Adaptive radio frequency interference cancellation method and system in a full duplex system

Abstract

The application discloses a kind of adaptive radio frequency interference cancellation method and system in full duplex system, including from the transmission link of full duplex system coupling out part transmission signal, as self-interference reference signal;Self-interference reference signal is fed into at least one adaptive adjustment branch;Each adaptive adjustment branch is independently digitally adjusted to the amplitude and phase of self-interference reference signal based on the control word generated by control algorithm, generates a cancellation signal;The received signal obtained from receiving antenna is synthesized with cancellation signal, to generate synthesis signal;By adjusting the amplitude and phase of cancellation signal, it is equal to the amplitude of self-interference component in received signal and opposite phase, so that the self-interference component in synthesis signal is cancelled, to realize the self-interference cancellation of radio frequency domain;The application significantly improves the self-interference suppression capability of radio frequency domain of full duplex system.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, specifically to an adaptive radio frequency interference cancellation method and system in a full-duplex system. Background Technology

[0002] With the explosive growth of mobile internet and IoT services, the spectrum efficiency of wireless communication systems has become a core bottleneck restricting network capacity improvement. Traditional duplex technologies, such as Frequency Division Duplex (FDD) and Time Division Duplex (TDD), achieve isolation of the transmit and receive links through spectrum resource allocation or time resource allocation, respectively, failing to maximize the utilization of spectrum resources. Full-duplex technology allows communication devices to transmit and receive signals simultaneously on the same frequency at the same time, theoretically doubling spectrum efficiency. It is considered one of the key enabling technologies for next-generation wireless communication systems, such as sixth-generation mobile communication, and has broad application prospects and significant market value.

[0003] The core challenge in achieving full-duplex communication lies in effectively suppressing the strong self-interference generated by the transmitted signal of the device on its own receiver. Existing self-interference cancellation technologies are mainly divided into two categories, but both have significant limitations.

[0004] The first type is antenna and spatial domain cancellation technology, which uses multiple transmitting antennas precisely arranged to form nulls in the signal beam at the receiving antenna to cancel interference. This type of technology has extremely stringent requirements for antenna spacing, azimuth, and signal amplitude and phase consistency. Even millimeter-level physical displacement or decibel-level amplitude error can cause the cancellation performance to deteriorate sharply from the theoretical optimal level to below 30dB. It has very small engineering tolerances, is difficult to adapt to dynamic environments, and is difficult to put into practical use.

[0005] The second type is radio frequency circuit cancellation technology, which couples a reference signal from the transmit link, modulates it using an analog phase shifter and attenuator, and then synthesizes it with the received signal. Traditional solutions often use analog phase modulators (delay lines) based on transmission lines of a specific length. Their core bottlenecks are: first, limited bandwidth—the delay line only has accurate phase shift near the designed center frequency; as the frequency shifts, the phase shift error increases, leading to a rapid decline in cancellation performance and making it difficult to support broadband signals; second, poor adjustment accuracy and flexibility—analog devices have limited adjustment accuracy and lack intelligent feedback mechanisms, making it impossible to track channel fluctuations caused by temperature changes, device aging, or multipath effects in real time, resulting in unstable performance in complex environments; and third, inadequate handling of multipath interference—a single cancellation path can only simulate one main interference path, offering limited cancellation effectiveness against the prevalent multipath self-interference in real-world environments. Summary of the Invention

[0006] The purpose of this invention is to address the problems of limited bandwidth, low adjustment accuracy, insufficient dynamic tracking capability, and poor multipath suppression capability in existing full-duplex self-interference cancellation technologies, and to provide an adaptive radio frequency interference cancellation method and system in a full-duplex system, so as to achieve radio frequency interference cancellation with broadband support, high-precision adjustment, adaptive tracking, and multipath suppression.

[0007] To achieve the above objectives, this invention specifically discloses an adaptive radio frequency interference cancellation method in a full-duplex system, comprising the following steps:

[0008] Step S1: From the transmission link of the full-duplex device, a portion of the transmitted signal is coupled out through a directional coupler or power divider as a reference signal for self-interference; wherein the self-interference reference signal retains all the modulation information and noise characteristics of the transmitted signal;

[0009] Step S2: Feed the self-interference reference signal into at least one adaptive adjustment branch; each branch includes a digitally controlled adjustable attenuator and a digitally controlled adjustable phase shifter connected in series; each adaptive adjustment branch independently and precisely sets the amplitude attenuation and phase rotation of the self-interference reference signal corresponding to the branch based on the digital control word generated by the control algorithm, thereby generating a cancellation signal corresponding to the self-interference signal of a specific path.

[0010] Step S3: Employ a closed-loop feedback control mechanism to achieve self-interference cancellation through the following iterative process: Perform vector synthesis of the current cancellation signal and the received signal received by the receiving antenna at the RF front end to generate a synthesized signal. The received signal contains the target signal attenuated by the spatial channel and the self-interference signal generated from the full-duplex system transmit link. Monitor the strength or characteristics of the residual interference signal in the synthesized signal in real time. The strength refers to the power or amplitude of the residual interference signal. The characteristics refer to at least one of the I / Q components, error vector amplitude, or correlation with the reference signal of the residual interference signal.

[0011] Based on the monitoring results, an adaptive algorithm, such as the least mean square algorithm and its variants, is run to dynamically calculate and output a digital control word. The adjustable attenuator and adjustable phase shifter in each adjustment branch are driven according to the digital control word to adjust the amplitude and phase of the cancellation signal. The process is iterated repeatedly until the amplitude of the cancellation signal and the self-interference component in the received signal are equal and the phase is opposite at the synthesis point, so as to maximize the cancellation of self-interference and significantly improve the signal-to-interference-plus-noise ratio of the received signal.

[0012] Furthermore, to effectively combat multiple self-interference replicas caused by multipath propagation, multiple adaptive adjustment branches can be deployed in parallel. Each branch can be adjusted independently to generate cancellation signals for different main interference paths. The outputs of all branches are combined and then synthesized with the received signal.

[0013] Furthermore, in the multi-path adaptive adjustment branch, each branch has a fixed phase offset link before or after the adjustable phase shifter chip, so that each branch has a different initial phase center, in order to expand the phase adjustment range and flexibility of interference cancellation, and more accurately fit the complex multipath channel response.

[0014] Based on the same inventive concept, this invention also discloses an adaptive radio frequency interference cancellation system, which performs the above-described method, specifically including:

[0015] The reference signal coupling module is used to couple out the interference reference signal from the transmit link of the full-duplex system. It is connected to the output of the transmit power amplifier or the transmit antenna.

[0016] At least one adaptive adjustment module is connected to the reference signal coupling module to receive the self-interference reference signal output by the reference signal coupling module. Each module includes a series digitally controlled adjustable attenuator and a digitally controlled adjustable phase shifter to perform joint amplitude and phase conditioning on the input reference signal. Based on the digital control word generated by the control algorithm, the amplitude and phase of the self-interference reference signal of the branch are digitally adjusted independently to generate a cancellation signal.

[0017] The signal synthesis module, employing an RF coupler or power combiner, connects one end to the receiving antenna and the other end to the total output of the adaptive adjustment module. It receives the canceled signal output from the adaptive adjustment module and the received signal from the receiving antenna, performs vector synthesis on the two signals, and outputs the synthesized signal.

[0018] The control module is connected to the adjustable attenuator and adjustable phase shifter in the adaptive adjustment module, and generates control words by running a control algorithm to adjust the amplitude and phase of the cancellation signal so that the self-interference component in the synthesized signal output by the signal synthesis module is cancelled.

[0019] Furthermore, the control module includes a microprocessor and a drive circuit connected to each other. The microprocessor is used to run an adaptive algorithm to dynamically update the digital control word according to the strength or characteristics of the residual interference signal in the synthesized signal output by the signal synthesis module. The drive circuit is used to send the updated digital control word to each adjustable attenuator and adjustable phase shifter respectively.

[0020] Furthermore, it also includes a balun module, which can be placed between the transmit link and the reference signal coupling module to convert the single-ended transmit signal into a pair of differential signals with equal amplitude and opposite phase. One path is used for normal transmission, and the other path is directly used as a high-quality "inverting" reference signal. This structure can further improve the inherent performance and operating bandwidth of the cancellation system.

[0021] Furthermore, the phase shifter employs a 6-bit digital control structure to achieve a minimum phase adjustment step of 5.625°; the attenuator employs a 7-bit digital control structure to achieve a fine amplitude step of 0.25 dB. Working together, they construct a fully digital, high-resolution amplitude and phase control link.

[0022] Compared with the prior art, the beneficial technical effects of the present invention using the above technical solution are as follows:

[0023] 1) This invention adopts a multi-path parallel programmable branch architecture, in which the amplitude and phase of each branch can be adjusted independently, and a composite cancellation waveform that matches the multipath self-interference signal can be synthesized. This fundamentally solves the problem of insufficient suppression capability of single-path cancellation architecture in multipath propagation environment, enabling the system to achieve efficient self-interference suppression under real complex channel conditions.

[0024] 2) This invention introduces an adaptive control algorithm based on real-time feedback, which enables the system to automatically track and compensate for channel disturbances, realize closed-loop dynamic tracking and automatic recovery of self-interference suppression, endow the system with "self-healing" capability, and significantly improve robustness in complex dynamic environments.

[0025] 3) This invention overcomes the inherent limitation of the linear change of phase with frequency in traditional delay lines by using a collaborative design of digital control chip and balun. It maintains excellent and consistent cancellation performance throughout the entire operating bandwidth, without the need for segmented compensation, and fully meets the requirements of broadband communication systems.

[0026] 4) This invention uses a 6-bit phase shifter and a 7-bit attenuator to achieve fully digital, high-resolution amplitude and phase control, eliminating the dependence on mechanical array precision, and achieving a stable cancellation depth of over 20 dB. The performance is repeatable and easy to mass-produce.

[0027] 5) The system architecture of this invention adopts a modular design, and the number of branches can be flexibly configured according to performance and cost requirements; the core hardware uses standard commercial programmable RF chips and general-purpose control chips, which are easy to integrate with existing RF front-ends and effectively reduce R&D and deployment costs. Attached Figure Description

[0028] Figure 1 This is a block diagram of the full-duplex self-interference cancellation system in the embodiment;

[0029] Figure 2 This is a schematic diagram of the principle of the digitally controlled adjustable attenuator chip used in the embodiment;

[0030] Figure 3 This is a schematic diagram of the principle of the digitally controlled adjustable phase shifter chip used in the embodiment;

[0031] Figure 4 This is a logic block diagram illustrating adaptive interference cancellation in the embodiment;

[0032] Figure 5 This is a comparison test diagram of the interference cancellation effect in the embodiments. Detailed Implementation

[0033] To further explain the technical content of the present invention, the following description is provided with reference to the accompanying drawings.

[0034] The core of the adaptive radio frequency interference cancellation method in the full-duplex system designed in this invention lies in accurately reconstructing an inverted signal with the same amplitude and opposite phase as the self-interference signal through circuit means, and then superimposing and canceling the inverted signal with the received signal at the radio frequency front end.

[0035] Example

[0036] The adaptive radio frequency interference cancellation method in the full-duplex system of the present invention can be expanded to multiple adaptive adjustment branches to achieve radio frequency interference cancellation with multipath countermeasures. This embodiment takes four adaptive adjustment branches as an example.

[0037] like Figure 1 As shown, this method is implemented by the following steps:

[0038] First, a portion of the transmitted signal is coupled out from the full-duplex system's transmit link via a directional coupler or power divider, serving as a reference signal for self-interference. This reference signal retains all the modulation information and noise characteristics of the transmitted signal.

[0039] The self-interference reference signal is then fed into at least one branch, each branch containing a digitally controlled adjustable attenuator and a digitally controlled adjustable phase shifter connected in series. Using digital control words provided by an external control module, the amplitude attenuation and phase rotation of the reference signal for that branch are independently and precisely set, thereby generating a cancellation signal corresponding to the self-interference signal of a specific path.

[0040] One or more canceled signals are vector-combined with the mixed signal received by the receiving antenna, which includes weak target signals and strong self-interference signals, at the radio frequency front end through a coupler or power combiner.

[0041] The system monitors the strength or characteristics of the received signal after cancellation and synthesis in real time; it determines whether the interference cancellation conditions are met. If they are met, the canceled and synthesized signal is directly output; if not, an adaptive algorithm, such as the least mean square algorithm and its variants, is run based on the feedback information from the monitoring. The algorithm is used to dynamically calculate and output the updated digital control word to drive the adjustable attenuators and adjustable phase shifters in each adjustment branch, so that the generated cancellation signal can track and match the amplitude and phase changes of the self-interference signal in the spatial channel in real time.

[0042] The interference cancellation condition is an engineering approximation of the ideal cancellation condition, and its threshold is dynamically or statically set according to the receiver's noise floor, useful signal power, and system linearity requirements. The ideal condition for interference cancellation is that the canceled signal and the self-interference component in the received signal have equal amplitude and opposite phase.

[0043] The interference cancellation condition here refers to the condition where, after cancellation and synthesis, the remaining interference characteristics obtained by monitoring meet a preset convergence threshold. These characteristics include, but are not limited to: remaining interference power, interference suppression ratio, mean square value of the error signal, or signal-to-interference-plus-noise ratio. When this characteristic is lower than or equal to the preset threshold, the interference cancellation condition is deemed met; otherwise, it is not.

[0044] Through the above adaptive adjustment, the self-interference components in the canceled signal and the received signal are made to have equal amplitude and opposite phase at the synthesis point, thereby canceling the self-interference to the maximum extent and significantly improving the signal-to-interference-plus-noise ratio of the received signal.

[0045] The principle of this process is as follows: Figure 2 As shown: A small portion of the transmitted signal is coupled out from the power amplifier output or the transmit antenna port via a directional coupler, serving as a self-interference reference signal X. This reference signal is then input to the adaptive adjustment branch. The core of this branch is a digitally controlled adjustable attenuator and a digitally controlled adjustable phase shifter. Based on the control word generated by the adaptive algorithm, the microcontroller sets the attenuation A of the attenuator and the phase shift Φ of the phase shifter, thereby adjusting the reference signal X into a cancellation signal. , where j is the imaginary unit. Simultaneously, the receiving antenna receives a weak target signal S from a distant location and a strong self-interference signal H·X propagating through space, potentially including direct and reflected paths, where H is the space channel response. The received signal is S + H·X. The canceled signal Y and the received signal are vector-combined in a combiner, such as a coupler or power combiner. Ideally, this is adjusted through an adaptive algorithm to make... The synthesizer output will then receive a signal. This effectively cancels out self-interference.

[0046] To address multipath effects in real-world environments, this method can employ multiple parallel adaptive adjustment branches, such as... Figure 2 The four extended adaptive adjustment branches within the dashed box are shown. Each branch includes a phase shifter and an attenuator connected in series. The phase shifter uses a 6-bit digital control structure to achieve a minimum phase adjustment step of 5.625°, and the attenuator uses a 7-bit digital control structure to achieve a fine amplitude step of 0.25 dB. The two work together to construct a fully digital, high-resolution amplitude and phase control link.

[0047] This embodiment also includes a balun network comprising three single-ended to differential baluns. The input of the first single-ended to differential balun is connected to the output of the transmit link, used to convert the single-ended transmit signal into a differential signal. The two differential outputs of the first single-ended to differential balun are respectively connected to the input of the second single-ended to differential balun and the input of the first attenuator; the two differential outputs of the second single-ended to differential balun are respectively connected to the input of the third single-ended to differential balun and the input of the second attenuator.

[0048] The second and third single-ended to differential baluns further convert their input differential signals. The third single-ended to differential balun, as the final stage balun, has its two differential outputs connected to the inputs of two attenuators in the transmit link.

[0049] The output terminals of the first to fourth attenuators are respectively connected to the input terminals of the first to fourth phase shifters.

[0050] With the above structure, each path independently generates a cancellation signal Y_i. All Y_i signals are combined before being synthesized with the received signal. Each path can be preset with a fixed phase offset, such as 0°, 90°, 180°, or 270°, to cover a more comprehensive phase adjustment range and more finely fit the multipath channel.

[0051] This is a schematic diagram illustrating the internal workings of the adjustable attenuator and adjustable phase shifter preferably used in this invention. Both employ a digital bit-controlled switch array to switch microstrip transmission paths of different lengths, thereby achieving discrete but high-precision amplitude attenuation or phase delay adjustment. For example, a 7-bit attenuator, such as... Figure 3 As shown, the chip contains seven serial attenuation traces, each with a parallel lossless trace and a switch. Switching allows selection of either lossy or lossless traces to create 128 (27) different attenuation levels. This digital control ensures precise and repeatable adjustment. Figure 4 As shown, the phase shifter adopts a switch-type structure, which is composed of multiple cascaded basic phase shifting units. Each phase shifting unit provides step values ​​of 5.6°, 11.2°, 22.5°, 45°, 90°, and 180° respectively. By controlling the on / off state of the switch, the units are combined and selected to achieve phase adjustment in 5.6° steps within the range of 0° to 360°.

[0052] like Figure 5As shown, without cancellation, the synthesizer output is a simple superposition of the two signals, resulting in high power. After finding the optimal combination of attenuation and phase shift through a control algorithm, the output signal power is significantly reduced, achieving an interference cancellation of approximately 30dB. Experiments demonstrate that this method is effective within a 2.45GHz center frequency and a 5MHz bandwidth. Since the RF chip used operates within a 2-4GHz bandwidth, this solution has the potential for wideband applications.

[0053] In summary, this invention provides a full-duplex self-interference cancellation solution that is stable in performance, has a large cancellation depth, can adapt to multipath environments, and is easy to integrate by constructing an adaptive adjustment circuit using a high-precision digital programmable radio frequency chip and combining it with a feedback control algorithm. This effectively promotes the practical application of full-duplex technology.

[0054] Meanwhile, the present invention also discloses an adaptive radio frequency interference cancellation system, which includes:

[0055] Reference signal coupling module, used to couple out interference reference signals from the transmit link of a full-duplex system;

[0056] At least one adaptive adjustment module is used to receive the self-interference reference signal output by the reference signal coupling module. Each module includes a series digitally controlled adjustable attenuator and a digitally controlled adjustable phase shifter, and performs independent digital adjustment on the amplitude and phase of the self-interference reference signal of the branch based on the digital control word generated by the control algorithm to generate a cancellation signal.

[0057] The signal synthesis module receives the cancellation signal output from the adaptive adjustment module and the received signal from the receiving antenna, and synthesizes the two signals to output the synthesized signal.

[0058] The control module is connected to the adjustable attenuator and adjustable phase shifter in the adaptive adjustment module, and generates control words by running a control algorithm to adjust the amplitude and phase of the cancellation signal so that the self-interference component in the synthesized signal output by the signal synthesis module is cancelled.

[0059] In a preferred embodiment, a balun is further included between the reference signal coupling module and the transmit link to convert the single-ended transmit signal into a pair of differential signals, one of which is used for transmission and the other is used as the self-interference reference signal.

[0060] In another preferred embodiment, the system includes multiple parallel adaptive adjustment modules, with the output of each module connected to a signal synthesis module. The control module independently or collaboratively controls the adjustable attenuators and adjustable phase shifters in each module. The control module includes an interconnected microprocessor and driving circuitry. The microprocessor runs an adaptive algorithm to dynamically update the digital control word based on the strength or characteristics of residual interference signals in the synthesized signal output by the signal synthesis module. The driving circuitry sends the updated digital control word to each adjustable attenuator and adjustable phase shifter.

[0061] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An adaptive radio frequency interference cancellation method in a full-duplex system, characterized in that, Includes the following steps: Step S1: Couple a portion of the transmitted signal from the full-duplex system's transmit link as a self-interference reference signal; The self-interference reference signal retains all the modulation information and noise characteristics of the transmitted signal; Step S2: Feed the self-interference reference signal into at least one adaptive adjustment branch; each adaptive adjustment branch performs independent digital adjustment on the amplitude and phase of the self-interference reference signal corresponding to the branch based on the digital control word generated by the control algorithm to generate a cancellation signal. Step S3: Combine the cancellation signal with the received signal obtained from the receiving antenna to generate a composite signal; iteratively adjust the amplitude and phase of the cancellation signal until its amplitude is equal to and phase is opposite to that of the self-interference component in the received signal, so that the self-interference component in the composite signal is canceled, thereby realizing self-interference cancellation in the radio frequency domain.

2. The adaptive radio frequency interference cancellation method in a full-duplex system according to claim 1, characterized in that, The received signal includes the target signal attenuated by the spatial channel and the self-interference signal generated from the full-duplex system transmission link.

3. The adaptive radio frequency interference cancellation method in a full-duplex system according to claim 1 or 2, characterized in that, In step S2, the amplitude adjustment of the self-interference reference signal is achieved by setting the attenuation amount of the digitally controlled adjustable attenuator chip; the phase adjustment of the self-interference reference signal is achieved by setting the phase shift amount of the digitally controlled adjustable phase shifter chip; the attenuation amount and the phase shift amount are set by the control word output by the control algorithm respectively.

4. The adaptive radio frequency interference cancellation method in a full-duplex system according to claim 3, characterized in that, The control algorithm is an adaptive algorithm. It detects residual interference signals in the synthesized signal in real time, and dynamically updates the digital control word according to the strength or characteristics of the residual interference signal. The updated digital control word is then sent to the adjustable attenuator chip and the adjustable phase shifter chip to adjust the attenuation and phase shift, track the changes in the self-interference channel, and achieve optimal interference cancellation.

5. The adaptive radio frequency interference cancellation method in a full-duplex system according to claim 3, characterized in that, Step S2 includes multiple parallel adaptive adjustment branches, each branch generating a cancellation signal; The multiple cancellation signals are combined with the received signal to cancel out multiple self-interference components caused by multipath propagation.

6. The adaptive radio frequency interference cancellation method in a full-duplex system according to claim 5, characterized in that, In the multi-path adaptive adjustment branch, each branch has a fixed phase offset link before or after the adjustable phase shifter chip, so that each branch has a different initial phase center, thereby expanding the phase adjustment range for interference cancellation.

7. An adaptive radio frequency interference cancellation system, characterized in that, The system performs the method according to any one of claims 1-6, comprising: Reference signal coupling module, used to couple out interference reference signals from the transmit link of a full-duplex system; At least one adaptive adjustment module is used to receive the self-interference reference signal output by the reference signal coupling module. Each module includes a series digitally controlled adjustable attenuator and a digitally controlled adjustable phase shifter, and performs independent digital adjustment on the amplitude and phase of the self-interference reference signal of the branch based on the digital control word generated by the control algorithm to generate a cancellation signal. The signal synthesis module receives the cancellation signal output from the adaptive adjustment module and the received signal from the receiving antenna, and synthesizes the two signals to output the synthesized signal. The control module is connected to the adjustable attenuator and adjustable phase shifter in the adaptive adjustment module, and generates control words by running a control algorithm to adjust the amplitude and phase of the cancellation signal so that the self-interference component in the synthesized signal output by the signal synthesis module is cancelled.

8. The system according to claim 7, characterized in that, The reference signal coupling module also includes a balun between itself and the transmission link, which is used to convert the single-ended transmission signal into a pair of differential signals, one of which is used for transmission and the other is used as the self-interference reference signal.

9. The system according to claim 7, characterized in that, The system includes multiple parallel adaptive adjustment modules, with the output of each module connected to the signal synthesis module; the control module independently or collaboratively controls the adjustable attenuators and adjustable phase shifters in each module.

10. The system according to claim 7 or 9, characterized in that, The control module includes a microprocessor and a driving circuit connected to each other. The microprocessor is used to run an adaptive algorithm to dynamically update the digital control word according to the strength or characteristics of the residual interference signal in the synthesized signal output by the signal synthesis module. The driving circuit is used to send the updated digital control word to each adjustable attenuator and adjustable phase shifter respectively.

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