GB2314977A - Adaptive nulling - Google Patents
Adaptive nulling Download PDFInfo
- Publication number
- GB2314977A GB2314977A GB8615893A GB8615893A GB2314977A GB 2314977 A GB2314977 A GB 2314977A GB 8615893 A GB8615893 A GB 8615893A GB 8615893 A GB8615893 A GB 8615893A GB 2314977 A GB2314977 A GB 2314977A
- Authority
- GB
- United Kingdom
- Prior art keywords
- signal
- correlation
- wave
- signals
- sum
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
- H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
- H01Q3/2605—Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays
- H01Q3/2611—Means for null steering; Adaptive interference nulling
- H01Q3/2617—Array of identical elements
Landscapes
- Noise Elimination (AREA)
- Radar Systems Or Details Thereof (AREA)
- Radio Transmission System (AREA)
Abstract
Methods and systems for adaptive nulling of wave signals received with a plurality of N receiving elements, e.g. radio signals received with antennae (ANT 1 -ANT N ), so as to improve the power ratio of a desired component in the signals to one or more undesired components, wherein signals from all the elements but one (ANT 2 -ANT N ) are weighted (W 2 -W N ) and summed with the unweighted signal from the one element (ANT ), correlated with the unweighted signals from all the elements but the one (ANT 2 -ANT N ), and the weights (W 2 -W N ) adjusted so as to tend to reduce the correlations. To take account of amplitude and phase errors in the system and to make the speed of nulling independent of the relative magnitudes of the components, the correlations are measured with N independent sets of values for the weights (W 2 -W N ); optimum values for tie weights can then be calculated from given equations. The specification also discloses a faster method involving the measurement of signal power, and a "boot-strapping" system (Figure 3) for providing improved separation of a desired component and an undesired component using a discriminator comprising a limiter (LIM) followed by a zonal filter (ZF).
Description
DESCRIPTION:
"ADAPTIVE NULLING"
The invention relates to adaptive nulling.
Two aspects of the invention relate to a method of obtaining from electrical signals representative of wave signals received at two spaced receiving elements, said electrical signals each having two components which are of substantially the same frequency and of which a first component is desired and the second component is undesired, an electrical signal in which the power ratio of the first component to the second component is approximately the inverse of that in a reference signal derived from the wave signals received at at least one of the receiving elements, the method comprising
receiving wave signals at said two elements and deriving first and second electrical signals which each have said two components and which are respectively representative of the wave signals received at a first and the second of the elements,
applying an adjustable weight W2 to the second electrical signal to derive a third, weighted signal representative of a weighted version of the wave signal received at the second element,
deriving from the first and third signals a fourth, sum signal representative of the sum of the wave signal received at the first element and said weighted version of the wave signal received at the second element, and
performing a correlation and adjustment process which comprises measuring the correlation C2 between said sum signal and said reference signal and adjusting the weight W2 so as to tend to reduce the correlation, whereby the sum signal then has approximate power inversion relative to said reference signal.
A further aspect of the invention relates to a method of obtaining, from electrical signals representative of wave signals received at a plurality of N(N > 2) mutually spaced receiving elements, said electrical signals each having a plurality of N components which are of substantially the same frequency and of which a first component is desired and the other components are undesired, an electrical signal in which the power ratio of the first component to each of the components is approximately the inverse of that in said electrical signals, the method comprising
receiving wave signals at said N elements and deriving N electrical signals which each have said plurality of components and of which the jth electrical signal (j = 1, 2, ... N) is respectively representative of the wave signal received at the jth element,
applying a respective adjustable weight Wi (i = 2, 3, ... N) to each of said electrical signals except the first to derive (N-l) weighted signals of which the ith weighted signal is respectively representative of a weighted version of the wave signal received at the ith element,
deriving from the first signal and said weighted signals a sum signal representative of the sum of the wave signal received at the first element and the weighted versions of the wave signals received at each of the other elements, and
performing a correlation and adjustment process which comprises measuring the correlations Ci between said sum signal and each of said electrical signals except the first and adjusting the weights
Wi so as to tend to reduce the correlations, whereby the sum signal then has approximate power inversion relative to said reference signal.
Still further aspects of the invention relate to systems for performing methods embodying the invention.
When wave signals such as radio signals or sonar signals are received, the signals may have, in addition to a desired component, one or more undesired components of similar frequency. If the undesired components are of greater magnitude than the desired component, it is desirable to process the received signals so as to alter the relative magnitudes of the components and to obtain a signal from which information in the desired component can be extracted. It is known that this may in principle be done by receiving the signals with an array of mutually spaced receiving elements (for example antennae in the case of radio signals, including radar signals) wherein there are at least as many components in the signal as receiving elements, weighting electrical signals derived from all but one of the receiving elements in both amplitude and phase, and summing the weighted signals with the unweighted signal from said one element. Provided the various signal components are received from sources in different respective orientations relative to the array of receiving elements, the effect of choosing suitable weights is to put nulls in the overall radiation pattern of the array on the directions of incidence of the undesired signal components, and hence the relative magnitude of the desired component can be improved.
The difficulty in performing adaptive nulling is how to choose appropriate weights quickly and accurately, particularly in the case where no prior knowledge of the nature of the desired signal component is available. A feedback technique proposed by Howells and Applebaum (see for example "Introduction to Adaptive Arrays" by
R.A. Monzingo and T.W. Miller, John Wiley, 1980, chapter 5) involves obtaining a weighted version of the signal from each of the receiving elements except a first, forming the sum of the weighted signals and the signal from the first element, correlating the sum signal with the unweighted signal from each element except the first, and adjusting the weights so as to tend to reduce the correlations to zero; a steering vector is often added to the weights. In practice, this technique has the disadvantages that it is rather slow, particularly when the undesired components are not of very much greater magnitude than the desired component, and in that case the improvement in the relative magnitude of the desired component, i.e. the extent of nulling, may not be as great as is desirable. An alternative, open-loop technique known as Direct
Matrix Inversion (ibid, chapter 6) involves cross-correlating weighted signals from each of the receiving elements. This technique has the advantage that it is potentially fast and that the speed is independent of the relative magnitudes of the components. However, it has the major disadvantage that being open-loop, the output of the system does not directly affect the weights applied to the signals from the receiving elements; consequently, the nulling is degraded if there are phase and/or amplitude errors in the system. Furthermore, a system with N receiving elements requires at least N(N+1)/2 correlators, which may be prohibitively large if N is large.
It is an object of the invention to provide improved methods and systems for adaptive nulling.
According to a first aspect of the invention, a method as set forth in the second paragraph of this specification is characterised in that the correlation and adjustment process comprises setting the weight W2 to each of two independent known values W2j (j = 1, 2), measuring the resultant correlation C2j for each value of W2j, calculating an optimum value W2opt for the weight W2 from the equation
W2opt = (C21W22 - C22W21)/(C21 - C22) and setting the weight W2 to W2opt According to a second aspect of the invention, a method as set forth in the second paragraph of this specification is characterised in that the correlation and adjustment process comprises setting the weight W2 to each of two independent known values W2j (j = 1, 2), measuring the resultant correlation C2j for each value of W2j, measuring the power P12 of the reference signal, calculating the quantity B where 3 = (W2n - i20pt) P12/C2n where n is either 1 or 2 and W2opt = (C21W22 - C22i21)/(C21 - C22) and storing the value of B, and when further wave signals of substantially the same frequency as before are received, setting the weight w2 to an independent known third value W23, measuring the resultant correlation C23 and the power P3 of the reference signal, calculating an optimum weight value W20PT where W20PT = W23 - (BC23/P3) and setting W2 to W2OPT.
According to a third aspect of the invention, a method as set forth in the third paragraph of this specification is characterised in that the correlation and adjustment process comprises setting the eights Wi to each of N sets of known respective values Wij, the N sets of known values being independent, measuring the resultant correlations Cjj for each set of values, calculating optimum values Wi opt for the weights from the equations Cii = Yj1 + W2jYj2 + W3jYi3 + ... + WNjYiN and = Yil + W20ptYi2 + W30ptYi3 + ... + WNoptYiNI and setting the weights Wi to We opt respectively.
The invention furthermore provides systems for performing methods respectively embodying each aspect of the invention, as set forth in Claims 8, 9 and 14 below.
The invention has the advantage of combining the following features, viz it can be quite fast, the speed is independent of the relative magnitudes of the components, and it takes account of amplitude and phase errors in the system. Furthermore, it requires only (N-l) correlators.
In methods and systems embodying the invention, a weighting factor may be used in deriving the first electrical signal representative of the wave signal received at the first element.
However, this weighting factor would not need to be altered in the correlation and adjustment process, and the value of the or each weight which does need to be adjusted in the correlation and adjustment process would be the product of this weighting factor and the value that the respective weight would have if the weighting factor were unity.
In a method embodying the first or second aspect of the invention, the reference signal may be representative of the wave signal received at the second element.
As an alternative, the method may further comprise applying an adjustable weight W1 to the first electrical signal to derive a fifth, weighted signal representative of a weighted version of the wave signal received at the first element,
deriving from the second and fifth signals a sixth, further sum signal representative of the sum of the wave signal received at the second element and said weighted version of the wave signal received at the first element,
performing a further correlation and adjustment process which comprises measuring the correlation C1 between the further sum signal and a further reference signal derived from the wave signal received at at least one of the receiving elements and adjusting said weight W1 so as to tend to reduce the correlation C1, wherein said reference signal and said further reference signal are respectively derived from said further sum signal and said sum signal, wherein either the derivation of only one out of said reference signal and said further reference signal comprises subjecting said further sum signal or said sum signal respectively to a discrimination process whereby to tend to increase the power of one of said components relative to the other, or the derivation of one out of said reference signal and said further reference signal comprises subjecting one out of said sum signal and said further sum signal to said discrimination process whereby to tend to increase the power of the first component relative to the second component and subjecting the other out of said sum signal and said further sum signal to said discrimination process whereby to tend to increase the power of the second component relative to the first component, and wherein said further correlation and adjustment process in respect of C1 and W1 is the same mutatis mutandis as the correlation and adjustment process in respect of C2 and W2. This is more complex, but may provide substantially better nulling of the undesired component. The discrimination process may comprise passing a signal through a hard limiter and then through a zonal bandpass filter, this can provide the desired change in the relative magnitudes of the components with various commonly-encountered signal modulations. Suitably, said correlation and adjustment process and said further correlation and adjustment process are repeated in alternation to further improve the nulling.
Embodiments of the invention will now be described1 by way of example, with reference to the diagrammatic drawings, in which:
Figure 1 depicts an adaptive nulling system embodying the invention and comprising an array of a plurality of antennae;
Figure 2 is a graph relating to relative signal magnitudes, and
Figure 3 depicts an adaptive nulling system embodying the invention and comprising two antennae, wherein a reference signal is obtained via a discriminator.
Figure 1 depicts schematically a system for adaptive nulling of radio signals without prior knowledge of the nature of the received signals. The system comprises N antennae ANT1, ANT2, ... ANTN respectively which suitably are substantially the same and suitably are omnidirectional. The output of each of the antennae except the first (ANT1) is connected to a respective weighting unit WT which multiplies the electrical signal supplied by the antenna when a radio signal is received by a respective weight W2 ... WN. The weights are in general complex quantities, so that both the amplitude and the phase of the antenna signals are affected by the weighting. The unweighted signal from the first antenna ANT1 and the weighted signals derived from antennae
ANT2-ANTN are fed to a summing unit SUM. The output of each of the antennae except the first is additionally supplied to a respective correlator CORR, to which the output of the summing unit
SUM is also connected. The outputs of the correlators are connected to a calculating and control unit CALC, the outputs of which respectively control the weights W2-WN. The output signal from the summing unit SUM also constitutes the output signal OP of the system.
In operation, upon reception of radio signals having N components of substantially the same frequency, it being desired to extract information from one of the components, the calculating unit CALC selects a first set of known values W21, W31 ... WN1 for the weights applied to the signals from each of the antennae except the first. The resulting respective correlations C21, C31 CNI CN1 between the sum signal from SUM and the unweighted signal from each of the antennae except the first are measured by the correlators CORR and stored in the calculating unit CALC. The process is then repeated with an independent second set of known weights W22 W32 ... WN2, and so on to a total of N independent set of weights.
The use of the N sets each of (N-l) known weights and the measurement of N sets of (N-l) correlations results in N simultaneous equations of the general form
Cij = Yj1 + W2jYj2 + W3jYi3 + ... + WNjYiN where i = 2,3 ... N and j = 1,2 ... N, and where Yij are N unknown coefficients. The calculating unit CALC solves the N simultaneous equations to derive the values of the N unknowns Yij.
These values are then used in (N-1) simultaneous equations of the general form = ti1 + W2optYi2 + W30ptYi3 + ... + WNoptViN where We opt are (N-l) unknown optimum values for the weights
W2-WN; the calculating unit solves these (N-l) simultaneous equations to derive the optimum weights, and sets the weights accordingly.
Although the above description with reference to Figure 1 relates to the general case of a system with a plurality of N receiving elements, it is of course applicable to the particular case of N=2. In that case, the two sets of simultaneous equations can be simplified to the single equation W2opt = (C21W22 - C22W21)/(C21 - C22).
It can be shown that the above-described method achieves approximate power inversion when the signals produced by the antennae have N components, of which one component is desired and the other components are undesired. This is to say, if for example an undesired component in the output signal of an antenna is 10 dB above the desired component, the undesired signal will be approximately 10dB below the desired component in the output signal
OP of the system. Figure 2 is a graph which relates to a 2-antenna system and which takes into account noise in the system. The graph shows the output desired signal-to-(noise plus undesired signal) ratio, OP DSNUSR, as a function of the input desired signal-to-noise ratio, IP DSNR, for various values of the input undesired signal-to-noise ratio, IP USNR. The curves are each of inverted V shape. To the left of the apex of each curve, where the input desired signal-to-noise ratio is relatively low, the value of that ratio mainly determines the output desired signal-to-(noise plus undesired signal) ratio. It is to the right of the apex of curve, where the input desired signal-to-noise ratio is relatively high, that results of greatest practical use are obtained: the output desired signal-to-(noise plus undesired signal) ratio is approximately equal to the input undesired signal-to-noise ratio minus the input desired signal-to-noise ratio. (It should be noted that if this difference is negative, i.e. the undesired component is weaker than the desired component in the input, the power inversion results in the undesired component being stronger than the desired component in the output.) The apex of each curve occurs when the input desired signal-to-noise ratio is approximately half the input undesired signal-to-noise ratio.
If the number of components in the received signal is less than the number of receiving elements being used, the system will tend to null the desired component. If a system having N receiving elements is used to receive a signal having less than N components, it is therefore necessary to reduce the number of receiving elements being used, for example by setting one or more weights to zero, so as to equalise the number of elements with the number of components. When the number of components in the received signal is unknown, the number of receiving elements being used may be progressively reduced from N until a useful output signal is obtained from the system. If the number of components in the received signal exceeds the number of receiving elements, the strongest components will be nulled, which will in general be a useful result. (The above has assumed that the undesired components are stronger than the desired component.)
With a system comprising only two receiving elements, it is not necessary to perform two correlation measurements (with different respective values of the weight W2) on each occasion that wave signals of a particular frequency are received, provided that signal powers can also be measured. In that case, the system may be calibrated in advance, as follows. When signals of a particular frequency are received, the correlation C2j is measured with two independent values of the weight W2j as usual, and the power P12 of the reference signal for the correlation, in this case the unweighted signal from the second antenna, is also measured. The optimum value W2opt of the weight W2 is calculated from the above-mentioned equation
Wopt = (C21W22 - C22W21)l(C21 - C22).
A calibration coefficient B is then calculated from the equation a = (W2n - W2opt) P12/C2n where n is either 1 or 2, and the value of B is stored. When further signals of substantially the same particular frequency are subsequently received, the weight W2 is set to a third value W23, and the resultant correlation C3 and the power P3 of the reference signal are measured. The optimum value W2OPT of the weight W2 in that situation is then calculated from the equation W20PT = W23 - aC3/P3.
For a system comprising only two receiving elements, the reference signal with which the sum signal, derived by adding the unweighted signal from the first element to the weighted signal from the second element, is correlated need not be the unweighted signal from the second receiving element: an alternative reference signal may be used, in particular a reference signal in which the power ratio of the undesired component to the desired component tends to be higher than in a signal derived directly from a receiving element. For example, the unweighted signal from the second element may for this purpose be subjected to a discrimination process which comprises passing the signal successively through a hard limiter and through a zonal filter which is a bandpass filter for selecting the fundamental frequency of the thus-limited signal. For many classes of signal, this has the desired effect. As a further example, the same discrimination process may be used in a "boot-strapping" signal-separation system embodying the invention, as will now be described with reference to
Figure 3.
The system depicted in simplified block diagram form in
Figure 3 may be considered to have two parallel and interconnected channels. Each channel comprises a respective antenna ANT1, ANT2 whose output is connected to a respective power-divider PD1A,
PD2A. One output of each power divider is connected to a respective weighting unit WT1, WT2 whose output is connected to one input of a respective summing unit SUM1, SUM2. The other input of each summing unit is connected to the other output of the power divider in the other channel. The outputs of the summing units are fed to respective mixers Mar1, MXR2 which are also fed by a common local oscillator LO, the signal frequency is thus converted to an intermediate frequency (IF). The IF signals are passed through respective band-pass filters BPF1, 8PF2 which are adapted to select the same frequency of interest, to further respective power-dividers PD1B, PD28. The signal derived from one output of each of these power-dividers is correlated in a respective correlator CORR1, CORR2 with a reference signal which is derived from the other output of the power-divider in the other channel and which, before being used as a reference signal, is subjected to a discrimination process which tends to increase the power of the stronger component relative to the weaker. As indicated above, the discriminators each consist in this case of a respective hard limiter LIM1, LIM2 followed by a zonal filter ZF. (Corresponding filters ZF are used in the connection to the other input of each correlator in order to equalise the delays.) The outputs of the correlators are fed to a calculating and control unit CALC which controls the weights W1, W2 in dependence on the outputs of the correlators CORR1, CORR2 respectively. An output signal may be taken from the system at the point marked OP1 or at the point marked OP2 following the respective summing units: in the general case where signal separation is achieved, one output signal will be predominantly the desired component and the other output signal will be predominantly the undesired component.
In operation, the weights W1 and W2 are adjusted repeatedly in alternation. Provided there is initially at least a slight difference between the signals in the two channels, the result of of the iterative weight adjustments will in general be to increase the difference to a substantial extent. The calculating and control unit CALC may begin the iteration by setting one of the weights, for example W1, to zero and performing a standard power inversion method embodying the invention, as described above with reference to Figure 1 for the case of N=2, i.e. the correlator
CORR2 is used to measure the correlation between the signal derived from OP2 (which is the sum of a weighted signal from the second antenna and an unweighted signal from the first antenna) with a reference signal derived from OP1 (which with W1=0 is simply an unweighted signal from the second antenna) for two known values of
W2, and W2 is then set to a calculated optimum value. (For this initial step, it is not necessary to use the limiter LIM1.) Using this value of W2, the unit CALC then performs the power inversion method of the invention to find a suitable value for W1, whereafter
W2 is readjusted using this new value for W1. The process may be repeated until there is little further change in the weights.
A simulation of an ideal system of the form depicted in
Figure 3 has indicated that such a system can generally provide substantial separation of two radio signals. Even if the received signals were to be of identical magnitudes, slight differences between the pass-band characteristics of the filters in the two channels would enable separation eventually to be achieved, although several iterations might be required before there were a substantial change in separation with succesive iterations. Using the above-described form of discriminator, signals which can be separated comprise:
two unmodulated carrier signals;
two frequency modulated signals;
a frequency modulated signal and an amplitude modulated
signal.
With two such discriminators (as shown in Figure 3), the ideal asymptotic rate of increase of separation is 12 dB per iterative cycle. However, using two such discriminators, separation cannot be achieved between a frequency modulated signal and a signal with single sideband modulation, since the bandpass limiter always enhances the FM signal, but separation (at an asymptotic rate of 5d3 per iterative cycle) can be achieved if only a single discriminator is used, i.e. one discriminator in Figure 3 is omitted. (The use of a single discriminator halves the rate of separation per iterative cycle of the previously mentioned signals.) Separation can also be achieved (with one or two discrininators) between an FM signal and one or more delayed versions (which may be attenuated) of itself, corresponding to multi path reception, the extent of separation is in this case limited, for example to 50dB, but this of course would be entirely adequate. It is expected that the use of at least one discriminator will enable various other kinds of signals to be separated.
It can be shown that adaptive nulling by methods and systems embodying the invention, as represented for example by the output desired signal to (undesired signal plus noise) ratio, is not affected by amplitude and phase errors in the system, whereas it would tend to be affected by such errors using other methods for directly calculating appropriate weights.
Claims (16)
1. A method of obtaining, from electrical signals representative of wave signals received at two spaced receiving elements, said electrical signals each having two components which are of substantially the same frequency and of which a first component is desired and the second component is undesired, an electrical signal in which the power ratio of the first component to the second component is approximately the inverse of that in a reference signal derived from the wave signals received at at least one of the receiving elements, the method comprising
receiving wave signals at said two elements and deriving first and second electrical signals which each have said two components and which are respectively representative of the wave signals received at a first and the second of the elements,
applying an adjustable weight W2 to the second electrical signal to derive a third, weighted signal representative of a weighted version of the wave signal received at the second element,
deriving from the first and third signals a fourth, sum signal represent4Rive of the sum of the wave signal received at the first element and said weighted version of the wave signal received at the second element, and
performing a correlation and adjustment process which comprises measuring the correlation C2 between said sum signal and said reference signal and adjusting the weight W2 so as to tend to reduce the correlation, whereby the sum signal then has approximate power inversion relative to said reference signal,
characterised in that the correlation and adjustment process comprises setting the weight W2 to each of two independent known values W2; (j = 1, 2), measuring the resultant correlation C2j for each value of W2j, calculating an optimum value W2opt for the weight W2 from the equation W2opt = (C21W22 - C22W21)/(C21 - C22) and setting the weight W2 to W2opt.
2. A method of obtaining, from electrical signals representative of wave signals received at two spaced receiving elements, said electrical signals each having two components which are of substantially the same frequency and of which a first component is desired and the second component is undesired, an electrical signal in which the power ratio of the first component to the second component is approximately the inverse of that in a reference signal derived from the wave signals received at at least one of the receiving elements, the method comprising
receiving wave signals at said two elements and deriving first and second electrical signals which each have said two components and which are respectively representative of the wave signals received at a first and the second of the elements,
applying an adjustable weight W2 to the second electrical signal to derive a third, weighted signal representative of a weighted version of the wave signal received at the second element,
deriving from the first and third signals a fourth, sum signal representative of the sum of the wave signal received at the first element and said weighted version of the wave signal received at the second element, and
performing a correlation and adjustment process which comprises measuring the correlation C2 between said sum signal and said reference signal and adjusting the weight W2 so as to tend to reduce the correlation, whereby the sum signal then has approximate power inversion relative to said reference signal,
characterised in that the correlation and adjustment process comprises setting the weight W2 to each of two independent known values W2j (j = 1, 2), measuring the resultant correlation C2j for each value of W2j, measuring the power P12 of the reference signal, calculating the quantity B where
B = (W2n - W2opt) P1z/C2n where n is either 1 or 2 and
W20pt = (C21W22 - C22W21)l(C21 - C22) and storing the value of B, and when further wave signals of substantially the same frequency as before are received, setting the weight W2 to an independent known third value W23, measuring the resultant correlation C23 and the power P3 of the reference signal, calculating an optimum weight value W2OPT where 20PT = W23 - (8C23/P3) and setting W2 to W2OPT.
3. A method as claimed in Claim 1 or 2 wherein the reference signal is representative of the wave signal received at the second element.
4. A method as claimed in any preceding claim wherein the method further comprises
applying an adjustable weight W1 to the first electrical signal to derive a fifth, weighted signal representative of a weighted version of the wave signal received at the first element,
deriving from the second and fifth signals a sixth, further sum signal representative of the sum of the wave signal received at the second element and said weighted version of the wave signal received at the first element,
performing a further correlation and adjustment process which comprises measuring the correlation C1 between the further sum signal and a further reference signal derived from the wave signal received at at least one of the receiving elements and adjusting said weight W1 so as to tend to reduce the correlation C1, wherein said reference signal and said further reference signal are respectively derived from said further sum signal and said sum signal, wherein either the derivation of only one out of said reference signal and said further reference signal comprises subjecting said further sum signal or said sum signal respectively to a discrimination process whereby to tend to increase the power of one of said components relative to the other, or the derivation of one out of said reference signal and said further reference signal comprises subjecting one out of said sum signal and said further sum signal to said discrimination process whereby to tend to increase the power of the first component relative to the second component and subjecting the other out of said sum signal and said further sum signal to said discrimination process whereby to tend to increase the power of the second component relative to the first component, and wherein said further correlation and adjustment process in respect of C1 and W1 is the same mutatis mutandis as the correlation and adjustment process in respect of C2 and W2.
5. A method as claimed in Claim 4 wherein said discrimination process comprises passing a signal through a hard limiter and then through a zonal bandpass filter.
6. A method as claimed in Claim 4 or 5 wherein said correlation and adjustment process and said further correlation and adjustment process are repeated in alternation.
7. A method of obtaining, from electrical signals representative of wave signals received at a plurality of N(N > 2) mutually spaced receiving elements, said electrical signals each having a plurality of N components which are of substantially the same frequency and of which a first component is desired and the other components are undesired, an electrical signal in which the power ratio of the first component to each of the other components is approximately the inverse of that in said electrical signals, the method comprising
receiving wave signals at said N elements and deriving N electrical signals which have said plurality of components and of which the jth electrical signal (j = 1, 2, ... N) is respectively representative of the wave signal received at the jth element,
applying a respective adjustable weight Wi (i = 2, 3, ... N) to each of said electrical signals except the first to derive (N-l) weighted signals of which the ith weighted signal is respectively representative of a weighted version of the wave signal received at the ith element,
deriving from the first signal and said weighted signals a sum signal representative of the sum of the wave signal received at the first element and the weighted versions of the wave signals received at each of the other elements, and
performing a correlation and adjustment process which comprises measuring the correlation Ci between said sum signal and each of said electrical signals except the first and adjusting the weights Wi so as to tend to reduce the correlations, whereby the sum signal then has approximate power inversion relative to said reference signal,
characterised in that the correlation and adjustment process comprises setting the weights Wi to each of N sets of known respective values Wij, the N sets of known values being independent, measuring the resultant correlations Cij for each set of values, calculating optimum values Wiopt for the weights from the equations
Cij = Yj1 + W2jYj2 + W3jYi3 + ... + WNjYiN and = Yi1 + W2optYi2 + W3optYi3 + ... + WNoptYiN, and setting the weights Wi to Wiopt respectively.
8. A system for performing a method as claimed in Claim 1 or any preceding claim appendant to Claim 1, the system comprising
receiving means, comprising two spaced receiving elements, for receiving wave signals and deriving first and second electrical signals respectively representative of the wave signals received at a first and the second of the elements,
weighting means for applying an adjustable weight W2 to the second electrical signal to derive a third, weighted signal representative of a weighted version of the wave signal received at the second element,
summing means for deriving from the first and third signals a fourth, sum signal representative of the sum of the wave signal received at the first element and said weighted version of the wave signal received at the second element,
correlating means for measuring the correlation C2 between said sum signal and a reference signal derived from the wave signal received at at least one of the receiving elements, and
calculating and control means for performing a correlation and weight adjustment process which comprises setting the weight W2 to each of two independent known values W2j (j = 1, 2), calculating from the resultant correlation C2j measured by the correlating means for each value of W2j an optimum value W20pt for the weight
W2 from the equation W20pt = (C21W2z - C22W21)/(C21 - C22) and setting the weight W2 to W2opt.
9. A system for performing a method as claimed in Claim 2 or any preceding claim appendant to Claim 2, the system comprising
receiving means, comprising two spaced receiving elements, for receiving wave signals and deriving first and second electrical signals respectively representative of the wave signals received at a first and the second of the elements,
weighting means for applying an adjustable weight W2 to the second electrical signal to derive a third, weighted signal representative of a weighted version of the wave signal received at the second element,
summing means for deriving from the first and third signals a fourth, sum signal representative of the sum of the wave signal received at the first element and said weighted version of the wave signal received at the second element,
correlating means for measuring the correlation C2 between said sum signal and a reference signal derived from the wave signal received at at least one of the receiving elements,
power measuring means for measuring the power of the reference signal, and
calculating and control means for performing a correlation and weight adjustment process which comprises setting the weight W2 to each of two independent known values W2j (j = 1, 2), calculating from the resultant correlation C2j measured by the correlating means for each value of W2; and from the power P12 of the reference signal measured by the measuring means the quantity B where
8 = (W2n - W2opt) P12/C2n where n is either 1 or 2 and W2opt = (C21W22 - C22W21)l(C2l - C22) and storing the value of B,
and wherein the system is responsive to the reception of further wave signals of substantially the same frequency as before to cause the calculating and control means to perform a further process which comprises setting the weight W2 to an independent known third value W23, calculating from the resultant correlation C23 measured by the correlating means and the power P3 of the reference signal measured by the power measuring means an optimum weight value W2OPT where W2OPT = W23 - (8C23/P3) and setting W2 to W2OPT.
10. A system as claimed in Claim 8 or 9 wherein the reference signal is the second electrical signal.
11. A system as claimed in any of Claims 8 to 10 for performing a method as claimed in any of Claims 4 to 6 wherein the system comprises
further weighting means for applying an adjustable weight W1 to the first electrical signal to derive a fifth, weighted signal representative of a weighted version of the wave signal received at the first element,
further summing means for deriving from the second and fifth signals a sixth, further sum signal representative of the sum of the wave signal received at the second element and said weighted version of the wave signal received at the first element,
further correlating means for measuring the correlation C1 between the further sum signal and a further reference signal derived from the wave signal received at at least one of the receiving elements,
means for deriving said reference signal and said further reference signal from said further sum signal and said sum signal respectively, comprising discriminating means for subjecting at least one out of said sum signal and said further sum signal to said discrimination process whereby to tend to increase the power of one component relative to the other, and
calculating and control means for performing a correlation and weight adjustment process in respect of C1 and W1 which is the same mutatis mutandis as the correlation and weight adjustment process in respect of C2 and W2.
12. A system as claimed in Claim 11 wherein the discriminating means comprises a hard limiter followed by a zonal bandpass filter.
13. A system as claimed in Claim 11 or 12 adapted to repeat said correlation and adjustment processes in respect of C1 and W1 and of C2 and W2 respectively in alternation.
14. A system for performing a method as claimed in Claim 7, the system comprising
receiving means, comprising a plurality of N(N 2) mutually spacing receiving elements, for receiving wave signals and deriving
N electrical signals of which the jth electrical signal (j = 1, 2, ... N) is respectively representative of the wave signal received at the jth element,
weighting means for applying a respective adjustable weight Wi (i = 2, 3, ... N) to each of said electrical signals except the first to derive (N - 1) weighted signals of which the ith weighted signal is respectively representative of a weighted version of the wave signal received at the ith element,
summing means for deriving from the first signal and said weighted signals a sum signal representative of the sum of the wave signal received at the first element and the weighted versions of the wave signals received at each of the other elements,
correlating means for measuring the correlation Ci between said sum signal and each of said electrical signals except the first, and
calculating and control means for performing a correlation and weight adjustment process which comprises setting the weights Wi to each of N sets of known respective values Wij, the N sets of known values being independent, calculating from the resultant correlations Cij measured by the correlating means for each set of weight values optimum values Wi opt for the weights from the equations
Cij = Yil + W2jYi2 + W3jYj3 + ... + WNjYiN and
0 = Yi1 + W2optYi2 + W3optYi3 + ... + WNoptYiN, and setting the weights Wi to We opt respectively.
15. An adaptive nulling method substantially as herein described with reference to Figure 1 or to Figure 3 of the drawings.
16. An adaptive nulling system substantially as herein described with reference to Figure 1 or to Figure 3 of the drawings.
16. An adaptive nulling system substantially as herein described with reference to Figure 1 or to Figure 3 of the drawings.
Amendments to the claims have been filed as follows
1. A method of obtaining, from electrical signals representative of wave signals received at two spaced receiving elements, said electrical signals each having two components which are of substantially the same frequency and of which a first component is desired and the second component is undesired, an electrical signal in which the power ratio of the first component to the second component is approximately the inverse of that in a reference signal derived from the wave signals received at at least one of the receiving elements, the method comprising
receiving wave signals at said two elements and deriving first and second electrical signals which each have said two components and which are respectively representative of the wave signals received at a first and the second of the elements,
applying an adjustable weight W2 to the second electrical signal to derive a third, weighted signal representative of a weighted version of the wave signal received at the second element,
deriving from the first and third signals a fourth, sum signal representative of the sum of the wave signal received at the first element and said weighted version of the wave signal received at the second element, and
performing a correlation and adjustment process which comprises measuring the correlation C2 between said sum signal and said reference signal and adjusting the weight W2 so as to tend to reduce the correlation, whereby the sum signal then has approximate power inversion relative to said reference signal,
characterised in that the correlation and adjustment process comprises setting the weight W2 to each of two independent known values W2j (j = 1, 2), measuring the resultant correlation C2j for each value of W2j, calculating an optimum value W2opt for the weight W2 from the equation
W20pt = (C21W22 - C22W21)/(C21 - C22) and setting the weight W2 to W20pt-
2. A method of obtaining, from electrical signals representative of wave signals received at two spaced receiving elements, said electrical signals each having two components which are of substantially the same frequency and of which a first component is desired and the second component is undesired, an electrical signal in which the power ratio of the first component to the second component is approximately the inverse of that in a reference signal derived from the wave signals received at at least one of the receiving elements, the method comprising
receiving wave signals at said two elements and deriving first and second electrical signals which each have said two components and which are respectively representative of the wave signals received at a first and the second of the elements,
applying an adjustable weight W2 to the second electrical signal to derive a third, weighted signal representative of a weighted version of the wave signal received at the second element,
deriving from the first and third signals a fourth, sum signal representative of the sum of the wave signal received at the first element and said weighted version of the wave signal received at the second element, and
performing a correlation and adjustnent process which comprises measuring the correlation C2 between said sum signal and said reference signal and adjusting the weight W2 so as to tend to reduce the correlation, whereby the sum signal then has approximate power inversion relative to said reference signal,
characterised in that the correlation and adjustment process comprises setting the weight W2 to each of two independent known values W2j (j = 1, 2), measuring the resultant correlation C2j for each value of W2j, measuring the power P12 of the reference signal, calculating the quantity B where a = (X2n - W20pt) P12/C2n where n is either 1 or 2 and
W2opt = (C21W22 - C22W21)/(C21 - C22) and storing the value of B, and when further wave signals of substantially the same frequency as before are received, setting the weight W2 to an independent known third value W23, measuring the resultant correlation C23 and the power P3 of the reference signal, calculating an optimum weight value W2OPT where 20PT = W23 - (3C23/P3) and setting W2 to W2OPT.
3. A method as claimed in Claim 1 or 2 wherein the reference signal is representative of the wave signal received at the second element.
4. A method as claimed in any preceding claim wherein the method further comprises
applying an adjustable weight W1 to the first electrical signal to derive a fifth, weighted signal representative of a weighted version of the wave signal received at the first element,
deriving from the second and fifth signals a sixth, further sum signal representative of the sum of the wave signal received at the second element and said weighted version of the wave signal received at the first element,
performing a further correlation and adjustment process which comprises measuring the correlation C1 between the further sum signal and a further reference signal derived from the wave signal received at at least one of the receiving elements and adjusting said weight W1 so as to tend to reduce the correlation C1, wherein said reference signal and said further reference signal are respectively derived from said further sum signal and said sum signal, wherein either the derivation of only one out of said reference signal and said further reference signal comprises subjecting said further sum signal or said surn signal respectively to a discrimination process whereby to tend to increase the power of one of said components relative to the other, or the derivation of one out of said reference signal and said further reference signal comprises subjecting one out of said sum signal and said further sum signal to said discrimination process whereby to tend to increase the power of the first component relative to the second component and subjecting the other out of said sum signal and said further sum signal to said discrimination process whereby to tend to increase the power of the second component relative to the first component, and wherein said further correlation and adjustment process in respect of C1 and W1 is the same mutatis mutandis as the correlation and adjustment process in respect of C2 and W2.
5. A method as claimed in Claim 4 wherein said discrimination process comprises passing a signal through a hard limiter and then through a zonal bandpass filter.
6. A method as claimed in Claim 4 or 5 wherein said correlation and adjustment process and said further correlation and adjustment process are repeated in alternation.
7. A method of obtaining, from electrical signals representative of wave signals received at a plurality of N(N)2) mutually spaced receiving elements, said electrical signals each having a plurality of N components which are of substantially the same frequency and of which a first component is desired and the other components are undesired, an electrical signal in which the power ratio of the first component to each of the other components is approximately the inverse of that in said electrical signals, the method comprising
receiving wave signals at said hi elements and deriving N electrical signals which have said plurality of components and of which the jth electrical signal (j = 1, 2, ... N) is respectively representative of the wave signal received at the jth element,
applying a respective adjustable weight Wi (i = 2, 3, ... ) to each of said electrical signals except the first to derive (N-l) weighted signals of which the ith weighted signal is respectively representative of a weighted version of the wave signal received at the ith element,
deriving from the first signal and said weighted signals a sum signal representative of the sum of the wave signal received at the first element and the weighted versions of the wave signals received at each of the other elements, and
performing a correlation and adjustment process which comprises measjring the correlation Ci between said sum signal and each of said electrical signals except the first and adjusting the weights Wi so as to tend to reduce the correlations, whereby the sum signal then has approximate power inversion relative to said reference signal,
characterised in that the correlation and adjustment process comprises setting the weights Wi to each of N sets of known respective values Wij, the N sets of known values being independent, measuring the resultant correlations Cii for each set of values, calculating optimum values We opt for the weights from the equations
Cii = Yil + 2jYi2 + W3jYi3 + ... + WNjYiN and 0 = Y j1 + W2optYi2 + W3optYi3 + ... + WNoptYiNw and setting the weights Wi to We opt respectively.
8. A system for performing a method as claimed in Claim 1 or any preceding claim appendant to Claim 1, the system comprising
receiving means, comprising two spaced receiving elements, for receiving wave signals and deriving first and second electrical signals respectively representative of the wave signals received at ) first and the second of the eLements, weighting means for applying an adjustable weight W2 to the second electrical signal to derive a third, weighted signal representative of a weighted version of the wave signal received at the second element,
summing means for deriving from the first and third signals a fourth, sum signal representative of the sum of the wave signal received at the first element and said weighted version of the wave signal received at the second element,
correlating means for measuring the correlation C2 between said sum signal and a reference signal derived from the wave signal received at at least one of the receiving elements, and
calculating and control means for performing a correlation and weight adjustment process which comprises setting the weight W2 to each of two independent known values W2; (j = 1, 2), calculating from the resultant correlation C2i measured by the correlating means for each value of W2j an optimum value W2opt for the weight i2 from the equation W2opt = (C21W22 - C22W21)/(C21 - C22) and setting the weight W2 to W2opt.
9. A system for performing a method as claimed in Claim 2 or any preceding claim appendant to Claim 2, the system comprising
receiving means, comprising two spaced receiving elements, for receiving wave signals and deriving first and second electrical signals respectively representative of the wave signals received at a first and the second of the elements,
weighting means for applying an adjustable weight W2 to the second electrical signal to derive a third, weighted signal representative of a weighted version of the wave signal received at the second element,
summing means for deriving from the first and third signals a fourth, sum signal representative of the sum of the wave signal received at the first element and said weighted version of the wave signal received at the second element,
correlating means for measuring the correlation C2 between said sum signal and a reference signal derived from the wave signal received at at least one of the receiving elements,
power measuring means for measuring the power of the reference signal, and
calculating and control means for performing a correlation and weight adjustment process which comprises setting the weight W2 to each of two independent known values W2j (j = 1, 2), calculating from the resultant correlation C2j measured by the correlating means for each value of W2j and from the power P12 of the reference signal measured by the measuring means the quantity B where B = (W2n - W2opt) P12/C2n where n is either 1 or 2 and W2opt = (C21W22 - C22W21)/(CZ1 measured by the power measuring means an optimum weight value W20PT where W20pT = W23 - (3C23/P3) and setting W2 to 420PT-
10. A system as claimed in Claim 8 or 9 wherein the reference signal is the second electrical signal.
11. A system as claimed in any of Claims 8 to 10 for performing a method as claimed in any of Claims 4 to 6 wherein the system comprises
further weighting means for applying an adjustable weight Wt to the first electrical signal to derive a fifth, weighted signal representative of a weighted version of the wave signal received at the first element,
further summing means for deriving from the second and fifth signals a sixth, further sum signal representative of the sum of the wave signal received at the second element and said weighted version of the wave signal received at the first element,
further correlating means for measuring the correlation C1 between the further sum signal and a further reference signal derived from the wave signal received at at least one of the receiving elements,
means for deriving said reference signal and said further reference signal from said further sum signal and said sum signal respectively, comprising discriminating means for subjecting at least one out of said sum signal and said further sum signal to said discrimination process whereby to tend to increase the power of one component relative to the other, and
calculating and control means for performing a correlation and weight adjustment process in respect of C1 and W1 which is the same mutatis mutandis as the correlation and weight adjustment process in respect of C2 and W2.
12. A system as claimed in Claim 11 wherein the discriminating means comprises a hard limiter followed by a zonal bandpass filter.
13. A system as claimed in Claim 11 or 12 adapted to repeat said correlation and adjustment processes in respect of C1 and W1 and of C2 and W2 respectively in alternation.
14. A system for performing a method as claimed in Claim 7, the system comprising
receiving means, comprising a plurality of N(N 2) mutually spacing receiving elements, for receiving wave signals and deriving
N electrical signals of which the jth electrical signal (j = 1, 2, ... N) is respectively representative of the wave signal received at the jth element,
weighting means for applying a respective adjustable weight Wi (i = 2, 3, ... N) to each of said electrical signals except the first to derive (N - 1) weighted signals of which the ith weighted signal is respectively representative of a weighted version of the wave signal received at the ith element,
summing means for deriving from the first signal and said weighted signals a sum signal representative of the sum of the wave signal received at the first element and the weighted versions of the wave signals received at each of the other elements,
correlating means for measuring the correlation Ci between said sum signal and each of said electrical signals except the first, and
calculating and control means for performing a correlation and weight adjustment process which comprises setting the weights Wi to each of N sets of known respective values Wij, the N sets of known values being independent, calculating from the resultant correlations Cij measured by the correlating means for each set of weight values optimum values We opt for the weights from the equations
Cij = Yil + W2jYi2 + W3jYi3 + .. + WNjYiN and 0 = Y j1 + W20ptYi2 + W30ptYi3 + ... + WNoptYiN, and setting the weights Wi to Wiopt respectively.
15. An adaptive nulling method substantially as herein described with reference to Figure 1 or to Figure 3 of the drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8615893A GB2314977B (en) | 1986-06-30 | 1986-06-30 | Adaptive nulling |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8615893A GB2314977B (en) | 1986-06-30 | 1986-06-30 | Adaptive nulling |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8615893D0 GB8615893D0 (en) | 1997-09-03 |
| GB2314977A true GB2314977A (en) | 1998-01-14 |
| GB2314977B GB2314977B (en) | 1998-06-24 |
Family
ID=10600309
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8615893A Expired - Fee Related GB2314977B (en) | 1986-06-30 | 1986-06-30 | Adaptive nulling |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2314977B (en) |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1556591A (en) * | 1976-10-21 | 1979-11-28 | Motorola Inc | Power rejection apparatus using a null constrained subarray for mti radar applications |
-
1986
- 1986-06-30 GB GB8615893A patent/GB2314977B/en not_active Expired - Fee Related
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1556591A (en) * | 1976-10-21 | 1979-11-28 | Motorola Inc | Power rejection apparatus using a null constrained subarray for mti radar applications |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2314977B (en) | 1998-06-24 |
| GB8615893D0 (en) | 1997-09-03 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3766559A (en) | Adaptive processor for an rf antenna | |
| EP2347531B1 (en) | Over-the-air test | |
| EP0992813B1 (en) | Radio wave arrival direction estimating antenna apparatus | |
| US6970722B1 (en) | Array beamforming with wide nulls | |
| EP1344276B1 (en) | Base station, base station module and method for direction of arrival estimation | |
| US5179386A (en) | Cylindrical phased array antenna system to produce wide open coverage of a wide angular sector with high directive gain and strong capability to resolve multiple signals | |
| CN100544231C (en) | Smart antenna implementation method and smart antenna based on software radio are realized system | |
| US10705176B2 (en) | Signal direction processing for an antenna array | |
| EP0809323A2 (en) | Signal processing apparatus and method for reducing the effects of interference and noise in wireless communications utilizing antenna array | |
| EP1032962B1 (en) | Discrimination procedure of a wanted signal from a plurality of cochannel interferents received from array antennas of base stations for cellular telecommunication and relative receiver | |
| CN114879226A (en) | Satellite navigation array anti-interference method based on intelligent sensing | |
| KR100532803B1 (en) | Method for evaluating direction | |
| US5933446A (en) | Beamformer with adaptive processors | |
| GB2314977A (en) | Adaptive nulling | |
| Chuku et al. | Adaptive array beamforming using an enhanced RLS algorithm | |
| US5434576A (en) | Optimized subarray amplitude tapers for array antennas | |
| US3725922A (en) | Convergence rate improvement for adaptive receiving array antennas of higher order than 2-pulse mti cancellers | |
| Lake et al. | Real-time digital equalization to enhance element-level digital beamforming | |
| CN113608179B (en) | Radar signal interference suppression method | |
| US7817091B2 (en) | Single input multiple output (SIMO) ranging and positioning systems | |
| Abohamra et al. | Direction of Arrival algorithms for user identification in cellular networks | |
| DE2650547A1 (en) | Adaptive radio reception aerial system - has main reflector aerial and several reference radiators producing minimum sensitivity in noise source directions | |
| CA2218309A1 (en) | Adaptive antenna | |
| Poutanen et al. | Correlation control in the multichannel fading simulators | |
| Stine | Beamforming Illustrations |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 730 | Substitution of applicants allowed (sect. 30/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19980924 |