System and method for improving narrowband interference performance
An orthogonal frequency division multiplexing (OFDM) receiver includes detection logic, offset generation logic, tone erasure logic, and correction generation logic. The detection logic is configured to detect a signal containing a block of samples that includes a narrowband interferer from a communication channel. The offset generation logic is configured to align a frequency of the narrowband interferer to a center of a subcarrier frequency of the communication channel to produce an offset signal thereby introducing inter-carrier interference (ICI). The tone erasure logic is configured to remove the subcarrier frequency from the offset signal to produce an interferer erased offset signal. The correction generation logic is configured to remove the ICI to produce an interferer erased signal.
1. A method for reducing narrowband interference (NBI) effects in orthogonal frequency division multiplexing (OFDM) systems comprising:
receiving a signal containing a block of samples that includes a first narrowband interferer from a communication channel;
aligning a frequency of the first narrowband interferer to a center of a first subcarrier frequency of the communication channel to produce a first offset signal and inter-carrier interference (ICI);
removing the first subcarrier frequency from the first offset signal to produce a first interferer erased offset signal; and
removing the ICI to produce a first interferer erased signal.
2. The method of claim 1 , further comprising:
detecting the frequency of the first narrowband interferer; and
detecting a frequency of a second narrowband interferer.
3. The method of claim 2 , further comprising:
in response to removing the ICI, aligning the frequency of the second narrowband interferer to a center of a second subcarrier frequency of the communication channel to produce a second offset signal and ICI;
removing the second subcarrier frequency from the second offset signal to produce a second interferer erased offset signal; and
removing the ICI to produce a second interferer erased signal.
4. The method of claim 1 , further comprising, decoding the block of samples.
5. The method of claim 1 , wherein aligning the frequency of the first narrowband interferer comprises:
determining a difference between the frequency of the first narrowband interferer and a center of a fast Fourier transform (FFT) bin frequency; and
multiplying the block of samples with a sinusoidal having a frequency that is negative of the difference.
6. The method of claim 1 , wherein removing the ICI comprises:
determining a difference between the frequency of the first narrowband interferer and a center of a fast Fourier transform (FFT) bin frequency; and
multiplying the first offset signal by a sinusoidal having a frequency that is the difference.
7. The method of claim 1 , wherein the aligning the frequency of the narrowband interferer, the removing the subcarrier frequency, and the removing the ICI comprises:
estimating an equivalent interference contribution in a time domain; and
subtracting the equivalent interference contribution from the signal.
8. An orthogonal frequency division multiplexing (OFDM) system, comprising:
a transmitting device configured to transmit a signal containing a block of samples that includes a narrowband interferer into a communication channel;
a receiver configured to:
detect a frequency of the narrowband interferer;
align the frequency of the narrowband interferer to a center of a subcarrier frequency of the communication channel to produce an offset signal and inter-carrier interference (ICI);
remove the subcarrier frequency from the offset signal to produce an interferer erased offset signal; and
remove the ICI to produce an interferer erased signal containing a corrected block of samples; and
data decode logic configured to decode the corrected block of samples.
9. The OFDM system of claim 8 , wherein the receiver is configured to align the frequency of the narrowband interferer to the center of the subcarrier frequency by:
determining a difference between the frequency of the first narrowband interferer and a center of a fast Fourier transform (FFT) bin frequency; and
multiplying the block of samples with a sinusoidal having a frequency that is negative of the difference.
10. The OFDM system of claim 8 , wherein the receiver is configured to remove the ICI by:
determining a difference between the frequency of the first narrowband interferer and a center of a fast Fourier transform (FFT) bin frequency; and
multiplying the first offset signal by a sinusoidal having a frequency that is the difference.
11. The OFDM system of claim 8 , wherein the receiver is configured to detect the frequency of the narrowband interferer by:
identifying the narrowband interferer, a corresponding fast Fourier transform (FFT) bin index, and FFT bin indices neighboring the corresponding FFT bin index; and
determining the frequency of the narrowband interferer based on a function of the signal power.
12. The OFDM system of claim 11 , wherein the receiver is configured to identify the narrowband interferer by:
determining an average of power of the signal on all tones in the communication channel;
determining a target threshold above the average;
in response to a tone exceeding the target threshold, identifying the tone as the narrowband interferer.