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Unformatted text preview: as a 1, and vice versa. For such a channel, if we know the transmitter’s
signaling levels and receiver’s digitizing threshold, we know (from the earlier lecture on
noise) how to calculate the probability of bit error (BER). For the most part, we will assume
a simple (but useful) model that follows from the properties of AWGN: a transmitted 0
bit may be digitized at the receiver as a 1 (after deconvolution) with some probability p
(the BER), and a transmitted 1 may be digitized as a 0 at the receiver (after deconvolution)
with the same probability p. Such a model is also called a binary symmetric channel, or BSC.
The “symmetric” refers to the property that a 0 becomes a 1 and vice versa with the same
probability, p.
BSC is perhaps the simplest error model that is realistic, but realworld channels exhibit
more complex behaviors. For example, over many wireless and wired channels as well as
on storage media (like CDs, DVDs, and disks), errors can occur in bursts. That is, the probability of any given bit being received wrongly depends on (recent) history: the probability
is higher if the bits in the rec...
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This document was uploaded on 02/26/2014 for the course CS 6.02 at MIT.
 Fall '13
 HariBalakrishnan

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