GB2544302B

GB2544302B - Pulse Data Word Throttling

Info

Publication number: GB2544302B
Application number: GB1519911.0A
Authority: GB
Inventors: Davies John; Pont Anthony; Lovegrove Graham; Lavery Richard
Original assignee: Thales Holdings UK PLC
Current assignee: Thales Holdings UK PLC
Priority date: 2015-11-11
Filing date: 2015-11-11
Publication date: 2019-11-20
Anticipated expiration: 2035-11-11
Also published as: GB2544302A; GB201519911D0

Description

Pulse Data Word Throttling

FIELD

Embodiments described herein relate to processing data received from a radar, in the form of pulse data words.

BACKGROUND

Radar receivers commonly output digital pulse data in the form of pulse data words. Each pulse data word bears information describing measurements such as measurement frequency and amplitude.

Relevant data can be occluded by the existence of high power radio frequency emissions. Due to increased commercial pressure to use radio frequencies for communications, such as digital broadcast television, such emissions are tending to encroach on frequencies habitually used for radar detection.

DESCRIPTION OF DRAWINGS

Figure 1 is a schematic diagram of a pulse data word throttle in accordance with an embodiment;

Figure 2 is a schematic diagram showing states of counts of the throttle in use; and

Figure 3 is a flow diagram showing function of the pulse data throttle of figure 1 in use.

DESCRIPTION OF EMBODIMENTS

An embodiment disclosed herein provides a pulse data word throttle which, in use, analyses an incoming stream of pulse data words and excludes, from an outgoing stream, pulse data words encoding frequencies which appear on the stream more times in a defined period than a permitted maximum.

An embodiment disclosed herein provides a method of throttling a train of pulse data words, each pulse data word encoding information relating to measured frequency of radiation received at a radar receiver, the method comprising defining a frequency detection range, and a plurality of disjoint frequency slots, wherein each frequency slot is within the frequency detection range, defining a counting period having a counting duration, establishing a plurality of counts, each count corresponding with a respective one of said frequency slots, for each received pulse data word, identifying if the pulse data word encodes frequency information corresponding to one of the frequency slots and, if so, if the count corresponding to the frequency slot encoded by that pulse data word is lower than a defined maximum count, passing the pulse data word to an output and incrementing the corresponding count, else discarding the pulse data word.

In one embodiment the union of the frequency slots comprises the frequency detection range. This provides for monitoring of a continuous region of the frequency spectrum, by non-overlapping but adjacent frequency slots. In alternative approaches, it may be appropriate to define frequency slots in certain parts of the spectrum, and not others, and the present disclosure does not exclude the possibility of monitoring several discontinuous portions of the spectrum at any one time.

In one embodiment, the frequency slots are of substantially equal frequency range. However, it may be appropriate, in certain embodiments, to define the slots as being of different ranges. For instance, it may be appropriate for the width of a frequency slot to be substantially variable with frequency. For instance, the width of a frequency slot may be in proportion with frequency. So, for example, a slot may be defined by bounds / (1 where f is the centre frequency of the slot and 5 is a dimensionless quantity expressing the slot width as a proportion of

The duration of the counting period may vary from one to the next. The duration may be a pseudorandom variable, defined with respect to a predetermined desired mean of the counting duration.

In one embodiment, the predetermined desired mean may be within a range of between 1 and 20ms. A range of possible values of the pseudorandom variable may be bounded to a predetermined range about the predetermined desired mean.

The predetermined range may be bounded by values 20% above and below the predetermined desired mean.

An overload counting period may be defined, such that, for an overload counting period, the method comprises counting the total number of pulse data words received and, if the total number exceeds a predetermined count limit within the overload counting period, reducing the defined maximum count and increasing the predetermined desired mean counting duration, wherein the duration of the overload counting period is set to be substantially greater than the predetermined desired mean of the counting duration.

The duration of the overload counting period may be at least 2 times greater than the predetermined desired mean of the counting duration. In one embodiment, the duration of the overload counting period is substantially 100 times the predetermined desired mean of the counting duration.

The value of the duration of the overload counting period may be defined by a user, through input to a device operating the method.

In an embodiment disclosed herein, the method comprises, during each counting period, resetting each count to zero. So, between the start and end of a counting period, all counts will have been set to zero once. In one embodiment, the counts are set to zero once and only once per counting period.

Rather than setting all counts to zero simultaneously, the counts may be set to zero in accordance with a sequence. Sequential resetting of the counts may be timed to progress over substantially the whole duration of a counting period. The method may comprise defining a plurality of intervals of the counting period, allocating each count to an interval, and, during each interval having an allocated count, resetting the allocated count to zero. The number of intervals may equal the number of counts.

Another embodiment comprises a throttle for throttling a train of pulse data words, each pulse data word encoding information relating to measured frequency of radiation received at a radar receiver, the throttle comprising a counting period timer for defining a counting period, the counting period having a counting duration, a plurality of counters, each counter being operable to establish a count corresponding to a respective one of a plurality of disjoint frequency slots defined within a frequency detection range, and a count processor operable, for each received pulse data word, to identify if the pulse data word encodes a frequency within one of the defined frequency slots and, if so, if the count corresponding to the identified frequency slot is lower than a defined maximum, to pass the pulse data word to an output and to increment the corresponding count, else to discard the pulse data word.

Another embodiment comprises a throttle in accordance with claim 18 wherein each pulse data word encodes frequency information within a predetermined range, and wherein each of the plurality of counts corresponds to a subdivision of that predetermined range of frequencies.

Another embodiment comprises a computer program product comprising computer executable instructions which, when executed by a computer processor, cause that processor to implement an embodiment as laid out above. A specific embodiment will now be described with reference to the drawings. A pulse data word throttle 100 is illustrated in figure 1. A functional description of the throttle 100 is shown by way of a flow diagram in figure 3, and steps of that flow diagram are introduced in this description also.

In general terms, the throttle 100 operates on a stream of pulse data words. The pulse data words are produced by equipment such as a radar detector, reporting detection of radio frequency (RF) pulses. Each pulse data word therefore bears information reporting measured characteristics of a detected RF pulse. This will include a measured frequency. The throttle 100 is placed in the stream to reduce excessive influence of a particular frequency on the stream. Situations could arise, such as where a television signal is detected by the radar equipment, whereby the incoming pulse data word stream is overwhelmingly influenced by the television broadcast frequency. This could inhibit analysis of RF activity of interest. A count processor 110 receives the input stream, and is operable to determine whether the pulse data words are to be permitted to pass through to an output stream.

To do this, a plurality of counters 112 are provided. Each counter 112 is assigned to a corresponding subdivision of the range of expected frequencies encoded on pulse data words. In one embodiment, the range of expected frequencies is 8GHz in width (S1-2), and 1000 counters 112 are provided (S1-4), hence each counter 112 is assigned to a subdivision of 8MHz in width (S1-6).

Each time a pulse data word is received by the count processor 110, the count processor 110 checks the counter 112 (S1-8) corresponding to the frequency encoded on that pulse data word. The count processor 110 stores a permitted maximum count value. If the count on the corresponding counter 112 is less than that permitted maximum count value (S1-10), then the count is incremented by one (S1-12), and the pulse data word is passed through to the output stream. In one embodiment, this permitted maximum count value is 255.

By contrast, if the count on the corresponding counter 112 is already at the permitted maximum value, then the pulse data word is discarded (S1-14). A counter reset 114 is provided, which is driven by a counting duration timer 116. The operating principle of the counter reset 114 is that, during a counting duration, set by the counting duration timer 116, each counter 112 will be supplied with a counter reset signal. The counter reset signal will trigger a reset of the count of that counter 112 to zero. The counter reset signal will be supplied to each counter once per counting duration.

In a particular embodiment, the counter reset signal is supplied to each counter 112 in turn, sequentially, over the period of a counting duration. In one embodiment, the counting duration is at a fixed and repetitive interval (S1-20). In one specific embodiment, a delay of substantially 5ms in duration is used. Therefore, if 1000 counters 112 are defined, counter reset signals will be sent, sequentially, to each counter 112 in turn every 5ps (S1-22).

As mentioned above, the counting duration, set and managed by the counting duration timer 116 is a fixed and repetitive interval. However, in one embodiment, the counting duration timer 116 is operable to vary this counting duration around a desired average. For example, in one embodiment, the average counting duration may be substantially 5ms, but the actual counting duration can at any particular time be anywhere between 4ms and 6ms. Variation of the counting duration is, in one specific embodiment, established pseudorandomly. That is, while the perception of randomness is achieved, to all intents and purposes, the generation of the pseudorandom variable can be carried out by a deterministic process. As the reader will appreciate, pseudorandom generation of a variable is generally more straightforward than achieving true randomness, and is acceptable in the context of performance of this embodiment.

The purpose of varying the counting duration, and preferably pseudorandomly, is to reduce effects which could be introduced by repetitively zeroing counts every 5ms. Repeatedly performing a processing step at regular intervals may introduce a periodicity into resultant data. Any process which introduces periodicity into data analysis may have an undesirable effect.

The counter reset 114 derives its process for issuing counter reset signals from the counting duration timer 116. That is, the counting duration timer 116 informs the counter reset 114 as to the next counting duration. The sequential zeroing of the counters 112 is then performed over the course of that counting duration. So, if the counting duration is more or less than the chosen fixed and repetitive interval, the sequence of counter reset signals will be retarded or accelerated accordingly.

An additional counter, described here as an overload counter 120, counts the number of pulse data words received at the count processor 110 over a further defined period. In this described embodiment, this defined period is 0.5s. The reader will observe that the overload count period is, in this example, 100 times the average count duration. This order of magnitude higher than the average count duration is appropriate, though strict compliance with this rule is not required. The overload counter 120 checks that the number of pulse data words does not exceed a preset total pulse value.

If the number of pulse data words exceeds the present total pulse value, then the overload counter 120 sends an overload signal to the counting duration timer 116, and to the count processor 110. The response of the counting duration timer 116 to the overload signal is to increase the average count duration (initially 5ms in one embodiment). The increased average count duration means that the counters 112 are more likely to reach their maximum value during a count duration. Also, the overload signal is sent to the count processor 110. The count processor 110 responds by reducing the permitted maximum count value for each counter 112. Again, this acts to impose a further constraint on the prospect of a pulse data word reaching the output stream. A user interface 118 is also provided, which can provide feedback information to a user as to the extent to which flow of pulse data words is being throttled by the throttle 100. It can also provide a facility for a user to alter operating parameters of the throttle, including initialising a maximum permitted count value (noting that this can be further reduced by the overload signal), the average counting duration, the width, in frequency, of each range of frequencies attributable to a particular count (initially 8MHz, but user variable), the number of counters to be employed, the range of permitted variation of the counting duration, the extent to which this variation should be pseudorandom, and the overall count to be monitored by the overload counter. All of these will impact on the sensitivity of the throttle 100 to conditions which merit the constraint of data from the input of the device to the output.

For simplicity, it may be desirable to present the user with simplified selectable states, each state mapping to preset values for all or some of these variables. So, in one embodiment, the user may be presented with a choice of “low” or “high” settings -choosing “low” will map to selection of values of all or some of these variables which place less constraint on data passing through the throttle, whereas choosing “high” will cause increased sensitivity to overload conditions.

Figure 2 illustrates a schematic representation of count values stored by the counters 112, in use. As can be seen, to the right of the drawing, count values are approaching the previously established maximum value, indicated by a broken horizontal line. Two of the illustrated bars has reached that maximum value. Thus, if the next pulse data word were to encode frequency information corresponding to a frequency represented by one of those bars, that pulse data word would be discarded.

One entry, as indicated in figure 2, is the most recently zeroed count. It is thus still at zero. Entries to the left of the most recently zeroed count are still at low levels, having only recently been zeroed. Counts to the right of the most recently zeroed count are next to be zeroed, and are thus at relatively high levels.

When a count, which previously had reached the maximum permitted value, is zeroed, the throttle then permits a further 255 words encoding frequencies corresponding to that count, until the maximum is reached. Thus, in essence, there will always be a permitted level of activity at each frequency. This will enable the admittance of pulse data words, carrying genuine data of interest, to pass through the throttle (at least, until the maximum is reached) whereas a filter might unduly exclude particular frequencies completely.

The above described throttle can be implemented on firmware of an FPGA, for instance using VHDL, though the reader will appreciate that other approaches, either involving hardware or software, could be envisaged.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

CLAIMS:

1. A method of throttling a train of pulse data words, each pulse data word encoding information relating to measured frequency of radiation received at a radar receiver, the method comprising: defining a frequency detection range, and a plurality of disjoint frequency slots, wherein each frequency slot is within the frequency detection range; defining a counting period having a counting duration; establishing a plurality of counts, each count corresponding with a respective one of said frequency slots, for each received pulse data word, identifying if the pulse data word encodes frequency information corresponding to one of the frequency slots and, if so, if the count corresponding to the frequency slot encoded by that pulse data word is lower than a defined maximum count, passing the pulse data word to an output and incrementing the corresponding count, else discarding the pulse data word.

2. A method in accordance with claim 1 wherein the union of the frequency slots comprises the frequency detection range.

3. A method in accordance with claim 1 or claim 2 wherein the frequency slots are of substantially equal frequency range.

4. A method in accordance with any preceding claim and further comprising, a plurality of counting periods, wherein each counting period is defined by a counting duration.

5. A method in accordance with claim 4 wherein defining the counting duration comprises assigning a value of a pseudorandom variable, the pseudorandom variable being defined with respect to a predetermined desired mean of the counting duration.

6. A method in accordance with claim 5 wherein the predetermined desired mean is within a range of between 1 and 20ms.

7. A method in accordance with claim 4 or claim 5 wherein the pseudorandom variable can assume a value within a predetermined range about the predetermined desired mean.

8. A method in accordance with claim 7 wherein the predetermined range is bounded by values 20% above and below the predetermined desired mean.

9. A method in accordance with any one of claims 4 to 8 and further comprising, for an overload counting period, counting the total number of pulse data words received and, if the total number exceeds a predetermined count limit within the overload counting period, reducing the defined maximum count and increasing the predetermined desired mean counting duration, wherein the duration of the overload counting period is set to be substantially greater than the predetermined desired mean of the counting duration.

10. A method in accordance with claim 9 wherein the duration of the overload counting period is at least 2 times greater than the predetermined desired mean of the counting duration.

11. A method in accordance with claim 9 or claim 10 wherein the duration of the overload counting period is substantially 100 times the predetermined desired mean of the counting duration.

12. A method in accordance with claim 9 comprising obtaining, from a user, a user defined value for the duration of the overload counting period.

13. A method in accordance with any one of the preceding claims comprising, during the counting period, resetting each count to zero.

14. A method in accordance with claim 13 wherein the resetting applies to each count on a single occasion per counting period.

15. A method in accordance with claim 14 comprising defining a zeroing sequence for the counts, and resetting the counts in accordance with the sequence.

16. A method in accordance with claim 15 wherein the sequential resetting of the counts is timed to progress over substantially the whole duration of a counting period.

17. A method in accordance with claim 16 comprising defining a plurality of intervals of the counting period, allocating each count to an interval, and, during each interval having an allocated count, resetting the allocated count to zero.

18. A method in accordance with claim 17, wherein the number of intervals equals the number of counts.

19. A throttle for throttling a train of pulse data words, each pulse data word encoding information relating to measured frequency of radiation received at a radar receiver, the throttle comprising: a counting period timer for defining a counting period, the counting period having a counting duration; a plurality of counters, each counter being operable to establish a count corresponding to a respective one of a plurality of disjoint frequency slots defined within a frequency detection range; and a count processor operable, for each received pulse data word, to identify if the pulse data word encodes a frequency within one of the defined frequency slots and, if so, if the count corresponding to the identified frequency slot is lower than a defined maximum, to pass the pulse data word to an output and to increment the corresponding count, else to discard the pulse data word.

20. A throttle in accordance with claim 19 wherein each pulse data word encodes frequency information within a predetermined range, and wherein each of the plurality of counts corresponds to a subdivision of that predetermined range of frequencies.

21. A throttle in accordance with claim 19 and wherein the subdivisions correspond to equal frequency ranges.

22. A throttle in accordance with any of claims 19 to 21 and wherein the counting duration timer is operable to vary the counting duration from one counting duration to the next.

23. A throttle in accordance with claim 22 and wherein the counting duration timer is operable to pseudorandomly vary the counting duration around a predetermined desired mean.

24. A throttle in accordance with claim 23 and wherein the counting duration timer is operable to vary the counting duration within a range about the predetermined desired mean.

25. A throttle in accordance with claim 24 wherein the range of counting duration is defined as 20% above and below the predetermined desired mean.

26. A throttle in accordance with any one of claims 23 to 25 and further comprising an overload counter operable to count, for an overload counting duration, the total number of pulse data words processed and, if the total number exceeds a predetermined count limit, operable to reduce the defined maximum count and to increase the predetermined desired mean count duration.

27. A throttle in accordance with claim 26 comprising an input unit operable to obtain, from a user, a user defined value for the overload count duration.

28. A throttle in accordance with claim 26 wherein the overload count duration is substantially greater than the predetermined desired mean count duration.

29. A throttle in accordance with claim 28 wherein the overload count duration is substantially 100 times the predetermined desired mean count duration.

30. A throttle in accordance with any one of claims 19 to 29 comprising a reset unit operable to reset each count to zero once for each counting duration.

31. A throttle in accordance with claim 30 wherein the reset unit is operable to sequentially reset the counts to zero.

32. A throttle in accordance with claim 31 wherein the reset unit is operable to define a plurality of equal intervals of the counting duration, each interval corresponding to a count, and each interval, to reset the corresponding count to zero.

33. Computer program product comprising computer executable instructions which, when executed by a computer processor, cause that processor to implement a method in accordance with any one of claims 1 to 18.