EOQ - Chp. 3 Multiuser Systems

Question 1

What is the difference between a broadcast and a multiple access channel?

Answer 1

m = 2 (could be more);

Broadcast channel -> one transmitter, m receivers
Multiple-access channel -> m transmitters, one receiver

Question 2

What are the three types of channels and what do they model.

Answer 2

1. Multiple Access Model; Models UL in mobile networks
2. Broadcast model; models DL in mobile networks
3. Interference model; models inteference case, edge of cell

Question 3

Why is SIC not done in MAC 5G?

Answer 3

Very difficult to implement.

Question 4

In a multi-antenna system, explain what is used in DL and UL.

Answer 4

1. DL -> MISO; signal combines coherently at the receiver.
2. UL -> SIMO

Question 5

Explain the diversity strategies in SIMO

Answer 5

1. Selection Combining; Select the strongest signal
2. Equal Gain Combining; Gives equal weight to signals SNR
3. Maximum Ratio Combinig; Gives strongest weight to strongest signal

Question 6

What is MIMO?

Answer 6

Send and multiple antennas to increase spatial diversity.

Question 7

What’s the difference between mutli-user and multiple access?

Question 8

Name the different multiple-access techniques and match them to their network (1G, 2G, 3G etc etc)

Question 9

What’s the difference between duplexing and multiplexing?

Question 10

Explain what ALOHA is. Is it an efficient protocal?

Question 11

What is multi-user gain

Question 12

What is the main idea in scheduling

Question 13

How does scheduling manifests itself in 5G+