KR102646840B1 - Method and apparatus for scheduling in mobile communication system - Google Patents

Abstract

A base station using a plurality of beams transmits a plurality of training beams, and receives measurement information about a first number of training beams with a large received signal strength from each of the plurality of terminals that have received the plurality of training beams, Based on the measurement information for the first number of training beams of each terminal, a received signal strength table indicating the received signal strength for each terminal and beam index is generated, and then the received signal strength table is used to transmit simultaneously among the plurality of terminals. Schedule terminals.

Description

Scheduling method and apparatus in mobile communication system {METHOD AND APPARATUS FOR SCHEDULING IN MOBILE COMMUNICATION SYSTEM}

The present invention relates to a scheduling method and device in a mobile communication system, and more specifically, to a scheduling method and apparatus in a mobile communication system that can easily and simply provide feedback from a terminal and scheduling at a base station in a mobile communication system using a directional beam. It's about devices.

After the emergence of mobile broadband services, mobile communication systems must meet the diverse needs of multiple users. In particular, in a voice-centric data environment where guaranteeing a certain minimum data rate is important, demand for wireless transmission of various multimedia such as music, video, and web surfing is rapidly increasing, and active scheduling (resource allocation) is required according to the amount and type of information currently requested by the terminal. ) is very important.

The 5th generation mobile communication system must not only support a data rate of up to 20Gbps for the terminal, but must also be able to maintain a data rate of 100Mbps to 1Gbps regardless of where the terminal is in the cell. In addition, it must support latency of less than 1ms and simultaneous connection of a very large number of devices. To achieve these technical goals, the adoption of the millimeter wave band in mobile communication systems has recently been in the spotlight. The millimeter wave band is very advantageous for high-speed data transmission as it is easy to secure a wide bandwidth, and has the advantage of lowering delays at the physical layer. However, there is severe radio wave attenuation depending on the transmission and reception distance, and there is blockage due to buildings, terrain, etc. Occurs.

Therefore, a mobile communication system using the millimeter wave band uses a directional beam at the transmitting and receiving end to compensate for severe attenuation of the channel. At this time, the base station must simultaneously support data to multiple terminals using multiple beams to maximize system performance. In other words, the implementation of a MU-MIMO (Multi-User Multiple-Input Multiple-Output) system is necessary. However, when operating multiple beams, inter-beam interference may occur and reduce system performance, so scheduling that takes inter-beam interference into consideration is essential.

In addition, the existing LTE (Long Term Evolution)/LTE-A (Advanced) CSI (Channel State Information) feedback structure is designed primarily to use different resources for each user, making it possible to implement a high-performance MU-MIMO system. It is very difficult. Therefore, in order to obtain maximum system performance in mobile communication systems using directional beams, a new CSI feedback structure and scheduling method is essential.

The problem to be solved by the present invention is to provide a scheduling method and device that can improve system performance in a mobile communication system using directional beams.

According to one embodiment of the present invention, a method of scheduling a plurality of terminals in a cell at a base station using a plurality of beams is provided. The scheduling method includes transmitting a plurality of training beams, receiving measurement information about a first number of training beams with large received signal strengths from each of the plurality of terminals that have received the plurality of training beams, and Based on measurement information about a first number of training beams, generating a received signal strength table indicating received signal strength for each terminal and beam index, and using the received signal strength table to select terminals to transmit simultaneously among the plurality of terminals. Includes a scheduling step.

The measurement information may include received signal strength, received phase, and beam index for each of the first number of training beams.

The scheduling step includes selecting a terminal with the largest sum of the squares of the received signal strengths of a first number of training beams of each terminal among the terminals in the schedulable terminal set, excluding the selected terminal from the terminal set, Excluding the first number of training beams of the selected terminal from the beam index set including the plurality of beams, the first number of training beams of each terminal among each terminal of the terminal set and the first number of training beams of the selected terminal Excluding from the terminal set a terminal in which the number of beams overlapping between training beams is greater than the maximum allowable number set, and repeating the selecting, generating, and excluding steps to schedule terminals to transmit simultaneously may include.

The scheduling step may further include generating a transmission beam to the selected terminal using the received signal strength of the first number of training beams of the selected terminal.

The scheduling method includes defining a beam set by merging a first number of training beams of each scheduled terminal, receiving signal strengths of beams that have not received feedback from each scheduled terminal among the beams in the merged beam set, and Assigning a value of 0 to the received phase, and designing minimum mean square error (MMSE) or zero-forcing (ZF) beam forming using the received signal strength and received phase of all beams of each scheduled terminal. Additional steps may be included.

The measurement information may include a received phase and beam index for each of the first number of training beams, and the sum of received signal strengths of the first number of training beams.

The scheduling step includes selecting a terminal with the largest sum of received signal strengths of the first number of training beams from a set of schedulable terminals, using the received phase of the first number of training beams of the selected terminal. Generating a transmission beam to the selected terminal, excluding the selected terminal from the terminal set, and excluding a first number of training beams of the selected terminal from the beam index set including the plurality of beams, Among each terminal in the terminal set, excluding from the terminal set a terminal in which the number of beams overlapping between the first number of training beams of each terminal and the first number of training beams of the selected terminal is greater than a set maximum allowable number, and It may include scheduling terminals to transmit simultaneously by repeating the selecting step, the generating step, and the excluding step.

The scheduling method may further include transmitting data of corresponding terminals through transmission beams of the scheduled terminals.

The measurement information may include a beam index for each of the first number of training beams and the sum of received signal strengths of the first number of training beams.

The scheduling step includes selecting a terminal with the largest sum of received signal strengths of the first number of training beams from a set of schedulable terminals, excluding the selected terminal from the terminal set, and including the plurality of beams. Excluding the first number of training beams of the selected terminal from the beam index set, beams overlapping between the first number of training beams of each terminal among each terminal of the terminal set and the first number of training beams of the selected terminal It may include excluding from the terminal set a number of terminals greater than a set maximum allowable number, and scheduling terminals to transmit simultaneously by repeating the selecting, generating, and excluding steps.

The scheduling method includes defining a beam set obtained by combining a first number of training beams of each scheduled terminal, requesting feedback from each scheduled terminal, and receiving beams in the merged beam set from each terminal. It may further include receiving signal strength and reception phase, and designing MMSE or ZF beamforming using the received signal strength and reception phase of beams in the merged beam set of each scheduled terminal.

According to another embodiment of the present invention, an apparatus for scheduling a plurality of terminals within a cell at a base station using a plurality of beams is provided. The scheduling device includes a transceiver and a processor. The transceiver transmits a plurality of training beams and receives measurement information about a first number of training beams with a large received signal strength from each of the plurality of terminals that have received the plurality of training beams. And the processor generates a received signal strength table indicating the received signal strength for each terminal and beam index based on measurement information about the first number of training beams of each terminal, and the received signal strength table according to the beamforming method of the base station. The plurality of terminals are scheduled using a table.

The measurement information may include received signal strength, received phase, and beam index for each of the first number of training beams.

The processor schedules a set number of terminals based on the sum of the squares of the received signal strengths of the first number of training beams of each of the terminals in the schedulable terminal set, and schedules the first number of terminals among the terminals in the terminal set. Terminals in which the number of beams overlapping between the training beam and the first number of training beams of each scheduled terminal is greater than the set maximum allowable number may be excluded from the scheduling.

The processor may generate the transmission beam for maximum ratio transmission (MRT) beamforming by combining received signal strengths for the first number of training beams of each scheduled terminal.

The processor assigns a value of 0 to the received signal strength and received phase of the beams that did not receive feedback from each scheduled terminal among the beams in the beam set obtained by combining the first number of training beams of each scheduled terminal, Minimum mean square error (MMSE) or zero-forcing (ZF) beamforming or random beamforming can be designed using the received signal strength and received phase of all scheduled beams of each terminal.

The measurement information may include a received phase and beam index for each of the first number of training beams, and the sum of received signal strengths of the first number of beams.

The processor schedules a set number of terminals based on the sum of the received signal strengths of the first number of training beams of each terminal in the schedulable terminal set, and determines the reception phase for the first number of training beams of each scheduled terminal. Combining them to generate a transmission beam for beamforming of the equal gain combining (EGC) method, the first number of training beams of each terminal among the terminals of the terminal set and the first number of the scheduled beams of each terminal Terminals in which the number of beams overlapping between training beams is greater than the maximum allowable number can be excluded from the scheduling.

The measurement information may include a beam index for each of the first number of training beams and the sum of received signal strengths of the first number of training beams.

The processor schedules a set number of terminals based on the sum of the squares of the received signal strengths of the first number of training beams of each of the terminals in the schedulable terminal set, and schedules the first number of terminals among the terminals in the terminal set. Terminals in which the number of overlapping beams between training beams and the first number of training beams of each of the scheduled terminals is greater than the maximum allowable number are excluded from the scheduling, and a beam obtained by combining the first number of training beams of each of the scheduled terminals is excluded from the scheduling. The received signal strength and reception phase of the beams in the set are requested from each scheduled terminal and received from each scheduled terminal, and the received signal strength and reception phase of the beams in the merged beam set are received from each scheduled terminal. You can design MMSE or ZF beamforming or arbitrary beamforming using .

According to an embodiment of the present invention, the amount of feedback of the terminal can be reduced, and system performance can be improved by efficiently scheduling the terminal even with the reduced feedback.

Figure 1 is a diagram showing an example of a path between a base station and a terminal according to an embodiment of the present invention.
Figure 2 is a diagram showing a number of terminals in an area covered by a base station according to an embodiment of the present invention.
Figure 3 is a diagram showing beam forming of a base station according to an embodiment of the present invention.
Figure 4 is a diagram showing an example of a received signal strength table generated by a base station according to an embodiment of the present invention.
5 to 7 are flowcharts showing a UE feedback and base station scheduling method according to the first to third embodiments of the present invention, respectively.
Figure 8 is a flowchart showing a UE feedback and base station beam forming method based on two section feedback according to the fourth embodiment of the present invention.
Figure 9 is a diagram showing a base station and a terminal according to an embodiment of the present invention.

Below, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts that are not related to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

Throughout the specification and claims, when a part is said to “include” a certain component, this means that it may further include other components rather than excluding other components, unless specifically stated to the contrary.

Now, a scheduling method and device in a mobile communication system according to an embodiment of the present invention will be described in detail with reference to the drawings.

Figure 1 is a diagram showing an example of a path between a base station and a terminal according to an embodiment of the present invention.

The millimeter wave band refers to the frequency band of 30GHz to 300GHz. The channel in the millimeter wave band has strong linearity, so it has poor diffraction and reflection characteristics due to objects in the path, and has large attenuation in the air. Therefore, only a very limited number of paths exist between the base station and the terminal.

For example, as shown in Figure 1, there may be three paths between the base station and terminal k. The first path is a path corresponding to Line-of-Sight (LoS), which is directed by the antenna of the base station. It exists in a position rotated by an angle of θ _k,1 relative to the bore-sight and has a channel gain of α _k,1 . The second and third paths are paths that are reflected in the cluster and then incident on terminal k, and exist at positions rotated by angles θ _k,2 and θ _k,3 relative to the bore site where the base station's antenna is aimed, respectively. , has channel gains α _k,2 and α _k,3 .

The channel between the base station and terminal k as shown in FIG. 1 is expressed as equation 1.

Here, L is the number of paths between the base station and UE k, M is the number of antennas installed at the base station, α _k,i is the complex channel gain corresponding to path i of UE k, a(θ _k,i ) can be expressed as Equation 2.

Equation 2 represents the response of the antenna array between the antenna array of the base station and the angle θ _k,i . Equation 2 represents the phase difference according to the time delay that occurs when a signal arrives at the antenna array.

Figure 2 is a diagram showing a number of terminals in an area covered by a base station according to an embodiment of the present invention.

Referring to FIG. 2, multiple terminals 200 may be located in a cell area served by one base station 100. The base station 100 selects (schedules) a terminal 200 to provide optimal performance among a plurality of terminals 200 in the cell area.

Figure 3 is a diagram showing beam forming of a base station according to an embodiment of the present invention.

Referring to FIG. 3, the base station 100 operating in the millimeter wave band uses multiple directional beams to completely cover the serviced cell area and support multiple users.

The simplest way to generate a directional beam is to use an antenna array, and in particular, the Uniform linear array (ULA) method can be used. ULA is a method in which antenna elements are arranged in a linear array structure while maintaining constant spacing between antenna elements.

When the base station 100 uses M antenna elements having a ULA structure, the base station 100 can generate M orthogonal training beams (w ₁ , w ₂ , ..., w _M ). Therefore, the base station 100 generates M training beams (w ₁ , w ₂ , ..., w _M ) and transmits them through specific resources so that the terminal 200 within the cell measures the channel between itself and the base station 100. make it possible The terminal 200 can measure the signal-to-noise ratio (SNR) or received signal strength for all training beams (w ₁ , w ₂ , ..., w _M ). However, since the base station 100 transmits data on the same resource using only a portion of the M training beams, the signal-to-interference and noise ratio (SINR) when receiving actual data is unknown. .

In a mobile communication system using multiple beams, one of the feedback and scheduling methods of the terminal 200 is that the terminal 200 feeds back the received signal strength (or SNR) for all M training beams used by the base station 100. , the base station 100 uses the received signal strength (or SNR) corresponding to the M training beams sent by all terminals 200 to determine the terminal to be used for actual data transmission through exhaustive search. This method can obtain the optimal performance given to the system, but the amount of feedback from the terminal 200 and the computational complexity are very high, making it difficult to apply to an actual system.

Accordingly, in an embodiment of the present invention, the terminal 200 uses the beam index corresponding to the N _FB training beams with the largest received signal strength among the M received signal strengths measured through the training beams and the received signal strength of the N _FB training beams. Feedback is provided to the base station 100. When feedback of the received signal strength and beam index of the N _FB training beams is provided from each terminal 200 in the cell, the base station 100 provides a received signal strength indicating the received signal strength corresponding to each terminal 200 and the beam index. You can create a table.

Figure 4 is a diagram showing an example of a received signal strength table generated by a base station according to an embodiment of the present invention.

Referring to FIG. 4, in the received signal strength table, the places where each terminal feeds back the received signal strength are expressed in black.

When generating the received signal strength table, the base station 100 assigns the corresponding received signal strength value to the beam index to which the terminal fed back the received signal strength among all beam indices (1 to M), and to the beam to which the received signal strength was not fed back. For the index, 0 or a specific value can be assigned. In Figure 4, for convenience, the points where each terminal feeds back the received signal strength are shown in black in the received signal strength table.

The channel h _k in the millimeter band, which can be expressed as Equation 1, is composed of the sum of L paths, and therefore the received signal strength of any training beam is determined by the direction of one or more of the L paths toward the terminal and which training beam is used. It is large when the heading direction is well matched.

When the received signal strength table as shown in FIG. 4 is generated, the base station 100 can schedule the terminal using the received signal strength table. As an example, the base station 100 may schedule the terminal using a greedy sequential scheduling algorithm using a received signal strength table. To briefly describe the greedy sequential scheduling algorithm, the base station 100 first selects the terminal and beam with the highest received signal strength in the received signal strength table, and then selects the total data rate among the remaining terminals and beams excluding the selected terminal and beam. Select the terminal and beam with the maximum (sum data rate). This process continues until the maximum number of schedulable terminals is reached.

This greedy sequential scheduling method is suitable when the base station 100 selects one beam among a plurality of training beams for each terminal and uses it for data transmission. However, selecting one training beam and transmitting data to the terminal in a millimeter band channel with multiple paths as shown in Equation 1 is not the optimal method. Therefore, a method is needed to generate and use a beam to transmit data appropriately for the estimated channel by combining a plurality of training beams.

In an embodiment of the present invention, a UE feedback method and a base station scheduling method are proposed when the base station 100 generates a beam to transmit data by combining a plurality of training beams.

By using the UE feedback method and the base station scheduling method proposed in the embodiment of the present invention, maximum ratio transmission (MRT) and equal gain combination are achieved at the base station 100 without the amount of feedback being high in the millimeter band channel. (equal gain combining, EGC) type beam forming can be implemented. Since the UE's feedback method and the base station's scheduling method are slightly different depending on the beamforming method of the base station, below is the UE's feedback appropriate for each beamforming method when the base station 100 performs MRT beamforming or EGC beamforming, respectively. And the scheduling method of the base station is described. Additionally, when the base station 100 uses the terminal feedback and the base station scheduling method used in MRT beamforming, minimum mean square error (MMSE) or zero forcing (Zero- This explains how to design forcing (ZF) beam forming. In addition, the base station 100 selects a beam to be used with the terminal based on the feedback method of the terminal that has a smaller feedback amount than the feedback amount of the terminal used in MRT and EGC beamforming in the first time section, and selects a beam to be used with the terminal in the second time section. This explains the UE feedback, base station scheduling, and beam forming design methods based on two-phase feedback, which designs MMSE or ZF beamforming by receiving feedback from the selected UE on channel information corresponding to the selected beam.

First, when the base station 100 uses MRT beamforming, the terminal's feedback and the base station's scheduling method suitable for MRT beamforming will be described with reference to FIG. 5. When the base station 100 uses EGC beamforming, The UE feedback and base station scheduling methods suitable for EGC beamforming will be described with reference to FIG. 6. In addition, when the base station 100 uses the terminal feedback and the base station scheduling method used in MRT beamforming, the method of designing MMSE or ZF beamforming will be explained with reference to FIG. 7, and the terminal feedback based on two-section feedback will be described with reference to FIG. , The scheduling and beam forming design method of the base station will be described with reference to FIG. 8.

Figure 5 is a flowchart showing a UE feedback and base station scheduling method according to the first embodiment of the present invention.

Referring to FIG. 5, the base station 100 transmits M training beams (S502).

A terminal that has received M training beams can select N _FB main training beams with high received signal strength. The N _FB training beams can be viewed as well-matched to the L paths between the base station and the terminal, and can be viewed as simulating the channel between the terminal and the base station.

는 단말 k에서 주요 트레이닝 빔 w_b의 수신 신호 세기를 나타낸다.

는 단말 k에서 주요 트레이닝 빔 w_b의 수신 위상을 나타낸다. 그리고

는 단말 k에서 선택한 수신 신호 세기가 큰 N_FB개의 주요 트레이닝 빔의 빔 인덱스 집합을 나타낸다. When the base station 100 uses MRT beamforming, the terminal feeds back the received signal strength, received phase, and index of the corresponding beam corresponding to each of the N _FB main training beams. The received signal strength, phase value, and index of the corresponding beam fed back by the terminal are each , and It can be expressed as:

represents the received signal strength of the main training beam w _b at terminal k.

represents the reception phase of the main training beam w _b at terminal k. and

represents the beam index set of N _FB main training beams with large received signal strengths selected by terminal k.

When the base station 100 receives feedback including the received signal strength, received phase, and index of the beam corresponding to each of the N _FB main training beams from each terminal (S504), it performs scheduling in the following manner.

The base station 100 has a set of schedulable terminals [ ] and the beam index set of the training beam [ ] and j are initialized (S506). Set of schedulable terminals[ ] is initialized to include all schedulable terminals, and the beam index set [ ] is initialized to include the entire beam index. And initialize it to j=1. Here, j represents the number of repetitions of the terminal scheduling algorithm.

The base station 100 uses Equation 3 to select the terminal with the highest received signal strength when using the main training beam among the set of schedulable terminals (S508). The terminal selected in the j th iteration is called k _j .

Next, the base station 100 generates a beam to be used when transmitting data to terminal k _j as shown in Equation 4 (S510). That is, when transmitting data to terminal k _j , the base station 100 combines the N _FB main training beams for terminal k _j to generate a beam to be used for transmission to terminal k _j . That is, MRT beamforming is performed by combining N _FB main training beams.

이 결정되면, 스케줄링 가능한 단말 집합을 수학식 5와 같이 업데이트하고(S512), 빔 인덱스 집합을 수학식 6과 같이 업데이트한다(S514). 즉, 스케줄링 가능한 단말 집합에서 단말 k_j을 제외시키고, 빔 인덱스 집합에서 빔

을 제외시킨다. In this way, the base station 100 selects a beam to be used when transmitting data to terminal k _j and terminal k _j .

Once this is determined, the set of schedulable terminals is updated as shown in Equation 5 (S512), and the beam index set is updated as shown in Equation 6 (S514). That is, exclude terminal k _j from the schedulable terminal set and beam from the beam index set.

exclude.

The base station 100 uses this method to determine the optimal terminal k _j And when the beam to be used for transmission to terminal k _j is determined, the following process is additionally performed to leave only terminals that generate less interference by the corresponding beam.

The base station 100 is a set of terminals that can schedule only terminals that generate less interference by the beam to be used for transmission to terminal k _j . A set of terminals that can be scheduled to remain in is updated according to Equation 7 (S516).

Here, N _OL is the maximum allowable number of main training beams that can overlap between different terminals.

A set of terminals that can be scheduled with terminals that satisfy Equation 7 When updated, the base station 100 creates a set of terminals that can schedule only terminals with low interference when scheduled at the same time as the currently selected terminal. You can leave it at .

If the base station 100 , , If all are satisfied (S518), j = j + 1 is increased (S520), then moves to step (S508) and repeats steps (S508 to S518). Otherwise, the scheduling algorithm is terminated (S522). Here, K _s,max (≤M) is a predetermined constant value (natural number).

When performing MRT beamforming at the base station 100, it can be seen that the amount of feedback from the UE when using this scheduling method is 2N _FB real numbers and N _FB integers.

Figure 6 is a flowchart showing the UE feedback and base station scheduling method according to the second embodiment of the present invention.

Referring to FIG. 6, the base station 100 transmits M training beams (S602).

A terminal that has received M training beams can select N _FB main training beams with high received signal strength.

를 기지국(100)에 피드백한다.When performing EGC-type beamforming at the base station 100, the terminal contains information corresponding to Equations 8 and 9 and a beam index set of N _FB main training beams with large received signal strengths.

is fed back to the base station 100.

When performing EGC-type beamforming at the base station 100, the terminal does not feed back the received signal strength of the N _FB main training beams with large received signal strengths, but feeds back the received signal strengths of the N _FB main training beams with large received signal strengths. Since only information about the sum of received signal strengths is fed back, the amount of feedback from the terminal can be reduced compared to the amount of feedback from the terminal when the base station 100 performs MRT-type beamforming.

를 포함하는 피드백을 수신하면(S604), 다음과 같은 방법으로 스케줄링을 수행한다. MRT 방식일 때와 비교하여 단말을 선택하는 방식 및 해당 단말에 데이터를 전송할 빔을 생성하는 방식이 다르다.The base station 100 receives the sum of the received signal strengths of the N _FB main training beams from each terminal, the received phase and beam index set of the N _FB main training beams.

Upon receiving feedback including (S604), scheduling is performed in the following manner. Compared to the MRT method, the method of selecting a terminal and the method of generating a beam to transmit data to the corresponding terminal are different.

The base station 100 has a set of schedulable terminals [ ] and the beam index set of the training beam [ ] and j are initialized (S606). Set of schedulable terminals[ ] is initialized to include all schedulable terminals, and the beam index set [ ] is initialized to include the entire beam index. And initialize it to j=1. Here, j represents the number of repetitions of the terminal scheduling algorithm.

The base station 100 uses Equation 10 to select the terminal with the highest received signal strength when using the main training beam among the set of schedulable terminals (S608). The terminal selected in the jth repetition is called k _j .

Next, the base station 100 performs EGC beamforming by generating a beam to be used when transmitting data to the terminal k _j as shown in Equation 11 (S610).

이 결정되면, 스케줄링 가능한 단말 집합을 수학식 12와 같이 업데이트하고(S612), 빔 인덱스 집합을 수학식 13과 같이 업데이트한다(S614). 즉, 스케줄링 가능한 단말 집합에서 단말 k_j을 제외시키고, 빔 인덱스 집합에서 빔

을 제외시킨다. In this way, the base station 100 selects a beam to be used when transmitting data to terminal k _j and terminal k _j .

Once this is determined, the schedulable terminal set is updated as shown in Equation 12 (S612), and the beam index set is updated as shown in Equation 13 (S614). That is, exclude terminal k _j from the schedulable terminal set and beam from the beam index set.

exclude.

When the base station 100 determines the optimal terminal k _j and the beam to be used for transmission to terminal k _j in this way, the base station 100 additionally performs the following process to leave only terminals that generate less interference by the corresponding beam. do.

The base station 100 is a set of terminals that can schedule only terminals that generate less interference by the beam to be used for transmission to terminal k _j . A set of terminals that can be scheduled to remain in is updated according to Equation 14 (S616).

Here, N _OL is the maximum allowable number of main training beams that can overlap between different terminals.

A set of terminals that can be scheduled with terminals that satisfy Equation 14 When updated, the base station 100 creates a set of terminals that can schedule only terminals with low interference when scheduled at the same time as the currently selected terminal. You can leave it at .

If the base station 100 , , If all are satisfied (S618), j = j + 1 is increased (S620), then moves to step (S608) and repeats steps (S608 to S618). Otherwise, the scheduling algorithm is terminated (S622). Here, K _s,max (≤M) is a predetermined constant value (natural number).

When the base station 100 uses ECG beamforming, the amount of feedback from the terminal when using this scheduling method is (N _FB + 1) real numbers and N _FB integers, which is less than the amount of feedback when using MRT beamforming. The amount of feedback from the terminal is reduced.

Figure 7 is a flowchart showing the UE feedback and base station scheduling method according to the third embodiment of the present invention.

Referring to FIG. 7, the base station 100 transmits M training beams (S702).

When the base station 100 receives feedback including the received signal strength, received phase, and corresponding beam index corresponding to each of the N _FB main training beams from each terminal (S704), it performs scheduling in the following manner.

The base station 100 has a set of schedulable terminals [ ] and the beam index set of the training beam [ ] and j are initialized (S706).

The base station 100 uses Equation 15 to select the terminal with the highest received signal strength when using the main training beam among the set of schedulable terminals (S708). The terminal selected in the jth repetition is called k _j .

을 제외시킨다. When the terminal k _j is determined, the base station 100 updates the schedulable terminal set as shown in Equation 16 (S710) and updates the beam index set as shown in Equation 17 (S712). That is, exclude terminal k _j from the schedulable terminal set and beam from the beam index set.

exclude.

Next, the base station 100 creates a set of terminals that can schedule only terminals whose main training beams overlap with the main training beam of terminal k _j . A set of terminals that can be scheduled to remain in is updated according to Equation 18 (S714).

Here, N _OL is the maximum allowable number of main training beams that can overlap between different terminals.

A set of terminals that can be scheduled as terminals that satisfy Equation 18 When updating, the base station 100 creates a set of terminals that can schedule only terminals whose channels are almost orthogonal to each other when scheduled at the same time as the currently selected terminal. You can leave it at .

If the base station 100 , , If all are satisfied (S716), j = j + 1 is increased (S718), then moves to step (S708) and repeats steps (S708 to S716). Otherwise, the terminal scheduling algorithm is terminated. Here, K _s,max (≤M) is a predetermined constant value (natural number).

In this way, after scheduling the terminals, the base station 100 can define a beam set B* by combining the main training beams of each scheduled terminal as shown in Equation 19.

Here, J is the j value when moving from step S716 to step S720.

The base station 100 is the main training beam set of each scheduled terminal k _j Only the received signal strength and received phase of the beams corresponding to are known. Therefore, for each terminal k _j Because the received signal strength and received phase of the beams corresponding to are not known, A value of 0 is assigned to the received signal strength and received phase of the beams corresponding to (S720). Then the base station 100 Within the subspace spanned by the beams corresponding to the beam index within the channel state information (CSI) of each terminal (i.e., the channel state information (CSI) of each terminal It can be considered that the received signal strength and received phase of all beams within the beam are accurately known. Based on accurate CSI information in this subspace, the base station 100 designs MMSE or ZF beamforming (S722). Additionally, the base station 100 may design arbitrary beamforming other than MMSE or ZF beamforming based on CSI information in this subspace.

It can be seen that when the base station 100 uses this scheduling method and beamforming, the amount of feedback from the UE is 2N _FB real numbers and N _FB integers, the same as when performing MRT beamforming.

Figure 8 is a flowchart showing a UE feedback and base station beam forming method based on two section feedback according to the fourth embodiment of the present invention.

Referring to FIG. 8, the base station 100 transmits M training beams (S802).

The base station 100 receives only the index of each of the N _FB main training beams and the sum of the received signal strengths of the main training beams as feedback from each terminal (S804).

The base station 100 has a set of schedulable terminals [ ] and the beam index set of the training beam [ ] and j are initialized (S806).

The base station 100 uses Equation 20 to select the terminal with the highest received signal strength when using the main training beam among the set of schedulable terminals (S808). The terminal selected in the j th iteration is called k _j .

을 제외시킨다. When the terminal k _j is determined, the base station 100 updates the schedulable terminal set as shown in Equation 21 (S810) and updates the beam index set as shown in Equation 22 (S812). That is, exclude UE k _j from the schedulable UE set, and the main training beam of UE k _j from the beam index set B.

exclude.

The base station 100 is a set of terminals that can schedule only terminals whose main training beams overlap with the main training beam of terminal k _j . A set of terminals that can be scheduled to remain in is updated according to Equation 23 (S814).

Here, N _OL is the maximum allowable number of main training beams that can overlap between different terminals.

A set of terminals that can be scheduled as terminals that satisfy Equation 23 When updating, the base station 100 creates a set of terminals that can schedule only terminals whose channels are almost orthogonal to each other when scheduled at the same time as the currently selected terminal. You can leave it at .

If the base station 100 , , If all are satisfied (S816), j = j + 1 is increased (S818), then moves to step (S808) and repeats steps (S808 to S816). Otherwise, the terminal scheduling algorithm is terminated. Here, K _s,max (≤M) is a predetermined constant value (natural number).

After scheduling the terminals, the base station 100 can define the B* set by combining the main training beams of each terminal as shown in Equation 24.

Here, J is the j value when moving from step S816 to step S820.

The base station 100 receives from each scheduled terminal By additionally requesting feedback on the received signal strength and received phase information of the beams corresponding to the beam index within the terminal, Feedback including the received signal strength and received phase information of the beams corresponding to the beam indices within the beam is received (S822).

When the base station 100 receives feedback from a terminal, the base station 100 Since the received signals and received phases of all beams within are known, Within the subspace spanned by the beams corresponding to the beam index within, the CSI of each terminal is accurately known. Based on this, the base station 100 designs MMSE or ZF beamforming based on CSI information in this subspace (S824). Additionally, the base station 100 may design arbitrary beamforming other than MMSE or ZF beamforming based on CSI information in this subspace.

The amount of feedback from the terminal when using this scheduling method and beamforming is 1 real number and N _FB integers in the feedback phase of the first section, and in the feedback phase of the second section, You can see that it was a mistake.

The scheduling method described above can also be applied to a structure that considers hybrid analog/digital beamforming in a situation where the number of RF chains (N _RF ) in the base station 100 is less than the number of antennas (M) of the base station. . Specifically, in a hybrid analog-digital beamforming situation, analog beam training is performed, and at this time, the terminal is scheduled according to the MRT and EGC-based scheduling methods described above, and an analog beam to be used when transmitting data to the corresponding terminal can be generated. However, since the number of terminals that can transmit simultaneously is limited to N _RFs , K _s,max ≤N _RF .

Figure 9 is a diagram showing a base station and a terminal according to an embodiment of the present invention.

Referring to FIG. 9, the scheduling device 910 of the base station includes a processor 912, a transceiver 914, and a memory 916. The processor 912 may be configured to implement the functions, operations, procedures, and methods for beamforming and scheduling in the base station described in the embodiment of the present invention. The processor 912 may execute instructions stored or loaded in the memory 916 to implement the functions, operations, procedures, and methods for scheduling in the base station described above. The transceiver 914 is connected to the processor 912 and transmits and/or receives wireless signals. The transceiver 914 may include a plurality of antenna elements. The memory 916 is connected to the processor 912 and stores various information for driving the processor 912. The memory 916 stores instructions to be executed by the processor 912 or loads instructions from a storage device (not shown) and temporarily stores them.

The feedback device 920 of the terminal includes a processor 922, a transceiver 924, and a memory 926. The processor 922 may be configured to implement the functions, operations, procedures, and methods for feedback in the terminal described in the embodiment of the present invention. The processor 922 may execute instructions stored or loaded in the memory 926 to implement the functions, operations, procedures, and methods for feedback in the terminal described above. The transceiver 924 is connected to the processor 922 and transmits and/or receives wireless signals. The memory 926 is connected to the processor 922 and stores various information for driving the processor 922. The memory 926 stores instructions to be executed by the processor 922 or loads instructions from a storage device (not shown) and temporarily stores them.

The processors 912 and 922 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed.

Memory 916, 926 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and/or other storage devices.

Embodiments of the present invention are not only implemented through the devices and/or methods described above, but may also be implemented through a program that implements functions corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. This implementation can be easily implemented by an expert in the technical field to which the present invention belongs based on the description of the embodiments described above.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements can be made by those skilled in the art using the basic concept of the present invention defined in the following claims. It falls within the scope of rights.

Claims (20)

A method of scheduling multiple terminals in a cell at a base station using multiple beams,
Transmitting a plurality of training beams,
Receiving a received signal strength indication (RSSI), a reception interval, and a beam index for each of the first number of training beams having the largest RSSI from each of the plurality of terminals that have received the plurality of training beams,
Based on measurement information about the first number of training beams of each terminal, generating an RSSI table representing the RSSIs of the terminal and beam indices, and
Scheduling terminals to transmit simultaneously among the plurality of terminals using the RSSI table,
Including,
The scheduling step is,
Selecting the terminal with the largest sum of squares of the RSSIs of the first number of training beams of each terminal among the terminals in the schedulable terminal set,
Excluding the selected terminal from the terminal set and excluding a first number of training beams of the selected terminal from the beam index set including the plurality of beams,
Among each terminal in the terminal set, excluding from the terminal set a terminal in which the number of beams overlapping between the first number of training beams of each terminal and the first number of training beams of the selected terminal is greater than the set maximum allowable number, and
A scheduling method comprising scheduling terminals to transmit simultaneously by repeating the selecting, generating, and excluding steps. In paragraph 1:
The measurement information includes received signal strength, received phase, and beam index for each of the first number of training beams. delete In paragraph 1:
The scheduling method further includes generating a transmission beam for the selected terminal using received signal strengths of a first number of training beams of the selected terminal. In paragraph 1:
Defining a beam set that combines the first number of training beams of each scheduled terminal,
Assigning a value of 0 to the received signal strength and received phase of beams that have not received feedback from each scheduled terminal among the beams in the merged beam set, and
A step of designing minimum mean square error (MMSE) or zero-forcing (ZF) beamforming using the received signal strength and received phase of all beams of each scheduled terminal.
A scheduling method further comprising: In paragraph 1:
The measurement information includes a received phase and beam index for each of the first number of training beams, and a sum of received signal strengths of the first number of training beams. In paragraph 6:
The scheduling step is
Selecting a terminal with the largest sum of received signal strengths of the first number of training beams from among the set of schedulable terminals,
Generating a transmission beam to the selected terminal using the reception phase for the first number of training beams of the selected terminal,
Excluding the selected terminal from the terminal set and excluding a first number of training beams of the selected terminal from the beam index set including the plurality of beams,
Among each terminal in the terminal set, excluding from the terminal set a terminal in which the number of beams overlapping between the first number of training beams of each terminal and the first number of training beams of the selected terminal is greater than the set maximum allowable number, and
A scheduling method comprising scheduling terminals to transmit simultaneously by repeating the selecting, generating, and excluding steps. In paragraph 7:
Transmitting data of corresponding terminals through the transmission beam of the scheduled terminals
A scheduling method further comprising: In paragraph 1:
The measurement information includes a beam index for each of the first number of training beams and a sum of received signal strengths of the first number of training beams. In paragraph 9:
The scheduling step is
Selecting a terminal with the largest sum of received signal strengths of the first number of training beams from among the set of schedulable terminals,
Excluding the selected terminal from the terminal set and excluding a first number of training beams of the selected terminal from the beam index set including the plurality of beams,
Among each terminal in the terminal set, excluding from the terminal set a terminal in which the number of beams overlapping between the first number of training beams of each terminal and the first number of training beams of the selected terminal is greater than the set maximum allowable number, and
A scheduling method comprising scheduling terminals to transmit simultaneously by repeating the selecting, generating, and excluding steps. In paragraph 10:
Defining a beam set obtained by combining the first number of training beams of each scheduled terminal,
Requesting feedback from each of the scheduled terminals, and receiving received signal strength and received phases of beams in the merged beam set from each terminal, and
Designing MMSE or ZF beamforming using the received signal strength and received phase of beams in the merged beam set of each scheduled terminal.
A scheduling method further comprising: A device for scheduling multiple terminals within a cell at a base station using multiple beams,
A transceiver that transmits a plurality of training beams and receives, from each of the plurality of terminals that have received the plurality of training beams, a reception interval and a beam index for each of the first number of training beams with the largest RSSI, and
Based on measurement information about the first number of training beams of each terminal, an RSSI table representing RSSIs of terminals and beam indices is generated, and the plurality of terminals are scheduled using the RSSI table according to the beamforming method of the base station. It includes a processor that
In order to perform the scheduling, the processor selects the terminal with the largest sum of squares of the RSSIs of the first number of training beams of each terminal among the terminals in the schedulable terminal set,
Excluding the selected terminal from the terminal set and excluding a first number of training beams of the selected terminal from the beam index set including the plurality of beams,
Among each terminal in the terminal set, exclude from the terminal set a terminal in which the number of beams overlapping between the first number of training beams of each terminal and the first number of training beams of the selected terminal is greater than the set maximum allowable number,
A scheduling device that schedules terminals to transmit simultaneously by repeating the selecting, generating, and excluding steps. In paragraph 12:
The measurement information includes received signal strength, received phase, and beam index for each of the first number of training beams. delete In paragraph 12:
The processor is a scheduling device for generating a transmission beam for maximum ratio transmission (MRT) beamforming by combining received signal strengths for the first number of training beams of each scheduled terminal. In paragraph 12:
The processor assigns a value of 0 to the received signal strength and received phase of the beams that did not receive feedback from each scheduled terminal among the beams in the beam set obtained by combining the first number of training beams of each scheduled terminal, A scheduling device that designs minimum mean square error (MMSE) or zero-forcing (ZF) beamforming or random beamforming using the received signal strength and received phase of all beams of each scheduled terminal. In paragraph 12:
The measurement information includes a received phase and a beam index for each of the first number of training beams, and a sum of received signal strengths of the first number of beams. In paragraph 17:
The processor schedules a set number of terminals based on the sum of the received signal strengths of the first number of training beams of each terminal in the schedulable terminal set, and determines the reception phase for the first number of training beams of each scheduled terminal. They are combined to generate a transmission beam for beamforming of the equal gain combining (EGC) method, and among the terminals in the terminal set, the first number of training beams of each terminal and the first number of the scheduled beams of each terminal are used. A scheduling device that excludes from the scheduling a terminal in which the number of beams overlapping between training beams is greater than a set maximum allowable number. In paragraph 12:
The measurement information includes a beam index for each of the first number of training beams and a sum of received signal strengths of the first number of training beams. In paragraph 19:
The processor schedules a set number of terminals based on the sum of the squares of the received signal strengths of the first number of training beams of each of the terminals in the schedulable terminal set, and schedules the first number of terminals among the terminals in the terminal set. Terminals in which the number of overlapping beams between training beams and the first number of training beams of each of the scheduled terminals is greater than the maximum allowable number are excluded from the scheduling, and a beam obtained by combining the first number of training beams of each of the scheduled terminals is excluded from the scheduling. The received signal strength and reception phase of the beams in the set are requested from each scheduled terminal and received from each scheduled terminal, and the received signal strength and reception phase of the beams in the merged beam set are received from each scheduled terminal. A scheduling device that designs MMSE or ZF beamforming or random beamforming using.

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