1. COVERAGE PLANNING Company Confidential 4/13/2018
Coverage in GSM network stands for the geographical area covered by the network from which mobile is accessible to the network.
In GSM Coverage area is planned in division of cells.Each cell covers a particular geographical area,the size of which depends on the terrain and other system configurations.Genrally the more the number of cells,the better the coverage ,but by just creating cells may not give good quality of coverrage.
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Author: Arif R.

2. Mobile Communications Propagation
Mobile Communications propagation is impacted by :
Path Loss
Reflection
Diffraction
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3. Path Loss Lfsl = 32.4 + 20 log d(in Kms)+ 20logf(in Mhz)
The basic path loss is the transmission loss in free space.
Lfsl = log d(in Kms)+ 20logf(in Mhz) d
At 900 Mhz, at a distance of 1km , Loss = 91.5 db
Actual prediction of loss cannot be done on this, since in a mobile environment the mobile will receive signals from several reflections.
The above formula is only valid under direct LOS and no reflection conditions.
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4. Reflection
Reflection occurs when a propagating electromagnetic wave impinges upon a surface which has very large dimensions as compared to the wavelength of the propagating wave.
Reflections occur from surface of earth, buildings,walls and water.
The wave is partially absorbed and partially reflected.
Amount of absorption will depend on the reflection coefficient of the reflecting surface.
Reflection coefficient is function of the material properties and depends on wave polarization , angle of incidence and the frequency.
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5. L2ray = 40 log d - ( 20 log ht + 20 log hr )
Reflection
Path loss for 2 -ray Model ( over flat conductive surface) ht hr d
L2ray = 40 log d - ( 20 log ht log hr )
Analytical formula, only valid for larger distances ( > 10 Km)
Loss increases at larger distance at a rate of 40db /dec.
At 900 Mhz, 10,000m distance , ht = 100m, hr = 1.5m
Lfs = db
L2ray = db
This indicates that in 2 ray path , additional loss of 5 db.
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6. Reflection
Reflection in actual mobile environment , would be from multiple paths.
So, reflection in mobile communications is Multipath reflection.
RSL will be resultant of levels coming from all paths.
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7. Diffraction ht hr Huygen's principle on phenomenon of diffraction
Diffraction allows radio signals to propagate around the curved surface of earth and behind obstruction. ht hr
Shadow region
RSL drops as the receiver moves deep into the shadow region
Huygen's principle on phenomenon of diffraction
All points on a wave-front can be considered as point sources for the production of secondary wavelets, and that these wavelets combine to produce a new wave-front in the direction of propagation.
Diffraction is caused by the propagation of secondary wavelets into the shadowed region
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8. Diffraction Diffraction is of two types in general
Smooth Sphere Diffraction
Knife Edge Diffraction
Smooth Sphere Diffraction
Diffraction takes place through almost a flat surface.
Knife Edge Diffraction
Hills, Mountains, Buildings will cause knife edge diffraction
In a Mobile environment most of the diffraction is knife edge.
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9. Calculation of Diffraction Loss
Fresnel zone geometry
Area around the LOS within which a diffraction can result into antiphase(180 deg) condition is the first fresnel zone. ht hr
If an object is within the fresnel zone or completely blocks the zone, then also energy will arrive at the receiver but will diffraction loss.
In Mobile environment, we are not worried about clearance, but only with the loss.
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10. Calculation of Diffraction Loss
Fresnel diffraction parameter (v)
Indicates the position of the object with reference to the fresnel zones ( 0 means , object tip on LOS, 1 means tip on 1st fresnel zone on upper side). h d1 d2
v = h
2 ( d1 + d2 )
d1.d2
( all values in "m" )
From "v" , we can compute the diffraction loss.
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11. Calculation of Diffraction Loss
Relation of "v" with diffraction loss
Loss(dB) = v < -1
Loss (dB) = 20 log ( v) < v < 0
Loss (dB) = 20 log ( 0.5 exp ( -0.95v) < v < 1
Loss (dB) = 20log ( ( v) ) 1 < v < 2.4
Loss (dB) = 20 log ( ) v > 2.4 v 2
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12. Calculation of Diffraction Loss
Relation of "v" with diffraction loss ( graphical ) 5 -5
-10
Knife edge diffraction gain (GadB)
-15
-20
-25
-30 -3 -2 -1 1 2 3 4 5
Fresnel diffraction parameter v
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13. Scattering
Radio wave when impinges on a rough surface , reflected energy is spread out in all directions due to scattering.
This is the reason actual RSL in a mobile environment is often stronger then what is predicted by reflection and diffraction.
Objects such as Lamp posts and trees tend to scatter energy in all directions, thereby providing additional radio energy at the receiver.
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14. Exercise !!!
Calculate the path loss at a distance of 4 km from the BTS. The height of Tx Antenna is 130m and Mobile Antenna is at 1.5m. There is a Hill at a distance of 2.4 km from the Tx, with a height of 35m above the LOS ?
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15. Path Loss Prediction
Formula's described earlier are based on simple models of the radio path.
Formula's don't take care of the type of the terrain of the radio path.
Realistic method of prediction would be to use empirical data of radio wave propagation over various types of terrain and land usage.
Empirical data of this type were collected by Okumura from his comprehensive radio wave propagation measurements
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16. Okumura Model
Okumura developed a set of curves giving the attenuation in excess to FSL in an urban area with base station effective height of 200m and and mobile antenna height of 3m.
These curves give the loss as a function of frequency and distance from base station.
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17. Okumura Model ( ) ( ) ( ) hte hre hre
Path loss for different heights can be calculated by these curves by using the formula.
Path Loss = Lfsl + A(f,d) - G(hte) - G(hre)
G(hte) and G(hre) are the effective Base Station and MS antenna heights
hte
200
( )
G(hte) = 20 log m > hte > 10m
hre 3
( )
G(hre) = 10 log hre < 3m
hre 3
( )
G(hre) = 20 log hre < 3m
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18. Okumura Model What is Effective Antenna Height ? hmsl hte 3 km 15 km
hte = Antenna height above msl(hmsl) - average ground level (havg)
( average ground level is calculated within km )
hmsl
hte
Average ground level (havg)
3 km
15 km
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19. Okumura Model
Okumura curves are only applicable for urban areas.
For other terrain's, Okumura has provided correction factors.
The correction factors are provided for 3 types of terrain in the form of curves related to frequency.
Open Area : corresponds to a rural , desert kind of terrain
Quasi Open Area : corresponds to rural , countryside kind of terrain
Suburban
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20. Okumura Model Path loss for other terrain's
Path Loss(o,q,s) = Lfsl + A(f,d) - G(hte) - G(hre) - G(area)
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21. Okumura Model Exercise
Calculate the path loss using the Okumura model, for urban , for suburban, open area , quasi-open and suburban type of terrain by using the below parameters :
Frequency = 900 MHz
Distance = 2.5 km
Base Station effective ht = 120m
Mobile ht = 1.5m
Compare this with the LOS path loss and 2 -ray Path loss models.
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22. Okumura Model Conclusion
Simplest, best and accurate prediction model but only for specific terrain's.
Slow response to rapid changes in terrain.
Model is fairly good for urban and suburban areas, but not as good in rural areas.
Standard deviations between predicted and measured loss values 10 dB to 14 dB.
Model is more graphical than mathematical, for computation we need formula's not graphs.
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23. Hata Model
Hata model is an empirical formulation of the graphical path loss data provided by Okumura.
Hata presented the urban area propagation loss as a standard formula and supplied correction equations for applications for other situations.
Formula's are designed for computer usage, but they are only rough approximations of Okumura's curves.
Since Terrain types profiles are practically infinite, modeling of the tool used for prediction because essential but taking several measurements and several times.
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24. Hata Model Urban terrain
L(urban) = log fc log hte - a(hre) + ( log hte ) log d
fc = frequency in MHz ( MHz)
hte = BTS antenna height ranging 30m to 200m
hre = effective receiver antenna height ranging 1m to 10m
d = Transmitter receiver separation distance ( km )
a(hre ) = correction factor for effective mobile antenna height which
is a function of size of the coverage area in db
Small to medium city
a(hre) = (1.1 log fc ) hre - ( 1.56 log fc ) db
For large city
a(hre) = 3.2 ( log hre ) 2
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25. Hata Model Correction for Suburban & Rural terrain's Loss for SUBURBAN
L(sub) = L (urban) - 2 [ log (fc/28) ] - 5.4 2
Loss for Rural Open Area
L(ro) = L (urban) ( log fc) log fc 2
Loss for Rural Quasi-Open Area
L(rqo) = L (urban) ( log fc) log fc 2
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26. Company Confidential
4/13/2018
COST Hata Model
COST -231working committee developed an extended version of HATA model for frequencies up to 2 GHz.
L(urb) = log fc log hte - a(hre) + ( log hte ) log d +Cm
fc = frequency in MHz ( MHz)
hte = BTS antenna height ranging 30m to 200m
hre = effective receiver antenna height ranging 1m to 10m
d = Transmitter receiver separation distance ( km )
a(hre ) = correction factor for effective mobile antenna height which
is a function of size of the coverage area in db
Cm = Correction factor for city size
COST : European Co-operative for Scientific and Technical research.
a(hre) = (1.1 log fc ) hre - ( 1.56 log fc ) db
Cm = 0 db for medium city and suburban centers with moderate tree density.
Cm = 3 db for metropolitan centers.
For rural areas , the earlier formula's will apply
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Author: Arif R.

27. Exercise !!!
Calculate the path loss using the HATA model, for urban-medium city, suburban , open area , quasi-open and suburban type of terrain by using the below parameters :
Frequency = 900 MHz
Distance = 2.5 km
Base Station effective ht = 120m
Mobile ht = 1.5m
Compare this with the LOS path loss and 2 -ray Path loss models.
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28. Path Loss Predictions for GSM
Selection of models for predicting path loss for GSM will depend on the cell ranges.
GSM has 3 cell ranges and different prediction model for each
Large Cells
Small Cells
Microcells
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29. Large Cells
Antenna is installed above the maximum height of the surrounding roof tops.
Propagation is mainly by diffraction and scattering at roof tops in the vicinity of the mobile i.e. the main rays propagate above the roof tops.
Cell radius is mainly 1 km and normally exceeds 3 km.
Hata's model and the COST 231-Hata model can be used to calculate path loss in such cells.
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30. Small Cells
Antenna is sited above the median but below the maximum height of the surrounding roof tops.
Propagation mechanism is same as large cell
Maximum range is typically less than kms.
Hata model cannot be used since it is applicable above 1 km.
COST 231-Walfish-Ikegami model is used for radius less than 5kms in urban environment.
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31. COST 231 - Walfish-Ikegami Model
Without free LOS between BS and MS
Frequency (f) = MHz
Transmitter height (hte) = m
Mobile height (hre) = m
Distance (d) = km
Height of buildings "Hroof" (m)
Width of road "w" (m)
Building separation "b" (m)
Road orientation with respect to the direct radio path Phi (o)
Free Space Loss (Lfsl)
Path Loss = Lfsl + Lrst + Lmsd
Lrts : roof-top-to-street diffraction and scatter loss
Lmsd : multiscreen diffraction loss
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32. COST 231 - Walfish-Ikegami Model
roof-top-to-street diffraction and scatter loss
Lrts = log(w) + 10 log(f) + 20 log(Hroof - Hre) + Lcri
Lcri = (Phi) for 0<= Phi < 35
Lcri = (Phi - 35) for 35<= Phi < 55
Lcri = (Phi - 55 ) for 55<= Phi < 90 o
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33. COST 231 - Walfish-Ikegami Model
multiscreen diffraction loss
Lmsd = Lbsh + ka + kd log(d) + kf log(f) - 9log(b)
with Lbsh = -18 log(1 + Hte - Hroof) for Hte > Hroof
= for Hte <= Hroof
ka = for Hte > Hroof
= (Hte - Hroof ) for d>=0.5 & Hte <=Hroof
= (Hte - Hroof ) (d/0.5) for d<0.5 & Hte <=Hroof
kd = for Hte > Hroof
= (Hte - Hroof)/Hroof for Hte <= Hroof
Kf = (f/ ) for medium sized and suburbs
= (f/ ) for metropolitan centers
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34. COST 231 - Walfish-Ikegami Model
With a free LOS between bs and ms ( Street Canyon )
Path Loss = log(d) + 20 log(f) for d > = km
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35. Indoor Loss
Additional loss which occurs at 900 MHz when moving into a house on the bottom floor on 1.5m height from the street.
Indoor loss near windows ( < 1m ) is typically 12 db.
Building loss as measured by Finish PTT varies between 37 db and -8db with an average of 18db taken over all floors and buildings.
In our predictions and calculations, as per GSM recommendations we will consider 15db as an average indoor loss.
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36. Microcells
Cell in which the base station antenna is mounted generally below roof top level.
Propagation is determined by diffraction and scattering around buildings ie. the main rays propagate in street canyons.
Microcells have a radius in the region of m .
Microcells can be supported by smaller and cheaper BTS's.
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37. Microcells Model With a free LOS between bs and ms ( Street Canyon )
Path Loss (GSM 900 ) = log(d) for d > = km
Path Loss (DCS 1800 ) = log(d) for d > = km
Propagation loss in microcells increases sharply as the receiver moves out of LOS , (ex : around a street corner ).
20db of loss could be added per street corner, up to two or three corners.
Beyod, this the COST231 - Walfish Ikegami model should be used
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38. Fading Fading in mobile environment is of 2 types: Small Scale Fading
A mobile radio signal envelope has continuos variations.
These variations continuously fluctuate the signal level and is referred to as the fading phenomenon.
Fading in mobile environment is of 2 types:
Small Scale Fading
Log-normal Fading
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39. Small Scale Fading SS Time
Rapid level fluctuation over a short period or travel distance (approx: half wavelength), so that large-scale path loss may be ignored.
MS antenna is lower in height as compared to surrounding objects, so several mulipath signals arrive with various phases and amplitudes and at certain times almost cancel out each other.
Short - term fading at certain times can be heard as annoying bursts. SS
Average
Time
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40. Small Scale Fading ro ro Rayleigh distribution
Observing the Short-term fading with reference to average level ro
(small-scale fading) ro
(db) = Average - instantaneous fluctuations
ro ranges in 40 db ( 10 db above and 30 db below the average )
ro follows a Rayleigh-distribution , since generally signals arrive from reflections only, hence small-scale fading is often called Rayleigh-Fading.
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41. Small Scale Fading Rayleigh distribution Pr avg level
As per Rayleigh distribution increase in fade depth is inversely proportional to the probability (ex: 10 db fade may occur for 40 % of the time, where the probability of 40db fade would be 10 % ) Pr
avg level
Fade Margin
min recv level of rcvr
deepest fades ( typically 30 db )
Area of poor quality
Probability that fade depths will enter area of poor quality is required to be less than 10 %.
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42. Small Scale Fading
If probability of small-scale fades is more below the minimum required signal level, then this could result in distorted speech.
To ensure this probability is less than 10 % , Transmit Power should be adjusted accordingly to achieve a high fade margin.
Space Diversity is quite effective for this kind of fades.
Rayleigh distribution only occurs when there are all reflected waves and no direct LOS signal. If there is a direct LOS signal present with reflections, then it is Ricean distribution of fading which is less severe , since the direct component is relatively much stronger than reflected waves and will restrict deep fades.
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43. Log-normal Fading SS Time Log-normal Fading
Small -scale signal variation when averaged out is called the local mean and is expressed in log scale of power , and is called Log-normal fading.
Log-normal variation is due to the terrain contour between the bs and ms.
If the terrain is an open area, then the change in signal will be with distance only, but normally there are obstructions ( buildings, trees etc. ) which cause a rapid variation of signal from its local mean over an area of 5 to 50m
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44. Log-normal Fading
Log -normal fading depths when exceeds the min receive level will result into shadow areas ( since this effect is over an area of m ) . This is also referred to as Coverage Holes.
Remedy for this is to keep an additional fade margin on top of min-rcv -level benchmark when predicting coverage.
This margin is called is log-normal shadow margin.
Log-normal shadow margin is in the range of 3-5db, with standard deviation of the local mean in the range of 4-8 db.
For, urban areas GSM recommends a margin of 5 db ( considering 7db as the deviation), this is to achieve 90% location probability on cell edges.
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45. Time Dispersion (Multipath)
Time Dispersion is the arrival of signals from multiple paths, but spread in time.
Equalizer in GSM can handle multipaths within a delay spread within 4 bit periods (15us) ( path difference of 4.5 kms ).
Any multipath component arriving after 15us will act as interference.
GSM needs a C/I ratio of 9 db, and the same applies to carrier to multipath (>15us) also. This ratio is known to Primary/Multipath (P/M )
Planning and BTS site selection should consider the location probability of Primary/Multipath ratio below 9 db.
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46. Time Dispersion (Multipath)SS
Impulse Response
should be > 9db
usecs
Delay spread : the spread in time of the pulse width because of multipath
It is very difficult isolate delay spread from multipath.
Only HP has the tool to do it, major NEMs are using this.
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47. Time Dispersion - Concern Situations
Eqlzr window (4bit)
>= 9db
Multipath - Primary > 4.5 km
(Since MS is near to BS , P/M is high)
Eqlzr window (4bit)
Multipath - Primary < 4.5 km
( P/M is low, but since MS is far from BS
and near to reflection , it is in window)
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48. Time Dispersion - Concern Situations
< = 9db
Eqlzr window (4bit)
Multipath - Primary > 4.5 km
(Since MS is away from BS and reflecting surface, the path difference is high and also the P/M is < 9db, so this is really an area of concern )
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49. Time Dispersion - Conclusions
Reflections outside the equalizer window are harmful
Reflections resulting into P/M < 9 dB are harmful ( if it meets the above condition )
Generally harmful conditions are those when a line of sight exists between BTS to reflector and also MS to reflector.
Reflectors near to the BTS may not be harmful since the reflection will come within the equalizer window.
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50. Reducing Time Dispersion Issues
Optimization and Countermeasures for Time Dispersion is something very interesting and can result into several issues like distorted voice, echo and even dropped calls !!
Certain countermeasures when adopted in the planning stage can reduce or eliminate these issues.
If problems occur later on, then optimization needs to be done.
Troubleshooting multipath problems is a big issue in live networks.
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51. Reducing Time Dispersion Issues
Site Location
Identify potential reflectors in the predicted cell area.
Locate sites for BTS near reflectors, this will bring the reflections within the window.
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52. Reducing Time Dispersion Issues
Directional Antenna's(Sectorization)
Using Sectored cells config, with the directional antenna pointing away from the reflector.
Antenna's front-back ratio is a very critical parameter.
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53. Reducing Time Dispersion Issues
Over Water Bodies
Time dispersion over water can make the quality worst
Covering the area from the other side of the water body will avoid large path differences between reflected signals.
Side lobes can still result into problems, where handovers should take care off, by properly setting neighbors& parameters
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54. Reducing Time Dispersion Issues
Tilting Antenna's
Tilting Antenna will reduce energy radiated towards the reflector.
Antenna's can be tilted horizontally or vertically.
Horizontal tilt will reduce the coverage to a large extent, hence vertical tilt is the most preferred one.
Reducing Output Power ???
Reduction in output power will reduce the energy from both direct as well reflected signal. Hence, P/M will not change.
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55. Doppler Shift fd = v fd = Shift in frequency in Hz
The shift in frequency relative to the speed of the mobile phone is Doppler Shift.
fd = v
fd = Shift in frequency in Hz
v = speed of the mobile in m/s
= wavelength in m
Actual received carrier frequency = fc + fd, when mobile is moving towards the transmitter.
Actual received carrier frequency = fc - fd, when mobile is moving away from the transmitter.
There is no shift , when the vehicle is moving perpendicular to the angle of arrival of the transmitted signal.
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56. Exercise !!!
Calculate the Doppler Shift under all the three conditions , when the vehicle is moving towards, away and perpendicular to the transmitter, which is transmitting at 960 MHz , and the speed of the vehicle is 110 kmph ?
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