Apparatus and method for frequency offset estimation
A user terminal transmits a preamble signal generated using a Zadoff-Chu sequence. A correlation processing unit calculates autocorrelation of a received preamble signal. A preamble detection unit detects a side peak position of the autocorrelation of the preamble signal and calculates the main correlation value representing correlation at the main peak position and the side correlation value representing correlation at the side peak position. A frequency offset estimation unit estimates frequency offset that has occurred in the wireless transmission path according to the main correlation value and the side correlation value.
1. A frequency offset estimation apparatus used in a wireless communication system transmitting a preamble signal generated using a sequence where a position of a side peak in an autocorrelation property of the sequence is not dependent on frequency offset and a correlation value of the side peak changes according to the frequency offset, comprising:
a correlation unit configured to calculate autocorrelation of a received preamble signal;
a detection unit configured to detect a position of a side peak of the autocorrelation of the preamble signal;
a calculation unit configured to calculate a main correlation value representing correlation at a position of a main peak of the autocorrelation and a side correlation value representing correlation at the position of the side peak; and
an estimation unit configured to estimate the frequency offset when a sum of the main correlation value and the two side correlation values is larger than a predetermined correlation threshold value, and the estimate of the frequency offset is performed by estimating the frequency offset within a range of frequency offset by comparing the main correlation value to each of the two side correlation values and, based on the comparing of the main correlation value, further comparing the two side correlation values to each other.
2. The frequency offset estimation apparatus according to claim 1 , wherein the sequence is Zadoff-Chu sequence.
3. The frequency offset estimation apparatus according to claim 2 , wherein correlation values at positions distant from the position of the main peak by dp and dm are calculated as side peaks, where (u·dp) modulo L=1, dm=L−dp.
4. The frequency offset estimation apparatus according to claim 2 , wherein
the Zadoff-Chu sequence is expressed in an expression below, where u represents a sequence number defining a pattern of the Zadoff-Chu sequence, n represents a symbol number identifying a symbol in the Zadoff-Chu sequence, and L represents a length of the Zadoff-Chu sequence
x
u
(
n
)
=
ⅇ
-
j
π
un
(
n
+
1
)
L
,
0
≤
n
≤
L
-
1.
5. The frequency offset estimation apparatus according to claim 4 , wherein
the detection unit specifies the sequence number using output of the correlation unit, and detects the position of the side peak according the specified sequence number.
6. A wireless base station having the frequency offset estimation apparatus according to claim 1 , comprising
a correction unit configured to correct a frequency of a received signal according to the frequency offset estimated by the frequency offset estimation unit.
7. The wireless base station according to claim 6 , further comprising:
a communication scheme decision unit configured to decide a communication scheme according to the frequency offset estimated by the frequency offset estimation apparatus, and
a transmission unit configured to transmit a signal to a user terminal using a communication scheme decided by the communication scheme decision unit.
8. The wireless base station according to claim 6 , further comprising:
a communication scheme decision unit configured to decide a communication scheme according to the frequency offset estimated by the frequency offset estimation apparatus, and
a notification unit configured to perform notification of the communication scheme decided by the communication scheme decision unit to a user terminal.
9. A frequency offset estimation method used in a wireless communication system transmitting a preamble signal generated using a sequence where a position of a side peak in an autocorrelation property of the sequence is not dependent on frequency offset and a correlation value of the side peak changes according to the frequency offset, comprising
calculating autocorrelation of a received preamble signal;
detecting a position of a side peak of the autocorrelation of the preamble signal;
calculating a main correlation value representing correlation at a position of a main peak of the autocorrelation and a side correlation value representing correlation at the position of the side peak; and
estimating the frequency offset when a sum of the main correlation value and the two side correlation values is larger than a predetermined correlation threshold value, and performing the estimating by estimating the frequency offset within a range of frequency offset by comparing the main correlation value to each of the two side correlation values and, based on the comparing of the main correlation value, further comparing the two side correlation values to each other.
10. The frequency offset estimation method of claim 9 , wherein the sequence is Zadoff-Chu sequence and correlation values at positions distant from the position of the main peak by dp and dm are calculated as side peaks, where (u·dp) modulo L=1, dm=L−dp.