Information Theory and coding Fourth stage By: MSC. Ridhab Sami Al-Mustaqbal University College Department of Computer Engineering Techniques Lecture 6 Mutual information for noisy channel Mutual information for noisy channel: Consider the
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Presentation Transcript
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Information Theory and coding
Β Fourth stage
By:
MSC. Ridhab Sami Al-Mustaqbal University College
Department of Computer Engineering Techniques<br>
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Lecture 6 Mutual information for noisy channel<br>
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Mutual information for noisy channel: Consider the set of symbols π₯1, π₯2,β¦.,π₯π, the transmitter ππ₯ my produce. The receiver π π₯ may receive π¦1, π¦2 β¦β¦β¦.π¦π. Theoretically, if the noise and jamming is neglected, then the set X=set Y.
The amount of information that π¦π provides about π₯π is called the mutual information between π₯π and π¦π.<br>
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Properties of π°(ππ , ππ): It is symmetric, πΌ(π₯π , π¦π) = πΌ(π¦π , π₯π).
πΌ(π₯π , π¦π) > 0 if aposteriori probability > a priori probability, π¦π provides +ve information about π₯π .
πΌ(π₯π , π¦π) = 0 if aposteriori probability = a priori probability, which is the case of statistical independence when π¦π provides no information about π₯π .
πΌ(π₯π , π¦π) < 0 if aposteriori probability < a priori probability, π¦π provides -ve information about π₯π , or π¦π adds ambiguity.<br>
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Joint entropy: In information theory, joint entropy is a measure of the uncertainty associated with a set of variables. P(x , y) joint probability Entropy Joint Entropy<br>
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2. Conditional entropy: In information theory, the conditional entropy quantifies the amount of information needed to describe the outcome of a random variable Y given that the value of another random variable X is known. P(x | y) conditional probability Conditional Entropy Entropy<br>
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3. Marginal Entropies: Marginal entropies is a term usually used to denote both source entropy H(X) defined as before and the receiver entropy H(Y) given by: Receiver Entropy Source Entropy<br>
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4. Relationship between joint, conditional and transinformation: Noise entropy: π»(π β£ π) = π»(π,π) β π»(π)
Loss entropy: π»(π β£ π) = π»(π,π) β π»(π) Also we have transinformation (average mutual information): πΌ(π,π) = π»(π) β π»(π β£ π)
πΌ(π,π) = π»(π) β π»(π β£ π)<br>
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Example: The joint probability of a system is given by: Find:
Marginal entropies.
Joint entropy.
Conditional entropies.
The transinformation.<br>
