In a few years to come, we will reach a point where the number of computing devices will cross the total human population. This phenomenal growth of the wireless technology brings new avenues to improve its efficiency and capacity. Days will not be far where you can turn these computing devices into sensor nodes and energy harvesters. The trend now is to make one device talk with the others.
The network engineers are already in the process of shifting to Ipv6 to inter-network this mammoth figure of mobile devices. A physical layer engineer is also very concerned since the modulation and coding schemes have to be modified from top to bottom. We can try to see some aspects of this upcoming scheme using a human analogy.
Alice wants to communicate some message to Bob. Now Bob is standing in a building which is adjacent to where Alice stays. If Alice shouts at the top of her voice, Bob will be able to hear. But Alice does not prefer that mainly because the message is confidential. So Alice does the following: Alice tells her assistant Charlie the message (not the complete message) and asks him to convey it to Bob. Alice will now call Bob from the balcony of her apartment and tell Bob the part of message not conveyed through Charlie.
It is nice to see some technical aspects of this message communication where Alice and Bob are the source and destination respectively and Charlie and Don are the relay nodes. We begin with the simple model where Alice has a direct channel with Bob.
Courtesy: www.citizenwarrior.com
The network engineers are already in the process of shifting to Ipv6 to inter-network this mammoth figure of mobile devices. A physical layer engineer is also very concerned since the modulation and coding schemes have to be modified from top to bottom. We can try to see some aspects of this upcoming scheme using a human analogy.
Alice wants to communicate some message to Bob. Now Bob is standing in a building which is adjacent to where Alice stays. If Alice shouts at the top of her voice, Bob will be able to hear. But Alice does not prefer that mainly because the message is confidential. So Alice does the following: Alice tells her assistant Charlie the message (not the complete message) and asks him to convey it to Bob. Alice will now call Bob from the balcony of her apartment and tell Bob the part of message not conveyed through Charlie.
Courtesy: ourcountryroad.blogspot.com
So has Alice lost her voice by shouting? If she if afraid of that, she would call her second assistant Don and pass the remaining part of the message through him.It is nice to see some technical aspects of this message communication where Alice and Bob are the source and destination respectively and Charlie and Don are the relay nodes. We begin with the simple model where Alice has a direct channel with Bob.
\( y_C = h_{AC} X_{AC}+Z_C \),
\( y_D = h_{AD} X_{AD}+Z_D \),
\( y_B = h_{AB} X_{AB}+ h_{CB} X_{CB} + h_{DB} X_{DB} + Z_B \)
\( y_D = h_{AD} X_{AD}+Z_D \),
\( y_B = h_{AB} X_{AB}+ h_{CB} X_{CB} + h_{DB} X_{DB} + Z_B \)
The goal now is to determine a coding scheme such that the common information in \(X_{AB}\), \(X_{CB}\) and \(X_{DB}\) is zero.
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