Multiple Access Techniques

Question 1

Define FDMA

Answer 1

All users have access to some of the bandwidth on a full time basis.

Question 2

Name and explain the two types of FDMA

Answer 2

Pre-assigned FDMA: Useful for continuous use, users are assigned a channel and do not compete for access.

Demand-assigned FDMA: Users are allocated a channel when needed, deallocating when the transmission is over.

Question 3

State the advantages and disadvantages of FDMA

Answer 3

Advantages: Easy to implement, inexpensive and widely available.

Disadvantages: Lack of flexibility to add new users, inter modulation interference between channels.

Question 4

Explain TDMA

Answer 4

All users have access to all of the bandwidth for a defined portion of time.

Question 5

What Does TDMA rely on?

Answer 5

The signal being digitised and divded into packets of data.

Question 6

State the advantages and disadvantages of TDMA

Answer 6

Advantages: High data rates, ability to exploit digital technologies, can employ EDAC.

Disadvantages: More expensive than FDMA, complex and precise synchronisation required.

Question 7

Explain CDMA

Answer 7

All users have access to all of the bandwidth on a full time basis.

Question 8

State the advantages and disadvantages of CDMA

Answer 8

Advantages: Users added easily, resistance to interference, low probability of intercept.

Disadvantages: More expensive than FDMA/TDMA, complex to design.