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CSC358 Tutorial 9 Notes

Below are some notes and sample solutions to the tutorial questions. These
notes are only meant to provide the necessary amount of information for you to
verify your own work and to help you recall the discussions in the tutorial.
Simply reading these solutions does NOT convey the same learning experience as
attending a tutorial (not even close). The tutorial materials are a mandatory
and important component of this course, so don't miss any of them!
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Question 1

Key points:

FDMA only reserves a fraction of the channel.

Slotted ALOHA needs a synchronized clock.

ALOHA allocates a fair share of the bandwidth to each node.

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Question 2

The efficiency is Np(1-p)^{2N-2}, take the derivative, set to 0 and find p*,
plug p* in and let N go to infinity.

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Quesiton 3

(a) A's average throughput is given by pA(1-pB) R. 

(b) B's average throughput is given by pB(1-pA) R. 

(c) Total efficiency is pA(1-pB) + pB(1-pA).

(d) In order to make pA(1-pB)= 2 pB(1-pA), we need that pA = 2pB / (1+pB)

(e) A's throughput is 2p(1-p)^(N-1) R, and any other node has throughput
p(1-p)^(N-2)(1-2p) R.

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Quesiton 4

Basically plotting Np(1-p)^(N-1) and Np(1-p)^(2N-2) 

When explaining the difference, compare the value of optimal p, the peak
throughput.