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tutorial5 - slotted ALOHA In this problem we complete the...

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EE3015 Tutorial 5 (Medium Access Control) 1. Suppose that the pure ALOHA protocol is used to share a 56 kbps satellite channel, and that frames are 2000 bits long. Find the maximum throughput of the system in frames/second. (Note: the throughput of pure ALOHA is 18.4%.) 2. Consider a broadcast channel with N nodes and a transmission rate of R bps. Suppose the broadcast channel uses polling (with an additional polling node) for multiple access control. There is a polling delay of d so that when a node completes its transmission, it takes d time units until the subsequent node is allowed to transmit. Within a polling round, a given node is allowed to transmit at most Q bits. What is the maximum throughput of the broadcast channel in bps? 3. In the lecture notes, we provided an outline of the derivation of the efficiency of
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Unformatted text preview: slotted ALOHA. In this problem, we complete the derivation. a) Recall that when there are N active nodes the efficiency of slotted ALOHA is Np (1 − p ) N − 1 . Find the value of p that maximizes this expression. b) Using the value of p found in (a), find the efficiency of slotted ALOHA by letting N approach infinity. Hint: (1 − 1/ N ) N approaches 1/ e as N approaches infinity. c) Compare your result in part (b) with the efficiency of pure ALOHA. Which protocol has a higher efficiency? Why? 4. Consider a slotted ALOHA system with two terminals, A and B. Terminal A transmits at the beginning of a time slot with probability 0.6, whereas terminal B transmits with probability 0.3. a) What is the throughput of terminal A? b) What is the throughput of terminal B?...
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