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Unformatted text preview: EE378 Statistical Signal Processing Lecture 2  04/09/2007 Gaussian Processes, Stationarity, Ergodicity Lecturer: Tsachy Weissman Scribe: Boon Sim Thian, Huixian Chen, Kamakshi S 1 Random Processes (discrete time) Throughout the course, we will mostly talk about discrete time processes.Some equivalent terms: • Stochastic Processes • Random Signals • Time Series Why should we mostly be concerned with discretetime processes? • Most of the processes that we would encounter will be discrete • Continuous processes can be approximated by discrete time processes arbitrarily well. • The mathematics involved is more tractable. Definition 1 (Random Process) . : A random process is a collection of random variables { X ( n ) } n ∈ Z . (Other notations: { X ( t ) } , { X ( n ) } , { X t } , { X n } ). A random process is fully specified by the finitedimensional distribution, i.e. distributions of ( X ( n 1 ) ,X ( n 2 ) ,...,X ( n k )) , ∀ k,n 1 ,n 2 ,...,n k . Theorem 2 (Kolmogorov’s Theorem) . Any consistent set of finitedimensional distribution uniquely speci fies a process. What do we mean by consistent? Colloquially it means, the marginal on the distributions of k + 1 dimensional vector must equal the distributions of kdimensional vector. More rigorously, we first define Definition 3 (The Distribution Functions of a Stochastic Process, { X t ,t ∈ T ⊂ R } ) . Let T be the set of all vectors { t = ( t 1 , ··· ,t n ) ∈ T n : t 1 < ··· < t n ,n = 1 , 2 ···} . Then the (finitedimensional) distribution functions of { X t ,t ∈ T } are the functions F t ( · ) , t ∈ T defined for t = ( t 1 , ··· ,t n ) by F t ( x ) = P ( X 1 ≤ x 1 , ··· ,X t n ≤ x n ) , x = ( x 1 , ··· ,x n ) ∈ R n (1) and the Kolmogorov Theorem from [Brockwell&Davis] is, Theorem 4 (Kolmogorov’s Theorem) . The probability distribution functions { F t ( · ) , t ∈ T } are the distri bution functions of some stochastic process if and only if for any n ∈ { 1 , 2 , ···} , t = { t 1 ,t 2 , ··· ,t n } ∈ T and 1 ≤ i ≤ n , lim x i →∞ F t ( x ) = F t ( i ) ( x ( i )) (2) where, t ( i ) and x ( i ) are the ( n 1)component vectors obtained by deleting the...
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This note was uploaded on 03/03/2011 for the course EE 378 taught by Professor Weissman,i during the Spring '07 term at Stanford.
 Spring '07
 Weissman,I
 Signal Processing

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