System and method for digital cancellation of self-interference in full-duplex communications

• US 9,847,865 B2
• Filed: 08/20/2014
• Issued: 12/19/2017
• Est. Priority Date: 08/20/2014
• Status: Active Grant

• Current Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Inventors: Moher, Michael
• Primary Examiner(s): Skripnikov, Alex
• Application Number:
  US14/464,117
• Publication Number:
  US 20160056946A1
• Time in Patent Office: 1,217 Days
• Field of Search: None
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04B 15/00 Suppression or limitation of noise or interference by means associated with receiver H04B1/10
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex

Abstract

Embodiments are provided for cancelling self-interference in a full-duplex communications system. The cancellation includes using a digital cancellation stage in additional to analog cancellation. In an embodiment, a method by a full-duplex communications device includes sampling a received signal, wherein the sampling provides a received digital signal corresponding to the received signal. The method further includes sampling a transmitted signal, wherein the sampling provides a transmitted digital signal corresponding to the transmitted signal. A channel distortion introducing self-interference in the received signal is then estimated according to the transmitted digital signal and the received digital signal. The method further includes estimating the self-interference in the received digital signal according to the estimated channel distortion.

Claims

1. A method for execution by a full-duplex communications device, the method comprising:

generating a baseband transmit signal and converting the transmit baseband signal to a first analog signal;

receiving a second analog signal while simultaneously transmitting the first analog signal, the received analog signal having first self-interference according to the transmitted analog signal;

removing the first self-interference from the received analog signal with one or more cancellation stages to produce a processed signal, the one or more cancellation stages introducing second self-interference in the processed signal, the second self-interference being a lower level of interference than the first self-interference, the second self-interference being linear distortions;

sampling the received analog signal to obtain a received digital signal corresponding to the received analog signal;

sampling the baseband transmit signal to obtain a transmitted digital signal corresponding to the transmitted analog signal;

estimating a first channel distortion in the processed signal, the first channel distortion corresponding to the first self-interference, the first channel distortion estimated with a linear model relating the received digital signal to the first channel distortion, noise in the received digital signal, and a data matrix produced according to the transmitted digital signal, the estimating comprising determining the first channel distortion from the linear model using a minimum mean square error solution for the first channel distortion; and

estimating the second self-interference in the received digital signal according to the estimated first channel distortion; and

removing the estimated second self-interference from the received digital signal.

2. The method of claim 1 further comprising, before estimating the first channel distortion, buffering the received digital signal according to a defined number of sampling points for the received analog signal.

3. The method of claim 1 further comprising obtaining an improved received analog signal by removing the estimated second self-interference from the received digital signal.

4. The method of claim 1 further comprising rejecting the transmitted analog signal from a reception path for the received analog signal at an isolation circuit positioned at an intersection of a transmission path for the transmitted analog signal and the reception path.

5. The method of claim 1, wherein the removing the estimated second self-interference is performed in a digital domain, and wherein the removing the first self-interference is performed in an analog domain and comprises:

before the sampling the received analog signal and the baseband transmit signal, estimating a second channel distortion in the received analog signal according to the transmitted analog signal and the received analog signal;

estimating the first self-interference in the received analog signal according to the estimated second channel distortion in the received analog signal; and

removing the estimated first self-interference in the received analog signal before removing the estimated second self-interference from the received digital signal, wherein the estimated second self-interference is residual self-interference after removing the estimated first self-interference.

6. A method by a full-duplex communications device, the method comprising:

sampling a transmit signal in the full-duplex communications device;

transmitting the transmit signal via an antenna;

receiving a receive signal via the antenna;

sampling the received signal at the full-duplex communications device;

estimating channel characteristics for first self-interference according to the sampled transmit signal, the sampled received signal, and a linear model relating the received signal to a data matrix produced according to the sampled transmit signal, to noise in the sampled received signal, and to the channel characteristics, wherein estimating the channel characteristics comprises solving for the channel characteristics in the linear model using a minimum mean square error solution for the channel characteristics; and

estimating the first self-interference in the received signal according to the estimated channel characteristics.

7. The method of claim 6 further comprising removing the estimated first self-interference from the received signal.

8. The method of claim 6, wherein the linear model relates a row vector of the sampled received signal to a product of the data matrix according to the sampled transmit signal and a column vector of the channel characteristics, and wherein estimating the channel characteristics comprises solving for the column vector in the linear model using the minimum mean square error solution.

9. The method of claim 8, wherein the row vector of the sampled received signal has a first length equal to a number of sampled signals, and wherein the column vector of the channel characteristics has a second length equal to a dimension suitable for the channel characteristics.

10. The method of claim 9, wherein the number of sampled signals exceeds the dimension for the channel characteristics.

11. A communications device for full-duplex communications, the communications device comprising:

a transmitter chain configured to transmit a first signal;

a receiver configured to receive a second signal;

an antenna coupled to the transmitter chain and the receiver;

a passive analog cancellation circuit positioned between the transmitter chain, the receiver, and the antenna, and configured to reject the first signal from a reception path between the passive analog cancellation circuit and the receiver; and

a digital cancellation circuit coupled to the receiver and the transmitter chain, and configured to sample the first signal and the second signal, and estimate first self-interference in the sampled second signal according to the sampled first signal and an estimate of a distortion channel inside the communications device; and

a processor configured to determine the estimate of the distortion channel with a linear model relating the second signal to the distortion channel, noise in the second signal, and a data matrix produced according to the first signal, wherein processor configured to determine the estimate of the distortion channel comprises the processor configured to determine the distortion channel from the linear model using a minimum mean square error solution for the distortion channel.

12. The communications device of claim 11, wherein the digital cancellation circuit is further configured to remove the estimated first self-interference from the sampled second signal.

13. The communications device of claim 11, wherein the distortion channel represents self-interference in the second signal due to multiple reflections of the first signal and the second signal along multiple paths in the communications device.

14. The communications device of claim 11, wherein the digital cancellation circuit is further configured to buffer a defined number of samples of the second signal before estimating the first self-interference.

15. The communications device of claim 11 further comprising an active analog cancellation circuit positioned between the passive analog cancellation circuit, the transmitter chain, and the receiver, and configured to estimate a second self-interference in the second signal according to the first signal and an estimate of a second distortion channel inside the communications device.

16. The communications device of claim 15, wherein the active analog cancellation circuit is further configured to remove the second self-interference from the second signal before removing the first self-interference from the sampled second signal, wherein the estimated first self-interference corresponds to residual self-interference after removing the estimated second self-interference.

17. The communications device of claim 15, wherein the active analog cancellation circuit includes:

a secondary receiver coupled to the passive analog cancellation circuit;

a secondary transmitter coupled to the receiver; and

a channel estimation circuit coupled to the secondary receiver, the secondary transmitter, and the transmitter chain.

18. The communications device of claim 11, wherein the transmitter chain includes a baseband transmitter and a radio frequency signal transmitter in series.

19. The communications device of claim 11 further comprising an analog to digital converter positioned between the receiver and the digital cancellation circuit.