CA1179780A

CA1179780A - Information and process control enhancement system

Info

Publication number: CA1179780A
Application number: CA000224059A
Authority: CA
Inventors: Richard L. Richardson; Bernard P. Hildebrand; Robert E. Mahan
Original assignee: Battelle Memorial Institute Inc
Current assignee: Battelle Memorial Institute Inc
Priority date: 1974-04-19
Filing date: 1975-04-08
Publication date: 1984-12-18
Also published as: GB1515122A; US3925646A; JPS5115940A; DE2517360A1

Abstract

INFORMATION AND PROCESS CONTROL ENHANCEMENT SYSTEM
Abstract An input signal is spectrally decomposed into a plurality of square waves each defined as a given Walsh func-tion, while a second signal, representative of a desired or undesired element in the first signal is similarly transformed to provide a second combination of square waves, each defining a Walsh function. The reciprocal of the last mentioned com-bination is obtained for multiplication with the first series of square waves for providing a filtered version of the ori-ginal input signal.

Description

~ :~ 7 9 .~

INFORMATION AND PROCESS CONTROL ENHANCEMENT SYSTEM

Linear and nonlinear processing or filtering of an input signal having one or rnore dimensions is faci:Litated by spectral decomposition thereof, while computing devices are suitably employed to process the various spectral compon-cnts. Processing of complex inputs, e.g., two dimcll.siollal imagcs, was formerly considered impractical because of the long operatilly times required, but has now bcell ma~c possible by the rediscovery of the Fast Fourier Transform algoritllm.
However, it would be preferable for the sake of speed and simplicity in the realm of computers to work entirely with binary functions rather than continuous functions.
A class of filtering which may be termed in-verse filtering involves recovery of an input signal in the presence of signal degradation, multiplicative noise, and the like. In a Fourier Transform system, an original input signal is theoretically restored by multiplying its Fourierspectrum point by point with a transfer function comprising the reciprocal of the Fourier Transform of the degradinc mechanism. This process fails in practice because it involves the inversion of zeros, ~ complete set of binary functions called Walsh functions would be well suited to relatively simple computer operation inasmuch as a Walsh function comprises a square wave having but two amplitude val.ues. ~lowever~
inverse filtering for ~alsh functions has notbeen considered possible because of a lack of a convolution theorem equivalentto the Fourier convolution theor-em, ~s a result, only relatively complex Fourier anal.ysis ancl approximation !
or combinations of ~alsh and Fourier analysis, have been considered practical in this area.
In accordance with the present invention, an input signal to be processed is converted to a form comprising a series of square wave spectral components which advantageously take -the form of Walsh functions. The conver-ted input is then multiplied in a multiplier circuit by the reciprocal of a second series of square waves -to produce an output. This output may comprise a filtered or restored version of the input, unity when the first and second series of square waves are the same, or other desired result.
In particul.ar, the reciprocal series of a series of Walsh functions representing the i.nformation to be filtered out is produced by an operation equivalent to solving a se-t of simultaneous equations for coefficients of the ~ ~.7(~7~

reciprocal series, the equations resulting from dyadically combined ~alsh functions. The set of equations is in effect obtained from the multiplication of the proposed reciprocal Walsh series by the terms of the Walsh series representing the information to be filtered out, wherein the product in-cludes Walsh functions identified by dyadic addition on series ~alsh function subscripts. The resulting reciprocal Walsh series is then readily combined with a Walsh series represent-ing the input. The whole filtering operation is simply and rapidly carried out employing binary apparatus.
It is accordingly an object of the present invention to provide an improved system for filtering or enhancing input information by spectral decomposition into square wave compon-ents and combination with other square wave components repre-sentative of noise or system degradation for the purpose of restoring the input.
It is another object of the present invention to provide a system for combining a square wave spectral decom-position of an input signal with the reciprocal of a square wave spectral decomposition of another signal.
It is another object of the present invention to provide computing apparatus which can operate in real-time for digitally accomplishing filtering of input signals hav-ing multiplied noise or the equivalent th,ereof.
It is a further object of the present invention to provide an improved control system employing computing appa-ratus which can operate on a real-time basis for producing a control function ln response to the square wave spectral decomposition of a desired performance signal and a signal representative of resulting system operation.

.

.. 9 7 ~ ~

Thus, in accordance with a broad aspect of the invention, there is provided apparatus Eor signal enhancement comprising: means for spectrally decomposing at least a portion oE an input signal into a series expansion of Walsh function representations, said spectrally decomposing means including an analog-to-digital converter for sampling said input signal and for digit-izing the samples produced, said spectrally decornposing means Eurther includ~
ing a Walsh transform converte:r for receiving sai.d digitized samples and pro~
viding an array of Walsh coefficients constituting the amplitudes of Walsh func-tions together representing sai.d poxtion of said input signal; second rneans for spectrally decomposing at least a portion of a second inpu-t function into a second series expansion of Walsh function representations, said second spectrally decomposing means including a Walsh transform converter for p:ro-viding an array of Walsh coefficients constituting the amplitudes of Walsh functions together representing said portion of said second input function means for generating the reciprocal of one of said Walsh function series expan~
sions in the form of coefficients of a recipxocal Walsh series expansion; and a multiplier for multiplying said reciprocal with the other of said Walsh func tion representations.

- 3a -~ ~7g7~0 The subject matter which we regard as our invention is particularly pointed out and distinctly claimed in the con-cluding portion of this specification. The invention, however, both as to organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference charac-ters refer to like elements.

Fig. 1 is a chart of Walsh functions;
Fig. 2 is a block diagram of a first system accord-ing to the present invention;
Fig. 3 is a block diagram of a second system accord-ing to the present invention;
Fig. 4 is a block diagram of a control system accord-ing to the present invention;
Fig. 5 is a block diagram illustrating a portion of the aforesaid systems in greater detail for providing Walsh function coefficient outputs;
E~ig. 6 is a block diagram illustrating the Fig. 5 apparatus in further detail and employing four input samples;
Fig. 7 is a block diagram of a generalized version of the Fig. 6 apparatus for greater than four samples;
Fig. ~ is a block diagram of an inverse Walsh trans-form converter utilized in systems of the present invention;
Fig. 9 is a block diagram of a multiplier circuit as employed according to the present invention;

Fig. 10 is a block diagram of a reciprocal Walsh transform converter employed according to the present inven-tion; and 1 ~ 7978~

Fig. 11 is a flow diagram of a program routine which alternatively may be employed according to the present inven-tion, for solving simultaneous equations.

Theoretical Background and Definitions The present system advantageously transforms input waveforms, or waveforms of information to be removed therefrom, into square wave components in the form of Walsh functions, rather than into sine wave components as in the case of Fourier Transformation. A series of harmonically related square waves known as Rademacher functions exist wherein a single square wave cycle is expressed as Ro~ two cycles as Rl, three cycles as R2, etc. I~owever, not every waveform can be simulated by a series of Rademacher functions.
Walsh functions comprise a series~of square waves of increasing "sequency" or axis crossings, which may be employed to simulate substantially any arbitrary waveform.
The first few Walsh functions as defined herein are illus-trated in Fig. 1.
Let Rk(x) denote the Rademacher functions and Wn~x) denote the Walsh functions for O<x<l, k=0,1,2,...

~ 1 if m is even~
Definition 1: Rk(x) -1 if m is odd m/2k~l ~ x ~ ~m + 1)/2k~1 m = 0,1,2, .... , 2k _ 1 .

Thus we first let k assume a givcn valuc, i.e. for the kth Rademacher function, and we then let m take on the various values, 0, 1, 2, etc., so long as x is greater than ~ero and less than or equal to 1. For example, the Rademachcr 7 ~3 ~Si ~ () function, Ro~ will have the value +l for 0 less than x less than or equal to 1~2, and will have the value -1 for 1/2 less than x less than or equal to 1. Walsh functions can be con-sidered as being made up of Rademacher functions.

nk Definition 2: Wn(x) = nk_o[Rk(x)]

n = ~ nk2k , nk~0,1}
k=0 The Walsh function Wn(x) thus equals a produet of Rademacher functions, as follows:
WO (x) = 1 Wl~x) = Ro(x) W2 (~C) = Rl (X) W3(x) = Ro(x)Rl(x) ete.
In definition 2 above, n is defined as a binary number, while nk, beinq in the set of 0,1, is a binary digit corresponding to the kth Rademacher function. The definition will indieate that if the subseript for the given Walsh function is taken in binary notation, then the digits thereof will indieate the mul-tiplicative presenee of certain Rademacher functions therein.
Therefore, ~3(X) = Wll(x) wherein the subscript is given in binary notation, and is indicative of the fact that such third Walsh function is provided by the product of the first and second Rademacher functions, Ro and Rl. Thus, starting at the lowest order digit in the subscript, the first and second digits are present.

In addition to the above definitions, the operation (~) in the dyadic group is used to evaluate the Walsh function equivalent to the product of two Walsh functions.

Definition 3: For integers m and n, m = ~ mk2 k-o n = ~ nk2 k=o mk~n],~O,l}

m ~ n = (mk ~ nk) 2 if mk = nk ~
~ 1 if mk ~ nk J

According to definition 3 if m and n are binary numbers, i,e,, with their digits in the set 0, 1, then the dyadic sum, m~n, equals their binary sum without carries. Thus, in such a system, 7~12=11, An exclusive or operation is performed on each of the binary representations, digit by digit.
Thus, 111 A property of the dyadic group useful in the sequel is: if A ~ B = C then A = B ~ C and B = A ~ C for binary integers A, B and C, Thus~ not only does 7 ~ 12 = 11, but 12 ~ 11 = 7, and 7 ~ 11 = 12, table of dyadic addition is given as follows:

~.

O . ~ 4 5 6 7 8 910 1112 13 14 15 1 1 _3__2_ 5 4 7 6 9 8 11 1013 12 15 14

2 2 3 0 1 6 7 4 5 10 11 8 914 15 12 13

3 3 2 1 0 7 6 5 4 11 10 9 8151.4 13 12 . _ _____ __

4 4 5 6 7 1 0 1 2 3 1.213 14 15 8 9 10 1l

5 5 4 7 6 1 1 0 3 2 13 12 1.514 9 ~ 11 10

6 6 7 4 5 1 2 3 0 1 14 15 1.2] 31011 8 9

7 7 6 5 4 1 3 2 1o 15 _14 _ 13__12 _ 11__~0 __9__ 8

8 8 910 11 12 1314 15 1 0 1 2 3 4 5 6 7

9 9 811 10 13 1215 14 1 1 0 3 2 5 4 7 6 1010 11 8 9 14 1512 13 ~ 2 3 0 1 6 7 4 5 1111 10 9 8 15 1413 12 ~ 3 2 1 0 7 6 5 4 1414 151.2 13 10 11 8 9 1 6 7 4 5 2 3 0 1515 1413 12 11 10 9 8 ~ 7 6 5 4 3 2 1 0 Table I - Dyadic Addi tion 7 ~ ~

The following theoremr proven by N.J. Fine~ ~On the ~alsh Functions", Transactions American Math Soc,, Volume 65~ pages 372~415, 1949, is useful in obtaining the product of two Walsh functions.
Theorem 1: Wm(x)wn(x) = Wm~n( Thus, there is a one-to-one correspondence between product opera~
tions on Walsh functions and dyadic addition of subscripts.
The definitions 1 and 2 yield a set of orthonormal (Walsh) func-tions that take on either the value (~1) or the value (-1) for each x~(0~1], Consequently, each Walsh function is identical with its reciprocal. How ever, this is true of the individual Walsh functions and not of a series of Walsh functions, Now we wish to spectrally decompose an input signal as well as information to be removed therefrom into respective series expansions of Walsh functions. Then, we wish to obtain the reciprocal of one series~
in order to obtain a useful means of eliminating undesired features from the other series.
If a linear com~ination of Walsh functions for which we desire the reciprocal equals the summation from j=0 to N of ajWj(x), then we can express its reciprocal series as follows:

~ akWk(x) = - ' (1) k=0 ~ ~jWj(x) {ak}, and M to be evaluated.

.. ..

7 ~

Removing the divisor and using Theorem l, k-0 j-0 k j k~j (2) The property of elements in the dyadic group mentioned in defin-ition 3 is used to eliminate the index j, leaving the index k in ascending order and arranging the index k~j in ascending order.
Let Q=k~j, then j=Q~k and max (k~j) M
Q- Q( k-0 ak~k~ l , The latter summation, from k=0 to M of ak~k~Q, represents the coefficient sum of terms for each Walsh function in the series, Linear independence of the Walsh function yields the set of equations:
M

k-0 k k~Q ~Q,0 ; Q = 0,1,2, ... , max (k~j) (3) ~Q 0 is the Kronecker delta equalling 1 if Q equals 0 but is otherwise 0, For a given value of Q, the summation is performed to provide an equation, Then the value of Q is changed and the summation repeated to yield a second equation, etc.
Expression (3) provides an evaluation of the {ak} if ~ l=2P, an integer. Adding ~k~Q= for lc~Q~N assures a square coeEEicient matrix yielding a unique solution set {ak} provided the deterrninant ¦~k~Q¦ ~ n;
i,.e., the given Walsh series ~ ~jWj(x) ~ 0, for all x~.(0,1l. Symbolically,

- 10 -3 ~7~ 7~3 2P-l k-O k k~Q ~Q,O ; Q = 0,1,2, ,.. , 2P--1 . (4) If ~,~ES where S is the set of Walsh function indices in the divi-sor series, then either S contains ~ or S must be enlarged to contain for every pair (~,~) of indices in S. We say S is complete if it con-tains all the elements (~ S. If we do not have a cornplete dyadi.c group of Walsh functions, then we may include further terms for completing the group. For example, if in expression (1), M=N=2, the complete dyadic group is not present according to the above criteria, With no loss or generality, we may then include the terrns ~3W3(x) and a3W3tx) in the given func-tions and evaluate the {ai} in terms of the {~i} Equations (1), (2), (3) and (4) in this discussion are evaluated with 2~=N=3, as follows:

~ a W (x) = 1 , {a.} unknown . (5) k O K k 3 Cl.~, (X) j=O

Clearing fractions, k o j-o k j k~j (6) Let Q= j~k, then j=Q-~k and max (k-~j)= 3:

Q~O Q k-O k k-~Q 1 . (7) ~ ~ ~ 9 7 ~ ~) Linear independence of the WQ(x) assures that ~_0 k k+Q ~Q,0 , Q = 0,1,2,3, (8) Expression (7) may be expanded as follows:

W0 (aO~0 + al~l + a2~2 3 3 Wl (aOC~l + al~O -~ a2~3 ~~ a3~2) +
W (a ~ + a ~ -~ a ~ + a ~ ) +

W3 (aO~3 + a3~0 + al~2 + a2~,1) = 1 The equations defined by expression (8) m,ay be written as follows:

alC~ a2(X2 + a3C~3 = 1 10 aO~l + altXO + a2~3 + a3C~2 aOo~2 + alC~3 + a2Lo + a3C~1 =
aO~3 -~ al~2 t a2~1 3 The sum of the coefficients for W0 are thus set equal to 1 and the sum of the coefficients for Wl, W2, and W3 are each set equal to zero, as a~rees, for example, with the Figure 1 representation of Walsh f~mctions. Then these equations are solved simultaneously for the values for the {ak}, :Eor -the desired reciprocal series.
If A = ¦~k+Q¦ ~ 0, Cramer's rule yields val.ues for the {ak}~

ak = Co:Eactor of element (k,l) in ~ dlvided by ~. (9) t g ~

C~0 C~ 3 (X2 ~ 2 C~ 3 ~ 2 C~ 3 Cl l a2 (~ 3 The numbers are 1 ~3aO~1 -1 ~3~0~1 ~0~3~2 1 ~0~3~2 ~2~ 2~1~0 1 ~2~1~0 1 a3~0~1 for k = O,1,2, and 3, respectively.
If x is sufficiently small, equation (5) will take on the value Cl .
j=O

Thus, given the coefficients of the Walsh series expansion of the function f(x), the algorithm described above provides the coefficients of the Walsh series expansion of the reciprocal g(x)=l/f(x) by a simple, fast equation solving routine. The algorithm holds even for g(x) non square integrable The algorithm addresses itself to what has been considered a form-idable problem, since the process of obtaining a series expansion for the reciprocal of a periodic function normally encounters difficulties when the function takes on the value O. However, when the function is expressed in ~alsh series and the algorithm is applied, singularities of the type present, for example, in x/sin x and l/x are automatically taken care of without elaborate programming.
Figure 2 illustrates a system to provide inverse filtering for the elimination of multiplied noise, signal degradation, or the like. ~n input signal S(t) is desired, but is contaminated with a noise factor N(t) The ~ 1~9~80 present system provides an enhanced output by '1divIding out" the undesired factor. It is assumed that the noise or degraaing factor can be character~
ized or estimated as a signal N(t) which signal is used as an additional input in the filtering process to remove N(t), The contaminated signal in Figure 2 is indicated as S(t)'N(t).
This analog signal is applied to analog to digital converter 10 having input means which samples the analog signal to provide a time series of analog samples. The analog to digital converter converts the samples to a digital array of numbers, with each number comprising the digitized amplitude value of a sample. Sampling and conversion are repeated on a cyclical basis to provide successive digital arrays during successive intervals of time on a "real time" basis. Walsh transform converter 14 then provides the fast Walsh transform corresponding to each successive interval, The actual output of converter 14 comprises an array of numbers representing amplitude coefficients of various Walsh functions of the Walsh series into which the original input may be spectrally decomposed. Converter 14 is further illus~
trated in Figures 5 and 6, and will subsequently be described in connection therewith, The noise estimate, N(t), is also coupled to an analog to digital converter 16 which samples the analog estimate, and converts the same to a second digital array, and Walsh transform converter 18 provides the fast Walsh transform corresponding to each successive interval of time, It will be understood Walsh transform converter 18 is suitably substantially identical to Walsh transform converter 14 hereinafter described. The output from Walsh transform converter ]8 is coupled to reciprocal Walsh trAnsform con-9 ~

verter 20, also hereinafter described, which effectively provides an output array corresponding to the reciprocal series of the series representing the noise estimate, N(t). Then this reciprocal array is multiplied by the transform of the con-taminated signal in multiplier 22 whereby to provide, for each interval, an array of nurnbers representing the Walsh transform of the desired signal, S(t). The multiplication in multiplier 22 suitably follows Theorem 1 as hereinbefore described, i.e. the multip:Lication is carried out employing dyadic addition. The output of multipl:ier 22 comprises the amplitude coefficients of a nurnber of square wave Walsh functions, which, when combined, would result in the desired waveform. The multiplication process wi-th the reciprocal in mul-tiplier 22 essentially "divides out" the undesired factor. The multiplier output is coupled to inverse transform converter 2~ which then drives digital to analog converter 26, the output of which is the desired analog signal, S(t), in continuous form, or a sig~
nal which is an enhanced analog replica of the original noisy input signal, While the apparatus is efficacious in removing multiplicative noise, expon~
entiation irnmediately following A to D converters 10 and 16 andalogari-thmic converter just prior to D to A converter 26 will proviae a system which filters added noise if such operation is desired In many instances it may be more suitable -to provide an estimate or model of the desired input signal rather than an estimate o:E the noise, For example, in radar systems and the like, one will know the characteristics of -the desired radar return. The sys-tern of F:igure 3 receives an i.n~)ut sig-nal contaminated wi-th noise, S(t) N(t), and there is a:Lso provided an estim-ate, S(t) oE the desired inpu-t signal. Arrow 2~ indicates the siqnal es-tim-~ ~ 7 ~

ate, S(t), is movable or adjustable in the time of periodic occurrence.
~ arious components of the Figure 3 system are referred to employing primed reference numerals, wherein the elements may be substantially identical to elements in Figure 2 identified by corresponding unprimed reference numer-als. However, an addi-tional reciprocal Walsh func-tion converter 30 is emp-loyed in the Figure 3 system for receivi.ng the output of multiplier 22'~
and an additional multiplier 32 combines the output of conver-ter 30 with the output of Walsh trans:i~orm converter 14', the product being applied -to in-verse Walsh transform converter 24'.
The Figure 3 system operates in the rnanner similar to that descrs ibed in connection with Figure 2 in that the contaminated signal, S(t)-N(t) is applied to analog to digi-tal converter 10' which provides digital values corresponding to successive analog samples of the input during a time inter val. Walsh transform converter 14' then supplies an array of Walsh coeffi-cients representing the amplitudes of the Walsh functions into which the in-put is converted. Instead of receiving a model or estimate of the noise, A to D converter 16' receives a model or estimate, S(t), of the input sig~
nal which is shiftable in time, and provides a plurality of digital represen-tations of those samples as an input to Walsh transform converter 18', Converter 18', in turn, generates an array of coefficients of Walsh functions representative of model., S(t), and this array is applied to reciprocal Walsh converter 20' wherein Walsh coefficients are provided representincl a reciprocal Walsh se:ries. The Walsh array from converter 14' :is mLIlt;l~l.ied by the Walsh array from conve:rter 20' in multil-)lier 22', but it will be r~

realized that the signal is divided out this time, rather than the noise.
Thus ! the output of multiplier 22' comprises an array of Walsh function coefficients which characterize the undesired noise or degrading factor.
Such output is applied to a second reciprocal Walsh transform converter 30, which may be substantially similar to converter 20', wherein coefficients of a Walsh series representing a reciprocal of a series representing the noise are generated. Thus, the output of converter 30 may be viewed as represent-ative of l/N, and is combined in multiplier 32, i.e. by means oE dyadic addition, with -the output of Walsh transform converter 14' to provide an array of coefficients of Walsh functions representing the desired outputr S(t), As before, inverse transform converter 24' is employed to produce samples for an enhanced continuous analog replica of the original input, Since these samples are digital in form, they are applied to D to A converter 26' from which an enhanced output is secured.
In operation, the ~(t) is cyclically generated at the same repetition rate as the desired signal, but the phase thereof relative to the desired signal is adjustable so that it may be made to correspond in time with rep-etitions of the desired signal as received, A further system according to the present inv~ntion is illustrated in Figure 4 and comprises a feedback control system. In the classical system a portion of the output is subtracted from the input and the result is used to drive the system. The conventional system thus seeks a null condition, In the present system, a reciprocal of the output is obtained and multiplied with the input to obtain the driving signal, Thus, the system seeks a constant. In Figure 4, reference signal generator 12 suitably comprises an 3 ~ ~ ~

oscillator or other signal source having a frequency which is to be determin-ative in this case of the speed of operation of DC motor 36. In a particular instance, signal generator 12 was an oscillator producing a sinusoidal signal which was sampled at the rate of eight samples per cycle at the input of ana-log to digital converter 38, A to D converter 38 digitizes the samples and provides the input for Walsh transform converter 40 wherein Walsh coefficients are generated for Walsh functions which together represent the reference signal, A tachometer 42 cornprising an alternator is driven by -the shaf-t of motor 36 and supplies an AC output to analog to digi-tal converter 44 wherein the output of tachometer 42 is sampled at a rate suitably the same as tha-t accomplished by A to D converter 38, ~ere again the samples are digiti~ed and coupled to a Walsh transform converter 46 which generates coefficients of Walsh functions representing the tachometer output. The array of coeffic-ients is coupled to reciprocal Walsh function converter 48 wherein coeffic-ients are produced for a series of Walsh functions which would comprise the reciprocal of the series represented from converter 46, and the output of converter 48 is multiplied by means of dyadic addition in multlplier 50 with the output of converter 40. The output of multiplier 50 will be unity providing the outputs of converters 40 and 48 are the same, indicative of motor operation at the desired speed. So long as the OUpilt frequency of the reference signal generator 12 remains constant, -the motor speed remains constant. A change in ou-tput speed or inpu-t signal resul-ts in a change in drive signal to restore the system to equilibrium, The change in drive sig-nal is rather large.

3, ~ ~

The output of multiplier 50 is applied to digital to analog conver~
ter 52 which may also include an inverse Walsh transform converter, ~owever, since the output sought from multiplier is unity, the circuitry in element 52 may be simplified and may comprise a summing amplifier receiving the Walsh coefficient outputs from multiplier 50. The converter 52 drives ampliEier device 54 which contains circuitry for supplying current to field winding 56 associated with motor 36. The current is changed in the field winding in a direction for restorincj system equilibriuml Considering Figure 5, a more detailed description will be given relative to the means for changing an input signal into a representation com-prising the coefficients of a series of Walsh functions. Input signals are sampled and the samples are converted to digital values in A to ~ conver-ter lO. ~hese digitized samples for a given interval are stored in the short term accumulating storage array 34, which may be considered a part of either A to D converter 10 or Walsh transform converter 14 The size of the storage array depends on the number of coefficients to be resolved, and also -the size of the Walsh transform converter array will. depend upon the nurnber of coeffic-ients desired. In converter 14 the transformation is produced by means of the Hadamard matrix, the matrix multiplication being more fully illustrated in the circuit of Figure 6.
Referring to Figure 6, control unit 36 causes the ~ to D converter 10 to sample at appropriate -times~ and consecutive samples are consccut:ively stored in the storage array 3~ having registers n~lmbc:red C)~ C )~ @j and . Altl~ough the illustrative circuit stores Eour ~amples pcr cycle( it ~ ~9~s~

will be understood that this number is by way of example only and a greater number can be employed for greater accuracy.
As soon as the four digital values are stored by storage array 34, the outputs of the individual registers are coupled to the Walsh transform converter 14 which here comprises a group of four dual adders that can per-form full carry addition and subtraction. In first level adders 37 and 39~
the sums and differences of 1 and 2, and of 3 and 4 are formed~ wherein the numbers correspond to samples from similarly numbered registers in array 34.
The partial results are coupled to the second leve] adders 41 and 43 where indica-ted sums and differences are again formed. The outputs of the second level adders are Walsh series coefficients of the input signal. Thus, the coefficient of Walsh function W0, i.e, ~0, equals (1+2+3+~)~ the coefficient of Walsh function Wl, i.e. ~1~ equals (1+2-3-4), the coefficient for Walsh function W2, i.e, ~2~ equals (1-2+3-~, and the coefficient of the Walsh func-tion W3, i.e. ~3, equals (1-2-3+4), mhe Hadamard matrix utili~ed by this particular four sample circuit will be seen to be as follows:

1 1 ~

The circuit is e~tended to larger arrays as illustrated in Figure 7. In Figure 7, s-torage array 34 comprises re~isters Ro ~hrou~lh ~, and Wals~h transform converter 14 comprises ~ ~ 7~780 an array of dual adders eo~prising Adder 0,0 through Adder N/2,N/2. For sixteen input signal samples, sixteen registers are required for array 34, and an 8 by 8 array of dual adders for Walsh transform converter 1~ for Hadamard transformation as will be understood by those skilled in the art. In the Fig. 7 circuit it is understood that a eontrol unit will be employed to bring about operation of A to D eonverter 10 in the manner hereinbefore deseribed, storage of digiti2ed sam-ples in array 34, and suecessive adding operations by the levels of adders from left to riqht in converter 14. Output identified c~0 through aN in Fig. 7 comprises the coeffieients for the Walsh functions W0 through WN in the Walsh series into whieh the input is being converted.
It is understood that the eireuit of Fig. 6 or the circuit of Fig. 7 may be employed to provide Walsh transform coefficients in the hereinbefore described embodiments. How-ever, the four-coefficient output of the Fig. 6 circuit will be referenced in the following discussion of circuitry.
Referring to Pig. 9, a eircuit is illustrated for implementing the multipliers indicated at 22, 22', 32 and 50 in Figs. 2 through 4. For the sake of identifying inputs and outputs in the following description, the Fig. 9 circuit will be considered as implementing the multiplier numbered 22 in the Fig. 1 embodiment. A series of,Walsh function coefficients aO...3 from Walsh transform converter 14 is stored in register 78 in Fig. 9 for multiplication with a series of Walsh function coefficients provided by reciproeal Walsh transform eonverter 20. The latter series of coeffi-cients is clesignated aO...a3 and is stored in register 80.

7 ~ ~
Selected of the coefficient values from registers 78 and 80 will be provided to a bank of 16 multipliers, Ml...M16, four of which are illustrated at 82, 84, 86 znd 88 in Fig. 9. The bank of multipliers provides inputs to a first level of eight adders, four of which are illustrated at 90, 92, 9~ and 96. In turn, the first level adders drive a second level of four adders represented by the adders desig-nated 98 and lO0. The product output produced comprises an array of four coefficients, C0, Cl, C2 and C3, wherein each of these coefficients is generated by one of the second level adders. The multipliers Ml...M16, the first level adders and the second level adders are successively actuated during a given cycle for producing these product coefficients. The particular manner of interconnection of these elements in the Fig. 9 circuit will become more apparent from the following discussion.
According to Theorem 1, the product M N M N
i-o i ij 1O jW~ aiajWi~j Let Q=i~j , then j=i~ , and M N max(i~j) N
~ aiWi ~ ajWj = ~ WQ ~ aiai~
i=0 j-0 Q=0 i-0 For M=3, N=3, max ti~ 3, iWi ~ ~jWj = ~ WQ ~ aiai~Q
i=0 j=0 Q=0 i=0 1 ~ 79780 Therefore, each Walsh function W~ in the product has a coef-ficient which we may indicate C~ =

~ ai~
i=O

. ~oaii~o ' ao~o+alal+a22+a3a3 1 ~

Cl = ~ ai~ ao~l~alaO~a23~a32 i=O

C2 = ~ aiai~2 = aOa2+al3+a2o+a3 1;0 C3 = ~ ai~i~3 = aoa3+al~2+a21+a3aO
i=O

Referring again to Fig. 9, multiplier 82 is employed to multiply the coefficients aO and ~0, while multiplier 84 multiplies the coefficients al and 1' Adder 90 provides the sum of these two multiplications, while adder 92 is employed in a similar manner for summing the products a22 and a3~3.
Adder 98 then provides the complete sum which is equal to C0.
Multiplier 86 in Fig. 9 provides the product a2al, while multiplier 88 multiplies a3 and 0. These two products, which are seen to be the last two terms in the solution for C3, are added in adder 96. Adder 100 receives as one input thereof the sum output from adder 96 and as the other input th~reof the sum output from adder 94 comprising the addition of the remaining terms in C3. Thus, adder 100 provides the final total equaling C3. The remaining indicated elements of the Fig. 9 circuit perform the successive multiplications and additions specified by the foregoing expressions for Co~C3 in a straightforward manner following the illustrated pattern.

~ :~ 7 '~

A circuit for inverse Walsh transform converter 24 (or 24') is illustrated in Fig. 8. The product coefficients, C0, Cl, C2 and C3, are stored respectively in registers 60, 62, 64 and 66. The first level adders 68 and 70 form the quantities C0+Cl~ C0-Cl~ C2~C3 and C2-C3. The second level adders 42 and 44 form the quantities Co+Cl+C2~C3-4f~to), C0+Cl C2 C3 ~f(tl), Co~Cl+C2~C3=4f(t2) and Co-cl-c2+c3=4f~t3)~
Operation of the registers for storing, operation of the first level adders, and operation of the second level adders in sequential order are controlled by unit 76. It will be seen that the inverse transformation takes place in substantially the same manner as the original forward Walsh transformation as illustrated, for example, according to the Fig. 6 circuit.
The outputs from second level adders 72 and 74 are larger than the required output values by a scale factor of 4, but this scale factor can be taken into consideration in the digital to analog converter 26 ~or 26') which receives digital outputs 4f(to)~ 4f(tl), 4f(t2) and 4f(t3) for conver-sion into continuous analog form.
Fig. 10 illustrates circuitry for the reciprocal Walsh transform converter 20, 20', or 48. Particularly con-sidering the Fig. 1 embodiment, Walsh transform converter 18 produces an additional set of Walsh function coefficients a0~ 2~ ~3 in the manner exemplified by the Fig. 6 cir-cuit. For a given cyc~le of operation, these four coefficients are separately stored in an input register 102 where they are available to the remainder of the Fig. 10 circuit via the switching network 104 operated under the control of control unit 114. Successive multiplications, additions, subtractions and divisions are performed as hereinafter described employing 1 ~797~
multiplier 108, adder/subtractor 110 and divider 112, with intermediate results being held in storage unit 106.
As hereinbefore described, the coefficients, ak, of a reciprocal series are obtained by simultaneous solution of equations defined by (4). In the case of the particular four term example, the four equations are given by expression ~8):

ak~k+Q = ~Q o ~ Q = 0,1,2,3.

~mploying Cramer's rule to solve the equations as indicated by expression (9), ak = 1 Cofactor (k,l). In the example, A =

aO 1 2 3 2 3 o 1 Also, ~ can be expressed as ~ k Cofactor (k,l) (11) k=0 Cofactor (k,l) =

. k +2i~k~i-ki~ i , k 0,1,2,3 (12) where ~ indicates product.

~ ~79~

If k=0, the Cofactor (k,l) =

aO 3 ~2 3 ~0 1 a2 al O

= 3 + 212a3 ~ O(al +~2 + 3 (13) a 3~2al23 - aO (al +a2 +~3 ) Then, aO = 3 (14) ~ k Cofactor (k,l) k=0 For the solution to the other coefficients, al, a2 and a3, the numerator of expression (14) is changed according to expression (12) for the particular k.
Returning to Fig. 10, the circuit solves for the {ak~ in the manner just described. The circuit first solves for and outputs the value of aO by implementing equation (14).
As indicated above, the numerator of expression (14) is the Cofactor for k=0, as given by expression (12). The following operations are consecutively performed by the Fig. 10 circuit under the control of control unit 114:
(a) Switching network 104 places the 0 value from register 102 on both output lines of network 104 leading to multiplier 108, multiplier 108 is operated by control unit 114, and the result, o2~ is coupled to temporary storage unit 106 by the switching network.
(b) The values of al2, 22 and a32 are similarly obtained and stored in unit 106.

g7~0 (c) The switching network couples ~o2 from storage unit 106 to one input lead of multiplier 108 while the value of aO from register 102 is coupled to the other multiplier input lead and the multiplier is operated to provide the value of aO3. The latter is stored in storage unit 106. As will be noted, the values of al3, 23 and a33 can be obtalned and stored in a ~imilar manner.
(d) The values a22 and a32 are directed by switch-ing network 104 from storage unit 106 to adder/subtractor 110 where the sum 22+a32 is formed under the control of control unit 114 and rerouted by the switching network to storage unit 106. Then switching network 104 routes the sum, ~22+32, and al2 from storage unit 106, to adder/subtractor 110 where the sum of the three is obtained for return to storage unit 106.
(e~ The sum, al2+22+a32 from register 106, is routed by the switching network to multiplier 108 via one input lead thereof, while aO is routed on the other input lead and the multiplier is operated by the control unit to provide the product ~0(~l2+~22+a32) for storage in storage unit 106.

(f) The results from step (e) and the value of aO3 from storage unit 106 are routed by the switching network to adder/subtractor 110 where a subtraction is performed yielding a03-ao(al2+22+a32) for re-entry. into storage unit 106.
(~) The switching network directs a2 and a3 to multiplier 10~ where the product is obtained for storage in storage unit 106. Then this result is redirected to multi-plier 10~ in conjunction with al for multiplication. The ~ 17978~

latter product is left-shifted by one binary bit to provide 2~1~2~3 which is returned to storage unit 106.
(h) The results of step (f) and step (g) are directed by the switching network to adder/subtractor 110, where the sum is formed for storage in unit 106. This sum comprises the numerator of expression (14), i.e. the Cofactor as defined by expression (13).
(i) The above steps are repeated, so far as inter-mediate values therefor are not already stored in storage unit 106, for the other three Cofactors as defined by expres-sion (12) for k=1,2,3, and the results are also stored in storage unit 106.
(j) The values of aO~ C2 and ~3 are consecu-tively directed by switching network 104 to multiplier 108 while at the same time corresponding Cofactors from storage unit 106 are consecutively provided as the other input to multiplier 108. The multiplier is actuated for consecutively supplying the products ~k Cofactor (k,l) for k=0,1,2,3.
These products are stored in storage unit 106.
(k) The four results of step (j) are added toge-ther. Since four terms are involved, a first pair and then a second pair are coupled from storage unit 106 to adder~
subtractor 110 for addition, after which the sums are stored in unit 106. The sums of the pairs are then inputted from the storage unit to the adder/subtractor where they are added together to provide the denominator of expression (14), i.e.
as defined by expression (11). The resultant is stored in storage unit 106.
(1) The result of step (h) is routed by the con-trol unit from storage unit 106 to divider 112, while the result of step (k) iq similarly directed to divider 112 where the former is divided by the latter to provide the solution for aO according to equation tl~) This digital value is outputted to register 80 in Fig. 9.
(m) The values of the Cofactors obtained in step tj) are also consecutively divided by ~ in divider 112 and the digital outputs produced are likewise coupled to register 80 in Fig. 9. This completes generation of the array of coefficients representative of the reciprocal series desired.
It should be noted the foregoing operations as performed by the various components of the Fig. 10 circuit are controlled or timed by control unit 114 via a plurality of interconnecting means generally represented in dashed line. Such interconnection from the control for bringing about the successive arithmetic operations above described is well within the understanding of those skilled in the art. The control unit may sequence the operations ~a) through ~j) by means of either hard-wired sequencing cir-cuitry, and/or by means of stored software, in a conventional manner with rcgard to the Fig. 10 computinq circuitry.
The particular means as described with reference to Fig. 10 for solving simultaneous equations to provide coefficients of the reciprocal series are illustrated by way of example and can be employed when a relatively small number of equations and unknowns are involved. A more com-plex implementation as hereinafter described is alternatively suitable particularly when solving for a greater number of terms. For example, general purpose digital computing appa-ratus may be employed at the location of circuit elements 20, 20' or 48 for cyclically solving sets of simultaneous cquations ~ ~-. 7 ~
identified by expression (4) utilizing the routine illustrated in the Figure

11 flow diagram. This routine, which is here expressed employing Fortran IV
terminology, is entitled "Crout" and is well known to those skilled in the art, Consideration of the manner in which the Crout reduction operates to solve simultaneous equations can be found in '1Introduction to Numerical Analysis"
by F.B. Ilildebrand, McGraw-~lill, 1956 ! p. 429 et seq. and p, 4~6 et seq, Examples of computinq apparatus for carrying out the Crout routine are the *IB~q 360/65 manufactured by International Business Machines, ~rmonk! New York;
the *CDC 6400 manufactured by Control Data Corporation, Minneapolis~ Minnesota and the *DEC PDP 11 manufactured by Digital Equipment Corporatic)n! Maynard, Massachusetts. The Crout routine is set forth herein by way of example r and various other programs for solving the simultaneous equations defined by expression (4) may be substituted therefor.
It will also be appreciated that any or all of the various digital functions performed by the transform converter, inverse transform converter, reciprocal transform converter, multipliers, storage devices and control means as hereinbefore described can likewise be implemented employing general or special purpose digital computers. The programming of general or special purpose computer apparatus to carry out -the various functions of addition, subtraction, multiplication! division and control, as disclosed with refer~
ence to Figures 6 -through 10, is straightforward, and any of the above mentioned general purpose computers may be employed in this way iF desirecl, In such case, the computer elemen-ts perEorm in essentially the same manner or in an equivalen-t manner to the circuitry hereinbeEore clisclosed, * Trade Marks J~ 7~

In the foregoing specification, the term "square wave" is meant to indicate a periodic wave that alternately assumes one of two relatively fixed values. It is not meant to imply that each square wave half cycle will have the same duration, or that there exists a constant ratio between dura-tion and magnitude of square wave half cycles. Furthermore, the transforn~ation of a function or signal into square wave component representation includes representation by the values thereof, e.g. digital values indicative of the mag-nitude of such square wave components.
In the foregoing circuits, an input signal or valuemay in some cases be considered unity, i.e. in the case of multiplication with another input signal or value. For instance, for some purposes it may be desired to obtain a reciprocal ~alsh series representation without further multiplication.
~ hile we have shown and described various embodi-ments of our invention, it will be apparent to those skilled in the art that many other changes and modifications may be ZO made without departing from our invention in its broader aspects. We, therefore, intend the appended claims to cover all such charlyes and modifications as fall within the truc spirit and scope of our invention.

"

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for signal enhancement comprising:
means for spectrally decomposing at least a portion of an input signal into a series expansion of Walsh function representations, said spectrally decomposing means including an analog-to-digital converter for sampling said input signal and for digitizing the samples produced, said spectrally decomposing means further including a Walsh transform converter for receiving said digitized samples and providing an array of Walsh coefficients constituting the amplitudes of Walsh functions together representing said portion of said input signal;
second means for spectrally decomposing at least a portion of a second input function into a second series expansion of Walsh function representations, said second spectrally decomposing means including a Walsh transform converter for providing an array of Walsh coefficients constituting the amplitudes of Walsh functions together representing said portion of said second input function;
means for generating the reciprocal of one of said Walsh function series expansions in the form of coefficients of a reciprocal Walsh series expansion;
and a multiplier for multiplying said reciprocal with the other of said Walsh function representations.

2. The apparatus according to claim 1 wherein said second input function comprises an estimate of noise to be divided from said input signal.

3. The apparatus according to claim 1 wherein said Walsh transform converters comprise Hadamard matrix converters for producing Hadamard transformation.

4. The apparatus according to claim 1 further including an inverse Walsh transform converter and a digital-to-analog converter for transforming the product of said multiplication into a substantially continuous signal output.

5. The apparatus according to claim 4 wherein said inverse Walsh transform converter comprises a Hadamard matrix converter for providing an inverse Hadamard transformation.

6. The apparatus according to claim 1 further including means for generating the reciprocal of the product produced by said multiplier in the form of coefficients of a second reciprocal Walsh series expansion, a second multiplier for multiplying the second reciprocal Walsh series expansion with the series expansion of Walsh function representations corresponding to said input signal to produce a second product, and an inverse Walsh transform converter and a digital-to-analog converter for transforming said second product into a substantially continuous signal output.

7. The apparatus according to claim 6 wherein said second input function comprises an estimate of a desired input signal.

8. The apparatus according to claim 1 further including a system to be controlled and means for generating feedback in response to system operation for providing said second input function, and means responsive to the product of said multiplier including a digital-to-analog converter for generating a restoring signal in said system.

9. The apparatus according to claim 1 wherein said means for generating the reciprocal comprises means for solving a set of simultaneous equations for coefficients of the reciprocal series wherein such set of equations is defined by multiplica-tion of the proposed reciprocal Walsh series by the terms of the Walsh series for which the reciprocal is desired.

10. The apparatus according to claim 1 wherein said means for developing the reciprocal comprises means for solving a set of simultaneous equations for coefficients of the reciprocal series, said equations having the form wherein the {ak} are representative of coefficients of the reciprocal Walsh series to be determined, the are representative of the coefficients of the given Walsh series for which the reciprocal is desired, and p is an integer.