Bit log likelihood ratio evaluation

• US 20060178755A1
• Filed: 01/11/2006
• Published: 08/10/2006
• Est. Priority Date: 01/11/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Bai, Jinxia, Ling, Fuyun, Chung, Seong Taek, Sun, Thomas
• Granted Patent: US 7,660,368 B2
• Time in Patent Office: Days
• US Class Current: 700/1
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0065 Serial concatenated codes
• CPC Class Codes: H04L 1/0066 Parallel concatenated codes
• CPC Class Codes: H04L 2001/0098 Unequal error protection
• CPC Class Codes: H04L 27/2604 Multiresolution systems by means of multiresolution subcarriers H04L27/183, H04L27/3488
• CPC Class Codes: H04L 27/3488 Multiresolution systems

Abstract

A system and method are provided for generating bit log likelihood ratio (LLR) values for two-layered Quadrature Phase-Shift Keying (QPSK) turbo decoding in a wireless communications user terminal (UT). The method includes receiving a two-layered QPSK signal with an energy ratio that is unknown, but typically defined as either k1² or k2². The method selects a mismatched energy ratio (k²) between k1² and k2², and generating bit LLR values for two-layered QPSK turbo decoding, using the mismatched k² energy ratio. For example, if the received two-layered QPSK signal is known to have an energy ratio of about 4 or about 6.25. Then, k² is selected to be about 5.0625. Alternately stated, the mismatched k² energy ratio in selected by determining the approximate midpoint between k1² and k2².

Claims

1. In a wireless communications user terminal (UT), a method for generating bit log likelihood ratio (LLR) values for two-layered quadrature phase-shift keying (QPSK) turbo decoding, the method comprising:

receiving a two-layered QPSK signal with an energy ratio selected from the group comprising k1² and k2²;

selecting a mismatched energy ratio (k²) between k1² and k2²; and

,

generating bit LLR values for two-layered QPSK turbo decoding, using the mismatched k² energy ratio.

2. The method of claim 1 wherein selecting the mismatched k² energy ratio includes:

determining the approximate midpoint between k1² and k2²; and

,

setting k² equal to the approximate midpoint.

3. The method of claim 1 wherein receiving the two-layered QPSK includes receiving a two-layered QPSK signal with an energy ratio selected from the group comprising about 4 and about 6.25;

and,

wherein selecting the mismatched k² energy ratio includes selecting k² to be about 5.0625.

4. The method of claim 3 wherein generating bit LLR values for two-layered QPSK turbo decoding includes decoding with a worst case degradation of less than about 0.1 dB.

5. The method of claim 1 wherein receiving the two-layered QPSK includes receiving a two-layered QPSK signal with in phase (I) and quadrature (Q) components per symbol;

and

wherein generating bit LLR values for two-layered QPSK turbo decoding includes determining LLR values for four bits (b3, b2, b1, and b0).

6. The method of claim 5 wherein determining the bit LLR values includes determining the LLR values for each b0 and b2 bit as follows:

${\mathrm{LLR}}_{2,0}=\frac{1}{N_0}\times <br><br>\frac{2}{1+k^2}\times <br><br>\left(<br><br>J<br><br>-k·<br><br>C^{*}·<br><br>C\right);<br><br>$

where J is v for b0, and w for b2;

v=√

{square root over (2(1+k²))}Re[C*r];

w=√

{square root over (2(1+k²))}Im[C*r];

r is the complex received signal;

C is the complex channel estimate; and

,

C* is the complex conjugate of C.

7. The method of claim 6 wherein determining the bit LLR values includes determining the LLR values for each b1 and b3 bit as follows:

${\mathrm{LLR}}_1=\frac{1}{N_0}\times <br><br>\frac{2}{1+k^2}\times <br><br>\mathrm{sgn}<br><br>\left(J\right)\times <br><br>\{\begin{array}{ccc}\left(k-1\right)<br><br><br><br>J<br><br>& \mathrm{if}& <br><br>J<br><br>\le <br><br>k·<br><br>C^{*}·<br><br>C\\ k<br><br>\left(<br><br>J<br><br>-C^{*}·<br><br>C\right)& \mathrm{if}& <br><br>J<br><br>><br><br>k·<br><br>C^{*}·<br><br>C\end{array}$

where J is v for b1, and w for b3;

sgn(J) is the sign bit of J.

8. A wireless communications user terminal (UT), for generating bit log likelihood ratio (LLR) values for two-layered quadrature phase-shift keying (QPSK) turbo decoding, the UT comprising:

a receiver having an air interface input to accept a two-layered QPSK signal with an energy ratio selected from the group comprising k1² and k2²; and

outputs to supply a complex received signal components and complex channel estimates; and

,

a LLR module having inputs to receive the complex received signal components and complex channel estimates, the LLR module selecting a mismatched energy ratio (k²) between k1² and k2², and supplying bit LLR values for two-layered QPSK turbo decoding at an output, using the k² energy ratio.

9. The UT of claim 8 wherein the LLR module selects k² as the approximate midpoint between k1² and k2².

10. The UT of claim 8 wherein the receiver accepts a two-layered QPSK signal with an energy ratio selected from the group comprising about 4 and about 6.25;

and,

wherein the LLR module selects k² to be about 5.0625.

11. The UT of claim 8 wherein the receiver accepts a two-layered QPSK signal with in phase (I) and quadrature (Q) components;

and

wherein the LLR module determines four bit LLR values (b3, b2, b1, and b0).

12. The UT of claim 11 wherein the LLR module determines the LLR values for each b0 and b2 bit as follows:

${\mathrm{LLR}}_{2,0}=\frac{1}{N_0}\times <br><br>\frac{2}{1+k^2}\times <br><br>\left(<br><br>J<br><br>-k·<br><br>C^{*}·<br><br>C\right);<br><br>$

where J is v for b0, and w for b2;

v=√

{square root over (2(1+k²))}Re[C*r];

w=√

{square root over (2(1+k²))}Im[C*r];

r is the complex received signal;

C is the complex channel estimate; and

,

C* is the complex conjugate of C.

13. The UT of claim 12 wherein the LLR module determines the LLR values for each b1 and b3 bit as follows:

${\mathrm{LLR}}_1=\frac{1}{N_0}\times <br><br>\frac{2}{1+k^2}\times <br><br>\mathrm{sgn}<br><br>\left(J\right)\times <br><br>\{\begin{array}{ccc}\left(k-1\right)<br><br><br><br>J<br><br>& \mathrm{if}& <br><br>J<br><br>\le <br><br>k·<br><br>C^{*}·<br><br>C\\ k<br><br>\left(<br><br>J<br><br>-C^{*}·<br><br>C\right)& \mathrm{if}& <br><br>J<br><br>><br><br>k·<br><br>C^{*}·<br><br>C\end{array}$

where J is v for b1, and w for b3; and

,

sgn(J) is the sign bit of J.

14. A processor for generating bit log likelihood ratio (LLR) values for two-layered quadrature phase-shift keying (QPSK) turbo decoding, the processor comprising:

inputs to receive complex received signals and complex channel estimates for QPSK symbols;

a log likelihood ratio (LLR) section having inputs to receive the complex received signals and complex channel estimates, the LLR section selecting a mismatched energy ratio (k²) between k1² and k2² and generating bit LLR values for two-layered QPSK turbo decoding using the k² energy ratio; and

,

outputs connected to a turbo decoder, to supply bit LLR values.

15. The processor of claim 14 wherein the LLR section selects k² as the approximate midpoint between k1² and k2².

16. The processor of claim 14 wherein the processor inputs accept complex received signal and complex channel estimates for two-layered QPSK signals with an energy ratio selected from the group comprising about 4 and about 6.25;

and,

wherein the LLR section selects k² to be about 5.0625.

17. A signal bearing medium tangibly embodying a program of machine-readable instructions executable by a digital processing apparatus to perform operations for generating bit log likelihood ratio (LLR) values for two-layered QPSK turbo decoding, the operations comprising:

receiving a two-layered QPSK signal with an energy ratio selected from the group comprising k1² and k2²;

selecting a mismatched energy ratio (k²) between k1² and k2²; and

,

generating bit LLR values for two-layered QPSK turbo decoding, using the mismatched k² energy ratio.

18. The operations of claim 17 wherein selecting the mismatched k² energy ratio includes:

determining the approximate midpoint between k1² and k2²; and

,

setting k² equal to the approximate midpoint.

19. The operations of claim 17 wherein receiving the two-layered QPSK includes receiving a two-layered QPSK signal with an energy ratio selected from the group comprising about 4 and about 6.25;

and,

wherein selecting the mismatched k² energy ratio includes selecting k² to be about 5.0625.

20. A wireless communications user terminal (UT), for generating bit log likelihood ratio (LLR) values for two-layered quadrature phase-shift keying (QPSK) turbo decoding, the UT comprising:

a means for accepting a two-layered QPSK signal with an energy ratio selected from the group comprising k1² and k2²;

a means for supplying a complex received signal components and complex channel estimates;

a means for selecting a mismatched energy ratio (k²) between k1² and k2², and,

a means for supplying bit LLR values for two-layered QPSK turbo decoding at an output, using the k² energy ratio.

21. The UT of claim 20 wherein the means for selecting the mismatched energy ratio selects k² as the approximate midpoint between k1² and k2².

22. The UT of claim 20 wherein the means for accepting the two-layered QPSK signal accepts a two-layered QPSK signal with an energy ratio selected from the group comprising about 4 and about 6.25;

and,

wherein the means for selecting the mismatched energy ratio selects k² to be about 5.0625.

23. A computer readable medium having computer executable instructions stored thereon to execute components of a wireless receiver, comprising:

receiving a two-layered QPSK signal with an energy ratio selected from the group comprising k12 and k22;

selecting a mismatched energy ratio (k2) between k12 and k22; and

,

generating bit LLR values for two-layered QPSK turbo decoding, using the mismatched k2 energy ratio.