BO CO BTL H THNG VIN THNG NHM 20 | 20161

TRNG I HC BCH KHOA H NI

VIN IN T - VIN THNG
----------

BO CO BI TP LN

MN H THNG VIN THNG

ti:

TM HIU V CELL SECTORING AND CELL SPLITTING

Ging vin hng dn : TS. Nguyn Thnh Chuyn

Sinh vin thc hin :
1. Nguyn Huyn Anh MSSV: 20146023 CNDTTT01 K59
2. Nguyn Thi H MSSV: 20146231 CNDTTT02 K59
3. Trn Trong i MSSV: 20135307 CNDTTT02 K58

H Ni 4/2017

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
MC LC
MC LC ............................................................................................................................ 2
DANH MC HNH NH .................................................................................................... 3
I. Gii thiu chung ............................................................................................................ 4
1.1. Hnh dng ca t bo...............................................................................................4
1.2. Cc nguyn l thng tin di ng..............................................................................5
1.3. H thng thng tin di ng s dng t bo ............................................................. 5
1.4. Cu trc h thng thng tin t bo .......................................................................... 7
II. Phn vng t bo (Cell Sectoring) .............................................................................. 8
2.1. Phn vng t bo vi anten ng hng bp sng rng ............................................ 8
2.2. Phn vng t bo vi anten chuyn bp sng ......................................................... 10
2.3. Cc k thut Trunkpool......................................................................................... 16
III. Cell splitting (Tch t bo) ....................................................................................... 17
3.1. Giai on 0 (Phase 0)......................................................................................... 20
3.2. Giai on 1 (Phase 1) Sector ha ...................................................................... 21
3.3. Giai on 2: Tch chia nh hn na v sau....................................................... 21
IV. Gii hn v hiu nng phn vng ti s dng trong mng di ng (reuse
partitioning) ........................................................................................................................ 23
4.1. Gii thiu .............................................................................................................. 23
4.2. Thut ton phn vng ti s dng ......................................................................... 24
4.2.1. Thut ton c bn ........................................................................................... 24
4.2.2. Thut ton m rng ........................................................................................ 27
4.3. Lu lng truy cp v m hnh ng. ................................................................... 30
4.4. Chnh sch gn knh ng .................................................................................... 32
4.5. Kt qu hiu nng ................................................................................................. 32
4.6. Kt lun ................................................................................................................. 38
V. Tng kt .................................................................................................................... 38
TI LIU THAM KHO .................................................................................................. 39

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BO CO BTL H THNG VIN THNG NHM 7 | 20162

DANH MC HNH NH

Hnh 1: Hnh dng t bo.......................................................................................................4

Hnh 2: H thng thng tin di ng s dng cu trc t bo ................................................ 6
Hnh 3. Khi nim v Cell (T bo) ..................................................................................... 7
Hnh 4. Bin gii ca mt Cell ............................................................................................. 8
Hnh 5. Trng hp CCI xu nht trn knh truyn i vi s phn vng t bo 120 ......... 9
Hnh 6. S Trunkpool cho cc anten switched-beam.....................................................10
Hnh 7. Kh nng bao ph khu vc, P1 cho knh phn hi, vi anten bp sng rng 30
(solid) v 15(dashed) .......................................................................................................... 13
Hnh 8. Kh nng bao ph khu vc, P1 cho knh truyn thng, vi antenna bp sng rng
30 (solid) v 15(dashed) ..................................................................................................... 14
Hnh 9. T l phn trm ca khu vc t bo, P2 cho knh phn hi, .................................. 15
Hnh 10. T l phn trm ca khu vc t bo, P2 cho knh truyn thng........................... 15
Hnh 11. Phn chia t bo ................................................................................................... 16
Hnh 12. Vic tch t bo c s dng ph hp vi vic load d liu bng cch a ra
cc t bo nh ..................................................................................................................... 17
Hnh 13. Phn chia Cell (t bo)......................................................................................... 18
Hnh 14. Cc Omni (360o) Cell ban u ............................................................................. 21
Hnh 15. Giai on 1 Sector ha (Sectorization) ............................................................. 21
Hnh 16. Tch chia Cell 1:3 thm ln na .......................................................................... 22
Hnh 17. Tch chia 1:4 (sau ln u chia 3) ....................................................................... 22
Hnh 18. Phn vng ti s dng t bo ............................................................................... 26
Hnh 19. T bo vi phn vng v hn .............................................................................. 29
Hnh 20. Ngi dng di ng gia cc Cell ....................................................................... 31
Hnh 21. Ngi s dng di ng gia cc subcells ............................................................ 31
Hnh 22. Ngi s dng c nh: ngn chn xc sut chng s lng ngi dng mi t
bo. ..................................................................................................................................... 34
Hnh 23. Ngi s dng c nh: chn hiu sut vi quyn truy cp c gii hn v hng
i. ...................................................................................................................................... 35
Hnh 24. Ngi s dng di chuyn: xc sut suy hao chng phn vng quang ph .......... 36
Hnh 25. Ngi dng di chuyn: xc sut li chuyn giao chng phn vng quang ph. 37
Hnh 26. Ngi dng di chuyn: nh hng ca hng i n hiu sut .......................... 37

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I. Gii thiu chung

H thng thng tin di ng t bo s dng mt s lng ln cc my pht v tuyn

cng sut thp to ln cc cell hay cn gi l t bo (n v a l c bn ca h thng
thng tin v tuyn. Thay i cng sut my pht nhm thay i cc kch thc cell theo
phn b mt thu bao. Khi thu bao di ng di chuyn t cell ny sang cell khc, cuc
m thoi ca h s c gi nguyn lin tc, khng gin on. Tn s s dng cell ny
c th c s dng li cell khc vi khong cch xc nh gia hai cell. [1]
1.1. Hnh dng t bo
H thng thng tin di ng s dng anten ng hng truyn thng tin
di dng sng trong mi trng khng kh. C th thy trong a s trng hp,
nng lng pht gim dn theo khong cch. Tc l mi trm thu pht s ph sng
c mt din tch mt t l hnh trn ly n lm tm v bn knh ph thuc vo
cng sut pht. Tuy nhin, ph sng cho mt din tch rng ln th i hi din
tch ph sng ca anten phi l mt hnh a gic. d hiu hn, ta hy xem xt
hnh sau:
Hnh 1

Vi hnh vung th khong cch t tm n im gn nht v xa nht

l chnh lch nhau nhiu
Hnh trn th s li nhng vng khng c ph sng c t bng
mu xm.
Hnh lc gic th va m bo bao ph hon ton va gn nh gi
c u im ca hnh trn l khong cch gia cc im trn cnh
lc gic vi tm l gn bng nhau.
Chnh v nhng l do trn m lc gic c chn lm hnh dng ca
t bo.

1.2. Cc nguyn l ca thng tin di ng

Mi thu bao di ng s dng mt knh v tuyn ring bit tm thi lin lc vi
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BO CO BTL H THNG VIN THNG NHM 7 | 20162
mi cell. Mi cell c th lin lc c vi nhiu thu bao di ng ti cng mt thi im,
mi thu bao c dng mt knh v tuyn ring. Mi knh v tuyn s dng mt cp tn
s lin lc, mt tn s cho ng xung (pht i t cell), mt tn s theo chiu ngc
li cell nhn cuc gi t thu bao. Nng lng sng v tuyn suy hao thoe khong cch
nn cc thu bao cn thit phi ng gn trm pht gi lin lc c lin tc. Cu trc
c bn ca mng di ng gm c th thng in thoi v dch v v tuyn. Ngoi ra h
thng thng tin di ng c th kt ni lin mng vi h thng PSTN.
1.3. H thng thng tin di ng s dng t bo

Khi nim t ong cu trc li h thng thng tin di ng theo cch khc. Thay v
s dng mt trm cng sut ln, ngi ta s dng nhiu trm cng sut nh trong vng ph
sng c n nh trc. Ly v d, bng cch phn chia mt vng trung tm thnh 100
vng nh hn (cc t bo), mi cell s dng mt my pht cng sut thp vi kh nng
cung cp 12 knh thoi cho mi my. Khi nng lc ca h thng v l thuyt c th tng
t 12 knh thoi s dng mt my pht cng sut ln ln n 2000 knh thoi bng cch
s dng 100 my pht cng sut thp.
Cc vn v nhiu sinh ra khi cc khi di ng s dng cng mt tn s ti cc
im gn nhau chng t rng tt c cc tn s khng th ti s dng mi cell. Vic ti
s dng ch c th trin khai cc cell c khong cch nht nh vi nhau. Cc nghin

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cu pht hin ra rng, cc nh hng ca nhiu khng phi do khong cch gia cc vng
m ph thuc vo t l ca khong cch vi bn knh ph sng ca vng.
Bng cch gim bn knh ca vng i 50%, nh cung cp dch v c th tng s kh
nng phc v ln 4 ln. H thng c trin khai trn vng c bn knh 1 Km c th cung
cp s knh ln hn gp 100 ln so vi h thng trin khai trn vng c bn knh 10 Km.
T thc t rt ra kt lun rng, bng cch gim bn knh vng i vi trm mt th nh cung
cp c th phc v thm vi triu cuc gi.
Khi nim cell (t bo) c s dng vi cc mc cng sut thp khc nhau, n cho
php cc cell (cc t bo) c th thay i vng ph sng tu theo mt , nhu cu ca thu
bao trong mt vng nht nh. Cc t bo c th c thm vo tng vng tu theo s pht
trin ca thu bao trong vng . Tn s t bo ny c th c ti s dng t bo khc,
cc cuc in thoi vn c duy tr lin tc khi thu bao di chuyn t t bo ny sang t
bo khc. [2]

Hnh 2. H thng thng tin di ng s dng cu trc t bo

Cc trm v tuyn t bo c th lin lc vi cc thu bao di ng trong mt khong

cch mc nh trc. Nng lng sng v tuyn suy hao theo khong cch, nn cc my
u cui di ng nht thit phi nm trong vng ph sng ca trm gc (BS Base Station).
Trong h thng thng tin di ng trc y, trm gc lin lc vi u cui di ng s dng
mt knh. Knh ny s dng mt cp tn s, tn s pht t trm gc v tn s thu t u
cui di ng ln trm gc.

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1.4. Cu trc h thng thng tin t bo
S lng thu bao ngy cng tng ln trong khi h thng thng tin di ng trc y
khng p ng kp v s lng thu bao cng nh cht lng dch v. y l sc p i
vi cc nh cung cp dch v, bt buc h phi tm gii php mi nhm nng cao cht lng
dch v, ng thi p ng nhu cu pht trin thu bao di ng tng nhanh. Ph tn s
dnh cho thng tin di ng l c hn, do s dng hiu qu tn s trong h thng thng
tin di ng t bo l rt cn thit. Cc tham s h thng nh s lng, kch thc cc cell,
s dng li tn s, qu trnh chuyn tip cuc gi gia cc cell (handover) l khc nhau tu
theo vng a l c th, nng thn hay thnh ph.
Cc t bo

Cell (t bo) l n v a l c bn ca h thng thng tin v tuyn theo m hnh t

bo. Cc vng ph sng bi cc trm c dng t bo nn ngi ta gi l h thng thng tin
theo m hnh t bo. Cc cell l cc trm gc pht sng n mt bn knh a l xung quang
v vng ph sng c dng gn ging hnh lc gic. Kch thc ph sng mi cell thay i
tu theo vng.
L n v c s mng, ti trm di ng MS tin hnh trao i thng tin vi mng
qua trm thu pht gc BTS. BTS trao i thng tin qua sng v tuyn vi tt c cc trm di
ng MS c mt trong Cell. [3]

Hnh 3. Khi nim v Cell (T bo)

Hnh dng l thuyt ca mt t bo l mt t ong hnh lc gic:

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BO CO BTL H THNG VIN THNG NHM 7 | 20162

Hnh 4. Bin gii ca mt Cell

Trn thc t, hnh dng ca mt cell l khng xc nh. [1]

II. Phn vng t bo (Cell Sectoring)

Phn vng t bo c s dng vo cc h thng thng tin di ng gim tc ng

ca CCI. Hai loi anten ng hng c cp: anten ng hng bp sng rng thng
thng (conventional wide beam directional antennas), anten chuyn bp sng (switched
beam antennas).
2.1. Phn vng t bo vi anten ng hng bp sng rng

Trong pha khi u ca mt h thng, anten bao ph mi hng c s dng

truyn hoc nhc dc liu, v t bo tng ng c gi n t bt k hng no. Trong
trng thi tip theo, h thng s dng anten ng hng cho c vic tng dung lng ca
h thng v gim hiu ng ca CCI. T bo ban u c chia thnh cc t bo khu vc,
ni m cc khu vc 120 (hoc 60) c mc bao ph c gii hn hn l bao dng
thng thng 360.
Phn vng t bo l phng thc rt ph bin, c s dng trong cc h thng t
bo tng kh hot ng C/I. Trn knh truyn i, anten ng hng gim s to ra CCI
bi vic chuyn giao tn hin n cc trm in thoi di ng (Mobile Stations) vi s tri
Angle-of-arrivel (AoA) hp hn l anten bao ph mi hng. Trn knh phn ngc li,
anten ng hng gim hiu ng ca CCI bi v chng phn hi CCI c to ra vi s
tri AoA hp hn v trm di ng.

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 BO CO BTL H THNG VIN THNG NHM 7 | 20162

D + 0.7R Serving
Base
Co- station
channel
Base Mobie
station D subcriber

Hnh 5. Trng hp CCI xu nht trn knh truyn i vi s phn vng t bo 120

Phn tch trng hp xu hn ca CCI trn knh truyn i vi s phn vng t bo

120. Nh hnh trn s phn vng 120 gim s lng cc nhiu knh truyn cng tn s t
6 xung 2. Hai tng nhiu u tin c ti khong cc xp x D v D + 0.7R. Kt qu C/I
trong trng hp xu nht l:

R
1


D (D 0.7R)
D D 0.7

R R

Vi ng mt s m = 3.5, trng hp xu nht ca C/I l: dB 21.1dB

Ni m anten bao ph mi hng c C/I l: dB 14.3dB

Cho N = 7, phn vng 120 to ra 6.8 dB li C/I cao hn trng hp khi s dng anten
bao ph mi hng.
nhn c li ch t vic phn vng, cc sng mang c phn n mi t bo phi
c chia ra. [2]

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2.2. Phn vng t bo vi anten chuyn bp sng

Cc anten Swicth-beam c th c s dng ti ni cc anten nh hng bp

rng/chm rng (wide-beam) theo quy c, ci thin v c kh nng ph sng v cng
sut h thng. Cc anten switched-beam l mt loi n gin ca anten thng minh m
nhiu bp/chm anten c s dng vi mi cell sector, v s li tia chm c thng
qua mt c ch la chn chm/bp n gin.

Hnh 6. S Trunkpool cho cc anten switched-beam

Cc anten MS c gi nh l ng hng. Vi anten ng hng BS, c su di

nhiu hng nht ng knh chuyn tip pha trc v ngc knh. S lng nhiu hng
nht c gim xung cn hai vi qut ph sng 120. Vi mt anten thng minh chuyn
bp sng, s nhiu ng knh hng nht trn cc knh pha trc l mt bin ngu nhin
khc nhau chy t 0 n 6, do bp sng hp.
Anten nh hng v s ph thuc ca cc chm tia kch hot trn cc v tr MS.
Nu CCI hnh thnh cc bp sng ph ca anten c b qua, c t nht mt nhiu trn
knh ngc li khi cc anten chuyn bp sng thng minh l t hn 40.
Hiu nng t bo vi anten chuyn bp sng

Hiu nng c nh gi vi cc gi thuyt sau:

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1. Mi t bo vng trn di dng mt t bo lc gic. Cc thit b di ng c phn
phi cng mt kiu trong mt t bo.
2. Ch nhiu ng knh tng u cn c quan tm
3. H thng c tn dng ti a ln ti 100%
4. Cc anten nh hng 120 c s dng trong h thng tham chiu c s nh hng
hon ho. Khng c cc thy bn. Tuy nhin cc thy bn gn k ti bp chnh c
cn nhc cho h thng anten thng minh switched-beam smart.
T l front-to-back ca smart antenna l 30dB, v s suy gim b sng gn k l 12dB.

Bi v iu khin nng lng c s dng trong h thng AMPS, hai trng hp

c cn nhc y l: iu khin nng lng v khng iu khin nng lng. Trong thc
t thut ton iu khin nng lng tc ng dn tng di tn hiu nhn c (C+I). Tuy
nhin cho n gin, thut ton iu khin nng lng ch quan tm n di di tn hiu
nhn c mong mun C, khi m CIR yu cu l 17dB trong h thng AMPS th nng
lng nhiu chng ta c th b qua, iu ny phn bit gia yu t s dng li tn s, k
thut trunkpool v antenna beam-with, khi switched-beam smart antennas c s dng:
Sma [reuse cluster size] [trunkpool type] [antenna beamwidth]
Trong :
- reuse cluster size: 7 cell hoc 4 cell
- trunkpool type: nh hng hoc sectored
- antenna beamwidth: 30 (12 phn t) hoc 15 (24 phn t)
a. Knh phn hi

Khi iu khin nng lng khng c s dng, tt c cc trm in thoi di ng c

d
gi thit vi nng nng lng nh nhau. CIR ti BS phc v l 1010
i

10
i
10

Vi d v i l ch s cc tn hiu mong mun v cc tn hiu giao thoa. Cc gi tr

ngu nhin d v i theo quy lut phn b Gauss. Cc s nhiu ng knh ph thuc vo
v tr mong mun v ng knh MS. Cc CIR s thay i nh l mt hm cc chm tia

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kch hot trong cc t bo ng knh. Ch rng h thng tham chiu c 2 nhnh la chn
trong knh phn hi. S lng ca nhiu ng knh ph thuc vo v tr mong mun v cc
MS ng knh. Khi iu khin nng lng c s dng, chng ta gi thit rng nng lng
nhn c i BS phc v cho mi MS duy tr ti 1 mc C c nh. Nng lng c phn
phi bi i mobile trong j t bo ti MSij vi khong cch dij ti BS phc v n l Pij Nng
lng nhn c ti BSj l:

C 1
i
i

C 10
10
10
10

i i

MSij cng ti khong cch di0 ti BS tham chiu BS, BS0 v s to ra CCI vi nng lng:
i 0 i 0 ij i
Ii 0 Pij10 10 10
C1010
C10

V C/I ti BS0 l

C 1
i i

C 10
10
10
10

i i

Gi thit rng ng dn mt.

b. Knh truyn thng

S khc bit ch yu gia knh truyn thng v knh phn hi l s lng nhiu
ng knh. Cng thc tnh ton C/I th vn ging nhau nhng h thng phn hi khng
khng c antenna nh hng.
c. Tiu chun hiu nng v kt qu

Hai tiu chun c s dng tnh ton hiu nng ca h thng anten chuyn mch
thng minh l
- Tiu chun 1: kh nng bao ph khu vc, P1 c nhn, C/I vt qu gi tr
mc tiu th

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
- Tiu chun 2: t l khu vc phn trm ca khu vc t bo, P2 nhn c, C/I
vt qu mc tiu th 75% ca thi gian
Tiu chun 1 c th c coi nh thc o hiu nng ton th. Tuy nhin cc v tr
s c ngy trang t hiu nng khu vc c bao ph bi cc v tr tt. y l s chnh
xc ring bit khi hiu nng l khng ng u trn c khu vc t bo. Trong trng hp
ny, tiu chun 2 hu dng. Mt nng cao hiu nng quan trng c tin hnh vi h
thng anten switch-beam thng minh, c bit cho knh truyn thng. Yu t chnh nh
hng n C/I trong khu vc bao c bao ph vi anten switched- beam thng minh l
rng bp sng ca antenv tn s c s dng li. K thut trunkpool khng ng vai tr
quan trng.

Hnh 7. Kh nng bao ph khu vc, P1 cho knh phn hi, vi anten bp sng rng 30
(solid) v 15(dashed)

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Hnh 8. Kh nng bao ph khu vc, P1 cho knh truyn thng, vi antenna bp sng rng
30 (solid) v 15(dashed)
Hnh 6 v Hnh 7 th hin hiu nng vi tiu chun 2. Trong trng hp ny ch c
khong 2dB c tng ln i vi h thng tham chiu. K thut Trunkpool c th hin
c nh hng quan trng trong hiu nng ca tiu chun 2. Hiu nng vi sectored
trunkpool tt hn so vi omni-trunkpool. H thng sma-4-sec-30 khng tt bng h thng
tham chiu.

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Hnh 9. T l phn trm ca khu vc t bo, P2 cho knh phn hi,

Ni C/I vt qu gi tr mc tiu, th, 75% of thi gian vi anten bp sng rng

30 (solid) v 15% vi antenna bp sng rng 15(dashed)

Hnh 10. T l phn trm ca khu vc t bo, P2 cho knh truyn thng
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BO CO BTL H THNG VIN THNG NHM 7 | 20162
Ni C/I vt qu gi tr mc tiu, th, 75% of thi gian vi anten bp sng rng
30 (solid) v 15% vi anten bp sng rng 15 (dashed).
Bad points: vi iu khin nng lng, bad points c th xy ra bt c ni no trong
t bo, khng ch trn ng bao. Bi v thut ton iu khin nng lng ch iu khin
nng lng ca tn hiu mong mun. Khi mt thit b di ng gn vi trm BS phc v n
th mc nng lng c gim xung. Do , nhiu nhiu hn c th s c tri qua
trn c knh truyn thng v knh phn hi, khi cc nhiu ng knh gn ti BS ny v xa
t cc BS phc v ca chng. Khi m antennas switched-beam thng minh c s dng,
hiu nng vi tiu chun mt c th c tng ln, v hiu nng vi tiu chun 2 c th
thay i mt lng nh.
im xu ca knh phn hi vi anten thng minh switched-beam c tp trung
trong radial sector v c gi l Bad area. S tng C/I l khng ng u trn ton b khu
vc t bo. Chng ta gi l hiu ng Cart-wheel. Tuy nhin, n khng th hin trong
knh truyn thng. Bad areas s lun lun tn ti trong h thng s dng anten switched-
beam thng minh khng quan tm rng bp sng hp ca anten v k c iu khin nng
lng c c s dng hay khng. D nhin, s lng Bad points c gim i khi anten
bp sng rng tng ln. gim nh hiu ng Cart-wheel, chng ta c th xoay mt vi t
bo Switched Beam hng ti cc t bo khc, c th phn phi Bad Point. Tuy nhin,
iu ch c th nh hng khi gc quay l ln hn s phn tri AOA ca tn hiu. Mt
cch tip cn khc l s dng linh ng phn knh trnh s dng chung knh khi mt
nhiu ng knh tim tng gn bn. [2]
2.3. Cc k thut Trunkpool

Mc d anten nh hng chm hp trong cc h thng anten thng minh switched-

beam lm gim s r r khng cn thit ca bc x v gim thiu nhng nh hng ca thi
gian knh phn tn, cc anten thng minh switched-beam s chuyn giao thng xuyn hn
m kt qu l gim hiu qu trunking

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
khc phc tnh trng gim hiu qu s dng trunking gy ra bi tia sectoring hp,
k hoch chia s cc k thut sector-trunkpool v omni-trunkpool c xut.
- Sector-trunkpool: C mt vi chm tia trong mi sector. Tt c cc chin lc
phn knh cho mt sector c chia s bi tt c cc chm tia trong sector .
Mi mt anten sector hot ng ph bin trong sector. Khng chuyn giao l cn
thit tr khi MS i qua sector hoc ranh gii t bo. Hiu qu s dng trunking
s vn ging nh cc h thng tham chiu trong mi sector wide beam c
cp pht knh ring.
- Omni-trunkpool: Bt k cc knh c cp pht cho mt t bo c th c
chuyn giao cho bt k mt trong hai chm c kch hot. Khng chuyn giao
l cn thit tr khi mt MS qua mt ranh gii t bo.
K thut Omni trunkpool th rt hu ch nng cao hiu qu trunking khi h
thng ng-ten thng minh c s dng. [3]
III. Cell splitting (Tch t bo)

Khi cc phng tin thng tin lin lc ngy mt tng ln, mt t bo c th c

chia thnh cc t bo nh hn ci thin vic s dng hiu qu ph tn (tn s ti s dng
thng xuyn hn). Thng thng, cc bn knh mi l mt na bn knh gc.
V d, bn knh ca mt t bo lm gim mt na v chia mt t bo c thnh bn t bo
nh mi (Hnh 11). Cc khu vc ca cc t bo phn chia l din tch ca cc t bo m,
sau vic load d liu c tng ln gp bn ln trong cng mt khu vc, nu mi t bo
mi mang cng mt ti lu lng ti a ca cc t bo c.

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 BO CO BTL H THNG VIN THNG NHM 7 | 20162

T bo gc

Hnh 11. Phn chia t bo

C hai cch chia: Trong hnh 11, t bo gc khng c s dng, mt t bo c chia

theo nhn 1 c nm trung im gia hai t bo c dn nhn 1. V cc t bo phn
chia nh hn, cng sut pht c th c gim. c tnh yu cu truyn ti in nng
trong cc t bo phn chia. Ch rng cng sut nhn c cho mt MS nm gc ca
mt t bo m:

R0 A0 A0 R

Trong khi cng sut nhn c ti bin ca t bo c phn chia l:

(Rs ) As Rs

Vi o v s l cng sut pht, Rs v Ro l bn knh t bo kt hp vi cc t bo

m v t bo phn chia tng ng. Cng sut pht mi:

Rs
s o
Ro

Vi =4, s o , v R R . V th, cc t bo phn chia c th lm gim mc

16
S

cng sut pht ca chng bng 12 dB. [3]

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BO CO BTL H THNG VIN THNG NHM 7 | 20162

Hnh 12. Vic tch t bo c s dng ph hp vi vic load d liu bng cch a ra
cc t bo nh.
trnh vi phm nhng hn ch ti s dng cho vic gii thiu cc t bo phn chia.
Mt cch tip cn rt chuyn tip thng l knh phn on, ni cc b knh trong cc t
bo ng knh c chia thnh hai nhm: cc t bo phn chia c gn cho mt nhm
cc knh, trong khi cc t bo ng knh m c phn chia nhm khc ca knh. Tuy
nhin, s sp xp ny hiu qu v cc t bo m c th khng s dng cc knh gn cho cc
t bo phn chia. Do , phn khc knh khng phi l mt la chn tt. Mt gii php
khc, cc t bo bn trong ni ph c a vo t bo m. Cc trm MS nm trong cc t
bo bn trong c che ph v cc t bo phn chia s dng mt nhm cc knh, trong khi
MS nm trong cc t bo bn ngoi s dng cc nhm khc ca cc knh. [1]

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BO CO BTL H THNG VIN THNG NHM 7 | 20162

Hnh 13. Phn chia Cell (t bo)

S khng thc t khi ngi ta chia nh ton b cc h thng ra cc vng nh hn

na v tng ng vi n l cc t bo. Nhu cu lu lng cng nh mt thu bao s
dng gia cc vng nng thn v thnh th c s khc nhau nn i hi cu trc mng
cc vng cng khc nhau.
Cc nh quy hoch s dng khi nim cells splitting phn chia mt khu vc c mt
thu bao cao, lu lng ln thnh nhiu vng nh hn cung cp tt hn cc dch v
mng. V d cc thnh ph ln c phn chia thnh cc vng a l nh hn vi cc t
bo c mc ph sng hp nhm cung cp cht lng dch v cng nh lu lng s
dng cao, trong khi khu vc nng thn nn s dng cc t bo c vng ph sng ln, tng
ng vi n s lng t bo s s dng t hn p ng cho lu lng thp v s ngi
dng vi mt thp hn.
3.1. Giai on 0 (Phase 0)
Khi mng li c thit lp, lu lng cn thp, s lng i trm cn t, mng
thng s dng cc omni cell vi cc anten v hng, phm vi ph sng rng.

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
Hnh 14. Cc Omni (360 ) Cell ban u
o

Khi mng c m rng, dung lng s tng ln, p ng c iu ny phi

dng nhiu sng mang hn hoc s dng li nhng sng mang c mt cch thuwongf
xuyn.
Tuy nhin, mi s thay i trong quy hoch cu trc tn s pho gn lin vi vic
quan tm ti t s C/I. Cc tn s khng th c n nh mt cch ngu nhin cho cc cell.
thc hin c iu ny, phng php ph bin l chia cell theo th t.
3.2. Giai on 1 (Phase 1) Sector ha

Thay anten v hng (omni) bng 3 anten ring bit nh hng di qut 120o l mt
gii php tch chia mt Cell thnh 3 Cells. l gii php di qut ha (sectorization
sector ha). Cch ny khng i hi thm mt bng cho cc Cell mi. Tuy cc cell mi
phn birtj nhau theo chc nng mng nhng chng vn ti mt bng c.
Khi , ti mi v tr c (Site) by gi c th phc v c 3 Cell mi, nhng Cell
ny nh hn v c 3 anten nh hng c t v tr ny, gc gia anten ny 120o
.

Hnh 15. Giai on 1 Sector ha (Sectorization)

3.3. Giai on 2: Tch chia nh hn na v sau

a. Tch chia Cell 1: 3 thm ln na

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
Ln tch ny s dng li mt bng c v thm mi gp i mt bng mi cho cc
BTS mi.
mt bng c, anten cn quay i 30o ngc chiu kim ng h. Nh vy tng s
mt bng gp 3 ln mt bng c tr gi cho s tng dung lng mng ln gp 3 ln.

Hnh 16. Tch chia Cell 1:3 thm ln na

b. Tch chia 1:4 (sau ln u chia 3)

Hnh 17. Tch chia 1:4 (sau ln u chia 3)

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
S tch chia ny khng i hi phi xoay hng anten tt c cc BTS c mt bng
c. S ln s dng li tn s, dung lng h thng v s lng mt bng BTS u tng 4
ln so vi trc khi tch. Ty theo dung lng h thng, vic chia Cell c th c thc
hin tip tc.
Bin php phn chia t bo lm gim kch thc ca t bo nhng cng lm tng
dung lng h thng. Bin php ny phi c p dng theo tng giai on pht trin ca
mng. Tuy nhin, bin php na cng c mt s hn ch nht nh bi kch thc cell cng
c gii hn. ng thi vic lp t cc v tr trm mi i hi kinh ph ln. [4]
IV. Gii hn v hiu nng phn vng ti s dng trong mng di ng (reuse
partitioning)
4.1. Gii thiu

Nhu cu i vi dch v in thoi di ng d kin s pht trin nhanh chng. Tng

cng sut ca h thng di ng hin i, tc l, s lng thu bao trn mt n v din tch
x l ti mt s cht lng dch v ti thiu, l mt trong nhng vn chnh trong cc
nghin cu v cc h thng ny. Trong vng ny mt vai tr quan trng c pht bng
ph v tuyn b gii hn c sn.
tng dung lng ca mt knh h thng, c ba phng php tip cn nh sau:

1. Gim kch thc t bo

2. Gim t l gia khong cch sng mang v cc bn knh t bo (D/R)
3. Ti u ha chnh sch phn b tn s.

Phng php u tin c mt nhc im i hi s gia tng s lng cc trm c s

tng ng vi mc cng sut tng c yu cu. Mc khc, vic gim t l D/R cng
nh vic gim thiu bng thng ca knh cho n ngi dng nh hng ca s giao thoa
nhiu n s iu ch v cc k thut m ha.
Cc khi nim ph bin trong tt c cc chin lc phn c nh hoc FCA (fixed
channel allocation) l vic phn b tp di hn ca sng v tuyn n tng t bo. Bi v
cng tn hiu v tuyn lm suy gim theo khong cch, cng mt tp cc tn s c

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
th c ti s dng bi mt t bo (cell cochannel) s khong cch xa. Khong cch ti
thiu gia hai t bo cochannel m cho php nhng ngi s dng in thoi di ng tng
ng giao tip m khng cn s can thip cochannel bt k v tr ca chng trong t bo
c gi l khong cch ti s dng ng knh (D)(cochannel reuse distance). S lng
ny ph thuc c SIR ti thiu (Signal Interferen Ratio) c cho php, trong xc nh
t l D/R, v trn bn knh t bo (R).
T s D/R ph thuc vo SIR min. Gim D c th t c bng cch chp nhn mt
SIR min thp hn hoc gim R. Mt SIR min thp hn c th chp nhn c nu c hiu
qu v s bin thin tt v phng thc m pht trin. mt hng khc, lm gim R,
khng c tng s trm c bn kt qu trong cht lng tn hiu song v tuyn khng c
chp nhn ngoi cng ca t bo. Tuy nhin n c th thc hin c nng cao nh
cch reuse ch tp hp vi tn s c kh nng kh dng.
Phng thc c lin quan ti vic phn vng ti s dng: Nguyn tc c s ca vic
phn vng ti s dng l mt knh m c dng, vi di ng gn trm c s tng ng,
knh c nhn vi cp ng cng sut cao hn knh xa mobiles. Chnh sch phn b.
chng ta c th chia n thnh 3 loi: chin lc c nh, chin lc linh hot, chin lc
ng lc. Khi nim ph bin hay FCA l phn b c nh ca mt thit lp sng v tuyn
cho mi t bo. Mt t bo c thit lp mt tn s f c nh. Trong FCA c bn mt yu
cu cuc gi trong mt t bo ch c th c phc v nu c mt knh rnh, kh dng
trong t bo. [5]
4.2. Thut ton phn vng ti s dng
4.2.1. Thut ton c bn

Mt dch v thng tin lin lc c cung cp cho mt khu vc a l s dng mt

tp hp Q sng mang (cariers). Nguyn tc ca mt mi trng thng tin di ng c chia
thnh cc t bo. Cc t bo thng c gi nh l lc gic m hnh mi trng mng
n gin nht. Gi nh mt trm c s c hiu lc trong mi mt t bo. T bo c ng
knh l R. Nguyn tc c bn ca mt mng di ng l carrier c th s dng ti cng mt
thi im ti vi t bo (cc t bo cng knh). Khong cch nh nht gia cc

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
t bo cng knh ging nhau l D. Cc t bo c chia thnh cc nhm. Mi nhm gm
M t bo ln cn c khc carrier. Cc k thut n gin nht phn b carrier cho t bo
l gn knh c nh (fixed channel assignment - FCA). Q sng mang c chia thnh cc
nhm q=Q/M sng. Mi n nh lu di cho cc t bo cng nhn. Do c trng k thut
ti s dng tn s ca mi trng t bo cho php tng dung lng c sn ca Q sng mang
bi mt yu t bng vi s cm (clusters). Vi hnh dng l t bo lc gic.

D .R

Khi mt SIR c chn theo tiu chun nng lng truyn dn, t s r= D/R gia
khong cch ti s dng nh nht v bn knh t bo c thit lp. Sau khi bn knh t bo
c la cho da trn s nghin cu. Thng s D t ng c c nh. in hnh SIR cho
php ti thiu 18dB. T s D/R t nht l 4.58, suy ra M c t nht l 7 t bo (cells). Cho
tng s t bo trong mt mng t bo (bng s tng s trm c s).
Mc tiu l tng dung lng truyn mng m khng tng s tn s sng mang. Mc
tiu c th t c bng cch cho php khong cch ti s dng nh hn ca mt tp
con Fs, ca tong b cc tp hp con sng mang kh dng trong mng, ch da vo vic
gim gi tr ca R. t s D/R khng i m khng cn p dng by k chng trnh iu
khin nng lng, cng sut gia s giao thoa cng knh gi tr c th chp nhn c.
Dl, Rl k hiu thay cho k hiu D, R lc u, v gi s rng mt sng mang fs thuc
Fs c s dng vi mt khong cch ti s dng Ds<Dl. T y, tng s lng v v tr
ca trm c s khng c thay i. Ds c th gi nh ch mt vi gi tr tng thch vi
dy cho trc ca trm c s, Do v khong cch ti s dng nh hn sng thit lp Fs.
Bn knh nh hng Rs phi tha mn:

Ds Dl

Rs Rl

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
R rng Rs<Rl, vng nh hn s c gi l li (trung tm), cn gii hn vng l
ngoi li v trong gii hn t bo.

Hnh 18. Phn vng ti s dng t bo

T cc phng trnh trn suy ra c: Rl

3M 3M
s l
Rs
Rs
Ms
V vy: Rl Ml

F l tp hp cc sng mang trong mng (|F|=Q). Cc tp F s c phn chia ph hp thnh

hai tp con Fl v Fs. Vi yu t Ql v Qs, c s dng vi khong cch ti s dng tng
ng Dl v Ds, cc tn s sng mang Fl v Fs c gi l long-haul frequencies (lhfs) v
short-hand frequencies (shfs). V vy mi t bo c ql=Ql/Ml lhf v qs = Ql/Ms vi tng s
sng mang q = qs+ql . hiu cch k thut phn vng ti s dng ny nh hng n hiu
sut mng, hai gi nh n gin ha sau:
- ql(qs) t l thut vi s lng ngi dng.
- Mt s dng thng nht trong mng.

Do cc gi nh ny nn c: qs R s 2 , ql R l R s
2 2 2

q R2 l q R2 l

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 BO CO BTL H THNG VIN THNG NHM 7 | 20162
Tng s lng sng mang c tnh ton:
Ms qs q
Q Q Q q M q q M M q
s l s s s l l l

1 s M q 4 1 2


Ml q q

S lng sng mang trn mt t bo q trong m trng di ng c in m khng

phn vng th q=Q/Ml. Do tng ti a cng sut mng li cung cp bi cc lc
phn vng ti s dng c thc hin khi hm: B( ) q '/ q c gi tr cc tiu.

Ngha l: B( ) 4
1 2

4.2.2. Thut ton m rng

Chn 2 khong cc ti s dng Ds, Dm, Dl= D (Ds<Dm<Dl). Chng ph hp vi mng

cho trc bi trm gc. m bo cc SIR ging nhau mi cp t bo cng knh. Ch
mt phn ca mi t bo (mt vng con) c th c ph bi sng mang, vi khong cch
ti s dng Ds v Dm. Do chng ta c th nh ngha hai t bo lc gic c chia ra
trong mi t bo vi ng tm v vi bn knh Rs, Rm. (Rs< Rm< Rl).

Ds Dm Dl

Rs Rm R
l

Ba khu vc c chia khng chng cho nhau, c gi l core(vng trong lc gic nh)
middle (vng trong lc gic ln v ngoi core) ring ( gia bin gii lc gic ln v bin
gii ca t bo)
Nh trong trng hp ch c mt phn vng t bo, quan h gia bn knh v khong cch
ti s dng cho mi vng ph t bo: Ds/Rs= Dm/Rm = Dl/Rl
Ds v Dm c chn, Dl c cho. Ba cm t bo khc nhau c xc nh gm Ms, Mm,
Rm
Ml t bo. Nu n biu th ch s Rm/Rl:
Rl

Tp hp F carriers kh dng trong mng (|F| = Q)

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
F s phn thnh 3 tp Fl, Fm, Fs. Vi s lng Ql, Qm, Qs, vi khong cch ti s dng Dl,
Dm, Ds.
Fm c gi l tn s tm trung. Do mi t bo:

ql= Ql/Ml; qs=Qs/Ms; qm= Qm/Mm;

Tng s sng mang trong mi t bo q= ql+ qm+ qs;

Tng dung lng mng c tnh nh cch trc trong 1 phn vng t bo. Gi dnh mt
ngi dng trong khu vc, phn b song mang ngi dng nh nhau ng u.

q R2
q R2
s s 2

q R 2 R2
q
m m 2
R
s
2 2
l

q R2 R 2
q
l l
R2
m
1 2
l

Tng s sng mang Q:

Q Qs Qm Ql
qs Ms qm Mm (q qqs qm q
)Ml

M q M s ms q M m
1 s
qm
l
Ml q Ml q q

M lq 4 2 ( 2 2 1 2 2 2 )
M q( 4 4 2 2 1 2 )
l

Hm C(,) q '/ q nh nht: C , 4 4 2 2 1 2

Khi v ch khi ,
1/ 3 2/3

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 BO CO BTL H THNG VIN THNG NHM 7 | 20162

Khi dung lng tng C 1 ( , ) 1.5. ngha vt l phn vng t bo ti u

1/ 3 2 /3
khi ba phn vng core middle, ring c din tch nh nhau bng 1/3 t bo.

Xem xt t bo P-1 phn vng.

- Ri: bn knh t bo lc gic ng tm vi chiu di gim dn (i= 0, P-1).

- R0: chiu di c bn ca t bo.

Hnh 19. T bo vi phn vng v hn

P phn vng con trong t bo: P-1 ring v 1 core

Chn 2 bn knh ln cn Ri, R(i+1) cho vng ph th i, c qi sng mang, Mi k hiu s t

bo trong cc cm lin quan phn vng th i.

i Ri . S dng P= 2, P = 3. Nh trng hp trc th cc vng ph c din tch

0

2 2 i1 1
ging nhau lm t bo c ti u ha. i
P

Do chng ta c s sng mang cho phn vng i:

qi q
2 2
i1
Tng s sng mang Q:

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 BO CO BTL H THNG VIN THNG NHM 7 | 20162

Q i0 M i qi
P1

i0 M 0 q
P1 2
2 2
i i i1

M q 2
2
P1 2

0 i0
i i i1

t gi tr nh nht
Hm C(i , P) C(i , P) i0 i i i1
P1 2
2 2

Ta c: P 1 v C 1 (P) 2P
C(P)
P 1
2P

Vi: lim C 1
(P) 2.
P

Suy ra: Gi tr ln nht tng l 2 ln. [6]

4.3. Lu lng truy cp v m hnh ng.

Qu trnh hnh thnh cuc gi ngi dng v linh ng c din t bng quy cho
trng hp ch mt phn chia t bo (mi t bo c chia thnh vng v li). V tr ca
ngi dng in thoi c nh ngha bi ch s t bo u ngi dng hin ti c
thy v theo tng kiu t bo (li v vng) bn trong t bo . Mt m hnh di ng n
gin c gii thiu m t s chuyn ng ngi dng gia cc vng dch v c chia.
Chng ta bc u xt rng mt t bo nh mt thc th n c. Hy cho thi gian i
qua t bo l gi tr ngu nhin vi hm mt xc sut cp s nhn t chi (pdf) v gi tr
trung bnh 1/ . Hy gi s u tin ngi dng ng, v th xc sut ca vic tm thy mt
ngi dng ti vng c cho l t l vi din tch vng, cho vng dch v by gi chia
thnh S t bo ging nhau.
Tc chuyn tip i ra t t bo xc nh c bit ( ), trong khi tc chuyn
tip khc thu c bi vic cn bng lu lng xt rng xc sut trng thi c nh ngha
bi 1/s (t bo nh du) v (s-1)/s (tt c cc t bo khc). Mt ngi dng ri khi t
bo v vo 6 t bo hng xm, l s la chn ngu nhin.
Gi phn bit v tr ngi dng gia vng tm v vng, chng ta chia trng thi t
bo c nh du. Tnh ton tc chuyn tip mi, cc gi nh sau c tao: xc sut

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
tm thy mt ngi s dngtrong mt khu vc nht nh t l vi din tch khu vc, tc
chuyn tip cho t bo khng thay i v thi gian i qua t bo trung bnh l t l

i .
vi bn knh t bo, Thi gian i qua li trung bnh l . Hnh 18 th hin

biu kt qu chuyn vng, ln na thy rng trng thi xc sut c nh ngha bi

2
v (S-1)/S t bo khc.
2 S (core) , 1 S (ring)

Hnh 20. Ngi dng di ng gia cc Cell

Hnh 21. Ngi s dng di ng gia cc subcells

Quan tm ti s hnh thnh qu trnh truy cp, mt ngi dng c m hnh nh

ngun Markovian on off. Ngi dng trong trang thi off(on) trong mt thi gian
ngu nin toff(ton) vi s m m pdf v 1 ( 1 ) l gi tr trung bnh. Mt yu cu thit

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
lp chim ly tng ng vi mt s chuyn tip off - on. Nu mng c th cung cp mt
knh rnh, cuc gi mi c chp nhn v ngi dng gi knh trong thi gian ton. Nu
khng, cuc gi b kha v ngi dng quay tr li trng thi off. Trong qu trnh mt cuc
gi ngi dng c th i qua bin gii mt t bo hoc bin gii li 0 vng v knh v tuy
hin ti khng di s dng. Khi mt chuyn vng phi thc hin. nu mt knh mi
ph hp khng c tm thy, mt chuyn vng xy ra li v cuc gi b ri. Ngi dng
khi b p v trng thi off. [4]
4.4. Chnh sch gn knh ng

Th tc cn bn x l cc sng mang, c ngha l, vic la chng nh song mang

gn v gii phng, v qun l trao i song mang c gn, n th hin phn vng ti
s dng v kt qu cp knh ng trong s tng thm ca di h thng c i chiu vi
h thng t bo c bn. Tuy nhin ngi s dng li truy cp c dch v shfs v lhfs ni
chung tt hn dch v ngi s dng vng. khc phc vi vn ny, mt tnh nng
n gin c gii thiu: Hn ch truy cp ngi s dng li lhfs. mc A (A<100)
c nh ngha rang, nu f.w knh hin ti c th h tr t bo b trung bnh f sng mang
lhfs phn chia cho t bo, khng nhiu hn Afw/100 knh c th c s dng bi ngi
dng li. A = 0 v A= 100 c nh ngha gii hn trng hp ca phn chia y ca
cc song mang gia li v vng, v s chia s lhfs gia ngi s dng gia li v vng.
Mt tnh nng c th ci thin hiu xut ca mng t bo l hng i ca hng i
FIFO trong mi trm c s, trong mi trm c s c th lu m nhng yu cu cuc
gi mi m khng th c p ng ngay lp t do khng c sn c v tr rnh trong song
mang c phn b cho t bo v mt sng mang c ng k ti t bo. Mi yu cu
ngi dng c th lc c phc v theo chnh sch FIFO ngay nh mt khe cm nhn
ri hoc mt sng mang mi kh dng trong t bo. Thng qua mt cuc gi m l li tm
thi vic cung cp dch v cho ngi s dng, v vy, trong mt thi gian m ti a phi
c thit lp ph hp cung cp mt cht lng mt dch v chp nhn c.
4.5. Kt qu hiu nng

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BO CO BTL H THNG VIN THNG NHM 7 | 20162
M hnh phn tch nh gi hiu sut ca h thng c nghin cu rt kh
pht trin, thc hin do s phc tp ca h thng. V l do ny bin php thc hin sau y
c tnh ton ch s dng m phng my tnh. Mt vng dch v romboidal m c
xem xt. Mt mng thng thng 10x10 trm c s cung cp ph song thng qua n ten
ng hng. Nh vy, chng ta tng tng khu vc dch v chia thnh 100 t bo lc gic
ging nhau. Cc ngun song v tuyn bao gm mt tp hp cc sng mang, nhng ci m
c gn cho cc t bo c lp nhau. Mi sng c t chc trong h thng gm c mt
s lng nht nh cc khe thi gian, v mi khe thi gian h tr cuc gi. Lng nh nht
ca ngun sng v tuyn c th gn c ti mt t bo l mt sng mang. Xc sut cuc
gi b chn c cho bi thut ton phn b knh ng vi phn vng ti s dng c m
t trong cc phn trc, c nh gi bng m phng my tnh. Lun lun gi nh
rng ngi dng li c truyn truy cp song mang trong tp FI. Cc tham s A s th hin
phn tram knh lhf c th c dng ngi dng li. Chng ta chn hai kch c cm Ml
= 7 v Ms = 3. Cc mng li truy cp v cc thng s gi nh y l Q= 35 sng mang.
Mi song mang gi w= 4 khe thi gian (cc knh), lu lng truy cp trung bnh mi ngi
dng = 0.025 vi thi gian gi trung bnh 1/ = 120s.
Hnh 19 th hin xc sut chn cuc gi vi ngi dng c inh. S ngi dng c
nh c s N trong Khong 600- 800 vi mt s khc nhau ca shfs Qs (s Ql lhf;s c
cho bi Ql = Q-Qs ). Mt tnh nng chn cuc goi c a ra bi cc k thut phn vng
ti s dng cho tt c cc gi tr ca phn vng quang ph so vi trng hp c bn khng
c phn vng quan ph (Qs=0). Ty vo s lng ngi dng s ci thin di t mt bc
ti vi bc ca kch thc. N c tin hnh mt s phn chia ti u cc tn s sng Q
thnh hai tp hp Qs v Ql, ci m thnh ra: Ql = 28 v Qs =7 cho tt c kch thc tp hp
c xem xt.

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Hnh 22. Ngi s dng c nh: ngn chn xc sut chng s lng ngi dng mi
t bo.
Tuy nhin, mc d s lng nh cc sng mang Qs phn b li, tri qua mt xc sut chn
thp hn do kh nng truy cp ca h ti tt c cc tn s, trong khi vng vng, ngi
dng ch truy cp lhfs. mc dng chnh lch nh vy, phn vng ti s dng vn cung cp
mt s ci thin trong ngay xc sut chn, ngay c trong tnh trng ti t nht, v d kinh
nghim ngi s dng vng c gi nh nh hiu sut ton b h thng (Hnh 19).
Hin nay, thm cc tnh nng hng i ti cc trm c s mt cuc gi mi c
thit lp bi trm v chn do khng c sn cc knh ph hp c xp trong thi gian gii
hn. Mt thng s hp l cho thi gian xp hng cuc gi c chn l 5s, c ngha l nu
cuc gi b b nu khng c mt v tr no kh dng hoc mt sng mang mi c to kh
dng trong t bo. Mt b m cho 30 cuc gi c gi nh. Tc ng ca hang i v
gii hn truy cp ti lhfs hin c nh gi cho mt phn vng ph Ql = 28, Qs = 7. Hnh
20 cho thy xc sut chn ton th vi hang i v vi mt yu t truy cp bin A so vi
trng hp c bn truy cp y khng hng i (A = 100).

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Hnh 23. Ngi s dng c nh: chn hiu sut vi quyn truy cp c gii hn v
hng i.
R rng xc sut chn tng bi v h s A gim. Tuy nhin, mt gi tr thch hp cho
h s kh nng truy cp lhfs tn ti m tm v vng nhn mt dch v tng c vi s
gim nh ca tng th hnh dng blocking. Trong trng hp ca chng ta xy ra vi A gn
vi 40. Ngi dng ng by gi c thm vo h thng vi tham s 1/ = 60s. By gi
cuc gi khng thnh cng do hai s kin khc nhau: chn ti thi gian thit lp cuc gi
hay mt do s chuyn vng khng thnh cng. Lu rng vi phn vng ti s dng ca
chng ta, chuyn vng l cn thit c bin gii t bo v ti bin gii li khi lhf ang
c s dng cho cuc gi. Xc sut chn cp n cc s kin ca chn cc cuc gi
mi, bi v cc ti khon ri chuyn vng khng thnh cng. Xc sut li s biu th tng
xc sut chn c tnh n c hai loi li. trong hon cnh ny vi tt c ngi dng in
thoi di ng xc sut th hin trong Hnh 21. Th hin gi tr nh nht ca chng cho t l
phn chia Q = 35 thnh Ql = 28 v Qs = 7, ci m thu c vi ngi dng c nh. Mt
ln na, nu khng c hin th trong hnh, ngi dng li nhn c dch v tt hn
ngi dng vng.

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Hnh 24. Ngi s dng di chuyn: xc sut suy hao chng phn vng quang ph

Hn na, Hnh 23 th hin xc xut ri trong khi chuyn vng do t to t bo chuyn

tip cao hn xc sut ging nhau do chuyn tip tm vng, tuy nhin, trong vng ca phn
chia ph ti u gi tr ca chng c th so snh. Hnh 24 cho xc sut khc cho N = 700
ngi dng so vi phn vng ph trong vng ca phn vng ti u khi hang i cho b
m cc cuc gi mi b chn c sn trong trm c s. S chn ca ca gim bt b m 1
cch ng k t l khng chp nhn ca cuc gi mi, nhng cho xc sut chn ton
th gim ch rt t. iu ny l do cc gi tr xc sut gim, m vn c ng k nh nhau.

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Hnh 25. Ngi dng di chuyn: xc sut li chuyn giao chng phn vng quang ph.

Hnh 26. Ngi dng di chuyn: nh hng ca hng i n hiu sut

Cc lc phn vng ti s dng xut t cng sut h thng cao hn trong khi
tng lng truy cp tn hiu cn thit x l chuyn vng. Thy rng gnh nng tn hiu
cn thit p dng lc phn vng ti s dng l hp l v hn ch khng th hin mt
s kh khn trong cc ng dng k thut ny. [7]

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4.6. Kt lun

Mt k hoch mi cho vic s dng c hiu qu hn nhiu ngun lc v tuyn trong

mt mng di ng chuyn mch c m t. tng c bn ca n l nh ngha 2 hay
nhiu hn tp hp song mang vi khong cch ti s dng khc. Theo mt k hoch ch
yu cu thm tn hiu thng bo do chuyn vng ca s kin chuyn vng khng tng s
trm c s n mi trng m khng cn phn vng quang ph. Ch rng iu khin
cng sut l khng cn thit mc d ng dng ca n c th ci thin hiu sut tng th
bng vic gim hn na s can nhiu. Mt s ci thin ang ch trong xc sut chn ginh
c cho tt c mng v thng s truy nhp. [5]
V. Tng kt

Thng qua bi tp ln vi ch TM HIU V CELL SECTORING AND CELL

SPLITTING, chng em hiu c thm cch nng cao dung lng h thng trong h thng
mng thng tin di ng t bo. Tuy nhin, do kin thc, kh nng su tm v dch ti liu
Ting Anh cn hn ch nn chng em cn tn ti rt nhiu thit st, knh mong thy gp
chng em hon thin hn.
Chng em xin chn thnh cm n thy gio giao ti chng em c t tm
hiu, tng hp ti liu v c c hi c lm vic theo nhm.

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TI LIU THAM KHO

[1] N. V. c, THNG TIN V TUYN, Nh xut bn k thut, 2006.

[2] N. H. Dng, "K s in," 20 3 2014. [Online]. Available:

https://kysudien.wordpress.com/2014/03/20/mang-thong-tin-di-dong-te-bao/.

[3] V. V. Ym, H THNG VIN THNG, Nh xut bn Bch Khoa, 2016.

[4] G. L. Stuber, Principles of Mobile communication, 2, Ed., Springer, 2009.

[5] L. Yong, "PCellular Architecture with Frequency Reuse," 2002-2002.

[6] R. S. Kshetrimayum, "Advanced Topics in Communication Systems".

[7] A. P. V. T. r. D. Lucatti, "Bounds and Performance of Reuse Partitioning in Cellular,"

International Journal of Wireless Inform ation Networks, vol. 4, no. 2, 1997.

[8] A. F. Molisch, Wireless Communications, John Wiley & Sons, 2005.

[9] T. S. Rappaport, Wireless Communications: Principles and Practice, PHI, 2007.

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