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Cc phng thc phn tp(diversity)Bi c Tin HVKTQS TVT6B1/24nh nghaPhn
tp l mt phng php truyn tn hiu bng cch truyn mt tn hiu ging nhau trn
nhiu knh truyn khc nhauVic ny nhm chng li fading v nhiu 2/242Phn
loi phn tpTheo cch thc trin khai:(1) phn tp pht (2) phn tp thuTheo
k thut phn tp:(1) phn tp khng gian Space Diversity(2) phn tp tn s
Frequency Diversity(3) phn tp thi gian Time Diversity(4) phn tp phn
cc Polarization Diversity(5) cc k thut kt hp3/24Phn tp khng gianTn
hiu c truyn trn nhiu ng khc nhauTrong truyn dn hu tuyn, ngi ta
truyn trn nhiu si cpTrong truyn dn v tuyn, ngi ta hay s dng phn tp
ng ten
4/24Phn tp thi gianPhn tp thi gian: tn hiu c truyn i nhng thi im
khc nhau. Nhc im : bn pha thu phi ch 1 khong thi gian x l tn
hiu5/24Phn tp tn sTn hiu c truyn trn nhiu tn s khc nhau Hoc trn mt
dy ph tn rng b tc ng bi fading la chn tn sNhc im: tiu tn ph
tn6/24Phn tp phn ccTn hiu c truyn i bng nhng sng phn cc khc nhau
(trc giao ch c 2 nhnh)Nhc: chia nh cng sut tn hiu v tn hiu phi chia
u cho cc nhnh => cht lng thu s gim7/24Kt hp phn tp khng gian
thuKt hp chn lc (Selection Combining)Kt hp t l ti a (Maximal Ratio
Combining)Kt hp ng li (Equal Gain Combining)Kt hp phn tp thu v tch
sng MLD8/24Kt hp chn lcL thuyt: chn nhnh c t s tn trn tp (SNR) ln
nhtThc t: o SNR kh nn tm nhnh c tng cng sut tn v tp ln nhtPhng php
ny c li phn tp thp nht
9/24Kt hp t l ti aTn hiu ca M nhnh c nhn vi trng s theo t l SNR
tng nhnhiu chnh ng pha ri cng vi nhauThc t: l phng php tt nht
10/24Kt hp ng liMRC tng i phc tp li khng ln hn nhiu so vi SCEGC
l mt trng hp c bit ca phng php t l ti a vi trng s cc nhnh l hng s
(n gin nht l hng s n v)11/24Kt hp phn tp thu v tch sng MLDS kt hp
MRC v tch sng ti u (Maximum Likehood Detection)
12/24Lut tch sng ti uSk tn hiuXc l biu phn phi im tn hiu (signal
constellation)D2 l bnh phng khong cch Euclid gia cc tn hiu thu c v
cc tn hiu khng cha tp m
13/24Kt hp phn tp khng gian phtT l ti a MRT (Maximum Ratio
Transmit)Phn tp pht gi chmPhn tp pht khng/thi gian14/24Phn tp pht t
l ti a (MRT)
15/24Phn tp pht gi chmCc bn sao ca d liu c truyn ti thi gian khc
nhau trn nhng anten khc nhau
16/24M ha khng gian- thi gian M khng gian-thi gian (Space-Time
Codes-STC) do Tarokh v cc ng s pht minh nm 1998 ti AT&T : l mt
phng php mang li hiu qu truyn tin trong vic phn tp pht trong mi
trng fading s dng nhiu anten
17/24M ha khng gian- thi gianGi s c N anten pht v M anten thuVi
mi k hiu sl u vo, b m ha to ra N k hiu m c pht ng thi t N anten pht
: cl,1; cl,2; cl,3,,cl,NVecto m cl= [cl,1; cl,2; cl,3,,cl,N] Pht dy
vecto m C = {C1, C2,, CL}Li xy ra khi b gii m quyt nh sai rng ta
pht 1 dy vecto m khc C = {C1, C2,, CL} Xt khung d liu c u vo l LMa
trn li A : A(C, C) = (Cl Cl)(Cl Cl)* vi * l k hiu lin hp phcT
18 Xc sut li cp PEP (Pairwise Error Probability) c gii hn trn
:
P(CC) ( Es / 4No )
-M-rMNng lng k hiuMt ph cng sut tp mHng ca ma trn li ATr ring
khc khng ca ma trn li A
( Es / 4No )-M-rM: tng ch m ha ca h thng: tng ch phn tp ca h
thng MN (do r N) MH =PT =M ha khng gian- thi gian19M ha khng gian-
thi gian Da vo cc thng s trn ngi ta phn loi cc b m ha ra lm 2 loi
chnh :
M khi khng gian thi gian STBC (Space-Time Block Coding)
+C PT+Khng c MH+ B gii m n ginM li khng gian thi gian STTC
(Space-Time Trellis Coding) (to ra s tng quan gia cc tn hiu pht)+C
PT+C MH+B gii m phc tp20/24M STTC(10)23(11)(00)01(10)
0001101100011011
00000110110100011011101110110010Cc k hiu trong chm sao tn hiu
QPSKK hiu 11 v 00 c pht ng thi trn 2 anten tng ngM STTC vi 4 v 8
trng thi s dng chm sao QPSK thit k cho 2 anten pht 1 m 4 trng thi 1
m 8 trng thi Hnh 1Hnh 221/24M STTCM STTC c thit k sao cho b gii m,
thut ton Viterbi thut ton gii m hp l cc i (Maximum Likelihood) c s
dng tnh ng hp l nht chy qua li c s o tch ly nh nht S o tch ly c xc
nh :
rt,m - s1 - s2
2 tng ch ng truyn t anten pht 1 n anten thu m tng ch ng truyn t
anten pht 2 n anten thu mTn hiu thu c anten m ti thi im tM STTC c
tm bng h thng my tnh cho cht lng tt hn hn cc m STTC trn (c thit k
bng phng php tnh ton th cng)22M STTC M STTC c tm bng h thng my tnh
cho cht lng tt hn hn cc m STTC trn (c thit k bng phng php tnh ton
th cng) :
M 4 trng thi QPSKHnh 3Hnh 423/24Kt lunQua cc nghin cu v l thuyt
cng kt qu m phng v k thut phn tp anten, c th khng nh:y l k thut rt
hiu qu trong vic gim nh hng ca fading ln tn hiuNng cao li h thng,
ci thin ng k cht lng cng nh dung lngm hnh phn tp anten ng dng vo h
thng MIMO c bit trong vic nng cao dung lng h thng mt yu cu ang rt c
quan tm ca cc cng ngh truyn thng hin i.24/24
