JP6095785B2 - Wireless communication system, control method therefor, and base station apparatus - Google Patents

Description

Import by reference

  This application claims the priority of Japanese Patent Application No. 2013-170033, which was filed on August 20, 2013, and is incorporated herein by reference.

  The present invention relates to a wireless communication system.

  In recent years, mobile traffic has increased rapidly due to the spread of smartphones and tablet terminals. In particular, in a hot spot where traffic is concentrated, a network operator installs a public wireless LAN that can be easily installed, and offloads the traffic. However, since all operators use the same frequency band, as the wireless LAN base stations are densely installed, the channel becomes congested and it becomes difficult to ensure sufficient communication quality. When the channel is congested, the user's quality of experience may be reduced when connected to a wireless LAN in order to offload mobile traffic. For this reason, it is necessary to take measures to offload traffic in the license band.

  In many cases, hot spots are crowded in a stopped state by users who use terminals. Therefore, in general, a small cell base station smaller than the macro cell base station may be installed at a specific location to offload traffic. In order to increase the throughput, there is a method of obtaining a cell split gain by making a cell smaller and communicating with a small number of users. In addition, many users who frequently handover are running on the road by car. Since it is difficult for a user driving a car to operate the terminal, high-load communication is difficult to occur. In order to accommodate low-load terminals and reduce the number of handovers, a macrocell base station with a wide cell is excellent.

  On the other hand, in public transportation such as trains and buses, the user stops in the car and moves with the vehicle at high speed. A hot spot that is highly likely to perform high-load communication occurs when the user is stopped. Such a hot spot is difficult to take because the terminal is moving at a high speed and has a high load.

  Conventionally, a terminal that moves at high speed is connected to a macro cell instead of offloading to a small cell in order to avoid an increase in data communication interruption time due to handover and an increase in signaling load (number of transactions) with Evolved Packet Core (EPC). The method to do was adopted. For example, in Japanese Patent Laid-Open No. 2013-90203, a base station determines a handover destination base station according to the stay time of a terminal in an adjacent cell that is a handover destination candidate. As information for determining the handover destination base station of the high-speed mobile terminal, the stay time information of the terminal having a moving speed of a certain value or more is measured and held in each base station. When a base station hands over a high-speed mobile terminal, an average stay time of the high-speed mobile communication terminal is obtained from an adjacent base station or a log server holding stay time information collected from each base station. An offset corresponding to the stay time is added to the handover reference value. The technology is described.

  In the prior art described above, a handover destination base station is selected so that a terminal moving at high speed does not frequently perform handover. However, since macrocell radio resources are shared by a large number of people, there is a problem that high-speed data communication cannot be provided.

  In addition, when a terminal that moves at high speed is offloaded to a small cell, there is a problem in that the data communication interruption time resulting from radio section signaling increases and the signaling load with the EPC increases. Due to the widespread use of smartphones, there are applications that are always connected to EPC even when the user is not operating the terminal, and handover is likely to occur. Signaling accompanying handover accounts for a large proportion of the number of EPC transactions, and increasing the number of handovers impairs the stability of the core network.

  Focusing on the radio section, the random access (RA) procedure for timing synchronization with the target cell not only at the time of handover failure (RLF, Too early / late HO, ping-ping, etc.) but also at the time of handover success. Redo may occur and data communication interruption time may increase.

  A terminal that moves at high speed generally has severe propagation path fluctuations, so that a long time is required to trigger a handover so that a ping-pong phenomenon does not occur. However, the communication quality may not be sufficiently ensured while the handover is extended, and a radio link failure (RLF) may occur. When RLF occurs, a recovery timer (for example, T310 in LTE) is set to cause a communication interruption of 1000 ms as an initial value.

  In addition, when a large number of terminals attempt handover at the same time and succeed in handover, control signal signaling occurs frequently and radio resources are wasted due to redoing the RA procedure in the handover execution procedure and the completion procedure to the target cell. Communication is stopped for about 50 ms by the signaling of the control signal. In high-speed railways, the maximum moving speed of a terminal is 350 km / h, and if the cell radius is 100 m, the terminal's stay time in the cell (ToS: Time of Stay) is about 1 second, which is derived from handover. The influence of the delay time in the radio section cannot be ignored.

  Therefore, in the present invention, a cellular radio system that suppresses handover is constructed to reduce signaling loss due to EPC and radio section control signals.

  A typical example of the invention disclosed in the present application is as follows. That is, a radio communication system including a plurality of base stations that transmit and receive radio signals to and from a terminal, wherein the base station transmits a downlink signal to the terminal using scheduled radio resources and receives an uplink signal from the terminal A plurality of radio devices, a scheduler that determines radio devices that allocate radio resources to the terminals and transmits signals using the allocated radio resources, and an aggregation device that processes signals transmitted and received by the radio devices. The plurality of wireless devices transmit common identification information to form a cell, and the scheduler determines a position of a moving terminal based on a propagation quality between each of the plurality of wireless devices and the terminal. And detecting resources from a part of the plurality of wireless devices based on the location of the terminal to transmit data to the terminal. Wireless communication system, characterized in that the shed Ri.

  According to the exemplary embodiment of the present invention, handover can be suppressed even if a terminal group moves. Problems, configurations, and effects other than those described above will become apparent from the description of the following embodiments.

It is a figure which shows the structure of the radio | wireless communications system with which the radio | wireless communications system of the C-RAN structure of the Example of this invention is provided by superimposition. It is a block diagram which shows the structure of the radio | wireless communications system of the C-RAN structure of a 1st Example. It is a figure which shows the structure of the radio | wireless communications system of a 1st Example. It is a sequence diagram of the radio | wireless communications system of 1st Example. It is a figure explaining operation | movement of the radio | wireless communications system of a 1st Example. It is a sequence diagram of the radio | wireless communications system of 2nd Example. It is a figure explaining operation | movement of the radio | wireless communications system of 2nd Example. It is a figure explaining operation | movement of the radio | wireless communications system of 2nd Example. It is a sequence diagram of the radio | wireless communications system of 3rd Example. It is a figure explaining the operation information management table of a 3rd Example. It is a figure explaining the RU management table of a 3rd Example. It is a block diagram which shows the structure of the radio | wireless communications system of the C-RAN structure of a 4th Example. It is a figure explaining operation | movement of the radio | wireless communications system of 5th Example. It is a figure explaining operation | movement of the radio | wireless communications system of 5th Example. It is a figure explaining operation | movement of the radio | wireless communications system of 5th Example. It is a figure explaining the RU management table of a 5th Example. It is a figure explaining operation | movement of the radio | wireless communications system of a 6th Example. It is a figure explaining the RU management table of a 6th Example.

  The mode for carrying out the present invention will be described with reference to some examples. These embodiments may be implemented individually, or a plurality of embodiments may be combined. In the following description, configurations denoted by the same reference numerals in the drawings perform the same operation, and thus description thereof is omitted.

  Hereinafter, as an embodiment of the present invention, in a cellular radio communication system having a heterogeneous network configuration composed of a plurality of small base stations and macro cell base stations, traffic of terminals moving at high speed is provided to an area provided by the small base stations. A wireless communication system that offloads and suppresses handover will be described.

  In the following description, the alphabet corresponds to the form of the connected base station, such as 1203-M for a terminal connected to the macro cell base station 1201-M and 1203-S for a terminal connected to the small cell base station 1201-S. Let

<Example 1>
FIG. 1 is a block diagram showing a configuration of a wireless communication system having a macro cell base station 1201-M having a unique cell ID.

  In the wireless communication system shown in FIG. 1, a macro cell base station 1201-M accommodates a terminal 1203 that moves at high speed on a public transportation such as a train. The macro cell base station system and the C-RAN are overlapped so that the cell provided by the wireless communication system shown in FIG. 1 and the cell provided by a base station having a C-RAN (Cloud-Radio Access Network) configuration shown in FIG. A system is provided in an overlapping manner.

  Macrocell base station 1201-M is connected to core network 1202, manages the mobility of terminal 1203, and mediates data communication services. The macro cell base station 1201-M is assigned a unique cell ID, and the core network 1202 manages the mobility of the terminal 1203 based on the cell ID and the address of the base station device. For example, ECGI (E-UTRA Cell Global ID) can be used as the cell ID, and an IP address can be used as the address.

  The base station 1201 can form a plurality of cells with one or more different cell IDs. When a plurality of cell IDs are assigned to the base station 1201, the correspondence relationship between the plurality of cell IDs managed by the base station and the IP address is managed from the core network 1202. When the core network 1202 transfers data to the terminal 1203 connected to the base station 1201 with a certain cell ID, the data is transferred to the serving base station 1201 with the cell ID, and the base station 1201 becomes the destination. A process of allocating data to the cell with the cell ID is executed.

  In the above-described processing, if the data reaches the terminal correctly, the base station 1201 suggests that the cell ID assigned to each cell can be switched within the range of one or more cell IDs to be managed.

  When a handover occurs in a plurality of cells managed by the base station 1201 due to the movement of the terminal (Intra-eNB Handover), the data transfer destination may be changed in the base station 1201. There is no need to replace the data transfer path. The handover in the base station 1201 requires less control signaling with the core network 1202 than the handover between the base stations 1201.

  In the C-RAN configuration as shown in FIG. 2, a centralized base station (CU: Center Unit) 1201-C that aggregates baseband functions of one or more base stations in one place is used for remote wireless communication. A large number of cells are formed in a transmitter (RU: Remote Unit) 1201-R. The number of baseband functions to be aggregated is the maximum number of cell IDs that can be used in the area of the C-RAN configuration. A configuration in which the number of baseband functions to be aggregated and one cell ID is used is conventionally referred to as a DAS (Distributed Antenna System), and is mainly used to configure a small-scale area for indoor use.

  In the DAS configuration, all handovers between RUs (1201-R) connected to one CU (1201-C) can be processed as Intra-eNB Handover. That is, there is a feature that there is little signaling with the core network 1202 at the time of handover.

  The CU (1201-C) includes an S1 / X2 coordinator 401, a cooperative radio resource scheduler 402, an L1 processing unit 403, and a switch 404. The S1 / X2 coordinator 401 transfers the data transferred from the core network 1202 to the cooperative radio resource scheduler 402. When the cooperative radio resource scheduler 402 is divided into a plurality of physical nodes, for example, when processing is performed at a node divided for each cell ID, the S1 / X2 coordinator has a relationship between the cell ID and the core network device. May serve as the coordinator function. This function is similar to the router function that associates the private address and local address of the IP router. The cooperative radio resource scheduler 402 determines terminals to which radio resources of a plurality of cells are allocated. The L1 processing unit 403 performs modulation and coding processing for generating a physical layer signal based on the radio resource allocation information determined by the cooperative radio resource scheduler 402, and the generated downlink communication IQ signal is transmitted to the switch 404. Output to. The switch 404 transfers the IQ signal to the RU (1201-R).

  Also, regarding uplink communication, the RU (1201-R) A / D converts the radio signal received from the terminal 1203, generates an IQ signal, and transfers the IQ signal to the switch 404. The switch 404 transfers the IQ signal to the L1 processing unit 403. The L1 processing unit 403 performs demodulation and decoding processing on the input IQ signal, extracts uplink communication data from the physical layer signal, and transfers the data to the cooperative radio resource scheduler 402. The cooperative radio resource scheduler 402 extracts information for each user from the uplink communication data input from the L1 processing unit 403 and transfers the information to the S1 / X2 coordinator 401.

  The S1 / X2 coordinator 401 transfers information in units of users to a necessary node through the core network 1202. The RU unit 1201-R desirably forms a beam so as to be an elongated cell along the line. The area may be formed by a leaky coaxial cable laid along the line instead of beam formation by an antenna. One RU unit 1201-R will be described assuming that one wireless I / F is accommodated. In a certain area, when a plurality of frequency bands are supported, a plurality of RUs (1201-R) may be accommodated in the same facility. When accommodating in the same equipment, equipment for transmitting radio waves such as an antenna may be shared.

  As described above, in the C-RAN configuration, even if the terminal 1203 enters a cell with a different cell ID and a handover occurs, signaling with the core network 1202 can be suppressed. Random access related signaling still occurs.

  FIG. 3 is a diagram illustrating the configuration of the wireless communication system according to the first embodiment.

  In order to reduce control signals in the radio section, consider forming a dedicated service area for railways with a C-RAN configuration. One CU (1201-C) is good enough to accommodate RU (1201-R) that covers the entire area through which one route passes, such as the Yamanote Line.

  By applying the C-RAN configuration, the cell ID can be freely set within the range of the cell ID managed by the CU (1201-C). Therefore, when the terminal 1203 moves, the cell formed by the RU (1201-R) The cell ID is dynamically changed. By changing the cell ID transmitted by the RU (1201-R) as the terminal 1203 moves, if the terminal 1203 can recognize that it is always communicating with the same cell, handover can be suppressed. When the movement route is known as in public transportation (for example, railroad), a cell is formed along the movement route, and the cell ID is shifted so that the RU (1201-R) is changed as the terminal 1203 moves. The cell ID of the cell to be formed can be changed dynamically.

  FIG. 4 is a sequence diagram of the wireless communication system according to the first embodiment.

  The baseband unit (BBU) 1201-B has a configuration of a CU (1201-C) including an S1 / X2 coordinator 401, a cooperative radio resource scheduler 402, and an L1 processing unit 403.

  In response to switch indication from BBU 1201-B, a signal of cell ID # 1 from RU group # 1 including one or more RUs, and a cell ID # 1 from RU group # 2 including one or more RUs The switch 404 switches the path so as to transmit a signal (for example, cell ID # 2) (P2001). For example, in LTE, a reference signal CRS (Cell-specific Reference Signal) is scrambled and operated by a cell ID. The terminal 1203 can recognize the cell ID based on the pattern of the reference signal.

  As illustrated in FIG. 5, an example will be described in which RU group # 1 is serving a terminal 1203-G in a train with cell ID # 1. Terminal 1203-G transmits an uplink data signal, a control signal, and a reference signal of cell ID # 1. For example, in LTE, SRS (Sounding Reference Signal) may be transmitted.

  In RU group # 1 and RU group # 2, the strength (RSSI) of the uplink signal transmitted from terminal 1203-G is measured (P2002). The channel to be measured may be a data signal, a control signal, a reference signal, or any combination thereof. The circuit for measuring the power may be included in the RU (1201-R) or the L1 processing unit 403, but the information on the measured power is periodically (desirably Are collected every 100 ms). The collection cycle is related to the link budget of the RU, and the smaller the cell radius, the shorter the collection cycle and the more precise control of this sequence is required.

  Based on the collected power information for each RU, the BBU 1201-B detects which RU the terminal is near (P2003). The detection method may be detected using a predetermined threshold value, or may be determined using a difference from the power information collected periodically. For example, the movement of the terminal can be detected using the power difference for each time.

  When it is detected that the terminal group 1203-G approaches the RU near the boundary with the RU group # 2 among the RUs belonging to the RU group # 1, among the RUs belonging to the RU group # 2, the RU group # 1 The cell ID transmitted by the RU near the boundary is changed to the cell ID # 1 used in the RU group # 1.

  Since RU group # 1 is composed of RUs that transmit cell ID # 1, the RU whose cell ID has been changed belongs to RU group # 1. The cell ID for each RU is switched by updating the path switch command to the switch 404. The BBU 1201-B issues a switching command to distribute the generated signal of the cell ID # 1 to the RU group # 1 and distribute the signal of the cell ID # 2 to the RU group # 2 (P2004). By changing the cell ID of the RU group # 2 existing in the traveling direction of the terminal group 1203-G to the cell ID # 1 by the above sequence, the terminal group 1203-G does not need to perform handover at the traveling destination. The RUs belonging to the RU group # 2 may sleep while the detection process described above is performed and the cell ID of the RU group # 1 is not used.

  In addition, a unique cell ID is preferably assigned to each train, and the cell ID of the RU is replaced every time the train passes so that the cell ID of the terminal group 1203-G in the train is maintained.

  After the train passes, until the next train arrives, the RU may be operated with the replaced cell ID. When the interval between trains is long, RUs with the same cell ID may increase. In this case, the number of RUs that can be operated with the same cell ID is limited by parameters, and cell IDs other than the cell IDs assigned for the terminals in the train are assigned in order from the old RU that has become the cell ID, or You may sleep.

  The number of RUs to which the same cell ID is assigned is preferably as small as possible from the viewpoint of control signal distribution. This is because the number of control signals that can be allocated becomes a bottleneck, and thus the number of accommodated terminals is limited. The reference signal must be transmitted by all RUs operating with the same cell ID. For example, in LTE, the reference signal is scrambled by the cell ID. For this reason, when the range of the same cell ID becomes wider, the reference signal (CRS) from the adjacent RU arrives as a multipath.

  If the control signal is transmitted so as to reach only a different terminal for each RU, the limitation on the number of accommodated terminals can be avoided, but the control signal must be decoded using the reference signal, so the reference signal is transmitted. If the number and transmission points of RUs and RUs that transmit control signals are different, there is a problem that reception performance is degraded. For this reason, it is necessary to provide a limit on the number of RUs operated with the same number of cell IDs.

  When changing the combination of the cell ID and the RU, if there is a terminal accommodated in the cell of the cell ID used in the RU to be changed, to the outside of the C-RAN system (for example, a macro cell base station) The cell ID is changed after the handover. By handing over a low-speed terminal that continues to stay in an area formed by a certain RU, the influence on the terminal can be reduced. In order to reduce the number of terminals to be handed over, an area provided by the RU from outside the C-RAN system (for example, a macro cell) may be provided with a restriction so that it is difficult to perform handover. Specifically, handover may be prohibited by the neighbor list management of the macro cell base station, or the power used for the handover criterion may be set larger than usual. Alternatively, by strictly controlling the area formed by the RU on the track, it is possible to reduce the possibility that the terminal is connected from outside the train while there is no train.

  When CA (Carrier Aggregation) is applied, if the above-described cell ID change processing (P2001 to P2004) is performed between RUs that transmit cell IDs of PCell (Primary Cell) managing mobility, handover is performed. Can be deterred. A similar cell ID change process may be performed for an SCell (Secondary Cell) configured to secure capacity. Since the SCell is not related to mobility, there is no effect of suppressing handover. However, even if the SCell moves, the SCell information does not change and a procedure for reconfiguring the SCell, for example, RRC (Radio Resource Control) reconfiguration, Activation / deactivation Processing does not occur, and CA reconfiguration becomes unnecessary in addition to handover-less.

  As described above, in the first embodiment of the present invention, it is possible to construct a system that suppresses the occurrence of handover when the base station changes the cell ID according to the movement of the terminal. In addition, when introducing a small cell, it is possible to solve the problem of a trade-off between system throughput and data communication interruption time. And since the terminal which moves at high speed can be accommodated in a small cell, the cell split gain by the offload from a macro cell to a small cell can be obtained. In addition, the throughput of high-speed mobile terminals can be improved, and the performance of real-time traffic can be improved by reducing the data communication interruption time.

  In the first embodiment, the coordinated radio resource scheduler 402 detects the moving terminal and its position based on the RSSI measurement result of the uplink signal of the terminal. Can be detected.

<Example 2>
In the first embodiment, the same signal is transmitted in the RU group having the same cell ID, but in the second embodiment, communication is performed with a different terminal for each RU in the RU group that transmits the same cell ID.

  FIG. 6 is a sequence diagram of the second embodiment. For example, when a train is passing through a cell formed by a plurality of RUs, the sequence shown in FIG. 6 is applied.

  The switch 404 so that the reference signal of the cell ID # 1 generated by the BBU 1201-B is transmitted from the RU group # 1 because it includes one or more RUs by the switch condition notification (Switch indication) from the BBU 1201-B. Switches paths (P2101).

  Each of the terminal groups UEG # 1, UEG # 2, and UEG # 3 including one or more terminals transmits an uplink reference signal for each terminal. For example, SRS can be used for the reference signal. Uplink signals transmitted from each terminal are received by a plurality of RUs. The BBU 1201-B collects the power value of the uplink signal transmitted from each terminal in each RU (P2102). The RU may measure the received power of the SRS and transfer it to the BBU 1201-B. The RU transmits only IQ data, and the BBU 1201-B calculates the received power for each RU from the IQ data transmitted from the RU. May be. A feature is that power measurement is performed before combining power received from a plurality of RUs in units of cell IDs.

  The BBU 1201-B collects the strength of the uplink power of each terminal at each RU, thereby detecting and grouping RUs near each terminal (P2103). For example, as illustrated in FIG. 7A, the terminal group UEG # 1 is a terminal group in which the reception power at RU # 1 satisfies the detection condition, but the reception power at RU # 2 does not satisfy the detection condition. The terminal group UEG # 2 is a terminal group in which the reception power in both RU # 1 and RU # 2 satisfies the detection condition. Terminal group UEG # 3 is a terminal group in which the received power at RU # 2 satisfies the detection condition, but the received power at RU # 1 does not satisfy the detection condition.

  The BBU 1201-B performs grouped terminal group switching processing and radio resource allocation processing for each RU (P2104).

  A data signal may be transmitted from one RU to the terminal groups UEG # 1 and 3 determined to be close to one RU. For example, data is transmitted from RU # 1 to the terminal group UEG # 1, and data is transmitted from RU # 2 to the terminal group UEG # 3. This process enables multi-user communication in which the same radio resource is allocated to a plurality of terminals within the same cell ID, and throughput can be improved. However, as described in the first embodiment, when the same cell ID is assigned to a plurality of RUs, the terminal receives the reference signal as a multipath signal.

  For example, even when only RU # 1 transmits a data signal to the terminal group UEG # 1, the reference signal is transmitted from RU # 1 and RU # 2, and therefore the path differs between the reference signal and the data signal. Channel estimation may not work correctly and reception performance may deteriorate. Therefore, in addition to reference signals transmitted from all RUs such as CRS, a reference signal for decoding a data signal transmitted by only one RU may be used for demodulation. For example, a demodulation reference signal (DMRS) can be used. Of course, when the multipath component of the reference signal transmitted by the RU other than the RU transmitting the data signal is sufficiently attenuated, a mode for decoding data communication using CRS may be used.

  On the other hand, as shown in FIG. 7B, for terminal group UEG # 2 in which power is detected by a plurality of RUs, a data signal is transmitted cooperatively (CoMP: Coordinated Multi) from a plurality of RUs (for example, RU # 1 and 2). Point). A power combining gain can also be obtained by cooperatively transmitting data signals. The cooperative transmission here includes the concept of transmission diversity in which exactly the same data is transmitted from a plurality of RUs. In the case of coordinated transmission, the same reference signal and data signal are transmitted from a plurality of RUs so that there is no deviation in channel estimation.

  Similarly to the case of transmitting data from a single RU, when the influence of CRS from the third RU cannot be ignored, a decoding reference signal (for example, DMRS) may be transmitted from the RU that transmits data. As a result, the transmission and reception paths for the data and the reference signal for decoding are aligned, so that the channel estimation accuracy does not deteriorate. Moreover, since CRS is not used for decoding, the influence of CRS from the third RU can be reduced.

  The BBU 1201-B forwards the signal transmitted to the terminal group UEG # 1 to the RU # 1 and forwards the signal transmitted to the terminal group UEG # 3 to the RU group # 2 with respect to the switch 404. A switch command is issued to the switch 404 to transfer the signal transmitted to the UEG # 2 to the RU group # 1 and the RU group # 2 (P2105). The second embodiment is different from the first embodiment in that an instruction to change the transfer destination RU is issued for each channel. For example, a channel for transmitting a reference signal and a control signal transmitted in common in all cells such as CRS (for example, CRS and PDCCH (Physical Downlink Control Channel in LTE)) is transmitted to all RUs, but is a data signal. A reference signal (for example, PDSCH (Physical Downlink Shared Channel) in LTE, DMRS) in LTE is branched to a transfer destination RU depending on a destination terminal group.

  Each of the terminal groups UEG # 1, 2, and 3 acquires broadcast information transmitted by the BBU 1201-B and scheduling information that is a result of scheduling from the control channel, demodulates and decodes the data channel, and extracts necessary information. (P2106). Terminal-specific control information is also obtained by these procedures. If there is data to be transmitted in the uplink, modulation / coding is performed to transmit the uplink data signal. Information such as HARQ (Hybrid-Automatic Repeat reQuest) response to downlink data signals and periodically transmitted SRS is also modulated and encoded.

  The uplink signal received by each RU is transferred to the BBU 1201-B via the switch 404 and demodulated by the BBU 1201-B (P2107). The BBU 1201-B may improve the reception quality of the uplink data signal by uplink CoMP that combines signals received by a plurality of RUs. In order to perform uplink CoMP, IQ data of uplink signals received by a plurality of RUs may be transferred via the switch 404 to the L1 processing unit 403 that demodulates the signal of the cell ID # 1.

  According to the second embodiment, it is possible to prevent the deterioration of the throughput even when the RU of the same cell ID increases. This is particularly effective when the interval at which RUs are installed is short.

<Example 3>
In the first embodiment described above, the RU near the terminal group in the train is determined by detecting the upstream power. On the other hand, there is a train operation management system in the railway, and this operation management system controls signals so that only one train exists in one closed section. When the BBU 1201-B acquires the correspondence relationship between the train travel position and the RU, the cell ID can be shifted more accurately than the detection of the upstream power.

  FIG. 8 is a sequence diagram of the third embodiment. The same processes as those in the above-described first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The BBU 1201-B periodically obtains data on the travel destination such as the information on the blocked section where the train is traveling, the route, and the traveling direction from the railway operation management system (P2204). The data acquisition cycle may be an interval of time (for example, several seconds) corresponding to the time that the train passes through the blockage section.

  As illustrated in FIG. 9A, data acquired from the operation management system is registered in the operation information management table 900. The operation information management table 900 includes train identification information (Train ID) 901, current blockage segment identification information (Current block ID) 902, and next blockage segment identification information (Next block ID) 903 in the traveling direction.

  As shown in FIG. 9B, the BBU 1201 -B holds an RU management table 910 that includes information associating the blocked section 912 and the RU identification information 911. And BBU1201-B updates cell ID913 used by the said RU using the information acquired from the operation management system (P2002A). If the identification information of the current blockage section and the identification information of the next blockage section are known, the cell ID of the RU in the traveling direction can be changed in advance to be the same as the ID of the current blockage section (P2003). For example, when the information illustrated in FIG. 9A is acquired, the cell ID # 1 used by the RU # 1 and RU # 2 in the association information illustrated in FIG. 9B is set in the traveling direction (identification information for the next block section 1001). (914). The cooperative radio resource scheduler 402 holds the RU management table 910 for managing the correspondence between the RU identification information 911 and the cell ID 913 shown in FIG. 9B, and manages the correspondence between the cell ID and the RU identification information. Also good.

  According to the third embodiment, train position information is acquired from the railway operation management system, and the cell ID is shifted in conjunction with the operation management system, so the cell ID is shifted accurately following the movement of the train. And handover in the system can be suppressed.

<Example 4>
In the first embodiment described above, the CPRI separation type C-RAN configuration (FIG. 2) has been described, but in the fourth embodiment, handoverless in the FAPI separation type C-RAN configuration as shown in FIG. The system will be described. The FAPI separation type is a configuration in which the functions of CU (1201-C) and RU (1201-R) are divided between L1 and L2 (cooperative radio resource scheduler 402). Signals transmitted and received between L2 and L1 may conform to FAPI (Femto Application Platform Interface) standards.

  The CU (1201-CF) of the fourth embodiment includes an S1 / X2 coordinator 401, a cooperative radio resource scheduler 402-A, and a switch 404-A. The RU (1201-RF) includes an L1 processing unit 403-A and a wireless I / F 405 having an AD / DA conversion function.

  The S1 / X2 coordinator 401 transfers the data transferred from the core network 1202 to the coordinated radio resource scheduler 402-A. The cooperative radio resource scheduler 402-A determines a terminal to allocate radio resources of a plurality of cells. The radio resource allocation information and the L2 payload information determined by the cooperative radio resource scheduler 402-A are transferred to the L1 processing unit 403-A via the switch 404-A. The L1 processing unit 403-A performs modulation and code processing, generates IQ data, and outputs the IQ data to the wireless I / F 405.

  Regarding uplink communication, the wireless I / F 405 performs AD conversion on an uplink signal received by an antenna or a leaky coaxial cable, and outputs the generated IQ data to the L1 processing unit 403-A. The L1 processing unit 403-A performs demodulation and decoding processing on the input IQ signal, extracts information on the L2 payload of uplink communication from the physical layer signal, and performs cooperative radio resource scheduler via the switch 404-A. Transfer to 402-A. The cooperative radio resource scheduler 402 -A extracts user unit information from the input uplink communication data and transfers the information to the S1 / X2 coordinator 401. The S1 / X2 coordinator 401 transfers information in units of users to a necessary node through the core network 1202.

  In the configuration of the fourth embodiment, since the RU performs the measurement of the uplink power in the sequence in P2002 of FIG. 4, the measured power value is transferred to the cooperative radio resource scheduler 402-A via the switch 404-A.

  According to the fourth embodiment, since the L1 processing unit is provided on the RU side, uplink CoMP that combines uplink power received by a plurality of RUs to improve channel estimation accuracy and obtain a combined gain is difficult. However, when signals from the same terminal are received by a plurality of RUs, the decoding process is performed by each RU, and the decoding success judgment (CRC OK) and L2 data are received from the L1 processing unit 403-A of the RU that has been successfully decoded. Is transmitted to the cooperative radio resource scheduler 402-A through the switch 404-A. The cooperative radio resource scheduler 402-A may use the same CRC OK and L2 data received from a plurality of RUs, and may proceed with the subsequent processes. Since determination is performed using data from a plurality of RUs, a selectivity gain can be obtained.

  Further, according to the fourth embodiment, since the CU and the RU are divided between the L2 (cooperative radio resource scheduler 402) and the L1, the split IQ signal is transmitted and received between the L1 and the RU. The amount of data transferred between the CU and the RU can be reduced to about 1/10 as compared with the C-RAN configuration. For this reason, the performance (for example, throughput) of the optical line which connects between CU and RU can be lowered.

  In particular, when Carrier Aggregation is introduced and the bandwidth of a cellular radio communication system is increased, the data size of the IQ signal is increased. When transferring 100 MHz band class data, compression of data transmitted between the CU and the RU is a great merit.

<Example 5>
In the fifth embodiment, a case where a plurality of lines are covered will be described. In many cases, a single railway line is double-tracked, and a plurality of railway lines may run in parallel in the city center.

  If one RU can form an area that covers only one line, a dedicated RU may be prepared for each line, and the cell ID may be shifted between the RUs according to the above-described embodiment. However, when the area formed by one RU covers a plurality of lines as shown in FIG. 11A, it is effective to change the operating frequency according to the traveling direction. That is, as shown in FIG. 11B, RUs (1201-R2) are arranged so as to cover the same area with cells having different cell IDs. A plurality of RUs covering the same area may be accommodated in the same facility.

  When the operating frequency cannot be changed according to the traveling direction of the train, as shown in FIG. 12A, it is preferable to determine a combination of RUs for shifting the cell ID for each line. The cooperative radio resource scheduler 402 classifies, for example, a RU (1201-RR) that shifts the cell ID in a certain direction (right direction) and a RU (1201-RL) that shifts the cell ID in the reverse direction (left direction). To manage RUs. That is, a combination of RUs covering a specific line may be created. For this reason, as shown in FIG. 12B, the RU management table 1210 of the fifth embodiment has route identification information 1214. Then, as shown in FIG. 12B, the cell ID can be shifted within the combination of RUs covering a specific line, but the cell ID shift between combinations of RUs covering another line is inhibited (or prohibited). Good.

  In addition, a range of cell IDs to be used within a combination of RUs is determined, and handover is inhibited beyond the range of cell IDs. This can prevent handover to a cell that covers different tracks when the trains pass by. By suppressing handover to cells covering different lines, it is possible to prevent occurrence of radio link failure (RLF) in which a terminal loses sight of a cell ID after a train passes.

  In the case shown in FIG. 12A, since the frequency used by the RUs covering the parallel tracks is the same, it is expected that interference occurs when the trains pass each other. For this reason, as shown to FIG. 11B, it is good to change an operating frequency band for every track | line.

  When equipment is shared and radio waves are transmitted from the same point, an RU (1201-RR) that shifts the cell ID in the right direction and an RU (1201-RL) that shifts the cell ID in the left direction are formed. Area interference increases. For this reason, as shown to FIG. 12A, it is good to arrange | position RU which covers a different track | line in a different position. For example, the RUs may be arranged at geographically distant locations such as arranging RUs on the opposite side across the line, or staggering the RUs with a half-cycle shift. Or, even if a plurality of RUs are accommodated at the same point, if the cells are formed so that the beam directions do not intersect for each covered line, the line area is similar to the case where the RUs are installed in geographically separated places. Interference between the two can be reduced.

  According to the fifth embodiment, the cooperative radio resource scheduler 402 controls the combination of cell IDs and RUs so as to shift the cell IDs by separating the RU combinations for each line on which the cells are to be formed. By doing so, handover can be suppressed even when a plurality of lines are laid close to each other.

<Example 6>
In the sixth embodiment, a case where the present invention is applied to a station will be described.

  In places other than the station platform (station building areas such as station bookstores, overpasses, underground passages, concourses, etc.), an area to which a fixed cell ID is assigned instead of the cell ID used in the track area is constructed. The cells in the station building area shown in FIG. 13A may be formed by RUs connected to C-RAN base stations, or may be formed by base stations other than C-RAN. The frequency used in the station building area may be different from the frequency of the cell covering the track.

  When the C-RAN base station accommodates RUs forming a station building area, the coordinated radio resource scheduler 402 manages the cell ID serving the area so that it does not shift.

  A handover occurs between a cell covering the station building area and a cell covering the track area. When a predetermined number or more of handovers from the cell ID in the station building area to the cell ID used in the track area are detected, a trigger for shifting the cell ID used in the track area may be used.

  For this reason, as shown in FIG. 13B, the BBU 1201-B holds an RU management table 1310 including information on RUs adjacent to the station building area. The RU management table 1310 may include route identification information 1214, a flag 1315 indicating whether it is adjacent to the station area, and the number of handovers 1316.

  In the example shown in FIG. 13B, the area of RU identifier # 1 and the area of RU identifier # 2 are adjacent to the station building area. An RU identifier larger than #m is an RU identifier for a station building area. The CU (1201-C) counts and records the number of handovers between the RU cell for the station building area and the RU cell adjacent to the station building area (1316). For example, the S1 / X2 coordinator 401 may have this function.

  When this number of handovers exceeds a predetermined number, it is determined that the passenger has started boarding the train and the cell ID of the cell adjacent to the station building area is followed by the movement of the terminal after the train has started. The cell ID shift may be started. By such determination, the shift of the cell ID can be accurately started.

  The RUs forming the cells adjacent to the station building area may be assigned a cell ID for a train that runs on the line regardless of the number of handovers. That is, after the cell ID shift starts, the cell ID assigned to the RU forming the cell adjacent to the station building area is changed, and a different cell ID is assigned for another train. As in the fifth embodiment described above, when a different RU is provided for each track, a unique cell ID may be assigned to each train. In this way, a unique cell ID can be assigned to each train.

  In addition, each Example mentioned above may be applied independently, and may be applied in combination. For example, it is possible to detect the position of the terminal with high accuracy by detecting the electric power of the RU, acquiring the position information of the train from the railway operation management system, and using the two pieces of information together. If the cell ID change accuracy increases, the probability of occurrence of handover can be lowered.

  As described above, according to the embodiment of the present invention, since the base station changes the cell ID according to the movement of the terminal, the occurrence of handover can be suppressed. As a result, when accommodating a high-speed mobile terminal in a small cell, it is possible to solve the problem that system throughput and data communication interruption time are traded off. This enables high-speed and real-time traffic transmission / reception, allows rich content such as moving images to be enjoyed even during high-speed movement, and improves end-user QoE. In addition, the use of a thin client, browsing of the Web and mail are smoothed, and a service with appealing power can be provided to business users.

  The present invention is not limited to the above-described embodiments, and includes various modifications and equivalent configurations within the scope of the appended claims. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to those having all the configurations described. A part of the configuration of one embodiment may be replaced with the configuration of another embodiment. Moreover, you may add the structure of another Example to the structure of a certain Example. In addition, for a part of the configuration of each embodiment, another configuration may be added, deleted, or replaced.

  In addition, each of the above-described configurations, functions, processing units, processing means, etc. may be realized in hardware by designing a part or all of them, for example, with an integrated circuit, and the processor realizes each function. It may be realized by software by interpreting and executing the program to be executed.

  Information such as programs, tables, and files that realize each function can be stored in a storage device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

  Further, the control lines and the information lines are those that are considered necessary for the explanation, and not all the control lines and the information lines that are necessary for the mounting are shown. In practice, it can be considered that almost all the components are connected to each other.

Claims (15)

A wireless communication system comprising a plurality of base stations that transmit and receive radio signals to and from a terminal,
The base station
A plurality of radio apparatuses that transmit downlink signals to the terminal using scheduled radio resources and receive uplink signals from the terminals;
A scheduler that determines a radio device that allocates radio resources to the terminal and transmits a signal using the allocated radio resource, and an aggregation device that processes signals transmitted and received by the radio device;
The plurality of wireless devices transmit common identification information to form a cell;
The scheduler detects a position of a moving terminal based on a propagation quality between each of the plurality of wireless devices and the terminal, and determines a part of the plurality of wireless devices based on the position of the terminal. A wireless communication system , wherein resources are allocated so that data is transmitted from a device to the terminal . The wireless communication system according to claim 1,
The scheduler detects a quality of propagation between each of the plurality of radio apparatuses and the terminal based on an uplink signal measurement result of the terminal . The wireless communication system according to claim 1,
The said scheduler acquires position information from the operation management system of a mobile body, and changes the allocation of the said resource based on the acquired position information, The radio | wireless communications system characterized by the above-mentioned. The wireless communication system according to claim 1,
The plurality of wireless devices are arranged along a railway line,
A wireless communication system, wherein a cell is formed on a railway line by a plurality of wireless devices included in the base station.   The wireless communication system according to claim 1,
  The scheduler acquires position information from a mobile operation management system, acquires propagation quality between each of the plurality of wireless devices and the terminal, and sends the terminal information based on the position information and the propagation quality. A wireless communication system, wherein a wireless device for transmitting data is determined. A wireless communication system comprising a plurality of base stations that transmit and receive radio signals to and from a terminal,
The base station
A plurality of radio apparatuses that transmit downlink signals to the terminal using scheduled radio resources, receive uplink signals from the terminals, and form cells of predetermined identification information;
A scheduler that determines a radio device that allocates radio resources to the terminal and transmits a signal using the allocated radio resource, and an aggregation device that processes signals transmitted and received by the radio device;
The scheduler detects the position of the moving terminal, hands over the terminal connected to the wireless device to which the terminal proceeds, from the cell provided by the base station, and then identifies cell identification information of the wireless device. Is changed to the identification information of the cell in which the terminal is detected . A wireless communication system comprising a plurality of base stations that transmit and receive radio signals to and from a terminal,
The base station
A plurality of radio apparatuses that transmit downlink signals to the terminal using scheduled radio resources, receive uplink signals from the terminals, and form cells of predetermined identification information;
A scheduler that determines a radio device that allocates radio resources to the terminal and transmits a signal using the allocated radio resource, and an aggregation device that processes signals transmitted and received by the radio device;
The scheduler detects the position of the moving terminal, changes the identification information of the cell to which the terminal proceeds, to the identification information of the cell in which the terminal is detected,
The scheduler further manages a combination of wireless devices that change cell identification information and a range of cell identification information for each line, and suppresses handover beyond the range of the cell identification information. Wireless communication system. A wireless communication system comprising a plurality of base stations that transmit and receive radio signals to and from a terminal,
The base station
A plurality of radio apparatuses that transmit downlink signals to the terminal using scheduled radio resources, receive uplink signals from the terminals, and form cells of predetermined identification information;
A scheduler that determines a radio device that allocates radio resources to the terminal and transmits a signal using the allocated radio resource, and an aggregation device that processes signals transmitted and received by the radio device;
The scheduler detects the position of a moving terminal when handover from a cell in a station building area to a cell adjacent to the station building area is performed a predetermined number of times or more , and identifies identification information of a destination cell of the terminal, A wireless communication system, wherein the terminal is changed to identification information of a detected cell . A wireless communication system according to claim 8,
The scheduler, after changing the identification information of a cell adjacent to the station area to the identification information of the cell in which the terminal is detected, assigns new cell identification information to the wireless device in which the terminal is detected. A wireless communication system. The wireless communication system according to claim 1,
The aggregation device is
A routing function for exchanging information of a plurality of cells formed by the base station with a core network and distributing data to the cells;
A modulation / demodulation unit that performs modulation / demodulation processing based on the radio resource allocation;
A switch that forwards the determined radio resource to the radio device;
The wireless communication system, wherein the switch is provided between the modulation / demodulation unit and the wireless device. The wireless communication system according to claim 1,
The aggregation device is
A routing function for exchanging information of a plurality of cells formed by the base station with a core network and distributing data to the cells;
A switch that forwards the determined radio resource to the radio device;
The wireless device has a modulation / demodulation unit that performs modulation / demodulation processing based on the allocation of the radio resource,
The wireless communication system, wherein the switch is provided between the scheduler and the modem unit. A wireless communication system according to claim 11, wherein
A radio communication system, wherein a format of a signal transmitted and received between the scheduler and the modem unit is FAPI. A wireless communication system according to claim 11, wherein
The modem unit decodes the received uplink signal of the terminal, sends the decoded data to the scheduler,
The wireless communication system, wherein the scheduler selects a decoding result of an uplink signal transmitted from the plurality of wireless devices. A control method of a wireless communication system comprising a plurality of base stations that transmit and receive radio signals to and from a terminal,
The base station transmits a downlink signal to the terminal with scheduled radio resources,
A scheduler that receives an uplink signal from the terminal and forms a cell of predetermined identification information; a scheduler that allocates radio resources to the terminal and determines a radio apparatus that transmits a signal using the allocated radio resource; An aggregation device that processes signals transmitted and received by the wireless device,
The method
The scheduler detects the position of the moving terminal,
After the scheduler has handed over the connection destination terminal to the radio device to which the terminal proceeds, from the cell provided by the base station , the cell identification information of the radio device is obtained from the cell detected by the terminal. A control method characterized by changing to identification information. A plurality of base station devices that transmit and receive radio signals to and from a terminal,
A radio apparatus that transmits a downlink signal to the terminal using scheduled radio resources, receives an uplink signal from the terminal, and forms a cell of predetermined identification information;
A scheduler that determines a radio device that allocates radio resources to the terminal and transmits a signal using the allocated radio resource, and includes an aggregation device that processes signals transmitted and received by the radio device;
The scheduler detects the position of the moving terminal, hands over the connection destination terminal from the cell provided by the base station to the destination radio apparatus of the terminal, and then identifies the cell identification information of the radio apparatus To the identification information of the cell in which the terminal is detected.

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