Robust fine frequency and time estimation in mobile multimedia multicast system receivers

1. A method of estimating a carrier frequency offset and a timing offset in a mobile multimedia multicast system, said method comprising:

receiving Orthogonal Frequency Division Multiplexing (OFDM) symbols;

interpolating pilots on odd or even symbols of the received OFDM symbols;

determining a phase difference between two successive symbols using the interpolated pilots;

obtaining an estimate of the carrier frequency offset and the timing offset from the determined phase difference between two successive symbols; and

correcting a sampling frequency in accordance with the estimated carrier frequency offset and timing offset.

2. The method of claim 1 , wherein determining the phase difference occurs using relation: Δφ k =2π(Δf+δ/T u ·k), wherein Δφ k is a differential phase between two successive symbols of sub-carrier index k in rad/symbol, Δf is the carrier offset between a receiver and a transmitter in said mobile multimedia multicast system in terms of sub-carrier bin duration, δ=T−T′/T′, where T is a transmitter sampling period and T′ is a receiver sampling period, k is the sub-carrier index, and T u is an OFDM symbol duration excluding a guard interval.

3. The method of claim 2 , further comprising:

determining Δφ k for multiple sub-carrier index k using said relation; and

representing the resulting values of Δφ k graphically.

4. The method of claim 3 , wherein the obtaining of the estimate of the carrier frequency offset is derived as the mean of intercept of the graphically represented values of Δφ k and the timing offset is derived as the slope of the graphically represented values of Δφ k .

5. The method of claim 1 , wherein an estimate of the timing offset φ Δ and the carrier frequency offset φ μ is obtained using:

φ

Δ

=

4

L

2

⁢

∑

k

=

0

L

2

-

1

⁢

(

Δφ

L

2

+

k

-

Δφ

k

)

,

⁢

φ

μ

=

1

L

⁢

∑

k

=

0

L

-

1

⁢

Δφ

k

wherein L is a total number pilots involved in the estimation within one OFDM symbol.

6. The method of claim 1 , wherein a relationship between the phase difference Δφ k , the timing offset represented by δ, and the carrier offset represented by Δf is given by:

Δφ

k

=

4

⁢

π

(

Δ

⁢

⁢

f

+

δ

T

u

·

k

)

,

wherein when there is no timing offset, Δf takes a maximum value when Δφ k =±π.

7. A non-transitory program storage device readable by computer, tangibly embodying a program of instructions executable by said computer to perform a method of estimating a carrier frequency offset and a timing offset in a mobile multimedia multicast system, said method comprising:

receiving Orthogonal Frequency Division Multiplexing (OFDM) symbols;

interpolating pilots on odd or even symbols of the received OFDM symbols;

determining a phase difference between two successive symbols using the interpolated pilots;

obtaining an estimate of the carrier frequency offset and the timing offset from the determined phase difference between two successive symbols; and

correcting a sampling frequency in accordance with the estimated carrier frequency offset and timing offset.

8. The program storage device of claim 7 , wherein determining the phase difference occurs using relation:

Δφ

k

=

2

⁢

π

⁡

(

Δ

⁢

⁢

f

+

δ

T

u

·

k

)

,

wherein Δφ k is a differential phase between two successive symbols of sub-carrier index k in rad/symbol, Δf is the carrier offset between a receiver and a transmitter in said mobile multimedia multicast system in terms of sub-carrier bin duration,

δ

=

T

-

T

′

T

′

,

where T is a transmitter sampling period and T′ is a receiver sampling period, k is the sub-carrier index, and T u is an OFDM symbol duration excluding a guard interval.

9. The program storage device of claim 8 , wherein said method further comprises:

determining Δφ k for multiple sub-carrier index k using said relation; and

representing the resulting values of Δφ k graphically.

10. The program storage device of claim 9 , wherein the obtaining of the estimate of the carrier frequency offset is derived as the mean of intercept of the graphically represented values of Δφ k and the timing offset is derived as the slope of the graphically represented values of Δφ k .

11. The program storage device of claim 7 , wherein an estimate of the timing offset φ Δ and the carrier frequency offset φ μ is obtained using:

φ

Δ

=

4

L

2

⁢

∑

k

=

0

L

2

-

1

⁢

(

Δφ

L

2

+

k

-

Δφ

k

)

,

⁢

φ

μ

=

1

L

⁢

∑

k

=

0

L

-

1

⁢

Δφ

k

wherein L is a total number pilots involved in the estimation within one OFDM symbol.

12. The program storage device of claim 7 , wherein a relationship between the phase difference Δφ k , the timing offset represented by δ, and the carrier offset represented by Δf is given by:

Δφ

k

=

4

⁢

π

(

Δ

⁢

⁢

f

+

δ

T

u

·

k

)

,

wherein when there is no timing offset, Δf takes a maximum value when Δφ k =±π.

13. An apparatus for estimating a carrier frequency offset and a timing offset in a mobile multimedia multicast system, said apparatus comprising:

a receiver adapted to receive Orthogonal Frequency Division Multiplexing (OFDM) symbols;

a processor adapted to interpolate pilots on odd or even symbols of the received OFDM symbols;

a calculator adapted to determine a phase difference between two successive symbols using the interpolated pilots;

an estimator adapted to obtain an estimate of the carrier frequency offset and the timing offset from the determined phase difference between two successive symbols; and

an integrator adapted to correct a sampling frequency in accordance with the estimated carrier frequency offset and timing offset.

14. The apparatus of claim 13 , wherein determining the phase difference occurs using relation:

Δφ

k

=

2

⁢

π

⁡

(

Δ

⁢

⁢

f

+

δ

T

u

·

k

)

,

wherein Δφ k is a differential phase between two successive symbols of sub-carrier index k in rad/symbol, Δf is the carrier offset between said receiver and a transmitter in said mobile multimedia multicast system in terms of sub-carrier bin duration,

δ

=

T

-

T

′

T

′

,

where T is a transmitter sampling period and T′ is a receiver sampling period, k is the sub-carrier index, and T u is an OFDM symbol duration excluding a guard interval.

15. The apparatus of claim 14 ,

wherein said

Δ

⁢

⁢

φ

k

⁢

o

=

2

⁢

⁢

π

⁡

(

Δ

⁢

⁢

f

+

δ

T

u

·

k

)

is determined for multiple sub-carrier index k, and wherein the resulting values of Δφ k are represented graphically.

16. The apparatus of claim 15 , wherein the obtaining of the estimate of the carrier frequency offset is derived as the mean of intercept of the graphically represented values of Δφ k and the timing offset is derived as the slope of the graphically represented values of Δφ k .

17. The apparatus of claim 13 , wherein an estimate of the timing offset φ Δ and the carrier frequency offset φ μ is obtained using:

φ

Δ

=

4

L

2

⁢

∑

k

=

0

L

2

-

1

⁢

(

Δφ

L

2

+

k

-

Δφ

k

)

,

⁢

φ

μ

=

1

L

⁢

∑

k

=

0

L

-

1

⁢

Δφ

k

wherein L is a total number pilots involved in the estimation within one OFDM symbol.

18. The apparatus of claim 13 , wherein a relationship between the phase difference Δφ k , the timing offset represented by δ, and the carrier offset represented by Δf is given by:

Δφ

k

=

4

⁢

π

(

Δ

⁢

⁢

f

+

δ

T

u

·

k

)

,

wherein when there is no timing offset, Δf takes a maximum value when Δφ k =±π.

19. The apparatus of claim 13 , further comprising a transmitter adapted to transmit said OFDM symbols.

20. The apparatus of claim 19 , further comprising a communication link between said receiver and said transmitter.