surya spent the last class giving us a quick and dirty overview of the history of radio and some technical fundamentals. key things:
- WWII submarine communication, frequency jamming, and frequency hopping
- relationship between frequency and bandwidth
- claude shannon and information theory
- wi-fi and packet types
- management frames in general. probe request frames and beacon frames in particular.
- OSI stack
i’m spending some time with claude shannon’s important paper, “a mathematical theory of communication”. i’m definitely not a math person, but i’m still finding the paper fascinating for the way it frames communication. for someone from a more art/lit theory-y background, talking about communication in this way is really new:
“Frequently the messages have meaning; that is they refer to or are correlated according to some system with certain physical or conceptual entities. These semantic aspects of communication are irrelevant to the engineering problem. The significant aspect is that the actual message is one selected from a set of possible messages.”
um. wow. he gives us this wonderfully symmetrical diagram:
but i think my favorite part is the way he defines these elements in words before representing them as mathematical entities that can be manipulated in/with equations. here’s how he breaks down the “information source” which produces a message that may be of various types:
- sequence of letters (like a telegraph)
- single function of time (like radio)
- function of time and other variables (like b&w tv). this would look like “function f (x, y, t) of two space coordinates and time, the light intensity at point (x, y) and time t on a pickup tube plate”
- 2+ functions of time (like multi-channel sound)
- 2+ functions of time and 2+ functions of space (like color tv or tv with associated audio channel). this would look like f (x, y, t), g(x, y, t), h(x, y, t).