Channel Spectral Characteristics

  • June 2020
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Channel Spectral Characteristics

Some Polyphase Filter Options

FDM-to TDM Standard Channelizer: Collection of Downconverters

FDM-to TDM Polyphase Channelizer: Input Commutator, M-Path Filter, and FFT

Conventional Channelizer Application Channelize and Downsample to Nyquist Rate, Interpolate to Two Times Symbol Rate

Enhanced Channelizer Solution Replace Interpolator Function With Buffer Addressing

Standard Downconverter: Heterodyne, Filter, Resample

Equivalency Theorem Heterodyne and Low Pass Filter Same as Band Pass Filter and Heterodyne

y (n, k ) = [ x (n )e =

− jθ k n

] ∗ h (n )

N −1

− j ( n − r )θ k x ( n − r ) e h (r ) ∑ r =0

=

N −1

jr θ k − jn θ k x ( n − r ) e h ( r ) e ∑ r =0

N −1

= e − jn θ k ∑ x ( n − r ) h ( r ) e jrθ k r =0

Slide Heterodyne Through Filter: Convert Low-Pass to Band-Pass

Slide Heterodyne Through Downsampler: Alias Frequency of Heterodyne

Select Input Center Frequency That Aliases to DC Under Resampling

Discard Trivial Heterodyne: Now a Scalar Multiply by Unity

Noble Identity Interchange Order of Filter and Resample

M-Path Partition of FIR Filter N −1

H ( Z ) = ∑ h( n) Z − n n=0

= h(0) + h(1) Z −1 + h(2) Z − 2 + h(3) Z − 3 + L + h( N − 1) Z −( N −1)

H(Z) = h(0)

+

h(M + 0) Z −M + h(2M + 0)Z −( 2M +0) +L

h(1)Z −1

+ h(M + 1)Z −( M +1) + h(2M + 1)Z −( 2M +1) +L

h(2)Z −2

+ h(M + 2)Z −(M +2) + h(2M + 2)Z −( 2M +2) +L

h(3)Z −3 M

+ h(M + 3)Z −( M +3) + h(2M + 3)Z −( 2M +3) +L M M M M M

h(M −1)Z −( M −1) + h(2M −1)Z −(2M −1) + h(3M −1)Z −(3M −1) +L H ( Z ) = H 0 ( Z M ) + Z −1 H1 ( Z M ) + Z −2 H 2 ( Z M ) + LL + Z −( M −1) H ( M −1) ( Z M ) M −1

H (Z ) = ∑ Z H r (Z ) r =0

−r

M

=

M −1

∑Z r =0

−r

( N / M ) −1

∑ h(r + nM )Z n =0

−M n

Example of Polyphase (M-Path) Partition

Block Diagram of M-Path Filter

Pull Resamplers Through Filters in Each path

Delays and Synchronous Rersamplers are Equivalent to Input Commutator

Input Series in Each Path of M-Path Filter have Offset Time Origins

Path Filters are Interpolators: Computing Output Samples with Common Time Origin

Phase Response of Paths in Ten Stage Polyphase Filter S pectral P has e Res pons e of Ten P olyphas e F ilters 0

-1

-2

Normalized P has e (φ /2π)

-3

-4

-5

-6

-7

-8

-9

0

0.05

0.1

0.15

0.2 0.25 0.3 Normaled Frequency (f/fs )

0.35

0.4

0.45

0.5

Group Delay of Paths in Ten-Stage Polyphase Filter S pectral Group Delay Res pons e of Ten P olyphas e Filters -7

-7.2

-7.4

s

Normalized Delay (∆ T/T )

-7.6

-7.8

-8

-8.2

-8.4

-8.6

-8.8

-9

0

0.05

0.1

0.15

0.2 0.25 0.3 Normaled Frequency (f/fs )

0.35

0.4

0.45

0.5

Modulation Property for Z-Transform if H ( Z ) = h( 0) + h(1) Z −1 + h( 2) Z − 2 + L + n( N − 1) Z −( N −1) N −1

= ∑ h( n) Z − n n =0

and G ( Z ) = h( 0) + h(1)e jθ Z −1 + h( 2)e j 2θ Z − 2 + L + h( N − 1)e j ( N −1)θ Z −( N −1) = h(0) + h(1)[e − jθ Z ]−1 + h( 2)[e − j 2θ Z ]− 2 + L + h( N − 1)[e − j ( N −1)θ Z ]−( N −1) N −1

= ∑ h(n)[e − jθ Z ]− n n =0

then G(Z) = H(Z) Z =e - jθ Z = H (e − jθ Z )

Polyphase Partition of Band-Pass Filter

Spectral Response of Signal in Resampled Pass Band Filter

Performance Specifications for 50-Channel Polyphase Channelizer

Required Spectral Response of Channel Filter at Output and at Input Rates

Time and Frequency Response of Remez Filter Design Impuls e Res pons e , P rototype F ilte r 0.025

10

x 10

Impuls e Res pons e , Detail

-4

0.02 0.015

5

0.01 0.005

0

0 -0.005

0

100

200

300

400

500

-5 -10

0

10

20

30

40

50

60

Frequency Res pons e , P rototype F ilte r 10 0 log magnitude (dB)

-10 -20 -30 -40 -50 -60 -70 -80

-30

-20

-10

0 Normalize d Frequenc y f/f

Channel

10

20

30

Time and Frequency response of Remez Filter Design with Modified End Points Impuls e Res pons e, P rototype Filter 0.025

10

x 10

Impuls e Res pons e, Detail

-4

0.02 0.015

5

0.01 0.005

0

0 -0.005

0

100

200

300

400

500

-5 -10

0

10

20

30

40

50

60

Frequency Res pons e, P rototype Filte r 10 0 log magnitude (dB)

-10 -20 -30 -40 -50 -60 -70 -80

-30

-20

-10

0 Normalized Frequency f/f

Channel

10

20

30

Time and Frequency Response of Prototype Filter at Output Sample Rate Impuls e Res pons e , P rototype F ilter

x 10 -3 20 15 10 5 0 -5

0

50

100

150

200

250

300

350

400

450

500

Frequency Res pons e, P rototype and Replicates at Output Ra te 10 0 log magnitude (dB)

-10 -20 -30 -40 -50 -60 -70 -80 -2

-1.5

-1

-0.5 0 Norma lized Frequency f/f

0.5

Channel

1

1.5

2

Commutators for Standard Input Buffer and for Circular Input Buffer

Standard Polyphase Channelizer and Modified Channelizer with Circular Buffers

Content of 64-Point Circular Input Buffer for Two Successive 48 Point Input Blocks

Shifting Time Origin for Input Data of Polyphase Filter and of Resetting FFT

Contents of Transfer Circular Buffer Aligning Origins for Successive Input Blocks

Input Time and Spectrum to 30 Channel, 40 Point FFT Channelizer real part of compos ite time s ignal 100

50

0

-50

-100 300

350

400

450

500

550

600

650

700

750

800

S pec trum: compos ite time s ignal 10 0 -10 -20 -30 -40 -50 -60 -20

-15

-10

-5

0

5

10

15

20

Time Series from 30 Channel Channelizer 10

10

10

10

10

10

0

0

0

0

0

0

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

10

10

10

10

10

10

0

0

0

0

0

0

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

10

10

10

10

10

10

0

0

0

0

0

0

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

10

10

10

10

10

10

0

0

0

0

0

0

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

10

10

10

10

10

10

0

0

0

0

0

0

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

-10

0

100

200

0

100

200

0

100

200

0

100

200

0

100

200

Spectra for 30 Channel Channelizer 0

0

0

0

0

0

-20

-20

-20

-20

-20

-20

-40

-40

-40

-40

-40

-40

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

0

0

0

0

0

-20

-20

-20

-20

-20

-20

-40

-40

-40

-40

-40

-40

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

0

0

0

0

0

-20

-20

-20

-20

-20

-20

-40

-40

-40

-40

-40

-40

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

0

0

0

0

0

-20

-20

-20

-20

-20

-20

-40

-40

-40

-40

-40

-40

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

0

0

0

0

0

-20

-20

-20

-20

-20

-20

-40

-40

-40

-40

-40

-40

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

-60 -1

0

1

0

1

0

1

0

1

0

1

Input Time and Spectrum to 50 Channel, 64 Point FFT Channelizer Compos ite Time S igna l 1

Amplitude

0.5

0

-0.5

-1 600

650

700

750

800 S ample Index

850

900

950

1000

S pec trum 10

Log Magnitude (dB)

0 -10 -20 -30 -40 -50 -60 -6000

-4000

-2000

0 Fre que nc y (kHz)

2000

4000

6000

Time Series from 50 Channel Matched Filter Channelizer 1

1

1

1

1

1

1

1

0

0

0

0

0

0

0

0

-1 1

0

100

200

0 -1 1

1

0

100

200

1

0

100

200

1

0

100

200

-1 1

-1 1

-1 1

0

100

200

-1 1

0

100

200

100

200

-1

1

0

100

200

-1 1

0

100

200

-1 1

0

100

200

100

200

-1 1

0

100

200

100

200

-1 1

0

100

200

100

200

-1

-1 1

-1 1

-1 1

0

100

200

-1 1

0

100 200

100

200

-1

1

0

100

200

-1 1

0

100 200

-1 1

0

100

200

100 200

-1 1

0

100

200

100 200

-1 1

0

100

200

100 200

-1

200

-1 1

-1 1

-1 1

0

100

200

-1 1

0

100

200

100

200

-1

1

0

100 200

-1 1

0

100

200

-1 1

0

100 200

100

200

-1 1

0

100 200

100

200

-1 1

0

100 200

100

200

-1

100

200

-1 1

0

100

200

-1 1

0

100

200

-1 1

0

100

200

0

100

200

0

100

200

0 0

100 200

0 0

0

0

0 0

1

0

0 0

-1

0

0

0 0

-1

0

0

0 0

100

0

0 0

1

0

0

0 0

-1

0

0

0 0

-1

0

0

0 0

100 200

0

0 0

1

0

0

0 0

-1

0

0

0 0

-1

0

0

0 -1

200

0

0 -1

100

0

0 -1

1

0

0

0 -1

-1

-1 1 0

0

100 200

-1

Spectra from 50 Channel Matched Filter Channelizer 0

0

0

0

0

0

0

0

-50

-50

-50

-50

-50

-50

-50

-50

-0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

-50 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0.5 -0.5

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0.5 -0.5 0

0.5 -0.5

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0.5 -0.5 0

0.5 -0.5

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0

0.5 -0.5 0

0.5

0

0.5

0

0.5

0

0.5

0

0.5

-50

-50 0.5 -0.5

0

-50

-50

0

0.5

-50

-50 0

0

-50

-50

-50 0

0

-50

-50

-50 0.5 -0.5

0

-50

-50

0

0.5 -0.5 0

-50

-50 0

0

-50

-50

-50 0

0

-50

-50

-50 0.5 -0.5

0

-50

-50

0

0.5 -0.5 0

-50

-50 0

0

-50

-50

-50 0

0

-50

-50

-50 -0.5

0.5 -0.5 0

-50

-50 -0.5 0

0

-50

-50 -0.5 0

0.5 -0.5 0

-50

-50 -0.5 0

0

-50 0

0.5 -0.5

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