Granted Patent B2

US 7,974,364 · App. 12/110,688 · Granted Jul 5, 2011

Abstract

Claims (82)

1. A method for Doppler frequency estimation and adaptation in a mobile multimedia multicast system, said method comprising:

receiving, in a receiver, a mobile multimedia multicast superframe comprising Orthogonal Frequency Division Multiplexing (OFDM) symbols;

dividing a Doppler frequency range into N ranges corresponding to N interpolation filters, wherein said N is an integer;

determining a correlation (τ) between two OFDM symbols separated by time τ;

estimating a Doppler frequency f D , by the correlation of OFDM symbols;

determining an α ratio of the correlation of OFDM symbols;

comparing the determined α ratio of the correlation of OFDM symbols with a look up table of α stored at said receiver to determine a corresponding Doppler frequency;

mapping α ranges stored at said look up table to suitable interpolation filters;

estimating an interpolation filter from the mapped α ranges mapped against said determined α ratio;

adapting Time Domain Interpolation (TDI) to the estimated interpolation filter; and

synchronizing said receiver to said mobile multimedia multicast superframe and the received OFDM symbols based on the adapted TDI filter.

2. The method of claim 1 , wherein said correlation (τ) between two OFDM symbols separated by time τ is expressed by: (τ)=E└h(n)h(n−τ)*┘=σ h 2 ℑ 0 (2πf D τ), where E└h(n)h(n−τ)*┘ is an expectation value of symbols h(n) and symbol h(n−τ), σ h 2 is a factor that depends on noise added to transmitted symbol h(n), and ℑ 0 (2πf D τ) is a Bessel function of a first kind of order 0.

3. The method of claim 1 , wherein said correlation (τ) between two OFDM symbols further comprises:

obtaining a correlation r 1 between OFDM symbols n and n+2; and

obtaining a correlation r 2 between OFDM symbols n and n+4,

wherein n represents an OFDM symbol.

4. The method of claim 3 , further comprising computing said α ratio of correlation of OFDM symbols based on: α=(r 2 /r 1 )=(ℑ 0 (2πf D *4τ)/ℑ 0 (2πf D *2τ)),

wherein α represents a ratio of r 2 /r 1 ,

wherein r 1 represents the correlation between OFDM symbols n and n+2,

wherein r 2 represents the correlation between OFDM symbols n and n+4,

wherein (ℑ 0 (2πf D *4τ)) represents a Bessel function of said OFDM symbols n and n+4,

wherein (ℑ 0 (2πf D *2τ)) represents a Bessel function of said OFDM symbols n and n+2,

wherein f D represents said Doppler frequency, and

wherein τ represents time.

5. The method of claim 1 , wherein said α ratio is based on instantaneously determined values of α.

6. The method of claim 5 , wherein said instantaneously determined α is α instantaneous , and wherein said determined α ratio is calculated by: α new =λ*α instantaneous +(1−λ)*α old , where λ is a dependency factor of α new on instantaneous calculated α, wherein said α old represents a previous value of said Doppler frequency.

7. The method of claim 6 , wherein said λ is large in a beginning stage in which said receiver synchronizes with a transmitter and α new ≈α instantaneous .

8. A non-transitory program storage device readable by computer, tangibly embodying a program of instructions executable by said computer to perform a method for Doppler frequency estimation and adaptation in a mobile multimedia multicast system, said method comprising:

receiving, in a receiver, a mobile multimedia multicast superframe comprising Orthogonal Frequency Division Multiplexing (OFDM) symbols;

dividing a Doppler frequency range into N ranges corresponding to N interpolation filters, wherein said N is an integer;

determining a correlation (τ) between two OFDM symbols separated by time τ;

estimating a Doppler frequency f D by the correlation of OFDM symbols;

determining an α ratio of the correlation of OFDM symbols;

comparing the determined α ratio of the correlation of OFDM symbols with a look up table of α stored at said receiver to determine a corresponding Doppler frequency;

mapping α ranges stored at said look up table to suitable interpolation filters;

estimating an interpolation filter from the mapped α ranges mapped against said determined α ratio;

adapting Time Domain Interpolation (TDI) to the estimated interpolation filter; and

synchronizing said receiver to said mobile multimedia multicast superframe and the received OFDM symbols based on the adapted TDI filter.

9. The program storage device of claim 8 , wherein said correlation (τ) between two OFDM symbols separated by time τ is expressed by: (τ)=E└h(n)h(n−τ)*┘=σ h 2 ℑ 0 (2πf D τ), where E└h(n)h(n−τ)*┘ is an expectation value of symbols h(n) and symbol h(n−τ), σ h 2 is a factor that depends on noise added to transmitted symbol h(n), and ℑ 0 (2πf D τ) is a Bessel function of a first kind of order 0.

10. The program storage device of claim 8 , wherein said correlation (τ) between two OFDM symbols further comprises:

obtaining a correlation r 1 between OFDM symbols n and n+2; and

obtaining a correlation r 2 between OFDM symbols n and n+4,

wherein n represents an OFDM symbol.

11. The program storage device of claim 10 , further comprising computing said α ratio of correlation of OFDM symbols based on:

α=(r 2 /r 1 )=(ℑ 0 (2πf D *4τ)/ℑ 0 (2πf D *2τ)),

wherein α represents a ratio of r 2 /r 1 ,

wherein r 1 represents the correlation between OFDM symbols n and n+2,

wherein r 2 represents the correlation between OFDM symbols n and n+4,

wherein (ℑ 0 (2πf D *4τ)) represents a Bessel function of said OFDM symbols n and n+4,

wherein (ℑ 0 (2πf D *2τ)) represents a Bessel function of said OFDM symbols n and n+2,

wherein f D represents said Doppler frequency, and

wherein τ represents time.

12. The program storage device of claim 8 , wherein said α ratio is based on instantaneously determined values of α.

13. The program storage device of claim 12 , wherein said instantaneously determined α is α instantaneous , and wherein said determined α ratio is calculated by: α new =λ*α instantaneous +(1−λ)*α old , where λ is a dependency factor of α new on instantaneous calculated α, wherein said α old represents a previous value of said Doppler frequency.

14. The program storage device of claim 13 , wherein said λ is large in a beginning stage in which said receiver synchronizes with a transmitter and α new ≈α instantaneous .

15. An apparatus for performing Doppler frequency estimation and adaptation in a mobile multimedia multicast system, said apparatus comprising:

a receiver that receives a mobile multimedia multicast superframe comprising Orthogonal Frequency Division Multiplexing (OFDM) symbols; and

a processor that:

divides a Doppler frequency range into N ranges corresponding to N interpolation filters, wherein said N is an integer;

determines a correlation (τ) between two OFDM symbols separated by time τ;

estimates a Doppler frequency f D by the correlation of OFDM symbols;

determines an α ratio of the correlation of OFDM symbols;

compares the determined α ratio of the correlation of OFDM symbols with a look up table of α stored at said receiver to determine a corresponding Doppler frequency;

maps α ranges stored at said look up table to suitable interpolation filters;

estimates an interpolation filter from the mapped α ranges mapped against said determined α ratio;

adapts Time Domain Interpolation (TDI) to the estimated interpolation filter; and

synchronizes said receiver to said mobile multimedia multicast superframe and the received OFDM symbols based on the adapted TDI filter.

16. The apparatus of claim 15 , wherein said correlation (τ) between two OFDM symbols separated by time τ is expressed by: (τ)=E└h(n)h(n−τ)*┘=σ h 2 ℑ 0 (2πf D τ), where E└h(n)h(n−τ)*┘ is an expectation value of symbols h(n) and symbol h(n−τ), σ h 2 is a factor that depends on noise added to transmitted symbol h(n), and ℑ 0 (2πf D τ) is a Bessel function of a first kind of order 0.

17. The apparatus of claim 15 , wherein said correlation (τ) between two OFDM symbols further comprises:

obtaining a correlation r 1 between OFDM symbols n and n+2; and

obtaining a correlation r 2 between OFDM symbols n and n+4,

wherein n represents an OFDM symbol.

18. The apparatus of claim 17 , wherein said processor computes said α ratio of correlation of OFDM symbols based on: α=(r 2 /r 1 )=(ℑ 0 (2πf D *4τ)/ℑ 0 (2πf D *2τ)),

wherein α represents a ratio of r 2 /r 1 ,

wherein r 1 represents the correlation between OFDM symbols n and n+2,

wherein r 2 represents the correlation between OFDM symbols n and n+4,

wherein (ℑ 0 (2πf D *4τ)) represents a Bessel function of said OFDM symbols n and n+4,

wherein (ℑ 0 (2πf D *2τ)) represents a Bessel function of said OFDM symbols n and n+2,

wherein f D represents said Doppler frequency, and

wherein τ represents time.

19. The apparatus of claim 15 , wherein said α ratio is based on instantaneously determined values of α.

20. The apparatus of claim 19 , wherein said instantaneously determined α is α instantaneous , wherein said determined α ratio is calculated by: α new =λ*α instantaneous +(1−λ)*α old , where λ is a dependency factor of α new on instantaneous calculated α, wherein said α old represents a previous value of said Doppler frequency, and wherein said λ is large in a beginning stage in which said receiver synchronizes with a transmitter and α new ≈α instantaneous .

Assignments (14)