Wireless communication method, wireless communication system, base station device, and relay device

Abstract

To provide a radio communication method, a radio communication system, a base station device, and a repeating device, capable of restricting communication efficiency degradation.SOLUTION: A radio communication method in a radio communication system 1 includes an acquisition step, an allocation step, and a reflection control step. The acquisition step is a step for acquiring moving information for each of mobile terminals 4. The allocation step is a step for allocating at least one of repeating devices 5 to one of the mobile terminals 4. Each of the repeating devices 5 is a device capable of repeating a radio signal carrying radio communication between a base station deice 3 and each of the mobile terminals 4 by reflection. The reflection control step is a step that the repeating device 5 allocated to either one mobile terminal 4 in the allocation step controls reflection of radio signal so as to track moving of the mobile terminal 4 based on the moving information of the mobile terminal 4 acquired in the acquisition step.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a wireless communication method, a wireless communication system, a base station device, and a relay device. [Background technology]

[0002] Non-Patent Document 1 discloses an example of a wireless communication system. In the wireless communication system, wireless communication is performed by radio signals between a base station device and each of a plurality of terminals. In the wireless communication system, a plurality of relay devices are provided that relay the radio signals between the base station device and the terminals by reflecting them. Each relay device controls the direction of reflection of the radio signals by shifting the phase of the incoming wave with a number of reflecting elements. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Qin Tao, Shuowen Zhang, Caijun Zhong and Rui Zhang, "Intelligent Reflecting Surface Aided Multicasting With Random Passive Beamforming," IEEE Wireless Communications Letters, Volume 10, Issue 1, January 2021. Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the wireless communication system of Non-Patent Document 1, training data for a terminal to wirelessly communicate with a base station device is transmitted every time the relay device changes the control state of reflection. On the other hand, if the control state of reflection by the relay device does not change, the destination of the terminal may be outside the range of wireless communication by radio signals. For this reason, if the relay device frequently changes the control state of reflection when a base station device wirelessly communicates with a moving terminal in the wireless communication system of Non-Patent Document 1, the overhead due to the training data becomes large, and the communication efficiency of the wireless communication system may decrease.

[0005] The present disclosure is directed to solving such problems. The present disclosure provides a wireless communication method, a wireless communication system, a base station device, and a relay device that can suppress a decrease in communication efficiency. [Means for solving the problem]

[0006] The wireless communication method according to the present disclosure includes an acquisition step of acquiring movement information of each of a plurality of mobile terminals; an assignment step of assigning at least one of a plurality of relay devices capable of relaying by reflection a radio signal that carries out wireless communication between a base station device and each of the plurality of mobile terminals to one of the plurality of mobile terminals; and a reflection control step in which a relay device among the plurality of relay devices assigned to one of the plurality of mobile terminals in the assignment step controls the reflection of the radio signal to follow the movement of the mobile terminal based on the movement information of the mobile terminal acquired in the acquisition step.

[0007] The wireless communication system according to the present disclosure comprises a base station device and a plurality of relay devices capable of relaying by reflection a radio signal that carries out wireless communication between the base station device and each of a plurality of mobile terminals, the base station device assigns at least one of the plurality of relay devices to one of the plurality of mobile terminals, and a relay device among the plurality of relay devices assigned to one of the plurality of mobile terminals controls the reflection of the radio signal to follow the movement of the mobile terminal.

[0008] A base station device according to the present disclosure includes a communication unit that transmits and receives radio signals that handle wireless communication with each of a plurality of mobile terminals, and an allocation unit that assigns to one of the plurality of mobile terminals at least one of a plurality of relay devices that are capable of relaying the radio signal by controlling the reflection of the radio signal so as to follow the movement of the mobile terminal between an assigned mobile terminal among the plurality of mobile terminals and the communication unit.

[0009] The relay device of the present disclosure includes a reflector that relays by reflection a radio signal that carries out wireless communication between a mobile terminal assigned by a base station device among a plurality of mobile terminals and the base station device, and a reflection control unit that controls the reflection of the radio signal by the reflector between the base station device and the mobile terminal so as to follow the movement of the mobile terminal based on movement information of the assigned mobile terminal obtained from the mobile terminal among the plurality of mobile terminals. Effect of the Invention

[0010] According to the wireless communication method, wireless communication system, base station device, or relay device disclosed herein, a decrease in communication efficiency is suppressed. [Brief description of the drawings]

[0011] [Figure 1] 1 is a configuration diagram of a wireless communication system according to a first embodiment. [Diagram 2] 1 is a functional block diagram of a wireless communication system according to a first embodiment. [Diagram 3] 3 is a diagram illustrating an example of control of a beam of a radio signal in the radio communication system according to the first embodiment. FIG. [Figure 4] FIG. 2 is a diagram showing an example of allocation in the wireless communication system according to the first embodiment. [Diagram 5] FIG. 2 is a diagram illustrating a model for predicting movement of a mobile terminal in the wireless communication system according to the first embodiment. [Figure 6] 5 is a flowchart showing an example of the operation of the wireless communication system according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The embodiments of the present disclosure will be described with reference to the accompanying drawings. In each drawing, the same or corresponding parts are given the same reference numerals, and duplicated descriptions are appropriately simplified or omitted. Note that the present disclosure is not limited to the following embodiments, and the embodiments may be freely combined, any component of each embodiment may be modified, or any component of each embodiment may be omitted, within the scope of the gist of the present disclosure.

[0013] Embodiment 1 FIG. 1 is a configuration diagram of a wireless communication system 1 according to the first embodiment.

[0014] The wireless signal of the wireless communication system 1 includes, for example, a high-frequency band signal including a millimeter wave or a terahertz wave. Here, since the high-frequency band signal has a high linearity, it is important to deal with the wireless communication system 1 in terms of blocking the wireless signal by a blocking object. There are multiple blocking objects in the communication range in which the wireless communication of the wireless communication system 1 of this example is performed. In this example, the multiple blocking objects include a blocking object 2a, a blocking object 2b, and a blocking object 2c. Here, when there is no need to distinguish between these blocking objects, they are simply referred to as a blocking object 2. The blocking object 2 is an object that blocks the wireless signal of the wireless communication system 1. The blocking object 2 may be, for example, a fixed object such as a building, or a moving object such as a vehicle.

[0015] The wireless communication system 1 includes a base station device 3. The base station device 3 has a function for transmitting and receiving wireless signals. The base station device 3 has a function for generating a beam that concentrates wireless signals in a desired direction, for example, by an array antenna. The wireless communication system 1 is responsible for wireless communication between the base station device 3 and multiple mobile terminals.

[0016] In this example, the multiple mobile terminals include a mobile terminal 4a, a mobile terminal 4b, and a mobile terminal 4c. Here, when there is no need to distinguish between these mobile terminals, they are simply referred to as a mobile terminal 4. The mobile terminal 4 is a mobile terminal device equipped with a wireless communication function. The mobile terminal 4 is, for example, a portable information terminal such as a smartphone, a tablet computer, or a laptop computer. At this time, the mobile terminal 4 moves with the user by being carried by the user who owns the mobile terminal 4. Alternatively, the mobile terminal 4 may be a communication module in a device equipped with a moving function such as an automatic driving car or a drone. At this time, the mobile terminal 4 moves by itself using the moving function, autonomously or according to remote control by an operator.

[0017] The wireless communication system 1 includes a plurality of relay devices. In this example, the plurality of relay devices include relay device 5a, relay device 5b, relay device 5c, relay device 5d, and relay device 5e. Here, when there is no need to distinguish between these relay devices, they are simply referred to as relay device 5. The relay device 5 is disposed in a communication range in which wireless communication by the wireless communication system 1 is performed so as to be able to relay a wireless signal propagating between the base station device 3 and the mobile terminal 4. The relay device 5 relays, for example, a wireless signal transmitted from the base station device 3 to the mobile terminal 4 by reflecting it. The relay device 5 is equipped with a function of dynamically controlling reflection characteristics such as the reflection direction of an incoming wave, for example, by shifting the phase of the incoming wave by a plurality of reflecting elements. In the relay device 5, such a function of dynamic control of reflection characteristics is implemented by a device such as an IRS (Intelligent Reflecting Surface). In the wireless communication system 1, some or all of the relay devices 5 are assigned to any of the mobile terminals 4. The relay device 5 relays a wireless signal propagating between the assigned mobile terminal 4 and the base station device 3 by reflection. In the wireless communication system 1, some or all of the relay devices 5 may be in an unused state in which they are not assigned to any mobile terminal 4. In the wireless communication system 1, multiple relay devices 5 may be assigned to a single mobile terminal 4.

[0018] In the wireless communication system 1 of this example, the base station device 3 performs multi-beam transmission. In this case, since a propagation path can be formed via a plurality of relay devices 5 at the same time, the effect of spatial multiplexing or spatial diversity can be obtained. Alternatively, in the wireless communication system 1, the base station device 3 may perform single-beam transmission. In this case, for a mobile terminal 4 to which a plurality of relay devices 5 are assigned, the base station device 3 selects one path by a beam from among a plurality of route candidates via the plurality of relay devices 5 assigned to the mobile terminal 4. In addition, the base station device 3 may directly communicate with the mobile terminal 4 without going through the relay device 5. The base station device 3 may perform multi-user transmission by multi-beam transmission.

[0019] In this example, the mobile terminal 4 is equipped with a function of estimating CSI (Channel State Information) based on, for example, a reference signal transmitted from the base station device 3. Here, the CSI of a wireless channel through which a wireless signal has propagated from the base station to the mobile terminal 4 represents information on the wireless channel, such as the amount of phase rotation and the amount of attenuation. The base station device 3 is equipped with a function of acquiring the CSI estimated by the mobile terminal 4. The estimation of CSI by the mobile terminal 4 and the control of the beam of the wireless signal based on the estimated CSI are performed, for example, as follows.

[0020] The base station device 3 generates a beam by sequentially changing the output direction of the radio signal so as to scan, and transmits a reference signal for each beam. The relay device 5 controls the reflection characteristics so as to scan the reflection direction for each beam transmitted by the base station device 3. The mobile terminal 4 observes the received power for each beam resulting from a combination of the output direction from the base station device 3 and the reflection direction at the relay device 5, and estimates the CSI. The mobile terminal 4 selects a beam to be used for communication based on the observed received power and the like. The mobile terminal 4 feeds back information on the selected beam and the estimated CSI and the like to the base station device 3 and the relay device 5 and the like. The wireless communication system 1 performs wireless communication with the mobile terminal 4 through the selected channel based on the information fed back from the mobile terminal 4. In this example, the mobile terminal 4 estimates the CSI of the wireless channel for direct communication with the base station device 3 and the CSI of the wireless channel for communication with the base station device 3 via the relay device 5.

[0021] When the beam of the radio signal is controlled in this manner, the mobile terminal 4 selects a beam to be used for communication from among the radio channels equal to the product of the number of relay devices 5 and the number of reflection directions scanned by each relay device 5. For this reason, if the beam of the radio signal based on the CSI is frequently controlled in this manner, the control overhead increases, decreasing the communication efficiency of the wireless communication system 1.

[0022] In addition, the base station device 3 is equipped with a function for acquiring movement information of each mobile terminal 4. The movement information of a mobile terminal 4 is information that represents the movement of the mobile terminal 4. The movement information of a mobile terminal 4 includes, for example, the movement direction, movement speed, and position of the mobile terminal 4.

[0023] The base station device 3 also has a function of acquiring information about each relay device 5. The information about the relay device 5 includes, for example, information about the position of the relay device 5, information about the state of reflection control of the relay device 5, and the like.

[0024] FIG. 2 is a functional block diagram of the wireless communication system 1 according to the first embodiment.

[0025] The base station device 3 includes a first communication unit 6, a first acquisition unit 7, a second acquisition unit 8, a third acquisition unit 9, an estimation unit 10, and an allocation unit 11.

[0026] The first communication unit 6 is a part that has a function of communicating with the mobile terminal 4 and the relay device 5. The first communication unit 6 includes, for example, an array antenna. The first communication unit 6 has, for example, a function of transmitting and receiving wireless signals.

[0027] The first acquisition unit 7 is a part that has a function of acquiring CSI. The first acquisition unit 7 acquires, for example, CSI estimated by the mobile terminal 4 or the like from the mobile terminal 4 via the first communication unit 6.

[0028] The second acquisition unit 8 is a part that acquires information of each relay device 5. The second acquisition unit 8 acquires the position of each relay device 5, for example, by reading information stored in advance in the base station device 3 or the like. Alternatively, the second acquisition unit 8 may acquire the position of the relay device 5 from a relay device 5 equipped with a self-position estimation function via the first communication unit 6 or the like. The self-position estimation function equipped in the relay device 5 may be implemented, for example, by a satellite positioning system or may be implemented by a positioning technology using a wireless signal of the wireless communication system 1.

[0029] The third acquisition unit 9 is a part that acquires the movement information of each mobile terminal 4. The third acquisition unit 9 acquires the position of the mobile terminal 4 from the mobile terminal 4 equipped with a function of self-location estimation through the first communication unit 6 or the like. At this time, the function of self-location estimation equipped in the mobile terminal 4 may be implemented, for example, by a satellite positioning system or may be implemented by a positioning technology using a wireless signal of the wireless communication system 1. In addition, the third acquisition unit 9 acquires information on the motion state of the mobile terminal 4 from the mobile terminal 4 equipped with a function of estimating its own motion state through the first communication unit 6 or the like. The information on the motion state of the mobile terminal 4 includes, for example, the moving direction and moving speed of the mobile terminal 4. At this time, the function of estimating its own motion state equipped in the mobile terminal 4 may be implemented, for example, by a sensor equipped in the mobile terminal 4.

[0030] The estimation unit 10 is a part equipped with a function of calculating a probability distribution for estimating a destination of the mobile terminal 4 at a time after the current time. The estimation unit 10 calculates the probability distribution based on the movement information of each mobile terminal 4 acquired by the third acquisition unit 9, etc.

[0031] The allocation unit 11 is a part that has a function of allocating some or all of the multiple relay devices 5 to any of the mobile terminals 4. The allocation unit 11 generates multiple allocation patterns that represent the correspondence between the relay devices 5 and the mobile terminals 4. Here, in any of the generated allocation patterns, there may be an available relay device 5 that is not allocated to any of the mobile terminals 4. The allocation unit 11 calculates the communication performance for the generated allocation pattern based on the probability distribution calculated by the estimation unit 10. The communication performance includes at least one of the visibility probability that represents the probability that there is a wireless channel available between the base station device 3 and the mobile terminal 4, and the throughput. The allocation unit 11 allocates the relay devices 5 by selecting an allocation pattern based on the calculated communication performance from among the generated allocation patterns.

[0032] Each relay device 5 includes a second communication unit 12 , a reflector 13 , a tracking unit 14 , and a reflection control unit 15 .

[0033] The second communication unit 12 is a part that includes a function for communicating with the base station device 3 and the relay device 5. The second communication unit 12 includes, for example, an antenna. The second communication unit 12 includes, for example, a function for transmitting and receiving wireless signals.

[0034] The reflector 13 is a portion that reflects a radio signal. The reflector 13 includes a device such as an IRS.

[0035] The tracking unit 14 is a part equipped with a function of tracking the movement route of the mobile terminal 4. The tracking unit 14 tracks the movement route of the mobile terminal 4 based on movement information acquired about the mobile terminal 4. The tracking unit 14 acquires, for example, the position of the mobile terminal 4 from the mobile terminal 4 equipped with a function of acquiring its own movement information through the second communication unit 12 or the like. Alternatively, the tracking unit 14 may acquire, for example, the movement information acquired from the mobile terminal 4 by the second acquisition unit 8 of the base station device 3 from the base station device 3 through the second communication unit 12 or the like.

[0036] The reflection control unit 15 is a part equipped with a function of controlling the reflection characteristics of the reflector 13. The reflection control unit 15 dynamically controls the reflection characteristics of the reflector 13 so that the wireless signal transmitted from the base station device 3 is reflected in the direction of the moving object to which the relay device 5 is assigned. At this time, the reflection control unit 15 controls the reflection characteristics so that the reflection of the wireless signal by the reflector 13 follows the movement of the moving object. In this example, the reflection control unit 15 controls the reflection characteristics so that the reflection of the wireless signal by the reflector 13 follows the movement path of the moving object tracked by the tracker 14.

[0037] FIG. 3 is a diagram showing an example of control of a beam of a radio signal in the radio communication system 1 according to the first embodiment.

[0038] The allocation unit 11 of the base station device 3 repeatedly allocates relay devices 5 in a set allocation period. The length of the allocation period corresponds to an update interval of the allocation of relay devices 5. In this example, when the allocation unit 11 performs allocation, the first acquisition unit 7 acquires CSI estimated by the mobile terminal 4. The allocation unit 11 allocates relay devices 5 using the CSI acquired by the first acquisition unit 7. In this example, the process of estimating CSI is performed in a set allocation period. The allocation unit 11 notifies the results of the allocation to each relay device 5 and each mobile terminal 4, for example, via the first communication unit 6.

[0039] The reflection control unit 15 of the relay device 5 assigned to the mobile terminal 4 by the assignment unit 11 controls the reflection characteristics of the reflector 13 so that the reflection direction of the radio signal follows the position of the mobile terminal 4. Thereafter, in the wireless communication system 1, data communication is performed between the base station device 3 and the mobile terminal 4 by radio signals relayed by the relay device 5 or the like.

[0040] The tracking unit 14 of the relay device 5 assigned to the mobile terminal 4 by the assignment unit 11 tracks the moving route of the mobile terminal 4. The tracking unit 14 continues to track the moving route of the mobile terminal 4 until the assignment of the multiple relay devices 5 by the assignment unit 11 is updated. The tracking unit 14 acquires moving information of the mobile terminal 4 at a set frequency, for example. The tracking unit 14 updates the moving route of the mobile terminal 4 based on the acquired moving information. The reflection control unit 15 dynamically controls the reflection characteristics of the reflector 13 based on the updated moving route so that the reflecting direction of the wireless signal follows the position of the mobile terminal 4. Thereafter, in the wireless communication system 1, data communication is performed by wireless signals between the base station device 3 and the mobile terminal 4 through relaying by the relay device 5 or the like.

[0041] In this way, in the wireless communication system 1, the relay device 5 assigned to the mobile terminal 4 dynamically controls the reflection characteristics of the reflector 13 so as to track the movement of the mobile terminal 4. This makes it possible to lengthen the cycle of processing such as CSI estimation, which involves large overhead, while suppressing the possibility that the mobile terminal 4 will go out of the communication range. Since the overhead of CSI estimation and the like is reduced, the decrease in communication efficiency of the wireless communication system 1 is suppressed.

[0042] On the other hand, while the relay device 5 is tracking the movement of a specific mobile terminal 4, the relay device 5 does not relay radio signals to other mobile terminals 4, so the other mobile terminals 4 cannot recognize the relay device 5. Therefore, the other mobile terminals 4 cannot estimate the CSI of the radio channel that passes through the relay device 5. Therefore, during the allocation period from when an allocation is made by the allocation unit 11 to when the next allocation is made, the relay device 5 cannot switch the mobile terminal 4 to be tracked. Therefore, the allocation unit 11 performs allocation using a probability distribution that estimates the destination of each mobile terminal 4 so that the mobile terminal 4 can use one of the radio channels even if the mobile terminal 4 moves during the allocation period.

[0043] In addition, while the relay device 5 is tracking the movement of a specific mobile terminal 4, if the wireless channel passing through the relay device 5 is blocked by the obstruction 2, the mobile terminal 4 may continue wireless communication with the base station device 3 using an available relay device 5. In other words, the available relay device 5 functions as a backup.

[0044] FIG. 4 is a diagram showing an example of allocation in the wireless communication system 1 according to the first embodiment.

[0045] In this example, relay device 5b and relay device 5c are assigned to mobile terminal 4a. Relay device 5d is assigned to mobile terminal 4c. Relay devices 5a and 5e are not assigned to any mobile terminal 4 and are in an unused state.

[0046] At this time, the mobile terminal 4a performs wireless communication with the base station device 3 through a wireless channel that passes through the relay device 5b and a wireless channel that passes through the relay device 5c. The mobile terminal 4c performs wireless communication with the base station device 3 through a wireless channel for direct communication that does not pass through the relay device 5, and a wireless channel that passes through the relay device 5d.

[0047] On the other hand, when the mobile terminal 4b moves to the position shown in Fig. 4, the wireless channel for direct communication that does not go through the relay device 5 is blocked by the shield 2b, and the wireless channel that goes through the relay device 5e is blocked by the shield 2c. At this time, the wireless communication between the mobile terminal 4b and the base station device 3 is cut off because there is no available wireless channel. At this time, if the relay device 5c is assigned to the mobile terminal 4b or the relay device 5c is available, the wireless channel that goes through the relay device 5c is not blocked by the shield 2, and the communication cutoff is avoided. The allocation unit 11 performs allocation using a probability distribution that estimates the destination of the mobile terminal 4 so as to avoid a situation in which such a communication cutoff may occur.

[0048] FIG. 5 is a diagram illustrating a model for predicting the movement of the mobile terminal 4 in the wireless communication system 1 according to the first embodiment.

[0049] In the wireless communication system 1 of this example, K mobile terminals 4 and N relay devices 5 are recognized as targets of allocation. Here, the K mobile terminals 4 and N relay devices 5 will be described using numbers sequentially assigned to each of them.

[0050] The estimation unit 10 calculates a probability distribution for estimating the destination of the mobile terminal 4 by modeling the movement of the mobile terminal 4. The estimation unit 10 estimates the destination from time t=0 to time t=T0. Here, time t=0 is the time immediately after an allocation is performed by the allocation unit 11. Also, time t=T0 is the time immediately before the next allocation is performed by the allocation unit 11. In this example, if the time corresponding to the overhead of the allocation process by the allocation unit 11 is subtracted from the allocation period, it corresponds to the time from time t=0 to time t=T0. The estimation unit 10 calculates a probability distribution of the location of the mobile terminal 4 at each of the times obtained by dividing the time from time t=0 to time t=T0 into multiple parts. Here, at the mth time point t m t m = mΔt, and at the Mth time point t M t M =MΔt=T0. The position of the kth mobile terminal 4 at the mth time point is expressed by the position vector r k,m =[x k,m ,y k,m ] T In this example, the origin of the position vector is taken as the position of the base station device 3 or the position of any relay device 5. Also, the velocity of the k-th mobile terminal 4 at the m-th time point is expressed by the velocity vector v k,m It is represented by:

[0051] In this example, the estimation unit 10 models the movement of each mobile terminal 4 by the Ornstein-Uhlenbeck process. m The speed v of the kth mobile terminal 4 in k,m Let, be the previous time t m-1 Velocity v at k,m-1 The drift component inherited from the previous equation is added with a random component, and is expressed as follows:

[0052]

number

[0053] Here, the coefficient α is a parameter that represents the proportion of the velocity component that is carried over from the previous time as the drift component. The parameter σ represents the magnitude of the random component. The vector w k,m-1 follows an isotropic two-dimensional Gaussian distribution with mean 0 and the identity matrix as its covariance matrix.

[0054] Using such a model, the estimation unit 10 calculates, as a probability distribution, a probability density function f k,m (r) is calculated using the following formula (2).

[0055]

number

[0056] Here, the probability density function f k,m (r) is the probability density function φ for each direction, assuming that the movements in the x and y directions are independent of each other. k,m (z), where the variable z represents either the x-coordinate or the y-coordinate of the mobile terminal 4. k,0 (z) and v k,0 (z) represents the x or y component of the position and velocity of the k-th mobile terminal 4 at time t0. In this manner, the estimation unit 10 calculates the probability distribution of the destination of each mobile terminal 4 at each time point between time t=0 and time t=T0.

[0057] The allocation unit 11 uses the probability distribution calculated by the estimation unit 10 to calculate the visibility probability, for example, as follows. m The expected value E[P n,k,LoS (t m )] is calculated using the following formula (3).

[0058]

number

[0059] Here, the position vector r n is a position vector whose origin is the position of the nth relay device 5. That is, the probability f k,m (r n )dx n dy n is the time t m The kth mobile terminal 4 is at position r n Area element dx around n dy n The parameter ψ corresponds to the density of the occlusion 2. The parameter ψ is, for example, the average density when the distribution of the occlusion 2 is modeled by a two-dimensional Poisson point process. The parameter ψ has the dimension of the inverse of the area. The expected value E[l k ] is the expected value of the length of the occlusion 2. The expected value E[l k ] is given in advance as a parameter, for example. m The expected value E[P B,k,LoS (t m )] is calculated in the same manner as in equation (3).

[0060] The allocation unit 11 calculates the visibility probability for the generated allocation pattern as the communication performance of the wireless communication system 1. For the k-th mobile terminal 4, the allocation unit 11 calculates the non-line-of-sight probability P B,k is calculated as follows:

[0061]

number

[0062] Here, the set N a (t m ) at time t m In equation (4), the product (*1) represents a set of relay devices 5 that are in an idle state and are not assigned to any mobile terminal 4 at time tm The product (*1) is the probability that the radio signal between the nth relay device 5 and the kth mobile terminal 4 is blocked by the obstacle 2 at time t m represents the probability that there will be no relay device 5 available for the kth mobile terminal 4 to use in the time period from time t=0 to time t=T0. Moreover, the product (*2) is obtained by multiplying the probability of the complementary event of the product (*1) for the time period from time t=0 to time t=T0. In other words, the product (*2) represents the probability that there is at least one relay device 5 available for the kth mobile terminal 4 to use in the time period from time t=0 to time t=T0. Moreover, the product (*3) represents the probability that there will be no relay device 5 available for the kth mobile terminal 4 to use in the time period from time t m The probability that the wireless signal between the base station device 3 and the kth mobile terminal 4 is not blocked by the obstruction 2 during the time period from time t=0 to time t=T0 is multiplied by the probability that the wireless signal between the base station device 3 and the kth mobile terminal 4 is not blocked by the obstruction 2 during the time period from time t=0 to time t=T0. In other words, the product (*3) represents the probability that the kth mobile terminal 4 can communicate with the base station device 3 through a wireless channel for direct communication that does not go through the relay device 5 during the time period from time t=0 to time t=T0. Therefore, the non-line-of-sight probability P B,k corresponds to the probability that all wireless channels available to the kth mobile terminal 4 are blocked by the obstruction 2 at least at any time between time t=0 and time t=T0. B,k The probability of the complementary event for (1-P B,k ) is the visibility probability for the kth mobile terminal 4. In this example, the allocation unit 11 calculates the average value of the visibility probabilities over the K mobile terminals 4 as the communication performance of the wireless communication system 1. In general, the more relay devices 5 that are in an idle state in an allocation pattern, the more relay devices 5 that can be used as backups, and therefore the visibility probability as a communication performance tends to be higher.

[0063] Furthermore, the allocation unit 11 calculates the throughput for the generated allocation pattern as the communication performance of the wireless communication system 1. The allocation unit 11 calculates the expected value E[γ k ] is calculated using the following formula (5).

[0064]

number

[0065] Here, the set N k (t m ) at time t m represents a set of relay devices 5 assigned to the k-th mobile terminal 4 in the k-th mobile terminal 4. B,k represents the received power at the k-th mobile terminal 4 for a wireless channel in direct communication that does not go through the relay device 5. n,k represents the received power at the kth mobile terminal 4 for the wireless channel passing through the nth relay device 5. The received power information is acquired from each mobile terminal 4, for example, via the first communication unit 6, when the first acquisition unit 7 acquires CSI from the mobile terminal 4. That is, the first term (*4) in the numerator represents the strength of the signal through the wireless channel by direct communication that does not pass through the relay device 5. Furthermore, the second term (*5) in the numerator represents the strength of the signal through the wireless channel that passes through the relay device 5. Furthermore, T, E[I], and σ th 2 represent the slot length, the expected value of interference power, and thermal noise, respectively. In this example, the allocation unit 11 calculates the average value of the throughput across K mobile terminals 4 as the communication performance of the wireless communication system 1. In general, the fewer the relay devices 5 that are in an idle state in the allocation pattern, the more relay devices 5 each mobile terminal 4 can use, on average, which enables large-capacity communication by multi-beam transmission or the like. In other words, the throughput as a communication performance tends to be higher.

[0066] In this way, there is a trade-off between the visibility probability and the throughput as communication performance with respect to the allocation of the relay device 5. For this reason, the allocation unit 11 selects an allocation pattern to be adopted from among the multiple allocation patterns V generated by multi-objective optimization as shown in the following equation (6).

[0067]

number

[0068] Here, F1(V) is an objective function corresponding to the visibility probability. Furthermore, F2(V) is an objective function corresponding to the throughput. The allocation unit 11 selects an allocation pattern to be adopted from among the weakly Pareto optimal allocation patterns for these objective functions. For example, the allocation unit 11 may select the weakly Pareto optimal allocation pattern that is found earliest, or may select one of the allocation patterns by imposing an additional condition on the weakly Pareto optimal allocation patterns that are found.

[0069] Next, an example of the operation of the wireless communication system 1 will be described with reference to FIG. FIG. 6 is a flowchart showing an example of the operation of the wireless communication system 1 according to the first embodiment.

[0070] In step S01, the first acquisition unit 7 acquires CSI for all wireless channels considered in the wireless communication system 1. Here, the CSI is estimated in each mobile terminal 4 based on, for example, a reference signal transmitted from the base station device 3. Thereafter, the process of the wireless communication system 1 proceeds to step S02.

[0071] In step S02, the second acquisition unit 8 acquires information such as the positions of all relay devices 5 considered in the wireless communication system 1. After that, the process of the wireless communication system 1 proceeds to step S03.

[0072] In step S03, the third acquisition unit 9 acquires movement information for all mobile terminals 4 considered in the wireless communication system 1. After that, the process of the wireless communication system 1 proceeds to step S04.

[0073] In step S04, the estimation unit 10 calculates a probability distribution for estimating the destination for each mobile terminal 4, based on, for example, equation (2), etc. After that, the process of the wireless communication system 1 proceeds to step S05.

[0074] In step S05, the allocation unit 11 generates a plurality of allocation patterns representing the correspondence between the relay device 5 and the mobile terminal 4. Here, the allocation unit 11 may generate all allocation patterns including possible correspondence between the relay device 5 and the mobile terminal 4, or may generate an allocation pattern by narrowing down the allocation patterns so as not to use wireless channels whose reception power at the mobile terminal 4 is smaller than a preset threshold. After that, the process of the wireless communication system 1 proceeds to step S06.

[0075] In step S06, the allocation unit 11 calculates the communication performance of the wireless communication system 1 for any of the generated allocation patterns based on, for example, equations (3) to (5), etc. After that, the process of the wireless communication system 1 proceeds to step S07.

[0076] In step S07, the allocation unit 11 judges whether the communication performance has been calculated for all the generated allocation patterns. If the judgment result is No, the process of the wireless communication system 1 proceeds to step S06. If the judgment result is Yes, the process of the wireless communication system 1 proceeds to step S08.

[0077] In step S08, the allocation unit 11 selects one of the generated allocation patterns as an allocation pattern to be adopted by multi-objective optimization such as that in equation (6). After that, the process of the wireless communication system 1 proceeds to step S09.

[0078] In step S09, the relay device 5 relays a wireless signal between the allocated mobile terminal 4 and the base station device 3 according to the allocation pattern selected by the allocation unit 11. At this time, the reflection control unit 15 of the relay device 5 controls the reflection characteristics of the reflector 13 so as to follow the movement of the mobile terminal 4. Thereafter, the processing of the wireless communication system 1 proceeds to step S10.

[0079] In step S10, the allocation unit 11 determines whether an allocation period has elapsed since the previous allocation. If the determination result is No, the process of the wireless communication system 1 proceeds to step S09. If the determination result is No, the process of the wireless communication system 1 proceeds to step S01.

[0080] As described above, the wireless communication method according to the first embodiment includes an acquisition step, an allocation step, and a reflection control step. The acquisition step is a step of acquiring movement information of each mobile terminal 4. The allocation step is a step of assigning at least any of the relay devices 5 to any of the mobile terminals 4. Each of the relay devices 5 is a device capable of relaying, by reflection, a radio signal that carries wireless communication between the base station device 3 and each of the mobile terminals 4. The reflection control step is a step in which the relay device 5 assigned to any of the mobile terminals 4 in the allocation step controls the reflection of the radio signal to follow the movement of the mobile terminal 4, based on the movement information of the mobile terminal 4 acquired in the acquisition step. Moreover, the wireless communication system 1 according to the first embodiment includes a base station device 3 and a plurality of relay devices 5. The base station device 3 assigns at least one of the relay devices 5 to one of the mobile terminals 4. The relay device 5 assigned to one of the mobile terminals 4 controls reflection of a wireless signal to follow the movement of the mobile terminal 4. Moreover, the base station device 3 according to the first embodiment includes a communication unit and an allocation unit 11. The communication unit transmits and receives radio signals that carry out radio communication with each mobile terminal 4. The allocation unit 11 allocates at least one of the relay devices 5 to one of the mobile terminals 4. Moreover, relay device 5 according to the first embodiment includes reflector 13 and reflection control unit 15. Reflector 13 relays, by reflection, a radio signal that is assigned by base station device 3 and is responsible for wireless communication between mobile terminal 4 and base station device 3. Reflection control unit 15 controls reflection of the radio signal by reflector 13 between base station device 3 and mobile terminal 4 so as to follow the movement of mobile terminal 4, based on movement information of the assigned mobile terminal 4 acquired from the mobile terminal 4.

[0081] With this configuration, the relay device 5 assigned to any one of the mobile terminals 4 dynamically controls the reflection characteristics to track the movement of the mobile terminal 4. Since the relay device 5 is fixedly assigned to any one of the mobile terminals 4, it becomes possible to reduce information required for estimating the CSI from the communicated information frame. This reduces the possibility that the mobile terminal 4 will be out of the communication range while reducing overhead such as CSI estimation, thereby suppressing a decrease in communication efficiency of the wireless communication system 1.

[0082] Moreover, the wireless communication method according to the first embodiment includes a tracking step, which is a step of tracking a moving path of each mobile terminal 4 based on the moving information acquired in the acquiring step. The reflection control step includes controlling reflection of the wireless signal so as to follow the moving path tracked in the tracking step.

[0083] With this configuration, the reflection characteristics are controlled based on the acquired movement information so that the wireless signal relayed by the relay device 5 more reliably tracks the mobile terminal 4. This further reduces the possibility that the mobile terminal 4 will go out of the communication range.

[0084] The allocation step also includes calculating a probability distribution for estimating a destination of each mobile terminal 4 based on the movement information acquired in the acquisition step. The allocation step includes calculating communication performance including at least one of a visibility probability and a throughput for each allocation pattern of the multiple relay devices 5 based on the calculated probability distribution. The allocation step includes selecting one of the allocation patterns based on the calculated communication performance.

[0085] With this configuration, the allocation is performed in consideration of the movement of the mobile terminal 4 and the situation beyond the time of the allocation. This reduces the possibility that the movement of the mobile terminal 4 will cause the communication performance of the wireless communication system 1 to decrease. In addition, by considering changes such as the movement of the mobile terminal 4, the solution space for the allocation is expanded, and the Pareto frontier in the trade-off relationship between the visibility probability and the throughput is improved. Note that the allocation step may evaluate either the visibility probability or the throughput as the communication performance, and select an allocation pattern based on the evaluated communication performance. In addition, in the evaluation of the communication performance, evaluation formulas other than formulas (3) to (5) may be used. For example, approximations of formulas (3) to (5) or formulas based on other evaluation methods may be used.

[0086] The wireless communication method according to the first embodiment may include a prediction step. The prediction step is executed, for example, instead of the tracking step or in parallel with the tracking step. The prediction step is executed, for example, by the base station device 3. In this case, the base station device 3 may include a prediction unit (not shown) that executes the prediction step. The prediction step is a step of predicting a movement path of each mobile terminal 4 based on the movement information acquired in the acquisition step. In this case, the reflection control step includes controlling the reflection of the wireless signal so as to follow the movement path predicted in the prediction step.

[0087] The base station device 3 may predict the movement route of the mobile terminal 4, for example, based on the position and speed of the mobile terminal 4, assuming that the mobile terminal 4 maintains the same speed. Alternatively, the base station device 3 may predict the movement route by, for example, modeling the movement of the mobile terminal 4 using the Ornstein-Uhlenbeck process. In this case, the base station device 3 may predict the movement route of the mobile terminal 4 by sampling according to a probability distribution such as that shown in equation (2).

[0088] In this way, by dynamically controlling the reflection characteristics of the relay device 5 according to the predicted moving path, it is possible to reduce the frequency of acquiring the moving information of the mobile terminal 4. This makes it possible to eliminate the information required for acquiring the moving information from the communicated information frame, thereby further reducing the overhead in the wireless communication system 1.

[0089] The allocating step may also include dynamically setting the update interval of the allocation of the multiple relay devices 5 based on the movement information acquired in the acquiring step. For example, the allocating unit 11 of the base station device 3 may set the length of the allocation period as a period until the next allocation based on the movement information of each mobile terminal 4 when performing the allocation. For example, the allocating unit 11 may set the length of the allocation period so that the faster the moving speed of the mobile terminal 4 is, the shorter the length of the allocation period is. Alternatively, the allocating unit 11 may set the length of the allocation period so that the length is shorter than the normal length when the moving speed of the mobile terminal 4 is faster than a preset threshold. Alternatively, the allocating unit 11 may set the length of the allocation period so that the length is longer than the normal length when the moving speed of the mobile terminal 4 is slower than a preset threshold. Here, the moving speed of the mobile terminal 4 may be the average speed or maximum speed of the multiple mobile terminals 4, or any speed of the multiple mobile terminals 4.

[0090] With this configuration, the allocation update interval is dynamically set according to the movement status of the mobile terminal 4, thereby achieving a balance between reducing the possibility that the mobile terminal 4 will go out of communication range and reducing a decrease in communication efficiency.

[0091] Further, some of the functions of the base station device 3 may be installed in each relay device 5. Alternatively, some of the functions of each relay device 5 may be installed in the base station device 3. For example, the tracking unit 14 may be installed in the base station device 3. At this time, information such as the position or direction of the mobile terminal 4 for tracking the mobile terminal 4 is notified from the base station device 3 to each relay device 5. The reflection control unit 15 of each relay device 5 controls the reflection characteristics of the reflector 13 according to the notification from the base station device 3.

[0092] Further, in the wireless communication system 1, wireless signals other than high frequency band signals may be used in combination. In the wireless communication system 1, different types of signals may be used depending on the type or capacity of data to be communicated. Furthermore, the wireless communication system 1 may also use wired communication in combination for communication between the stationary base station device 3 and the relay device 5.

[0093] Next, an example of the hardware configuration of the device of the wireless communication system 1 including the base station device 3 and each relay device 5 will be described. The device of the wireless communication system 1 has, as hardware, a processing circuit having, for example, a processor and a memory. The processor is, for example, a CPU, an arithmetic unit, a microprocessor, or a microcomputer. The memory is, for example, a non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, and EEPROM, or a storage medium such as a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD. The memory stores, for example, a program as software or firmware. The device of the wireless communication system 1 performs a preset process by the processor executing the program stored in the memory, and realizes each function as a result of the hardware and software working together. Each function of the device of the wireless communication system 1 may be realized by a processing circuit. Alternatively, some or all of the functions of the device of the wireless communication system 1 may be realized collectively by a processing circuit. In addition, the processing circuit may be realized by, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, or an FPGA, or a combination of these. [Explanation of symbols]

[0094] REFERENCE SIGNS LIST 1 wireless communication system, 2, 2a, 2b, 2c shield, 3 base station device, 4, 4a, 4b, 4c mobile terminal, 5, 5a, 5b, 5c, 5d, 5e relay device, 6 first communication unit, 7 first acquisition unit, 8 second acquisition unit, 9 third acquisition unit, 10 estimation unit, 11 allocation unit, 12 second communication unit, 13 reflector, 14 tracking unit, 15 reflection control unit

Claims

1. An acquisition step of acquiring movement information of each of a plurality of mobile terminals; an assignment step of assigning at least one of a plurality of relay devices capable of relaying, by reflection, a radio signal carrying radio communication between a base station device and each of the plurality of mobile terminals to any one of the plurality of mobile terminals; a reflection control step in which a relay device among the plurality of relay devices assigned to one of the plurality of mobile terminals in the assignment step controls reflection of a radio signal so as to follow the movement of the mobile terminal based on the movement information of the mobile terminal acquired in the acquisition step; Equipped with The allocating step includes: Dynamically setting an update interval for the allocation of the plurality of relay devices based on the movement information acquired in the acquiring step. Including, A wireless communication method.

2. a tracking step of tracking a moving route of each of the plurality of mobile terminals based on the moving information acquired in the acquiring step; Equipped with The reflex control step includes: controlling the reflection of the radio signal so as to follow the movement path tracked in the tracking step; Including, The wireless communication method according to claim 1 .

3. A prediction step of predicting a movement route of each of the plurality of mobile terminals based on the movement information acquired in the acquisition step. Equipped with The reflex control step includes: controlling reflection of the radio signal so as to follow the movement path predicted in the prediction step; Including, The wireless communication method according to claim 1 .

4. The allocating step includes: calculating a probability distribution for estimating a destination of each of the plurality of mobile terminals based on the movement information acquired in the acquiring step; calculating communication performance including at least one of a visibility probability and a throughput for each allocation pattern of the plurality of relay devices based on the calculated probability distribution; and selecting one of the allocation patterns of the plurality of relay devices based on the calculated communication performance; Including, The wireless communication method according to any one of claims 1 to 3.

5. A base station device, a plurality of relay devices capable of relaying, by reflection, a radio signal carrying out radio communication between the base station device and each of a plurality of mobile terminals; Equipped with the base station device assigns at least one of the plurality of relay devices to one of the plurality of mobile terminals; A relay device among the plurality of relay devices, which is assigned to any one of the plurality of mobile terminals, controls reflection of a radio signal so as to follow the movement of the mobile terminal; the base station device dynamically sets update intervals of allocation of the plurality of relay devices based on movement information acquired from at least one of the plurality of mobile terminals; Wireless communication system.

6. A communication unit that transmits and receives radio signals for wireless communication with each of a plurality of mobile terminals; an allocation unit that allocates to one of the plurality of mobile terminals at least one of a plurality of relay devices that are capable of relaying the wireless signal by controlling reflection of the wireless signal so as to follow the movement of the mobile terminal between the allocated mobile terminal among the plurality of mobile terminals and the communication unit; Equipped with the allocation unit dynamically sets update intervals of allocation of the plurality of relay devices based on movement information acquired from at least one of the plurality of mobile terminals. Base station equipment.

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