EP0371357A2
Expired / Lapsed
EP
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Method of determination of signal reception time by means of correlation technique
Assignee: Motorola Solutions Danmark AS
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Filing: 1989-11-17
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Granted: —
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Expires: 2009-11-17
Abstract
Abstract A method of determining the reception time of a signal containing a predetermined code, e.g. a Barker code. The code may be present at the start of a telegram to be received by a mobile radio from a base station. The signal is correlated with a corresponding code stored in memory. The correlation is carried out at different offsets in time. This gives a correlation curve (figure 2). The apex represents peak correlation. The timing of optimum correlation is determined by extrapolating the sides to the apex. The invention also provides a zero crossing detector for timing zero crossing events whereby sufficiently accurate timing of receipt of the code is possible to enable meaningful correlation.
Inventors
- 👤 Per. E. Pedersen
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 13:35
CPC Classifications
H; H04; H04L; H04L7/00; H04L7/04; H04L7/041; H04L7/042; H04L7/08
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
152 words
A method of determining the timing of receipt of a signal containing a predetermined code, the method comprising the steps of: i) providing a first digital representation of the received code; ii) correlating the first representation of the received code with a stored true version of the code to provide a first number (R₁) of points of correlation therebetween; iii) providing a second digital representation of the received code, shifted by an incremental offset (T₂ - T₁) in time relative to the first representation and repeating the correlation to provide at least a second number (R₂) of points of correlation; iv) extrapolating the numbers of points of correlation in a period of increasing correlation and in a period of decreasing correlation; and v) determining the time at which the extrapolated increase coincides with the extrapolated decrease, thereby to determine the time of optimum correlation to an accuracy greater than the incremental offset.
Claim 2
Independent Claim
152 words
A method of determining the timing of receipt of a signal containing a predetermined code, the method comprising the steps of: i) providing a first digital representation of the received code; ii) correlating the first representation of the received code with a stored true version of the code to provide a first number (R₁) of points of correlation therebetween; iii) providing a second digital representation of the received code, shifted by an incremental offset (T₂ - T₁) in time relative to the first representation and repeating the correlation to provide at least a second number (R₂) of points of correlation; iv) extrapolating the numbers of points of correlation in a period of increasing correlation and in a period of decreasing correlation; and v) determining the time at which the extrapolated increase coincides with the extrapolated decrease, thereby to determine the time of optimum correlation to an accuracy greater than the incremental offset.
Claim 3
Dependent Claim
33 words
A method according to claim 1, wherein the rate of increase and decrease per incremental offset for the basis of extrapolation is taken to be equal to the predetermined number of logic states.
Claim 4
Dependent Claim
70 words
A method according to claim 2, wherein the time of optimum correlation is calculated in accordance with the formula: where: T-start is the time of optimum correlation; T1 and T2 are points in time within+/- 1 incremental offset of T-start; R1 and R2 are the number of points of correlation at times T1 and T2 respectively; and alpha is the rate of increase/decrease of points of correlation per incremental offset.
Claim 5
Dependent Claim
26 words
A method according to claim 1, wherein the rates of increase and decrease are measured by repeating the correlation at a plurality of incremental offset shifts.
Claim 6
Dependent Claim
131 words
Apparatus for determining the timing of receipt of a signal containing a predetermined code, comprising: i) means for providing at least first and second digital representations of the received code separated by an incremental offset in time; ii) means (13) for storing a true version (15) of the code; iii) means (12) for correlating the representations of the received code with the true version to provide at least first and second numbers of points of correlation therebetween; iv) means for extrapolating the number of points of correlation in a period of increasing correlation and in a period of decreasing correlation and for determining the time at which the extrapolated increase coincides with the extrapolated decrease, thereby to determine the time of optimum correlation to an accuracy greater than the incremental offset.
Claim 7
Dependent Claim
131 words
Apparatus for determining the timing of receipt of a signal containing a predetermined code, comprising: i) means for providing at least first and second digital representations of the received code separated by an incremental offset in time; ii) means (13) for storing a true version (15) of the code; iii) means (12) for correlating the representations of the received code with the true version to provide at least first and second numbers of points of correlation therebetween; iv) means for extrapolating the number of points of correlation in a period of increasing correlation and in a period of decreasing correlation and for determining the time at which the extrapolated increase coincides with the extrapolated decrease, thereby to determine the time of optimum correlation to an accuracy greater than the incremental offset.
Claim 8
Independent Claim
89 words
A method of signal processing of a signal comprising the steps of: (i) confirming that the signal represents a first or second logic state when a valid zero crossing to that state has been registered and a predetermined threshold above or below a datum level, respectively, is exceeded; ii) determining whether the signal crosses the datum level to detect a potential zero crossing when this occurs; and (iii) registering the potential zero crossing as a valid zero crossing only if the potential zero crossing follows a confirmed logic state,
Claim 9
Independent Claim
89 words
A method of signal processing of a signal comprising the steps of: (i) confirming that the signal represents a first or second logic state when a valid zero crossing to that state has been registered and a predetermined threshold above or below a datum level, respectively, is exceeded; ii) determining whether the signal crosses the datum level to detect a potential zero crossing when this occurs; and (iii) registering the potential zero crossing as a valid zero crossing only if the potential zero crossing follows a confirmed logic state,
Claim 10
Dependent Claim
68 words
A method according to claim 6, wherein the signal contains a stream of data bits having a predetermined baud rate and is sampled by analog-to-digital conversion means at a rate substantially higher than the baud rate and wherein, upon registering of a valid zero crossing, the timing of the valid zero crossing is registered, whereby said timing can be measured to an accuracy dependent on the sampling rate.
Claim 11
Dependent Claim
34 words
A method according to claim 6 or 7, comprising the further step of suppressing any further registrations of valid zero crossings for a predetermined period of time after a valid zero crossing is registered.
Claim 12
Independent Claim
38 words
A method according to any one of claims 6 to 8, wherein the peak-to-peak value of the signal is measured and the datum level is determined from the peak-to-peak value as being the mid level of the signal
Claim 13
Independent Claim
44 words
A method according to any one of claims 6 to 9, wherein the peak-to-peak value of the signal is measured and the predetermined threshold is removed from the dataum level by an amount equal to a predetermined fraction of the peak to peak value.
Claim 14
Independent Claim
77 words
A method according to any one of claims 6 to 10 wherein the dataum level is determined from the following steps: (i) measuring, over a period when the signal represents a predetermined code, the ratio of periods of one logic state to periods of another logic state; (ii) comparing this ratio with a predetermined expected ratio for that predetermined code and (iii) adjusting the datum level in accordance with the comparison between the measured and expected ratios.
Claim 15
Dependent Claim
106 words
A zero crossing detector comprising: (i) comparator means for comparing a signal with a datum level and detecting potential and valid zero crossings of the signal to first and second logic states; (ii) comparator means for comparing the signal with a predetermined threshold above or below the datum level and confirming that the signal represents the logic state to which the signal has cross when a valid zero crossing to that state has been registered and the respective threshold has been exceeded. (iii) means for registering a potential zero crossing as a valid zero crossing only if the potential zero crossing follows a confirmed logic state.
Claim 16
Dependent Claim
106 words
A zero crossing detector comprising: (i) comparator means for comparing a signal with a datum level and detecting potential and valid zero crossings of the signal to first and second logic states; (ii) comparator means for comparing the signal with a predetermined threshold above or below the datum level and confirming that the signal represents the logic state to which the signal has cross when a valid zero crossing to that state has been registered and the respective threshold has been exceeded. (iii) means for registering a potential zero crossing as a valid zero crossing only if the potential zero crossing follows a confirmed logic state.
Claim 17
Dependent Claim
97 words
A zero crossing detector according to claim 10, for demodulation of a signal (21) having a predetermined baud rate, comprising an analog-to-digital (A/D) converter (14) and a clock having a rate substantially higher than the baud rate, the A/D converter being arranged to sample the signal at said clock rate, and to determine the timing of samples in accordance with said clock count, wherein the means for registering a valid zero crossing are arranged to indicate the time of the valid zero crossing in accordance with the clock count at the time of that valid zero crossing.
References Cited (Backward Citations)
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