WO2024216513A1

WO2024216513A1 - Joint transmission based on grouping of network devices

Info

Publication number: WO2024216513A1
Application number: PCT/CN2023/089065
Authority: WO
Inventors: Hao Liu; Tao Yang
Original assignee: Nokia Shanghai Bell Co., Ltd; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2023-04-18
Filing date: 2023-04-18
Publication date: 2024-10-24

Abstract

Example embodiment of the present disclosure discloses a solution for joint transmission based on grouping of network devices. In an aspect, a terminal device determines a first preliminary group and a second preliminary group of network devices among network devices serving the terminal device. The terminal device transmits group information indicative of the first and the second preliminary groups. The terminal device receives first data jointly transmitted from a first group and second data jointly transmitted from a second group of network devices. The first data and the second data are different or common between the first group and the second group which are determined based on at least the group information. Example embodiments of the present disclosure can alleviate the sensitivity of phase errors and harvest the potential superiority of joint transmission in communication systems.

Description

JOINT TRANSMISSION BASED ON GROUPING OF NETWORK DEVICES

FIELD

Example embodiments of the present disclosure generally relate to the field of communication, and in particular, to a terminal device, a network device, methods, apparatuses, and a computer readable medium for joint transmission based on grouping of network devices.

BACKGROUND

Cell-free massive multiple input multiple output (CF-mMIMO) , also known as distributed MIMO (dMIMO) , is an emerging technology where multiple network devices such as access points (APs) jointly serve a number of user equipments (UEs) on the same time-frequency resources. dMIMO systems are envisioned to increase coverage and spectral efficiency (SE) compared to traditional cellular networks without cooperation. The superior SE performance can be achieved by adopting coherent joint transmission (CJT) , where the symbols sent to the UE are coherently transmitted from multiple adjacent serving APs. The performance advantage relies on strict phase-synchronization among multiple serving APs.

In practice, due to hardware defects (e.g., low resolution analog-to-digital converters (ADC) , phase instability in local oscillator (LO) ) , and hardware impairments (e.g., the performance of hardware is different in different environments) , etc., the phase errors among the APs are inevitable. Therefore, the effect of phase errors on CJT should be considered in the dMIMO application.

SUMMARY

In general, example embodiments of the present disclosure provide solutions for joint transmission based on grouping of network devices.

In a first aspect, there is provided a terminal device. The terminal device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device at least to: determine at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device; transmit group information indicative of the first preliminary group and the second preliminary group; and receive first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices, wherein the first group and the second group are determined based on at least the group information.

In a second aspect, there is provided a network device. The network device comprises: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network device at least to: receive group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device; determine, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and configure the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.

In a third aspect, there is provided a method. The method comprises: determining at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device; transmitting group information indicative of the first preliminary group and the second preliminary group; and receiving first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices, wherein the first group and the second group are determined based on at least the group information.

In a fourth aspect, there is provided a method. The method comprises: receiving group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device; determining, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and configuring the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.

In a fifth aspect, there is provided an apparatus. The apparatus comprises: means for determining at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device; means for transmitting group information indicative of the first preliminary group and the second preliminary group; and means for receiving first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices, wherein the first group and the second group are determined based on at least the group information.

In a sixth aspect, there is provided an apparatus. The apparatus comprises: means for receiving group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device; means for determining, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and means for configuring the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.

In a seventh aspect, there is provided a non-transitory computer-readable storage medium comprising program instructions. The program instructions, when executed by an apparatus, cause the apparatus to perform at least the following: determining at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device; transmitting group information indicative of the first preliminary group and the second preliminary group; and receiving first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices, wherein the first group and the second group are determined based on at least the group information.

In an eighth aspect, there is provided a non-transitory computer-readable storage medium comprising program instructions. The program instructions, when executed by an apparatus, cause the apparatus to perform at least the following: receiving group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device; determining, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and configuring the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.

In a ninth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: determine at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device; transmit group information indicative of the first preliminary group and the second preliminary group; and receive first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices, wherein the first group and the second group are determined based on at least the group information.

In a tenth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: receive group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device; determine, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and configure the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.

In an eleventh aspect, there is provided a terminal device. The terminal device comprises: determining circuitry configured to determine at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device; transmitting circuitry configured to transmit group information indicative of the first preliminary group and the second preliminary group; and receiving circuitry configured to receive first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices, wherein the first group and the second group are determined based on at least the group information.

In a twelfth aspect, there is provided a network device. The network device comprises: receiving circuitry configured to receive group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device; determining circuitry configured to determine, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and configuring circuitry configured to configure the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described with reference to the accompanying drawings, in which:

FIG. 1A illustrates an example communication network in which embodiments of the present disclosure may be implemented;

FIG. 1B illustrates an example of average-UE SE in the presence of AP side phase errors under fully-connected architecture;

FIG. 1C illustrates another example of average-UE SE in the presence of AP side phase errors under fully-connected architecture;

FIG. 2 illustrates an example of a process flow in accordance with some example embodiments of the present disclosure;

FIG. 3 illustrates a grouped joint transmission system in accordance with some example embodiments of the present disclosure;

FIG. 4 illustrates another example of a process flow in accordance with some example embodiments of the present disclosure;

FIG. 5 illustrates performance of different transmission schemes under max-min power allocation in accordance with some example embodiments of the present disclosure;

FIG. 6 illustrates a flowchart of an example method implemented at a terminal device in accordance with some embodiments of the present disclosure;

FIG. 7 illustrates another flowchart of an example method implemented at a network device in accordance with some embodiments of the present disclosure;

FIG. 8 illustrates a simplified block diagram of a device that is suitable for implementing some example embodiments of the present disclosure; and

FIG. 9 illustrates a block diagram of an example of a computer-readable medium in accordance with some example embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar elements.

DETAILED DESCRIPTION

Principles of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an embodiment, ” “an example embodiment, ” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof. As used herein, “at least one of the following: <a list of two or more elements>” and “at least one of <a list of two or more elements>” and similar wording, where the list of two or more elements are joined by “and” or “or” , mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) :

(i) a combination of analog and/or digital hardware circuit (s) with software/firmware and

(ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (for example, firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

As used herein, the term “network” , “communication network” or “data network” refers to a network following any suitable communication standards, such as long term evolution (LTE) , LTE-advanced (LTE-A) , wideband code division multiple access (WCDMA) , high-speed packet access (HSPA) , narrow band Internet of things (NB-IoT) , wireless fidelity (Wi-Fi) and so on. Furthermore, the communications between a terminal device and a network device/element in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the fourth generation (4G) , 4.5G, the future fifth generation (5G) , IEEE 802.11 communication protocols, and/or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP) or a transmission and reception point (TRP) , for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a NR NB (also referred to as a gNB) , a remote radio unit (RRU) , a radio header (RH) , a remote radio head (RRH) , a WiFi device, a relay, a low power node such as a femto, a pico, a central processing unit (CPU) connected to multiple access points, and so forth, depending on the applied terminology and technology. In the following description, the terms “network device” , “AP device” , “AP” and “access point” may be used interchangeably.

The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE) , a Subscriber Station (SS) , a Portable Subscriber Station, a Mobile Station (MS) , a station (STA) or station device, or an Access Terminal (AT) . The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA) , portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) , an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD) , a vehicle, a drone, a medical device and applications (for example, remote surgery) , an industrial device and applications (for example, a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts) , a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. In the following description, the terms “station” , “station device” , “STA” , “terminal device” , “communication device” , “terminal” , “user equipment” and “UE” may be used interchangeably.

In a dMIMO system, multiple APs are connected to a central processing unit (CPU) and jointly serve a number of UEs on the same time-frequency resources. Ideally, all APs may jointly serve all UEs, which is called a fully-connected architecture and has high macro diversity gain. However, due to the requirement of high fronthaul capacity, the fully-connected architecture is not scalable in terms of practical deployment. Therefore, the user-centric architecture is widely adopted at present, where a UE may only be served by partial APs surrounding this UE.

dMIMO systems are envisioned to increase coverage and spectral efficiency (SE) compared to traditional cellular networks without cooperation. The superior SE performance can be achieved by adopting coherent joint transmission (CJT) , where the symbols sent to the UE are coherently transmitted from multiple adjacent serving APs. The performance advantage relies on strict phase-synchronization among multiple serving APs. However, in practice, due to hardware defects (e.g., low resolution analog-to-digital converters (ADC) , phase instability in local oscillator (LO) ) , and hardware impairments (e.g., the performance of hardware is different in different environments) , etc., the phase errors among the APs are inevitable. Therefore, the effect of phase errors on CJT should be considered in the dMIMO application. There is a need to further improve transmission reliability and robustness for dMIMO application as well as other MIMO applications against the phase errors.

For illustrative purposes, principles and example embodiments of the present disclosure will be described below with reference to FIG. 1A to FIG. 9. However, it is to be noted that these embodiments are given to enable the skilled in the art to understand inventive concepts of the present disclosure and implement the solution as proposed herein, and not intended to limit scope of the present application in any way.

FIG. 1A illustrates an example of an application scenario 100 in which some example embodiments of the present disclosure may be implemented. The application scenario 100, which is a part of a communication network, includes terminal devices and network devices.

In the descriptions of the example embodiments of the present disclosure, the network environment 100 may also be referred to as a communication system 100 (for example, a portion of a communication network) . For illustrative purposes only, various aspects of example embodiments will be described in the context of one or more terminal devices and network devices that communicate with one another. It should be appreciated, however, that the description herein may be applicable to other types of apparatus or other similar apparatuses that are referenced using other terminology.

As illustrated in FIG. 1A, the communication network 100 may include multiple network devices 130-1, 130-2, and 130-3 (collectively “130” ) . Each of the network devices 130 may also be referred to as an AP 130, gNB 130, BS 130 and the like. The communication network 100 may further include multiple terminal devices 120-1, and 120-2 (collectively “120” ) , which may also be referred to UE 120. Each of the terminal devices 120 may be served by a plurality of the network devices 130 in the communication network 100, for example, via joint transmission. When all of the network devices 130 collectively serve the terminal devices 120, the communication network 100 may be called full-connected. When a subset of the network devices 130 serve one or more of the terminal devices 120, it may be called user-centric clustering.

As illustrated, the communication network 100 comprises a network device 110 connected to the network devices 130 via e.g. fronthaul. The network device 110 may be a central processing unit (CPU) . As shown, the network device 110 is separate from the network devices 130 serving the terminal devices 120. Alternatively, the network device 110 may be included in one or more of the network devices 130. Alternatively, the network device 110 may also be a network device serving terminal devices 120 as an access point.

Under control of the network device 110, the network devices 130 provide services to the terminal devices 120. The network devices 130 and the terminal devices 120 may communicate data and control information with each other. In some embodiments, the network devices 130 and the terminal devices 120 may communicate with direct links/channels.

In the communication system 100, a link from network device (s) 130 to a terminal device 120 is referred to as a downlink (DL) , while a link from the terminal device 120 to the network device (s) 130 is referred to as an uplink (UL) . In downlink, the network device (s) 130 is a transmitting (TX) device (or a transmitter) and the terminal device 120 is a receiving (RX) device (or a receiver) . In uplink, the terminal device 120 is a transmitting (TX) device (or a transmitter) and the network device (s) 130 is a RX device (or a receiver) . It is to be understood that the links shown in FIG. 1A is for illustrative purposes without suggesting any limitation. It is also to be understood that the network device (s) 130 may provide one or more serving cells. As illustrated in FIG. 1A, the network device (s) 130 provides one serving cell 102, and the terminal device 120 camps on the serving cell 102. In some embodiments, the network device (s) 130 can provide multiple serving cells and the terminal device 120 may switch from a source cell to a target cell between the serving cells during its mobility. It is to be understood that the number of serving cell (s) shown in FIG. 1A is for illustrative purposes without suggesting any limitation.

Communications in the network environment 100 may be implemented according to any proper communication protocol (s) , comprising, but not limited to, cellular communication protocols of the fourth generation (4G) and the fifth generation (5G) and on the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA) , Frequency Division Multiple Access (FDMA) , Time Division Multiple Access (TDMA) , Frequency Division Duplex (FDD) , Time Division Duplex (TDD) , Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Division Multiple (OFDM) , Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and/or any other technologies currently known or to be developed in the future.

It is to be understood that the number of devices and their connection relationships and types shown in FIG. 1A are for illustrative purposes without suggesting any limitation. The communication system 100 may comprise any suitable number of devices adapted for implementing embodiments of the present disclosure.

As mentioned, the performance of the communication network 100 (e.g. spectral efficiency (SE) ) is impacted by phase errors on coherent joint transmission (CJT) . FIG. 1B illustrates an example of average-UE SE in the presence of AP side phase errors under fully-connected architecture of the communication network 100. In FIG. 1B, the performance impact of cross-AP phase errors on CJT is illustrated for two different CJT processing methods under fully-connected architecture. The first one is the centralized processing dMIMO (C-dMIMO) , which means that a network device 110 (e.g. CPU) uses global channel state information (CSI) to calculate the precoding matrices (e.g., zero forcing (ZF) ) for the served UEs 120. The other one is the distributed processing dMIMO (D-dMIMO) , which means that each AP 130 uses its local channel state information (CSI) to calculate the precoding matrix (e.g., ZF) for its served UEs 120. From FIG. 1B, it is observed that, with the increase of root mean squared error (RMSE) of phase errors, the performance of both C-dMIMO and D-dMIMO deteriorates, meanwhile the C-dMIMO is more sensitive to the phase errors due to stringent requirement of inter-AP CSI accuracy and phase synchronization. Therefore, distributed processing is more robust to inter-AP phase errors than centralized processing for dMIMO CJT scheme, and is a preferred transmission scheme for dMIMO deployment.

It is also observed in the communication network 100 that the phase errors at the APs 130 degraded the system performance, while the phase and amplitude errors at UE side do not affect the system performance. Therefore, it is beneficial to focus on the effect of the phase errors at the AP side. In order to eliminate the effect of phase errors, non-coherent joint transmission (NCJT) scheme is applied, where different APs 130 may send different data symbols to a given UE 120 and the data of each AP 130 are decoded separately at the UE side. The performance of CJT and NCJT according to the communication network 100 is plotted in FIG. 1C. It can be seen that NCJT is not affected by the phase errors, but it suffers severe performance decrease due to the interference of data symbols from multiple APs, especially at the region of low phase errors. In view of this, a dMIMO scheme that can simultaneously be insensitive to phase errors and still guarantee high SE performance faces great challenges.

Due to the large overhead of the phase error calibration and the inherent hardware impairments of the dMIMO system, the influence of the phase errors on the CJT may exist in practice. As the phase errors of the cooperative APs increase, the CJT performance drops sharply, as shown in FIG. 1B and FIG. 1C. Thus, to harvest the potential superiority of CJT in dMIMO systems, an AP chunking/grouping-based CJT (or chunked/grouped CJT) system is provided herein, which may alleviate the impact of phase errors on the system performance. Note that terms “grouping” and “grouped” in the present disclosure may be interchangeably used with terms “chunking” and “chunked” respectively, and terms “batch” and “batches” may be interchangeably used with terms “group” and “groups” respectively.

FIG. 2 illustrates an example of a process flow 200 in accordance with some example embodiments of the present disclosure. For ease of understanding, the process flow 200 will be described with reference to FIG. 1A. It would be appreciated that although the process flow 200 has been described referring to the communication network 100 of FIG. 1A, this process flow 200 may be likewise applied to other similar communication scenarios.

The terminal device 120 determines (201) at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices 130 serving the terminal device 120. In some embodiments, the plurality of network devices 130 serving the terminal device 120 may be a subset of the network devices in the communication network 100 formed by the network device 110. For example, the network device 110 may perform AP clustering and select the serving network devices 130 for the terminal device 120 from a set of network devices based on large-scale information, such as distance between the terminal device and the network devices 130, strength indication of received signals, and the like.

In some embodiments, the terminal device 120 may determine the at least a first preliminary group of network devices and the second preliminary group of network devices based on downlink beamforming reference signals (RSs) from the network devices 130. The terminal device 120 may transmit sounding reference signals (SRSs) to the network devices 130, and receive RSs from the respective network devices 130. Then, the terminal device 120 may determine the DL channels (e.g. effective channels) for plurality of network devices based on the RSs, and then determine, based on the DL channels, which group each of the network devices 130 belongs to. In some embodiments, the terminal device 120 may determine the first preliminary group of network devices and the second preliminary group of network devices based on received power information or phase information of the DL channels.

As such, the terminal device 120 may obtain group information indicative of the first preliminary group and the second preliminary group of the network devices 130. In some embodiments, the group information may comprise a bit map where each bit indicates a group (the first preliminary group or the second preliminary group) that a corresponding network device belongs to. For example, “0” may indicate the first group and “1” may indicate the second group, and vice versa. Alternatively or additionally, group information may comprise a number of network devices included in one of the first preliminary group and the second preliminary group and an index indicative of network devices in the corresponding group. In some embodiments, the terminal device 120 may determine one of the groups that has less network devices, and determine an index indicating the network devices in that group. The index may be determined based on combinatorial function of network devices in that group over all of the serving network devices of the terminal device 120. In this way, the index may be mapped to a particular combination of network devices 130.

The terminal device 120 transmits (202) the group information (203) . Accordingly, the network device 110 receives (204) the group information (203) . In some embodiments, the network device 110 may be a separate device from the network devices 130, for example, a CPU connected to the network devices 130 in a dMIMO system. In this case, it may receive (204) the group information (203) from the one of network devices 130 which receives the group information from the terminal device 120. That is, the network device 110 may receive (204) the group information (203) from the terminal device 120 indirectly. Alternatively, the network device 110 may comprise or be included in one or more of the plurality of network devices serving the terminal device 120. In this case, the network device 110 may receive (204) the group information (203) from the terminal device 120 directly.

In some embodiments, the terminal device 120 may further indicate the network device 110 about whether to actually divide the network devices 130 into groups for DL transmission. The terminal device 120 may determine whether sizes of the first preliminary group and the second preliminary group are similar. Similar sizes may imply that the impact of phase errors in the system are relatively large, and it would be more beneficial to divide the network devices 130 into groups for DL transmission. Based on determining that the sizes of the first preliminary group and the second preliminary group are similar, the terminal device 120 may transmit an indictor indicative of division of the plurality of network devices into the first group and the second group for DL transmission.

Upon reception of the group information, the network device 110 determines (205) , based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices 130. In some embodiments, the network device 110 may receive the indictor indicative of division of the plurality of network devices 130 into the first group and the second group for DL transmission, and based on receiving the indicator, divide the plurality of network devices 130 into the first group and the second group.

In some embodiments, the network device 110 may solely rely on the group information to perform the division. Alternatively or additionally, the network device 110 may divide the plurality of network devices 130 into the first group and the second group based on, in addition to the group information, network conditions including actual connection situation, service capability, and power consumption of the plurality of network devices 130. Thus, the network device 110 finally determines the first group and the second group of network devices 130 for serving the terminal device 120.

In some embodiments, the network device 110 may adjust the grouping of the network devices 130 periodically. The periodicity of the adjustment may be based on the stability of phase errors in the communication system. In some embodiments, the network device 110 may obtain a feedback periodicity for transmitting the group information and configure the terminal device 120 to transmit the group information based on the feedback periodicity. For example, when the network device 110 determines that the phase errors mainly depend on the hardware implement and operating conditions, which are relatively constant, it may obtain a larger feedback periodicity. When the network device 110 determines that the phase errors changes dramatically, it may obtain a smaller feedback periodicity such that the terminal device 120 may transmit the group information more frequently.

The network device 110 configures (206) the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device 120. The first data and the second data may be different or common between the first group of network devices and the second group of network devices. In some embodiments, the network device 110 may perform power allocation for the first group and the second group of network devices for the data transmission.

In some embodiments, the network device 110 may perform maximum-minimum power allocation for DL transmission based on convex optimization. The network device 110 may adapt the convex optimization with a relaxed maximum-minimum power allocation algorithm, because the division of network devices may cause the loss of convex condition. By the relaxed maximum-minimum power allocation method, a sum of modulus squared of a sum of desired signals from the first group of network devices and modulus squared of a sum of desired signals from the second group of network devices is relaxed to be a square of a sum of modulus of desired signals from the plurality of network devices.

Then, the first group and the second group of the network devices are configured (207) under the control of the network device 110. Afterwards, the terminal device 120 receives (208) first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices 130. The first data and the second data may be different or common between the first group of network devices and the second group of network devices. According to the joint transmission, the same group of the network devices may transmit the same data. In some embodiments, a transmission mode of the first data and the second data may comprise transmit diversity. Alternatively or additionally, the transmission mode may comprise spatial multiplexing.

FIG. 3 illustrates a grouped joint transmission system 300 in accordance with some example embodiments of the present disclosure. The system 300 may be example system implementing the process flow 200 illustrated in FIG. 2. In FIG. 3, a CPU 310 is an example implementation of the network device 110, UE 320 is an example implementation of the terminal device 120, and the APs 330 are example implementations of the network devices 130.

The network device 110 may first configure a user-centric network 312 for the terminal device 320. The user-centric network 312 contains a plurality of APs 330 to serve the UE 320. The CPU 310 divides the APs 330 into two batches 314 and 316. The phase errors between cooperative APs within each batch are as small as possible to guarantee the SE performance of CJT for the UE 320, and then the NCJT transmission (e.g., spatial multiplexing or spatial diversity) is executed between the batches 314 and 316 to guarantee the robustness to phase errors for the UE 320.

By grouping the network devices for joint transmission, the embodiments of the disclosure may alleviate the impact of phase errors on the system performance. Some embodiments of the disclosure may include the following features, which will be described later in detail with reference to FIG. 4.

As a first feature, in order to improve the robustness of CJT to phase errors across the cooperative APs, some embodiments of the disclosure propose an AP chunking-based CJT scheme, i.e., the phase errors between cooperative APs within each batch is as small as possible to ensure the performance advantage of CJT, and NCJT is used between the batches to ensure robustness.

As a second feature, in order to minimize the performance loss of the chunked CJT, some embodiments of the disclosure propose an optimal batched algorithm based on receiving (Rx) power. Alternatively, a batched algorithm based on Rx phase information is also proposed. The proposed two algorithms can give full play to the performance advantages of the chunked CJT comparing with the random batched algorithm.

As a third feature, to provide fair and high-quality services to UE in the network, some embodiments of the disclosure propose a relaxed max-min power allocation algorithm for the chunked CJT scheme.

As a fourth feature, to facilitate the application of the proposed scheme in the 3GPP standard, some embodiments of the disclosure propose a standard oriented process along with a low feedback overhead strategy. Further, according to the channel conditions, two modes i.e., quasi-static mode or dynamic mode, are proposed to realize chunked CJT feedback and transmission.

The implementation steps of some embodiments may include one or more of the following steps. Firstly, CPU forms a user-centric network containing multiple APs to serve a UE, and each AP relies on the UL sounding reference signal (SRS) transmitted by the UE to calculate the DL preprocessing matrix locally.

Next, each AP sends downlink (DL) beamformed reference signal (RS) to UE it serves, then UE receives DL beamformed RS and uses the heuristic batched algorithms based on DL effective channel to divide the APs serving the UE into two disjoint batches. Each UE then reports the chunked results with a small amount of feedback indicating which batch is selected for each AP, then CPU relies on the feedback information, the actual connection situation, the service capability and power consumption of the AP to make the final chunked results.

The CPU performs the relaxed max-min power allocation based on chunked results to correct the previous DL preprocessing matrix. Finally, the multiple APs serving the UE can transmit data in the form of spatial multiplexing, i.e., APs in the same batch send the same data symbols, while APs in different batches send different data symbols; it can also transmit data in the form of transmit diversity, i.e., the two batches jointly transmit in an Alamouti mode.

In general, phase errors depend on the hardware implementation and operating conditions. Thus, the phase errors can be assumed to be constant over many propagation channel coherence intervals, so division of the APs by CPU and reporting of the chunked results by UE are typically performed infrequently, i.e., after UE measurement of DL effective channel and feedback of chunked results, this result is used for DL chunked data transmission on multiple coherent intervals in the future. Extensive simulations verify the advantages of the proposed solution. For example, the chunked CJT according to the proposed solution is always better than the NCJT under any phase errors. As the phase errors increase, the performance advantage of the proposed solution gradually increases compared with CJT. When the phase error RMSE is 100° at clustering threshold η=60dB, compared with CJT, the Average-UE SE and 5%-pile cell edge UE SE of the chunked CJT have 14%and 60%improvement respectively. Therefore, the chunked CJT proposed in this disclosure greatly improves the robustness of phase errors while maintaining high SE performance.

FIG. 4 illustrates another example of a process flow 400 in accordance with some example embodiments of the present disclosure. The process flow 400 may be implemented in the communication network 100 in FIG. 1A, wherein the CPU 410 is an example implementation of the network device 110, the UE 420 is an example implementation of the terminal device 120, and the APs 430 are example implementations of the network devices 130.

The chunked CJT proposed according to embodiments of the disclosure can greatly reduce the impact of the phase errors on dMIMO performance. In some embodiments, the UE relies on the measurement of DL effective channel to divide the AP cluster serving it into two disjoint batches and feeds back the chunked situation to one or more APs, then APs in the same batch send the same data symbols in CJT mode, and APs in different batches send different or same data symbols in NCJT mode.

Consider DL of a CF mMIMO system with M APs each equipped with N antennas and K single antenna UEs. The main process is UL SRS transmission, DL beamformed RS transmission, UE reporting chunked results, CPU processing and deriving final chunked results, and DL chunked joint data transmission. The detailed implementation of the invention is summarized as follows:

At 401 (Forming a user-centric network) , there are many ways to form a user centered network, such as using the distance between APs 430 and UE 420, using the strength indication of received signals, etc. Here, the CPU 410 may performs AP clustering according to the large-scale channel information between the UE 420 and the AP 430, i.e., when the large-scale value of a pair of AP-UE is smaller than a predefined threshold η, the element c_mk=1, m=1, …, M, k=1, …, K, representing the connection between AP m and UE k, otherwise c_mk=0 representing no connection between them, thus the CPU 410 obtains a connection matrix C= [C₁, …, C_M] ∈R^K×M, where C_m= [c_m1, …, c_mK] ^T. The set of APs serving UE k, D_k, can be defined as

where β_mk represents the large-scale fading coefficient between AP m and UE k.

At 402 (UL SRS transmission) , focusing on the effect of phase errors on DL performance, for simplicity, it is assumed that the AP m has a perfect UL channel matrix G_m= [g_m1, …, g_mK] ∈C^N×K after the UE transmits SRS;
G_m=B_mH_m (2)

where H_m= [h_m1, …, h_mK] ∈C^N×K is the aggregated UL physical propagation channel connecting AP m and each of K UEs, and B_m∈C^N×N is the frequency response matrix due to phase errors induced by hardware problems. It is assumed that AP only depends on channel reciprocity, so the transpose of UL channel is directly used as the corresponding DL channel.

At 403, according to the connection relationship C_m, AP m performs ZF locally to obtain the DL precoding matrix W_m= [w_m1, …, w_mK] ∈C^N×K;

whereis the UL partial channel matrix obtained by AP m according to the connection relation, diag (·) is to take the diagonal matrix. Then AP does normalization and equal power allocation to obtain the DL preprocessing matrix

At 404 (DL beamformed RS transmission) : each of the APs 430 transmits DL beamformed references signals to the UE 420.

At 405 (RS receiving and chunking) , the UE 420 relies on the DL beamformed RSs transmitted by the serving APs 430 to measure the DL effective channel, UE k divides the APs in the D_k into two disjoint batches based on DL effective channel according to the following two algorithms respectively.

In algorithm 1, at the initialization stage, two APs having the largest inferences in consideration of received power are found. At the loop stage, other APs are distributed one by one to an appropriate batch such that APs in the same batch have the least impact from inter-AP phase errors.

Alternatively, a heuristic batched algorithm based on phase information of the DL effective channel is also proposed. The specific algorithm steps are shown as follows:

In algorithm 2, at the initialization stage, two APs having the largest inferences in consideration of phases are found. At the loop stage, other APs are distributed one by one to an appropriate batch such that APs in the same batch have similar phrases.

At 406 (UE reporting chunked results) : when the phase errors are small, the performance of the traditional CJT is similar to that of the proposed embodiments of the disclosure, and the chunked results, andshow a large difference between the two batches. At this time, UE 420 may recommend that the CPU 410 adopts the traditional CJT, instead of chunked CJT. But as the phase errors increase, the performance advantage of the proposed embodiments of the disclosure gradually increases, so UE 420 may need to feed back chunked resultsandFor this purpose, the UE 420 first need to report one bit indicating the transmission mode, e.g., 1→chunked CJT, 0→traditional CJT. If the chunked CJT is chosen, the following two feedback methods are specified to show the detailed chunked results for its served APs 430.

Feedback method 1: Let 0 represent APs that belong to batch 1, and 1 represent APs that belong to batch 2, so the UE k only needs to feed back Λ_k bits, where Λ_k is the number of elements in the set D_k, that is, the number of coordinated APs in the cluster specific to UE k;

Feedback method 2: The UE feeds back two parts of bit information. The first part of the bit information is to report the number of APs in one batch, which is less than the number of APs in another batch. The second part of the bit information of the UE is to report the index of the APs in the smaller batch. So the CPU is aware of the chunked results for the two batches. The feedback amount O_k of UE k is expressed as

where L_k is the number of APs in the smaller batch serving UE k and is equal to or less than is the ceiling function (representing the smallest integer greater than or equal to itself) and C (n, m) is combinatorial function, where n is the total number of elements and m is the number of elements involved in the selection. Feedback method 2 is better than feedback method 1 in most cases, but when the AP numbers of the two batches are similar, the feedback method 1 is slightly better than the feedback method 2.

At 407 (obtaining final chunked results) , the CPU 410 finally determines the sets andaccording to the information fed back by the UE 420, the actual connection situation, the service capability and power consumption of the AP. According to the actual degree of phase change, there are two modes.

Quasi-static mode: In general, the phase errors depend on the hardware implement and operating conditions, such as temperature drift. Thus, the phase errors can be assumed to be constant over many propagation channel coherence intervals, so UE measurements of DL effective channel and feedback of chunked results (i.e., 405 and 406) are typically performed infrequently, e.g., once in an hour. In other words, after UE measurement of DL effective channel and feedback of chunked result, this result is used for DL chunked data transmission on multiple coherent intervals in the future.

Dynamic mode: When the phase errors change drastically on special occasions, the UE 420 performs chunking and feedback more frequently during this period, and the CPU 410 also makes the final chunked results in time and performs DL data transmission according to the chunked results.

At 408 (power allocation for data transmission) , in some embodiments, the preprocessing matrix at 403 may be directly used for DL data transmission. Alternatively, maximum-minimum power allocation may be used to maximize the minimum UE rate, so as to achieve fairness between UEs in the region. Letrepresent the power coefficient between AP m and UE k, and σ_n is noise power. In order to solve the optimization problem with cvx toolbox (a modeling system for constructing and solving disciplined convex programs (DCPs) ) , the following inequality is adopted to relax the maximum-minimum power control of chunked CJT.
|s₁+s₂|²+|s₃+s₄|²≤ (|s₁+s₂|+|s₃+s₄|) ²≤ (|s₁|+|s₂|+|s₃|+|s₄|) ² (9)

It is assumed that s₁ and s₂ are the desired signals provided by APs in batch 1 for a UE, and s₃ and s₄ are the desired signals provided by APs in batch 2 for the UE. According to equation (9) . a sum of modulus squared of a sum of desired signals from the batch 1 and modulus squared of a sum of desired signals from the batch 2 is relaxed to be a square of a sum of modulus of desired signals from all of APs serving the UE. The relaxed maximum-minimum power allocation algorithm for the chunked CJT is given below:

At 409 (DL data transmission) , the APs 430 may have two transmission schemes for NCJT. If the channel quality is poor, the APs 430 may transmit data in the form of transmit diversity; otherwise, APs 430 may transmit data in the form of spatial multiplexing.

Spatial multiplexing: The same batch of APs send the same data symbol in CJT mode, while different batches of APs send different data symbols in spatial multiplexing mode, that is, APs in batch 1 transmit x_1, _k, and APs in batch 2 transmit x_2, _k;

where x_z, _k, z∈ {1, 2} is the data symbol sent by the APs in batch z for UE k.

Transmit diversity: Two batches of APs jointly transmit in an Alamouti mode, i.e., the different data symbols x_1, _k and x_2, _k sent to the UE k are encoded according to the following space-time codeword matrix:

In the first time slot, APs in batch 1 transmit x_1, _k, and APs in batch 2 transmit x_2,k; in the second time slot, the APs in batch 1 transmitand the APs in batch 2 transmitConsidering the reason of Alamouti decoding, it is assumed that the effective channel of the two time slots is unchanged. Then UE k uses the complex orthogonality of Alamouti codes to solve the desired data symbols.

Some simulation results and performance analysis based on some example embodiments of the present disclosure are as below. The simulation parameters are shown in Table 1.

Table 1: Simulation parameters

To demonstrate the advantages brought by the batched algorithms proposed in the disclosure, the performance of the random batched algorithm is simulated, i.e., the number of APs in the two batches is similar and the APs in the batch are randomly selected, which is the most straightforward batched algorithm.

FIG. 5 illustrates performance of different transmission schemes under max-min power allocation in accordance with some example embodiments of the present disclosure. In Fig 5, the performances of various transmission schemes are plotted against the cross-AP phase errors at clustering threshold η=60dB and the performance gains of the patented scheme under more clustering thresholds are shown in Table 2.

Table 2: Performance gains from Rx power based solution

According to the simulation results, the following conclusions can be drawn. Using NCJT as the benchmark, the chunked CJT according to embodiments of the disclosure outperforms the NCJT under any clustering threshold and phase error, but the random chunked CJT performs worse than the NCJT when the phase errors are large. Using CJT as the benchmark, when the number of APs connected to the UE is large (or the clustering threshold η is large) and the phase errors are small, average-UE SE of chunked CJT according to embodiments of the disclosure is slightly better than that of the CJT, but as the increase of the phase errors, the performance gap of the solution proposed in the patent gradually increases. When the phase error RMSE is 100° at clustering threshold η=60dB, compared with CJT, the average-UE SE and 5%-pile cell edge UE SE of the chunked CJT have 14%and 60%improvement respectively.

In view of above, the chunked CJT scheme according to embodiments of the disclosure can significantly alleviate the sensitivity of phase errors and harvest the potential superiority of CJT in dMIMO systems.

FIG. 6 illustrates a flowchart of an example method 600 implemented at a terminal device in accordance with some other embodiments of the present disclosure. For ease of understanding, the method 600 will be described from the perspective of the terminal device 120 with reference to FIG. 1A.

At block 610, the terminal device 120 determines at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device.

In some embodiments, the terminal device 120 may transmit sounding reference signals (SRSs) to the plurality of network devices, and receive the reference signals from the plurality of network device. In some embodiments, the terminal device 120 may determine downlink (DL) channels for the plurality of network devices based on reference signals from the plurality of network device. The terminal device 120 may determine the first preliminary group of network devices and the second preliminary group of network devices based on the DL channel.

In some embodiments, the terminal device 120 may determine the first preliminary group of network devices and the second preliminary group of network devices based on received power information of the DL channel. Alternatively or additionally, the terminal device 120 may determine the first preliminary group of network devices and the second preliminary group of network devices based on phase information of the DL channels.

In some embodiments, the terminal device 120 may further obtain a feedback periodicity for transmitting the group information. The terminal device 120 may further transmit the group information based on the feedback periodicity.

At block 620, the terminal device 120 transmits group information indicative of the first preliminary group and the second preliminary group. The first group and the second group are determined based on at least the group information.

In some embodiments, the group information may comprise a bitmap. Alternatively or additionally, the group information may comprise a number of network devices in one of the first preliminary group and the second preliminary group and an index indicative of the network device in the corresponding group.

In some embodiments, the terminal device 120 may further determine whether sizes of the first preliminary group and the second preliminary group are similar. Based on determining that the sizes of the first preliminary group and the second preliminary group are similar, the terminal device 120 may transmit an indictor indicative of division of the plurality of network devices into the first group and the second group for DL transmission.

At block 630, the terminal device 120 receive first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices. The first data and the second data are different or common between the first group of network devices and the second group of network devices.

In some embodiments, a transmission mode of the first data and the second data may comprise transmit diversity. Alternatively or additionally, the transmission mode may comprise spatial multiplexing.

FIG. 7 illustrates another flowchart of an example method implemented at a network device in accordance with some embodiments of the present disclosure. For ease of understanding, the method 700 will be described from the perspective of the network device 110 with reference to FIG. 1A.

At 710, the network device 110 receives group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device.

In some embodiments, the network device 110 may determine large-scale channel information between the terminal device and a set of network device. The network device 110 may further select the plurality of network devices from the set of network devices for serving the terminal device based on the large-scale channel information.

In some embodiments, the network device 110 may obtain a feedback periodicity for transmitting the group information, and configure the terminal device to transmit the group information based on the feedback periodicity.

At 720, the network device 110 determines, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices.

In some embodiments, the network device 110 may receive an indictor indicative of division of the plurality of network devices into the first group and the second group for DL transmission. Based on receiving the indicator, the network device 110 may divide the plurality of network devices into the first group and the second group.

In some embodiments, the network device 110 may divide the plurality of network devices into the first group and the second group based on the group information and at least one of actual connection situation, service capability, and power consumption of the plurality of network devices.

At 730, the network device 110 configures the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device. The first data and the second data are different or common between the first group of network devices and the second group of network device.

In some embodiments, the network device 110 may further perform maximum-minimum power allocation for DL transmission based on convex optimization. In the convex optimization, a sum of modulus squared of a sum of desired signals from the first group of network devices and modulus squared of a sum of desired signals from the second group of network devices is relaxed to be a square of a sum of modulus of desired signals from the plurality of network devices.

In some embodiments, the network device 110 may comprise one or more of the plurality of network devices serving the terminal device. Alternatively or additionally, the network device 110 may comprise a central process unit (CPU) connected to the plurality of network devices in a distributed multiple-in multiple-out (dMIMO) system.

In some embodiments, an apparatus capable of performing the method 600 (for example, the terminal device 120) may comprise means for performing the respective steps of the method 600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for determining at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device; means for transmitting group information indicative of the first preliminary group and the second preliminary group; and means for receiving first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices, wherein the first group and the second group are determined based on at least the group information.

In some embodiments, means for determining at least a first preliminary group of network devices and a second preliminary group of network devices may comprise means for determining downlink (DL) channels for the plurality of network devices based on reference signals from the plurality of network devices, and means for determining the first preliminary group of network devices and the second preliminary group of network devices based on the DL channels.

n some embodiments, means for determining at least a first preliminary group of network devices and a second preliminary group of network devices may comprise means for determining the first preliminary group of network devices and the second preliminary group of network devices based on received power information or phase information of the DL channels.

In some embodiments, the group information comprises one or more of: a bitmap; or a number of network devices in one of the first preliminary group and the second preliminary group and an index indicative of the network device in the corresponding group.

In some embodiments, the apparatus may further comprise: means for determining whether sizes of the first preliminary group and the second preliminary group are similar; and means for transmitting, based on determining that the sizes of the first preliminary group and the second preliminary group are similar, an indictor indicative of division of the plurality of network devices into the first group and the second group for DL transmission.

In some embodiments, means for transmitting group information indicative of the first preliminary group and the second preliminary group may comprise means for obtaining a feedback periodicity for transmitting the group information and means for transmitting the group information based on the feedback periodicity.

In some embodiments, a transmission mode of the first data and the second data may comprise at least one of transmit diversity and spatial multiplexing.

In some embodiments, the apparatus may further comprise means for transmitting sounding reference signals (SRSs) to the plurality of network device and means for receiving the reference signals from the plurality of network devices.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 600. In some embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

In some embodiments, an apparatus capable of performing the method 700 (for example, the network device 110) may comprise means for performing the respective steps of the method 700. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for receiving group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device; means for determining, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network device; and means for configuring the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.

In some embodiments, the apparatus may further comprise: means for determining large-scale channel information between the terminal device and a set of network devices, and means for selecting the plurality of network devices from the set of network devices for serving the terminal device based on the large-scale channel information.

In some embodiments, means for determining at least a first group of network devices and a second group of network devices may comprise means for receiving an indictor indicative of division of the plurality of network devices into the first group and the second group for DL transmission and means for dividing, based on receiving the indicator, the plurality of network devices into the first group and the second group.

In some embodiments, means for determining at least a first group of network devices and a second group of network devices may comprise means for dividing the plurality of network devices into the first group and the second group based on the group information and at least one of actual connection situation, service capability, and power consumption of the plurality of network devices.

In some embodiments, the apparatus may further comprise: means for obtaining a feedback periodicity for transmitting the group information; and means for configuring the terminal device to transmit the group information based on the feedback periodicity.

In some embodiments, the apparatus may further comprise means for performing maximum-minimum power allocation for DL transmission based on convex optimization, wherein a sum of modulus squared of a sum of desired signals from the first group of network devices and modulus squared of a sum of desired signals from the second group of network devices is relaxed to be a square of a sum of modulus of desired signals from the plurality of network devices.

In some embodiments, the apparatus may be or included in one or more of the plurality of network devices serving the terminal device or a central process unit (CPU) connected to the plurality of network devices in a distributed multiple-in multiple-out (dMIMO) system.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 700. In some embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

FIG. 8 illustrates a simplified block diagram of a device 800 that is suitable for implementing some example embodiments of the present disclosure. The device 800 may be provided to implement a communication device, for example, the network device 110 or the terminal device 120 as shown in FIG. 1A. As shown, the device 800 includes one or more processors 810, one or more memories 820 coupled to the processor 810, and one or more communication modules 840 coupled to the processor 810.

The communication module 840 is for bidirectional communications. The communication module 840 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network elements.

The processor 810 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 800 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 820 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 824, an electrically programmable read only memory (EPROM) , a flash memory, a hard disk, a compact disc (CD) , a digital video disk (DVD) , and other magnetic storage and/or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 822 and other volatile memories that will not last in the power-down duration.

Acomputer program 830 includes computer executable instructions that are executed by the associated processor 810. The program 830 may be stored in the ROM 824. The processor 810 may perform any suitable actions and processing by loading the program 830 into the RAM 822.

The embodiments of the present disclosure may be implemented by means of the program 830 so that the device 800 may perform any process of the disclosure as discussed with reference to FIGS. 6 and 7. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some example embodiments, the program 830 may be tangibly contained in a computer-readable medium which may be included in the device 800 (such as in the memory 820) or other storage devices that are accessible by the device 800. The device 800 may load the program 830 from the computer-readable medium to the RAM 822 for execution. The computer-readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like.

FIG. 9 illustrates a block diagram of an example of a computer-readable medium 900 in accordance with some example embodiments of the present disclosure. The computer-readable medium 900 has the program 830 stored thereon. It is noted that although the computer-readable medium 900 is depicted in form of CD or DVD in FIG. 9, the computer-readable medium 900 may be in any other form suitable for carry or hold the program 830.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the method 600 or 700 as described above with reference to FIG. 6 or 7. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer-readable medium, and the like.

The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. A computer-readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer-readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. The term “non-transitory, ” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM) .

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A terminal device comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device at least to:

determine at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device;

transmit group information indicative of the first preliminary group and the second preliminary group; and

receive first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices,

wherein the first group and the second group are determined based on at least the group information.
The terminal device of claim 1, wherein the terminal device is further caused to determine at least a first preliminary group of network devices and a second preliminary group of network devices by:

determining downlink (DL) channels for the plurality of network devices based on reference signals from the plurality of network devices; and

determining the first preliminary group of network devices and the second preliminary group of network devices based on the DL channels.
The terminal device of claim 2, wherein determining the first preliminary group of network devices and the second preliminary group of network devices based on the DL channels comprises:

determining the first preliminary group of network devices and the second preliminary group of network devices based on received power information or phase information of the DL channels.
The terminal devices of any of claims 1 to 3, wherein the group information comprises one or more of:

a bitmap; or

a number of network devices in one of the first preliminary group and the second preliminary group and an index indicative of the network device in the corresponding group.
The terminal device of any of claims 1 to 4, wherein the terminal device is further caused to:

determine whether sizes of the first preliminary group and the second preliminary group are similar; and

based on determining that the sizes of the first preliminary group and the second preliminary group are similar, transmit an indictor indicative of division of the plurality of network devices into the first group and the second group for DL transmission.
The terminal device of any of claims 1 to 5, wherein the terminal device is caused to transmit the group information by:

obtaining a feedback periodicity for transmitting the group information; and

transmitting the group information based on the feedback periodicity.
The terminal device of any of claims 1 to 6, wherein a transmission mode of the first data and the second data comprises at least one of transmit diversity and spatial multiplexing.
The terminal device of any of claims 1 to 7, wherein the terminal device is further caused to:

transmit sounding reference signals (SRSs) to the plurality of network devices; and

receive the reference signals from the plurality of network devices.
A network device comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the network device at least to:

receive group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device;

determine, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and

configure the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.
The network device of claim 9, wherein the network device is further caused to:

determine large-scale channel information between the terminal device and a set of network devices; and

select the plurality of network devices from the set of network devices for serving the terminal device based on the large-scale channel information.
The network device of claims 9 or 10, wherein the group information comprises one or more of:

a bitmap; or

a number of network devices in one of the first preliminary group and the second preliminary group and an index indicative of the network device in the corresponding group.
The network device of any of claims 9 to 11, wherein the network device is further caused to determine at least a first group of network devices and a second group of network devices among the plurality of network devices by:

receiving an indictor indicative of division of the plurality of network devices into the first group and the second group for DL transmission; and

based on receiving the indicator, dividing the plurality of network devices into the first group and the second group.
The network device of any of claims 9 to 12, wherein the network device is further caused to determine at least a first group of network devices and a second group of network devices among the plurality of network devices by

dividing the plurality of network devices into the first group and the second group based on the group information and at least one of actual connection situation, service capability, and power consumption of the plurality of network devices.
The network device of any of claims 9 to 13, wherein the network device is further caused to receive the group information by:

obtaining a feedback periodicity for transmitting the group information; and

configuring the terminal device to transmit the group information based on the feedback periodicity.
The network device of any of claims 9-14, wherein the network device is further caused to:

perform maximum-minimum power allocation for DL transmission based on convex optimization,

wherein a sum of modulus squared of a sum of desired signals from the first group of network devices and modulus squared of a sum of desired signals from the second group of network devices is relaxed to be a square of a sum of modulus of desired signals from the plurality of network devices.
The network device of any of claims 9 to 15, wherein a transmission mode of the first data and the second data comprises at least one of transmit diversity or spatial multiplexing.
The network device of any of claims 9 to 16, wherein the network device comprises one or more of:

one or more of the plurality of network devices serving the terminal device; or

a central process unit (CPU) connected to the plurality of network devices in a distributed multiple-in multiple-out (dMIMO) system.
A method comprising:

determining at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device;

transmitting group information indicative of the first preliminary group and the second preliminary group; and

receiving first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices,

wherein the first group and the second group are determined based on at least the group information.
A method comprising:

receiving group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device;

determining, based on the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and

configuring the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.
An apparatus comprising:

means for determining at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device;

means for transmitting group information indicative of the first preliminary group and the second preliminary group; and

means for receiving first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices,

wherein the first group and the second group are determined based on at least the group information.
An apparatus comprising:

means for receiving group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device;

means for determining, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and

means for configuring the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.
A non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least:

determining at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving the terminal device;

transmitting group information indicative of the first preliminary group and the second preliminary group; and

receiving first data jointly transmitted from a first group of network devices among the plurality of network devices and second data jointly transmitted from a second group of network devices among the plurality of network devices, the first data and the second data being different or common between the first group of network devices and the second group of network devices,

wherein the first group and the second group are determined based on at least the group information.
A non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least:

receiving group information indicative of at least a first preliminary group of network devices and a second preliminary group of network devices among a plurality of network devices serving a terminal device;

determining, based on at least the group information, at least a first group of network devices and a second group of network devices among the plurality of network devices; and

configuring the first group of network devices to jointly transmit first data and the second group of network devices to jointly transmit second data to the terminal device, the first data and the second data being different or common between the first group of network devices and the second group of network devices.