Mobile Networks

Question 1

Give the formula for the EM wave encoding

Answer 1

f(t) = A * sin(2piF + P)

with A = Amplitude
F = Frequency
P = Phase

Question 2

How does CSMA work?

Answer 2

Listen to channel and sense if someone is transmitting

• > transmit if free
• > else backoff and wait

Question 3

How does CSMA/CD work?

Answer 3

Like CSMA but the sender listens to a channel to detect collisions which might not occur during the propagation delay.

Question 4

How does CSMA/CA work?

Answer 4

Hidden and exposed station prevents CD approach.

Therefore: handshake process: Request To Send -> Clear To Send
Backoff if other senders hear RTS or CTS

Question 5

Describe the main difference between 3G, 4G and 5G networks

Answer 5

3G: switching at BSController between Internet and voice subsystems

4G: Nodes forward to Evolved packet core which handles both, internet and voice.

5G: Virtual core, NFV, abstraction & integration of multiple protcols, network slicing