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

• US 20060104254A1
• Filed: 11/15/2005
• Published: 05/18/2006
• Est. Priority Date: 11/15/2004
• Status: Active Grant

• 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: Jung, Young-Ho, Lee, Yong-Hoon, Hwang, Chan-Soo, Joung, Jin-Gon, Shin, Won-Yong
• Granted Patent: US 7,630,463 B2
• Time in Patent Office: Days
• US Class Current: 370/343
• 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;

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.

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 2, wherein the step of modeling the power delay profile in the time-varying frequency selective fading channel conditions by the specific function comprises a step of modeling the function to have characteristics of an exponential function and to be detected by means of information representing a sum of average power of signals received through a multi-path of 1.

4. The method as claimed in claim 3, 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 N_CP, the function is,

${\alpha }_{}$

k = C k ,

wherein k represents an k^th multi-path of the N_CP number of multi-paths and C is a constant expressed by,

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

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

${\Lambda }_{}$

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, τ

represents the symbol timing offset, ε

represents the frequency offset, σ

_s² represents average power of transmitted signals s(•

),σ

_w² represents Additive White Gaussian Noise (AWGN), and γ

(n) and the Φ

(n) are respectively,

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

wherein ρ

_n represents a correlation coefficient absolute value between an n^th sample and an (n+N)^th sample in received signals, and

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

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

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

^ ML = arg ⁢

 

⁢

max τ

⁢

{ 

γ

⁡

( τ

) 

- Φ

⁡

( τ

) } ,

wherein {circumflex over (τ

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

7. The method as claimed in claim 5, wherein the an estimation value of the frequency offset is,

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

^ ML = - 1 2 ⁢

π

⁢

∠

γ

⁡

( τ

^ ML ) ,

wherein {circumflex over (ε

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

8. 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

performing a synchronization acquisition unit for inputting the signal for which the FFT has been performed, detecting a log probability distribution function of a timing offset and a frequency offset in consideration of a correlation between the received signal and received multi-path signal in time-varying frequency selective fading channel conditions, and estimating a timing offset and a frequency offset which maximize the log probability distribution function of the timing offset and the frequency offset.

9. The apparatus as claimed in claim 8, wherein a power delay profile in the time-varying frequency selective fading channel conditions has been modeled by a specific function, the function has characteristics of an exponential function and has been modeled by a function which can be detected with information representing a sum of average power of signals received through a multi-path of 1.

10. The apparatus as claimed in claim 9, 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 N_CP, the function is expressed as,

${\alpha }_{}$

k = C k ,

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

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

11. The apparatus as claimed in claim 10, 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, τ

represents the symbol timing offset, ε

represents the frequency offset, σ

_s² represents average power of transmitted signals s(•

),σ

_w² represents 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 an n^th sample and an (n+N)^th sample in received signals, and

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

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

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

^ ML = arg ⁢

 

⁢

max τ

⁢

{ 

γ

⁡

( τ

) 

- Φ

⁡

( τ

) } ,

wherein {circumflex over (τ

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

13. The apparatus as claimed in claim 11, wherein the an estimation value of the frequency offset is,

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

^ ML = - 1 2 ⁢

π

⁢

∠

γ

⁡

( τ

^ ML ) ,

wherein {circumflex over (ε

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