SPE-T 2009
Guillaume VILLEMAUD – Advanced Radio Communications
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Some references Advanced Wireless Communications – 4G, Savo G Glisic, Wiley Ed. UWB – Theory and Applications, Ian Oppermann - Matti Hamalainen – Jari Iinatti, Wiley Ed. WiMax Forum: http://www.wimaxforum.org/ 3GPP-LTE: http://www.3gpp.org/article/lte WiMedia Alliance: http://www.wimedia.org/ Agilent Technologies: http://www.home.agilent.com/
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Just a fact...
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A wired and wireless world
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Focus Lots of new emerging technologies to increase data rate and/or mobility key points ?
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Outline This course presents advanced techniques used to enhance wireless communications capabilities through 3 different examples: WiMax, LTE and UWB. Each technology could be further understood by the way of simulation and analysis tools. Introduction and Common Concepts Wireless Broadband Access: WiMAX 3GPP Long-Term Evolution for Mobile Ultra Wide Band technologies Simulation Project: ADS and VSA study
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Roadmap
source Alcatel Guillaume VILLEMAUD – Advanced Radio Communications
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Brief overview Standard
LTE
Family
Primary Use
Radio Tech
Downlin k (Mbit/s)
Uplink (Mbit/s)
Notes
UMTS/4G
General 4G
OFDMA/MIMO/SCOFDMA/MIMO/SCFDMA
326.4
86.4
LTELTE-Advanced update to offer over 1 Gbit/s Gbit/s speeds.
WiMAX
Mobile Internet
MIMOMIMO-SOFDMA
70
70
WiMAXWiMAX-m update to offer over 1 Gbit/s Gbit/s speeds, (comparable to LTE advanced). advanced).
FlashFlash-OFDM
FlashFlashOFDM
Mobile Internet mobility up to 200mph (350km/h)
FlashFlash-OFDM
5.3 10.6 15.9
1.8 3.6 5.4
Mobile range 18miles (30km) extended range 34 miles (55km)
HIPERMAN
HIPERMA N
Mobile Internet
OFDM
56.9
56.9
Wibro
WiBro
Mobile Internet
OFDMA
50
50
Mobile range (900 m)
iBurst
iBurst 802.20
Mobile Internet
HCHCSDMA/TDD/MIMO
64
64
3–12 km
EDGE Evolution
GSM
Mobile Internet
TDMA/FDD
1.9
0.9
3GPP Release 7
UMTSUMTS-TDD
UMTS/3GS M
Mobile Internet
CDMA/TDD
16
16
Reported speeds according to IP Wireless using 16QAM modulation similar to HSDPA+HSUPA
1xRTT
CDMA2000
Mobile phone
CDMA
0.144
0.144
Succeeded by EVEV-DO
EVEV-DO 1x Rev. Rev. 0 EVEV-DO 1x Rev.A EVEV-DO Rev.B
CDMA2000
Mobile Internet
CDMA/FDD
2.45 3.1 4.9xN
0.15 1.8 1.8xN
Rev B note: N is the number of 1.25 MHz chunks of spectrum used. used. Not yet deployed. deployed.
802.16e
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Different kinds of links
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Wireless everywhere We can observe a growing number of antennas on rooftops in all cities. Not only different use or standard, but also different operators.
Eiffel tower
© ANRF : http://www.cartoradio.fr Guillaume VILLEMAUD – Advanced Radio Communications
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Network structures The more visible wireless network is probably broadcast systems (ex: TV, AM or FM radio…). Features : 1 simplex link (downlink) 1 omnidirectional emitter Directional or omnidirectional receivers
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Radio relay High capacity radio point to point link, used to realize wireless bridges. Features : 1 simplex or duplex link 2 Tx/Rx with high gain antennas Possible repeaters
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Point to Multi-point Fixed architecture with Gateways (base stations, access points…). Features : 1 duplex link 1 omnidirectional or sectorial Tx/Rx 1 highly Directional Tx/Rx for user Application: WLL
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Mobile radio Transmission between one fixed access point and mobile users. Features: 1 duplex link 2 omnidirectional Tx/Rx Application: police, firemen,emergency…
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Cellular Networks Cellular: extension of geographical region of coverage and increase of the number of possible users. Features: duplex links Omnidirectional or sectorial Tx/Rx for BS (cells) Omnidirectional Tx/Rx for MU
BSC
MSC HLR VLR AUC EIR
BSC
OMC
GMSC
ISC Guillaume VILLEMAUD – Advanced Radio Communications
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Ad hoc and sensor networks Large scale networks with light (or null) infrastructure. Features: duplex links M2M omnidirectional Tx/Rx Low energy resources and cost Application: monitoring, detection, domotics…
Sink Station Sink Station Sensed Area
Sensor Event Monitored Area
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TT
rr aa
nn
ss
mm
ii ss
ss
ii oo
nn
ss
cc
hh
ee
mm
ee
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RF Vision
RF chains dimensioning depends on the dynamic of signals to deal with and tolerated distortions.
G u illau m e V IL L E M A U D – A d van ced R ad io C o m m u n icatio n s
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Radio Channel Vision
Pu M n ct ob ua ili l p ty ro mo ce de ss l
Sp pr atia oc l es ran s, or do m de r2 Te pr mp oc or es al s, ra or nd de om r2
Tends to express an analytical expression of radio channel variations.
Emitted Power Pi
A(xi,xj)
S(xi,xj)
Fij(t)
X
X
X
Random process with 2N+1 dimensions
/
RSB
γ ij (t )
Noise Power Nj Guillaume VILLEMAUD – Advanced Radio Communications
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Global Vision Emitter MAC
BB
RF
Receiver RF
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BB
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MAC
Modulation
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Transmitting information
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Phase shift keying 1 symbol = 1 bit BPSK
Increasing modulation order increases the encoded number of bits per emitted symbol.
1 symbol = 2 bits Q
I QPSK
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IQ modulation Information is mapped in a complex plane, modulated on an in-phase and in-quadrature branches.
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Quadrature Amplitude Modulation 1 symbol = 4 bits
64 QAM 16 QAM 1 symbol = 6 bits
256 QAM 1 symbol = 8 bits Guillaume VILLEMAUD – Advanced Radio Communications
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Symbol Error Rate Comparison
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Some snapshots sequence: 0100010110
BPSK
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BPSK constellation
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QPSK in time sequence: 10 00 11 01
QPSK
01
11
00
10
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QPSK constellation
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QAM in time 16QAM
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QAM constellation
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BPSK
W=B
S/N = 10.5
f
W = B/2 QPSK
S/N = 13.5
QPSK
f
Wide Bandwidth
BPSK
Low S/N
Channel capacity
W = B/4 16 QAM
S/N = 20.5
16 QAM
f
W = B/6 S/N = 26.5
64 QAM
f
256 QAM
W = B/8 S/N = 32.6
256 QAM
f
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Narrow Bandwidth
64 QAM
High S/N
For a fixed W, the capacity depends on the available SNR (basis of adaptive modulation schemes).
Spectrally viewing...
No filter Rectangular
Cosine
So don’t forget the filters !!! Guillaume VILLEMAUD – Advanced Radio Communications
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Wireless Channel
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A look on topology
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Propagation channel To estimate radio link quality, we need to know the effective received power.
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Link budget Free space Friis’ formula
λ Pr = 4π r
2
⋅Ge ⋅G
r
⋅ Pe
Pr : received power at Rx Pe : emitted power at Tx Ge : Tx antenna gain Gr : Rx antenna gain r : Tx/Rx distance Guillaume VILLEMAUD – Advanced Radio Communications
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Antenna gain
Multiplying factor allowing to render the power density created in a particular direction. This factor does not depend on feeding power but includes losses of the antenna (matching and materials).
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More details Fading
Slow variation due to obstacle
Fast variation due to multi-path
(dB)
(dB)
Attenuation proportional to the distance
Shadowing
(dB)
Path loss
Distance Tx-Rx
Distance Tx-Rx
Distance Tx-Rx
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Reality In a real environment, the 3 phenomenon are added (in dB, multiplied in linear scale !)
Path loss + Shadowing + Fading Guillaume VILLEMAUD – Advanced Radio Communications
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Back to the SER
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More complete Friis’ formula
Long term
Short term
Pe: constant Ge and Gr function of direction (spatial filters) k and n depending on environment
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General modeling
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Signal attenuation Ground effect Need a lot of informations on the real environment to evaluate line-of-sight conditions.
250 200 150 100 50 0 0
1
2
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250 200 150 100 50 0 4 km
3
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Two-ray model
E LOS (d ' , t ) =
E0 ⋅ d 0 ⋅ exp( j (ω c t − βd ' ) ) d'
E0 ⋅ d 0 EGND (d " , t ) = R ⋅ ⋅ exp( j (ω c t − βd " ) ) d"
ETOT (d , t ) =
E0 ⋅ d 0 ⋅ exp( j (ωct − βd ' ) ) ⋅ [1 + R ⋅ exp( − jβ∆ )] d
d PL ≈ 22 + 20 log( ) − 20 log 1 + R ⋅ exp(− jβ∆ )
λ
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Geometrical model d’ ht ht-hr
ELOS d’’
ht ht+hr
∆=
EGND
hr
(ht + hr )2 + d 2 − (ht − hr )2 + d 2
2ht ⋅ hr ≈ d
for d>> ht,hr
PL becomes : d ϕ PL ≈ 22 + 20 log − 20 log sin λ 2
with : ϕ =
2π∆
λ
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At long distance PL becomes :
d ϕ PL ≈ 22 + 20 log − 20 log sin λ 2
if d >
with : ϕ =
20 ⋅ hr ⋅ ht (sin ϕ ϕ) λ⋅
we obtain :
PL = 40 log d − 20 log hT − 20 log hR
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2π∆
λ
Example : GSM, λ=30cm, hE=15m; hR=1,5m -30
losses : -PL(d)
Dry ground : εr=5
-40
Two-ray model
-50 -60 -70 -80
free-space model -90 -100 -110 -120 1 10
2
10
3
10
4
5
10
10
k (distance d = k.λ)
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Example : GSM, λ=30cm, hE=15m; hR=1,5m -30
losses : -PL(d)
Dry ground : -40 εr=5
Simplified model R=-1
-50 -60 -70 -80 -90 -100 -110 -120 1 10
2
10
3
10
4
5
10
10
k (distance d = k.λ)
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Example : GSM, λ=30cm, hE=15m; hR=1,5m -30
losses : -PL(d)
Dry ground : -40 εr=5
Real Model
-50 -60 -70 -80 -90 -100 -110 -120 1 10
2
10
3
10
4
5
10
10
k (distance d = k.λ)
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Example : GSM, λ=30cm, hE=15m; hR=1,5m losses : -PL(d)
40dB/dec
20dB/dec
d = 4π
Two-slope model
hr ⋅ ht
λ
h ⋅h PL = 20 log16π 2 r 2 t λ Guillaume VILLEMAUD – Advanced Radio Communications
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NLOS case
No direct visibility… A pure geometrical approach would predict no signal
10,3 dB 250 200 150 100 50 0 0
250 200 150 100 50 0 1
2
3
4
5
6
7
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Geometrical model
? h hR
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hE
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Geometrical model
? hR
∆h d2
d1
hE
∆h 2 (d1 + d 2 ) ∆= ⋅ 2 d1 ⋅ d 2
2(d1 + d 2 ) ν = ∆h ⋅ λ ⋅ d1 ⋅ d 2
πν 2 Φ= 2
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Fresnel Zone nλd1d 2 rn = d1 + d 2
ν = 2⋅n φ = π ⋅n
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Fresnel Zone
All points corresponding to the same phase
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Interception rn=3 rn=1
rn=-1
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Statistical Formulations In multi-path environment , statiscal laws are based on distributions
NLOS Rayleigh’s law
avec
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Rice’s law Line-of-sight conditions plus multi-path.
K factor can variate from 0 (Rayleigh) to infinity (AWGN)
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Loi de Nakagami Line-of-sight conditions plus multi-path.
Facteur m factor can variate from 1/2 (mono-lateral gaussian fading) and infinity (perfect) m=1 correspond à Rayleigh
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Time domain aspect Shadowing and fading parameters are time-variant. Emitted signals are then dimensioned depending of time-domain behavior of the wireless channel. L
h(t ,τ ) = ∑ hn (t )δ (τ − τ n (t )) n =1
hn (t ) = α n (t )e
jθ n ( t )
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Coherence bandwidth
Numerous parameters are linked to the channel behavior: frame duration, equalizers length, training sequences...
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Multi-path Multi-path produce important recieved power variations but also multiple delayed copies of te signal.
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Impulse response Usual parameters
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Example
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Some values
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The point is…
We can evaluate Pr versus Pe, but what about the radio link quality ?
We need to know the noise level
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Noise sources • galactic (15MHz, 100GHz) • thermal (Johnson): white noise (up to infrared...) • artificial: evolving, non predictible (dB)
Urban zone Residential zone Rural zone Desert rural zone Galactic noise
120 100
Noise level relative to minimal thermal noise
80 60 40
Receiver noise
20 0
10-1
100
101 102 Frequency (MHz)
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103
Random aspect of noise
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Thermal noise :
PN = k ⋅ T ⋅ B
avec k=1.379.10-23 W.Hz-1.K-1
example : GSM : B=270kHz, T=290°K
• Noise factor • Noise figure
N eq N out / G F= = k .T .B k .T .B
FdB = 10. log10 (F )
• Noise temperature N eq = k .T .B + k .Teq .B Guillaume VILLEMAUD – Advanced Radio Communications
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Interference -120dBm -90dBm
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Orthogonality trends
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Spreading techniques A way of strengthening a signal against channel effects and interference is to spread it spectrally. Two kinds of spreading: FHSS (ex: Bluetooth) and DSSS (ex:802.11b). The consequence is that the total bandwidth is increased but the power is spreaded. By using the DSSS principle with a set of orthogonal codes allows to re-use the same band for multiple users: CDMA (basis of 3G technologies).
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Direct sequence spreading
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DSSS spectrum
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WiFi 802.11b
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CDMA
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3G technology
W-CDMA -50
dBm(Spectre_Reception2) dBm(Spectre_Reception1) dBm(Spectre_Reception)
Spreading factor used -100
-150
-200
-250 2.105 2.110 2.115 2.120 2.125 2.130 2.135 2.140 2.145 2.150 2.155 2.160 2.165 2.170 2.175
freq, GHz
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OFDM Orthogonal Frequency Division Multiplexing is in use in every emerging technologies (802.11a/g/n, WiMAX, LTE, DVB…)
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Cyclic prefix A cyclic prefix is introduce at the beginning of each OFDM symbol to prevent from ISI
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A simple example: If one sends a million symbols per second using conventional single-carrier modulation over a wireless channel, then the duration of each symbol would be one microsecond or less. This imposes severe constraints on synchronization and necessitates the removal of multipath interference. If the same million symbols per second are spread among one thousand sub-channels, the duration of each symbol can be longer by a factor of a thousand, i.e. one millisecond, for orthogonality with approximately the same bandwidth. Assume that a guard interval of 1/8 of the symbol length is inserted between each symbol. Intersymbol interference can be avoided if the multipath time-spreading (the time between the reception of the first and the last echo) is shorter than the guard interval, i.e. 125 microseconds. This corresponds to a maximum difference of 37.5 kilometers between the lengths of the paths.
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Multiplexing structure
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Example of values
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802.11g
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Interest in multi-path
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Drawback: high PAPR An OFDM signal exhibits a high peak-to-average power ratio (PAPR) because the independent phases of the sub-carriers mean that they will often combine constructively.
High resolution DAC/ADC needed. Also needs of fine synchronization and linearity Guillaume VILLEMAUD – Advanced Radio Communications
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Access sharing
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Multiple Access Beyond the unitary link capacity, wireless systems need to share the resource between multiple users. Different approaches: TDMA, FDMA, CDMA, SDMA, OFDMA, CSMA-CA.
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Possible combinations
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More recent techniques
SDMA
OFDMA
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CSMA-CA To avoid centralized and highly synchronized architectures, each emitter senses the medium before sending data.
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RF part
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Receiver threshold
Tr(d,f)
– Modulation, coding, BER acceptable SNR : (notations : SNR, SINR, C/I, Eb/No). Decibels :
bruit
Eb C I = 10 ⋅ log10 N0
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Sensitivity Key parameter for system dimensioning, it allows to know the amount of received power needed to ensure a desired level at the mixer input.
Mean SNR at the antenna
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Back to white noise…
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Example of GSM Source Nokia
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Dimensioning
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Noise figure
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Some words on baseband
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Main steps of receiving AGC
CIR calculation
Sampling Power detection
Equalization Frame synchro
Channel selection Demod Coarse synchro De-interleaving Down-sampling Frequency correction
Channel decoding Source decoding
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A/D Conversion Limitations
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SNR for ADC Plus distortions SNDR
N represents considered number of bits for ADC, fs the sampling frequency and fmax the maximum frequency contained in the signal to digitize. Effective number of bits:
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Gain control
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44 Mo/s data rate (I & Q signals) Standard characterization (802.11b or 802.11g)
802.11b sampling
802.11g sampling
44 Mo/s
40 Mo/s
Time synchronization (barker reference)
Time synchronization (Short preamble reference)
Under sampling
Under sampling
44 11 Mo/s
44 20 Mo/s
- Frequency Offset correction
- Frequency Offset correction
- CIR computation
- Long preamble synchronization
- RAKE equalization - SFD synchronization
- Guard Interval removing - FFT 44 PCMo/s
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