Electronically controllable reflector and system

Abstract

An electronically controllable reflector (RIS) comprising at least one reflector element (RE), each reflector element having: at least one first antenna element (AE-RX) configured to receive a receive signal (DS-TX) as an input signal (S-RX) with a first polarization (POL1); and an amplifier device (AMP, UNI-AMP, Bi-AMP) configured to electronically amplify the input signal (S-RX) and output as an output signal (S-TX); and at least one second antenna element (AE-TX) configured to transmit the output signal (S-TX) as a transmission signal (DS-RX) at a second polarization (POL2); and a control device (CRTL) configured to control the amplitude and / or phase of the output signal (S-TX) with an electronic control device to form a controllable antenna characteristic of the reflector, and the second polarization (POL2) is different from the first polarization (POL1).

Description

[0001] Regardless of the grammatical gender of a particular term, it includes both male and female. Technical Field

[0002] The present invention relates to an electronically controllable reflector and a system having an electronically controllable reflector. Background Technology

[0003] Electronically controlled reflectors (RIS) can improve radio communication at higher frequencies (e.g., above 20 GHz) and in situations where there are obstacles between the transmitter and receiver. RIS typically consists of multiple antenna elements, which are usually identical in size and geometry. These antenna elements are arranged geometrically on the surface of a carrier, often following specific rules. For example, circular antenna elements may be arranged in a hexagonal pattern with a spacing of, for example, 0.8 wavelengths.

[0004] Antenna elements receive the incident power wave from the transmitter at a specific gain according to their respective antenna characteristics. This energy is reflected and its amplitude and / or phase is altered using electronics within the elements. The manipulation of the electronics in each element is selected such that the sum of the individual reflections of the antenna elements is constructively superimposed at the receiver.

[0005] By using electronically controlled reflectors, communication between the transmitter and receiver can be ensured even when the connection is obstructed ("non-line of sight"). The coverage area of ​​the radio communication is determined, for example, by level planning, which is the sum of power losses from transmitter to receiver, taking into account transmit power, receiver sensitivity, and noise power. The reflection losses of the electronically controlled reflectors are also considered in the level planning. Summary of the Invention

[0006] The technical objective of this invention is to keep the reflection loss of the electronically controllable reflector as small as possible, and to achieve reflection gain where possible.

[0007] In the existing technology, there are several technical possibilities to keep the loss of electronically controlled reflectors low and increase the reflector's reflection gain: • Use a large RIS surface with many individual antenna elements. • Use individual antenna elements with high efficiency, such as antenna elements with low ohmic loss and high antenna gain. • Control electronics using individual antenna elements with low reflection loss or even amplification. • Collaborate to optimize the control settings of individual antenna elements to achieve optimal field strength superposition of reflections from individual antenna elements at the receiver's location.

[0008] The problem is that all of these points are subject to limitations and constraints, thus requiring further improvements.

[0009] In existing systems, there is a potential tendency for self-oscillation due to amplification in the RIS-controlled electronic devices. To date, this amplification has typically had to be reduced to a level where the oscillation tendency no longer exists. As a result, while losses in the RIS are thus compensated, only very small amplification can be selected otherwise.

[0010] This results in limitations, such as transmit-receive isolation, which represents the ratio between the signal injected into the radiating element and the signal reflected back from the radiating element. In this context, radiating elements are also equipped with directional couplers, isolators, etc.

[0011] Furthermore, inter-component isolation is also limited; inter-component isolation refers to isolation from adjacent RIS antenna components.

[0012] Achievable isolation is low and highly dependent on the immediate environment. Especially at frequencies above 20 GHz in the millimeter wave range, manufacturing tolerances and component tolerances also have a significant impact on isolation.

[0013] Therefore, the objective of this invention is to overcome the shortcomings of the prior art through a simple and efficient solution.

[0014] This task is solved by an electronically controllable reflector, which includes at least one reflector element, wherein each reflector element comprises: • At least one first antenna element, configured to receive a first polarized signal as an input signal, and • An amplifier device configured to electronically amplify an input signal and output it as an output signal, and • At least one second antenna element configured to transmit the output signal as a transmit signal with a second polarization. • The second polarization differs from the first polarization, and • A control device configured to use electronic control to control the amplitude and / or phase of an output signal to form controllable antenna characteristics of a reflector, and the control device is further configured to receive a provided polarization control signal. • The amplifier device includes a bidirectional signal amplifier with two settable amplification directions, the bidirectional signal amplifier being configured to set the effective amplification direction of the bidirectional signal amplifier according to a polarization control signal.

[0015] This allows for significantly higher isolation, which in turn significantly improves amplification in RIS components compared to existing technologies.

[0016] The second polarization is preferably orthogonal to the first polarization; that is, in the case of linear polarization, it is preferably rotated by 90°, or in the case of circular polarization, it is rotated in a different direction, for example, the first polarization is left-handed and the second polarization is right-handed, or vice versa. This advantageously decouples the input and output channels of the antenna element.

[0017] As long as the amplification is less than the isolation level, RIS can achieve stable operation, i.e., oscillatory operation. This applies to both transmit-receive isolation and inter-component isolation.

[0018] The amplifier device includes a bidirectional signal amplifier, which can amplify the signal back to the receiving direction or the transmitting direction.

[0019] The transmitted and received signals have different polarizations. However, in the context of this invention, it is clear that signal polarization can also be undesirably affected by various effects during signal transmission, such as reflections. These undesirable effects are not considered separately in the context of this invention, and the aforementioned polarization difference between the two signals does not apply to the features according to the invention, in which the signal with the second polarization differs from the signal with the first polarization.

[0020] Therefore, by using a bidirectional amplifier switched by a control signal, polarization can be easily adapted when the transmission direction is reversed (i.e., when switching from receiver to transmitter mode) by having the corresponding transmitter indicate to the reflector with a control signal which polarization to transmit in. This keeps the system complexity simple and enables bidirectional communication to be performed in a simple and efficient manner with alternating polarization via the reflector.

[0021] The RIS can also be configured to form antenna characteristics that minimize the attenuation of radio signals between the transmitter, reflector, and receiver. This can be achieved by selectively choosing individual antenna elements and manipulating their amplitude and / or phase accordingly.

[0022] Electronically controllable reflectors can have a large number of reflector elements, such as 10, 50, 100 or more.

[0023] Antenna elements can be implemented in different arrangements.

[0024] For example, antenna elements for receiving and antenna elements for transmitting can be arranged alternately to form a reflector.

[0025] Alternatively, for example, two reflectors can be arranged side by side. One reflector uses its antenna element as a receiver with a first polarization, while the other reflector acts as a transmitter with a second polarization, or, in the case of linear polarization, the other reflector can be mounted with its antenna element rotated 90° relative to the receiver.

[0026] This solution enables high amplification while maintaining stable operation, thereby avoiding amplifier oscillation.

[0027] Furthermore, the number of antenna elements can be reduced while achieving the same reflector effect. For example, a 3 dB amplification can halve the number of required elements, or halve the area required for the RIS.

[0028] Because of the reduced number of required components, the beamwidth of the RIS beamwidth oriented toward the receiver increases. Therefore, less precise "aiming" is needed, or movement in the scene has less impact, and fewer iterations are required to locate radio participants (e.g., by scanning at two spatial angles), resulting in faster completion.

[0029] In addition, this solution is also beneficial for energy consumption optimization.

[0030] Electronic control devices for controlling the amplitude and / or phase of signals are known in the prior art, such as electronic phase shifters, voltage dividers, or electronic amplifiers in digital or analog form, wherein, for example, in a digital phase shifter, two or more states can be controlled.

[0031] In an improved embodiment of the invention, the reflector is configured to operate at an operating frequency of at least 20 GHz.

[0032] Especially when the RIS operates at a frequency exceeding 20 GHz, a sufficient number of antenna elements can be implemented.

[0033] In an improved embodiment of the invention, it is proposed that at least one first antenna element and at least one second antenna element are constituted by a common antenna structure.

[0034] When using a bidirectional amplifier instead of a unidirectional amplifier in alternating RIS elements, timing control allows the RIS to receive and reflect horizontally and vertically at one time, and receive and reflect with the opposite polarization at another time. The advantage here is that if the RIS knows which polarity is currently arriving as the input signal, additional elements configured accordingly in that polarity can also contribute to amplification.

[0035] From the perspective of the radio system, it can be seen that there is no significant difference in the channel characteristics between the uplink and downlink. There are no restrictions on the radio system used.

[0036] Furthermore, from a radio system perspective, using a specific polarization is advantageous because simple terminal equipment typically only supports one polarization, or there are environmental conditions that favor or weaken a particular polarization. Therefore, bidirectional amplified RIS enables the use of their respective optimal connections.

[0037] Another extension is provided by a control electronics device that can operate purely passively on the one hand, and amplified (unidirectional and / or bidirectional) on the other.

[0038] The advantage of this solution is that it allows users to choose whether amplification is needed, thus requiring more power, or not. RIS can be set up and operated with energy optimization while maintaining sufficient performance. This feature is particularly important for high-availability applications (i.e., 24 / 7 / 365 operation).

[0039] Therefore, the reflector can be pre-set to a preferred polarization plane, thereby reducing reception loss.

[0040] Electronic devices for setting polarization are known in the prior art, such as using separate feed points on the corresponding antenna (e.g., patch antenna) or using orthogonally arranged dipole antennas.

[0041] This task is solved by a system comprising: a radio transmitter for transmitting a data transmission signal, the radio transmitter having electronic means for controlling the polarization of the data signal; an electronically controllable reflector for reflecting the data transmission signal according to any one of the preceding claims; a radio receiver for receiving the reflected data signal; and a system control device connected to the radio transmitter via a communication device, wherein the radio transmitter is configured to set a predetermined polarization using its electronic means and to transmit information about this polarization to the system control device via the communication device, and the system control device is configured to set the polarization on the reflector by means of the corresponding electronic means for setting the polarization when receiving the data signal.

[0042] Therefore, the reflector can be pre-set to a preferred polarization, thereby reducing reception loss.

[0043] In an improved embodiment of the invention, the system is proposed to include a first radio transmitter and a second radio transmitter according to the invention, and a first radio receiver and a second radio receiver according to the invention, wherein the first radio transmitter and the first radio receiver constitute a first transceiver, the second radio transmitter and the second radio receiver constitute a second transceiver, and a controllable reflector according to the invention is configured to connect the first transceiver and the second transceiver via a radio connection through the reflector, and the first radio transmitter is configured to transmit a first data signal with a first polarization at a first moment, and the second radio transmitter is configured to transmit a second data signal with a second polarization different from the first polarization at a subsequent second moment.

[0044] The reflector can be configured such that the first transceiver transmits and receives in a first polarization, while the second transceiver transmits and receives in a second polarization.

[0045] Therefore, when extending a radio system via RIS, there is no need to change or adapt the existing transmission technology between transceivers. They can continue to use the same antennas for transmitting and receiving, and thus also use the same polarization.

[0046] In an improved embodiment of the invention, a transmitter is configured to transmit polarization information about a first polarization to a controllable reflector according to the invention, and the reflector is configured to receive the polarization information and set the amplification direction of a bidirectional signal amplifier such that the amplification direction corresponds to the first polarization.

[0047] Therefore, by using a bidirectional signal amplifier, polarization can be adapted in a simple way based on the polarization of the signal transmitted by the transmitter.

[0048] In other words, this achieves the transformation of the transmit path in the combined antenna into the receive path of the combined antenna, and the transformation of the receive path into the transmit path of the combined antenna.

[0049] For a combined antenna, a first polarization direction is set for a switchable transmit / receive path, and a second polarization direction is set for a second switchable transmit / receive path, wherein the first polarization direction and the second polarization direction are different, and preferably the first polarization direction and the second polarization direction are orthogonal to each other.

[0050] This statement, as an improvement to the present invention, can also be understood as an independent system, independent of the system description described above. Attached Figure Description

[0051] The present invention will now be explained in more detail with reference to the embodiments shown in the accompanying drawings. In the drawings: Figure 1 A schematic diagram of an electronically controllable reflector is shown. Figure 2 A block diagram of an electronically controllable reflector is shown. Figure 3 A schematic diagram of a prior art antenna element is shown. Figure 4 An embodiment of an antenna element with an inserted unidirectional amplifier and two antenna terminals for different polarizations is shown. Figure 5 An embodiment with two antenna elements is shown, each with an inserted unidirectional amplifier and two antenna terminals for different polarizations. Figure 6 An embodiment of an antenna element with an inserted bidirectional amplifier and two antenna terminals for different polarizations is shown. Detailed Implementation

[0052] Figure 1 An example of an electronically controllable reflector RIS is schematically shown, which has a large number of circular antenna elements AE arranged on a planar circuit carrier with a hexagonal profile.

[0053] Figure 2 A block diagram of an electronically controllable reflector (RIS) and a radio communication system is shown.

[0054] The electronically controllable reflector RIS comprises a large number of reflector elements RE, each of which includes a receiving antenna element AE-RX and a transmitting antenna element AE-TX. The reflector RIS may include a large number of reflector elements RE.

[0055] Each reflector element RE has a first antenna element AE-RX, which is configured to receive the signal DS-TX transmitted by the transmitter TX as the input signal S-RX with the first polarization POL1 as the receive signal.

[0056] In addition, an amplifier device AMP is provided, which is configured to electronically amplify the input signal S-RX and output it as the output signal S-TX to the transmitting antenna element AE-TX.

[0057] Each reflector element RE has a second antenna element AE-TX, which is configured to send the output signal S-TX as a transmit signal DS-RX to the receiver RX with the second polarization POL2.

[0058] In addition, a control device CRTL is provided, which is configured to use an electronic control device to control the amplitude and / or phase of the output signal S-TX to form a controllable antenna feature of the reflector, and to make the second polarization POL2 (e.g., vertical polarization) different from the first polarization POL1 (e.g., horizontal polarization).

[0059] The amplifier device AMP can be included by the reflector element RE.

[0060] The reflector RIS is preferably designed to operate at a frequency of at least 20 GHz.

[0061] The first antenna element AE-RX and the second antenna element AE-TX are optionally composed of a common antenna structure AE, which together with the amplifier device AMP constitutes the reflector element RE.

[0062] The amplifier device AMP may include a bidirectional signal amplifier.

[0063] In one specific embodiment, the amplifier device AMP is controlled such that antenna element AE-RX or AE-TX, which ensures better transmission quality of the signal DS-TX with polarization POL1, is used as a receiving element. Simultaneously, another antenna element AE-TX or AE-RX is used to transmit the signal DS-RX with polarization POL2. This setting or control can optionally be performed via control signal POL-C transmitted by the transmitter TX. In this figure, the control POL-C of the system control device CTRL is shown separately from the data transmission signal DS-TX. This representation is merely a logical representation, as the data transmission signal DS-TX and the signal POL-C used to control polarization can optionally be transmitted via the same radio channel, but alternatively, they can be transmitted via separate transmission channels.

[0064] In another embodiment, the system includes: a radio transmitter TX for transmitting a data transmission signal DS-TX, having electronic means for controlling the polarization POL1 of the data signal; an electronically controllable reflector RIS according to the invention for reflecting the data transmission signal DS-TX; a radio receiver RX for receiving the reflected data signal DS-RX; and a system control device CTRL.

[0065] The system control device CTRL is configured to set the polarization POL2 by means of a corresponding electronic device for setting the polarization when the data signal DS-RX is sent on the reflector RIS.

[0066] Electronic devices for setting polarization are known in the prior art, such as using separate feed points on the corresponding antenna (e.g., patch antenna) or using orthogonally arranged dipole antennas.

[0067] The radio transmitter TX can also be configured to transmit a first data signal with a first polarization at a first moment, and transmit a second data signal with a second polarization different from the first polarization at a subsequent second moment.

[0068] Here, the controllable reflector can be configured to reflect the first and second data signals to a radio receiver that receives both signals.

[0069] The system shown represents only a unidirectional signal path from the transmitted signal TX via the reflector RIS to the receiver RX. However, it is clear that the system can also operate bidirectionally, and the transmitter TX and receiver RX can each be composed of transceivers capable of transmitting and receiving data. This also means that the system control unit CTRL is operated by the transmitter, including the transceiver of the receiver RX, in the corresponding transmission mode. In other words, the system control unit CTRL can optionally be connected to the transceivers of both the transmitter TX and the receiver RX. However, this function is not shown for clarity.

[0070] Another advantage is that the RIS connects to only one transceiver, i.e., when that transceiver is included by a "base station". In the base station, all data regarding the transmission and reception times, as well as the transmission directions (uplink / downlink) of all participants, are known.

[0071] In one specific embodiment, a system is proposed, comprising: a radio transmitter TX for transmitting a data transmission signal DS-TX, having electronic means for controlling the polarization POL1 of the data signal, an electronically controllable reflector RIS for reflecting the data transmission signal DS-TX, a radio receiver RX for receiving the reflected data signal DS-RX, and a system control device CTRL connected to the radio transmitter TX via a communication device.

[0072] The radio transmitter TX is configured to set a predetermined polarization POL1 using its electronic devices and transmit information about this polarization POL1 to the system control device CTRL via the communication device.

[0073] The predetermined polarization POL1 is set on the radio transmitter TX using its electronics.

[0074] The polarization POL1 is transmitted to the system control unit CTRL via a communication device.

[0075] The system control unit CTRL is configured to set the polarization POL1 on the reflector RIS by means of a corresponding electronic device for setting the polarization when receiving the data signal DS-TX.

[0076] In another specific embodiment, a system is proposed, including a first radio transmitter TX and a second radio transmitter, as well as a first radio receiver RX and a second radio receiver.

[0077] The first radio transmitter TX and the first radio receiver RX constitute the first transceiver.

[0078] The second radio transmitter and the second radio receiver constitute the second transceiver.

[0079] The controllable reflector RIS is configured to connect the first transceiver to the second transceiver via a radio connection and the reflector RIS.

[0080] The first radio transmitter TX is configured to transmit a first data signal with a first polarization at a first moment.

[0081] The second radio transmitter is configured to transmit a second data signal at a subsequent second time point in a second polarization different from the first polarization.

[0082] Figure 3 An antenna element of the prior art is shown.

[0083] The antenna element AE receives the signal and sends it to the distributor circuit DIV. The received signal is amplified by the unidirectional amplifier UNI-AMP, and the amplified signal is sent back to the antenna element AE via the distributor DIV for transmission.

[0084] Here, if the amplification of the UNI-AMP is set too high, it will cause the device to oscillate undesirably.

[0085] Figure 4 An embodiment of an antenna element with an inserted unidirectional amplifier and two antenna terminals for different polarizations is shown.

[0086] The antenna element AE receives the signal via a first feed terminal that detects only the vertical polarization plane VER, amplifies the received signal using a unidirectional amplifier UNI-AMP, and then sends the amplified signal back to the antenna element AE for transmission, but via a second feed terminal that has a horizontal polarization plane HOR that is different from the polarization plane VER of the first feed terminal.

[0087] The vertical polarization plane VER corresponds to the first polarization POL1 according to the preceding figure, while the horizontal polarization plane HOR corresponds to the second polarization POL2 according to the preceding figure, which is different from the first polarization POL1.

[0088] Figure 5 An embodiment of two antenna elements is shown, each having an inserted unidirectional amplifier and two antenna terminals for different polarizations HOR and VER.

[0089] This arrangement corresponds to the dual implementation arrangement according to the previous figure, but provides independent signal paths for two different polarization planes, HOR and VER.

[0090] Figure 6 An embodiment of an antenna element with an inserted bidirectional amplifier BI-AMP and two antenna terminals of different polarizations for a shared, combined antenna AE is shown, wherein a single signal path is set for two feed terminals for a first horizontal polarization plane HOR and a second vertical polarization plane VER via the bidirectional amplifier BI-AMP.

[0091] A bidirectional signal amplifier (BI-AMP) can be implemented, for example, by means of two anti-parallel unidirectional amplifiers connected by a controllable switcher, i.e., two unidirectional amplifiers connected in anti-parallel and switchably via two high-frequency switches (SPDT, "singlepole, double throw").

[0092] In other words, Figure 6 The nodes of the bidirectional amplifier BI-AMP shown can each be replaced and manipulated by an SPDT switch to set only the effective amplification direction of the bidirectional signal amplifier BI-AMP.

[0093] Alternatively, the two anti-parallel connected unidirectional amplifiers of the bidirectional signal amplifier BI-AMP can be operated by activating or deactivating their respective branches with unidirectional amplifiers to switch the effective amplification direction of the bidirectional signal amplifier BI-AMP.

[0094] This can be done by switching the power supply voltage on or off, or by changing, for example, the control voltage used to set the respective operating point on each unidirectional amplifier, so as to set only the effective amplification direction of the bidirectional signal amplifier BI-AMP.

[0095] The polarization direction can be changed by altering the effective amplification direction of the bidirectional signal amplifier (BI-AMP).

[0096] Therefore, the transmit path in the combined antenna AE becomes the receive path of the combined antenna AE, and the receive path becomes the transmit path of the combined antenna AE.

[0097] For a combined antenna AE used for two polarization planes HOR and VER, a first polarization direction HOR is set for a switchable transmit / receive path, and a second polarization direction VER is set for a second switchable transmit / receive path, wherein the first polarization direction HOR and the second polarization direction VER are different. Preferably, the first polarization direction HOR and the second polarization direction VER are orthogonal to each other.

[0098] List of reference numerals in the attached diagram: AE, AE-RX, AE-TX antenna elements DIV Directional Coupler The signal sent by the DS-RX to the receiver, and the signal transmitted by the reflector. DS-TX is the signal transmitted by the transmitter TX and received by the reflector. HOR horizontal polarization POL1, POL2 polarization POL-C polarization control signal RIS Electronically Controlled Reflector AMP, UNI-AMP, BI-AMP amplifiers RE reflector element RX receiver TX transmitter VER Vertical Polarization

Claims

1. An electronically controllable reflector (RIS) comprising a plurality of reflector elements (REs), each reflector element comprising: The first antenna element (AE-RX) is configured to receive the received signal (DS-TX) with the first polarization (POL1) as the input signal (S-RX). An amplifier device (AMP, UNI-AMP, BI-AMP) configured to electronically amplify the input signal (S-RX) and output it as an output signal (S-TX); as well as The second antenna element (AE-TX) is configured to transmit the output signal (S-TX) as a transmit signal (DS-RX) with a second polarization (POL2), wherein the second polarization (POL2) is different from the first polarization (POL1); as well as A control unit (CRTL) configured to use an electronic control device to control the amplitude and / or phase of the output signal (S-TX) to form controllable antenna characteristics of the reflector. The control device (CRTL) is characterized in that it is further configured to receive the provided polarization control signal (POL-C). The amplifier device (AMP) includes a bidirectional signal amplifier (BI-AMP) having two settable amplification directions, the bidirectional signal amplifier being configured to set the effective amplification direction of the bidirectional signal amplifier (BI-AMP) according to the polarization control signal (POL-C).

2. The reflector (RIS) of claim 1, wherein the reflector (RIS) is configured to operate at an operating frequency of at least 20 GHz.

3. The reflector (RIS) according to any one of the preceding claims, wherein the at least one first antenna element (AE-RX) and the at least one second antenna element (AE-TX) are constituted by a common antenna structure (AE).

4. A system comprising: A radio transmitter (TX) for transmitting a data transmission signal (DS-TX) has electronic means for controlling the polarization (POL1) of the data signal; an electronically controllable reflector (RIS) according to any one of the preceding claims for reflecting the data transmission signal (DS-TX); a radio receiver (RX) for receiving the reflected data signal (DS-RX); and a system control unit (CTRL) connected to the radio transmitter (TX) via a communication device, wherein the radio transmitter (TX) is configured to set a predetermined polarization (POL1) using its electronic means and transmit information (POL-C) about the polarization (POL1) to the system control unit (CTRL) via the communication device, and the system control unit (CTRL) is configured to set the polarization (POL1) by means of a corresponding electronic means for setting the polarization when receiving the data signal (DS-TX) on the reflector (RIS).

5. The system of claim 4, comprising a first radio transmitter (TX) and a second radio transmitter of claim 4, and a first radio receiver (RX) and a second radio receiver of claim 4, wherein the first radio transmitter (TX) and the first radio receiver (RX) constitute a first transceiver, and the second radio transmitter and the second radio receiver constitute a second transceiver, and a controllable reflector (RIS) of claim 4, the controllable reflector being configured to connect the first transceiver and the second transceiver via a radio connection and the reflector (RIS), and the first radio transmitter (TX) being configured to transmit a first data signal with a first polarization at a first moment, and the second radio transmitter being configured to transmit a second data signal with a second polarization different from the first polarization at a subsequent second moment.

6. The system according to any one of the preceding claims, wherein the transmit signal (TX) is configured to transmit polarization information (POL-C) with respect to a first polarization (POL1) to a controllable reflector (RIS) according to any one of claims 1 to 3, and the reflector is configured to receive the polarization information (POL-C) and set the amplification direction of the bidirectional signal amplifier (BI-AMP) such that the amplification direction corresponds to the first polarization (POL1).

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