JP6899423B2 - Communication system and handover control method - Google Patents

Description

The present invention relates to a communication system having an overlay cell configuration and a handover control method.

In recent years, as a countermeasure against disasters and out-of-service areas, from mobile base stations in the sky built into aircraft such as aircraft, artificial satellites, HAPS, balloons, helicopters, and drones, to the ground, water, or low altitude air. The expansion of the three-dimensional large zone cell (first cell) to be formed is considered to be effective. In an overlay cell configuration in which ground cells (second cell) such as normal macro cells and small cells are superimposed in this large zone cell, the frequency utilization efficiency is expanded by operating the large zone cell using the same frequency as the ground cell. can do.

In the overlay cell configuration, the interference from the large zone cell to the terrestrial cell increases, which may reduce the communication quality (throughput) of the UE (user device), which is a mobile station connected to the terrestrial cell. Further, in the overlay cell configuration, since the sky cell of the same frequency is deployed above the ground cell, the UE located in the area outside the ground cell area in the sky cell not only connects to the sky cell, but also the signal of the sky cell is transmitted. When a UE in a strong environment (for example, a cell boundary between ground cells or a UE located outdoors) is handed over to a sky cell, a large number of UEs are located in the sky cell and communication traffic is concentrated on the sky cell. There is a risk. When communication traffic is concentrated on the sky cell, UEs that really need to connect to the sky cell (for example, mountainous areas, rural areas away from urban areas, the sea, the center of a large lake, the sky, etc.) The communication quality of UEs located in out-of-service areas or out-of-service areas in the event of a disaster will deteriorate.

Conventionally, as a technique for reducing cell-to-cell interference between a macro cell base station and a small cell base station in an overlay cell configuration in which a macro cell and a small cell overlap, the macro cell base station and the small cell base station are time-synchronized with each other. An inter-cell interference control technique (eICIC: enhanced Inter-Cell Interference Coordination) in a time domain (subframe unit) is known on the premise of this (see, for example, Patent Document 1). In this inter-cell interference control technology (eICIC), ABS (Almost Blank Subframe) for stopping the transmission of downlink signals of each cell is set to avoid inter-cell interference on the time axis.

Japanese Unexamined Patent Publication No. 2017-005451

However, when the cell-to-cell interference control technology (eICIC) of Patent Document 1 is used, in order to avoid cell-to-cell interference on the time axis, time synchronization is performed with the base station of a large zone cell having an overlay cell configuration. It is necessary for the base stations of all the terrestrial cells in the large zone cell to have a time synchronization function, and there is a problem that the frequency utilization efficiency is lowered because the transmission signal is stopped in subframe units.

In the communication system of the first aspect according to one aspect of the present invention, a first cell base station forming the first cell and a plurality of second cells having a cell size smaller than that of the first cell are placed in the first cell. A plurality of second cell base stations to be formed are provided, and the plurality of second cells include a second cell having a different frequency using a frequency different from that of the first cell, a second cell having a different frequency, and the entire area. Alternatively, it is a communication system including a second cell having the same frequency that partially overlaps and uses the same frequency as the first cell. In this communication system, a means for determining whether or not a mobile station located in a second cell having the same frequency as the first cell is being interfered with by the first cell, and the mobile station is the first cell. When the cell is interfering with the mobile station, the mobile station is provided with a means for controlling the handover of the mobile station so that the mobile station is handed over from the second cell having the same frequency to the second cell having a different frequency.

In the communication system of the first aspect, the second cell base station of the same frequency is described in the measurement report of the same frequency received from the mobile station located in the second cell of the same frequency as the first cell. When it is determined whether or not the cell identifier of the same frequency is included and the cell identifier of the first cell is included in the measurement report of the same frequency, the movement from the second cell of the same frequency to the second cell of the different frequency. A handover request for forcibly executing the handover of the station is transmitted to the second cell base station of the different frequency, and the handover of the mobile station from the second cell of the same frequency to the second cell of the different frequency. The process may be executed.
In the communication system of the first aspect, the second cell base station of the same frequency is described in the measurement report of the same frequency received from the mobile station located in the second cell of the same frequency as the first cell. When it is determined whether or not the cell identifier of the cell is included and the cell identifier of the first cell is included in the measurement report of the same frequency, the received power P1 from the first cell base station and the reception from the first cell are received. The difference between the power P1 and the received power P2s from the own station (P1-P2s) or the ratio of the received power P1 from the first cell to the received power P2s from the own station (P1 / P2s) is predetermined. It is determined whether or not the frequency is equal to or higher than the threshold value, and if the determination is affirmative, the handover for forcibly executing the handover of the mobile station from the second cell of the same frequency to the second cell of the different frequency. The request may be transmitted to the second cell base station of the different frequency, and the handover process of the mobile station from the second cell of the same frequency to the second cell of the different frequency may be executed.

In the communication system of the first aspect, the second cell base station of the same frequency is described in the measurement report of the same frequency received from the mobile station located in the second cell of the same frequency as the first cell. If the cell identifier of the first cell is included in the measurement report of the same frequency, the handover of the mobile station from the second cell of the same frequency to the first cell is performed. When the handover request for executing the above is transmitted to the first cell base station and the permission response to the handover request is received from the first cell base station, the second cell of the same frequency to the first cell. When the handover process of the mobile station is executed and the rejection response to the handover request is received from the first cell base station, the mobile station of the mobile station from the second cell of the same frequency to the second cell of the different frequency. A handover request for executing the handover is transmitted to the second cell base station of the different frequency, and the handover process of the mobile station from the second cell of the same frequency to the second cell of the different frequency is executed. May be good.
Here, the first cell base station may selectively transmit the permission response and the rejection response based on the number of mobile stations connected to the first cell and in the service area. Further, the first cell base station determines whether or not the amount of communication traffic of the mobile station in the first cell is equal to or greater than a predetermined threshold value, and if the determination is affirmative, the said The permission response may be transmitted, and if the judgment is negative, the rejection response may be transmitted.

In the communication system of the first aspect, the second cell base station of the same frequency is located in the second cell of the same frequency prior to the handover from the second cell of the same frequency to the second cell of the different frequency. When the measurement report of the different frequency is received from the mobile station in the service area and the measurement report of the different frequency includes a plurality of cell identifiers of the second cell of the different frequency, the first of the plurality of different frequencies The handover request may be transmitted to the second cell having the highest received power among the two cells and having a different frequency.

In the communication system of the first aspect, the second cell base station of the same frequency is located in the second cell of the same frequency prior to the handover from the second cell of the same frequency to the second cell of the different frequency. When the measurement report of the different frequency is received from the mobile station in the service area and the measurement report of the different frequency includes a plurality of cell identifiers of the second cell of the different frequency, the first of the plurality of different frequencies The handover request may be transmitted to the second cell having a different frequency having the best reception quality among the two cells.

In the communication system of the first aspect, the second cell base station of the same frequency is described in the measurement report of the same frequency received from the mobile station located in the second cell of the same frequency in the first cell. If the cell identifier of the first cell is included in the measurement report of the same frequency, the handover of the mobile station from the second cell of the same frequency to the first cell is performed. Is transmitted to the first cell base station, the handover process of the mobile station from the second cell of the same frequency to the first cell is executed, and the measurement report of the same frequency is executed. If the cell identifier of the first cell is not included in, the handover request to the first cell base station is not transmitted, and the first cell base station moves from the second cell of the same frequency to the first cell. After the handover process of the mobile station is completed, a handover request for forcibly executing the handover of the mobile station from the first cell to the second cell of the different frequency is sent to the second cell of the different frequency. It may be transmitted and the handover process of the mobile station from the first cell to the second cell of the different frequency may be executed.
Here, the first cell base station selectively transmits the handover request to the second cell base station having a different frequency based on the number of mobile stations in the first cell. May be good. Further, the first cell base station determines whether or not the amount of communication traffic of the mobile station in the first cell is equal to or greater than a predetermined threshold value, and if the determination is affirmative, the permission is granted. A response may be sent, and if the judgment is negative, a rejection response may be sent.
Further, the second cell base station of the same frequency is located in the second cell of the same frequency prior to the handover from the second cell of the same frequency to the second cell of the different frequency via the first cell. When the measurement report of the different frequency is received from the mobile station in the service area and the measurement report of the different frequency includes a plurality of cell identifiers of the second cell of the different frequency, the first of the plurality of different frequencies The handover request is made by adding the cell identification information of the second cell of the different frequency having the largest received power so as to cause the second cell of the different frequency having the largest received power among the two cells to perform the handover from the first cell. It may be transmitted to the first cell base station.
Further, the second cell base station of the same frequency is located in the second cell of the same frequency prior to the handover from the second cell of the same frequency to the second cell of the different frequency via the first cell. When the measurement report of the different frequency is received from the mobile station in the service area and the measurement report of the different frequency includes a plurality of cell identifiers of the second cell of the different frequency, the first of the plurality of different frequencies The handover request is made by adding the cell identification information of the second cell having the best reception quality to the second cell having the best reception quality and having the different frequency from the first cell. It may be transmitted to the first cell base station.

In the communication system of the second aspect according to still another aspect of the present invention, the first cell base station forming the first cell and a plurality of second cells having a cell size smaller than that of the first cell are included in the first cell. A plurality of second cell base stations formed therein are provided, and the plurality of second cells include a second cell having a different frequency using a frequency different from that of the first cell, and a second cell and an area having a different frequency. It is a communication system including a second cell of the same frequency which uses the same frequency as the first cell, in which all or a part of the above overlaps. In this communication system, a means for determining whether or not a mobile station located in a second cell having a different frequency is being interfered with by the first cell, and a mobile station interfering with the first cell. When receiving, the means for controlling the handover of the mobile station so as to cause the mobile station to be handed over from the second cell of the different frequency to the second cell of the same frequency is provided.
In the communication system of the second aspect, different cell identifiers are set for the first cell and the second cell of the same frequency, and the second cell base station of the different frequency is the second cell of the different frequency. It is determined whether or not the cell identifier of the first cell is included in the measurement report of the same frequency received from the mobile station in the cell, and the cell of the first cell is included in the measurement report of the same frequency. When the identifier is not included, a handover request for forcibly executing the handover of the mobile station from the second cell of the different frequency to the second cell of the same frequency is sent to the second cell base station of the same frequency. It may be transmitted and the handover process of the mobile station from the second cell of the different frequency to the second cell of the same frequency may be executed.
In the communication system of the second aspect, different cell identifiers are set for the first cell and the second cell of the same frequency, and the second cell base station of the different frequency is the second cell of the different frequency. It is determined whether or not the cell identifier of the first cell is included in the measurement report of the same frequency received from the mobile station in the cell, and the cell of the first cell is included in the measurement report of the same frequency. When the identifier is included, the received power P1 from the first cell base station, the difference between the received power P1 from the first cell and the received power P2s from the second cell of the same frequency (P1-P2s), or It is determined whether or not the ratio (P1 / P2s) of the received power P1 from the first cell to the received power P2s from the second cell of the same frequency is equal to or less than a predetermined threshold, and the determination is affirmative. In this case, a handover request for forcibly executing the handover of the mobile station from the second cell of the different frequency to the second cell of the same frequency is transmitted to the second cell base station of the same frequency. The handover process of the mobile station from the second cell of the different frequency to the second cell of the same frequency may be executed.

In the communication system of the second aspect, the second cell base station of the different frequency is described in the measurement report of the same frequency received from the mobile station located in the second cell of the different frequency in the first cell. If the measurement report of the same frequency does not include the cell identifier of the first cell, the second cell of the different frequency to the second cell of the same frequency is said to be included. When a handover request for executing the handover of a mobile station is transmitted to the second cell base station of the same frequency and a permission response to the handover request is received from the second cell base station of the same frequency, the different frequency The handover process of the mobile station from the second cell of the above to the second cell of the same frequency may be executed.
Here, the second cell base station of the same frequency may selectively transmit the allow response and the deny response based on the number of mobile stations in the second cell of the same frequency. .. Further, the second cell base station having the same frequency determines whether or not the amount of communication traffic of the mobile station located in the second cell of the same frequency is equal to or greater than a predetermined threshold value, and the determination is made. If is affirmative, a rejection response may be sent, and if the judgment is negative, the permission response may be sent.

In any of the communication systems of the second aspect, the second cell base station of the different frequency has the second cell of the different frequency prior to the handover from the second cell of the different frequency to the second cell of the same frequency. When a measurement report of the same frequency is received from a mobile station located in a cell and the measurement report of the same frequency includes a plurality of cell identifiers of the second cell of the same frequency, the plurality of identical cell identifiers are included. The handover request may be transmitted to the second cell of the same frequency having the highest received power among the second cells of the frequency.

In any of the communication systems of the second aspect, the second cell base station of the different frequency has the second cell of the different frequency prior to the handover from the second cell of the different frequency to the second cell of the same frequency. When a measurement report of the same frequency is received from a mobile station located in a cell and the measurement report of the same frequency includes a plurality of cell identifiers of the second cell of the same frequency, the plurality of identical cell identifiers are included. The handover request may be transmitted to the second cell of the same frequency having the best reception quality among the second cells of the frequency.

In the method of the third aspect according to still another aspect of the present invention, a first cell base station forming the first cell and a plurality of second cells having a cell size smaller than that of the first cell are placed in the first cell. The plurality of second cells include a plurality of second cell base stations formed in the above, and the plurality of second cells include a second cell having a different frequency using a frequency different from that of the first cell, and a second cell having a different frequency and an area. This is a handover control method in a communication system including a second cell having the same frequency, which is entirely or partially overlapped and uses the same frequency as the first cell. This handover control method determines whether or not a mobile station located in the second cell of the same frequency is being interfered by the first cell, and the mobile station interferes with the first cell. In the case of receiving, the handover of the mobile station is controlled so as to cause the mobile station to be handed over from the second cell of the same frequency to the second cell of the different frequency.

In the method of the fourth aspect according to still another aspect of the present invention, a first cell base station forming the first cell and a plurality of second cells having a cell size smaller than that of the first cell are placed in the first cell. The plurality of second cells include a plurality of second cell base stations formed in the above, and the plurality of second cells include a second cell having a different frequency using a frequency different from that of the first cell, and a second cell having a different frequency and an area. This is a handover control method in a communication system including a second cell having the same frequency, which is entirely or partially overlapped and uses the same frequency as the first cell. This handover control method determines whether or not a mobile station located in the second cell having a different frequency is interfering with the first cell, and the mobile station interferes with the first cell. In the case of receiving, the handover of the mobile station is controlled so as to cause the mobile station to be handed over from the second cell of the different frequency to the second cell of the same frequency.

In the communication systems of the first aspect and the second aspect, and the handover control methods of the third aspect and the fourth aspect, the second cell base station having the same frequency is a small cell base station installed on the ground or water. Alternatively, it is a small cell base station installed in an air vehicle flying at an altitude lower than that of the first cell base station, and the second cell base station having a different frequency is a macro cell base station installed on the ground or water or the above. It is a macro cell base station installed in an air vehicle flying at a lower altitude than the first cell base station, and the first cell base station is a base station arranged at the same position as or higher than the second cell base station. It may be.
Further, the first cell base station may be a macro cell base station, and the second cell base station having the same frequency and the second cell base station having different frequencies may be small cell base stations, respectively.

According to the present invention, in an overlay configuration in which a plurality of second cells having a small cell size are located in the first cell, all the second cells have a time synchronization function for time synchronization with the base station of the first cell. It is possible to avoid the concentration of communication traffic in the first cell while suppressing the decrease in frequency utilization efficiency without providing the base station in the above.

An explanatory diagram showing an example of a schematic configuration of a mobile communication system having an overlay cell configuration in which a plurality of ground cells are arranged in a large zone cell according to an embodiment of the present invention. The explanatory view which shows an example of the format in the time axis direction of the wireless communication frame of the LTE downlink. Explanatory drawing which shows an example of the format in the time axis and frequency axis direction of the LTE downlink wireless communication frame. Explanatory drawing which shows an example of the format of a part of the subframe which constitutes a wireless communication frame. It is explanatory drawing which shows an example of the state of transmission stop in the subframe by ABS adopted by the inter-cell interference control technology (eICIC) of the same frequency which concerns on a reference example. The explanatory view which shows an example of the inter-frequency handover in the overlay cell configuration of the communication system which concerns on this embodiment. The sequence diagram which shows an example of the inter-frequency handover processing in the overlay cell configuration of the communication system which concerns on this embodiment. The sequence diagram which shows another example of the inter-frequency handover processing in the overlay cell configuration of the communication system which concerns on this embodiment. FIG. 5 is a sequence diagram showing still another example of inter-frequency handover processing in the overlay cell configuration of the communication system according to the present embodiment. FIG. 5 is a sequence diagram showing still another example of inter-frequency handover processing in the overlay cell configuration of the communication system according to the present embodiment. The explanatory view which shows another example of the inter-frequency handover processing in the overlay cell configuration of the communication system which concerns on this embodiment. FIG. 5 is a sequence diagram showing still another example of inter-frequency handover processing in the overlay cell configuration of the communication system according to the present embodiment. FIG. 5 is a sequence diagram showing still another example of inter-frequency handover processing in the overlay cell configuration of the communication system according to the present embodiment. FIG. 5 is a sequence diagram showing still another example of inter-frequency handover processing in the overlay cell configuration of the communication system according to the present embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, an embodiment of the present invention will be described on the premise of application to LTE / LTE-Advanced, but the concept of the present invention can be applied to any system as long as it is a system using a similar cell configuration and physical channel configuration. Applicable.

First, the overall configuration of a mobile communication system to which the present invention can be applied will be described.
FIG. 1 is an explanatory diagram showing an example of a schematic configuration of a mobile communication system having an overlay cell configuration in which a plurality of ground cells 20A and 30A are arranged in a large zone cell 10A according to an embodiment of the present invention. As a measure against disasters and elimination of out-of-service areas, it is effective to deploy a large-sized large zone cell 10A formed from the air-floating type communication relay device 15 toward the ground or water. Further, as a countermeasure against the rapidly increasing mobile communication traffic in the large zone cell 10A, it is effective to apply an overlay cell configuration in which a plurality of ground cells 20A and 30A are superimposed in the large zone cell 10A.

In FIG. 1, the plurality of terrestrial cells 20A and 30A have the same frequency (frequency band) as that of the large zone cell 10A for wireless communication with a user terminal device (hereinafter, also referred to as “UE”) which is a mobile station. It includes a small cell 20A as a second cell and a macro cell 30A as a second cell having a different frequency (frequency band) different from that of the large zone cell 10A for wireless communication with the UE. The UE 41 in FIG. 1 is located in the large zone cell 10A and is connected to the cell 10A. Further, the UE 42 in FIG. 1 is in the small cell 20A and is connected to the cell 20A, and the UE 43 is in the macro cell 30A and is connected to the cell 30A.

In the overlay cell configuration of FIG. 1, the frequency utilization efficiency can be expanded by using the same frequency between the large zone cell 10A and the small cell 20A having the same frequency, and the boundary area of the small cell 20A having the same frequency is required. By handing over the UE 42 in the area to another macro cell 30A having a different frequency, interference from the large zone cell 10A can be avoided, so that the communication quality (for example, throughput) in the UEs 41, 42, 43 can be increased. ..

In FIG. 1, the mobile communication system of the present embodiment is a communication system conforming to next-generation standard specifications such as LTE (Long Term Evolution) / LTE-Advanced or 5th generation, and is mounted on the communication relay device 15. A mobile large zone cell base station 10 as a first cell base station and a ground cell base as a plurality of second cell base stations fixedly arranged in a large zone cell 10A which is a wireless communication area of the large zone cell base station 10. It has stations 20 and 30. The terrestrial cell base stations 20 and 30 are, for example, small cell bases as second cell base stations of the same frequency that use the same frequency as the large zone cell base station 10 (hereinafter, also referred to as “frequency A”) for wireless communication with the UE. The station 20 includes a macro cell base station 30 as a second cell base station having a different frequency that uses a frequency different from the frequency A (hereinafter, also referred to as “frequency B”) for wireless communication with the UE. Further, the frequencies A and B used in the cells 10A, 20A and 30A may be, for example, a frequency in the microwave band of 300 MHz to 30 GHz or a frequency in the millimeter wave band higher than 30 GHz. Further, the frequency A is 700 MHz to 1 GHz (also referred to as “platinum band”), and the frequency B may be a frequency higher than 1 GHz.

The small cell 20A and the macro cell 30A, which are the wireless communication areas of the small cell base station 20 and the macro cell base station 30, are included inside the large zone cell 10A of the large zone cell base station 10. The number of small cells 20A arranged in the large zone cell 10A may be 1 to 6, or may be 8 or more. Further, the number of macro cells 30A arranged in the large zone cell 10A may be 1 to 2, or 4 or more. Further, in the example of FIG. 1, one or a plurality of small cells 20A are located in the macro cell 30A, and the entire small cell 20A overlaps the macro cell 30A, but a part of the small cell 20A overlaps the macro cell 30A. You may.

The large zone cell base station 10 is a base station (for example, eNodeB, gNodeB) as a relay communication station mounted on an airborne communication relay device 15 composed of an air vehicle that can move in the sky, and is a feeder on the mobile communication network side. The wireless communication of the link FL and the wireless communication of the service link SL on the mobile station side can be relayed.

Although FIG. 1 shows an example in which the relay communication station mounted on the communication relay device 15 in the sky is the large zone cell base station 10, the large zone cell base station 10 may be provided at the gateway station on the ground side. Alternatively, it may be provided in a device connected to a gateway station on the ground side. In this case, the relay communication station mounted on the communication relay device 15 performs wireless communication of the feeder link FL with the large zone cell base station 10 and wireless communication of the service link SL with the UE (mobile station). Functions as a relay repeater.

Further, FIG. 1 shows an example in which the communication relay device 15 equipped with the large zone cell base station 10 is an airship as an airship capable of moving over the sky, but the communication relay device 15 can move or fly over the sky. Drone, balloon, aircraft, helicopter, solar plane type HAPS ("high altitude platform station" or "high altitude pseudo satellite") or LAPS ("low altitude platform station" or "low altitude pseudo satellite"), airship type It may be another unmanned or manned aircraft such as HAPS or LAPS, artificial satellites. Further, the communication relay device 15 is controlled to move to a predetermined position in the sky located at the time of operation for wireless relay, and then stay at that position or circulate in a predetermined range of flight space including the position. You may.

The aircraft is located in the airspace at an altitude of 100 [km] or less from the ground, sea surface, or water surface such as a river or lake, by autonomous control or external control, or by the control of the operator boarding the aircraft. It may be controlled as follows. Further, the flight airspace of the flying object may be a stratospheric airspace having an altitude of 11 [km] or more and 50 [km] or less. Further, the flight airspace of the flying object may be an airspace having an altitude of 15 [km] or more and 25 [km] or less in which the weather conditions are relatively stable, and particularly an airspace having an altitude of approximately 20 [km]. May be good.

Further, the large zone cell base station 10 is located at a higher position (position in the atmosphere and outer space) than the ground cell base station (second base station) such as the small cell base station 20 and the macro cell base station 30. It may be a base station installed in (including). The small cell base station 20 and the macro cell base station 30 may be installed on the ground or on the water, respectively, or may be installed on an aircraft flying at an altitude lower than that of the large zone cell base station 10. Further, the large zone cell base station 10 is a macro cell base station, and a second cell base station having the same frequency as the macro cell base station and a second cell base station having a different frequency from the macro cell base station are small cells. It may be a base station.

The macrocell base station 30 is a high-power base station that covers a ground cell that is usually installed outdoors in a mobile communication network and has a wide area with a radius of about several hundred meters to several tens of kilometers. The macrocell base station 30 is connected to another base station by, for example, a wired communication line, and can communicate with a predetermined communication interface. Further, the macro cell base station 30 is connected to the core network of the mobile communication network via a communication line such as a line termination device and a dedicated line, and is connected to various nodes such as a server on the core network by a predetermined communication interface. Communication is possible.

Unlike the wide-area macrocell base station 30, the small cell base station 20 has a wireless communication range of several meters to several hundreds of meters, and can be installed inside a building such as a general household, a store, or an office. It is a small output base station. The small cell base station 20 is also connected to the core network of the mobile communication network via a line termination device and a communication line such as an ADSL (Asymmetric Digital Subscriber Line) line or a broadband public communication line such as an optical line, and is on the core network. It is possible to communicate with various nodes such as the server device of the above using a predetermined communication interface.

The small cell base station 20 and the macro cell base station 30 in the large zone cell 10A may be base stations installed on the ground or on the water, or may be installed on a low-altitude air vehicle such as a drone, a balloon, a helicopter, or an aircraft. It may be a base station.

In FIG. 1, the first mobile station, UE 41, is a user terminal device (MUE) located in the large zone cell 10A of frequency A and connected to the large zone cell base station 10, via the large zone cell base station 10. It is in a state where wireless communication for telephone and data communication is possible.

The UE 42, which is a part of the second mobile station, is a user terminal device (SUE) located in the small cell 20A of the frequency A and connected to the small cell base station 20, and is a user terminal device (SUE) connected to the small cell base station 20 via the small cell base station 20. Wireless communication for telephone and data communication is possible. Since the UE 42 uses the same frequency A as the large zone cell 10A, if the small cell 20A is located in a boundary area close to the boundary with the large zone cell 10A, it is susceptible to interference from the large zone cell 10A.

The other second mobile station, the UE 43, is a user terminal device (SUE) located in the macro cell 30A of the frequency B and connected to the macro cell base station 30, and is a telephone or data via the small cell base station 20. Wireless communication for communication etc. is possible.

When the UEs 41, 42, and 43 are in the large zone cell 10A, the small cell 20A, and the macro cell 30A, respectively, the large zone cell base station 10, the small cell base station 20, and the macro cell base station 30 corresponding to the cells in the area are located. Wireless communication can be performed between them using a predetermined communication method and wireless communication resource. Each of the UEs 41, 42, and 43 is configured by using hardware such as a computer device having a CPU and a memory, an external communication interface unit for a core network, and a wireless communication unit, and a base station is executed by executing a predetermined program. Wireless communication with 10, 20, 30, etc. can be performed.

In the present embodiment, the large zone cell base station 10, the small cell base station 20, and the macro cell base station 30, respectively, provide hardware such as a computer device having a CPU and memory, an external communication interface unit for a core network, and a wireless communication unit, respectively. By executing a predetermined program, various processes such as handover for suppressing interference described later can be executed, and UEs 41, 42, 43 and UEs 41, 42, 43 can be executed by using a predetermined communication method and wireless communication resources. Can perform wireless communication between.

Each of the base stations 10, 20, and 30 is a base station capable of wireless communication of an OFDM (Orthogonal Frequency Division Multiplexing) downlink to a UE which is a mobile station. The base stations 10, 20, and 30 include, for example, an antenna, a radio signal path switching unit, a transmission / reception duplexer (DUP: Duplexer), a downlink radio reception unit and an OFDM (Orthogonal Frequency Division Multiplexing) demodulation unit, an uplink radio reception unit, and SC-. It is equipped with an FDMA (Single-Carrier Frequency-Division Multiple Access) demodulation unit and the like. Further, each of the base stations 10, 20 and 30 includes an OFDM modulation unit, a downlink radio transmission unit, a control unit and the like.

The SC-FDMA demodulation unit executes an SC-FDMA demodulation process on the received signal received by the uplink radio reception unit, and passes the demodulated data to the control unit. The OFDM modulation unit modulates the downlink signal data received from the control unit and transmitted to the UE in the cell of its own station by the OFDM method so that it is transmitted with a predetermined power. Further, when the base station receives the information of the subframe to be stopped for transmission from the server, for example, the OFDM modulation unit is controlled to stop the downlink transmission only for a specific subframe in the wireless communication frame. The downlink radio transmission unit transmits the transmission signal modulated by the OFDM modulation unit via the transmission / reception duplexer, the radio signal path switching unit, and the antenna.

The control units of the base stations 10, 20, and 30 are composed of, for example, a computer device, and control each unit or execute various processes by reading and executing a predetermined program. The control unit also functions as a means for performing processing for handover of the UEs 41, 42, and 43 in cooperation with the external communication interface unit for the core network.

FIG. 2 is an explanatory diagram showing an example of the format of the LTE downlink wireless communication frame in the time axis direction. FIG. 3 is an explanatory diagram showing an example of a format in the time axis and frequency axis directions of the LTE downlink wireless communication frame.
As shown in FIG. 2, the wireless communication frame 100 having a predetermined length (10 [ms] in the illustrated example), which is one unit of the LTE downlink signal, has a predetermined number (10 in the illustrated example) of a predetermined length (10 in the illustrated example). In the illustrated example, it is composed of 1.0 [ms]) subframes 110. Since the TTI (Transmission Time Interval), which is the minimum time unit for LTE downlink scheduling, is one subframe, a resource block (RB), which is the minimum unit of radio resources, is assigned to the scheduled UE for each subframe. .. Each subframe 110 has a control channel area 110A and a data channel area 110B as described later.

Further, as shown in FIG. 3, in each subframe 110, a maximum of 100 resource blocks (RB) are allocated in the frequency axis direction. As will be described later, the primary synchronization signal (PSS) 121 and the secondary synchronization signal (SSS) are located in the central 6RB of the first (# 0) and sixth (# 5) subframes in the frequency axis direction from the beginning. ) 122 is arranged.

FIG. 4 is an explanatory diagram showing an example of a partial format of a subframe constituting a wireless communication frame. In FIG. 4, each subframe 110 is composed of, for example, 8 subcarriers (15 [kHz]) in the frequency axis direction and 14 OFDM symbols in the time axis direction, for a total of 112 REs (Resource Elements). When Extended Cyclo Prefix is used, 12 OFDM symbols are transmitted in one subframe. Here, the "symbol" is a unit of information transmitted by wireless communication. Further, one symbol is generated by one modulation of the information to be transmitted, and the amount of information (number of bits) of one symbol is determined by the modulation method. Scheduling is performed for each subframe, which frequency / time resource mapping is performed for each UE, what modulation format (modulation method, code rate) is used for the data signal to each UE, and the like. The result is notified to the UE.

As shown in FIG. 4, in each subframe 110, the RE of the data channel signal and the upper control channel signal is mapped to the control channel area 110A of the head portion to which the RE of the downlink L1 / L2 control channel signal is mapped. It has a data channel area 110B. The control channel area 110A can be assigned the OFDM symbols 1 to 3 at the beginning of the subframe (1 OFDM symbol in the example of FIG. 4).

A PDCCH (Physical Downlink Control Channel), which is an L1 / L2 control channel, is set in the control channel area 110A of the subframe 110. The PDCCH is used for determining the scheduling of the upper and lower links and transmitting control information (DCI: Downlink Control Information) such as an uplink power control command. The DCI includes downlink scheduling allocations that include PDSCH resource instructions, transmission formats, HARQ information, and control information about spatial multiplexing. The DCI also includes PUSCH resource instructions, transmission formats, HARQ-related information, and uplink grants, which are uplink scheduling information.

Further, a physical shared channel (PDSCH: Physical Downlink Shared Channel) is set in the data channel area 110B of the subframe 110. PDSCH is a physical channel for transmitting downlink data, and in addition to MIMO diversity as a MIMO transmission method, LTE supports MIMO multiplexing of up to 4 layers, and LTE-Advanced supports MIMO multiplexing of up to 8 layers. In addition, SIB which is notification information other than MIB, paging information which is a call when receiving an incoming call, and other control messages of the upper layer, for example, control information of the RRC (Radio Resource Control protocol) layer are also transmitted by PDSCH. The UE decodes the PDSCH based on the information such as the radio resource allocation position, the modulation method, and the data size (TB: Transport Block size) acquired from the PDCCH.

Further, in LTE, cell-specific reference signals (CRS) are distributed and regularly arranged in the first, fifth, eighth, and twelfth OFDM symbols among the 14 OFDM symbols in the time domain in the subframe 110. This cell reference signal CRS plays two roles of a reference signal for measuring channel quality information (CSI) in the UE and a reference signal for data demodulation. The cell reference signal CRS is subject to a frequency shift of the subcarrier position that is mapped to different scrambling depending on the cell ID. In the example of FIG. 4, the cell reference signal CRS for the first antenna # 0 and the cell reference signal CRS for the second antenna # 1 used in the case of MIMO using two antennas are shown. There is.

In the communication system having the overlay cell configuration, the large zone cell 10A and the small cell (ground cell) 20A use the same frequency in order to improve the frequency utilization efficiency. Therefore, the increased interference from the large zone cell 10A to the small cell 20A may reduce the communication quality (throughput) of the UE 42 connected to the small cell 20A. Further, in the overlay cell configuration, since the large zone cell (sky cell) 10A having the same frequency is deployed above the small cell (ground cell) 20A, the UE located in the area outside the small cell area within the large zone cell 10A is the large zone cell 10A. In addition to connecting to the large zone cell 10A, a UE in an environment where the signal of the large zone cell 10A is strong (for example, a cell boundary between small cells or a UE located outdoors) is handed over to the large zone cell 10A, so that a large number of UEs are connected to the large zone cell 10A. UE is in the area, and communication traffic may be concentrated on the large zone cell 10A. When communication traffic is concentrated on the large zone cell 10A, a UE that truly needs to be connected to the large zone cell 10A (for example, a mountainous area, a rural area away from an urban area, the sea, the center of a large lake, or the sky) is conventional. The communication quality of UEs located in the out-of-service area of the cell or the out-of-service area at the time of a disaster is deteriorated.

The cell-to-cell interference control technique (eICIC) is known as a technique for reducing cell-to-cell interference of the same frequency in an overlay cell configuration.

FIG. 5 is an explanatory diagram showing an example of a state in which transmission is stopped in a subframe by ABS adopted in the cell-cell interference control technology (eICIC) having the same frequency according to a reference example. In eICIC, for example, as shown in FIG. 5, the data channel is set by setting ABS in some subframes of the large zone cell 10A (subframes # 1, # 3, # 6, # 8 in the illustrated example). It is possible to stop the signal transmission in the region and reduce the interference of the data channel in the UE 42 connected to the ground cell (small cell) 20A. Further, for example, as shown in FIG. 5, some subframes of the ground cell (small cell) 20A (subframes of # 0, # 2, # 4, # 5, # 7, # 9 in the illustrated example) Similarly, by setting the ABS, it is possible to reduce the interference of the data channel in the UE 41 connected to the large zone cell 10A.

However, when the cell-to-cell interference control technology (eICIC) by ABS is applied, the time for time synchronization with the large zone cell base station 10 having an overlay cell configuration is required to avoid cell-to-cell interference on the time axis. It is necessary for all the small cell base stations 20 in the large zone cell 10A to have a synchronization function, and there is a problem that the frequency utilization efficiency is lowered because the transmission signal is stopped in subframe units.

Therefore, in the present embodiment, as shown below, the frequency at which the UE 42 is handed over to the macro cell 30A having a different frequency B only when it is determined that the UE 42 in the small cell 20A is being interfered with by the large zone cell 10A. Interfering with the UE 42 is avoided by performing inter-handover. On the other hand, when it is determined that the UE 42 is not interfered with by the large zone cell 10A, the UE 42 is left connected to the small cell 20A without performing the handover to the macro cell 30A of the different frequency B, or , Another small cell 20A of the same frequency A is handed over. In this way, only the small cell 20A that requires the handover is subjected to the inter-frequency handover to avoid the interference of the UE 42.

When the UE returns to the small cell 20A after performing the inter-frequency handover to the macro cell 30A, the macro cell base station 30 maintains the connection of the UE to the macro cell 30A until the communication of the UE after the handover is completed. , Inter-frequency handover to the small cell 20A may be performed at the timing when the communication is completed. Further, the macro cell base station 30 may monitor the traffic (load balance) in the macro cell 30A to determine whether or not the UE returns to the small cell 20A. For example, the macro cell base station 30 sets the threshold parameter (for example, A4offset to be compared with the received power [dBm] of the adjacent cell) for controlling whether or not the UE returns to the small cell 20A, in the small cell 20A and It may be changed based on the traffic (load balance) in the macro cell 30A. Here, the macro cell base station 30 may receive information on the traffic in the small cell 20A through the inter-base station interface.

[Example 1 of inter-frequency handover]
FIG. 6 is an explanatory diagram showing an example of inter-frequency handover in the overlay cell configuration of the communication system according to the present embodiment, and FIG. 7 is a sequence diagram showing an example of inter-frequency handover processing of FIG. In the illustrated example, the frequency A of the large zone cell 10A and the small cell 20A is the frequency of the 2 GHz frequency band (Band 1), and the frequency B of the macro cell 30A is the frequency of the platinum band 900 MGz frequency band (Band 8). is there.

In this example, the physical cell identifier (PCI) is assigned and set to the large zone cell 10A, the small cell 20A, and the macro cell 30A (S101 in FIG. 7). In the illustrated example, PCI = 100 is assigned to the large zone cell 10A, PCI = 101 is assigned to the small cell 20A, and PCI = 201 is assigned to the macro cell 30A.

When the UE 42 located in the small cell 20A moves to the cell boundary area (the area at the right end in the figure) of the small cell 20A, the UE 42 is strongly interfered with by the large zone cell 10A. Under this circumstance, the UE 43 transmits a measurement report (MR) including information on the physical cell identifier (PCI) of the adjacent cell measured at the frequency A and the frequency B and the received power [dBm] to the small cell base station 20 ( S102 in FIG. 7). In the illustrated example, the measurement report (MR) including the information of the large zone cell 10A PCI = 100, −84 [dBm] and the information of the macro cell 30A PCI = 101, −87 [dBm] as the information of the adjacent cell. Is transmitted from the UE 42 to the small cell base station 20.

Next, the small cell base station 20 determines whether or not the measurement report (MR) of the frequency A received from the UE 42 includes the physical cell identifier (PCI = 100) of the large zone cell 10A. In the illustrated example, since the measurement report (MR) of frequency A includes the physical cell identifier (PCI = 100) of the large zone cell 10A, the small cell base station 20 determines the handover of frequency B to macrocell 30A (FIG. FIG. 7 S103).

Next, the small cell base station 20 forces HO as a handover request for forcibly executing the handover of the UE 42 from the small cell 20A of the frequency A to the macro cell 30A of the frequency B to the macro cell base station 30 of the frequency B. A command is transmitted (S104 in FIG. 7).

When the small cell base station 20 receives an acknowledgment (ACK) as a response to the forced HO command (handover request response) (S105 in FIG. 7), the small cell base station 20 performs "RRC CONNECTION RECONFIGURATION" for starting the handover process to the macro cell 30A. It is transmitted to the UE 42 (S106 in FIG. 7). As a result, processing for subsequent handover is executed between the small cell base station 20 and the UE 43.

In this example, when the measurement report (MR) of the frequency A does not include the physical cell identifier (PCI = 100) of the large zone cell 10A, the small cell base station 20 does not perform the handover of the frequency B to the macro cell 30A. , Do not send the above forced HO command.

As described above, according to this example, the small cell base station 20 is not provided with a time synchronization function for time synchronization with the large zone cell base station 10, and the frequency utilization efficiency of the frequency A is suppressed from being lowered. It is possible to avoid the concentration of communication traffic on the zone cell 10A.

In this example, in order to avoid the concentration of communication traffic in the macro cell 30A, the small cell base station 20 acquires the traffic information of the adjacent cell macro cell 30A through the inter-base station interface and performs a handover to the macro cell 30A. The set value of the threshold parameter for control (for example, A4offset to be compared with the received power [dBm] of the adjacent cell) may be changed. For example, when the communication traffic of the macro cell 30A is large, the threshold parameter is changed to a high value, and when the traffic of the macro cell 30A is small, the threshold parameter is changed to a low value. Then, when the small cell base station 20 includes the physical cell identifier (PCI = 100) of the large zone cell 10A in the measurement report (MR) of the frequency A, the received power of the macro cell 30A and the threshold parameter (for example, A4offset) are further measured. When the received power of the macro cell 30A is larger than the threshold parameter by comparing with the set value, the handover to the macro cell 30A of the frequency B may be determined and the forced HO command may be transmitted to the macro cell base station 30.

Further, in this example, in order to suppress the deterioration of the communication quality of the UE handed over to the macro cell 30A, the small cell base station 20 reports the physical cell identifier (PCI = 100) of the large zone cell 10A in the measurement report (MR) of the frequency A. ) Is included, the received power P1 from the large zone cell base station 10, the difference between the received power P1 from the large zone cell base station 10 and the received power P2s from the own station (P1-P2s), or the large zone cell base station 10 It is determined whether or not the ratio (P1 / P2s) of the received power P1 from the source to the received power P2s from the own station is equal to or higher than a preset predetermined threshold, and if the determination is affirmative, the macrocell base station A forced HO command may be sent to 30.

Further, in this example, the small cell base station 20 reports the measurement of the frequency B, which is a different frequency, from the UE 42 located in the cell boundary area of the small cell 20A prior to the handover from the small cell 20A to the macro cell 30A. (MR) is received, and if the measurement report (MR) of the frequency B contains a plurality of physical cell identifiers (PCI) of the cell of the frequency B (for example, the macro cell 30A or another small cell), the plurality of physical cell identifiers (PCI) are included. The handover request may be transmitted to the cell of frequency B having the highest received power among the cells of frequency B. In this case, it is possible to suppress the deterioration of the communication quality of the UE after handing over to the cell of frequency B.

[Inter-frequency handover example 2]
8 and 9 are sequence diagrams showing other examples of inter-frequency handover processing in the overlay cell configuration of the communication system according to the present embodiment, respectively. These examples are examples in which handover to the large zone cell 10A is attempted prior to the inter-frequency handover processing. Since the PCI allocation setting and MR reception (S201, S202) in FIGS. 8 and 9 are common to the above-mentioned case of FIG. 7, their description will be omitted.

When the measurement report (MR) of the frequency A received from the UE 42 includes the physical cell identifier (PCI = 100) of the large zone cell 10A, the small cell base station 20 first includes the large zone cell 10A of the same frequency A from the own cell 20A. A HO command as a normal handover request for executing the handover of the UE 42 to is transmitted to the large zone cell base station 10 (S203 in FIG. 8).

When the large zone cell base station 10 receives the HO command from the small cell base station 20, the number of UEs 41 connected to the own station 10 is equal to or higher than a preset threshold value based on the communication traffic status of the own cell 10A. If it is determined that the communication traffic of the own station 10 is large, a negative response (NACK) is returned to the small cell base station 20 as a response to the HO command (handover request response) so as to reject the handover to the own cell 10A. (S204 in FIG. 8).

When the small cell base station 20 receives a negative response (NACK) from the large zone cell base station 10, it is a handover request for forcibly executing the handover of the UE 42 from the small cell 20A of the frequency A to the macro cell 30A of the frequency B. Forced HO command is transmitted (S205 in FIG. 8).

When the small cell base station 20 receives an acknowledgment (ACK) as a response to the forced HO command (handover request response) (S206 in FIG. 8), the small cell base station 20 performs "RRC CONNECTION RECONFIGURATION" for starting the handover process to the macro cell 30A. It is transmitted to the UE 42 (S207 in FIG. 8). As a result, processing for subsequent handover is executed between the small cell base station 20 and the UE 43.

In this example, when the measurement report (MR) of the frequency A does not include the physical cell identifier (PCI = 100) of the large zone cell 10A, the small cell base station 20 does not perform the trial of handover to the large zone cell 10A. Therefore, as a result, the above forced HO command is not transmitted.

When the large zone cell base station 10 receives the HO command from the small cell base station 20, for example, the number of UEs 41 connected to the own station 10 is a preset threshold value based on the communication traffic status of the own cell 10A. If it is determined that the communication traffic of the own station 10 is smaller, an acknowledgment (ACK) is returned to the small cell base station 20 as a response to the HO command (handover request response) so as to allow the handover to the own cell 10A. (S208 in FIG. 9).

When the small cell base station 20 receives an acknowledgment (ACK) from the large zone cell base station 10, the small cell base station 20 performs "RRC CONNECTION RECONFIGURATION" for starting the handover process of the UE 42 from the own cell 20A to the large zone cell 10A of the same frequency A. It is transmitted to the UE 42 (S209 in FIG. 9). As a result, processing for subsequent handover is executed between the small cell base station 20 and the UE 42.

As described above, according to this example, the small cell base station 20 is not provided with a time synchronization function for time synchronization with the large zone cell base station 10, and the frequency utilization efficiency of the frequency A is suppressed from being lowered. It is possible to avoid the concentration of communication traffic on the zone cell 10A.

In particular, according to this example, when the handover to the large zone cell 10A is attempted prior to the inter-frequency handover processing from the small cell 20A to the macro cell 30A, and the number of UEs 41 connected to the large zone cell 10A is small and the communication traffic is small, the same is true. Since the handover is performed to the large zone cell 10A of the frequency A, it is possible to more accurately achieve the suppression of the decrease in the frequency utilization efficiency of the frequency A and the avoidance of the concentration of the communication traffic on the large zone cell 10A.

In this example, the large zone cell base station 10 selectively transmits the allow response (ACK) and the deny response (NACK) based on the number of UEs connected to the own cell 10A and in the service area. You may. For example, when the number of UEs connected to the own cell 10A is small and the communication traffic is small, the large zone cell base station 10 returns the authorization response (ACK) to the small cell base station 20 and causes the large zone cell 10A to perform a handover. On the other hand, when the number of UEs connected to the own cell 10A is large and the communication traffic is large, the large zone cell base station 10 returns the rejection response (NACK) to the small cell base station 20 and handovers from the small cell 20A to the macro cell 30A. Let me. Thereby, it is possible to suppress the decrease in the frequency utilization efficiency of the frequency A and avoid the concentration of the communication traffic on the large zone cell 10A more accurately.

Further, in this example, when the small cell base station 20 transmits a handover request (forced HO request) to the adjacent cell, the macro cell 30A, in order to avoid the concentration of the communication traffic of the macro cell 30A, the traffic information of the macro cell 30A. Is acquired by the inter-base station interface, and the set value of the threshold parameter (for example, A4offset to be compared with the received power [dBm] of the adjacent cell) for controlling the handover to the macro cell 30A may be changed. For example, when the traffic of the macro cell 30A is large, the threshold parameter is changed to a high value, and when the traffic of the macro cell 30A is small, the threshold parameter is changed to a low value. Then, the small cell base station 20 compares the received power of the macro cell 30A with the set value of the threshold parameter (for example, A4offset), and when the received power of the macro cell 30A is larger than the threshold parameter, issues a forced HO command to the macro cell base. It may be transmitted to the station 30.

Further, in this example, in order to suppress the deterioration of the communication quality of the UE handed over to the macro cell 30A, the small cell base station 20 reports the physical cell identifier (PCI = 100) of the large zone cell 10A in the measurement report (MR) of the frequency A. ) Is included, the received power P1 from the large zone cell base station 10, the difference between the received power P1 from the large zone cell base station 10 and the received power P2s from the own station (P1-P2s), or the large zone cell base station 10 It is determined whether or not the ratio (P1 / P2s) of the received power P1 from the source to the received power P2s from the own station is equal to or higher than a preset predetermined threshold, and if the determination is affirmative, the large zone cell base A normal HO command may be sent to the station 10.

Further, in this example, after receiving the rejection response (NACK) from the large zone cell base station 10, the small cell base station 20 is placed in the cell boundary area of the small cell 20A prior to the handover from the small cell 20A to the macro cell 30A. A measurement report (MR) of frequency B, which is a different frequency, is received from the UE 42 in the service area, and the measurement report (MR) of frequency B is sent to the cell of frequency B (for example, macro cell 30A or other small cell). When a plurality of physical cell identifiers (PCI) are included, the handover request may be transmitted to the cell of the frequency B having the highest received power among the cells of the plurality of frequencies B. In this case, it is possible to suppress the deterioration of the communication quality of the UE after handing over to the cell of frequency B.

[Example 3 of inter-frequency handover]
FIG. 10 is a sequence diagram showing another example of the inter-frequency handover process in the overlay cell configuration of the communication system according to the present embodiment. In this example, the small cell 20A is temporarily handed over to the large zone cell 10A, and then the inter-frequency handover is performed from the large zone cell 10A to the macro cell 30A. Since the PCI allocation setting and MR reception (S301, S302) in FIG. 10 are common to the case of FIG. 7 described above, their description will be omitted.

When the measurement report (MR) of the frequency A received from the UE 42 includes the physical cell identifier (PCI = 100) of the large zone cell 10A, the small cell base station 20 first includes the large zone cell 10A of the same frequency A from the own cell 20A. A HO command as a normal handover request for executing the handover of the UE 42 to the large zone cell base station 10 is transmitted to the large zone cell base station 10 (S303).

When the large zone cell base station 10 receives the HO command from the small cell base station 20, it gives an acknowledgment (ACK) as a response to the HO command (handover request response) so as to allow the handover to its own cell 10A. Reply to the base station 20 (S304).

When the small cell base station 20 receives an acknowledgment (ACK) from the large zone cell base station 10, the small cell base station 20 starts the normal handover process of the UE 42 from the own cell 20A to the large zone cell 10A of the same frequency A, "RRC CONNECTION RECONFIGURATION". Is transmitted to the UE 42 (S305). As a result, processing for subsequent handover is executed between the small cell base station 20 and the UE 42.

Next, the large zone cell base station 10 transmits a forced HO command as a handover request for forcibly executing the handover of the UE 42 from the own cell 10A to the macro cell 30A of the different frequency B (the macro cell base station 30). S306).

When the macro cell base station 30 receives the HO command from the large zone cell base station 10, it gives an acknowledgment (ACK) as a response to the HO command (handover request response) so as to allow the handover to its own cell 30A. Reply to station 10 (S307).

When the large zone cell base station 10 receives an acknowledgment (ACK) from the macro cell base station 30, it performs "RRC CONNECTION RECONFIGURATION" for starting the inter-frequency handover process of the UE 42 from its own cell 10A to the macro cell 30A of a different frequency B. It is transmitted to the UE 42 (S308). As a result, processing for subsequent handover is executed between the large zone cell base station 10 and the UE 42.

As described above, according to this example, the small cell base station 20 is not provided with a time synchronization function for time synchronization with the large zone cell base station 10, and the frequency utilization efficiency of the frequency A is suppressed from being lowered. It is possible to avoid the concentration of communication traffic on the zone cell 10A.

In this example, since the small cell 20A is once handed over to the large zone cell 10A and then the large zone cell 10A is handed over to the macro cell 30A, the large zone cell base station 10 is based on the number of UEs connected to the own cell 10A. Then, it may be determined whether or not the UE 41 once handed over from the small cell 20A is further handed over to the macro cell 30A. For example, when the number of UEs connected to the own cell 10A is small and the communication traffic is small, the large zone cell base station 10 keeps the connection to the large zone cell 10A, and the number of UEs 41 connected to the own cell 10A is large and the communication traffic is high. In the case of a large number, the UE 41 once handed over from the small cell 20A can be further handed over to the macro cell 30A. Therefore, it is possible to suppress the decrease in the frequency utilization efficiency of the frequency A and avoid the concentration of the communication traffic on the large zone cell 10A more accurately.

Further, in this example, in order to avoid the concentration of communication traffic of the macro cell 30A, when the large zone cell base station 10 transmits a handover request (forced HO request) to the macro cell 30A, the traffic information of the macro cell 30A is transmitted between the base stations. The set value of the threshold parameter (for example, A4offset to be compared with the received power [dBm] of the adjacent cell) for controlling the handover to the macro cell 30A, which is acquired by the interface, may be changed. For example, when the traffic of the macro cell 30A is large, the threshold parameter is changed to a high value, and when the traffic of the macro cell 30A is small, the threshold parameter is changed to a low value. Then, the large zone cell base station 10 compares the received power of the macro cell 30A with the set value of the threshold parameter (for example, A4offset), and when the received power of the macro cell 30A is larger than the threshold parameter, issues a forced HO command to the macro cell base. It may be transmitted to the station 30.

Further, in this example, in order to suppress the deterioration of the communication quality of the UE handed over to the macro cell 30A, the small cell base station 20 reports the physical cell identifier (PCI = 100) of the large zone cell 10A in the measurement report (MR) of the frequency A. ) Is included, the received power P1 from the large zone cell base station 10, the difference between the received power P1 from the large zone cell base station 10 and the received power P2s from the own station (P1-P2s), or the large zone cell base station 10 It is determined whether or not the ratio (P1 / P2s) of the received power P1 from the source to the received power P2s from the own station is equal to or higher than a preset predetermined threshold, and if the determination is affirmative, the large zone cell base A normal HO command may be sent to the station 10.

Further, in this example, the large zone cell base station 10 receives a measurement report (MR) of a frequency B having a different frequency from the UE 41 located in the large zone cell 10A prior to the handover from the large zone cell 10A to the macro cell 30A. When the received and the measurement report (MR) of the frequency B contains a plurality of physical cell identifiers (PCI) of the cell of the frequency B (for example, the macro cell 30A or another small cell), the cells of the plurality of frequencies B are included. The handover request may be transmitted to the cell of the frequency B having the highest received power. In this case, it is possible to suppress the deterioration of the communication quality of the UE after handing over to the cell of frequency B.

[Example 4 of inter-frequency handover]
FIG. 11 is an explanatory diagram showing another example of the inter-frequency handover in the overlay cell configuration of the communication system according to the present embodiment, and FIG. 12 is a sequence diagram showing an example of the inter-frequency handover of FIG. This example is an example in which the UE 43 before handover is in the macro cell 30A. In the illustrated example, the frequency A of the large zone cell 10A and the small cell 20A is the frequency of the 2 GHz frequency band (Band 1), and the frequency B of the macro cell 30A is the frequency of the platinum band 900 MGz frequency band (Band 8). is there.

In this example, the large zone cell 10A, the small cell 20A, and the macro cell 30A are assigned different physical cell identifiers (PCI) and set (S401 in FIG. 12). In the illustrated example, PCI = 100 is assigned to the large zone cell 10A, PCI = 101 is assigned to the small cell 20A, and PCI = 201 is assigned to the macro cell 30A.

When the UE 43 located in the macro cell 30A of the frequency band (Band 8) of 900 MGz, which is a platinum band, moves to the cell boundary area of the macro cell 30A, the UE 43 is strongly interfered with by the large zone cell 10A. Under this circumstance, the UE 43 transmits a measurement report (MR) including information on the physical cell identifier (PCI) of the adjacent cell measured at the frequency A and the frequency B and the received power [dBm] to the macrocell base station 30 (FIG. FIG. 12 S402). In the illustrated example, the measurement report (MR) including the information of the large zone cell 10A PCI = 100, −84 [dBm] and the information of the small cell 20A PCI = 101, −87 [dBm] as the information of the adjacent cell. ) Is transmitted from the UE 43 to the small cell base station 20.

Next, the macro cell base station 30 determines whether or not the measurement report (MR) of the frequency A received from the UE 43 includes the physical cell identifier (PCI = 100) of the large zone cell 10A. In the illustrated example, since the measurement report (MR) of frequency A includes the physical cell identifier (PCI = 100) of the large zone cell 10A, the macrocell base station 30 determines the handover of frequency A to the small cell 20A (FIG. FIG. 12 S403).

Next, the macro cell base station 30 forces the small cell base station 20 of the frequency A to perform a compulsory HO as a handover request for forcibly executing the handover of the UE 43 from the macro cell 30A of the frequency B to the small cell 20A of the frequency A. A command is sent (S404 in FIG. 12).

When the macro cell base station 30 receives an acknowledgment (ACK) as a response to the forced HO command (handover request response) (S405 in FIG. 12), the macro cell base station 30 performs "RRC CONNECTION RECONFIGURATION" for starting the handover process to the small cell 20A. It is transmitted to the UE 43 (S406 in FIG. 12). As a result, processing for subsequent handover is executed between the macro cell base station 30 and the UE 43.

In this example, when the measurement report (MR) of the frequency A does not include the physical cell identifier (PCI = 100) of the large zone cell 10A, the macro cell base station 30 does not perform the handover of the frequency A to the small cell 20A. , Do not send the above forced HO command.

As described above, according to this example, the small cell base station 20 is not provided with a time synchronization function for time synchronization with the large zone cell base station 10, and the frequency utilization efficiency of the frequency A is suppressed from being lowered. It is possible to avoid the concentration of communication traffic on the zone cell 10A.

In this example, in order to avoid the concentration of communication traffic in the macro cell 30A, the macro cell base station 30 acquires the traffic information of the adjacent small cell 20A through the inter-base station interface and hands over to the small cell 20A. The set value of the threshold parameter (for example, A4offset to be compared with the received power [dBm] of the adjacent cell) for controlling the above may be changed. For example, when the communication traffic of the small cell 20A is large, the threshold parameter is changed to a high value, and when the traffic of the small cell 20A is small, the threshold parameter is changed to a low value. Then, when the macro cell base station 30 includes the physical cell identifier (PCI = 100) of the large zone cell 10A in the measurement report (MR) of the frequency A, the received power of the small cell 20A and the threshold parameter (for example, A4offset) are further measured. When the received power of the small cell 20A is larger than the threshold parameter by comparing with the set value, the handover of the frequency A to the small cell 20A may be determined and the forced HO command may be transmitted to the small cell base station 20. ..

Further, in this example, in order to suppress the deterioration of the communication quality of the UE 43 handed over to the small cell 20A, the macro cell base station 30 reports the physical cell identifier (PCI = 100) of the large zone cell 10A in the measurement report (MR) of the frequency A. ) Is included, the received power P1 from the large zone cell base station 10, the difference between the received power P1 from the large zone cell base station 10 and the received power P2s from the own station (P1-P2s), or the large zone cell base station 10 It is determined whether or not the ratio (P1 / P2s) of the received power P1 from the source to the received power P2s from the own station is equal to or less than a predetermined threshold set in advance, and if the determination is affirmative, the small cell base is used. A forced HO command may be sent to station 20.

Further, in this example, the macro cell base station 30 receives a frequency A measurement report (MR) from the UE 43 located in the cell boundary area of the macro cell 30A prior to the handover from the macro cell 30A to the small cell 20A. If the measurement report (MR) of the frequency A contains a plurality of physical cell identifiers (PCI) of the cell of the frequency A (for example, the small cell 20A or another small cell), the cell of the plurality of frequencies A The handover request may be transmitted to the cell having the frequency A having the highest received power. In this case, the deterioration of the communication quality of the UE 43 after the handover to the cell of the frequency A can be suppressed.

[Example 5 of inter-frequency handover]
13 and 14 are sequence diagrams showing still another example of the inter-frequency handover process in the overlay cell configuration of the communication system according to the present embodiment, respectively. In these examples, the UE 43 before the handover is in the macro cell 30A, and the handover to the large zone cell 10A is attempted prior to the inter-frequency handover processing. Since the PCI allocation setting and MR reception (S501 and S502) in FIGS. 13 and 14 are common to the above-mentioned case of FIG. 12, their description will be omitted.

When the measurement report (MR) of the frequency A received from the UE 43 in the own cell 30A includes the physical cell identifier (PCI = 100) of the large zone cell 10A, the macrocell base station 30 first starts with the frequency from the own cell 30A. A HO command as a normal handover request for executing the handover of the UE 43 to the large zone cell 10A of A is transmitted to the large zone cell base station 10 (S503 in FIG. 13).

When the large zone cell base station 10 receives the HO command from the macro cell base station 30, the number of UEs connected to the own station 10 is, for example, equal to or greater than a preset threshold value based on the communication traffic status of the own cell 10A. When it is determined that the communication traffic of the own station 10 is large, a negative response (NACK) is returned to the macro cell base station 30 as a response to the HO command (handover request response) so as to reject the handover to the own cell 10A ( S504 in FIG. 13).

When the macro cell base station 30 receives a negative response (NACK) from the large zone cell base station 10, it serves as a handover request for forcibly executing the handover of the UE 43 from the macro cell 30A of the frequency B to the small cell 20A of the frequency A. A forced HO command is transmitted (S505 in FIG. 13).

When the macro cell base station 30 receives an acknowledgment (ACK) as a response to the forced HO command (handover request response) (S506 in FIG. 13), the macro cell base station 30 performs "RRC CONNECTION RECONFIGURATION" for starting the handover process to the small cell 20A. It is transmitted to the UE 43 (S507 in FIG. 13). As a result, processing for subsequent handover is executed between the macro cell base station 30 and the UE 43.

In this example, when the measurement report (MR) of the frequency A does not include the physical cell identifier (PCI = 100) of the large zone cell 10A, the macro cell base station 30 does not try to hand over to the large zone cell 10A. As a result, the above forced HO command is not transmitted.

When the large zone cell base station 10 receives the HO command from the macro cell base station 30, the number of UEs connected to the own station 10 is, for example, from a preset threshold value based on the communication traffic status of the own cell 10A. If it is determined that the communication traffic of the own station 10 is small and the communication traffic of the own station 10 is small, an acknowledgment (ACK) is returned to the macro cell base station 30 as a response to the HO command (handover request response) so as to allow the handover to the own cell 10A ( S508 in FIG. 14).

When the macro cell base station 30 receives an acknowledgment (ACK) from the large zone cell base station 10, the macro cell base station 30 sets the UE 43 with an “RRC CONNECTION RECONFIGURATION” for starting the handover process of the UE 43 from the own cell 30A to the large zone cell 10A having a frequency A. It is transmitted (S509 in FIG. 14). As a result, processing for subsequent handover is executed between the macro cell base station 30 and the UE 43.

As described above, according to this example, the macro cell base station 30 is not provided with the time synchronization function for time synchronization with the large zone cell base station 10, and the large zone cell is suppressed while suppressing the decrease in the frequency utilization efficiency of the frequency A. It is possible to avoid the concentration of communication traffic on the 10A.

In particular, according to this example, the frequency is determined when the number of UEs connected to the large zone cell 10A is small and the communication traffic is small by attempting the handover to the large zone cell 10A prior to the inter-frequency handover process from the macro cell 30A to the small cell 20A. Since the handover is performed to the large zone cell 10A of A, it is possible to suppress the decrease in the frequency utilization efficiency of the frequency A and avoid the concentration of communication traffic on the large zone cell 10A more accurately.

In this example, the large zone cell base station 10 selectively transmits the allow response (ACK) and the deny response (NACK) based on the number of UEs connected to the own cell 10A and in the service area. You may. For example, when the number of UEs connected to the own cell 10A is small and the communication traffic is small, the large zone cell base station 10 returns the authorization response (ACK) to the macro cell base station 30 and causes the large zone cell 10A to perform a handover. On the other hand, when the number of UEs connected to the own cell 10A is large and the communication traffic is large, the large zone cell base station 10 returns the rejection response (NACK) to the macro cell base station 30 and causes the macro cell 30A to hand over to the small cell 20A. .. Thereby, it is possible to suppress the decrease in the frequency utilization efficiency of the frequency A and avoid the concentration of the communication traffic on the large zone cell 10A more accurately.

Further, in this example, in order to avoid the concentration of communication traffic of the small cell 20A, when the macro cell base station 30 transmits a handover request (forced HO request) to the adjacent cell 20A, the small cell 20A The set value of the threshold parameter (for example, A4offset to be compared with the received power [dBm] of the adjacent cell) for controlling the handover to the small cell 20A by acquiring the traffic information by the inter-base station interface may be changed. For example, when the traffic of the small cell 20A is large, the threshold parameter is changed to a high value, and when the traffic of the small cell 20A is small, the threshold parameter is changed to a low value. Then, the macro cell base station 30 compares the received power of the small cell 20A with the set value of the threshold parameter (for example, A4offset), and when the received power of the small cell 20A is larger than the threshold parameter, the forced HO command is small. It may be transmitted to the cell base station 20.

Further, in this example, in order to suppress the deterioration of the communication quality of the UE handed over to the small cell 20A, the macro cell base station 30 reports the physical cell identifier (PCI = 100) of the large zone cell 10A in the measurement report (MR) of the frequency A. ) Is included, the received power P1 from the large zone cell base station 10, the difference between the received power P1 from the large zone cell base station 10 and the received power P2s from the own station (P1-P2s), or the large zone cell base station 10 It is determined whether or not the ratio (P1 / P2s) of the received power P1 from the source to the received power P2s from the own station is equal to or higher than a preset predetermined threshold, and if the determination is affirmative, the large zone cell base A normal HO command may be sent to the station 10.

Further, in this example, the macro cell base station 30 is located in the cell boundary area of the macro cell 30A after receiving the rejection response (NACK) from the large zone cell base station 10 and prior to the handover from the macro cell 30A to the small cell 20A. The measurement report (MR) of the frequency A is received from the UE 43, and the physical cell identifier (PCI) of the cell of the frequency A (for example, the small cell 20A or another small cell) is sent to the measurement report (MR) of the frequency A. ) Is included, the handover request may be transmitted to the cell of the frequency A having the highest received power among the cells of the plurality of frequencies A. In this case, it is possible to suppress the deterioration of the communication quality of the UE after handing over to the cell of frequency A.

Further, in the present embodiment, the case of the overlay configuration of the ground cell (small cell 20A, macro cell 30A) and the large zone cell 10A has been described, but the present invention is not limited to this configuration, and the present invention has a plurality of sizes different from each other. It can be applied to the overlay configuration of cells.

Further, in the present embodiment, the description has been made on the premise of application to LTE / LTE-Advanced, but downlink wireless communication, wireless communication frame, and OFDM of the OFDM (Orthogonal Frequency Division Multiplexing) method similar to LTE / LTE-Advanced. The concept of the present invention can be applied to any system as long as it is a system using symbols and the like, and is not limited to the transmitter and receiver configurations shown in the present embodiment.

In addition, the processing process described herein and the components of the mobile communication system, large zone cell base station, ground cell base station (small cell base station, macro cell base station), and user terminal device (mobile station) are various. It can be implemented by means. For example, these steps and components may be implemented in hardware, firmware, software, or a combination thereof.

Regarding hardware implementation, means such as a processing unit used to realize the above steps and components in an entity (for example, various wireless communication devices, Node Bs, terminals, hard disk drive devices, or optical disk drive devices) One or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processors (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors , Controllers, microprocessors, microprocessors, electronic devices, other electronic units designed to perform the functions described herein, computers, or combinations thereof.

For firmware and / or software implementation, means such as processing units used to implement the above components are programs (eg, procedures, functions, modules, instructions) that perform the functions described herein. , Etc.) may be implemented. Generally, any computer / processor readable medium that clearly embodies the firmware and / or software code is a means such as a processing unit used to implement the steps and components described herein. May be used to implement. For example, the firmware and / or software code may be stored in memory and executed by a computer or processor, for example, in a control device. The memory may be implemented inside the computer or processor, or may be implemented outside the processor. Further, the firmware and / or software code may be, for example, a random access memory (RAM), a read-only memory (ROM), a non-volatile random access memory (NVRAM), a programmable read-only memory (PROM), or an electrically erasable PROM (EEPROM). ), FLASH memory, floppy (registered trademark) discs, compact discs (CDs), digital versatile discs (DVDs), magnetic or optical data storage devices, etc. Good. The code may be executed by one or more computers or processors, or the computers or processors may be made to perform functional embodiments described herein.

Further, the medium may be a non-temporary recording medium. Further, the code of the program may be read and executed by a computer, a processor, or another device or device machine, and the format thereof is not limited to a specific format. For example, the code of the program may be any of source code, object code, and binary code, or may be a mixture of two or more of these codes.

Also, the description of the embodiments disclosed herein is provided to allow one of ordinary skill in the art to manufacture or use the disclosure. Various amendments to this disclosure will be readily apparent to those of skill in the art and the general principles defined herein are applicable to other variations without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not limited to the examples and designs described herein, but should be accepted in the broadest range consistent with the principles and novel features disclosed herein.

10 large zone cell base stations (1st base station, relay communication station)
10A large zone cell (1st cell)
15 Communication relay device 20A small cell (second cell of the same frequency)
30A macro cell (second cell with different frequency)
41 UE (mobile station) connected to a large zone cell
42 UE (mobile station) connected to the small cell
43 UE (mobile station) connected to the macro cell

Claims (25)

A plurality of first cell base stations forming a first cell and a plurality of second cell base stations forming a plurality of second cells having a cell size smaller than that of the first cell in the first cell are provided. The second cell uses the same frequency as the first cell because the second cell having a different frequency using a frequency different from that of the first cell and the second cell having a different frequency and a part of the area overlap with each other. A communication system that includes a second cell of the same frequency.
A means for determining whether or not a mobile station located in the second cell of the same frequency is being interfered with by the first cell, and
When the mobile station is interfered with by the first cell, the handover of the mobile station is controlled so that the mobile station is handed over from the second cell of the same frequency to the second cell of the different frequency. A communication system comprising means and means. In the communication system of claim 1,
The second cell base station of the same frequency
It is determined whether or not the measurement report of the same frequency received from the mobile station located in the second cell of the same frequency includes the cell identifier of the first cell.
When the measurement report of the same frequency includes the cell identifier of the first cell, the handover for forcibly executing the handover of the mobile station from the second cell of the same frequency to the second cell of the different frequency. A communication system comprising transmitting a request to a second cell base station having a different frequency and executing a handover process of the mobile station from a second cell having the same frequency to a second cell having a different frequency. In the communication system of claim 1,
The second cell base station of the same frequency
It is determined whether or not the measurement report of the same frequency received from the mobile station located in the second cell of the same frequency includes the cell identifier of the first cell.
When the cell identifier of the first cell is included in the measurement report of the same frequency, the received power P1 from the first cell base station, the received power P1 from the first cell, and the received power P2s from the own station It is determined whether or not the difference (P1-P2s) or the ratio (P1 / P2s) of the received power P1 from the first cell to the received power P2s from the own station is equal to or higher than a predetermined threshold, and the above-mentioned If the determination is affirmative, a handover request for forcibly executing the handover of the mobile station from the second cell of the same frequency to the second cell of the different frequency is made to the second cell base station of the different frequency. A communication system characterized by transmitting to a mobile station and executing a handover process of the mobile station from a second cell having the same frequency to a second cell having a different frequency. In the communication system of claim 1,
The second cell base station of the same frequency
It is determined whether or not the measurement report of the same frequency received from the mobile station located in the second cell of the same frequency includes the cell identifier of the first cell.
When the measurement report of the same frequency includes the cell identifier of the first cell, the first request for performing the handover of the mobile station from the second cell of the same frequency to the first cell is made. Send to cell base station,
When the permission response to the handover request is received from the first cell base station, the handover process of the mobile station from the second cell of the same frequency to the first cell is executed.
When a rejection response to the handover request is received from the first cell base station, the handover request for executing the handover of the mobile station from the second cell of the same frequency to the second cell of the different frequency is made. A communication system characterized in that it transmits to a second cell base station of a different frequency and performs a handover process of the mobile station from the second cell of the same frequency to the second cell of the different frequency. In the communication system of claim 4,
The first cell base station is a communication system characterized in that the permit response and the deny response are selectively transmitted based on the number of mobile stations in the first cell. In the communication system of claim 4,
The first cell base station determines whether or not the amount of communication traffic of the mobile station in the first cell is equal to or greater than a predetermined threshold value, and if the determination is affirmative, the permission response. And send
A communication system characterized in that if the determination is negative, the rejection response is transmitted. In the communication system according to any one of claims 2 to 6.
The second cell base station of the same frequency
Prior to the handover from the second cell of the same frequency to the second cell of the different frequency, the measurement report of the different frequency is received from the mobile station located in the second cell of the same frequency.
When the measurement report of the different frequency includes a plurality of cell identifiers of the second cell of the different frequency, the handover is performed in the second cell of the different frequency having the largest received power among the second cells of the plurality of different frequencies. A communication system characterized by transmitting a request. In the communication system according to any one of claims 2 to 6.
The second cell base station of the same frequency
Prior to the handover from the second cell of the same frequency to the second cell of the different frequency, the measurement report of the different frequency is received from the mobile station located in the second cell of the same frequency.
When the measurement report of the different frequency includes a plurality of cell identifiers of the second cell of the different frequency, the handover is performed in the second cell of the different frequency having the best reception quality among the second cells of the plurality of different frequencies. A communication system characterized by transmitting a request. In the communication system of claim 1,
The second cell base station of the same frequency
It is determined whether or not the measurement report of the same frequency received from the mobile station located in the second cell of the same frequency includes the cell identifier of the first cell.
When the measurement report of the same frequency includes the cell identifier of the first cell, the first request for performing the handover of the mobile station from the second cell of the same frequency to the first cell is made. It is transmitted to the cell base station, the handover process of the mobile station from the second cell of the same frequency to the first cell is executed, and the handover process is executed.
When the measurement report of the same frequency does not include the cell identifier of the first cell, the handover request to the first cell base station is not transmitted, and the handover request is not transmitted.
The first cell base station is the mobile station from the first cell to the second cell of a different frequency after the handover process of the mobile station from the second cell of the same frequency to the first cell is completed. A handover request for forcibly executing the handover of the above is transmitted to the second cell of the different frequency, and the handover process of the mobile station from the first cell to the second cell of the different frequency is executed. A communication system characterized by. In the communication system of claim 9,
The first cell base station selectively transmits the handover request to the second cell base station having a different frequency based on the number of mobile stations connected to the first cell and in the service area. A communication system characterized by. In the communication system of claim 9,
The first cell base station determines whether or not the amount of communication traffic of the mobile station in the first cell is equal to or greater than a predetermined threshold value, and if the determination is affirmative, issues an authorization response. Send and
A communication system characterized in that a rejection response is transmitted when the determination is negative. In the communication system of claim 9 or 10.
The second cell base station of the same frequency
Prior to the handover from the second cell of the same frequency to the second cell of the different frequency via the first cell, the measurement of the different frequency is performed from the mobile station located in the second cell of the same frequency. Receive the report,
When a plurality of cell identifiers of the second cell of the different frequency are included in the measurement report of the different frequency, the second cell of the different frequency having the largest received power among the second cells of the plurality of different frequencies is referred to. A communication system characterized in that a cell identification information of a second cell having a different frequency having the largest received power is added and a handover request is transmitted to the first cell base station so as to perform a handover from one cell. In the communication system of claim 9 or 10.
The second cell base station of the same frequency
Prior to the handover from the second cell of the same frequency to the second cell of the different frequency via the first cell, the measurement of the different frequency is performed from the mobile station located in the second cell of the same frequency. Receive the report,
When the measurement report of the different frequency includes a plurality of cell identifiers of the second cell of the different frequency, the second cell of the different frequency having the best reception quality among the second cells of the plurality of different frequencies is referred to. A communication system characterized in that the handover request is transmitted to the first cell base station by adding the cell identification information of the second cell of a different frequency having the best reception quality so that the handover is performed from one cell. A plurality of first cell base stations forming a first cell and a plurality of second cell base stations forming a plurality of second cells having a cell size smaller than that of the first cell in the first cell are provided. The second cell uses the same frequency as the first cell because the second cell having a different frequency using a frequency different from that of the first cell and the second cell having a different frequency and a part of the area overlap with each other. A communication system that includes a second cell of the same frequency.
A means for determining whether or not a mobile station located in the second cell having a different frequency is being interfered with by the first cell, and
When the mobile station is interfered with by the first cell, the handover of the mobile station is controlled so that the mobile station is handed over from the second cell of the different frequency to the second cell of the same frequency. A communication system comprising means and means. In the communication system of claim 14,
Different cell identifiers are set for the first cell and the second cell having the same frequency.
The second cell base station having a different frequency is
It is determined whether or not the measurement report of the same frequency received from the mobile station located in the second cell of the different frequency includes the cell identifier of the first cell.
When the cell identifier of the first cell is not included in the measurement report of the same frequency, the handover of the mobile station from the second cell of the different frequency to the second cell of the same frequency is forcibly executed. A communication system characterized in that a handover request is transmitted to the second cell base station of the same frequency, and the handover process of the mobile station from the second cell of the different frequency to the second cell of the same frequency is executed. .. In the communication system of claim 14,
Different cell identifiers are set for the first cell and the second cell having the same frequency, and the second cell base station having a different frequency has a different cell identifier.
It is determined whether or not the measurement report of the same frequency received from the mobile station located in the second cell of the different frequency includes the cell identifier of the first cell.
When the cell identifier of the first cell is included in the measurement report of the same frequency, the received power P1 from the first cell base station, the received power P1 from the first cell and the second cell of the same frequency The difference from the received power P2s (P1-P2s) or the ratio of the received power P1 from the first cell to the received power P2s from the second cell of the same frequency (P1 / P2s) is equal to or less than a predetermined threshold. If the determination is affirmative, a handover request for forcibly executing the handover of the mobile station from the second cell of the different frequency to the second cell of the same frequency is made. , A communication system characterized by transmitting to a second cell base station of the same frequency and executing a handover process of the mobile station from the second cell of the different frequency to the second cell of the same frequency. In the communication system of claim 14,
The second cell base station having a different frequency is
It is determined whether or not the measurement report of the same frequency received from the mobile station located in the second cell of the different frequency includes the cell identifier of the first cell.
When the measurement report of the same frequency does not include the cell identifier of the first cell, a handover request for executing the handover of the mobile station from the second cell of the different frequency to the second cell of the same frequency is requested. , Transmit to the second cell base station of the same frequency,
When a permission response to the handover request is received from the second cell base station of the same frequency, the handover process of the mobile station from the second cell of the different frequency to the second cell of the same frequency is executed. Communication system. In the communication system of claim 17,
The second cell base station having the same frequency selectively transmits the allow response and the deny response based on the number of mobile stations in the second cell of the same frequency. Communications system. In the communication system of claim 17,
The second cell base station having the same frequency determines whether or not the amount of communication traffic of the mobile station located in the second cell of the same frequency is equal to or greater than a predetermined threshold value, and the determination is affirmed. In the case of, send a rejection response and
A communication system characterized in that if the determination is negative, the permission response is transmitted. In the communication system according to any one of claims 14 to 18.
The second cell base station having a different frequency is
Prior to the handover from the second cell of the different frequency to the second cell of the same frequency, the measurement report of the same frequency is received from the mobile station located in the second cell of the different frequency.
When the measurement report of the same frequency includes a plurality of cell identifiers of the second cell of the same frequency, a handover request is made to the second cell of the same frequency having the largest received power among the plurality of second cells of the same frequency. A communication system characterized by transmitting. In the communication system according to any one of claims 14 to 19.
The second cell base station having a different frequency is
Prior to the handover from the second cell of the different frequency to the second cell of the same frequency, the measurement report of the same frequency is received from the mobile station located in the second cell of the different frequency.
When the measurement report of the same frequency includes a plurality of cell identifiers of the second cell of the same frequency, a handover request is made to the second cell of the same frequency having the best reception quality among the plurality of second cells of the same frequency. A communication system characterized by transmitting. In the communication system according to any one of claims 1 to 21
The second cell base station having the same frequency is a base station installed on the ground or water, or a base station installed on an air vehicle flying at an altitude lower than that of the first cell base station.
The second cell base station having a different frequency is a base station installed on the ground or water, or a base station installed on an air vehicle flying at an altitude lower than that of the first cell base station.
The first cell base station is a communication system characterized in that it is a base station arranged at the same position as or higher than the second cell base station. In the communication system according to any one of claims 1 to 21
A communication system characterized in that the first cell base station is a macro cell base station, and the second cell base station having the same frequency and the second cell base station having different frequencies are small cell base stations, respectively. A plurality of first cell base stations forming a first cell and a plurality of second cell base stations forming a plurality of second cells having a cell size smaller than that of the first cell in the first cell are provided. The second cell uses the same frequency as the first cell because the second cell having a different frequency using a frequency different from that of the first cell and the second cell having a different frequency and a part of the area overlap with each other. A handover control method in a communication system including a second cell having the same frequency.
To determine whether or not a mobile station located in the second cell of the same frequency is being interfered with by the first cell, and
When the mobile station is interfered with by the first cell, the handover of the mobile station is controlled so that the mobile station is handed over from the second cell of the same frequency to the second cell of the different frequency. A handover control method comprising the above. A plurality of first cell base stations forming a first cell and a plurality of second cell base stations forming a plurality of second cells having a cell size smaller than that of the first cell in the first cell are provided. The second cell uses the same frequency as the first cell because the second cell having a different frequency using a frequency different from that of the first cell and the second cell having a different frequency and a part of the area overlap with each other. A handover control method in a communication system including a second cell having the same frequency.
To determine whether or not the mobile station located in the second cell of the different frequency is being interfered with by the first cell, and
When the mobile station is interfered with by the first cell, the handover of the mobile station is controlled so that the mobile station is handed over from the second cell of the different frequency to the second cell of the same frequency. A handover control method comprising the above.

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