TRB 2006 -Question 8

The order in which the following satellite communication is accessed is

a) FDMA   TDMA   CDMA

b) CDMA   FDMA   TDMA

c) FDMA   CDMA   TDMA

d) Cellular   Telephony  AMPS   FDMA

Correct Answer: Option A

We can answer this question using, uplink power requirements

FDMA:

Using,

$$\frac{C}{N_0}=\frac{E_b}{N_0}+R$$

We can say Power level of carrier (C) depends on modulation rate.

In FDMA, we can say modulation rate (R) will be less, as total frequency spectrum is divided among earth stations and hence the EIRP (Equivalent isotropic radiated power) is less for uplink.

TDMA:

We can say TDMA uses modulation rate higher than FDMA and hence higher EIRP is required for the earth stations to uplink. 

Hence FDMA is most preferable than TDMA.

Likewise CDMA also has high modulation rate because of generation of pseudo noise like sequence.

FDMA > TDMA > CDMA