ng Thanh Bnh

Chng 2
S lan truyn v tuyn
Ni dung
C bn v sng v tuyn (radio wave)
Antenna
Cc c ch lan truyn (propagation mode)
Tnh ton cng sut
Truyn thng Line-of-Sight
Hin tng m (fading)
Cc m hnh suy hao ngoi tri
Hiu ng Doppler
Delay spread, ISI v cohenrent bandwidth

2
C BN V SNG V TUYN
Electromagnetic Wave (Sng in t)
The Physics Classroom
Sng in t l sng c th di chuyn qua chn
khng trong khng gian.
Sng c hc (mechanical wave) cn s tn ti ca vt
liu truyn dn truyn ti nng lng ca n t
im ny n im khc

4
To ra sng in t
Nguyn tc c bn: lc cc ht in tch
truyn thng tin, s dao ng cc ht in tch
phi kim sot c, ngha l cc ht in tch
nn dao ng ln v xung mt cch nhp nhng.
Qu trnh ny to ra bc x c th lp li chnh n
lm iu ny, s dng mt mch in c cun
cm (inductor) v t (capacitor) to ra dng
in dao ng
Truyn dng in ny vo 1 anten.
5
Spark Gap Transmitter
Cun dy (tuning coil) v cc
bnh Leyden ng vai tr
inductor v capacitor
Khi nhn telegraph key, ngun
pin s to ra chnh lch in th
b nh la (spark gap), lm
pht ra 1 tia in gia 2 u ca
b nh la.
Vic ny lm ng mch v cung
cp dng in n mch c
to ra bi cun dy v bnh
Leyden.
Dng in s di chuyn vi tn
s ca mch ny, sau y c
a n anten v truyn i

6
Electromagnetic Wave (Sng in t)
Sng c to ra c c t tnh v in tnh, c kh
nng lan truyn qua khng gian.
Bc x (radiation) in t to ra t trng
(Magnetic Field) v in trng (Electric Field).
Hai trng ny vung gc vi nhau v hng di
chuyn cng vung gc vi c 2 trng.
Tc dao ng ca electron quyt nh tn s
sng.

7
Electromagnetic Wave (Sng in t)
Mt phng ca in trng s xc nh s phn
cc (polarization) ca sng

8
Sng radio l g?
Radio: v tuyn
Sng v tuyn l mt loi bc x in t c bc
sng trong ph in t di hn tia hng ngoi.
Sng v tuyn c tn s 300 GHz n mc 3 kHz,
tng ng vi bc sng 1 millimeter (0.039 in)
n 100 kilometer (62 mi)
Ging nh cc loi sng in t khc, sng radio
di chuyn vi tc nh sng

9
Ph in t

10
Sng radio lan truyn nh th no?
Theo Maxwell:
Do thnh phn in v t lun tng tc, sn sinh ra
nhau nn sng lun c mt in t trng
Cc ht mang in v t ny tng tc vi cc ht ln
cn (trong trng in t ca n) trong mi trng
ng cht nn cc ht ny cng nhim in t v tip
tc lm nhim in t cc ht ln cn
C th, sng s lan truyn i xa n khi ht cng sut
pht hoc b di li (do phn x hay khc x)
Trong mi trng khc cht, sng s b phn x hay
khc x
11
Cc c tnh ca sng in t
Wavelength (Bc sng)
Frequency (Tn s)
Amplitude (Bin )
Phase (Pha)

12
Cc c tnh ca sng in t

13
Cc c tnh ca sng in t
Phase (Pha)
S khc bit (o bng )
gia cc sng hnh sin
chng ln nhau
Lch pha (Out of phase)
o t 0-360
0 cng pha (in phase)
90 lch pha (quarter
out of phase)
180 hy tn hiu ban u
(cancels out original)

14
Tc , bc sng v tn s
Tc nh sng = Bc sng x Tn s
= 3 x 108 m/s = 300,000 km/s

15
ANTENNA
Antenna
Antenna (aerial) l 1 thit b in c nhim v
chuyn nng lng in thnh sng v tuyn v
ngc li.
Truyn (Transmission) anten nhn dng in dao
ng tn s nh trc t transmitter v truyn
n u anten, sau bc x nng lng ca dng
in thnh sng in t
Nhn (Reception) thu thp nng lng in t t
khng kh, to thnh dng in c in th thp,
chuyn n receiver. , dng in s c
khuch i v x l tip
17
Phn loi Antenna
C 2 loi antenna chnh:
Anten ng hng (Isotropic antenna
Omnidirectional antenna)
Pht ra nng lng nh nhau theo mi hng
Anten nh hng (Directional antenna hoc Beam
antenna)
Pht sng c nh hng

18
Anten ng hng
Vertical antenna
Whip antenna
Monopole antenna

19
Anten ng hng
Dipole antenna Half Wave Dipole Antenna
Angten lng cc
Gm 2 linh kin
dn (conductor)
pht sng v 2
hng
Thng c chiu
di bng na
bc sng

20
Anten ng hng
in trng v t trng ca dipole antenna
Xanh: in trng
: T trng

21
Anten nh hng
Anten Yagi

22
Anten nh hng
Log-periodic antenna

23
Mt s thit k antenna khc
Phased array

24
Mt s thit k antenna khc
Trm thu pht BTS

25
Mt s thit k antenna khc
Parabolic antenna

26
 li ca antenna - Antenna Gain
li ca antenna (Antenna gain)
o tnh c hng ca antenna
L cng sut pht ra theo 1 hng c th so vi
thng s chun ca 1 antenna ng hng
(omnidirectional antenna hay isotropic antenna)
Khu vc hiu dng
Ty thuc vo kch thc vt l v hnh dng ca
antenna

27
Lan truyn trong khng gian t do

)
Received power PR
Transmitted power PT
d

Omni-directional
transmitting antenna Receiving antenna, area AR

Vi l tham s hiu nng

Mc tp trung: c xc nh bng kch thc antenna trong

bc sng (bc sng l ):

vi l tham s hiu nng ca antenna truyn 28

Antenna nh hng
Transmitted power PT Received power PR

(
Transmitting antenna, area AT
d

)
Receiving antenna, area AR

Directional antenna gain GT > 1

Tng t vi slide trc:

Mc nng lng nhn c:

29
CC HIU NG LAN TRUYN V
TUYN
Lan truyn v tuyn
Lan truyn v tuyn (radio propagation) l mt
hnh vi ca sng radio khi chng c pht t
mt im n mt im khc, hoc khi chng di
chuyn gia nhng phn khc nhau ca bu kh
quyn
V cng l sng in t, sng radio cng b nh
hng bi cc hin tng: reflection (phn x),
refraction (khc x), diffraction (nhiu x),
absorption (hp th), polarization (phn cc), v
scattering (tn x)
31
Cc hiu ng lan truyn khng dy
Phn x (Reection)
Xy ra khi bc x in t gp mt vt cn ln hn
nhiu so vi bc sng (chng hn: b mt tri t,
nh cao tng, ).

32
Cc hiu ng lan truyn khng dy
Khc x (Refraction)
Tn hiu b b cong khi n i qua 1 cht liu c mt
khc bit so vi mi trng trc
Thay i hng i ca sng.

33
Cc hiu ng lan truyn khng dy
Nhiu x (Diffraction)
ng i gia transmitter v receiver b cn bi 1
vt c cnh trn.
Sng vng qua vt cn, ngay c khi tm nhn thng
(Line of Sight LoS) khng tn ti

34
Cc hiu ng lan truyn khng dy
Tn x (Scattering)
Khi vt th nh hn so vi bc sng ca sng ang
lan truyn (chng hn: bin bo, ct n, )
Tn hiu b phn tn thnh nhiu ng tn hiu c
cng yu hn.

35
Lan truyn a tuyn (Multipath)
L hin tng lan truyn m tn hiu nhn
c thit b thu n t nhiu ng khc
nhau
Nguyn nhn l cc hiu ng din ra trong qu
trnh truyn
Tc ng:
Interference (xung t) c tc ng tt v tc ng
xu
Lm chuyn dch pha ca tn hiu
Hin tng Rayleigh fading
Rician fading
36
Lan truyn a tuyn (Multipath)

37
Lan truyn a tuyn (Multipath)

38
Lan truyn a tuyn (Multipath)
M hnh ton hc ca multipath:
http://en.wikipedia.org/wiki/Multipath_propagation

39
Lan truyn a tuyn (Multipath)
Downfade (suy gim)
Lm suy hao cng tn hiu
Khi nhiu ng tn hiu RF n receiver vo cng
thi im v lch pha so vi sng chnh,
Lch pha trong khong 121 v 179 s to nn
hin tng suy gim

40
Lan truyn a tuyn (Multipath)
Upfade (tng cng)
Gia tng cng tn hiu.
Khi nhiu ng tn hiu RF n receiver vo cng
thi im v cng pha hoc lch pha 1 phn vi
sng chnh
Lch pha t 0 n 120 s gy ra hin tng
upfade.
Cng tn hiu nhn c cui cng khng bao
gi ln hn cng tn hiu pht i ban u.

41
Lan truyn a tuyn (Multipath)
Nulling (trit tiu)
Kt qu gy ra: trit tiu tn hiu.
Khi nhiu ng tn hiu RF n receiver cng thi
im v lch pha 180 so vi sng chnh.
Tn hiu RF b trit tiu hon ton.

42
CC C CH LAN TRUYN
Cc c ch lan truyn v tuyn
Ground wave propagation (<2 MHz): Sng c tn s
thp
i trn mt t v c th truyn khong cch di
AM(LF,MF) radio.
Sky wave propagation (230 MHz): sng ngn, b
phn x tng in ly.
Di ln v xung gia b mt tri t v tng in ly, di
chuyn vng quanh th gii
Pht thanh phm vi quc t
Space Wave propagation (>30 MHz): sng c tn s
cao (>30MHz) v ch i theo ng thng (line of
sight).
in thoi di ng, h thng v tinh, 44
Cc c ch lan truyn v tuyn
Ground wave: Sng mt t
Space wave: Sng khng gian
Sky wave: Sng tri
Troposphere: tng i lu
Stratosphere: tng bnh lu
Mesosphere: tng gia
Ionosphere: tng in ly

45
Bng tn v tuyn

46
Bng thng - Bandwidth
Bandwidth (BW)
L s khc bit gia tn s mc cao v tn s mc
thp trong 1 di tn s lin tc

47
TNH TON CNG SUT
n v o cng sut

n v o cng sut n v so snh

(n v tuyt i) (n v tng i)
watt (W) decibel (dB)
milliwatt (mW) dBi
dBm dBd

49
n v o cng sut
Watt
n v o cng sut c s
Cng sut ca dng in 1 ampere vi hiu in th
1 volt
Volts x Amps
MilliWatt (mW)
1/1000 watt
Hu ht thit b dng trong mng IEEE 802.11 c
cng sut c o bng milliwatt

50
n v o cng sut
Decibel (dB)
n v c s dng so snh
So snh cng sut pht ca 2 transmitter
So snh cng sut pht ra ti transmitter v nhn
c ti receiver
Bel da trn logarith. S dng log10 tnh ton
101=10 Log10(10)=1
102=100 Log10(100)=2
103=1000 Log10(1000)=3
104=10000 Log10(10000)=4
51
n v o cng sut
Decibel (dB) Miliwatts Decibel change
Cng thc: 0.001 -30

= 0.01 -20


= 0.1 -10

P1, P2 l cc gi tr cng 1 0
sut 10 +10
100 +20
1000 +30
10000 +40
100000 +50 52
n v o cng sut
dBi
Decibels Isotropic
khuch i so vi 1 b pht sng ng hng
(isotropic radiator) l thuyt
dBd
Decibel Dipole
S decibel khuch i (gain) so vi dipole antenna
C th chuyn i qua li vi dBi
Antenna dipole chun: 2.14 dBi
Nu 1 antenna c gi tr gain l 3 dBd th: 2.14+3=5.14 dBi

53
n v o cng sut
dBm
n v o tuyt i
S decibel ng vi s mW nng lng
Gi tr tham chiu: 1 mW=0 dBm
Do : 100 mW= +20dBm
C th dng cng thc
1
= 10
V sao dng dBm?
D vit -100dBm hn .0000000001 mW

54
Tnh ton cng sut
Lut 6dB
Nu tng gp i khong cch gia receiver v
transmitter, tn hiu nhn c s suy hao 6 dB.
Mi 6dBi khuch i s tng gp i khong cch hiu
dng ca sng v tuyn

55
Tnh ton cng sut
Lut 3s v lut 10s
Vi mi 3 dB khuch i, nhn s mW cho 2.
Vi mi 3 dB suy hao, chia i gi tr mW.
Vi mi 10 dB khuch i, nhn s mW cho 10.
Vi mi 10 dB suy hao, chia s mW cho 10.

56
Noise Floor Nhiu nn
Cn gi l background noise
Nhiu nn l mc nng lng radio nn trn 1
knh truyn c th
Bt k th g c in t tnh u c kh nng lm
tng bin ca nhiu nn
Bng tn 2.4 GHz ISM (Industrial, Scientific and
Medical Frequency Band) c nhiu nn khong
100 dBm

57
Signal-to-Noise Ratio (SNR)
V bn cht, SNR l s khc bit, tnh bng
decibel, gia received signal v background noise
level (noise floor). N khng hn l 1 t l.
V d, mt thit b nhn c tn hiu 85 dBm
v noise floor l 100 dBm, s khc bit gia
received signal v background noise l 15 dB
SNR l 15 dB.
SNR >= 25 dB: tn hiu tt
SNR <= 10 dB: tn hiu c cht lng rt km

58
Signal-to-Noise Ratio (SNR)

59
TRUYN THNG LINE-OF-SIGHT
Lan truyn Line-of-Sight

61
Lan truyn Line-of-Sight
Yu cu tn s trn 30 MHz
Anten truyn v anten nhn phi nhn thy nhau
Truyn thng v tinh tn hiu trn 30 MHz khng b
phn x bi tng i-n
Truyn thng mt t
Tc ca sng in t l 1 hm theo mc
m c ca mi trng truyn
Khi thay i mi trng truyn, tc thay i

62
Cc c ch lan truyn khng dy
Kt qu ca cc c ch lan truyn l 3 hin
tng gn nh c lp nhau:
Suy hao trn ng truyn - Path loss
Hin tng m chm - Slow fading (shadowing)
Hin tng m nhanh - Fast fading (multipath
fading)

63
Cng tn hiu nhn c - RSSI
Suy hao (Loss/Attenuation): L hin tng suy
gim cng tn hiu sau qu trnh truyn ti
cng tn hiu o c 1 thi im bt
k thp hn so vi cng o 1 thi im
trc
Khuch i (Gain): l hin tng cng tn
hiu c tng cng
Cng tn hiu nhn c (Received Signal
Strength Indicator RSSI): Cng tn hiu ti
thit b thu.
64
Cng tn hiu nhn c - RSSI
Cc yu t nh hng n cng tn hiu ti
receiver
Khong cch (hoc delay) (m hnh Path Loss Model)
Path attenuation (suy hao trn ng truyn)
Slow fading (hin tng m chm) hoc Shadowing
(do vt cn)
Fast fading (hin tng m nhanh) (do s di ng,
)
Hiu ng Doppler
Multipath Lch pha

65
Nhiu - Noise
Thermal Noise Nhiu nhit
Intermodulation noise
Crosstalk xuyn m
Impulse Noise

66
Thermal Noise Nhiu nhit
Cn gi l white noise
Do s bt nh ca cc electron
Tn ti trong cc thit b in t v cc phng
tin truyn dn
Khng th b trit tiu hon ton
L mt hm theo nhit
L yu t c nh hng ng k trong truyn
thng v tinh

67
Thermal Noise Nhiu nhit
Tng lng nhiu thermal trong khong bng
thng 1 Hz ca mt thit b bt k l:

68
Thermal Noise Nhiu nhit
Tng lng nhiu thermal trong khong bng
thng B Hz ca mt thit b bt k l:

69
Cc khi nim khc v nhiu
Intermodulation noise xy ra khi tn hiu trn
cc tn s khc nhau chia s chung ng truyn
Crosstalk hai lung tn hiu khc nhau quyn
vo nhau
Impulse noise cc xung tn hiu khng d on
trc
C thi gian ngn v cng kh cao
To ra bi cc sng in t bn ngoi hoc do li ca
h thng truyn thng

70
M HNH LAN TRUYN
M hnh lan truyn khng dy
Mt m hnh lan truyn khng dy (radio
propagation model) l mt m hnh ton hc
c xy dng m t qu trnh lan truyn v
tuyn di dng hm ca tn s, khong cch
v cc iu kin khc
Cc m hnh c s dng d on nng
lng nhn c hoc vic suy hao trn ng
truyn gy ra bi cc hiu ng refraction,
reflection, scattering,

72
Phn loi m hnh lan truyn khng dy
Line-of-Sight Model (M hnh ng nhn thng)
Free Space Model (M hnh khng gian t do)
Path Loss Model (M hnh suy hao trn ng truyn)
Land Propagation Model (M hnh lan truyn mt
t)
M hnh lan truyn phm vi rng
M hnh lan truyn phm vi hp
Empirical Model (m hnh thc nghim)
M hnh cho mi trng ngoi tri (outdoor)
M hnh cho mi trng trong nh (indoor)

73
M hnh lan truyn v tuyn - Mc tiu

74
M hnh Free Space Propagation
Dng d on cng tn hiu nhn c
khi transmitter v receiver c ng line-of-
sight (LOS) r rng v khng b che khut.
Vd: satellite, kt ni microwave line-of-sight.
M hnh free space d on rng mc nng
lng nhn c suy gim theo 1 hm khong
cch (d) gia thit b pht v thit b thu (T-R).
Nng lng s gim:
Tng ng vi d2
T l nghch vi 2
75
M hnh Free Space Propagation

Mc nng lng nhn c bi 1 anten pha

nhn (cng thc free space Friis)

76
M hnh Free Space Propagation

Pt = cng tn hiu ti anten pht

Pr = cng tn hiu ti anten thu
= bc sng ca sng mang (m)
Gt = mc khuch i (gain) ca anten pht
Gr = mc khuch i (gain) ca anten thu
d = khong cch gia cc anten (T-R) o bng mt (>0)
L : tham s suy hao ca h thng do suy hao trn ng
dy (ni b, trong thit b, phn cng), suy hao do cc b
lc, suy hao ca anten (L >= 1)
L = 1 ngha rng khng c suy hao do phn cng.
77
M hnh Path Loss
Path Loss (Suy hao trn ng truyn): Mc
suy hao tn hiu c o bng dB v l 1 i
lng >0, c nh ngha l s khc nhau gia
mc nng lng hiu dng pht ra bi
transmitter v mc nng lng nhn c.
Cng tn hiu suy gim theo hm m ca
khong cch d gia transmitter v receiver;
Ty theo mi trng, mc suy hao t l vi
mt gi tr trong khong d2 v d4

78
M hnh Path Loss
nh ngha path loss

79
M hnh Line of Sight Vn
Cc m hnh line of sight (LOS) n gin, chng
hn nh m hnh free space, khng tnh n
nhiu yu t thc t, vd nh:
a hnh g gh
Cc ta nh
Phn x
CHNH
S di ng XC THP
Che chn
Gii php: M hnh thc nghim (Empirical
Model)
80
Lan truyn mt t (Land Propagation)
Mt knh truyn thng di ng mt t (land
mobile radio channel) c xc nh khi c mt
phin truyn thng t/n mt trm c nh
(base station BS) n/t mt trm di ng
(mobile station MS)
N tr thnh mt knh lan truyn a tuyn c
suy hao t nhin
Tn hiu (signal) n ch theo nhiu ng i
do cc hiu ng/c ch lan truyn trn ng
truyn, vd nh phn x, nhiu x, tn x,
81
Lan truyn mt t (Land Propagation)
Cng tn hiu nhn c (RSSI) v thi gian
n ch ca thng tin c th khc bit nhau ty
vo mi trng
Vic lan truyn sng trong knh a tuyn
(multipath channel) ph thuc vo mi trng
thc t, k c cc yu t nh chiu cao ca
anten, nh ca, ng s, a hnh.
Cn m t hot ng ca knh truyn di ng
bng mt c ch ph hp

82
Lan truyn mt t (Land Propagation)
Cng tn hiu nhn c:

Vic lan truyn sng trong knh di ng c

m hnh ha bng ba yu t: path loss, slow
fading (shadowing), v fast fading. Hm lan
truyn L c m t nh sau:

83
HIN TNG M (FADING)
Hin tng m (Fading)
Tnh cht ca qu trnh truyn khng ch c
xc nh bi khi nim suy hao (attenuation).
Suy hao c th dao ng ln xung theo khong
cch v thi gian FADING.
Fading xy ra khi tn hiu mt i nhng c tnh
t nhin ca n v tr nn ngu nhin (random)
Fading thng c m hnh ha di dng
mt tin trnh ngu nhin (random process)

85
Hin tng m (Fading)

86
Fading

87
Delay Spread-Hin tng tr lan truyn
Khi tn hiu lan truyn t transmitter n
receiver, tn hiu chu mt hoc nhiu ln
phn x, tn x, iu ny lm cho tn hiu i
thnh nhiu ng.
Mi ng c di khc nhau, nn thi gian
n ch trn tng ng l khc nhau
Hiu ng ny c gi l Delay Spread.
Tr lan truyn l khong thi gian t thi im
thnh phn a tuyn u tin n ch n khi
thnh phn a tuyn cui cng n ch
88
Delay Spread
Tr lan truyn c dng th hin mc
ph bin ca hiu ng a tuyn trong knh
truyn thng

89
Delay Spread

90
Tc ng ca tc di chuyn

91
HIU NG DOPPLER
Hiu ng Doppler
L 1 hiu ng vt l trong tn s v bc
sng ca cc sng m, sng in t b thay i
khi ngun pht sng chuyn ng tng i vi
ngi quan st
Christian Andreas Doppler (1803-1853) l nh
ton hc v vt l hc ngi o

93
Hiu ng Doppler

94
Hiu ng Doppler

95
Hiu ng Doppler
Ngun pht m thanh ng yn. Tc di
chuyn ca sng l c

96
Hiu ng Doppler
Cng ngun m thanh nhng my pht di
chuyn tc 0.7c (Mach 0.7) v 1c (Mach 1)

97
Hiu ng Doppler
Tc di chuyn v=1.4c (Mach 1.4)

98
ISI, CCI V COHERENT BANDWIDTH
Intersymbol Interference (ISI)
Hin tng xung t k hiu/giao thoa tn hiu
c to ra do nhiu ng tn hiu n ch
khng cng lc vi nhau. Tn hiu ca ng
n sau c nhn trong lc nhn symbol k
tip
Tc ng ln mc li burst ca channel
Vi bit-error-rate (BER) thp R 1
2d
R (tc truyn) b gii hn bi delay spread d
100
Intersymbol Interference (ISI)
Transmission
signal 1 1
Time
0

Received signal
(short delay)
Time

Propagation time
Delayed signals
Received signal
(long delay)
Time

101
Xung t knh - Cochannel Interference
Cc t bo (cell) c cng tn s xung t ln
nhau.
rd l tn hiu mun nhn (desired signal)
ru l tn hiu gy xung t (undesired signal)
l h s bo v (protection ratio), trong
rd ru (nh th sng t xung t nht)
Nu P(rd ru ) th rd ru ,
Cochannel probability Pco = P(rd ru )

102
Coherence Bandwidth
Bng thng kt hp Bc:
Th hin s tng quan (correlation) gia 2 tn hiu
fading tn s f1 v f2.
L 1 hm ca delay spread.
S dng trong cc h thng nhn tn hiu diversity
(a dng)
Nhiu phin bn ca thng ip c truyn trn cc tn
s khc nhau.
Chng hn, h thng s dng MIMO

103