BIT LOG LIKELIHOOD RATION EVALUATION

• US 20100098192A1
• Filed: 12/23/2009
• Published: 04/22/2010
• Est. Priority Date: 01/11/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Chung, Seong Taek, Bai, Jinxia, Ling, Fuyun, Sun, Thomas
• Granted Patent: US 8,102,949 B2
• Time in Patent Office: Days
• US Class Current: 375/332
• 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. A non-transitory computer readable medium comprising:

instructions for causing a wireless communications user terminal (UT) to generate a bit log likelihood ratio (LLR) values for two-layered quadrature phase-shift keying (QPSK) turbo decoding by;

receiving a two-layered QPSK signal with in phase (I) and quadrature (Q) components per symbol and with an energy ratio selected from a group comprising k1² and k2²;

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

generating the bit LLR values for the two-layered QPSK turbo decoding, using the mismatched k² energy ratio and including determining the bit LLR values for four bits (b3, b2, b1, and b0), wherein determining the bit LLR values includes determining the bit LLR values for each b0 and b2 bit as follows;

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

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.

2. The non-transitory computer readable medium of claim 2 wherein determining the bit LLR values includes determining the LLR values for each b1 and b3 bit as follows:

$L<br><br><br><br>L<br><br><br><br>R_1=\frac{1}{N_0}\times <br><br>\frac{2}{1+k^2}\times <br><br>\mathrm{sgn}<br><br>\left(J\right)\times <br><br>\{\begin{array}{ccc}\left(k-1\right)<br><br><br><br>J<br><br>& \mathrm{if}& <br><br>J<br><br>\le <br><br>k·<br><br>C^{*}·<br><br>C\\ k<br><br>\left(<br><br>J<br><br>-C^{*}·<br><br>C\right)& \mathrm{if}& <br><br>J<br><br>><br><br>k<br><br>·<br><br>C^{*}·<br><br>C\end{array}$

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

sgn(J) is the sign bit of J.

3. 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:

receiver means for accepting a two-layered QPSK signal having an energy ratio selected from a group comprising k1² and k2² with in phase (I) and quadrature (Q) components and supplying a complex received signal components and complex channel estimates; and

LLR module means for receiving the complex received signal components and complex channel estimates, determining four bit LLR values (b3, b2, b1, and b0), 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 mismatched energy ratio (k²), wherein the LLR module means determines the bit LLR values for each b0 and b2 bit as follows;

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

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.

4. The UT of claim 3 wherein the LLR module means determines the bit LLR values for each b1 and b3 bit as follows:

$L<br><br><br><br>L<br><br><br><br>R_1=\frac{1}{N_0}\times <br><br>\frac{2}{1+k^2}\times <br><br>\mathrm{sgn}<br><br>\left(J\right)\times <br><br>\{\begin{array}{ccc}\left(k-1\right)<br><br><br><br>J<br><br>& \mathrm{if}& <br><br>J<br><br>\le <br><br>k·<br><br>C^{*}·<br><br>C\\ k<br><br>\left(<br><br>J<br><br>-C^{*}·<br><br>C\right)& \mathrm{if}& <br><br>J<br><br>><br><br>k<br><br>·<br><br>C^{*}·<br><br>C\end{array}$

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

,

sgn(J) is the sign bit of J.