Processing A Noisy Analogue Signal

Abstract

A device is provided for correlating at least one noisy analogue signal which is one of a plurality of signals obtained by a plurality of receivers. The device comprises a 1-bit quantisation element to which is supplied, in use, the noisy signal; a comparator configured to compare the quantised signal with a reference signal which is a consensus signal obtained by averaging data from the plurality of receivers; and an up/down counter that is configured to be incremented by a subset of the comparison signal.

Description

FIELD

The present invention relates to a method of, and a device for, correlating at least one noisy analogue signal which is one of a plurality of signals obtained by a plurality of receivers.

BACKGROUND

The correlation of one or more noisy analogue signals may be effective even when the signal is polluted by noise that is of greater amplitude than the signal. One known approach is to correlate the noisy analogue signal with another signal, such as a reference signal of known characteristics. This is achieved by multiplying together the two signals and then integrating the result. When the integral is near-zero, the signals are not correlated. When the integral is strongly positive, the signals are correlated and when the integral is strongly negative, the signals are correlated, but one is inverted in relation to the other.

However, analogue integrators are prone to drift. Furthermore, the multiplication and integration of the two signals is quite resource intensive.

The present invention has been devised in part to address these issues.

SUMMARY

According to a first aspect of the present invention there is provided a method of correlating at least one noisy analogue signal, wherein the noisy signal is one of a plurality of signals obtained by a plurality of receivers; the method comprising the steps of:

• • 1-bit quantising the noisy signal;
  • comparing the quantised signal with a quantised reference signal, wherein the reference signal is a consensus signal obtained by averaging data from the plurality of receivers; and
  • sampling the comparison signal (in other words a signal resulting from the comparing step) to increment an up/down counter.

When working with a very noisy signal, digitising the signal using 1-bit quantisation extracts the majority of the available information from the noisy signal. The presence of a lot of noise means that the provision of additional resolution in the digital signal would not add any further information.

The step of sampling the comparison signal to increment an up/down counter, effectively performs the integration required to identify the correlation, or lack thereof, between the signals. The use of an up/down counter, in place of the integrator required in the analogue approach known in the art, provides a much less computationally intensive operation, by merely adding rather than performing an integration.

The presence of a large amount of random noise affects the value of the count proportional to the signal-to-noise ratio of the noisy signal. The strength of the required signal can be measured and optimised even when the noise is much stronger.

Noise contributed by each receiver is generally independently from noise contributed by the other receivers. Thus, correlating the signals in this way can reduce the noise associated with the reference or consensus signal.

Each of the plurality of signals may originate from a single source. The signal from the source may be an n-state phase-shift keyed signal.

The method may comprise: identifying, i.e. determining, the phase offset between the phase of the noisy signal and the phase of the reference signal by considering the value of the up/down counter; and altering the phase of the noisy signal to correct for the phase offset.

The method may comprise: 1-bit quantising each of in-phase and quadrature components of the noisy signal; comparing each of the quantised in-phase and quadrature components of the noisy signal with each of quantised in-phase and quadrature components of the reference signal; if the quantised in-phase components of the noisy signal and the reference signal are equal, incrementing or decrementing a first up/down counter in a first direction (e.g. up) and, if not, incrementing or decrementing the first up/down counter in a second direction (e.g. down); if the quantised quadrature components of the noisy signal and the reference signal are equal, incrementing or decrementing the first up/down counter in the first direction and, if not, incrementing or decrementing the first up/down counter in the second direction; if the quantised in-phase component of the noisy signal and the quantised quadrature component of the reference signal are equal, incrementing or decrementing a second up/down counter in a first direction and, if not, incrementing or decrementing the second up/down counter in a second direction; and if the quantised quadrature component of the noisy signal and the quantised in-phase component of the reference signal are equal, incrementing or decrementing the second up/down counter in the second direction and, if not, incrementing or decrementing the second up/down counter in the first direction.

The method may comprise stopping the first and second up/down counters when one of the first and second up/down counters reaches full scale.

The method may comprise: determining the phase offset between the phase of the noisy signal and the phase of the reference signal by considering the values of the first and second up/down counters; altering the phase of the noisy signal in order to correct for the phase offset; and resetting the first and second up/down counters.

The method may comprise inverting the quantised signal if there is a strong negative correlation.

The method may comprise excluding the noisy signal from the consensus signal if the noisy signal consistently sits beyond a predetermined range of the consensus signal.

According to a second aspect of the present invention there is provided a device for correlating at least one noisy analogue signal, wherein the noisy signal is one of a plurality of signals obtained by a plurality of receivers, the device comprising:

• • a 1-bit quantisation element to which is supplied, in use, the noisy signal;
  • a comparator configured to compare the quantised signal with a reference signal, wherein the reference signal is a consensus signal obtained by averaging data from the plurality of receivers; and
  • an up/down counter that is configured to be incremented by a subset of the comparison signal (in other words a signal provided by the comparator).

The device may comprise a sampling device configured to sample the comparison signal, and the up/down counter may be configured to be incremented each time, or just after each time, the sampling device samples the comparison signal.

The comparator may be an XOR logic operator.

The device may be configured to alter the phase of the noisy analogue signal. The phase alteration of the noisy signal is performed in order to optimise the correlation.

The device may further comprise a control block configured to reset the or each up/down counter.

There may be provided apparatus comprising the plurality of receivers, each of the plurality of receivers comprising the device.

Further optional features of the present invention are specified in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present invention are described below, by way of example only, with reference to the accompanying FIG. 1 which illustrates a device for correlating at least one noisy analogue signal.

Certain embodiments of the present invention are described below, by way of example only, with reference to the accompanying FIG. 1 which illustrates a device for correlating at least one noisy analogue signal.

DETAILED DESCRIPTION OF THE CERTAIN EMBODIMENTS

FIG. 1 shows a device 100, or phase controlled receiver, for correlating at least one noisy analogue signal 200, being a Phased Shift Keyed signal. The noisy analogue signal 200 is obtained from one of a plurality of receivers. The signal from each of the receivers is combined to provide a consensus signal 210. The consensus signal 210 has components I_OUT and Q_OUT that is the summation of the in-phase and quadrature components of the analogue signals received from each of the receivers.

FIG. 1 shows a device 100, or phase controlled receiver, for correlating at least one noisy analogue signal 200, being a Phased Shift Keyed signal. The noisy analogue signal 200 is obtained from one of a plurality of receivers. The signal from each of the receivers is combined to provide a consensus signal 210. The consensus signal 210 has components I_OUT and Q_OUT that is the summation of the in-phase and quadrature components of the analogue signals received from each of the receivers.

The noisy analogue signal 200 is provided modulated onto a microwave frequency carrier. It is introduced to low noise amplifier 102 then to multipliers 104 which brings the signal back to baseband. The signal is then filtered at filter 106 which removes signals outside the baseband frequency band.

Once the noisy signal 200 has been prepared, it can then be digitised in the 1-bit quantisation elements 110. Similar 1-bit quantisation elements 130 are provided to digitise the consensus signal 210. The elements 110, 130 identify whether or not the signal exceeds a predetermined level and allocate a binary value as appropriate. The noisy signal 200 is then provided to an XOR gate which has its other input controlled in order to either maintain or invert the signal. The provision of the XOR gates enables a strongly negative correlation to be inverted to provide a strongly positive correlation or vice versa.

A comparator 120 is provided to compare the prepared, and potentially inverted, noisy signal 200 (In, Qn) with the consensus signal 210 (ΣI, ΣQ). The comparator 120 comprises four XOR gates 122, 124, 126 and 128. XOR gates 124 and 126 give correlation of the amplitude of the signal. Whilst XOR gates 122 and 128 give correlation of the phase of the signal.

The outputs of the four XOR gates control the UP/DOWN status of a counter block 140 which is clocked at intervals as frequent as is justified by the frequency bandwidth of the signal being received. There is a counter that gives the amplitude of correlation and a counter that gives the phase error. The counter that gives the amplitude of correlation is incremented or decremented according to:

• • If In=ΣI count up
  • If Qn=ΣQ count up
  • If In≠ΣI count down
  • If Qn≠ΣQ count down

The counter that gives the phase error is incremented or decremented according to:

• • If In=ΣQ count up
  • If In≠ΣQ count down
  • If Qn=ΣI count down
  • If Qn≠ΣI count up

When one of the counters reaches full scale, either positive or negative, counting is stopped on the counters. By considering the value of the counters, the phase offset can be identified and the control block 150 is configured to control an oscillator 160 which alters the phase of the signal in the multipliers 104 in order to correct the phase. A signal from the control block 150 resets the counters, i.e. to their mid range zero position. Another reading may be then commenced. Accordingly, the phase offset is driven to zero.

The phase offset is equal to an angle defined by the values of the counters. In particular, if the value (hereinafter referred to as the “phase counter value”) of the counter that gives the phase error is plotted on the x-axis and the value of the counter that gives the amplitude of correlation (hereinafter referred to as the “amplitude counter value”) is plotted on the y-axis, then the phase error is defined as the angle between the (vertical) line which is the positive part of the y-axis and the line from the origin to the point whose x- and y-coordinates are defined by the phase counter value and amplitude counter value respectively. The angle is defined such that is can vary between −180 degrees (minus 180 degrees) and +180 degrees (plus 180 degrees). The angle is negative if the phase counter value is negative and vice versa. Accordingly, the angle is given by the arctangent of the ratio of the phase counter value to the (full-scale) amplitude counter value for angles between −45 degrees and +45 degrees, by 90 degrees minus the arctangent of the ratio of the amplitude counter value to the (full-scale) phase counter value for angles between +45 degrees and +135 degrees, etc.

It is not necessary to determine the phase offset when one of the counters has reached full scale. The phase offset can be determined from any pair of phase and amplitude counter values.

In order to preserve the integrity of the consensus signal 210, one or more of the receivers, or parts thereof, may have to be disregarded. This is achieved using a control circuit 170.

Signals from receivers can only be included in the consensus signal if they are within a predetermined percentage of the consensus signal. If the noisy signal 200 consistently sits beyond the predetermined range, despite inverting the signal with the XOR gates 112 and changing the phase by up to 90° using the oscillator 160 then the control circuit 170 can exclude it from the consensus signal. This enhances the integrity of the consensus signal.

The control block 150 is also provided with a power on reset facility 180 which ensures that the up/down counters are all reset to their midrange zero point when the device 100 is initialised.

It will be appreciated that many other modifications may be made to the embodiments hereinbefore described.

Claims

1-17. (canceled)

18. A method comprising: obtaining a quantised signal from a received signal that is one of a plurality of received signals;obtaining a quantised reference signal from a combined signal that is a combination of a plurality of output signals, wherein each output signal is obtained from one of the plurality of received signals;obtaining a comparison signal by at least comparing the quantised signal with the quantised reference signal; andusing at least the comparison signal to change a counter value, wherein the counter value is for correlating an output signal obtained from the received signal with the plurality of output signals.

19. The method of claim 18, wherein the output signal corresponds to the quantised signal.

20. The method of claim 19, further comprising: using at least the counter value to alter a phase of the quantised signal.

21. The method of claim 20, further comprising: resetting the counter value after the use thereof.

22. The method of claim 18, wherein each of the plurality of received signals corresponds to a n-state phase shift keyed signal.

23. The method of claim 18, wherein: the quantised signal is obtained from a first type of component of the received signal; andeach output signal is obtained from one of the first type and a second type of component of one of the plurality of received signals.

24. The method of claim 23, comprising: obtaining a further quantised signal from the second type of component of the received signal;obtaining a further quantised reference signal from a further combined signal that is a combination of a plurality of further output signals, wherein each further output signal is obtained from the other of the first and second types of component of one of the plurality of received signals;obtaining the comparison signals and at least one further comparison signal by comparing at least one of the quantised signals and the further quantised signal with at least one of the quantised reference signal and the further quantised reference signal; andusing the comparison signal and the at least one further comparison signal to change at least one of the counter value and at least one further counter value.

25. The method of claim 24, wherein the first and second types of components correspond to in-phase and quadrature components, respectively.

26. The method of claim 24, further comprising using the counter value and the at least one further counter value to determine a phase offset between the output signal and the combined signal.

27. The method of claim 18, further comprising performing at least one of: selectively inverting the quantised signal before the comparing thereof with the quantised reference signal; andselectively excluding the output signal from the combined signal.

28. The method of claim 18, wherein obtaining the quantised signal comprises 1-bit quantising a signal obtained from the received signal.

29. The method of claim 18, wherein the combined signal is obtained by at least one of averaging and summing the plurality of output signals.

30. A device comprising: a quantisation element to enable a quantised signal to be obtained from a received signal that is one of a plurality of received signals;a comparator to enable a comparison signal to be obtained by at least comparing the quantised signal with a quantised reference signal obtained from a combined signal that is a combination of a plurality of output signals, wherein each output signal is obtained from one of the plurality of received signals; anda control block to use a counter value to enable correlation of an output signal obtained from the received signal with the plurality of output signals, wherein the counter value is changed using at least the comparison signal.

31. The device of claim 30, further comprising a multiplier to enable the received signal to be demodulated prior to quantisation.

32. The device of claim 30, further comprising a further quantisation element to enable the quantised reference signal to be obtained from the combined signal.

33. The device of claim 30, wherein the comparator comprises an exclusive-ORr gate.

34. The device of claim 30, wherein the control block is configured to provide a signal for altering a phase of the quantised signal.

35. The device of claim 30, further comprising circuitry to selectively include the output signal in the combined signal.

36. The device of claim 30, wherein: the device comprises the quantisation element and a further quantisation element to enable in-phase component and quadrature component versions of the quantised signal to be obtained;wherein the comparator is configured to enable the comparison signal and at least one further comparison signal to be obtained by comparing at least one of the in-phase component and quadrature component versions of the quantised signal with at least one of in-phase component and quadrature component versions of the quantised reference signal;wherein the control block is configured to use at least one of the counter value and at least one further counter value, wherein at least one of the counter value and the at least one further counter value is changed using the comparison signal and the at least one further comparison signal.

37. A system comprising: first and second conductors; anda plurality of devices, wherein each device comprises:quantisation elements to enable in-phase and quadrature quantised signals to be obtained from in-phase and quadrature components of a received signal, respectively;a first output for providing an in-phase output signal corresponding to the in-phase quantised signal to the first conductor;a second output for providing a quadrature output signal corresponding to the quadrature quantised signal to the second conductor;a first input for obtaining an in-phase combined signal from the first conductor;a second input for obtaining a quadrature combined signal from the second conductor;further quantisation elements to enable in-phase and quadrature quantised reference signals to be obtained from the in-phase and quadrature combined signals, respectively;a comparator to enable at least two comparison signals to be obtained by comparing at least one of the in-phase and quadrature quantised signals with at least one of the in-phase and quadrature quantised reference signals; anda control block to use at least one counter value to enable correlation of the in-phase and quadrature output signals with the in-phase and quadrature combined signals, respectively, wherein the at least one counter value is changed using the at least two comparison signals.