Soft decision gain compensation for receive filter attenuation

• US 20030104797A1
• Filed: 12/04/2001
• Published: 06/05/2003
• Est. Priority Date: 12/04/2001
• Status: Active Grant

• Current Assignee: Intellectual Ventures I LLC (Intellectual Ventures LLC)
• Original Assignee: Conexant Incorporated (Synaptics Incorporated)
• Inventors: Webster, Mark A., Garrett, Albert L., Chiuchiolo, Paul J.
• Granted Patent: US 6,973,296 B2
• Time in Patent Office: Days
• US Class Current: 455/296
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2695 with channel estimation, e.g. determination of delay spread, derivative or peak tracking channel estimation H04L25/0202

Abstract

A wireless receiver including a receive chain, a synchronization processor, a memory, a combiner and a soft decision processor. The synchronization processor determines a frequency response of the wireless channel using synchronization data transmitted in the wireless channel. The memory stores a compensation vector indicative of a frequency response of receive chain filtering. The combiner combines the compensation vector with the wireless channel frequency response to provide a compensated frequency response. The soft decision processor uses the compensated frequency response to evaluate data decisions. The compensation vector is based on measurement or estimation of the frequency response of the receive chain. The combiner may be based on multiplication or addition. The wireless receiver may include an FEQ. The synchronization processor generates FEQ coefficients for programming the FEQ taps. The FEQ provides an equalized data value and a compensated frequency response value to the soft decision processor for each sub-carrier.

Claims

1. A wireless receiver that receives radio frequency (RF) signals via a wireless channel in which data is transmitted using a plurality of sub-carriers, comprising:

a receive chain;

a synchronization processor that determines a frequency response of the wireless channel using synchronization data;

a memory that stores a compensation vector indicative of a frequency response of the receive chain;

a combiner that combines the compensation vector with the wireless channel frequency response to provide a compensated frequency response; and

a soft decision processor that uses the compensated frequency response to evaluate data decisions.

2. The wireless receiver of claim 1, wherein the receive chain includes a plurality of filtering circuits that collectively have a variant frequency response and a relatively flat signal to noise ratio (SNR).

3. The wireless receiver of claim 2, wherein the compensation vector is based on a measurement of the variant frequency response of the receive chain.

4. The wireless receiver of claim 2, wherein the compensation vector is based on an estimation of the variant frequency response of the receive chain.

5. The wireless receiver of claim 2, wherein the compensation vector is based on a compensation curve derived from the variant frequency response of the receive chain.

6. The wireless receiver of claim 2, wherein the compensation vector corrects for variations in the variant frequency response of the receive chain across the plurality of sub-carriers.

7. The wireless receiver of claim 1, wherein:

the compensation vector comprises a plurality of compensation factors; and

wherein the combiner comprises a plurality of multipliers.

8. The wireless receiver of claim 1, wherein:

the compensation vector comprises a plurality of compensation offsets; and

wherein the combiner comprises a plurality of adders.

9. The wireless receiver of claim 1, further comprising:

a frequency domain equalizer (FEQ) having programmable taps for equalizing each of the plurality of sub-carriers in an attempt to remove phase and amplitude variations;

the FEQ receiving compensated frequency response values and providing an equalized data value and a corresponding compensated frequency response value for each sub-carrier to the soft decision processor;

the synchronization processor generating FEQ coefficients used to program the taps of the FEQ and generating receive chain frequency response values that are provided to the combiner; and

the combiner receiving the receive chain frequency response values and providing corresponding compensated frequency response values to the FEQ.

10. A radio frequency (RF) transceiver for communicating via a wireless channel, comprising:

an antenna;

a radio including receive chain circuitry coupled to the antenna that converts received RF packets into Baseband information;

a Baseband processor, coupled to the radio, including a receive processor for processing the Baseband information, the receive processor comprising;

a synchronization processor that determines a plurality of frequency response values using synchronization data transmitted via the wireless channel;

a memory that stores a plurality of compensation values indicative of a frequency response of the receive chain circuitry;

a combiner that modifies the plurality of frequency response values using the plurality of compensation values to provide a plurality of compensated frequency response values; and

a soft decision processor that uses the plurality of compensated frequency response values to evaluate decisions of corresponding data values.

11. The RF transceiver of claim 10, wherein the receive chain circuitry includes a plurality of filtering and down conversion circuits that collectively have a variant frequency response and a relatively flat signal to noise ratio (SNR).

12. The RF transceiver of claim 11, wherein the plurality of compensation values are based on a compensation curve derived from the variant frequency response of the receive chain circuitry.

13. The RF transceiver of claim 12, wherein the plurality of compensation values correct for variations in the variant frequency response of the receive chain circuitry for each of a plurality of sub-carriers.

14. The RF transceiver of claim 10, wherein:

the plurality of compensation values comprise a plurality of frequency response compensation factors; and

wherein the combiner comprises a plurality of multipliers.

15. The RF transceiver of claim 10, wherein:

the plurality of compensation values comprise a plurality of frequency response compensation offsets; and

wherein the combiner comprises a plurality of adders.

16. The RF transceiver of claim 10, further comprising:

an analog to digital converter (ADC) that converts the Baseband information from analog to digital format for processing by the receive processor;

the receive processor comprising;

a frequency transform converter that converts time domain Baseband digital information into frequency domain Baseband digital information; and

a frequency domain equalizer (FEQ) having programmable taps for equalizing the frequency domain Baseband digital information in an attempt to remove phase and amplitude variations for each of a plurality of sub-carriers, the FEQ receiving the plurality of compensated frequency response values and providing an equalized data value and a corresponding compensated frequency response value for each of the plurality of sub-carriers to the soft decision processor;

wherein the synchronization processor generates FEQ coefficients used to program the taps of the FEQ and generates receive chain circuitry frequency response values that are provided to the combiner; and

wherein the combiner receives the receive chain frequency response values and provides corresponding compensated frequency response values to the FEQ.

17. The RF transceiver of claim 16, wherein the synchronization processor further comprises:

a frequency offset estimator that determines phase adjustment and asserts phase adjustment signals indicative thereof;

a gain adjust circuit that compares the synchronization data with a target gain signal and asserts gain adjustment signals indicative thereof; and

an FEQ initializer that employs a selected constellation and that receives the phase adjustment signals and the gain adjustment signals to provide the FEQ coefficients in an attempt to remove rotation and correct amplitude variations caused by the wireless channel, the FEQ initializer further determining a frequency response of the wireless channel and providing the plurality of frequency response values indicative thereof.

18. A method of compensating channel state information for a wireless receiver that receives radio frequency (RF) signals via a wireless channel in which data is incorporated on a plurality of sub-carriers and in which the receiver employs soft decision processing, comprising:

determining a frequency response of the wireless channel based on synchronization data transmitted in the wireless channel;

modifying the frequency response by a compensation vector indicative of filtering of the receive chain to provide a corresponding compensated frequency response;

processing data received from the wireless channel through the receive chain to provide estimated data values; and

determining quality of data value decisions based on the compensated frequency response values.

19. The method of claim 18, further comprising:

measuring a frequency response of the receive chain;

inverting the measured frequency response; and

determining the compensation vector based on the inverted frequency response.

20. The method of claim 18, further comprising:

approximating a frequency response of the receive chain;

inverting the approximated frequency response; and

determining the compensation vector based on the inverted frequency response.

21. The method of claim 18, wherein the compensation vector comprises a plurality of compensation factors, wherein the frequency response comprises a plurality of frequency response values, and wherein said modifying comprises multiplying each of the compensation factors by a corresponding one of the frequency response values.

22. The method of claim 18, wherein the compensation vector comprises a plurality of compensation offsets, wherein the frequency response comprises a plurality of frequency response values, and wherein said modifying comprises adding each of the compensation offsets by a corresponding one of the frequency response values.

23. The method of claim 18, further comprising:

determining frequency equalizer (FEQ) coefficients using the synchronization data;

programming an FEQ based on the FEQ coefficients;

processing data from the receive chain through the FEQ to provide equalized data values; and

making data value decisions based on the equalized data values.