1. COSC 393: Lecture 2
Radio Fundamentals

2. Radio signals Spectrum Transmitter Signal propagation Modulation
Radio Communication
Radio signals
Spectrum
Transmitter
Signal propagation
Modulation

3. Radio Wave
s(t) = At sin(2  ft t + t)

4. Frequency and Wave length
Relationship:
 = c/f
wave length ,
speed of light c  3x108m/s,
frequency f

5. Radio Spectrum

6. VLF = Very Low Frequency LF = Low Frequency MF = Medium Frequency
twisted pair
coax cable
optical transmission
1 Mm
300 Hz
10 km
30 kHz
100 m
3 MHz
1 m
300 MHz
10 mm
30 GHz
100 m
3 THz
1 m
300 THz
VLF LF MF HF
VHF
UHF
SHF
EHF
infrared UV
visible light
VLF = Very Low Frequency
LF = Low Frequency
MF = Medium Frequency
HF = High Frequency
VHF = Very High Frequency
UHF = Ultra High Frequency
SHF = Super High Frequency
EHF = Extra High Frequency
UV = Ultraviolet Light

7. Antennas
Isotropic radiator: Equal radiation in all directions (3D) - theoretical antenna
Real antennas always have directive effects (vertically and/or horizontally)
Different antennas have different radiation pattern.

8. Example: Radiation pattern of a simple Hertzian dipole
Dipoles with lengths /4 or Hertzian dipole with length /2 (length proportional to wavelength)
Example: Radiation pattern of a simple Hertzian dipole
Gain: maximum power in the direction of the main lobe compared to the power of an isotropic radiator (with the same average power)
/2
/4 y y z
simple
dipole x z x
side view (xy-plane)
side view (yz-plane)
top view (xz-plane)

9. Often used for base stations in a cellular system (e. g
Often used for base stations in a cellular system (e.g., covering a valley) y y z
directed
antenna x z x
side view (xy-plane)
side view (yz-plane)
top view (xz-plane) z z
sectorized
antenna x x
top view, 3 sector
top view, 6 sector

10. Effect of a transmission
Transmission range
communication possible
low error rate
Detection range
detection of the signal possible
no communication possible
Interference range
signal may not be detected
signal adds to the background noise
sender
transmission
distance
detection
interference
No effect

11. Signal propagation property
Radio signal behaves like light in free space (straight line)
Receiving power proportional to 1/d² (d = distance between sender and receiver)
So ideally, the transmitter and a receiver must see each other!
Really?

12. Three means of propagation
Ground wave
Tropospheric wave
Ionospheric or sky wave

13. Ground Wave travels in contact with earth’s surface
reflection, refraction and scattering by objects on the ground
transmitter and receiver need NOT see each other
affects all frequencies
at VHF or higher, provides more reliable propagation means
signal dies off rapidly as distance increases

14. Tropospheric Wave bending(refraction) of wave in the lower atmosphere
VHF communication possible over a long distance
bending increases with frequency – so higher frequency more chance of propagation
More of an annoyance for VHF or UHF (cellular)

15. Ionospheric or Sky Wave
Reflected back to earth by ionospheric layer of the earth atmosphere
By repeated reflection, communication can be established over 1000s of miles
Mainly at frequencies below 30MHz
More effective at times of high sunspot activity

16. 4 possible events Radio wave Radio wave Radio wave shadowing
scattering
Radio wave
reflection
diffraction

17. Multipath Characteristics
A signal may arrive at a receiver
- many different times
- many different directions
- due to vector addition
. Reinforce
. Cancel
- signal strength differs from place to place

18. Mobile System Usually Base Station is not mobile
Receiver could be moving (65mph!)
Whenever relative motion exists
- Doppler shift
- Fading
Even the motion of scatterers cause fading

19. Free Space Propagation
Suppose we have unobstructed line-of-sight
Pr(d) = (Pt Gt Gr l^2)/(4p)^2 d^2 L)
-Pt transmitted power
-Gt, Gr Antenna gain
-l wavelength in meters
- d distance in meters
- L (>= 1) system loss factor (not related to propagation.

20. Propagation Losses Two major components - Long term fading m(t)
- Short term fading r(t)
Received signal s(t)
s(t) = m(t) r(t)

21. dB - decibel
Decibel, a logarithmic unit of intensity used to indicated power lost or gained between two signals.  Named after Alexander Graham Bell.
10 log (P1/P2)

22. Radio Signal Fading Short term fading Signal strength (dB)
Long term fading T
Time

23. Short term fading
Also known as fast fading – caused by local multi paths.
Observed over distance = ½ wave length
30mph will experience several fast fades in a sec.
Given by Rayleigh Distribution
This is nothing but the square root of sum of the square of two Gaussian functions.
r = square root ( Ac * Ac + As * As)
Ac and As are two amplitude components of the field intensity of the signal

24. Long term fading
Long term variation in mean signal level is also known as slow fading
Caused by movement over large distances.
The probability density function is given by a log-normal distribution
- normal distribution on a log scale
P(m) = (1/m s(m) 2p) e^[-(log m – E(m))^2/(2 s(m)^2)]

25. Delay Spread Signal follows different paths to reach same destination.
So same signal may arrive many times at different time intervals. t

26. Delay Spread
In digital system, delay spread causes intersymbol interference.
Therefore, there is a limit on the maximum symbol rate of a digital multipath channel.
Obviously, delay spreads are different in different environment.
(roughly between 0.2 to 3 microseconds)

27. Capacity of Channel
What is the maximum transmission rate so that the channel has very high reliability?
- error free capacity of a channel
C.E. Shannon’s work suggest that signaling scheme exists for error-free transmission if the rate of transmission is lower than the channel capacity.

28. Shannon’s work C - channel capacity (bits/s)
B – transmission bandwidth (Hz)
E – energy per bit of received signal (Joule)
R – information rate (bits/s)
S = E R – signal power
N – single-sided noise power spectral density (W/Hz)
(C/B) = log [1+(S/(NB))] = log [1+(E/N)(R/B)]
Suppose R = C we have
(C/B) = log [1+(E/N)(C/B)]

29. Shannon’s work - continued
Solving for (E/N) (aka. signal to noise ratio)
(E/N) = (2^a –1)/a
where a = (C/B).
So given C= 19.2kb/s and bandwidth = 30kHz
What is E/N required for error-free transmission?
R/B = 19.2/30 = 0.64
Substituting we get E/N = = dB
So control transmission power to obtain this E/N.

30. Propagation models in built-up areas
Propagation is strongly influenced by the environment
- building characteristics
- vegetation density
- terrain variation
Perfect conductors reflect the wave where as nonconductors absorb some energy!

31. Empirical models to predict propagation losses
Okumura’s model
- based on free space path loss + correction factors for suburban and rural areas, irregular terrain, street orientations
Sakagmi and Kuboi model
- extend Okumura’s model using regression analysis of data.
Hata’s model
- empirical formula to describe Okumura’s data

32. More models Ibrahim and Parsons model
- equations developed to best fit data observed at London. (freq MHz)
Lee’s model
Use at 900MHZ
3 parameters (median trasmission loss, slope of the path loss curve and adjustment factor)

33. Freq. for mobile communication
VHF-/UHF-ranges for mobile radio
simple, small antenna
SHF and higher for directed radio links, satellite communication
small antenna, focusing
large bandwidth available
Wireless LANs use frequencies in UHF to SHF spectrum
limitations due to absorption by water and oxygen
weather dependent fading, signal loss due to by heavy rainfall etc.
2.2.1

34. Modulation Digital modulation Analog modulation Motivation
digital data is translated into an analog signal
ASK, FSK, PSK (… Shift Keying)
differences in spectral efficiency, power efficiency, robustness
Analog modulation
shifts center frequency of baseband signal up to the radio carrier
Motivation
smaller antennas (e.g., /4)

35. Types of Modulation Amplitude modulation Frequency modulation
Phase modulation
Combination modulation

36. analog
baseband
signal
digital
data
digital
modulation
analog
modulation
radio transmitter
radio
carrier
analog
baseband
signal
digital
data
analog
demodulation
synchronization
decision
radio receiver
radio
carrier

37. Amplitude Modulation

38. Frequency Modulation

39. Phase Modulation

40. Digital modulation Amplitude Shift Keying (ASK):1 1
Amplitude Shift Keying (ASK):
simple
low bandwidth
susceptible to interference
Frequency Shift Keying (FSK):
somewhat larger bandwidth
Phase Shift Keying (PSK):
more complex (both ends)
robust against interference t 1 1 t 1 1 t