Suppose that you wish to offer a voice over IP wireless service. The target pack

Question

Suppose that you wish to offer a voice over IP wireless service. The target packet
error rate (or drop rate) is 10^-3 and you determine that if the signal is confined to
within a coherence band, about 20% of the packets are dropped due to fading. To
solve this problem, you introduce frequency diversity by spreading the signal over
multiple coherence bands.
Now suppose that an error correction code is introduced into the original
(narrowband) system that reduces the packet drop rate to 5%. How does this change
the bandwidth your system requires?

Explanation / Answer

a. If each coherence band is 100 kHz and experiences independent fading, about how much bandwidth does your system require? (Hint: calculate the probability that at least one of the coherence bands will not be faded according to the slides on selection diversity.) b. Now suppose that an error correction code is introduced into the original (narrowband) system that reduces the packet drop rate to 5%. How does this change the bandwidth your system requires?

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