Synchronization method, receiver, network element, communication device, electronic device, computer program product and computer program distribution medium

1. A method, comprising:

determining a coarse time-offset and a coarse frequency-offset estimation;

estimating errors in the coarse time-offset and the coarse frequency-offset estimation, wherein the errors are estimated by using a maximum-likelihood time-offset estimation and a joint optimization of time-offset and frequency-offset;

estimating a frequency-offset and a time-offset based on the error estimates in a closed tracking loop; and

removing the time-offset from a received signal by delaying or advancing the received signal in a circular buffer by using the time-offset estimate.

2. The method of claim 1 , further comprising:

generating the maximum-likelihood time-offset estimation by maximizing a log-likelihood function over possible coarse time-offset estimates.

3. The method of claim 1 , further comprising:

determining the frequency offset estimation as follows:

ɛ

^

⁡

(

m

)

=

G

inst

G

ave

⁢

g

⁢

⁢

ɛ

^

ML

⁡

(

m

)

+

(

1

-

G

inst

G

ave

⁢

g

)

⁢

ɛ

^

⁡

(

m

-

1

)

,

wherein

G inst denotes an instantaneous signal-to-noise ratio estimate,

G ave denotes an average signal-to-noise ratio,

g denotes a fixed loop gain,

{circumflex over (ε)} ML (m) is a maximum-likelihood estimate of a frequency-offset, and

{circumflex over (ε)}(m−1) is an maximum-likelihood frequency-offset output of a closed tracking loop for a previous orthogonal frequency division multiplexed symbol.

4. The method of claim 1 , further comprising:

determining the time offset estimation as follows:

ϕ

^

⁡

(

m

)

=

G

inst

G

ave

⁢

g

⁢

⁢

ϕ

^

ML

⁡

(

m

)

+

(

1

-

G

inst

G

ave

⁢

g

)

⁢

ϕ

^

⁡

(

m

-

1

)

,

wherein

G inst denotes an instantaneous signal-to-noise ratio estimate,

G ave denotes an average signal-to-noise ratio,

g denotes a fixed loop gain,

{circumflex over (φ)} ML (m) denotes an estimated time error term at the m th orthogonal frequency division multiplexed symbol, and

{circumflex over (φ)}(m−1) denotes an estimated time error term at the (m−1) th orthogonal frequency division multiplexed symbol.

5. An apparatus, comprising:

a processor;

memory including computer program instructions;

the memory and the computer program instructions configured to, working with the processor, cause the apparatus to perform at least the following:

determine a coarse time offset and a coarse frequency offset estimation;

estimate errors in the coarse time offset and the coarse frequency offset estimation, wherein the errors are estimated by using a maximum-likelihood time-offset estimation and a joint optimization of time-offset and frequency-offset;

estimate frequency offset and time offset based on the error estimates in a closed tracking loop having an adaptive loop gain; and

remove the time-offset from a received signal by one of delaying the signal in a circular buffer or advancing the signal in a circular buffer, by using the time-offset estimate.

6. The apparatus of claim 5 , wherein the receiver is further configured to generate the maximum-likelihood time-offset estimation by maximizing a log-likelihood function over the coarse time-offset estimates.

7. The apparatus of claim 5 , wherein the receiver is further configured to determine the frequency offset estimation as follows:

ɛ

^

⁡

(

m

)

=

G

inst

G

ave

⁢

g

⁢

⁢

ɛ

^

ML

⁡

(

m

)

+

(

1

-

G

inst

G

ave

⁢

g

)

⁢

ɛ

^

⁡

(

m

-

1

)

,

wherein

G inst denotes an instantaneous signal-to-noise ratio estimate,

G ave denotes an average signal-to-noise ratio,

g denotes a fixed loop gain,

{circumflex over (ε)} ML (m) is a maximum-likelihood estimate of a frequency-offset, and

{circumflex over (ε)}(m−1) is an maximum-likelihood frequency-offset output of a closed tracking loop for a previous orthogonal frequency division multiplexed symbol.

8. The apparatus of claim 5 , wherein the receiver is further configured to determine the time offset estimation as follows:

ϕ

^

⁡

(

m

)

=

G

inst

G

ave

⁢

g

⁢

⁢

ϕ

^

ML

⁡

(

m

)

+

(

1

-

G

inst

G

ave

⁢

g

)

⁢

ϕ

^

⁡

(

m

-

1

)

,

wherein

G inst denotes an instantaneous signal-to-noise ratio estimate,

G ave denotes an average signal-to-noise ratio,

g denotes a fixed loop gain,

{circumflex over (φ)} ML (m) denotes an estimated time error term at the m th orthogonal frequency division multiplexed symbol, and

{circumflex over (φ)}(m−1) denotes an estimated time error term at the (m−1) th orthogonal frequency division multiplexed symbol.

9. The apparatus of claim 5 , wherein the apparatus comprises a network element.

10. The apparatus of claim 5 , wherein the apparatus comprises a communication device.

11. The apparatus of claim 5 , wherein the apparatus comprises an electronic device.

12. A computer program embodied on a computer-readable medium comprising a computer program of instructions for executing a computer process for synchronization, the process comprising:

determining a coarse time offset and a coarse frequency offset estimation;

estimating errors in the coarse time-offset and frequency offset estimation, wherein the errors are estimated by using a maximum-likelihood time-offset estimation and a joint optimization of time-offset and frequency-offset;

estimating frequency offset and time offset based on the error estimates in a closed tracking loop; and

removing the time-offset from a received signal by delaying or advancing the received signal in a circular buffer by using the time-offset estimate.

13. The computer program embodied on the computer-readable medium of claim 12 , wherein the computer-readable medium comprises at least one of a program storage medium, a record medium, a computer readable memory, a computer readable software distribution package and a computer readable compressed software package.

14. An apparatus, comprising:

determining means for determining a coarse time offset and a coarse frequency offset estimation;

error estimating means for estimating errors in the coarse time offset and the coarse frequency offset estimation, wherein the errors are estimated by using a maximum-likelihood time-offset estimation and a joint optimization of time-offset and frequency-offset;

offset estimating means for estimating frequency offset and time offset based on the error estimates in a closed tracking loop having an adaptive loop gain; and

removing means for removing the time-offset from a received signal by delaying or advancing the received signal in a circular buffer by using the time-offset estimate.

15. The apparatus of claim 14 , wherein the determining means, error estimating means, offset estimating means, and removing means are comprised in a receiver.