1. Signal Propagation
Propagation: How the Signal are spreading from the receiver to sender.
Transmitted to the Receiver in the spherical shape.
sender
When the signal transmit from sender to receiver , the character of signal may not be changed in the wired network.
But wired signal there is a change in character, like packet loss, external factors .etc,.

2. Signal Propagation Ranges
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

3. Path Loss of Radio Signals
When Propagation in free space always like light (straight line).
The signal passes sender to receiver in a straight line is called Line-of-sight (LOS)
If there is a vacuum between sender receiver , it’s a free space loss.
Received power by the receiver is P. Distance between sender and receiver is d.
The received power by the receiver
Pr is proportional to 1/d2.
Pr α 1/d2.
The sender emits signals with certain energy.
If there is a vacuum space, the sends at the speed of light with spherical shape.
If there is no obstacle continuously grows the surface of sphere (s) and it moves to the particular distance d. According to the equation
s=4πd2

4. Path Loss of Radio Signals
The additional parameters are important .
The receiver power depends on the wavelength and gain of receiver and transmitter.
The external factors are affects the signals . The path loss not occures in short distance.
The atmosphere influences in long distance travel signal.
Heavy Rain - Mobile Phone
Depending upon the frequency , it penetrate objects
A short wave length with lower frequencies
penetrate easily
A long wave length with higher frequencies can be blocked by external factors

5. Fundamental Propagation Behaviors
Ground Wave
< 2 MHz . LF and MF
Low frequency follow the earth surface
Used in Submarine Communication and AM Radio
Sky Wave
2 to 20 MHz
Waves bounce from the ionosphere to
earth. The short waves are reflected
Used in International broadcasts

6. Signal propagation Depending on the density of a medium Shadowing
Making the signal weak
Reflection at large obstacles
Refraction
Depending on the density of a medium
Changing in Direction
Scattering at small obstacles
The signal meets one point and scatter as many
Diffraction at edges

7. Multipath propagation
Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction. i.e radio signals reaching the receiving antenna by two or more paths
The signals travelling along different path, different length and different time. This effects is delay spread

8. A Real Example of Multiplexing
How ???

9. Multiplexing
Transmission of multiple data communication sessions over a common wire or medium
Minimum of interference and a maximum of medium utilization.

10. Space Division Multiplexing
The channels k1 to k3 can be mapped onto the three ‘spaces’ s1 to s3
Separate the channels and prevent the interference ranges from overlapping
channels ki k1 k2 k3 k4 k5 k6 c
k4 to k6 is allocated for some others. t c s1
Analog Telephone t s2 f f c t s3 f

11. Frequency Division Multiplexing
The total bandwidth available in a communication medium is divided into a
series of non-overlapping frequency sub-bands
Each of which is used to carry a separate signal

12. Frequency Division Multiplex
Separation of the whole spectrum into smaller frequency bands
Advantages:
no dynamic coordination necessary
works also for analog signals
Disadvantages:
waste of bandwidth if the traffic is distributed unevenly
inflexible
guard spaces
E.g FM Radio k1 k2 k3 k4 k5 k6 c f t

13. Time Division Multiplexing
The time domain is divided into several recurrent time slots of fixed
length
A sample byte sub-channel 1 is transmitted during time slot 1, sub-
channel 2 during time slot 2, etc

14. Time Division Multiplex
A channel gets the whole spectrum for a certain amount of time
Advantages:
only one carrier in the medium at any time
throughput high even for many users
Mobile Phone for a Time k1 k2 k3 k4 k5 k6 c f t

15. Time and frequency multiplex
Combination of both methods
A channel gets a certain frequency band for a certain amount of time
Example: GSM
Advantages:
better protection against tapping
protection against frequency selective interference
higher data rates compared to code multiplex
but: precise coordination required k1 k2 k3 k4 k5 k6 c f t

16. Code Division Multiplexing (CDM)
Also known as code division multiple access (CDMA)
An advanced technique that allows multiple devices to transmit on the same frequencies at the same time using different codes
Used for mobile communications.
Each mobile device is assigned a unique 64-bit code (chip spreading code)
To send a binary 1, mobile device transmits the unique code
To send a binary 0, mobile device transmits the inverse of code

17. Code Division Multiplex
Each channel has a unique code
All channels use the same spectrum at the same time
Advantages:
bandwidth efficient
no coordination and synchronization necessary
good protection against interference and tapping
Disadvantages:
lower user data rates
more complex signal regeneration
Implemented using spread spectrum technology k1 k2 k3 k4 k5 k6 c f t