Communication control device, program, and communication control method

There is provided a communication control device including an acquisition unit configured to acquire a reception timing at which a second radio communication device receives a downlink signal from a base station performing radio communication with a first radio communication device or the second radio communication device, and a decision unit configured to decide a transmission timing at which the second radio communication device transmits a signal to the first radio communication device through inter-device communication based on the reception timing. The decided transmission timing is a timing later than a timing at which the second radio communication device transmits an uplink signal.

TECHNICAL FIELD

The present disclosure relates to a communication control device, a program, and a communication control method.

BACKGROUND ART

Near field inter-terminal communication or device-to-device communication (D2D communication) is a communication form in which a signal is directly transmitted between terminal devices, unlike a communication form in which a signal passes through a base station in cellular communication. Therefore, in the D2D communication, new use forms of terminal devices unlike the existing cellular communication are expected to appear. For example, various applications such as information sharing by data communication between near terminal devices or a group of near terminal devices, information distribution from installed terminal devices, and autonomous communication between devices called Machine to Machine (M2M) can be considered.

With regard to the significant increase in data traffic with the recent increase of smartphones, the D2D communication can also he considered to be utilized in off-loading of data. In recent years, for example, demands for transmission and reception of streaming data of moving images have rapidly increased. However, since moving images generally have large data amounts, the moving images have a problem in that they consume many resources in a Radio Access Network (RAN). Accordingly, when terminal devices are in a state suitable for the D2D communication such as a case in which a distance between terminal devices is small, resource consumption and process loads in the RAN can be suppressed by off-loading moving image data in the D2D communication. Thus, the D2D communication is useful for both communication providers and users. Therefore, at present, the D2D communication is recognized and noticed as one of the important technical areas necessary for Long Term Evolution (LTE) of the 3rd Generation Partnership Project (3GPP) standardization commission as well.

In the related art, as disclosed in the following patent literature, communication schemes such as Bluetooth (registered trademark) and WiFi (registered trademark) have been adopted in the D2D communication and combinations of such communication schemes and communication schemes of cellular communication such as Wideband Code Division Multiple Access (WCDMA) (registered trademark) and LTE have been combined as an example.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, when the same communication scheme as the communication scheme (for example, LTE) of the cellular communication is adopted in the D2D communication and the cellular communication and the D2D communication are not properly combined, transmission and reception of signals in the D2D communication may be obstructed. Specifically, for example, since a distance between terminal devices at the time of the D2D communication is less than a distance between a base station and a terminal device, propagation delay in the D2D communication is less than propagation delay in cellular communication. For this reason, when the terminal device does not transmit a signal of the D2D communication in consideration of transmission and reception timings in cellular communication, there is a possibility of the signal of the D2D communication not being properly received.

Accordingly, it is desirable to provide a structure capable of improving a possibility of a signal being properly received in D2D communication in which the same communication scheme as a communication scheme of cellular communication is adopted.

Solution to Problem

According to the present disclosure, there is provided a communication control device including an acquisition unit configured to acquire a reception timing at which a second radio communication device receives a downlink signal from a base station performing radio communication with a first radio communication device or the second radio communication device, and a decision unit configured to decide a transmission timing at which the second radio communication device transmits a signal to the first radio communication device through inter-device communication based on the reception timing. The decided transmission timing is a timing later than a timing at which the second radio communication device transmits an uplink signal.

According to the present disclosure, there is provided a program causing a computer to function as an acquisition unit configured to acquire a reception timing at which a second radio communication device receives a downlink signal from a base station performing radio communication with a first radio communication device or the second radio communication device, and a decision unit configured to decide a transmission timing at which the second radio communication device transmits a signal to the first radio communication device through inter-device communication based on the reception timing. The decided transmission timing is a timing later than a timing at which the second radio communication device transmits an uplink signal.

According to the present disclosure, there is provided a communication control method including acquiring a reception timing at which a second radio communication device receives a downlink signal from a base station performing radio communication with a first radio communication device or the second radio communication device, and deciding a transmission timing at which the second radio communication device transmits a signal to the first radio communication device through inter-device communication based on the reception timing. The decided transmission timing is a timing later than a timing at which the second radio communication device transmits an uplink signal.

Advantageous Effects of Invention

According to an embodiment of the present disclosure described above, it is possible to improve a possibility of a signal being properly received in D2D communication in which the same communication scheme as a communication scheme of cellular communication is adopted.

DESCRIPTION OF EMBODIMENTS

The description will be made in the following order.

1.1. Transmission and Reception Timings of Signals in Cellular Communication Scheme

1.2. Technical Problem in D2D Communication

2. Schematic Configuration of Radio Communication System

3. Configuration of Terminal Device

4. Flow of Process

5. Modification Examples

6.1. Application to Terminal Device

6.2. Application to Base Station

First, transmission and reception timings of signals in a cellular communication scheme and a technical problem in D2D communication will be described with reference toFIGS. 1 to 9.

<1.1. Transmission and Reception Timings of Signals in Cellular Communication Scheme>

Transmission and reception timings of signals in a cellular communication scheme will be described with reference toFIGS. 1 to 7. Here, the timings of the transmission and reception of the signals in, for example, LTE will be described.

(Configuration of Radio Communication System)

FIG. 1is an explanatory diagram illustrating an example of a radio communication system which is a premise of description ofFIGS. 2 to 7. Terminal devices10and a base station20are illustrated inFIG. 1. The terminal device10is referred to user equipment (UE) and the base station20is referred to as an evolved node B (eNB). A cell21formed by the base station20is also illustrated. In such a radio communication system, radio communication is performed as cellular communication between each terminal device10and the base station20. Radio communication is performed as D2D communication between the terminal devices10. For example, the terminal devices10A and10B perform the D2D communication.

In this example, the terminal device10A is located to be more distant than the terminal device10B from the base station20. That is, a distance between the terminal device10A and the base station20is longer than a distance between the terminal device10B and the base station20.

In LTE, Orthogonal Frequency Division Multiplexing (OFDM) is adopted in a downlink. Fourteen OFDM symbols are transmitted for each of the subframes which are units of times of radio communication. Hereinafter, a specific example of this point will be described with reference toFIG. 2.

FIG. 2is an explanatory diagram illustrating a downlink signal transmitted in radio communication according to LTE. A downlink signal transmitted with one subframe in radio communication according to LTE is illustrated inFIG. 2. In LTE, fourteen OFDM symbols are generally included in one subframe. In other words, one subframe includes two slots and one slot includes seven OFDM symbols. Each OFDM symbol includes a cyclic prefix (CP) in its beginning.

The CP is a guard interval for removing inter-symbol interference in which a delay wave of the OFDM symbol has an influence on the subsequent OFDM symbol. The CP is generated, for example, by copying signal corresponding to a predetermined time of the last end of the OFDM symbol. A terminal device receiving the OFDM symbol neglects the signal of the CP in the OFDM symbol and demodulates the remaining signals of the OFDM symbol. The cyclic prefix contributes to removal of inter-subcarrier interference.

In the case of a normal cyclic prefix, the length of the OFDM symbol is about 66.67 microseconds. The length of the cyclic prefix included in the beginning of each symbol is about 4.687 microseconds.

Uplink

In LTE, on the other hand, a Single Carrier Frequency Division Multiple Access (SC-FDMA) is adopted in an uplink. The SC-FDMA symbol is transmitted in a time direction. The SC-FDMA symbol also includes a CP as in the OFDM symbol.

(Transmission and Reception Timings of Signals)

In a downlink of LTE, the base station20transmits a downlink signal simultaneously at a certain frame timing. That is, the base station20transmits the downlink signal to each terminal device10at the same timing. This is because resource blocks for transmitting data destined for the terminal devices10are subjected to signal processing in parallel at the same frame timing and the resource blocks are transmitted simultaneously from an antenna after amplification in the base station20.

On the other hand, the terminal device10receives a downlink signal after propagation delay according to a distance between the terminal device10and the base station20rather than the frame timing. A specific example of this point will be described with reference toFIGS. 3 and 4.

FIG. 3is an explanatory diagram schematically illustrating an example of timings at which terminal devices receive the downlink signals. Timings at which the base station20transmits downlink signals to the terminal devices10A and10B with the subframes are illustrated inFIG. 3. Thus, the base station20transmits the downlink signals simultaneously at a certain frame timing. Further, timings at which the terminal devices10A and10B receive the downlink signals are also illustrated inFIG. 3. Thus, the terminal devices10A and10B start receiving the downlink signal later than the frame timing.

FIG. 4is an explanatory diagram illustrating the details of an example of timings at which the terminal devices receive the downlink signals. The timings at which the terminal devices10A and10B illustrated inFIG. 3receive the downlink signals are illustrated in more detail inFIG. 4. In this example, as illustrated inFIG. 1, the terminal device10A is more distant from the base station20than the terminal device10B. Therefore, propagation delay PD(B→TA) in a path from the base station20to the terminal device10A is greater than propagation delay PD(B→TB) in a path from the base station20to the terminal device10B. That is, “PD(B →TA)>PD(B→TB)” is satisfied. Accordingly, a timing at which the terminal device10A starts receiving the downlink signal is later than a timing at which the terminal device10B starts receiving the downlink signal. Thus, the reception timing of the downlink signal of the terminal device10is decided depending on where the terminal device10is located within the cell21.

Uplink

In an uplink of LTE, the base station20receives uplink signals simultaneously at a given frame timing. That is, the base station20receives the uplink signals from the respective terminal devices10at the same timing.

On the other hand, the terminal device10starts transmitting the uplink signal earlier than the frame timing rather than the frame timing in consideration of the propagation delay according to the distance between the terminal device10and the base station20. A specific example of this point will be described with reference toFIGS. 5 and 6.

FIG. 5is an explanatory diagram schematically illustrating an example of timings at which the terminal devices transmit the uplink signals. The timings at which the base station20receive the uplink signals from the terminal devices10A and10B with the subframes are illustrated inFIG. 5. Thus, the base station20receives the uplink signals simultaneously at a certain frame timing. The timings at which the terminal devices10A and10B transmit the uplink signals are also illustrated inFIG. 5. Thus, the terminal devices10A and10B start transmitting the uplink signals earlier than the frame timing.

FIG. 6is an explanatory diagram illustrating the details of an example of timings at which the terminal devices transmit the uplink signals. The timings at which the terminal devices10A and10B illustrated inFIG. 5receive the uplink signals are illustrated in more detail inFIG. 6. In this example, as illustrated inFIG. 1, the terminal device10A is more distant from the base station20than the terminal device10B. Therefore, propagation delay PD(TA→B) in a path from the terminal device10A to the base station20is greater than propagation delay PD(TB→B) in a path from the terminal device10B to the base station20. That is, “PD(TA→B) >PD(TB→B)” is satisfied. Accordingly, a timing at which the terminal device10A starts transmitting the uplink signal is earlier than a timing at which the terminal device10B starts transmitting the uplink signal. Thus, the transmission timing of the uplink signal of the terminal device10is decided depending on where the terminal device10is located within the cell21.

Thus, a technology for enabling the terminal devices10to transmit the uplink signals so that the uplink signals from the respective terminal devices10simultaneously reach the base station20is referred to as timing advance (TA). Hereinafter, the more detailed content of this point will be described with reference toFIG. 7.

FIG. 7is an explanatory diagram illustrating the timing advance. A transmission timing of the uplink signal of the terminal device10A and a transmission timing of the downlink signal of the terminal device10A are illustrated inFIG. 7. Thus, the transmission timing of the uplink signal is earlier than the frame timing by the same time as the propagation delay PD(TA→B). The reception timing of the downlink signal is later than the frame timing by the propagation delay PD(B→TA). In general, the propagation delay PD(TA→B) is the same as the propagation delay PD(B→TA). That is, “PD(TA→B)=PD(B→TA)” is satisfied. Accordingly, the terminal device100A transmits the uplink signal earlier than a timing at which the downlink signal is to be received by a time twice the propagation delay PD(B→TA) (or the propagation delay PD(TA→B)).

The terminal device10knows the timing at which the downlink signal is to be received since the terminal device10receives the downlink signal. The terminal device10receives a timing advance value (TA value) as information used to decide a timing at which the uplink signal is transmitted from the base station. For example, the terminal device10is notified of an initial value of the TA value with a random access response at the time of random access. The terminal device10decides a timing earlier than the timing at which the downlink signal is transmitted by a time corresponding to the TA value as a timing at which the uplink signal is transmitted. That is, the time corresponding to the TA value corresponds to a time generally twice the propagation delay between the terminal device10and the base station. For example, a TA value corresponding to a longer time than the terminal device10located nearer the center of the cell is given to the terminal device10located in a cell edge of the cell21. The TA value in LTE is an 11-bit value from 0 to 1282. A pitch width of the TA value for adjusting the transmission timing is about 0.52 microseconds. Accordingly, the transmission timing of the terminal device10can be adjusted up to 0.67 milliseconds.

As described above, signals are transmitted and received in the cellular communication. On the other hand, it is not preferable to apply the transmission and reception timings of the signals in the cellular communication directly to the D2D communication between the terminal devices10. Hereinafter, a specific example of this point will be described with reference toFIGS. 8 and 9. In this example, the OFDM is adopted in the D2D communication.

FIG. 8is an explanatory diagram illustrating a first example when the transmission and reception timings of signals in the cellular communication are applied to the D2D communication. In the example ofFIG. 8, the terminal device10B is a transmission side device of the D2D communication and the terminal device10A is a reception side device of the D2D communication. A transmission timing at which the base station20transmits a downlink signal and a reception timing at which the terminal device10A receives the downlink signal are illustrated inFIG. 8. These timings have been described with reference toFIG. 4.

A transmission timing at which the terminal device10B transmits a D2D communication signal through the D2D communication and a reception timing at which the terminal device10A actually receives the D2D communication signal are also illustrated inFIG. 8. In this example, since the transmission and reception timings in the cellular communication are directly applied, the transmission timing at which the terminal device10B transmits the D2D communication signal is the same as the transmission timing at which the terminal device10B transmits the uplink signal. A reception timing at which the terminal device10A actually receives the D2D communication signal is later than the transmission timing at which the terminal device10B transmits the D2D communication signal by propagation delay PD(TA→TB). Since the distance between the terminal devices10A and10B is small at the time of the D2D communication, the propagation delay PD(TA→TB) becomes very small.

As a result, as illustrated inFIG. 8, a large deviation may occur between a reception timing at which the terminal device10A receives the downlink signal and a reception timing at which the terminal device10A actually receives the D2D communication signal. When the terminal device10A demodulates a signal after the reception timing at which the terminal device10A receives the downlink signal, a part of the D2D communication signal is not demodulated. The part includes not only the CP but also a signal other than the CP. Accordingly, the signal is not properly received.

FIG. 9is an explanatory diagram illustrating a second example when the transmission and reception timings of signals in the cellular communication are applied to the D2D communication. In the example ofFIG. 9, the terminal device10A is a transmission side device of the D2D communication and the terminal device10B is a reception side device of the D2D communication. A transmission timing at which the base station20transmits a downlink signal and a reception timing at which the terminal device10B receives the downlink signal are illustrated inFIG. 9. These timings have been described with reference toFIG. 4.

A transmission timing at which the terminal device10A transmits a D2D communication signal in the D2D communication and a reception timing at which the terminal device10B actually receives the D2D communication signal are also illustrated inFIG. 9. In this example, since the transmission and reception timings in the cellular communication are directly applied, the transmission timing at which the terminal device10A transmits the D2D communication signal is the same as the transmission timing at which the terminal device10A transmits the uplink signal. A reception timing at which the terminal device10B actually receives the D2D communication signal is later than the transmission timing at which the terminal device10A transmits the D2D communication signal by propagation delay PD(TB→TA). Since the distance between the terminal devices10A and10B is not distant at the time of the D2D communication, the propagation delay PD(TB→TA) becomes very small.

As a result, as illustrated inFIG. 9, a large deviation may occur between a reception timing at which the terminal device10B receives the downlink signal and a reception timing at which the terminal device10B actually receives the D2D communication signal. When the terminal device10A demodulates signals after the reception timing at which the terminal device10B receives the downlink signal, some of the D2D communication signals are not demodulated. Some of the signals include not only the CP but also a signal other than the CP. Accordingly, the signal is not properly received.

As described above with reference toFIGS. 8 and 9, when an adjustment width (that is, a time corresponding to the TA value) of an uplink transmission timing by the TA is large, a portion other than the CP of the D2D communication signal is not demodulated and the D2D communication signal is not properly received. Since the D2D communication is assumed to be frequency used mainly in a cell edge distant from the base station20, the TA value in regard to the terminal device10performing the D2D communication is assumed to be a relatively large value. Accordingly, there is a possibility of the D2D communication signal not being properly demodulated.

The above-mentioned problem will be described using more detailed numerical values. For example, the terminal devices10A and10B are assumed to be present in a cell edge of a cell with a radius of 1 kilometer. In this case, propagation delay in a path from the base station20to the terminal device10is about 3.33 microseconds. Accordingly, when the distance between the terminal devices10is neglected, deviation of a reception timing between the terminal devices10is about 6.66 microseconds. On the other hand, the length of the CP is 4.687 microseconds. Accordingly, when the deviation of the reception timing exceeds the length of the CP, the D2D communication signals are not properly received.

In the above-described example, the distance between the terminal device10and the base station20is 1 kilometer. However, when this distance is shorter, the D2D communication signals can be properly received. For example, when the distance between the terminal device10and the base station20is 700 meters, the propagation delay is 2.33 microseconds. In this case, the deviation of the reception timing is about 4.66 microseconds. Accordingly, the propagation delay permitted in the D2D communication is 0.021 microseconds in consideration of the fact that the cyclic prefix has a length of 4.687 microseconds. This propagation delay corresponds to a distance of 6.3 meters. However, under the constraint of the propagation delay or the distance, a large influence on the D2D communication can occur due to, for example, a slight change in the propagation delay caused by movement of the terminal device10or a change in a propagation path. Accordingly, reliable communication is considered not to be ensured.

Thus, when the transmission and reception timings optimized for the communication with the base station20are used in the terminal device10, whether the D2D communication is possible depends on the distance between the terminal device10and the base station20and the distance between the terminal devices10performing the D2D communication. That is, large constraint may be imposed on the D2D communication.

Accordingly, in the embodiment, a possibility of signals being properly received in the D2D communication in which the same communication scheme as the communication scheme of the cellular communication is adopted can be configured to be improved. More specifically, it is possible to loosen or remove the constraints in the D2D communication, such as the distance between the base station20and the terminal devices10performing the D2D communication, the distance between the terminal devices10performing the D2D communication, and the like.

<<2. Schematic Configuration Of Radio Communication System>>

Next, a schematic configuration of the radio communication system1according to an embodiment of the present disclosure will be described with reference toFIG. 10.FIG. 10is an explanatory diagram illustrating an example of the schematic configuration of the radio communication system1according to the embodiment. Referring toFIG. 10, the radio communication system1includes terminal devices100and a base station200. The radio communication system1adopts, for example, LTE as a communication scheme of the cellular communication.

The terminal device100performs radio communication with the base station200when the terminal device100is located within a cell21formed by the base station200. That is, the terminal device100receives a downlink signal transmitted by the base station200and transmits an uplink signal to the base station200. For example, the terminal device100receives the downlink signal according to the OFDM and transmits an uplink signal according to the SC-FDMA.

The terminal device100performs D2D communication with another terminal device100. For example, the terminal device100transmits a signal through the D2D communication according to a predetermined radio communication scheme and receives a signal according to the predetermined radio communication scheme. The predetermined radio communication scheme is, for example, a radio communication scheme used by the base station200to transmit a downlink signal. That is, the predetermined radio communication scheme is the OFDM. That is, the terminal device100transmits and receives signals according to the OFDM through the D2D communication.

The base station200performs the radio communication with the terminal device100located within the cell21. That is, the base station200transmits a downlink signal to the terminal device100and receives an uplink signal from the terminal device100. For example, the base station200transmits a downlink signal according to the OFDM and receives an uplink signal according to the SC-FDMA.

<<3. Configuration Of Terminal Device>>

An example of the configuration of the terminal device100according to the embodiment will be described with reference toFIGS. 11 to 19.FIG. 11is a block diagram illustrating an example of the configuration of the terminal device100according to the embodiment. Referring toFIG. 11, the terminal device100includes an antenna unit110, a radio communication unit120, a storage unit130, and a control unit140.

The antenna unit110receives the radio signal and outputs the received radio signal to the radio communication unit120. The antenna unit110transmits a transmission signal output by the radio communication unit120.

The radio communication unit120performs the radio communication with another device. For example, when the terminal device100is located within the cell21formed by the base station200, the radio communication unit120performs the radio communication with the base station200. That is, the radio communication unit120receives the downlink signal transmitted by the base station200and transmits the uplink signal to the base station200. For example, the radio communication unit120receives the downlink signal according to the OFDM and transmits the uplink signal according to the SC-FDMA.

In particular, in the embodiment, the radio communication unit120performs the D2D communication with another terminal device100. For example, the radio communication unit120transmits a signal according to a predetermined radio communication scheme through the D2D communication and receives a signal according to the predetermined radio communication scheme. The predetermined radio communication scheme is, for example, a radio communication scheme used by the base station200to transmit the downlink signal. That is, the predetermined radio communication scheme is the OFDM. The radio communication unit120transmits and receives the signals according to the OFDM through the D2D communication.

The storage unit130stores a program and data for an operation of the terminal device100.

The control unit140supplies various functions of the terminal device100. The control unit140includes an information acquisition unit141and a transmission timing decision unit143.

The information acquisition unit141acquires a reception timing (hereinafter referred to as a “downlink reception timing”) at which the terminal device100(the radio communication unit120) receives the downlink signal from the base station200performs radio communication with the terminal device100or the other terminal device100. For example, the terminal device100and the other terminal device100are located within the same cell21and the base station200is a base station of the cell21. That is, the terminal device100and the other terminal device100receive downlink signals from the same base station200. Then, the information acquisition unit141acquires the downlink reception timing at which the terminal device100(the radio communication unit120) receives the downlink signal from the base station200. For example, the information acquisition unit141acquires the downlink reception timing from a detection result of the downlink signal by the radio communication unit120.

For example, the information acquisition unit141further acquires timing advance information (TA information) to decide a timing (hereafter referred to as an uplink transmission timing) at which the terminal device100(the the radio communication unit120) transmits the uplink signal. The TA information is, for example, a TA value. As described above, since the terminal device100is notified of the TA value with a random access response at the time of random access, the information acquisition unit141acquires the TA value notified of with the random access response via the radio communication unit120.

The information acquisition unit141may further acquire the TA information to decide a timing (that is, an uplink transmission timing of the other terminal device100) at which the other terminal device100transmits the uplink signal. In this case, for example, the base station200may acquire the TA value of the other terminal device100and transmit the TA value to the terminal device100. When the radio communication unit120receives the TA value of the other terminal device100, the information acquisition unit141may acquire the TA value of the other terminal device100.

The transmission timing decision unit143decides the transmission timing at which the terminal device100transmits a signal.

For example, the transmission timing decision unit143decides a transmission timing (hereinafter referred to as an “uplink transmission timing”) at which the terminal device100(the radio communication unit120) transmits the uplink signal to the base station200. More specifically, for example, the transmission timing decision unit143decides a timing earlier than the downlink reception timing by a time corresponding to the acquired TA value as the uplink transmission timing. Then, the transmission timing decision unit143causes the radio communication unit120to transmit the uplink signal at the decided uplink transmission timing.

In particular, in the embodiment, the transmission timing decision unit143decides a transmission timing (hereinafter referred to as a “D2D transmission timing”) at which the terminal device100(the radio communication unit120) transmits a signal to the other terminal device100through the D2D communication based on the acquired downlink reception timing. The decided D2D transmission timing is a timing later than a timing (that is, the uplink transmission timing) at which the terminal device100(the radio communication unit120) transmits the uplink signal.

As described above, when the D2D transmission timing of a transmission side device of the D2D communication is the same as the uplink transmission timing, the D2D communication signal may arrive at a reception side device quite earlier than the downlink reception timing of the reception side device of the D2D communication. For this reason, there is a possibility of a portion other than the CP in the D2D communication signal not being demodulated according to distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device.

On the other hand, in the embodiment, when the D2D transmission timing is a timing later than the uplink transmission timing, the downlink reception timing and the D2D reception timing of a partner side are closer. Accordingly, there is a high possibility of the D2D communication signal being properly received. In other words, it is possible to loosen constraints (for example, the distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device) for proper reception of the D2D communication signal. As a result, off-loading can be performed more effectively, which considerably contributes to an increase a system capacity.

Hereinafter, a more specific example of the decided D2D transmission timing will be described.

First Example of D2D Transmission Timing

As a first example, the transmission timing decision unit143decides the D2D transmission timing based on the downlink reception timing of the terminal device100and the TA information of the terminal device100. As described above, the TA information is, for example, a TA value. Since the TA information (for example, a TA value) is an existing parameter of which the terminal device100is notified at the time of the random access, it is not necessary for the base station200to transmit a new control signal.

For example, the decided D2D transmission timing is a timing earlier than the downlink reception timing. For example, the transmission timing decision unit143multiples a time corresponding to the TA value of the terminal device100by a coefficient P (where 0<P<1). Then, the transmission timing decision unit143decides the timing earlier than the downlink reception timing by a time of the multiplication result as the D2D transmission timing. Then, the transmission timing decision unit143causes the radio communication unit120to transmit the D2D communication signal at the decided D2D transmission timing.

In this way, it is possible to prevent a period in which the partner device actually receives the D2D communication signal from not entering a period in which the partner device receives the downlink signal because the D2D transmission timing is too late.

For example, the decided D2D transmission timing is a timing later than a timing (hereinafter referred to as a “downlink transmission timing”) at which the base station200transmits the downlink signal. For example, the downlink transmission timing is a timing earlier than the downlink reception timing by half of the time corresponding to the TA information of the terminal device100.

Specifically, for example, the transmission timing decision unit143multiples a time corresponding to the TA value of the terminal device100by the coefficient P (where 0<P≦1/2). Then, the transmission timing decision unit143decides a timing earlier than the downlink reception timing by a time of the multiplication result as the D2D transmission timing.

In this way, the D2D transmission timing is later than the downlink transmission timing of the base station. Since the downlink reception timing of the partner device is at least later than the downlink transmission timing, the downlink reception timing and the D2D transmission timing are closer. Accordingly, there is a high possibility of the D2D communication signal being properly received. In other words, it is possible to loosen constraints (for example, the distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device) for proper reception of the D2D communication signal.

As a specific example, the decided D2D transmission timing is a timing (that is, the downlink transmission timing) at which the base station200transmits the downlink signal. As described above, for example, the downlink transmission timing is a timing earlier than the downlink reception timing by half of the time corresponding to the TA information of the terminal device100. For example, the transmission timing decision unit143multiples the time corresponding to the TA value of the terminal device100by a coefficient 1/2. Then, the transmission timing decision unit143decides the timing earlier than the downlink reception timing by the time of the multiplication result as the D2D transmission timing.

In this way, the D2D transmission timing becomes nearly constant between the terminal devices100. That is, a variation in the D2D transmission timing by the terminal device100is small irrespective of the position of each terminal device100within the cell21, a frequency band used for the D2D communication, and a duplex communication scheme (for example, an FDD scheme or a TDD scheme).

Hereinafter, a specific example will be described with reference toFIGS. 12 and 13.

FIG. 12is a first explanatory diagram illustrating a first example of a D2D transmission timing according to the embodiment. In the example ofFIG. 12, the terminal device100B is a transmission side device of the D2D communication and the terminal device100A is a reception side device of the D2D communication. A downlink transmission timing at which the base station200transmits a downlink signal and a downlink reception timing at which the terminal device100A receives the downlink signal are illustrated inFIG. 12. This point is the same as that of the example illustrated inFIG. 8.

A D2D transmission timing at which the terminal device100B transmits a D2D communication signal in the D2D communication and a D2D reception timing at which the terminal device100A actually receives the D2D communication signal are also illustrated inFIG. 12. In this example, the D2D transmission timing of the terminal device100B is almost the same as the downlink transmission timing of the base station200. As a result, a deviation between the reception timings (that is, a deviation between the D2D reception timing and the downlink reception timing in the terminal device100A) illustrated inFIG. 12is less than the deviation between the reception timings illustrated inFIG. 8. As a result, the deviation between the reception timings is less than the length of the CP and the terminal device100A can properly receive the D2D communication signal.

FIG. 13is a second explanatory diagram illustrating the first example of the D2D transmission timing according to the embodiment. In the example ofFIG. 13, the terminal device100A is a transmission side device of the D2D communication and the terminal device100B is a reception side device of the D2D communication. A downlink transmission timing at which the base station200transmits a downlink signal and a downlink reception timing at which the terminal device100B receives the downlink signal are illustrated inFIG. 13. This point is the same as that of the example illustrated inFIG. 9.

A D2D transmission timing at which the terminal device100A transmits a D2D communication signal in the D2D communication and a D2D reception timing at which the terminal device100B actually receives the D2D communication signal are also illustrated inFIG. 13. In this example, the D2D transmission timing of the terminal device100A is almost the same as the downlink transmission timing of the base station200. As a result, a deviation between the reception timings (that is, a deviation between the D2D reception timing and the downlink reception timing in the terminal device100B) illustrated inFIG. 12is less than the deviation between the reception timings illustrated inFIG. 9. As a result, the deviation between the reception timings is less than the length of the CP and the terminal device100B can properly receive the D2D communication signal.

Second Example of D2D Transmission Timing

As a second example, a decided D2D transmission timing is a reception timing (that is, a downlink reception timing) at which the terminal device100receives the downlink signal. That is, the transmission timing decision unit143decides the acquired downlink reception timing as the D2D transmission timing. Then, the transmission timing decision unit143causes the radio communication unit120to transmit the D2D communication signal at the decided D2D transmission timing.

In general, the terminal devices100(for example, the terminals100A and100B) performing the D2D communication are located nearby. That is, the distance between the terminal devices100is small. Therefore, a difference between the downlink reception timing of the transmission side device and the downlink reception timing of the reception side in the D2D communication is small. Further, in the D2D communication, propagation delay from the transmission side device to the reception side device is small. Accordingly, when the transmission side device (for example, the terminal device100A) of the D2D communication transmits a D2D communication signal at a downlink reception timing of the own device, the reception side device (for example, the terminal device100B) can receive the D2D communication signal at a timing close to the downlink reception timing of the own device. Accordingly, there is a high possibility of the D2D communication signal being properly received. In other words, it is possible to loosen constraints (for example, the distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device) for proper reception of the D2D communication signal.

In this case, information other than the reception timing is not necessary. Accordingly, even when the TA value is not yet acquired (for example, the terminal device100does not perform random access and is in an idle state), the terminal device100can transmit the D2D communication signal at a proper D2D transmission timing.

Hereinafter, a specific example will be described with reference toFIGS. 14 and 15.

FIG. 14is a first explanatory diagram illustrating a second example of the D2D transmission timing according to the embodiment. In the example ofFIG. 14, the terminal device100B is a transmission side device of the D2D communication and the terminal device100A is a reception side device of the D2D communication. A downlink transmission timing at which the base station200transmits a downlink signal and a downlink reception timing at which the terminal device100A receives the downlink signal are illustrated inFIG. 14. This point is the same as those of the examples illustrated inFIGS. 8 and 12.

A D2D transmission timing at which the terminal device100B transmits a D2D communication signal in the D2D communication and a D2D reception timing at which the terminal device100A actually receives the D2D communication signal are also illustrated inFIG. 14. In this example, the D2D transmission timing of the terminal device100B is the same as the downlink reception timing of the terminal device100B. As a result, a deviation between the reception timings (that is, a deviation between the D2D reception timing and the downlink reception timing in the terminal device100A) illustrated inFIG. 14is less than the deviation between the reception timings illustrated inFIG. 8. As a result, the deviation between the reception timings is less than the length of the CP and the terminal device100A can properly receive the D2D communication signal.

FIG. 15is a second explanatory diagram illustrating the second example of the D2D transmission timing according to the embodiment. In the example ofFIG. 15, the terminal device100A is a transmission side device of the D2D communication and the terminal device100B is a reception side device of the D2D communication. A downlink transmission timing at which the base station200transmits a downlink signal and a downlink reception timing at which the terminal device100B receives the downlink signal are illustrated inFIG. 15. This point is the same as that of the example illustrated inFIG. 9.

A D2D transmission timing at which the terminal device100A transmits a D2D communication signal in the D2D communication and a D2D reception timing at which the terminal device100B actually receives the D2D communication signal are also illustrated inFIG. 15. In this example, the D2D transmission timing of the terminal device100A is the same as the downlink reception timing of the terminal device100A. As a result, a deviation between the reception timings (that is, a deviation between the D2D reception timing and the downlink reception timing in the terminal device100B) illustrated inFIG. 15is less than the deviation between the reception timings illustrated inFIG. 9. In this example, the D2D reception timing is slightly later than the downlink reception timing. Accordingly, when a reception period of the downlink signal is set to be slightly longer than the length of the OFDM symbol, the terminal device100B can properly receive the D2D communication signal.

The above-described D2D transmission timing may be applied to a case in which a predetermined condition is satisfied. For example, when a time advance group (TAG) of the transmission side device (for example, the terminal device100A) is the same as a TAG of the reception side device (for example, the terminal device100B), the above-described D2D transmission timing may be applied.

The fact that the TAG of the transmission side device is the same as the TAG of the reception side device means that the TA value of the transmission side device is the same as the TA value of the reception side device. Accordingly, when the TAG of the transmission side device is the same as the TAG of the reception side device, the downlink reception timing of the transmission side device is the same as the downlink reception timing of the reception side device. Accordingly, the downlink reception timing and the D2D reception timing in the reception side device can be closer.

When the TAGs of two terminal devices performing the D2D communication are not the same, the D2D transmission timings may be individually adjusted by an offset value of the transmission timing.

Such determination of whether the TAGs are the same and adjustment of the transmission timings by the offset value are performed by the base station200. Then, for example, the base station200notifies the terminal device100performing the D2D communication.

Third Example of D2D Transmission Timing

As a third example, the transmission timing decision unit143decides the D2D transmission timing based on the downlink reception timing of the terminal device100, the TA information of the terminal device100, and the TA information of another terminal device100.

For example, the decided D2D transmission timing is a timing (that is, a downlink reception timing of the other terminal device100) at which the other terminal device100(that is, a reception side terminal device of the D2D communication) receives a downlink signal from the base station200. For example, the downlink reception timing of the other terminal device100is a timing later than a timing (that is, a downlink transmission timing) at which the base station200transmits the downlink signal by half of a time corresponding to the TA information of the other terminal device100.

Specifically, for example, the transmission timing decision unit143multiples the time corresponding to the TA value of the terminal device100by a coefficient 1/2. Then, the transmission timing decision unit143calculates a timing earlier than the downlink transmission timing by a time of a multiplication result as the downlink transmission timing of the base station200. The transmission timing decision unit143calculates a timing later than the calculated downlink transmission timing by half of a time corresponding to the TA information of the other terminal device100as the downlink reception timing of the other terminal device100. The half time corresponds to propagation delay from the base station200to the other terminal device100. The transmission timing decision unit143decides the downlink reception timing of the other terminal device100as a D2D transmission timing of the terminal device100. The transmission timing decision unit143causes the radio communication unit120to transmit the D2D communication signal at the decided D2D transmission timing.

In general, the terminal devices100(for example, the terminals100A and100B) performing the D2D communication are located nearby. That is, the distance between the terminal devices100is small. Therefore, in the D2D communication, propagation delay from the transmission side device to the reception side device is small. Accordingly, when the transmission side device (for example, the terminal device100A) of the D2D communication transmits a D2D communication signal at a downlink reception timing of the reception side device (for example, the terminal device100B), the reception side device can receive the D2D communication signal at a timing close to the downlink reception timing of the own device. Accordingly, there is a high possibility of the D2D communication signal being properly received. In other words, it is possible to loosen constraints (for example, the distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device) for proper reception of the D2D communication signal.

Hereinafter, a specific example will be described with reference toFIGS. 16 and 17.

FIG. 16is a first explanatory diagram illustrating a third example of the D2D transmission timing according to the embodiment. In the example ofFIG. 16, the terminal device100B is a transmission side device of the D2D communication and the terminal device100A is a reception side device of the D2D communication. A downlink transmission timing at which the base station200transmits a downlink signal and a downlink reception timing at which the terminal device100A receives the downlink signal are illustrated inFIG. 16. This point is the same as those of the examples illustrated inFIGS. 8, 12, and 14.

A D2D transmission timing at which the terminal device100B transmits a D2D communication signal in the D2D communication and a D2D reception timing at which the terminal device100A actually receives the D2D communication signal are also illustrated inFIG. 16. In this example, the D2D transmission timing of the terminal device100B is almost the same as the downlink reception timing of the terminal device100A. As a result, a deviation between the reception timings (that is, a deviation between the D2D reception timing and the downlink reception timing in the terminal device100A) illustrated inFIG. 16is less than the deviation between the reception timings illustrated inFIG. 8. In this example, the D2D reception timing is slightly later than the downlink reception timing. Accordingly, when a reception period of the downlink signal is set to be slightly longer than the length of the OFDM symbol, the terminal device100A can properly receive the D2D communication signal.

FIG. 17is a second explanatory diagram illustrating the third example of the D2D transmission timing according to the embodiment. In the example ofFIG. 17, the terminal device100A is a transmission side device of the D2D communication and the terminal device100B is a reception side device of the D2D communication. A downlink transmission timing at which the base station200transmits a downlink signal and a downlink reception timing at which the terminal device100B receives the downlink signal are illustrated inFIG. 17. This point is the same as that of the example illustrated inFIG. 9.

A D2D transmission timing at which the terminal device100A transmits a D2D communication signal in the D2D communication and a D2D reception timing at which the terminal device100B actually receives the D2D communication signal are also illustrated inFIG. 17. In this example, the D2D transmission timing of the terminal device100A is almost the same as the downlink reception timing of the terminal device100B. As a result, a deviation between the reception timings (that is, a deviation between the D2D reception timing and the downlink reception timing in the terminal device100B) illustrated inFIG. 17is less than the deviation between the reception timings illustrated inFIG. 9. In this example, the D2D reception timing is slightly later than the downlink reception timing. Accordingly, when a reception period of the downlink signal is set to be slightly longer than the length of the OFDM symbol, the terminal device100B can properly receive the D2D communication signal.

Case of One-to-multiple D2D Communication

Here, a D2D transmission timing of a case in which a terminal device100performs the D2D communication with two or more other terminal devices100will be described with reference toFIGS. 18 and 19.

FIG. 18is an explanatory diagram illustrating a first case in which a terminal device performs D2D communication with two or more other terminal devices. InFIG. 18, a terminal device100B performs the D2D communication with both of terminal devices100A and100C. As an example of this case, the terminal device100B is connected to a content delivery server via the base station200and transmits content to the terminal devices100A and100C.

FIG. 19is an explanatory diagram illustrating a second case in which the terminal device performs the D2D communication with two or more other terminal devices. InFIG. 19, in the case ofFIG. 18, the terminal devices100A and100C further mutually perform the D2D communication. As an example of this case, the terminal devices100A,100B, and100C perform communication in a group.

As described above, when the terminal device100performs the D2D communication with two or more other terminal devices100, it is preferable to apply the first example or the second example of the D2D transmission timing described above rather than applying the third example of the D2D transmission timing described above. This is because since the TA value of the communication partner of the D2D communication is acquired in the third example of the D2D transmission timing described above, the TA value of which the base station200notifies increases, and thus the process and communication increase and become complicated.

<<4. Flow Of Process>>

Next, an example of the communication control process according to the embodiment will be described with reference toFIG. 20.FIG. 20is a sequence diagram illustrating an example of a schematic flow of the communication control process according to the embodiment.

In step S401, the control unit140of the terminal device100A causes the radio communication unit120to transmit a start request of the D2D communication. Then, the base station200receives the start request.

Next, in step S403, the base station200performs paging. In the paging, information indicating the D2D communication is transmitted. The terminal device100B is called by the paging.

Then, in step S405, the terminal device100B and the base station200perform a random access procedure. During the random access procedure, the control unit140of the terminal device100B causes the radio communication unit120to transmit a random access request. The base station200transmits a random access response in response to the random access request. The base station200notifies the terminal device100B of the TA value of the terminal device100B in the random access response.

In step S407, the transmission timing decision unit143of the terminal device100A decides the D2D transmission timing based on the downlink reception timing of the terminal device100A and the TA value acquired in advance. For example, as in the first example of the D2D transmission timing described above, the downlink transmission timing of the base station200calculated from the downlink reception timing and the TA value is decided as the D2D transmission timing of the terminal device100A.

In step S409, the transmission timing decision unit143of the terminal device100B decides the D2D transmission timing based on the downlink reception timing of the terminal device100B and the TA value acquired in the random access procedure. For example, as in the first example of the D2D transmission timing described above, the downlink transmission timing of the base station200calculated from the downlink reception timing and the TA value is decided as the D2D transmission timing of the terminal device100B.

In step S411and step S413, the base station200instructs the terminal devices100A and100B to transmit a pilot signal in the D2D communication and to perform measurement in regard to the pilot signal in the D2D communication.

In step S415, the control unit140of the terminal device100A causes the radio communication unit120to transmit the pilot signal. Then, the radio communication unit120of the terminal device100B receives the pilot signal and the control unit140of the terminal device100B performs the measurement in regard to the pilot signal.

In step S417, the control unit140of the terminal device100B causes the radio communication unit120to transmit the pilot signal. The radio communication unit120of the terminal device100A receives the pilot signal and the control unit140of the terminal device100A performs the measurement in regard to the pilot signal.

In step S419and step S421, the terminal devices100A and100B report measurement results in regard to the pilot signal to the base station200via the radio communication unit120.

In step S423, the base station200determines whether to permit the D2D communication based on the reported measurement results. For example, the base station200determines to permit the D2D communication when communication quality of the D2D communication satisfies a predetermined quality requirement.

In step S425and step S427, the base station200notifies the terminal devices100A and100B of the permission of the D2D communication. Thereafter, the D2D communication starts between the terminal devices100A and100B.

One example of the communication control process according to the embodiment has been described. When the third example of the D2D transmission timing described above is used, the base station200notifies the terminal device100A of the TA value of the terminal device100B before step S407and notifies the terminal device100B of the TA value of the terminal device100A before step S409.

Next, modification examples of the embodiment will be described with reference toFIGS. 21 to 24.

In the above-described embodiment, the example in which two terminal devices100(for example, the terminal devices100A and100B) performing the D2D communication are located within the same cell has been described. Accordingly, examples in which two terminal devices100performing the D2D communication are located within different cells will be described as modification examples of the embodiment.

(Example of Cells in Which Terminal Devices Performing D2D Communication are Located)

First, a specific example of cells which is a premise will be described with reference toFIGS. 21 and 22.

FIG. 21is an explanatory diagram illustrating a first example of cells when the terminal devices performing the D2D communication are located in the different cells. Adjacent cells21A and20B are illustrated inFIG. 21. The base station200A of the cell21A and the terminal device100A located in the cell21A are illustrated. The base station200B of the cell21B and the terminal device100B located in the cell21B are illustrated. For example, thus, the terminal devices100performing the D2D communication are located in the two mutually adjacent cells21.

FIG. 22is an explanatory diagram illustrating a second example of cells when the terminal devices performing the D2D communication are located in the different cells. A macro cell23and a small cell25overlapping with the macro cell23are illustrated inFIG. 22. A base station203of the macro cell23and the terminal device100A located within the macro cell23are illustrated. A base station205of the small cell25and the terminal device100B located within the small cell25are illustrated. For example, thus, the terminal devices100performing the D2D communication are located in the macro cell23and the small cell25, respectively.

As in the above-described example, even when two terminal devices100performing the D2D communication are located within different cells, a proper D2D transmission timing can be decided. Modification examples of the embodiment will be described below using the example ofFIG. 21as the premise. This description can also be applied similarly to the example ofFIG. 22.

Since a decision scheme when transmission and reception timings between two cells are synchronized and a decision scheme when transmission and reception timings between two cells are not synchronized are slightly different, the two cases will be described.

(When Synchronization is Achieved Between Cells)

When the synchronization is achieved between the cells, the downlink transmission timings by the base station200between the cells21are the same. As in the case in which two terminal devices100performing the D2D communication are located in the same cell, the D2D transmission timing can be decided. For example, as in the first to third examples of the D2D transmission timing described above, the D2D transmission timing can be decided.

In the third example of the D2D transmission timing, as described above, the terminal device100A (the transmission timing decision unit143) decides the D2D transmission timing based on the downlink reception timing of the terminal device100A, the TA information of the terminal device100A, and the TA information of the other terminal device100B. The TA information of the terminal device100A is TA information of the terminal device100A in the cell21A in which the terminal device100is located. On the other hand, when the terminal devices100A and100B performing the D2D communication are located within different cells, the TA information of the terminal device100B is TA information of the terminal device100B in the cell21B in which the terminal device100B is located. Therefore, the base station200B transmits the TA information of the terminal device100B to the base station200A, and then the base station200A transmits the TA information of the terminal device100B to the terminal device100A. Then, the terminal device100A (the information acquisition unit141) acquires the TA information of the terminal device100B.

(When Synchronization is not Achieved Between Cells)

When the synchronization is not achieved between the cells, the downlink transmission timings by the base station200between the cells21are different. Therefore, the followings are different compared to the case in which two terminal devices100performing the D2D communication are located in the same cell.

First Example of D2D Transmission Timing

In the first example of the D2D transmission timing, as described above, the terminal device100A decides the D2D transmission timing based on the downlink reception timing of the terminal device100A and the TA information of the terminal device100A. When the terminal devices100A and100B performing the D2D communication are located within different cells, the downlink reception timing of the terminal device100A and the TA information of the terminal device100A are as follows.

First, the downlink reception timing of the terminal device100A is a reception timing at which the terminal device100A receives the downlink signal (that is, the downlink signal of the cell21B) from the base station200B performing radio communication with the terminal device100B. Therefore, the information acquisition unit141of the terminal device100A causes the radio communication unit120to receive the downlink signal (for example, a primary synchronization signal, a secondary synchronization signal, or the like) of the cell21B and acquires the reception timing of the downlink signal.

The TA information of the terminal device100A is TA information (that is, TA information of the terminal device100A in the cell21B) used to decide a timing at which the terminal device100A transmits an uplink signal to the base station200B. Therefore, the information acquisition unit141causes the terminal device100A to perform random access to the cell21B and acquires the TA information of the terminal device100A in the cell21B.

According to the downlink reception timing of the terminal device100A and the TA information of the terminal device100A, the terminal device100A can calculate, for example, a timing at which the base station200B transmits the downlink signal. That is, the terminal device100A can calculate the downlink transmission timing in the cell21B in which the terminal device100B which is a partner side device of the D2D communication is located.

Using the fact that the terminal devices100A and100B are located nearby as the premise, the information acquisition unit141may acquire and use the TA information of the terminal device100B in the cell21B as a substitute of the TA information of the terminal device100A in the cell21B. In this case, the base station200B may transmit the TA information of the terminal device100B to the base station200A and the base station200A may transmit the TA information of the terminal device100B to the terminal device100A.

Second Example of D2D Transmission Timing

In the second example of the D2D transmission timing, as described above, the terminal device100A decides the D2D transmission timing based on the downlink reception timing of the terminal device100A. When the terminal devices100A and100B performing the D2D communication are located within different cells, the downlink reception timing of the terminal device100A is as follows.

As in the first example of the D2D transmission timing described above, the downlink reception timing of the terminal device100A is a reception timing at which the terminal device100A receives the downlink signal of the cell21B.

According to the downlink reception timing of the terminal device100A, the terminal device100A can know a reception timing at which the terminal device100A receives the downlink signal from the base station21B. That is, the terminal device100A can calculate the downlink transmission timing in the cell21B in which the terminal device100B which is a partner side device of the D2D communication is located.

Third Example of D2D Transmission Timing

In the third example of the D2D transmission timing, as described above, the terminal device100A decides the D2D transmission timing based on the downlink reception timing of the terminal device100A, the TA information of the terminal device100A, and the TA information of the terminal device100B. When the terminal devices100A and100B performing the D2D communication are located within different cells, the downlink reception timing of the terminal device100A, the TA information of the terminal device100A, the TA information of the terminal device100B are as follows.

First, the downlink reception timing of the terminal device100A is a reception timing at which the terminal device100A receives the downlink signal of the cell21B as in the first example of the D2D transmission timing described above. The TA information of the terminal device100A is TA information of the terminal device100A in the cell21B as in the first example of the D2D transmission timing described above.

The TA information of the terminal device100B is TA information (that is, TA information of the terminal device100B in the cell21B) used to decide a timing at which the terminal device100B transmits an uplink signal to the base station200B. Therefore, the base station200B transmits the TA information of the terminal device100B to the base station200A and the base station200A transmits the TA information of the terminal device100B to the terminal device100A. Then, the information acquisition unit141acquires the TA information of the terminal device100B.

According to the downlink reception timing of the terminal device100A, the TA information of the terminal device100A, and the TA information of the terminal device100B, the terminal device100A can calculate, for example, a timing at which the terminal device100B which is a partner side device of the D2D communication receives the downlink signal from the base station200B. That is, the terminal device100A can calculate a timing at which the terminal device100B receives the downlink signal of the cell21B.

Next, examples of the communication control process according to modification examples of the embodiment will be described with reference toFIGS. 23 and 24.

When Synchronization is Achieved Between Cells

FIG. 23is a sequence diagram illustrating a first example of a schematic flow of the communication control process according to a modification example of the embodiment.

In step S501, the control unit140of the terminal device100A causes the radio communication unit120to transmit a start request of the D2D communication. Then, the base station200A receives the start request. Then, in step S503, the base station200A transmits the start request to the base station200B.

In step S505, the base station200A transmit inter-cell synchronization information indicating whether the cells21A and21B are synchronized, to the terminal device100A. In this case, the inter-cell synchronization information indicates that the cells21A and21B are synchronized. In this way, the terminal device100A knows that the cells21A and21B are synchronized. In this example, the inter-cell synchronization information is acquired in step S505, but the acquisition of the inter-cell synchronization information is not limited to this example. The inter-cell synchronization information may be announced in advance using the system information to the terminal device100or may be announced in advance separately using signaling from the base station200to the terminal device100. When all of the cells or some of the cells in the system are synchronized, information regarding whether synchronization is achieved between the cells may be stored in the terminal devices100.

In step S507, the base station200B perform paging. In the paging, information indicating the D2D communication is transmitted. The terminal device100B is called by the paging.

Then, in step S509, the terminal device100B and the base station200B perform a random access procedure. During the random access procedure, the control unit140of the terminal device100B causes the radio communication unit120to transmit a random access request. The base station200B transmits a random access response in response to the random access request. The base station200B notifies the terminal device100B of the TA value of the terminal device100B in the random access response. The TA value is the TA value of the terminal device100B in the cell21B.

In step S511, the transmission timing decision unit143of the terminal device100A decides the D2D transmission timing based on the downlink reception timing of the terminal device100A in the cell21A and the TA value (the TA value of the terminal device100A in the cell21A) acquired in advance. For example, as in the first example of the D2D transmission timing described above, the downlink transmission timing of the base station200A calculated from the downlink reception timing and the TA value is decided as the D2D transmission timing of the terminal device100A.

In step S513, the transmission timing decision unit143of the terminal device100B decides the D2D transmission timing based on the downlink reception timing of the terminal device100B in the cell21B and the TA value (the TA value of the terminal device100B in the cell21B) acquired in the random access procedure. For example, as in the first example of the D2D transmission timing described above, the downlink transmission timing of the base station200B calculated from the downlink reception timing and the TA value is decided as the D2D transmission timing of the terminal device100B.

In step S515, the base station200A instructs the terminal device100A to transmit the pilot signal in the D2D communication and perform measurement in regard to the pilot signal in the D2D communication.

In step S517, the base station200B instructs the terminal device100B to transmit the pilot signal in the D2D communication and perform measurement in regard to the pilot signal in the D2D communication.

In step S519, the control unit140of the terminal device100A causes the radio communication unit120to transmit the pilot signal. Then, the radio communication unit120of the terminal device100B receives the pilot signal and the control unit140of the terminal device100B performs the measurement in regard to the pilot signal.

In step S521, the control unit140of the terminal device100B causes the radio communication unit120to transmit the pilot signal. The radio communication unit120of the terminal device100A receives the pilot signal and the control unit140of the terminal device100A performs the measurement in regard to the pilot signal.

In step S523, the terminal device100B reports a measurement result in regard to the pilot signal to the base station200B via the radio communication unit120.

In step S525, the terminal device100A reports a measurement result in regard to the pilot signal to the base station200A via the radio communication unit120.

In step S527, the base stations200A and200B determine whether to permit the D2D communication based on the reported measurement results. For example, the base stations200A and200B determine to permit the D2D communication when communication quality of the D2D communication satisfies a predetermined quality requirement. In step S529, the base station200A notifies the terminal device100A of the permission of the D2D communication. In step S531, the base station200B notifies the terminal device100B of the permission of the D2D communication. Thereafter, the D2D communication starts between the terminal devices100A and100B.

The first example of the communication control process according to the modification example of the embodiment has been described. When the third example of the D2D transmission timing described above is used, the base station200A notifies the terminal device100A of the TA value of the terminal device100B in the cell21B before step S511. The base station200B notifies the terminal device100B of the TA value of the terminal device100A in the cell21A before step S513.

When Synchronization is not Achieved Between Cells

FIG. 24is a sequence diagram illustrating a second example of the schematic flow of the communication control process according to a modification example of the embodiment. Here, only step S551, step S553, step S555, step S557, and step S559which are differences between the first example of the schematic flow of the communication control process illustrated inFIG. 23and the second example of the schematic flow of the communication control process illustrated inFIG. 24will be described.

In step S551, the base station200A transmits inter-cell synchronization information indicating whether the cells21A and21B are synchronized, to the terminal device100A. In this example, the inter-cell synchronization information indicates that the cells21A and21B are not synchronized. In this way, the terminal device100A knows that the cells21A and21B are not synchronized. In this example, the inter-cell synchronization information is acquired in step S551, but the acquisition of the inter-cell synchronization information is not limited to this example. The inter-cell synchronization information may be announced in advance using the system information to the terminal device100or may be announced in advance separately using signaling from the base station200to the terminal device100. When all of the cells or some of the cells in the system are synchronized, information regarding whether synchronization is achieved between the cells may be stored in the terminal devices100.

Then, in step S553, the terminal device100A and the base station200B perform a random access procedure. During the random access procedure, the control unit140of the terminal device100A causes the radio communication unit120to transmit a random access request. The base station200B transmits a random access response in response to the random access request. The base station200B notifies the terminal device100A of the TA value of the terminal device100A in the random access response. The TA value is the TA value of the terminal device100A in the cell21B.

Then, in step S555, the terminal device100B and the base station200A perform a random access procedure. During the random access procedure, the control unit140of the terminal device100B causes the radio communication unit120to transmit a random access request. The base station200A transmits a random access response in response to the random access request. The base station200A notifies the terminal device100B of the TA value of the terminal device100B in the random access response. The TA value is the TA value of the terminal device100B in the cell21A.

In step S557, the transmission timing decision unit143of the terminal device100A decides the D2D transmission timing based on the downlink reception timing of the terminal device100A in the cell21B and the TA value (the TA value of the terminal device100A in the cell21B) acquired in the random access procedure. For example, as in the first example of the D2D transmission timing described above, the downlink transmission timing of the base station200B calculated from the downlink reception timing and the TA value is decided as the D2D transmission timing of the terminal device100A.

In step S559, the transmission timing decision unit143of the terminal device100B decides the D2D transmission timing based on the downlink reception timing of the terminal device100B in the cell21A and the TA value (the TA value of the terminal device100B in the cell21A) acquired in the random access procedure. For example, as in the first example of the D2D transmission timing described above, the downlink transmission timing of the base station200A calculated from the downlink reception timing and the TA value is decided as the D2D transmission timing of the terminal device100B.

The second example of the communication control process according to the modification example of the embodiment has been described. When the third example of the D2D transmission timing described above is used, the base station200A notifies the terminal device100A of the TA value of the terminal device100B in the cell21B before step S557. The base station200B notifies the terminal device100B of the TA value of the terminal device100A in the cell21A before step S559.

The technology related to the present disclosure can be applied to various products. The terminal device100may be realized as, for example, a mobile terminal such as a smartphone, a tablet personal computer (PC), a notebook PC, a portable game console, a portable/dongle-style mobile router, or a digital camera, or as an in-vehicle terminal such as a car navigation device. In addition, the terminal device100may also be realized as a terminal that conducts machine-to-machine (M2M) communication (also called a machine-type communication (MTC) terminal). Furthermore, the terminal device100may be a radio communication module mounted onboard these terminals (for example, an integrated circuit module configured on a single die).

For example, the base station200may be realized as one kind of evolved NodeB (eNB) such as a macro eNB or a small eNB. The small eNB may be an eNB that covers a smaller cell, such as a pico eNB, a micro eNB, or a home (pemto) eNB, than a macro cell. Instead, the base station200may be realized as another kind of base station such as a NodeB or a base transceiver station (BTS). The base station200may include a main body (also referred to as a base station device) controlling radio communication and at least one remote radio head (RRH) disposed at a different location than the main body. The above-described various kinds of terminals may perform a base station function temporarily or semi-permanently to operate as the base station200.

<<6.1. Applications Related to Terminal Device>>

The processor901may be a CPU or system-on-a-chip (SoC), for example, and controls functions in the application layer and other layers of the smartphone900. The memory902includes RAM and ROM, and stores programs executed by the processor901as well as data. The storage903may include a storage medium such as semiconductor memory or a hard disk. The external connection interface904is an interface for connecting an externally attached device, such as a memory card or Universal Serial Bus (USB) device, to the smartphone900.

The camera906includes an image sensor such as a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) sensor, and generates a captured image. The sensor907may include a sensor group such as a positioning sensor, a gyro sensor, a geomagnetic sensor, and an acceleration sensor, for example. The microphone908converts audio input into the smartphone900into an audio signal. The input device909includes devices such as a touch sensor that detects touches on a screen of the display device910, a keypad, a keyboard, buttons, or switches, and receives operations or information input from a user. The display device910includes a screen such as a liquid crystal display (LCD) or an organic light-emitting diode (OLED) display, and displays an output image of the smartphone900. The speaker911converts an audio signal output from the smartphone900into audio.

The radio communication interface912supports a cellular communication scheme such as LTE or LTE-Advanced, and executes radio communication. Typically, the radio communication interface912may include a BB processor913, an RF circuit914, and the like. The BB processor913may conduct processes such as encoding/decoding, modulation/demodulation, and multiplexing/demultiplexing, for example, and executes various signal processing for radio communication. Meanwhile, the RF circuit914may include components such as a mixer, a filter, and an amp, and transmits or receives a radio signal via an antenna916. The radio communication interface912may also be a one-chip module integrating the BB processor913and the RF circuit914. The radio communication interface912may also include a plurality of BB processors913and a plurality of RF circuits914as illustrated inFIG. 25. Note that althoughFIG. 25illustrates an example of the radio communication interface912including a plurality of BB processors913and a plurality of RF circuits914, the radio communication interface912may also include a single BB processor913or a single RF circuit914.

Furthermore, in addition to a cellular communication scheme, the radio communication interface912may also support other types of radio communication schemes such as a short-range wireless communication scheme, a near field wireless communication scheme, or a wireless local area network (LAN) scheme. In this case, a BB processor913and an RF circuit914may be included for each radio communication scheme.

Each antenna switch915switches the destination of an antenna916among a plurality of circuits included in the radio communication interface912(for example, circuits for different radio communication schemes).

Each antenna916includes a single or a plurality of antenna elements (for example, a plurality of antenna elements constituting a MIMO antenna), and is used by the radio communication interface912to transmit and receive radio signals. The smartphone900may also include a plurality of antennas916as illustrated inFIG. 25. Note that althoughFIG. 25illustrates an example of the smartphone900including a plurality of antennas916, the smartphone900may also include a single antenna916.

Furthermore, the smartphone900may also be equipped with an antenna916for each radio communication scheme. In this case, the antenna switch915may be omitted from the configuration of the smartphone900.

The bus917interconnects the processor901, the memory902, the storage903, the external connection interface904, the camera906, the sensor907, the microphone908, the input device909, the display device910, the speaker911, the radio communication interface912, and the auxiliary controller919. The battery918supplies electric power to the respective blocks of the smartphone900illustrated inFIG. 25via power supply lines partially illustrated with dashed lines in the drawing. The auxiliary controller919causes minimal functions of the smartphone900to operate while in a sleep mode, for example.

In the smartphone900illustrated inFIG. 25, the information acquisition unit141and the transmission timing decision unit143described with reference toFIG. 11may be implemented in the radio communication interface912. Also, at least some of these functions may also be implemented in the processor901or the auxiliary controller919.

FIG. 26is a block diagram illustrating an example of a schematic configuration of a car navigation device920to which technology according to an embodiment of the present disclosure may be applied. The car navigation device920is equipped with a processor921, memory922, a Global Positioning System (GPS) module924, a sensor925, a data interface926, a content player927, a storage medium interface928, an input device929, a display device930, a speaker931, a radio communication interface933, one or more antenna switches936, one or more antennas937, and a battery938.

The processor921may be a CPU or SoC, for example, and controls a car navigation function and other functions of the car navigation device920. The memory922includes RAM and ROM, and stores programs executed by the processor921as well as data.

The GPS module924measures the position of the car navigation device920(for example, the latitude, longitude, and altitude) by using GPS signals received from GPS satellites. The sensor925may include a sensor group such as a gyro sensor, a geomagnetic sensor, and a barometric pressure sensor, for example. The data interface926is connected to an in-vehicle network941via a port not illustrated in the drawing, and acquires data generated on the vehicle side, such as vehicle speed data.

The content player927plays content stored on a storage medium (for example, a CD or DVD) inserted into the storage medium interface928. The input device929includes devices such as a touch sensor that detects touches on a screen of the display device930, buttons, or switches, and receives operations or information input from a user. The display device930includes a screen such as an LCD or OLED display, and displays a navigation function or an image of played-back content. The speaker931outputs audio of a navigation function or played-back content.

The radio communication interface933supports a cellular communication scheme such as LTE or LTE-Advanced, and executes radio communication. Typically, the radio communication interface933may include a BB processor934, an RF circuit935, and the like. The BB processor934may conduct processes such as encoding/decoding, modulation/demodulation, and multiplexing/demultiplexing, for example, and executes various signal processing for radio communication. Meanwhile, the RF circuit935may include components such as a mixer, a filter, and an amp, and transmits or receives a radio signal via an antenna937. The radio communication interface933may also be a one-chip module integrating the BB processor934and the RF circuit935. The radio communication interface933may also include a plurality of BB processors934and a plurality of RF circuits935as illustrated inFIG. 26. Note that althoughFIG. 26illustrates an example of the radio communication interface933including a plurality of BB processors934and a plurality of RF circuits935, the radio communication interface933may also include a single BB processor934or a single RF circuit935.

Furthermore, in addition to a cellular communication scheme, the radio communication interface933may also support other types of radio communication schemes such as a short-range wireless communication scheme, a near field wireless communication scheme, or a wireless LAN scheme. In this case, a BB processor934and an RF circuit935may be included for each radio communication scheme.

Each antenna switch936switches the destination of an antenna937among a plurality of circuits included in the radio communication interface933(for example, circuits for different radio communication schemes).

Each antenna937includes a single or a plurality of antenna elements (for example, a plurality of antenna elements constituting a MIMO antenna), and is used by the radio communication interface933to transmit and receive radio signals. The car navigation device920may also include a plurality of antennas937as illustrated inFIG. 26. Note that althoughFIG. 26illustrates an example of the car navigation device920including a plurality of antennas937, the car navigation device920may also include a single antenna937.

Furthermore, the car navigation device920may also be equipped with an antenna937for each radio communication scheme. In this case, the antenna switch936may be omitted from the configuration of the car navigation device920.

The battery938supplies electric power to the respective blocks of the car navigation device920illustrated inFIG. 26via power supply lines partially illustrated with dashed lines in the drawing. Also, the battery938stores electric power supplied from the vehicle.

In the car navigation device920illustrated inFIG. 26, the information acquisition unit141and the transmission timing decision unit143described with reference toFIG. 11may be implemented in the radio communication interface933. Also, at least some of these functions may also be implemented in the processor921.

In addition, technology according to the present disclosure may also be realized as an in-vehicle system (or vehicle)940that includes one or more blocks of the car navigation device920discussed above, the in-vehicle network941, and a vehicle-side module942. The vehicle-side module942generates vehicle-side data such as the vehicle speed, number of engine revolutions, or malfunction information, and outputs the generated data to the in-vehicle network941.

<<10.1. Applications Related to Base Station>>

FIG. 27is a block diagram illustrating a first example of a schematic configuration of an eNB to which technology according to an embodiment of the present disclosure may be applied. An eNB800includes one or more antennas810, and a base station device820. The respective antennas810and the base station device820may be connected to each other via an RF cable.

Each antenna810includes a single or a plurality of antenna elements (for example, a plurality of antenna elements constituting a MIMO antenna), and is used by the base station device820to transmit and receive radio signals. The eNB800may include a plurality of antennas810as illustrated inFIG. 27, and the plurality of antennas810may respectively correspond to a plurality of frequency bands used by the eNB800, for example. Note that althoughFIG. 27illustrates an example of the eNB800including a plurality of antennas810, the eNB800may also include a single antenna810.

The base station device820is equipped with a controller821, memory822, a network interface823, and a radio communication interface825.

The controller821may be a CPU or DSP, for example, and causes various higher-layer functions of the base station device820to operate. For example, the controller821generates a data packet from data inside a signal processed by the radio communication interface825, and forwards the generated packet via the network interface823. The controller821may also generate a bundled packet by bundling data from a plurality of baseband processors, and forward the generated bundled packet. In addition, the controller821may also include logical functions that execute controls such as Radio Resource Control (RRC), Radio Bearer control, mobility management, admission control, or scheduling. Also, such controls may also be executed in coordination with a nearby eNB or core network node. The memory822includes RAM and ROM, and stores programs executed by the controller821as well as various control data (such as a terminal list, transmit power data, and scheduling data, for example).

The network interface823is a communication interface for connecting the base station device820to a core network824. The controller821may also communication with a core network node or another eNB via the network interface823. In this case, the eNB800and the core network node or other eNB may be connected to each other by a logical interface (for example, the S1 interface or the X2 interface). The network interface823may also be a wired communication interface, or a wireless communication interface for wireless backhaul. In the case in which the network interface823is a wireless communication interface, the network interface823may use a higher frequency band for wireless communication than the frequency band used by the radio communication interface825.

The radio communication interface825supports a cellular communication scheme such as Long Term Evolution (LTE) or LTE-Advanced, and provides a radio connection to a terminal positioned inside the cell of the eNB800via an antenna810. Typically, the radio communication interface825may include a baseband (BB) processor826, an RF circuit827, and the like. The BB processor826may conduct processes such as encoding/decoding, modulation/demodulation, and multiplexing/demultiplexing, for example, and executes various signal processing in respective layers (for example, L1, Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP)). The BB processor826may also include some or all of the logical functions discussed earlier instead of the controller821. The BB processor826may be a module including memory that stores a communication control program, a processor that executes such a program, and related circuits. The functions of the BB processor826may also be modifiable by updating the program. Also, the module may be a card or a blade inserted into a slot of the base station device820, or a chip mounted onboard the card or the blade. Meanwhile, the RF circuit827may include components such as a mixer, a filter, and an amp, and transmits or receives a radio signal via an antenna810.

The radio communication interface825may also include a plurality of BB processors826as illustrated inFIG. 27, and the plurality of BB processors826may respectively correspond to a plurality of frequency bands used by the eNB800, for example. In addition, the radio communication interface825may also include a plurality of RF circuits827as illustrated inFIG. 27, and the plurality of RF circuits827may respectively correspond to a plurality of antenna elements, for example. Note that althoughFIG. 27illustrates an example of the radio communication interface825including a plurality of BB processors826and a plurality of RF circuits827, the radio communication interface825may also include a single BB processor826or a single RF circuit827.

FIG. 28is a block diagram illustrating a second example of a schematic configuration of an eNB to which technology according to an embodiment of the present disclosure may be applied. An eNB830includes one or more antennas840, a base station device850, and an RRH860. The respective antennas840and the RRH860may be connected to each other via an RF cable. Also, the base station device850and the RRH860may be connected to each other by a high-speed link such as an optical fiber cable.

Each antenna840includes a single or a plurality of antenna elements (for example, a plurality of antenna elements constituting a MIMO antenna), and is used by the RRH860to transmit and receive radio signals. The eNB830may include a plurality of antennas840as illustrated inFIG. 28, and the plurality of antennas840may respectively correspond to a plurality of frequency bands used by the eNB830, for example. Note that althoughFIG. 28illustrates an example of the eNB830including a plurality of antennas840, the eNB830may also include a single antenna840.

The radio communication interface855supports a cellular communication scheme such as LTE or LTE-Advanced, and provides a radio connection to a terminal positioned inside a sector corresponding to the RRH860via the RRH860and an antenna840. Typically, the radio communication interface855may include a BB processor856and the like. The BB processor856is similar to the BB processor826described with reference toFIG. 27, except for being connected to an RF circuit864of the RRH860via the connection interface857. The radio communication interface855may also include a plurality of BB processors856as illustrated inFIG. 28, and the plurality of BB processors856may respectively correspond to a plurality of frequency bands used by the eNB830, for example. Note that althoughFIG. 28illustrates an example of the radio communication interface855including a plurality of BB processors856, the radio communication interface855may also include a single BB processor856.

The connection interface857is an interface for connecting the base station device850(radio communication interface855) to the RRH860. The connection interface857may also be a communication module for communication on the high-speed link connecting the base station device850(radio communication interface855) and the RRH860.

In addition, the RRH860is equipped with a connection interface861and a radio communication interface863.

The connection interface861is an interface for connecting the RRH860(radio communication interface863) to the base station device850. The connection interface861may also be a communication module for communication on the high-speed link.

The radio communication interface863transmits and receives a radio signal via an antenna840. Typically, the radio communication interface863may include an RF circuit864. The RF circuit864may include components such as a mixer, a filter, and an amp, and transmits or receives a radio signal via an antenna840. The radio communication interface863may also include a plurality of RF circuits864as illustrated inFIG. 28, and the plurality of RF circuits864may respectively correspond to a plurality of antenna elements, for example. Note that althoughFIG. 28illustrates an example of the radio communication interface863including a plurality of RF circuits864, the radio communication interface863may also include a single RF circuit864.

The example in which the terminal device100decides the D2D transmission timing of the own device has been described. However, instead of the terminal device100, the base station200may decide a D2D transmission timing of the terminal device100and notify the terminal device100of the transmission timing. That is, the information acquisition unit141and the transmission timing decision unit143descried with reference toFIG. 11may not be included by terminal device100, but may be instead included by the base station200. In this case, in the eNB800and the eNB830illustrated inFIGS. 28 and 29, the information acquisition unit141and the transmission timing decision unit143described with reference toFIG. 11may be implemented in the radio communication interface825as well as the radio communication interface855and/or the radio communication interface863. Also, at least some of these functions may also be implemented in the controller821and the controller851.

The communication devices and each process according to the embodiment have been described above with reference toFIGS. 1 to 24. According to the embodiment of the present disclosure, the reception timing (that is, the downlink reception timing) at which the terminal device100receives the downlink signal from the base station200performing the radio communication with the terminal device100or the other terminal device100is acquired. The transmission timing (that is, the D2D transmission timing) at which the terminal device100performing the D2D communication transmits a signal to the other terminal device100is decided based on the acquired reception timing. Then, the decided D2D transmission timing is a timing later than the timing (that is, the uplink transmission timing) at which the terminal device100transmits the uplink signal.

When the D2D transmission timing of a transmission side device of the D2D communication is the same as the uplink transmission timing, the D2D communication signal may arrive at a reception side device quite earlier than the downlink reception timing of the reception side device of the D2D communication. For this reason, there is a possibility of a portion other than the CP in the D2D communication signal not being demodulated according to distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device.

On the other hand, in the embodiment, when the D2D transmission timing is a timing later than the uplink transmission timing, the downlink reception timing and the D2D reception timing of a partner side are closer. Accordingly, there is a high possibility of the D2D communication signal being properly received. In other words, it is possible to loosen constraints (for example, the distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device) for proper reception of the D2D communication signal. As a result, off-loading can be performed more effectively, which considerably contributes to an increase a system capacity.

For example, the TA information used to decide the timing (that is, the uplink transmission timing) at which the terminal device100transmits the uplink signal is further acquired. As the first example of the D2D transmission timing, the D2D transmission timing is decided based on the downlink reception timing of the terminal device100and the TA information of the terminal device100.

Since the TA information (for example, the TA value) is an existing parameter of which the terminal device100is notified at the time of the random access, it is not necessary for the base station200to transmit a new control signal.

For example, the decided D2D transmission timing is the timing earlier than the downlink reception timing.

In this way, it is possible to prevent a period in which the partner device actually receives the D2D communication signal from not entering a period in which the partner device actually receives the downlink signal because the D2D transmission timing is too late.

For example, the decided D2D transmission timing is a timing later than a timing (hereinafter referred to as a “downlink transmission timing”) at which the base station200transmits the downlink signal. For example, the downlink transmission timing is a timing earlier than the downlink reception timing by half of the time corresponding to the TA information of the terminal device100.

In this way, the D2D transmission timing is later than the downlink transmission timing of the base station. Since the downlink reception timing of the partner device is at least later than the downlink transmission timing, the downlink reception timing and the D2D transmission timing of the partner side are closer. Accordingly, there is a high possibility of the D2D communication signal being properly received. In other words, it is possible to loosen the constraints (for example, the distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device) for proper reception of the D2D communication signal.

As a specific example, the decided D2D transmission timing is a timing (that is, the downlink transmission timing) at which the base station200transmits the downlink signal.

In this way, the D2D transmission timing becomes nearly constant between the terminal devices100. That is, a variation in the D2D transmission timing by the terminal device100is small irrespective of the position of each terminal device100within the cell21, a frequency band used for the D2D communication, and a duplex communication scheme (for example, an FDD scheme or a TDD scheme).

As the second example of the D2D transmission timing, the decided D2D transmission timing is the reception timing (that is, the downlink reception timing) at which the terminal device100receives the downlink signal.

In general, the terminal devices100(for example, the terminals100A and100B) performing the D2D communication are located nearby. That is, the distance between the terminal devices100is small. Therefore, a difference between the downlink reception timing of the transmission side device and the downlink reception timing of the reception side in the D2D communication is small. Further, in the D2D communication, propagation delay from the transmission side device to the reception side device is small. Accordingly, when the transmission side device (for example, the terminal device100A) of the D2D communication transmits a D2D communication signal at a downlink reception timing of the own device, the reception side device (for example, the terminal device100B) can receive the D2D communication signal at a timing close to the downlink reception timing of the own device. Accordingly, there is a high possibility of the D2D communication signal being properly received. In other words, it is possible to loosen the constraints (for example, the distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device) for proper reception of the D2D communication signal.

In this case, information other than the reception timing is not necessary. Accordingly, even when the TA value is not yet acquired (for example, the terminal device100does not perform random access and is in an idle state), the terminal device100can transmit the D2D communication signal at a proper D2D transmission timing.

As the third example of the D2D transmission timing, the TA information used to decide the timing (that is, the uplink transmission timing of another terminal device100) at which the other terminal device100transmits the uplink signal is further acquired. The D2D transmission timing is decided based on the downlink reception timing of the terminal device100, the TA information of the terminal device100, and the TA information of the other terminal device100.

More specifically, for example, the decided D2D transmission timing is the timing (that is, the downlink reception timing of the other terminal device100) at which the other terminal device100(that is, the reception side terminal device of the D2D communication) receives the downlink signal from the base station200. For example, the downlink reception timing of the other terminal device100is the timing later than a timing (that is, a downlink transmission timing) at which the base station200transmits the downlink signal by half of a time corresponding to the TA information of the other terminal device100.

In general, the terminal devices100(for example, the terminals100A and100B) performing the D2D communication are located nearby. That is, the distance between the terminal devices100is small. Therefore, in the D2D communication, propagation delay from the transmission side device to the reception side device is small. Accordingly, when the transmission side device (for example, the terminal device100A) of the D2D communication transmits a D2D communication signal at the downlink reception timing of the reception side device (for example, the terminal device100B), the reception side device can receive the D2D communication signal at the timing close to the downlink reception timing of the own device. Accordingly, there is a high possibility of the D2D communication signal being properly received. In other words, it is possible to loosen the constraints (for example, the distances between the base station200, and the reception side device and the transmission side device and the distance between the reception side device and the transmission side device) for proper reception of the D2D communication signal.

For example, the example in which the terminal device decides the D2D transmission timing of the own device has been described, but an embodiment of the present disclosure is not limited thereto. For example, as described even in the applications, the D2D transmission timing of the terminal device may be decided by a device forming a part of the base station. For example, in the described example, the information acquisition unit and the transmission timing decision unit included in the terminal device may be included in the base station (or the device forming a part of the base station). The base station may notify the terminal device of the D2D transmission timing.

Also, the processing steps in a communication control process in this specification are not strictly limited to being executed in a time series following the sequence described in a flowchart. For example, the processing steps in a communication control process may be executed in a sequence that differs from a sequence described herein as a flowchart, and furthermore may be executed in parallel.

In addition, it is possible to create a computer program for causing hardware such as a CPU, ROM, and RAM built into a communication control device (for example, terminal device) to exhibit functions similar to each structural element of the foregoing communication control device. It becomes also possible to provide a storage medium which stores the computer program.

A communication control device including:

an acquisition unit configured to acquire a reception timing at which a second radio communication device receives a downlink signal from a base station performing radio communication with a first radio communication device or the second radio communication device; and

a decision unit configured to decide a transmission timing at which the second radio communication device transmits a signal to the first radio communication device through inter-device communication based on the reception timing,

wherein the decided transmission timing is a timing later than a timing at which the second radio communication device transmits an uplink signal.(2)

The communication control device according to (1),

wherein the acquisition unit further acquires first timing advance information to decide the timing at which the second radio communication device transmits the uplink signal, and

wherein the decision unit decides the transmission timing based on the reception timing and the first timing advance information.(3)

The communication control device according to (2), wherein the decided transmission timing is a timing earlier than the reception timing.(4)

The communication control device according to (2) or (3), wherein the decided transmission timing is a timing later than a timing at which the base station transmits the downlink signal.(5)

The communication control device according to (4), wherein the decided transmission timing is the timing at which the base station transmits the downlink signal.(6)

The communication control device according to (4) or (5), wherein the timing at which the base station transmits the downlink signal is a timing earlier than the reception timing by half of a time corresponding to the first timing advance information.(7)

The communication control device according to (1), wherein the decided transmission timing is the reception timing.(8)

The communication control device according to (2),

wherein the acquisition unit further acquires second timing advance information to decide a timing at which the first radio communication device transmits an uplink signal, and

wherein the decision unit decides the transmission timing based on the reception timing, the first timing advance information, and the second timing advance information.(9)

The communication control device according to (8), wherein the decided transmission timing is a timing at which the first radio communication device receives the downlink signal from the base station.(10)

The communication control device according to (9), wherein the timing at which the first radio communication device receives the downlink signal is a timing later than a timing at which the base station transmits the downlink signal by half of a time corresponding to the second timing advance information.(11)

wherein the first radio communication device and the second radio communication device are located in a same cell, and

wherein the base station is a base station of the same cell.(12)

wherein the first radio communication device is located in a first cell,

wherein the second radio communication device is located at a second cell different from the first cell, and

wherein the base station is a base station of one of the first cell and the second cell.(13)

The communication control device according to any one of (1) to (12), wherein the first radio communication device and the second radio communication device transmit a signal according to a predetermined radio communication scheme through the inter-device communication and receive a signal according to the predetermined radio communication scheme.(14)

The communication control device according to (13), wherein the predetermined radio communication scheme is a radio communication scheme used by the base station to transmit the downlink signal.(15)

The communication control device according to (14), wherein the predetermined radio communication scheme is an orthogonal frequency division multiplexing scheme.(16)

The communication control device according to any one of (1) to (15), wherein the communication control device is the second radio communication device.(17)

The communication control device according to any one of (1) to (15), wherein the communication control device is a device forming a part of the base station.(18)

A program causing a computer to function as:

an acquisition unit configured to acquire a reception timing at which a second radio communication device receives a downlink signal from a base station performing radio communication with a first radio communication device or the second radio communication device; and

a decision unit configured to decide a transmission timing at which the second radio communication device transmits a signal to the first radio communication device through inter-device communication based on the reception timing,

wherein the decided transmission timing is a timing later than a timing at which the second radio communication device transmits an uplink signal.(19)

A communication control method including:

acquiring a reception timing at which a second radio communication device receives a downlink signal from a base station performing radio communication with a first radio communication device or the second radio communication device; and

deciding a transmission timing at which the second radio communication device transmits a signal to the first radio communication device through inter-device communication based on the reception timing,

wherein the decided transmission timing is a timing later than a timing at which the second radio communication device transmits an uplink signal.

REFERENCE SIGNS LIST