Fast joint traffic-to-pilot ratio and spatial scheme detection

• US 10,420,116 B1
• Filed: 04/05/2018
• Issued: 09/17/2019
• Est. Priority Date: 04/05/2018
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Tahmasbi, Amir, Cho, Jun Hyok
• Primary Examiner(s): Harper, Kevin C.
• Assistant Examiner(s): Rose, Derrick V
• Application Number:
  US15/946,606
• Publication Number:
  US 20190313415A1
• Time in Patent Office: 530 Days
• Field of Search: None
• CPC Class Codes: H04B 7/0486 taking channel rank into account
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• CPC Class Codes: H04J 11/0046 using joint detection algorithms
• CPC Class Codes: H04J 11/0059 Out-of-cell user aspects
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 25/03305 Joint sequence estimation and interference removal joint detection of several desired signals H04L25/03331
• CPC Class Codes: H04W 72/541 using the level of interference

Abstract

Methods, systems, and devices for wireless communications are described. A wireless device such as a User Equipment (UE) in communication with a serving cell, may perform interference cancellation from an interfering cell. A UE may determine a rank of an unprecoded channel matrix associated with the interfering cell, estimate a traffic-to-pilot ratio (TPR) for an interfering transmission, based in part on a unit-norm property of a plurality of precoding matrix hypotheses for the interfering transmission, calculate respective log-likelihood functions for joint demodulation of the serving and interfering cell transmissions, select a subset of the plurality of precoding matrix hypotheses, and perform joint demodulation of the transmissions to obtain a set of demapped symbols, by assuming a uniform distribution hypothesis for the serving cell transmission, and a Gaussian distribution hypothesis for the interfering transmission.

Claims

1. A method for interference cancellation performed by a User Equipment (UE) in communication with a serving cell, the method comprising:

determining a rank of an unprecoded channel matrix associated with an interfering cell;

estimating, based at least in part on the determined rank, a Traffic-to-Pilot Ratio (TPR) for an interfering transmission from the interfering cell over time and frequency resources associated with a serving cell transmission from the serving cell, wherein estimating the TPR of the interfering transmission is based at least in part on a unit-norm property of a plurality of precoding matrix hypotheses for the interfering transmission;

calculating, based at least in part on the estimated TPR for the interfering transmission, respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission according to the plurality of precoding matrix hypotheses;

selecting a subset of the plurality of precoding matrix hypotheses based at least in part on the respective log-likelihood functions; and

performing joint demodulation of the serving cell transmission and the interfering transmission to obtain a set of demapped symbols for the serving cell transmission, the joint demodulation being based at least in part on a uniform distribution hypothesis for the serving cell transmission and a non-uniform distribution hypothesis for the interfering transmission.

2. The method of claim 1, wherein the estimating the TPR for the interfering transmission comprises:

applying a complex random vector model for the interfering transmission to an observed symbol model over the time and frequency resources.

3. The method of claim 1, wherein the estimating the TPR for the interfering transmission comprises:

applying a complex random vector model for the serving cell transmission to an observed symbol model over the time and frequency resources.

4. The method of claim 1, wherein the estimating the TPR for the interfering transmission comprises:

calculating a result of a closed-form equation for the TPR, the closed-form equation applying the unit-norm property of the plurality of precoding matrix hypotheses to an observed symbol model over the time and frequency resources.

5. The method of claim 4, further comprising:

rounding the result of the closed-form equation for the TPR to an upper bound TPR estimate, and rounding the TPR to a lower bound TPR estimate;

selecting a precoding matrix hypothesis associated with each of the upper bound TPR estimate and the lower bound TPR estimate from the plurality of precoding matrix hypotheses for the interfering transmission;

calculating, based at least in part on the upper bound TPR estimate and the lower bound TPR estimate, respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission; and

reporting one of the upper bound TPR estimate or the lower bound TPR estimate, and a respective precoding matrix hypothesis for the interfering transmission, based at least in part on a maximum of the respective log-likelihood functions.

6. The method of claim 1, wherein the performing the joint demodulation of the serving cell transmission and the interfering transmission comprises:

calculating, according to the uniform distribution hypothesis for the serving cell transmission and the non-uniform distribution hypothesis for the interfering transmission, second respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission according to the subset of the plurality of precoding matrix hypotheses; and

selecting a precoding matrix hypothesis for the interfering transmission corresponding to a maximum of the second respective log-likelihood functions.

7. The method of claim 1, wherein the plurality of precoding matrix hypotheses for the interfering transmission include a space frequency block coding spatial scheme, a transmit diversity spatial scheme, an open-loop spatial multiplexing spatial scheme, or a closed-loop spatial multiplexing spatial scheme.

8. The method of claim 1, wherein the estimating the TPR for the interfering transmission is performed for a plurality of resource blocks over the time and frequency resources.

9. The method of claim 1, wherein the estimating the TPR for the interfering transmission is based on the rank of the unprecoded channel matrix associated with the interfering cell being a full rank.

10. The method of claim 1, wherein a number of hypotheses in the selected subset of the plurality of precoding matrix hypotheses for the interfering transmission is determined based at least in part on a difference between a highest of the respective log-likelihood functions and a second-highest of the respective log-likelihood functions.

11. The method of claim 1, further comprising:

determining that a second rank of a second unprecoded channel matrix associated with a second interfering cell does not correspond to a full rank;

calculating second respective log-likelihood functions for joint demodulation of a second serving cell transmission and a second interfering transmission from the second interfering cell according to a plurality of TPR and precoding matrix hypotheses for the interfering transmission, the plurality of TPR and precoding matrix hypotheses comprising a second plurality of precoding matrix hypotheses for each of a plurality of TPR value hypotheses;

selecting a subset of the plurality of TPR and precoding matrix hypotheses for the interfering transmission based at least in part on the second respective log-likelihood functions; and

performing second joint demodulation of the second serving cell transmission and the second interfering transmission to obtain a second set of demapped symbols for the second serving cell transmission.

12. An apparatus for interference cancellation performed by a User Equipment (UE) in communication with a serving cell, comprising:

means for determining a rank of an unprecoded channel matrix associated with an interfering cell;

means for estimating, based at least in part on the determined rank, a traffic-to-pilot Ratio (TPR) for an interfering transmission from the interfering cell over time and frequency resources associated with a serving cell transmission from the serving cell, wherein estimating the TPR of the interfering transmission is based at least in part on a unit-norm property of a plurality of precoding matrix hypotheses for the interfering transmission;

means for calculating, based at least in part on the estimated TPR for the interfering transmission, respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission according to the plurality of precoding matrix hypotheses;

means for selecting a subset of the plurality of precoding matrix hypotheses based at least in part on the respective log-likelihood functions; and

means for performing joint demodulation of the serving cell transmission and the interfering transmission to obtain a set of demapped symbols for the serving cell transmission, the joint demodulation being based at least in part on a uniform distribution hypothesis for the serving cell transmission and a non-uniform distribution hypothesis for the interfering transmission.

13. The apparatus of claim 12, wherein the estimating the TPR for the interfering transmission comprises:

means for applying a complex random vector model for the interfering transmission to an observed symbol model over the time and frequency resources.

14. The apparatus of claim 12, wherein the estimating the TPR for the interfering transmission comprises:

means for applying a complex random vector model for the serving cell transmission to an observed symbol model over the time and frequency resources.

15. The apparatus of claim 12, wherein the estimating the TPR for the interfering transmission comprises:

means for calculating a result of a closed-form equation for the TPR, the closed-form equation applying the unit-norm property of the plurality of precoding matrix hypotheses to an observed symbol model over the time and frequency resources.

16. The apparatus of claim 15, further comprising:

means for rounding the result of the closed-form equation for the TPR to an upper bound TPR estimate, and rounding the TPR to a lower bound TPR estimate;

means for selecting a precoding matrix hypothesis associated with each of the upper bound TPR estimate and the lower bound TPR estimate from the plurality of precoding matrix hypotheses for the interfering transmission;

means for calculating, based at least in part on the upper bound TPR estimate and the lower bound TPR estimate, respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission; and

means for reporting one of the upper bound TPR estimate or the lower bound TPR estimate, and a respective precoding matrix hypothesis for the interfering transmission, based at least in part on a maximum of the respective log-likelihood functions.

17. The apparatus of claim 12, wherein the performing the joint demodulation of the serving cell transmission and the interfering transmission comprises:

means for calculating, according to the uniform distribution hypothesis for the serving cell transmission and the non-uniform distribution hypothesis for the interfering transmission, second respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission according to the subset of the plurality of precoding matrix hypotheses; and

means for selecting a precoding matrix hypothesis for the interfering transmission corresponding to a maximum of the second respective log-likelihood functions.

18. The apparatus of claim 12, wherein the estimating the TPR for the interfering transmission is based on the rank of the unprecoded channel matrix associated with the interfering cell being a full rank.

19. The apparatus of claim 12, wherein a number of hypotheses in the selected subset of the plurality of precoding matrix hypotheses for the interfering transmission is determined based at least in part on a difference between a highest of the respective log-likelihood functions and a second-highest of the respective log-likelihood functions.

20. The apparatus of claim 12, further comprising:

means for determining that a second rank of a second unprecoded channel matrix associated with a second interfering cell does not correspond to a full rank;

means for calculating second respective log-likelihood functions for joint demodulation of a second serving cell transmission and a second interfering transmission from the second interfering cell according to a plurality of TPR and precoding matrix hypotheses for the interfering transmission, the plurality of TPR and precoding matrix hypotheses comprising a second plurality of precoding matrix hypotheses for each of a plurality of TPR value hypotheses;

means for selecting a subset of the plurality of TPR and precoding matrix hypotheses for the interfering transmission based at least in part on the second respective log-likelihood functions; and

means for performing second joint demodulation of the second serving cell transmission and the second interfering transmission to obtain a second set of demapped symbols for the second serving cell transmission.

21. An apparatus for interference cancellation performed by a User Equipment (UE) in communication with a serving cell, comprising a processor, memory in electronic communication with the processor, and instructions stored in the memory and operable, when executed by the processor, to cause the apparatus to:

determine a rank of an unprecoded channel matrix associated with an interfering cell;

estimate, based at least in part on the determined rank, a traffic-to-pilot ratio (TPR) for an interfering transmission from the interfering cell over time and frequency resources associated with a serving cell transmission from the serving cell, wherein estimating the TPR of the interfering transmission is based at least in part on a unit-norm property of a plurality of precoding matrix hypotheses for the interfering transmission;

calculate, based at least in part on the estimated TPR for the interfering transmission, respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission according to the plurality of precoding matrix hypotheses;

select a subset of the plurality of precoding matrix hypotheses based at least in part on the respective log-likelihood functions; and

perform joint demodulation of the serving cell transmission and the interfering transmission to obtain a set of demapped symbols for the serving cell transmission, the joint demodulation being based at least in part on a uniform distribution hypothesis for the serving cell transmission and a non-uniform distribution hypothesis for the interfering transmission.

22. The apparatus of claim 21, wherein the estimating the TPR for the interfering transmission comprises:

apply a complex random vector model for the interfering transmission to an observed symbol model over the time and frequency resources.

23. The apparatus of claim 21, wherein the estimating the TPR for the interfering transmission comprises:

apply a complex random vector model for the serving cell transmission to an observed symbol model over the time and frequency resources.

24. The apparatus of claim 21, wherein the estimating the TPR for the interfering transmission comprises:

calculate a result of a closed-form equation for the TPR, the closed-form equation applying the unit-norm property of the plurality of precoding matrix hypotheses to an observed symbol model over the time and frequency resources.

25. The apparatus of claim 24, wherein the instructions are further executable by the processor to cause the apparatus to:

round the result of the closed-form equation for the TPR to an upper bound TPR estimate, and rounding the TPR to a lower bound TPR estimate;

select a precoding matrix hypothesis associated with each of the upper bound TPR estimate and the lower bound TPR estimate from the plurality of precoding matrix hypotheses for the interfering transmission;

calculate, based at least in part on the upper bound TPR estimate and the lower bound TPR estimate, respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission; and

report one of the upper bound TPR estimate or the lower bound TPR estimate, and a respective precoding matrix hypothesis for the interfering transmission, based at least in part on a maximum of the respective log-likelihood functions.

26. The apparatus of claim 21, wherein the performing the joint demodulation of the serving cell transmission and the interfering transmission comprises:

calculate, according to the uniform distribution hypothesis for the serving cell transmission and the non-uniform distribution hypothesis for the interfering transmission, second respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission according to the subset of the plurality of precoding matrix hypotheses; and

select a precoding matrix hypothesis for the interfering transmission corresponding to a maximum of the second respective log-likelihood functions.

27. The apparatus of claim 21, wherein the estimating the TPR for the interfering transmission is based on the rank of the unprecoded channel matrix associated with the interfering cell being a full rank.

28. The apparatus of claim 21, wherein a number of hypotheses in the selected subset of the plurality of precoding matrix hypotheses for the interfering transmission is determined based at least in part on a difference between a highest of the respective log-likelihood functions and a second-highest of the respective log-likelihood functions.

29. The apparatus of claim 21, wherein the instructions are further executable by the processor to cause the apparatus to:

determine that a second rank of a second unprecoded channel matrix associated with a second interfering cell does not correspond to a full rank;

calculate second respective log-likelihood functions for joint demodulation of a second serving cell transmission and a second interfering transmission from the second interfering cell according to a plurality of TPR and precoding matrix hypotheses for the interfering transmission, the plurality of TPR and precoding matrix hypotheses comprising a second plurality of precoding matrix hypotheses for each of a plurality of TPR value hypotheses;

select a subset of the plurality of TPR and precoding matrix hypotheses for the interfering transmission based at least in part on the second respective log-likelihood functions; and

perform second joint demodulation of the second serving cell transmission and the second interfering transmission to obtain a second set of demapped symbols for the second serving cell transmission.

30. A non-transitory computer-readable medium storing code for interference cancellation performed by a User Equipment (UE) in communication with a serving cell, the code comprising instructions executable by a processor to:

determine a rank of an unprecoded channel matrix associated with an interfering cell;

estimate, based at least in part on the determined rank, a traffic-to-pilot ratio (TPR) for an interfering transmission from the interfering cell over time and frequency resources associated with a serving cell transmission from the serving cell, wherein estimating the TPR of the interfering transmission is based at least in part on a unit-norm property of a plurality of precoding matrix hypotheses for the interfering transmission;

calculate, based at least in part on the estimated TPR for the interfering transmission, respective log-likelihood functions for joint demodulation of the serving cell transmission and the interfering transmission according to the plurality of precoding matrix hypotheses;

select a subset of the plurality of precoding matrix hypotheses based at least in part on the respective log-likelihood functions; and

perform joint demodulation of the serving cell transmission and the interfering transmission to obtain a set of demapped symbols for the serving cell transmission, the joint demodulation being based at least in part on a uniform distribution hypothesis for the serving cell transmission and a non-uniform distribution hypothesis for the interfering transmission.