MicroWave Transmission Basics
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Transcript of MicroWave Transmission Basics
April 11, 2023, Slide No 1
Transmission System
Introduction. Low capacity transmission. High capacity transmission. Optical Fibre. Network configuration.
April 11, 2023, Slide No 2
The Transport Network is divided into two parts:Access network
Users are grouped together by being connected to the same switching node; the local exchange or access node (AN).
Trunk network Trunk network connects ANs and network nodes (NN) with other ANs and NNs.
Transmission Media’sCopper CableRadio linkOptical fibre
Access and Trunk Network
April 11, 2023, Slide No 3
MS Mobile Station = phone + SIM card
BTS Base Transceiver Station
MSCVLR
PSTNFixed network
BSC
SMSC
EIR
INTERNET
PABXPSTNInternational
BSC
Telenor Nett
IN
PrePaidNode
VMS
HLR
MSC
AUC
April 11, 2023, Slide No 4
Media
Copper cable Low bandwidth (-) Sensitive to crosstalk and noise(-) Attenuation per Km depends on wire diameter (0.4-1.1mm) and frequency.Reliable(+)
*** Attenuation is the loss of signal energy is measured in decibel,db.
Attenuation = 10log(P1/P2) P1=transmitted signal power P2=received signal power.
***Noise is the random variation in current and voltage produced by all electrical circuits.
***Crosstalk is the interference from another conversation/line.
April 11, 2023, Slide No 5
Media
Radio Flexibility +
Quick installation +
Sensitive to ambient disturbance. (Rain and Multipath fading).-
Time and frequency dependent.+
Modulation /Demodulation.+
Low bit error (BER) in bursts.+
QAM (Quadrature Amplitude Modulation) [PSK+AM] .
Radio license fees.-
***Non modulated signal is called Baseband signal
April 11, 2023, Slide No 6
Media
Optical Fibre
High transmission quality. (minimum attenuation). + High transmission capacity. + Resistance to ambient disturbance. + Long Implementation time. -
.
April 11, 2023, Slide No 7
Plesiochronous Digital Hierarchy (PDH)
As the semiconductor development proceeded successfully higher hierarchic levels have been standardized, each level handling timing transparency.
PDH is a standardized bit interleaved multiplexing hierarchy for digital plesiochronous signals, using bit justification to achieve timing transparency.
Actually there are three PDH hierarchies- two are based on 1.5 Mbits and used in North America & Japan. The European hierarchy is 2Mbits .
April 11, 2023, Slide No 8
140Mbps
34Mbps
8Mbps
2Mbps
x4
x4
x4
x31
64 Kbps
2Mbps
8Mbps
64Kbps
8Kbps
x31
x120
x4
400Mbps
100 Mbps
32Mbps
6Mbps
1.5Mbps
nx45Mbps
45mbps
6Mbps
x4
x3
x5
x4 x4
x24
64Kbps
Europe and Most other countries
Japan North America
Synchronous
Plesiochronous
April 11, 2023, Slide No 9
Radio Path Calculation
Radio wave propagationPropagation mechanismEarth Properties
Fading free conditionFree space lossGas absorbtionObstacle loss
Fading ConditionFade MarginFading MechanismLink Budget
RepeatersActive or Passive
April 11, 2023, Slide No 10
• Free space• Absorption• Diffraction• Reflection/scattering• Refraction• Multipath propagation
• Atmosphere• Earth topography• Electrical properties of earth
surface• Earth curvature
Earth properties Propagation mechanisms
Attenuation of the radio wave
April 11, 2023, Slide No 11
Fading free condition
Pr(dbm)=Pt(dbm)+Gt(db)+Gr(db)-20logf(ghz)-20logd(km)-92.4
Free space loss= 20logf(ghz)+20logd(km)+92.4
Fading Free Condition Free space loss Gas absorbtion Obstacle loss
April 11, 2023, Slide No 12
The Fresnel zone
ReflectedhA hB
The radiated power is distributed in a zone surrounding the direct line-of-sight
Direct
Refracted
d
da db
1st fresnel zone : da+db-d=λ/2
April 11, 2023, Slide No 13
Ground clearance and k factor
ReflectedhA hB
Radio optical line of sight
Direct
Refracted
d
da db
Due to refraction in the atmosphere the radio beam is bent normally slightly downwardsThe bending effect is described by the earth factor kK =157/157+dn/dh=4/3 ; where dn/dh=- 40, N= densityH=height
K=α K=4/3
K=1
K=2/3Ground clearance
Geometrical line of sight
April 11, 2023, Slide No 14
Trans-mitter
Receiver
OutputPower(dBm)
Effective radiated power(dBW)
Path loss
Cable loss
Antenna gainAntenna gain
Cable loss
Wave propagation loss•Free-space loss•Gas absorption•Obstacle loss
ReceivedPower(dBm)
Terminology
April 11, 2023, Slide No 15
When the size of an obstacle is large compared with the wavelength,diffraction may occur giving obstacle loss
20 dB16 dB12 dB6 dB0 dB0 dB
Obstacle loss
April 11, 2023, Slide No 16
Fading Mechanisms
Fading Mechanisms
Rain Fading Multipath Fading K- fading
Flat fading Frequency selective fadingReflections
Atmospheric fading ( Absorbtion, refraction)Ground based fading( Tidesand other variations)Man made fading( temporary constructions, boats , aircrafts)
Atmospheric fading ( Absorption, refraction) Ground based fading( Tides and other variations)
Man made fading( temporary constructions, boats , aircrafts)
Variation in signal strength in time, phase or polarization Attenuation that is changing temporarily.
April 11, 2023, Slide No 17
antenna gain
feeder lossreceived power
fade margin
receiver thresholdvalue
wave propagation losses
antennagain
outputpower
feeder loss
POWER
Free space loss +gas absorption +
obstacle loss
Link budget & Fade Margin
Free space loss +gas absorption +
obstacle loss
Fade marginShould be large enough toguarantee that quality and availability objectives are metduring fading conditionsFM=P (n) – P (th)Maximum attenuation before giving out of service
Fade Margin is required for proper performanceIf Rx power is high from the level of the fade margin then
Interference will occur.
April 11, 2023, Slide No 18
• Free space• Absorption• Diffraction• Reflection/scattering• Refraction• Multipath propagation
• Atmosphere• Earth topography• Electrical properties of earth
surface• Earth curvature
Earth properties Propagation mechanisms
Attenuation of the radio wave
April 11, 2023, Slide No 19
Obstacle lossReflection loss
Predictableif present
Link budget
Quality & availability
Fading prediction
Free-space attenuationGas attenuation Rain fading
Multipath fading
Always present andpredictable
Not always presentbut statistically pre-dictable
Maximum values
Free space 130 dB
Gas 5 dB
Obstacle < 20 dB
Reflection 15 dB
Loss and fading
April 11, 2023, Slide No 20
Recommendations from ITU-T
G.821
Error performance of a digital connection below the primary rate (commonly used in PDH Network)
G.826
Error performance of a digital connection at or above the primary rate (Commonly used in SDH network)
Quality and availability Targets
April 11, 2023, Slide No 21
Errored second (ES) A one-second period in which one or more bits are in error.
Severely errored second (SES) A one-second period which has a bit error ratio higher than 10
-3.
Definitions of bit errors
Errored blocks (EB)A block in which one or more bits are in error.
Errored second (ES) A one-second period in which one or more blocks are in error.
Severely errored second (SES) A one-second period which contains >30% errored blocks.
Background block error (BBE)An errored block not occurring as part of an SES
G.821
G.826
April 11, 2023, Slide No 22
Definitions of availability (G.826)
T1306430-95
Time
10 secsec< 10 10 sec
Unavailability detected Availability detected
Unavailable period Available period
Severely Errored Second
Errored Second (non-SES)
Error-free Second
April 11, 2023, Slide No 23
Thank you!