Fundamental Communication Engineering

1. Ron Milione Ph.D.Ron Milione Ph.D.
W2TAPW2TAP

2. Information Modulator Amplifier
Ant
Feedline
Transmitter
Information Demodulator Pre-Amplifier
Ant
Feedline
Receiver
Filter
Filter
RF Propagation
This presentation concentrates
on the propagation portion

3.  As the wave propagates, the
surface area increases
 The power flux density
decreases proportional to
1/d2
• At great enough distances
from the source, a portion of
the surface appears as a
plane
• The wave may be modeled
as a plane wave
• The classic picture of an EM
wave is a single ray out of
the spherical wave

4.  Most real antennas do not
radiate spherically
 The wavefront will be
only a portion of a sphere
• The surface area of the wave
is reduced
• Power density is increased!
• The increase in power
density is expressed as
Antenna Gain
• dB increase in power along
“best” axis
• dBi = gain over isotropic
antenna
• dBd = gain over dipole
antenna
Gain in
this area

5.  Radiated power often referenced to power radiated
by an ideal antenna
ttGPEIRP =
Pt
= power of transmitter
Gt
= gain of transmitting antenna system
• The isotropic radiator radiates power uniformly in all
directions
• Effective Isotropic Radiated Power calculated by:
Gt = 0dB = 1 for isotropic antenna
This formula assumes power and gain is expressed linearly. Alternatively,
you can express power and gain in decibels and add them: EIRP = P(dB) + G(dB)
The exact same formulas and
principles apply on the
receiving side too!

6. λ
2
2D
d f =
• Large-scale (Far Field) propagation model
• Gives power where random environmental effects
have been averaged together
• Waves appear to be plane waves
• Far field applies at distances greater than the
Fraunhofer distance:
D = largest physical dimension of antenna
λ = wavelength
• Small-scale (Near Field) model applies for shorter
distances
• Power changes rapidly from one area/time to the next

7. 2
2
2
2
)4()4(
)(
c
fdd
P
P
linlossFree
r
t π
λ
π
===
For Free Space (no buildings, trees, etc.)
dBdf
c
fd
dBlossFree 56.147log20log20
4
log10)( 1010
2
10 −+=





=
π
f = frequency
d = distance (m)
λ= wavelength (m)
c = speed of light
hb
= base station antenna height (m)
hm
= mobile antenna height (m)
a(hm
) is an adjustment factor for the type of environment and the
height of the mobile.
a(hm
) = 0 for urban environments with a mobile height of 1.5m.
Note: Hata valid only with d in range 1000-20000, hb in range 30-200m
)3)(loglog55.60.44(
)(log82.13)6(log16.2655.69)(
1010
1010
−−+
−−−+=
dh
hahfdBlossHata
b
mb
For Urban environments, use the Hata model

8. A transmission system transmits a signal at 960MHz with a power of 100mW using
a 16cm dipole antenna system with a gain of 2.15dB over an isotropic antenna.
At what distance can far-field metrics be used?
λ = 3.0*108
m/s / 960MHz = 0.3125 meters
Fraunhofer distance = 2 D2
/ λ = 2(0.16m)2
/0.3125 = 0.16m
What is the EIRP?
Method 1: Convert power to dBm and add gain
Power(dBm) = 10 log10 (100mW / 1mW) = 20dBm
EIRP = 20dBm + 2.15dB = 22.15dBm
Method 2: Convert gain to linear scale and multiply
Gain(linear) = 102.15dB/10
= 1.64
EIRP = 100mW x 1.64 = 164mW
Checking work: 10 log10 (164mW/1mW) = 22.15dBm

9. A transmission system transmits a signal at 960MHz with a power of 100mW
using a 16cm dipole antenna system with a gain of 2.15dB over an isotropic
antenna.
What is the power received at a distance of 2km (assuming free-space
transmission and an isotropic antenna at the receiver)?
Loss(dB) = 20 log10(960MHz) + 20 log10(2000m) – 147.56dB
= 179.6dB + 66.0dB – 147.56dB = 98.0dB
Received power(dBm) = EIRP(dB) – loss
= 22.15dBm – 98.0dB = -75.85dBm
Received power(W) = EIRP(W)/loss(linear)
= 164mW / 1098.0dB/10
= 2.6 x 10-8
mW = 2.6 x 10-11
W
Checking work: 10 -75.85dBm/10
= 2.6x 10-8
mW
What is the power received at a distance of 2km (use Hata model with base
height 30 m, mobile height 1.5 m, urban env.)?
Loss(dB) = 69.55+26.16(log(f)-6) – 13.82(log(hb)) – a(hm)+ 44.9-6.55(log(hb))(log(d)-3)
=69.55 + 78.01 – 27.79 – 0 + (35.22)(0.30)
= 130.34 dB  Received power = 22.15dBm – 130.34dB = -108.19dBm

10.  A Link Budget analysis determines if there is
enough power at the receiver to recover the
information
Information Modulator Amplifier
Ant
Feedline
Transmitter
Information Demodulator Pre-Amplifier
Ant
Feedline
Receiver
Filter
Filter
RF Propagation
Gain
Gain
Loss

11.  Begin with the power output of the transmit amplifier
 Subtract (in dB) losses due to passive components in the transmit
chain after the amplifier
 Filter loss
 Feedline loss
 Jumpers loss
 Etc.
 Add antenna gain
 dBi
 Result is EIRP
Information Modulator Amplifier
Ant
Feedline
Transmitter
Filter
RF Propagation

12. dBi12Antenna gain
dB(1.5)150 ft. at 1dB/100 footFeedline loss
dB(1)Jumper loss
dB(0.3)Filter loss
dBm4425 WattsPower Amplifier
ScaleValueComponent
dBm53Total
All values are example values

13.  The Receiver has several gains/losses
 Specific losses due to known environment around the receiver
 Vehicle/building penetration loss
 Receiver antenna gain
 Feedline loss
 Filter loss
 These gains/losses are added to the received signal strength
 The result must be greater than the receiver’s sensitivity
InformationDemodulatorPre-Amplifier
Ant
Feedline
Receiver
Filter

14.  Sensitivity describes the weakest signal power level
that the receiver is able to detect and decode
 Sensitivity is dependent on the lowest signal-to-noise ratio
at which the signal can be recovered
 Different modulation and coding schemes have different
minimum SNRs
 Range: <0 dB to 60 dB
 Sensitivity is determined by adding the required
SNR to the noise present at the receiver
 Noise Sources
 Thermal noise
 Noise introduced by the receiver’s pre-amplifier

15.  Thermal noise
 N = kTB (Watts)
 k=1.3803 x 10-23
J/K
 T = temperature in Kelvin
 B=receiver bandwidth
 Thermal noise is usually very small for reasonable
bandwidths
 Noise introduced by the receiver pre-amplifier
 Noise Factor = SNRin/SNRout (positive because
amplifiers always generate noise)
 May be expressed linearly or in dB

16.  The smaller the sensitivity, the better the receiver
 Sensitivity (W) =
kTB * NF(linear) * minimum SNR required (linear)
 Sensitivity (dBm) =
10log10(kTB*1000) + NF(dB) + minimum SNR
required (dB)

17.  Example parameters
 Signal with 200KHz bandwidth at 290K
 NF for amplifier is 1.2dB or 1.318 (linear)
 Modulation scheme requires SNR of 15dB or 31.62 (linear)
 Sensitivity = Thermal Noise + NF + Required SNR
 Thermal Noise = kTB =
(1.3803 x 10-23
J/K) (290K)(200KHz)
= 8.006 x 10-16
W = -151dBW or -121dBm
 Sensitivity (W) = (8.006 x 10-16
W )(1.318)(31.62) = 3.33 x 10-14
W
 Sensitivity (dBm) = -121dBm + 1.2dB + 15dB = -104.8dBm
 Sensitivity decreases when:
 Bandwidth increases
 Temperature increases
 Amplifier introduces more noise

18.  Transmit/propagate chain produces a received
signal has some RSS (Received Signal Strength)
 EIRP minus path loss
 For example 50dBm EIRP – 130 dBm = -80dBm
 Receiver chain adds/subtracts to this
 For example, +5dBi antenna gain, 3dB feedline/filter
loss  -78dBm signal into receiver’s amplifier
 This must be greater than the sensitivity of the
receiver
 If the receiver has sensitivity of -78dBm or lower, the
signal is successfully received.

19. Information Modulator Amplifier
Ant
Feedline
Transmitter
Information Demodulator Pre-Amplifier
Ant
Feedline
Receiver
Filter
Filter
RF Propagation
EIRP
Prop Loss
RSS
Sensitivity

20.  A Link Budget determines what maximum path loss a system can
tolerate
 Includes all factors for EIRP, path loss, fade margin, and
receiver sensitivity
 For two-way radio systems, there are two link budgets
 Base to mobile (Forward)
 Mobile to base (Reverse)
 The system link budget is limited by the smaller of these two
(usually reverse)
 Otherwise, mobiles on the margin would have only one-way
capability
 The power of the more powerful direction (usually forward) is
reduced so there is no surplus
 Saves power and reduces interference with neighbors

21.  Forward (Base to Mobile)
 Amplifier power 45dBm
 Filter loss (2dB)
 Feedline loss (3dB)
 TX Antenna gain 10dBi
 Path loss X
 Fade Margin (5dB)
 Vehicle Penetration
(12dB)
 RX Antenna gain 3dBi
 Feedline loss (3dB)
 Signal into mobile’s LNA has
strength 33dBm – path loss
 If Mobile Sensitivity is -100dBm
 Maximum Path loss = 133dB
• Reverse (Mobile to Base)
• Amplifier power 28dBm
• Filter loss (1dB)
• Feedline loss (3dB)
• TX Antenna gain 3dBi
• Fade Margin (5dB)
• Vehicle Penetration (12dB)
• Path Loss X
• RX Antenna gain 10dBi
• Feedline loss (3dB)
• Signal into base’s LNA has
strength 17dBm – path loss
• If Base Sensitivity is -105dBm
• Maximum Path loss = 122dB
Unbalanced – Forward path can tolerate 11dB more loss (distance) than reverse