Demodulation in VAMOS receivers

• US 8,934,589 B2
• Filed: 05/29/2013
• Issued: 01/13/2015
• Est. Priority Date: 05/29/2013
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Jacob, Naveen
• Primary Examiner(s): Corrielus, Jean B
• Application Number:
  US13/904,905
• Publication Number:
  US 20140355721A1
• Time in Patent Office: 594 Days
• Field of Search: 375/285, 375/261, 375/267, 375324-325, 375/346, 375/347, 375/349
• US Class Current: 375/346
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 15/00 Suppression or limitation of noise or interference by means associated with receiver H04B1/10
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/03318 Provision of soft decisions
• CPC Class Codes: H04L 27/2017 in which the phase changes are non-linear, e.g. generalized and Gaussian minimum shift keying, tamed frequency modulation H04L27/201 takes precedence
• CPC Class Codes: H04L 27/362 Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated H04L27/366 takes precedence
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits
• CPC Class Codes: H04L 5/12 the signals being represented by different phase modulations of a single carrier

Abstract

A desired signal and interfering signal are transmitted in the same timeslot and on the same frequency using an Adaptive Quadrature Phase Shift Keying (AQPSK) modulated carrier. When the Subchannel Power Imbalance Ratio (SCPIR) for the AQPSK modulated carrier is large and favors the interfering signal, SIC is used to cancel the interfering signal from the received signal. Following interference cancellation, the desired signal is demodulated using two different estimates of the channel and the demodulated soft bits from demodulated soft bits from each demodulation process are combined to obtain a combined estimate.

Claims

1. A method of receiving a signal, the method implemented by a wireless terminal in a wireless communication network and comprising:

receiving a desired signal in one or more data bursts on a first subchannel of a quadrature modulated carrier;

receiving an interfering signal in the one or more data bursts on a second subchannel of the quadrature modulated carrier;

computing a power imbalance ratio indicative of a power distribution between the first and second subchannels; and

if the power imbalance ratio meets a threshold;

generating a first channel estimate for the first subchannel;

demodulating the desired signal using the first channel estimate to obtain first demodulated soft bits corresponding to the desired signal;

generating a second channel estimate for the first subchannel based on the interfering signal;

demodulating the desired signal using the second channel estimate to obtain second demodulated soft bits corresponding to the desired signal; and

combining the first and second demodulated soft bits to obtain combined demodulated soft bits.

2. The method of claim 1 wherein receiving the desired signal on the first subchannel of the quadrature modulated carrier comprises receiving the desired signal on one of an in-phase component and a quadrature component of the quadrature modulated carrier, and wherein receiving the interfering signal on the second subchannel of the quadrature modulated carrier comprises receiving the interfering signal on the other one of the in-phase component and the quadrature component of the quadrature modulated carrier.

3. The method of claim 1 wherein generating the first channel estimate comprises generating the first channel estimate from training symbols in the desired signal.

4. The method of claim 1 wherein generating the second channel estimate based on the interfering signal comprises generating the second channel estimate from training symbols in the interfering signal.

5. The method of claim 4 wherein generating the second channel estimate from training symbols in the interfering signal comprises:

generating a third channel estimate for the second subchannel from the training symbols in the interfering signal; and

transforming the third channel estimate to obtain the second channel estimate.

6. The method of claim 1 wherein generating the second channel estimate based on the interfering signal comprises generating the second channel estimate from demodulated soft bits corresponding to the interfering signal.

7. The method of claim 6 wherein generating the second channel estimate from the demodulated soft bits corresponding to the interfering signal comprises:

generating a third channel estimate for the second subchannel using the demodulated soft bits corresponding to the interfering signal; and

transforming the third channel estimate to obtain the second channel estimate.

8. The method of claim 7 wherein generating the third channel estimate for the second subchannel using demodulated soft bits corresponding to the interfering signal comprises generating the third channel estimate using demodulated soft bits located near an end of the one or more data bursts.

9. The method of claim 1 wherein generating the first channel estimate comprises generating the first channel estimate from training symbols in the interfering signal.

10. The method of claim 9 wherein generating the second channel estimate based on the interfering signal comprises generating the second channel estimate from demodulated soft bits corresponding to the interfering signal.

11. The method of claim 10 wherein generating the second channel estimate from the demodulated soft bits corresponding to the interfering signal comprises:

generating a third channel estimate for the second subchannel using demodulated soft bits corresponding to the interfering signal; and

transforming the third channel estimate to obtain the second channel estimate.

12. The method of claim 11 wherein generating the third channel estimate for the second subchannel using demodulated soft bits corresponding to the interfering signal comprises generating the third channel estimate using demodulated soft bits located near an end of the one or more data bursts.

13. The method of claim 1 wherein demodulating the desired signal using the first channel estimate comprises:

whitening the desired signal based on the first channel estimate to obtain a first whitened desired signal; and

demodulating the first whitened desired signal.

14. The method of claim 13 wherein demodulating the desired signal using the second channel estimate comprises:

whitening the desired signal based on the second channel estimate to obtain a second whitened desired signal; and

demodulating the second whitened desired signal.

15. The method of claim 1 further comprising canceling interference in the desired signal attributable to the interfering signal before demodulating the desired signal using either the first channel estimate or the second channel estimate.

16. A wireless terminal comprising:

receiver circuits configured to receive a quadrature modulated carrier containing a desired signal on a first subchannel of the quadrature modulated carrier and an interfering signal on a second subchannel of the quadrature modulated carrier; and

a processing circuit configured to;

compute a power imbalance ratio indicative of a power distribution between the first and second subchannels; and

if the power imbalance ratio meets a threshold;

generate a first channel estimate for the first subchannel;

demodulate the desired signal using the first channel estimate to obtain first demodulated soft bits corresponding to the desired signal;

generate a second channel estimate for the first subchannel based on the interfering signal;

demodulate the desired signal using the second channel estimate to obtain second demodulated soft bits corresponding to the desired signal; and

combine the first and second demodulated soft bits to obtain combined demodulated soft bits.

17. The wireless terminal of claim 16 wherein the receiver circuits are configured to receive the desired signal on one of an in-phase component and a quadrature component of the quadrature modulated carrier, and to receive the interfering signal on the other one of the in-phase component and the quadrature component of the quadrature modulated carrier.

18. The wireless terminal of claim 16 wherein the processing circuit comprises a first channel estimation circuit configured to generate the first channel estimate from training symbols in the desired signal.

19. The wireless terminal of claim 18 wherein the processing circuit further comprises a second channel estimation circuit configured to generate the second channel estimate from training symbols in the interfering signal.

20. The wireless terminal of claim 19 wherein the second channel estimation circuit is configured to:

generate a third channel estimate for the second subchannel from the training symbols in the interfering signal; and

transform the third channel estimate to obtain the second channel estimate.

21. The wireless terminal of claim 18 wherein the processing circuit further comprises a second channel estimation circuit configured to generate the second channel estimate using demodulated soft bits corresponding to the interfering signal.

22. The wireless terminal of claim 19 wherein the second channel estimation circuit is configured to generate the second channel estimate from demodulated soft bits located near an end of one or more data bursts.

23. The wireless terminal of claim 22 wherein the second channel estimation circuit is configured to:

generate the third channel estimate for the second subchannel using demodulated soft bits corresponding to the interfering signal; and

transform the third channel estimate to obtain the second channel estimate.

24. The wireless terminal of claim 16 wherein the processing circuit comprises a first channel estimation circuit is configured to generate the first channel estimate from training symbols in the interfering signal.

25. The wireless terminal of claim 24 wherein the processing circuit further comprises a second channel estimation circuit is configured to generate the second channel estimate from demodulated soft bits corresponding to the interfering signal.

26. The wireless terminal of claim 25 the second channel estimation circuit is configured to:

generate a third channel estimate for the second subchannel using demodulated soft bits corresponding to the interfering signal; and

transform the third channel estimate to obtain the second channel estimate.

27. The wireless terminal of claim 26 wherein the second channel estimation circuit is configured to generate the third channel estimate for the second subchannel using demodulated soft bits located near an end of one or more data bursts.

28. The wireless terminal of claim 16 further comprising a first whitening filter to whiten the desired signal using the first channel estimate to obtain a first whitened desired signal and a first demodulator to demodulate the first whitened desired signal.

29. The wireless terminal of claim 28 further comprising a second whitening filter to whiten the desired signal using the second channel estimate to obtain a second whitened desired signal and a second demodulator to demodulate the second whitened desired signal.

30. The wireless terminal of claim 16 further comprising an interference cancellation circuit configured to cancel interference in the desired signal attributable to the interfering signal before demodulation of the desired signal using either the first channel estimate or the second channel estimate.