Wireless communication system and base station

A wireless communication system including a phased array comprising a plurality of antennas configured to emit a respective radio wave based on a respective antenna signal. Further, the system includes a plurality of power amplifiers each coupled to one of the plurality of antennas via a feed line and configured to output the antenna signal to the feed line. Also, the system includes a plurality of directional couplers each coupled into one of the feed lines and comprising a third port configured to output a fraction of a power received at a first port coupled to the power amplifier via the feed line, likewise a fourth port configured to output a fraction of a power received at a second port. Additionally, the system includes switching circuitry configured to alternately couple the third port to a first feedback receiver, and to alternately couple the fourth port to a second feedback receiver.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to European Application 21215432.2, filed on Dec. 17, 2021. The content of this earlier filed application is incorporated by reference herein in its entirety.

BACKGROUND

In active phased arrays such as for 5G millimeter wave (mmWave), Power Amplifiers (PAs) face a beamsteering angle dependent load. Each PA response changes with beam direction change (in high power regime) due to load pull of different PAs and lack of space to insert a circulator (as deployed in todays 5G systems below 6 GHz).

Digital Pre-Distortion (DPD) offers various significant benefits, especially in improving the PA efficiency and increasing Root Mean Square (RMS) transmit power. Hence, there is a strong desire to enable DPD also for active phased arrays such as mmWave beamforming systems. However, the above described angle-dependent load modulation requires that the DPD is adapted according to the beamsteering angle. Furthermore, the DPD shall linearize the phased array beam output instead of each single PA output.

Conventional sub-6 GHz systems include an isolator between antenna and PA output in order to DPD linearize the PA without complexity of antenna to antenna coupling. The insertion loss of the isolator significantly reduces to the overall transmit efficiency of such a system.

Hence, there may be a demand for improved wireless communication systems.

DETAILED DESCRIPTION

FIG.1illustrates a wireless communication system100comprising a phased array110. The wireless communication system100comprises a plurality of antennas111-1, . . . ,111-4forming the phased array110. In the example ofFIG.1, four antennas are illustrated. However, it is to be noted that present disclosure is not limited thereto. In general any number n≥2 of antennas may be used. For example, the phased array110may comprise 4, 8, 16, 32, 64, 128 or more antennas.

The plurality of antennas111-1, . . . ,111-4may be arranged in a linear array (i.e. a one-dimensional array) as indicated inFIG.1. In other examples, the plurality of antennas111-1, . . . ,111-4may be arranged in a planar array (i.e. a two-dimensional array). For example, the plurality of antennas111-1, . . . ,111-4may be patch antennas. However, the present disclosure is not limited thereto. The plurality of antennas111-1, . . . ,111-4may in general be any type of antenna.

The plurality of antennas111-1, . . . ,111-4are configured to receive a respective (analog) antenna signal121-1, . . . ,121-4and to emit a respective radio wave based on the respective antenna signal121-1, . . . ,121-4. The radio waves emitted by the plurality of antennas interfere with each other such that at one or more solid angle constructive interference of the emitted radio waves occurs while at others destructive interference of the emitted radio waves occurs. Accordingly, one or more main beam (main lobe) is formed by interference of the emitted radio waves. Further, one or more side beams (side lobes) may occur due to the interference of the emitted radio waves.

The antenna signals121-1, . . . ,121-4are phase/delay and/or amplitude shifted with respect to each other such that also the emitted radio waves are phase and/or amplitude shifted with respect to each other. By shifting the phase/delay and/or amplitude of the antenna signals121-1, . . . ,121-4and, hence, the emitted radio waves, the one or more solid angle at which constructive interference of the emitted radio waves occurs may be controlled. In other words, the (spatial beam) direction of the one or more main beam formed by interference of the emitted radio waves may be controlled by shifting the phase/delay and/or amplitude of the antenna signals121-1, . . . ,121-4and, hence, the emitted radio waves. The direction of the main beam formed by interference of the emitted radio waves may also be denoted as beam angle or beamsteering angle.

This is exemplarily illustrated inFIGS.2to4. InFIG.2, a first phase/delay and/or amplitude relation between the antenna signals121-1, . . . ,121-4is adjusted such that the main beam199formed by interference of the emitted radio waves is directed to a first spatial direction (the lower left). InFIG.3, a different second phase/delay and/or amplitude relation between the antenna signals121-1, . . . ,121-4is adjusted such that the main beam199formed by interference of the emitted radio waves is directed to a second spatial direction, which is different from the first spatial direction. InFIG.4, a different third phase/delay and/or amplitude relation between the antenna signals121-1, . . . ,121-4is adjusted such that the main beam199formed by interference of the emitted radio waves is directed to a third spatial direction (the lower right), which is different from the first spatial direction and the second spatial direction.

In the examples ofFIGS.2to4, the phased array comprises 32 antennas to highlight that the present disclosure is not limited four antennas as illustrated inFIG.1.

Part of the power received by the respective antenna111-1, . . . ,111-4via the respective antenna signal121-1, . . . ,121-4is reflected back to the respective PA120-1, . . . ,120-4by the antenna. The amount of power reflected back to the respective PA is determined by the refection coefficient Γiof the respective antenna. The respective refection coefficient Γifor each individual antenna of the phased array110is defined as follows:

The power reflected back to the respective PA120-1, . . . ,120-4loads the respective PA120-1, . . . ,120-4. The amount of power reflected back to the respective PA120-1, . . . ,120-4depends on the (spatial beam) direction of the one or more main beam formed by interference of the emitted radio waves. In other words, the amount of power reflected back to the respective PA120-1, . . . ,120-4depends on the phase and/or amplitude relation between the antenna signals121-1, . . . ,121-4. Accordingly, a beam angle-dependent load modulation occurs.

The beam angle-dependent modulation of the load seen by the plurality of PAs120-1, . . . ,120-4may be compensated or at least mitigated by DPD. For adjusting the DPD to the beam angle-dependent load modulation, information about the forward power and the reflected power is needed.

For providing the information about the forward power and the reflected power, the wireless communication system100comprises a plurality of directional couplers130-1, . . . ,130-4and switching circuitry140.

As illustrated inFIG.1, each of the plurality of directional couplers130-1, . . . ,130-4is coupled into a respective one of the feed lines125-1, . . . ,125-4.

Each of the directional couplers130-1, . . . ,130-4comprises a respective first port coupled to the respective power amplifier via the respective feed line125-1, . . . ,125-4. Further, each of the directional couplers130-1, . . . ,130-4comprises a respective second port coupled to the respective antenna111-1, . . . ,111-4via the respective feed line125-1, . . . ,125-4.

The power output by the respective PA120-1, . . . ,120-4to the respective feed line125-1, . . . ,125-4via the respective antenna signal121-1, . . . ,121-4is received at the respective first port of each directional coupler130-1, . . . ,130-4. Each of the directional couplers130-1, . . . ,130-4comprises a respective third port configured to output a fraction of the respective power received at the respective first port of the directional coupler.

The power reflected back to the respective feed line125-1, . . . ,125-4and, hence, the respective PA120-1, . . . ,120-4by the respective antenna111-1, . . . ,111-4is received at the respective second port of each directional coupler130-1, . . . ,130-4. Each of the directional couplers130-1, . . . ,130-4comprises a respective fourth port configured to output a fraction of the respective power received at the respective second port of the directional coupler.

The above is exemplarily illustrated inFIG.1for the directional coupler130-1coupled into the feed line125-1coupling the PA120-1and the antenna111-1. The PA120-1outputs the antenna signal121-1to the feedline125-1. The first port131of the directional coupler130-1is coupled to the output of the PA120-1via the feedline125-1and receives the antenna signal121-1. The antenna signal121-1passes the directional coupler120-1and is output to the feedline125-1at the second port132of the directional coupler130-1such that is propagates to the antenna111-1, which is coupled to the second port132of the directional coupler130-1. Part of the antenna signal121-1′ power is coupled out from the antenna signal121-1by the directional coupler130-1, and is output at the third port133of the directional coupler130-1. Analogously, the second port132of the directional coupler130-1receives via the transmission line125-1the power reflected back by the antenna111-1. The reflected power passes the directional coupler120-1and is output to the feedline125-1at the first port131of the directional coupler130-1such that is propagates to the PA120-1and loads the PA120-1. Part of the reflected power is coupled out by the directional coupler130-1, and is output at the fourth port134of the directional coupler130-1.

The switching circuitry140is coupled to the respective third port of the plurality of directional couplers130-1, . . . ,130-4and the respective fourth port of the plurality of directional couplers130-1, . . . ,130-4. Further, the switching circuitry140is coupled to a first feedback receiver150and a second feedback receiver155. The switching circuitry140is configured to alternately couple the respective third port of one of the plurality of directional couplers130-1, . . . ,130-4to the first feedback receiver150. Further, the switching circuitry140is configured to alternately couple the respective fourth port of one of the plurality of directional couplers130-1, . . . ,130-4to the second feedback receiver140. In particular, the switching circuitry140is configured to simultaneously couple the respective third port and the respective fourth port of the respective one of the plurality of directional couplers130-1, . . . ,130-4to the respective one of the first feedback receiver150and the second feedback receiver155. For example, the switching circuitry140may first simultaneously couple the third port133and the fourth port134of the directional coupler130-1to the respective one of the first feedback receiver150and the second feedback receiver155, then simultaneously couple the third port and the fourth port of the directional coupler130-2to the respective one of the first feedback receiver150and the second feedback receiver155, then simultaneously couple the third port and the fourth port of the directional coupler130-3to the respective one of the first feedback receiver150and the second feedback receiver155, and then simultaneously couple the third port and the fourth port of the directional coupler130-4to the respective one of the first feedback receiver150and the second feedback receiver155. However, it is to be noted that the present disclosure is not limited thereto. In other examples, the switching circuitry140may use another order (sequence) for coupling the respective third port and the respective fourth port of the plurality of directional couplers130-1, . . . ,130-4to the respective one of the first feedback receiver150and the second feedback receiver155.

The switching circuitry140may, e.g., comprise a plurality of semiconductor switches such as a plurality of transistors or a plurality of transistor networks for the selective coupling of the individual ports of the directional couplers130-1, . . . ,130-4to the respective one of the first feedback receiver150and the second feedback receiver155.

The plurality of directional couplers130-1, . . . ,130-4and the switching circuitry140allow to extract for each PA120-1, . . . ,120-4the forward power, i.e., the power output by the respective PA120-1, . . . ,120-4to the respective feed line125-1, . . . ,125-4. Analogously, the plurality of directional couplers130-1, . . . ,130-4and the switching circuitry140allow to extract for each PA120-1, . . . ,120-4the reflected power, i.e. the power reflected back to the feed line125-1, . . . ,125-4and, hence, the respective PA120-1, . . . ,120-4by the respective antenna111-1, . . . ,111-4. The information for each PA120-1, . . . ,120-4about the respective forward power and the respective reflected power allow to adjust DPD for the wireless system, which will be explained below with more details.

The first feedback receiver150and the second feedback receiver155are schematically illustrated inFIG.1.

The first feedback receiver150comprises an amplifier or attenuator151(e.g. a Low Noise Amplifier, LNA, or a programmable attenuator such as a Digital Step Attenuator, DSA) configured to amplify or attenuate a first output (signal)141of the switching circuitry140. The first output141is based on (corresponds to) the power (signal) output by the respective third port coupled to the first feedback receiver150by the switching circuitry140. The first feedback receiver150further comprises circuitry152for processing the amplified first output141. The further circuitry152may comprise various circuitry such as one or more filter, one or more Analog-to-Digital Converter (ADC), an equalizer, one or more mixer (down-converter or IQ down-converter), etc. The first feedback receiver is configured to generate a first digital feedback signal153based on the first output141. The first digital feedback signal153is indicative of the forward power of the respective PA120-1, . . . ,120-4, i.e., the power output by the respective PA120-1, . . . ,120-4to the respective feed line125-1, . . . ,125-4.

Analogously, the second feedback receiver155comprises an amplifier or attenuator156(e.g. an LNA or a DSA) configured to amplify or attenuate a second output (signal)142of the switching circuitry140. The second output142is based on (corresponds to) the power (signal) output by the respective fourth port coupled to the second feedback receiver155by the switching circuitry140. The second feedback receiver155further comprises circuitry157for processing the amplified second first output142. The further circuitry157may comprise various circuitry such as one or more filter, one or more ADC, an equalizer, one or more mixer (down-converter or IQ down-converter), etc. The second feedback receiver155is configured to generate a second digital feedback signal158based on the second output142. The second digital feedback signal158is indicative of the reflected power loading the respective PA120-1, . . . ,120-4, i.e. the power reflected back to the feed line125-1, . . . ,125-4and, hence, the respective PA120-1, . . . ,120-4by the respective antenna111-1, . . . ,111-4.

Training circuitry160is coupled to the first feedback receiver150and the second feedback receiver155. For example, the training circuitry160may be a single dedicated processor, a single shared processor, or a plurality of individual processors, some of which or all of which may be shared, a digital signal processor (DSP) hardware, an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The training circuitry160may optionally be coupled to, e.g., read only memory (ROM) for storing software, random access memory (RAM) and/or non-volatile memory. The training circuitry160is configured to receive the first digital feedback signal153and the second digital feedback signal158. Further, the training circuitry160is configured to determine (calculate) one or more pre-distortion coefficient based on the first digital feedback signal153and the second digital feedback signal158.

The one or more distortion coefficient are used by DPD circuitry170for pre-distorting a digital transmit signal101. The digital transmit signal101may, e.g., be a baseband signal or a digital signal derived therefrom. Similar to the training circuitry160, the DPD circuitry170may, e.g., be a single dedicated processor, a single shared processor, or a plurality of individual processors, some of which or all of which may be shared, a DSP hardware, an ASIC or a FPGA. Although illustrated as separate elements inFIG.1, the training circuitry160and the DPD circuitry170may be implemented integrally in other examples of the present disclosure. The DPD circuitry170is configured to receive the digital transmit signal101and to pre-distort the digital transmit signal101using the one or more pre-distortion coefficient. The DPD circuitry170is further configured to output a pre-distorted digital transmit signal102.

As indicated inFIG.1, also the training circuitry160may optionally be configured to receive the digital transmit signal101. Accordingly, the training circuitry160may be configured to determine the one or more pre-distortion coefficient further based on the digital transmit signal101. Alternatively or additionally, the training circuitry160may optionally be configured to receive the pre-distorted digital transmit signal102and to determine the one or more pre-distortion coefficient further based on the pre-distorted digital transmit signal102.

The wireless communication system100further comprises a transmitter180configured to receive the pre-distorted digital transmit signal102. The transmitter180is further configured to generate an analog radio frequency signal103based on the pre-distorted digital transmit signal102. The transmitter180may comprise various circuitry such as one or more filter, a Digital-to-Analog Converter (DAC), one or more mixer (up-converter), etc.

Additionally, the wireless communication system100comprises beamforming circuitry190coupled to the transmitter180and the plurality of PAs120-1, . . . ,120-4. The beamforming circuitry190is configured to generate a plurality of radio frequency transmit signals191-1, . . . ,191-4for the plurality of PAs120-1, . . . ,120-4based on the analog radio frequency signal103output by the transmitter180, i.e., effectively based on the pre-distorted digital transmit signal102. As illustrated inFIG.1, the beamforming circuitry190is configured to generate a respective radio frequency transmit signal191-1, . . . ,191-4for each of the plurality of PAs120-1, . . . ,120-4.

The beamforming circuitry190is configured to adjust a respective phase/delay and/or a respective amplitude of the radio frequency transmit signals191-1, . . . ,191-4for controlling the direction (i.e. the beam angle) of the main beam formed by interference of the corresponding radio waves emitted by the antennas111-1, . . . ,111-4. For example, the beamforming circuitry190may comprise a plurality of phase shifters/delay circuits and/or amplitude shifters for adjusting the respective phase/delay and/or the respective amplitude of the radio frequency transmit signals191-1, . . . ,191-4. However, it is to be noted that the present disclosure is not limited to the specific analog beamforming circuitry190illustrated inFIG.1. In general, any beamforming circuitry configured to perform the above described functionality may be used.

In the example ofFIG.1, the beamforming circuitry190is implemented as analog beamforming circuitry. However, the present disclosure is not limited thereto. In alternative examples, the beamforming circuitry190may be implemented as digital beamforming circuitry which performs the phase and/or amplitude adjustment in the digital domain rather than in the analog domain. Accordingly, the analog-to-digital conversion performed by the transmitter180in the example ofFIG.1may be performed subsequent to the phase and/or amplitude adjustment in the digital domain.

The training circuitry160may use one or more training model or algorithm for determining the one or more pre-distortion coefficient based on the first digital feedback signal153and the second digital feedback signal158(and optionally further the digital transmit signal101and/or the pre-distorted digital transmit signal102). For example, the training circuitry160may be configured to determine the one or more pre-distortion coefficient using a training model for minimizing an overall non-linear distortion of the main beam formed by interference of the radio waves emitted by the antennas111-1, . . . ,111-4. In other words, the training circuitry160may be configured to determine the one or more pre-distortion coefficient such that the overall non-linear distortion of the main beam is minimized rather than individual non-linear distortions of the individual PAs120-1, . . . ,120-4. Accordingly, one or more of the plurality of the PAs120-1, . . . ,120-4may exhibit a rather high individual non-linear distortion despite the DPD. However, this is negligible as the overall non-linear distortion of the main beam is minimized. In other words, the training circuitry160may use a training model aiming to minimize the combined non-linearity of all the PAs120-1, . . . ,120-4rather than the individual non-linearities of single ones of the plurality of the PAs120-1, . . . ,120-4.

Those skilled in the art are aware of suitable training models or algorithms for determining one or more pre-distortion coefficient based on at least a first digital signal indicative of the forward power of the respective PA and a second digital signal indicative of the reflected power loading the respective PA. Therefore, only a few explanations will be given in the following with respect to the determination of the one or more pre-distortion coefficient.

As described above, the second digital feedback signal158is indicative of the reflected power loading the respective PA120-1, . . . ,120-4. Hence, the second digital feedback signal158allows to determine (characterize) the load modulation of the plurality of PAs120-1, . . . ,120-4. Accordingly, the training circuitry160may be configured to determine a load modulation of the plurality of PAs120-1, . . . ,120-4based on the second digital feedback signal158. In other words, the beam angle-dependent load of the plurality of PAs120-1, . . . ,120-4may be determined based on the second digital feedback signal158. Accordingly, the one or more pre-distortion coefficient may be determined by the training circuitry160based on the determined load modulation of the plurality of PAs120-1, . . . ,120-4.

As described above, the first digital feedback signal153is indicative of the forward power of the respective PA120-1, . . . ,120-4. Hence, the first digital feedback signal153allows to determine the far field radiation pattern of the phased array110. While the near field of the phased array110is the region right next to the phased array110(i.e. the immediate vicinity of the phased array110), the far field of the phased array110is the region that comes after the near field. An intended recipient of the radio waves emitted by the phased array110(e.g. a mobile phone) is usually located in the far field region of the phased array110. Accordingly, the training circuitry160may be configured to determine the far field radiation pattern of the phased array110based on the first digital feedback signal153. Accordingly, the one or more pre-distortion coefficient may be determined by the training circuitry160based on the determined far field radiation pattern. For example, techniques such as anti-beamforming may be used by the training circuitry160to determine the far field radiation pattern. However, it is to be noted that the present disclosure is not limited thereto. Other techniques may be used as well.

One or more antenna of the phased array may further be used for measuring the near field radiation pattern of the phased array110. For example, one (or more) of the plurality of PAs120-1, . . . ,120-4may be configured (controlled) to provide no antenna signal to the respective antenna of the phased array110during a time slot, i.e., during a given period of time. Accordingly, the respective antenna of the phased array110does not emit a radio wave during the time slot and may, hence, be used as probe for measuring the near field radiation pattern of the phased array110. The switching circuitry140may be configured to couple the fourth port of the directional coupler coupled to the one of the plurality of PAs (not providing an antenna signal to respective antenna of the phased array110) during the time slot to the second feedback receiver155. For example, the PA120-1may be configured to provide no antenna signal to the antenna111-1during the time slot such that the antenna111-1can be used as probe for measuring the near field radiation pattern of the phased array110. Accordingly, the switching circuitry140may be configured to couple the fourth port134of the directional coupler130-1during the time slot to the second feedback receiver155. As a consequence, a signal section of the second digital feedback signal158, which is generated by the second feedback receiver155based on the second output (signal)142of the switching circuitry during the time slot, is indicative of the near field radiation pattern of the phased array110.

The training circuitry160may accordingly be configured to determine the near field radiation pattern of the phased array110based on the signal section of the second digital feedback signal158, which is generated by the second digital feedback signal155based on the second output (signal)142of the switching circuitry during the time slot. The one or more pre-distortion coefficient may be determined by the training circuitry160based on the determined near field radiation pattern of the phased array110.

According to the present disclosure, a respective coupler measuring incoming and outgoing wave on each PA is used. This elegantly solves the area problem or small number of receiving antennas, and allows to capture PA loading depending on the bemasteering angle.

The wireless communication system100may be used for various beamforming applications. For example, the wireless communication system100may be used for millimeter wave applications such as 5G mmWave. Accordingly, the radio waves emitted by the plurality of antennas111-1, . . . ,111-4of the phased array110may be millimeter waves. In other words, the radio waves emitted by the plurality of antennas111-1, . . . ,111-4of the phased array110may exhibit a frequency of 24 GHz or more. The proposed architecture may enable DPD on mmWave phased arrays and, hence, enable an increased RMS transmit power and much higher power efficiency (e.g., up to 20%) resulting in very significant power saving for wireless operators. Also, system thermal design may be drastically simplified, translating into lower costs for base station suppliers.

However, the present disclosure is not limited to millimeter wave applications. The wireless communication system100may be used for emitting radio waves of shorter wavelength (i.e. lower frequency) as well. For example, the wireless communication system100may be used for sub-6 GHz applications such as classical cellular communication. Accordingly, the radio waves emitted by the plurality of antennas111-1, . . . ,111-4of the phased array may exhibit a frequency of 6 GHz or less. The further benefits of the present architecture for sub-6 GHz wireless communication will become evident from the example ofFIG.5.FIG.5illustrates another wireless communication system500according to the present disclosure for sub-6 GHz wireless communication. For reasons of simplicity, only a single antenna511together with the corresponding transmit path circuitry is illustrated inFIG.5. However, it is to be noted that the wireless communication system500may comprise a plurality of antennas and transmit paths similar to what is described below.

Similar to what is described above, the wireless communication system500comprises DPD circuitry570configured to receive a digital transmit signal501and to pre-distort the digital transmit signal501using one or more pre-distortion coefficient. A transmitter580receives the pre-distorted digital transmit signal502and generates an analog radio frequency transmit signal591. The transmitter580may comprise various circuitry such as one or more filter, a DAC, one or more mixer (up-converter), etc. In the example ofFIG.5, the beamforming circuitry for adjusting a phase and/or an amplitude of the analog radio frequency transmit signal591is included in the transmitter580for reasons of simplicity.

A PA520receives the analog radio frequency transmit signal591and generates an antenna signal521for the antenna511by amplifying the analog radio frequency transmit signal591. The PA520outputs the antenna signal521to a feedline525coupling the antenna511and the PA520. A bandpass filter595is coupled into the feedline525. Further, a directional coupler530is coupled into the feedline525analogously to what is described above.

A first port of the directional coupler530is coupled to the output of the PA520via the feedline525and receives the antenna signal521. The antenna signal521passes the directional coupler530and is output to the feedline525at a second port of the directional coupler530such that is propagates to the antenna511, which is coupled to the second port of the directional coupler530. Part of the antenna signal521′ power is coupled out from the antenna signal521by the directional coupler530, and is output at a third port of the directional coupler530. Analogously, the second port of the directional coupler530receives via the transmission line525the power reflected back by the antenna511. The reflected power passes the directional coupler530and is output to the feedline525at the first port of the directional coupler530such that is propagates to the PA520and loads the PA520. Part of the reflected power is coupled out by the directional coupler530, and is output at a fourth port of the directional coupler530.

The third port of the directional coupler530is coupled to a first feedback receiver550. The fourth port of the directional coupler530is coupled to a second feedback receiver555. In the example ofFIG.5, no switching circuitry is illustrated for reasons of simplicity as only a single transmit path is illustrated. It is evident from the above description that the feedback receivers550and555may be shared among multiple transmit paths (e.g. four or more) and be coupled to the respective transmit path via switching circuitry. Further illustrated are two bandpass filters596and597coupled between the directional coupler530and the respective one of the first feedback receiver550and the second feedback receiver555.

The first feedback receiver550generates a first digital feedback signal553based on the power received from the third port of the directional coupler530. Analogously, the second feedback receiver555generates a second digital feedback signal558based on the power received from the fourth port of the directional coupler530.

The power output at the third port of the directional coupler530and, hence, the first digital feedback signal553is indicative of the forward power of the PA520, i.e., the power output by the PA520to the feed line525. The power output at the fourth port of the directional coupler530and, hence, the second digital feedback signal558is indicative of the reflected power loading the PA520, i.e. the power reflected back to the feed line525and, hence, the PA520by the antenna511. The first digital feedback signal553and the second digital feedback signal558are supplied to the DPD circuitry570, which includes the above described training circuitry. Accordingly, the one or more pre-distortion coefficient are determined based on the first digital feedback signal553and the second digital feedback signal558.

Measuring the forward power and the reflected power enables linearization of the PA520and beamforming by means of DPD according to the above described principles. Contrary to conventional sub-6 GHz systems, the proposed architecture allows to omit an isolator505between the PA520and the antenna511. The insertion loss of the isolator505would significantly reduce to the overall transmit efficiency of the system. Accordingly, the proposed architecture allows to increase the overall transmit efficiency also for sub-6 GHz systems.

A receive path coupled to the antenna511is indicated by the LNA598coupled to the feedline525between the PA520and the antenna511.

FIG.6illustrates an exemplary directional coupler600which may be used in a wireless communication system according to one or more aspect of the architecture described above. However, it is to be noted that wireless communication systems according to the present disclosure are not limited to using the directional coupler600. Other directional coupler structures may be used as well for the plurality of directional couplers.

The directional coupler600comprises a first transmission line601coupling a first port610and a second port620. Further, the directional coupler600comprises a second transmission line702coupling the a third port630and a fourth port640.

The first transmission line601and the second transmission line602are spaced apart from each other at a distance d enabling power passing through one of the first transmission line601and the second transmission line602to couple into the other one of the first transmission601line and the second transmission line602.

For example, if the first port610is coupled to a PA and the second port620is coupled to an antenna as described above, the first port610receives power output from the PA. The power passes through the first transmission line601to the second port620, where it is output to the antenna. Due to the spacing of the first transmission line601and the second transmission line602, a fraction of the power received from the PA couples into the second transmission line602and can be extracted at the third port630for further processing as described above. Analogously, the second port620receives power reflected back by the antenna. The power passes through the first transmission line601to the first port610, where it is output to the PA and loads the PA. Due to the spacing of the first transmission line601and the second transmission line602, a fraction of the power received from the antenna couples into the second transmission line602and can be extracted at the fourth port640for further processing as described above.

A length l of the coupled straight sections of the first transmission line601and the second transmission line602may be λ/4, wherein λ denotes a wavelength of the power passing through the transmission line601(e.g. a wavelength of an antenna signal for driving the antenna). Hence, the length l of the coupled sections of the first transmission line601and the second transmission line602depends on the frequency of the power (i.e. the signals) passing through the transmission line601.

An example of an implementation using a wireless communication system according to one or more aspect of the architecture described above in connection withFIGS.1to6or one or more example described above in connection withFIGS.1to6is illustrated inFIG.7.FIG.7schematically illustrates an example of a radio base station700(e.g. for a femtocell, a picocell, a microcell or a macrocell) comprising a wireless communication system710as proposed.

The wireless communication system710is configured as described above. For illustrative purposes only, the phased array730of the wireless communication system710is illustrated as separate element inFIG.7. The phased array730is indicated by a single antenna in the example ofFIG.7.

The base station700further comprises baseband circuitry (e.g. a baseband processor)720coupled to the wireless communication system710. The baseband circuitry720is configured to generate a baseband signal721. The wireless communication system710is configured to receive and process the baseband signal721. Accordingly, the antenna signals supplied to the antennas of the phased array730are based on the baseband signal721. For example, the baseband circuitry720may be configured to generate the baseband signal721based on data (e.g. user data) to be transmitted wirelessly.

To this end, a base station enabling DPD for a phased array may be provided.

The base station700may comprise further elements such as, e.g., an application processor, memory, a network controller, a user interface, power management circuitry, a satellite navigation receiver, a network interface controller or power tee circuitry.

In some aspects, the application processor may include one or more Central Processing Unit CPU core and one or more of cache memory, a Low-DropOut (LDO) voltage regulator, interrupt controllers, serial interfaces such as Serial Peripheral Interface (SPI), Inter-Integrated Circuit (I2C) or universal programmable serial interface module, Real Time Clock (RTC), timer-counters including interval and watchdog timers, general purpose Input-Output (IO), memory card controllers such as Secure Digital (SD)/MultiMedia Card (MMC) or similar, Universal Serial Bus (USB) interfaces, Mobile Industry Processor Interface Alliance (MIPI) interfaces and Joint Test Access Group (JTAG) test access ports.

In some aspects, the baseband circuitry may be implemented, for example, as a solder-down substrate including one or more integrated circuit, a single packaged integrated circuit soldered to a main circuit board or a multi-chip module containing two or more integrated circuits.

In some aspects, the memory may include one or more of volatile memory including Dynamic Random Access Memory (DRAM) and/or Synchronous Dynamic Random Access Memory (SDRAM), and Non-Volatile Memory (NVM) including high-speed electrically erasable memory (commonly referred to as Flash memory), Phase change Random Access Memory (PRAM), Magnetoresistive Random Access Memory (MRAM) and/or a three-dimensional crosspoint (3D XPoint) memory. The memory may be implemented as one or more of solder down packaged integrated circuits, socketed memory modules and plug-in memory cards.

In some aspects, the power management integrated circuitry may include one or more of voltage regulators, surge protectors, power alarm detection circuitry and one or more backup power sources such as a battery or capacitor. Power alarm detection circuitry may detect one or more of brown out (under-voltage) and surge (over-voltage) conditions.

In some aspects, the power tee circuitry may provide for electrical power drawn from a network cable to provide both power supply and data connectivity to the base station using a single cable.

In some aspects, the network controller may provide connectivity to a network using a standard network interface protocol such as Ethernet. Network connectivity may be provided using a physical connection which is one of electrical (commonly referred to as copper interconnect), optical or wireless.

In some aspects, the satellite navigation receiver module may include circuitry to receive and decode signals transmitted by one or more navigation satellite constellation such as the Global Positioning System (GPS), GLObalnaya NAvigatSionnaya Sputnikovaya Sistema (GLONASS), Galileo and/or BeiDou. The receiver may provide data to the application processor which may include one or more of position data or time data. The application processor may use time data to synchronize operations with other radio base stations.

In some aspects, the user interface may include one or more of physical or virtual buttons, such as a reset button, one or more indicators such as Light Emitting Diodes (LEDs) and a display screen.

The wireless communication system and the base station according to the proposed architecture or one or more of the examples described above may be configured to operate according to one of the 3rd Generation Partnership Project (3GPP)-standardized mobile communication networks or systems. The mobile or wireless communication system may correspond to, for example, a 5thGeneration New Radio (5G NR), a Long-Term Evolution (LTE), an LTE-Advanced (LTE-A), High Speed Packet Access (HSPA), a Universal Mobile Telecommunication System (UMTS) or a UMTS Terrestrial Radio Access Network (UTRAN), an evolved-UTRAN (e-UTRAN), a Global System for Mobile communication (GSM), an Enhanced Data rates for GSM Evolution (EDGE) network, or a GSM/EDGE Radio Access Network (GERAN). Alternatively, the wireless communication circuits may be configured to operate according to mobile communication networks with different standards, for example, a Worldwide Inter-operability for Microwave Access (WIMAX) network IEEE 802.16 or Wireless Local Area Network (WLAN) IEEE 802.11, generally an Orthogonal Frequency Division Multiple Access (OFDMA) network, a Time Division Multiple Access (TDMA) network, a Code Division Multiple Access (CDMA) network, a Wideband-CDMA (WCDMA) network, a Frequency Division Multiple Access (FDMA) network, a Spatial Division Multiple Access (SDMA) network, etc.

In other examples, the wireless communication system and the base station according to the proposed architecture or one or more of the examples described above may be configured to operate according to a standardized wireless communication satellite system. Accordingly, the emitted radio waves may exhibit a frequency in one of the frequency bands used for satellite communication such as the L-band (approx. 1-2 GHz), the S-band (approx. 2-4 GHz), the C-band (approx. 4-8 GHz), the X-band (approx. 8-12 GHz), the Ku-band (approx. 12-18 GHz), the K-B and (approx. 18-26 GHz) or the Ka-band (approx. 26-40 GHz).

Examples of the present disclosure provide a feedback path for mmWave DPD.

The examples described herein may be summarized as follows:

An example (e.g. example 1) relates to a wireless communication system, comprising: a phased array comprising a plurality of antennas configured to emit a respective radio wave based on a respective antenna signal; a plurality of power amplifiers each coupled to a respective one of the plurality of antennas via a respective feed line and configured to output the respective antenna signal to the respective feed line; a plurality of directional couplers each coupled into a respective one of the feed lines and comprising a respective third port configured to output a fraction of a respective power received at a respective first port coupled to the respective power amplifier via the respective feed line, and a respective fourth port configured to output a fraction of a respective power received at a respective second port coupled to the respective antenna via the respective feed line; and switching circuitry configured to alternately couple the respective third port of one of the plurality of directional couplers to a first feedback receiver, and to alternately couple the respective fourth port of one of the plurality of directional couplers to a second feedback receiver.

Another example (e.g. example 2) relates to a previously described example (e.g. example 1), wherein the antenna signals are phase and/or amplitude shifted with respect to each other.

Another example (e.g. example 3) relates to a previously described example (e.g. example 1 or example 2), wherein the first feedback receiver is configured to generate a first digital feedback signal, wherein the second feedback receiver is configured to generate a second digital feedback signal, and wherein the wireless communication system further comprises: digital pre-distortion circuitry configured to pre-distort a digital transmit signal using one or more pre-distortion coefficient, wherein the antenna signals are based on the digital transmit signal; and training circuitry configured to determine the one or more pre-distortion coefficient based on the first digital feedback signal and the second digital feedback signal.

Another example (e.g. example 4) relates to a previously described example (e.g. example 3), wherein the training circuitry is configured to determine the one or more pre-distortion coefficient further based on the digital transmit signal.

Another example (e.g. example 5) relates to a previously described example (e.g. example 3 or example 4), wherein the training circuitry is configured to: determine a load modulation of the plurality of power amplifiers based on the second digital feedback signal; and determine the one or more pre-distortion coefficient based on the determined load modulation of the plurality of power amplifiers.

Another example (e.g. example 6) relates to a previously described example (e.g. one of examples 3 to 5), wherein the training circuitry is configured to: determine a far field radiation pattern of the phased array based on the first digital feedback signal; and determine the one or more pre-distortion coefficient based on the determined far field radiation pattern.

Another example (e.g. example 7) relates to a previously described example (e.g. one of examples 3 to 6), further comprising beamforming circuitry coupled to the plurality of power amplifiers, wherein the beamforming circuitry is configured to: generate a plurality of radio frequency transmit signals for the plurality of power amplifiers based on the pre-distorted digital transmit signal, wherein the plurality of power amplifiers generate the antenna signals by amplifying the plurality of radio frequency transmit signals; and adjust a phase and/or an amplitude of the radio frequency transmit signals for controlling a direction of a main beam formed by interference of the emitted radio waves.

Another example (e.g. example 8) relates to a previously described example (e.g. example 7), wherein the training circuitry is configured to determine the one or more pre-distortion coefficient using a training model for minimizing an overall non-linear distortion of the main beam.

Another example (e.g. example 9) relates to a previously described example (e.g. one of examples 3 to 8), wherein one of the plurality of power amplifiers is configured to provide no antenna signal to the respective antenna of the phased array during a time slot, wherein the switching circuitry is configured to couple the fourth port of the directional coupler coupled to the one of the plurality of power amplifiers during the time slot to the second feedback receiver, and wherein the training circuitry is configured to: determine a near field radiation pattern of the phased array based on a signal section of the second digital feedback signal, which is generated by the second feedback receiver based on an output of the switching circuitry during the time slot; and determine the one or more pre-distortion coefficient based on the determined near field radiation pattern.

Another example (e.g. example 10) relates to a previously described example (e.g. one of examples 1 to 9), wherein the switching circuitry is configured to simultaneously couple the respective third port and the respective fourth port of the respective one of the plurality of directional couplers to the respective one of the first feedback receiver and the second feedback receiver.

Another example (e.g. example 11) relates to a previously described example (e.g. one of examples 1 to 10), wherein the radio waves are millimeter waves, and/or wherein the radio waves exhibit a frequency of 24 GHz or more.

Another example (e.g. example 12) relates to a previously described example (e.g. one of examples 1 to 10), wherein the radio waves exhibit a frequency of 6 GHz or less.

Another example (e.g. example 13) relates to a previously described example (e.g. one of examples 1 to 12), wherein at least one of the plurality of directional couplers comprises: a first transmission line coupling the respective first port and the respective second port; and a second transmission line coupling the respective third port and the respective fourth port, wherein the first transmission line and the second transmission line are spaced apart from each other at a distance enabling power passing through one the first transmission line and the second transmission line to couple into the other one of the first transmission line and the second transmission line.

Another example (e.g. example 14) relates to a previously described example (e.g. one of examples 1 to 13), wherein the plurality of antennas are patch antennas.

Another example (e.g. example 15) relates to a base station, comprising: a wireless communication system according to a previously described example (e.g. one of examples 1 to 14); and baseband circuitry coupled to the wireless communication system and configured to generate a baseband signal, wherein the antenna signals are based on the baseband signal.

Another example (e.g. example 16) relates to a previously described example (e.g. example 15), wherein the baseband circuitry is configured to generate the baseband signal based on data to be transmitted wirelessly.