Question

In your own words, describe the two wireless problems, hidden station and exposed station. Provide an example (preferably from real life) that can describe them. Also, what are the solutions (if any) that solved those two problems

Answer 1

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1)Hidden station problem

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a)definition and example

-when two sending nodes which are not in range of each other , send data simultaneously to a receiving node which is in range of both senders, which results in collision

-e.g take two 3 nodes ,l ,m,n

- sending node 1 ---->l

-sending node 2-------> m

-receiving node 1------>n

- l and m are both hidden from each other

- n is in range of both l and m

- l and m both send data at same time to n which results in collision

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b)solution

-expand the range of each node so that other sending nodes are also in range .,so that nodes can detect on going transmission and wait

-use omni-directional antennas instead of directional antenna

-get rid of barriers that block the range of a node

-change the position of nodes so that they come in each others range

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2)Exposed station problem

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a)definition and example

- in it a node cannot send data to other node because it is blocked due to transmission by a nearby node

-e.g take two 3 nodes s,t,r,q

- sending node 1 ----> s

-sending node 2-------> t

-receiving node 1------>r

-receiving node 2------>q

- s and t are both in range of each other

- s is transmitting already data to r

- so t is blocked because it is neighborhood of s and , so t cannot transmit data to q

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b)solution

-a mechanism that involves two kind of messages rts and cts can be used to solve it

-a node who wants to transmit data sends rts (request to send) to receiving node

-the receiving node in return sends cts (clear to send ) message to sender to signal that it can send data

-so when a exposed node sends rts , and it will not receive cts in return which helps it to understand that it is exposed state

-so then it can send data to other neighboring node

Not only these there are several wireless problems, by using different technologies, techniques solve these problems..

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