Strong Signal Tolerant OFDM Receiver and Receiving Methods

• US 20100159858A1
• Filed: 12/19/2008
• Published: 06/24/2010
• Est. Priority Date: 12/19/2008
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Mattisson, Sven, Dent, Paul Wilkinson
• Granted Patent: US 8,090,320 B2
• Time in Patent Office: Days
• US Class Current: 455/131
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

Circuits and methods are disclosed for compensating for received signal distortion caused by non-linearities in wideband receivers. An exemplary receiver includes a distortion waveform generator configured to approximate non-linear response characteristics of a downconverter circuit used to downconvert the received radio frequency signal. The resulting estimated distortion waveform is filtered, using filter(s) substantially similar to those used for filtering an intermediate frequency signal that includes the desired signal and non-linear distortion products caused by strong interfering signals. The filtered estimated distortion waveform and intermediate frequency signal are sampled, to obtain a sampled distortion signal and a sampled signal of interest. The sampled distortion signal and the sampled signal of interest are divided into a plurality of frequency channels. For a selected number of frequency channels, the sampled distortion signal for a frequency channel is scaled, and subtracted from the corresponding sampled signal of interest for the same frequency channel to obtain reduced-interference signal samples for the frequency channel.

Claims

1. A receiver circuit, comprising:

a downconverter unit configured to downconvert a received radio frequency signal, comprising a desired signal and one or more interfering signals, to a processing frequency, to obtain a processing frequency signal;

a distortion waveform generator configured to generate an estimated distortion waveform from the one or more interfering signals, the estimated distortion waveform comprising one or more intermodulation products of the interfering signals;

first and second filters configured to filter the processing frequency signal and the estimated distortion waveform, respectively;

first and second sampling units configured to sample the filtered processing frequency signal and the filtered estimated distortion waveform to obtain a sampled signal of interest and a sampled distortion signal, respectively;

first and second transform units to divide the sampled signal of interest and the sampled distortion signal, respectively, into a plurality of frequency channels; and

an interference subtracting unit configured to combine the sampled distortion signal for each of a selected number of frequency channels with the corresponding sampled signal of interest for each of the same frequency channels to obtain interference-reduced signal samples for each of the selected number of frequency channels.

2. The receiver circuit of claim 1, wherein the first and second transform units comprise first and second discrete Fourier transform units.

3. The receiver circuit of claim 1, wherein the distortion waveform generator comprises a non-linear circuit configured to approximate one or more non-linear response characteristics of the downconverter unit.

4. The receiver circuit of claim 1, wherein the interference subtraction unit comprises:

a first correlator configured to correlate the sampled signal of interest for each of the selected number of frequency channels with the corresponding sampled distortion signal for each of the same frequency channels to obtain a first factor for each of the selected number of frequency channels;

a second correlator configured to correlate the sampled distortion signal for each of the selected number of frequency channels with itself to obtain a second factor for each of the selected number of frequency channels;

a scaling unit configured to scale the sampled distortion signal for each of a second selected number of frequency channels based on the first and second factors; and

a subtracting unit configured to subtract the scaled, sampled, distortion signal for each of the second selected number of frequency channels from the corresponding sampled signal of interest for each of the same second selected number of frequency channels to obtain the interference-reduced signal samples for each of the second selected number of frequency channels.

5. The receiver circuit of claim 4, wherein the interference subtraction unit further comprises:

a first averaging unit to average the first factor for each of the selected number of frequency channels over a plurality of OFDM symbol periods;

a second averaging unit to average the second factor for each of the selected number of frequency channels over a plurality of OFDM symbol periods; and

a divider to divide the averaged first and second factors generated for each of the same frequency channels to generate a scaling factor for each of the selected number of frequency channels

6. The receiver circuit of claim 5, wherein the selected number of frequency channels comprises all of the plurality of frequency channels, and wherein the second selected number of frequency channels equals the selected number of frequency channels.

7. The receiver circuit of claim 5, wherein the selected number of frequency channels comprises a subset of the plurality of frequency channels comprising fewer than the plurality of frequency channels.

8. The receiver circuit of claim 7, wherein the scaling unit is configured to scale the sampled distortion signal for each of the selected number of frequency channels using the scaling factor generated for each of the same frequency channels and to reuse the determined scaling factors to scale the sampled distortion signal for the remaining frequency channels.

9. The receiver circuit of claim 1, wherein the interference subtraction unit comprises a plurality of interference subtraction units, and wherein each interference subtraction unit corresponds to a different frequency channel.

10. The receiver circuit of claim 1, wherein the downconverter unit comprises a quadrature downconverter configured to downconvert the received radio frequency signal to obtain in-phase and quadrature signals at the processing frequency, and wherein the first sampling circuit is configured to sample the filtered processing frequency signal by sampling the in-phase and quadrature signals to obtain in-phase and quadrature samples of the signal of interest.

11. The receiver circuit of claim 1, wherein the processing frequency comprises one of an intermediate frequency, a low intermediate frequency, and a baseband frequency.

12. A method for reducing interference from intermodulation distortion in a receiver, the method comprising:

downconverting a received radio frequency signal comprising a desired signal and one or more interfering signals to obtain a processing frequency signal;

generating an estimated distortion waveform from the one or more interfering signals, the estimated distortion waveform comprising one or more intermodulation products of the interfering signals;

filtering the processing frequency signal and the estimated distortion waveform with first and second filters, respectively;

sampling the filtered processing frequency signal and the filtered estimated distortion waveform to obtain a sampled signal of interest and a sampled distortion signal, respectively;

dividing each of the sampled signal of interest and the sampled distortion signal into a plurality of frequency channels; and

combining the sampled distortion signal for each of a selected number of frequency channels with the corresponding sampled signal of interest for each of the same frequency channels to obtain interference-reduced signal samples for each of the selected number of frequency channels.

13. The method of claim 12, wherein dividing each of the sampled signal of interest and the sampled distortion signal into a plurality of frequency channels comprises applying a discrete Fourier transform to each of the sampled signal of interest and the sampled distortion signal.

14. The method of claim 12, wherein generating an estimated distortion waveform from the one or more interfering signals comprises applying the one or more interfering signals to a non-linear circuit approximating one or more non-linear response characteristics of a downconverter unit used to downconvert the received radio signal.

15. The method of claim 12, wherein combining the sampled distortion signals with the corresponding sampled signals of interest comprises:

correlating the sampled signal of interest for each of the selected number of frequency channels with the corresponding sampled distortion signal for each of the same frequency channels to obtain a first factor for each of the selected number of frequency channels;

correlating the sampled distortion signal for each of the selected number of frequency channels with itself to obtain a second factor for each of the selected number of frequency channels;

scaling the sampled distortion signal for each of a second selected number of frequency channels based on the first and second factors; and

subtracting the scaled, sampled, distortion signal for each of the second selected number of frequency channels from the corresponding sampled signal of interest for each of the same second selected number of frequency channels to obtain the interference-reduced signal samples for each of the second selected number of frequency channels.

16. The method of claim 15, further comprising:

averaging the first factor for each of the selected number of frequency channels over a plurality of OFDM symbol periods;

averaging the second factor for each of the selected number of frequency channels over a plurality of OFDM symbol periods; and

dividing the averaged first and second factors generated for each of the same frequency channels to generate a scaling factor for each of the selected number of frequency channels.

17. The method of claim 16, wherein the selected number of frequency channels comprises all of the plurality of frequency channels, and wherein the second selected number of frequency channels equals the selected number of frequency channels.

18. The method of claim 16, wherein the selected number of frequency channels comprises a subset of the plurality of frequency channels comprising fewer than the plurality of frequency channels.

19. The method of claim 18, wherein scaling the sampled distortion signal comprises scaling the sampled distortion signal for each of the selected number of frequency channels using the scaling factor generated for each of the same frequency channels and reusing the determined scaling factors to scale the sampled distortion signal for the remaining frequency channels.

20. The method of claim 12, wherein combining the sampled distortion signal for each of the selected number of frequency channels with the corresponding sampled signal of interest for each of the same frequency channels comprises combining the sampled distortion signal with the corresponding sampled signal of interest for different frequency channels in separate interference subtraction units associated with the different frequency channels.

21. The method of claim 12, wherein downconverting the received radio frequency signal comprises downconverting the received radio frequency signal with a quadrature downconverter to obtain in-phase and quadrature signals at the processing frequency, and wherein sampling the filtered processing frequency signal comprises sampling the in-phase and quadrature signals to obtain in-phase and quadrature samples of the signal of interest.

22. The method of claim 12, wherein the processing frequency comprises one of an intermediate frequency, a low intermediate frequency, and a baseband frequency.