ISRO CS 2023 Q.15: solution and answer

Official answer: ASource: ISRO's revised and final answer key of 16 February 2024

1. Recall the nominal peak data rates of the 802.11 amendments. These are standard reference values.

2. 802.11b works in the $2.4\text{GHz}$ band with DSSS/CCK and has a maximum rate of $11\text{Mbps}$, so (iv) matches (Q).

3. 802.11a ($5\text{GHz}$) and 802.11g ($2.4\text{GHz}$) both use OFDM with a maximum rate of $54\text{Mbps}$, so (ii) matches (R).

4. 802.11ad (WiGig) works in the $60\text{GHz}$ band and reaches about $7\text{Gbps}$, so (iii) matches (P).

5. The only rate left is (S), $3.5\text{Gbps}$. This is the figure usually quoted for 802.11ac ($5\text{GHz}$, wide channels, MU-MIMO), so (i) matches (S). It is also the only pairing that leaves each rate used once.

6. The matching (i)-(S), (ii)-(R), (iii)-(P), (iv)-(Q) is option (a).

7. Check the other options. Option (b) pairs 802.11b with $7\text{Gbps}$ and 802.11ad with $11\text{Mbps}$. Options (c) and (d) pair 802.11ac with $54\text{Mbps}$, which is the rate of the older 802.11a/g, so they fail.