Method and apparatus for self-interference cancellation in a frequency division duplex system

Abstract

The present invention relates to a fifth generation (5G) or 5G communication system for supporting higher data rates beyond a fourth generation (4G) communication system, such as Long Term Evolution (LTE). A method and apparatus for self-interference cancellation in a communication device. The communication device includes an antenna configured to transmit a transmission signal and receive a reception signal through a duplexer in FDD communication, a first analog-to-digital converter (ADC) configured to convert the reception signal from analog to digital, a coupler configured to couple a sample of the transmission signal to a second ADC configured to convert the sample of the transmission signal from analog to digital, and a self-interference cancellation circuit configured to process the digital sample of the transmission signal to generate a self-interference cancellation signal and apply the self-interference cancellation signal to the digital reception signal to cancel the amount of interference caused by the transmission signal in the reception signal. The SIC process provides additional isolation between the TX signal and the RX signal. The additional isolation can be used to relax the isolation requirements of the duplexer, reducing the duplexer cost and form factor.

Description

Technical Field

[0001] The present disclosure generally relates to self-interference cancellation in radio antenna systems. Embodiments of the present disclosure relate to self-interference cancellation that reduces the isolation requirements of duplexers in frequency division duplex (FDD) systems. Background Art

[0002] In order to meet the demand for wireless data traffic since the deployment of the fourth generation (4G) communication systems, efforts have been made to develop improved 5G or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also referred to as "beyond 4G networks" or "post-LTE systems".

[0003] 5G communication systems are considered to be implemented in higher frequency (MMWave) bands (e.g., 60 GHz band) to achieve higher data rates. In order to reduce the propagation loss of radio waves and increase the transmission distance, beamforming, massive multiple input multiple output (MIMO), full-dimension MIMO (FD-MIMO), array antennas, analog beamforming, and large antenna technologies have been discussed in 5G communication systems.

[0004] In addition, in 5G communication systems, system network improvements are being developed based on advanced small cells, cloud radio access network (RAN), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, coordinated multi-point (CoMP), receiver interference cancellation, etc.

[0005] In 5G systems, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) have been developed as advanced coding modulation (ACM), and filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) have been developed as advanced access technologies.

[0006] In many regions of the world, the expansion of mobile wireless network capacity is largely due to the expansion of the geographical coverage of wireless data networks. Technically and economically, this poses a series of challenges to the maintenance and expansion of the coverage of LTE and 5G cellular communication systems. Most LTE and 5G bands are in high frequencies, which have higher path loss, wider bandwidth, and lower power spectral density (PSD) compared to low-frequency bands. Therefore, in order to improve the signal-to-noise ratio (SNR) of the base station (BS) for better reception, it is usually necessary to allocate less than the full bandwidth of the available spectrum to cell-edge users.

[0007] Most frequency bands are allocated as Frequency Division Duplex (FDD) bands, where two separate frequency bands or channels are allocated for simultaneous (i.e., full-duplex) Downlink (DL) and Uplink (UL) communications. Although FDD has the advantage of a larger coverage area as it can accommodate higher transmission power, higher frequency resource efficiency without the need to allocate guard time, and may reduce latency due to continuous transmission and reception, sufficient guard bands are required to separate the transmit and receive channels so that they do not interfere with each other and ensure clear and uninterrupted transmission. Despite a large frequency separation band being allocated between the UL and DL bands, a very high degree of isolation is required between the UL and DL signal paths in an FDD wireless communication device to mitigate interference between the UL and DLL bands. Summary of the Invention

[0008] Technical Problem

[0009] Embodiments of the present invention provide a method and apparatus for self-interference cancellation in a communication device.

[0010] Technical Solution

[0011] In one embodiment, a communication device includes: an antenna configured to transmit a transmit signal and receive a receive signal in full-duplex communication; a first Radio Frequency (RF) Analog-to-Digital Converter (RFADC) configured to convert the receive signal from analog to digital; a coupler configured to couple a sample of the transmit signal to a second RFADC, where the second RFADC is configured to convert the sample of the transmit signal from analog to digital; and a self-interference cancellation circuit configured to process the digital samples of the transmit signal to generate a self-interference cancellation signal and apply the self-interference cancellation signal to the digital receive signal to cancel the amount of interference caused by the transmit signal in the receive signal. The RFADC can be replaced by a conventional Receive (RX) path of a Low Noise Amplifier (LNA), a downconverter, an analog baseband filter, and an Analog-to-Digital Converter (ADC).

[0012] In one embodiment, a method for self-interference cancellation includes generating, by a transmit path circuit, a transmit signal to be transmitted via an antenna in a transmit band, and receiving, via the antenna, a receive signal in a receive band. The method further includes converting, by a first RF analog-to-digital converter (RFADC) in a receive path circuit, the receive signal from an analog receive signal to a digital receive signal, converting, by a second RFADC in a coupling path circuit, samples of the transmit signal from analog samples of the transmit signal to digital samples of the transmit signal, processing, by a self-interference cancellation circuit, the digital samples of the transmit signal to generate a self-interference cancellation signal, and applying, by the self-interference cancellation circuit, the self-interference cancellation signal to the digital receive signal to cancel an amount of interference caused by the transmit signal in the receive signal. The RFADC can be replaced with a conventional RX path including an LNA, a downconverter, an analog baseband filter, and an analog-to-digital converter (ADC).

[0013] Those skilled in the art will readily appreciate other technical features from the following drawings, description, and claims.

[0014] Before proceeding with the following detailed description, it is desirable to set forth definitions of certain words and phrases used in this patent document. The term "couple" and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with each other. The terms "transmit," "receive," and "communicate," and their derivatives, include both direct and indirect communication. The terms "include" and "comprise," and their derivatives, mean including but not limited to. The term "or" is inclusive and means and / or. The phrase "associated with," and its derivatives, means including, included within, interconnected with, contained in, contained within, connected to or associated with, coupled to or communicating with, cooperating with, interlacing, juxtaposed, proximate to, bound to or associated with, having, having attributes of, related to or associated therewith, etc. The term "controller" refers to any device, system, or component thereof that controls at least one operation. Such a controller can be implemented in hardware or a combination of hardware and software and / or firmware. The functions associated with any particular controller can be centralized or distributed, whether locally or remotely. When used with a list of items, the phrase "at least" means that different combinations of one or more of the listed items can be used, and it may be necessary to use only one of the items in the list. For example, "at least one of A, B, and C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.

[0015] In addition, the various functions described below can be implemented or supported by one or more computer programs, each of which is formed of computer-readable program code and embodied in a computer-readable medium. The terms "application program" and "program" refer to one or more computer programs, software components, instruction sets, procedures, functions, objects, classes, instances, related data, or portions thereof, adapted to be implemented in appropriate computer-readable program code. The phrase "computer-readable program code" includes any type of computer code, including source code, object code, and executable code. The phrase "computer-readable medium" includes any type of medium that a computer can access, such as read-only memory (ROM), random access memory (RAM), hard disk drive, optical disk (CD), digital video disk (DVD), or any other type of memory. A "non-transitory" computer-readable medium does not include a wired, wireless, optical, or other communication link that transmits transient electrical or other signals. Non-transitory computer-readable media include media that permanently store data and media that store data and then rewrite it, such as rewritable optical disks or erasable storage devices.

[0016] Definitions of other specific words and phrases are provided in this patent document. One of ordinary skill in the art should understand that, in many if not most instances, such definitions apply to the prior and future use of such defined words and phrases. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The patent or application file contains at least one color drawing. Copies of this patent or patent application publication, as well as the color drawings, will be provided by the Patent Office upon request and payment of the necessary fees.

[0018] To more fully understand the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:

[0019] Figure 1 An example wireless system for transmitting signals in accordance with the principles of the present invention is shown;

[0020] Figure 2 An example base station (BS) in accordance with an embodiment of the present invention is shown;

[0021] Figure 3 An example user equipment (UE) in accordance with an embodiment of the present invention is shown;

[0022] Figure 4 A block diagram of an example FDD communication device in accordance with an embodiment of the present invention is shown;

[0023] Figure 5 A block diagram of an example FDD communication device in accordance with an embodiment of the present invention is shown;

[0024] Figure 6A Shows an example set of frequency bands allocated for communication in an FDD system according to an embodiment of the present invention;

[0025] Figure 6B Shows a power spectral density (PSD) graph of a self-interference cancellation (SIC) process according to an embodiment of the present invention;

[0026] Figure 7 Shows a block diagram of an example FDD communication device according to an embodiment of the present invention;

[0027] Figure 8 Shows a block diagram of an example FDD communication device according to an embodiment of the present invention; and

[0028] Figure 9A , Figure 9B , Figure 9C and Figure 9D Shows embodiments of the self-interference cancellation process according to various embodiments of the present invention. DETAILED DESCRIPTION

[0029] The following discussion Figures 1 to 9D and the various embodiments used in this patent document to describe the principles of the present invention are merely illustrative and should not be construed in any way as limiting the scope of the present invention. Those skilled in the art will understand that the principles of the present invention can be implemented in any suitably arranged system or device.

[0030] Embodiments of the present invention recognize that even when a large separation frequency band (usually tens of megahertz or even hundreds of megahertz) is allocated between the UL and DL frequency bands in an FDD system, the FDD duplexer still faces two challenges. First, due to the power amplifier (PA) nonlinearity that causes adjacent channel leakage and due to antenna coupling, the transmitter (TX) leaks into the receiver (RX). If the TX leakage in the RX frequency band cannot be reduced to below the input reference RX noise floor at the input of the RX chain, the TX leakage will reduce the receiver sensitivity, thereby reducing the coverage.

[0031] Second, due to the high noise figure of the digital-to-analog converter (DAC) in the TX chain and the high gain of the TX chain from the DAC output to the PA output, the TX noise floor is also much higher than the RX noise floor. If the TX noise coupled to the RX chain input is not lower than the RX input reference noise floor, it will also reduce the UL receiver sensitivity, thereby further reducing the coverage. The RX input reference noise floor will be referred to as the RX noise floor.

[0032] Embodiments of the present invention recognize that, to solve the above problems, a duplexer with isolation is implemented in an FDD wireless communication device to isolate the UL and DL bands. Through the high isolation in the duplexer, the TX leakage and TX background noise can be reduced to below the RX background noise, thus ensuring the sensitivity of the UL receiver, and the design of the duplexer does not affect TX power transmission, except for introducing insertion loss. However, the isolation requirements to achieve this goal can be very high. For example, in an FDD BS, due to the large gap between the high transmission power of the DL TX band and the low sensitivity level of the UL RX band, a duplexer with an isolation of more than 100 dB may be required. Therefore, due to the provision of more cavity taps to meet the extremely high isolation requirements, the duplexer is costly and has a large volume factor.

[0033] Therefore, embodiments of the present invention provide an active self-interference cancellation (SIC) system in the digital domain to provide active SIC, achieving high system TX-RX isolation and large TX power handling through a low-cost and small-size duplexer. The SIC system provides effective TX-RX isolation by adding the duplexer isolation and the digital-domain isolation generated by SIC processing to calculate the overall system TX-RX isolation. That is, the SIC system reduces the isolation burden on the duplexer, thus allowing the use of a smaller and lower-cost duplexer while achieving the same total TX-RX isolation as a larger and higher-cost duplexer. It can be understood that reducing the isolation burden on the duplexer in an FDD wireless communication device is an application of the SIC system, and the SIC system can be used in other devices for different applications. An example can be that the frequency response of the isolation provided by the duplexer can be reconfigured by turning on SIC and turning off SIC to return to the baseline response.

[0034] Embodiments of the present invention provide an active SIC system by sampling the TX signal at the input of the duplexer, equalizing the sampled TX signal with the RX signal, and subtracting the equalized TX from the RX signal to eliminate the influence of TX leakage and TX background noise caused by the TX signal within the RX signal. Embodiments of the present invention implement the SIC process in the digital domain. Before being input into the SIC process, the sampled TX signal can be preprocessed to reduce the noise introduced into the sampled TX signal after sampling, and the sampled TX can be filtered to improve the dynamic range of the sampled TX and prevent nonlinear and saturation effects during the conversion from the analog domain to the digital domain.

[0035] Embodiments of the present invention also recognize that the disclosed SIC solution can be used as an alternative SIC solution in a cross-divided duplex (XDD) system. XDD enhances the UL coverage of the TDD carrier without sacrificing the DL data throughput. XDD allows the UE to transmit uplink signals while the BS transmits downlink signals simultaneously in the same spectrum within the same TDD band. That is, XDD allows full-duplex communication similar to FDD, but within the TDD band. The uplink of the UE can be arranged with more opportunities in the time domain and frequency domain, so the coverage can be extended compared with the TDD system.

[0036] Embodiments of the present invention use analog-to-digital converters (ADCs) and digital-to-analog converters (DACs). The terms ADC and DAC are sometimes synonymous with direct RF sampling ADC (RFADC) and direct RF sampling DAC (RFDAC), respectively. RFADC and RFDAC do not require additional RF downconversion or RF upconversion. For example, an RFADC can digitize an RF signal input and perform downconversion to the baseband in the digital domain through the RFADC. Similarly, an RFDAC can receive a baseband or intermediate frequency (IF) input, perform upconversion in the digital domain, and output an analog RF signal.

[0037] Figure 1 An example wireless system 100 for transmitting signals according to the principles of the present invention is shown. In the illustrated embodiment, the wireless system 100 includes a transmission point (e.g., evolved Node B (eNB), Node B), such as a base station (BS) 102. The BS 102 can communicate with other base stations and the Internet or a similar IP-based system (not shown).

[0038] The BS 102 provides Internet wireless broadband access to user equipment (UE) 104 (e.g., mobile phone, mobile station, or user station) within the coverage area of the BS 102. The UE 104 can access voice, data, video, video conferencing, and / or other broadband services through the Internet. The UE 104 can be associated with an access point (AP) of a WiFi WLAN. The UE 104 can be any of a plurality of mobile devices, including a wireless-enabled laptop computer, a wireless-enabled personal computer, a personal digital assistant, a notebook, a handheld device, or other wireless-enabled devices. Although Figure 1 only one base station and one user equipment are described, it can be understood that the wireless system 100 can provide wireless broadband access to other user equipment.

[0039] In this embodiment, the wireless system 100 uses frequency-division duplex (FDD) operation, having two separate frequency bands or channels for downlink (DL) and uplink (UL) communications. From the perspective of the BS 102, DL communication is the transmission of signals, and UL communication is the reception of signals. From the perspective of the UE 104, DL communication is the reception of signals, and UL communication is the transmission of signals. A guard band (GB) 110 is allocated between the DL band 106 and the UL band 108 to reduce interference between the DL band 106 and the UL band 108 during operation. The guard band can be several tens of megahertz or several hundreds of megahertz. Despite the guard band, due to the transmission power of the transmission point being significantly higher than the reception power of the reception point, the transmission power still significantly leaks into the reception band.

[0040] Figure 2 An example BS 102 according to an embodiment of the present invention is shown. Figure 2 The embodiment of the BS 102 shown in is for illustration only, Figure 1 and the BS 102 in can have the same or similar configuration. However, there are various configurations of the BS, Figure 2 and the scope of the present invention is not limited to any specific implementation of the BS.

[0041] As Figure 2 shown, the BS 102 includes a plurality of antennas 205a - 205n, a plurality of RF transceivers 210a - 210n, a transmit (TX) processing circuit 215, and a receive (RX) processing circuit 220. The BS 102 also includes a controller / processor 225, a memory 230, and a backhaul or network interface 235.

[0042] The RF transceivers 210a - 210n receive incoming RF signals from the antennas 205a - 205n, such as signals transmitted by the UE 104 or other UEs in the system 100. The RF transceivers 210a - 210n down-convert the incoming RF signals to generate IF or baseband signals. The IF or baseband signals are sent to the RX processing circuit 220, which generates a processed baseband signal by filtering, decoding, and / or digitizing the baseband or intermediate-frequency signal. The RX processing circuit 220 sends the processed baseband signal to the controller / processor 225 for further processing.

[0043] The TX processing circuit 215 receives digital data (such as voice data, network data, e-mail, or interactive video game data) from the controller / processor 225. The TX processing circuit 215 encodes, multiplexes, and / or digitizes the outgoing baseband data to generate a processed baseband or IF signal. The RF transceivers 210a - 210n receive the outgoing processed baseband or IF signal from the TX processing circuit 215 and up-convert the baseband or IF signal to an outgoing RF signal transmitted through the antennas 205a - 205n.

[0044] The RF transceivers 210a - 210n are FDD transceivers, and each transceiver includes a duplexer to facilitate simultaneous reception of incoming RF signals and transmission of outgoing RF signals. The duplexer also provides isolation between the incoming and outgoing RF signals. In some embodiments, the RF transceivers 210a - 210n include an active SIC process operating in the digital domain to further isolate the incoming RF signal from the outgoing RF signal, as described below. In other embodiments, the RX processing circuit 220 includes this active SIC process. The active SIC process can be implemented using dedicated digital domain hardware, such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). In some embodiments, the active SIC process is implemented in the RFIC. The active SIC process can also be implemented in the controller / processor 225.

[0045] The controller / processor 225 may include one or more processors or other processing devices that control the overall operation of the BS 102. For example, the controller / processor 225 can control the RF transceivers 210a - 210n, the RX processing circuit 220, and the TX processing circuit 215 to receive forward channel signals and transmit reverse channel signals according to well-known principles. The controller / processor 225 can also support additional functions, such as more advanced wireless communication functions.

[0046] For example, the controller / processor 225 can support beamforming or directional routing operations, where the outgoing signals from the multiple antennas 205a - 205n are weighted differently to effectively steer the outgoing signals in the desired direction. The controller / processor 225 can support various other functions in the BS 102.

[0047] The controller / processor 225 is also capable of executing programs and other processing residing in the memory 230, such as an operating system (OS). The controller / processor 225 can move data into or out of the memory 230 as needed for performing the processing.

[0048] The controller / processor 225 is also connected to a backhaul or network interface 235. The backhaul or network interface 235 allows the BS 102 to communicate with other devices or systems via a backhaul connection or network. The interface 235 can support communication via any suitable wired or wireless connection. For example, when the BS 102 is implemented as part of a cellular communication system (such as a system supporting 5G, LTE, or LTE-A), the interface 235 can allow the BS 102 to communicate with other BSs via a wired or wireless backhaul connection. When the BS 102 is implemented as an access point, the interface 235 can allow the BS 102 to communicate via a wired or wireless local area network or a wired or wireless connection to a larger network (such as the Internet). The interface 235 includes any suitable structure that supports communication via a wired or wireless connection, such as an Ethernet or RF transceiver.

[0049] The memory 230 is coupled to the controller / processor 225. A portion of the memory 230 may include random access memory (RAM), and another portion of the memory 230 may include flash memory or other read-only memory (ROM).

[0050] Although Figure 2 an example of the BS 102 is shown, Figure 2 there may be different variations. For example, the BS 102 may include Figure 2 any number of each component shown in. As a specific example, an access point may include a number of interfaces 235, and the controller / processor 225 may support routing functions to route data between different network addresses. As another specific example, although shown as including a single instance of the TX processing circuit 215 and a single instance of the RX processing circuit 220, the BS 102 may include multiple instances of each (for example, one for each RF transceiver). Additionally, Figure 2 the various components in can be combined, further subdivided, or omitted, and other components can also be added according to specific needs.

[0051] Figure 3 An example UE 104 according to an embodiment of the present invention is shown. Figure 3 The embodiment of the UE 104 shown is for illustrative purposes only, Figure 1 and the UE 04 can have the same or similar configuration. There are various configurations for the UE, Figure 3 and the scope of the present invention is not limited to any specific implementation of the UE.

[0052] As Figure 3As shown, the UE 104 includes an antenna 305, a radio frequency (RF) transceiver 310, a TX processing circuit 315, a microphone 320, and a receive (RX) processing circuit 325. The UE 104 also includes a speaker 330, a processor 340, an input / output interface (I / O IF) 345, a touch screen 350, a display 355, and a memory 360. The memory 360 includes an OS 361 and one or more applications 362.

[0053] The RF transceiver 310 receives an incoming RF signal transmitted by a BS of the system 100, such as the BS 102, from the antenna 305. The RF transceiver 310 down-converts the incoming RF signal to generate an intermediate frequency (IF) or baseband signal. The IF or baseband signal is sent to the RX processing circuit 325 to generate a processed baseband signal by filtering, decoding, and / or digitizing the baseband or IF signal. The RX processing circuit 325 transmits the processed baseband signal to the speaker 330 (such as for voice data) or the processor 340 for further processing (such as for web browsing data).

[0054] The TX processing circuit 315 receives analog or digital voice data from the microphone 320, or other outgoing baseband data from the processor 340 (such as network data, email, or interactive video game data). The TX processing circuit 315 encodes, multiplexes, and / or digitizes the outgoing baseband data to generate a processed baseband or IF signal. The RF transceiver 310 receives the outgoing processed baseband or IF signal from the TX processing circuit 315 and up-converts the baseband or IF signal to an outgoing RF signal transmitted through the antenna 305.

[0055] The RF transceiver 310 is an FDD transceiver that includes a duplexer to facilitate simultaneous reception of incoming RF signals and transmission of outgoing RF signals. The duplexer also provides isolation between the incoming and outgoing RF signals. In some embodiments, the RF transceiver 310 includes an active SIC process operating in the digital domain to further isolate the incoming RF signal from the outgoing RF signal, as described below. In other embodiments, the RX processing circuit 325 includes the active SIC process. The active SIC process can be implemented using dedicated digital domain hardware, such as an ASIC or FPGA. In some embodiments, the active SIC process is implemented in an RFIC. The active SIC process can also be implemented in the processor 340.

[0056] The processor 340 may include one or more processors or other processing devices and execute the OS 361 stored in the memory 360 to control the overall operation of the UE 104. For example, the processor 340 may control the RF transceiver 310, the RX processing circuit 325, and the TX processing circuit 315 to receive forward channel signals and transmit reverse channel signals according to well-known principles. In some embodiments, the processor 340 includes at least one microprocessor or microcontroller.

[0057] The processor 340 is also capable of executing other processes and programs residing in the memory 360, such as the process for CSI feedback on the uplink channel. The processor 340 may move data into or out of the memory 360 as needed for performing the processes. In some embodiments, the processor 340 is configured to execute the application 362 based on the OS 361 or in response to signals received from the base station or the operator. The processor 340 is also coupled to the I / O interface 345, providing the UE 104 with the ability to connect to other devices, such as laptop computers and handheld computers. The I / O interface 345 is the communication path between these accessories and the processor 340.

[0058] The processor 340 is also coupled to the touch screen 350 and the display 355. The operator of the UE 104 may use the touch screen 350 to input data into the UE 104. The display 355 may be a liquid crystal display, a light-emitting diode display, or other display capable of presenting text and / or at least limited graphics, such as from a website.

[0059] The memory 360 is coupled to the processor 340. A part of the memory 360 may include RAM, and another part of the memory 360 may include flash memory or other ROM.

[0060] Although Figure 3 one example of the UE 104 is shown, Figure 3 various changes may be made. For example, Figure 3 the various components in Figure 3 may be combined, further subdivided, or omitted, and other components may be added according to specific requirements. As a specific example, the processor 340 may be divided into multiple processors, such as one or more central processing units (CPUs) and one or more graphics processing units (GPUs). Additionally, although

[0061] Figure 4FIG. 0 shows a block diagram of an exemplary FDD communication device 400 according to an embodiment of the present invention. For convenience, the FDD communication device 400 is hereinafter discussed as being implemented in an FDD BS, but it will be understood that the communication device 400 may be implemented in an FDD UE. In some embodiments, the FDD communication device 400 may be implemented in Figures 1 - 3 BS 102 or UE 104 of. It will be understood that any number of communication devices 400 may be included in a single BS 102 or UE 104. For example, an FDD BS or UE using a multiple-input multiple-output (MIMO) antenna array may include a communication device 400 for each antenna of the array.

[0062] The FDD communication device 400 includes an antenna 402, a duplexer 404, a SIC process 406, and a coupler 407. The antenna 402 is coupled to the duplexer 044. The duplexer 404 supports FDD communication and facilitates frequency-division duplex transmission and reception via the antenna 402. The duplexer 404 accordingly has a TX port 409 for transmitting the DL TX signal to radiation via the antenna 402 and an RX port 411 for receiving the UL RX signal via the antenna 402. The duplexer 404 provides isolation between the DL TX band and the UL RX band. This isolation of the duplexer 404 reduces TX leakage and TX background noise induced in the UL RX band in the TX circuit.

[0063] The coupler 407 couples a sample of the DL TX signal from the TX port 409 to the SIC process 406. In some embodiments, the sample of the DL TX may be less than 1% of the total power of the DL TX signal. The remaining power of the DL TX signal is transferred to the TX port 409.

[0064] The SIC process 406 provides effective isolation between the DL TX band and the UL RX band, which adds to the isolation provided by the duplexer 404 to provide the total TX-RX isolation of the FDD communication device 400. The SIC process 406 is implemented in the digital domain. Thus, before being input to the SIC process 406, the UL RX signal passes through an RX chain 426, which may include a first direct RF sampling analog-to-digital converter (RFADC) 428 (although for clarity, the RFADC 428 is shown separately from the RX chain 428 here). The signal path from the RX port 411 to the SIC process 406 is herein referred to as the main path, and the signal input to the SIC process 406 from the main path is herein referred to as the main path signal.

[0065] In addition, since the SIC process 406 is implemented in the digital domain, samples of the DL TX signal from the coupler 407 pass through the second RFADC 429 before being input to the SIC process 406. This signal path, from the TX port 409 through the coupler 407 to the SIC process 406, is herein referred to as the coupling path (or the coupled path), and the signal input to the SIC process 406 from the coupling path is herein referred to as the coupling path signal. In this embodiment, since direct RF sampling is used in the RFADCs 428 and 429, additional downconversion is not performed on the samples of the RX signal in the main path or the DL TX signal in the coupling path before being input to the RFADCs 428 and 429 respectively, in order to reduce the frequency range of the DL RX signal.

[0066] In some embodiments, the SIC process equalizes the coupling path signal to the main path signal and then subtracts the equalized signal from the main path signal. Therefore, since the coupling path only contains TX-related signals, including TX leakage and TX background noise in the UL RX band, the output of the SIC process 406 is the SIC residual with the unmodified UL RX signal. The SIC residual corresponds to the spectrogram 422, and the TX leakage and TX background noise are eliminated to a level lower than the RX background noise.

[0067] One embodiment of this process is interpreted as minimizing the error between the coupled signal x[n] and the received signal y[n] in the UL band through the equalizer h, where n is the time index. This can be calculated as a calibration at the factory for the filter:

[0068] h^=argmin h ||h*x[n]-y[n]|| (1)

[0069] The FIR equalizer is calculated as:

[0070]

[0071] Using the least squares (LS) solution:

[0072] h=(X T X+λI) -1 X T y (3)

[0073] where λ is the regularization factor proposed by Tikhonov (see Tikhonov, A. et al., Nonlinear Ill-posed problems, London: Chapman & Hall, ISBN 0412786605, Aug 2018), which is selected to improve the numerical stability of the LS problem.

[0074] In some embodiments, the requirements for the amount of isolation provided by the duplexer 404 can be determined based on the input constraints of the SIC process 406, and the SIC process 406 can be parameterized to provide additional effective isolation sufficient to reduce the TX leakage and TX background noise in the UL RX band below the RX background noise. This ensures that the quality of the UL RX signal is sufficient for RX processing by the RX process 430. Spectrograms 408, 410, and 422 illustrate such embodiments.

[0075] Spectrogram 408 shows the spectrum at the TX port 409, and spectrogram 410 shows the spectrum at the RX port 411. The TX background noise 412a and TX leakage 414a at the TX port 409 are the result of the DL TX signal processing effects in the TX chain 432, which may include the PA 434 (although the PA 434 is shown separately from the TX chain 432 for clarity). Comparing the TX background noise 412a and TX leakage 414a at the TX port 409 with the TX noise ceiling 412b and TX leakage 414b at the RX port 411, at the RX port 4101, the amplitudes of the TX leakage and TX background noise are reduced by a first amount corresponding to the duplexer isolation 416 provided by the duplexer 404. At this point, the TX background noise 412b and TX leakage 414b are still higher than the RX background noise 418, which would degrade the recovery if the UL RX signal 420 were transmitted to the RX process 430.

[0076] Spectrogram 422 shows the spectrum at the output of the SIC process 406. Comparing the TX background noise 412b and TX leakage 414b at the RX port 411 with the TX background noise 412c and TX leakage 414c at the output of the SIC process 406, the amplitudes of the TX leakage and TX background noise are reduced by a second amount at the output of the SIC process 406. This second amount corresponds to the effective SIC isolation 424 provided by the SIC process 406. Comparing the TX background noise 412c and TX leakage 414c at the output of the SIC process 406 with the original TX background noise 412a and TX leakage 414a in spectrogram 408, it can be seen that the total TX - RX isolation provided by the duplexer 404 and the SIC process 406 is the sum of the duplexer isolation 416 and the effective SIC isolation 424. This result is comparable to what could be achieved with a larger, more costly duplexer, equivalent to the sum of the duplexer isolation 416 and the effective SIC isolation 424.

[0077] Although Figure 4 an example of the FDD communication device 400 is shown, Figure 4 there may be various variations. For example, Figure 4 the various components in [[ ]] can be combined, further subdivided, or omitted, and additional components can be added according to specific needs.

[0078] Figure 5 FIG. 3 shows a block diagram of an exemplary FDD communication device 500 according to an embodiment of the present invention. The FDD communication device 500 is Figure 4 an embodiment of the FDD communication device 400 in [reference]. In this embodiment, the FDD communication device 500 operates using direct RF sampling ADCs of RFADCs 428 and 429. That is, no additional down-conversion is performed on the RX signal in the main path or the DL TX signal samples in the coupling path, and the frequency range of the DL RX signal is reduced before being input to the RFADCs 428 and 429, respectively.

[0079] In the main path, the RX chain 426 includes a low-noise amplifier (LNA) 504 and a gain block 506. The UL band-pass filter (BPF) 508 may optionally be included in the design. If the circuit includes the UL BPF 508, it filters out frequencies outside the UL RX band and has a steep transition response to select only the UL RX band from the UL RX signal. This improves the dynamic range of the UL RX signal input to the first RFADC 428 without distorting the UL RX signal. This is very beneficial for improving the signal-to-noise ratio of the coupled signal.

[0080] The coupler 407 couples samples of the DL TX signal into the coupling path as a coupling path signal. The DL TX signal is output by the PA 434 after being generated by the TX process 516 and the TX chain 432. In this embodiment, the TX chain 442 includes an image rejection (IR) filter 518 that filters out the image spectrum in the Nyquist region outside the region of interest from the DL TX signal. The output of the IR filter 518 passes through a gain block 520 that acts as a pre-driver before being input to the PA 434.

[0081] In some embodiments, the coupling path has its own background noise that is independent of the TX background noise and RX background noise in the main path. Due to this independence, when the coupling path signal is equalized with the main path signal in the SIC process 406, the coupling path background noise component is not affected, and attempting to subtract the equalized coupling path signal from the main path signal will result in adding the coupling path background noise to the RX background noise in the main path. The coupling path is designed to minimize the coupling path background noise during equalization-based cancellation.

[0082] To further improve the SNR of the coupled-path signal, before being input to the second RFADC 429, the power level of the coupled-path signal can be amplified to obtain a very high signal power in the target UL RX band. A gain block 512 is included in the coupled path to perform this amplification. However, since the main power component in the coupled-path signal is the DL TX signal component in the DL TX band, amplifying the coupled-path signal to have a high signal power in the target UL RX band will result in an even higher signal power in the DL TX band, which may generate nonlinear products or saturate the second RFADC 429.

[0083] To solve this problem, the DL TX signal samples from the coupler 407 are input to a DL band-stop filter (BSF) 514, also known as a band-rejection filter. The DL BSF 514 filters out the frequencies in the DL TX band from the samples of the DL TX signal before the gain block 512 amplifies it. This also improves the dynamic range of the DL TX signal input to the second RFADC 429.

[0084] At this time, the coupled-path signal input from the second RFADC 429 to the SIC process 406 and the main-path signal input from the first RFADC 428 to the SIC process 406 are mainly controlled by the signal components in the target UL RX band. Therefore, the SIC process 406 is performed only on the target UL RX band, rather than on the entire frequency band of the system. The output of the SIC process 406 is the SIC residual provided to the RX process 430 for further RX processing.

[0085] Although Figure 5 an example of the FDD communication device 500 is shown, Figure 5 there may be various variations. For example, Figure 5 the various components in [[ ]] can be combined, further subdivided, or omitted, and additional components can be added according to specific requirements.

[0086] Figure 6A An example set of frequency bands allocated for communication in an FDD system (such as Figure 1 the wireless system 100 in [[ ]]) according to an embodiment of the present invention is shown. In this example, the system has a 10 MHz UL band 108 centered at 2432 MHz, and two 10 MHz DL bands 106 centered at 2450 MHz and 2460 MHz, respectively. An 8 MHz guard band 110 is allocated between the UL band 108 and the nearest DL band 106.

[0087] It can be understood that Figure 6AIs an example, and other frequency bands can be used with embodiments of the present invention. For example, in the LTE system, the 3rd Generation Partnership Project (3GPP) has allocated many FDD frequency band configurations. These configurations include Band 1, with a UL frequency band of 1920 - 1980 MHz paired with a DL frequency band of 2110 - 2170 MHz, and a guard band of 190 MHz; Band 2, with a UL frequency band of 1850 - 1910 MHz paired with a DL frequency band of 1930 - 1990 MHz, and a guard band of 80 MHz; Band 3, with a UL frequency band of 1710 - 1785 MHz paired with a DL frequency band of 1805 - 1880 MHz, and a guard band of 95 MHz; and Band 4, with a UL frequency band of 1710 - 1755 MHz paired with a DL frequency band of 2110 - 2155 MHz, and a guard band of 400 MHz.

[0088] Figure 6B FIG. 600 shows the power spectral density (PSD) of the SIC process according to an embodiment of the present invention. For example, the PSD diagram 600 can represent the PSD of the signal related to the SIC process 406, as described above with respect to Figures 4 - 5 stated. In this embodiment, the PSD diagram 600 represents the signal PSD generated based on Figure 6A an example set of frequency bands. It can be understood that the PSD diagram 600 is only an example, and the PSD of the signal in the FDD communication device 400 or 500 may vary significantly.

[0089] The PSD diagram 600 includes the coupled path signal PSD 602 at the input of the SIC process 406, the main path signal PSD 604 at the input of the SIC process 406, the equalized signal PSD 406 generated by the SIC process 406, and the SIC residual PSD 608 output by the SIC process 406. In an embodiment corresponding to the embodiment of Figure 5 the SIC processing is only performed on the target UL RX frequency band. Therefore, the frequency components outside the UL RX frequency band are filtered out and not shown in Figure 6B it.

[0090] The coupled path signal PSD 602 is the PSD of the digitized coupled path signal at the output of the second RFADC 429, including the PSD of the TX leakage and TX background noise within the UL RX frequency band, which is related to the TX leakage and TX background noise caused in the main path signal within the UL RX frequency band. The main path signal PSD 604 is the PSD of the digitized main path signal at the output of the first RFADC 428, including the TX leakage and TX background noise caused by the DL TX signal in the main path signal. For the purpose of illustrating the SIC process, there is no UL RX signal in this example.

[0091] The equalized signal PSD 606 represents the result of equalizing the coupled path signal to the main path signal through the SIC process 406. The equalized signal PSC 606 is almost identical to the main path signal PSD 60. That is to say, the equalized signal PST 606 almost exactly matches the PSD of the interference caused by TX leakage and TX background noise in the UL RX band.

[0092] As described above, the equalized signal is subtracted from the main path signal. The PSD of the result of this subtraction is the SIC residual PSD 608. In this example, the RX background noise is -111.5 dBm / 10 kHz, which means that the SIC residual PSD 609 is just the RX background noise PSD, and the effects of TX leakage and TX background noise have been eliminated to a scale far less than the RX background noise.

[0093] In Figure 6A and Figure 6B 's example, the effective TX-RX isolation provided by the SIC process 406 is 28 dB. Therefore, the isolation requirement for the duplexer in this system is reduced by 28 dB. For example, if the TX-RX isolation requirement of the system is 86 dB, a 58 dB duplexer can be combined with the SIC process 406 to achieve a total TX-RX isolation of 86 dB. The isolation requirement for the duplexer is reduced from 86 dB to 58 dB, thus saving cost and hardware size for the system.

[0094] Although Figure 6A and Figure 6B show an example set of frequency bands allocated for communication in an FDD system, and an example PSD diagram of the SIC process, however Figure 6A and Figure 6B various changes may occur. For example, different frequency bands can be allocated, and different signals can be used as the transmitted signal.

[0095] Figure 7 shows a block diagram of an example FDD communication device 700 according to an embodiment of the present invention. The FDD communication device 700 is Figure 4 an embodiment of the FDD communication device 400 in Figure 5 Specifically, the FDD communication device 700 is an improvement of the FDD communication device 500 in Figure 5 In this embodiment, the FDD communication device 700 operates using direct RF sampling ADCs of RFADCs 428 and 429. That is to say, the downconversion is not performed on the DL RX signal samples in the main path or the DL TX signal samples in the coupled path, and the frequency range of the DL RX signal is reduced before being input to the RFADCs 428 and 429 respectively.

[0096] The FDD communication device 700 shares many of the same components as the FDD communication device 500. The FDD communication device 700 also includes a digital predistorter (DPD) 702 and a DAC 704, which are part of the TX chain. The DPD 702 uses feedback from the TX path of the FDD communication device 700, similar to the SIC process 406, but the DPD 701 does not use the same preprocessing as the SIC process 406. Specifically, the DPD 703 operates on the DL TX signal itself, so filtering the coupled path signal to suppress the DL TX band would be problematic. Therefore, the FDD communication device 700 shares the coupled path between the SIC process 406 and the DPD 702, and uses switches 706, 708, and 710 to change the coupled path as needed depending on whether the SIC process 406 or the DPD 701 is in use.

[0097] When the SIC process 406 is in use, switches 706 and 708 route the coupled path through the preprocessing hardware for the SIC process 406. In this embodiment, only the DL suppression filter 514 is used for preprocessing. In other embodiments, the gain block 512 may also be included in this section of the coupled path. Additionally, switch 710 routes the output of the second RFADC 429 to the SIC process 406.

[0098] When the DPD 702 is in use, switches 706 and 708 bypass the preprocessing hardware (e.g., the DL suppression filter 514) for the SIC process 406 and instead feed samples of the DL TX signal directly into the second RFADC 429. Then, switch 710 routes the output of the second RFAD 429 to the DPD 702.

[0099] Since the DPD 702 and the SIC process 406 cannot operate simultaneously, they are able to share the second RFADC 429 to digitize the feedback signals from both processes. Therefore, the FDD communication device 700 can save costs and reduce the size of the FDD communication device.

[0100] Although Figure 7 one example of the FDD communication device 700 is shown, Figure 7 there may be various variations. For example, Figure 7 the various components in

[0101] Figure 8 A block diagram of an example FDD communication device 800 according to an embodiment of the present invention is shown. The FDD communication device 800 is Figure 4 the FDD communication device 400 or Figure 5An embodiment of the FDD communication device 500. In this embodiment, the FDD communication device 800 uses an IF sampling transceiver. That is, before being input into the ADCs 428 and 429 respectively, the DL RX signals in the main path and the coupled path are down-converted. Superheterodyne receivers and IF sampling transceivers are typically deployed in the implementation of FDD base stations. As Figure 8 shown in the embodiment of, the SIC process 406 can also be implemented in these types of traditional transceivers.

[0102] The FDD communication device 800 includes the SIC process 406 and the coupled path components of the FDD communication device 400, as well as the DL rejection filter 514 in the coupled path, as disclosed above with respect to Figure 5 the FDD communication device 500. However, the ADCs 428 and 429 are IF or baseband ADCs, and the DAC 704 is an IF or baseband DAC. Therefore, the FDD communication device 800 also includes an IF to RF up-conversion component 802 and an RF to IF down-conversion component 804.

[0103] The TX-side signal from the DAC 704 is up-converted using the IF to RF up-conversion component 802 before being amplified by the PA 434 to generate the DL TX signal. The coupled path samples of the DL TX signal and the main path UL RX signal on the RX side pass through an independent down-converter and an independent analog IF filter in the RF to IF down-conversion component 804 before being input into the ADCs 428 and 429 respectively. In this embodiment, the mixer in the coupled path of the down-conversion component 804 is driven by the local oscillator (LO) used by the RX main path. In other embodiments, the mixer in the coupled path of the down-conversion component 804 can be driven by the LO in the up-conversion component 802 (used by the TX path) instead of the LO of the RX main path.

[0104] In addition, the operation of the SIC process 406 is as described above. Furthermore, it can be understood that the SIC process 406 can be similarly implemented into a baseband FDD transceiver. For example, the FDD communication device 800 can be modified to perform RF to baseband down-conversion and baseband to RF up-conversion.

[0105] Although Figure 8 shows an example of the FDD communication device 800, Figure 8 there can be various variations. For example, Figure 8 the various components in can be combined, further subdivided, or omitted, and additional components can be added according to specific requirements.

[0106] Figure 9A , Figure 9B , Figure 9C and Figure 9DAn embodiment of a process for self-interference cancellation according to various embodiments of the present disclosure is shown. For example, Figure 9A , Figure 9B , Figure 9C and Figure 9D the processes described in Figures 1 - 3 can be performed by the BS 102 or the UE 104 of Figure 9A Various embodiments of the processes described in Figure 4 , Figure 5 , Figure 7 and Figure 8 can be implemented using the FDD communication devices 400, 500, 700, and 800 of

[0107] The process begins with the transmission path circuit generating a transmission signal to be transmitted through the antenna in the transmission band (step 905). For example, in step 905, a DL TX signal is generated through the antenna of the FDD BS for transmission in the FDD TX band. As described above, the DL TX signal is provided to the duplexer in the transmission path circuit, and the duplexer provides a first amount of isolation between the DL TX band and the UL RX band.

[0108] Next, the process receives a received signal in the receive band via the antenna (step 910). For example, in step 910, the FDD BS antenna receives the UL RX signal in the FDD UL band. In some embodiments, the UL RX signal is received simultaneously with the transmission of the DL TX signal in step 905 (i.e., in full-duplex communication, by separating the TX and RX antennas and providing isolation between the two antennas, duplexer isolation can be replaced. As described above, this may result in TX leakage and TX background noise from the DL TX signal being introduced into the UL RX band, as described above. To reduce the effects of TX leakage and TX background noise, the UL RX signal is provided from the antenna through the duplexer before the process continues to step 915. The duplexer provides a first amount of isolation between the DL TX band and the UL RX band, as described above.

[0109] Then, the process suppresses frequencies outside the receive band from the received signal using a bandpass filter (step 915). For example, in step 915, the UL BPF can filter out frequencies outside the UL RX band from the UL RX signal. This can improve the dynamic range and SNR of the UL RX signal without distorting the UL RX signal for input to the first ADC in the following step 920.

[0110] Next, the process uses a first ADC in the receive path circuit to convert the received signal from an analog received signal to a digital received signal (step 920). In this embodiment, the first ADC is an RFADC and does not require downconversion of the analog received signal before being input to the first ADC. Subsequently, the digital received signal is combined with the output of the SIC cancellation circuit of step 945.

[0111] Steps 925 and 930 occur in an embodiment of a process implemented on a communication device such as Figure 5 an FDD communication device. In these embodiments, the process then uses a band rejection filter in the coupling path circuit to suppress frequencies in the transmit band from the samples of the transmit signal, thereby generating filtered samples of the transmit signal (step 925). For example, the samples of the transmit signal can be signals sampled from the DL TX signal using a coupler, which can introduce a small amount of power (e.g., less than 1% of the total DL TX signal power) into the coupling path circuit. In step 925, the band rejection filter is a DL BSF that filters out frequencies in the DL TX band so as to largely remove the DL TX signal component from the sampled DL TX signal before amplification in step 930. This also improves the dynamic range of the DL TX signal samples before being output to the second ADC in step 935 below.

[0112] In an embodiment corresponding to Figure 5 the process then uses an amplifier in the coupling path circuit to amplify the filtered samples of the transmit signal (step 930). This amplifies the TX leakage and TX background noise components in the UL RX band to reduce the impact of noise in the coupling path circuit. In turn, this improves the SNR of the TX leakage and TX background noise components in the UL RX band, which can be used in the self-interference cancellation process of step 940 below.

[0113] Then, the process uses a second ADC in the coupling path circuit to convert the samples of the transmit signal from analog samples of the transmit signal to digital samples of the transmit signal (step 935). In this embodiment, the second ADC is an RFADC and does not require downconversion of the analog received signal before being input to the second ADC. In embodiments involving steps 925 and 930, the samples of the transmit signal are the filtered samples of the transmit signal, and the digital filtered samples of the transmit signal are generated in step 935. In embodiments not including steps 925 and 930, the samples of the transmit signal are directly coupled from the TX path to the second ADC.

[0114] Next, the SIC circuit processes the digital samples of the transmitted signal to generate a SIC signal (step 940), and the SIC circuit applies the SIC signal to the digital received signal to cancel out the amount of interference caused by the transmitted signal in the received signal (step 945). For example, in step 945, the SIC signal is subtracted from the digital UL RX signal, and the amount of TX leakage and TX background noise interference is cancelled out from the UL RX signal in the UL RX band. The output of the process is the SIC residual, which can be further processed for RX in the FDD BS.

[0115] Figure 9B More details of an embodiment showing the SIC processing of step 940 are shown. In this embodiment, the digital samples of the transmitted signal are equalized to the digital received signal by the SIC circuit (step 941). For example, step 941 includes determining the time-domain equalizer coefficients based on the first channel response of the receive path circuit and the second channel response of the coupling path circuit. Next, the SIC circuit applies the time-domain equalizer coefficients to the digital samples of the transmitted signal to generate a SIC signal (step 942). It should be understood that this is one embodiment of SIC processing, and other types of SIC processing can be used.

[0116] Figure 9C Shows the use of Figure 8 implemented by the FDD communication device 800 Figure 9A More details of an embodiment of the process are shown. The FDD communication device 800 includes an IF sampling transceiver, and thus, Figure 9C the process includes steps related to IF processing. Unless otherwise specified, Figure 9C the process is after Figure 9A the steps of the process.

[0117] Instead of Figure 9A step 915, steps 916 and 917 are performed in Figure 9C the process. In step 916, the process uses a first downconverter to downconvert the analog signal from the RF band to the IF band or the baseband before inputting it to the bandpass filter. The BPF is an IF or baseband BPF.

[0118] In step 917, the IF or baseband BPF suppresses frequencies outside the target downconversion bandwidth from the downconverted analog received signal. For example, steps 916 and 917 prepare the analog UL RX signal for input to Figure 9A the first ADC in step 920 of

[0119] Figure 9C Steps 931 and 932 of the process are performed after Figure 9A step 930 and before step 935 of Figure 9Aas indicated by markers A and B in). Since the FDD communication device 800 can be implemented based on the FDD communication device 400 of Figure 4 or the FDD communication device 500 of Figure 5 , the FDD communication device 800 can be implemented with or without Figure 9A the DL TX band suppression filtering and subsequent amplification in steps 925 and 930. Figure 9C The process.

[0120] The process uses a second downconverter to downconvert the analog samples of the transmitted signal from the RF band to the IF band or baseband (step 931). Then, the process uses a second IF or baseband BPF to suppress frequencies outside the second target downconversion bandwidth from the downconverted analog samples of the transmitted signal (step 932). For example, steps 931 and 932 prepare samples of the DL TX signal for input to the second ADC of Figure 9A step 935. In this embodiment, the second ADC is an IF or baseband ADC.

[0121] Figure 9D shows further details of an embodiment of the process implemented using the FDD communication device 700 of Figure 7 . The FDD communication device 700 includes a digital predistorter (DPD) that shares a coupling path and a second ADC with the SIC process to obtain feedback from the DL TX signal. Therefore, Figure 9A the process includes steps related to connecting the coupling path between the switched SIC process and the DPD. Unless otherwise specified, Figure 9D the process is after the steps of Figure 9D the process. Figure 9A The process of

[0122] Figure 9D starts after step 935 of Figure 9A , as indicated by marker C in Figure 9A . The process receives digital samples of the transmitted signal from the second ADC without the filtering or amplification of steps 925 and 930. For example, as described below, in steps 965 - 975, there is a band suppression filter in step 925 in the communication device, but it is bypassed to obtain digital samples of the transmitted signal.

[0123] The process uses the DPD to generate a predistorted digital transmitted signal based on the digital samples of the transmitted signal (step 950). For example, the DPD is part of the TX chain of the FDD BS and receives the digital DL TX signal from the TX processing section of the FDD BS for predistortion. In step 950, the DPD uses the digital samples of the transmitted signal as feedback for generating the predistorted digital DL TX signal based on the digital DL TX signal. This predistortion prepares the signal for input to the power amplifier (PA) in step 960.

[0124] Then, the process uses a DAC to convert the predistorted digital transmit signal into a predistorted analog transmit signal (step 955). Next, the process uses a PA to amplify the predistorted analog transmit signal to generate a transmit signal (step 960). For example, in step 960, the PA amplifies the predistorted digital DL TX signal to generate a final DL TX signal, which will be input to the duplexer of the FDD BS. This step is similar to Figure 9A step 905 of

[0125] At decision block 961, the process determines whether the coupling path circuit is to be used to route samples of the transmit signal to the DPD or SIC circuit. If samples of the DL TX signal are used for the SIC process, the process continues to step 965b, as described below. If samples of the DL TX signal are used for feedback to the DPD, the process continues to step 965a.

[0126] When it is determined at decision block 961 that samples of the DL TX signal are used for feedback to the DPD, the process bypasses the band rejection filter using the first and second switches such that samples of the transmit signal are directly provided to the second ADC (step 965a). For example, in step 965a, samples of the DL TX signal are to be used as feedback to the DPD in step 950. For proper operation, band rejection filtering used by the applied SIC circuit should not be performed on the DPD input.

[0127] Next, the process connects the second ADC to the DPD using the third switch (step 970a). The process also uses the second ADC to convert samples of the transmit signal from analog samples of the transmit signal to digital samples of the transmit signal (step 975). Then, the DPD can use the digital samples of the DL TX signal as feedback, as discussed in step 950.

[0128] When it is determined at decision block 961 that samples of the DL TX signal are to be used by the SIC circuit, the process connects the band rejection filter in the coupling path using the first and second switches such that samples of the transmit signal are provided to the band rejection filter and the output of the band rejection filter is provided to the second ADC (step 965b). Then, the process connects the second ADC to the SIC circuit using the third switch (step 970b).

[0129] Then, the process continues to Figure 9A step 925 of Figure 9A as marked D in Figure 9D In this way, the process of Figure 9A is able to adjust the coupling path to provide the necessary signals to perform the SIC process included in Figure 9D digital predistortion, if needed.

[0130] The above flowcharts illustrate example methods that can be implemented in accordance with the principles of the present disclosure, and various changes can be made to the methods shown in the flowcharts herein. For example, although shown as a series of steps, the individual steps in each figure may overlap, occur in parallel, occur in a different order, or occur multiple times. In another example, other steps may be omitted or replaced.

[0131] Although the present invention has been described in terms of exemplary embodiments, those skilled in the art can make various changes and modifications. The present invention is intended to cover such changes and modifications that fall within the scope of the appended claims. No description in this application should be construed as implying that any particular element, step, or function is an essential element that must be included within the scope of the claims. The scope of the patent subject matter is defined by the claims.

Claims

1. A method for self-interference cancellation in a communication device, comprising: generating a transmission signal to be transmitted through an antenna in a transmission band by a transmission path circuit; receiving a received signal in a reception band via the antenna; converting the received signal from an analog received signal to a digital received signal by a first analog-to-digital converter (ADC) in a reception path circuit; converting a sample of the transmission signal from an analog sample of the transmission signal to a digital sample of the transmission signal by a second ADC in a coupling path circuit; processing the digital sample of the transmission signal by a self-interference cancellation circuit to generate a self-interference cancellation signal; and applying the self-interference cancellation signal to the digital received signal by the self-interference cancellation circuit to cancel an amount of interference caused by the transmission signal in the received signal, wherein the method further comprises: using a first switch and a second switch to bypass a band rejection filter such that the sample of the transmission signal is provided to the second ADC, wherein the band rejection filter suppresses frequencies in the transmission band from the sample of the transmission signal to generate a filtered sample of the transmission signal; and using a third switch to connect the second ADC to one of the self-interference cancellation circuit or a digital pre-distorter (DPD), wherein the DPD generates a pre-distorted digital transmission signal based on the digital sample of the transmission signal, and wherein converting the sample of the transmission signal from the analog sample of the transmission signal to the digital sample of the transmission signal comprises: converting the sample of the transmission signal from the analog sample of the transmission signal to the digital sample of the transmission signal by the second ADC based on the band rejection filter being bypassed and the second ADC being connected to the DPD.

2. The method according to claim 1, wherein converting the sample of the transmission signal comprises converting the filtered sample of the transmission signal from the analog filtered sample of the transmission signal to the digital filtered sample of the transmission signal by the second ADC.

3. The method according to claim 2, further comprising amplifying the filtered sample of the transmission signal by an amplifier before the conversion.

4. The method according to claim 2, further comprising: converting the pre-distorted digital transmission signal to a pre-distorted analog transmission signal by a digital-to-analog converter (DAC); and amplifying the pre-distorted analog transmission signal by a power amplifier (PA) to generate the transmission signal.

5. The method according to claim 1, further comprising processing the digital sample of the transmission signal by the self-interference cancellation circuit by equalizing the digital sample of the transmission signal to the digital received signal.

6. The method according to claim 5, further comprising: equalizing the digital sample of the transmission signal to the digital received signal by the self-interference cancellation circuit by determining a time-domain equalizer coefficient based on a first channel response of the reception path circuit and a second channel response of the coupling path circuit; and applying the time-domain equalizer coefficient to the digital sample of the transmission signal by the self-interference cancellation circuit to generate the self-interference cancellation signal.

7. The method according to claim 1, further comprising: providing isolation between the receive band and the transmit band by a duplexer operatively connected to the antenna to reduce a second amount of the interference caused by the transmit signal in the receive signal; receiving the transmit signal by the duplexer from the transmit path circuit; and outputting the receive signal by the duplexer to the receive path circuit.

8. The method according to claim 7, wherein the duplexer is operatively connected to the transmit path circuit and the receive path circuit, the method further comprises reducing, by the duplexer, a total amount of power entering the receive path circuit to ensure that the receive path circuit operates within a linear range of the receive path circuit, and wherein, when a non-linear component generated in the receive path circuit is less than the background noise, applying the self-interference cancellation signal to the digital receive signal cancels the interference caused in the receive signal to the background noise.

9. The method according to claim 1, further comprises suppressing frequencies outside the receive band from the analog receive signal by a band-pass filter before inputting to the first ADC.

10. The method according to claim 1, further comprising: based on the receive path circuit being equipped with an intermediate frequency (IF) sampling receiver architecture, down-converting the analog receive signal from a radio frequency (RF) band to an IF band or a baseband by a first down-converter before inputting to the band-pass filter; suppressing frequencies outside a target down-conversion bandwidth from the down-converted analog receive signal by the band-pass filter, wherein the band-pass filter is an IF or a baseband band-pass filter; down-converting analog samples of the transmit signal from the RF band to the IF band or the baseband by a second down-converter; and suppressing frequencies outside a second target down-conversion bandwidth from the down-converted analog samples of the transmit signal by a second IF or baseband band-pass filter before inputting to the second ADC.

11. A communication device, comprising: an antenna configured to receive a receive signal in a receive band and transmit a transmit signal in a transmit band; a transmit path circuit configured to generate the transmit signal, the transmit path circuit including a digital pre-distorter (DPD) configured to generate a pre-distorted digital transmit signal based on digital samples of the transmit signal; a receive path circuit configured to process the receive signal, the receive path circuit including a first analog-to-digital converter (ADC) configured to convert the receive signal from an analog receive signal to a digital receive signal; The coupling path circuit includes a coupler, a band rejection filter, a first switch, a second switch, a third switch, and a second ADC. The coupler is configured to couple a sample of the transmit signal to the band rejection filter, the first switch, and the second ADC. The band rejection filter is configured to output a filtered sample of the transmit signal to the second ADC by suppressing frequencies in the transmit band from the sample of the transmit signal. The first switch and the second switch are configured to allow the band rejection filter to be bypassed such that a sample of the transmit signal is provided to the second ADC. The third switch is configured to switchably connect the output of the second ADC to the self-interference cancellation circuit and the DPD. The second ADC is configured to convert a sample of the transmit signal from an analog sample of the transmit signal to a digital sample of the transmit signal based on the band rejection filter being bypassed and the second ADC being connected to the DPD; and the self-interference cancellation circuit, which is configured to: process the digital sample of the transmit signal output by the second ADC to generate a self-interference cancellation signal, and apply the self-interference cancellation signal to the digital receive signal output by the first ADC to cancel an amount of interference caused by the transmit signal in the receive signal.

12. The communication device according to claim 11, wherein, the second ADC is configured to convert a filtered sample of the transmit signal from an analog filtered sample of the transmit signal to a digital filtered sample of the transmit signal for output to the self-interference cancellation circuit.

13. The communication device according to claim 12, wherein, the coupling path circuit further includes an amplifier configured to amplify a filtered sample of the transmit signal before input to the second ADC.

14. The communication device according to claim 12, wherein, the transmit path circuit further includes a digital-to-analog converter DAC and a power amplifier PA. The DAC is configured to convert the predistorted digital transmit signal to a predistorted analog transmit signal. The PA is configured to amplify the predistorted analog transmit signal to generate the transmit signal.

15. The communication device according to claim 11, wherein, the communication device is configured to perform the method according to any one of claims 5-10.

Images