JP6568964B2 - Mobile communication system, base station and inter-base station controller - Google Patents

Description

  The present invention relates to a mobile communication system capable of performing communication by a mobile terminal, a base station used in the mobile communication system, and an inter-base station control apparatus.

  Small cell base stations ("mini cell base stations", "pico cell base stations", "femto cells") with smaller cells (wireless communication areas) than conventional macro cell base stations to cope with the rapid increase in traffic in recent mobile communication systems Demand for “base stations” is increasing. In particular, as a traffic countermeasure, a heterogeneous cellular network (HetNet: Heterogeneous Cell Size) in which small cells are arranged in a plane in an area where a lot of traffic such as hot spots in a macro cell of a conventional macro cell base station is concentrated. Heterogeneous Network) configuration is effective.

  Conventionally, as a technique for reducing inter-cell interference between a macro cell and a small cell, a radio frame in the time domain (subframe unit) on the assumption that the macro cell base station and the small cell base station are time-synchronized with each other. There is known an inter-cell interference control technique for adjusting and controlling (for example, see Patent Document 1 and Non-Patent Document 1). This inter-cell interference control technology is a technology based on LTE (Long Term Evolution) -Advanced standards, and is also called eICIC (enhanced Inter-Cell Interference Coordination).

JP 2012-129793 A

“Overview of 3GPP”, Release 10, V0.2. 1 (2014-06).

  In addition, when the conventional inter-cell interference control technology is applied in the HetNet configuration, time resources (time slots) allocated between the macro cell and the small cell are completely divided, so that interference between the macro cell and the small cell is avoided. However, there is a problem that the maximum transmission rate (peak throughput) of the macro cell and the small cell is reduced. In particular, if a large number of time resources are allocated to small cells in order to increase the transmission rate of the small cells, there is a problem that the time resources allocated to the macro cells where there are many users are reduced and the transmission rate of the macro cells is reduced. Therefore, a technique that can particularly improve the reduction in the transmission rate (throughput) of the macro cell is desired.

A mobile communication system according to an aspect disclosed in the present specification includes a first base station forming a first cell, at least an antenna disposed in the first cell, and at least partly overlapping the first cell. A mobile communication system comprising one or a plurality of second base stations forming a second cell, wherein the first base station and the second base station are time-synchronized with respect to transmission timing, A transmission weight for suppressing an interference signal from the first cell received by a terminal located in the cell is calculated, and the transmission signal from the first base station is multiplied by the transmission weight to be transmitted from the second base station. Send.
In the mobile communication system, a transmission interference suppression signal is generated by multiplying the transmission signal received from the first base station by the transmission weight, and the transmission time of the transmission signal from the first base station and the second base station The transmission interference suppression signal may be transmitted from the second base station by adjusting the transmission time so that the transmission time of the transmission interference suppression signal from the same time becomes the same time.
In the mobile communication system, when there are a plurality of the second base stations, the transmission weight is individually calculated for each second base station, and the transmission from the first base station is performed for each second base station. The signal may be transmitted by multiplying the transmission weight individually.
Further, in the mobile communication system, the transmission weight is determined from a propagation path characteristic of a first received signal from the first base station measured by a mobile station located in the second cell and from the second base station. You may calculate based on the propagation path characteristic of a 2nd received signal. Here, the terminal located in the second cell obtains information on the propagation path characteristics of the first reception signal from the first base station and the propagation path characteristics of the second reception signal from the second base station. The second base station that transmits to the base station and receives the information may calculate the transmission weight. Alternatively, a terminal located in the second cell calculates a transmission weight based on the propagation path characteristic of the first reception signal from the first base station and the propagation path characteristic of the second reception signal from the second base station. The transmission weight information may be transmitted to the second base station.

In the mobile communication system, the transmission weight may be calculated so as not to exceed a predetermined maximum value while maintaining a vector direction of the transmission weight.
In the mobile communication system, the transmission weight is a signal power pair (noise power + interference power) in the terminal under a condition that the total transmission power transmitted from the second base station does not exceed a predetermined maximum transmission power. The ratio may be calculated so as to maximize the SINR (Signal power to Interference power and Noise power Ratio).

The mobile communication system may further include an inter-base station control device that performs control between the first base station and the second base station.
The inter-base station control device calculates the transmission weight, multiplies the transmission signal received from the first base station by the transmission weight, creates a transmission interference suppression signal, and transmits the transmission from the first base station. The transmission interference suppression signal may be transmitted to the second base station in synchronization with a signal, and the second base station may transmit the transmission interference suppression signal received from the inter-base station controller.
In addition, the inter-base station control device calculates the transmission weight and transmits it to the second base station, the second base station receives the transmission weight from the inter-base station control device, and the first base station A transmission interference suppression signal may be generated by multiplying the transmission signal received from the base station by the transmission weight, and the transmission interference suppression signal may be transmitted in synchronization with the transmission signal from the first base station.
In the inter-base station controller, the propagation path characteristics of the first received signal from the first base station and the propagation of the second received signal from the second base station measured by the terminal located in the second cell Information on the path characteristics may be received via the second base station, and the transmission weight may be calculated based on the information received via the second base station.

In the mobile communication system, the second base station calculates the transmission weight at its own station, multiplies the transmission signal received from the first base station by the transmission weight, and creates a transmission interference suppression signal, The transmission interference suppression signal may be transmitted in synchronization with the transmission signal from the first base station.
In the mobile communication system, the second base station receives the transmission weight from a terminal located in the second cell, and multiplies the transmission signal received from the first base station by the transmission weight. Then, a transmission interference suppression signal may be generated, and the transmission interference suppression signal may be transmitted in synchronization with the transmission signal from the first base station.

The mobile communication system further includes a common baseband processing unit connected to each of the first base station and the second base station via a communication line, and the first base station and the second base station are respectively The transmission signal generated by the baseband processing unit may be received via a communication line and transmitted from the antenna of each base station.
Further, in the mobile communication system, the first base station is a macro cell base station in which at least an antenna is arranged on the ground or the sea so as to form a macro cell as the first cell, and the second base station It may be a small cell base station in which at least an antenna is arranged on the ground or the sea so as to form a small cell as the second cell.

Further, in the mobile communication system, the first base station is provided on a flying body or a levitation body located in the sky so as to form the first cell, and the second base station includes the second cell. It may be a macro cell base station or a small cell base station in which at least an antenna is arranged on the ground or the sea so as to form. Here, the flying body may include at least one of a battery and a photovoltaic power generation system, and may fly with electric power.
In the mobile communication system, the first base station may be provided in an artificial satellite, a HAPS, an airship, a balloon, or a drone.

An inter-base-station control apparatus according to another aspect disclosed in the present specification includes: a first base station that forms a first cell; and a second cell that at least partially overlaps the first cell. An inter-base station control apparatus that performs control with a plurality of second base stations, and calculates a transmission weight for suppressing an interference signal from a first cell received by a terminal located in the second cell Then, a transmission interference suppression signal is created by multiplying the transmission signal received from the first base station by the transmission weight, and the transmission time of the transmission signal from the first base station and the transmission from the second base station The transmission time is adjusted so that the transmission time of the interference suppression signal is the same, and the transmission interference suppression signal is transmitted from the second base station.
In addition, an inter-base station control apparatus according to still another aspect disclosed in the present specification includes a first base station that forms a first cell, and at least an antenna disposed in the first cell. An inter-base station control apparatus that performs control with one or a plurality of second base stations that form a second cell that overlaps at least partly, and receives a first received by a terminal located in the second cell A transmission weight for suppressing an interference signal from the cell is calculated, and the transmission weight is transmitted to the second base station.

  According to the mobile communication system, the base station, and the inter-base station control device disclosed in the present specification, it is possible to suppress transmission interference from a macro cell having a HetNet configuration to a small cell. There is no need to divide (time slot), and a decrease in the maximum transmission rate (peak throughput) of the macro cell and the small cell can be suppressed.

FIG. 1 is a diagram showing an example of the overall configuration of a mobile communication system according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an arrangement example of time slots of radio resources set in each of the macro cell and the small cell in the inter-cell interference control technology (eICIC) of the conventional example. FIG. 3 is a diagram illustrating an arrangement example of time slots of radio resources set in each of the macro cell and the small cell in the mobile communication system according to the present embodiment. FIG. 4 is an explanatory diagram illustrating a configuration example of a communication system in which the transmission interference suppression technique according to the present embodiment can be introduced. FIG. 5 is an explanatory diagram illustrating an example of a basic operation (downlink) of transmission interference suppression control according to the present embodiment. FIG. 6 is an explanatory diagram illustrating an example of a basic operation (uplink) of transmission interference suppression control according to the present embodiment. FIG. 7 is an explanatory diagram illustrating an example of transmission interference suppression control according to the present embodiment. FIG. 8 is a block diagram illustrating another example of transmission interference suppression control according to the present embodiment. FIG. 9 is a block diagram showing still another example of transmission interference suppression control according to the present embodiment. FIG. 10 is a block diagram showing still another example of transmission interference suppression control according to the present embodiment. FIG. 11 is a diagram showing an example of the overall configuration of a mobile communication system according to another embodiment of the present invention. FIG. 12 is a block diagram showing an example of transmission interference suppression control in the mobile communication system of FIG.

  Various embodiments will be described below with reference to the drawings. Each figure only schematically shows the shape, size, and positional relationship to the extent that the contents of the present invention can be understood. Therefore, the present invention shows the shape, size, and position illustrated in each figure. It is not limited to relationships only. Moreover, the numerical value illustrated below is only a suitable example of this invention, Therefore, this invention is not limited to the illustrated numerical value.

  FIG. 1 is a diagram showing an example of a configuration of a heterogeneous cellular network (HetNet) of a heterogeneous cell size mixed type in a mobile communication system (mobile phone system) according to an embodiment of the present invention. In FIG. 1, the mobile communication system of the present embodiment includes macro cell base stations (first base stations) 20A and 20B and small cell base stations (second base stations) 30A as a plurality of base stations capable of wireless communication with a terminal 10. , 30B. At least antennas of the small cell base station 30A are arranged at four locations in the macro cell (first cell) 200A of one macro cell base station 20A, and small cell bases are respectively provided at six locations in the macro cell 200B of the other macro cell base station 20B. At least the antenna of the station 30B is arranged.

  The configuration of the mobile communication system in FIG. 1 is a traffic countermeasure in which small cells (second cells) 300A and 300B are arranged in a plane in an area where a lot of traffic such as hot spots in the macro cells 200A and 200B is concentrated. It is a valid “HetNet configuration”. In this system, the macro cell and the small cell use the same frequency. In particular, in an urban area where high-rise buildings 40 are lined up as in the example of FIG. 1, there are many cases where traffic is concentrated in large-scale offices on high floors, and small cells are placed in such places. The “original space HetNet configuration (three-dimensional spatial cell configuration)” is very effective. In the three-dimensional space cell configuration of FIG. 1, a plurality of outdoor small cells are arranged in the plane direction, and a plurality of indoor small cells are arranged in the height direction.

  The terminal 10 is a mobile phone, a smart phone, a mobile personal computer having a mobile communication function, or the like, and is also called a user apparatus (UE), a mobile station, a mobile device, or a mobile communication terminal. When the terminal 10 is located in one macro cell 200A, the terminal 10 communicates with the mobile communication network side via the macro cell base station 20A corresponding to the macro cell 200A. Further, when the terminal 10 moves to any of the overlapping small cells 300A in the macro cell 200A, the terminal 10 communicates with the mobile communication network side via any of the small cell base stations 30A. Similarly, when the terminal 10 is located in the other macro cell 200B, the terminal 10 communicates with the mobile communication network side via the macro cell base station 20B corresponding to the macro cell 200B. Further, when the terminal 10 moves to any of the overlapping small cells 300B in the macro cell 200B, the terminal 10 communicates with the mobile communication network side via the small cell base station 30B.

  In addition, in FIG. 1, the number of each of the macro cell base station and the small cell base station is arbitrary. For example, the macro cell base station may be provided in one place or three places or more, and the small cell base station is provided in each macro cell. You may provide in 1 place-3 places or 7 places or more. The macro cell base station and the small cell base station are time-synchronized with each other.

  Each of the macrocell base stations 20A and 20B is a wide-area base station that covers a macrocell that is a wide-area area having a radius of about several hundred m to several km that is installed outdoors in a mobile communication network. , “Macro e-Node B”, “MeNB”, etc. The macrocell base stations 20A and 20B are connected to other base stations via, for example, a wired communication line, and can communicate with each other through a predetermined communication interface. The macrocell base stations 20A and 20B are connected to a core network of a mobile communication network via a line termination device and a communication line such as an optical line or a dedicated line, and between various nodes such as a server device on the core network. Communication is possible through a predetermined communication interface.

  Each of the small cell base stations 30A and 30B, unlike a macro cell base station in a wide area, has a wireless communication range of about several tens to several hundreds of meters, and can be installed indoors such as ordinary homes, stores, and offices. It is a small capacity base station. Since the small cell base stations 30A and 30B are provided so as to cover an area smaller than the area covered by the wide-area macro cell base station in the mobile communication network, they are referred to as “small cell base stations” or “Small e-Node”. It may be called “B” or “Small eNB”. The small cell base stations 30A and 30B are also connected to a core network of a mobile communication network via a line termination device and a communication line such as an optical line or a dedicated line, and between various nodes such as a server device on the core network. Communication is possible through a predetermined communication interface.

  The same radio transmission method and the same frequency band are used for radio communication between the macro cell base stations 20A and 20B and the small cell base stations 30A and 30B and the terminal 10. As a wireless transmission method, for example, a communication method of a third generation mobile communication system (3G) such as WCDMA (registered trademark) (Wideband Code Division Multiple Access) or CDMA-2000, LTE (Long Term Evolution) or LTE-Advanced A communication system, a 4th generation mobile phone communication system, a 5th generation mobile phone communication system, etc. can be employed.

  The terminal 10 is configured using hardware such as a computer device having a CPU, a memory, and the like, and a wireless communication unit, for example, and the macro cell base stations 20A and 20B and the small cell base stations 30A and 30B are executed by executing predetermined programs. Wireless communication and the like between them can be performed. The macro cell base stations 20A and 20B and the small cell base stations 30A and 30B are each configured using hardware such as a computer device having a CPU, a memory, etc., an external communication interface unit for a core network, a wireless communication unit, and the like. By executing the predetermined program, it is possible to perform wireless communication with the terminal 10 or communication with the core network side.

  The terminal 10 may be a modular mobile station incorporated in a mobile body such as an automobile or a drone, or may be a terminal device of a device for IoT (Internet of Things).

  In the three-dimensional space cell configuration as shown in FIG. 1, estimation of pre-interference and interference between macro cells, between macro cells and small cells, and between small cells is very complicated, as indicated by arrows in the figure. In addition, it is extremely difficult to construct a three-dimensional spatial cell configuration that avoids mutual interference by spatially separating the cells. In order to realize a three-dimensional spatial cell configuration, advanced interference control is indispensable.

  As an inter-cell interference control technique applicable to the above-described HetNet configuration, an inter-cell interference control technique called eICIC conforming to the above-mentioned LTE-Advanced standard is known.

  FIG. 2 is a diagram illustrating an arrangement example of time slots of radio resources set in each of the macro cell and the small cell in the inter-cell interference control technology (eICIC) of the conventional example. As shown in FIG. 2, in the above-described inter-cell interference control technique called eICIC, radio resources in the same frequency band are time-divided and different time slots are allocated to the macro cell and the small cell, respectively. Thereby, interference in the same frequency band between the macro cell and the small cell can be avoided. However, in the conventional inter-cell interference control technology (eICIC), the radio resource (time slot) is divided in each of the macro cell and the small cell and a part of each is not used. Therefore, the maximum transmission rate (peak) of the macro cell and the small cell is not used. (Throughput) is reduced. For example, in the example of FIG. 2, the maximum transmission rates of the macro cell and the small cell are both reduced to 5/10 = 1/2 compared to the case where all the radio resources are used. Therefore, a technique that can improve the decrease in the maximum transmission rate of the macro cell and the small cell is desired. In particular, a technique that can improve a decrease in transmission rate (throughput) of a macro cell in which many users (terminals) exist is desired.

  Therefore, in the present embodiment, in order to solve the problem of avoiding interference between cells and improving the decrease in the maximum transmission rate of the macro cell and the small cell, as shown in FIG. Introducing transmission interference suppression technology (transmission interference cancellation technology) that suppresses (cancels) interference from macro cells to small cells, as shown below, while realizing simultaneous use of (all time slots). Yes.

  FIG. 4 is an explanatory diagram illustrating a configuration example of a communication system in which the transmission interference suppression technique according to the present embodiment can be introduced. The communication system of FIG. 4 shows an example based on a C-RAN (centralized radio access network) configuration, but is a communication system having another configuration such as a D-RAN (distributed radio access network). There may be.

  In the communication system having the C-RAN configuration of the present embodiment, the macrocell base station 20 and the small cell base station 30 are each a wired communication line or a wireless communication line such as an optical fiber, an interface between base stations (for example, x2 interface in LTE), etc. Base station transceiver including RRH (remote radio header) (also referred to as “overhang base station” or “light overhang device”) 21 and 31 and a baseband signal processor connected to each other via a communication line 90 (Baseband processing unit). The base station transceivers of the base stations 20 and 30 are integrated into a common BBU (baseband unit) 50 installed at one place. The RRHs 21 and 31 of the base stations 20 and 30 are connected to the BBU 50 via an inter-base station network cooperation control device (hereinafter referred to as “inter-base station control device”) 60 and a communication line 90. The RRHs 21 and 31 are also called overhang base stations, and have an RF unit, an amplification device, and the like. The RRHs 21 and 31 convert the transmission signal from the BBU 50 into a radio signal and transmit it from the antenna with a predetermined transmission power, or convert the radio signal received by the antenna into a reception signal and send it to the BBU 50. The inter-base station control device 60 executes a transmission interference canceller that suppresses interference from a macro cell to a small cell, which will be exemplified below.

FIG. 5 is an explanatory diagram illustrating an example of a basic operation (downlink) of transmission interference suppression control according to the present embodiment.
In FIG. 5, the transmission signal (small cell transmission signal) si (i = 1, 2, −−−) of each small cell 300 is transmitted from the BBU 50 via the inter-base station control device 60 to the RRH 31 of each small cell base station. Sent to. A transmission signal (macro cell transmission signal) s0 of the macro cell 200 is transmitted from the BBU 50 to the RRH 21 of the macro cell base station via the inter-base station control device 60 and to the RRH 31 of each small cell base station. The RRH 31 of the i-th small cell base station transmits the small cell transmission signal si received from the inter-base station control device 60 from the antenna. In the figure, i = 1 and 2 are set. Further, the RRH 31 of each small cell base station multiplies the macro cell transmission signal s0 received from the inter-base station control device 60 by a predetermined transmission weight wi to obtain a transmission interference suppression signal (wi · s0) (“transmission interference cancellation signal”). And transmit from the antenna. With this transmission interference suppression signal (wi · s0), it is possible to suppress or cancel an interference signal (macrocell transmission signal s0) received by the terminal 10 located in the small cell 300 from the macrocell base station 20.

FIG. 6 is an explanatory diagram illustrating an example of a basic operation (uplink) of transmission interference suppression control according to the present embodiment.
In FIG. 6, the terminal 10 (Mi) of the i-th small cell 300 determines the propagation path characteristic hi0 between the macro cell base station 20 (B0) and the RRH 21 and the i-th small cell base station 30 (Bi). A propagation path characteristic hii is measured.

The terminal Mi of the i-th small cell transmits the following feedback information FB (1) or (2) to the i-th small cell base station Bi. The following (2) FB information has the advantage that the amount of transmission information is smaller than the (1) FB information.
(1) Information on propagation path characteristics hi0 and hii measured by terminal Mi (2) Transmission weight wi calculated from propagation path characteristics hi0 and hii measured by terminal Mi

  The i-th small cell base station Bi receives and acquires the FB information from the terminal Mi, and transmits the FB information to the small cell transmission weight calculation unit 61 provided in the inter-base station control device 60.

  The small cell transmission weight calculation unit 61 calculates a transmission weight wi based on the FB information received from the small cell base station Bi, multiplies the transmission weight wi by the macro cell transmission signal s0, and transmits a transmission interference suppression signal (wi · s0). ) Is generated.

  FIG. 7 is an explanatory diagram illustrating an example of transmission interference suppression control according to the present embodiment. The example of FIG. 7 is an example in which there are a plurality of small cells in the macro cell 200, and the terminal Mi calculates a transmission weight wi to generate a transmission interference suppression signal (wi · s0). In FIG. 7, the same reference numerals are given to portions common to those in FIGS. 1 and 4 to 6 described above, and description thereof is omitted.

  In FIG. 7, the RRH 21 of the macrocell base station 20 is assumed to be the macrocell base station B0, the terminal 10 located in the macrocell 200 is assumed to be M0, and the transmission signal (macrocell transmission signal) of the macrocell 200 is assumed to be s0. Also, let RRH 31 of the i-th small cell base station 30 be the small cell base station Bi, let the terminal 10 located in the small cell 300 be Mi, and let the transmission signal (small cell transmission signal) of the small cell 300 be si. Further, the RRH 31 of the small cell base station 30 other than the i-th small cell base station Bi is defined as a small cell base station Bj (i ≠ j).

  Further, the propagation path characteristic between the macro cell base station B0 and the terminal Mi of the i-th small cell is hi0, the propagation path characteristic between the small cell base station Bi and the terminal Mi is hi, and the other small cell base stations Bj. And the propagation path characteristic of the terminal Mi is hij.

The received signal yi of the terminal Mi of the i-th small cell is given by the following equation.

  Here, hii · si is a received signal of the terminal Mi transmitted from the i-th small cell.

  The terminal Mi of the i-th small cell measures the propagation path characteristic hi0 of the macrocell transmission signal s0 and the propagation path characteristic hii of the small cell transmission signal as information necessary for interference suppression of the macrocell transmission signal. Then, the terminal Mi calculates a transmission weight wi = −hi0 / hii for suppressing the macrocell transmission signal.

  Next, the terminal Mi of the i-th small cell transmits (A) information on the propagation path characteristics hi0 and hii measured by the terminal Mi to the i-th small cell base station Bi by a feedback signal, or ( B) Information on the transmission weight wi calculated by the terminal Mi is transmitted.

  Next, in the case of (A) above, the small cell base station Bi calculates (determines) the transmission weight wi = −hi0 / hii based on the information of hi0 and hii transmitted from the terminal Mi, and the above (B) In this case, a transmission interference suppression signal (−hi0 / hii · s0) is generated by multiplying the transmission weight wi by the macrocell transmission signal s0 using the transmission weight wi (= −hi0 / hii) transmitted from the terminal Mi. The transmission interference suppression signal is transmitted from the small cell base station Bi.

Next, if the reception signal of the terminal Mi when the transmission signal si from the small cell base station Bi and the transmission interference suppression signal are simultaneously transmitted is set as yci, the reception signal yci is set to yi as an interference suppression signal hii · Since wi · s0 is added and received, the following equation is obtained.

  As a result, yci = h11 · s1 + I, and interference from the macro cell 200 in the received signal of the terminal Mi can be completely suppressed (cancelled).

  In the transmission interference suppression control of the present embodiment, hi0 may be very large or hii may be very small with respect to transmission weight wi = −hi0 / hii. In such a case, the transmission weight wi becomes a very large value, and the transmission power of the transmission interference suppression signal becomes very large. In general, since the transmission power of the base station is limited, it is not possible to transmit with a transmission power exceeding the transmission power.

Therefore, in another control example of the transmission interference suppression control of the present embodiment, the transmission weight w may be limited as an actual value. For example, if the maximum value of the transmission weight w is set as wmax, the limited transmission weight wilim is given by the following equation. Here, Min (a, b) is a function that gives the minimum values of a and b.

  According to the control example of this example, it is possible to prevent the transmission weight w from exceeding wmax by the limited transmission weight wiim without changing the vector direction of the transmission weight wi. Therefore, the transmission power of the small cell base station Bi can be made lower than a predetermined value, and interference from the macro cell 200 in the received signal of the terminal Mi can be suppressed (cancelled) within the range of wmax.

  In yet another control example of the transmission interference suppression control of the present embodiment, the optimal transmission weight wi is determined so as to maximize the SINR that is the ratio of the signal power of the terminal Mi to (noise power + interference power). Good.

  In this control example, when the maximum transmission power of the small cell is specified, the i-th small cell base station Bi optimally distributes the transmission power of the small cell transmission signal si and the transmission interference suppression signal s0, and accordingly Each signal is multiplied by the optimum transmission weight and transmitted to the terminal Mi.

  The criterion for the optimum transmission weight is a weight that maximizes the SINR that is the ratio of the signal power of the terminal Mi to (noise power + interference power). Here, when the maximum transmission power is defined, if the small cell transmission signal is βi · si, the transmission interference suppression signal is αi · (wi · s0), and the total transmission power is P, the following equation (1) is obtained. It is necessary to satisfy. Here, βi is a correction coefficient for the small cell transmission signal si, and αi is a correction coefficient for the ideal transmission interference suppression signal (wi · s0).

The optimum transmission weight is determined by the following procedure.
First, the following equation (1) is set as a standard for the maximum transmission power of the i-th small cell.

Next, assuming that the SINR of the terminal Mi is λi, λi can be expressed by the following equation (2). However, the thermal noise power of the terminal Mi is normalized as 1.

  Αi and βi to maximize Expression (2) are determined on the condition of Expression (1). An example of the procedure for determining αi and βi is shown below.

In the above formula (1), for example, P = 1 (reference value) can be set without impairing generality. Substituting equation (1) into equation (2), λi can be expressed as:

Further, when the formula (1) is substituted into the formula (2), the following formula is obtained.

In Expression (3), αi and βi at which λi is maximized are as follows.

  Using Expression (4), the transmission signal from the small cell base station Bi is βi · si, and the transmission interference suppression signal is αi · (wi · s0).

  According to this control example, when the maximum transmission power of the small cell base station Bi is determined, the terminal Mi is configured to maximize the communication quality (SINR) of the received signal from the small cell base station Bi of the terminal Mi. Interference signal from the macro cell 200 can be optimally suppressed (cancelled).

  In the present embodiment, the calculation of the transmission weight wi and the generation of the transmission interference suppression signal (wi · s0) may be performed by a device other than the small cell base station Bi (for example, the inter-base station control device 60).

  FIG. 8 is a block diagram illustrating another example of transmission interference suppression control according to the present embodiment. The example of FIG. 8 is an example in which the inter-base station control device 60 calculates a transmission weight wi and generates a transmission interference suppression signal (wi · s0). In FIG. 8, the same reference numerals are given to the portions common to the above-described FIG. 1 and FIGS. 4 to 7, and description thereof is omitted.

  In FIG. 8, the inter-base station control device 60 includes a small cell transmission weight calculation unit 61 and a transmission signal processing unit 62. The transmission weight calculation unit 61 includes small cell base stations B1, Bi,. . . Received from the feedback information FB1,. . . , FBi,. . . Based on the transmission weights w1,. . . , Wi,. . . Calculate

  The transmission signal processing unit 62 includes transmission weights w1,. . . , Wi,. . . Is multiplied by the macro transmission signal s0 to reduce the transmission interference suppression signal w1 · s0,. . . , Wi · s0,. . . Is generated. The transmission interference suppression signals w1 · s0,. . . , Wi · s0,. . . In addition, transmission signals (desired signals) s1, s0,. . . To the small cell transmission signal s1 '(= w1 · s0 + s1),. . . , Si ′ (= wi · s0 + si),. . . Is generated.

  Further, the transmission signal processing unit 62 includes a macro transmission signal s0 and small cell transmission signals s1 ',. . . , Si ',. . . , Macro transmission signal s0 and transmission interference suppression signal w1 · s0,. . . , Wi · s0,. . . The time synchronization adjustment control is performed with respect to the transmission timing so that the transmission times are the same. This time synchronization adjustment control includes, for example, a macro transmission signal s0 and small cell transmission signals s1 ',. . . , Si ',. . . Each of them is sent to a predetermined delay time τ0, τ1, τi,. . . Shifted by a distance of each base station B0, B1, Bi,. . . Send to. For example, the delay time τ0 of the macro transmission signal s0 and the small cell transmission signals s1 ',. . . , Si,. . . Delay times τ1,. . . , Τi,. . . Are the macrocell base station B0 and the small cell base stations B1,. . . , Bi,. . . Can be determined in advance based on information on the spatial positional relationship between the mobile station and information such as a propagation delay time difference between each base station and the terminal. The delay time τ0 of the macro transmission signal s0 may be set to 0 seconds.

  According to this control example, since there is no limit on the interference transmission power, as in the case of FIG. 7, the terminals M1,. . . , Mi,. . . Interference from the macro cell in the received signal can be completely suppressed (cancelled).

  FIG. 9 is a block diagram showing still another example of transmission interference suppression control according to the present embodiment. The example of FIG. 9 is an example in which the inter-base station control device 60 generates a transmission interference suppression signal (w1lim · s0,..., Willim · s0,...) Using the limited transmission weight described above. is there. In FIG. 9, the same reference numerals are given to portions common to those in FIG. 1 and FIGS. 4 to 8 described above, and descriptions thereof are omitted.

  In the example of FIG. 9, the above-described limited transmission weights w1lim,. . . , Wilim,. . . Is multiplied by the macro transmission signal s0 to reduce the transmission interference suppression signals w1lim · s0, wilim · s0,. . . Is generated.

  According to the control example of this example, it is possible to prevent the transmission weight w from exceeding wmax by the limited transmission weight wilim, so that the small cell base stations B1,. . . , Bi,. . . Of the terminals M1, Mi,. . . Interference from the macro cell 200 in the received signal can be appropriately suppressed (cancelled) within the limited transmission power.

  FIG. 10 is a block diagram showing still another example of transmission interference suppression control according to the present embodiment. In the example of FIG. 10, the inter-base station controller 60 is configured such that the terminals M1,. . . , Mi,. . . To generate a transmission interference suppression signal (α1 · w1 · s0,..., Αi · wi · s0,...) And a small cell transmission signal (β1 · s1,. This is an example of generating βi · si,. In FIG. 10, the same reference numerals are given to portions common to those in FIGS. 1 and 4 to 8 described above, and description thereof is omitted.

  In the example of FIG. 10, the transmission weight calculation unit 61 includes the terminals M1,. . . , Mi,. . . Corrected transmission weights α1 · w1,. . . , Αi · wi,. . . , And correction coefficients β1,. . . , Βi,. . . , Multiplied by the macro transmission signal s0, and corrected transmission interference suppression signals α1, w1, s0,. . . , Αi · wi · s0,. . . , And the small transmission signals s1,. . . , Si,. . . And the corrected small cell transmission signals β1 · s1, βi · si,. . . Is generated. The transmission signal processing unit 62 uses these corrected signals to each small cell base station B1, Bi,. . . , Corrected small cell transmission signals s1 ′ (= β1 · s1 + α1 · w1 · s0),. . . , Si ′ (= βi · si + αi · wi · s0),. . . Is generated.

  According to this control example, the terminals M1,. . . , Mi,. . . , M1, Mi,. . . Interference from the macro cell 200 in the received signal can be optimally suppressed (cancelled) within the limited transmission power.

  FIG. 11 is a diagram showing an example of the overall configuration of a mobile communication system according to another embodiment of the present invention. FIG. 12 is a block diagram showing an example of transmission interference suppression control in the mobile communication system of FIG. 11 and 12, the same reference numerals are given to portions common to those in FIGS. 1 and 4 to 10, and the description thereof is omitted.

  A general macrocell base station B0 is installed on the ground, but includes an artificial satellite 71, a solar plane type HAPS ("high altitude pseudo satellite", "high altitude platform station") 72, an airship type HAPS 73, a drone 74, a balloon 75, the relay radio apparatus 700 may be mounted on an aircraft 70 such as an aircraft that floats at various altitudes, such as an airplane. The body 70 may include a battery, a solar power generation system, and the like.

  The relay radio apparatus 700 includes a macro cell base station 711 (B0) as a first base station, and a relay transceiver 712. The macro cell base station 711 (B0) of the relay radio apparatus 700 mounted on the airframe 70 can configure a macro cell 701 as a wide-area two-dimensional or three-dimensional first cell. Note that the second ground cell included in the macro cell 701 may be the small cell 300 formed by the ground small cell base station 30 as shown in FIG. 11 or may be formed by the above-described ground macro cell base station 20. The macro cell 200 may be used.

  Since the macrocell base station 711 (B0) and the inter-base station controller 60 cannot be connected by a wired communication line such as an optical fiber, a wireless relay system is used. The wireless relay system includes, for example, a gate station (also referred to as a “gateway station”, “GW station”, “repeater master”, or “feeder station”) 80 that includes an antenna and a relay transceiver, and an antenna and relay. It is configured using a relay transceiver 712 of the relay radio apparatus 700 that is configured by a transmitter / receiver and is mounted on the airframe 70 in the sky. The feeder link relay frequency f1 between the gate station 80 and the relay transceiver 712 is different from the service link frequency f2 used for communication between the macrocell base station 711 (B0) and the terminal 10 in the macrocell 701. A frequency may be used.

  The airframe 70 on which the relay wireless device 700 is mounted is controlled so as to float or fly in a high altitude airspace (floating airspace) of 100 km or less from the ground or sea surface by autonomous control or external control, for example. May be. The airspace in which the airframe 70 is located may be, for example, a stratospheric airspace whose altitude is 11 [km] or more and 50 [km] or less. This airspace may be an airspace with an altitude of 15 [km] or more and 25 [km] or less, in which the weather conditions are relatively stable, and particularly an airspace with an altitude of approximately 20 [km].

  As described above, according to each embodiment, since transmission interference from the macro cell 200 having the HetNet configuration to the small cell 300 can be suppressed, it is not necessary to divide time resources (time slots) allocated between the macro cell 200 and the small cell 300, A decrease in the maximum transmission rate (peak throughput) of the macro cell 200 and the small cell 300 can be suppressed.

  Note that the processing steps described in this specification and the components of the communication system, the wireless device, the base station, the wireless relay station (feeder station), and the terminal (user device, mobile station, mobile device) are implemented by various means. can do. For example, these processing steps and components may be implemented in hardware, firmware, software, or a combination thereof.

  For hardware implementation, to realize the above-described steps and components in an entity (for example, various wireless communication devices, wireless relay devices, NodeBs, servers, gateways, exchanges, computers, hard disk drive devices, or optical disk drive devices) The processing unit or the like used in the process includes one or more application specific IC (ASIC), digital signal processor (DSP), digital signal processor (DSPD), programmable logic device (PLD), field Programmable gate array (FPGA), processor, controller, microcontroller, microprocessor, electronic device, other electronic unit designed to perform the functions described herein, a computer, or it It may be implemented in a combination of.

  Also, for firmware and / or software implementation, the means used to implement the above components are code (eg, procedures, functions, modules, instructions, etc.) that perform the functions described herein. ). In general, any computer / processor readable medium that specifically embodies firmware and / or software code is means such as a processing unit used to implement the steps and components described herein. May be used to implement For example, the firmware and / or software code may be stored in a memory, for example, in a control device, and executed by a computer or processor. The memory may be implemented inside the computer or processor, or may be implemented outside the processor. The firmware and / or software code may be, for example, random access memory (RAM), read only memory (ROM), nonvolatile random access memory (NVRAM), programmable read only memory (PROM), electrically erasable PROM (EEPROM) ), FLASH memory, floppy disk, compact disk (CD), digital versatile disk (DVD), magnetic or optical data storage, etc. Good. The code may be executed by one or more computers or processors, and may cause the computers or processors to perform the functional aspects described herein.

  Also, descriptions of embodiments disclosed herein are provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to the present disclosure will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. The present disclosure is therefore not limited to the examples and designs described herein, but should be accorded the widest scope consistent with the principles and novel features disclosed herein.

10 terminal (mobile station)
20, 20A, 20B Macrocell base station 21 Macrocell base station RRH (remote radio header)
200, 200A, 200B Macrocell 30, 30A, 30B Small cell base station 300, 300A, 300B Small cell 31 RRH (remote radio header)
40 high-rise building 50 BBU (baseband unit)
60 Inter-base station network cooperation controller (inter-base station controller)
61 Transmission Weight Calculation Unit 62 Transmission Signal Processing Unit 70 Aircraft Over Sky 700 Relay Radio Device 701 Macro Cell 711 Macro Cell Base Station RRH (Remote Radio Header)
712 Relay transceiver 80 Gate station 90 Communication line

Claims (11)

A first base station that forms a first cell; and one or a plurality of second base stations that form a second cell included in the first cell, the first base station, the second base station, Are mobile communication systems that are time-synchronized with respect to transmission timing,
Calculating a transmission weight for suppressing an interference signal from the first cell received by a terminal located in the second cell;
Creating a transmission interference suppression signal transmitted from the second base station by multiplying the transmission signal output from the baseband processing unit of the first base station and transmitted from the antenna by the transmission weight ;
The transmission time is adjusted so that the transmission time of the transmission signal from the first base station is the same as the transmission time of the transmission interference suppression signal from the second base station, and the transmission signal is A mobile communication system , wherein the transmission interference suppression signal is transmitted from one base station, and the transmission interference suppression signal is transmitted from the second base station. The mobile communication system according to claim 1, wherein
The transmission weight includes a propagation path characteristic of the first reception signal from the first base station and a propagation path characteristic of the second reception signal from the second base station measured by a terminal located in the second cell. The mobile communication system is calculated based on The mobile communication system according to claim 1 or 2,
The mobile communication system, wherein the transmission weight is calculated so as not to exceed a predetermined maximum value while maintaining a vector direction of the transmission weight. The mobile communication system according to any one of claims 1 to 3,
The transmission weight is a signal power to SINR (Signal power to signal power) ratio in the terminal under the condition that the total transmission power transmitted from the second base station does not exceed a predetermined maximum transmission power. A mobile communication system that is calculated so as to maximize an interference power and noise power ratio. The mobile communication system according to any one of claims 1 to 4,
Further comprising an inter-base station controller for controlling between the first base station and the second base station,
The inter-base station controller is
Information on the propagation path characteristics of the first received signal from the first base station and the propagation path characteristics of the second received signal from the second base station measured by the terminal located in the second cell, 2 via base stations,
Calculating the transmission weight based on the information received via the second base station;
Creating a transmission interference suppression signal transmitted from the second base station by multiplying the transmission signal output from the baseband processing unit of the first base station and transmitted from the antenna before the transmission weight;
As the transmission time of the transmission interference suppression signal from the second base station and the transmission time of the transmission signal from the first base station are the same time, transmission of the transmission signal of the to the first base station And transmission of the transmission interference suppression signal to the second base station, each shifted by a predetermined delay time,
The first base station transmits the transmission signal received from the inter-base station controller,
The mobile communication system, wherein the second base station transmits the transmission interference suppression signal received from the inter-base station controller. The mobile communication system according to any one of claims 1 to 4,
The second base station is
Information on the propagation path characteristics of the first reception signal from the first base station and the propagation path characteristics of the second reception signal from the second base station, measured by the terminal located in the second cell, from the terminal. Receive
Calculating the transmission weight based on the information received from the terminal;
A transmission interference suppression signal is created by multiplying the transmission signal received from the first base station by the transmission weight, and the transmission time of the transmission signal from the first base station and the transmission interference from the second base station A mobile communication system, wherein a transmission time is adjusted so that a transmission time of a suppression signal is the same time, and the transmission interference suppression signal is transmitted from the second base station. The mobile communication system according to any one of claims 1 to 4,
The terminal located in the second cell determines the transmission weight based on the measured propagation path characteristic of the first reception signal from the first base station and the propagation path characteristic of the second reception signal from the second base station. And transmitting the transmission weight information to the second base station,
The second base station receives the transmission weight information from the terminal, multiplies the transmission signal received from the first base station by the transmission weight, and creates a transmission interference suppression signal. The first base station The transmission time is adjusted so that the transmission time of the transmission signal from the second base station and the transmission time of the transmission interference suppression signal from the second base station become the same time, and the transmission interference suppression signal from the second base station The mobile communication system characterized by transmitting. The mobile communication system according to any one of claims 1 to 7,
A common baseband processing unit connected to each of the first base station and the second base station via a communication line;
Each of the first base station and the second base station receives a transmission signal generated by the baseband processing unit via a communication line and transmits it from an antenna of each base station. system. The mobile communication system according to any one of claims 1 to 8,
The first base station is provided on a flying object or levitation body located in the sky so as to form the first cell,
The mobile communication system, wherein the second base station is a macro cell base station or a small cell base station in which at least an antenna is arranged on the ground or the sea so as to form the second cell. The mobile communication system according to claim 9, wherein
The mobile communication system, wherein the first base station is provided in an artificial satellite, HAPS, airship, balloon or drone. An inter-base station controller that performs control between a first base station that forms a first cell and one or more second base stations that form a second cell included in the first cell,
Information on the propagation path characteristics of the first received signal from the first base station and the propagation path characteristics of the second received signal from the second base station measured by the terminal located in the second cell, 2 via base stations,
Based on the information received via the second base station, a transmission weight for suppressing an interference signal from the first cell received by a terminal located in the second cell is calculated,
Creating a transmission interference suppression signal transmitted from the second base station by multiplying the transmission signal output from the baseband processing unit of the first base station and transmitted from the antenna by the transmission weight;
The transmission time is adjusted so that the transmission time of the transmission signal from the first base station is the same as the transmission time of the transmission interference suppression signal from the second base station, and the transmission signal is An inter-base-station control apparatus that transmits from one base station and transmits the transmission interference suppression signal from the second base station.