METHOD FOR IMPLEMENTING AN EQUALIZER OF AN OFDM BASEBAND RECEIVER

• US 20070237244A1
• Filed: 04/05/2006
• Published: 10/11/2007
• Est. Priority Date: 04/05/2006
• Status: Active Grant

• Current Assignee: VIA Technologies Incorporated (VIA Technologies)
• Original Assignee: VIA Technologies Incorporated (VIA Technologies)
• Inventors: Lin, Jeff, Huang, Jian-Wei
• Granted Patent: US 8,335,282 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 25/03292 with channel estimation circuitry
• CPC Class Codes: H04L 25/03318 Provision of soft decisions

Abstract

A method for implementing an equalizer of an orthogonal frequency division multiplexing (OFDM) baseband receiver is provided. The OFDM baseband receiver includes a channel estimation and tracking module for estimating a channel impulse response of an input signal of the equalizer. A conjugate of the channel impulse response is first calculated. The input signal and the conjugate of the channel impulse response are then multiplied to generate a product signal. The product signal is then taken as the output signal of the equalizer without dividing the product signal by a channel state information, wherein the channel state information represents a square of an absolute value of the channel impulse response.

Claims

1. A method for implementing an equalizer of an orthogonal frequency division multiplexing (OFDM) baseband receiver, wherein the OFDM baseband receiver includes a channel estimation and tracking module for estimating a channel impulse response of an input signal of the equalizer, the method comprising:

calculating a conjugate of the channel impulse response;

multiplying the input signal and the conjugate of the channel impulse response to generate a product signal; and

taking the product signal as the output signal of the equalizer directly without dividing the product signal by a channel state information;

wherein the channel state information represents a square of an absolute value of the channel impulse response.

2. The method as claimed in claim 1, wherein the method further comprises:

adjusting the amplitudes of a plurality of constellation points in a constellation according to the multiplication factor of the channel state information;

finding a first constellation point which is the most approximate to the output signal from the plurality of constellation points in the constellation; and

obtaining the data represented by the first constellation point to demodulate the output signal.

3. The method as claimed in claim 1, wherein the method further comprises:

adjusting the locations of a plurality of decision boundaries in a constellation according to a multiplication factor of the channel state information, wherein a plurality of constellation points are delimited by the plurality of decision boundaries in the constellation;

deriving a plurality of boundary values from the plurality of decision boundaries;

calculating a plurality of soft decision values according to the boundary values and the output signal;

finding a first constellation point which is the most approximate to the output signal from the plurality of constellation points in the constellation according to the signs of soft decision values; and

obtaining the data represented by the first constellation point to demodulate the output signal.

4. The method as claimed in claim 1, wherein the equalizer equalizes the input signal according to the following algorithm:

X_k=Y_k×

conj(H_k);

wherein X_k represents the output signal of the equalizer, Y_k represents the input signal of the equalizer, H_k represents the channel impulse response estimated by the channel estimation and tracking module, conj( ) is a conjugate function, and the suffix k represents the index of OFDM subcarrier.

5. The method as claimed in claim 1, wherein the method further comprises:

estimating the channel impulse response of the input signal with a preamble of the input signal; and

refining the channel impulse response of the input signal according to a channel tracking algorithm.

6. The method as claimed in claim 5, wherein the channel tracking algorithm is an algorithm selected from the group consisting of a recursive least square tracking algorithm and a least mean square tracking algorithm.

7. The method as claimed in claim 2, wherein the method further comprises:

calculating an estimate of the channel impulse response according to the first constellation point;

feeding back the estimate of the channel impulse response to the channel estimation and tracking module for adjusting the channel impulse response.

8. An orthogonal frequency division multiplexing (OFDM) baseband receiver, comprising:

a channel estimation and tracking module, for estimating a channel impulse response of an input signal and calculating a conjugate of the channel impulse response; and

an equalizer, coupled to the channel state module, for multiplying the input signal and the conjugate of the channel impulse response to generate an output signal, and outputting the output signal without dividing the output signal by a channel state information;

wherein the channel state information represents a square of an absolute value of the channel impulse response.

9. The OFDM baseband receiver as claimed in claim 8, wherein the OFDM baseband receiver comprises:

a demapper, coupled to the equalizer, for adjusting the amplitudes of a plurality of constellation points in a constellation according to the multiplication factor of the channel state information, finding a first constellation point which is the most approximate to the output signal from the plurality of constellation points in the constellation, and obtaining the data represented by the first constellation point to demodulate the output signal.

10. The OFDM baseband receiver as claimed in claim 8, wherein the OFDM baseband receiver further comprises a demapper for demodulating the output signal, and the demapper comprises:

a soft demapper, coupled to the equalizer and the channel estimation and tracking module, for adjusting the locations of a plurality of decision boundaries in a constellation according to a multiplication factor of the channel state information, deriving a plurality of boundary values from the plurality of decision boundaries, and calculating a plurality of soft decision values according to the boundary values and the output signal; and

a hard demapper, coupled to the soft demapper, for finding a first constellation point which is the most approximate to the output signal from a plurality of constellation points in the constellation according to the signs of soft decision values, and obtaining the data represented by the first constellation point to demodulate the output signal;

wherein the plurality of constellation points are delimited by the plurality of decision boundaries in the constellation.

11. The OFDM baseband receiver as claimed in claim 8, wherein the equalizer equalizes the input signal according to the following algorithm:

X_k=Y_k×

conj(H_k);

wherein X_k represents the output signal of the equalizer, Y_k represents the input signal of the equalizer, H_k represents the channel impulse response estimated by the channel estimation and tracking module, conj( ) is a conjugate function, and the suffix k represents the index of OFDM subcarrier.

12. The OFDM baseband receiver as claimed in claim 8, wherein the channel estimation and tracking module further comprises:

a channel estimation module, for estimating the channel impulse response of the input signal with a preamble of the input signal; and

a channel tracking module, coupled to the channel estimation module and the equalizer, for refining the channel impulse response of the input signal according to a channel tracking algorithm.

13. The method as claimed in claim 12, wherein the channel tracking algorithm is an algorithm selected from the group consisting of a recursive least square tracking algorithm and a least mean square tracking algorithm.

14. The OFDM baseband receiver as claimed in claim 9, wherein an estimate of the channel impulse response is calculated according to the first constellation point by the demapper, and the estimate of the channel impulse response is fed back to the channel estimation and tracking module for adjusting the channel impulse response.

15. An maximal ratio combining (MRC)—

orthogonal frequency division multiplexing (OFDM) baseband receiver, wherein the MRC-OFDM baseband receiver receives an OFDM signal with a plurality of spatially correlated antennas to generate a plurality of input signals, the MRC-OFDM baseband receiver comprising;

a channel estimation and tracking module, for estimating a plurality of channel impulse response of the plurality of input signals and calculating the conjugates of the channel impulse responses; and

an equalizer, coupled to the channel estimation module, for respectively multiplying the input signals and the conjugates of the channel impulse responses to generate a plurality of product signals, summing the product signals together to generate an output signal, and outputting the output signal directly without dividing the output signal by a channel state information;

wherein the channel estimation information represents a summation of the squares of the absolute values of the channel impulse responses.

16. The MRC-OFDM baseband receiver as claimed in claim 15, wherein the MRC-OFDM baseband receiver further comprises:

a demapper, coupled to the equalizer, for adjusting the amplitudes of a plurality of constellation points in a constellation according to the multiplication factor of the channel state information, finding a first constellation point which is the most approximate to the output signal from from the plurality of constellation points in the constellation, and obtaining the data represented by the first constellation point to demodulate the output signal.

17. The MRC-OFDM baseband receiver as claimed in claim 15, wherein the MRC-OFDM baseband receiver further comprises a demapper for demodulating the output signal, and the demapper comprises:

a soft demapper, coupled to the equalizer and the channel estimation and tracking module, for adjusting the locations of a plurality of decision boundaries in a constellation according to a multiplication factor of the channel state information, deriving a plurality of boundary values from the plurality of decision boundaries, and calculating a plurality of soft decision values according to the boundary values and the output signal; and

a hard demapper, coupled to the soft demapper, for finding a first constellation point which is the most approximate to the output signal from a plurality of constellation points in the constellation according to the signs of soft decision values, and obtaining the data represented by the first constellation point to demodulate the output signal;

wherein the plurality of constellation points are delimited by the plurality of decision boundaries in the constellation.

18. The MRC-OFDM baseband receiver as claimed in claim 15, wherein the equalizer equalizes the input signal according to the following algorithm:

X_k=Y_k¹×

conj(H_k¹)+Y_k²×

conj(H_k²)+ . . . +Y_k¹×

conj(H_k¹)+ . . . Y_kⁿ×

conj(H_kⁿ);

wherein X_k represents the output signal of the equalizer, Y_kⁱ represents the input signal of the equalizer, H_kⁱ represents the channel impulse response estimated by the channel estimation and tracking module, conj( ) is a conjugate function, the suffix k represents the index of OFDM subcarrier, i represent the index, among the plurality of input signals, and n is the number of the input signals.

19. The MRC-OFDM baseband receiver as claimed in claim 15, wherein the channel estimation and tracking module further comprises:

a channel estimation module, for estimating the channel impulse responses of the input signals with preambles of the input signals; and

a channel tracking module, coupled to the channel estimation module and the equalizer, for refining the channel impulse responses of the input signals according to a channel tracking algorithm.

20. The method as claimed in claim 19, wherein the channel tracking algorithm is an algorithm selected from the group consisting of a recursive least square tracking algorithm and a least mean square tracking algorithm.

21. The MRC-OFDM baseband receiver as claimed in claim 16, wherein a plurality of estimates of the channel impulse responses are calculated according to the first constellation point by the demapper, and the estimates of the channel impulse responses are fed back to the channel estimation and tracking module for adjusting the channel impulse responses.