Detection & Estimation Lecture 1 -...
Transcript of Detection & Estimation Lecture 1 -...
9/9/2019
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Detection & EstimationLecture 1Intro, MVUE, CRLB
Xiliang Luo
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General Course Information
• Textbooks & References• 1. Fundamentals of Statistical Signal Processing: Estimation Theory/Detection Theory,
Steven M. Kay, Prentice Hall, 1993.• 2. Principles of Signal Detection and Parameter Estimation, Benard C. Levy, Springer,
2008.• 3. Detection, Estimation, and Modulation Theory, Part I, Harry L. Van Trees, John
Wiley & Sons, Inc., 2001.
• Lecturer• Dr. Xiliang Luo (1C‐403A)• Office hour: Tuesday, Thursday, 10:30‐12:00pm
• TA• Mr. Zixin Wang (1A‐413)• Office hour: Tuesday, Wednesday, 7:30‐9:15pm
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General Course Information
• Grading• Homework: 30%
• weekly
• due at the beginning of each lecture
• Midterm: 30%
• Final: 40%
• You must complete the weekly HW independently
• Discussions among students are allowed but solutions must be your own
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General Course Information
• Course websitefaculty.sist.shanghaitech.edu.cn/faculty/luoxl/class/2019Fall_EE251/EE251.htm
• Course forumBlackboard
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Estimation
• Radar
• Sonar
• Speech
• Image analysis
• Biomedicine
• Communication
• Control
• Seismology
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Radar
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Sonar
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Cell Search
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Cell Search
0 20 40 60 80 100 120 140 160 180 20010
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Cell Search
SNR=‐10dB
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Cell Search
0 20 40 60 80 100 120 140 160 180 200-60
-40
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SNR=‐10dB
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Cell Search
SNR=‐20dB
0 20 40 60 80 100 120 140 160 180 200-150
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Estimation Problem
• Given a data set• 𝑥 0 , 𝑥 1 , … , 𝑥 𝑁 1
• We want to determine the value of an unknown parameter as:• 𝜃 𝑔 𝑥 0 , 𝑥 1 , … , 𝑥 𝑁 1• this function is an estimator
• Date back to Gauss, 1795• least squares planetary movement
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Least Squares
• "Least squares" means that the overall solution minimizes the sum of the squares of the residuals made in the results of every single equation.
𝑦 𝐴𝜃 𝑤
𝜃 𝐴 𝐴 𝐴 𝑦
For example: 𝐴 1, … , 1 , we have sample mean!
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Least Squares• 1805, Legendre:
• the first clear and concise exposition of
the method of least squares
• The technique is described as an
algebraic procedure for fitting linear
equations to data and Legendre
demonstrates the new method by
analyzing the same data as Laplace for
the shape of the earth. The value of
Legendre's method of least squares was
immediately recognized by leading
astronomers and geodesists of the time.
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Least Squares• 1809, Carl Friedrich Gauss:
• Published his method of calculating the orbits of celestial bodies.
• In that work he claimed to have been in possession of the method of least squares since 1795.
• This naturally led to a priority dispute with Legendre.
• However, to Gauss's credit, he went beyond Legendre and succeeded in connecting the method of least squares with the principles of probability and to the normal distribution.
• Gauss showed that arithmetic mean is indeed the best estimate of the location parameter for the Gauss distribution
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Estimation Problem
• The data has to be dependent on the unknown parameter
• pdf: 𝑝 𝑥 0 , … , 𝑥 𝑁 1 ; 𝜃• the semicolon denotes the dependence
• Example: Gaussian pdf
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Classical vs Bayesian
• Classical estimation• the unknown parameter is deterministic
• Bayesian estimation• the unknown parameter is itself random
• we are estimating one realization of the random parameter
• the data are characterized by the joint pdf• 𝑝 𝑥, 𝜃 𝑝 𝑥 𝜃 𝑝 𝜃• 𝑝 𝜃 : the prior pdf
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Estimator Performance
• 𝑥 𝑛 𝐴 𝑤 𝑛
• 𝐴 ∑𝑥 𝑛
• Question:• How is this estimator?
• find the mean,variance
• Best estimator?• topic next
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Unbiased Estimator
• On average, the estimator should yield the true value this estimator is unbiased• E 𝜃 𝜃, 𝜃 ∈ 𝑎, 𝑏
• Example: • 𝑥 𝑛 𝐴 𝑤 𝑛
• 𝐴 ∑ 𝑥 𝑛
• “An estimator is unbiased” does not mean it is a good estimator
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Minimum Variance
• In order to find one “optimal” estimator, we need to specify the criterion• one natural criterion is the Mean Square Error (MSE)
• 𝑚𝑠𝑒 𝜃 𝐸 𝜃 𝜃 𝑣𝑎𝑟 𝜃 𝑏 𝜃
• Example:
𝐴 𝑎1𝑁
𝑥 𝑛
𝑚𝑠𝑒 𝐴𝑎 𝜎
𝑁𝑎 1 𝐴
𝑎𝐴
𝐴 𝜎 /𝑁
Not realizable!
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MVUE• Minimize the variance while being unbiased
• Question: whether MVUE exists?• unbiased estimator with minimum variance for all values of the unknown parameter
• Example: [Example 2.3, Kay]
𝑥 0 ∼ 𝒩 𝜃, 1 𝑥 1 ∼𝒩 𝜃, 1 , 𝑖𝑓 𝜃 0 𝒩 𝜃, 2 , 𝑖𝑓 𝜃 0
𝜃12
𝑥 0 𝑥 1
𝜃13
2𝑥 0 𝑥 1
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MVUE
• No known “turn‐the‐crank” procedure to produce the MVUE
• Next, we will discuss• Cramer‐Rao lower bound
• Rao‐Blackwell‐Lehmann‐Scheffe theorem
• best linear estimator
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Cramer‐Rao Lower Bound
• We need to place a lower bound on the variance of any unbiased estimator!• Check whether our estimator is MVUE
• Check how far our estimator is from the optimal one• even the optimal one may not exist
• Tells us it is impossible to find an estimator that can beat the bound
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Likelihood Function
• When the pdf is views a function of the unknown parameter, it is referred to as the “likelihood function”
• Example: 𝑥 0 𝐴 𝑤 0
ln 𝑝 𝑥 0 ; 𝐴 ln 2𝜋𝜎1
2𝜎𝑥 0 𝐴
𝜕 ln 𝑝 𝑥 0 ; 𝐴𝜕 𝐴
1𝜎
𝑝 𝑥 0 ; 𝐴1
2𝜋𝜎𝑒
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CRLB• Regularity condition:
• For any unbiased estimator, we have:
• Furthermore, one unbiased estimator achieving the bound exists iff:
• 𝜃 𝑔 𝑥 is the MVUE and the min variance is given by 1/𝐼 𝜃
𝐸𝜕 ln 𝑝 𝒙; 𝜃
𝜕𝜃0, ∀𝜃
𝑣𝑎𝑟 𝜃 𝐸𝜕 ln 𝑝 𝒙; 𝜃
𝜕 𝜃
𝜕 ln 𝑝 𝒙; 𝜃𝜕𝜃
𝐼 𝜃 𝑔 𝒙 𝜃
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Regularity Condition
• 𝑥 𝑛 , n=0,…,N‐1, IID according to U[0,𝜃], let’s check the regularity condition
𝜕 ln 𝑝 𝒙; 𝜃𝜕𝜃
𝑁𝜃
What is going on here?
𝜕 ln 𝑝 𝑥; 𝜃𝜕𝜃
𝑑𝑥 ? 0
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Some Examples
• DC level in white noise
𝑥 𝑛 𝐴 𝑤 𝑛 , 𝑛 0,1, … , 𝑁 1
𝜕 ln 𝑝 𝑥; 𝐴𝜕𝐴
𝑁𝜎
∑𝑥 𝑛𝑁
𝐴
𝑝 𝑥; 𝐴1
2𝜋𝜎𝑒
∑
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Fisher Information
• Fisher Information
• Nonnegative• Additive for independent observations
𝐼 𝜃 𝐸𝜕 ln 𝑝 𝒙; 𝜃
𝜕𝜃𝐸
𝜕ln 𝑝 𝒙; 𝜃𝜕𝜃
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Proof of CRLB
• Setup: • 1. pdf depends on 𝜃• 2. we need to estimate one scalar parameter 𝛼 𝑔 𝜃
• We consider all unbiased estimators for the parameter 𝛼• 𝛼 𝑓 𝑥 0 , 𝑥 1 , … , 𝑥 𝑁 1• 𝐸 𝛼 𝑔 𝜃
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Proof of CRLB
𝛼𝑝 𝑥; 𝜃 𝑑𝑥 𝑔 𝜃 𝛼𝜕𝑝 𝑥; 𝜃
𝜕𝜃𝑑𝑥
𝜕𝑔 𝜃𝜕𝜃
𝛼𝜕 ln 𝑝 𝑥; 𝜃
𝜕𝜃𝑝 𝑥; 𝜃 𝑑𝑥
𝜕𝑔 𝜃𝜕𝜃
𝛼 𝛼𝜕 ln 𝑝 𝑥; 𝜃
𝜕𝜃𝑝 𝑥; 𝜃 𝑑𝑥
𝜕𝑔 𝜃𝜕𝜃
𝜕𝑔 𝜃𝜕𝜃
𝛼 𝛼 𝑝 𝑥; 𝜃 𝑑𝑥 𝜕 ln 𝑝 𝑥; 𝜃
𝜕𝜃𝑝 𝑥; 𝜃 𝑑𝑥
𝑣𝑎𝑟 𝛼
𝜕𝑔 𝜃𝜕𝜃
𝐸𝜕 ln 𝑝 𝑥; 𝜃
𝜕𝜃31
Proof of CRLB
• Equality condition (Cauchy‐Schwarz inequality)
• If equality holds and for 𝛼 𝑔 𝜃 𝜃, we have 𝑐 𝜃 𝐼 𝜃
𝜕𝑔 𝜃𝜕𝜃
𝛼 𝛼 𝑝 𝑥; 𝜃 𝑑𝑥 𝜕 ln 𝑝 𝑥; 𝜃
𝜕𝜃𝑝 𝑥; 𝜃 𝑑𝑥
𝜕 ln 𝑝 𝑥; 𝜃𝜕𝜃
𝑐 𝜃 𝛼 𝛼
𝜕 ln 𝑝 𝑥; 𝜃𝜕𝜃
𝐼 𝜃 𝜃 𝜃
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Example
• General CRLB for Signals in WGN
𝑥 𝑛 𝑠 𝑛; 𝜃 𝑤 𝑛 , 𝑛 0, … , 𝑁 1
var 𝜃𝜎
∑ 𝜕𝑠 𝑛; 𝜃𝜕𝜃
• Sinusoidal Frequency Estimation
𝑠 𝑛; 𝑓 𝐴 cos 2𝜋𝑓 𝑛 𝜙 , 𝑓 ∈ 0, 0.5
Apply the above results:
var 𝑓𝜎
𝐴 ∑ 2𝜋𝑛sin 2𝜋𝑓 𝑛 𝜙33
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
f0
1
1.5
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2.5
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3.5
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4.5
510-4 =0, A2/ 2=1, N=10
Example• Sinusoidal Frequency Estimation
𝑠 𝑛; 𝑓 𝐴 cos 2𝜋𝑓 𝑛 𝜙 , 𝑓 ∈ 0, 0.5
var 𝑓𝜎
𝐴 ∑ 2𝜋𝑛sin 2𝜋𝑓 𝑛 𝜙
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Example
• Range Estimation [Example 3.13 in Kay’s book]
𝑥 𝑡 𝑠 𝑡 𝜏 𝑤 𝑡 , 𝑡 ∈ 0, 𝑇
Sample at Nyquist rate (2B):
𝑥 𝑛Δ 𝑠 𝑛Δ 𝜏 𝑤 𝑛Δ , 𝑛 0, … , 𝑁 1
𝑥 𝑛 𝑠 𝑛Δ 𝜏 𝑤 𝑛 , 𝑛 0, … , 𝑁 1
𝑥 𝑛𝑤 𝑛 , 𝑛 ∈ 0, 𝑛 1
𝑠 𝑛Δ 𝜏 , 𝑛 ∈ 𝑛 , 𝑛 𝑀 1𝑤 𝑛 , 𝑛 ∈ 𝑛 𝑀, 𝑁 1
M: length of signal𝑛 𝜏 /Δ: delay in samples
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Example
• Range Estimation
var 𝜏𝜎
1Δ
𝑑𝑠 𝑡𝑑𝑡 𝑑𝑡
1ℇ
𝑁 /2 𝐹
𝐹
𝑑𝑠 𝑡𝑑𝑡 𝑑𝐹
𝑠 𝑡 𝑑𝐹
2𝜋𝐹 𝑆 𝐹 𝑑𝐹
𝑆 𝐹 𝑑𝐹mean‐square BW of the signal
var 𝜏𝜎
∑ 𝜕𝑠 𝑛; 𝜏𝜕𝜏
𝜎
∑ 𝜕𝑠 𝑛Δ 𝜏𝜕𝜏
𝜎
∑ 𝑑𝑠 𝑡𝑑𝑡 |
Parseval’s Theorem 36
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Example
• Range Estimation
var 𝜏𝜎
1Δ
𝑑𝑠 𝑡𝑑𝑡 𝑑𝑡
1ℇ
𝑁 /2 𝐹
𝐹
𝑑𝑠 𝑡𝑑𝑡 𝑑𝐹
𝑠 𝑡 𝑑𝐹
2𝜋𝐹 𝑆 𝐹 𝑑𝐹
𝑆 𝐹 𝑑𝐹mean‐square BW of the signal
For the Gaussian pulse 𝑠 𝑡 exp , we have
𝑆 𝐹𝜎
2𝜋exp
2𝜋𝐹
𝜎
𝐹𝜎2 37
Vector Parameter• For vector parameters: 𝜽 𝜃 , … , 𝜃
• Regularity condition:
• For any unbiased estimator 𝜽, we have:
• Furthermore, one unbiased estimator achieving the bound exists iff:
• 𝜽 𝒈 𝒙 is the MVUE and the min variance is given by 𝐼 𝜽
𝐸𝜕 ln 𝑝 𝒙; 𝜽
𝜕𝜽𝟎, ∀𝜽
𝐶𝜽 𝐼 𝜽 0
𝜕 ln 𝑝 𝒙; 𝜽𝜕𝜽
𝐼 𝜽 𝒈 𝒙 𝜽
𝐼 𝜽 , 𝐸𝜕 ln 𝑝 𝒙; 𝜽
𝜕𝜃 𝜕𝜃
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Example
• DC Level in WGN: 𝜽 𝐴, 𝜎 are unknown
𝑥 𝑛 𝐴 𝑤 𝑛 , 𝑛 0,1, … , 𝑁 1
𝐼 𝜽𝐸
𝜕 ln 𝑝 𝒙; 𝜽𝜕𝐴
𝐸𝜕 ln 𝑝 𝒙; 𝜽
𝜕𝐴𝜕𝜎
𝐸𝜕 ln 𝑝 𝒙; 𝜽
𝜕𝜎 𝜕𝐴𝐸
𝜕 ln 𝑝 𝒙; 𝜽
𝜕𝜎
𝑁𝜎
0
0𝑁
2𝜎
Note: typically, the more unknowns, the higher the CRLB!
𝑝 𝑥; 𝐴, 𝜎1
2𝜋𝜎exp
∑ 𝑥 𝑛 𝐴2𝜎
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Vector CRLB for Transformation
• Scalar parameter 𝛼 𝑔 𝜃
• Vector parameter 𝜶 𝒈 𝜽 , r‐dimensional function
𝑣𝑎𝑟 𝛼
𝜕𝑔 𝜃𝜕𝜃
𝐸𝜕 ln 𝑝 𝑥; 𝜃
𝜕𝜃
𝑪𝜶𝜕𝒈 𝜽
𝜕𝜽𝑰 𝜽
𝜕𝒈 𝜽𝜕𝜽
0
Jacobian
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Example• DC Level in WGN: 𝜽 𝐴, 𝜎 are unknown, we want
to estimate the SNR: 𝛼
𝑥 𝑛 𝐴 𝑤 𝑛 , 𝑛 0,1, … , 𝑁 1
𝐼 𝜽𝐸
𝜕 ln 𝑝 𝒙; 𝜽𝜕𝐴
𝐸𝜕 ln 𝑝 𝒙; 𝜽
𝜕𝐴𝜕𝜎
𝐸𝜕 ln 𝑝 𝒙; 𝜽
𝜕𝜎 𝜕𝐴𝐸
𝜕 ln 𝑝 𝒙; 𝜽
𝜕𝜎
𝑁𝜎
0
0𝑁
2𝜎
𝑣𝑎𝑟 𝛼2𝐴𝜎
,𝐴𝜎
𝐼 𝜃2𝐴𝜎
,𝐴𝜎
4𝛼 2𝛼N
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Asymptotic CRLB
• For a WSS Gaussian random process 𝑥 𝑛 with zero mean, whose PSD depends on parameter 𝜃, Fisher information matrix element can be approximated as
𝐼 𝜃𝑁2
𝜕 ln 𝑃 𝑓; 𝜃𝜕𝜃
𝜕 ln 𝑃 𝑓; 𝜃𝜕𝜃
𝑑𝑓
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Fd=10Hz
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Asymptotic CRLB
• Almost any WSS Gaussian random process 𝑥 𝑛 can be represented as the output of a filter with white input
• The PSD is then
𝑥 𝑛 ℎ 𝑘 𝑢 𝑛 𝑘 ,
𝑃 𝑓 𝐻 𝑓 𝜎
𝐻 𝑓 ℎ 𝑘 𝑒
ℎ 0 1
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Asymptotic CRLB
• For large 𝑁 (much larger than the impulse response length, or the correlation time of 𝑟 𝑘 ), we have
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Asymptotic CRLB
• Parseval’s Theorem:
• 𝒖 𝒖 ∑ 𝑢 𝑛 𝑈 𝑓 𝑑𝑓
• Fourier Transform relationship between 𝑢 𝑛 and 𝑥 𝑛• 𝑋 𝑓 𝐻 𝑓 𝑈 𝑓
• We have
•𝒖 𝒖 𝑑𝑓
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Asymptotic CRLB
• Asymptotic pdf is:
ln𝑝 𝒙; 𝜽𝑁2
ln 2𝜋𝜎12
𝑋 𝑓𝑃 𝑓
𝑑𝑓
• To eliminate 𝜎 , we use the following:
= 0
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Asymptotic CRLB
• Asymptotic pdf:
ln 𝑝 𝒙; 𝜽𝑁2
ln 2𝜋𝑁2
ln 𝑃 𝑓
𝑋 𝑓𝑁
𝑃 𝑓𝑑𝑓
• CRLB can be found as:
𝐼 𝜃𝑁2
𝜕 ln 𝑃 𝑓; 𝜃𝜕𝜃
𝜕 ln 𝑃 𝑓; 𝜃𝜕𝜃
𝑑𝑓
Note: Periodogram spectral estimator:
𝐸𝑋 𝑓
𝑁𝑃 𝑓 , 𝑎𝑠 𝑁 → ∞
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Center Frequency of Process
• PSD depends on the center frequency. Some time a want to estimate the center frequency
𝑃 𝑓; 𝑓 𝑄 𝑓 𝑓 𝑄 𝑓 𝑓 𝜎
𝑄 𝑓 𝑒
𝑣𝑎𝑟 𝑓12𝜎
𝑁
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