# Patent

## Title
Circuits and methods for performing self-interference cancelation in full-duplex transceivers

## Abstract

Full duplex transceivers are provided, the transceivers comprising: a transmitter section that includes an analog portion having analog baseband signals and a digital portion having digital baseband signals; a receiver section that includes an analog portion having analog baseband signals and a digital portion having digital baseband signals; an analog self-interference canceller that, in response to the analog baseband signals in the analog portion of the transmitter section, produces analog cancellation signals that cancel first self-interference in the analog baseband signals in the analog portion of the receiver section; and a digital self-interference canceller that, in response to the digital baseband signals in the digital portion of the transmitter section, produces digital cancellation signals that cancel second self-interference in the digital baseband signals in the digital portion of the receiver section.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Patent Application No. 62/271,297, filed Dec. 27, 2015, and U.S. Provisional Patent Application No. 62/346,977, filed Jun. 7, 2016, and is a continuation-in-part of International Patent Application No. PCT/US2016/065456, filed Dec. 7, 2016, which claims the benefit of U.S. Provisional Patent Application No. 62/264,312, filed Dec. 7, 2015, U.S. Provisional Patent Application No. 62/271,297, filed Dec. 27, 2015, and U.S. Provisional Patent Application No. 62/346,977, filed Jun. 7, 2016. Each of the applications listed in the foregoing sentence is hereby incorporated by reference herein in its entirety.


STATEMENT REGARDING GOVERNMENT FUNDED RESEARCH
This invention was made with government support under contracts FA8650-14-1-7414 and HR0011-12-1-0006 awarded by the Defense Advanced Research Projects Agency. The government has certain rights in the invention.


BACKGROUND
Full-duplex communications, in which a transmitter and a receiver of a transceiver operate simultaneously on the same frequency band, is drawing significant interest for emerging 5G communication networks due to its potential to double network capacity compared to half-duplex communications.
However, one of the biggest challenges in implementing full-duplex communications is managing self-interference. Self-interference is interference present in a receiver channel of a transceiver that is caused by signals transmitted from a transmitter channel of the transceiver.
Accordingly, new mechanisms for implementing self-interference cancellation in full-duplex transceivers are desirable.
SUMMARY
In accordance with some embodiments, full duplex transceivers are provided, the transceivers comprising: a transmitter section that includes an analog portion having analog baseband signals and a digital portion having digital baseband signals; a receiver section that includes an analog portion having analog baseband signals and a digital portion having digital baseband signals; an analog self-interference canceller that, in response to the analog baseband signals in the analog portion of the transmitter section, produces analog cancellation signals that cancel first self-interference in the analog baseband signals in the analog portion of the receiver section; and a digital self-interference canceller that, in response to the digital baseband signals in the digital portion of the transmitter section, produces digital cancellation signals that cancel second self-interference in the digital baseband signals in the digital portion of the receiver section.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an example of a full duplex transceiver incorporating an analog self-interference canceller and a digital self-interference canceller in accordance with some embodiments.
FIG. 2 is a schematic of an example of a portion a full duplex transceiver that can be used as a portion of the full duplex transceiver of FIG. 1 in accordance with some embodiments.
FIG. 3 is an illustration of a non-linear tapped delay line that can be used to implement digital self-interference cancellation in a full duplex transceiver in accordance with some embodiments.



DETAILED DESCRIPTION
In accordance with some embodiments, mechanisms for providing self-interference cancellation in a full duplex transceiver in accordance with some embodiments are provided. In some embodiments, digital self-interferences can be provided using a non-linear tapped delay line.
Turning to FIG. 1, an example 100 of a block diagram of a full duplex transceiver incorporating self-interference cancellation mechanisms in accordance with some embodiments is shown. As illustrated, transceiver 100 includes a digital-to-analog converter (DAC) 104, a mixer 106, a local oscillator generator 108, a power amplifier (PA) 110, an antenna interface 112, an antenna 114, a low-noise amplifier (LNA) 116, a mixer 118, an analog self-interference (SI) canceller 120, an analog-to-digital converter (ADC) 122, an adder 124, and a digital self-interference (SI) canceller 126.
During operation of transceiver 100, DAC 104 converts a signal to be transmitted from digital form to analog form resulting in a transmitter (TX) analog baseband signal 128. The transmitter analog baseband signal is then upconverted by mixer 106 using a local oscillator from local oscillator generator 108. The upconverted signal is then amplified by power amplifier (PA) 110. The signal output by PA 110 is represented in FIG. 1 by signal 130, which includes a PTX component, which is an amplified form of the transmitter signal, and a self-interference (SI) third-order inter-modulation (IM3) distortion component. The signal output by PA 110 is provided to antenna interface 112, which directs the signal to antenna 114 for transmission. A signal received at antenna 114 is represented in FIG. 1 by signal 132, which includes a desired signal component and a noise component. The signal received at the antenna is directed by antenna interface 112 to the input of low noise amplifier 116, which amplifies the received signal. As illustrated by signals 134, the signals received at the antenna are combined with interference from the signal output by PA 110 that is not isolated by antenna interface 112. Mixer 118 then downconverts the amplified signal using a local oscillator from generator 108. Based on transmitter analog baseband signal 128, analog self-interference canceller 120 provides a signal that cancels at least some of the self-interference in the output of mixer 118. The combined output of mixer 118 and canceller 120 is represented by receiver (RX) analog baseband signals 136. The RX analog baseband signal is then converted to digital form by ADC 122 and provided to adder 124. Digital SI canceller 126, based on signals at the input to DAC 104, provides digital cancellation signals to adder 124 that, when added to the output of ADC 122, further cancels the self-interference from the PTX signal and the SI IM3 distortion. The is represented by signals 138.
DAC 104 and ADC 122 can be implemented in any suitable manner using any suitable digital-to-analog and analog-to-digital converters.
In some embodiments, analog self-interference canceller 120 can be implemented as described below in connection with analog baseband self-interference canceller 228 of FIG. 2.
Mixers 106 and 118 can be implemented in any suitable manner using any suitable mixers in some embodiments.
Generator 108 can be implemented in any suitable manner using any suitable local oscillator generator in some embodiments.
Power amplifier 110 can be implemented in any suitable manner using any suitable power amplifier in some embodiments.
LNA 116 can be implemented in any suitable manner using any suitable low noise amplifier in some embodiments.
Adder 124 can be implemented in any suitable manner using any suitable adder in some embodiments.
Antenna 114 can be implemented in any suitable manner using any suitable antenna in some embodiments.
Antenna interface 112 can be implemented in any suitable manner using any suitable antenna interface, such as non-reciprocal circulator or an electrical balance duplexer, in some embodiments.
In some embodiments, rather than using antenna interface 112 and a single antenna 114, two antennas 114 can be used, one connected to the output of power amplifier 110 and the other connected to the input of LNA 116, and antenna interface 112 can be omitted.
Turning to FIG. 2, a more detailed example 200 of portion 140 of transceiver 100 in accordance with some embodiments is shown. Box 299 represents a chip on which the encompassed components can be implemented in some embodiments. In some embodiments, such a chip can be implemented in 65 nm CMOS technology.
As illustrated, transceiver portion 200 is implemented using transmit baseband buffers 202 and 204, a transmit modulator 206, a power amplifier 208, a non-reciprocal circulator 210 (of which inductors 214 are a part), an antenna 212, a circulator local oscillator (LO) generator 216, inductors 218 and 220, a common-gate, common-source low-noise transconductance amplifier (LNTA) 222, a receiver (RX) LO generator 224, a four-phase passive mixer 226, an analog baseband (BB) self-interference canceller (SIC) 228, transimpedance amplifiers (TIAs) 234, and analog baseband recombination circuitry 236.
Transmit baseband buffers 202 and 204 can be implemented in any suitable manner using any suitable baseband buffers in some embodiments.
Transmit modulator 206 can be implemented in any suitable manner using any suitable modulator in some embodiments. For example, in some embodiments, modulator 206 can be implemented using part number TRF370417 available from Texas Instruments (of Dallas, Tex.).
Power amplifier 208 can be implemented in any suitable manner using any suitable power amplifier in some embodiments.
Non-reciprocal circulator 210 can be implemented in any suitable manner using any suitable non-reciprocal circulator in some embodiments. For example, in some embodiments, non-reciprocal circulator can be implemented using non-reciprocal circulator as described in connection with FIG. 4 of International Patent Application No. PCT/US2016/065456, filed Dec. 7, 2016, which is hereby incorporated by reference herein in its entirety.
Antenna 212 can be implemented in any suitable manner using any suitable antenna in some embodiments.
Inductors 218 and 220 can be implemented in any suitable manner using any suitable inductors for use with LNTA 222 in some embodiments.
Common-gate, common-source low-noise transconductance amplifier (LNTA) 222 can be implemented in any suitable manner using any suitable LNTA in some embodiments. For example, in some embodiments, LNTA 222 can be implemented as shown in the schematic of FIG. 2.
Four-phase passive mixer 226 can be any suitable four-phase passive mixer in some embodiments. For example, in some embodiments, mixer 226 can be implemented as shown in the schematic of FIG. 2.
Transimpedance amplifiers (TIAs) 234 can be implemented in any suitable manner using any suitable TIAs in some embodiments. For example, in some embodiments, TIAs 234 can be implemented as shown in the schematic of FIG. 2.
Analog baseband recombination circuitry 236 can be implemented in any suitable manner using any suitable analog baseband recombination circuitry in some embodiments. For example, recombination circuitry 236 can be implemented using voltage to current converting gm cells as shown in circuitry 734 of FIG. 7 of International Patent Application No. PCT/US2016/065456, filed Dec. 7, 2016, which is hereby incorporated by reference herein in its entirety. The recombination circuit may be formed from multiple pairs of gms to form I/Q outputs of the receiver.
During operation, transmit signals received at baseband I and Q inputs 201 are amplified by buffers 202 and 204, modulated by modulator 206, amplified by amplifier 208, directed to antenna 212 by circulator 210, and transmitted by antenna 212. Signals received at antenna 212 are directed by circulator 210 to LNTA 222, amplified by LNTA 222, down-converted by mixer 226, amplified by TIAs 234, converted to I and Q baseband outputs by circuitry 236, and output at outputs 203. Analog BB SIC 228 taps from the transmit baseband signals between the baseband buffers 202 and 204, adjusts the amplitude and the phase of the tapped signals, and injects cancellation currents at the inputs to TIA 234.
Amplitude and phase scaling in analog BB SIC 228 is achieved through two five-bit digitally-controlled phase rotators 230 and 232 injecting into the I-paths and the Q-paths of the RX analog BB, respectively. Each phase rotator can include 31 (or any other suitable number) identical cells with independent controls 238 (these controls can determine the contribution of each cell to the analog BB SIC current). Each cell, which can be implemented in any suitable manner in some embodiments (e.g., such as shown in box 229), of the phase rotator adopts a noise-canceling common-gate (CG) and common-source (CS) topology, allowing partial cancellation of the noise from the CG devices (dependent on the phase rotator setting at controls 238).
Circulator 210 can be implemented in any suitable manner in some embodiments, such as described in connection with FIGS. 4 and 6 of International Patent Application No. PCT/US2016/065456, filed Dec. 7, 2016, which is hereby incorporated by reference herein in its entirety.
Circulator 210 receives from circulator LO generator 216 two sets of eight non-overlapping clock signals each with 12.5% duty cycle. These clock signals are used to control the switches in the eight paths of the N-path filter of circulator 210.
Generator 216 can be implemented in any suitable manner in some embodiments. For example, in some embodiments, to generate these clock signals, generator 216 receives two differential (0 degree and 180 degree) input clocks that run at four times the desired commutation frequency. A divide-by-two frequency-divider circuit 244 generates four quadrature clocks with 0 degree, 90 degree, 180 degree, and 270 degree phase relationship. These four clock signals drive two parallel paths for the two sets of switches.
In a first of the two paths, a programmable phase shifter 246 that allows for arbitrary staggering between the two commutating switch sets is provided. Programmable phase shifter 246 enables switching between −90 degree and +90 degree staggering, which allows dynamic reconfiguration of the circulation direction. The phase shifter also allows for fine tuning of the staggered phase shift to optimize the transmission loss in the circulation direction and isolation in the reverse direction. After phase shifting, another divide-by-two circuit 248 and a non-overlapping 12.5% duty-cycle clock generation circuit 250 create the clock signals that control the commutating transistor switches in the first path.
In a second of the two paths, directly after first divide-by-two frequency-divider circuit 244, another divide-by-two circuit 252 and a non-overlapping 12.5% duty-cycle clock generation circuit 254 create the clock signals that control the commutating transistor switches in the second path.
Divide-by-two circuits 244, 248, and 252, phase shifter 246, and non-overlapping 12.5% duty-cycle clock generation circuits 250 and 254 can be implemented in any suitable manner.
In some embodiments, circulator LO generator 216 may use static 90 degree phase-shifts or digital phase interpolators that preserve the square-wave nature of the clock.
At RX LO port 242, RX LO generator 224 receives two differential (0 degree and 180 degree) input clocks that run at two times the operating frequency of the receiver (e.g., 750 MHz). A divide-by-two frequency-divider circuit (which can be implemented in any suitable manner) in generator 224 generates four quadrature clocks with 0 degree, 90 degree, 180 degree, and 270 degree phase relationship.
In some embodiments, although not shown, an impedance tuner can be provided to counter reflections due to antenna impedance mismatch. The tuner can be used at the ANT port for joint optimization of SIC bandwidth (BW) between the circulator and the analog BB canceller.
In some embodiments, transceivers take advantage of inherent down-conversion of an N-path filter to merge a circulator and a receiver.
Turning back to FIG. 1, in accordance with some embodiments, digital self-interference canceller 126 can be implemented using a non-linear tapped delay line. In some embodiments, a non-linear tapped delay line can be implemented in any suitable hardware processor (such as a digital signal processor, microprocessor, etc.) that is programmed to perform a non-linear tapped delay line function. For example, in accordance with some embodiments, such a non-linear tapped delay line can be implemented as illustrated in FIG. 3, which essentially models the self-interference channel in digital as a truncated Volterra series:




  
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where y[n] is the digital SI canceller output, x[n] and x[n−k] (k represents the delay index) are the current and past TX digital baseband signals, N corresponds to the maximum delay in the modeled SI channel, and hi[k] (i=1, 2, 3, . . . , p) is the i-th order digital canceller coefficient for delay index of k.

In some embodiments, truncating the Volterra series can be used to reduce the digital SI canceller complexity to a manageable level. For example, in some embodiments, non-linear terms up to 4th order (i.e., p=4) can be considered with a delay spread length of 41 samples (i.e., N=40), resulting in 164 total unknown canceller coefficients.
In some embodiments, the digital SI canceller coefficients can be determined using a two-tone pilot signal. More particularly, given an M-length pilot sequence Y (y[0], y[1], . . . , y[M−1]) and a N-length nonlinear coefficient sequence H (h1[0], h1[1], . . . ), and taking noise into account, we have the following linear equation:

Y=XH+n 

where X is a M*N matrix that consists of TX digital baseband signals (x[0], x[1], x2[0], x3[0], . . . ), and n is the noise from the SI channel. The goal is to find a Ĥ that minimizes |XĤ−Y|. When the received data points are more than the number of unknown coefficients (M>N), this becomes a least-squares problem, and Ĥ can be found as:

Ĥ=A+Y 

where A+ is the pseudo-inverse of matrix A.

Although the disclosed subject matter has been described and illustrated in the foregoing illustrative implementations, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the details of implementation of the disclosed subject matter can be made without departing from the spirit and scope of the disclosed subject matter, which is limited only be the claims that follow. Features of the disclosed implementations can be combined and rearranged in various ways.

## Claims

1. A full duplex transceiver comprising:
a transmitter section that includes an analog portion having analog baseband signals and a digital portion having digital baseband signals;
a receiver section that includes an analog portion having analog baseband signals and a digital portion having digital baseband signals;
an analog self-interference canceller that, in response to the analog baseband signals in the analog portion of the transmitter section, produces analog cancellation signals that cancel first self-interference in the analog baseband signals in the analog portion of the receiver section; and
a digital self-interference canceller that, in response to the digital baseband signals in the digital portion of the transmitter section, produces digital cancellation signals that cancel second self-interference in the digital baseband signals in the digital portion of the receiver section, wherein the digital self-interference canceller performs a non-linear tapped delay line function on the digital baseband signals in the digital portion of the transmitter section to produce the digital cancellation signals.

2. The full duplex transceiver of claim 1, wherein the transmitter section comprises a digital-to-analog converter that separates the digital portion of the transmitter section from the analog portion of the transmitter section.

3. The full duplex transceiver of claim 1, wherein the receiver section comprises an analog-to-digital converter that separates the analog portion of the receiver section from the digital portion of the receiver section.

4. The full duplex transceiver of claim 1, wherein the non-linear tapped delay line function is:




  
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where y[n] is an output of the delay line, k is a delay index, x[n−k] is current and past values of the digital baseband signals of the transmitter section, N corresponds to a maximum delay, and hi[k] (i=1, 2, 3, . . . , p) is an i-th order digital canceller coefficient for delay index of k.

5. A full duplex transceiver comprising:
a transmitter section that includes an analog portion having analog baseband signals and a digital portion having digital baseband signals;
a receiver section that includes an analog portion having analog baseband signals and a digital portion having digital baseband signals;
an analog self-interference canceller that, in response to the analog baseband signals in the analog portion of the transmitter section, produces analog cancellation signals that cancel first self-interference in the analog baseband signals in the analog portion of the receiver section, wherein the analog self-interference canceller performs amplitude and phase scaling on the analog baseband signals in the analog portion of the transmitter section to produces analog cancellation signals; and
a digital self-interference canceller that, in response to the digital baseband signals in the digital portion of the transmitter section, produces digital cancellation signals that cancel second self-interference in the digital baseband signals in the digital portion of the receiver section.

6. The full duplex transceiver of claim 1, where an output of the transmitter section and an input of the receiver section are connected to an antenna interface that is also connected to an antenna that transmits signals from the transmitter section and receives signals provided to the receiver section.

7. The full duplex transceiver of claim 6, wherein the antenna interface is a non-reciprocal circulator.

8. The full duplex transceiver of claim 6, wherein the antenna interface is an electrical balance duplexer.

9. The full duplex transceiver of claim 5, wherein the transmitter section comprises a digital-to-analog converter that separates the digital portion of the transmitter section from the analog portion of the transmitter section.

10. The full duplex transceiver of claim 5, wherein the receiver section comprises an analog-to-digital converter that separates the analog portion of the receiver section from the digital portion of the receiver section.

11. The full duplex transceiver of claim 5, where an output of the transmitter section and an input of the receiver section are connected to an antenna interface that is also connected to an antenna that transmits signals from the transmitter section and receives signals provided to the receiver section.

12. The full duplex transceiver of claim 11, wherein the antenna interface is a non-reciprocal circulator.

13. The full duplex transceiver of claim 11, wherein the antenna interface is an electrical balance duplexer.