Apparatus and method for acquiring synchronization in mobile communication system using OFDM scheme

• US 7,630,463 B2
• Filed: 11/15/2005
• Issued: 12/08/2009
• Est. Priority Date: 11/15/2004
• Status: Expired due to Fees

• Current Assignee: Korea Advanced Institute of Science and Technology, Samsung Electronics Co. Ltd.
• Original Assignee: Korea Advanced Institute of Science and Technology, Samsung Electronics Co. Ltd.
• Inventors: Shin, Won-Yong, Jung, Young-Ho, Lee, Yong-Hoon, Hwang, Chan-Soo, Joung, Jin-Gon
• Primary Examiner(s): Perilla; Jason M.
• Application Number:
  US11/274,577
• Publication Number:
  US 20060104254A1
• Time in Patent Office: 1,484 Days
• Field of Search: 375/260, 375/295, 375/316, 375324-327, 375/344, 375/346
• US Class Current: 375/344
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2676 Blind, i.e. without using known symbols

Abstract

Disclosed is a method for acquiring synchronization in a mobile communication system using an Orthogonal Frequency Division Multiplexing (OFDM) scheme. The method includes modeling a power delay profile in time-varying frequency selective fading channel conditions by a specific function; detecting a log probability distribution function of a timing offset and a frequency offset in consideration of a correlation between a received signal and the received multi-path signal in the time-varying frequency selective fading channel conditions having the power delay profile modeled as the specific function; and estimating a timing offset and a frequency offset which maximize the log probability distribution function of the timing offset and the frequency offset.

Claims

1. A method for acquiring synchronization in a mobile communication system using an Orthogonal Frequency Division Multiplexing (OFDM) scheme, the method comprising:

modeling a power delay profile in time-varying frequency selective fading channel conditions by a specific function;

receiving a signal by an OFDM receiver of the system;

generating a log probability distribution function of a timing offset and a frequency offset using a correlation between an n^th sample from samples included in the received signal and an (n+N)^th sample from samples included in the received signal; and

estimating, using a maximum likelihood technique, a timing offset and a frequency offset of the n^th sample based on the power delay profile and the log probability distribution function,

wherein the estimating of the timing offset and the frequency offset is considered within a permissible range of values associated with a number of samples of the received signal.

2. The method as claimed in claim 1, wherein the log probability distribution function includes a correlation part component and an energy part component of the received signal.

3. The method as claimed in claim 1, wherein, when the mobile communication system using the OFDM scheme has N_CP number of multi-paths and guard interval signals have a length of the N_CP, the specific function is expressed as

${\alpha }_{}$

k = C k ,

wherein k represents a k^th multi-path of the N_CP multi-paths and C is a constant expressed as

$C=\sqrt{\frac{1}{\underset{k=1}{\overset{N_{\mathrm{CP}}}{\sum <br><br>}}<br><br>k^2}}.$

4. The method as claimed in claim 3, wherein the log probability distribution function is expressed as

${\Lambda }_{}$

2 ⁢

nd ⁡

( τ

, ɛ

) = 2 σ

s 2 + σ

w 2 ⁡

[ Re ⁢

{ γ

⁡

( τ

) } ⁢

cos ⁡

( 2 ⁢

π

ɛ

) - Im ⁢

{ γ

⁡

( τ

) } ⁢

sin ⁡

( 2 ⁢

π

ɛ

) - Φ

⁡

( τ

) ] = 2 σ

s 2 + σ

w 2 ⁡

[ 

γ

⁡

( τ

) 

⁢

cos ⁡

( 2 ⁢

π

ɛ

+ ∠

γ

⁡

( τ

) ) - Φ

⁡

( τ

) ] ,

wherein Λ

_2nd(τ

, ε

) represents the log probability distribution function, T represents the symbol timing offset, ε

represents frequency offset, σ

_s² represents average power of transmitted signals s(•

), σ

_w² represents an average power of Additive White Gaussian Noise (AWGN), and γ

(n) and the Φ

(n) are respectively expressed as

$\mathrm{\gamma <br><br>}<br><br>\left(n\right)\equiv <br><br>\underset{n=\mathrm{\tau <br><br>}}{\overset{\mathrm{\tau <br><br>}+N_{\mathrm{CP}}-1}{\sum <br><br>}}<br><br>\frac{{\mathrm{\rho <br><br>}}_n}{1-{\mathrm{\rho <br><br>}}_n^2}<br><br>r<br><br>\left(n\right)<br><br>r*\left(n+N\right),$

wherein ρ

_n represents a correlation coefficient absolute value between the n^th sample and the (n+N)^th sample of the received signal r(n), and

$\mathrm{\Phi <br><br>}<br><br>\left(n\right)\equiv <br><br>\frac{1}{2}<br><br>\underset{n=\mathrm{\tau <br><br>}}{\overset{\mathrm{\tau <br><br>}+N_{\mathrm{CP}}-1}{\sum <br><br>}}<br><br>\frac{{\mathrm{\rho <br><br>}}_n^2}{\left(1-{\mathrm{\rho <br><br>}}_n^2\right)}<br><br>\left\{{<br><br>r<br><br>\left(n\right)<br><br>}^2+{<br><br>r<br><br>\left(n+N\right)<br><br>}^2\right\}.$

5. The method as claimed in claim 4, wherein an estimation value of the timing offset is expressed as

${\stackrel{}{\tau }}_{}$

^ ML = arg ⁢

⁢

max τ

⁢

{ 

γ

⁡

( τ

) 

- Φ

⁡

( τ

) } ,

wherein {circumflex over (τ

)}_ML represents the estimation value of the timing offset.

6. The method as claimed in claim 4, wherein an estimation value of the frequency offset is expressed as

${\stackrel{}{\varepsilon }}_{}$

^ ML = - 1 2 ⁢

π

⁢

∠

γ

⁡

( τ

^ ML ) ,

wherein {circumflex over (ε

)}_ML represents the estimation value of the frequency offset.

13. The method as claimed in claim 1, wherein the power delay profile represents a power profile of a time-varying frequency selective fading channel.

14. The method as claimed in claim 1, wherein the specific function is a square root of an average power in a k^th multi-path, and the square root of the average power in the k^th multi-path is proportional to an inverse of k, and k is a natural number.

7. An apparatus for acquiring synchronization in a mobile communication system using an Orthogonal Frequency Division Multiplexing (OFDM) scheme, the apparatus comprising:

a receiver for receiving a Radio Frequency (RF) signal, converting the received RF signal to a baseband signal, and performing a Fast Fourier Transform (FFT) on the baseband signal; and

a synchronization acquisition unit for inputting the signal for which the FFT has been performed, modeling a power delay profile in time-varying frequency selective fading channel conditions by a specific function, generating a log probability distribution function of a timing offset and a frequency offset using a correlation between an n^th sample from samples included in the inputted signal and an (n+N)^th sample from samples included in the inputted signal, and estimating, using a maximum likelihood technique, a timing offset and a frequency offset of the n^th sample based on the power delay profile and the log probability distribution function, wherein the estimating of the timing offset and the frequency offset is considered within a permissible range of values associated with a number of samples of the received signal.

8. The apparatus as claimed in claim 7, wherein the log probability distribution function includes a correlation part component and an energy part component of the received signal.

9. The apparatus as claimed in claim 7, wherein, when the mobile communication system using the OFDM scheme has N_CP number of multi-paths and guard interval signals have a length of the N_CP, the specific function is expressed as

${\alpha }_{}$

k = C k ,

wherein k represents a k^th multi-path of the N_CP multi-paths and C is a constant expressed as

$C=\sqrt{\frac{1}{\underset{k=1}{\overset{N_{\mathrm{CP}}}{\sum <br><br>}}<br><br>k^2}}.$

10. The apparatus as claimed in claim 9, wherein the log probability distribution function is expressed as

$\begin{array}{c}{\Lambda }_{}\end{array}$

2 ⁢

nd ⁡

( τ

, ɛ

) = ⁢

2 σ

s 2 + σ

w 2 ⁡

[ Re ⁢

{ γ

⁡

( τ

) } ⁢

cos ⁡

( 2 ⁢

π

ɛ

) - Im ⁢

{ γ

⁡

( τ

) } ⁢

sin ⁡

( 2 ⁢

π

ɛ

) - Φ

⁡

( τ

) ] = ⁢

2 σ

s 2 + σ

w 2 ⁡

[ 

γ

⁡

( τ

) 

⁢

cos ⁡

( 2 ⁢

π

ɛ

+ ∠

γ

⁡

( τ

) ) - Φ

⁡

( τ

) ] ,

wherein Λ

_2nd(τ

, ε

) represents the log probability distribution function, T represents symbol timing offset, ε

represents frequency offset, σ

_s² represents average power of transmitted signals s(•

), σ

_w² represents an average power of Additive White Gaussian Noise (AWGN), and γ

(n) and the Φ

(n) are respectively expressed as

$\mathrm{\gamma <br><br>}<br><br>\left(n\right)\equiv <br><br>\underset{n=\mathrm{\tau <br><br>}}{\overset{\mathrm{\tau <br><br>}+N_{\mathrm{CP}}-1}{\sum <br><br>}}<br><br>\frac{{\mathrm{\rho <br><br>}}_n}{1-{\mathrm{\rho <br><br>}}_n^2}<br><br>r<br><br>\left(n\right)<br><br>r^{*}<br><br>\left(n+N\right),$

wherein ρ

_n represents a correlation coefficient absolute value between the n^th sample and the (n+N)^th sample of the received signal r(n), and

$\mathrm{\Phi <br><br>}<br><br>\left(n\right)\equiv <br><br>\frac{1}{2}<br><br>\underset{n=\mathrm{\tau <br><br>}}{\overset{\mathrm{\tau <br><br>}+N_{\mathrm{CP}}-1}{\sum <br><br>}}<br><br>\frac{{\mathrm{\rho <br><br>}}_n^2}{\left(1-{\mathrm{\rho <br><br>}}_n^2\right)}<br><br>\left\{{<br><br>r<br><br>\left(n\right)<br><br>}^2++<br><br>{<br><br>r<br><br>\left(n+N\right)<br><br>}^2\right\}.$

11. The apparatus as claimed in claim 10, wherein an estimation value of the timing offset is expressed as

${\stackrel{}{\tau }}_{}$

^ ML = arg ⁢

⁢

max τ

⁢

{ 

γ

⁡

( τ

) 

- Φ

⁡

( τ

) } ,

wherein {circumflex over (τ

)}_ML represents the estimation value of the timing offset.

12. The apparatus as claimed in claim 10, wherein an estimation value of the frequency offset is expressed as

${\stackrel{}{\varepsilon }}_{}$

^ ML = - 1 2 ⁢

π

⁢

∠

γ

⁡

( τ

^ ML ) ,

wherein {circumflex over (ε

)}_ML represents the estimation value of the frequency offset.

15. The apparatus as claimed in claim 7, wherein the power delay profile represents a power profile of a time-varying frequency selective fading channel.

16. The apparatus as claimed in claim 7, wherein the specific function is a square root of an average power in a k^th multi-path, and the square root of the average power in the k^th multi-path is proportional to an inverse of k, and k is a natural number.