1 emlab wireless propagations. 2 emlab channel rf dsp 데이터 송신 rf dsp 수신 데이터 1....
Post on 14-Dec-2015
217 Views
Preview:
TRANSCRIPT
1
EMLAB
Wireless propagations
2
EMLAB
channelRFDSP데이터
송신
RF DSP
수신
데이터
1. Wireless channel model
• 무선 통신 기기 사이의 전파 송수신 예측 어려움 .
• 단말기 설계를 위해 channel 특성 파악 필요 .
3
EMLAB
근사 모델 #1: Free space model
2
4
RGGPP RTTR
R
Rc
j
RT eR
GGH
4)(
(Friis formula)
• 거리 감쇄 효과만 고려 .
• 초기 설계에 유용 .
4
EMLAB
Antenna modeling
)/(4
cRtR
R
)ˆˆ(),(4 hT,vT, TT
jkR
TTTT
in hhR
eG
P
E
안테나에서 나온 신호는 거리 R 떨어진 지점에서 진폭이 1/R로 줄어들고 시간 지연이 R/c 만큼 생긴다 .
)(t
5
EMLAB
Field test route (outdoor)
Guidelines for drive testing to accurately estimate average cell radius or for tun-ing a path loss model.
6
EMLAB
Field test route (indoor)
Typical in-building measurement route and signal strength.
7
EMLAB
Measured path loss
8
EMLAB
Physical model
Impu
lse
resp
onse
Time
dthstxt
R )()()(
)(th
Measurement Simplified model
9
EMLAB
Propagation channel model
tfjtfjii
iiR
cic eettstx 2)(2)]([)(Re
Impu
lse
resp
onse
Time
Spec
tru
m
Frequency
Amplitude variation
time spread
Mathematical model
αi(t), τi(t) 가 channel 특성 결정 .
10
EMLAB
Hierarchical fading process : statistical model
11
EMLAB
Propagation loss mechanisms : scaled model
1. Large Scale Fading:due to distance
2. Medium Scale Fading: shadowing and obstacles
3. Small Scale Fad-ing: due to multipath
12
EMLAB
The three scales of mobile signal variation
13
EMLAB
(1) Large scale fading
)/()(][)( 00 dddPLdBdPL
( 거리와 path loss 를 fitting 하여 β 값을 찾음 .)
14
EMLAB
근사 모델 #2 : Two-ray Ground Reflection
21
21
4)(
R
eR
R
eGGH
Rc
j
S
Rc
j
RT
15
EMLAB
• Measure PL(d0) or calculate Free Space Path Loss.
• Take measurements and derive empirically.
근사 모델 #3 : Log-Distance Model
Environment Exponent (β)
Free space 2
Urban area 2.7~3.5
Shadowed urban area 3~5
Indoor LOS 1.6~1.8
Indoor non-LOS 4~6
)/()(][)( 00 dddPLdBdPL
16
EMLAB
Classification of large scale propagation models1. Macro cell model
① Empirical model
a. Log-distance path loss
b. Okumura-Hata
② Physical model
a. COST231/Walfisch-Ikegami Model
③ ITU-R model
2. Micro cell model
④ Empirical model
a. Dual slope model
⑤ Physical model
a. Two-ray model
b. Street canyon model
c. Random waveguide model
d. Ray tracing model
⑥ ITU-R model
3. Pico cell model
⑦ Empirical model
⑧ Physical model
17
EMLAB
Okumura-Hata model (COST207)
1. 150MHz~1.5GHz 에서 유용 .
2. 측정을 통해 얻은 데이터임 .
3. Open area, Suburban area, Urban area 로 분류함 .
ERBALdB log
CRBALdB log
DRBALdB log
1.1)56.0log56.1()7.0log1.1(
3001.1))54.1(log(29.8
30097.4))75.11(log(2.3
94.40log33.18)(log78.4
4.5))28/(log(*2
log55.69.44
log82.13log16.2655.69
2
2
2
2
CmC
Cm
Cm
CC
C
b
bC
fhfE
MHzfh
MHzfhE
ffD
fC
hB
hfA
For large cities
For medium to small cities
frequencycarrier :[MHz]f
mobile andstation base
between distance circlegreat :R[km]
1.5m) (oftemheight
antennastation mobile:][
C
mhm
Urban areas :
Suburban areas :
Open areas :
18
EMLAB
COST231-Hata model
GERBFLdB log
areasan metropolit3
areassuburban and cities sized medium0
log82.13log9.333.46
G
hfF bC
1. 1.5GHz~2GHz 로 Hata 모델 확장
2. 측정을 통해 얻은 데이터임 .
3. Open area, Suburban area, Urban area 로 분류함 .
19
EMLAB
Walfisch-Ikegami Propagation Model
sdmsdFdB LLLL Lf : free space loss
Lmsd:multiple knife edge diffraction
Lsd : single diffraction
20
EMLAB
(2) Medium scale model : shadowing
SdB LLL 50
21
EMLAB
Typical variation of shadowing with mobile position at fixed BS distance
Probability density function of shad-owing. Measured values are pro-duced by subtracting the empirical model.
Log-normal distribution : shadowing
2
2
2exp
2
1)(
S
S
L
S
LLp
22
EMLAB
LzxSz SS
zQdx
xdLLpzL
L /
2
2exp
2
1)(Pr
Shadowing effect on coverage
23
EMLAB
(3) Small scale fading
tfjc
cetuttftats 2)(Re)(2cos)()(
)()()()( )( tjytxetatu tj
Probability density function of real part of NLOS fading signal→ Gaussian
Multi-path fading : NLOS
24
EMLAB
Equal delay ellipse : multi-path fading
25
EMLAB
Complex samples of NLOS fading signal Theoretical and experimental Rayleigh distributions
Rayleigh fading
26
EMLAB
Rician fading
2
2 2/
s
P
Pk
NLOS
LOS
kr
Ieer
rp kr 2)( 0
)2/(2
22
Rice factor :
27
EMLAB
c
,1
12
)cos1()( υk
][ || tυrrr
c
kυ
kkk ||
][|| HυEEE
][|| EυHHH
HE,
HE ,k
υ
동일한 전자기 현상이지만 관찰자의 상대적 운동에 의해 E, H, k, 주파수 등이 변한다
2c
ttrυ
Frequency shift by Doppler effect
28
EMLAB
1f
2f
Beat frequency due to Doppler effect
)cos1( ff
υ
다중 경로 신호의 주파수가 달라져 beat frequency 관찰됨 .
29
EMLAB
The received signal of a time varying channel where the transmitted signal is a time-harmonic signal with frequency f =10Hz.
Time varying channel – Doppler shift
Dc f
T16
9
30
EMLAB
Time varying channel : auto-correlation
Power spectral density
)2()()( 0* Dlll fJPtataE
otherwise0
if)/(1
2
)2()( 20
D
DDD
ffffffJFfS
( fD : maximum Doppler frequency.)
( )S F
Dff
Jakes model
For time delay profile
Dc f
T16
9Coherence time :
31
EMLAB
Wideband fast fading
c
rr 21
]1[
)()(])([
1
])([2
])([1
11
2211
jtj
tjtj
eea
eaeaH
)]cos(1[2)( 1 aH
32
EMLAB
Multi-path Fading
Impu
lse
resp
onse
Time
• Flat fading :
• low data rate.
• Ex) AMPS, ASK, ...
Time
Impu
lse
resp
onse
Sd T
• Frequency selective fading :
• high data rate 인 경우에 생김 .
• Ex) WCDMA, DMB 등 ...
Sd TInter-symbol interference
ST
STSymbol Time
d
d
33
EMLAB
Multi-path Fading
Multi-path Fading 의 영향
•협대역 신호인 경우 영향이 작다 .
광대역 신호인 경우 신호 spec-trum 에 미치는 영향이 크다 .
34
EMLAB
l
tffjll
llcetxtaty ))((2)()(Re)(
…shift in time …
…shift in frequency …
… attenuation…
(this causes small scale time variations)
paths
Wide-band fast fading channel model
35
EMLAB
Channel sounding
n
iii
T
PP
10
n
iii
Trms P
P20
21
rmscB 2
3
Coherent B. W. :
36
EMLAB
Overcoming narrow band fading
Diversity
37
EMLAB
Overcoming wide band fading
Linear equalizer
38
EMLAB
Adaptive equalizer
39
EMLAB
OFDM receivers
OFDM Subcarriers in the Frequency Domain
40
EMLAB
. . .
0w 1w 2Nw 1Nw
12
각도 추정
.
.
.0w 1w 2Nw 1Nw
RF, modem
다중 빔 안테나
각도 추정 알고리즘 다중 빔 생성
Adaptive antenna
top related