Multiple Access

Question 1

Name the three main modes of multiple access

Answer 1

CDMA - Code division
FDMA - Frequency division
TDMA - Time division

Question 2

How does TDMA work?

Answer 2

K users each get allocated a slot of duration Tu = Tf/K in each frame of length Tf - each uses the whole bandwidth for their time, then stops broadcasting

Question 3

What is FDMA and how does it work?

Answer 3

FDMA is frequency division - each user is allocated a specific frequency within the bandwidth. There should be no overlap between uses (typically beyond the first lobe overlap is deemed acceptable). Frequency band required should be found from Fourier (or the question).

Question 4

What is CDMA and how does it work?

Answer 4

For Code division, each user is given a unique signature that is orthogonal to other signatures over the symbol period, such that the received signal can be multiplied with the correct signature to extract the signal.