Method and electronic device for hierarchical beam search based on multi-AP in wireless communication system

Abstract

The present disclosure relates to a hierarchical beam search method using a plurality of APs. The method performed by an electronic device of the present disclosure may comprise: a step in which a first AP, performing a search first among a plurality of APs, performs a first beam search on a service area by using a first beam set predetermined for searching the service area among a plurality of beam sets allocated to the first AP; a step for selecting, from the first beam set, a first beam to be used for simultaneous transmission according to the result of the first beam search; determining, on the basis of the first beam, a second AP performing a search second and a second beam set to be used for a second beam search among a plurality of beam sets allocated to the second AP; a step in which the second AP performs the second beam search by using the second beam set; a step for selecting, from the second beam set, a second beam to be used for simultaneous transmission according to the result of the second beam search; and a step for performing simultaneous transmission to a terminal by using the selected beams.

Description

Method and electronic device for hierarchical beam seeking based on multi-AP in a wireless communication system

[0001] The present disclosure relates to a wireless communication system, and more specifically, to a method and electronic device for performing hierarchical beam search based on a multi-AP in a wireless communication system.

[0002] A multi-AP (Access Point) based cooperative transmission system is a technology in which multiple APs cooperate to transmit data, and it is an important method for improving network performance.

[0003] To implement a multi-AP cooperative transmission system, a central controller that controls multiple APs may be used. In this case, the central controller can exchange information with the multiple APs, collect information, and coordinate transmission using the multiple APs. Alternatively, to implement a multi-AP cooperative transmission system, multiple APs may communicate directly with each other using a backhaul network, coordinate transmission, and cooperate. The information exchanged between the multiple APs and the central controller, and / or between the multiple APs, may include information measuring channel conditions received from a terminal. For example, at least some of the multiple APs may transmit a reference signal to the terminal using beam sweeping, and the terminal may measure the channel condition based on the reference signal. The terminal reports information related to the channel condition to the APs, and based on the information received from the terminal, the APs and / or the central controller may perform operations necessary for multi-AP cooperative transmission.

[0004] In a multi-AP cooperative transmission system, multiple APs can simultaneously transmit the same data or different data to terminals. By utilizing multi-AP cooperative transmission, latency and interference between APs can be minimized, and throughput and resource utilization efficiency can be improved, thereby significantly enhancing system capacity and network performance. However, there are challenges to address, such as implementation complexity and overhead management.

[0005] The present disclosure aims to provide a beam search method and apparatus that minimizes the overhead caused by beam search in a multi-AP cooperative transmission system and further improves the speed and resource utilization efficiency of cooperative transmission.

[0006] A method performed by an electronic device of the present disclosure for solving the above-described problem may include: an operation of performing a first beam search for a service area by a first AP that performs a search first among a plurality of APs, using a first beam set designated (predetermined) for searching a service area among a plurality of beam sets assigned to the first AP; an operation of selecting a first beam to be used for simultaneous transmission among the first beam sets according to the result of the first beam search; an operation of determining a second beam set to be used for a second beam search among a plurality of beam sets assigned to a second AP and a second AP that performs a search second based on the first beam; an operation of performing a second beam search by the second AP using the second beam set; an operation of selecting a second beam to be used for simultaneous transmission among the second beam sets according to the result of the second beam search; and an operation of performing simultaneous transmission to a terminal using the selected beams.

[0007] An electronic device for performing simultaneous transmission to a terminal located in a service area according to one embodiment of the present disclosure may include a transceiver that communicates with a plurality of APs; and a control unit coupled to the transceiver. The control unit may be configured to perform a first beam search for a service area using a first beam set assigned to the first AP, which performs the first search among the plurality of APs, and to select a first beam to be used for simultaneous transmission among the first beam sets based on the result of the first beam search, and to determine a second beam set to be used for a second beam search among the plurality of beam sets assigned to the second AP and the second AP based on the first beam, and to perform a second beam search using the second beam set by the second AP, and to select a second beam to be used for simultaneous transmission among the second beam sets based on the result of the second beam search, and to perform simultaneous transmission to the terminal using the selected beams.

[0008] An electronic device for performing simultaneous transmission to a terminal located in a service area according to one embodiment of the present disclosure may include a plurality of APs; a transceiver; and a control unit coupled to the transceiver. The control unit may be configured to perform a first beam search for a service area using a first beam set assigned to the first AP, which performs the first search among the plurality of APs, and to select a first beam to be used for simultaneous transmission among the first beam sets based on the result of the first beam search, and to determine a second beam set to be used for a second beam search among the plurality of beam sets assigned to the second AP and the second AP based on the first beam, and to perform a second beam search using the second beam set by the second AP, and to select a second beam to be used for simultaneous transmission among the second beam sets based on the result of the second beam search, and to perform simultaneous transmission to the terminal using the selected beams.

[0009] According to one embodiment of the present disclosure, candidate search regions to be used for hierarchical beam search and an optimal beam set to be used for each of the candidate search regions are pre-set, so the time or resources consumed for beam search can be minimized compared to conventional empirical methods. In conventional empirical methods, the beam set is determined during hierarchical beam search by obtaining data rates for a plurality of terminals and a plurality of beam sets based on the results of beam search and determining the beam set where the data rate is maximized.

[0010] According to one embodiment of the present disclosure, the optimal beam set to be used for each of the candidate search regions can be determined based on a beam set that maximizes the region average signal-to-noise ratio (SNR). In the present disclosure, the region average SNR can be determined by dividing the candidate search region into a number of sub-regions equal to the number of beams and summing the SNRs of each beam for each sub-region. Thus, a higher data transmission rate can be achieved through interference minimization and SNR improvement, and the capacity of the overall system can be enhanced.

[0011] Furthermore, the number of beams in this case refers to the number of beams used when actually searching the candidate search area; since fewer beams can be used as the width of the candidate search area narrows, the overhead associated with beam training can be reduced as the candidate search area narrows during hierarchical beam search. Alternatively, regarding the number of beams used when determining the area average SNR, a narrower candidate search area allows for more precise beam search even with the same number of beams, thereby concentrating the signal toward the user terminal and significantly increasing transmission capacity.

[0012] According to one embodiment of the present disclosure, as hierarchical beam search progresses, if the search area where beam search is actually required decreases, the number of APs assigned to a pre-specified beam set for searching the narrowed search area decreases, and thus the number of beam searches can be reduced.

[0013] FIG. 1 illustrates a beamforming communication method according to one embodiment.

[0014] FIG. 2 illustrates a beamforming communication method in a multi-AP-based cooperative transmission method according to one embodiment.

[0015] FIG. 3 is a diagram illustrating the process of predetermining a beam set of an AP for searching a search area according to one embodiment.

[0016] FIG. 4 is a diagram illustrating the region average SNR according to one embodiment.

[0017] Figure 5 is a diagram illustrating an experience-based method for determining a beam set.

[0018] FIG. 6 is a diagram illustrating a hierarchical beam search method using a plurality of APs according to one embodiment.

[0019] FIG. 7 is a diagram illustrating that the search area is gradually narrowed as beam search proceeds according to one embodiment.

[0020] FIG. 8 is a diagram illustrating that the search area is gradually narrowed as beam search proceeds according to one embodiment.

[0021] FIG. 9 is a diagram illustrating that the search area gradually narrows as beam search proceeds according to one embodiment.

[0022] FIG. 10 is a diagram illustrating that the search area is gradually narrowed as beam search proceeds according to one embodiment.

[0023] FIG. 11 is a diagram illustrating that beam search according to one embodiment influences the determination of the beam set to be used for the next beam search.

[0024] FIG. 12 is a drawing for explaining a beam set designated for a search area according to one embodiment.

[0025] FIG. 13 is a diagram illustrating beam search according to one embodiment.

[0026] FIG. 14 is a flowchart of a method performed by an electronic device in one embodiment.

[0027] FIG. 15 is a flowchart of a method performed by an electronic device in one embodiment.

[0028] FIG. 16 is a diagram illustrating the data rate performance and the number of beam searches of a hierarchical beam search method according to one embodiment.

[0029] FIG. 17 is a diagram illustrating the data rate performance and the number of beam searches of a hierarchical beam search method according to one embodiment.

[0030] FIG. 18 is a diagram illustrating the data rate performance and the number of beam searches of a hierarchical beam search method according to one embodiment.

[0031] FIG. 19 is a block diagram showing an example of the configuration of a terminal according to one embodiment.

[0032] FIG. 20 is a block diagram showing an example of the configuration of an electronic device according to one embodiment of the present disclosure.

[0033] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings.

[0034] In describing the embodiments, technical details that are well known in the technical field to which this disclosure belongs and are not directly related to this disclosure are omitted. This is intended to convey the essence of this disclosure more clearly without obscuring it by omitting unnecessary explanations.

[0035] For the same reason, some components in the attached drawings have been exaggerated, omitted, or schematically depicted. Additionally, the dimensions of each component do not entirely reflect their actual dimensions. Identical or corresponding components in each drawing have been assigned the same reference numbers.

[0036] The advantages and features of the present disclosure, and the methods for achieving them, will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure is complete and to fully inform those skilled in the art of the scope of the disclosure, and the present disclosure is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components. Furthermore, in describing the present disclosure, if it is determined that a detailed description of related functions or configurations might unnecessarily obscure the essence of the present disclosure, such detailed description is omitted. Additionally, the terms described below are defined considering their functions in the present disclosure, and these may vary depending on the intentions or conventions of the user or operator. Therefore, their definitions should be based on the content throughout the specification.

[0037] Hereinafter, a base station is an entity that performs resource allocation for terminals and may be at least one of a gNode B, eNode B, Node B, BS (Base Station), wireless access unit, base station controller, or a node on a network. A terminal may include a UE (User Equipment), MS (Mobile Station), cellular phone, smartphone, computer, or a multimedia system capable of performing communication functions. In this disclosure, a downlink (DL) refers to a wireless transmission path of a signal transmitted by a base station to a terminal, and an uplink (UL) refers to a wireless transmission path of a signal transmitted by a terminal to a base station. Furthermore, while LTE, LTE-A, or 5G systems may be described as examples below, embodiments of this disclosure may also be applied to other communication systems having similar technical backgrounds or channel types. For example, 5th generation mobile communication technology (5G, new radio, NR) developed after LTE-A may be included therein, and the 5G below may be a concept that includes existing LTE, LTE-A, and other similar services. In addition, the present disclosure may be applied to other communication systems with some modifications made at the discretion of a person with skilled technical knowledge, without significantly departing from the scope of the present disclosure.

[0038] At this point, it will be understood that each block of the process flow diagrams and combinations of the flow diagrams can be executed by computer program instructions. Since these computer program instructions can be loaded into the processor of a general-purpose computer, a special-purpose computer, or other programmable data processing equipment, the instructions executed through the processor of the computer or other programmable data processing equipment create means to perform the functions described in the flow diagram block(s). Since these computer program instructions can also be stored in computer-available or computer-readable memory that can be directed toward the computer or other programmable data processing equipment to implement the function in a specific way, the instructions stored in computer-available or computer-readable memory can also produce a manufactured item containing the means of instruction to perform the function described in the flow diagram block(s). Since computer program instructions can be loaded onto a computer or other programmable data processing equipment, instructions that perform a series of operation steps on the computer or other programmable data processing equipment to create a process executed by the computer can also provide steps for executing the functions described in the flowchart block(s).

[0039] Additionally, each block may represent a module, segment, or part of code containing one or more executable instructions for executing a specific logical function(s). It should also be noted that in some alternative execution examples, the functions mentioned in the blocks may occur out of order. For example, two blocks described in succession may actually be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order according to their corresponding functions.

[0040] In this embodiment, the term "part" refers to a software or hardware component such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit), and the "part" performs certain roles. However, the meaning of "part" is not limited to software or hardware. The "part" may be configured to reside in an addressable storage medium or configured to run one or more processors. Accordingly, as an example, the "part" includes components such as software components, object-oriented software components, class components, and task components, as well as processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and "parts" may be combined into a smaller number of components and "parts" or further separated into additional components and "parts." In addition, the components and 'parts' may be implemented to utilize one or more CPUs within the device or secure multimedia card. Furthermore, in the embodiment, the 'part' may include one or more processors.

[0041] Wireless communication systems are evolving from providing early voice-oriented services to broadband wireless communication systems that provide high-speed, high-quality packet data services, such as communication standards like 3GPP’s HSPA (High Speed ​​Packet Access), LTE (Long Term Evolution or E-UTRA (Evolved Universal Terrestrial Radio Access)), LTE-Advanced (LTE-A), LTE-Pro, 3GPP2’s HRPD (High Rate Packet Data), UMB (Ultra Mobile Broadband), and IEEE’s 802.16e.

[0042] As a representative example of the above-mentioned broadband wireless communication system, the LTE system employs the Orthogonal Frequency Division Multiplexing (OFDM) method for the downlink (DL) and the Single Carrier Frequency Division Multiple Access (SC-FDMA) method for the uplink (UL). The uplink refers to a wireless link through which a terminal (User Equipment (UE) or Mobile Station (MS)) transmits data or control signals to a base station (eNode B, gNode B, or base station (BS)), and the downlink refers to a wireless link through which a base station transmits data or control signals to a terminal. The above-mentioned multiple access method can distinguish the data or control information of each user by allocating and operating time-frequency resources to be sent for each user so that they do not overlap, that is, so that orthogonality is established.

[0043] As a future communication system following LTE, that is, a 5G communication system, it must be able to freely reflect the diverse requirements of users and service providers, and therefore, services that satisfy various requirements simultaneously must be supported. Services being considered for the 5G communication system include enhanced Mobile Broadband (eMBB), massive Machine Type Communication (mMTC), and Ultra Reliability Low Latency Communication (URLLC).

[0044] eMBB aims to provide data transmission speeds that are superior to those supported by existing LTE, LTE-A, or LTE-Pro. For example, in a 5G communication system, eMBB must be able to provide a peak data rate of 20 Gbps in the downlink and 10 Gbps in the uplink from the perspective of a single base station. Furthermore, while providing these peak data rates, the 5G communication system must also provide an increased user-perceived data rate. To satisfy these requirements, it necessitates improvements in various transmission and reception technologies, including enhanced Multi-Input Multi-Output (MIMO) transmission technology. Additionally, while LTE transmits signals using a maximum bandwidth of 20 MHz in the 2 GHz band, the 5G communication system can meet the data transmission speeds required by using a frequency bandwidth wider than 20 MHz in frequency bands of 3–6 GHz or above 6 GHz.

[0045] Simultaneously, mMTC is being considered to support application services such as the Internet of Things (IoT) in 5G communication systems. To efficiently provide IoT, mMTC requires support for a large number of terminal connections within a cell, improved terminal coverage, enhanced battery life, and reduced terminal costs. Since IoT devices are attached to various sensors and equipment to provide communication functions, the system must be able to support a large number of terminals within a cell (e.g., 1,000,000 terminals / km²). Furthermore, due to the nature of the service, terminals supporting mMTC are likely to be located in dead zones not covered by cells, such as building basements; therefore, they may require wider coverage compared to other services provided by 5G communication systems. Terminals supporting mMTC must consist of low-cost devices, and since it is difficult to frequently replace terminal batteries, a very long battery life of 10 to 15 years may be required.

[0046] Finally, URLLC is a mission-critical cellular-based wireless communication service. Examples include services used for remote control of robots or machinery, industrial automation, unmanned aerial vehicles, remote health care, and emergency alerts. Therefore, the communication provided by URLLC must offer very low latency and very high reliability. For instance, services supporting URLLC must satisfy an air interface latency of less than 0.5 milliseconds and simultaneously require a packet error rate of 10^-5 or less. Consequently, for services supporting URLLC, 5G systems must provide a Transmission Time Interval (TTI) smaller than other services, and design considerations may be required to allocate wide resources within the frequency band to ensure the reliability of the communication link.

[0047] The three 5G services, namely eMBB, URLLC, and mMTC, can be multiplexed and transmitted within a single system. In this case, different transmission and reception techniques and parameters may be used between the services to satisfy the different requirements of each service. Of course, 5G is not limited to the three services mentioned above.

[0048] To increase system capacity, a joint transmission method based on multiple access points (APs) or multiple transmission / reception points (TRPs) was introduced.

[0049] As the number of APs used for cooperative transmission increases, the number of beams used for beam seeking also increases, thereby improving beamforming performance; however, if each AP performs the beam seeking process independently, the overhead associated with beam seeking increases proportionally to the number of APs.

[0050] The present disclosure aims to provide a beam search method and apparatus that minimizes the overhead caused by beam search in a multi-AP cooperative transmission system and further improves the speed and resource utilization efficiency of cooperative transmission.

[0051] The present disclosure relates to hierarchical beam search and can provide a method and apparatus for narrowing the search area to be searched next based on the results of a previous beam search. Since the total number of beam searches can be reduced as the search area is gradually reduced, transmission overhead can be reduced. Furthermore, since the number of beams available to a single AP is fixed and the search area is reduced, the ratio of the number of available beams to the width of the search area increases accordingly. Consequently, even when reducing the number of beams used for beam search to reduce transmission overhead, the beamforming effect does not decrease, and even when utilizing all available beams for search to increase the beamforming effect, transmission overhead may not increase. Additionally, as the number of beams available to a single AP increases, the number of cases for selecting the number of beams to be used for actual beam selection increases; thus, performance and efficiency can be optimized by flexibly adjusting the number of beams according to system requirements.

[0052] According to one embodiment of the present disclosure, as beam search proceeds and the search area is narrowed, beam selection is possible without performing beam search for some APs, and time and resources can be saved by simplifying the beam search procedure.

[0053] According to one embodiment of the present disclosure, by integrating information based on received signals using beams in multiple directions, the quality of data transmission can be improved, interference reduced, signal strength maximized in specific environments, and communication efficiency increased.

[0054] According to one embodiment of the present disclosure, beam sets for each of a plurality of APs that maximize the area average SNR for search areas including service areas are already designated. Unlike conventional technology, where beam set modification is performed during hierarchical beam search and a large amount of time is consumed in beam search by modifying the beam set according to the result of beam search, the electronic device of the present disclosure can minimize time consumption due to beam set modification during beam search by simply using a pre-designated AP and its beam set that has the maximum SNR for the changed search area when the search area is changed according to the result of beam search.

[0055] In addition, according to one embodiment of the present disclosure, a beam set for searching a search area is designated as a beam set that maximizes the area average SNR, so there is no need to record beam sets for a large number of terminals, and thus the time and resources allocated to the prior preparation of beam sets can be minimized. In addition, there is no need to record a new beam set even if there is a change in channel conditions, such as a change in the location of a terminal.

[0056] Hereinafter, a method and apparatus for hierarchical beam seeking based on the multi-AP of the present disclosure will be described with reference to the drawings.

[0057] FIG. 1 illustrates a beamforming communication method according to one embodiment.

[0058] FIG. 1 illustrates a base station (110) and terminals (120, 130) as part of nodes utilizing a wireless channel in a wireless communication system. FIG. 1 illustrates one base station and two terminals, but this is merely an example. For example, the wireless communication system of FIG. 1 may further include other base stations identical or similar to the base station (110) and other terminals.

[0059] A base station (110) is a network infrastructure that provides wireless access to terminals (120, 130). The base station (110) has coverage defined as a certain geographical area based on the distance at which it can transmit signals. In addition to being a base station, the base station (110) may be referred to as an 'access point (AP)', 'evolved Node B (eNB)', 'next generation node B (gNB)', '5G node (5th generation node)', 'wireless point', 'transmission / reception point (TRP)', or other terms having an equivalent technical meaning.

[0060] A terminal (120, 130) is a device used by a user and can perform communication with a base station (110) via a wireless channel. The terminal (120, 130) can be operated without user involvement. For example, the terminal (120, 130) may be a device that performs machine type communication (MTC) and may not be carried by a user. The terminal (120, 130) may be referred to as 'user equipment (UE)', 'mobile station', 'subscriber station', 'customer premises equipment (CPE)', 'remote terminal', 'wireless terminal', 'electronic device', or 'user device', or other terms having an equivalent technical meaning.

[0061] The base station (110) and terminal (120) of the present disclosure may each be a transmitting apparatus, a transmitting node, a receiving apparatus, and / or a receiving node. For example, the base station (110) may transmit a radio frequency (RF) signal to the terminal (120). The base station (110) may receive an RF signal from the terminal (120). As another example, the terminal (120) may transmit an RF signal to the base station (110) or another network entity of the wireless communication system. The terminal (120) may receive an RF signal from the base station (110) or another network entity.

[0062] The base station (110) and terminals (120, 130) can transmit and / or receive wireless signals in the millimeter wave (mmWave) band (e.g., 28 GHz, 30 GHz, 38 GHz, 60 GHz). At this time, to improve channel gain, the base station (110) and / or terminals (120, 130) can perform beamforming.

[0063] Beamforming may include transmission beamforming and / or reception beamforming. That is, the base station (110) and / or terminal (120, 130) may give directivity to the transmission signal or the reception signal. To give directivity to the reception signal, the base station (110) and / or terminal (120, 130) may select serving beams through a beam search, beam management, or beam optimization procedure.

[0064] According to one embodiment, in order to select serving beams, a base station (110) may transmit a synchronization signal block (SSB) to a terminal (120, 130) using beam sweeping. The SSB may include a primary synchronization signal (PSS) for time synchronization between a cell associated with the base station (110) and the terminal (120, 130), a secondary synchronization signal (SSS) providing additional synchronization information, a physical broadcast channel (PBCH) providing essential system information required for initial connection, and a demodulation reference signal (PBCH DMRS) which is a reference signal used for channel estimation to accurately demodulate the PBCH. The terminal (120, 130) may identify the symbol timing and frame boundary of the cell based on the PSS. The additional synchronization information included in the SSS may include a cell ID associated with the base station (110) within a cell group, and the terminal (120, 130) may identify the cell associated with the base station (110) from other cells based on the SSS. The PBCH may include a master information block (MIB) containing essential system information such as subcarrier spacing. Referring to FIG. 1, the base station (110) may transmit an SSB using eight different beams. A terminal (120, 130) that receives the SSB may detect the presence of the base station (110), perform time and frequency synchronization, and obtain essential information necessary to connect to the base station (110). The terminal (120, 130) may measure the received power (e.g., RSRP) of the received SSB and report the index of the beam with the highest received power to the base station (110).

[0065] In a codebook-based beam search procedure, the base station (110) receives a beam index from the terminal (120, 130) and can identify a beam corresponding to the beam index. The base station (110) can perform additional beam sweeping based on the identified beam. The base station (110) can perform beam sweeping with narrower beams in a narrower range associated with the identified beam. The terminal (120, 130) can report to the base station (110) the beam with the highest received power among the narrower beams. For example, in FIG. 1, the terminal (120) can report the index of beam (112) to the base station (110), and the terminal (130) can report the index of beam (113).

[0066] The base station (110) receives a report from the terminal (120, 130) and can repeatedly transmit to the terminal using the reported beam. The terminal (120) can tune the terminal's receiver based on the beam that the base station repeatedly transmits. For example, in FIG. 1, the terminal (120) can determine the receiving beam (121) based on the beam that the base station (110) repeatedly transmits, and the terminal (130) can determine the receiving beam (131).

[0067] After serving beams are selected, subsequent communication can be performed through resources that are in a quasi-co-located (QCL) relationship with the resource that transmitted the serving beams. For example, a terminal can perform simultaneous transmission to the terminal using the selected beams of the APs.

[0068] In this way, the base station (110) and the terminal (120, 130) can perform beam training to find the optimal beam pair. The overhead associated with beam training can lower the overall resource utilization and thus reduce the data transmission rate. Additionally, since frequent beam training is required in environments where the terminal is moving, the beam training overhead can increase significantly. In the case of a system using a large number of beams, the number of RSRP measurements required to find the optimal beam pair increases, so the beam training overhead can increase significantly. For example, if the base station (110) uses 64 beams and the terminal (120) uses 8 beams, 512 measurements are performed to find the optimal beam pair between the base station and the terminal, and the overhead associated with beam training can increase as many times as the measurements are performed.

[0069] FIG. 2 illustrates a beamforming communication method in a multi-AP-based cooperative transmission method according to one embodiment.

[0070] The following description is based on the downlink between an AP and a terminal, but this is merely an example and does not limit the present disclosure. For example, the multi-AP-based cooperative transmission method of the present disclosure may also be applied to cooperative transmission of an uplink in which a terminal transmits data to multiple APs.

[0071] Referring to FIG. 2, N APs can simultaneously service a single terminal. Each AP may include an array antenna to form multiple beams. For example, each AP may be configured with a structure in which Nt multiple antenna elements are arranged in a straight line (e.g., a uniform linear array (ULA) structure). Each AP may be configured to include at least one RF chain to convert RF signals received from the antenna elements into electrical signals, or to convert intermediate frequency signals into RF signals and amplify them.

[0072] Information obtained using N APs illustrated in FIG. 2 can be processed by a central device. The central device can aggregate information from N APs and transmit control commands for beam search and data transmission / reception to each AP. The central device may be referred to as an electronic device that performs cooperative communication with terminals existing in a service area using multiple APs.

[0073] For example, if the central device or electronic device illustrated in FIG. 2 includes a communication unit and a control unit coupled to the communication unit, the control unit can control the communication unit to transmit control commands for beam search and data transmission and reception to N APs. After beam selection for N APs is performed, the electronic device can perform simultaneous transmission to terminals located in the service area using the beams selected for the N APs.

[0074] The terminal shown in FIG. 2 includes a single antenna, but this is merely an example and does not limit the present disclosure, and may include a plurality of antennas as in the terminal (120, 130) of FIG. 1.

[0075] As illustrated in FIG. 2, each AP may perform beam search using up to B beams. However, this is merely an example and does not limit the present disclosure. For example, the maximum number of beams that an AP can use for beam search may vary from AP to AP. Additionally, according to one embodiment, an AP may not use all available beams, and the number of beams actually used by the AP when performing beam search may vary depending on which beam search the same AP is used for during hierarchical beam search. As the beam search order of the AP is later, the AP searches a narrower search area, so it may be configured to use fewer beams for beam search. For example, assuming that the maximum number of beams that AP1 can use for beam search in FIG. 2 is 5, if AP1 performs beam search for the first time, it uses 5 beams; if AP1 performs beam search for the second time, it uses 2 beams; and if AP1 needs to select a beam for the Nth time, AP1 may not perform beam search.

[0076] The AP repeatedly transmits a reference signal while changing the beam angle, and the terminal can continuously receive the reference signal. The terminal can select the beam with the highest received signal quality or strength among the beams transmitted by each AP and feed it back to each AP. For example, the terminal [can select] the beams transmitted by AP 1 (i.e., 1, 2, ..., *(1) , ..., B The highest signal quality for ) * The index of (1) can be fed back to AP 1. Alternatively, the terminal can feed back the beams transmitted by AP N (i.e., 1, ..., *(N) , ..., B-1 , BThe highest signal quality for ) * The index of (N) can be fed back to AP N.

[0077] If each AP searches beams independently of each other and each AP performs B beam searches, the beams used for searching are beam angles. Depending on It can be defined as follows. When the number of subcarriers used by a base station or AP during beam search is defined as k', the selected beam of the nth AP can be expressed as follows.

[0078] [Mathematical Formula 1]

[0079]

[0080] Each signal can be transmitted using the OFDM method with K subcarriers. At this time, can mean the channel of the k-th subcarrier between the n-th AP and the terminal.

[0081] After beam selection, each AP can simultaneously beamform using the selected beam during data transmission. If each AP searches for beams independently of each other and each AP performs B beam searches, the data rate performance can be expressed as follows using a rate formula model that has no attenuation due to phase differences between AP signals.

[0082] [Mathematical Formula 2]

[0083]

[0084] In contrast, according to one embodiment of the present disclosure, a beam search is performed using at least one of a plurality of APs, and the result of the beam search performed first may affect the next beam search. Therefore, the beam search of the present disclosure is dependent on the beam search performed first.

[0085] The present disclosure may provide a hierarchical beam search (HBS) method in which the beam search results influence the beam search of the next AP. According to one embodiment, each AP may perform a hierarchical beam search for a narrowed area in the same way. In the hierarchical beam search (HBS) method according to one embodiment, because the area where a UE is expected to exist changes at the time each AP performs a beam search, the same AP may use a different beam set depending on which beam search is performed.

[0086] Before performing beam search using at least one of the plurality of APs, a beam set to be used for beam search of each AP may be determined in advance. A plurality of beam sets may be assigned to each AP, and this assigned beam set may be closely related to the search area for performing beam search. Among the plurality of beam sets assigned to the AP, each beam set may be designated for a different search area. At least one AP may perform beam search for a search area using one of the plurality of beam sets, and that beam set may be designated for searching that search area.

[0087] For example, in FIG. 2, multiple beam sets for AP 1 may be pre-allocated. Among the multiple beam sets for AP 1, each beam set consists of four beams ( 1, 2, 3, 4) includes (i.e., B=2), and if two beam sets are predetermined for AP 1, the two beam sets are beam set 1 (e.g., 1= 0.125, 2= ​​0.375, 3= 0.625, 4= 0.875) and beam set 2 ( 1= 0.14, 2= ​​0.41, 3= 0.67, It may include 4 = 0.9). In this case, beam search using AP 1 selects beam set 2 from beam set 1 and beam set 2 determined for AP 1, performs beam search using beam set 2, and the beam selected as a result of the beam search ( Simultaneous transmission to the terminal can be performed using 2 = 0.41).

[0088] As another example, in Fig. 2, three beam sets can be predetermined for AP 1, and the three beam sets include beam set 3 (e.g., in addition to the aforementioned beam set 1 and beam set 2) 1= 0.65, 2= ​​0.75, 3= 0.83, It may include 4 = 0.95). In this case, beam search using AP 1 selects Beam Set 2 from Beam Set 1, Beam Set 2, and Beam Set 3 determined for AP 1, performs beam search using Beam Set 2, and the beam selected as a result of the beam search ( Simultaneous transmission to the terminal can be performed using 2 = 0.41).

[0089] As with the example above, in FIG. 2, a plurality of beam sets for AP 2, ..., a plurality of beam sets for AP N may be predetermined and exist. In the present disclosure, a set of beam sets for each of AP 1 to AP N may be referred to as a beam book. That is, the beam book may include a plurality of beam sets that AP 1 can use for beam searching, a plurality of beam sets that AP 2 can use for beam searching, ..., a plurality of beam sets that AP N can use for beam searching. A plurality of beam sets that AP N can use for beam searching may be referred to as a plurality of beam sets assigned to AP N. Each of a plurality of beam sets assigned to AP N may be a beam set designated to search each of a plurality of search regions.

[0090] Alternatively, the beam book may include a plurality of beam sets designated to search a first search area, a plurality of beam sets designated to search a second search area, ..., a plurality of beam sets designated to search a Nth search area. For example, in FIG. 2, the plurality of beam sets designated to search the Nth search area may include a beam set designated for AP 1 to search the Nth search area, a beam set designated for AP 2 to search the Nth search area, ..., a beam set designated for AP N to search the Nth search area.

[0091] In the present disclosure, the search area may refer to an area where an AP performs beam search. The AP may search the search area to select a beam corresponding to the location of a terminal. In the present disclosure, the search area may be gradually narrowed as hierarchical beam search proceeds. The first search area where beam search is performed for the first time may be referred to as a service area. The service area may have a range pre-set for simultaneous transmission using multiple APs and may include an area where a terminal is initially expected to exist. When a beam is selected by the result of the first beam search performed during hierarchical beam search, it may be expected that a terminal exists in a portion of the first search area (or service area) corresponding to the direction of the selected beam, and it may be expected that a terminal does not exist in other areas corresponding to the unselected beam among the beams used in the first beam search. Therefore, in the second beam search, only a portion of the area corresponding to the direction of the beam selected in the first beam search, which is the newly expected area where a terminal exists, may be searched. That is, the second search area may include a portion of the first search area corresponding to the direction of the beam selected in the first beam search.

[0092] FIG. 3 is a diagram illustrating the process of predetermining a beam set of an AP for searching a search area according to one embodiment.

[0093] AP 1 shown in FIG. 3 is one of multiple APs used in a multi-AP-based cooperative transmission system. The beam set to be used for beam search of AP 1 is 1, It may include 2. The area represented by the position (x, y) (where x1 < x < x2 and y1 < y < y2) in the xy coordinate plane illustrated in FIG. 3 may refer to a search area where beam search of AP 1 is performed. It is expected that a terminal exists within the search area of ​​FIG. 3. For convenience of explanation, the search area illustrated in FIG. 3 may refer to the first search area, i.e., the service area. The service area may have a pre-specified range to provide simultaneous transmission services to the terminal using multiple APs. Of course, FIG. 3 is merely an example and does not limit the present disclosure. For example, the process of predetermining the beam set of the AP for searching the search area described in FIG. 3 may also be applied to the second and third search areas. Furthermore, the shape of the first search area is not limited to a rectangle, and it is sufficient if it is an area having a specified range.

[0094] A beam set may refer to a set of beams that maximizes the area average signal-to-noise ratio (SNR) for a search area. The area average SNR is calculated by dividing the search area into multiple sub-regions and summing the SNRs for each of the divided sub-regions. In this case, the number of sub-regions may be equal to the number of beams that each AP uses to search the search area. The number of beams that each AP uses to search the search area may be specified within the range of the maximum number of beams available for beam search by each AP. The maximum number of beams available for beam search by AP 1 shown in FIG. 3 may be four, determined based on the antenna included by the AP, or it may be specified that the search area is searched using two beams in practice. The number of beams that the AP uses to search the search area may change as the search area changes.

[0095] In Fig. 3, the region average SNR for the search region of AP 1 (i.e., x1 < x < x2 and y1 < y < y2) can be determined as follows. The beam set of AP 1 beam 1 and beam If 2 is included, the sin value is sin 1 and sin Angles with an average of 2 The search area can be divided into two sub-regions based on . The two sub-regions are, Sub-region 1 (x1 < x < x2, y1 < y < y2, 0 < < m) and sub-region 2 (x1 < x < x2, y1 < y < y2, m < < It can be expressed as end).

[0096] To determine the SNR for each of the divided sub-regions, sub-region 1 (x1 < x < x2, y1 < y < y2, 0 < < Regarding m), the beam Determine SNR using 1, and sub-region 2 (x1 < x < x2, y1 < y < y2, m < < Regarding the end), the beam You can determine the SNR using 2.

[0097] The region average SNR for the search area can be determined by summing the SNRs for each of the divided sub-regions. For example, In this case, the region average SNR for the search area is calculated by performing an integral with respect to distance r as shown in the following Equation 3. It can be expressed as an expression for.

[0098] [Mathematical Formula 3]

[0099]

[0100] In the integral of mathematical equation 3 function for cast It can be expressed as Equation 4 by performing a linear approximation on the integration interval of.

[0101] [Mathematical Formula 4]

[0102]

[0103] By substituting Equation 4 into Equation 3 and rearranging, the approximate formula for the region average SNR can be expressed as Equation 5.

[0104] [Mathematical Formula 5]

[0105]

[0106] In addition, beamforming gain function to simplify the integration process It can be expressed as a sum of cosine functions as follows.

[0107] [Mathematical Formula 6]

[0108]

[0109] Indefinite integral using the Taylor series for the cosine function is expressed as in mathematical equation 7, and the indefinite integral It can be expressed as in mathematical formula 8.

[0110] [Mathematical Formula 7]

[0111]

[0112] [Mathematical Formula 8]

[0113]

[0114] The result of the indefinite integral of mathematical equations 7 and 8 and Region average SNR using To summarize, it is as follows.

[0115] [Mathematical Formula 9]

[0116]

[0117] The beam set for the search area is the area average SNR for the search area This may refer to a set of beams that maximize this. According to one embodiment, as in Equation 9 cast It is approximate, and The set of beams 1 and 2 that maximizes can be determined as the beam set for the search area.

[0118] The operations of mathematical formulas 3 through 9 can also be applied to an extended embodiment in which one beam set includes B beams.

[0119] FIG. 4 is a diagram illustrating the region average SNR according to one embodiment.

[0120] Referring to Fig. 4, AP is S1+S2+ ...+S B For a search area S composed of, a beam set ( 1, ..., B Beam selection can be performed using ). The beam set can be determined based on the search area S. For example, if AP intends to use a beam set containing B beams, the AP's area average SNR with respect to the search area S It can be expressed as in mathematical equation 10. For example, the probability that a terminal exists in the search area S can be represented by a uniform distribution.

[0121] [Mathematical Formula 10]

[0122]

[0123] In mathematical formula 10, ε is the beamforming gain function, which represents a numerical value of the signal quality improvement obtainable through beamforming. Since the degree of signal concentration varies depending on the beam angle, the beamforming gain function is a function of the angle. The beamforming gain function can quantitatively represent the degree of SNR improvement. is a path loss function based on the distance r from the AP.

[0124] By performing the operations of mathematical formulas 3 through 9 on mathematical formula 10 A beam set that maximizes ( 1, ..., B ) can be obtained. The obtained beam set is the search area S1+S2+ ...+S B The beam set to be used by the AP can be determined for this. In a multi-AP-based hierarchical beam search method, each AP can perform beam search using a predetermined beam set for searching the search area.

[0125] In this way, the beam set ( 1, ..., B ) is the area average SNR for the search area It refers to the set of beams that maximize this, and the beam set ( 1, ..., B The search area may be determined differently depending on the search area. In the present disclosure, the search area of ​​AP 1 may be determined based on the result of a beam search performed by another AP prior to the beam search by AP 1 (e.g., AP 1 of FIG. 2), and the search area of ​​AP 1 may differ from the case where AP 1 performs the first beam search among a plurality of APs and the case where AP 1 performs the second beam search. Accordingly, the beam set of AP 1 designated to search the first search area and the beam set of AP 1 designated to search the second search area may be different. The beam book may include a beam set designated for each of the search areas that AP 1 can search.

[0126] Using the above mathematical formulas 3 through 10, beam sets can be determined for AP 1, AP 2, ..., AP N. The beam book of the present disclosure may include beam sets for each of the search regions that AP 1 can search, beam sets for each of the search regions that AP 2 can search, and beam sets for each of the search regions that AP N can search. An electronic device according to one embodiment may perform beam search using beam sets included in the beam book.

[0127] According to one embodiment, a DeepMIMO channel model may be used to determine beam sets for multiple search regions for multiple APs.

[0128] Figure 5 is a diagram illustrating an experience-based method for determining a beam set.

[0129] Referring to FIG. 5, the experience-based beam set determination method may mean a method for determining a beam set for each of a plurality of APs such that the sum of the terminal data rates for a search area S is maximized. For example, according to the experience-based beam set determination method, the beam set of AP 1 ( 1 (1) , ..., B (1) The terminal's data rate for area S using ), AP 2's beam set ( 1 (2) , ..., B (2) Data rate of the terminal for area S using ), ..., beam set of AP n( 1 (n) , ..., B (n) Summing the data rates of the terminals for area S using ), and the beam set of AP 1 where the average becomes maximum ( 1 (1) , ..., B (1) ), AP 2's beam set( 1 (2) , ..., B (2) ), ..., beam set of AP n( 1 (n) , ..., B (n) ) can be obtained. The beam set of AP n obtained based on an experience-based beam set determination method ( 1 (n) , ..., B (n) ) can be expressed as in mathematical formula 11.

[0130] [Mathematical Formula 11]

[0131]

[0132] Ru can mean the data rate of the u-th terminal.

[0133] The empirical method using Equation 11 is inefficient because it determines different beam sets based on the locations of multiple beam sets and multiple terminals. In contrast, as shown in Fig. 3, the method of dividing the search area where beam search is performed into multiple sub-regions based on the beams included in the beam set used for beam search, and determining the beam set that maximizes the sum of the SNRs for each of the divided sub-regions (i.e., the method of determining the beam set that maximizes the area average SNR) is efficient because the beam set can be determined through a simple calculation using the approximation of Equation 10.

[0134] FIG. 6 is a diagram illustrating a hierarchical beam search method using a plurality of APs according to one embodiment.

[0135] Referring to FIG. 6, four APs may be used to perform simultaneous transmission to terminals located in the service area. The service area may refer to a pre-designated range of areas to provide services to terminals using multiple APs.

[0136] Each AP may include an array antenna to form multiple beams. For example, the array antenna may be a ULA antenna configured with a uniform linear array (ULA) structure. For example, each AP may include an antenna with four antenna elements arranged to form two or more beams.

[0137] At least one of the APs shown in FIG. 6 can perform beam search. Specifically, at least one AP can transmit an SSB to a terminal located in the search area using a beam set determined according to the search area, and receive beam index information for beam selection from the terminal. The search area may include at least a portion of the area included in the service area, and multiple search areas included in the service area may overlap or be exclusive of each other. Each AP can perform beam search for the search area using a beam set corresponding to the search area.

[0138] According to one embodiment, the N+1th area to be searched (N+1th search area) may include at least a portion of the area to be searched Nth (Nth search area), wherein at least a portion of the area may be a limited area corresponding to a beam selected through the Nth beam search. For example, the first area to be searched may be a service area, and the second area to be searched may be a narrower area than the service area, determined based on the beam selected by the first beam search among the service areas.

[0139] Among the APs shown in FIG. 6, there may be APs that are not used for beam search or do not perform beam search. Specifically, when a search area where a terminal is expected to exist is determined as a result of at least one beam search, among the APs that are not yet used for beam search, there may be APs that have only one or zero beams capable of transmitting to the determined search area. In this way, if the number of beams associated with the search area among the beams assigned to an AP is less than two, the AP can perform simultaneous transmission to the terminal using the remaining single beam without needing to perform beam selection, so the AP may not be used for beam search.

[0140] Information obtained using the four APs illustrated in FIG. 6 can be processed by a control unit of an electronic device that performs multi-AP-based hierarchical beam search. For example, the information obtained using the APs may include information regarding beam search and / or beam selection. For example, the information obtained using the APs may include information regarding beam selection and / or information regarding a search area determined based on beam selection.

[0141] The electronic device may include a communication unit and a control unit coupled to the communication unit, and the control unit may control the communication unit to transmit control commands for beam search and data transmission and reception to four APs. After beam selection for the four APs is performed, subsequent communication may be performed through a resource that is in a quasi-co-located (QCL) relationship with the resource that transmitted the selected beams. After beam selection, the terminal may tune its receiver based on the beams repeatedly transmitted by the base station. After beam selection, the electronic device may perform simultaneous transmission to terminals located in the service area using the beams selected for the four APs.

[0142] FIGS. 7 to 10 are drawings for explaining that the search area is gradually narrowed as beam search proceeds according to one embodiment.

[0143] Among the multiple APs depicted in FIG. 6, AP1 can perform beam search first as shown in FIG. 7. Referring to FIG. 8, AP1, which performs beam search first among the APs, can search for a service area. Specifically, the beam set used by AP1 for searching for the service area ( 1, 2) may be a beam set pre-specified for the service area.

[0144] The beam set that AP1 uses for service area discovery ( 1, 2) may refer to a set of beams that maximizes the area average SNR for the service area. Referring to Fig. 8, the beam set assigned to AP1 includes up to 2 beams, and among them, beam ( 1) and beam( 2) can be associated with the service area that AP1 will explore. The service area is the beam( 1) and beam( 2) is divided into two sub-regions (710, 720), and a beam (for sub-region (710) 1) SNR and beam for sub-region (720) 2) Area average SNR for the service area by summing the SNRs You can obtain the area average SNR for the service area. A beam that maximizes 1, beam A set of 2 can be determined as the beam set of AP1 for the service area.

[0145] Referring to FIG. 7, the AP performing the second beam search can be determined based on the beam selected as a result of the first beam search. Specifically, the second search area can be determined corresponding to the beam selected as a result of the first beam search. Among the APs that have not yet performed a beam search, APs that have two or more beams suitable for the determined search area are used for beam search, while APs that have one or fewer beams suitable for the determined search area do not need to be used for beam search. For example, as a result of the beam search of AP1, the beam of AP1 ( 1) If selected, beam ( Based on 1), the area where a terminal is expected to exist can be specified as a search area (710). Referring to FIG. 9, the beam set of AP2 ( 1, Even if beam search for the search area (710) is not actually performed using 2), the signal quality measured by the terminal located in the search area (710) is beam ( 1) than beam( 2) is expected to be higher. Therefore, without the need to perform beam search using AP2, beam( 2) This can be selected. Likewise, for AP3, even if beam search for the search area (710) is omitted, a beam ( 2) can be selected. Therefore, when the search area (710) is specified by the first beam search, for each of AP2 and AP3 among the plurality of APs, the beam ( 2) can be selected. In the case of AP4, referring to FIG. 10, depending on the location of the terminal within the search area (710), the beam set of AP4 ( 1, 2) Since it is impossible to predict which beam will be selected, beam search using AP4 is required. The AP used for the second beam search can be determined from at least one AP among multiple APs in which the number of beams included in the beam set designated to search the search area (710) is two or more. At this time, the beams included in the beam set designated to search the search area (710) can be referred to as beams associated with the search area (710). In FIG. 7, since AP4 is the only AP that has two or more beams associated with the specific search area (710) after the first search, AP4 performs the second beam search.

[0146] Referring to FIG. 7, the AP performing the third beam search can be determined based on the beam selected as a result of the second beam search. Specifically, the search area for the third beam search can be determined based on the beam selected as a result of the second beam search. For example, the beam of AP1 as a result of the beam search of AP1 ( 2) If this is selected, the beam ( Based on 2), an area where a terminal is expected to exist can be designated as a search area (720). In FIG. 7, each of AP2, AP3, and AP4 may have a beam set designated for searching the search area (720), and each beam set may include multiple beams. Among the multiple APs, AP2, AP3, and AP4, which have two or more beams associated with the search area (720), the AP to perform the second beam search may be determined. For example, among AP2, AP3, and AP4, AP2 may be used for the second beam search. AP2 has a beam set ( 1, Perform beam search using 2), and AP2 beams from the terminal ( Based on receiving the index of 1), AP2's beam ( 1) can be selected. The beam of AP2 selected as a result of the second beam search by AP2 ( Based on 1), the terminal AP2's beam ( It may be expected that there is a search area (730) corresponding to 1). A third beam search may be performed using a beam set containing multiple beams among the beam sets designated to search the search area (730). Among the APs assigned beam sets containing multiple beams among the beam sets designated for the search area (730), the AP to be used for the third beam search may be determined. Among AP3 and AP4, which have not yet performed a beam search, AP3 has two beams associated with the search area (730), and AP4 has one beam associated with the search area (730). In FIG. 7, among the beam sets designated for the search area (730), the AP assigned beam sets containing multiple beams is AP3, which has two beams associated with the search area (730); therefore, the AP used for the third beam search may be determined to be AP3. Afterwards, as a result of searching the search area (730) using AP3 and two beams of AP3, the beam of AP3 ( 1) or beam( 2) If this is selected, it can be expected that a terminal exists in the area corresponding to the selected beam. Beam search using AP4 may be omitted. After the search area (730) resulting from the beam search of AP2 is determined, the beam of AP4 ( 2) This can be selected.

[0147] A beam from an AP that is not performing beam search may be selected at a predetermined time. A predetermined time may refer to a time determined by specific conditions or circumstances. For example, regarding an area corresponding to a beam selected as a result of the most recent beam search, if all beam sets containing multiple beams among the beam sets designated to search that area have been used for beam search, a beam for APs that have not yet performed beam search may be selected. APs that have not performed beam search may use this beam for cooperative transmission. As another example, at a preset time interval, if there is an area corresponding to a beam selected as a result of the most recent beam search and a beam set containing a specified number (e.g., 1) or fewer of the beams among the beam sets designated to search that area, the beam of the AP to which that beam set is assigned may be selected. As yet another example, whenever beam search is performed, if there is an area corresponding to a beam selected as a result of the beam search and a beam set containing a specified number or fewer of the beams among the beam sets designated to search that area, the beam of the AP to which that beam set is assigned may be selected.

[0148] Referring to FIG. 7, the AP performing the fourth beam search can be determined based on the beam selected as a result of the third beam search. For example, the beam of AP1 as a result of the beam search of AP1 ( 2) If this is selected, the beam ( Based on 2), an area where a terminal is expected to exist can be designated as a search area (720). Among the APs assigned a beam set containing multiple beams among the multiple beam sets designated to search the search area (720), the AP to be used for the second beam search can be determined. In FIG. 7, among AP2, AP3, and AP4 having two or more beams associated with the search area (720) among the multiple APs, AP2 can be used for the second beam search. AP2 is a beam set ( 1, Perform beam search using 2), and AP2 beams from the terminal ( Based on receiving the index of 2), AP2's beam ( 2) This can be selected. The beam of AP2 selected as a result of the second beam search by AP2 ( Based on 2), the terminal AP2's beam ( It can be expected that it exists in the search area (740) corresponding to 2). Among the remaining APs that have not yet performed beam search, the AP to search the search area may be determined from at least one AP that has two or more beams associated with the search area. In FIG. 7, since AP3 and AP4, which have not yet performed beam search, each have two beams associated with the search area (740), one of AP3 or AP4 may be determined as the AP for the third beam search. When AP3 performs the third beam search, AP3's beam ( 2) Based on the selection, the area where the terminal is expected to exist can be designated as the search area (750). Since AP4, which has not yet performed beam search, has two beams associated with the search area (750), beam search can be performed using the beams of AP4. On the other hand, the beam of AP3 ( 1) If the area where the terminal is expected to exist is specified as the search area (760) based on the selection, the beam set of AP4 designated for searching the search area (760) includes one beam, or since the number of beams of AP4 associated with the search area (760) is one, AP4 is not used for beam searching. Beam searching by AP4 is omitted, and one beam associated with the search area (760) among the beams assigned to AP4 can be selected.

[0149] In FIGS. 7 through 10, it is explained that as beam search progresses, the search area is gradually narrowed, at least one AP among a plurality of APs included in the cooperative transmission system performs beam search, while the remaining APs do not perform beam search, and the result of the beam search influences the determination of the search area to be searched in the next beam search, the AP to be searched, and the beam set thereof. FIGS. 7 through 10 illustrate a cooperative transmission system including four APs, but this is merely an example and does not limit the present disclosure.

[0150] FIG. 11 is a diagram illustrating that beam search according to one embodiment influences the determination of the beam set to be used for the next beam search.

[0151] The beam used for the N+1th beam search may be determined based on the search area specified by the Nth beam search. For example, the beam used for the N+1th beam search may be pre-specified for the specified search area. Referring to FIG. 11, the search area (710) or search area (720) resulting from the Nth beam search of AP1 may be determined as the N+1th search area. AP4 may be assigned a beam set for searching each of the multiple search areas. The multiple beam sets assigned to AP4 may include a beam set specified for searching the search area (710) and a beam set specified for searching the search area (720). The beam to be used by AP4 to search the search area (710) may be pre-specified in association with the search area (710), and the beam to be used by AP4 to search the search area (720) may be pre-specified in association with the search area (720). Likewise, referring to FIG. 7, the beam that AP4 will use to search each of the search area (740), search area (750), and search area (760) can be pre-assigned in association with each of the search area (740) and search area (750).

[0152] According to one embodiment, a beam set of each AP that maximizes the region average SNR can be assigned for each of the search regions. The method of the present disclosure does not modify the beam set according to the result of the beam search during the hierarchical beam search, but rather a beam set of each AP that maximizes the SNR for each of the search regions is assigned in advance, and when a search region is identified according to the result of the beam search, the beam set assigned to that identified search region is used, thereby minimizing the time consumed by the beam search.

[0153] The area average SNR for the AP's search area can be obtained by dividing the search area into multiple sub-regions and summing the SNRs for each of the divided sub-regions. The number of sub-regions may be equal to the number of beams the AP uses to search the search area. The number of beams the AP uses to search the search area may be specified within a range within the maximum number of beams available to the AP. While the maximum number of beams available to the AP is a fixed value based on the antennas included by the AP, the number of beams the AP uses to search the search area may change as the search area changes. For example, since a large number of beams may not be required to search a narrow area, beam overhead can be reduced by decreasing the number of beams used as the search area becomes narrower.

[0154] For example, a beam set (which AP4 uses for searching the search area (710) 1, 2) may refer to a set of beams that maximizes the area average SNR for the search area (710). In FIG. 11, if each of the multiple beam sets assigned to AP4 contains up to two beams, the beam set that AP4 uses to search the search area (710) is a beam set ( 1 (2) , 2 (2)Arbitrarily determined as ), and area average SNR for the search area (710) A beam that maximizes 1 (2) , beam 2 (2) By acquiring the beam set ( 1 (2) , 2 (2) ) can be determined. For example, the search area (710) can be beam ( 1 (2) The first sub-region and beam ( 2 (2) Divided into a second sub-region for ), and a beam for the first sub-region ( 1 (2) SNR of ) and beam for the second sub-region ( 2 (2) Area average SNR for the search area (710) by summing the SNRs of ) It can be obtained. Area average SNR for the search area (710). A beam that maximizes 1 (2) , beam 2 (2) The set of can be determined as the beam set of AP4 for the search area (710).

[0155] For each of the search area (710), search area (740), search area (750), and search area (760), a beam set of AP4 that maximizes the area average SNR for each search area may be predetermined. Additionally, for each of the search area (730) and search area (760), a beam set of AP4 that maximizes the area average SNR for each search area may be predetermined. A beam set designated to search each of the search area (730) and search area (760) may include a single beam. Alternatively, a single beam designated to search each of the search area (730) and search area (760) may be pre-selected. When a search area resulting from multiple beam searches is identified as the search area (730) or the search area (760), AP4 may provide service to the terminal using a single beam included in the designated beam set or a pre-selected beam.

[0156] FIG. 12 is a drawing for explaining a beam set designated for a search area according to one embodiment.

[0157] FIG. 12 illustrates the change in the search area when AP1 performs the first beam search in a multi-AP-based hierarchical beam search method. AP1 can search the first search area using the beam set of AP1 assigned to AP1 and designated in the first search area (e.g., the service area (700) in FIG. 7). The result area A or area B of AP1's first beam search can be determined as the second search area to be searched. A third beam search and a fourth beam search were performed until there was no longer a need for beam search.

[0158] A beam book according to one embodiment may include a beam set of each AP to search the search areas illustrated in FIG. 12. For example, the beam book may include a beam set of AP2 for searching area A or area B, respectively. The beam set of AP2 for searching area A may be specified by obtaining the area average SNR of the beams for area A according to the number of AP2 beams to be used to search area A (e.g., 1), and determining the angle of the beams that maximizes the area average SNR. Alternatively, the beam set of AP2 for searching area B may be specified by dividing area B into two sub-areas according to the number of AP2 beams to be used to search area B (e.g., 2), obtaining the area average SNR by obtaining and summing the SNR of each beam for each sub-area, and determining the angle of the beams that maximizes the area average SNR.

[0159] As another example, the beam book may include a beam set of AP3 for searching either region E or region F. The beam set of AP3 for searching region E may be specified by dividing region E into two sub-regions according to the number of AP3 beams to be used to search region E (e.g., two), obtaining the SNR of each beam for each sub-region and summing them to obtain a region average SNR, and determining the angles of the beams that maximize the region average SNR. Alternatively, the beam set of AP3 for searching region F may be specified by dividing region F into two sub-regions according to the number of AP3 beams to be used to search region F (e.g., two), obtaining the SNR of each beam for each sub-region and summing them to obtain a region average SNR, and determining the angles of the beams that maximize the region average SNR.

[0160] In the same way, beam sets for each of AP1 to AP4 can be assigned for each of the regions A to L shown in FIG. 12. FIG. 12 illustrates only the search regions when beam search is performed in the order from AP1 to AP4 for convenience of explanation, but various search regions not shown in FIG. 12 can be determined by changing the order of beam search. A beam book according to one embodiment may include beam sets for each AP assigned for searching each of the possible search regions according to the multi-AP-based hierarchical beam search method of FIG. 12.

[0161] FIG. 13 is a diagram illustrating beam search according to one embodiment.

[0162] Referring to FIG. 13, the electronic device can perform simultaneous transmission to a terminal located in service area S(0) using a plurality of APs. To select a beam to perform simultaneous transmission, at least one of the plurality of APs can perform beam search. Each of the plurality of APs has a beam set (including 4 beams) 1 (1) , 2 (1) , 3 (1) , 4 (1) Beam search can be performed using ). AP1 performs the first beam search for service area S(0), and as a result, AP1's beam( 1 (1) ) and beam( 1 (1A search area S (1) corresponding to )) may be selected. Among the multiple APs, excluding AP1, AP2 may perform a second beam search among at least one AP in which the number of beams associated with the search area S (1) is two or more. Unlike AP1, which performed a beam search using four beams, AP2 may perform a beam search using two beams. AP2 may use up to four beams, but the beam set of AP2 designated to search AP2's area S (1) may include two beams. AP2's beam set ( 1(1), By specifying 2(1)), beams 3 and 4 of AP 2 are not used when searching area S(1), so the training overhead associated with beam searching can be reduced.

[0163] At this time, the beam of AP2 to be used for searching the search area S(1) 1(2)), beam( 2(2)) can be predetermined as a value that maximizes the area average SNR for the search area S(1). The beam associated with the search area S(1) ( 1(2)), beam( The search area S(1) is divided into a first sub-area and a second sub-area by 2(2)), and a beam (for the first sub-area) SNR of 1(2)) and beam for the second sub-region ( By summing the SNRs of 2(2)), the area average SNR for the search area S(1) You can obtain.

[0164] As shown in the example of FIG. 13, according to one embodiment, when the search area of ​​the Nth beam search result is specified, the number of beams used for the N+1th beam search may be reduced based on the specified search area. At this time, since the number of beams assigned to each AP is greater than 2, when the search area of ​​the Nth beam search result (e.g., search area S(1) in FIG. 13) is specified, some beams of the AP (e.g., AP2 in FIG. 13) performing the N+1th beam search (e.g., the beams of AP2 in FIG. 13 3 (2) ) and beam( 4 (2) Even if )) is excluded from the beam set for beam search, AP2 is a beam associated with the search area (e.g., search area S(1) in FIG. 13) (e.g., the beam of AP2 in FIG. 13 ( 1 (2) ) and beam( 2 (2) There can be two or more )). For example, if there are more than two beams assigned to an AP, the number of beams when using the AP for the N+1th beam search may be equal to or less than the number of beams when using the AP for the Nth beam search.

[0165] FIG. 14 is a flowchart of a method performed by an electronic device in one embodiment.

[0166] An electronic device that performs simultaneous transmission to terminals located in a service area using multiple APs can perform the following operations.

[0167] In operation 1410, the electronic device may perform a first beam search for a service area by using a first beam set designated for searching a service area among a plurality of beam sets assigned to the first AP, by the first AP that performs the search first among a plurality of APs. The first beam search may mean a beam search by the first AP that performs the search first. The service area may mean a range of areas designated in advance to provide services to a terminal using a plurality of APs. For example, the service area may correspond to at least one of the area represented by x1 < x < x2 and y1 < y < y2 in FIG. 3, area S in FIG. 4, the service area in FIG. 6, the service area (700) in FIG. 7 and FIG. 11, and the service area S (0) in FIG. 13.

[0168] At this time, the first beam set may be a beam set that maximizes the area average signal-to-noise ratio (SNR) for the service area among the plurality of beam sets assigned to the first AP. The area average SNR of the first beam set designated for searching the service area among the plurality of beam sets assigned to the first AP may be the sum of the SNR values ​​for the plurality of sub-areas included in the service area based on the beams included in the designated first beam set. To calculate the area average SNR, the service area may be divided into a plurality of sub-areas according to the number of beams included in the first beam set. Specifically, the first beam set that maximizes the area average SNR for the service area is a beam set ( 1, 2) Arbitrarily determine and the service area is beam( 1) The first sub-region and beam ( Divided into a second sub-region for 2), and a beam for the first sub-region ( 1) SNR and beam for the second sub-region ( 2) Sum the SNRs to obtain a function of the region average SNR, and a beam set that maximizes the region average SNR ( 1, 2) can be designated by determining.

[0169] The first AP may be allocated multiple beam sets for searching multiple search areas. Among the multiple beam sets allocated to the first AP, a first beam set for searching a service area may also be included. The first beam set of the first AP may refer to a beam set of the first AP that maximizes the area average SNR for the service area.

[0170] The first AP that performs beam search first among a plurality of APs may be selected from at least one AP (e.g., AP1, AP2, AP3 and / or AP4 in FIG. 6) that is assigned a beam set including a plurality of beams and maximizes the area average SNR for the service area. To perform beam search for the service area, the electronic device may select the first AP among at least one AP having a beam set specified for the service area.

[0171] An operation 1410 in which an electronic device according to one embodiment performs a first beam search may include an operation of transmitting a reference signal to a terminal using a first beam set and an operation of receiving an index of the first beam from the terminal. The first beam may be the one with the highest reception power of the reference signal among the first beam set. Specifically, a terminal that receives a reference signal from a first AP using the first beam set may determine the index of the first beam with the highest reception power of the reference signal and report the index of the first beam to the first AP, and the electronic device may obtain the index of the first beam from the first AP. The first AP or the electronic device that receives the index of the first beam according to the result of the first beam search may select a first beam to be used for simultaneous transmission among the first beam set in operation 1420.

[0172] In operation 1430, the electronic device can determine, based on the first beam, a second AP that performs a second search and a plurality of beam sets assigned to the second AP, a second beam set to be used for the second beam search.

[0173] A second search area can be determined corresponding to the beam selected as a result of the first beam search. Specifically, if the first beam is selected as a result of the first beam search, it can be expected that a terminal exists in a first area determined based on the first beam. The first area may include at least a portion of the service area corresponding to the first beam. Since the area where the terminal is expected to exist has been narrowed to the first area by the first beam selected as a result of the first beam search, a second beam search can be performed on the first area. A second beam search can be performed in the second search area that has been narrowed compared to the first search area as a result of the first beam search. The first area may correspond, for example, to the search area (710), search area (720) of FIG. 7, and search area S (1) of FIG. 13.

[0174] According to one embodiment, a plurality of APs may be assigned a beam set designated to search each of a plurality of search areas. Accordingly, when a first beam is selected and a first area is identified as a result of a first beam search, one beam set may be selected from among the beam sets of each of the plurality of APs designated to search the first area. The selected beam set may be used for beam search of the first area.

[0175] The electronic device may determine the AP that performs the second beam search based on the beam selected as a result of the first beam search. Specifically, the electronic device may determine the second AP to perform the second beam search among at least one AP assigned a beam set designated for the search of a first area. The beam set designated for the search of the first area includes a plurality of beams, and a plurality of beams may be used for the second beam search. According to one embodiment, a beam set associated with the first area may be pre-designated for at least one of the plurality of APs.

[0176] For example, if the first area is the search area (720) of FIG. 7, the beam set of AP2, the beam set of AP3, and the beam set of AP4 that maximize the area average SNR for the search area (720) may each be pre-specified. The electronic device may search the search area (720) using one of the beam sets of AP2, the beam set of AP3, and the beam set of AP4 that maximize the area average SNR for the search area (720).

[0177] In operation 1440, the electronic device may perform a second beam search using the second beam set of the second AP. The electronic device may control the second AP to perform a second beam search using the second beam set. The second beam set is one of a plurality of beam sets assigned to the second AP and may be a beam set predetermined for the search of a first region by the second AP. In this case, the first region may correspond to the first beam selected in operation 1430. The second beam set is a beam set that maximizes the region average SNR for the first region, and the region average SNR for the first region may be determined by summing the SNR values ​​for each of a plurality of mutually exclusive sub-regions included in the first region. In this case, the number of sub-regions is equal to the number of beams included in the second beam set.

[0178] An operation 1440 in which an electronic device according to one embodiment performs a second beam search may include an operation of transmitting a reference signal to a terminal using a second beam set and an operation of receiving an index of the second beam from the terminal. The second beam may be the one with the highest reception power of the reference signal among the second beam set. Specifically, a terminal that receives a reference signal from a second AP using a second beam set may determine the index of the second beam with the highest reception power of the reference signal and report the index of the second beam to the second AP, and the electronic device may obtain the index of the second beam from the second AP. The second AP or the electronic device that receives the index of the second beam according to the result of the second beam search may select a second beam to be used for simultaneous transmission among the second beam set in operation 1450.

[0179] FIG. 15 is a flowchart of a method performed by an electronic device in one embodiment. Beam search may be performed using at least some of the APs among the plurality of APs, and operations 1430 to 1450 may be repeated for the remaining APs among at least some of the APs, excluding the first AP and the second AP. If the plurality of APs further includes a third AP that performs a third beam search, in operation 1510, the electronic device may determine a search area for the third beam search based on the beam selected as a result of the second beam search, and determine the AP that performs the third beam search based on the determined search area. Specifically, the electronic device may specify a second area as an area corresponding to the second beam among the first areas based on the second beam selected according to the result of the second beam search, determine the third beam set to be used for the third beam search among the third AP that performs the third search and the plurality of beam sets assigned to the third AP, and perform a beam search for the second area using the third beam set to select the third beam. At this time, the third beam set of the third AP may be a beam set designated for the second area.

[0180] Additionally, if the plurality of APs further includes a fourth AP that performs a fourth beam search, similar to operation 1510, the electronic device may determine a search area for a fourth beam search based on the beam selected as a result of the third beam search, and determine an AP that performs a fourth beam search based on the determined search area.

[0181] According to one embodiment, among a plurality of APs, there may be APs that are not used for beam search. If an area selected according to the result of a plurality of beam searches does not have a beam set designated for search by any AP or contains only one beam, that AP may not be used for beam search. For example, if the beam set assigned to that AP in the area selected according to the result of beam search contains only one beam, in operation 1520, the electronic device may select the one beam assigned to the AP that is not used for beam search among the plurality of APs. As another example, if there is no beam set assigned to that AP in the area selected according to the result of beam search, the electronic device may not use that AP among the plurality of APs when performing simultaneous transmission to the terminal.

[0182] In operations 1460 and 1530, the electronic device can perform simultaneous transmission to the terminal using the selected beams. At this time, the selected beams may include the first beam and the second beam selected in operations 1420 and 1450. Additionally, the selected beams may further include the third beam selected in operation 1510 and one beam selected in operation 1520.

[0183] FIGS. 16 to 18 are diagrams illustrating the data rate performance and the number of beam searches of a hierarchical beam search method according to one embodiment. FIG. 16 illustrates the beam sets of AP1 and AP4 used for beam search when attempting to perform simultaneous transmission to a terminal existing in a service area such as FIGS. 6 to 11. FIG. 18 indicates the number of beam searches performed to select the beams of all APs when beam search is performed by at least one of AP1 to AP4 in the environment of FIGS. 6 to 11. As a result of beam search being performed by at least one of AP1 to AP4, if a beam is selected, simultaneous transmission to the terminal can be performed using the selected beam. FIG. 18 indicates the data rate during simultaneous transmission to the terminal.

[0184] Referring to FIG. 16, beam set (1610), beam set (1620), and beam set (1630) are beam sets assigned at the same angle to all APs. Beam set (1610) is for AP1 to AP4. 1=0.25, 2=0.75 can be used. The beam set (1620) utilizes the area average SNR and is a beam set that maximizes the area average SNR of each of AP1 and AP4 for the service area. The beam set (1620) for AP1 to AP4 1=0.28, 2=0.80 can be used. The beam set (1630) is a beam set created through an experience-based beam set determination method, and is a beam set in which the sum of the data rates of terminals for the service area is maximized. The beam set (1630) is for AP1 to AP4 1=0.30, 2=0.82 can be used. The beam set (1620) is pre-specified for the service area before beam search, but the beam set (1630) is determined based on the data rate of the actual data transmitted to the terminal during the beam search process.

[0185] Beam set (1640) and beam set (1650) are beam sets used for a hierarchical beam search method, and each AP may include a different beam set. Beam set (1640) utilizes area average SNR and is a beam set of AP1 that maximizes the area average SNR for a service area (e.g., service area (700) in FIG. 7) and a beam set of AP4 that maximizes the area average SNR for a search area (e.g., search area (710) or search area (720) in FIG. 7). Therefore, the beam set of AP1 and the beam set of AP4 may have different beam angles. According to beam set (1640), AP1 has a beam set ( 1=0.28, 2=0.80) is assigned, and AP4 has a beam set ( 1=0.20, 2=0.64) and the beam set assigned to the search area (720) 1=0.52, 2=0.89) can be assigned.

[0186] The beam set (1650) is a beam set created through an experience-based beam set determination method, and is a beam set that maximizes the sum of the data rates of terminals for a service area (e.g., service area (700) in FIG. 7) and a beam set of AP4 that maximizes the sum of the data rates of terminals for a search area (e.g., search area (710) or search area (720) in FIG. 7). Therefore, the beam set of AP1 and the beam set of AP4 may have different beam angles. According to the beam set (1650), AP1 has a beam set (where the data rate for terminals in the service area (700) is maximized) =0.28, 2=0.81) is assigned, and AP4 has a beam set (where the data rate for the terminal in the search area (710) is maximum) 1=0.23, A beam set with the maximum data rate for the terminal in the search area (2=0.67) and the search area (720) 1=0.52, 2=0.88) can be assigned.

[0187] Referring to FIGS. 17 and 18, independent beam search and hierarchical beam search were performed using a beam set (1610).

[0188] Experimental Examples (1710) to (1730) are experimental examples in which, unlike the hierarchical beam search method in the preceding embodiments in which beam search was performed on a search area that gradually narrowed as beam search progressed, each AP performed beam search independently of each other. Experimental Examples (1715) to (1735), Experimental Example (1740), and Experimental Example (1750) are experimental examples in which a hierarchical beam search was performed to reduce the search area according to the result of the beam search performed first. In Experimental Examples (1710) to (1730), beam sets (1610) to (1630) were used respectively, and in Experimental Examples (1715) to (1735), beam sets (1610) to (1630) were also used respectively. In experimental example (1740) and experimental example (1750), beam set (1640) to beam set (1650) were used, respectively. Referring to FIG. 17, when performing independent beam search, a total of 8 beam searches must be performed until beam selection of all APs is completed, but by performing hierarchical beam search, the number of beam searches until beam selection of all APs is completed can be reduced to less than 7. FIG. 17 is for an environment including 4 APs, and as the number of APs increases, the effect of reducing beam training overhead can be greater.

[0189] Referring to FIG. 18, experimental examples (1740) and (1750) that perform hierarchical beam search using a beam set for a search area that narrows as the number of beam searches increases can achieve a higher data rate compared to experimental examples (1725) and (1735) that use the same beam set in all beam searches.

[0190] Referring to FIG. 18, experimental example (1740) shows similar performance to experimental example (1750), experimental example (1720) shows similar performance to experimental example (1730), and experimental example (1725) shows similar performance to experimental example (1735). That is, according to one embodiment, the data speed when using a beam set (1620, 1640) designated for the search area is as high as when using a beam set (1630, 1650) found by calculating the data speed of the terminal each time a beam search is performed. The hierarchical beam search method according to one embodiment only uses a beam set (1620, 1640) pre-designated for the search area, and since the process of calculating the data speed of the terminal to determine the beam set for the next beam search is unnecessary, the time required for beam search for the entire service area can be greatly reduced while maintaining excellent performance.

[0191] Additionally, by comparing experimental example (1715), experimental example (1725), and experimental example (1735), beam performance related to the area average SNR method can be evaluated. Experimental example (1725) is an experimental example (1725) in which beam search is performed using a beam set (1620) in which the area average SNR is maximized, and simultaneous transmission to a terminal is performed using the beam selected as a result. It can be seen that the data rate of experimental example (1725) is higher than when using a conventional beam set (1610), and is as high as when using a beam set (1630) found by calculating the terminal's speed while performing beam search.

[0192] FIG. 19 is a block diagram showing an example of the configuration of a terminal according to one embodiment.

[0193] As illustrated in FIG. 19, the terminal of the present disclosure may include a control unit (control unit) (1930), a transceiver (1910), and a storage unit (memory) (1920). However, the components of the terminal are not limited to the examples described above. For example, the terminal may include more components or fewer components than those described above. Furthermore, the control unit (1930), the transceiver (1910), and the storage unit (1920) may be implemented in the form of a single chip. According to one embodiment, the transceiver (1910) of FIG. 19 may include the transceiver (2304) and the receiver (2308) of FIG. 23. Additionally, the control unit (1930) of FIG. 19 may include at least one processor or controller.

[0194] According to one embodiment, the control unit (1930) can control a series of processes that allow the terminal to operate according to the embodiments of the present disclosure described above. For example, according to the embodiments of the present disclosure, the components of the terminal can be controlled to perform a transmission and reception method of the terminal depending on whether the terminal mode is a terminal energy saving mode or a terminal general mode. The control unit (1930) may be one or a plurality of units, and the control unit (1930) can perform a transmission and reception operation of the terminal in a wireless communication system applying the carrier band of the present disclosure described above by executing a program stored in the storage unit (1920).

[0195] The transceiver (1910) can transmit and receive signals with a base station. The signals transmitted and received with the base station may include control information and data. The transceiver (1910) may be composed of an RF transmitter that up-converts and amplifies the frequency of a transmitted signal, and an RF receiver that low-noise amplifies a received signal and down-converts the frequency. However, this is merely an example of the transceiver (1910), and the components of the transceiver (1910) are not limited to an RF transmitter and an RF receiver. Additionally, the transceiver (1910) can receive a signal through a wireless channel and output it to a control unit (1930), and transmit the signal output from the control unit (1930) through a wireless channel.

[0196] According to one embodiment, the storage unit (1920) may store programs and data necessary for the operation of the terminal. Additionally, the storage unit (1920) may store control information or data included in signals transmitted and received by the terminal. The storage unit (1920) may be composed of a storage medium such as ROM, RAM, hard disk, CD-ROM, and DVD, or a combination of storage media. Additionally, the storage unit (1920) may be a plurality of units. According to one embodiment, the storage unit (1920) may store a program for performing the transmission and reception operation of the terminal depending on whether the terminal mode, which is one of the embodiments of the present disclosure described above, is a terminal energy saving mode or a terminal general mode.

[0197] FIG. 20 is a block diagram showing an example of the configuration of an electronic device according to one embodiment of the present disclosure.

[0198] As illustrated in FIG. 20, the electronic device of the present disclosure may include a control unit (2030), a transceiver (2010), and a storage unit (memory) (2020). However, the components of the electronic device are not limited to the examples described above. For example, the electronic device may include more components or fewer components than those described above. Furthermore, the control unit (2030), the transceiver (2010), and the storage unit (2020) may be implemented in the form of a single chip. The control unit (2030) of FIG. 20 may include at least one processor or controller.

[0199] The control unit (2030) can control a series of processes to enable the electronic device to operate according to the embodiments of the present disclosure described above. For example, the components of the electronic device can be controlled to perform a hierarchical beam search and cooperative transmission method using a plurality of APs according to the embodiments of the present disclosure. The control unit (2030) may be one or a plurality of units, and the control unit (2030) can perform the hierarchical beam search and cooperative transmission method using the plurality of APs described above by executing a program stored in the storage unit (2020).

[0200] Specifically, as shown in operation 1410 of FIG. 14, the control unit (2030) can perform a first beam search using a first beam set using a first AP. The control unit (2030) can determine the first AP to perform the search among a plurality of APs and control the transceiver unit (2010) to transmit a signaling to control the first beam search of the first AP. The first AP can perform a first beam search using a first beam set designated for searching a service area based on the signaling received from an electronic device. According to one embodiment, the signaling to control the first beam search of the first AP may include information about the first beam set assigned to the first AP for searching a service area.

[0201] Additionally, as shown in operation 1420 of FIG. 14, the control unit (2030) can select a first beam to be used for cooperative transmission among the first beam set according to the beam search result of the first AP. Specifically, after the first beam is selected by the terminal as a result of the beam search of the first AP, the control unit (2030) can control the transceiver unit (2010) to receive information about the first beam selected from the first AP or from the terminal. The control unit (2030) can determine the first beam as the beam of the first AP for cooperative transmission.

[0202] Based on the selection of the first beam, the control unit (2030) may limit the area to be searched next from the service area to the first area corresponding to the first beam. The control unit (2030) may select the first area based on the first beam and determine the AP and beam set for the second search among the APs designated for the search of the first area and the beam set of each AP. As in operation 1430 of FIG. 14, the control unit (2030) may determine the second AP to perform the second search and the second beam to be used for the second beam search among the plurality of beam sets assigned to the second AP.

[0203] In operation 1440 of FIG. 14, the control unit (2030) can perform a second beam search using a second beam set using the second AP. The control unit (2030) can control the transceiver (2010) to transmit signaling for controlling the second beam search of the second AP. The second AP can perform a second beam search using a second beam set designated for searching a service area based on the signaling received from the electronic device. According to one embodiment, the signaling for controlling the second beam search of the second AP may include information about the second beam set assigned to the second AP for searching a service area.

[0204] In operation 1450 of FIG. 14, the control unit (2030) can select a second beam to be used for cooperative transmission among the second beam sets according to the beam search result of the second AP. Specifically, after the second beam is selected by the terminal as a result of the beam search of the second AP, the control unit (2030) can control the transceiver unit (2010) to receive information about the selected second beam from the second AP or from the terminal. The control unit (2030) can determine the second beam as the beam of the second AP for cooperative transmission.

[0205] As shown in operation 1520 of FIG. 15, the control unit (2030) may select one beam for the AP that is not used for beam search when there is an AP among a plurality of APs that is not used for beam search. Based on the search area limited by the results of a plurality of beam search, if there is a beam set that includes one beam among a plurality of beam sets designated for the search area, the control unit (2030) may select one beam included in the beam set as the beam of the AP for cooperative transmission for the AP to which the beam set is assigned.

[0206] As in operation 1460 or operation 1530, the control unit (2030) can perform cooperative transmission to the terminal using selected beams. The control unit (2030) can control the transceiver unit (2010) to transmit signaling for data transmission to the APs. The signaling for data transmission may include information about the beam selected for each AP.

[0207] The transmitting and receiving unit (2010) can transmit and receive signals to and from terminals, APs, other network entities, etc. At this time, the signals transmitted and received may include control information and data.

[0208] The transceiver (2010) may include a wired / wireless interface. In one embodiment, the transceiver (2010) may further include a wired backhaul interface and may communicate through a wired backhaul link established between the transceiver and the AP. The transceiver (2010) may further include a plurality of APs and an RF transmitter and an RF receiver for transmitting and receiving signals with the plurality of APs, wherein each AP may include an antenna capable of adjusting its position and angle to control the directionality of the RF signal and perform beamforming. In one embodiment, the transceiver (2010) may be composed of an RF transmitter that up-converts and amplifies the frequency of a transmitted signal, and an RF receiver that low-noise amplifies a received signal and down-converts the frequency. However, this is merely an example of the transceiver (2010), and the components of the transceiver (2010) are not limited to an RF transmitter and an RF receiver.

[0209] Additionally, the transmitting and receiving unit (2010) receives a signal through a wired or wireless channel and outputs it to the control unit (2030), and can transmit the signal output from the control unit (2030) through the wired or wireless channel.

[0210] According to one embodiment, the storage unit (2020) may store programs and data necessary for the operation of the base station. Additionally, the storage unit (2020) may store control information or data included in signals transmitted and received by the base station. The storage unit (2020) may be composed of a storage medium such as ROM, RAM, hard disk, CD-ROM, and DVD, or a combination of storage media. Additionally, the storage unit (2020) may be a plurality of units. According to one embodiment, the storage unit (2020) may store a program for performing a method of scheduling a terminal according to whether the base station mode, which is one of the embodiments of the present disclosure described above, is a base station energy saving mode or a base station general mode.

[0211] A method performed by an electronic device that performs simultaneous transmission to a terminal located in a service area using a plurality of APs of the present disclosure may include: an operation of performing a first beam search for a service area by a first AP that performs a search first among the plurality of APs, using a first beam set designated (predetermined) for searching the service area among a plurality of beam sets assigned to the first AP; an operation of selecting a first beam to be used for simultaneous transmission among the first beam sets according to the result of the first beam search; an operation of determining a second beam set to be used for a second beam search among a plurality of beam sets assigned to a second AP and a second AP that performs a search second based on the first beam; an operation of performing a second beam search by the second AP using the second beam set; an operation of selecting a second beam to be used for simultaneous transmission among the second beam sets according to the result of the second beam search; and an operation of performing the simultaneous transmission to the terminal using the selected beams. At this time, the service area may have a pre-configured range for the simultaneous transmission using the plurality of APs.

[0212] According to one embodiment, the designated first beam set is a beam set having the maximum area average signal-to-noise ratio (SNR) for the service area, and the area average SNR for the service area is the sum of the SNR values ​​for each of a plurality of mutually exclusive sub-areas included in the service area, and the number of beams included in the first beam set may be equal to the number of the plurality of sub-areas.

[0213] Specifically, a first beam set that maximizes the area average SNR for a service area can be designated by arbitrarily determining a beam set to be used by the first AP to search the service area, dividing the service area into multiple sub-areas according to the number of multiple beams included in the beam set, dividing each beam into sub-areas, summing the SNRs of the beams for each sub-area to obtain a function of the area average SNR, and determining a beam set that maximizes the area average SNR. The beam set that maximizes the area average SNR can be determined based on Equations 2 to 10.

[0214] According to one embodiment, the second AP is determined among at least one AP to which a predetermined beam set is assigned for searching a first area corresponding to the first beam, the first area includes at least a portion of the service area, and the beam set assigned for searching the first area may include a plurality of beams.

[0215] According to one embodiment, the second beam set is designated (predetermined) for searching a first region corresponding to the first beam, and maximizes the region average SNR for the first region, wherein the region average SNR for the first region is the sum of the SNR values ​​for each of a plurality of mutually exclusive sub-regions included in the first region, and the number of beams included in the second beam set may be equal to the number of the plurality of sub-regions. The beam set that maximizes the region average SNR may be determined based on Equations 2 to 10.

[0216] According to one embodiment, the number of beams included in the second beam set may be determined based on at least one of the maximum number of beams available to the second AP, the size of the first area, or the size of the beam width used for beam search. Specifically, the number of beams included in the second beam set is limited to the maximum number of beams available to the second AP. If the size of the first area is small, the option to reduce the number of beams is available, and as the size of the first area becomes smaller, the number of options (e.g., not reducing the number of beams, reducing the number of beams by 1, reducing the number of beams by 2, ...) may increase. By setting the number of beams included in the beam set in various ways in this manner, transmission overhead (or hardware resources, signal processing burden) and beamforming performance (e.g., precision, capacity) can be flexibly adjusted. As the beam width used for beam search becomes wider, the area covered by each beam increases, so the number of beams required to cover the same search area may decrease. As the beam width used for beam search becomes narrower, the number of beams required to cover the same search area may increase.

[0217] According to one embodiment, the method may further include an operation of determining a third AP that performs a third search based on the second beam selected according to the result of the second beam search, and a third beam set to be used for the third beam search among a plurality of beam sets assigned to the third AP. Specifically, the electronic device may specify a second area as an area corresponding to the second beam among a first area based on the second beam selected according to the result of the second beam search, and select a third beam set assigned to the third AP among a plurality of beam sets designated to search the second area, thereby performing a third beam search using the third beam set of the third AP.

[0218] According to one embodiment, the method further includes an operation of selecting one beam assigned to an AP that is not used for beam search among the plurality of APs, and the one beam may be included in a beam set of the AP not used for beam search that is predetermined for searching an area selected according to the result of the plurality of beam searches. For example, if there is no beam set designated for an AP to search an area selected according to the result of the plurality of beam searches, or if it contains only one beam, that AP may not be used for beam search. In this way, there may be APs among the plurality of APs that are not used for beam search. As another example, if there is no beam set assigned to that AP in an area selected according to the result of beam search, the electronic device may not use that AP among the plurality of APs when performing simultaneous transmission to a terminal.

[0219] According to one embodiment, the operation of performing the first beam search may include the operation of transmitting a reference signal to the terminal using the first beam set; and the operation of receiving an index of the first beam from the terminal. Specifically, the first beam may be the one with the highest received power of the reference signal among the first beam set. Specifically, the terminal that receives the reference signal from the first AP using the first beam set may determine the index of the first beam with the highest received power of the reference signal and report the index of the first beam to the first AP, and the electronic device may obtain the index of the first beam from the first AP. Likewise, the operation of performing the second beam search may include the operation of transmitting a reference signal to the terminal using the second beam set; and the operation of receiving an index of the second beam from the terminal. The second beam may be the one with the highest received power of the reference signal among the second beam set.

[0220] An electronic device for performing simultaneous transmission to a terminal located in a service area according to one embodiment of the present disclosure may include a transceiver (2010) that communicates with a plurality of APs; and a control unit (2030) coupled to the transceiver. The control unit may be configured to perform a first beam search for a service area using a first beam set assigned to the first AP, which performs the first search among the plurality of APs, and to select a first beam to be used for simultaneous transmission among the first beam sets based on the result of the first beam search, and to determine a second beam set to be used for a second beam search among the plurality of beam sets assigned to the second AP and the second AP based on the first beam, and to perform a second beam search using the second beam set by the second AP, and to select a second beam to be used for simultaneous transmission among the second beam sets based on the result of the second beam search, and to perform simultaneous transmission to the terminal using the selected beams.

[0221] According to one embodiment, the designated first beam set is a beam set having the maximum area average signal-to-noise ratio (SNR) for the service area, and the area average SNR for the service area is the sum of the SNR values ​​for each of a plurality of mutually exclusive sub-areas included in the service area, and the number of beams included in the first beam set may be equal to the number of the plurality of sub-areas.

[0222] According to one embodiment, the control unit may be further configured to determine a third beam set to be used for the third beam search among a plurality of beam sets assigned to the third AP and a third AP that performs a third search based on the second beam selected according to the result of the second beam search.

[0223] According to one embodiment, the second AP is determined among at least one AP to which a predetermined beam set is assigned for searching a first area corresponding to the first beam, the first area includes at least a portion of the service area, and the beam set assigned for searching the first area may include a plurality of beams.

[0224] According to one embodiment, the second beam set is designated (predetermined) for searching a first region corresponding to the first beam, and maximizes the region average SNR for the first region, wherein the region average SNR for the first region is the sum of the SNR values ​​for each of a plurality of mutually exclusive sub-regions included in the first region, and the number of beams included in the second beam set may be equal to the number of the plurality of sub-regions.

[0225] According to one embodiment, the number of beams included in the second beam set may be determined based on at least one of the maximum number of beams that the second AP can use, the size of the first area, or the size of the beam width used for beam search.

[0226] According to one embodiment, the control unit is further configured to select one beam assigned to an AP that is not used for beam searching among the plurality of APs, and the one beam may be included in a beam set of the APs not used for beam searching that is predetermined for searching an area selected according to the result of the plurality of beam searches.

[0227] According to one embodiment, the control unit can transmit a reference signal to the terminal using the first beam set and receive an index of the first beam from the terminal.

[0228] According to one embodiment, the service area may have a pre-set range for the simultaneous transmission using the plurality of APs.

[0229] According to one embodiment, the control unit may be configured to transmit a reference signal to the terminal using the second beam set and to receive an index of the second beam from the terminal.

[0230] An electronic device for performing simultaneous transmission to a terminal located in a service area according to one embodiment of the present disclosure may include a plurality of APs; a transceiver (2010); and a control unit (2030) coupled to the transceiver. The control unit may be configured to perform a first beam search for a service area using a first beam set assigned to the first AP, which performs the first search among the plurality of APs, and to select a first beam to be used for simultaneous transmission among the first beam sets based on the result of the first beam search, and to determine a second beam set to be used for a second beam search among the plurality of beam sets assigned to the second AP and the second AP based on the first beam, and to perform a second beam search using the second beam set by the second AP, and to select a second beam to be used for simultaneous transmission among the second beam sets based on the result of the second beam search, and to perform simultaneous transmission to the terminal using the selected beams.

[0231] Methods according to the embodiments described in the claims or specification of the present invention may be implemented in the form of hardware, software, or a combination of hardware and software.

[0232] When implemented in software, a computer-readable storage medium may be provided for storing one or more programs (software modules). One or more programs stored in the computer-readable storage medium are configured for execution by one or more processors within an electronic device. One or more programs include instructions that cause the electronic device to execute methods according to embodiments described in the claims or specification of the present invention.

[0233] Such programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, ROM (Read Only Memory), Electrically Erasable Programmable Read Only Memory (EEPROM), magnetic disc storage devices, Compact Disc-ROM (CD-ROM), Digital Versatile Discs (DVDs), or other forms of optical storage devices, magnetic cassettes. Alternatively, they may be stored in memory composed of some or all of these. Additionally, each constituent memory may include multiple units.

[0234] In addition, the above program may be stored on an attachable storage device that can be accessed via a communication network such as the Internet, Intranet, Local Area Network (LAN), Wide LAN (WLAN), or Storage Area Network (SAN), or a combination thereof. Such a storage device may be connected to a device performing an embodiment of the present invention through an external port. Additionally, a separate storage device on a communication network may be connected to a device performing an embodiment of the present invention.

[0235] In the specific embodiments of the present invention described above, the components included in the invention are expressed in a singular or plural form according to the specific embodiments presented. However, the singular or plural expression is selected to suit the situation presented for convenience of explanation, and the present invention is not limited to singular or plural components; even if a component is expressed in the plural form, it may be composed in the singular form, or even if a component is expressed in the singular form, it may be composed in the plural form.

[0236] Meanwhile, although specific embodiments have been described in the detailed description of the present invention, it is understood that various modifications are possible within the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims set forth below as well as equivalents thereof.

Claims

1. A method performed by an electronic device that performs simultaneous transmission to terminals located in a service area using multiple APs, An operation of performing a first beam search for a service area by a first AP that performs the first search among the plurality of APs, using a first beam set designated (predetermined) for searching the service area among a plurality of beam sets assigned to the first AP; An operation to select a first beam to be used for simultaneous transmission among the first beam set according to the result of the first beam search; Based on the first beam, an operation to determine a second AP that performs a second search and a second beam set to be used for a second beam search among a plurality of beam sets assigned to the second AP; An operation of performing the second beam search using the second beam set by the second AP; An operation of selecting a second beam to be used for simultaneous transmission among the second beam set according to the result of the second beam search; and A method comprising the operation of performing the simultaneous transmission to the terminal using the selected beams.

2. In Paragraph 1, The first beam set designated above is a beam set having the maximum area average signal-to-noise ratio (SNR) for the service area, and The area average SNR for the above service area is the sum of the SNR values ​​for each of a plurality of mutually exclusive sub-areas included in the above service area, and A method in which the number of beams included in the first beam set is equal to the number of the plurality of sub-regions.

3. In Paragraph 1, A method further comprising determining a third AP that performs a third search based on the second beam selected according to the result of the second beam search, and determining a third beam set to be used for the third beam search among a plurality of beam sets assigned to the third AP.

4. In Paragraph 1, The above 2 AP is, A predetermined beam set for searching a first region corresponding to the first beam is determined among at least one AP to which it is assigned, and The first area above includes at least a portion of the service area, and A method in which a beam set designated for the exploration of the first area includes a plurality of beams.

5. In Paragraph 1, The above second beam set is, It is designated (predetermined) for searching a first region corresponding to the first beam, and maximizes the region average SNR for the first region, and The region average SNR for the first region above is, It is the sum of the SNR values ​​for each of a plurality of mutually exclusive sub-regions included in the first region above, and A method in which the number of beams included in the second beam set is equal to the number of the plurality of sub-regions.

6. In Paragraph 5, A method in which the number of beams included in the second beam set is determined based on at least one of the maximum number of beams that the second AP can use, the size of the first area, or the size of the beam width used for beam search.

7. In Paragraph 1, The operation further includes selecting one beam assigned to an AP that is not used for beam search among the plurality of APs mentioned above, and A method in which the above-mentioned single beam is included in a beam set of APs not used in the beam search, which is specified (predetermined) for the search of a region selected according to the result of the above-mentioned multiple beam searches.

8. In Paragraph 1, The above service area is, A method having a pre-set range for simultaneous transmission using the above plurality of APs.

9. An electronic device that performs simultaneous transmission to terminals located in a service area using multiple APs, A transceiver that performs communication with the above plurality of APs; and It includes a control unit coupled to the above-mentioned transmitting and receiving unit, and the control unit, A first beam search for a service area is performed by a first AP that performs the first search among the plurality of APs above, using a first beam set designated (predetermined) for searching the service area among the plurality of beam sets assigned to the first AP, and Based on the result of the first beam search above, a first beam to be used for simultaneous transmission among the first beam set is selected, and Based on the first beam above, a second AP that performs a second search and a second beam set to be used for the second beam search among a plurality of beam sets assigned to the second AP are determined, and By the above second AP, the second beam search is performed using the above second beam set, and Based on the result of the second beam search above, a second beam to be used for simultaneous transmission among the second beam set is selected, and An electronic device configured to perform the simultaneous transmission to the terminal using the selected beams.

10. In Paragraph 9, The first beam set designated above is a beam set having the maximum area average signal-to-noise ratio (SNR) for the service area, and The area average SNR for the above service area is the sum of the SNR values ​​for each of a plurality of mutually exclusive sub-areas included in the above service area, and An electronic device in which the number of beams included in the first beam set is equal to the number of the plurality of sub-regions.

11. In Paragraph 9, The above control unit is, An electronic device further configured to determine a third AP that performs a third search based on the second beam selected according to the result of the second beam search, and a third beam set to be used for the third beam search among a plurality of beam sets assigned to the third AP.

12. In Paragraph 9, The above 2 AP is, A predetermined beam set for searching a first region corresponding to the first beam is determined among at least one AP to which it is assigned, and The first area above includes at least a portion of the service area, and The beam set designated for the search of the first region above is an electronic device comprising a plurality of beams.

13. In Paragraph 9, The above second beam set is, It is designated (predetermined) for searching a first region corresponding to the first beam, and maximizes the region average SNR for the first region, and The region average SNR for the first region above is, It is the sum of the SNR values ​​for each of a plurality of mutually exclusive sub-regions included in the first region above, and An electronic device in which the number of beams included in the second beam set is the same as the number of the plurality of sub-regions.

14. In Paragraph 13, An electronic device in which the number of beams included in the second beam set is determined based on at least one of the maximum number of beams that the second AP can use, the size of the first area, or the size of the beam width used for beam searching.

15. In Paragraph 9, The above control unit is further configured to select one beam assigned to an AP that is not used for beam search among the plurality of APs, and The above-mentioned single beam is an electronic device included in a beam set of APs not used in the beam search, which is designated (predetermined) for searching an area selected according to the result of the above-mentioned multiple beam searches.

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