Method of and apparatus for detecting impulsive noise, method of operating a demodulator, demodulator and radio receiver
First Claim
1. A method of detecting impulsive noise in a stream of sets of signal samples in a radio receiver, wherein each of said sets comprises at least one of said samples, said method comprising the steps of:
- (a) comparing a value based on an amplitude of said at least one sample of each said set with each of a number J of thresholds Tj, where J is greater than zero;
(b) determining each number nj of said sets in each Nj consecutive ones of said sets for which said value is greater than Tj for each value of j such that 1≦
j≦
j; and
(c) indicating a noise impulse when each said number nj is greater than a respective first number Xj;
wherein;
said step (a) is performed for each said set of samples, Si in turn in order of arrival with a first threshold, where i indicates order of arrival;
said step (b) compromises determining each said nj from each said Nj consecutive sets, of which a most recent is Si;
said step (c) compromises indicating a start of said noise impulse when every said nj rises above said respective first number Xj and indicating an end of said noise impulse when every said nj falls below a respective number Yj; and
each said second number Yj is smaller than said respective first number Xj.
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Accused Products
Abstract
In a digital receiver for receiving COFDM modulated television signals or the like, consecutive samples are compared with a detection threshold and the number of samples having amplitudes greater than the threshold is determined. This is compared with a further threshold and, if the number of such samples exceeds the further threshold, affected samples are blanked to zero. Similarly, an automatic gain control loop is disabled when the samples are blanked. A demodulator forms the difference in phase of pilot carriers from symbol to symbol. If the variance of the phase differences exceeds an averaged value, this indicates the presence of impulsive noise and is used to inhibit signal correction techniques within the demodulator. Noise energy is thus reduced and propagation of effects resulting from impulsive noise from symbol to symbol is substantially reduced.
71 Citations
34 Claims
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1. A method of detecting impulsive noise in a stream of sets of signal samples in a radio receiver, wherein each of said sets comprises at least one of said samples, said method comprising the steps of:
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(a) comparing a value based on an amplitude of said at least one sample of each said set with each of a number J of thresholds Tj, where J is greater than zero; (b) determining each number nj of said sets in each Nj consecutive ones of said sets for which said value is greater than Tj for each value of j such that 1≦
j≦
j; and(c) indicating a noise impulse when each said number nj is greater than a respective first number Xj; wherein; said step (a) is performed for each said set of samples, Si in turn in order of arrival with a first threshold, where i indicates order of arrival; said step (b) compromises determining each said nj from each said Nj consecutive sets, of which a most recent is Si; said step (c) compromises indicating a start of said noise impulse when every said nj rises above said respective first number Xj and indicating an end of said noise impulse when every said nj falls below a respective number Yj; and
each said second number Yj is smaller than said respective first number Xj.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. An apparatus for detecting impulsive noise in a stream of sets of samples in a radio receiver, wherein each of said sets comprises at least one of said samples, said apparatus comprising:
- a comparator for comparing a value based on an amplitude of each said sample of each said set with each of a number J of thresholds Tj, where J is greater than zero;
determining means for determining each number nj of said sets in each Nj consecutive ones of said sets for which the value is greater than Tj for each value of j such that 1≦
j≦
J; and
indicating means for indicating a noise impulse when every said number nj is greater than a respective first number Xj wherein;
said comparator is arranged to perform a comparison for each said set of signal samples, Si in turn in order of arrival with each said first threshold, wherein i indicates said order of arrival;
said determining means is arranged to determine each said nj from the or each said Nj consecutive sets of samples, of which a most recent is Si;
said indicating means is arranged to indicate a start of said noise impulse when ever said nj rises above said respective first number Xj; and
an end of said noise impulse when every said nj falls below a respective second number Yj; and
each said second number Yj is smaller than said respective first number Xj. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
- a comparator for comparing a value based on an amplitude of each said sample of each said set with each of a number J of thresholds Tj, where J is greater than zero;
Specification