Method and device for synchronisation in OFDM
View Patent ↗A method of synchronizing an Orthogonal Frequency Division Multiplexed (OFDM) IEEE 802.11a data packet at a receiver is disclosed. The 802.11a data packet has a series of short training sequence (STS) symbols as a preamble. Cross-correlation at the receiver of the STS in the 802.11a packet PLCP preamble with the modified reference STS, that is 10 circular shifted by eight samples, results in a main correlation peak but with reduced pre- and post-lobes. To locate the cross-correlation peak, a running second derivative of the cross-correlation function is performed. Peak selection employs a running comparison of the position and magnitude of all peaks in the intermediate neighborhood of the local peaks. Following selection of a peak from within the cross-correlation function of the first STS in the PLOP preamble, both the position and magnitude of the first STS is compared to those of the second STS. Based on the two independent calculations, the start of the OFDM frame is estimated.
1. A method of generating a signal, r y,STS , indicating the presence of at least one predefined identification data marker, STS, of length X samples, in at least one received digital data frame, y, transmitted over a communication link comprising a plurality of received samples, each received sample being identified as v(n), for n>0, the method comprising:
having an integrated circuit generate a first signal, STS ref , based on said predefined identification data marker according to an expression
STS ref ={STS k ,STS k+1 ,STS k+2 , . . . ,STS X ,STS 1 ,STS 2 , . . . ,STS k−1 }.
wherein k is a predefined amount; and
having the integrated circuit generate a plurality of output signal values each according to the expression
r
y
,
STS
(
n
)
=
∑
l
=
0
N
-
n
-
1
y
(
n
)
·
STS
ref
*
(
l
+
n
)
,
where STS* ref is the complex conjugate of STS ref ;
wherein the presence of the at least one predefined identification marker is indicated by a peak in r y,STS .
2. A method as claimed in claim 1 , wherein said first signal is based on said predefined identification data marker with a left circular shift.
3. A method as claimed in claim 1 , wherein said predefined amount is 8 samples.
4. An Application Specific Integrated Circuit (ASIC) arranged to generate a signal, r y,STS , indicating the presence of at least one predefined data identification marker, STS, of length X samples, in at least one received digital data frame, y, transmitted over a communication link comprising a plurality of received samples, each received sample being identified as v(n) for n>0, comprising:
means for generating a first signal, STS ref , based on said predefined identification data marker according to the expression
STS ref ={STS k ,STS k+1 ,STS k+2 , . . . ,STS X ,STS 1 ,STS 2 , . . . , STS k−1 },
wherein k is a predefined amount; and
means for generating a plurality of output signal values each according to the expression
r
y
,
STS
(
n
)
=
∑
l
=
0
N
-
n
-
1
y
(
n
)
·
STS
ref
*
(
l
+
n
)
,
where STS* ref is the complex conjugate of STS ref , and
wherein the presence of the at least one predefined identification marker is indicated by a peak in r y,STS .
5. A storage medium comprising software code portions, which, when executed by a computer, carry out the method of claim 1 .
6. A method of identifying the presence of at least one predefined data identification marker, the method comprising:
having an integrated circuit to generate an indicating signal according to the method of claim 1 ; and
having the integrated circuit to generate at least one peak in the indicating signal.