Mode detection for OFDM signals

• US 7,433,296 B2
• Filed: 05/29/2003
• Issued: 10/07/2008
• Est. Priority Date: 05/29/2003
• Status: Expired due to Fees

• Current Assignee: Silicon Integrated Systems Corporation (Silicon Integrated Systems Corporation Taiwan)
• Original Assignee: Silicon Integrated Systems Corporation (Silicon Integrated Systems Corporation Taiwan)
• Inventors: Tsuie, Yih-Ming
• Primary Examiner(s): Vu; Huy D.
• Assistant Examiner(s): Skripnikov; Alex
• Application Number:
  US10/447,154
• Publication Number:
  US 20040240379A1
• Time in Patent Office: 1,958 Days
• Field of Search: 370204-211, 370/203, 708422-426
• US Class Current: 370/203
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

A method and apparatus for detecting the transmitted mode and guard interval length. The mode detection is adopted by the DVB-T system to increase system flexibility and combat multi-path interference in the transmission environment, of the received OFDM signals by applying the concepts of down-sampling and correlation. The unique combination of down-sampling and correlation method requires far less memory than the traditional correlation methods. By comparing the indicators resulting from output of each correlation module, the transmitted mode and guard interval length are detected with much greater reliability.

Claims

1. A method for processing a RF OFDM signal transmitted from an OFDM transmitter, comprising the steps of:

receiving and converting the RF OFDM signal into an IF OFDM signal;

converting the IF OFDM signal into a digital OFDM signal composed of an original sample sequence;

detecting a transmission mode and guard interval length of the OFDM signal, comprising steps of;

down-sampling the original sample sequence by a first, second, third and fourth factors to generate a first, second, third and fourth down-sampled sequence;

delaying the original sample sequence by a first and second number of samples, and down-sampling the delayed sample sequences by the third factor to generate a fifth and sixth down-sampled sequence;

applying a first, second and third correlation function to the first, second and fourth down-sampled sequence, and a fourth correlation function to the third, fifth and sixth down-sampled sequence, to derive a first, second, third, fourth, fifth and sixth correlation powers respectively;

down-sampling the original sample sequence by a fifth, sixth, seventh and eighth factor to generate a seventh, eighth, ninth and tenth down-sampled sequence;

delaying the original sample sequence by a third and fourth number of samples, and down-sampling the delayed sample sequences by the seventh factor to generate an eleventh and twelfth down-sampled sequence;

applying the first, second and third correlation function to the seventh, eighth and ninth down-sampled sequence, and the fourth correlation function, to the tenth, eleventh and twelfth down-sampled sequence, to derive seventh, eighth, ninth, tenth, eleventh and twelfth correlation powers respectively; and

determining the transmission mode and guard interval length by the first, second, third, seventh, eighth and ninth correlation powers, the maximum of the fourth, fifth and sixth correlation powers, and the maximum of the tent, eleventh and twelfth correlation powers;

implementing digital processing of the OFDM signal in time domain and frequency domain; and

implementing channel decoding and de-interleaving of the OFDM signal.

2. The method as claimed in claim 1, wherein the first, second, third, fourth, fifth, sixth, seventh and eighth factors are 64, 128, 256, 512, 256, 512, 1024 and 2048 respectively.

3. The method as claimed in claim 1, wherein the first, second, third and fourth numbers are 1, 2, 4 and 8.

4. The method as claimed in claim 1, wherein the first, second, third and fourth correlation functions are respectively c=Σ

y(33n)y*(33n+32), c=Σ

y(17n)y*(17n+16), c=Σ

y(9n)y*(9n+8) and c=Σ

y(5n)y*(5n+4) where c and y are the output and input of the correlation functions, and n=0, 1, . . . , M−

1, and M is a predetermined value.

5. The method as claimed in claim 4, wherein the correlation powers are |c|².

6. The method as claimed in claim 1, wherein the first, second, third, seventh, eighth and ninth correlation powers, the maximum of the fourth, fifth and sixth correlation powers, and the maximum of the tenth, eleventh and twelfth correlation powers are respectively represented by indicators I1, I2, I3, I4, I5, I6, I7 and I8, and the transmission mode and guard interval length is determined by the steps of:

(a) sorting the indicators I1,I2, I3 and I4, and deriving a result {S1, S2, S3, S4};

(b) Implementing the procedure;

{If S1>

α

S2  

 

2K_Tu_Comparison_Valid=TRUE  

 

2K_Tu_Possible_RTg=RTgS1  

Elseif S3>

β

S4  

 

2K_Tu_Comparison_Valid=TRUE  

 

2K_Tu_Possible_RTg=RTgS4  

Else  

 

Tu_Comparison_Valid=FALSE  

2K_Tu_Average_Indicator=I1+I2+I3+I4},

 

wherein α and

β

are predetermined values and are both larger than 1, RTgS1 is 1/32, 1/16, ⅛ and

¼

if S1 is I1, I2, I3 and I4 respectively, and RTgS4 is 1/32, 1/16, ⅛ and

¼

if S4 is I1, I2, I3 and I4 respectively;

(c) sorting the indicators I5, I6, I7 and I8, and deriving a result {S5, S6, S7, S8};

(d) Implementing the procedure;

{If S5>

α

S6  

 

8K_Tu_Comparison_Valid=TRUE  

 

8K_Tu_Possible_RTg=RTgS5  

Elseif S7>

β

S8  

 

8K_Tu_Comparison_Valid=TRUE  

 

8K_Tu_Possible_RTg=RTgS8  

Else  

 

Tu_Comparison_Valid=FALSE  

8K_Tu_Average_Indicator=I5+I6+I7+I8},

 

wherein α and

β

are predetermined values and are both larger than 1, RTgS5 is 1/32, 1/16, ⅛ and

¼

if S5 is I5, I6, I7 and I8 respectively, and RTgS8 is 1/32, 1/16, ⅛ and

¼

if S8 is I5, I6, I7 and I8 respectively; and

(e) implementing the procedure;

{If 2K_Comparison_Valid=TRUE and  

 

8K_Comparison_Valid=TRUE,  

 

 

MD_Flag=SUCCESS  

If 2K_Average_Indicator>

8K_Average_Indicator  

 

 

Tu_Flag=2K  

 

 

 

RTg_Flag=2K_Possible_RTg  

 

Else  

 

 

 

Tu_Flag=8K  

 

 

 

RTg_Flag=8K_Possible_RTg  

If 2K_Comparison_Valid= TRUE and 8K_Comparison_Valid=  

 

 

FALSE,  

 

MD_Flag=SUCCESS  

 

Tu_Flag=2K  

 

RTg_Flag=2K_Possible_RTg  

If 2K_Comparison_Valid= FALSE and 8K_Comparison_Valid=  

 

 

TRUE,  

 

MD_Flag=SUCCESS  

 

Tu_Flag=8K  

 

RTg_Flag=8K_Possible_RTg If 2K_Comparison_Valid= FALSE and 8K_Comparison_Valid=  

 

 

FALSE,  

 

MD_Flag=FAIL},

 

wherein Tu₁₃ Flag is the transmission mode, the product of RTg<sub>—

Flag and Tu</sub>_Flag is the guard interval length and MD_Flag indicates the success or failure of the mode detection.

7. A method of mode detection for an OFDM signal comprising the steps of:

down-sampling the original sample sequence by a first, second, third and fourth factors to generate a first, second, third and fourth down-sampled sequence;

delaying the original sample sequence by a first and second number of samples, and down-sampling the delayed sample sequences by the third factor to generate a fifth and sixth down-sampled sequence;

applying a first, second, and third correlation function to the first, second and fourth down-sampled sequence, and a fourth correlation function to the third, fifth and sixth down-sampled sequence, to derive first, second, third, fourth, fifth and sixth correlation powers respectively;

down-sampling the original sample sequence by a fifth, sixth, seventh and eighth factor to generate a seventh, eighth, ninth and tenth down-sampled sequence;

delaying the original sample sequence by a third and fourth number of samples, and down-sampling the delayed sample sequences by the seventh factor to generate a eleventh and twelfth down-sampled sequence;

applying the first, second and third correlation function to the seventh, eighth and ninth down-sampled sequence, and the fourth correlation function to the tenth, eleventh and twelfth down-sampled sequence, to derive seventh, eighth, ninth, tenth, eleventh and twelfth correlation powers respectively; and

determining the transmission mode and guard interval length by the first, second, third, seventh, eighth and ninth correlation powers, the maximum of the fourth, fifth and sixth correlation powers, and the maximum of the tenth, eleventh and twelfth correlation powers.

8. The method as claimed in claim 7, wherein the first, second, third, fourth, fifth, sixth, seventh and eighth factors are 64, 128, 256, 512, 256, 512, 1024 and 2048 respectively.

9. The method as claimed in claim 7, wherein the first, second, third and fourth number are 1, 2, 4 and 8.

10. The method as claimed in claim 7, wherein the first, second, third and fourth correlation functions are respectively c=Σ

y(33n)y*(33n+32), c=Σ

y(17n)y*(17n+16), c=Σ

y(9n)y*(9n+8) and c=Σ

y(5n)y*(5n+4) where c and y are the output and input of the correlation functions, and n=0, 1, . . . , M−

1, and M is a predetermined value.

11. The method as claimed in claim 10, wherein the correlation powers are |c|².

12. The method as claimed in claim 7, wherein the first, second, third, seventh, eighth and ninth correlation powers, the maximum of the fourth, fifth and sixth correlation powers, and the maximum of the tenth, eleventh and twelfth correlation powers are respectively represented by indicators I1, I2, I3, I4, I5, I6, I7 and I8, and the transmission mode and guard interval length is determined by the steps of:

(a) sorting the indicators I1, I2, I3 and I4, and deriving a result {S1, S2, S3, S4};

(b) Implementing the procedure;

{If S1>

α

S2  

 

2K_Tu_Comparison_Valid=TRUE  

 

2K_Tu_Possible_RTg=RTgS1  

Elseif S3>

β

S4  

 

2K_Tu_Comparison_Valid=TRUE  

 

2K_Tu_Possible_RTg=RTgS4  

Else  

 

Tu_Comparison_Valid=FALSE  

2K_Tu_Average_Indicator=I1+I2+I3+I4},

 

wherein α and

β

we predetermined values and are both larger than 1, RTgS1 is 1/32, 1/16, ⅛ and

¼

if S1 is I1, I2, I3 and I4 respectively, and RTgS4 is 1/32, 1/16, ⅛ and

¼

if S4 is I1, I2, I3 and I4 respectively;

(c) sorting the indicators I5, I6, I7 and I8, and deriving a result {S5, S6, S7, S8};

(d) Implementing the procedure;

{If S5>

α

S6  

 

8K_Tu_Comparison_Valid=TRUE  

 

8K_Tu_Possible_RTg=RTgS5  

Elseif S7>

β

S8  

 

8K_Tu_Comparison_Valid=TRUE  

 

8K_Tu_Possible_RTg=RTgS8  

Else  

 

Tu_Comparison_Valid=FALSE  

8K_Tu_Average_Indicator=I5+I6+I7+I8},

 

wherein α and

β

are predetermined values and are both larger than 1, RTgS5 is 1/32, 1/16, ⅛ and

¼

if S8 is I5, I6, I7 and I8 respectively, and RTgS8 is 1/32, 1/16, ⅛ and

¼

if S8 is I5, I6, I7 and I8 respectively; and

(e) implementing the procedure;

 

 

{If 2K_Comparison_Valid=TRUE and  

 

 

 

8K_Comparison_Valid=TRUE,  

 

 

 

 

MD_Flag=SUCCESS  

 

 

If 2K_Average_Indicator>

8K_Average_Indicator  

 

 

 

 

Tu_Flag=2K  

 

 

 

 

RTg_Flag=2K_Possible_RTg  

 

 

Else  

 

 

 

 

Tu_Flag=8K  

 

 

 

 

RTg_Flag=8K_Possible_RTg  

If 2K_Comparison_Valid= TRUE and 8K_Comparison_Valid=  

 

 

 

FALSE,  

 

 

MD_Flag=SUCCESS  

 

 

Tu_Flag=2K  

 

 

RTg_Flag=2K_Possible_RTg  

If 2K_Comparison_Valid= FALSE and 8K_Comparison_Valid=  

 

 

 

TRUE,  

 

 

MD_Flag=SUCCESS  

 

 

Tu_Flag=8K  

 

 

RTg_Flag=8K_Possible_RTg If 2K_Comparison_Valid= FALSE and 8K_Comparison_Valid=  

 

 

 

FALSE,  

 

 

MD_Flag=FAIL},

 

wherein Tu_Flag is the transmission mode, the product of RTg_Flag and Tu_Flag is the guard interval length and MD_Flag indicates the success or failure of the mode detection.

13. An OFDM receiver comprising:

a front end receiving and converting the RF QFDM signal into an IF OFDM signal;

an A/D converter converting the IF OFDM signal into a digital OFDM signal;

a mode detector detecting a transmission mode and guard interval length of the digital OFDM signal by the steps of;

down-sampling the original sample sequence by first, second, third and fourth factors to generate a first, second, third and fourth down-sampled sequence;

delaying the original sample sequence by a first and second number of samples, and down-sampling the delayed sample sequences by the third factor to generate a fifth and sixth down-sampled sequence;

applying a first, second and third correlation function to the first, second and fourth down-sampled sequence, and a fourth correlation function to the third, fifth and sixth down-sampled sequence, to derive first, second, third, fourth, fifth and sixth correlation powers respectively;

down-sampling the original sample sequence by a fifth, sixth, seventh and eighth factor to generate a seventh, eighth, ninth and tenth down-sampled sequence;

delaying the original sample sequence by a third and fourth number of samples, and down-sampling the delayed sample sequences by the seventh factor to generate an eleventh and twelfth down-sampled sequence;

applying the first, second and third correlation function to the seventh, eighth and ninth down-sampled sequence, and the fourth correlation function to the tenth, eleventh and twelfth down-sampled sequence, to derive seventh, eighth, ninth, tenth, eleventh and twelfth correlation powers respectively; and

determining the transmission mode and guard interval length by the first second, third, seventh, eighth and ninth correlation powers, the maximum of the fourth, fifth and sixth correlation powers, and the maximum of the tenth, eleventh and twelfth correlation powers;

frequency and time domain digital processors implementing digital processing of the OFDM signal in time domain and frequency domain; and

a channel decoder and de-interleaver implementing channel decoding and de-interleaving of the OFDM signal.

14. The OFDM receiver as claimed in claim 13, wherein the first, second, third, fourth, fifth, sixth, seventh and eighth factors are 64, 128, 256, 512, 256, 512, 1024 and 2048 respectively.

15. The OFDM receiver as claimed in claim 13, wherein the first second, third and fourth numbers are 1,2,4 and 8.

16. The OFDM receiver as claimed in claim 13, wherein the first, second, third and fourth correlation functions are respectively c=Σ

y(33n)y*(33n+32), c=Σ

y(17n)y*(17n+16), c=Σ

y(9n)y*(9n+8) and c=Σ

y(5n)y*(5n+4) where c and y are the output and input of the correlation functions, and n=0, 1, . . . , M−

1, and M is a predetermined value.

17. The OFDM receiver as claimed in claim 16, wherein the correlation powers are |c|².

18. The OFDM receiver as claimed in claim 16, wherein the first, second, third, seventh, eighth and ninth correlation powers, the maximum of the fourth, fifth and sixth correlation powers, and the maximum of the tenth, eleventh and twelfth correlation powers are respectively represented by indicators I1, I2, I3, I4, I5, I6, I7 and I8, and the transmission mode and guard interval length is determined by the steps of:

(a) sorting the indicators I1, I2, I3 and I4, and deriving a result {S1, S2, S3, S4};

(b) Implementing the procedure;

{If S1>

α

S2  

 

2K_Tu_Comparison_Valid=TRUE  

 

2K_Tu_Possible_RTg=RTgS1  

Elseif S3>

β

S4  

 

2K_Tu_Comparison_Valid=TRUE  

 

2K_Tu_Possible_RTg=RTgS4  

Else  

 

Tu_Comparison_Valid=FALSE  

2K_Tu_Average_Indicator=I1+I2+I3+I4},

 

wherein α and

β

are predetermined values and are both larger than 1, RTgS1 is 1/32, 1/16, ⅛ and

¼

if S1 is I1, I2, I3 and I4 respectively, and RTgS4 is 1/32, 1/16, ⅛ and

¼

if S4 is I1, I2, I3 and I4 respectively;

(c) sorting the indicators I5, I6, I7 and I8, and deriving a result {S5, S6, S7, S8};

(d) Implementing the procedure;

{If S5>

α

S6  

 

8K_Tu_Comparison_Valid=TRUE  

 

8K_Tu_Possible_RTg=RTgS5  

Elseif S7>

β

S8  

 

8K_Tu_Comparison_Valid=TRUE  

 

8K_Tu_Possible_RTg=RTgS8  

Else  

 

Tu_Comparison_Valid=FALSE  

8K_Tu_Average_Indicator=I5+I6+I7+I8},

 

wherein α and

β

are predetermined values and are both larger than 1, RTgS5 is 1/32, 1/16, ⅛ and

¼

if S5 is I5, I6, I7 and I8 respectively, and RTgS8 is 1/32, 1/16, ⅛ and

¼

if S8 is I5, I6, I7 and I8 respectively; and

(e) implementing the procedure;

{If 2K_Comparison_Valid=TRUE and  

 

8K_Comparison_Valid=TRUE,  

 

 

MD_Flag=SUCCESS  

If 2K_Average_Indicator>

8K_Average_Indicator  

 

 

Tu_Flag=2K  

 

 

RTg_Flag=2K_Possible_RTg  

Else  

 

 

Tu_Flag=8K  

 

 

 

RTg_Flag=8K_Possible_RTg  

If 2K_Comparison_Valid= TRUE and 8K_Comparison_Valid=  

 

 

FALSE,  

 

MD_Flag=SUCCESS  

 

Tu_Flag=2K  

 

RTg_Flag=2K_Possible_RTg  

If 2K_Comparison_Valid= FALSE and 8K_Comparison_Valid=  

 

 

TRUE,  

 

MD_Flag=SUCCESS  

 

Tu_Flag=8K  

 

RTg_Flag=8K_Possible_RTg If 2K_Comparison_Valid= FALSE and 8K_Comparison_Valid=  

 

 

FALSE,  

 

MD_Flag=FAIL},

 

wherein Tu_Flag is the transmission mode, the product of RTg_Flag and Tu_Flag is the guard interval length and MD_Flag indicates the success or failure of the mode detection.

19. A mode detector detecting a transmission mode and guard interval length of the digital OFDM signal by the steps of:

down-sampling the original sample sequence by first, second, third and fourth factors to generate a first, second, third and fourth down-sampled sequence;

delaying the original sample sequence by a first and second number of samples, and down-sampling the delayed sample sequences by the third factor to generate a fifth and sixth down-sampled sequence;

applying a first, second and third correlation function to the first, second and fourth down-sampled sequence, and a fourth correlation function to the third, fifth and sixth down-sampled sequence, to derive first, second, third, fourth, fifth and sixth correlation powers respectively;

down-sampling the original sample sequence by a fifth, sixth, seventh and eighth factor to generate a seventh, eighth, ninth and tenth down-sampled sequence;

delaying the original sample sequence by a third and fourth number of samples, and down-sampling the delayed sample sequences by the seventh factor to generate an eleventh and twelfth down-sampled sequence;

applying the first, second and third correlation function to the seventh, eighth and ninth down-sampled sequence, and the fourth correlation function to the tenth, eleventh and twelfth down-sampled sequence, to derive seventh, eighth, ninth, tenth, eleventh and twelfth correlation powers respectively; and

determining the transmission mode and guard interval length by the first, second, third, seventh, eighth and ninth correlation powers, the maximum of the fourth, fifth and sixth correlation powers, and the maximum of the tenth, eleventh and twelfth correlation powers.

20. The mode detector as claimed in claim 19, wherein the first, second, third, fourth, fifth, sixth, seventh and eighth factors are 64, 128, 256, 512, 256, 512, 1024 and 2048 respectively.

21. The mode detector as claimed in claim 19, wherein the first, second, third and fourth number are 1, 2, 4 and 8.

22. The mode detector as claimed in claim 19, wherein the first, second, third and fourth correlation functions are respectively c=Σ

y(33n)y*(33n+32), c=Σ

y(17n)y*(17n+16), c=Σ

y(9n)y*(9n+8) and c=Σ

y(5n)y*(5n+4) where c and y are the output and input of the correlation functions, and n=0, 1, . . . , M−

1, and M is a predetermined value.

23. The mode detector as claimed in claim 22, wherein the correlation powers are |c|².

24. The mode detector as claimed in claim 19, wherein the first, second, third, seventh, eighth and ninth correlation powers, the maximum of the fourth, fifth and sixth correlation powers, and the maximum of the tenth, eleventh and twelfth correlation powers are respectively represented by indicators I1, I2, I3, I4, I5, I6, I7 and I8, and the transmission mode and guard interval length is determined by the steps of:

(a) sorting the indicators I1, I2, I3 and I4, and deriving a result {S1, S2, S3, S4};

(b) Implementing the procedure;

{If S1>

α

S2  

 

2K_Tu_Comparison_Valid=TRUE  

 

2K_Tu_Possible_RTg=RTgS1  

Elseif S3>

β

S4  

 

2K_Tu_Comparison_Valid=TRUE  

 

2K_Tu_Possible_RTg=RTgS4  

Else  

 

Tu_Comparison_Valid=FALSE  

2K_Tu_Average_Indicator=I1+I2+I3+I4},

wherein α and

β

are predetermined values and are both larger than 1, RTgS1 is 1/32, 1/16, ⅛ and

¼

if S1 is I1, I2, I3 and I4 respectively, and RTgS4 is 1/32, 1/16, ⅛ and

¼

if S4 is I1, I2, I3 and I4 respectively;

(c) sorting the indicators I5, I6, I7 and I8, and deriving a result {S5, S6, S7, S8};

(d) Implementing the procedure;

{If S5>

α

S6  

 

8K_Tu_Comparison_Valid=TRUE  

 

8K_Tu_Possible_RTg=RTgS5  

Elseif S7>

β

S8  

 

8K_Tu_Comparison_Valid=TRUE  

 

8K_Tu_Possible_RTg=RTgS8  

Else  

 

Tu_Comparison_Valid=FALSE  

8K_Tu_Average_Indicator=I5+I6+I7+I8},

 

wherein α and

β

are predetermined values and are both larger than 1, RTgS5 is 1/32, 1/16, ⅛ and

¼

if S5 is I5, I6, I7 and I8 respectively, and RTgS8 is 1/32, 1/16, ⅛ and

¼

if S8 is I5, I6, I7 and I8 respectively; and

(e) implementing the procedure;

 

 

{If 2K_Comparison_Valid=TRUE and  

 

 

 

8K_Comparison_Valid=TRUE,  

 

 

 

 

MD_Flag=SUCCESS  

 

 

If 2K_Average_Indicator>

8K_Average_Indicator  

 

 

 

 

Tu_Flag=2K  

 

 

 

 

RTg_Flag=2K_Possible_RTg  

 

 

Else  

 

 

 

 

Tu_Flag=8K  

 

 

 

 

RTg_Flag=8K_Possible_RTg  

If 2K_Comparison_Valid= TRUE and 8K_Comparison_Valid=  

 

 

 

FALSE,  

 

 

MD_Flag=SUCCESS  

 

 

Tu_Flag=2K  

 

 

RTg_Flag=2K_Possible_RTg  

If 2K_Comparison_Valid= FALSE and 8K_Comparison_Valid=  

 

 

 

TRUE,  

 

 

MD_Flag=SUCCESS  

 

 

Tu_Flag=8K  

 

 

RTg_Flag=8K_Possible_RTg If 2K_Comparison_Valid= FALSE and 8K_Comparison_Valid=  

 

 

 

FALSE,  

 

 

MD_Flag=FAIL},

 

wherein Tu_Flag is the transmission mode, the product of RTg_Flag and Tu_Flag is the guard interval length and MD_Flag indicates the success or failure of the mode detection.