backgound trafic 5 backgound trafic 10 backgound trafic Sau khi mo phong, gia tri tmng binh PSNR cua 3 thuat toan dupc cho a bang 3.
Bang 3. So sdnh trung binh PSNR cua cdc thudt todn qua lung trudng hgp Average PSNR(dB)
802.1 le EDCA STATIC MAPING ADAPTIVE MAPING
CAC TRLTdNG HOP THI
35.68 35.45 35.73
TH2 34.57 34.57 34.91
TH3 33.61 33.80 34 03
TH4 30.93 32.82 33.13
TH5 30.17 31.45 32.15
+ Khi tai mang thap (doi voi taiong hpp THI va trucmg hpp TH2) thi thuat toan Static mappmg da xay ra hien mpng mat goi tin la khong cin thiit, boi vi thuSt toan Static mapping da cho cac goi tin vao nhirng hang dpi c6 dp uu tien thip nen k i t qua la co gia
DANH GIA HIEU NANG CUA M O T SO GIAI PHAP TRUYEN VIDEO-
tri PSNR tucmg duang hoac co thd thip han 802.1 le EDCA. Trong Iiic do thuat toan Adaptive mapping co ca che quan Ii hang dgi de kiem soat tinh trang mang va anh xa goi tin vao timg hang dgi mpt each hgp Ii. Vi vay thuat toan nay da cho ket qua trung binh PSNR tuang tu nhu 802.1 le EDCA va cao han thuat toan anh xa tmh.
+ Trong dieu kidn tai mang cao (doi vai TH3, TH4 va THS), thuat toan Static mapping CO ti Id mat khung it han va co gia tri tmng binh PSNR cao han 802.1 le EDCA. Thuat toan Adaptive mappmg co gia tri tmng binh PSNR cao han thuat toan Static mapping va 802.1 le EDCA.
Tir cac kdt gua a hinh 6 cho ta thay: trong 3 giai phap thi giai phap Adaptive mapping hoat dpng tot trong moi didu kidn tai mang khac iJiau. Do giai phap nay da sii dung ca chd quan ly hang dpi co giam sat tinh trang tai mang, thong qua kich thuac hang dgi hidn thai de cho goi tin co dp quan trpng vao timg hang dgi mpt each hgp Ii.
cAcnu/dNG HOP M 6 PHONG
Hinh 6. Dd thi so sdnh gid tri trung binh PSNR qua cdc tnrdng hgp 5. KET LUAN VA H U O N G PHAT TRIEN
Qua qua farinh nghien ciiu cac giai phap tmydn video trdn mang WLAN, tac gia da cai dat va mo phong thanh cong mgt so giai phap trdn phan mem mo phong NS2. Tii ket qua mo phong, tac gia da tidn hanh phan tich, so sanh, danh gia dugc cac uu va nhugc didm ciia cac giai phap tren. Thong qua kdt qua mo phong, tac gia nhan thiy ring giai phap Adaptive mapping c6 uu didm nhat trong vide tmydn video qua WLAN trong mpi didu kien tai mang khac nhau. Trong tuong lai, tac gia tidp tuc nghien cim cac vin dd vd tmydn video tren mang WLAN. Bdn canh do, tac gia tien hanh sii dung cac mo hmh toan hgc dd danh gia cac giai phap mpt each chinh xac hon, dong thai xac dinh gia tri RN t6i uu trong giai phap Adaptive mapping.
TAI LIEU THAM KHAO
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Signal Processing: Image Communication 15, pp. 281-298
[4] Ksentini, A., Naimi, M., and Gueroui. A. (2006). Toward an improvement of H.264 video transmission over IEEE 802.1 Ie through a cross-layer architecture, IEEE Communications Magazine.
[5] Mangold, S., Choi, S., Hiertz, G. R., Klein, O., & Walke, 3.(2003). Analysis of IEEE 802.1 le for QoS support in wireless LANs, In IEEE wireless communications mag (pp. 40-50).
[6] Takeuchi, S., Sezaki, K., & Yasuda, Y. (2005). Dynamic adaptation of contention window sizes in IEEE 802.lie wireless LAN, In Fifth international conference on information, communications and signal processing (pp. 659-663).
[7] Wang, Y., & Huang, B. (2004). Performance improvement of IEEE 802.1 le". In The 13th IEEE workshop on local and metropol itanareanetworks, pp. 51-54.
[8] Illgner K, Muller F (1995). Hierarchical coding of molionveclor fields. In International conference on image processing. Vol. I, pp. 566-569.
[9] "The Network Simulator ns-2", truy cap ngay 19/12/2013, http://www.isi.edu/nsnani/ns/.
Title: PERFORMANCE EVALUATION OF SOME VIDEO TRANSMISSION SOLUTIONS ON WIRELESS LOCAL AREA NETWORKS (WLANs)
Abstract: This paper aims at smdying some solutions for transmitting videos over WLANs.
These solutions are based on algorithms combined with encoding video in MPEG-4 standard, to ensure the transmission of video files and efficiently utilisation the space of queues. Testing results have been analyzed, compared, evaluated performance by relying on the video file received after Iransmission, packet loss rale and PSNR «ith some different conditions of loading network.
Keywords: MPEG-4, 802.1 le video, wireless networks
ThS. LE TAN
Khoa Tin hoc, Truong Dai hpc Su pham - Dai hoe Hui DT: 0914 050 001, Email: [email protected]