Wireless communication method and wireless communication system

Abstract

This wireless communication method uses dual connectivity of a plurality of transmission points and a user terminal. With this wireless communication method, generation of a wireless link is performed using at least one dynamic reflective plate between each of the plurality of transmission points and the user terminal. Meanwhile, with this wireless communication method, transmission, to the user terminal, of different data streams from each of the plurality of transmission points via the at least one dynamic reflective plate is performed.

Description

Technical Field

[0001] The present disclosure relates to a wireless communication method and a wireless communication system, and more particularly, to a wireless communication method and a wireless communication system using a dynamically controllable reflector.

Background Art

[0002] In recent years, a dynamically controllable reflector (RIS: Reconfigurable Intelligent Surface) has attracted attention. Hereinafter, in this specification, a dynamically controllable reflector is referred to as a dynamic reflector. The dynamic reflector can dynamically control the phase and amplitude of radio waves and artificially control the radio wave characteristics in the propagation path space.

[0003] On the other hand, in recent wireless communication systems, in order to achieve high speed in a planar manner, a method called CoMP (Coordinated Multipoint) that deploys a large number of transmission points and supports users from multiple transmission points has also attracted attention. In particular, Non-Patent Document 1 proposes to assist CoMP transmission with a dynamic reflector. Hereinafter, in this specification, a transmission method that uses a dynamic reflector to assist CoMP transmission is referred to as RIS-assisted CoMP transmission.

[0004] RIS-assisted CoMP transmission includes a first method schematically shown in FIG. 4 and a second method schematically shown in FIG. 5. The first method is a method that uses one transmission point and a plurality of dynamic reflectors. In the example shown in FIG. 4, two identical data streams A transmitted from one transmission point Tx are reflected by two dynamic reflectors RIS1 and RIS2 and transmitted to the user terminal UE. The second method is a method that uses a plurality of transmission points and one dynamic reflector. In the example shown in FIG. 5, the same data stream A transmitted separately from two transmission points TxA and TxB is reflected by a common dynamic reflector RIS and transmitted to the user terminal UE. In any method, the parameters of the dynamic reflector are controlled by a controller CR related to the transmission point.

[0005] According to RIS-assisted CoMP transmission, high effects can be expected in improving the received power of cell-edge users. However, although coverage improvement can be expected, there is room for improvement in communication capacity and communication speed in RIS-assisted CoMP transmission. Specifically, the data rate R achievable by the user terminal UE in RIS-assisted CoMP transmission is limited to a speed approximately equal to the data rate R_A of the data stream A.

[0006] In addition to Patent Document 1, the following Patent Documents 2 to 6 can be exemplified as documents showing the technical level at the time of filing in the technical field of the present disclosure.

Prior Art Documents

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a technology capable of improving coverage and also improving communication capacity and communication speed.

Means for Solving the Problems

[0009] To achieve the above object, the present disclosure provides a wireless communication method. The wireless communication method of the present disclosure is a wireless communication method using dual connectivity between a plurality of transmission points and a user terminal, and includes at least the following steps. The first step is to generate a wireless link between each of the plurality of transmission points and the user terminal using at least one dynamic reflector. The second step is to transmit different data streams from each of the plurality of transmission points to the user terminal via the at least one dynamic reflector.

[0010] To achieve the above object, the present disclosure provides a wireless communication system. The wireless communication system of the present disclosure includes a plurality of transmission points, a user terminal capable of communicating using dual connectivity, and a plurality of dynamic reflectors. A wireless link is generated between each of the plurality of transmission points and the user terminal using at least one of the plurality of dynamic reflectors. Then, different data streams are transmitted from each of the plurality of transmission points to the user terminal via the at least one dynamic reflector.

Advantages of the Invention

[0011] According to the wireless communication method and the wireless communication system according to the present disclosure, by using a dynamic reflector to assist communication using dual connectivity, it is possible to improve coverage and also improve communication capacity and communication speed.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0013] 1. Wireless communication system First, the configuration of a wireless communication system according to an embodiment of the present disclosure will be described with reference to FIG. 1. The wireless communication system 100 shown in FIG. 1 is a system that provides wireless communication using dual connectivity to user terminals UE within a service area.

[0014] The wireless communication system 100 includes two transmission points TxA and TxB. The two transmission points TxA and TxB are, for example, base stations that provide different wireless communications. In that case, the transmission point TxA may be a primary base station and the transmission point TxB may be a secondary base station. However, the frequency bands used by the two transmission points TxA and TxB may be the same frequency band, different frequency bands, or different frequency channels within the same frequency band. Note that the two transmission points TxA and TxB are connected by a backhaul line.

[0015] The wireless communication system 100 includes two dynamic reflectors RIS1 and RIS2. The dynamic reflectors RIS1 and RIS2 are electromagnetic wave reflectors composed of a large number of passive reflection elements. The reflection elements included in the dynamic reflectors RIS1 and RIS2 are composed of, for example, metamaterials whose characteristics can be dynamically changed. By appropriately changing the reflection characteristics of each reflection element, a wireless link that bypasses obstacles can be generated, and wireless communication that is not affected by obstacles can be realized. In the example shown in FIG. 1, the dynamic reflector RIS1 is used to generate a wireless link connecting the transmission point TxA and the user terminal UE. Also, the dynamic reflector RIS2 is used to generate a wireless link connecting the transmission point TxB and the user terminal UE.

[0016] The reflection characteristics of each of the dynamic reflectors RIS1 and RIS2 can be controlled by appropriately setting its parameters. The configurable parameters are, for example, phase and amplitude. In the example shown in FIG. 1, controllers CR-A and CR-B are provided for each of the dynamic reflectors RIS1 and RIS2. The controller CR-A sets the parameters of the dynamic reflector RIS1 based on an instruction from the transmission point TxA. The controller CR-B sets the parameters of the dynamic reflector RIS2 based on an instruction from the transmission point TxB. Note that the controller may be provided for each transmission point, for each dynamic reflector, or in a higher-level network.

[0017] A data stream A is transmitted from the transmission point TxA to the user terminal UE via the dynamic reflector RIS1. A data stream B different from the data stream A is transmitted from the transmission point TxB to the user terminal UE via the dynamic reflector RIS2. Thus, in the wireless communication system 100, the dynamic reflectors RIS1 and RIS2 are used with the help of dual connectivity transmission (DC transmission). Hereinafter, the transmission method newly proposed by the present disclosure, that is, the transmission method using a dynamic reflector with the help of DC transmission, is referred to as RIS-assisted DC transmission.

[0018] According to RIS-assisted DC transmission, both the coverage and the communication capacity and speed can be improved. For example, according to the RIS-assisted DC transmission realized in the system configuration shown in FIG. 1, when wireless resources are allocated based on the proportional fairness criterion, the downlink system throughput can be improved by about 1.5 times compared with the conventional DC transmission.

[0019] In the example shown in FIG. 1, there are two transmission points and one dynamic reflector per wireless link. However, the RIS-assisted DC transmission proposed in the present disclosure is also applicable to wireless communication systems with three or more transmission points or wireless communication systems with two or more dynamic reflectors per wireless link. Also, the dynamic reflectors may be shared among different wireless links. Further, in the wireless communication system that realizes the RIS-assisted DC transmission proposed in the present disclosure, not only one user terminal but also multiple user terminals can be supported.

[0020] 2. Wireless Communication Method Next, the wireless communication method realized in the above-described wireless communication system 100, that is, the wireless communication method using RIS-assisted DC transmission will be described with reference to the flowchart of FIG. 2. In this flowchart, the processes of the transmission points TxA, TxB, the dynamic reflectors RIS1, RIS2, and the user terminal UE, which are the components of the wireless communication system 100, and the signal exchanges between the components are shown in time series.

[0021] First, in step S101A, the transmission point TxA allocates a dynamic reflector (RIS) to the user terminal UE. Also, in step S101B, the transmission point TxB allocates a dynamic reflector to the user terminal UE. However, instead of the transmission points TxA and TxB, a higher-level network may allocate the dynamic reflectors corresponding to the respective transmission points TxA and TxB to the user terminal UE.

[0022] The method of allocating the dynamic reflector to the user terminal UE may use any method. For example, in the first method, each transmission point TxA, TxB (or network) sets the reflection direction for the dynamic reflector. Then, inspection signals are transmitted from each transmission point TxA, TxB to the user terminal UE via the dynamic reflector. If the user terminal UE can confirm the reception of the inspection signal, the dynamic reflector that can generate the radio link connecting the transmission points TxA, TxB and the user UE is allocated to the user UE.

[0023] As a second method of allocating the dynamic reflector to the user UE, each transmission point TxA, TxB (or network) may collect the location information of the user terminal UE and allocate the dynamic reflector closest to the user terminal UE. Or, a group of dynamic reflectors within a certain range from the user terminal UE may be identified and allocated to the user terminal UE collectively.

[0024] In the example shown in FIG. 2, the transmission point TxA allocates the dynamic reflector RIS1 to the user terminal UE, and the transmission point TxB allocates the dynamic reflector RIS2 to the user terminal UE. The allocation result is notified from each transmission point TxA, TxB (or network) to each dynamic reflector RIS1, RIS2.

[0025] Next, in step S102A, the parameters (RIS parameters) of the dynamic reflector RIS1 are set. Also, in step S102B, the parameters of the dynamic reflector RIS2 are set. Specifically, the parameters are phase and amplitude. The method and setting values of the parameters are arbitrary. For example, the channel between the transmission point passing through the dynamic reflector and the user terminal may be estimated, and the parameter setting values may be calculated using the estimated channel information, or the direction in which the dynamic reflector should reflect may be estimated using location information, etc.

[0026] Next, in step S103A, the user terminal UE is connected to the transmission point TxA by the exchange of connection signals between the transmission point TxA and the user terminal UE. Also, in step S103B, the user terminal UE is connected to the transmission point TxB by the exchange of connection signals between the transmission point TxB and the user terminal UE. These processes are called association.

[0027] After the association between the transmission point TxA and the user terminal UE is completed, in step S104A, the transmission point TxA transmits a reference signal for communication quality measurement to the user terminal UE. Also, after the association between the transmission point TxB and the user terminal UE is completed, in step S104B, the transmission point TxB transmits a reference signal for communication quality measurement to the user terminal UE.

[0028] In step S105A, the user terminal UE measures the SINR using the reference signal transmitted from the transmission point TxA. However, the communication quality to be measured is not limited to the SINR. The SNR, RSSI, or other communication quality may be measured, or multiple types of communication quality may be measured. Then, in step S106A, the user terminal UE transmits the communication quality measured in step S105A to the transmission point TxA.

[0029] Also, in step S105B, the user terminal UE measures the SINR using the reference signal transmitted from the transmission point TxB. The communication quality to be measured is not limited to the SINR, but it is preferable to measure the same type of communication quality between the transmission point TxB as that measured between the transmission point TxA. Then, in step S106B, the user terminal UE transmits the communication quality measured in step S105B to the transmission point TxB.

[0030] In step S107A, the transmission point TxA determines whether the user terminal UE is a DC user that should perform communication via DC transmission, based on the communication quality obtained in step S106A. For example, when the communication quality obtained in step S106A is equal to or higher than a preset threshold, the user terminal UE may be determined as a DC user for the transmission point TxA; otherwise, it may be determined that the user terminal UE is not a DC user.

[0031] Also, in step S107B, the transmission point TxB determines whether the user terminal UE is a DC user that should perform communication via DC transmission, based on the communication quality obtained in step S106B. For example, when the communication quality obtained in step S106B is equal to or higher than a preset threshold, the user terminal UE may be determined as a DC user for the transmission point TxB; otherwise, it may be determined that the user terminal UE is not a DC user.

[0032] Next, in step S108, the transmission points TxA and TxB perform communication using a backhaul line and share the determination result of step S107A and the determination result of step S107B. Then, in steps S109A and S109B, each of the transmission points TxA and TxB makes a final determination as to whether to regard the user UE as a DC user, using the information shared in step S108. The final determination is made according to the following table. According to this table, the user UE is determined as a DC user of the wireless communication system 100 only when the determination result of step S107A is yes and the determination result of step S107B is also yes.

Table 1

[0033] Next, in step S110A, the transmission point TxA performs scheduling to calculate time resources to be allocated to the user terminal UE. Similarly, in step S110B, the transmission point TxB performs scheduling to calculate time resources to be allocated to the user terminal UE.

[0034] In scheduling, for each dynamic reflector (r) at each transmission point (j) and for each user (u), a schedule time ratio δ that is globally optimized for the entire system is calculated. Note that the parameters used in scheduling are defined as shown in the following table.

Table 2

[0035] In scheduling, parameters that maximize the sum of transmission rates are calculated using the following objective function P1.

Equation

[0036] In the calculation of the objective function P1, the fairness index α may be set in advance, or the objective function P1 may be calculated including the determination of the index α. If the index α is 1, it is proportional fairness, and if the index α is made infinite, it becomes Max-Min fairness. Increasing the index α improves the minimum data rate of the system.

[0037] In the calculation of the objective function P1, for the calculation of the schedule time ratio δ, for example, the following scheduling formula derived using the Karush-Kuhn-Tucker conditions is used.

Equation

[0038] The link rate l is calculated using the communication quality obtained in steps S105A and S105B. For example, the Shannon capacity formula is used. The association variables x and d are obtained in steps S101A, S101B, and S108. Among the obtained results, trials are made to associate or not associate, and the association variables x and d that maximize the objective function P1 are finally determined. β and θ are those obtained in steps S102A and 102B and are used.

[0039] Also, in the above objective function P1, the transmission rate per user terminal is represented by the following formula.

Equation

[0040] Note that the following two formulas are the setting conditions for the scheduling time ratio.

Equation

Equation

[0041] Also, the setting conditions for each parameter are as follows.

Equation

Equation

Equation

Equation

Equation

[0042] After the completion of the scheduling at both transmission points TxA and TxB, in step S111, the transmission points TxA and TxB communicate using a backhaul line and share the scheduling result of step S110A and the scheduling result of step S110B. Then, based on the ratio of the transmission rates assigned by each transmission point TxA and TxB to the user terminal UE, the transmission information to be transmitted to the user terminal UE is distributed to each of the transmission points TxA and TxB. The transmission rate is calculated as a value obtained by multiplying the data rate calculated from the communication quality (SINR) between the transmission point and the user terminal by the time resource assigned by the transmission point to the user terminal. Also, in step S111, synchronization processing is executed between the transmission points TxA and TxB as necessary.

[0043] Finally, in step S112A, the transmission point TxA transmits the transmission information distributed to the transmission point TxA in step S111 to the user terminal UE using the time resource assigned by the transmission point TxA to the user terminal UE in step S110A. Also, in step S112B, the transmission point TxB transmits the transmission information distributed to the transmission point TxB in step S111 to the user terminal UE using the time resource assigned by the transmission point TxB to the user terminal UE in step S110B.

[0044] FIG. 3 is a diagram showing an example of a timeline according to the above-described wireless communication method. In this timeline, the number of user terminals UE existing in the service area is five, namely, ♯1, ♯2, ♯3, ♯4, and ♯5. Among these, user terminals UE♯1 and UE♯2 are both connected to transmission points TxA and TxB, and wireless communication is performed between transmission points TxA and TxB by DC transmission, more specifically, RIS-assisted DC transmission. User terminals UE♯3 and UE♯4 are each connected only to transmission point TxA, and wireless communication using RIS is performed between the transmission point TxA and the user terminals. User terminal UE♯5 is connected only to transmission point TxB, and wireless communication using RIS is performed between the transmission point TxA and the user terminal. As shown in FIG. 3, scheduling is performed so that signals are transmitted from each of transmission points TxA and TxB at an overall optimized time ratio, including user terminals UE♯1 and UE♯2 that perform DC transmission and user terminals UE♯3, UE♯4, and UE♯5 that do not perform DC transmission.

[0045] 3. Others The above embodiments can be variously modified and implemented without departing from the gist of the present disclosure. That is, when numbers such as the number, quantity, amount, and range of each element are mentioned in the above embodiments, unless otherwise specifically stated or clearly specified by the principle, the technology according to the present disclosure is not limited to the mentioned numbers. Also, the structures and the like described in the above embodiments are not necessarily essential to the technology according to the present disclosure, unless otherwise specifically stated or clearly specified by the principle.

Explanation of Reference Numerals

[0046] 100 Wireless communication system TxA, TxB Transmission points UE User terminal RIS1, RIS2 Dynamic reflectors CR-A, CR-B Controllers

Claims

1. A wireless communication method using dual connectivity between a plurality of transmission points and a user terminal, comprising: generating a wireless link between each of the plurality of transmission points and the user terminal using at least one dynamic reflector; transmitting different data streams from each of the plurality of transmission points to the user terminal via the at least one dynamic reflector; allocating transmission information to be transmitted to the user terminal to the different data streams transmitted from each of the plurality of transmission points. A wireless communication method characterized by the above.

2. The wireless communication method according to Claim 1, further comprising: measuring the communication quality between each of the plurality of transmission points and the user terminal via the at least one dynamic reflector; performing communication using the dual connectivity to the user terminal upon receiving confirmation that the communication quality exceeds a threshold at all of the plurality of transmission points. A wireless communication method characterized by the above.

3. The wireless communication method according to Claim 2, wherein confirmation that the communication quality exceeds the threshold at all of the plurality of transmission points is performed by sharing the confirmation results of the communication quality obtained at each of the plurality of transmission points among the plurality of transmission points. A wireless communication method characterized by the above.

4. The wireless communication method according to any one of Claims 1 to 3, further comprising: calculating time resources to be allocated to the user terminal by each of the plurality of transmission points; allocating the transmission information to each of the different data streams based on the time resources allocated to the user terminal by each of the plurality of transmission points. A wireless communication method characterized by the above.

5. The wireless communication method according to Claim 4, wherein allocating the transmission information to each of the different data streams includes allocating based on the communication quality between each of the plurality of transmission points and the user terminal via the at least one dynamic reflector. A wireless communication method characterized by the above.

6. The wireless communication method according to Claim 4 or 5, wherein allocating the transmission information to each of the different data streams is performed by sharing the time resources allocated to the user terminal by each of the plurality of transmission points among the plurality of transmission points. A wireless communication method characterized by the above.

7. In the wireless communication method according to any one of Claims 4 to 6, after performing synchronization processing among the plurality of transmission points, each of the plurality of transmission points transmits the different data streams to which the transmission information is allocated using time resources allocated to the user terminal. The wireless communication method is characterized by the above.

8. A plurality of transmission points, A user terminal capable of communicating using dual connectivity, A plurality of dynamic reflectors, and A wireless link is generated between each of the plurality of transmission points and the user terminal using at least one of the plurality of dynamic reflectors, Different data streams are transmitted from each of the plurality of transmission points to the user terminal via the at least one dynamic reflector, The transmission information transmitted to the user terminal is allocated to the different data streams transmitted from each of the plurality of transmission points. The wireless communication system is characterized by the above.

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