Method and apparatus of using a bank of filters for excision of narrow band interference signal from CDMA signal

A process of removing narrowband interference signals from transmitted signals, comprising:

• dividing the transmitted signal up into a plurality of narrow sub band signals with sufficiently overlapping frequency limits to avoid blind spots or spots of limited sensitivity in the broadband spectrum to be analyzed for the presence of narrow band noise;
• analyzing the signals in each sub band to determine if a narrow band interference source is present in said sub band;
• removing or attenuating all narrow band interference sources from all sub bands in which they are found;
• and
• reconstructing the transmitted signal from the individual sub band signals after any narrowband interference signals have been removed;
• and
• wherein the step of analyzing the signals in each sub band comprises the step of calculating the variance of the amplitude or power of the signals in each sub band and determining if the variance within the sub band has a magnitude which exceeds an acceptable level of variance.

A narrowband interference signal excision circuit, comprising:

• a bank of perfect or near perfect reconstruction filters connected in parallel to have a shared input for receiving a transmitted signal and a shared output at which a reconstructed transmitted signal is output, said bank comprised of a plurality of individual perfect or near perfect reconstruction filters each having an analysis filter with an input coupled to said shared input and an output and a synthesis filter having an input and having an output coupled to said shared output, said bank of filters having an overall frequency response which covers the spectrum of said transmitted signals and which is comprised of a plurality of individual overlapping frequency responses of the individual filters, each having a different center frequency;
• and
• a detection and cancellation matrix comprised of a plurality of individual detection and cancellation circuits, each having an input coupled to an output of a different analysis filter and an output coupled to an input of a different synthesis filter, each detection and cancellation circuit comprising a first means for setting the amplitude of the input signal to the synthesis filter to which the detection and cancellation circuit is connected to zero or attenuating some or all of the frequencies in the signal from the output of said analysis filter in a first state, and, in a second state, coupling the output of said analysis filter to the input of the synthesis filter without attenuation, and a second means for determining if a narrowband interference signal is present in the output from the analysis filter to which it is connected, and, if not, causing said first means to enter said second state, and, if so, causing said first means to enter said first state.

A process for removing narrowband interference from a digital input signal sample stream, comprising:

• passing said input sample stream through M decimators coupled in parallel to lower the sample rate by a factor of M;
• filtering the output sample stream from each decimator using a digital polyphase passband analysis filter, each having filter coefficients to establish a sub band of frequencies centered on a different center frequency and so as to establish overlapping bandwidth with the sub bands established by each neighboring analysis filter;
• analyzing the signals in each sub band to determine if an interfering signal is present in the sub band;
• suppressing or eliminating at least the interfering signal in each sub band;
• passing the sample stream of each sub band after any interfering signals have been removed or suppressed through a polyphase synthesis filter;
• interpolating the output sample stream from each polyphase synthesis filter to raise the sample rate and re-create a sample stream that accurately represents the input signal but with the elimination or reduction of interference signals.