Method and appratus for avoiding inteference in terminal with plural heterogeneous communication modules in wireless communication system

A method for avoiding mutual interference when heterogeneous communication modules such as LTE, wireless LAN, Bluetooth, and GPS coexist in a terminal in a wireless communication system is provided. The terminal may reduce mutual interference when a plurality of communication modules simultaneously operate to efficiently communicate therewith.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system. More particularly, the present invention relates to a method for avoiding interference between a plurality of heterogeneous wireless communication modules when the heterogeneous wireless communication modules coexist in a terminal.

2. Description of the Related Art

In recent years, with rapid supply of smart phones, demand and use of wireless LAN, Bluetooth, and GPS have rapidly increased. Various communication technologies, such as conventional cellular network technology (LTE/UMTS), wireless LAN and Bluetooth, and GNSS/GPS, frequently coexist. When heterogeneous communication technologies are used simultaneously, a mutual interference problem arises. In-Device Coexistence (IDC) has been discussed in the 3rdGeneration Partnership Project (3GPP). A heterogeneous communication technology other than LTE refers to interfering Communication Technology (CT).

LTE/UMTS communication technology operates at various frequency bands, whereas a communication technology such as Bluetooth or wireless LAN operates at an Industrial, Scientific and Medical (ISM) band of 2400˜2483.5 MHz. In particular, among various bands using the LTE/UMTS communication technology, because Band 4 (2300-2400 MHz) and uplink band (2500-2570 MHz) of Band 7 are adjacent to an ISM band used by the Bluetooth and the wireless LAN, when they communicate simultaneously, a transmission signal in one communication technology is treated as a received signal in another communication technology, and may cause significant interference.

Accordingly, when a plurality of heterogeneous communication modules coexist in a terminal, there is a need for research into an approach capable of reducing interference between heterogeneous communication modules.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a method for avoiding interference between heterogeneous communication modules, such as Long Term Evolution (LTE) and Wi-Fi, LTE and Bluetooth, LTE and a Global Positioning System (GPS), and the like when the heterogeneous communication modules coexist in a terminal, and an apparatus thereof.

According to an aspect of the present invention, when heterogeneous communication modules (e.g., wireless LAN or Bluetooth) in a terminal operate, a terminal reports a list of preference or non-preference frequency bands to a network to introduce handover.

According to an aspect of the present invention, a terminal does not camp-on (wait for a base station signal in an idle state of the terminal) bands that may cause an interference problem because of communication modules (e.g., wireless LAN or Bluetooth) therein. The terminal voluntarily controls an access priority order of a base station. The terminal reports a list of preference or non-preference frequency bands in a network re-entering (e.g., Radio Resource Control (RRC) connection setup of LTE) procedure.

In accordance with an aspect of the present invention, a method for controlling interference in a terminal with a plurality of heterogeneous communication modules in a wireless communication system is provided. The method includes accessing a cellular network through a first communication module performing cellular communication, receiving a driving request for a second communication module, and controlling driving of the second communication module so as not to interfere with communication of the first communication module.

In accordance with another aspect of the present invention, a method for controlling interference in a terminal with a plurality of heterogeneous communication modules in a wireless communication system is provided. The method includes receiving a driving request for a second communication module, determining preference bands or non-preference bands based on operating frequency bands of a first communication module performing cellular communication and a second communication module, setting a priority order for accessing a base station according to the preference bands or the non-preference bands, and performing an access procedure of a base station according to the set priority order.

In accordance with another aspect of the present invention, an apparatus for controlling interference occurring between a first communication module performing cellular communication and a second communication module performing communication other than communication of the first communication module is provided. The first communication module includes a transceiver for exchanging signals with a base station, an interference communication detecting/determining unit for detecting a driving request of the second communication module and for determining whether driving of the second communication module interferes with communication of the first communication module, and a controller for controlling the driving of the second communication module so as not to interfere with the communication of the first communication module when a notification of interference is received from the interference communication detecting/determining unit in an access state of a cellular network.

In accordance with another aspect of the present invention, an apparatus for controlling interference occurring between a first communication module performing cellular communication and a second communication module performing communication other than communication of the first communication module is provided. The first communication module includes a transceiver for exchanging signals with a base station, an interference communication detecting/determining unit for detecting a driving request of the second communication module and for determining whether a driving of the second communication module interferes with communication of the first communication module, and a controller for determining preference bands or non-preference bands using operating frequency bands of the first communication module and the second communication module when interference notification is received from the interference communication detecting/determining unit in an idle state, for setting a priority order for accessing a base station according to the preference bands or the non-preference bands, and for controlling execution of an access procedure for the base station according to the set priority order.

In accordance with an aspect of the present invention, a terminal is provided. The terminal includes a first communication module for performing cellular communication, a second communication module for performing communication different from the cellular communication, an interference unit for detecting operation of the second communication module and for determining whether the communication of the second communication module interferes with the communication of the first communication module, and a controller for controlling the second module so as not to interfere with the first communication module when the interference unit determines that the communication of the second communication module interferes with the communication of the first communication module.

According to aspects of the present invention, a terminal having heterogeneous communication modules may reduce use of frequency bands having strong interference to easily perform communication.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

For convenience of description, a cellular communication (or mobile communication) technology of the present invention is explained based on a Long Term Evolution (LTE) system. Exemplary embodiments of the present invention are also applicable to other cellular communication technologies.

FIG. 1is a view illustrating a frequency band adjacent to an Industrial Scientific Medical Band (IMS) band among frequency bands used for mobile communication in a current 3rdGeneration Partnership Project (3GPP) according to an exemplary embodiment of the present invention.

Referring toFIG. 1, when a mobile communication cell uses Band 40 and a wireless LAN uses a channel number 1, interference is strong. Similarly, when the mobile communication cell uses Band 7 and a wireless LAN uses a channel number 13 or 14, interference is also strong.

Such an interference phenomenon may dynamically change according to locations and used frequencies of mobile communication base stations, a used channel, and a traffic pattern of a wireless LAN. Accordingly, there is a need for an interference avoiding technology suited to the situation.

A method is described below for reducing use of a frequency band having strong interference a terminal having heterogeneous communication modules to perform communication easily. The method may avoid interference in a terminal in an access state and avoid inference in a terminal in a non-access state in a cellular network.

A terminal according to an exemplary embodiment of the present invention may include heterogeneous communication modules, such as a first communication module performing wireless communication with a cellular network and a second communication module perform near or long distance wireless communication with a network other than the cellular network or an access point. The first communication module may be a cellular communication module using a mobile base station. The second communication module may include at least one of a wireless LAN (Wi-Fi module), a Bluetooth module, or a Global Positioning System (GPS) performing communication that may interfere with cellular communication (e.g., LTE communication) of a terminal.

FIG. 2is a diagram illustrating a method for avoiding interference in a terminal in an access state to a cellular network according to an exemplary embodiment of the present invention.FIG. 2illustrates operations of a terminal (UE)201and a base station (ENB)203.

The terminal201accesses the base station203(RRC connection setup) through a network access procedure in step205. The terminal201detects the driving of a second communication module or detects that driving of the second communication module is requested in step207. The terminal detects that potential interference communication technology (referred to as interfering communication technology (CT) hereinafter) for cellular communication (e.g., LTE communication technology) is to be started. The foregoing detecting method may use a method for enabling the terminal201to detect turning-on a start button (or power button) of a GPS device, a wireless LAN, or a Bluetooth by a user, or a method for measuring and detecting a received signal from a cellular base station.

After detection, the terminal201communicates with the base station203to exchange data therewith such that the terminal201does not operate at an LTE band to be expected interfering with interfering CT through steps209and211. For this operation, the terminal201may select preference bands having relatively weak interference with the interfering CT. The selection procedure is as follows.

1. The terminal201identifies an operation band of an interference CT which immediately starts or operates. This is denoted as a band A.

2. The terminal201identifies a band of a cellular system (e.g., LTE/UMTS/GSM system) which is now operating. This is denoted as a band B.

3. The terminal201sets bands where a band B is spaced apart from a band A by greater than a preset distance (e.g., x MHz) as preference bands. The terminal201sets bands where a band B is spaced apart from a band A by less than a preset distance (e.g., x MHz) as non-preference bands. The preset distance x may be a fixed value, be received from a base station, or be determined by signal filtering ability. The terminal201may create and store a preference band list or a non-preference band list through the foregoing procedure.

FIG. 2illustrates a procedure creating the preference band list or the non-preference band list after a terminal201receives an interference communication request. However, exemplary embodiments of the present invention are not limited to the foregoing order. For example, since a frequency band using interfering CT uses a fixed value, the terminal may include a preference band list or a non-preference band list a time taken out of the warehouse.

After creating the preference band list or the non-preference band list, the terminal201determines whether a current operating frequency of cellular communication is included in preference bands. If the current operating frequency of cellular communication is included in the preference bands, the terminal201starts an interfering CT at once in step215. If the terminal is performing the interfering CT, the terminal201continues performing the interfering CT.

When the current operating frequency of cellular communication is not included in preference bands but is included in non-preference bands, i.e., when the interfering CT interferes with cellular communication which is being performed by greater than a preset threshold, the terminal201may delay starting of the interfering CT before performing handover to one of preference bands.

The terminal201may generate and transmit an interference information report message to the base station in step209. In this case, the interference information report message may be a Radio Resource Control (RRC) (layer controlling layer 2 in LTE system) message containing a preference band list and/or a non-preference band list and/or an identification identifying a type of interference CT (e.g., which one of wireless LAN, GPS, or Bluetooth interferes with). The non-preference band denotes a band that may have interference from interfering CT upon performing cellular communication, and more particularly refer to a band spaced apart from a band used by the interfering band by less than x MHz, as discussed above.

When the base station receives the RRC message, the base station203determines whether a current operation band of the terminal201for cellular communication is included in preference bands.

If the terminal201operates at the preference band, the base station203may store the preference band of the terminal201, and then use the stored preference band to determine a target base station when handover of the terminal201is required.

If the terminal210does not operate at the preference band, the base station203determines whether the terminal201can perform handover to the preference band. If the terminal201can perform handover to the preference band, the base station203transmits an interference information report response message to the terminal201to instruct a handover procedure of the terminal201in step211. The interference information report response message may be an RRC message containing information presence of handover of the terminal201.

If the handover is performed, the terminal201may start interfering CT in step215. After performing the handover, the terminal201may simultaneously use heterogeneous communication technologies (e.g., LTE and interfering CT).

If the terminal201detects that the interfering CT operation has stopped in step217, the terminal201informs, in step219, the base station203using an RRC message that the preference bands or the non-preference bands are required no longer and/or the interfering CT operation stops. Upon receiving the RRC message, the base station203releases restrictions related to preference or non-preference bands applied to a corresponding terminal201.

If it is impossible to perform handover of the terminal201to a preference band (e.g., due to lack available resource of a base station operating at a preference band), the base station203informs the terminal201not to perform handover of the terminal201to the preference band through an RRC message in step213. When the terminal201receives the RRC message, the terminal201informs a user of the fact so that the user may determine whether to start the interfering CT.

The foregoing exemplary embodiment has illustrated a method for reducing interference of the interfering CT with a terminal accessing a cellular system (e.g., LTE/UMTS/GSM). The interfering CT may affect an idle terminal that is not currently accessing the cellular system. For example, the terminal might not be able to receive a signal that the terminal should receive from a base station of the cellular system due to an interference signal of the interfering CT.

An terminal in an idle state does not ‘camp-on’ (an idle state of a terminal in a base station to receive a phone or data) a base station operating at a cellular network band adjacent to an operating band of the interfering CT. This is achieved by controlling cell selection/reselection priority order or omitting a specific (interfering) frequency band at cell reselection time. When the terminal enters an access mode after terminating access to a network, the terminal may report preference or non-preference bands.

FIG. 3is a diagram illustrating a method for avoiding interference in a terminal in an idle state from a cellular network according to an exemplary embodiment of the present invention.FIG. 3illustrates operations of a terminal (UE)301and a base station ENB303.

Referring toFIG. 3, the terminal301in an idle state detects driving of a second communication module in step305. This denotes detecting that the terminal301in an idle state starts interfering CT. The foregoing detecting method may use a method for detecting turning-on a start button (or power button) of a GPS device, a wireless LAN, or a Bluetooth by the user, or a method for measuring and detecting a received signal from a cellular base station.

After the detection, the terminal301determines preference bands and non-preference bands in step307. A standard for distinguishing the preference bands from the non-preference bands is described above, and thus a detailed description thereof is omitted.

The terminal301sets a cell selection/reselection priority order of the smallest value for a non-reference band to minimize ‘camping-on a cell operating at a non-preference band in step309. The cell selection/reselection priority order is to control a degree of camping-on a specific frequency band or a specific cellular communication network by the terminal in an idle state. The base station303provides the cell selection/reselection priority order to the terminal301. The terminal301compares a priority order of a frequency band of a current camping on cell with that of another frequency band provided from a current zone.

If a channel situation of a frequency band having a high priority order is higher than a predetermined reference value, the frequency band having a high priority order is preferentially selected even though a channel situation of a frequency band having a low priority order is better.

According to an exemplary embodiment of the present invention, to set a priority order of a non-preference frequency band to the lowest value by the terminal301denotes that the terminal301does not camp on the non-reference frequency band if another frequency band providing channels higher than predetermined quality exist at a periphery. The terminal301disregards a cell selection/reselection priority order allotted for a frequency band corresponding to a non-preference frequency and sets the lowest cell selection/reselection priority order with reference to a frequency band of a current camping on cell and a peripheral frequency band provided from system information of the current camping on cell when there is a frequency band corresponding to a non-preference frequency band.

The terminal301continues an idle state and then changes to an access state. The terminal301transmits a RRC connection setup request to the base station303in step311. The base station303transmits an RRC connection setting message to the terminal301in step313. The terminal301transmits an RRC connection setup complete message to the base station303in response thereto in step315. The terminal301reports an RRC message containing preference bands and/or non-preference band and/or an identification of interfering CT to the base station301in step315. The reported information should be reported to the base station rapidly if possible to prevent unnecessary handover to the non-reference bands.

The message to be transmitted to an LTE cellular network when the terminal301accesses the base station may be an RRC connection setup report message transmitted at step311. Since the message is restricted in size, the message may not be suitable for the report information. A more suitable message including the report information is an RRC connection setup complete message transmitted at step315. According to an exemplary embodiment of the present invention, the terminal301adds the report information to the RRC connection setup complete message and transmits the addition result message.

The base station303may reject an RRC connection setup request of the terminal301. In this case, the base station303receives an RRC connection setup request message from the terminal and then transmits an RRC connection setup reject message. The message contains information regarding a frequency band for a next access attempt. This information is used for performing a next access attempt by the terminal301through a base station having a sufficient (busy less) wireless resource. However, an RRC connection setup reject message for redirection is transmitted before receiving an RRC connection setup complete message. The RRC connection setup reject message may be created to instruct the terminal to attempt a next access to a non-preference band of the terminal301. In this case, the terminal301disregards redirection information of an RRC connection setup reject message and selects an optional band from preference bands to attempt access.

FIG. 4Ais a flowchart illustrating a method for controlling interference in a terminal accessing a cellular network according to an exemplary embodiment of the present invention.

Referring toFIG. 4A, the terminal201accesses a cellular system in step401. In step403, it is determined whether interference occurs in the terminal201by measuring a received signal or receiving corresponding information from a heterogeneous network communication technology.

If interference is detected from a heterogeneous communication network or power of the heterogeneous communication network is turned-on through measurement of the received signal in step405, the terminal201transmits an interference information report message to report interference information (preference and/or non-preference bands, identification of interfering CT or measured received signal value) to the base station203in step407. For example, the information about the preference or non-preference bands may be an Absolute Radio Frequency Channel Number (ARFCN) associated with the preference or non-preference bands or a frequency band number (bandEUTRA defined in 36.331 in LTE) of the preference or non-preference bands.

The terminal201determines whether an interference information report response message is received within a limited time from the base station203in step409. When the interference information report response message is not received, the process returns to step403and repeats the foregoing procedures.

When the interference information report response message is received within a limited time from the base station203, the terminal201goes to step411. When the interference information report response message contains a handover command, the terminal201performs handover according to a command from the base station in step413.

If the interference information report response message does not contain the handover command, i.e., if a message capable of not performing handover is received, the process terminates the routine.

FIG. 4Bis a flowchart illustrating a method for controlling interference in a terminal201accessing a cellular network by a base station203according to an exemplary embodiment of the present invention.

Referring toFIG. 4B, the base station203enables an access attempt of a terminal201through an RRC connection procedure in step451. The base station203receives an interference information report message from the terminal201in step453. The interference information report message contains at least one of a preference band list and/or a non-preference band list, an identification of interfering CT, or a measured received signal value.

The base station203determines to perform handover of the terminal201using the interference information provided from the terminal201in step455. If the handover is performed, the base station203determines whether handover of the terminal201to a preference band is possible in step457. When the handover is possible, the base station203instructs the terminal201to perform the handover in step461. The base station203transmits an interference information report response message containing a handover command to the terminal201. When handover is impossible, the base station203transmits an interference information report response message containing information indicating that the handover is impossible to the terminal201in step459.

FIGS. 5A and 5Bare flowcharts illustrating a method for controlling interference in a terminal301in an idle state from a cellular system according to an exemplary embodiment of the present invention.

Referring toFIG. 5A, the terminal301is in an idle state in step501. The terminal301determines the presence of interference through measurement of a received signal in step503. The terminal301receives corresponding information from a heterogeneous communication module and selects preference and/or non-preference bands based on the received information in step505. The terminal301determines an access priority order of a base station303in step507, and selects the base station303according to the determined access priority order thereof in step509.

To perform an entering procedure to a network, the terminal301transmits an RRC connection setup request message in step511. After transmission of the RRC connection setup request message, when the terminal301does not receive an RRC connection setup message or an RRC connection reject message in step513, the terminal301returns to step511and retransmits an RRC connection set request message.

When the terminal301receives an RCC connection setup message in step515, the terminal301reports an RRC connection setup complete message including reference or non-reference bands and/or an identification of interfering CT and/or a measured received value to the base station303in step517, and terminates a corresponding procedure.

When receiving an RRC connection rejection message at step515, the terminal301determines whether the RRC connection rejection message includes redirect information with a command to another frequency band in step519. When the RRC connection rejection message includes redirect information with a command to another frequency band, the terminal301determines whether non-reference bands set thereby are identical with redirect information in step521. When the set non-reference bands differ from the redirect information, the terminal301stores the redirect information to use corresponding information upon entering a next network in step523.

When the set non-reference bands are identical with the redirect information at step521, the terminal301disregards redirect information received from the base station303and terminates a corresponding procedure in step525.

FIG. 5Bis a flowchart illustrating a method for controlling interference in a terminal301in an idle state by a base station303in a cellular system according to an exemplary embodiment of the present invention.

Referring toFIG. 5B, the base station303receives a network entering request from an optional terminal301in step551. The base station303determines whether a measured received signal value and/or preference and/or non-preference bands, and an identification of interfering CT is received (corresponding to step517by a terminal) in step553. When the measured received signal value and/or the preference and/or non-preference bands, and the identification of interfering CT are received, the base station303stores corresponding values in step555.

Subsequently, the terminal310finishes a network entering procedure, and continuously reports signal strength to the base station303for handover in step557. When it is determined that handover of a terminal301is required according to a signal strength provided from the terminal301at step559, the base station303determines whether interference information is received from the terminal301at a previous step553in step561. When interference information has been received from the terminal301, the base station303selects a target base station based on interference information stored at step555to instruct the terminal301to perform handover in step563.

FIG. 6is a block diagram illustrating a configuration of a terminal according to an exemplary embodiment of the present invention.

Referring toFIG. 6, a terminal201according to an exemplary embodiment of the present invention may include a first communication module and a second communication module. The first communication module is a module for performing cellular communication using a mobile base station. The second communication module may include at least one of a Wi-Fi module, a Bluetooth module, or a Global Positioning System (GPS) module that may interfere with cellular communication (e.g., LTE communication) of the terminal As shown inFIG. 6, the second communication module may denote an interfering CT device513.

The terminal201exchanges data with an upper layer605, and transmits and receive control messages through a control message processor607. Upon transmission, the terminal201multiplexes data by a multiplexer/demultiplexer603and transmits the multiplexed data through a transceiver601under the control of a controller609.

Upon reception, the terminal201receives a physical signal by the transceiver601under the control of the controller609, demultiplexes the received physical signal by the multiplexer/demultiplexer603, and transfers the demultiplexed signal to an upper layer device505or the control message processor607.

An interfering CT device613may inform an interfering CT sensing/determining unit611that power of a second communication module is turned-on or the second communication module is beginning to operate. A signal615transmitted from the interfering CT device613acts as a strong interference signal617to the transceiver601of the first communication module, and the controller607may sense the strong interference signal617to directly inform the interfering CT sensing/determining unit611of an interference situation.

If the interfering CT sensing/determining unit611senses interference with the second communication module, it determines whether it is necessary to avoid interfering CT. When it is necessary to avoid interfering CT, the interfering CT sensing/determining unit611informs the controller609of this fact. When an interference influence is greater than a preset threshold, the interfering CT sensing/determining unit611may determine that it is necessary to avoid interference. Accordingly, the controller609informs a control message processor607of interfering CT related information according to a state (access mode or idle mode) of the terminal, and transmits the corresponding information to allow the base station to recognize the information.

When the terminal is in an access mode, upon reception of a driving request for a second communication module, the controller609controls driving of the second communication module not to interfere with communication of the first communication module. The controller609selects preference bands or non-preference bands using operating frequency bands of the first communication module and the second communication module, and creates and transmits interference information with one of the preference bands or the non-preference bands to the base station. The controller609may determine a frequency band where an operating frequency band of the second communication module is spaced apart from an operating frequency band of the first communication module by greater than a preset distance as preference bands. The controller609may determine a frequency band where an operating frequency band of the second communication module is spaced apart from an operating frequency band of the first communication module by less than a preset distance as non-preference bands.

When an operating frequency band of the first communication module is a preference band, the controller609controls the second communication module to be driven. When an operating frequency band of the first communication module is a non-preference band, the controller609determines whether a handover command is received from the base station. When the handover command is received, the controller609controls to perform handover of the terminal to the preference band.

When the terminal is in an idle mode, the controller609sets a priority order for accessing a base station according to preference bands or non-preference bands. The controller609may set the non-preference bands as the lowest priority order for accessing a base station.

When the terminal attempts to access the base station, the controller609controls transmission of an RRC connect setup request message to the base station to change the terminal to an access state. When receiving the RRC connection setup message from the base station according to the transmission, the controller609may control transmission of an RRC connection setup complete message including at least one of the preference bands or the non-preference bands to the base station.

Upon reception of an RRC connection reject message from the base station according to transmission of the RRC connection setup request message, the controller609may analyze redirection information included in the RRC connection reject message. If the non-preference bands of the terminal differ from the redirect information, the controller609may control storage of the redirect information.

FIG. 7is a block diagram illustrating a configuration of a base station according to an exemplary embodiment of the present invention.

Referring toFIG. 7, the base station may include a transceiver710, a memory720, and a controller730.

The transceiver710performs transmission and reception of signals, data, and messages between a base station and a terminal or between the base station and a cellular network node. The transceiver710may include a wired or wireless interface.

The memory720may store programs necessary to operate the base station203according to an exemplary embodiment of the present invention. The memory720may store interference information provided from the terminal. The interference information may contain a preference band list, a non-preference band list, and/or interference communication identification.

The controller730controls overall operations of a base station. The controller730may include an interference controller731to control interference occurring in a terminal by the base station.

When the terminal is in an access state, the interference controller731senses reception of an interference information report message provided from the terminal. The interference controller731determines whether to perform handover of the terminal using the interference information provided from the terminal. For the terminal to perform handover, the interference controller731determines whether handover of the terminal to a preference band is possible. When the handover of the terminal to the preference band is possible, the interference controller731instructs the terminal to perform the handover. The interference controller731transmits an interference information report response message including a handover command to the terminal.

When the handover is impossible, the interference controller731transmits an interference information report response message including information indicating that the handover is impossible to the terminal.

The interference controller731may sense that the terminal receives a network entering request from an idle terminal in an idle state. Accordingly, the interference controller731determines whether a measured received signal value, preference bands, non-preference bands, and/or an identification of interfering CT are received. When the measured received signal value, the preference bands, the on-preference bands, and/or the identification of interfering CT are received, the interference controller731stores the corresponding values in the memory720.

The interference controller731receives signal strength from the terminal, and determines whether handover of the terminal is necessary. When the handover of the terminal is necessary, the interference controller731instructs handover of the terminal to a target base station using interference information received from the terminal. The foregoing approaches avoid interference from a current interference situation or potential interference factors to minimize interference, such that the terminal may communicate with a cellular network.