Method and apparatus for packet detection via cross-correlation in the presence of frequency offset
View Patent ↗An apparatus and method for packet detection using cross-correlation in the presence of frequency offset. The method comprises: segmenting a received signal; and cross-correlating each segment with an expected signal. The apparatus comprises a slicer that segments a received signal; and a cross correlator that cross-correlates each segment with an expected signal.
1. A method implemented with a packet detector, comprising:
segmenting, with a segmenter of the packet detector, a received signal;
cross-correlating, with a cross-correlator of the packet detector, each segment with an expected signal; and
correcting a phase of each correlated segment, with the cross-correlator, by de-rotation according to an expected phase offset due to assumed frequency offset,
wherein the cross correlation as a function of frequency offset is:
y
(
Δ
f
)
≈
x
(
0
)
+
∑
n
=
1
K
-
1
2
(
x
(
-
n
)
+
x
(
n
)
)
·
cos
(
2
π
·
Δ
f
·
Δ
t
·
N
K
·
n
)
+
j
·
(
x
(
-
n
)
-
x
(
n
)
)
·
sin
(
2
π
·
Δ
f
·
Δ
t
·
N
K
·
n
)
2
wherein Δf is the assumed frequency offset correction, K is the number of segments, N is a number of samples, Δt is an inverse of sampling clock frequency, and x is the cross-correlation of each segment.
2. The method of claim 1 , wherein the expected phase offset is a constant at a beginning of each segment.
3. The method of claim 1 , wherein the expected phase offset is a constant at any same location of each segment.
4. The method of claim 1 , wherein 3 values of Δf are used and and the values are a fraction of a maximum frequency offset.
5. The method of claim 4 , wherein the maximum frequency offset is approximately 325 kHz.
6. The method of claim 1 , further comprising coherently summing the cross-correlations after the de-rotation.
7. The method of claim 1 , wherein a sign of the expected signal is used in place of the expected signal.
8. A packet detector, comprising:
a slicer that segments a received signal; and
a cross correlator that cross-correlates each segment with an expected signal,
wherein the cross correlator corrects a phase of each correlated segment by de-rotation according to an expected phase offset due to assumed frequency offset,
wherein the cross correlation as a function of frequency offset is:
y
(
Δ
f
)
≈
x
(
0
)
+
∑
n
=
1
K
-
1
2
(
x
(
-
n
)
+
x
(
n
)
)
·
cos
(
2
π
·
Δ
f
·
Δ
t
·
N
K
·
n
)
+
j
·
(
x
(
-
n
)
-
x
(
n
)
)
·
sin
(
2
π
·
Δ
f
·
Δ
t
·
N
K
·
n
)
2
wherein Δf is the assumed frequency offset correction, K is the number of segments, N is a number of samples, Δt is an inverse of sampling clock frequency, and x is the cross-correlation of each segment.
9. The detector of claim 8 , wherein the expected phase offset is a constant at a beginning of each segment.
10. The detector of claim 8 , wherein the expected phase offset is a constant at any same location of each segment.
11. The detector of claim 8 , wherein 3 values of Δf are used and wherein the values are a fraction of a maximum frequency offset.
12. The detector of claim 11 , wherein the maximum frequency offset is approximately 325 kHz.
13. The detector of claim 8 , further comprising coherently summing the cross-correlations after the de-rotation.
14. The detector of claim 8 , wherein a sign of the expected signal is used in place of the expected signal.
15. A receiver, comprising:
a receiving block that receives a signal;
an analog front end coupled to the receiving block that produces I and Q signals from the received signal;
an analog-to-digital converter coupled to the front end that converts the I and Q signals to digital form;
a packet detector coupled to the analog-to-digital converter, the packet detector comprising a slicer that segments the I and Q signals; and a cross correlator that cross-correlates each segment with an expected signal;
a frame synch block coupled to the packet detector that established frame synchronization; and
a signal processing block coupled to the frame synch block that processes the signal,
wherein the cross correlator corrects a phase of each correlated segment by de-rotation according to an expected phase offset due to assumed frequency offset,
wherein the cross correlation as a function of frequency offset is:
y
(
Δ
f
)
≈
x
(
0
)
+
∑
n
=
1
K
-
1
2
(
x
(
-
n
)
+
x
(
n
)
)
·
cos
(
2
π
·
Δ
f
·
Δ
t
·
N
K
·
n
)
+
j
·
(
x
(
-
n
)
-
x
(
n
)
)
·
sin
(
2
π
·
Δ
f
·
Δ
t
·
N
K
·
n
)
2
wherein Δf is the assumed frequency offset correction, K is the number of segments, N is a number of samples, Δt is an inverse of sampling clock frequency, and x is the cross-correlation of each segment.