WO2023206089A1

WO2023206089A1 - Systems and methods for ul reference signal transmission

Info

Publication number: WO2023206089A1
Application number: PCT/CN2022/089368
Authority: WO
Inventors: Peng Lin; Zhenguo Ma; Chenguang Lu; Yezi HUANG
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2022-04-26
Filing date: 2022-04-26
Publication date: 2023-11-02

Abstract

Systems and methods for transmitting a UL reference signal to enable beamforming based on UL and DL channel reciprocity in the FDD system are provided. In some embodiments, a method performed by a wireless device in a FDD system may include transmitting a UL reference signal in a DL band allocated for DL transmission in the FDD system, in response to a UL reference signal transmission configuration in the DL band being configured. The UL reference signal is to be used for DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource. By enabling the wireless device to send the UL reference signal in the DL band, the reference signal may be received and used at the base station side to perform beamforming for the DL band based on channel reciprocity, and it is thus possible to improve the MIMO performance in DL.

Description

SYSTEMS AND METHODS FOR UL REFERENCE SIGNAL TRANSMISSION

Technical Field

The present disclosure relates to transmitting uplink (UL) reference signal for beamforming based on channel reciprocity.

Background

Massive multiple-input multiple-output (MIMO) is an essential part of 4G, 5G and its evolution to 6G due to its high system capacity and energy efficiency. Achieving the aforementioned potential gains of massive MIMO in practical systems hinges on the accuracy of channel state information (CSI) at the base station. CSI will determine link parameters like modulation and coding scheme (MCS) and precoder/beamforming configurations (e.g. beamforming weights, rank, precoder matrix indication (PMI) ) for next downlink (DL) transmissions.

Currently, there are two ways to get CSI in base station. One is that the user equipment (UE) feedbacks CSI to base station. Figure 1 shows a feedback-based beamforming process for DL band in a frequency division duplex (FDD) system. As shown in Figure 1, this processing consists of two stages, including downlink channel estimation at the UE side and UE feedback of CSI reports. Firstly, the CSI reference signals (CSI-RSs) are transmitted by base station, and UE estimates the DL channel based on the CSI-RS observation. Then UE sends the estimated CSI to base station through the UL control channel (PUCCH) . The CSI from UE feedback includes rank index (RI) , precoder matrix index (PMI) and channel quality index (CQI) , which respectively correspond to the number of layers, the recommended beam index corresponding to the beam weights defined in a codebook for base station to precode each layer, and signal-to-noise ratio (SNR) indication for selecting MCS. These parameters are pre-defined in 3GPP. Another way is based on the channel reciprocity between DL and UL to obtain the CSI in base station. In a time division duplex (TDD) system where UL and DL transmission use the same frequency channel, the channel reciprocity allows DL channels to be estimated through the reference signals such as sounding reference signals (SRS) transmitted in UL by UE. Basically, base station uses the received SRS signals transmitted from different UEs to estimate the UL channel between UE antennas and base station antennas. Then, DL channel estimates are derived based on the UL channel estimates, leveraging UL and DL channel reciprocity which is enabled by a proper UL/DL antenna calibration to calibrate out the differences in amplitude and phase in UL and DL transceiver components. Then, the base station will use the derived DL channel estimates to schedule multiple layers for one or multiple UEs and calculate the corresponding beamforming weights to beamform these layers to the corresponding UEs. For single-user MIMO (SU-MIMO) , reciprocity-based beamforming performs better than the feedback-based precoding/beamforming when the reciprocity-based DL channel estimates are of good quality, e.g. when UL SNR of the SRS signal is good. It is more important that reciprocity-based beamforming is very effective for multi-user MIMO (MU-MIMO) enabling transmit data to multiple users simultaneously using the same frequency-time resources, while feedback-based beamforming doesn't perform well in MU-MIMO. Therefore, reciprocity-based beamforming can significantly increase cell capacity by serving more UEs simultaneously using MU-MIMO, as well as increasing single user throughput significantly using SU-MIMO.

For the FDD system illustrated in Figure 1, reciprocity-based beamforming is not applicable since the UL and DL transmissions in the FDD system use different part of the spectrum of a FDD band, denoted as fu for UL and fd for DL. Thus, in FDD, feedback-based beamforming based on codebooks is used. Base station transmits the CSI-RS to UE, and UE sends back the CSI report based on a predefined codebook, e.g., Type I or Type II codebook specified in 3GPP. Base station uses the CSI report to determine the precoding/beamforming configuration for the next DL transmissions.

Figure 2A shows a general front-end structure of a FDD transceiver, which can be used for either UE or base station. In the illustrated front-end structure, a duplexer allows bi-directional (duplex) communication of transmit and receive frequencies (e.g., fu for UL and fd for DL) within the same FDD band using the same antenna. For the receiver path, after the duplex filter, the received signal is amplified by a low noise amplifier (LNA) . A bandpass filter (BPF) is usually required after LNA to further clean the spectrum, followed by a component which consists of local oscillator and mixer (down-converter) to convert the RF signal to an intermediate frequency (IF) signal. The signal will be converted to digital IQ samples by the analog-to-digital converter (ADC) and the digital IQ samples will be processed in baseband processing part of the receiver. For the transmitter path, the processing is opposite to the receiver path. Specifically, after baseband signal goes through the digital-to-analog converter (ADC) , the component consisted with LO and mixer will up-convert the signal to RF signal, which will be amplified by the power amplifier (PA) . After the duplexer, the filtered RF signal is sent out from the antenna.

Figure 2B shows a general front-end structure of a TDD transceiver, which can be used for either UE or base station. In Figure 2B, a single pole double throw (SPDT) switch is used to switch between transmitter and receiver in a TDD system. UL and DL are separated using different time slots but using same frequency band. Rest of procedures including BPF, LNA/PA, down/up-converter and ADC/DAC are similar as those in the FDD system.

No matter in the FDD or TDD system, when the UE received the CSI-RS from the base station, the CSI report comprising RI, PMI and CQI can be determined based on the CSI-RS channel estimation and the codebook used.

For the FDD system, since codebook-based precoder is used for DL beamforming, the MIMO performance is limited due to the constraint of the feedback bandwidth which limits the accuracy of the CSI report, and therefore it would not achieve an optimal performance. Further, codebook-based precoding/beamforming is not effective in MU-MIMO, which is an important feature to significantly increase cell capacity of 5G and its evolution towards 6G using massive MIMO and distributed MIMO technologies.

Summary

Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges. Systems and methods for transmitting a UL reference signal to enable beamforming based on UL and DL channel reciprocity in the FDD system are provided.

In some embodiments, a method performed by a wireless device in a FDD system (operating on a FDD spectrum) may include transmitting a UL reference signal in a DL band originally allocated for DL transmission in the FDD system, in response to a UL reference signal transmission configuration in the DL band being configured. The UL reference signal is to be used for DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource.

In some embodiments, a method performed by a base station in a FDD system may include: receiving, from a wireless device in the FDD system, an UL reference signal in a DL band originally allocated for DL transmission in the FDD system; and performing DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource, based on the received UL reference signal.

In some embodiments, a wireless device operating in a FDD system may include one or more processors, and memory storing instructions executable by the one or more processors. The wireless device may be operable to perform an operation of transmitting a UL reference signal in a DL band originally allocated for DL transmission in the FDD system, in response to a UL reference signal transmission configuration in the DL band being configured. The UL reference signal is to be used for DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource.

In some embodiments, a base station operating in a FDD system may include one or more processors, and memory comprising instructions to cause the base station to perform operations of receiving, from the wireless device in the FDD system, an UL reference signal in a DL band allocated for DL transmission in the FDD system, and performing DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource, based on the received UL reference signal.

The proposed solutions enable the wireless device to send the UL reference signal in the DL band, and such reference signal may be received and used at the base station side to perform reciprocity-based beamforming for the DL band. Since full channel information is available on the base station side, it is possible to improve the MIMO performance in DL. Especially, in DL, SU-MIMO performance can be improved, and MU-MIMO capability can be enabled. This would significantly increase the DL cell capacity especially for massive MIMO and distributed MIMO systems, where many antennas are used on the base station side.

Brief Description of the Drawings

The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

Figure 1 shows a feedback-based beamforming process for DL band in the FDD system;

Figure 2A shows a general front-end structure of a FDD transceiver;

Figure 2B shows a general front-end structure of a TDD transceiver;

Figure 3 illustrates one example of a cellular communications system in which embodiments of the present disclosure may be implemented;

Figure 4 is a flowchart illustrating a method performed by a wireless device in a FDD system according to some embodiments of the present disclosure;

Figure 5 is a flowchart illustrating a method performed by a base station in a FDD system according to some embodiments of the present disclosure;

Figure 6 is a conceptual diagram illustrating an example of time-frequency configuration for UL reference signal transmission in the DL band according to some embodiments of the present disclosure;

Figure 7 is a schematic graph illustrating DL throughput comparison between the existing precoding scheme and the beamforming scheme according to some embodiments of the present disclosure;

Figure 8 illustrates an example of an operation flow between the wireless device and the base station according to some embodiments of the present disclosure;

Figure 9 is a schematic block diagram of a wireless device operating in a FDD system according to some embodiments of the present disclosure;

Figure 10 is a schematic block diagram of a base station operating in a FDD system according to some embodiments of the present disclosure;

Figures 11 to 14 show examples of the front-end structures designed for the wireless device of Figure 9, according to some embodiments of the present disclosure;

Figures 15 to 17 show examples of the front-end structures designed for the base station of Figure 10, according to some embodiments of the present disclosure;

Figure 18 shows examples of arrangements of antennas for the base station of Figure 10, according to some embodiments of the present disclosure;

Figure 19 illustrates a telecommunication network connected via an intermediate network to a host computer in accordance with some embodiments of the present disclosure;

Figure 20 is a generalized block diagram of a host computer communicating via a base station with a UE over a partially wireless connection in accordance with some embodiments of the present disclosure;

Figure 21 is a flowchart illustrating a method implemented in a communication system in accordance with one embodiment of the present disclosure;

Figure 22 is a flowchart illustrating a method implemented in a communication system in accordance with one embodiment of the present disclosure;

Figure 23 is a flowchart illustrating a method implemented in a communication system in accordance with one embodiment of the present disclosure; and

Figure 24 is a flowchart illustrating a method implemented in a communication system in accordance with one embodiment of the present disclosure.

Detailed Description

The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

Radio Node: As used herein, a “radio node” is either a radio access node or a wireless communication device.

Radio Access Node: As used herein, a “radio access node” or “radio network node” or “radio access network node” is any node in a radio access network of a cellular communications network that operates to wirelessly transmit and/or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., a New Radio (NR) base station (gNB) in a Third Generation Partnership Project (3GPP) Fifth Generation (5G) NR network or an enhanced or evolved Node B (eNB) in a 3GPP Long Term Evolution (LTE) network) , a high-power or macro base station, a low-power base station (e.g., a micro base station, a pico base station, a home eNB, or the like) , a relay node, a network node that implements part of the functionality of a base station (e.g., a network node that implements a gNB Central Unit or a network node that implements a gNB Distributed Unit) or a network node that implements part of the functionality of some other type of radio access node.

Core Network Node: As used herein, a “core network node” is any type of node in a core network or any node that implements a core network function. Some examples of a core network node include, e.g., a Mobility Management Entity (MME) , a Packet Data Network Gateway (P-GW) , a Service Capability Exposure Function (SCEF) , a Home Subscriber Server (HSS) , or the like. Some other examples of a core network node include a node implementing a Access and Mobility Function (AMF) , a User Plane Function (UPF) , a Session Management Function (SMF) , an Authentication Server Function (AUSF) , a Network Slice Selection Function (NSSF) , a Network Exposure Function (NEF) , a Network Function (NF) Repository Function (NRF) , a Policy Control Function (PCF) , a Unified Data Management (UDM) , or the like.

Communication Device: As used herein, a “communication device” is any type of device that has access to an access network. Some examples of a communication device include, but are not limited to: mobile phone, smart phone, sensor device, meter, vehicle, household appliance, medical appliance, media player, camera, or any type of consumer electronic, for instance, but not limited to, a television, radio, lighting arrangement, tablet computer, laptop, or Personal Computer (PC) . The communication device may be a portable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data via a wireless or wireline connection.

Wireless Communication Device: One type of communication device is a wireless communication device, which may be any type of wireless device that has access to (i.e., is served by) a wireless network (e.g., a cellular network) . Some examples of a wireless communication device include, but are not limited to: a User Equipment device (UE) in a 3GPP network, a Machine Type Communication (MTC) device, and an Internet of Things (IoT) device. Such wireless communication devices may be, or may be integrated into, a mobile phone, smart phone, sensor device, meter, vehicle, household appliance, medical appliance, media player, camera, or any type of consumer electronic, for instance, but not limited to, a television, radio, lighting arrangement, tablet computer, laptop, or PC. The wireless communication device may be a portable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data via a wireless connection.

Network Node: As used herein, a “network node” is any node that is either part of the radio access network or the core network of a cellular communications network/system.

Note that the description given herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system.

Note that, in the description herein, reference may be made to the term “cell” ; however, particularly with respect to 5G NR concepts, beams may be used instead of cells and, as such, it is important to note that the concepts described herein are equally applicable to both cells and beams. Sector is another term that is sometimes also used to represent a cell.

Herein, the terms “scheduled” and “configured” may be used exchangeable with each other, and the terms “schedule” and “configure” may also be used exchangeable with each other.

Note that, in the description herein, beamforming based on/utilizing UL and DL channel reciprocity may also be referred to as “reciprocity-based beamforming. ”

Figure 3 illustrates one example of a cellular communications system 300 in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communications system 300 is a 5G system (5GS) including a NR RAN. In this example, the RAN includes base stations 302-1 and 302-2, which in 5G NR are referred to as gNBs (e.g., LTE RAN nodes connected to 5GC, which are referred to as gn-eNBs) , controlling corresponding (macro) cells 304-1 and 304-2. The base stations 302-1 and 302-2 are generally referred to herein collectively as base stations 302 and individually as base station 302. Likewise, the (macro) cells 304-1 and 304-2 are generally referred to herein collectively as (macro) cells 304 and individually as (macro) cell 304. The RAN may also include a number of low power nodes 306-1 through 306-4 controlling corresponding small cells 308-1 through 308-4. The low power nodes 306-1 through 306-4 can be small base stations (such as pico or femto base stations) or Remote Radio Heads (RRHs) , or the like. Notably, while not illustrated, one or more of the small cells 308-1 through 308-4 may alternatively be provided by the base stations 302. The low power nodes 306-1 through 306-4 are generally referred to herein collectively as low power nodes 306 and individually as low power node 306. Likewise, the small cells 308-1 through 308-4 are generally referred to herein collectively as small cells 308 and individually as small cell 308. The cellular communications system 300 also includes a core network 310, which in the 5GS is referred to as the 5G core (5GC) . The base stations 302 (and optionally the low power nodes 306) are connected to the core network 310.

The base stations 302 and the low power nodes 306 provide service to wireless communication devices 312-1 through 312-5 in the corresponding cells 304 and 308. The wireless communication devices 312-1 through 312-5 are generally referred to herein collectively as wireless communication devices 312 and individually as wireless communication device 312. In the following description, the wireless communication devices 312 are oftentimes UEs, but the present disclosure is not limited thereto.

In a FDD system, reciprocity-based beamforming is not applicable since the UL and DL transmissions use different part of the spectrum of a FDD band. Instead, codebook-based precoder is used for DL beamforming. Unfortunately, due to the constraint of the feedback bandwidth which limits the accuracy of the CSI report, the MIMO performance is limited in the FDD system. Especially, codebook-based precoding/beamforming is not effective in MU-MIMO, which is an important feature to significantly increase cell capacity of 5G and its evolution towards 6G using massive MIMO and distributed MIMO technologies.

Systems and methods for transmitting a UL reference signal to enable beamforming based on UL and DL channel reciprocity in the FDD system are provided. Figure 4 is a flowchart illustrating a method performed by a wireless device which is operating in a FDD system or operating in a FDD spectrum, according to some embodiments of the present disclosure. The method may include transmitting a UL reference signal in a DL band which is originally allocated for DL transmission in the FDD system, in response to a UL reference signal transmission configuration in the DL band being configured, where the UL reference signal is to be used for DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource (step 402) . In some embodiments, the method may also optionally include, as shown in dashed-line blocks in Figure 4, one or more of: prior to transmitting the UL reference signal, receiving, from a base station in the FDD system, a DL signaling for signaling the UL reference signal transmission configuration in the DL band (step 400) ; maintaining or pausing, in a period corresponding to the UL reference signal transmission in the DL band, UL transmission in a UL band allocated for UL transmission in the FDD system (step 404) ; and resuming reception of a DL signal in the DL band after the UL reference signal transmission in the DL band is completed (step 406) . In some embodiments, the reference signals may be sent periodically, semi-periodically, or aperiodically in the same mechanism as defined for normal SRS, for example. In some embodiments, the UL reference signal in the DL band may be transmitted periodically, semi-periodically or aperiodically in accordance with the UL reference signal transmission configuration in the DL band, or transmitted when a base station requires for the reference signal. The UL reference signal transmission configuration may be configured and informed to the wireless device by the base station through a DL signaling, for example, through PDCCH or PDSCH. This enables a flexible configuration for transmitting the UL reference signal in the DL band.

Traditionally in the FDD system, the DL band only allows the DL transmission while the UL band only allows the UL transmission. Differently, in the present disclosure, some embodiments enable the wireless device, such as UE, to send UL signals, such as reference signals (e.g., SRS, demodulation reference signal (DMRS) ) in the DL band. Based on channel reciprocity between UL and DL channels, such reference signals may be used at the base station side to perform reciprocity-based beamforming for the DL band. In this way, for the DL band of the FDD system, SU-MIMO performance can be improved, and MU-MIMO capability is enabled since the full channel information is available on the base station side.

In some embodiments, the wireless device may transmit the UL reference signal by switching from DL reception to UL transmission in the DL band in response to the UL reference signal transmission configuration in the DL band, and transmitting the UL reference signal in the DL band. For an antenna of the wireless device through which the UL reference signal transmission in the DL band is to be performed, the antenna may be switched to be uncoupled from a DL receiver chain for receiving a DL signal in the DL band, and to be coupled to a UL transmit chain for transmitting a UL signal in the DL band. The UL transmit chain for the DL band may include a transmit bandpass filter (BPF) for DL band, a power amplifier (PA) , an up-converter and a digital-to-analog converter (DAC) in an arrangement similar to an existing UL transmit chain for transmitting UL signals in the UL band in the front-end part of the wireless device. A switching element, such as SPDT switch, may be provided between the antenna and the UL transmit chain and the DL receiver chain for the DL band. The UL transmit chain may be provided per antenna or provided for being shared by part or all of multiple antennas of the wireless device. In the latter case, an antenna through which the UL reference signal transmission in the DL band is to be performed may be switched to be coupled to the UL transmit chain, while keeping the other antennas be uncoupled to the UL transmit chain.

In some embodiments, the wireless device may switch from UL transmission to DL reception in the DL band after the UL reference signal transmission is completed. Specifically, for an antenna through which the UL reference signal transmission in the DL band is completed, the antenna may be switched to be uncoupled to the UL transmit chain to stop the UL reference signal transmission in the DL band, and to be coupled to the DL receiver chain to resume reception of the DL signal in the DL band.

Figure 5 is a flowchart illustrating a method performed by a base station in a FDD system according to some embodiments of the present disclosure. In some embodiments, a method performed by a base station in the FDD system may include: receiving, from a wireless device in the FDD system, a UL reference signal in a DL band originally allocated for DL transmission in the FDD system (step 502) ; and performing DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource, based on the received UL reference signal (step 504) . In some embodiments, as shown in dashed-line blocks in Figure 5, the method may also optionally include one or more of: prior to receiving the UL reference signal, transmitting, to the wireless device, a DL signaling for signaling UL reference signal transmission configuration in the DL band (step 500) ; when there is no UL reference signal transmission configured in the DL band in a predefined period configured for UL reference signal transmission, configuring and performing DL transmission in the DL band in this period to the wireless device or one or more different wireless device in the FDD system (step 506) ; resuming DL transmission in the DL band after the UL reception of the reference signal is completed (step 508) . In some embodiments, the base station may receive the UL reference signal in the DL band in a periodic, semi-periodic or aperiodic manner. In some embodiments, the base station may perform the DL beamforming by performing UL channel estimation based on the UL reference signal to obtain UL channel estimates of the UL channel in the DL band, deriving DL channel estimates from the UL channel estimates utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource, and performing DL beamforming based on the DL channel estimates. With the reciprocity-based beamforming scheme, the DL beamforming may be based on channel information of higher accuracy, and therefore may perform much better than the codebook-based beamforming/precoding at the base station side.

In some embodiments, for example in the SU-MIMO mode, the base station may receive UL reference signal transmission in the DL band from different antennas included in a single wireless device at different symbols or slots, or from all antennas or selected antennas included in the wireless device simultaneously. In this situation, with the received UL reference signals transmitted from multiple antennas of the single wireless device, the base station may obtain channel estimates of a channel between the multiple antennas of the single wireless device and the antennas of the base station, and then perform channel estimation based on the obtained channel estimates. This may enable better channel estimation and beamforming for the DL band.

In some embodiments, when there are multiple wireless devices in the FDD system, the base station may receive UL reference signal transmission in the DL band from the multiple wireless devices simultaneously or at different symbols or slots. In one example, for example in subband full-duplexing mode, the multiple wireless devices may be allocated with respective subbands of the DL band, and may transmit their UL reference signals in the respective subbands at the same time. When one of the wireless devices transmits its UL reference signal in a suband of the DL band, transmission of a DL signal in the subband may be paused during the period of the UL reference signal transmission window, while the base station may maintain, configure or transmit a DL signal in one or more subbands, different from the subband used for UL reference signal transmission, of the DL band to one or more different wireless device. In another example, the UL reference signal in the DL band may be transmitted from the wireless devices by multiplexing between the wireless devices, for example, frequency domain multiplexing (FDM, e.g. using COMB where wireless devices use different subcarriers within each resource block (e.g. comprising 12 subcarriers) to transmit their reference signals) , time domain multiplexing (TDM, e.g. using different symbols) , code domain multiplexing (CDM, e.g. using different codes on the same frequency-time resources) .

In some embodiments, for example in the MU-MIMO mode, each wireless device normally is configured to transmit only one or two layers. Therefore, the reference signal only needs to be transmitted from one or two antennas, that is, the base station may receive UL reference signal transmission in the DL band from part of multiple antennas included in each of the wireless devices. The part of antennas may be selected by either the wireless device itself or the base station based on channel information. If antenna selection is made by the wireless device, it may use previous DL channel information estimated by the wireless device, e.g., based on CSI-RS, DL DMRS, etc. If antenna selection is made by the base station, it may use the channel information available at the base station side, e.g., the UL channel information estimated by the base station (e.g., based on SRS, UL DMRS) , the CSI report from the wireless device, etc. In this case, the base station may inform the wireless device the result of antenna selection by DL signaling, e.g., through PDCCH or PDSCH. As an example, one or more antennas with better channel qualities, e.g., having higher SINRs or having higher channel gains, may be selected. With such embodiment of transmitting and receiving UL reference signal in the DL band from part of the antennas included in the wireless device, overhead of transmitting reference signals per UE (wireless device) may be reduced. Specifically, when it is known from available channel information that only part of the antennas are needed for reference signal transmission (to get the channel information regarding these antennas) , only requesting these antennas to transmit reference signals would reduce the overhead, especially when antenna switching is used for reference signal transmission. In this case, complexity due to additional UL reference signal transmission in the DL band may also be reduced at both of the wireless device side and the base station side.

In some embodiments, the base station may receive the UL reference signal by switching from DL transmission to UL reception in the DL band, and receiving the UL reference signal in the DL band. Specifically, for an antenna of the base station through which the UL reference signal reception in the DL band is to be performed, the base station may switch the antenna to be uncoupled from a DL transmit chain for transmitting a DL signal in the DL band, and to be coupled to a UL receiver chain for receiving a UL signal in the DL band. The UL receiver chain may be provided per antenna, and include a DL-band receiver bandpass filter (BPF) , a low noise amplifier (LNA) , a down-converter and an analog-to-digital converter (ADC) in an arrangement similar to an existing UL receiver chain for receiving UL signals in the UL band in the front-end part of the base station. A switching element, for example, SPDT switch, may be provided between the antenna and the UL receiver chain and the DL transmit chain for the DL band.

In some embodiments, the base station may switch from UL reception to DL transmission in the DL band after the UL reference signal transmission is completed. Specifically, for an antenna through which the UL reference signal reception in the DL band is completed, the base station may switch the antenna to be uncoupled to the UL receiver chain to stop the UL reference signal reception in the DL band, and to be coupled to the DL transmit chain to resume transmission of DL signal in the DL band.

Figure 6 is a conceptual diagram illustrating an example of time-frequency configuration for UL reference signal transmission in the DL band according to some embodiments of the present disclosure. The horizontal axis denotes “time, ” and the vertical axis denotes “frequency. ” In the FDD system, UL and DL use different frequency spectra of the whole band. In UL, wireless devices transmit UL signals to the base station, e.g., gNB, using the frequency spectrum allocated for UL transmissions, referred to as UL band (denoted as “UL” in Figure 6) . In DL, the base station transmits DL signals to wireless devices, using the frequency spectrum allocated for DL transmissions, referred to as DL band (denoted as “DL” in Figure 6) . As shown in Figure 6, a UL transmission window, denoted as shaded area, may be defined in the DL band for the wireless devices to transmit reference signals, e.g., SRS or DMRS, to the base station. In some embodiments, the UL transmission window in the DL band may be defined as a periodic, semi-periodic or aperiodic pattern in accordance with the UL reference signal transmission configuration in the DL band. In some embodiments, the UL transmission window in the DL band may have a time length of multiple symbols. The length may be adjustable in accordance with the UL reference signal transmission configuration in the DL band. The multi-symbol time may include a guard period for the wireless device to switch from DL reception to UL transmission in the DL band, and a transmission period for the wireless device to transmit the UL reference signal in the DL band. For example, the UL transmission window may have a length of 3-symbol time, which may include 1-symbol time for guard time for the wireless device to switch from DL reception to UL transmission and 2-symbol time for sending the reference signal.

In the example of Figure 6, the UL transmission window is defined periodically in the DL band, similarly to the TDD pattern defined in a TDD system. For example, the UL transmission window may have a length of 3-symbol time and provided every 5 slots (e.g. 1 slot is 0.5 ms long for a 5G NR system with 30kHz subcarrier spacing) in the DL band. Given that each slot consists of 14 symbols, the overhead of UL transmission in DL band is 4.3%which is very low and would not cause much loss in DL time-domain resources. Since reciprocity-based beamforming will increase bit rate significantly, there is still a big net gain in DL than traditional FDD systems.

As denoted by shaded areas, the wireless device may suspend reception of a DL signal in the DL band within the UL transmission window, and resume DL reception after the UL transmission window lapses. In this case, resource of time and frequency may be wasted when there is no UL reference signal transmission scheduled in DL band within the UL transmission window. Fortunately, the overhead of the UL transmission window is very low as mentioned above, and advantages may be achieved that it would not cause any interference between the UL reference signal transmission and the DL transmissions in different cells, since the UL transmission window is reserved for UL transmissions in all cells. Overall, the system performance would benefit from the fact that reciprocity-based beamforming is enabled, as compared with the existing FDD system which uses codebook based precoder to do beamforming and has worse performance. Simulation is performed to compare the SU-MIMO performance of codebook-based precoding and reciprocity-based beamforming. It shall be understand that also the simulation shown here is for SU-MIMO. MU-MIMO simulations may be similarly conducted. The simulation parameters are listed in Table 1 below, in which the SRS is transmitted in a UL transmission window defined with a length of 2-symbol time and provided every 5 slots in the DL band, and UE represents wireless device. Technical specifications, for example, 3GPP TS. 38.211 and 3GPP TS. 38.214, may be referred to with respect to parameters in Table 1.

Table 1 Simulation Parameters

With the simulation parameters in Table 1, the schematic graph of Figure 7 and the following table, Table 2, illustrate DL throughput (e.g., UE PDSCH throughput) comparison between the existing precoding scheme and the beamforming scheme according to some embodiments of the present disclosure.

Table 2 DL throughput Comparison

It shows significant throughput improvement in medium and high SNR region for SU-MIMO. The maximum throughput improvement ratio may reach 42.08%. Here, DL-UL SNR offset is assumed 20 dB. For MU-MIMO with massive MIMO, the low and medium SNR region would also benefit. In particularly, the DL-UL SNR offset is usually smaller for distributed MIMO. In this case, the gain of using reciprocity-based beamforming will be even higher. In the above simulation, SU-MIMO results are given as an example. MU-MIMO is supposed to achieve even higher gains in cell capacity/throughput since more layers can be scheduled with MU-MIMO, while codebook-based precoding can only be effective for SU-MIMO with fewer layers.

In some embodiments, the UL transmission window in DL band may be not reserved for UL transmission only. The UL transmission window may be defined as available for the base station to configure DL transmission to wireless devices in the FDD system. For example, when there is no UL reference signal transmission in the UL transmission window, the base station may configure and transmit a DL signal in the UL transmission window to one or more different wireless device. In one embodiment, the base station may opportunistically schedule DL transmissions in the UL transmission window in DL band when it determines it would not suffer from interferences from the UL reference signal transmissions of other cells and would not cause the interferences to the UL reference signal reception of other cells. In this case, resource used for DL transmission may be the same as in the existing FDD system (i.e., DL band is only used for DL transmission) . This may be most beneficial when the traffic load is low. This may avoid waste of resource and improve resource utilization.

In some embodiments, UL transmission in the UL band may be maintained or pause in a period corresponding to the UL transmission window. Dashed areas in the UL band corresponding to the shaded areas of the UL transmission window in Figure 6 may indicate such a period. A wireless device may transmit UL signals in the UL band in the period simultaneously with its UL reference signal transmission in the DL band, if the wireless device has capability to transmit on both DL and UL bands simultaneously. In this way, transmission efficiency may be improved for the same wireless device. Alternatively, the wireless device may stop its UL transmission in the UL band in the period corresponding to the UL transmission window, if it does not have capability to transmit on both DL and UL bands simultaneously. This may reduce complexity at the wireless device side, while the system capacity may not be impacted with multiple users. As another example, time and frequency resource within the period may be used for other wireless device (s) to transmit UL data. This may be useful, because if the wireless device transmitting the reference signal doesn't have data to send or capacity to transmit on both DL and UL bands simultaneously, allowing other wireless devices to transmit their data will improve resource utilization. In some embodiments, the base station may schedule UL data transmission from the wireless devices during the period corresponding to the UL transmission window according to capabilities of these wireless devices and traffic demand.

Although not shown in Figure 6, in some embodiments, each of the UL and DL bands in the FDD system may be divided into subbands allocated to different, multiple wireless devices. UL transmission windows may be defined/reserved, for example, by the base station, for the multiple wireless devices respectively in the respective subbands of the DL band. The wireless devices may transmit UL reference signals in the respective subbands, respectively, simultaneously or at different symbols or slots.

In some other embodiments, the UL transmission window in DL band may be used by multiple wireless devices by multiplexing between them. The multiplexing may be FDM (e.g. using COMB) , TDM (e.g. using different symbols) , CDM (e.g. using different codes on the same frequency-time resources) , etc.

Figure 8 illustrates an example of an operation flow between the wireless device and the base station according to some embodiments of the present disclosure. First, the base station may send for example, through PDCCH or PDSCH to the wireless device, a DL signaling for configuring a UL reference signal transmission configuration in the DL band (operation 800) . In some embodiments, the configuration may include reserving or defining a UL transmission window in the DL band. In response to receiving the DL signaling, the wireless device may transmit a reference signal (e.g., SRS or DMRS) in the defined/reserved UL transmission window in the DL band to the base station (operation 802) . In some embodiments, the wireless device may stop receiving DL signals in the UL transmission window. The wireless device may resume the DL signal reception in the DL band after the UL transmission window lapses (operation 806) . The base station may receive and use the UL reference signal for performing reciprocity-based beamforming in the DL band for the wireless device (operation 804) . In some embodiments, the base station may stop transmit DL signals in the UL transmission window. The base station may resume the DL signal transmission in the DL band after the UL transmission window lapses (operation 808) . The base station may perform next DL transmission to the wireless device by using DL beamforming configurations. In case of multiple wireless devices, the base station may use the received reference signals transmitted from the different wireless devices to estimate the UL channel. Then, DL channel estimates may be derived based on the UL channel estimates, leveraging UL and DL channel reciprocity which is enabled a proper UL/DL antenna calibration to calibrate out the differences in UL and DL transceiver components. Then, the base station may use the derived DL channel estimates to schedule multiple layers for the multiple wireless devices and calculate the corresponding beamforming weights to beamform these layers to the corresponding wireless devices. For SU-MIMO, reciprocity-based beamforming performs better than the feedback-based precoding/beamforming, when the reciprocity-based DL channel estimates are of good quality, e.g. when UL SNR of the SRS signal is good. Furthermore, reciprocity-based beamforming is effective for MU-MIMO enabling multiple users to transmit simultaneously using the same frequency-time resources, while feedback-based beamforming doesn't perform well in MU-MIIMO. Therefore, reciprocity-based beamforming may significantly increase cell capacity by serving more wireless devices simultaneously.

Figure 9 is a schematic block diagram of a wireless device operating in a FDD system according to some embodiments of the present disclosure. As illustrated, the wireless device 900 includes one or more processors 902 (e.g., CPUs, ASICs, FPGAs, and/or the like) , memory 904, and one or more transceivers 906 each including one or more transmitters and one or more receivers coupled to one or more antennas 912. The transceiver (s) 906 includes radio-front end circuitry connected to the antenna (s) 912 that is configured to condition signals communicated between the antenna (s) 912 and the processor (s) 902, as will be appreciated by on of ordinary skill in the art. The processors 902 are also referred to herein as processing circuitry. The transceivers 906 are also referred to herein as radio circuitry. In some embodiments, the functionality of the wireless device 900 described above may be fully or partially implemented in software that is, e.g., stored in the memory 904 and executed by the processor (s) 902. Note that the wireless communication device 900 may include additional components not illustrated in Figure 9 such as, e.g., one or more user interface components (e.g., an input/output interface including a display, buttons, a touch screen, a microphone, a speaker (s) , and/or the like and/or any other components for allowing input of information into the wireless communication device 900 and/or allowing output of information from the wireless communication device 900) , a power supply (e.g., a battery and associated power circuitry) , etc.

In some embodiments, a computer program is provided to include instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the wireless device 900 according to any of the embodiments described herein, for example, one or more of the steps included in the method shown in Figure 4. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory) .

In some embodiments, the wireless device 900 may include one or more modules, each of which is implemented in software. The module (s) provide the functionality of the wireless device 900 according to any of the embodiments described herein.

Figure 10 is a schematic block diagram of a base station operating in a FDD system according to some embodiments of the present disclosure. As illustrated, the base station 1000 includes one or more processors 1002 (e.g., CPUs, ASICs, FPGAs, and/or the like) , memory 1004, one or more transceivers 1006 each including one or more transmitters and one or more receivers coupled to one or more antennas 1012, and network interface 1014. The transceiver (s) 1006 includes radio-front end circuitry connected to the antenna (s) 1012 that is configured to condition signals communicated between the antenna (s) 1012 and the processor (s) 1002, as will be appreciated by on of ordinary skill in the art. The processors 1002 are also referred to herein as processing circuitry. The transceivers 1006 are also referred to herein as radio circuitry. The network interface 1014 may be configured to provide communications with other network nodes (e.g., with other base stations) and/or core network. In some embodiments, the functionality of the base station 1000 described above may be fully or partially implemented in software that is, e.g., stored in the memory 1004 and executed by the processor (s) 1002. Note that the base station 1000 may include additional components not illustrated in Figure 10, such as a power supply and associated power circuitry, etc.

In some embodiments, a computer program is provided to include instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the base station 1000 according to any of the embodiments described herein, for example, one or more of the steps included in the method shown in Figure 5. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory) .

In some embodiments, the base station 1000 includes one or more modules, each of which is implemented in software. The module (s) provide the functionality of the base station 1000 according to any of the embodiments described herein.

Below description will be made on modifications of radio-front end structures in the wireless device and the base station for implementation of UL transmission of reference signals in the DL band of a FDD system. The modifications may be made on the radio-front end circuitries of the wireless device 900 in Figure 9 and the base station 1000 in Figure 10.

Figures 11 to 14 show examples of modified front-end structures designed for the wireless device of Figure 9, according to some embodiments of the present disclosure.

Compared with a general front-end part of a wireless device, the front-end part of the wireless device as illustrated in Figure 11 may further include a UL transmit chain 1102 for transmitting a UL signal in the DL band, which may be referred to as “first UL transmit chain. ” Now the wireless device may has a front-end structure including two UL transmit chains (in which the UL transmit chain 1104 for transmitting a UL signal in the UL band may be referred to as “second UL transmit chain” ) and one DL receiver chain 1100 between an antenna 1108 and the baseband processing part. The first UL transmit chain 1102 may include a DL-band transmit bandpass filter (TX BPF) , a power amplifier (PA) , an up-converter and a digital-to-analog converter (DAC) , similarly to the components of the second UL transmit chain 1104. The DL receiver chain 1100 may include a DL-band receiver bandpass filter (RX BPF) , a low noise amplifier (LNA) , a down-converter and an analog-to-digital converter (ADC) in the same manner as the components of the conventional receiver chain. The front-end part of the wireless device may further include a switching element 1112 provided between the antenna 1108 and the first UL transmit chain 1102. In the example of Figure 11, the switching element 1112 is implemented with a SPDT switch. This is just an example, and various types of switching elements may be used as long as it may be used to switch the antenna between the first UL transmit chain 1102 and the DL receiver chain 1100.

With reference to Figure 11, when UL reference signal in DL band is not configured/scheduled by the base station, the SPDT switch turns to couple the antenna 1108 to the DL receiver chain 1100. The wireless device sends and receives signals in the UL and DL bands as in the conventional FDD process. When transmission of UL reference signal in DL band is configured, the SPDT switch may turn to decouple the antenna 1108 from the DL receiver chain 1100, and to couple the antenna 1108 to the first UL transmit chain 1102. Then the wireless device may use the DL band to send the UL reference signal to the base station. Since the antenna 1108 is decoupled from the DL receiver chain 1100, DL reception in the DL band is stopped. On the other hand, the wireless device may maintain UL signal transmission in the UL band, that is, retaining the sending mode on two frequency bands of DL and UL bands and simultaneously sending the UL reference signal in the DL band and UL data in the UL band. Alternatively, the wireless device may suspend the UL transmission in the UL band. After the UL reference signal transmission in DL band is completed, the SPDT switch may turn back to the DL receiver chain 1100, until next UL reference signal transmission in DL band. The rest of the process may be same as conventional FDD system.

Figure 12 shows an example of modified front-end structure designed for the wireless device of Figure 9, according to some embodiments of the present disclosure. Description will be focused on differences from the example of Figure 11, while repeated description will be omitted. The DL receiver chain 1200 in Figure 12 may be the same as the DL receiver chain 1100 in Figure 11. The first UL transmit chain 1202 and the second UL transmit chain 1204 may be functionally the same as the first UL transmit chain 1102 and the second UL transmit chain 1104, while one DAC is shared between the two transmit chains. Specifically, a switching element 1214, denoted as “SPDT switch #2” in Figure 12, may be provided adjacent to the DAC, and switch to place the DAC either in the first UL transmit chain 1202 or the second UL transmit chain 1204. When UL reference signal in DL band is not configured/scheduled by the base station, the switching element 1212 (denoted as “SPDT switch #1” ) and the switching element 1214 may turn to couple the antenna 1208 and the DAC to the DL receiver chain 1200 and the second UL transmit chain 1204, respectively. The wireless device may conduct normal UL transmission in the UL band and DL reception in the DL band. If UL reference signal transmission in DL band is configured, the

switching elements

1212 and 1214 may turn to decouple the antenna 1208 and the DAC from the DL receiver chain 1200 and the second UL transmit chain 1204, respectively, and to couple the antenna 1208 and the DAC to the first UL transmit chain 1202. Then the wireless device may use the DL band to send the UL reference signal to the base station. In this example, the wireless device may only send the UL reference signal in DL band to the base station, while stopping DL reception in the DL band and UL transmission in the UL band. After transmission of UL reference signal in DL band is completed, the

switching elements

1212 and 1214 may turn back to the DL receiver chain 1200 and the second UL transmit chain 1204, respectively, until the next transmission of UL reference signal in DL band. The rest of the process may be same as conventional FDD system.

In this example, one DAC is shared between the two transmit chains, and this may reduce complexity in designing the front-end part of the wireless device. Further, by making the wireless device and the base station work on only one band to transmit and receive the UL reference signal in DL band, it is possible to reduce complexity of baseband processing.

Figure 13 shows an example of modified front-end structure designed for the wireless device of Figure 9, according to some embodiments of the present disclosure. Description will be focused on differences from the example of Figure 11, while repeated description will be omitted. The DL receiver chain 1300 in Figure 12 may be the same as the DL receiver chain 1100 in Figure 11. The first UL transmit chain 1302 and the second UL transmit chain 1304 may be functionally the same as the first UL transmit chain 1102 and the second UL transmit chain 1104, while the first and second UL transmit chains 1302 and 1304 share the same PA, up-converter and DAC as shown in Figure 13. In this case, the PA may be implemented with a wideband PA covering both the DL and UL band, and the DAC may be implemented with a high-speed DAC operating at a higher speed than the DAC in the example of Figures 11 and 12. Similarly to the example of Figure 11, a switching element 1312 is provided between the antenna 1308 and the first UL transmit chain 1302. The switching element 1312 may be implemented with a SPDT switch. When transmission of UL reference signal in DL band is configured, the SPDT switch may turn to decouple the antenna 1308 from the DL receiver chain 1300, and to couple the antenna 1308 to the first UL transmit chain 1302. Then the wireless device may use the DL band to send the UL reference signal to the base station. Since the antenna 1308 is decoupled from the DL receiver chain 1300, DL reception in the DL band is stopped. On the other hand, the wireless device may maintain UL signal transmission in the UL band, that is, retaining the sending mode on two frequency bands of DL and UL bands and simultaneously sending the UL reference signal in the DL band and UL data in the UL band. Alternatively, the wireless device may suspend the UL transmission in the UL band. After the UL reference signal transmission in DL band is completed, the SPDT switch may turn back to the DL receiver chain 1300, until next UL reference signal transmission in DL band. The rest of the process may be same as conventional FDD system.

In this example, by sharing components including the PA, the up-converter and the DAC between the two transmit chains, it is possible to further reduce complexity in designing the front-end part of the wireless device, and acceptance of the increased complexity at the wireless device side is therefore feasible. Further, it is possible to make the wireless device and the base station work on only one band to transmit and receive the UL reference signal in DL band, and thus to further reduce complexity of baseband processing.

Although Figures 11 to 13 show that the first UL transmit chain is provided per antenna, they are illustrated merely as examples, and the UL transmit chain for the DL band may be provided for being shared by part or all of multiple antennas in the wireless device, as shown in Figure 14 described in the following.

Figure 14 shows an example of modified front-end structure designed for the wireless device of Figure 9, according to some embodiments of the present disclosure. Description will be focused on differences from the example of Figure 11, while repeated description will be omitted. Each of the DL receiver chain 1400-1 and 1400-2 in Figure 14 may be the same as the DL receiver chain 1100 in Figure 11, and each of the UL transmit chains 1404-1 and 1404-2 in Figure 14 may be the same as the second UL transmit chain 1104 in Figure 11.

As shown in Figure 14, a single UL transmit chain 1402 ( “first UL transmit chain” ) for transmitting a UL signal in the DL band is provided for being shared between two antennas 1408-1 and 1408-2. This is just an example, and one first UL transmit chain 1402 may be shared among three or more antennas included in the wireless device. Switching elements 1412-1 and 1412-2 are provided respectively between the antennas 1408-1 and 1408-2 and the first UL transmit chain 1402. The switching elements may be implemented with SPDT switches. When UL reference signal in DL band is not configured/scheduled by the base station, the SPDT switch turns to couple the antennas 1408-1 and 1408-2 to the DL receiver chains 1400-1 and 1400-2, respectively. The wireless device sends and receives signals in the UL and DL bands as in the conventional FDD process. When transmission of UL reference signal in DL band is configured for one of the antennas 1408-1 and 1408-2, for example, the antenna 1408-1, the SPDT switch 1412-1 may turn to decouple the antenna 1408-1 from the DL receiver chain 1400-1, and to couple the antenna 1408-1 to the first UL transmit chain 1402. Then the wireless device may use the DL band to send the UL reference signal to the base station from the antenna 1408-1. Since the antenna 1408-1 is decoupled from the DL receiver chain 1400-1, DL reception in the DL band is stopped for the antenna 1408-1. After the UL reference signal transmission in DL band is completed for the antenna 1408-1, the SPDT switch 1412-1 may turn back to the DL receiver chain 1400-1. When transmission of UL reference signal in DL band is configured for the other antenna 1408-2, the SPDT switch 1412-2 may turn to decouple the antenna 1408-2 from the DL receiver chain 1400-2, and to couple the antenna 1408-2 to the first UL transmit chain 1402. Then the wireless device may use the DL band to send the UL reference signal to the base station from the antenna 1408-2. Since the antenna 1408-2 is decoupled from the DL receiver chain 1400-2, DL reception in the DL band is stopped for the antenna 1408-2. After the UL reference signal transmission in DL band is completed for the antenna 1408-2, the SPDT switch 1412-2 may turn back to the DL receiver chain 1400-2. With this embodiment providing only one transmit chain in the DL band, the required complexity of structural modification can be significantly reduced at the wireless device side.

In the example where a single UL transmit chain for transmitting a UL signal in the DL band is provided for being shared between multiple antennas, the antennas may be switched to be coupled to the single UL transmit chain at different time slots, where each time slot here may correspond to a UL transmission window for transmitting UL reference signal in DL band. At each time slot the wireless device may switch one of the antennas to be coupled to the single UL transmit chain to transmit the UL reference signal, while keeping the rest of the antennas be uncoupled to the UL transmit chain. In this way, channel information of all the antennas may be obtained by transmitting UL reference signal from the respective antennas at different time slots, and channel estimates of a channel between the multiple antennas of the wireless device and the antennas of the base station may be obtained based on the received UL reference signals transmitted from the multiple antennas of the wireless device. This is usually the case for SU-MIMO.

For MU-MIMO where there are multiple wireless devices and each of them has multiple antennas, each wireless device is normally configured to transmit a reference signal at only one or two layers. Therefore, instead of transmitting from all the antennas, each wireless device may transmit the reference signal from only one or two antennas, which may be are selected by either the wireless device itself or by the base station based on channel information. If the antenna selection is made by the wireless device, it may use the previous DL channel information estimated by itself, e.g., based on CSI-RS, DL DMRS etc. If the antenna selection is made by the base station, it may use the available channel information at the base station side, e.g., the UL channel information estimated by the base station (e.g., based on SRS, UL DMRS) , the CSI report from the wireless device etc. In this case, the base station may inform the wireless device information of the antenna selection by a DL signaling, e.g., through PDCCH or PDSCH. As an example, one or two antennas with better channel qualities, e.g., having higher SINRs or having higher channel gains, may be selected.

Figures 15 to 17 show examples of modified front-end structures designed for the base station of Figure 10, according to some embodiments of the present disclosure. Embodiments of the present disclosure may require structural modifications in the base station, which would increase its complexity and costs. However, it is generally acceptable to increase complexity at the base station side. For example, a feature called “subband full-duplexing” increases complexity of base station substantially, but it is currently being discussed in 3GPP. Therefore, modifications introduced to the base station side are foreseen acceptable from complexity point of view.

Compared with a general front-end part of a base station, the front-end part of the base station as illustrated in Figure 15 may further include a UL receiver chain 1502 for receiving a UL signal in the DL band, which may be referred to as “first UL receiver chain. ” Now the wireless device may has a front-end structure including two UL receiver chains (in which the UL transmit chain 1504 for receiving a UL signal in the UL band may be referred to as “second UL receiver chain” ) and one DL transmit chain 1500 between an antenna 1508 and the baseband processing part. The first UL receiver chain 1502 may include a DL-band receiver bandpass filter (RX BPF) , a low noise amplifier (LNA) , a down-converter and an analog-to-digital converter (ADC) , similarly to the components of the second UL receiver chain 1504. The DL transmit chain 1500 may include a DL-band transmit bandpass filter (TX BPF) , a power amplifier (PA) , an up-converter and a digital-to-analog converter (DAC) in the same manner as the components of the conventional transmit chain. The front-end part of the wireless device may further include a switching element 1512 provided between the antenna 1508 and the first UL receiver chain 1502. The switching element 1512 may be implemented with a SPDT switch. This is just an example, and various types of switching elements may be used as long as it may be used to switch the antenna between the first UL receiver chain 1502 and the DL transmit chain 1500.

With reference to Figure 15, when UL reference signal in DL band is not configured/scheduled, the SPDT switch turns to couple the antenna 1508 to the DL transmit chain 1500. The base station sends and receives signals in the UL and DL bands as in the conventional FDD process. When UL reference signal in DL band is sent from the wireless device side, the SPDT switch may turn to decouple the antenna 1508 from the DL transmit chain 1500, and to couple the antenna 1508 to the first UL receiver chain 1502. Then the base station may use the DL band to receive the UL reference signal from the wireless device. Since the antenna 1508 is decoupled from the DL transmit chain 1500, DL reception in the DL band is stopped. On the other hand, the base station may maintain UL signal reception in the UL band, that is, retaining the receiving mode on two frequency bands of DL and UL bands and simultaneously receiving the UL reference signal in the DL band and UL data in the UL band. Alternatively, the base station may suspend the UL reception in the UL band. After the UL reference signal transmission in DL band is completed, the SPDT switch may turn back to the DL transmit chain 1500, until next UL reference signal transmission in DL band. The rest of the process may be same as conventional FDD system.

Figure 16 shows an example of modified front-end structure designed for the base station of Figure 10, according to some embodiments of the present disclosure. Description will be focused on differences from the example of Figure 15, while repeated description will be omitted. The DL transmit chain 1600 in Figure 15 may be the same as the DL transmit chain 1500 in Figure 15. The first UL receiver chain 1602 and the second UL receiver chain 1604 may be functionally the same as the first UL receiver chain 1502 and the second UL receiver chain 1504, while one ADC is shared between the two receiver chains. Specifically, a switching element 1614, denoted as “SPDT switch #2” in Figure 16, may be provided adjacent to the ADC, and switch to place the ADC either in the first UL receiver chain 1602 or the second UL receiver chain 1604. When UL reference signal in DL band is not configured/scheduled, the switching element 1612 (denoted as “SPDT switch #1” ) and the switching element 1614 may turn to couple the antenna 1608 and the ADC to the DL transmit chain 1600 and the second UL receiver chain 1604, respectively. The base station may conduct normal DL transmission in the DL band and UL reception in the UL band. If UL reference signal in DL band is transmitted from the wireless device side, the

switching elements

1612 and 1614 may turn to decouple the antenna 1608 and the ADC from the DL transmit chain 1600 and the second UL receiver chain 1604, respectively, and to couple the antenna 1608 and the ADC to the first UL receiver chain 1602. Then the base station may use the DL band to receive the UL reference signal from the wireless device. In this example, the base station may only receive the UL reference signal in DL band, while stopping DL transmission in the DL band and UL reception in the UL band. After reception of UL reference signal in DL band is completed, the

switching elements

1612 and 1614 may turn back to the DL transmit chain 1600 and the second UL receiver chain 1604, respectively, until the next transmission of UL reference signal in DL band. The rest of the process may be same as conventional FDD system.

In this example, one ADC is shared between the two receiver chains, and this may reduce complexity in designing the front-end part of the base station. Further, by making the wireless device and the base station work on only one band to transmit and receive the UL reference signal in DL band, it is possible to reduce complexity of baseband processing.

Figure 17 shows an example of modified front-end structure designed for the base station of Figure 10, according to some embodiments of the present disclosure. Description will be focused on differences from the example of Figure 15, while repeated description will be omitted. The DL transmit chain 1700 in Figure 17 may be the same as the DL transmit chain 1500 in Figure 15. The first UL receiver chain 1702 and the second UL receiver chain 1704 may be functionally the same as the first UL receiver chain 1502 and the second UL receiver chain 1504, while the first and second

UL receiver chains

1702 and 1704 share the same LNA, down-converter and ADC as shown in Figure 17. In this case, the LNA may be implemented with a wideband LNA covering both the DL and UL band, and the ADC may be implemented with a high-speed ADC operating at a higher speed than the ADC in the example of Figures 15 and 16. Similarly to the example of Figure 15, a switching element 1712 is provided between the antenna 1708 and the first UL receiver chain 1702. The switching element 1712 may be implemented with a SPDT switch. When a UL reference signal in DL band is transmitted from the wireless device side, the SPDT switch may turn to decouple the antenna 1708 from the DL transmit chain 1700, and to couple the antenna 1708 to the first UL receiver chain 1702. Then the base station may use the DL band to receive the UL reference signal from the wireless device. Since the antenna 1708 is decoupled from the DL transmit chain 1700, DL reception in the DL band is stopped. On the other hand, the base station may maintain UL signal reception in the UL band, that is, retaining the receiving mode on two frequency bands of DL and UL bands and simultaneously receiving the UL reference signal in the DL band and UL data in the UL band. Alternatively, the wireless device may suspend the UL reception in the UL band. After the UL reference signal transmission in DL band is completed, the SPDT switch may turn back to the DL transmit chain 1700, until next UL reference signal transmission in DL band. The rest of the process may be same as conventional FDD system.

In this example, by sharing components including the LNA, the down-converter and the ADC between the two transmit chains, it is possible to further reduce complexity in designing the front-end part of the base station, and the increased complexity at the base station side is therefore acceptable, for example, in future 6G system. Further, it is possible to make the wireless device and the base station work on only one band to transmit and receive the UL reference signal in DL band, and thus to further reduce complexity of baseband processing.

Figure 18 shows examples of arrangements of antennas for the base station of Figure 10, according to some embodiments of the present disclosure. The base station may have multiple antennas including an array of receive antennas for receiving in the UL band and an array of transmit antennas for transmission in the DL band. The array of receive antennas and the array of transmit antennas may be provided in two panels respectively, or in two sub-panels on one panel. As shown in Figure 18, the base station may have a two-panel ( “Panel 0” and “Panel 1” ) design where one panel includes multiple receive antennas for FDD UL band, and the other panel includes multiple antennas for FDD DL band, while supporting both DL transmission and UL reference signal reception in the DL band. The two panels may be two separate panels. Alternatively, the base station may have a two-subpanel ( “Sub-panel 0” and “Sub-panel 1” ) design where two sub-panels on one panel are provided to include multiple receive antennas for FDD UL band and multiple antennas for FDD DL band, respectively. This follows the modular-design principles such that it can reuse the existing designs of FDD and TDD on different panels, respectively, and therefore reduce design and manufacture costs at the base station side. Figure 18 shows just examples of antenna arrangement, and variants thereof may also be envisioned and applied at the base station side.

Figure 19 illustrates a telecommunication network connected via an intermediate network to a host computer in accordance with some embodiments of the present disclosure. With reference to Figure 19, in accordance with an embodiment, a communication system includes a telecommunication network 1900, such as a 3GPP-type cellular network, which comprises an access network 1902, such as a RAN, and a core network 1904. The access network 1902 comprises a plurality of

base stations

1906A, 1906B, 1906C, such as Node Bs, eNBs, gNBs, or other types of wireless Access Points (APs) , each defining a

corresponding coverage area

1908A, 1908B, 1908C. Each

base station

1906A, 1906B, 1906C is connectable to the core network 1904 over a wired or wireless connection 1910. A first UE 1912 located in coverage area 1908C is configured to wirelessly connect to, or be paged by, the corresponding base station 1906C. A second UE 1914 in coverage area 1908A is wirelessly connectable to the corresponding base station 1906A. While a plurality of

UEs

1912, 1914 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 1906.

The telecommunication network 1900 is itself connected to a host computer 1916, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server, or as processing resources in a server farm. The host computer 1916 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider.

Connections

1918 and 1920 between the telecommunication network 1900 and the host computer 1916 may extend directly from the core network 1904 to the host computer 1916 or may go via an optional intermediate network 1922. The intermediate network 1922 may be one of, or a combination of more than one of, a public, private, or hosted network; the intermediate network 1922, if any, may be a backbone network or the Internet; in particular, the intermediate network 1922 may comprise two or more sub-networks (not shown) .

The communication system of Figure 19 as a whole enables connectivity between the connected

UEs

1912, 1914 and the host computer 1916. The connectivity may be described as an Over-the-Top (OTT) connection 1924. The host computer 1916 and the connected

UEs

1912, 1914 are configured to communicate data and/or signaling via the OTT connection 1924, using the access network 1902, the core network 1904, any intermediate network 1922, and possible further infrastructure (not shown) as intermediaries. The OTT connection 1924 may be transparent in the sense that the participating communication devices through which the OTT connection 1924 passes are unaware of routing of uplink and downlink communications. For example, the base station 1906 may not or need not be informed about the past routing of an incoming downlink communication with data originating from the host computer 1916 to be forwarded (e.g., handed over) to a connected UE 1912. Similarly, the base station 1906 need not be aware of the future routing of an outgoing uplink communication originating from the UE 1912 towards the host computer 1916.

Example implementations, in accordance with an embodiment, of the UE, base station, and host computer discussed in the preceding paragraphs will now be described with reference to Figure 20. In a communication system 2000, a host computer 2002 comprises hardware 2004 including a communication interface 2006 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 2000. The host computer 2002 further comprises processing circuitry 2008, which may have storage and/or processing capabilities. In particular, the processing circuitry 2008 may comprise one or more programmable processors, ASICs, FPGAs, or combinations of these (not shown) adapted to execute instructions. The host computer 2002 further comprises software 2010, which is stored in or accessible by the host computer 2002 and executable by the processing circuitry 2008. The software 2010 includes a host application 2012. The host application 2012 may be operable to provide a service to a remote user, such as a UE 2014 connecting via an OTT connection 2016 terminating at the UE 2014 and the host computer 2002. In providing the service to the remote user, the host application 2012 may provide user data which is transmitted using the OTT connection 2016.

The communication system 2000 further includes a base station 2018 provided in a telecommunication system and comprising hardware 2020 enabling it to communicate with the host computer 2002 and with the UE 2014. The hardware 2020 may include a communication interface 2022 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 2000, as well as a radio interface 2024 for setting up and maintaining at least a wireless connection 2026 with the UE 2014 located in a coverage area (not shown in Figure 20) served by the base station 2018. The communication interface 2022 may be configured to facilitate a connection 2028 to the host computer 2002. The connection 2028 may be direct or it may pass through a core network (not shown in Figure 20) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, the hardware 2020 of the base station 2018 further includes processing circuitry 2030, which may comprise one or more programmable processors, ASICs, FPGAs, or combinations of these (not shown) adapted to execute instructions. The base station 2018 further has software 2032 stored internally or accessible via an external connection. The base station 2018 may be an example of the base station 1000 shown in Figure 10, and configured to carry out the functionality of the base station 1000 according to any of the embodiments described herein, with the software 2032 and the processing circuitry 2030. For example, the processing circuitry 2030 may be configured to execute a computer program included in the software 2032 to perform one or more of the steps of the method in Figure 5. The radio interface 2024 may be implemented to have any of the front-end structures of Figures 15 to 17 according to the embodiments described herein.

The communication system 2000 further includes the UE 2014 already referred to. The UE's 2014 hardware 2034 may include a radio interface 2036 configured to set up and maintain a wireless connection 2026 with a base station serving a coverage area in which the UE 2014 is currently located. The hardware 2034 of the UE 2014 further includes processing circuitry 2038, which may comprise one or more programmable processors, ASICs, FPGAs, or combinations of these (not shown) adapted to execute instructions. The UE 2014 further comprises software 2040, which is stored in or accessible by the UE 2014 and executable by the processing circuitry 2038. The software 2040 includes a client application 2042. The client application 2042 may be operable to provide a service to a human or non-human user via the UE 2014, with the support of the host computer 2002. In the host computer 2002, the executing host application 2012 may communicate with the executing client application 2042 via the OTT connection 2016 terminating at the UE 2014 and the host computer 2002. In providing the service to the user, the client application 2042 may receive request data from the host application 2012 and provide user data in response to the request data. The OTT connection 2016 may transfer both the request data and the user data. The client application 2042 may interact with the user to generate the user data that it provides. The UE 2014 may be an example of the wireless device 900 shown in Figure 9, and configured to carry out the functionality of the wireless device 900 according to any of the embodiments described herein, with the software 2040 and the processing circuitry 2038. For example, the processing circuitry 2038 may be configured to execute a computer program included in the software 2040 to perform one or more of the steps of the method in Figure 4. The radio interface 2036 may be implemented to have any of the front-end structures of Figures 11 to 14 according to the embodiments described herein.

It is noted that the host computer 2002, the base station 2018, and the UE 2014 illustrated in Figure 20 may be similar or identical to the host computer 1916, one of the

base stations

1906A, 1906B, 1906C, and one of the

UEs

1912, 1914 of Figure 19, respectively. This is to say, the inner workings of these entities may be as shown in Figure 20 and independently, the surrounding network topology may be that of Figure 19.

In Figure 20, the OTT connection 2016 has been drawn abstractly to illustrate the communication between the host computer 2002 and the UE 2014 via the base station 2018 without explicit reference to any intermediary devices and the precise routing of messages via these devices. The network infrastructure may determine the routing, which may be configured to hide from the UE 2014 or from the service provider operating the host computer 2002, or both. While the OTT connection 2016 is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network) .

The wireless connection 2026 between the UE 2014 and the base station 2018 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE 2014 using the OTT connection 2016, in which the wireless connection 2026 forms the last segment. More precisely, the teachings of these embodiments may improve the e.g., data rate, latency, power consumption, etc. and thereby provide benefits such as e.g., reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc.

A measurement procedure may be provided for the purpose of monitoring data rate, latency, and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 2016 between the host computer 2002 and the UE 2014, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 2016 may be implemented in the software 2010 and the hardware 2004 of the host computer 2002 or in the software 2040 and the hardware 2034 of the UE 2014, or both. In some embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 2016 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which the

software

2010, 2040 may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 2016 may include message format, retransmission settings, preferred routing, etc. ; the reconfiguring need not affect the base station 2018, and it may be unknown or imperceptible to the base station 2018. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer 2002's measurements of throughput, propagation times, latency, and the like. The measurements may be implemented in that the

software

2010 and 2040 causes messages to be transmitted, in particular empty or ‘dummy' messages, using the OTT connection 2016 while it monitors propagation times, errors, etc.

Figure 21 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station, and a UE which may be those described with reference to Figures 19 and 20. For simplicity of the present disclosure, only drawing references to Figure 21 will be included in this section. In step 2100, the host computer provides user data. In sub-step 2102 (which may be optional) of step 2100, the host computer provides the user data by executing a host application. In step 2104, the host computer initiates a transmission carrying the user data to the UE. In step 2106 (which may be optional) , the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step 2108 (which may also be optional) , the UE executes a client application associated with the host application executed by the host computer.

Figure 22 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station, and a UE which may be those described with reference to Figures 19 and 20. For simplicity of the present disclosure, only drawing references to Figure 22 will be included in this section. In step 2200 of the method, the host computer provides user data. In an optional sub-step (not shown) the host computer provides the user data by executing a host application. In step 2202, the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In step 2204 (which may be optional) , the UE receives the user data carried in the transmission.

Figure 23 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station, and a UE which may be those described with reference to Figures 19 and 20. For simplicity of the present disclosure, only drawing references to Figure 23 will be included in this section. In step 2300 (which may be optional) , the UE receives input data provided by the host computer. Additionally or alternatively, in step 2302, the UE provides user data. In sub-step 2304 (which may be optional) of step 2300, the UE provides the user data by executing a client application. In sub-step 2306 (which may be optional) of step 2302, the UE executes a client application which provides the user data in reaction to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE initiates, in sub-step 2308 (which may be optional) , transmission of the user data to the host computer. In step 2310 of the method, the host computer receives the user data transmitted from the UE, in accordance with the teachings of the embodiments described throughout this disclosure.

Figure 24 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station, and a UE which may be those described with reference to Figures 19 and 20. For simplicity of the present disclosure, only drawing references to Figure 24 will be included in this section. In step 2400 (which may be optional) , in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE. In step 2402 (which may be optional) , the base station initiates transmission of the received user data to the host computer. In step 2404, the host computer receives the user data carried in the transmission initiated by the base station.

Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs) , special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM) , Random Access Memory (RAM) , cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more embodiments of the present disclosure.

While processes in the figures may show a particular order of operations performed by certain embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc. ) .

Embodiments

Group A Embodiments

Embodiment 1: A method performed by a wireless device (operating in a FDD spectrum) in a Frequency Division Duplex (FDD) system, the method comprising: transmitting an uplink (UL) reference signal in a downlink (DL) band originally allocated for DL transmission in the FDD system, in response to a UL reference signal transmission configuration in the DL band being configured, wherein the UL reference signal is to be used for DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource.

Embodiment 2: The method of embodiment 1 wherein transmitting the UL reference signal comprises: transmitting the UL reference signal in the DL band periodically, semi-periodically or aperiodically in accordance with the UL reference signal transmission configuration in the DL band.

Embodiment 3: The method of any of embodiments 1 to 2 wherein transmitting the UL reference signal comprises: transmitting the UL reference signal in a UL transmission window defined in the DL band for UL reference signal transmission.

Embodiment 4: The method of any of embodiments 1 to 3 further comprising: pausing reception of a DL signal in the DL band during the UL transmission window; or pausing reception of a DL signal in a subband of the DL band in the case that the wireless device is operating on the subband.

Embodiment 5: The method of any of embodiments 1 to 4 wherein the UL transmission window in the DL band is defined with a time length of multiple symbols, and wherein the length is adjustable in accordance with the UL reference signal transmission configuration in the DL band.

Embodiment 6: The method of embodiment 5 wherein the multi-symbol time comprises a guard period for the wireless device to switch from DL reception to UL transmission in the DL band, and a transmission period for the wireless device to transmit the UL reference signal in the DL band.

Embodiment 7: The method of any of embodiment 3 to 6 wherein the method further comprises: resuming reception of a DL signal in the DL band after the UL transmission window lapses; and/or maintaining or pausing, in a period corresponding to the UL transmission window, UL transmission in an uplink (UL) band allocated for UL transmission in the FDD system; and/or wherein frequency-time resource in the UL band in the period corresponding to the UL transmission window is available for UL transmission by one or more wireless devices different from the wireless device in the FDD system.

Embodiment 8: The method of any of embodiments 3 to 7 wherein the UL transmission window is available for a base station to configure DL transmission to the wireless device or one or more different wireless devices in the FDD system.

Embodiment 9: The method of any of embodiments 1 to 8 further comprising receiving, from a base station in the FDD system, a DL signaling for signaling the UL reference signal transmission configuration in the DL band.

Embodiment 10: The method of any of embodiments 1 to 9 wherein transmitting the UL reference signal comprises: transmitting the UL reference signal in the DL band from part of multiple antennas included in the wireless device.

Embodiment 11: The method of embodiment 10 wherein the part of multiple antennas is selected by the wireless device, or selected and informed by a base station.

Embodiment 12: The method of embodiment 11 wherein the part of multiple antennas is selected by the wireless device based on channel information including DL channel information estimated by the wireless device; or the part of multiple antennas is selected by the base station based on channel information including UL channel information estimated by the base station and/or channel state information (CSI) report from the wireless device, and informed by the base station through a DL signaling.

Embodiment 13: The method of any of embodiments 1 to 12 wherein transmitting the UL reference signal comprises: transmitting the UL reference signal in the DL band from different antennas included in the wireless device in different symbols or slots, or from all antennas or selected antennas included in the wireless device simultaneously.

Embodiment 14: The method of any of embodiments 1 to 13 wherein transmitting the UL reference signal comprises: switching from DL reception to UL transmission in the DL band in response to the UL reference signal transmission configuration in the DL band; and transmitting the UL reference signal in the DL band.

Embodiment 15: The method of embodiment 14 wherein switching from DL reception to UL transmission in the DL band comprises: for an antenna of the wireless device through which the UL reference signal transmission in the DL band is to be performed, switching the antenna to be uncoupled from a DL receiver chain for receiving a DL signal in the DL band, and to be coupled to a UL transmit chain for transmitting a UL signal in the DL band.

Embodiment 16: The method of embodiment 15 wherein the UL transmit chain is provided per antenna.

Embodiment 17: The method of embodiment 15 wherein the UL transmit chain is provided for being shared by part or all of multiple antennas of the wireless device, and switching the antenna to be coupled to the UL transmit chain comprises: for an antenna through which the UL reference signal transmission in the DL band is to be performed, switching the antenna to be coupled to the UL transmit chain, while keeping the rest of the antennas be uncoupled to the UL transmit chain.

Embodiment 18: The method of any of the previous embodiments, further comprising: switching from UL transmission to DL reception in the DL band after the UL reference signal transmission is completed.

Embodiment 19: The method of embodiment 18, wherein switching from UL transmission to DL reception in the DL band comprises: for an antenna through which the UL reference signal transmission in the DL band is completed, switching the antenna to be uncoupled to the UL transmit chain to stop the UL reference signal transmission in the DL band, and to be coupled to the DL receiver chain to resume reception of the DL signal in the DL band.

Group B Embodiments

Embodiment 20: A method performed by a base station in a Frequency Division Duplex (FDD) system comprises: receiving, from the wireless device in the FDD system, an uplink (UL) reference signal in a downlink (DL) band allocated for DL transmission in the FDD system; and performing DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource, based on the received UL reference signal..

Embodiment 21: The method of embodiment 20 wherein performing DL beamforming comprises: performing UL channel estimation based on the UL reference signal to obtain UL channel estimates of the UL channel in the DL band; deriving DL channel estimates from the UL channel estimates utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource; and performing DL beamforming based on the DL channel estimates.

Embodiment 22: The method of any of embodiments 20 to 21 wherein receiving the UL reference signal comprises receiving the UL reference signal in the DL band in a periodic, semi-periodic or aperiodic manner.

Embodiment 23: The method of any of embodiments 20 to 22 wherein receiving the UL reference signal comprises receiving the UL reference signal in a UL transmission window defined in the DL band.

Embodiment 24: The method of embodiment 23 further comprising one or more of: pausing transmission of a DL signal in the DL band during the UL transmission window; pausing transmission of a DL signal in a subband of the DL band during the UL transmission window in the case that the UL reference signal is received on the subband from the wireless device; resuming transmission of a DL signal in the DL band after the UL transmission window lapses; configuring and transmitting a DL signal in the DL band in the UL transmission window to the wireless device or one or more different wireless device in the FDD system, when there is no UL reference signal transmission configured in the UL transmission window; and in the case that the UL reference signal is received on a subband of the DL band from the wireless device, configuring and transmitting a DL signal in one or more subbands, different from the subband, of the DL band in the UL transmission window to one or more wireless device in the FDD system different from the wireless device.

Embodiment 25: The method of any of embodiments 20 to 24 further comprises transmitting, to the wireless device, a DL signaling for signaling UL reference signal transmission configuration in the DL band.

Embodiment 26: The method of any of embodiments 20 to 25 wherein receiving the UL reference signal comprises: receiving UL reference signal transmission in the DL band from different antennas included in the wireless device at different symbols or slots, or from all antennas or selected antennas included in the wireless device simultaneously.

Embodiment 27: The method of embodiment 26 wherein performing DL beamforming comprises: obtaining channel estimates of a channel between multiple antennas of the wireless device and antennas of the base station based on the received UL reference signal transmitted from the multiple antennas of the wireless device.

Embodiment 28: The method of any of embodiments 20 to 27 wherein there are multiple wireless devices in the FDD system, and wherein receiving the UL reference signal comprises: receiving UL reference signal transmission in the DL band from the multiple wireless devices simultaneously or at different symbols or slots.

Embodiment 29: The method of embodiment 28 wherein each of the wireless devices comprises multiple antennas, and wherein receiving the UL reference signal comprises: receiving the UL reference signal transmission in the DL band from part of the multiple antennas of each of the wireless devices.

Embodiment 30: The method of embodiment 29 wherein the part of multiple antennas is selected by the wireless device based on channel information including DL channel information estimated by the wireless device.

Embodiment 31: The method of embodiment 29 wherein the part of multiple antennas is selected by the base station, and wherein the method further comprises: selecting the part of multiple antennas based on channel information including UL channel information estimated by the base station and/or channel state information (CSI) report from the wireless device, and informing the wireless device of a result of the selection through a DL signaling.

Embodiment 32: The method of any of embodiments 20 to 31 wherein receiving the UL reference signal comprises: switching from DL transmission to UL reception in the DL band; and receiving the UL reference signal in the DL band.

Embodiment 33: The method of embodiment 32 wherein switching from DL transmission to UL reception in the DL band comprises: for an antenna of the base station through which the UL reference signal reception in the DL band is to be performed, switching the antenna to be uncoupled from a DL transmit chain for transmitting a DL signal in the DL band, and to be coupled to a UL receiver chain for receiving a UL signal in the DL band.

Embodiment 34: The method of embodiment 33 wherein the UL receiver chain is provided per antenna.

Embodiment 35: The method of any of embodiments 20 to 34 wherein the base station comprises multiple antennas comprising an array of receive antennas for receiving in the UL band and an array of transmit antennas for transmission in the DL band, and the array of receive antennas and the array of transmit antennas are provided in two panels respectively, or in two sub-panels on one panel.

Embodiment 36: The method of any of embodiments 20 to 35, further comprising: switching from UL reception to DL transmission in the DL band after the UL reference signal transmission is completed.

Embodiment 37: The method of embodiment 36, wherein switching from UL reception to DL transmission in the DL band comprises: for an antenna through which the UL reference signal reception in the DL band is completed, switching the antenna to be uncoupled to the UL receiver chain to stop the UL reference signal reception in the DL band, and to be coupled to the DL transmit chain to resume transmission of the DL signal in the DL band.

Group C Embodiments

Embodiment 38: A wireless device operating in a Frequency Division Duplex (FDD) system, the wireless device comprising: one or more processors; and memory storing instructions executable by the one or more processors, whereby the wireless device is operable to perform any of the steps of any of the Group A embodiments.

Embodiment 39: The wireless device of embodiment 38, further comprising: a first UL transmit chain for transmitting a UL signal in the DL band; wherein the first UL transmit chain is provided for each antenna in the wireless device, or provided for being shared by part or all of multiple antennas in the wireless device, and each of the antennas is switchably coupled to or uncoupled from the first UL transmit chain.

Embodiment 40: The wireless device of embodiment 39, wherein the first UL transmit chain comprises a DL-band transmit bandpass filter (BPF) , a power amplifier (PA) , an up-converter and a digital-to-analog converter (DAC) , wherein the wireless device further comprises a switching element provided between each antenna and the first UL transmit chain, and the antenna is coupled to or uncoupled from the first UL transmit chain through the switching element.

Embodiment 41: The wireless device of embodiment 40, wherein the PA is a wideband PA, and the DAC is a high-speed DAC, wherein the wideband PA and the high-speed DAC are shared with a second UL transmit chain for transmitting a UL signal in a UL band allocated for UL transmission in the FDD system.

Embodiment 42: The wireless device of embodiment 40 or 41, wherein for an antenna through which the UL reference signal transmission in the DL band is to be performed, the switching element is switched to uncouple the antenna from a DL receiver chain for receiving a DL signal in the DL band, and to couple the antenna to the first UL transmit chain to perform the UL reference signal transmission in the DL band.

Embodiment 43: The wireless device of embodiment 40, wherein the first UL transmit chain comprises a DL-band transmit bandpass filter (BPF) , a power amplifier (PA) , an up-converter, and a digital-to-analog converter (DAC) shared with a second UL transmit chain for transmitting a UL signal in a UL band allocated for UL transmission in the FDD system, wherein the wireless device further comprises a first switching element provided between each antenna and the first UL transmit chain, and a second switching element provided adjacent to the shared DAC; and the antenna is switchably coupled to or uncoupled from the first UL transmit chain through the first switching element, and the shared DAC is switchably placed in either the first UL transmit chain or the second UL transmit chain through the second switching element.

Embodiment 44: The wireless device of embodiment 43, wherein for an antenna through which the UL reference signal transmission in the DL band is to be performed, the first switching element is switched to uncouple the antenna from a DL receiver chain for receiving a DL signal in the DL band and to couple the antenna to the first UL transmit chain, while the second switching element is switched to uncouple the shared DAC from the second UL transmit chain and to place the shared DAC in the first UL transmit chain.

Embodiment 45: The wireless device of any of embodiment 39 to 44, wherein in the case of the first UL transmit chain being shared by part or all of multiple antennas in the wireless device, for an antenna through which the UL reference signal transmission in the DL band is to be performed, the antenna is switched to be coupled to the first UL transmit chain, while keeping the rest of the multiple antennas be uncoupled to the first UL transmit chain.

Embodiment 46: A base station operating in a Frequency Division Duplex (FDD) system, the base station comprising: one or more processors; and memory comprising instructions to cause the base station to perform any of the steps of any of the Group B embodiments.

Embodiment 47: The base station of embodiment 46 further comprising: a first UL receiver chain for receiving a UL signal in the DL band, and wherein the first UL receiver chain is provided for each of multiple antennas in the base station, and each of the antennas is switchably coupled to or uncoupled from the first UL receiver chain.

Embodiment 48: The base station of embodiment 47, wherein the first UL receiver chain comprises a DL-band receiver bandpass filter (BPF) , a low noise amplifier (LNA) , an down-converter and an analog-to-digital converter (ADC) , wherein the base station further comprises a switching element provided between each antenna and the first UL receiver chain, and the antenna is coupled to or uncoupled from the first UL transmit chain through the switching element.

Embodiment 49: The base station of embodiment 48, wherein the LNA is a wideband LNA, and the ADC is a high-speed ADC, and wherein the wideband LNA and the high-speed ADC are shared with a second UL receiver chain for receiving a UL signal in a UL band allocated for UL reception in the FDD system.

Embodiment 50: The base station of embodiment 48 or 49, wherein for an antenna through which the UL reference signal reception in the DL band is to be performed, the switching element is switched to uncouple the antenna from a DL transmit chain for transmitting a DL signal in the DL band, and to couple the antenna to the first UL receiver chain to perform the UL reference signal reception in the DL band.

Embodiment 51: The base station of embodiment 47, wherein the first UL receiver chain comprises a DL-band receiver bandpass filter (BPF) , a low noise amplifier (LNA) , an down-converter, and an analog-to-digital converter (ADC) shared with a second UL receiver chain for receiving a UL signal in a UL band allocated for UL reception in the FDD system, wherein the base station further comprises a first switching element provided between each antenna and the first UL receiver chain, and a second switching element provided adjacent to the shared ADC; the antenna is coupled to or uncoupled from the first UL receiver chain through the first switching element, and the shared ADC is switchably placed in either the first UL receiver chain or the second UL receiver chain through the second switching element.

Embodiment 52: The base station of embodiment 51, wherein for an antenna through which the UL reference signal reception in the DL band is to be performed, the first switching element is switched to uncouple the antenna from a DL transmit chain for transmitting a DL signal in the DL band, and to couple the antenna to the first UL receiver chain to perform the UL reference signal reception in the DL band, while the second switching element is switched to uncouple the shared ADC from the second UL receiver chain, and to place the shared ADC in the first UL receiver chain.

Embodiment 53: The base station of any of embodiments 46 to 52, wherein the base station comprises multiple antennas comprising an array of receive antennas for receiving in the UL band and an array of transmit antennas for transmission in the DL band, and the array of receive antennas and the array of transmit antennas are provided in two panels respectively, or in two sub-panels on one panel.

Embodiment 54: A User Equipment, UE, for transmitting feedback, the UE comprising: an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to perform any of the steps of any of the Group A embodiments.

Embodiment 55: A communication system including a host computer comprising: processing circuitry configured to provide user data; and a communication interface configured to forward the user data to a cellular network for transmission to a User Equipment, UE; wherein the cellular network comprises a base station having a radio interface and processing circuitry, the base station's processing circuitry configured to perform any of the steps of any of the Group B embodiments.

Embodiment 56: The communication system of embodiment 55 further including the base station.

Embodiment 57: The communication system of embodiment 55 or 56, further including the UE, wherein the UE is configured to communicate with the base station.

Embodiment 58: The communication system of any of embodiments 55 to 57, wherein: the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; and the UE comprises processing circuitry configured to execute a client application associated with the host application.

Embodiment 59: A method implemented in a communication system including a host computer, a base station, and a User Equipment, UE, the method comprising: at the host computer, providing user data; and at the host computer, initiating a transmission carrying the user data to the UE via a cellular network comprising the base station, wherein the base station performs any of the steps of any of the Group B embodiments.

Embodiment 60: The method of embodiment 59, further comprising, at the base station, transmitting the user data.

Embodiment 61: The method of embodiment 59 or 60, wherein the user data is provided at the host computer by executing a host application, the method further comprising, at the UE, executing a client application associated with the host application.

Embodiment 62: A method implemented in a communication system including a host computer, a base station, and a User Equipment, UE, the method comprising: at the host computer, providing user data; and at the host computer, initiating a transmission carrying the user data to the UE via a cellular network comprising the base station, wherein the UE performs any of the steps of any of the Group A embodiments.

Embodiment 63: The method of the previous embodiment, further comprising at the UE, receiving the user data from the base station.

Embodiment 64: A method implemented in a communication system including a host computer, a base station, and a User Equipment, UE, the method comprising: at the host computer, receiving user data transmitted to the base station from the UE, wherein the UE performs any of the steps of any of the Group A embodiments.

Embodiment 65: The method of the previous embodiment, further comprising, at the UE, providing the user data to the base station.

Embodiment 66: The method of embodiment 64 or 65, further comprising: at the UE, executing a client application, thereby providing the user data to be transmitted; and at the host computer, executing a host application associated with the client application.

Embodiment 67: The method of any of embodiments 64 to 66, further comprising: at the UE, executing a client application; and at the UE, receiving input data to the client application, the input data being provided at the host computer by executing a host application associated with the client application; wherein the user data to be transmitted is provided by the client application in response to the input data.

Embodiment 68: A communication system including a host computer comprising a communication interface configured to receive user data originating from a transmission from a User Equipment, UE, to a base station, wherein the base station comprises a radio interface and processing circuitry, the base station's processing circuitry configured to perform any of the steps of any of the Group B embodiments.

Embodiment 69: The communication system of the previous embodiment further including the base station.

Embodiment 70: The communication system of embodiment 68 or 69, further including the UE, wherein the UE is configured to communicate with the base station.

Embodiment 71: The communication system of any of embodiments 68 to 70, wherein: the processing circuitry of the host computer is configured to execute a host application; and the UE is configured to execute a client application associated with the host application, thereby providing the user data to be received by the host computer.

Embodiment 72: A method implemented in a communication system including a host computer, a base station, and a User Equipment, UE, the method comprising: at the host computer, receiving, from the base station, user data originating from a transmission which the base station has received from the UE, wherein the UE performs any of the steps of any of the Group A embodiments.

Embodiment 73: The method of the previous embodiment, further comprising at the base station, receiving the user data from the UE.

Embodiment 74: The method of embodiment 72 or 73, further comprising at the base station, initiating a transmission of the received user data to the host computer.

At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used above. If listed multiple times below, the first listing should be preferred over any subsequent listing (s) .

● 3GPP Third Generation Partnership Project

● 5G Fifth Generation

● 5GC Fifth Generation Core

● 5GS Fifth Generation System

● ACK Acknowledgement

● ACK/NACK Acknowledgement/Negative Acknowledgement

● AF Application Function

● AMF Access and Mobility Function

● AN Access Network

● AP Access Point

● AUSF Authentication Server Function

● CE Control Element

● CORESET Control Resource Set

● CPU Central Processing Unit

● CSI Channel State Information

● CSI-RS Channel State Information Reference Signal

● CQI Channel Quality Index

● DCI Downlink Control Information

● DL Downlink

● DMRS Demodulation Reference Signal

● DN Data Network

● DSP Digital Signal Processor

● eMBB Enhanced Mobile Broadband

● eNB Enhanced or Evolved Node B

● FDD Frequency Division Duplex

● GEO Geostationary Earth Orbit

● gNB New Radio Base Station

● HARQ Hybrid Automatic Repeat Request

● HSS Home Subscriber Server

● IoT Internet of Things

● IP Internet Protocol

● ITS In-the-Sky

● LEO Low Earth Orbit

● LTE Long Term Evolution

● MAC Medium Access Control

● MEO Medium Earth Orbit

● MIMU Multiple-Input Multiple-Output

● MME Mobility Management Entity

● MU-MIMU Multi-User Multiple-Input Multiple-Output

● MTC Machine Type Communication

● NACK Negative Acknowledgement

● NEF Network Exposure Function

● NF Network Function

● NR New Radio

● NRF Network Function Repository Function

● NSSF Network Slice Selection Function

● NTN Non-Terrestrial Network

● OTT Over-the-Top

● PC Personal Computer

● PCF Policy Control Function

● PDSCH Physical Downlink Shared Channel

● PDCCH Physical Downlink Control Channel

● P-GW Packet Data Network Gateway

● PHY Physical Layer

● PMI Precoder Matrix Index

● PUCCH Physical Uplink Control Channel

● RAM Random Access Memory

● RAN Radio Access Network

● RI Rank Index

● ROM Read Only Memory

● RRC Radio Resource Control

● RRH Remote Radio Head

● RTT Round Trip Time

● SAW Stop-and-Wait

● SCEF Service Capability Exposure Function

● sCell Secondary Cell

● SCS Subcarrier Spacing

● SIB System Information Block

● SMF Session Management Function

● SNR Signal-to-Noise Ratio

● SRS Sounding Reference Signal

● SU-MIMU Single-User Multiple-Input Multiple-Output

● TBS Transport Block Size

● TCI Transmission Configuration Indicator

● TDD Time Division Duplex

● TDL Tapped Delay Line

● UDM Unified Data Management

● UE User Equipment

● UL Uplink

● UPF User Plane Function

● URLLC Ultra Reliable and Low Latency Communication

● ZP Zero Power

Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

Claims

A method performed by a wireless device (900) in a Frequency Division Duplex (FDD) system, the method comprising:

transmitting (402, 802) an uplink (UL) reference signal in a downlink (DL) band allocated for DL transmission in the FDD system, in response to a UL reference signal transmission configuration in the DL band being configured,

wherein the UL reference signal is to be used for DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource.
The method of claim 1, wherein transmitting the UL reference signal comprises: transmitting the UL reference signal in the DL band periodically, semi-periodically or aperiodically in accordance with the UL reference signal transmission configuration in the DL band.
The method of any of claims 1 to 2, wherein transmitting the UL reference signal comprises:

transmitting the UL reference signal in a UL transmission window defined in the DL band for UL reference signal transmission.
The method of any of claims 1 to 3, further comprising:

pausing reception of a DL signal in the DL band during the UL transmission window; or

pausing reception of a DL signal in a subband of the DL band in the case that the wireless device is operating on the subband.
The method of any of claims 1 to 4, wherein the UL transmission window in the DL band is defined with a time length of multiple symbols, and

wherein the length is adjustable in accordance with the UL reference signal transmission configuration in the DL band.
The method of claim 5, wherein the multi-symbol time comprises a guard period for the wireless device to switch from DL reception to UL transmission in the DL band, and a transmission period for the wireless device to transmit the UL reference signal in the DL band.
The method of any of claims 3 to 6, wherein the method further comprises:

resuming reception of a DL signal in the DL band after the UL transmission window lapses; and/or

maintaining or pausing, in a period corresponding to the UL transmission window, UL transmission in an uplink (UL) band allocated for UL transmission in the FDD system; and/or

wherein frequency-time resource in the UL band in the period corresponding to the UL transmission window is available for UL transmission by one or more wireless devices different from the wireless device in the FDD system.
The method of any of claims 3 to 7, wherein the UL transmission window is available for a base station to configure DL transmission to the wireless device or one or more different wireless devices in the FDD system.
The method of any of claims 1 to 8 further comprises:

receiving, from a base station in the FDD system, a DL signaling for signaling the UL reference signal transmission configuration in the DL band.
The method of any of claims 1 to 9, wherein transmitting the UL reference signal comprises:

transmitting the UL reference signal in the DL band from part of multiple antennas included in the wireless device.
The method of claim 10, wherein the part of multiple antennas is selected by the wireless device, or selected and informed by a base station.
The method of claim 11, wherein the part of multiple antennas is selected by the wireless device based on channel information including DL channel information estimated by the wireless device; or

the part of multiple antennas is selected by the base station based on channel information including UL channel information estimated by the base station and/or channel state information (CSI) report from the wireless device, and informed by the base station through a DL signaling.
The method of any of claims 1 to 12, wherein transmitting the UL reference signal comprises:

transmitting the UL reference signal in the DL band from different antennas included in the wireless device in different symbols or slots, or from all antennas or selected antennas included in the wireless device simultaneously.
The method of any of claims 1 to 13, wherein transmitting the UL reference signal comprises:

switching from DL reception to UL transmission in the DL band in response to the UL reference signal transmission configuration in the DL band; and

transmitting the UL reference signal in the DL band.
The method of claim 14, wherein switching from DL reception to UL transmission in the DL band comprises:

for an antenna of the wireless device through which the UL reference signal transmission in the DL band is to be performed, switching the antenna to be uncoupled from a DL receiver chain for receiving a DL signal in the DL band, and to be coupled to a UL transmit chain for transmitting a UL signal in the DL band.
The method of claim 15, wherein the UL transmit chain is provided per antenna.
The method of claim 15, wherein the UL transmit chain is provided for being shared by part or all of multiple antennas of the wireless device, and

switching the antenna to be coupled to the UL transmit chain comprises:

for an antenna through which the UL reference signal transmission in the DL band is to be performed, switching the antenna to be coupled to the UL transmit chain, while keeping the rest of the antennas be uncoupled to the UL transmit chain.
The method of any of claims 1 to 17 further comprising:

switching from UL transmission to DL reception in the DL band after the UL reference signal transmission is completed.
The method of claim 18, wherein switching from UL transmission to DL reception in the DL band comprises:

for an antenna through which the UL reference signal transmission in the DL band is completed, switching the antenna to be uncoupled to the UL transmit chain to stop the UL reference signal transmission in the DL band, and to be coupled to the DL receiver chain to resume reception of the DL signal in the DL band.
A method performed by a base station (1000) in a Frequency Division Duplex (FDD) system, the method comprising:

receiving (502, 804) , from a wireless device (900) in the FDD system, an uplink (UL) reference signal in a downlink (DL) band allocated for DL transmission in the FDD system; and

performing (504, 804) DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource, based on the received UL reference signal.
The method of claim 20, wherein performing DL beamforming comprises:

performing UL channel estimation based on the UL reference signal to obtain UL channel estimates of the UL channel in the DL band;

deriving DL channel estimates from the UL channel estimates utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource; and

performing DL beamforming based on the DL channel estimates.
The method of any of claims 20 to 21, wherein receiving the UL reference signal comprises:

receiving the UL reference signal in the DL band in a periodic, semi-periodic or aperiodic manner.
The method of any of claims 20 to 22, wherein receiving the UL reference signal comprises:

receiving the UL reference signal in a UL transmission window defined in the DL band.
The method of claim 23 further comprising one or more of:

pausing transmission of a DL signal in the DL band during the UL transmission window;

pausing transmission of a DL signal in a subband of the DL band during the UL transmission window in the case that the UL reference signal is received on the subband from the wireless device;

resuming transmission of a DL signal in the DL band after the UL transmission window lapses;

configuring and transmitting a DL signal in the DL band in the UL transmission window to the wireless device or one or more different wireless device in the FDD system, when there is no UL reference signal transmission configured in the UL transmission window;

in the case that the UL reference signal is received on a subband of the DL band from the wireless device, configuring and transmitting a DL signal in one or more subbands, different from the subband, of the DL band in the UL transmission window to one or more wireless device in the FDD system different from the wireless device.
The method of any of claims 20 to 24 further comprising:

transmitting, to the wireless device, a DL signaling for signaling UL reference signal transmission configuration in the DL band.
The method of any of claims 20 to 25, wherein receiving the UL reference signal comprises:

receiving UL reference signal transmission in the DL band from different antennas included in the wireless device at different symbols or slots, or from all antennas or selected antenenas included in the wireless device simultaneously.
The method of claim 26, wherein performing DL beamforming comprises:

obtaining channel estimates of a channel between multiple antennas of the wireless device and antennas of the base station based on the received UL reference signal transmitted from the multiple antennas of the wireless device.
The method of any of claims 20 to 27, wherein there are multiple wireless devices in the FDD system, and

wherein receiving the UL reference signal comprises:

receiving UL reference signal transmission in the DL band from the multiple wireless devices simultaneously or at different symbols or slots.
The method of claim 28, wherein each of the wireless devices comprises multiple antennas, and

wherein receiving the UL reference signal comprises:

receiving the UL reference signal transmission in the DL band from part of the multiple antennas of each of the wireless devices.
The method of claim 29, wherein the part of multiple antennas is selected by the wireless device based on channel information including DL channel information estimated by the wireless device.
The method of claim 29, wherein the part of multiple antennas is selected by the base station, and

wherein the method further comprises:

selecting the part of multiple antennas based on channel information including UL channel information estimated by the base station and/or channel state information (CSI) report from the wireless device, and informing the wireless device of a result of the selection through a DL signaling.
The method of any of claims 20 to 31, wherein receiving the UL reference signal comprises:

switching from DL transmission to UL reception in the DL band; and

receiving the UL reference signal in the DL band.
The method of claim 32, wherein switching from DL transmission to UL reception in the DL band comprises:

for an antenna of the base station through which the UL reference signal reception in the DL band is to be performed, switching the antenna to be uncoupled from a DL transmit chain for transmitting a DL signal in the DL band, and to be coupled to a UL receiver chain for receiving a UL signal in the DL band.
The method of claim 33, wherein the UL receiver chain is provided per antenna.
The method of any of claims 20 to 34, wherein the base station comprises multiple antennas comprising an array of receive antennas for receiving in the UL band and an array of transmit antennas for transmission in the DL band, and

the array of receive antennas and the array of transmit antennas are provided in two panels respectively, or in two sub-panels on one panel.
The method of any of claims 1 to 35 further comprising:

switching from UL reception to DL transmission in the DL band after the UL reference signal transmission is completed.
The method of claim 36, wherein switching from UL reception to DL transmission in the DL band comprises:

for an antenna through which the UL reference signal reception in the DL band is completed, switching the antenna to be uncoupled to the UL receiver chain to stop the UL reference signal reception in the DL band, and to be coupled to the DL transmit chain to resume transmission of the DL signal in the DL band.
A wireless device (900) operating in a Frequency Division Duplex (FDD) system, the wireless device (900) comprising:

one or more processors (902) ; and

memory (904) storing instructions executable by the one or more processors (902) , whereby the wireless device (900) is operable to perform a method comprising:

transmitting (402, 802) an uplink (UL) reference signal in a downlink (DL) band allocated for DL transmission in the FDD system, in response to a UL reference signal transmission configuration in the DL band being configured,

wherein the UL reference signal is to be used for DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource.
The wireless device of claim 38, wherein the instructions further cause the wireless device to perform the method of any one of claims 2 to 19.
The wireless device of any of claims 38 to 39 further comprising:

a first UL transmit chain for transmitting a UL signal in the DL band;

wherein the first UL transmit chain is provided for each antenna in the wireless device, or provided for being shared by part or all of multiple antennas in the wireless device, and

each of the antennas is switchably coupled to or uncoupled from the first UL transmit chain.
The wireless device of claim 40, wherein the first UL transmit chain comprises a DL-band transmit bandpass filter (BPF) , a power amplifier (PA) , an up-converter and a digital-to-analog converter (DAC) ,

wherein the wireless device further comprises a switching element provided between each antenna and the first UL transmit chain, and

the antenna is coupled to or uncoupled from the first UL transmit chain through the switching element.
The wireless device of claim 41, wherein the PA is a wideband PA, and the DAC is a high-speed DAC,

wherein the wideband PA and the high-speed DAC are shared with a second UL transmit chain for transmitting a UL signal in a UL band allocated for UL transmission in the FDD system.
The wireless device of any of claims 41 to 42, wherein for an antenna through which the UL reference signal transmission in the DL band is to be performed, the switching element is switched to uncouple the antenna from a DL receiver chain for receiving a DL signal in the DL band, and to couple the antenna to the first UL transmit chain to perform the UL reference signal transmission in the DL band.
The wireless device of claim 40, wherein the first UL transmit chain comprises a DL-band transmit bandpass filter (BPF) , a power amplifier (PA) , an up-converter, and a digital-to-analog converter (DAC) shared with a second UL transmit chain for transmitting a UL signal in a UL band allocated for UL transmission in the FDD system,

wherein the wireless device further comprises a first switching element provided between each antenna and the first UL transmit chain, and a second switching element provided adjacent to the shared DAC; and

the antenna is switchably coupled to or uncoupled from the first UL transmit chain through the first switching element, and the shared DAC is switchably placed in either the first UL transmit chain or the second UL transmit chain through the second switching element.
The wireless device of claim 44, wherein for an antenna through which the UL reference signal transmission in the DL band is to be performed, the first switching element is switched to uncouple the antenna from a DL receiver chain for receiving a DL signal in the DL band and to couple the antenna to the first UL transmit chain, while the second switching element is switched to uncouple the shared DAC from the second UL transmit chain and to place the shared DAC in the first UL transmit chain.
The wireless device of any of claims 40 to 46, wherein in the case of the first UL transmit chain being shared by part or all of multiple antennas in the wireless device, for an antenna through which the UL reference signal transmission in the DL band is to be performed, the antenna is switched to be coupled to the first UL transmit chain, while keeping the rest of the multiple antennas be uncoupled to the first UL transmit chain.
A base station (1000) operating in a Frequency Division Duplex (FDD) system, the base station (1000) comprising:

one or more processors (1002) ; and

memory (1004) comprising instructions executable by the one or more processors, whereby the base station (1000) is operable to perform a method comprising:

receiving (502, 804) , from a wireless device (900) in the FDD system, an uplink (UL) reference signal in a downlink (DL) band allocated for DL transmission in the FDD system; and

performing (504, 804) DL beamforming utilizing reciprocity of channel between UL and DL transmissions on the same frequency resource, based on the received UL reference signal.
The base station of claim 47, wherein the instructions further cause the base station to perform the method of any one of claims 21 to 37.
The base station of any of claims 48 to 49 further comprising:

a first UL receiver chain for receiving a UL signal in the DL band, and

wherein the first UL receiver chain is provided for each of multiple antennas in the base station, and

each of the antennas is switchably coupled to or uncoupled from the first UL receiver chain.
The base station of claim 49, wherein the first UL receiver chain comprises a DL-band receiver bandpass filter (BPF) , a low noise amplifier (LNA) , an down-converter and an analog-to-digital converter (ADC) ,

wherein the base station further comprises a switching element provided between each antenna and the first UL receiver chain, and

the antenna is coupled to or uncoupled from the first UL transmit chain through the switching element.
The base station of claim 50, wherein the LNA is a wideband LNA, and the ADC is a high-speed ADC, and

wherein the wideband LNA and the high-speed ADC are shared with a second UL receiver chain for receiving a UL signal in a UL band allocated for UL reception in the FDD system.
The base station of any of claim 50 to 51, wherein for an antenna through which the UL reference signal reception in the DL band is to be performed, the switching element is switched to uncouple the antenna from a DL transmit chain for transmitting a DL signal in the DL band, and to couple the antenna to the first UL receiver chain to perform the UL reference signal reception in the DL band.
The base station of claim 49, wherein the first UL receiver chain comprises a DL-band receiver bandpass filter (BPF) , a low noise amplifier (LNA) , an down-converter, and an analog-to-digital converter (ADC) shared with a second UL receiver chain for receiving a UL signal in a UL band allocated for UL reception in the FDD system,

wherein the base station further comprises a first switching element provided between each antenna and the first UL receiver chain, and a second switching element provided adjacent to the shared ADC;

the antenna is coupled to or uncoupled from the first UL receiver chain through the first switching element, and

the shared ADC is switchably placed in either the first UL receiver chain or the second UL receiver chain through the second switching element.
The base station of claim 53, wherein for an antenna through which the UL reference signal reception in the DL band is to be performed, the first switching element is switched to uncouple the antenna from a DL transmit chain for transmitting a DL signal in the DL band, and to couple the antenna to the first UL receiver chain to perform the UL reference signal reception in the DL band, while the second switching element is switched to uncouple the shared ADC from the second UL receiver chain, and to place the shared ADC in the first UL receiver chain.
The base station of any of claims 47 to 54, wherein the base station comprises multiple antennas comprising an array of receive antennas for receiving in the UL band and an array of transmit antennas for transmission in the DL band, and

the array of receive antennas and the array of transmit antennas are provided in two panels respectively, or in two sub-panels on one panel.