chapter 8 dsp algorithm implementation wang weilian [email protected] school of information science...
TRANSCRIPT
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CHAPTER 8 DSP Algorithm Implementation
CHAPTER 8 DSP Algorithm Implementation
Wang Weilian
School of Information Science and Technology
Yunnan University
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OUTLINEOUTLINE
• Concepts Relating to DSP Algorithm
– Matrix Representation
– Precedence Graph
– Structure Verification
• Structure Simulation and Verification Using MATLAB
• Computation of DFT
– Goertzel’s Algorithm
– FFT
– Inverse DFT computation
• Summary
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MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
• Consider the structure figure:
• The structure can be described by a set of equations:
1 5
2 1 3
13 2
4 3 2
15 4
1 5
( ) ( ) ( )
( ) ( ) ( )
( ) ( )
( ) ( ) ( )
( ) ( )
( ) ( ) ( )
W z X z W z
W z W z W z
W z z W z
W z W z W z
W z z W z
Y z W z W z
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MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
• In the time-domain, the equivalent set of equations is as follows:
• The above set of equations are non-computable in the present order.
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MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
• Reorder the above equations as follows:
• The above ordered set of equations can be implemented in the sequential order and is computable.
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MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
• A simple way to examine the computability of structure equations is by writing the equations in a matrix form.
• Define four matrices as follows:
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MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
• The first ordered set of equations can be described in the compact matrix form:
• The matrix equation is not computable because all elements of the matrix F on the diagonal and above diagonal are not all zeros.
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MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
MATRIX REPRESENTATION OF THE DIGITAL FILTER STRUCTURE
• Computability condition: all elements of the F matrix on the diagonal and above diagonal must be zeros.
• The F matrix for the second ordered set of equations is
• It can be seen that the above F matrix satisfies the computability condition.
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PRECEDENCE GRAPHPRECEDENCE GRAPH
• Precedence graph can be used to test the computability of a digital filter structure. It is developed from the signal flow-graph of the digital filter structure.
• The signal flow-graph description of
is shown below
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PRECEDENCE GRAPHPRECEDENCE GRAPH
• The reduced signal flow-graph is
• The precedence graph of the above figure is
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STRUCTURE VERIFICATIONSTRUCTURE VERIFICATION
• A digital filter structure is verified to ensure that no computational and / or other errors taken place and that the structure is indeed characterized by H (z).
• Consider a causal 3rd order IIR transfer function
• Its unit sample response is {h[n]}, then
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STRUCTURE VERIFICATIONSTRUCTURE VERIFICATION
• From the above equation, we arrive at
in the time-domain, the equivalent convolution sum is
for n=0,1,2,…,6, we have
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STRUCTURE VERIFICATIONSTRUCTURE VERIFICATION
• The above equations can be written in the matrix form
in the partitioned form, it can be written as
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STRUCTURE VERIFICATIONSTRUCTURE VERIFICATION
where
• Solving the second equation, we get
• Substituting above in the first equation, we arrive at
• In the case of N-th order IIR filter, the coefficients of its transfer function can be determined from the first 2N+1 impulse response samples.
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STRUCTURE VERIFICATIONSTRUCTURE VERIFICATION
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STRUCTURE VERIFICATIONSTRUCTURE VERIFICATION
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Structure Simulation & Verification Using MATLAB
Structure Simulation & Verification Using MATLAB
• As shown earlier, the set of equations describing the filter structure must be ordered properly to ensure computability.
• The procedure is to express the output of each adder and filter output variable in terms of all incoming variables.
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Structure Simulation & Verification Using MATLAB
Structure Simulation & Verification Using MATLAB
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• From the computed impulse response samples, the structure can be verified by determining the transfer function coefficients using the M-file strucver.
• The M-file filter implements IIR filter in the transposed direct form II structure shown below for a 3rd order filter.
• As indicated in the figure, d(1) has been assumed to be equal to 1.
Structure Simulation & Verification Using MATLAB
Structure Simulation & Verification Using MATLAB
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Structure Simulation & Verification Using MATLAB
Structure Simulation & Verification Using MATLAB
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Structure Simulation & Verification Using MATLAB
Structure Simulation & Verification Using MATLAB
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COMPUTATION OF DFTCOMPUTATION OF DFT
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GOERTZEL’S ALGORITHMGOERTZEL’S ALGORITHM
• Goertzel’s algorithm is a recursive DFT computation scheme making use of the identity
• We can write
• Define
1kNNW
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GOERTZEL’S ALGORITHMGOERTZEL’S ALGORITHM
then we have
• is the direct convolution of the causal sequence
with a causal sequence
[ ]ky n
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GOERTZEL’S ALGORITHMGOERTZEL’S ALGORITHM
• A second order realization
• According to the above figure, DFT computation equations are
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GOERTZEL’S ALGORITHMGOERTZEL’S ALGORITHM
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FAST FOURIER TRANSFORM ALGORITHMS
FAST FOURIER TRANSFORM ALGORITHMS
• The basic idea behind the fast Fourier transform ( FFT)
– Decompose the N-point DFT computation into computations of smaller-size DFTs
– Take advantage of the periodicity and symmetry of the complex number .
kNNW
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
• Consider a sequence of length . Using 2-band polyphase decomposition, we can express its z-transform as
[ ]x n 2uN
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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• Examination of the above flow-graph reveals that each stage of the DFT computation process employs the same basic computational module
• Basic computational module is called butterfly computation.
DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-TIME FFT ALGORITHMDECIMATION-IN-TIME FFT ALGORITHM
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DECIMATION-IN-FREQUENCY FFT ALGORITHM
DECIMATION-IN-FREQUENCY FFT ALGORITHM
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DECIMATION-IN-FREQUENCY FFT ALGORITHM
DECIMATION-IN-FREQUENCY FFT ALGORITHM
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DECIMATION-IN-FREQUENCY FFT ALGORITHM
DECIMATION-IN-FREQUENCY FFT ALGORITHM
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DECIMATION-IN-FREQUENCY FFT ALGORITHM
DECIMATION-IN-FREQUENCY FFT ALGORITHM
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DECIMATION-IN-FREQUENCY FFT ALGORITHM
DECIMATION-IN-FREQUENCY FFT ALGORITHM
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DECIMATION-IN-FREQUENCY FFT ALGORITHM
DECIMATION-IN-FREQUENCY FFT ALGORITHM
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INVERSE DFT COMPUTATIONINVERSE DFT COMPUTATION
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INVERSE DFT COMPUTATIONINVERSE DFT COMPUTATION
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INVERSE DFT COMPUTATIONINVERSE DFT COMPUTATION
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DFT AND IDFT COMPUTATION USING MATLAB
DFT AND IDFT COMPUTATION USING MATLAB
• The following functions in the MATLAB package can be used to compute DFT and IDFT:
fft(x) ifft(x) fft(x,N) ifft(x,N)
• Since vectors in MATLAB are indexed from 1 to N, the DFT and the IDFT computed in the above MATLAB functions make use of the expressions:
( 1)( 1)
1
( 1)( 1)
1
[ ] [ ] ,1
1[ ] [ ] ,1
Nn kN
n
Nn k
Nk
X k x n W k N
x n X k W n NN
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SUMMARYSUMMARY
• Some common factors in the implementation of DSP algorithm
• The implementation carried out by the set of equations describing the algorithm
• The computability condition of these equations
• Fast Fourier transform (FFT)
• MATLAB-based implementation of digital filtering algorithms