Adaptive quantization method and apparatus for an OFDM receiver

• US 7,756,222 B2
• Filed: 05/04/2006
• Issued: 07/13/2010
• Est. Priority Date: 05/04/2006
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Integrated System Solution Corp.
• Inventors: Lee, Yumin, Lin, Yuh-Chun, Chen, Jeng-Hong
• Primary Examiner(s): Liu; Shuwang
• Assistant Examiner(s): Singh; Hirdepal
• Application Number:
  US11/381,625
• Publication Number:
  US 20070258531A1
• Time in Patent Office: 1,531 Days
• Field of Search: 375242-245, 375322-324, 375342-345, 375/295, 375/306, 375/316, 375/340, 375/354, 375/359, 375259-260, 375/267, 375/348, 375/350, 375/371, 370/204, 370/208, 370/310, 370/476, 455/52, 455/59, 455/69
• US Class Current: 375/324
• CPC Class Codes: H04L 25/067 providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

A quadrature frequency division multiplexing (“OFDM”) wireless receiver, including methods and devices for adaptive quantization of OFDM signals according to modulation and coding schemes and sub-carrier frequency responses, is provided. Efficient quantization may be utilized to reduce the large dynamic range of signals to achieve circuit simplification and chip area reduction. In one embodiment, a quantization circuit includes a quantization selector to select quantization thresholds according to modulation and coding schemes and sub-carrier frequency responses, and a non-uniform quantizer to reduce input dynamic range so that an output is represented by fewer bits than an input.

Claims

1. A method of dynamic quantization in an orthogonal frequency division multiplexing (OFDM) system, the method comprising:

receiving quadrature amplitude modulation (QAM) symbols for each of a number of “

m”

sub-carrier channels, m being an integer greater than 1;

computing a channel power P_CH(i)=|G_CH(i)|² for each of the m sub-carrier channels, where G_ch(i) is the i^-th sub-carrier channel frequency response, i being an integer from 0 to m−

1;

computing

2. The method of claim 1 further comprising:

quantizing the received QAM symbol x_i into a q-bit output including 2^q levels according to the (2^q−

1) quantization thresholds, θ

₀,±

θ

₁, . . . ,±

θ

<sub>2q−

1−

1</sub>.

3. The method of claim 2, wherein

4. The method of claim 3, wherein S_t is approximated to an integer.

5. The method of claim 3, wherein

6. The method of claim 5, wherein S₂=2 and S₃=4 and wherein the quantization thresholds θ

₀,±

θ

₁,±

θ

₂,±

θ

₃ for a 3-bit quantized output are computed as follows;

θ

₀=0, θ

₁=K′

×

D, θ

₂=θ

₁×

2 and θ

₃=θ

₁×

4.

7. The method of claim 5, wherein S₂=2.5 and S₃=5 and wherein the quantization thresholds θ

₀,±

θ

₁,±

θ

₂,±

θ

₃ 3-bit quantized output are computed as follows;

θ

₀=0, θ

₁=K′

×

D , θ

₂=θ

₁×

2.5 and θ

₃=θ

₁×

5.

8. The method of claim 1 further comprising:

computing the total channel power to determine a dynamic range

9. The method of claim 8 further comprising a look-up table to provide values of K′

based on the first and second FSI values from the channel frequency selectivity detector and sub-carrier modulation and coding scheme (MCS) information, wherein K=K′

×

D.

10. The method of claim 1, wherein the first FSI value is set to one and the second FSI value is set to zero.

11. A receiver for dynamic quantization in an orthogonal frequency division multiplexing (OFDM) system, the receiver comprising:

a channel power calculator to compute a channel power P_CH(i)=|G_CH(i)|² for each of “

m”

sub-carrier channels, where G_ch(i) is the i^-th sub-carrier channel frequency response, i being an integer from 0 to m−

1; and

a channel frequency selectivity detector to compute

12. The receiver of claim 11, wherein the first FSI value is set to 1 and the second FSI value is set to 0.

13. The receiver of claim 11,

wherein the quantization parameter, K, is selected according to the first or second FSI values.

14. The receiver of claim 11 comprising:

quantizing the received QAM symbol x_i into a q-bit into a q-bit output including 2^q levels according to the (2^q−

1) quantization thresholds, θ

₀,±

θ

₁, . . . ,±

θ

<sub>2q−

1−

1</sub>.

15. The receiver of claim 14, wherein

16. The receiver of claim 15, wherein

17. The receiver of claim 16, wherein S₂=2 and S₃=4 and wherein the quantization thresholds θ

₀,±

θ

₁,±

θ

₂,±

θ

₃ for a 3-bit quantized output are computed as follows;

θ

₀=0, θ

₁=K′

×

D, θ

₂=θ

₁×

2 and θ

₃=θ

₁×

4.

18. The receiver of claim 16, wherein S₂=2.5 and S₃=5 and wherein the quantization thresholds θ

₀,±

θ

₁,±

θ

₂,±

θ

₃ for a 3-bit quantized output are computed as follows;

θ

₀=0, θ

₁=K′

×

D , θ

₂=θ

₁×

2.5 and θ

₃=θ

₁×

5.

19. The receiver of claim 15, wherein S_t is approximated to an integer.

20. The receiver of claim 11 further comprising:

computing the total channel power to determine a dynamic range

21. The receiver of claim 20 further comprising a look-up table to provide values of K′

based on the first and second FSI values from the channel frequency selectivity detector and sub-carrier modulation and coding scheme (MCS) information, wherein K=K′

×

D.