SFO estimation technique for MIMO-OFDM frequency synchronization
A receiver is configured to determine an estimation of a Sampling Frequency Offset an OFDM signal received from an emitter over a transmission channel. The received OFDM signal is constituted of symbols. The receiver receives symbols from the emitter through a first path of said transmission channel, and receives the symbols from the emitter through a second path of the transmission channel. On the second path, the symbols are characterized by a different ratio between a first duration of a total OFDM symbol and a second duration of useful data portion of the OFDM symbol, than on the first path. The receiver determines the estimation according to received symbols through the first and second paths.
1. A method for determining an estimation of a Sampling Frequency Offset of an Orthogonal Frequency-Division Multiplexing, OFDM, signal sent by an emitter to a receiver over a transmission channel, said signal being constituted of symbols, said method comprising:
sending symbols by said emitter through a first path of said transmission channel;
sending said symbols by said emitter through a second path of said transmission channel, said second path being characterized by a different ratio than the first path, between a first duration of a total OFDM symbol and a second duration of a useful data portion of the total OFDM symbol;
determining said estimation according to the symbols received through said first and second paths; and compensating for said Sampling Frequency Offset of said OFDM signal according to said estimation.
2. The method according to claim 1 , wherein said estimation {circumflex over (t)} Δ is determined as
t
^
Δ
=
1
2
π
k
(
1
-
c
)
·
(
T
s
T
u
)
p
1
·
arg
(
R
l
,
k
,
p
1
′
R
l
,
k
,
p
2
′
)
,
wherein R l,k,p1 and R l,k,p2 corresponds to said received symbols from, respectively said first path p 1 and said second path p 2 , and wherein Ts and Tu are said first duration and said second duration, respectively, k represents a subcarrier, and c is a parameter.
3. The method according to claim 1 , wherein said estimation is determined as an average value taken for all pilot subcarriers.
4. The method according to claim 1 , wherein said estimation is determined as an average value taken for all subcarriers.
5. The method according to claim 1 wherein said first duration is equal to 4 μs for said first path, p 1 , and for said second path, p 2 , and said second duration differs between said first path and said second path, so that (T s /T u ) p1 =c*(T s /T u ) p2 , where c is a parameter.
6. The method according to claim 2 , wherein said parameter is transmitted by said emitter inside preamble symbols of said OFDM signal.
7. A receiver for determining an estimation of a Sampling Frequency Offset an Orthogonal Frequency-Division Multiplexing (OFDM) signal received from an emitter over a transmission channel, said signal being constituted of symbols, said receiver comprising:
means for receiving symbols from said emitter through a first path of said transmission channel and receiving said symbols from said emitter through a second path of said transmission channel, said second path being characterized by a different ratio between the durations of a total OFDM symbol and a useful data portion of the total OFDM symbol, than the first path;
means for determining said estimation based on said symbols received through said first path and through said second path; and
means for compensating for said Sampling Frequency Offset of said OFDM signal according to said estimation.
8. The receiver according to claim 7 , wherein said means for determining said estimation {circumflex over (t)} Δ is determined as:
t
^
Δ
=
1
2
π
k
(
1
-
c
)
·
(
T
s
T
u
)
p
1
·
arg
(
R
l
,
k
,
p
1
′
R
l
,
k
,
p
2
′
)
,
wherein R l,k,p1 and R l,k,p2 corresponds to said received symbols from, respectively said first path and said second path, and wherein Ts and Tu are said first duration and said second duration, respectively, k represents subcarrier, and c is a parameter.
9. The receiver according to claim 7 , wherein said estimation is determined as an average value taken for all pilot subcarriers.
10. The receiver according to claim 7 , wherein said estimation is determined as an average value taken for all subcarriers.
11. The receiver according to claim 7 , wherein said first duration is equal to 4 μs for said first path and said second path, and said second duration differs between said first path and said second path, so that (T s /T u ) p1 =c*(T s /T u ) p2 .
12. The receiver according to claim 8 , wherein said parameter is received from said emitter inside preamble symbols of said OFDM signal.
13. A method performed by a receiver, for determining an estimation of a Sampling Frequency Offset of an Orthogonal Frequency-Division Multiplexing, OFDM, signal including symbols, said method comprising:
receiving said symbols sent via a first path of a transmission channel;
receiving said symbols sent via a second path of said transmission channel, said second path being characterized by a different ratio than the first path, between a first duration of a total OFDM symbol and a second duration of a useful data portion of the total OFDM symbol;
determining said estimation according to the symbols received through said first and second paths; and
compensating for said Sampling Frequency Offset of said OFDM signal according to said estimation.
14. The method according to claim 13 , wherein said estimation {circumflex over (t)} Δ is determined as
t
^
Δ
=
1
2
π
k
(
1
-
c
)
·
(
T
s
T
u
)
p
1
·
arg
(
R
l
,
k
,
p
1
′
R
l
,
k
,
p
2
′
)
,
wherein R l,k,p1 and R l,k,p2 corresponds to said received symbols from, respectively said first path p 1 and said second path p 2 , and wherein Ts and Tu are said first duration and said second duration, respectively, k represents a subcarrier, and c is a parameter.
15. The method according to claim 13 , wherein
said estimation is determined as an average value taken for all pilot subcarriers, or
said estimation is determined as an average value taken for all subcarriers.
16. The method according to claim 13 , wherein said first duration is equal to 4 μs for said first path, p 1 , and for said second path, p 2 , and said second duration differs between said first path and said second path, so that (T s /T u ) p1 =c*(T s /T u ) p2 , where c is a parameter.
17. The method according to claim 14 , wherein said parameter is received inside preamble symbols of said OFDM signal.