Method for cancelling a narrow-band interference signal
A method of canceling a narrow-band interference signal in a receiver is provided. A reference signal (ref_in) is subtracted from a received input signal (in). the phase of a result of the subtraction is calculated on the basis of an arctangent function. An unwrap function on the output signal from the arctangent function is performed by removing the modulo 2Π limitation introduced with the arctangent function, in order to produce an absolute phase representation. A frequency offset is determined by comparing phase representation values which are shifted predetermined in time. The narrow-band interference signal is canceled based on the result of the determined frequency offset.
1. A method of canceling a narrow-band interference signal in a receiver, comprising the steps of:
subtracting a reference signal from a received input signal;
calculating the phase of a result of the subtraction on the basis of an arctangent function,
performing an unwrap function on the output signal from the arctangent function, by removing the modulo 2Π limitation introduced with the arctangent function, thereby producing an absolute phase representation,
determining a frequency offset by comparing phase representation values which are shifted predetermined in time, and
canceling the narrow-band interference signal based on the result of the determined frequency offset,
wherein the unwrap function accumulates k times 2Π, where k depends on the wrapped function so that k will be increased by 1 if the difference between the last corrected sample and the current sample is smaller than −Π, and k will be decreased by 1 if the difference between the last corrected sample and the current sample is greater than Π.
2. A method according to claim 1 , characterized in that the subtracting step can be put on a hold a predetermined period of time, if there is no reference signal available to perform the subtraction.
3. A method according to claim 1 , characterized in that the unwrap function can be put on a hold a predetermined period of time, if there is no reference signal available to perform the unwrap function.
4. A method according to claim 1 , characterized in that the canceling the narrow-band interference signal is performed by selecting a filter from within a filter-bank based on the value of k.
5. A method according to claim 1 , characterized in that the canceling the narrow-band interference signal is performed by generating a second narrow-band signal, which corresponds to the narrow-band interference signal, and by subtracting the second narrow-band signal from the distorted desired wide-band signal.
6. An apparatus characterized in that the apparatus comprises
a subtracting unit for subtracting a reference signal from a received input signal;
a complex phase calculator for calculating the phase of a result of the subtraction signal on a sample-by-sample basis of the in-phase and quadrature components of the signal and performing an arctangent function on the in-phase and quadrature components of the incoming signal,
a phase unwrap module for removing discontinuities in the phase if the phase passes the in-phase axes in the complex plane with an absolute value greater than Π,
a comparator module arranged to compare the difference in phase signal values at predetermined time intervals, the difference in said values representing a frequency offset in the subtracting signal, and
a canceling means for canceling the narrow-band interference signal based on the result of the determined frequency offset,
wherein the phase unwrap module is configured to accumulate k times 2Π, where k depends on the wrapped function so that k will be increased by 1 if the difference between the last corrected sample and the current sample is smaller than −Π, and k will be decreased by 1 if the difference between the last corrected sample and the current sample is greater than Π.
7. An apparatus according to claim 6 , characterized in that the canceling means comprises a filter-bank, wherein the narrow-band interference signal is canceled by selecting a filter from within said filter-bank based on the value of k.
8. An apparatus according to claim 6 , characterized in that the canceling means comprises a generating means for generating a second narrow-band signal, which corresponds to the narrow-band interference signal, and a subtracting means for subtracting the second narrow-band signal from the distorted desired wide-band signal.