Detecting narrow band interference in wireless networks using spectral analysis
A method detects narrow band interference in wireless networks by first thresholding each block of samples to produce thresholded samples. The samples are normalized frequency magnitudes obtained from a spectrum of a wireless signal in a channel. Each block of the thresholded samples is summed to produce a thresholded value for each block. Then, thresholded values are autocorrelated to determine whether a bandwidth of the wireless signal is consistent with narrow band interference.
1. A method for detecting narrow band interference in wireless networks, comprising:
thresholding each block of samples to produce thresholded samples, wherein the samples are normalized frequency magnitudes obtained from a spectrum of a wireless signal in a channel;
summing each block of the thresholded samples to produce a thresholded value for each block; and
autocorrelating the thresholded values to determine whether a bandwidth of the wireless signal is consistent with narrow band interference, wherein the steps are performed in a processor, wherein the summing produces the thresholded value according to
y
(
n
)
=
∑
j
=
1
N
fft
(
X
j
,
n
-
X
threshold
)
+
,
where j indexes the a number of samples in the block n and N fft is a positive integer, X j,n are the samples, X threshold is the threshold, and an operator (x) + is defined by
(
x
)
+
=
{
x
x
>
0
0
x
≤
0
.
wherein the autocorrelation is obtained according to
r(m)=E[y(n)y(n+m)],
where E[.] is an expectation and m represents a delay at which the auto correlation is evaluated.
2. The method of claim 1 , wherein the spectrum is unregulated.
3. The method of claim 1 , wherein the interference is emitted by a microwave oven.
4. The method of claim 1 , further comprising:
determining a periodicity of interference to characterize a type of device causing the interference.
5. The method of claim 1 , wherein a fast Fourier transform is applied, to the samples before the normalization.
6. The method of claim 1 , wherein the processor is contained in a wireless device and the threshold is set according to a noise floor of device.
7. The method of claim 1 , further comprising:
storing the thresholded values in a buffer for the autocorrelation.
8. The method of claim 1 , wherein the blocks are acquired periodically.