Virtual Labs

Flat Fading

1. What is the primary disadvantage of a baseline SISO (Single-Input Single-Output) system in a flat fading channel?

a: It has a very high Level Crossing Rate (LCR). Explanation

Explanation

b: It has a very long Average Fade Duration (ADF). Explanation

Explanation

c: It is highly susceptible to deep fades, leading to high outage probability. Explanation

Explanation

d: It cannot be used for high data rates. Explanation

Explanation

2. What do both Selection Combining (SC) and Maximal-Ratio Combining (MRC) require at the receiver to provide diversity gain?

a: A single, very high-gain antenna. Explanation

Explanation

b: Multiple receive antennas or signal paths. Explanation

Explanation

c: A very fast signal processor. Explanation

Explanation

d: A perfect knowledge of the data being sent. Explanation

Explanation

3. What is the primary implementation advantage of Selection Combining (SC) when compared to Maximal-Ratio Combining (MRC)?

a: SC provides a higher signal-to-noise ratio. Explanation

Explanation

b: SC is much simpler, as it only needs to select one signal, not combine them. Explanation

Explanation

c: SC works better when the user is moving fast. Explanation

Explanation

d: SC completely eliminates all fading. Explanation

Explanation

4. How does Maximal-Ratio Combining (MRC) achieve the best possible performance?

a: It selects the two strongest signals and averages them. Explanation

Explanation

b: It inverts the phase of weak signals to cancel them. Explanation

Explanation

c: It aligns the phases of all signals and sums them, weighted by their strength. Explanation

Explanation

d: It switches between antennas at a very high speed. Explanation

Explanation

5. If a mobile user increases their speed (e.g., from walking to driving), what is the most likely effect on the Level Crossing Rate (LCR)?

a: The LCR will increase. Explanation

Explanation

b: The LCR will decrease. Explanation

Explanation

c: The LCR will not change. Explanation

Explanation

d: The LCR will become zero. Explanation

Explanation

6. If a mobile user increases their speed, what is the corresponding effect on the Average Fade Duration (ADF)?

a: The ADF will increase. Explanation

Explanation

b: The ADF will decrease. Explanation

Explanation

c: The ADF will not change. Explanation

Explanation

d: The ADF will become infinitely long. Explanation

Explanation

7. If the system's acceptable signal quality threshold is *raised* (i.e., a better signal is required), what happens to the outage probability?

a: The outage probability decreases. Explanation

Explanation

b: The outage probability stays the same. Explanation

Explanation

c: The outage probability increases. Explanation

Explanation

d: The outage probability depends only on the LCR. Explanation

Explanation

8. How does receiver diversity (like SC or MRC) fundamentally reduce outage probability?

a: It increases the total transmitted power from the base station. Explanation

Explanation

b: It makes the signal travel a shorter distance. Explanation

Explanation

c: It relies on the low probability that all receive paths are in a deep fade at the same time. Explanation

Explanation

d: It changes the flat fading into frequency-selective fading. Explanation

Explanation

9. When comparing SC and MRC with the same number of receiver antennas, which statement is true regarding performance?

a: SC always has a lower outage probability than MRC. Explanation

Explanation

b: MRC always has a lower outage probability than SC. Explanation

Explanation

c: SC and MRC always have the identical outage probability. Explanation

Explanation

d: SC is better for LCR, while MRC is better for ADF. Explanation

Explanation

10. Compared to a single-antenna (SISO) system, what is the general effect of using either SC or MRC on the Average Fade Duration (ADF)?

a: ADF increases. Explanation

Explanation

b: ADF decreases. Explanation

Explanation

c: ADF is not affected by diversity. Explanation

Explanation

d: ADF becomes equal to the LCR. Explanation

Explanation