WO2015025838A1 - 同期信号送信方法及び基地局装置 - Google Patents
同期信号送信方法及び基地局装置 Download PDFInfo
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- WO2015025838A1 WO2015025838A1 PCT/JP2014/071632 JP2014071632W WO2015025838A1 WO 2015025838 A1 WO2015025838 A1 WO 2015025838A1 JP 2014071632 W JP2014071632 W JP 2014071632W WO 2015025838 A1 WO2015025838 A1 WO 2015025838A1
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- synchronization signal
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
- H04W16/24—Cell structures
- H04W16/28—Cell structures using beam steering
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/001—Synchronization between nodes
Definitions
- the present invention relates to a synchronization signal transmission method and a base station apparatus in a next-generation mobile communication system.
- LTE Long Term Evolution
- Non-patent Document 1 a successor system of LTE is also being studied for the purpose of further broadbandization and higher speed from LTE (for example, LTE advanced or LTE enhancement (hereinafter referred to as “LTE-A”)).
- LTE-A LTE advanced or LTE enhancement
- the mobile station apparatus UE when the mobile station apparatus UE communicates with the network, a cell search process for establishing synchronization is required.
- the mobile station apparatus UE detects a synchronization signal (SS: Synchronization Signal) transmitted from the base station apparatus at a constant time interval, and the frequency of the cell (located cell) where the mobile station apparatus UE is located Acquire synchronization, timing synchronization, and cell ID (PCI: Physical Cell ID). Based on the acquired information, the mobile station apparatus UE determines a serving cell. Then, by transmitting RACH (Random Access CHannel), the cell is notified of the service area and communication resources are secured.
- SS Synchronization Signal
- PCI Physical Cell ID
- MIMO Massive MIMO (Multi Input Multi Output)
- MIMO Multi Input Multi Output
- Massive-MIMO Multi Input Multi Output
- beam forming is a technique that can change the directivity and beam shape of a transmission / reception beam by controlling the amplitude and phase of each transmission / reception signal in a plurality of antenna elements.
- the higher the number of antenna elements the higher control is possible.
- the number of beams according to the number of antenna elements, the shape of each beam (the width of the beam in the horizontal plane, the width of the beam in the vertical plane, etc., hereinafter referred to as “beam width” as appropriate), the direction and gain of the beam in detail.
- beam width the width of the beam in the horizontal plane, the width of the beam in the vertical plane, etc., hereinafter referred to as “beam width” as appropriate
- the direction and gain of the beam in detail can be controlled.
- high gain power density
- the present invention has been made in view of the above points, and an object of the present invention is to provide a synchronization signal transmission method and a base station apparatus that can sufficiently exert the performance of a communication system to which Massive-MIMO is applied.
- a synchronization signal transmission method of the present invention is a synchronization signal transmission method for controlling a transmission direction of a transmission beam for a synchronization signal used for cell search by beam forming using a plurality of antenna elements included in a base station apparatus, A synchronization signal processing step of generating a synchronization signal including information capable of identifying a transmission beam for a signal, and changing a beamforming weight for the synchronization signal at a predetermined time interval, and according to each of the beamforming weights And transmitting the synchronization signal generated in the downlink.
- the base station apparatus of the present invention is a base station apparatus that controls the transmission direction of a transmission beam for a synchronization signal used for cell search by beam forming using a plurality of antenna elements, and identifies the transmission beam for the synchronization signal
- a synchronization signal processing unit configured to generate a synchronization signal including possible information and change a beamforming weight for the synchronization signal at a predetermined time interval; and the synchronization signal generated according to each of the beamforming weights
- the present invention it is possible to provide a synchronization signal transmission method and a base station apparatus capable of sufficiently exerting the performance of a communication system to which Massive-MIMO is applied.
- FIG. 10 is a schematic diagram of a beam group transmitted by a BF-SS signal transmission method according to a first modification. It is explanatory drawing of the transmission method of the BF-SS signal which concerns on a 2nd modification. It is explanatory drawing of the transmission method of the BF-SS signal which concerns on a 3rd modification.
- a high frequency band of 10 GHz or more can be suitably used.
- the size of the antenna element is proportional to the wavelength of the transmission signal.
- the wavelength of the transmission signal is relatively short, and the size of the antenna element can be reduced.
- the high frequency band has a relatively low utilization rate compared to the low frequency band, and it is easy to secure resources with a wide bandwidth.
- propagation loss increases in signal transmission using a high frequency band. Therefore, even when signal transmission is performed with the same transmission power, the received signal strength in the mobile station apparatus UE can be reduced as compared with signal transmission using a low frequency band. However, such a decrease in received signal strength can be covered by the beamforming gain.
- FIG. 1 is an explanatory diagram of a transmission beam reachable range in the Massive-MIMO base station.
- FIG. 1A shows a reach range of a transmission beam output from a general base station apparatus (a base station apparatus to which Massive-MIMO is not applied), and
- FIG. 1B shows a transmission beam output from a Massive-MIMO base station. The reach of is shown.
- a case is shown where signal transmission using the high frequency band is performed in the Massive-MIMO base station shown in FIG. 1B and signal transmission using the low frequency band is performed in the base station apparatus shown in FIG. 1A. Yes.
- the Massive-MIMO base station grasps the position (direction, distance) of the mobile station apparatus UE to be transmitted, forms a transmission beam having directivity at the position by beam forming, and transmits user data Is preferably transmitted.
- the mobile station apparatus UE When performing wireless communication with such a Massive-MIMO base station, the mobile station apparatus UE needs to perform a cell search process for establishing synchronization, as in LTE and LTE-A.
- a synchronization signal (SS: Synchronization Signal) is transmitted without beamforming from the Massive-MIMO base station, if the mobile station apparatus UE exists at a position away from the Massive-MIMO base station, synchronization is performed. The reception power of the signal is reduced, and a situation where the cell search process cannot be performed properly may occur.
- SS Synchronization Signal
- the gist of the present invention is a synchronization signal transmission method for controlling the transmission direction of a transmission beam for a synchronization signal used for cell search by beam forming using a plurality of antenna elements included in a Massive-MIMO base station.
- the beamforming weight for the synchronization signal is changed at a predetermined time interval, and the generated synchronization signal is downloaded according to each beamforming weight. It is sent on a link.
- the synchronization signal since a synchronization signal in which the beamforming weight is changed is generated and transmitted every predetermined time interval, the synchronization signal can reach a position at a long distance from the Massive-MIMO base station. it can. Thereby, since the cell search process can be appropriately performed in the mobile station apparatus UE, it is possible to suppress a decrease in throughput characteristics due to a defect in the cell search process or the like.
- each synchronization signal since each synchronization signal includes information capable of identifying the transmission beam for the synchronization signal, the mobile station apparatus UE can identify the transmission beam for the synchronization signal. Therefore, even when beam forming is applied to the synchronization signal, the cell search process can be appropriately performed.
- FIG. 2 is a diagram illustrating an example of a network configuration to which the base station apparatus according to the present embodiment is applied.
- FIG. 2 shows a case where the base station apparatus according to the present embodiment is applied to a network (eg, heterogeneous network) configuration in which the Massive-MIMO cell MM is overlaid in the cell area of the macro cell M. ing.
- the network to which the Massive-MIMO base station according to the present embodiment is applied is not limited to an overlay network, and can be changed as appropriate.
- a base station apparatus hereinafter referred to as “macro base station” as appropriate
- MeNB Massive-MIMO forming the macro cell M
- a base station apparatus hereinafter referred to as “Massive-MIMO base station (MM base station)”
- MMeNB forming the cell MM is connected to a central control station CC disposed in the macro cell M.
- the central control station CC is connected to a core network (not shown).
- the central control station CC includes, for example, an access gateway device, a radio network controller (RNC), a mobility management entity (MME), and the like, but is not limited thereto.
- RNC radio network controller
- MME mobility management entity
- a mobile station apparatus (hereinafter simply referred to as “mobile station”) UE is configured to be able to communicate with a macro base station MeNB when located in the macro cell M, and to a macro base station MeNB when located in the Massive-MIMO cell MM. In addition, it is configured to be able to communicate with the MM base station MMeNB.
- the mobile station UE wirelessly communicates with the macro base station MeNB and the MM base station MMeNB, but more generally, the user equipment (UE including both the mobile terminal apparatus and the fixed terminal apparatus) : User Equipment)
- a control plane (C (Control) -plane) that handles control messages is supported by the macro cell M.
- a user plane (U (User) -plane) for handling user data is supported by the Massive-MIMO cell MM.
- the macro cell M and the massive-MIMO cell MM can be operated in different frequency bands.
- the C-plane supported by the macro cell M can be operated in the 2 GHz band
- the U-plane supported by the Massive-MIMO cell MM can be operated in the 10 GHz band.
- the MM base station MMeNB and the mobile station UE may be connected by a line-of-sight (LoS) that does not have an obstacle.
- LoS line-of-sight
- a propagation path having a low frequency selectivity is generally formed.
- the overlay network configuration shown in FIG. 2 shows a case where the MM base station MMeNB according to the present embodiment is arranged so as to overlap the macro cell M.
- the target to which the MM base station MMeNB according to the present embodiment overlaps is not limited to this.
- the MM base station MMeNB according to the present embodiment does not necessarily have to be placed on another radio base station or a network so as to overlap.
- the MM base station MMeNB can perform signal transmission to the mobile station UE located in the Massive-MIMO cell MM using the Massive-MIMO transmission scheme. More specifically, the MM base station MMeNB forms a transmission beam having directivity toward the mobile station UE by controlling the amplitude and phase of each signal in a plurality of antenna elements ( Signal transmission can be performed by beam forming.
- MM base station MMeNB applies beamforming not only to user data for mobile station UE but also to a synchronization signal (hereinafter referred to as “SS signal”) necessary for cell search processing. More specifically, the MM base station MMeNB applies beam forming to the SS signal to generate and transmit a transmission beam having a narrow beam width.
- SS signal synchronization signal
- an SS signal to which beam forming is applied is referred to as a “BF-SS signal”.
- SA Massive-MIMO cell MM
- a decrease in received power in the synchronization signal can be prevented. Thereby, even when the mobile station UE exists in a position away from the MM base station MMeNB, the mobile station UE can detect the synchronization signal and appropriately perform the cell search process.
- a plurality of modes of a method for transmitting a synchronization signal (BF-SS signal) in the MM base station MMeNB according to the present embodiment will be described.
- FIG. 3 is an explanatory diagram of a BF-SS signal transmission method according to the first aspect.
- FIG. 3A schematically shows a transmission image of a BF-SS signal transmitted from the MM base station MMeNB to the SA.
- FIG. 3B the BF-SS signal transmitted from the MM base station MMeNB is shown on the time axis and the frequency axis.
- a transmission beam having a narrow beam width (hereinafter abbreviated as “narrow beam”) is generated for the transmission of the BF-SS signal. To do. Then, by changing the transmission direction of this narrow beam in the azimuth direction at every time interval ⁇ , the BF-SS signal is transmitted to the entire SA of the Massive-MIMO cell MM at a predetermined total time T.
- the transmission method of the BF-SS signal according to the first aspect is such that the transmission direction of the narrow beam for transmitting the BF-SS signal is changed in the azimuth direction at every time interval ⁇ , so that the Massive-MIMO cell This is a transmission method of scanning all mobile stations UE located in the MM SA.
- the azimuth direction is equal to the beam width ⁇ at timing t 2.
- the transmission direction is shifted to a narrow beam (see FIG. 3A).
- transmission of a narrow beam is repeated by shifting the transmission direction in the azimuth direction by the beam width ⁇ at every time interval ⁇ .
- the BF-SS signal S (t) can be obtained by, for example, the following (Equation 1).
- W n (t, f) represents a beamforming weight (hereinafter referred to as “BF weight”)
- S SS (t) represents an SS signal.
- the total time T for transmitting the BF-SS signal to the entire SA (omnidirectional) of the Massive-MIMO cell MM is, for example, 2).
- T 360 ⁇ / ⁇
- ⁇ represents the time interval of the BF-SS signal
- ⁇ represents the beam width of the BF-SS signal.
- the time interval ⁇ and the beam width ⁇ can be selected as parameters in the communication system.
- the time interval ⁇ can be determined according to the signal length of the SS signal.
- the time interval ⁇ can be increased when the signal length of the SS signal is long, while the time interval ⁇ can be decreased when the signal length of the SS signal is short.
- the beam width ⁇ can be determined according to the number of antenna elements, transmission power, frequency band, bandwidth, and total time T. When the number of antenna elements is large, the beam width ⁇ can be narrowed, whereas when the number of antenna elements is small, the beam width ⁇ can be widened.
- the beam width ⁇ can be widened, while when the transmission power is small, the beam width ⁇ can be narrowed.
- the frequency band is high, the beam width ⁇ can be narrowed, whereas when the frequency band is low, the beam width ⁇ can be widened.
- the bandwidth is wide, the beam width ⁇ can be narrowed, while when the bandwidth is narrow, the beam width ⁇ can be widened.
- the total time T is long, the beam width ⁇ can be narrowed, whereas when the total time T is short, the beam width ⁇ can be widened.
- the cell radius is large, the beam width ⁇ can be reduced, while when the cell radius is small, the beam width ⁇ can be increased.
- the time interval ⁇ and the beam width ⁇ may be determined according to predetermined contents. Further, the time interval ⁇ and the beam width ⁇ may be adaptively calculated depending on the communication environment. As for the communication environment, for example, the number of mobile stations UE in the Massive-MIMO cell MM, the distance to an adjacent cell (such as the Massive-MIMO cell MM), and the like are assumed. In addition, about the information regarding this communication environment, it can acquire from the macrocell M (more specifically, macro base station MeNB) arrange
- each BF-SS signal can be identified by the mobile station UE.
- unique identification information (beam ID)
- a beam ID is generated by the MM base station MMeNB and is included in the synchronization signal as well as system information such as a cell ID. Since it is included in the synchronization signal, it is possible to receive the synchronization signal appropriately by the mobile station UE as with the system information.
- a cell-specific orthogonal sequence that can identify a base station as a cell ID.
- the identification information is not limited to the beam ID.
- Arbitrary identification information can be adopted as long as a narrow beam transmitted in each direction can be identified.
- a plurality of types of SS signals may be prepared in advance, such as PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal) in LTE, and different system information may be assigned to each.
- PSS Primary Synchronization Signal
- SSS Secondary Synchronization Signal
- BF weight in (Expression 1) described above can be used as identification information.
- the synchronization signal (BF-SS signal) in which the beamforming weight is changed is generated and transmitted every time interval ⁇ .
- the synchronization signal can be made to reach a long distance from the Massive-MIMO base station MMeNB.
- each synchronization signal includes a beam ID that can identify the transmission beam for the synchronization signal. Since the signal transmission beam can be identified, the cell search process can be appropriately performed even when beam forming is applied to the synchronization signal.
- BF weights corresponding to various beam directions and beam shapes (widths) are generated in advance, and the database It is preferable as an embodiment that the stored information is stored in the Massive-MIMO base station MMeNB (or in the network) and only the BF weight is selected according to the beam direction and width at the time of beamforming. In this case, since the process of generating the BF weight based on the beam direction and width can be omitted, it is possible to reduce the load when generating the synchronization signal (BF-SS signal) in the Massive-MIMO base station MMeNB. Become.
- the elevation angle direction is added to the transmission direction of the narrow beam for transmitting the BF-SS signal. It differs from the transmission method. That is, the BF-SS signal transmission method according to the second aspect changes the transmission direction of a narrow beam for transmission of the BF-SS signal to the azimuth angle direction and the elevation angle direction at every time interval ⁇ , so that A transmission method that scans all mobile stations UE located in the SA of the MIMO cell MM.
- the description will focus on differences from the BF-SS signal transmission method according to the first aspect.
- the elevation direction is orthogonal to the horizontal direction, and the direction indicated by an angle in which the angle indicating the downward (or upward) direction is 0 ° and the angle indicating the horizontal direction is 90 °. It is defined as
- FIG. 4 is an explanatory diagram of a BF-SS signal transmission method according to the second aspect.
- FIG. 4A it is explanatory drawing of the elevation angle direction of the BF-SS signal transmitted from MM base station MMeNB.
- FIG. 4B schematically shows a transmission image of a BF-SS signal transmitted from the MM base station MMeNB to the SA.
- FIG. 4C the BF-SS signal transmitted from the MM base station MMeNB is shown on the time axis and the frequency axis.
- the MM base station MMeNB is arranged at a position away from the ground.
- the MM base station MMeNB used in the BF-SS signal transmission method according to the second aspect transmits to the position corresponding to the radius of the SA of the Massive-MIMO cell MM as shown in FIG. 4A.
- the beam is arranged at a position having an angle ⁇ in the elevation direction.
- the MM base station MMeNB used in the BF-SS signal transmission method according to the second aspect has a transmission beam having an angle ⁇ 1 in the elevation direction and an angle ⁇ 2 in the elevation direction.
- the BF-SS signal can be transmitted toward three regions included in the SA of the Massive-MIMO cell MM by generating the transmission beam having the angle ⁇ 3 in the elevation angle direction.
- the BF-SS signal transmission method generates different transmission beams in the radial direction of the Massive-MIMO cell MM.
- -Different from the SS signal transmission method is performed by, for example, a beam forming technique that provides directivity in the vertical direction (3D beam forming).
- the beam width ⁇ of the transmission beam in the radial direction of the Massive-MIMO cell MM is a length corresponding to half of the radius of the Massive-MIMO cell MM.
- FIG. 4B and FIG. 4C a case where two different transmission beams are generated in the radial direction of the Massive-MIMO cell MM will be described.
- the number of transmission beams generated in the radial direction of the Massive-MIMO cell MM is not limited to this and can be changed as appropriate.
- a narrow beam is transmitted by shifting the transmission direction outward (see FIG. 4B). Further, after transmitting a narrow beam by shifting the transmission direction by the beam width ⁇ in azimuth at a timing t 21, by shifting the transmission direction by beamwidth ⁇ elevation inwardly at the timing t 22 to transmit the narrow beam (FIG. 4B). Similarly, transmission of a narrow beam is repeated by shifting the transmission direction in the elevation direction or azimuth direction by the beam width ⁇ at every time interval ⁇ .
- the entire SA (all directions) of the Massive-MIMO cell MM can be scanned. .
- the BF-SS signal S (t) can be obtained by, for example, (Equation 1) described above.
- the total time T when the BF-SS signal is transmitted to the entire SA (omnidirectional) of the Massive-MIMO cell MM is, for example, 3).
- T 360 ⁇ / ⁇ 2
- ⁇ indicates the time interval of the BF-SS signal
- ⁇ indicates the angle of the maximum elevation angle of the transmission beam
- ⁇ indicates the beam width of the BF-SS signal.
- the time interval ⁇ and the beam width ⁇ can be configured to be selectable as parameters in the communication system, as in the first aspect. Further, as in the first mode, the time interval ⁇ and the beam width ⁇ may be determined according to predetermined contents, or may be calculated adaptively depending on the communication environment.
- the total time T when the BF-SS signal is transmitted to the entire SA (omnidirectional) of the Massive-MIMO cell MM can be obtained by, for example, (Equation 4) below.
- T 360 ⁇ / ( ⁇ H ⁇ V )
- ⁇ represents the time interval of the BF-SS signal
- ⁇ represents the angle of the maximum elevation angle of the transmission beam
- ⁇ H represents the horizontal beam width of the BF-SS signal
- ⁇ V represents the BF-SS signal. Indicates the vertical beam width.
- parameters such as beam width and time interval are selected in consideration of such a phenomenon and the uniformity and efficiency of scanning of the BF-SS signal within the SA. This is preferable as an embodiment.
- the beam width and the time interval between when the elevation angle is high and when the elevation angle is low the total power of the beam can be shared, and the uniformity of BF-SS signal scanning can be ensured.
- the transmission beam scanning order and scanning range can also be selected as parameters in the communication system.
- FIG. 4B illustrates a case where scanning is performed from the same direction side in the radial direction of the Massive-MIMO cell MM when the transmission direction of the transmission beam is changed in the azimuth direction.
- the scanning order of the transmission beams is not limited to this, and can be changed as appropriate.
- the transmission direction of the transmission beam in the azimuth direction it is possible to scan from different direction sides in the radial direction of the Massive-MIMO cell MM.
- the transmission beam before the change is outside the Massive-MIMO cell MM, the transmission beam may be transmitted to the inside which is a different direction side. Good.
- FIG. 4B illustrates a case where the entire SA of the Massive-MIMO cell MM is used as the scanning range.
- the scanning range of the transmission beam is not limited to this, and can be changed as appropriate. For example, only a certain area of the Massive-MIMO cell MM can be scanned with the transmission beam. Such selection of the local scanning range is assumed when the position of the mobile station UE can be acquired in advance from the macro cell M (more specifically, the macro base station MeNB) arranged in an overlapping manner. .
- the beamforming weight is changed at each time interval ⁇ , as in the BF-SS signal transmission method according to the first aspect. Since the synchronization signal (BF-SS signal) is generated and transmitted, the synchronization signal can reach a position at a long distance from the Massive-MIMO base station MMeNB. Thereby, since the cell search process can be appropriately performed in the mobile station UE, it is possible to suppress a decrease in throughput characteristics due to a defect in the cell search process or the like. Since each synchronization signal includes a beam ID that can identify the transmission beam for the synchronization signal, the mobile station UE can identify the transmission beam for the synchronization signal. Even when forming is applied, cell search processing can be performed appropriately.
- the scanning mode according to the BF-SS signal transmission method according to the first aspect is referred to as a two-dimensional (2D) scanning mode
- the scanning mode according to the BF-SS signal transmission method according to the second aspect is referred to as a three-dimensional (3D) scanning mode.
- These scanning modes can be configured to be selectable as parameters in the communication system.
- the 3D scanning mode can be selected when the SA of the Massive-MIMO cell MM is relatively large, while the 2D scanning mode can be selected when the SA is relatively small.
- the 2D scanning mode can be selected when the beam having a wide beam width on the vertical plane can be covered with respect to SA.
- the communication environment such as the arrangement status of the mobile station UE is determined.
- the 2D scanning mode and the 3D scanning mode can be dynamically switched.
- these scanning modes can be switched by selecting a BF weight that controls the BF-SS signal transmission direction in the azimuth direction and a BF weight that controls the azimuth direction and the elevation direction. Since the 2D scanning mode and the 3D scanning mode can be switched by selecting the BF weight in this way, the synchronization signal necessary for the cell search process can be flexibly switched without requiring complicated control.
- FIG. 5 is an explanatory diagram showing an example of an operation sequence between the MM base station MMeNB and the mobile station UE in the BF-SS signal transmission method according to the first and second aspects.
- the synchronization signal (BF-SS signal) transmitted from the MM base station MMeNB includes a beam ID as transmission beam identification information.
- the MM base station MMeNB first generates a BF-SS signal by applying beamforming to the SS signal (multiplying the BF weight) (step (hereinafter referred to as “ST”) 501. ).
- the MM base station MMeNB generates a BF-SS signal by the calculation of (Equation 1) described above.
- the MM base station MMeNB transmits the generated BF-SS signal (ST502).
- This BF-SS signal is transmitted toward a certain area of the Massive-MIMO cell MM specified by the BF weight.
- the BF-SS signal includes a cell ID, a beam ID, and the like.
- the mobile station UE performs cell search processing when power is turned on or when returning from outside the cell area (outside the small cell area) to the cell area (ST503).
- the mobile station UE monitors the BF-SS signal from the MM base station MMeNB.
- a frequency is specified from the BF-SS signal and timing synchronization is taken.
- the mobile station UE acquires cell ID, beam ID, reception quality information (for example, reception power information) of the BF-SS signal, and the like.
- the cell search process is completed by acquiring these pieces of information.
- the mobile station UE acquires all received beam IDs, reception quality, and the like. It is to be noted that the beam ID, reception quality, etc. of the top M transmission beams (BF-SS signals) with good reception quality are acquired, or that the transmission beam (BF-SS signal) is higher than the predetermined reception quality. It is also possible to acquire ID, reception quality, and the like. In these cases, the number of transmission beams (M) and the threshold of reception quality can be selected as parameters in the communication system.
- the mobile station UE After completing the cell search process, the mobile station UE generates a RACH preamble based on the cell ID and beam ID acquired in the cell search process and its own terminal ID (UE-ID) (ST504). Then, the generated RACH preamble is transmitted to the MM base station MMeNB together with the reception quality information of the transmission beam (BF-SS signal) (ST505).
- UE-ID the cell ID and beam ID acquired in the cell search process and its own terminal ID
- the mobile station UE when a plurality of transmission beams (BF-SS signals) are received, for example, the mobile station UE generates a RACH preamble for all the transmission beams, and MM together with reception quality information of each transmission beam. Transmit to the base station MMeNB. It is also possible to generate and transmit a RACH preamble for the top M transmission beams with good reception quality, and to generate and transmit a RACH preamble for a transmission beam with a predetermined reception quality or higher. Furthermore, it is also possible to transmit the reception quality information of the transmission beam (BF-SS signal) separately from the RACH preamble.
- BF-SS signals reception quality information of the transmission beam
- the MM base station MMeNB After transmitting the BF-SS signal in ST502, the MM base station MMeNB monitors the RACH preamble from the mobile station UE. And if a RACH preamble is received, a RACH response will be transmitted to the mobile station UE (ST506).
- the RACH response includes information such as a preamble number detected by the MM base station MMeNB and transmission timing information.
- the mobile station UE monitors the RACH response from the MM base station MMeNB. Then, when receiving the RACH response (ST507), the mobile station UE transmits the system bandwidth, system frame number (SFN), transmission antenna from the MIB (Master Information Block) included in the PBCH (Physical Broadcast Channel). Get basic information such as numbers. And based on these information, it connects with MM base station MMeNB.
- SFN system frame number
- MIB Master Information Block
- FIG. 6 is a block diagram for explaining a configuration example of the MM base station MMeNB used in the BF-SS signal transmission method according to the first and second aspects.
- FIG. 7 is a block diagram for explaining a configuration example of the mobile station UE used in the BF-SS signal transmission method according to the first and second aspects.
- the configurations of the MM base station MMeNB and the mobile station UE shown in FIGS. 6 and 7 are simplified to explain the present invention, and the configurations of the normal base station device and the mobile station device are provided. It shall be.
- the component regarding data communication is abbreviate
- the information acquisition units 611 and 711 that acquire various types of information (external information) from the macro cell M and the like are described. However, these components can be omitted.
- the MM base station MMeNB includes a synchronization signal (SS) signal control unit 61, an SS signal processing unit 62, a data signal processing unit 63, a transmission unit 64, and a reception unit 65.
- the SS signal control unit 61 includes an information acquisition unit 611 and an SS control information generation unit 612.
- the SS signal processing unit 62 includes an SS signal generation unit 621, a storage unit 622, a BF weight generation unit 623, and a BF-SS signal generation unit 624.
- the data signal processing unit 63 includes a data generation unit 631, a storage unit 632, a data weight generation unit 633, and a transmission / reception signal generation unit 634.
- the transmission unit 64 includes a transmission control unit 641 and a signal transmission unit 642.
- the reception unit 65 includes a reception control unit 651 and a signal reception unit 652.
- the SS signal control unit 61 provides the SS signal processing unit 62, the data signal processing unit 63, the transmission unit 64, and the reception unit 65 with information (SS control information) necessary for generating or transmitting a BF-SS signal. To do.
- SS control information based on the external information is generated and provided to the SS signal processing unit 62 or the like.
- the information acquisition unit 611 acquires external information from the macro cell M or the like. Then, the acquired external information is output to the SS control information generation unit 612.
- information on the communication environment such as the number of mobile stations UE in the Massive-MIMO cell MM and the distance to the adjacent Massive-MIMO cell MM is acquired.
- the SS control information generation unit 612 generates SS control information used in the MM base station MMeNB based on the external information received from the information acquisition unit 611.
- This SS control information includes, for example, the beam width ⁇ for the BF-SS signal, the time interval ⁇ for switching the transmission direction, and the scanning method (including the scanning mode). Then, the SS control information generation unit 612 transmits the generated SS control information to the storage unit 622 and the BF weight generation unit 623 of the SS signal processing unit 62, the storage unit 632 and the data weight generation unit 633 of the data signal processing unit 63, and transmission. Output to the transmission control unit 641 of the unit 64 and the reception control unit 651 of the reception unit 65.
- the SS control information generation unit 612 generates SS control information based on the external information received from the information acquisition unit 611.
- the beam width ⁇ for the BF-SS signal, the time interval ⁇ for switching the transmission direction, and the scanning method are, for example, in the communication system. It is configured to be selectable as a parameter.
- the SS control information generation unit 612 generates SS control information based on these parameters.
- the SS signal processing unit 62 generates a BF-SS signal based on the SS control information received from the SS signal control unit 61 and outputs the BF-SS signal to the transmission unit 64.
- the storage unit 622 includes a database that stores SS control information and information generated based on the SS control information (SS generation information). In this database, for example, SS control information received from the SS control information generation unit 612 and SS generation information generated by the SS signal generation unit 621 and the BF weight generation unit 623 are stored.
- the SS generation information includes an SS signal and an SS signal BF weight (BF weight). Note that it is also possible to manage the BF weights in advance as a table.
- the SS signal generation unit 621 generates an SS signal based on the SS control information stored in the storage unit 622 (database). Then, the generated SS signal is output to the BF-SS signal generation unit 624 and the storage unit 622.
- the BF weight generation unit 623 generates a BF weight based on the SS control information received from the SS control information generation unit 612. Then, the generated BF weight is output to the BF-SS signal generation unit 624 and the storage unit 622.
- the SS generation information (SS signal, BF weight) stored in the storage unit 622 can be used, the SS signal generation unit 621 and the BF weight generation unit 623 call them and output them to the BF-SS signal generation unit 624.
- the BF-SS signal generation unit 624 generates a BF-SS signal based on the SS signal from the SS signal generation unit 621 and the BF weight from the BF weight generation unit 623. Then, the generated BF-SS signal is output to the transmission unit 64.
- the data signal processing unit 63 generates a beam-formed transmission signal (BF transmission signal) based on the data source and control information instructed by the upper layer, and outputs the transmission signal to the transmission unit 64.
- the data generation unit 631 generates transmission data from a data source for transmission data and control information.
- the storage unit 632 stores weight generation information for transmission data received from the SS control information generation unit 612.
- the data weight generation unit 633 generates a data weight (transmission weight) based on the weight generation information stored in the storage unit 632. Then, the generated data weight is output to the transmission / reception signal generation unit 634 and the storage unit 632.
- the transmission / reception signal generation unit 634 generates a beam-formed transmission signal (BF transmission signal) based on the transmission data from the data generation unit 631 and the transmission weight from the data weight generation unit 633. Then, the generated BF transmission signal is output to the transmission unit 64.
- BF transmission signal beam-formed transmission signal
- the data signal processing unit 63 extracts the data source and control information from the reception signal received by the reception unit 65.
- the storage unit 632 stores weight generation information for received data received from the SS control information generation unit 612.
- the data weight generation unit 633 generates a data weight (reception weight) based on the weight generation information stored in the storage unit 632. Then, the generated data weight is output to the transmission / reception signal generation unit 634 and the storage unit 632.
- the transmission / reception signal generation unit 634 receives the reception signal output from the reception unit 65. Also, the transmission / reception signal generation unit 634 generates a reception signal based on the reception weight received from the data weight generation unit 633. Then, the generated reception signal is output to the data generation unit 631.
- the data generation unit 631 generates reception data based on this reception signal. Then, the generated reception data is output to a higher-level component (not shown) (for example, an application processing unit).
- the transmission unit 64 transmits the BF-SS signal or the BF transmission signal from the SS signal processing unit 62 or the data signal processing unit 63 on the downlink.
- the transmission control unit 641 controls the BF-SS signal transmission processing by the signal transmission unit 642 based on the SS control information received from the SS control information generation unit 612. For example, the transmission control unit 641 controls the time interval ⁇ of transmission of the BF-SS signal by the signal transmission unit 642.
- the signal transmission unit 642 transmits a BF-SS signal and a BF transmission signal under the control of the transmission control unit 641.
- the receiving unit 65 receives a reception signal from the mobile station UE and outputs it to the data signal processing unit 63.
- the reception control unit 651 controls reception processing such as a RACH preamble by the signal reception unit 652 based on the SS control information received from the SS control information generation unit 612.
- the signal reception unit 652 receives a RACH preamble and a reception signal under the control of the reception control unit 651.
- the received RACH preamble and received signal are output to the data signal processing unit 63.
- the mobile station UE includes a cell search (CS) control unit 71, an SS signal processing unit 72, a connection request unit 73, a reception unit 74, and a transmission unit 75.
- the CS control unit 71 includes an information acquisition unit 711 and a CS control information generation unit 712.
- the SS signal processing unit 72 includes an SS related information extraction unit 721, a reception quality measurement unit 722, and a storage unit 723.
- the connection request unit 73 includes a reception quality information generation unit 731, a RACH preamble generation unit 732, and a transmission signal generation unit 733.
- the reception unit 74 includes a reception control unit 741 and a signal reception unit 742.
- the transmission unit 75 includes a transmission control unit 751 and a signal transmission unit 752.
- the CS control unit 71 provides the SS signal processing unit 72, the connection request unit 73, the reception unit 74, and the transmission unit 75 with information (CS control information) necessary for the cell search process.
- CS control information based on the external information is generated and provided to the SS signal processing unit 72 or the like.
- the information acquisition unit 711 acquires external information from the macro cell M or the like. For example, as external information from the macro cell M or the like, information such as a candidate list (Massive-MIMO cell ID or cell position coordinate) of the Massive-MIMO cell MM is acquired. Further, the information acquisition unit 711 acquires SS related information input from the SS related information extraction unit 721 of the SS signal processing unit 72. Then, the acquired external information and SS related information are output to the CS control information generation unit 712.
- the CS control information generation unit 712 generates CS control information used in the mobile station UE based on the external information and the SS related information received from the information acquisition unit 711.
- This CS control information includes, for example, information such as the beam direction, beam width, signal length, frequency, bandwidth, scanning timing, and scanning method of the transmission beam of the BF-SS signal. Then, the CS control information generation unit 712 converts the generated CS control information into the storage unit 723 of the SS signal processing unit 72, the transmission signal generation unit 733 of the connection request unit 73, the reception control unit 741 and the transmission unit 75 of the reception unit 74. To the transmission control unit 751.
- CS control information generation unit 712 generates CS control information based on the external information received from the information acquisition unit 711.
- CS control information such as the beam direction and beam width of the transmission beam of the BF-SS signal is configured to be selectable as a parameter in the communication system, for example.
- the CS control information generation unit 712 generates SS control information based on these parameters.
- the SS signal processing unit 72 extracts and stores information related to the SS signal (SS related information) from the received signal from the receiving unit 74 and outputs it to the CS control unit 71.
- the SS related information extraction unit 721 extracts SS related information from the reception signal received from the reception unit 74.
- the extracted SS related information includes the beam ID included in the BF-SS signal.
- the SS related information extraction unit 721 outputs the extracted SS related information to the storage unit 723 and the information acquisition unit 711 of the CS control unit 71.
- the reception quality measurement unit 722 measures the reception quality from the reception signal received from the reception unit 74. Then, the measured reception quality is output to the storage unit 723.
- the storage unit 723 includes a database that stores the SS related information and the reception quality received from the SS related information extraction unit 721 and the reception quality measurement unit 722.
- the connection request unit 73 generates a transmission signal including the RACH preamble and the reception quality information based on the CS control information from the CS signal control unit 71, the SS related information stored in the SS signal processing unit 72, and the reception quality.
- the data is output to the transmission unit 75.
- the reception quality information generation unit 731 reads the reception quality from the storage unit 723 of the SS signal processing unit 72 and generates reception quality information. Then, the generated reception quality information is output to transmission signal generation section 733.
- the RACH preamble generation unit 732 reads the SS related information from the storage unit 723 of the SS signal processing unit 72 and generates a RACH preamble. Then, the generated RACH preamble is output to transmission signal generating section 733.
- the transmission signal generation unit 733 generates a transmission signal including the RACH preamble and reception quality information. Then, the generated transmission signal is output to the transmission unit 75.
- the receiving unit 74 receives a reception signal from the MM base station MMeNB and outputs it to the SS signal processing unit 72.
- the reception control unit 741 controls reception processing of a BF-SS signal and the like by the signal reception unit 742 based on the CS control information received from the CS control information generation unit 712. For example, the reception control unit 741 controls the reception timing of the BF-SS signal by the signal reception unit 742.
- the signal reception unit 742 receives the BF-SS signal under the control of the reception control unit 741. Then, the received BF-SS signal is output to the SS signal processing unit 72.
- the transmission unit 75 transmits the transmission signal from the connection request unit 73 to the MM base station MMeNB via the uplink.
- the transmission control unit 751 controls transmission processing of a transmission signal by the signal transmission unit 752 based on the CS control information received from the CS control information generation unit 712. For example, the transmission control unit 751 controls the transmission timing of the transmission signal by the signal transmission unit 752 and the like.
- the signal transmission unit 752 transmits a transmission signal under the control of the transmission control unit 751.
- FIG. 8 and 9 are flowcharts for explaining a BF-SS signal transmission operation from the MM base station MMeNB used in the BF-SS signal transmission method according to the first and second aspects.
- 10 and 11 are flowcharts for explaining the reception operation of the BF-SS signal of the mobile station UE used in the BF-SS signal transmission method according to the first and second aspects. Note that FIG. 9 is obtained by partially changing the operation flow shown in FIG. 8, and the processes common to those in FIG. FIG. 11 is a partial change of the operation flow shown in FIG. 10, and the processes common to those in FIG.
- the SS signal control unit 61 when transmitting a BF-SS signal, in the MM base station MMeNB, the SS signal control unit 61 generates SS control information based on the external information (ST801).
- the SS control information generated in ST801 is output to the database in the storage unit 622 of the SS signal processing unit 62, the BF weight generation unit 623, and the transmission control unit 641 of the transmission unit 64.
- Storage section 622 stores this SS control information in a database (ST802).
- the SS control information generation unit 612 selects a BF parameter (ST803). For example, the SS control information generation unit 612 selects the beam width ⁇ for the BF-SS signal, the time interval ⁇ for switching the transmission direction, and the scanning method (including the scanning mode). SS signal generation section 621 generates an SS signal based on these BF parameters (ST804). The generated SS signal is output to the BF-SS signal generation unit 624.
- the BF parameter selected by the SS control information generation unit 612 is output and stored in the database.
- the SS signal generation unit 621 can also generate an SS signal based on the BF parameters stored in the database.
- BF weight generation section 623 generates a BF weight (SS signal BF weight) based on the SS control information received from SS signal control section 61 (ST805). Then, the generated BF weight is output to the BF-SS signal generation unit 624.
- BF-SS signal generation section 624 generates a BF-SS signal according to these SS signal and BF weight (ST806).
- the generated BF-SS signal is output to the signal transmission unit 642 of the transmission unit 64.
- Signal transmission section 642 transmits this BF-SS signal in the downlink (ST807).
- the transmission control unit 641 controls the transmission of the BF-SS signal by the signal transmission unit 642 based on the SS control information received from the SS signal control unit 61.
- the transmit beam (BF-SS signal) is transmitted to the transmission direction of the timing t 1 shown in FIG. 3A.
- the MM base station MMeNB monitors whether the reception control unit 651 of the reception unit 65 receives the signal (RACH preamble) from the mobile station UE (ST808). Using the above example, it is monitored whether or not the RACH preamble is received from the mobile station UE that has received the transmission beam at timing t 1 .
- the SS signal control unit 61 can further generate SS control information based on information included in the RACH preamble.
- SS signal control section 61 determines whether scanning has been completed for all SAs in Massive-MIMO cell MM (that is, whether BF-SS signals have been transmitted to all SAs) (ST809). If scanning has not been completed for all SAs in Massive-MIMO cell MM, the process returns to ST803, and the processes of ST803 to ST809 are repeated. Using the above example, after transmitting the transmission beam at timing t 1 , the transmission beam (BF-SS signal) is transmitted in the transmission direction at timing t 2 . If it is determined in ST809 that scanning has been completed for all SAs in the Massive-MIMO cell MM, the process ends. When it is determined that scanning has been completed for all SAs in the Massive-MIMO cell MM, for example, a BF-SS signal is transmitted in all directions shown in FIG. 3A.
- the SS signal control unit 61 completes scanning for all SAs of the Massive-MIMO cell MM (that is, all SAs are transmitted). (Whether a BF-SS signal has been transmitted) is determined (ST901). If scanning has not been completed for all SAs in Massive-MIMO cell MM, the process returns to ST803, and the processes of ST803 to ST807 and ST901 are repeated.
- reception control section 651 of reception section 65 receives a signal (RACH preamble) from mobile station UE (ST902). ).
- RACH preamble a signal
- information included in the RACH preamble is output to the SS signal control unit 61 (information acquisition unit 611).
- the process ends when a certain time has elapsed after the last BF-SS signal is transmitted.
- the synchronization signal (BF-SS signal) in which the beamforming weight is changed is generated at each time interval ⁇ , the long distance from the Massive-MIMO base station MMeNB is transmitted.
- the synchronization signal can be made to reach the position.
- the CS signal control unit 71 When receiving the BF-SS signal, in the mobile station UE, as shown in FIG. 10, the CS signal control unit 71 generates CS control information based on the external information (ST1001).
- the CS control information generated in ST1001 is output to the storage unit 723 of the SS signal processing unit 72, the reception control unit 741 of the reception unit 74, the transmission signal generation unit 733 of the connection request unit 73, and the transmission control unit 751 of the transmission unit 75. Is done.
- the CS control information output to the storage unit 723 is stored in a database.
- the signal receiving unit 742 of the receiving unit 74 monitors reception of the BF-SS signal. Then, when receiving the BF-SS signal (ST1002), the signal receiving unit 742 outputs the BF-SS signal to the SS related information extracting unit 721 of the SS signal processing unit 72. In this case, the reception control unit 741 controls the reception of the BF-SS signal by the signal reception unit 742 based on the CS control information received from the CS signal control unit 71.
- the SS related information extraction unit 721 Upon receiving the BF-SS signal, the SS related information extraction unit 721 extracts SS related information included in the BF-SS signal (ST1003). The extracted SS related information is output to the storage unit 723.
- This SS related information includes a beam ID uniquely given to the BF-SS signal. That is, when receiving the BF-SS signal, the mobile station UE extracts the beam ID given to the BF-SS signal in the storage unit 723 and outputs it to the storage unit 723.
- reception quality measuring section 722 measures the reception quality of the BF-SS signal (ST1004).
- the measured reception quality is output to the storage unit 723.
- Storage section 723 stores the SS-related information and reception quality in a database (ST1005).
- ST1005 the aspect which measures reception quality after extraction of SS related information is demonstrated here, these order may be reverse.
- the reception control unit 741 of the reception unit 74 determines whether or not the reception of the BF-SS signal is completed (ST1006). If reception of the BF-SS signal is not completed, the process returns to ST1002, and the processes of ST1002 to ST1006 are repeated. On the other hand, if reception of the BF-SS signal is completed, the process proceeds to ST1007.
- the connection request unit 73 generates a transmission signal (reply signal) to the MM base station MMeNB. More specifically, the reception quality information generation unit 731 generates reception quality information based on the reception quality in the storage unit 723 (database), while the RACH preamble is based on SS related information in the storage unit 723 (database).
- the generation unit 732 generates a RACH preamble. In this case, the RACH preamble generated by the RACH preamble generation unit 732 includes the beam ID given to the BF-SS signal.
- the transmission signal generation unit 733 generates a transmission signal including the reception quality information and the RACH preamble.
- the transmission signal generation unit 733 generates a transmission signal based on the CS control information received from the CS control information generation unit 712.
- the transmission signal generation unit 733 can also generate a transmission signal based on the CS control information stored in the database.
- the generated transmission signal is output to the transmission unit 75.
- signal transmission section 752 of transmission section 75 transmits a transmission signal (reply signal) to MM base station MMeNB (ST1008).
- the transmission control unit 752 controls transmission of a transmission signal (reply signal) by the signal transmission unit 752 based on the CS control information received from the CS signal control unit 71.
- the reception control unit 741 monitors whether a RACH response is received from the MM base station MMeNB. Then, the mobile station UE exchanges information using a RACH response or the like, and connects to the MM base station MMeNB (ST1009). Information acquired by this information exchange is output to the CS control unit 71 and used to generate CS control information.
- the mobile station UE determines whether the cell search (CS) process is completed (ST1010). If the cell search process is not completed, the process returns to ST1002, and the processes of ST1002 to ST1010 are repeated. On the other hand, when the cell search process is completed, the series of processes is terminated.
- CS cell search
- the reception completion of the BF-SS signal is determined in ST1006, and when the reception of the BF-SS signal is completed, a transmission signal (reply signal) to the MM base station MMeNB is generated. Yes.
- the operation flow shown in FIG. 11 is different from the operation flow shown in FIG. 10 in that the step of determining completion of reception of the BF-SS signal is omitted.
- the mobile station UE when receiving the BF-SS signal, the mobile station UE generates a RACH preamble including information (beam ID) that can identify the BF-SS signal, and transmits the transmission signal including the RACH preamble to the MM base station MMeNB.
- a connection request is made by sending to.
- the mobile station UE can identify the BF-SS signal and appropriately perform the cell search process. The resulting reduction in throughput characteristics can be suppressed.
- the load of the cell search process can be reduced by using the external information.
- external information include system parameters such as timing information and resource allocation information, Massive-MIMO cell MM candidate list (Massive-MIMO cell ID and cell position coordinates), and beam direction of a BF-SS signal transmission beam , Information such as beam width, signal length, frequency, bandwidth, scanning timing and scanning method are included.
- These external information may be obtained from, for example, the connected macro base station MeNB or the adjacent MM base station MMeNB.
- These macro base station MeNB and MM base station MMeNB comprise an external communication apparatus.
- the mobile station UE by acquiring these external information in advance, for example, part of the process of generating the CS control information and the process of generating the RACH preamble can be omitted, so the burden of the cell search process is reduced. It becomes possible to reduce.
- the connection request can be made even when the connection is not established with the MM base station MMeNB performing the connection request.
- the present invention is not limited to the above embodiment, and can be implemented with various modifications.
- the number of carriers, the carrier bandwidth, the signaling method, the number of processing units, and the processing procedure in the above description can be appropriately changed and implemented without departing from the scope of the present invention.
- Other modifications can be made without departing from the scope of the present invention.
- a single narrow beam is generated by beam forming and the BF-SS signal is transmitted.
- the form of the transmission beam for transmitting the BF-SS signal is not limited to this and can be changed as appropriate.
- a plurality of narrow beams can be simultaneously generated by beam forming to transmit a BF-SS signal.
- each narrow beam constituting the narrow beam group (beam group) is referred to as a sub beam.
- FIG. 12 is an explanatory diagram of a BF-SS signal transmission method according to the first modification.
- FIG. 12A schematically shows a transmission image of a BF-SS signal transmitted from the MM base station MMeNB to the SA.
- FIG. 12B the BF-SS signal transmitted from the MM base station MMeNB is shown on the time axis and the frequency axis.
- a beam group including five sub-beams having different transmission directions (the beam width of each sub-beam is ⁇ ) at the same time at the timing t 1.
- Send. Then transmits the beams by shifting the transmission direction 5 times only in the azimuthal direction of the beam width ⁇ at timing t 2.
- transmission of the beam group is repeated by shifting the transmission direction in the azimuth direction by 5 times the beam width ⁇ at each time interval ⁇ .
- a beam group including a plurality of sub-beams having different transmission directions is transmitted at the same time, and the transmission direction of these beam groups is changed at every time interval ⁇ .
- the scanning time T ′ for the entire SA can be shortened to 1 / b of the total time T required for transmission of the BF-SS signal according to the first mode. it can.
- each sub-beam included in the beam group includes, for example, some antenna elements (for example, 10 antennas included in 100 antenna elements). Element).
- the sub-beams included in the beam group are orthogonal to each other.
- the orthogonal relationship between the sub-beams is realized by frequency multiplexing using different frequency bands, spatial multiplexing using 3D beam forming, a combination of these frequency multiplexing and spatial multiplexing, or the like.
- FIG. 13A schematically shows a beam group having an orthogonal relationship generated by spatial multiplexing using 3D beamforming.
- FIG. 13B schematically shows a beam group having an orthogonal relationship generated by a combination of spatial multiplexing and frequency multiplexing using 3D beamforming.
- the mobile station UE can obtain in advance control information (for example, the number of sub-beams and multiplexing direction) regarding sub-beams constituting the beam group.
- control information for example, the number of sub-beams and multiplexing direction
- BF-SS signal can be easily received.
- such sub-beam control information is previously received from the connected base station apparatus such as the macro base station MeNB in the mobile station UE. It is preferable to obtain.
- identifiers that can be identified for each sub-beam are used.
- ID By assigning (ID), it becomes possible to specify each sub-beam on the mobile station UE side. Furthermore, by using sequences orthogonal to each other in each beam ID, it becomes possible to simplify the processing on the mobile station UE side.
- the BF-SS signal transmitted at every time interval ⁇ is transmitted using the bandwidth of the entire system of the communication system.
- the mode of the transmission beam for transmitting the BF-SS signal (hereinafter referred to as “SS beam” as appropriate) is not limited to this and can be changed as appropriate.
- SS beam the mode of the transmission beam for transmitting the BF-SS signal
- a BF-SS signal transmitted every time interval ⁇ can be transmitted using a part of the bandwidth of the communication system.
- FIG. 14 is an explanatory diagram of a BF-SS signal transmission method according to the second modification.
- FIG. 14A schematically shows a transmission image of a BF-SS signal transmitted from the MM base station MMeNB to the SA.
- FIG. 14B the BF-SS signal transmitted from the MM base station MMeNB is shown on the time axis and the frequency axis.
- the reception power density can be improved by narrowing the bandwidth of the SS beam.
- the power line density can be improved by concentrating the transmission power in a narrow bandwidth, and the SS signal can be transmitted to a long distance.
- the SS beam bandwidth can be selected as a parameter in the communication system, for example.
- the BF-SS signal transmission method according to the second modification can be combined with the BF-SS signal transmission method according to the first modification.
- the BF-SS signal is transmitted by switching the transmission direction of the transmission beam with a fixed beam width.
- the mode of the SS beam is not limited to this and can be changed as appropriate.
- the BF-SS signal can be transmitted by adjusting the beam width of the SS beam in stages.
- a plurality of SS beam widths are prepared in advance, and the SS beam having a narrow beam width is changed in order from the SS beam having a wide beam width. It is possible. More specifically, the area where the mobile station UE exists is selected by scanning all SAs with the SS beam having the widest beam width in the first stage. Then, only the area where the mobile station UE exists is scanned with the SS beam having the next narrowest beam width, and the area where the mobile station UE exists is further selected. These scanning processes are repeated until the SS beam having the narrowest beam width is reached.
- FIG. 15 is an explanatory diagram of an example of a BF-SS signal transmission method according to the third modification.
- the widest beam width of the SS beam is set to 1 ⁇ 4 of the SA beam width and the narrowest beam width of the SS beam is set to 1/32 beam width of the SA will be described. To do.
- the entire SA is scanned using an SS beam having a beam width of 1/4 of the SA.
- the beam width of the SS beam is reduced by one step, and the mobile station UE exists due to the SS beam having a beam width that is 1/8 of the SA. Scanning is limited to the area to be performed. In this way, the beam width of the SS beam is gradually reduced, and finally, as shown in FIG. 15C, the SS beam having a beam width of 1/32 of the SA is used to make the area where the mobile station UE exists. Limited scan.
- the mobile station UE is scanned by adjusting the beam width of the SS beam step by step.
- the scanning area can be reduced. This makes it possible to perform scanning processing (BF-SS signal transmission processing) while reducing the processing load on the MM base station MMeNB.
- the BF-SS signal transmission method for example, when a wider beam is used in the first half scan, such as in the first stage, the power density is lower than that of the narrow beam used in the second half scan. Therefore, the range that the beam can reach is shortened. Even in such a case, the same range can be covered with beams having different widths by combining with the second modification (narrow bandwidth).
- the narrowest beam the beam with the highest gain
- the narrowest beam used in the final-stage scanning is set to the same width as the beam used during data communication.
- the MM base station MMeNB can acquire in advance communication environment information such as the distribution and location information of the mobile station UE and the distance to the adjacent cell. And the scanning process using a wide beam width until the area where the mobile station UE exists can be omitted. For this reason, when the BF-SS signal transmission method according to the third modification is applied, it is preferable that such communication environment information is obtained in advance from the macro base station MeNB in the MM base station MMeNB.
- the BF-SS signal transmission method according to the third modification can be combined with the BF-SS signal transmission method according to the first and second modifications.
- the BF-SS signal transmission method according to the first to third modifications described above can also be applied to the BF-SS signal transmission method according to the second aspect.
- the irradiation range (power density) corresponding to the elevation angle of the SS beam as described above It is preferable to select parameters such as beam width and time interval in consideration of changes, uniformity of scanning of the BF-SS signal in SA, and efficiency. In this case, for example, by adjusting the beam width between when the elevation angle is high and when the elevation angle is low, the power density can be shared, and the uniformity of BF-SS signal scanning can be ensured.
- the external information is based on the acquired external information.
- the BF weight may be calculated adaptively.
- specific examples of the external information from the external communication device include distribution and location information of each mobile station UE, user priority, location information of adjacent base station devices, and the like.
- the communication state in the Massive-MIMO cell MM can also be controlled.
- By controlling the communication state in such a Massive-MIMO cell MM it becomes possible to control the communication state in consideration of, for example, interference with other communication systems, load balance of the entire communication system, user satisfaction, and the like. .
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Abstract
Description
まず、本実施の形態に係る基地局装置に適用されるMassive-MIMO伝送方式の概要について説明する。Massive-MIMO伝送方式においては、例えば、100個以上のアンテナ素子を用いてデータを送信することでデータレート(周波数利用効率)を向上させる。100個以上のアンテナ素子を用いてデータを送信することから、少数のアンテナ素子を用いる場合と比べて多重化に伴う伝送効率を改善でき、従来よりも高速な無線通信が可能となる。また、ビームフォーミング時におけるアンテナ素子の組み合わせの選択肢を多様化でき、従来よりも高度なビームフォーミングが可能となる。このような高度なビームフォーミングにより、ビームフォーミング利得による受信信号電力の増加や、干渉低減及び無線リソースの有効利用などの効果を期待できる。
まず、第1の態様に係るBF-SS信号の送信方法について説明する。図3は、第1の態様に係るBF-SS信号の送信方法の説明図である。図3Aにおいては、MM基地局MMeNBからSAに対して送信されるBF-SS信号の送信イメージを模式的に示している。図3Bにおいては、MM基地局MMeNBから送信されるBF-SS信号を時間軸及び周波数軸上に示している。
(式1)
S(t) = Wn(t,f)・SSS(t)
ここで、Wn(t,f)はビームフォーミングウェイト(以下、「BFウェイト」という)を示し、SSS(t)はSS信号を示す。
(式2)
T = 360τ/Φ
ここで、τはBF-SS信号の時間間隔を示し、ΦはBF-SS信号のビーム幅を示す。
次に、第2の態様に係るBF-SS信号の送信方法について説明する。第2の態様に係るBF-SS信号の送信方法においては、BF-SS信号の送信用の狭いビームの送信方向に仰角方向が追加される点で、第1の態様に係るBF-SS信号の送信方法と相違する。すなわち、第2の態様に係るBF-SS信号の送信方法は、BF-SS信号の送信用の狭いビームの送信方向を、方位角方向及び仰角方向に時間間隔τ毎に変更することで、Massive-MIMOセルMMのSAに位置する全ての移動局UEを走査する送信方法である。以下においては、第1の態様に係るBF-SS信号の送信方法との相違点を中心に説明する。なお、本明細書において、仰角方向とは水平方向に直交し、かつ、下方(または上方)に向かう向きを示す角度を0°とし、水平方向を示す角度を90°とする角度によって示される方向と定義する。
(式3)
T = 360ατ/Φ2
ここで、τはBF-SS信号の時間間隔を示し、αは送信ビームの最大仰角方向の角度を示し、ΦはBF-SS信号のビーム幅を示す。
(式4)
T = 360ατ/(ΦHΦV)
ここで、τはBF-SS信号の時間間隔を示し、αは送信ビームの最大仰角方向の角度を示し、ΦHはBF-SS信号の水平ビーム幅を示し、ΦVはBF-SS信号の垂直ビーム幅を示す。
例えば、第1の態様に係るBF-SS信号の送信方法においては、ビームフォーミングにより単一の狭いビームを生成してBF-SS信号を送信している。しかしながら、BF-SS信号の送信のための送信ビームの態様については、これに限定されず適宜変更が可能である。例えば、ビームフォーミングにより狭いビームを同時に複数生成してBF-SS信号を送信することができる。以下においては、狭いビーム群(ビーム群)を構成するそれぞれの狭いビームをサブビームと呼ぶものとする。
第1の態様に係るBF-SS信号の送信方法においては、時間間隔τ毎に送信されるBF-SS信号を、通信システムのシステム全体の帯域幅を利用して送信している。しかしながら、BF-SS信号の送信のための送信ビーム(以下、適宜「SSビーム」という)の態様については、これに限定されず適宜変更が可能である。例えば、時間間隔τ毎に送信されるBF-SS信号を、通信システムの一部の帯域幅を利用して送信することができる。
第1の態様に係るBF-SS信号の送信方法においては、ビーム幅を固定した送信ビームの送信方向を切り替えてBF-SS信号を送信している。しかしながら、SSビームの態様については、これに限定されず適宜変更が可能である。例えば、SSビームのビーム幅を段階的に調整してBF-SS信号を送信することができる。
Claims (9)
- 基地局装置が有する複数のアンテナ素子を用いたビームフォーミングによりセルサーチに用いられる同期信号用の送信ビームの送信方向を制御する同期信号送信方法であって、
同期信号用の送信ビームを識別可能な情報を含む同期信号を生成すると共に、前記同期信号に対するビームフォーミング用ウェイトを所定の時間間隔で変更する同期信号処理ステップと、それぞれの前記ビームフォーミング用ウェイトに応じて生成された前記同期信号を下りリンクで送信する送信ステップとを具備することを特徴とする同期信号送信方法。 - 前記同期信号処理ステップにおいて、前記同期信号用の送信ビームの送信方向を方位角方向に制御する前記ビームフォーミング用ウェイトと、方位角方向及び仰角方向に制御する前記ビームフォーミング用ウェイトとを選択可能であることを特徴とする請求項1記載の同期信号送信方法。
- 少なくとも前記ビームフォーミング用ウェイトを変更する時間間隔と、前記同期信号用の送信ビームのビーム幅とを含むビームフォーミング用パラメータを選択する選択ステップを更に具備し、前記同期信号処理ステップにおいて、前記選択ステップで選択された前記ビームフォーミング用パラメータに基づいて前記ビームフォーミング用ウェイト及び当該ビームフォーミング用ウェイトを変更する時間間隔を制御することを特徴とする請求項1記載の同期信号送信方法。
- 前記選択ステップにおいて、前記同期信号の信号長に基づいて前記ビームフォーミング用ウェイトを変更する時間間隔を決定することを特徴とする請求項3記載の同期信号送信方法。
- 前記選択ステップにおいて、基地局装置におけるアンテナ素子の数、送信電力、周波数帯、帯域幅及びビーム照射範囲の少なくとも1つに基づいて前記同期信号用の送信ビームのビーム幅を決定することを特徴とする請求項3記載の同期信号送信方法。
- 前記同期信号処理ステップにおいて、前記同期信号用の送信ビームを複数含むビーム群を同時に生成する前記ビームフォーミングウェイトを選択することを特徴とする請求項1記載の同期信号送信方法。
- 前記送信ステップにおいて、通信システムの一部の帯域幅を利用して前記同期信号用の送信ビームを送信することを特徴とする請求項1記載の同期信号送信方法。
- 外部通信装置から前記同期信号用の送信ビームの生成のための情報を取得する取得ステップを更に具備し、前記同期信号処理ステップにおいて、前記取得ステップで取得された情報に基づいて前記ビームフォーミング用ウェイトを選択することを特徴とする請求項1記載の同期信号送信方法。
- 複数のアンテナ素子を用いたビームフォーミングによりセルサーチに用いられる同期信号用の送信ビームの送信方向を制御する基地局装置であって、
同期信号用の送信ビームを識別可能な情報を含む同期信号を生成すると共に、前記同期信号に対するビームフォーミング用ウェイトを所定の時間間隔で変更する同期信号処理部と、それぞれの前記ビームフォーミング用ウェイトに応じて生成された前記同期信号を下りリンクで送信する送信部とを具備することを特徴とする基地局装置。
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Also Published As
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US20160212631A1 (en) | 2016-07-21 |
CN105493547A (zh) | 2016-04-13 |
JP6336728B2 (ja) | 2018-06-06 |
JP2015041817A (ja) | 2015-03-02 |
US10051484B2 (en) | 2018-08-14 |
CN105493547B (zh) | 2019-06-18 |
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