Node for transmission and reception of radio signals

Abstract

The present invention relates to a node for transmission and reception of radio signals, and more specifically to one with multiple transmission antennas and at least one reception antenna capable of cancelling self-interference, or interference caused in the reception chain(s) by the transmission chains, also reducing the number of electronic components necessary for such cancellation.

Description

[0001] NODE FOR TRANSMISSION AND RECEPTION OF RADIOELECTRIC SIGNALS

[0002] Technical field of the invention

[0003] The present invention is directed to a node for transmitting and receiving radio signals and, more specifically, to one with multiple transmitting antennas and at least one receiving antenna capable of cancelling self-interference, or interference caused in the receiving chain(s) by the transmitting chains, also reducing the number of electronic components necessary for such cancellation.

[0004] Background of the invention

[0005] In the field of telecommunications, and particularly in wireless radio frequency (or simply radio) communications, multiple input-multiple output (MIMO) systems are well-known. These systems allow the capacity of a radio link to be multiplied by using multiple transmitting and receiving antennas to exploit multipath propagation. These systems are present, for example, in devices with some of the most common wireless communication standards: IEEE 802.11 n (Wi-Fi 4), IEEE 802.11 ac (Wi-Fi 5), HSPA+ (3G), WiMAX, and Long Term Evolution (LTE).

[0006] MIMO systems allow more than one data signal to be sent and received simultaneously over the same physical medium, taking advantage of the differences in propagation channels observed between different antennas (e.g., due to multipath effects). They also allow the transmission of multiple data signals sent to different receivers with one or more receiving antennas.

[0007] On the other hand, In-Band Full Duplex (IBFD) technologies allow transmission and reception on the same frequency simultaneously, achieving greater efficiency (measured in bits / s / Hz) in communications (even doubling it compared to non-IBFD technologies) and reducing latency compared to Time-Division Duplex (TDD) systems by eliminating the need to wait for the next transmission interval to transmit what you want to transmit. However, these IBFD technologies, by transmitting and receiving simultaneously on the same frequency, have the main drawback that they can generate self-interference.

[0008] Until now, MIMO systems have not applied IBFD technologies to avoid the problem of self-interference and have been limited to time division duplexing (without using IBFD technology) or directly to frequency division duplexing (FDD), obviously depriving themselves of the improvements that IBFD technologies allow to achieve.

[0009] For this reason, it is more than necessary to find some type of solution that allows combining MIMO systems with IBFD technology in such a way that the advantages of these systems can be combined with those of the technology.

[0010] Description of the invention

[0011] The present invention proposes a solution to the above problems by means of a radio signal transmission and reception node and a radio signal transmission and reception system, as defined below.

[0012] In a first inventive aspect, the invention provides a node for transmitting and receiving radio signals, characterized in that it comprises: at least a first transmission chain and a second transmission chain, configured to transmit a first transmission signal and a second transmission signal, respectively, and at least one reception chain, configured to receive a reception signal, wherein the reception chain also receives at least self-interference signals from the first and second transmission signals, the reception chain comprising a self-interference canceller, which in turn comprises, for each transmission chain: a linear cancellation stage, configured to generate a linear self-interference cancellation signal component from a sample of the corresponding transmission signal, and a non-linear cancellation stage,configured to generate a non-linear self-interference canceling signal component from a sample of the corresponding transmit signal, wherein the canceller is configured to feed the combination of the linear cancelling signal components, converted to radio frequency, to a combiner in the receive chain; and wherein the canceller is configured to feed the combination of the non-linear cancelling signal components to a combiner in the receive chain.

[0013] Throughout this document, a node will be understood as an element of a telecommunications system capable of receiving and / or transmitting signals; in a preferred embodiment, the node is one end of a communications link, for example, a transceiver, and in another embodiment, it is a signal repeater, configured to receive a signal and retransmit it to another node. The terms transmission chain, or simply transmitter, and reception chain, or simply receiver, are understood to mean a set of elements configured to transmit or receive a given signal.

[0014] In a preferred embodiment, a transmission chain comprises one or more signal amplifiers, an antenna, a digital-to-analog converter (DAC), an upconverter block and other auxiliary blocks such as pre-distortion stages, etc.

[0015] In a preferred embodiment, a receiving chain comprises an antenna, one or more combiners, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), a downconverter, a linear cancellation stage, a non-linear cancellation stage, etc.

[0016] A signal sample is a copy of a signal obtained from a chain, in particular a transmission chain, and which is used as a self-interference model or pattern to compare with the received signal in order to cancel the corresponding interference component.

[0017] The components of a given signal are understood to be the constituent parts of that signal that, when superimposed, give rise to that signal; in particular, the components of a transmission signal that, after being modulated, amplified, and emitted, are received by an antenna in the receiving chain, and which are the self-interference signals. Self-interference signals can be broken down into a linear component, primarily due to the result of amplifying the signal, and a non-linear component, due to an unwanted phenomenon in the amplification process itself. The linear component accounts for the majority of the power of the interfering signal.

[0018] A cancellation stage or self-cancellation stage refers to the element or set of elements configured to cancel a component of an interfering signal, particularly a linear component or a non-linear component. A self-interference canceller is an element comprising at least one linear cancellation stage and one non-linear cancellation stage.

[0019] A combiner is understood to mean an element capable of adding or combining two or more signals and, in particular, capable of combining one or more cancellation signal components with a reception signal, or several cancellation signal components with each other.

[0020] In general, it should be understood that the above elements and components can be implemented either by means of separate analog and / or electronic components dedicated to a specific function, or by means of general-purpose integrated processors or reconfigurable logic devices, configured to execute one or more of the above functions, or even as a combination of both configurations.

[0021] Advantageously, the node for transmitting and receiving radio signals makes it possible to transmit at least two transmission signals and to cancel the interference generated by these at least two transmission signals in the signal received by the node in the reception chain; to cancel this self-interference, the node uses the transmission signals as a reference to generate, on the one hand, a linear component of the cancellation signal, and on the other hand, a non-linear component of the cancellation signal; each of these components is superimposed, by means of a combiner, on the reception signal, resulting in the cancellation of the unwanted self-interference signal. Particularly advantageously, the linear and non-linear cancellation signals are combined with the reception signal separately, so as to avoid saturation of the amplifiers, frequency-lowering stages and analog-to-digital converters of the receiver.Furthermore, the configuration object of the present invention allows the number of transmission and / or reception chains to be expanded very easily, as it is a fundamentally modular design. Likewise, the node architecture can be adapted to other frequencies and bandwidths more easily than other known solutions, in many cases without modifications to the hardware. Specifically, the Stanford architectures (see Balatsoukas-Stimming, A., Austin, A.C., Belanovic, P. et al. “Baseband and RF hardware impairments in full-duplex wireless systems: experimental characterisation and suppression”, J Wireless Com Network 2015, 142 (2015), http: / / www.wirelesscom.org / en / library / 201501001000 / baseband-and-rf-hardware-impairments-in-full-duplex-wireless-systems / ), support reduced bandwidths compared to the proposed architecture, and in general, when the working band changes, they require a redesign of the cancellation stages.Classic Rice architectures are generally more flexible than Stanford architectures in terms of operating frequency, but significant changes in signal bandwidth would still require a hardware redesign. In contrast, the architecture of the node object of the present invention would only require the construction of new hardware if the operating frequencies exceeded the sampling rate of the system's analog-to-digital and digital-to-analog converters. However, current technologies make it possible to build converters with a bandwidth of several GHz, which covers a large number of bands and frequencies used in practice. Thus, if the proposed in-band full duplex (IBFD) mode system is desired to be used at other frequencies or with higher-bandwidth signals, the corresponding architecture could use the same hardware, simply by reconfiguring the firmware of the digital signal processing device.This is possible even if the operating frequency and / or bandwidth vary by several orders of magnitude.

[0022] In a particular embodiment, the linear cancellation stage, the non-linear cancellation stage, or both, comprise a filter bank whose response is defined by a set of coefficients.

[0023] In this document, the coefficients of the coefficient set will be understood as a set of values ​​or adjustment parameters that allow a given frequency response to be obtained in a signal filter; depending on the specific implementations, the coefficients will be understood as consisting of design parameters of a physical filter, in the embodiment in which such filters are used, or variables of a software program or reconfigurable logic device configured to reproduce the claimed function in those embodiments that include a filter digitally implemented by software. Advantageously, the coefficients define the behavior of the filter and can be adjusted to obtain a particular result.

[0024] In a particular embodiment, the linear cancellation stage, the non-linear cancellation stage, or both, comprise a coefficient calculation block configured to generate coefficients for the filter bank.

[0025] Advantageously, the filter coefficients can preferably be modified dynamically based on the error signal obtained by comparing the signal obtained by cancelling the self-interferences with a reference signal, such that a closed control loop is implemented for the cancellation.

[0026] In a particular embodiment, the coefficient calculation block is configured to implement a least squares algorithm such as: Filtered-X Least Mean Square, Recursive Least Square, Normalized Least Mean Square.

[0027] Advantageously, the coefficients are associated with functions or algorithms that model the desired behavior, allowing the power of the error signal obtained to be minimized. Furthermore, the adaptive algorithms used to achieve self-interference cancellation at the node are transparent to the transmitted signal; that is, no specific characteristics are required in the transmitted waveform. Thus, the cancellation system would be applicable to multiple use cases, including communications systems such as communications modems and communications relays, as well as outside of communications systems, where self-interference also occurs, as in the case of intelligent jammers or radars, or spectral sensing systems with simultaneous transmission of communications signals (Integrated Sensing and Communication - ISAC).

[0028] In a particular embodiment, the linear cancellation stage is fed by a sample of the baseband reception signal, taken after the corresponding combiner, for the calculation of coefficients.

[0029] Advantageously, the baseband reception signal is fed to the block to calculate the coefficients and thus perform the generation of the linear cancellation component in a convenient and effective manner.

[0030] In a particular embodiment, the linear cancellation stage comprises a phase correction block.

[0031] Advantageously, the phase correction block makes it possible to compensate for any phase shifts that may occur between the generation of the cancellation signal and its combination with the received signal, ensuring system stability.

[0032] In a particular embodiment, the non-linear cancellation stage is fed by a sample of the baseband reception signal, after the combiner, for the calculation of coefficients.

[0033] Advantageously, the receiving signal after the combiner is free of both self-interference signal components and contains only the receiving signal as it was emitted at the output of the transmitter that generated it; this interference-free receiving signal is used as a reference for calculating the coefficients that generate the nonlinear component of the cancellation signal.

[0034] In a particular embodiment, the non-linear cancellation stage comprises a non-linear component generation block, configured to model the transfer function of the elements of a transmission chain together with the self-interference channel response.

[0035] Advantageously, the non-linear component generation block allows the coefficients to be adjusted so that their response matches the behavior of one or more elements in the transmission chain that alter the transmission signal and contribute to self-interference.

[0036] In a particular embodiment, the non-linear component generation block is configured to implement a polynomial non-linearity model.

[0037] Advantageously, the non-polynomial linearity model is a non-linear model, which is used to model the non-linear response of certain components, particularly those components that generate non-linear self-interference, such as digital-to-analog converters, frequency-raising blocks and power amplifiers.

[0038] In a particular embodiment, the node further comprises additional transmission chains and / or reception chains.

[0039] Advantageously, the node can be expanded with as many transmission chains or reception chains as desired, depending on the needs or requirements of the telecommunications system.

[0040] In a particular embodiment, the transmission chains comprise frequency uplink blocks, digital-to-analog converters, power amplifiers and antennas.

[0041] Advantageously, frequency-raising units, or upconverters, allow a signal's frequency to be adjusted and, in particular, increased in a controlled manner, for example, to adapt it to the desired transmission frequency; digital-to-analog converters allow a digital signal modulated according to a message to be transmitted to be transformed into an equivalent analog signal; power amplifiers allow the power of a radio frequency signal to be amplified prior to its transmission through the antenna.

[0042] In a particular embodiment, the at least one reception chain comprises a frequency downlink block, an analog-to-digital converter and an antenna.

[0043] Advantageously, frequency-lowering units, or downconverters, allow a signal's frequency to be adjusted and, in particular, lowered in a controlled manner, for example, to convert it from a reception frequency to a frequency suitable for processing by a demodulator; analog-to-digital converters allow an analog signal to be transformed into a digital signal that preserves the received information; and antennas allow radio frequency signals to be captured.

[0044] In a second inventive aspect, the invention provides a system for transmitting and receiving radio signals, comprising at least two nodes according to any of the preceding claims.

[0045] Advantageously, an assembly with more than one node such as that of the first inventive aspect allows implementing a MIMO communications system, with an improved reception signal thanks to the cancellation of self-interference.

[0046] These and other features and advantages of the invention will become apparent from the description of the preferred, but not exclusive, embodiments, which are illustrated by way of non-limiting example in the accompanying drawings.

[0047] Brief description of the drawings

[0048] Figure 1 This figure shows an example of the implementation of the radio signal transmission and reception node with two transmission branches and one reception branch.

[0049] Figure 2 This figure shows another example of the implementation of the radio signal transmission and reception node with a number n of transmission branches and m reception branches.

[0050] Detailed description of an embodiment

[0051] In the following detailed description, numerous specific details are presented in the form of examples to provide a thorough understanding of the relevant teachings. However, it will be apparent to those skilled in the art that the present teachings can be implemented without such details.

[0052] Figure 1 shows a preferred embodiment of a multi-antenna node, representing a case with two transmitters (Tx1, Tx2) and one receiver (Rx1). In other embodiments, the node could include any number of transmitting and receiving antennas, provided there are at least two transmitters and one receiver; an example of this configuration, with n transmitters and m receivers, is shown in Figure 2.

[0053] The simplest example is shown in Figure 1, comprising two transmitters (Tx1 , Tx2), each emitting a different signal through its antenna, and a receiver Rx1 ). In general, each transmitting antenna generates a self-interference component towards each existing receiver, which must be adequately cancelled to achieve an IBFD system; more specifically, in the described example, each of the two transmitting antennas generates a self-interference component on the receiving antenna. This principle can be extended both by increasing the number of transmitting antennas (in which case each receiving antenna would receive as many self-interference components as there are transmitting antennas) and by increasing the number of receivers (in which case, each additional receiver would receive a self-interference component from each transmitting antenna), as shown in Figure 2.

[0054] In the example shown in Figure 1 , the transmission chains (Tx1 , Tx2) are identical, and comprise an upconverter (UC), a digital-to-analog (D / A) converter, a power amplifier (PA), and an antenna. The reception chain (Rx1 ) comprises an antenna, an analog-to-digital (A / D) converter, a downconverter (DC), and two combiners (S), one arranged between the antenna and the analog-to-digital (A / D) converter, and another arranged at the output of the downconverter (DC); the function of these combiners (S) is to combine the reception signal with the linear or non-linear component of the cancellation signal, as appropriate.

[0055] The described node allows the components of each self-interference signal received by the receiver (Rx1 ) to be cancelled separately; for this purpose, two cancellation components, linear and non-linear, are calculated separately, necessary to eliminate the self-interference signal generated by each of the two transmitters (Tx1 , Tx2). In the receiver (Rx1 ), the cancellation components generated separately are combined into a single signal, which is then added to the received signal in one of the combiners (S).

[0056] These components are generated in the self-interference canceller, which comprises a linear cancellation (CL) stage and a non-linear cancellation (CN) stage for each transmission chain (Tx1, Tx2). As shown in Figure 1, each linear cancellation (CL) stage and each non-linear cancellation (CN) stage is fed by a sample of the transmission signal from one of the transmission chains (Tx1, Tx2) before passing through the upconverter (UC).

[0057] The linear cancellation (CL) stages sum the generated cancellation signals and feed them to an upconverter (UC) and a digital-to-analog (D / A) converter to convert them to radio frequency before feeding them to the reception chain (Rx1 ) by means of a combiner (S) arranged between the antenna and the analog-to-digital (A / D) converter. The non-linear cancellation (CN) stages sum the generated cancellation signals and feed them to the received signal in the reception chain (Rx1 ), by means of a combiner (S) arranged at the output of the downconverter (DC); the resulting signal after combining the two signals is fed to the two non-linear cancellation (CN) stages to implement a closed control loop and facilitate the calculation of the coefficients.

[0058] In the example described, each linear canceller, or linear cancellation (CL) stage, includes a finite impulse response (FIR) filter whose coefficients are adaptively calculated based on the transmitted signal and the degree of self-interference observed in the cancellation result. The filter takes the transmitted signal and modifies it so that it resembles the self-interference received by the receiver (Rx1) as much as possible, so that the desired cancellation is then achieved in an analog signal combiner (S). Prior to a coefficient adaptation block, a phase correction block is included on the received signal to correct hardware imperfections.

[0059] Coefficient adaptation algorithms can be based on one or more mathematical models, for example, filtered-X LMS, Recursive Least Square (RLS) or Normalized LMS (NLMS).

[0060] The nonlinear cancellation (NC) stage consists of three parts: a first block that applies a nonlinear transformation to the transmitted signal to generate a series of nonlinear components; a set of FIR filters that process these components and generate a cancellation signal; and a coefficient matching block that recalculates the coefficients of these filters from a sample of the received signal. The NC stage is based on a polynomial model of the power amplifier (PA), according to which its nonlinear components are generated from a memory polynomial transfer function (memory polynomial model).The order of the implemented polynomial model will depend on the power amplifier (PA) used: if an amplifier with relatively linear behavior is chosen, a low order should be sufficient to cancel self-interference, while if the device has a more marked nonlinear character, a higher order should be used in the canceller. Furthermore, each of the coefficient calculation blocks can apply, for example, the previously mentioned LMS, RLS, or NLMS algorithms to perform coefficient adaptation of the FIR filters. Finally, the signal generated by the filters is combined into a single cancellation signal, which is then added to the received signal already processed by the linear cancellation (CL) stage through a combiner (S).

[0061] In the proposed example, all digital blocks can be implemented on a single integrated circuit, or chip. Consequently, the transmitting and receiving node can be implemented as a compact and simple hardware element, eliminating the need to design custom radio frequency components, as is the case, for example, with analog cancellers in Stanford architectures. Furthermore, this implementation allows the system to occupy a smaller area and weight, as well as resulting in lower power consumption. Specifically, if the chip integrates analog-to-digital converters and digital-to-analog converters, since analog elements are not required to implement the upconverters and downconverters, the transmitted and received signals are less affected by imperfections in these types of components, such as intermodulation, oscillator leakage, the presence of spurious components, or I / Q balance problems.

[0062] The transmitting and receiving node of the example described above, and shown in Figure 1 , can be extended with additional transmit and receive chains, as many as are practical or advantageous. An example of a generic node with n transmit chains (Tx1 ,...,Txn) and m receive chains (Rx1 ,..., Rxm) is shown in Figure 2. The constituent elements are analogous to those described in the previous example, and only their number changes. In Figure 2, two chains are represented on the transmitter and receiver sides, plus a generic one (Txn, Rxm) which represents, in dashed lines, a generic number of transmit chains.

[0063] The proposed multi-antenna cancellation architecture requires a single analog combiner per receiver. This combiner applies a linear cancellation signal that eliminates the linear self-interference components of all transmitters in the system. This is in particular contrast to Stanford architectures, where eliminating each self-interference component would require a dedicated analog cancellation block. Therefore, if a Stanford system includes N transmitters and M receivers, it would typically incorporate a total of NxM cancellation blocks, while the proposed architecture solves the problem with M analog combiners. Consequently, the proposed system is more scalable depending on the number of antennas used.This is especially attractive in current communications systems, as a significant number of antennas can now be used; for example, in 5G systems, up to 8 transmitting antennas and 8 receiving antennas can be used, and in fact, Radio Frequency System-on-Chip (RFSoC) devices incorporate up to 16 A / D and D / A converters.

Claims

CLAIMS 1. A node for transmitting and receiving radio signals, characterized in that it comprises: at least a first transmission chain (Tx1) and a second transmission chain (Tx2), configured to transmit a first transmission signal and a second transmission signal, respectively, and at least one reception chain (Rx1), configured to receive a reception signal, wherein the reception chain (Rx1) also receives at least self-interference signals from the first and second transmission signals, the reception chain (Rx1) comprising a self-interference canceller, which in turn comprises, for each transmission chain (Tx1, Tx2): a linear cancellation stage (CL), configured to generate a linear self-interference cancellation signal component from a sample of the corresponding transmission signal, and a non-linear cancellation stage (CN),configured to generate a non-linear self-interference canceling signal component from a sample of the corresponding transmit signal, wherein the canceller is configured to feed the combination of the linear cancelling signal components, converted to radio frequency, to a combiner (S) of the receive chain; and wherein the canceller is configured to feed the combination of the non-linear cancelling signal components to a combiner (S) of the receive chain.

2. Node according to the preceding claim, wherein the linear cancellation stage (CL), the non-linear cancellation stage (CN), or both, comprise a filter bank whose response is defined by a set of coefficients.

3. Node according to the preceding claim, wherein the linear cancellation stage (CL), the non-linear cancellation stage (CN), or both, comprise a coefficient calculation block configured to generate coefficients for the filter bank.

4. Node according to the preceding claim, wherein the coefficient calculation block is configured to implement an algorithm among: Filtered-X Least Mean Square, Recursive Least Square, Normalized Least Mean Square.

5. Node according to any of claims 2-4, wherein the linear cancellation stage (CL) is fed by a sample of the baseband reception signal, before the combiner (S), for the calculation of coefficients.

6. Node according to any of the preceding claims, wherein the linear cancellation (CL) stage comprises a phase correction block.

7. Node according to any of claims 2-6, wherein the non-linear cancellation (CN) stage is fed by a sample of the baseband reception signal, after the combiner, for the calculation of coefficients.

8. Node according to any of the preceding claims, wherein the non-linear cancellation (CN) stage comprises a non-linear component generation block, configured to model the transfer function of the elements of a transmission chain together with the response of the self-interference channel.

9. Node according to the preceding claim, wherein the non-linear component generation block is configured to implement a polynomial non-linearity model.

10. Node according to any of the preceding claims, further comprising additional transmission chains (Txn) and / or reception chains (Rxm).

11. Node according to any of the preceding claims, wherein the transmission chains (Tx1, Tx2) comprise frequency uplink blocks (UC), digital-to-analog converters (D / A), power amplifiers (PA) and antennas.

12. Node according to any of the preceding claims, wherein the at least one reception chain (Rx1) comprises a frequency downlink block (DC), an analog-to-digital converter (A / D) and an antenna.

13. System for transmitting and receiving radioelectric signals, comprising at least two nodes according to any of the preceding claims.

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