Digital filter tree
First Claim
Patent Images
1. A frequency multiplex circuit including a plurality of digital filter cells, each including a digital filter bank for effecting conversion between a frequency multiplexed signal and a plurality of weighted filter signals, and a discrete Fourier transformation means connected to the respective filter bank, the cells being connected to one another in successive stages in an outwardly branching tree structure such that, starting with the first stage, the frequency multiplexed signal is separated into L.sub.ν
- individual complex signals appearing on separate lines at the ν
th stage, where ν
=1, 2, . . . , the Fourier transformation means of each cell effecting a discrete Fourier transformation between the weighted filter signals of the cell and the L.sub.ν
individual complex signals, and the sampling rate is reduced at the ν
th stage by M.sub.ν
≦
L.sub.ν
, wherein for all of said cells for each cell of the ν
th stage;
the frequency multiplexed signal contains component signals each associated with a respective individual complex signal and having a bandwidth B.sub.ν
;
the weighted filter signals have the form ##EQU12## where i.sub.ν
=p·
L.sub.ν
+q,q=0, 1, 2, . . . L.sub.ν
-1, andi.sub.ν
, p, q=(0, 1, 2, 3, . . . )the frequency multiplexed signal is s.sub.ν
(k) and has a sampling rate of fAν
;
h(i.sub.ν
) is a coefficient representing a pulse response of a finite length for i.sub.ν
=0, 1, 2 . . . N.sub.ν
-1;
the discrete Fourier transformation has the form ##EQU13## where Sl.sbsb.ν
(kM.sub.ν
) represents the individual complex signals andDFT {·
} is the discrete Fourier transformation, M.sub.ν
is a sampling rate reduction factor, M.sub.ν
≦
L.sub.ν
, and the discrete Fourier transformation involves sampling with respect to every M.sub.ν
th value of the weighted filter signals;
each component signal of the frequency multiplexed signal is associated with a respective channel having a channel number, l.sub.ν
, and a center channel frequency fl.sbsb.ν
=l.sub.ν
·
B.sub.ν
+B.sub.ν
/2 and l.sub.ν
=0, 1, 2, . . . L.sub.ν
-1,the frequency multiplexed signal is a complex signal, sD (kT.sub.ν
)=srν
(kT.sub.ν
)+jsiν
(kT.sub.ν
) with a real portion Re=srν
(kT.sub.ν
) and an imaginary portion Im=siν
(kT.sub.ν
), and k is a time factor= . . . , -1, 0, +1 . . . ; and
each filter bank in the ν
th stage comprising;
two chains of N.sub.ν
-1 delay members each having a delay of T.sub.ν
+1 and each processing a respective portion of the complex signal, where N.sub.ν
is the number of samples of the frequency multiplexed signal associated with each set of weighted filter signal values output by the filter banks of the ν
th stage and T.sub.ν
=1/fAν
;
sampling means for sampling the signals associated with each delay member at a rate corresponding to the sampling rate of the frequency multiplexed signal reduced by M.sub.ν
;
first processing means for effecting conversion between each sample signal associated with a given delay member and an associated weighted sample signal; and
second processing means for effecting conversion between selected weighted filter signals and selected weighted sample signals;
for all stages ν
, the sampling rate reduction factor M.sub.ν
=2 and the number of individual complex signals appearing on separate lines at the ν
th stage L.sub. =4 are fixed, with only two signals of the L.sub.ν
=4 being utilized;
the frequency multiplex signal for the first stage ν
=1 at the input side is real and the sampling rate at the input of the first stage is cut in half.
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Abstract
The invention relates to a digital filter tree composed of a plurality of digital filter banks arranged in a tree structure one behind the other to branch out in stages with a separation into L.sub.ν individual signals taking place in each stage and the sampling rate being reduced each time by the factor M.sub.ν where ν=1,2, . . . identifies the νth stage. The filter tree employs a prototype filter with half-band functions for channel center frequencies fl =l·B+B/2, with a real frequency multiplex input signal being separated into L.sub.ν complex channel signals for further processing by means of a discrete Fourier transformation. For all stages M.sub.ν =2 and L.sub.ν =4 are fixed, with only two signals of the L.sub.ν =4 being utilized. The arrangement permits adaptation of a hierarchical multi-stage method also to numbers of channels which are not equal to a power of two without changing the input sampling frequency and without the causing channels, whose number is fixed by the difference from the next higher power of two, to idle.
93 Citations
2 Claims
-
1. A frequency multiplex circuit including a plurality of digital filter cells, each including a digital filter bank for effecting conversion between a frequency multiplexed signal and a plurality of weighted filter signals, and a discrete Fourier transformation means connected to the respective filter bank, the cells being connected to one another in successive stages in an outwardly branching tree structure such that, starting with the first stage, the frequency multiplexed signal is separated into L.sub.ν
- individual complex signals appearing on separate lines at the ν
th stage, where ν
=1, 2, . . . , the Fourier transformation means of each cell effecting a discrete Fourier transformation between the weighted filter signals of the cell and the L.sub.ν
individual complex signals, and the sampling rate is reduced at the ν
th stage by M.sub.ν
≦
L.sub.ν
, wherein for all of said cells for each cell of the ν
th stage;the frequency multiplexed signal contains component signals each associated with a respective individual complex signal and having a bandwidth B.sub.ν
;the weighted filter signals have the form ##EQU12## where i.sub.ν
=p·
L.sub.ν
+q,q=0, 1, 2, . . . L.sub.ν
-1, andi.sub.ν
, p, q=(0, 1, 2, 3, . . . )the frequency multiplexed signal is s.sub.ν
(k) and has a sampling rate of fAν
;h(i.sub.ν
) is a coefficient representing a pulse response of a finite length for i.sub.ν
=0, 1, 2 . . . N.sub.ν
-1;the discrete Fourier transformation has the form ##EQU13## where Sl.sbsb.ν
(kM.sub.ν
) represents the individual complex signals andDFT {·
} is the discrete Fourier transformation, M.sub.ν
is a sampling rate reduction factor, M.sub.ν
≦
L.sub.ν
, and the discrete Fourier transformation involves sampling with respect to every M.sub.ν
th value of the weighted filter signals;each component signal of the frequency multiplexed signal is associated with a respective channel having a channel number, l.sub.ν
, and a center channel frequency fl.sbsb.ν
=l.sub.ν
·
B.sub.ν
+B.sub.ν
/2 and l.sub.ν
=0, 1, 2, . . . L.sub.ν
-1,the frequency multiplexed signal is a complex signal, sD (kT.sub.ν
)=srν
(kT.sub.ν
)+jsiν
(kT.sub.ν
) with a real portion Re=srν
(kT.sub.ν
) and an imaginary portion Im=siν
(kT.sub.ν
), and k is a time factor= . . . , -1, 0, +1 . . . ; andeach filter bank in the ν
th stage comprising;
two chains of N.sub.ν
-1 delay members each having a delay of T.sub.ν
+1 and each processing a respective portion of the complex signal, where N.sub.ν
is the number of samples of the frequency multiplexed signal associated with each set of weighted filter signal values output by the filter banks of the ν
th stage and T.sub.ν
=1/fAν
;
sampling means for sampling the signals associated with each delay member at a rate corresponding to the sampling rate of the frequency multiplexed signal reduced by M.sub.ν
;
first processing means for effecting conversion between each sample signal associated with a given delay member and an associated weighted sample signal; and
second processing means for effecting conversion between selected weighted filter signals and selected weighted sample signals;for all stages ν
, the sampling rate reduction factor M.sub.ν
=2 and the number of individual complex signals appearing on separate lines at the ν
th stage L.sub. =4 are fixed, with only two signals of the L.sub.ν
=4 being utilized;the frequency multiplex signal for the first stage ν
=1 at the input side is real and the sampling rate at the input of the first stage is cut in half.
- individual complex signals appearing on separate lines at the ν
-
2. A frequency multiplex circuit including a plurality of digital filter cells, each including a digital filter bank for effecting conversion between a frequency multiplexed signal and a plurality of weighted filter signals, and a discrete Fourier transformation means connected to the respective filter bank, the cells being connected to one another in successive stages in an outwardly branching tree structure such that, starting with the first stage, the frequency multiplexed signal is separated into L.sub.ν
- individual complex signals appearing on separate lines at the ν
th stage, where ν
=1, 2, . . . , the Fourier transformation means of each cell effecting a discrete Fourier transformation between the weighted filter signals of the cell and the L.sub.ν
individual complex signals, and the sampling rate is reduced at the ν
th stage by M.sub.ν
≦
L.sub.ν
, wherein for all of said cells for each cell of the ν
th stage;the frequency multiplexed signal contains component signals each associated with a respective individual complex signal and having a bandwidth B.sub.ν
;the weighted filter signals have the form ##EQU14## where i.sub.ν
=p·
L.sub.ν
+q,q=0, 1, 2, . . . L.sub.ν
-1, andi.sub.ν
, p, q=(0, 1, 2, 3, . . . )the frequency multiplexed signal is s.sub.ν
(k) and has a sampling rate of fAν
;h(i.sub.ν
) is a coefficient representing a pulse response of a finite length for i.sub.ν
=0, 1, 2 . . . N.sub.ν
-1;the discrete Fourier transformation has the form ##EQU15## where sl.sbsb.ν
(kM.sub.ν
) represents the individual complex signals andDFT{·
} is the discrete Fourier transformation, M.sub.ν
is a sampling rate reduction factor, M.sub.ν
≦
L.sub.ν
, and the discrete Fourier transformation involves sampling with respect to every M.sub.ν
th value of the weighted filter signals;each component signal of the frequency multiplexed signal is associated with a respective channel having a channel number, l.sub.ν
, and a center channel frequency
space="preserve" listing-type="equation">f.sub.l.sbsb.ν
=l.sub.ν
·
B.sub.ν
+B.sub.ν
/2 and l.sub.ν
=0, 1, 2, . . . L.sub.ν
-1,the frequency multiplexed signal is a complex signal, sD (kT.sub.ν
)=srν
(kT.sub.ν
)+jsiν
(kT.sub.ν
) with a real portion Re=srν
(kT.sub.ν
) and an imaginary portion Im=siν
(kT.sub.ν
), and k is a time factor= . . . , -1, 0, +1 . . . ; andeach filter bank in the ν
th stage comprising;
two chains of N.sub.ν
-1 delay members each having a delay of T.sub.ν
+1 and each processing a respective portion of the complex signal, where N.sub.ν
is the number of frequency multiplexed signal values associated with each set of weighted filter signal values output by the filter banks of the ν
th stage and T.sub.ν
=1/fAν
;
sampling means for sampling the signals associated with each delay member at a rate corresponding to the sampling rate of the frequency multiplexed signal reduced by M.sub.ν
;
first processing means for effecting conversion between each sample signal associated with a given delay member and an associated weighted sample signal; and
second processing means for effecting conversion between selected weighted filter signals and selected weighted sample signals;
wherein for all stages ν
the sampling rate reduction factor M.sub.ν
=2 and the number of individual complex signals appearing on separate lines at the ν
th stage L.sub.ν
=4 are fixed,the first stage (ν
=1) forms a true four-branch system having four output signals s0 (2kT1), s1 (2kT1), s2 (2kT1), s3 (2kT1), are each fed to the subsequent stage, andonly two output signals of each of the cells of the next following stages are input to subsequent stages; and the circuit further comprising a prefilter having an output coupled to the first stage (ν
=1) for producing the complex input signal sD to the first stage by sampling at the rate 2fA1 from a real frequency multiplex input signal SD (kT0), andmeans for spectrally offsetting the two partial spectra of s1 and s3 output by the first stage, which do not come to lie directly in the band 0 to fA1 /4.
- individual complex signals appearing on separate lines at the ν
Specification
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Current AssigneeANT Nachrichtentechnik GmbH Patentabteilung
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Original AssigneeAnt Nachrichtentechnik GmbH
-
InventorsGockler, Heinz
-
Primary Examiner(s)Griffin, Robert L.
-
Assistant Examiner(s)Chin, Wellington
-
Application NumberUS07/246,692Time in Patent Office266 DaysField of Search370/50, 370/70, 370/19, 370/23, 370/123US Class Current370/210CPC Class CodesH03H 17/0213 Frequency domain filters us...H03H 17/0266 Filter banksH03H 17/0292 Time multiplexed filters; T...
