WIRELESS COMMUNICATIONS SYSTEM, TERMINAL, BASE STATION AND PROCESSING METHOD

A wireless communications system includes a first terminal configured to use a first detection signal of a first band and detect a second terminal capable of performing direct wireless communication with the first terminal in the first band, the first terminal determining whether the first terminal is able to perform direct wireless communication with the second terminal in a second band, by transmitting a second detection signal of the second band addressed to the detected second terminal, the first terminal performing direct wireless communication with the second terminal in at least one of the first band and the second band, based on a result of determination; and a base station to which the first terminal is connected, the base station controlling transmission of the first detection signal and the second detection signal.

FIELD

The embodiments discussed herein relate to a wireless communications system, a terminal, a base station, and a processing method.

BACKGROUND

According to a studied technique, in a cellular wireless communications system, in addition to a primary component carrier (PCC) that is a communication carrier operated in a band for which the communication common carrier of the cellular wireless communications system has a license (a licensed band), a band that is available without any license (an unlicensed band) and that is conventionally used in a wireless local area network (LAN) or the like is used as a secondary component carrier (SCC) bundled with the PCC.

Use of an unlicensed band not only for the communication between a base station and a terminal but also for device-to-device (D2D) communication among terminals to directly communicate with each other without use of a base station therebetween is under investigation.

For example, according to a known technique, a base station makes a reservation for necessary resources in an unlicensed band in response to a request for the D2D communication from a mobile station, and notifies the mobile station of information concerning the reservation (see, for example, US Patent Application Publication No. 2012/0077510).

SUMMARY

According to an aspect of an embodiment, a wireless communications system includes a first terminal configured to use a first detection signal of a first band and detect a second terminal capable of performing direct wireless communication with the first terminal in the first band, the first terminal determining whether the first terminal is able to perform direct wireless communication with the second terminal in a second band, by transmitting a second detection signal of the second band addressed to the detected second terminal, the first terminal performing direct wireless communication with the second terminal in at least one of the first band and the second band, based on a result of determination; and a base station to which the first terminal is connected, the base station controlling transmission of the first detection signal and the second detection signal.

DESCRIPTION OF THE INVENTION

Embodiments of a wireless communications system, a terminal, a base station, and a processing method according the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1Ais a diagram of an example of the wireless communications system according to a first embodiment.FIG. 1Bis a diagram of an example of signal flow in the wireless communications system depicted inFIG. 1A. As depicted inFIG. 1AandFIG. 1B, the wireless communications system100according to the first embodiment includes terminals110and120, and a base station130. The base station130is the base station to which at least the terminal110of the terminals110and120is connected wirelessly.

The terminals110and120are devices capable of mutually performing direct wireless communication using at least a first band or a second band when the terminals110and120are close to each other. The second band is a frequency band different from the first band.

The terminal110includes a detecting unit111and a communicating unit112. The detecting unit111detects another terminal capable of performing direct wireless communication with the terminal110in the first band using a first detection signal of the first band. For example, the terminal110may detect among terminals present around the terminal110, another terminal capable of performing direct wireless communication with the terminal110, by receiving the first detection signal of the first band transmitted from each of the terminals present around the terminal110. This detection is, for example, passive scanning. It is assumed in the example depicted inFIG. 1Athat the detecting unit111detects the terminal120as another terminal capable of performing direct wireless communication with the terminal110.

The detecting unit111determines whether the terminal110can perform direct wireless communication with the terminal120in the second band, by transmitting a second detection signal of the second band, addressed to the detected terminal120. For example, the detecting unit111transmits the second detection signal of the second band addressed to the detected terminal120. The detecting unit111receives a response signal from the terminal120in response to the transmitted second detection signal and may thereby determine whether the terminal110can perform direct wireless communication with the terminal120in the second band. This process is, for example, active scanning. The detecting unit111outputs the result of the determination to the communicating unit112.

The communicating unit112performs direct wireless communication with the terminal120in at least either the first band or the second band based on the result of the determination output from the detecting unit111. For example, when the detecting unit111determines that the terminal110can perform direct wireless communication with the terminal120in the second band, the communicating unit112performs the direct wireless communication with the terminal120in the second band.

When the detecting unit111determines that the terminal110cannot perform direct wireless communication with the terminal120in the second band, the communicating unit112performs the direct wireless communication with the terminal120in the first band. When the detecting unit111determines that the terminal110can perform direct wireless communication with the terminal120in the second band, the communicating unit112may perform the direct wireless communication with the terminal120in both of the first band and the second band.

As described, according to the first embodiment, after the detection in the first band, a terminal transmits the second detection signal addressed to the detected other terminal and can thereby execute the detection in the second band. The direct wireless communication in the second band is thereby enabled even when the frequencies of the first band and the second band differ from each other. The other terminal with which the direct wireless communication can be performed can be detected efficiently even when the frequencies of the first band and the second band differ from each other.

The transmission of each of the first detection signal and the second detection signal is controlled by, for example, a control unit131included in the base station130. For example, the control unit131controls the terminal120such that the terminal120transmits the first detection signal of the first band. The control unit131controls the terminal110such that the detecting unit111of the terminal110transmits the second detection signal of the second band. For example, the control unit131controls the terminals110and120by wirelessly transmitting control signals between the terminals110and120.

For example, the base station130transmits a signal that instructs transmission of the first detection signal, to a terminal connected to the base station (for example, the terminal120). The base station130receives from the terminal110, the result of the detection of the terminal120using the first detection signal and transmits based on the received result, a signal that instructs transmission of the second detection signal to the terminal110. The base station130may thereby control the transmission of each of the first detection signal and the second detection signal.

For example, the base station130assigns to the terminal110, radio resources of the second band for the terminal110to transmit the second detection signal. In response to this, the terminal110transmits the second detection signal using the radio resources assigned thereto by the base station130. Thus, collision may be suppressed between the second detection signal and transmission by other terminals connected to the base station130.

The first band may be set to be a band dedicated to the wireless communications system100(the wireless communications system100). The second band may be set to be a band shared between the wireless communications system100and another wireless communications system. The other wireless communications system is, for example, a wireless communications system whose communication scheme is different from that of the wireless communications system100.

When plural terminals including the terminals110and120execute the detection in the first band, each of the detected terminals may determine whether the terminal can perform direct wireless communication with the other terminals in the second band, by mutually transmitting the second detection signal of the second band.

For example, it is assumed that at least both of the terminals110and120detect each other by transmitting and receiving the first detection signal of the first band. In this case, each of the detected terminals110determines whether direct wireless communication can be performed mutually in the second band, by mutually transmitting the second detection signal of the second band. This process is, for example, passive scanning.

When terminals are present that detect each other in addition to the terminals110and120, the terminals each also determine whether direct wireless communication can be performed mutually in the second band, by mutually transmitting the second detection signal of the second band (passive scanning).

In this manner, in the first embodiment, after the detection in the first band, limited to the detected terminals, the detected terminals may execute the detection in the second band by mutually transmitting the second detection signal of the second band. In this case, the direct wireless communication in the second band may also be performed even when the frequencies of the first band and the second band differ from each other. Other terminals with which the direct wireless communication may be performed, may be efficiently be detected even when the frequencies of the first band and the second band differ from each other.

For example, the base station130transmits a signal that instructs transmission of the first detection signal to the terminal connecting to the base station130(for example, the terminal120). The base station130receives from the terminal110, the result of the detection of the terminal120using the first detection signal and transmits to each of the terminals110and120based on the received result, a signal that instructs transmission of the second detection signal. The base station130may thereby control the transmission of the first detection signal and the second detection signal.

For example, the base station130assigns to the terminal110, radio resources of the second band for the terminal110to transmit the second detection signal. In response to this, the terminal110transmits the second detection signal using the radio resources assigned thereto by the base station130. Thus, collision may be suppressed between the second detection signal and transmission by the other terminal connected to the base station130.

The base station130transmits using the second band, a reservation signal that reserves the radio resources of the second band to transmit the second detection signal. In this case, each of the terminals110and120mutually transmits the second detection signal using the radio resources reserved by the reservation signal. Thus, collision may be suppressed between the second detection signal and other signals in the second band.

The base station130may transmit in the first band, the reservation signal that reserves the radio resources of the second band to transmit the second detection signal. Thus, collision may be suppressed between the second detection signal and other signals in the first band and the second band.

The first band may be set to be, for example, a band dedicated to the wireless communications system100(the wireless communications system100). The second band may be set to be a band shared between the wireless communications system100and another wireless communications system. The other wireless communications system is, for example, a wireless communications system whose communication scheme is different from that of the wireless communications system100.

FIG. 2is a diagram of an example of a wireless communications system according to a second embodiment. As depicted inFIG. 2, the wireless communications system200according to the second embodiment includes eNBs211to213and UEs231to239.

The eNBs211to213(evolved Node Bs) are macro base stations that respectively form macro cells221to223. The UEs231to233(User Equipment: user terminals) are present in the macro cell221and may perform wireless communication with the eNB211. The UEs234to236are present in the macro cell222and may perform wireless communication with the eNB212. The UEs237to239are present in the macro cell223and may perform wireless communication with the eNB213.

In the example depicted inFIG. 2, in the macro cell221, the UE231performs wireless communication with the eNB211. In the macro cell221, the UEs232and233execute, for example, D2D communication with each other under the control of the eNB211.

The wireless communications system100depicted inFIG. 1AandFIG. 1Bmay be realized by, for example, the eNB211and the UEs231to233. In this case, for example, the terminals110and120depicted inFIG. 1AandFIG. 1Bmay be applied to the UEs231to239. The base station130depicted inFIGS. 1A and 1Bmay be applied to the eNBs211to213.

A case will be described where the wireless communications system100is applied to the eNB211and the UEs in the macro cell221(for example, the UEs232and233).

FIG. 3Ais a diagram of an example of the eNB according to the second embodiment.FIG. 3Bis a diagram of an example of signal flow in the eNB depicted inFIG. 3A. The eNB211depicted inFIG. 2may be realized by, for example, an eNB300depicted inFIG. 3AandFIG. 3B. The eNB300includes an antenna301, a radio processing unit302, an FFT processing unit303, a demodulating unit304, a decoding unit305, an MAC•RLC processing unit306, a radio resource control unit307, an MAC control unit308, and a packet generating unit309. The eNB300also includes an MAC scheduling unit310, an encoding unit311, a modulating unit312, a multiplexing unit313, an IFFT processing unit314, a radio processing unit315, and an antenna316.

The antenna301receives a signal transmitted wirelessly from another wireless communications apparatus. The antenna301outputs the received signal to the radio processing unit302. The radio processing unit302executes radio processing of the signal output from the antenna301. The radio processing by the radio processing unit302includes, for example, frequency conversion from a high frequency band to a baseband. The radio processing unit302outputs the signal on which the radio processing is executed, to the FFT processing unit303.

The FFT processing unit303executes an FFT (Fast Fourier Transform) process for the signal output from the radio processing unit302. The signal is thereby converted from the signal in the time domain to a signal in the frequency domain. The FFT processing unit303outputs the signal on which the FFT process is executed, to the demodulating unit304.

The demodulating unit304demodulates the signal output from the FFT processing unit303. The demodulating unit304outputs the signal obtained by the demodulation, to the decoding unit305. The decoding unit305decodes the signal output from the demodulating unit304. The decoding unit305outputs the data obtained by the decoding, to the MAC•RLC processing unit306.

The MAC•RLC processing unit306executes processing for each of an MAC (Media Access Control) layer and an RLC (Radio Link Control) layer based on the data output from the decoding unit305. The MAC•RLC processing unit306outputs data obtained by the processing executed for the layers. The signal output from the MAC•RLC processing unit306is input into, for example, a processing unit in a higher-order layer of the eNB300. The MAC•RLC processing unit306outputs control information such as feedback information included in the data obtained by the processing executed for the layers, to the radio resource control unit307.

The radio resource control unit307executes radio resource control based on the control information output from the MAC•RLC processing unit306. This radio resource control is a processing for an RRC layer. The radio resource control unit307outputs the control information based on the radio source control to the MAC control unit308. The radio resource control unit307outputs resource information for D2D based on the radio resources control, to the packet generating unit309.

The MAC control unit308executes control of the MAC layer based on the control information output from the radio resource control unit307. The MAC control unit308outputs individual control information for the UE based on the control of the MAC layer, to the multiplexing unit313. The individual control information is, for example, a PDCCH (Physical Downlink Control Channel). The MAC control unit308outputs control information based on the control of the MAC layer, to the MAC scheduling unit310.

The packet generating unit309generates packets including user data output from a higher-order layer of the eNB300and the resource information for D2D output from the MAC control unit308. The packet generating unit309outputs the generated packets to the MAC scheduling unit310.

The MAC scheduling unit310executes scheduling for the MAC layer of the packets output from the packet generating unit309, based on the control information output from the MAC control unit308. The MAC scheduling unit310outputs the packets to the encoding unit311based on the result of the scheduling.

The encoding unit311encodes the packets output from the MAC scheduling unit310. The encoding unit311outputs the encoded packets to the modulating unit312. The modulating unit312executes modulation based on the packets output from the encoding unit311. The modulating unit312outputs the signal obtained by the modulation to the multiplexing unit313.

The multiplexing unit313multiplexes the individual control information output from the MAC control unit308and the signal output from the modulating unit312with each other. The multiplexing unit313outputs the signal obtained by the multiplexing to the IFFT processing unit314.

The IFFT processing unit314executes an IFFT (Inverse Fast Fourier Transform) process on the signal output from the multiplexing unit313. The signal is thereby converted from the signal in the frequency domain into a signal in the time domain. The IFFT processing unit314outputs the signal on which the IFFT process is executed, to the radio processing unit315.

The radio processing unit315executes radio processing on the signal output from the IFFT processing unit314. The radio processing by the radio processing unit315includes frequency conversion, for example, from the baseband to the high frequency band. The radio processing unit315outputs to the antenna316, the signal on which the radio processing is executed. The antenna316wirelessly transmits the signal output from the radio processing unit315to another wireless communications apparatus.

The control unit131depicted inFIG. 1AandFIG. 1Bmay be realized by, for example, the configurations except the MAC control unit308of the configurations depicted inFIG. 3AandFIG. 3B. Alternatively, the control unit131depicted inFIG. 1AandFIG. 1Bmay be realized by, for example, the configurations (including the MAC control unit308) depicted inFIG. 3AandFIG. 3B.

FIG. 3Cis a diagram of an example of hardware configuration of an eNB.FIG. 3Dis a diagram of an example of signal flow in the hardware configuration depicted inFIG. 3C. The eNB300may be realized by, for example, a wireless communications apparatus350depicted inFIG. 3CandFIG. 3D.

The wireless communications apparatus350includes, for example, a transmitting and receiving antenna351, an amplifier352, a multiplying unit353, an analog-digital converter354, a processor355, and a memory356. The wireless communications apparatus350also includes a digital-analog converter357, a multiplying unit358, an amplifier359, and an oscillator360. The wireless communications apparatus350may include an interface that executes wired communication with an external communications apparatus.

The transmitting and receiving antenna351receives signals wirelessly transmitted from the vicinity of the wireless communications apparatus350, and outputs the received signals to the amplifier352. The transmitting and receiving antenna351wirelessly transmits the signal output from the amplifier359to the vicinity of the wireless communications apparatus350.

The amplifier352amplifies the signal output from the transmitting and receiving antenna351. The amplifier352outputs the amplified signal to the multiplying unit353. The multiplying unit353multiplies the signal output from the amplifier352by a clock signal output from the oscillator360to thereby execute frequency conversion from the high frequency band to the baseband. The multiplying unit353outputs the frequency-converted signal to the analog-digital converter354.

The analog-digital converter354(A/D) is an ADC (Analog/Digital Converter) that converts the signal output from the multiplying unit353from an analog signal to a digital signal. The analog-digital converter354outputs the signal converted into the digital signal to the processor355.

The processor355supervises overall control of the wireless communications apparatus350. The processor355may be realized by, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). The processor355executes a reception process for the signal output from the analog digital converter354. The processor355generates a signal to be transmitted by the wireless communications apparatus350, and executes a transmission process to output the generated signal to the digital-analog converter357.

The memory356includes, for example, a main memory and an auxiliary memory. The main memory is, for example, a RAM (Random Access Memory). The main memory is used as a working area of the processor355. The auxiliary memory is a non-volatile memory such as, for example, a magnetic disk or a flash memory. The auxiliary memory stores therein various types of programs that operate the processor355. The programs stored in the auxiliary memory are loaded onto the main memory to be executed by the processor355. The auxiliary memory stores therein, for example, various types of threshold values determined in advance.

The digital-analog converter357is a DAC (Digital/Analog Converter) that converts the signal output from the processor355from a digital signal to an analog signal. The digital-analog converter357outputs the signal converted into the analog signal, to the multiplying unit358.

The multiplying unit358multiplies the signal output from the digital-analog converter357by the clock signal output from the oscillator360to thereby execute frequency conversion from the baseband to the high frequency band. The multiplying unit358outputs the frequency-converted signal to the amplifier359. The amplifier359amplifies the signal output from the digital-analog converter357. The amplifier359outputs the amplified signal to the transmitting and receiving antenna351.

The oscillator360oscillates the clock signal (an AC signal of a continuous wave) at a predetermined frequency. The oscillator360outputs the oscillated clock signal to the multiplying units353and358.

The antennas301and316depicted inFIG. 3AandFIG. 3Bmay be realized by, for example, the transmitting and receiving antenna351. The radio processing unit302and the radio processing unit315depicted inFIG. 3AandFIG. 3Bmay be realized by, for example, the amplifier352, the multiplying unit353, an analog-digital converter354, the digital-analog converter357, the multiplying unit358, the amplifier359, and the oscillator360. The other configurations depicted inFIG. 3AandFIG. 3Bmay be realized by, for example, the processor355and the memory356.

FIG. 4Ais a diagram of an example of a UE according to the second embodiment.FIG. 4Bis a diagram of an example of signal flow in the UE depicted inFIG. 4A. Each of the UEs231to233depicted inFIG. 2may be realized by, for example, a UE400depicted inFIG. 4AandFIG. 4B.

The UE400includes an antenna401, a radio processing unit402, an FFT processing unit403, an equalization processing unit404, an IFFT processing unit405, a demodulating unit406, a decoding unit407, and a response signal detecting unit408. The UE400also includes a discovery signal detecting unit409, a carrier sensing unit410, a control information processing unit411, and a discovery signal generating unit412. The UE400further includes a data processing unit413, a multiplexing unit414, a symbol mapping unit415, a multiplexing unit416, an FFT processing unit417, a frequency mapping unit418, an IFFT processing unit419, and a radio processing unit420.

The antenna401receives a signal wirelessly transmitted from another wireless communications apparatus. The antenna401outputs the received signal to the radio processing unit402. The antenna401wirelessly transmits to another wireless communications apparatus, a signal output from the radio processing unit420.

The radio processing unit402executes radio processing of the signal output from the antenna401. The radio processing by the radio processing unit402includes, for example, frequency conversion from a high frequency band to a baseband. The radio processing unit402outputs the signal on which the radio processing is executed, to the FFT processing unit403, the discovery signal detecting unit409, and the carrier sensing unit410.

The FFT processing unit403executes an FFT process on the signal output from the radio processing unit402. The signal is thereby converted from the signal in the time domain to a signal in the frequency domain. The FFT processing unit403outputs the signal on which the FFT process is executed, to the equalization processing unit404.

The equalization processing unit404executes an equalization process om the signal output from the FFT processing unit403. The equalization processing unit404outputs the signal on which the equalization process is executed to the IFFT processing unit405. The IFFT processing unit405executes an IFFT process on the signal output from the equalization processing unit404. The signal is thereby converted from the signal in the frequency domain into a signal in the time domain. The IFFT processing unit405outputs to the demodulating unit406, the signal on which the IFFT process is executed.

The demodulating unit406demodulates the signal output from the IFFT processing unit405. The demodulating unit406outputs to the decoding unit407, the signal obtained by the demodulation. The decoding unit407decodes the signal output from the demodulating unit406. The decoding unit407outputs data obtained by the decoding. The data output from the decoding unit407is input into, for example, a processing unit in a higher-order layer of the UE400and the response signal detecting unit408. The data output from the decoding unit407includes, for example, user data.

The response signal detecting unit408detects a response signal transmitted from the other wireless communications apparatus and included in the data output from the decoding unit407. The response signal detecting unit408outputs to the control information processing unit411, detection information indicating the result of the detection of the response signal.

The discovery signal detecting unit409detects a discovery signal transmitted from another wireless communications apparatus and included in the signal output from the radio processing unit402. The discovery signal includes, for example, an active scan signal and a passive scan signal. The discovery signal detecting unit409outputs detection information indicating the result of the detection of the discovery signal to the control information processing unit411.

The carrier sensing unit410executes carrier sensing based on the signal output from the radio communicating unit402. The carrier sensing unit410outputs carrier sensing result information indicating the result of the carrier sensing to the control information processing unit411.

The control information processing unit411executes processing for, for example, the pieces of control information for the MAC layer and an RRC (Radio Resources Control) layer. For example, the control information processing unit411determines whether a response is present for the active scan signal transmitted from the UE400, based on the detection information output from the response signal detecting unit408.

The control information processing unit411executes control of transmission of a response signal in response to the active scan signal transmitted from the other UE, reception of the passive scan signal transmitted from the other UE, and the like, based on the detection information output from the discovery signal detecting unit409. The control information processing unit411checks availability of the radio resources for the UE400to execute the communication, based on the carrier sensing result information output from the carrier sensing unit410.

The control information processing unit411outputs a discovery signal transmission instruction that instructs the transmission of the discovery signal, to the discovery signal generating unit412, based on the control signals received from the base station. The control information processing unit411outputs the response signal and pieces of control information such as the radio resource assignment information to the multiplexing unit414, based on the processing results.

The discovery signal generating unit412generates a discovery signal, based on the discovery signal transmission instruction output from the control information processing unit411. The discovery signal generating unit412outputs the generated discovery signal to the multiplexing unit416.

The data processing unit413executes various types of data processing and outputs to the multiplexing unit414, data to be transmitted based on the result of the data processing. The multiplexing unit414multiplexes the control information output from the control information processing unit411and the data to be transmitted output from the data processing unit413with each other, and outputs to the symbol mapping unit415, a signal to be transmitted that is obtained by the multiplexing.

The symbol mapping unit415executes symbol mapping for the signal to be transmitted output from the multiplexing unit414. The symbol mapping unit415outputs to the multiplexing unit416, the signal to be transmitted and for which the symbol mapping is executed.

The multiplexing unit416multiplexes the discovery signal output from the discovery signal generating unit412, the signal to be transmitted output from the symbol mapping unit415, and a pilot signal and a synchronization signal from the UE400, with each other. The multiplexing unit416outputs the signal acquired by the multiplexing to the FFT processing unit417.

The FFT processing unit417executes an FFT process for the signal output from the multiplexing unit416. The signal is thereby converted from the signal in the time domain into a signal in the frequency domain. The FFT processing unit417outputs to the frequency mapping unit418, the signal for which the FFT process is executed. The frequency mapping unit418executes frequency mapping for the signal output from the FFT processing unit417. The frequency mapping unit418outputs the signal for which the frequency mapping is executed to the IFFT processing unit419.

The IFFT processing unit419executes an IFFT process on the signal output from the frequency mapping unit418. The signal is thereby converted from the signal in the frequency domain into a signal in the time domain. The IFFT processing unit419outputs the signal on which the IFFT process is executed to the radio processing unit420.

The radio processing unit420executes radio processing on the signal output from the IFFT processing unit419. The radio processing by the radio processing unit420includes, for example, the frequency conversion from the baseband to the high frequency band. The radio processing unit420outputs the signal on which the radio processing is executed to the antenna401.

A case has been described where the same antenna401is used for the wireless transmission and the wireless reception in the example depicted inFIG. 4AandFIG. 4Bwhile an antenna for the wireless transmission and another antenna for the wireless reception may be disposed in the UE400. The detecting unit111depicted inFIG. 1AandFIG. 1Bmay be realized by, for example, the antenna401, the radio processing unit402, the FFT processing unit403, the equalization processing unit404, the IFFT processing unit405, the demodulating unit406, the decoding unit407, the response signal detecting unit408, the discovery signal detecting unit409, the carrier sensing unit410, the control information processing unit411, the discovery signal generating unit412, the multiplexing unit416, the FFT processing unit417, the frequency mapping unit418, the IFFT processing unit419, and the radio processing unit420.

The communicating unit112depicted inFIG. 1AandFIG. 1Bmay be realized by, for example, the antenna401, the radio processing unit402, the FFT processing unit403, the equalization processing unit404, the IFFT processing unit405, the demodulating unit406, the decoding unit407, the response signal detecting unit408, the control information processing unit411, the discovery signal generating unit412, the data processing unit413, the multiplexing unit414, the symbol mapping unit415, the multiplexing unit416, the FFT processing unit417, the frequency mapping unit418, the IFFT processing unit419, and the radio processing unit420.

The UE400may be realized by, for example, the wireless communications apparatus350depicted inFIG. 3CandFIG. 3D. In this case, the wireless communications apparatus350may omit an interface that executes wired communication with an external communications apparatus.

The antenna401depicted inFIG. 4AandFIG. 4Bmay be realized by, for example, the transmitting and receiving antenna351. The radio processing unit402and the radio processing unit420depicted inFIG. 4AandFIG. 4Bmay each be realized by, for example, the amplifier352, the multiplying unit353, the analog-digital converter354, the digital-analog converter357, the multiplying unit358, the amplifier359, and the oscillator360. The other configurations depicted inFIG. 4AandFIG. 4Bmay be realized by, for example, the processor355and the memory356.

FIG. 5is a flowchart of an example of a start control process for the D2D communication by the eNB according to the second embodiment. The eNB300according to the second embodiment executes, for example, process steps depicted inFIG. 5as the start control process for the D2D communication.

The eNB300transmits a PCC discovery start instruction to each of the UEs (step S501). The PCC discovery start instruction is a signal that instructs the start of discovery on the PCC. The transmission at step S501may be executed at various timings such as, for example, at that of the request from the UE connected to the eNB300.

The eNB300determines whether the eNB300receives from each of the UEs, a report of the discovery result in response to the PCC discovery start instruction transmitted at step S501(step S502) and waits until the eNB300receives the report (step S502: NO). The report of the discovery result includes, for example, information indicating the D2D communication counterpart determined by each of the UEs.

When the eNB300determines at step S502that the eNB300has received the report (step S502: YES), the eNB300advances to the operation at step S503. The eNB300individually transmits an active scan instruction to each of the UEs to execute the D2D communication, based on the D2D communication counterpart indicated by the report received at step S502(step S503). The active scan instruction is a signal that instructs active scanning in the SCC.

The eNB300determines whether the eNB300receives a report of the result of the active scanning in response to the active scan instruction transmitted at step S503(step S504) and waits until the eNB300receives the report (step S504: NO). The report of the result of the active scanning includes, for example, information indicating whether each of the UEs to execute the D2D communication can execute the D2D communication in the SCC.

When the eNB300determines at step S504that the eNB300has received the report (step S504: YES), the eNB300advances to the operation at step S505. The eNB300determines whether each of the UEs to execute the D2D communication can execute the D2D communication in the SCC, based on the report of the result of the active scanning received at step S504(step S505).

When the eNB300determines at step S505that the UE can execute the D2D communication in the SCC (step S505: YES), the eNB300determines the radio resources for the D2D communication in the SCC (step S506) and advances to the operation at step S508. The radio resources are, for example, a frequency resource and a time resource. When the eNB300determines that the UE cannot execute the D2D communication in the SCC (step S505: NO), the eNB300determines the radio resources for the D2D communication in the PCC (step S507).

The eNB300transmits D2D resource information indicating the radio resources determined at either step S506or S507, to each of the UEs (step S508) and causes the series of process steps for the start control process for the D2D communication to come to an end. Each of the UEs thereby starts the D2D communication using the radio resources (the PCC or the SCC) indicated by the D2D resource information transmitted at step S508.

FIG. 6is a flowchart of an example of a start process of the D2D communication by the UE according to the second embodiment. The UE400according to the second embodiment executes, for example, the steps depicted inFIG. 6as the start process of the D2D communication.

The UE400determines whether the UE400receives a PCC discovery start instruction from the eNB300(step S601) and waits until the UE400receives the PCC discovery start instruction (step S601: NO). The PCC discovery start instruction is a signal that instructs the start of each discovery in the PCC. When the UE400determines that the UE400has received the PCC discovery start instruction (step S601: YES), the UE400executes device service discovery in the PCC (step S602).

The device service discovery includes, for example, device discovery to detect other UEs present around the UE400(a proximity degree detection function) and service discovery to detect services and application software supplied by the detected UE. The device service discovery is executed by transmitting and receiving the passive scan signal. For example, device service discovery defined in Release 12 of the LTE (Long Term Evolution) may be applied to the above device service discovery.

The UE400determines the D2D communication counterpart based on the result of the discovery sessions executed at step S602(step S603). For example, the UE400determines the D2D communication counterpart from the UEs present around the UE400and each capable of executing a predetermined D2D communication service with the UE400.

The UE400transmits the report of the result of the discovery sessions executed at step S602to the eNB300(step S604). The report transmitted at step S604is a signal that includes, for example, information concerning the terminal detected at step S602(the identification number of the terminal, the reception level of the discovery signal, service information, and the like) and information indicating the D2D communication counterpart determined at step S603.

The UE400determines whether the UE400receives the active scan instruction (step S605) and waits until the UE400receives the active scan instruction (step S605: NO). The active scan instruction is a signal that instructs active scanning. When the UE400determines that the UE400has received the active scan instruction (step S605: YES), the UE400executes the active scanning in the SCC by transmitting and receiving the active scan signal of the SCC (step S606).

The UE400transmits a report of the result of the active scanning executed at step S606to the eNB300(step S607). The report transmitted at step S607is, for example, a signal that indicates whether the D2D communication in the SCC is executable with the D2D communication counterpart determined at step S603.

The UE400determines whether the UE400receives D2D resource information from the eNB300(step S608) and waits until the UE400receives the D2D resource information (step S608: NO). The D2D resource information is information that indicates the radio resources for the D2D communication. When the UE400determines that the UE400has received the D2D resource information (step S608: YES), the UE400starts the D2D communication based on the received D2D resource information (step S609) and causes the series of process steps for the D2D communication start process to come to an end.

FIG. 7Ais a diagram of a first operation example of the wireless communications system according to the second embodiment. The wireless communications system200according to the second embodiment operates according to the process steps depicted in, for example,FIG. 7A. The eNB211transmits a PCC discovery start instruction that instructs the start of the discovery sessions (step S701). It is assumed in the example depicted inFIG. 7Athat the PCC discovery start instruction transmitted at step S701is received by the UEs232and233.

The UE232executes the device service discovery in the PCC, based on the PCC discovery start instruction transmitted at step S701(step S702). The UE233executes the device service discovery in the PCC, based on the PCC discovery start instruction transmitted at step S701(step S703).

The UE232determines the D2D communication counterpart based on the result of the discovery sessions executed at step S702(step S704). It is assumed in this case that the UE232detects the UE233as the UE located near the UE232and capable of executing the D2D communication service with the UE232, and determines that the UE233is the D2D communication counterpart thereof.

The UE233determines the D2D communication counterpart, based on the result of the discovery sessions executed at step S703(step S705). It is assumed in this case that the UE233detects the UE232as the UE located near the UE233and capable of executing the D2D communication service with the UE233, and determines that the UE232is the D2D communication counterpart thereof.

The UE232reports the result of the device service discovery executed at step S702to the eNB211(step S706). For example, the UE232transmits to the eNB211, a report that indicates that D2D communication in the PCC is executable (communication executable) and that includes information indicating the D2D communication counterpart (the UE233) determined at step S704.

The UE233reports the result of the device service discovery executed at step S703to the eNB211(step S707). For example, the UE233transmits to the eNB211a report that indicates that the D2D communication in the PCC is executable (communication executable) and that includes information indicating the D2D communication counterpart (the UE232) determined at step S705.

The eNB211transmits an individual active scan instruction that instructs the active scanning to each of the UEs232and233, based on the reports from the UEs232and233transmitted at steps S706and S707(step S708). At this step, eNB211may assign to the UEs232and233, the radio resources for the UEs232and233to transmit the active scan signals, and may notify the UEs232and233of the radio resources assigned thereto using the active scan instructions.

The UEs232and233mutually execute the active scanning in the SCC (step S709). For example, the UEs232and233execute the active scanning by mutually transmitting and receiving the active scan signals. Because it is however already assured by the service discovery executed at steps S702and S703that the UEs232and233each support a predetermined D2D communication service, whether the UEs232and233can mutually communicate in the SCC only has to be checked at step S709. The device discovery therefore only has to be executed and the service discovery does not have to be executed at step S709.

The UE232reports to the eNB211, the result of the active scanning executed at step S709(step S710). In the example depicted inFIG. 7A, the UE232transmits a report indicating that the D2D communication in the SCC is executable (communication executable) to the eNB211. The UE233reports to the eNB211, the result of the active scanning executed at step S709(step S711). In the example depicted inFIG. 7A, the UE233transmits a report indicating that the D2D communication in the SCC is executable (communication executable) to the eNB211.

The eNB211determines the radio resources for the D2D communication executed by the UEs232and233in the SCC, based on the reports from the UEs232and233transmitted at steps S710and S711(step S712).

The eNB211transmits the D2D resource information that indicates the SCC radio resources determined at step S712, to each of the UEs232and233(step S713). The UEs232and233mutually start the D2D communication in the SCC using the radio resources in the SCC indicated by the D2D resource information transmitted at step S713(step S714).

FIG. 7Bis a diagram of a second operation example of the wireless communications system according to the second embodiment. The wireless communications system200according to the second embodiment may operate according to the process steps depicted in, for example,FIG. 7B. Steps S721to S731depicted inFIG. 7Bare same as steps S701to S711depicted inFIG. 7A. It is however assumed in the example depicted inFIG. 7Bthat the UEs232and233determine in the active scanning executed at step S729that the UEs232and233cannot mutually execute the D2D communication in the SCC.

In this case, at step S730, the UE232transmits a report indicating that the D2D communication in the SCC is not executable (communication not executable) to the eNB211. At step S731, the UE233transmits a report indicating that the D2D communication in the SCC is not executable (communication not executable) to the eNB211.

The eNB211determines the radio resources for the D2D communication executed by the UEs232and233in the PCC, based on the reports from the UEs232and233transmitted at steps S730and S731(step S732).

The eNB211transmits D2D resource information that indicates the PCC communication carrier determined at step S732to each of the UEs232and233(step S733). The UEs232and233mutually start the D2D communication in the PCC using the radio resources in the PCC indicated by the D2D resource information transmitted at step S733(step S734).

As described, according to the second embodiment, the active scanning (Probing) in the SCC is executed after the discovery in the PCC. For example, in the PCC, the device service discovery (the passive scanning) using a discovery signal having a relatively large size is executed. In the SCC, the active scanning (communication confirmation with a specific counterpart) is executed.

Because the service discovery is unnecessary in the active scanning, the size of the discovery signal may be reduced to be relatively small. The traffic for the discovery in the SCC may therefore be reduced and reduction of the congestion of the SCC may be facilitated by executing the active scanning in the SCC. For example, even when the SCC is an unlicensed band to be a channel shared with other communication systems, the communication therefore may be executed efficiently, suppressing any influence on the other communication systems.

Even when the D2D communication in the SCC is not executable as a result of the active scanning in the SCC, because it is already assured that the D2D communication in the PCC is executable, for example, the D2D communication is executable in the PCC even when discovery is not again executed.

A third embodiment will be described for portions different from the second embodiment.

FIG. 8is a flowchart of an example of a start control process of the D2D communication by the eNB according to the third embodiment. The eNB300according to the third embodiment executes, for example, the process steps depicted inFIG. 8as the start control process of the D2D communication. Steps S801and S802are same as steps S501and S502depicted inFIG. 5.

Subsequent to step S802, the eNB300executes determination of a UE subset and assignment of the radio resources for the discovery, based on the D2D communication counterpart indicated by the report of the result of the discovery sessions received at step S802(step S803).

The UE subset is a set of UEs that each reports to the eNB300that the UE can execute the D2D communication. The UE subset is a sum set of pairs of UEs for which the pairing for the D2D links is completed based on the PCC discovery start instruction transmitted at step S801. The radio resources for the discovery are the radio resources for the device discovery in the SCC.

The eNB300transmits an RTS (Request To Send) signal in the PCC and the SCC (step S804). The RTS signal transmitted at step S804is a RTS signal to request the reservation of the radio resources assigned as the radio resources for the discovery at step S803.

The eNB300transmits the SCC discovery start instruction for the UEs in the subset determined at step S803(step S805). The SCC discovery start instruction is a signal that instructs the device discovery executed by the passive scanning in the SCC.

The eNB300determines whether the eNB300has received a report of the result of the device discovery in response to the SCC discovery start instruction transmitted at step S805(step S806) and waits until the eNB300receives the report of the result of the device discovery (step S806: NO). The report of the result of the device discovery includes, for example, information indicating the D2D communication counterpart determined by each of the UEs. When eNB300determines that the eNB300has received the report of the result of the device discovery (step S806: YES), the eNB300advances to the operation at step S807.

Steps S807to S810depicted inFIG. 8are the same as at steps S505to S508depicted inFIG. 5. The eNB300however assigns the radio resources for the D2D communication in the SCC to each pair of UEs reporting that the pair can execute the D2D communication in the SCC, in the UE subset. The eNB300assigns the radio resources for the D2D communication in the PCC to each pair of UEs reporting that the pair cannot execute the D2D communication in the SCC in the UE subset. Each of the UEs starts the D2D communication using the radio resources (in the PCC or the SCC) for the D2D communication assigned thereto by the eNB300.

FIG. 9is a flowchart of an example of a start process of the D2D communication by a UE according to the third embodiment. The UE400according to the third embodiment executes, for example, the process steps depicted inFIG. 9as the start process of the D2D communication. Steps S901to S904depicted inFIG. 9are the same as at steps S601to S604depicted inFIG. 6.

Subsequent to step S904, the UE400determines whether the UE400receives the SCC discovery start instruction (step S905) and waits until the UE400receives the SCC discovery start instruction (step S905: NO). When the UE400determines that the UE400has received the SCC discovery start instruction (step S905: YES), the UE400executes the device discovery in the SCC (step S906). The device discovery executed at step S906may be executed by, for example, the passive scanning to transmit and receive the passive scan signal.

The UE400transmits a report of the result of the device discovery executed at step S906to the eNB300(step S907). The report of the result of the discovery sessions transmitted at step S907includes, for example, information indicating whether the D2D communication in the SCC is executable with the D2D communication counterpart determined at step S903. Steps S908and S909are the same as at steps S608and S609depicted inFIG. 6.

FIG. 10Ais a diagram of a first operation example of the wireless communications system according to the third embodiment. The wireless communications system200according to the third embodiment operates according to the process steps depicted in, for example,FIG. 10A. Steps S1001to S1007depicted inFIG. 10Aare the same as steps S701to S707depicted inFIG. 7A.

It is assumed in the example depicted inFIG. 10Athat not only the UEs232and233but also plural pairs of UEs report to the eNB211that the UEs are mutually capable of the D2D communication as the result of the device service discovery. In response to this, the eNB211executes the determination of the UE subset and the assignment of the radio resources for the discovery, based on the reports from the UEs (step S1008).

The eNB300transmits the RTS signal that requests the reservation of the radio resources assigned as the radio resources for the discovery at step S1008, in the PCC and the SCC (step S1009).

The eNB300transmits the SCC discovery start instruction to the UEs included in the UE subset determined at step S1008(step S1010).

The UEs included in the UE subset (including the UEs232and233) mutually execute the device discovery in the SCC (step S1011). At step S1011, for example, the UEs each execute the passive scan by mutually transmitting and receiving the passive scan signals.

It is however already assured by the service discovery executed at steps S1002and S1003that the UEs support the predetermined D2D communication service and, at step S1011, therefore, it only has to be checked whether the UEs can mutually execute communication in the SCC. At step S1011, the device discovery only has to be executed and the service discovery does not have to be executed.

The UE232reports the result of the device discovery executed at step S1011to the eNB211(step S1012). In the example depicted inFIG. 10A, the UE232transmits to the eNB211, a report that indicates that the D2D communication in the SCC is executable (communication executable) and that includes the information indicating the D2D communication counterpart (the UE233) determined at step S1004.

The UE233reports the result of the active scanning executed at step S1011to the eNB211(step S1013). In the example depicted inFIG. 10A, the UE233transmits to the eNB211a report that indicates that the D2D communication in the SCC is executable (communication executable) and that includes the information indicating the D2D communication counterpart (the UE232) determined at step S1005.

The eNB211may thereby determine that the UEs232and233can execute the D2D communication in the SCC. Each UE different from the UEs232and233of the UEs included in the UE subset also reports to the eNB211similarly to the UEs232and233. Steps S1014to S1016depicted inFIG. 10Aare the same as steps S712to S714depicted inFIG. 7A.

The eNB211also assigns the radio resources for the D2D communication in the SCC to the UEs that are different from the UEs232and233of the UEs included in the UE subset and that each report that the UE can execute the D2D communication in the SCC. When the UEs included in the UE subset can execute the D2D communication in the SCC, the radio resources of the SCC are assigned to the UEs and the UEs can each start the D2D communication in the SCC.

FIG. 10Bis a diagram of a second operation example of the wireless communications system according to the third embodiment. Steps S1021to S1033depicted inFIG. 10Bare the same as steps S1001to S1013depicted inFIG. 10A. It is however assumed in the example depicted inFIG. 10Bthat the UEs232and233determine that the UEs232and233cannot mutually execute the D2D communication in the SCC.

In this case, at step S1032, the UE232transmits to the eNB211, a report indicating that the D2D communication in the SCC is not executable (communication not executable). At step S1033, the UE233transmits to the eNB211, a report indicating that the D2D communication in the SCC is not executable (communication not executable).

The eNB211determines the radio resources for the D2D communication to be used by the UEs232and233in the PCC, based on the reports from the UEs232and233transmitted at steps S1032and S1033(step S1034).

The eNB211transmits the D2D resource information that indicates the PCC radio resources determined at step S1034, to each of the UEs232and233(step S1035). The UEs232and233mutually start the D2D communication in the PCC using the radio resources in the PCC indicated by the D2D resource information transmitted at step S1035(step S1036).

FIG. 11is a diagram of an example of the transmission of the discovery signal in the SCC. InFIG. 11, the horizontal axis represents the time resources (t) and the vertical axis represents the frequency resources (f). “PCC” on the vertical axis represents the band of the PCC that is a licensed band. “SCC” on the vertical axis represents the band of the SCC that is an unlicensed band.

It is assumed in the example depicted inFIG. 11that the UE subset determined by the eNB211at step S1008ofFIG. 10Aincludes, for example, eight UEs of UEs #1 to #8. It is also assumed as an example that the UE #1 and the UE #5 form a pair of UEs that each determines that the UEs can mutually execute the D2D communication in the PCC. It is also assumed that the UE #2 and the UE #6, the UE #3 and the UE #7, and the UE #4 and the UE #8 are each the D2D communication counterparts of each other.

A resource reservation time period1101is, for example, a time period of the radio resources for the discovery assigned by the eNB211at step S1008ofFIG. 10A.

For example, at step S1009ofFIG. 10A, the eNB211transmits an RTS signal1102of the PCC. The eNB211transmits an RTS signal1104of the SCC after carrier sensing1103. Each of the RTS signals1102and1104is an RTS signal that requests the reservation of the SCC in the resource reservation time period1101.

When the UEs other than those in the UE subset each receive, for example, the RTS signal1104of the SCC, these UEs do not execute any radio transmission in the SCC in the resource reservation time period1101indicated by the RTS signal1104. Each of the UEs in the UE subset may thereby occupy a channel for the RTS signal1104.

For example, at step S1011ofFIG. 10A, the UEs #1 to #8 execute the device discovery1105in the SCC using the radio resources of the SCC for the discovery indicated by the RTS signals1102and1104. At this time, the UEs #1 to #8 may execute the device discovery1105using arbitrary radio resources of the SCC in the resource reservation time period1101.

For example, the UEs #1 and #5 (for example, the UEs232and233) determining that the UEs #1 and #5 can mutually execute the D2D communication in the PCC determine whether the UEs #1 and #5 can mutually execute the D2D communication also in the SCC, by transmitting and receiving the passive scan signals at different times in the SCC in the resource reservation time period1101. In the time period in which a UE transmits a signal, the UE usually cannot receive a signal at the equal carrier frequency. The UEs #1 and #5 cannot respectively receive the passive scan signals transmitted by the UEs #2 to #4 and #6 to #8.

When the UEs #1 and #5 determine that the UEs #1 and #5 can mutually execute the D2D communication also in the SCC, the UEs #1 and #5 report the determination at, for example, steps S1012and S1013ofFIG. 10A. The eNB211thereby assigns the SCC radio resources for the D2D to the UEs #1 and #5, and the UEs #1 and #5 can start the D2D communication in the SCC.

When the UEs #1 and #5 determine that the UEs #1 and #5 cannot mutually execute the D2D communication in the SCC, the UEs #1 and #5 report such indication at, for example, steps S1032and S1033ofFIG. 10B. The eNB211thereby assigns the radio resources of the PCC for the D2D to the UEs #1 and #5, and the UEs #1 and #5 can start the D2D communication in the PCC.

When the SCC is an unlicensed band similar to a radio LAN (Local Area Network), an RTS signal defined in the radio LAN may be used as the RTS signal1104. Thus, interference may be suppressed from the radio LAN to the device discovery1105.

In this case, for example, the LTE terminal cannot recognize the RTS signal1104. To cope with this, interference may be suppressed from the LTE terminal to the device discovery1105, by also transmitting the RTS signal1102of the PCC that is recognizable by the LTE terminal.

As described, interferences may be suppressed from both of the LTE terminal and the radio LAN to the device discovery1105by transmitting the RTS signal1102recognizable by the LTE terminal in the PCC and transmitting the RTS signal1104defined in the radio LAN in the SCC.

As described, according to the third embodiment, the passive scanning with the limited UEs is executed in the SCC after the discovery in the PCC. For example, the eNB211determines the UE subset whose UEs are caused to mutually scan in the SCC based on the result of the discovery in the PCC, and assigns the radio resources for the discovery to the UE subset. Each of the UEs included in the UE subset can thereby execute the passive scanning in the SCC using the radio resources for the discovery assigned thereto by the eNB211.

Thus, transmission and reception of the discovery signal by the UE not executing the D2D communication may be suppressed and the traffic for the discovery in the SCC may be reduced, enabling reduction of the congestion of the SCC to be facilitated. The UEs transmitting and receiving the discovery signals are reduced, whereby increase of the time period necessary for the discovery may be reduced, which is a problem in the case, for example, where the discovery is executed in the SCC that is a shared channel.

Compared to, for example, a case where active scanning is used in executing the discovery in the SCC, no individual active scan instruction may be transmitted to each of the UEs that each execute the discovery in the SCC. The traffic for the discovery in the SCC may be reduced and the reduction of the congestion of the SCC may be facilitated.

Thus, communication may be efficiently executed suppressing any effects on other communication systems even when, for example, the SCC is an unlicensed band to be the shared channel with the other communication systems.

The D2D communication may be executed in the PCC even without, for example, executing again any discovery because it is already assured that the D2D communication in the PCC is executable even when the D2D communication in the SCC is not executable as the result of the passive scanning in the SCC.

FIG. 12AandFIG. 12Bare diagrams of an example of the discovery message. A mechanism is discussed for the LTE-Advanced to realize direct wireless communication between terminals. For example, a method is discussed according to which each terminal transmits a discovery signal, another terminal present around the terminal detects the discovery signal, and the device capable of executing the direct communication and information concerning the services supplied by the device are obtained.

It is discussed that each terminal transmits, for example, a discovery message1210depicted inFIG. 12Aor a discovery message1220depicted inFIG. 12B, as the discovery signal in the above case. The discovery message1210is a 192-bit discovery message in “Non-public safety open discovery use case”. The discovery message1220is a discovery message in “Public safety use case”.

For example, the discovery message1210or the discovery message1220including the information concerning the services supplied by the device is usable as the passive scan signal. On the other hand, a discovery message not including any information concerning the services supplied by the device is usable as the active scan message.

As described, according to the wireless communications system, the terminal, the base station, and the processing method, the D2D communication in the SCC is enabled even when the frequencies of the PCC and the SCC differ from each other.

For example, conventionally, a method has been discussed according to which an unlicensed band is used as an additional carrier in the LTE that uses a licensed band taking into consideration an impact to the current LTE specification. In this method, as to the transmission of control information, use of, for example, a carrier of a licensed band is discussed.

For this method, for example, a method of coexisting with a radio LAN in an unlicensed band, and the like are discussed. A scenario is also discussed to use the unlicensed band not only for the communication between an eNB and a UE but also for the D2D communication.

For example, in a case where the discovery is executed in the PCC (a licensed band) and the SCC (unlicensed band), when the frequencies of the PCC and the SCC differ from each other (for example, that of the PCC is 2 [GHz] and that of the SCC is 5.8 [GHz]), mismatching occurs. For example, such cases can be considered as where a device detected in the PCC cannot communicate because the propagation property is different in the SCC.

In contrast, a method may be considered according to which the procedure for the discovery executed in the PCC is executed as it is in the SCC while, in this case, the following problem arises. The SCC is a shared channel and CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) or the like is therefore used for the access control of the channel. The base station therefore cannot execute accurate scheduling and cannot execute access control for each sub-band as a unit, and the efficiency of the discovery may therefore be low compared to that of the PCC.

In contrast, according to the embodiments, in the PCC, the device and service discovery using the discovery signal having a relatively large size (the passive scanning) may be executed. In the SCC, the active scanning with which the size of the discovery signal may be reduced or the passive scanning for limited terminals may be executed.

In the discovery for the communication between devices, any mismatching of the discovery may thereby be avoided when the frequencies of the PCC and the SCC differ from each other. The traffic for the discovery in the SCC may be reduced. Thus, improvement of the efficiency of the discovery in the SCC may be facilitated when the D2D communication is executed in the PCC and the SCC whose frequencies differ from each other.

However, with conventional techniques, the frequencies of the PCC and the SCC may differ from each other when, for example, an unlicensed band is used as the SCC. When the D2D communication is executed, for example, the case may be present where a terminal detects on the PCC other terminals each capable of executing D2D communication and present around the terminal and, as a result, execution of the D2D communication on the SCC whose frequency differs from that of the PCC is difficult even between the terminals each determined to be capable of executing the D2D communication.

According to an aspect of the present invention, an effect is achieved in that a terminal may be detected that can execute the D2D communication on the SCC even when the frequencies of the PCC and the SCC differ from each other.