JP5095259B2 - COMMUNICATION METHOD AND BASE STATION DEVICE USING THE SAME - Google Patents

Description

  The present invention relates to communication technology, and more particularly, to a communication method for assigning a channel to a terminal device and a base station device using the communication method.

In a mobile communication system composed of a radio base station and a radio mobile station, the radio base station allocates a channel as a resource to the radio mobile station. Further, communication is performed between the radio base station and the radio mobile station while using the allocated channel (see, for example, Patent Document 1).
JP 2006-270941 A

  In general, effective use of limited frequency resources is desired in wireless communication. In particular, as the communication speed increases, the demand is further increased. One technique for meeting this requirement is the OFDMA (Orthogonal Frequency Division Multiple Access) system, which can be combined with TDMA / TDD. OFDMA is a technique for frequency-multiplexing a plurality of terminal devices using OFDM. In such OFDMA, a subchannel is formed by a plurality of subcarriers, and a multicarrier signal is formed by a plurality of subchannels.

  Further, by combining with TDMA, the multicarrier signal is divided into a plurality of time slots on the time axis. As a result, the base station apparatus performs data communication with the terminal apparatus by assigning the subchannel in at least one time slot to the terminal apparatus. When a broadband application is used, the terminal device requires a plurality of resources, that is, a plurality of subchannels. In order for many terminal devices to use such an application, it is necessary to assign subchannels so that each terminal device can secure subchannels from a plurality of base station devices.

  On the other hand, the distance between the base station apparatus and the terminal apparatus varies depending on the terminal apparatus unit. The terminal device must transmit the packet signal of the assigned subchannel so as to fit in the time slot defined by the base station device. However, if the distance between the base station apparatus and the terminal apparatus is long, the packet signal transmitted by the terminal apparatus may be received by the base station apparatus at a timing delayed from the time slot. At that time, the base station apparatus performs time alignment. In time alignment, the base station apparatus instructs the terminal apparatus to advance the packet signal transmission timing. When the terminal device is assigned a subchannel from each of the plurality of base station devices, and when another time slot included in the same time slot is assigned, the terminal device is assigned to each of the plurality of base station devices. Receive time alignment instructions from. As a result, the transmission timing becomes unknown in the terminal device.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a communication technique for reliably executing a time alignment instruction to a terminal device capable of assigning subchannels from a plurality of base station devices. There is.

  In order to solve the above problems, a base station apparatus according to an aspect of the present invention is a base station apparatus that forms a frame by time multiplexing of a plurality of time slots while forming a time slot by frequency multiplexing of a plurality of subchannels. An allocating unit that allocates at least two subchannels to the terminal device, and a communication unit that performs communication while performing time alignment for the terminal device to which the allocating unit has allocated at least two subchannels. . The assigning unit determines at least two subchannels to be assigned to the terminal apparatus so that the number of time slots including at least two subchannels is reduced.

  Another aspect of the present invention is a communication method. In this method, a time slot is formed by frequency multiplexing of a plurality of subchannels, and a frame is formed by time multiplexing of a plurality of time slots, and at least two subchannels are allocated to a terminal device, and at least two And performing communication while executing time alignment for the terminal device to which the subchannel is allocated. The assigning step determines at least two subchannels to be assigned to the terminal device such that the number of time slots including at least two subchannels is reduced.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the instruction | indication of time alignment can be reliably performed with respect to the terminal device which can allocate a subchannel from several base station apparatuses.

  Before describing the present invention specifically, an outline will be given first. Embodiments of the present invention relate to a communication system including a base station device and at least one terminal device. In the communication system, each frame is formed by time-division multiplexing a plurality of time slots, and each time slot is formed by frequency-division multiplexing a plurality of subchannels. Each subchannel is formed by a multicarrier signal. Here, OFDM signals are used as multicarrier signals, and OFDMA (Orthogonal Frequency Division Multiple Access) is used as frequency division multiplexing. The OFDMA scheme is a technique for frequency multiplexing a plurality of terminal devices using OFDM.

  The base station apparatus performs communication with the plurality of terminal apparatuses by assigning each of the plurality of subchannels included in each time slot to the terminal apparatus. On the other hand, when the distance between the terminal device and the base station device is large, the packet signal transmitted from the terminal device may not fit in the time slot defined in the base station device. At that time, the base station apparatus instructs the terminal apparatus to correct the transmission timing of the packet signal by executing time alignment. As described above, when a terminal device is assigned subchannels from a plurality of base station devices, if these subchannels are included in the same time slot, the terminal devices may receive different times from the plurality of base station devices. May receive alignment instructions. As a result, in the terminal device, it is unclear which time alignment instruction should be followed. In order to cope with this, the communication system according to the present embodiment executes the following processing.

  When allocating a plurality of subchannels to the terminal device, the base station apparatus selects a subchannel included in one time slot without selecting a subchannel that spans a plurality of time slots. That is, the base station apparatus selects a plurality of subchannels so that the number of time slots including a plurality of subchannels is reduced. Further, the base station apparatus performs communication with the terminal apparatus by assigning the selected subchannel to the terminal apparatus. As a result, the terminal device uses a time slot allocated from another base station device.

  FIG. 1 shows a configuration of a communication system 100 according to an embodiment of the present invention. The communication system 100 includes a first terminal device 12a, a second terminal device 12b, and a third terminal device 12c, which are collectively referred to as a base station device 10 and a terminal device 12.

  The base station device 10 has a terminal device 12 connected to one end via a wireless network and a wired network (not shown) connected to the other end. Further, the terminal device 12 is connected to the base station device 10 via a wireless network. The base station apparatus 10 performs communication with the plurality of terminal apparatuses 12 by assigning communication channels to the plurality of terminal apparatuses 12. Specifically, the base station device 10 broadcasts a control signal, and the terminal device 12 recognizes the presence of the base station device 10 by receiving the control signal. Thereafter, the terminal apparatus 12 transmits a channel allocation request signal to the base station apparatus 10, and the base station apparatus 10 allocates a communication channel to the terminal apparatus 12 in response to the received request signal.

  In addition, the base station apparatus 10 transmits information on the communication channel assigned to the terminal apparatus 12, and the terminal apparatus 12 performs communication with the base station apparatus 10 while using the assigned communication channel. As a result, the data transmitted from the terminal device 12 is output to the wired network via the base station device 10 and finally received by a communication device (not shown) connected to the wired network. Data is also transmitted in the direction from the communication device to the terminal device 12. 1 shows one base station apparatus 10, the communication system 100 may include a plurality of base station apparatuses 10, and the terminal apparatus 12 communicates with one of the base station apparatuses 10. If a channel is assigned, communication can be executed. Whether or not the terminal device 12 can communicate with the base station device 10 generally depends on the relative positional relationship between the base station device 10 and the terminal device 12.

  In the above description, the communication channel is specified by the combination of the subchannel and the time slot described above. In addition, since the base station apparatus 10 has a plurality of time slots and a plurality of subchannels, the base station apparatus 10 executes OFDMA using a plurality of subchannels while executing TDMA using the plurality of time slots. Here, the terminal apparatus 12 transmits data so as to fit in the time slot defined in the base station apparatus 10. On the other hand, if the terminal device 12 exists at a position away from the base station device 10, the propagation delay from the terminal device 12 to the base station device 10 becomes long. Therefore, the data transmitted from the terminal device 12 may be later than the time slot timing. In order to reduce the occurrence of such a state, the base station apparatus 10 performs time alignment. That is, when the base station apparatus 10 receives data from the terminal apparatus 12 at a timing later than the time slot, the base station apparatus 10 instructs the terminal apparatus 12 to advance the transmission timing.

  2A to 2C show a frame configuration in the communication system 100. FIG. The horizontal direction in the figure corresponds to the time axis. A frame is formed by time multiplexing of eight time slots. The eight time slots are composed of four upstream time slots and four downstream time slots. Here, four uplink time slots are indicated as “first uplink time slot” to “fourth uplink time slot”, and four downlink time slots are indicated as “first downlink time slot” to “fourth downlink time slot”. . Further, the illustrated frame is repeated continuously.

  The configuration of the frame is not limited to that shown in FIG. 2A. For example, the frame configuration may be configured by four time slots or 16 time slots. The configuration will be described with reference to FIG. For the sake of brevity, it is assumed that the upstream time slot and the downstream time slot have the same configuration. For this reason, only one of the uplink time slot and the downlink time slot may be described, but the same description is valid for the other time slot. Furthermore, a super frame is formed by continuing a plurality of frames shown in FIG. Here, as an example, it is assumed that a super frame is formed by “20” frames.

  FIG. 2B shows the configuration of one time slot in FIG. The vertical direction in the figure corresponds to the frequency axis. As illustrated, one time slot is formed by frequency multiplexing of “16” subchannels from “first subchannel” to “16th subchannel”. In addition, the plurality of subchannels are frequency division multiplexed. Since each time slot is configured as shown in FIG. 2B, the above-described communication channel is specified by the combination of the time slot and the subchannel. Also, the frame configuration corresponding to one subchannel in FIG. 2B may be as shown in FIG. Note that the number of subchannels arranged in one time slot may not be “16”. Here, it is assumed that the allocation of the subchannel in the uplink time slot and the allocation of the subchannel in the downlink time slot are the same. Further, it is assumed that at least one control signal is assigned in units of superframes. For example, a control signal is assigned to one subchannel of one time slot among a plurality of downlink time slots included in a superframe. The same applies to the uplink.

  FIG. 2 (c) shows the configuration of one subchannel in FIG. 2 (b). Similar to FIG. 2A and FIG. 2B, the horizontal direction in the figure corresponds to the time axis, and the vertical direction in the figure corresponds to the frequency axis. Further, numbers “1” to “29” are assigned to the frequency axis, and these indicate subcarrier numbers. In this way, the subchannel is composed of multicarrier signals, and in particular is composed of OFDM signals. “TS” in the figure corresponds to a training symbol and is constituted by a known value. Further, it is assumed that a control signal may be included in “TS”. “GS” corresponds to a guard symbol, and no substantial signal is arranged here. “PS” corresponds to a pilot symbol, and is configured by a known value. “DS” corresponds to a data symbol and is data to be transmitted. “GT” corresponds to a guard time, and no substantial signal is arranged here.

  FIG. 3 shows an arrangement of subchannels in the communication system 100. In FIG. 3, the frequency axis is shown on the horizontal axis, and the spectrum for the time slot shown in FIG. 2B is shown. As described above, 16 subchannels from the first subchannel to the 16th subchannel are frequency division multiplexed in one time slot. Each subchannel is configured by a multicarrier signal, here, an OFDM signal.

  FIG. 4 shows the configuration of the base station apparatus 10. The base station apparatus 10 includes a first RF unit 20a, a second RF unit 20b, an NRF unit 20n, a baseband processing unit 22, a modem unit 24, an IF unit 26, a radio control unit 28, and a storage unit 30. including. The radio control unit 28 includes a control channel determination unit 32 and a radio resource allocation unit 38.

  As a reception process, the RF unit 20 performs frequency conversion on a radio frequency multicarrier signal received from a terminal device 12 (not shown) to generate a baseband multicarrier signal. Here, the multicarrier signal is formed as shown in FIG. 3, and corresponds to the uplink time slot of FIG. Further, the RF unit 20 outputs a baseband multicarrier signal to the baseband processing unit 22. In general, a baseband multicarrier signal is formed by an in-phase component and a quadrature component, and therefore should be transmitted by two signal lines. For the sake of clarity, a single signal line is used here. Only. The RF unit 20 also includes an AGC and an A / D conversion unit.

  As a transmission process, the RF unit 20 performs frequency conversion on the baseband multicarrier signal input from the baseband processing unit 22 to generate a radiofrequency multicarrier signal. Further, the RF unit 20 transmits a radio frequency multicarrier signal. The RF unit 20 transmits a multicarrier signal while using the same radio frequency band as the received multicarrier signal. That is, as shown in FIG. 2A, TDD (Time Division Duplex) is used. The RF unit 20 also includes a PA (Power Amplifier) and a D / A conversion unit.

  The baseband processing unit 22 inputs a baseband multicarrier signal from each of the plurality of RF units 20 as a reception operation. Since the baseband multi-carrier signal is a time domain signal, the baseband processing unit 22 converts the time domain signal to the frequency domain by FFT and performs adaptive array signal processing on the frequency domain signal. To do. Further, the baseband processing unit 22 executes timing synchronization, that is, FFT window setting, and also deletes the guard interval. Since a known technique may be used for timing synchronization and the like, description thereof is omitted here. The baseband processing unit 22 outputs the result of adaptive array signal processing to the modem unit 24. As a transmission operation, the baseband processing unit 22 receives a multi-carrier signal in the frequency domain from the modulation / demodulation unit 24 and performs dispersion processing using weight vectors.

  As a transmission operation, the baseband processing unit 22 converts the frequency domain signal to the time domain by IFFT on the frequency domain multicarrier signal input from the modem unit 24, and converts the converted time domain signal to the RF unit. 20 output. The baseband processing unit 22 also adds a guard interval, but the description is omitted here. Here, the frequency domain signal includes a plurality of subchannels as shown in FIG. 2B, and each of the subchannels includes a plurality of subcarriers as in the vertical direction of FIG. 2C. For the sake of clarity, it is assumed that the signals in the frequency domain are arranged in the order of subcarrier numbers to form a serial signal.

  The modem unit 24 performs demodulation on the multi-carrier signal in the frequency domain from the baseband processing unit 22 as reception processing. The multicarrier signal converted into the frequency domain has components corresponding to each of the plurality of subcarriers as shown in FIGS. Demodulation is performed in units of subcarriers. The modem unit 24 outputs the demodulated signal to the IF unit 26. Further, the modem unit 24 performs modulation as transmission processing. The modem unit 24 outputs the modulated signal to the baseband processing unit 22 as a multi-carrier signal in the frequency domain.

  The IF unit 26 receives the demodulation result from the modulation / demodulation unit 24 as a reception process, and separates the demodulation result for each terminal device 12. That is, the demodulation result is composed of a plurality of subchannels as shown in FIG. Therefore, when one subchannel is assigned to one terminal apparatus 12, the demodulation result includes signals from a plurality of terminal apparatuses 12. The IF unit 26 separates such a demodulation result for each terminal device 12. The IF unit 26 outputs the separated demodulation result to a wired network (not shown). At that time, the IF unit 26 performs transmission according to information for identifying the destination, for example, an IP (Internet Protocol) address.

  Further, the IF unit 26 inputs data for the plurality of terminal devices 12 from a wired network (not shown) as a transmission process. The IF unit 26 assigns data to subchannels and forms a multicarrier signal from a plurality of subchannels. That is, the IF unit 26 forms a multicarrier signal composed of a plurality of subchannels as shown in FIG. The subchannel to which data is to be assigned is determined in advance as shown in FIG. 2 (c), and an instruction related thereto is received from the radio control unit 28. The IF unit 26 outputs the multicarrier signal to the modem unit 24.

  The radio control unit 28 controls the operation of the base station device 10. The radio control unit 28 defines time slots formed by frequency multiplexing of a plurality of subchannels and frames formed by time multiplexing of a plurality of time slots, as shown in FIGS. . The radio resource allocation unit 38 notifies the control signal from the modem unit 24 via the RF unit 20. Here, the control signal includes information such as its own identification number and the number of empty subchannels. The control signal is assigned to a subchannel determined by a control channel determination unit 32 described later. The radio resource allocation unit 38 receives a subchannel allocation request from the terminal device 12 (not shown) from the RF unit 20 via the modem unit 24.

  The radio resource allocation unit 38 allocates a subchannel to the terminal device 12 that has received the allocation request. Here, the radio resource assignment unit 38 assigns the subchannels included in the uplink time slot and the downlink time slot to the terminal device 12. In particular, it is assumed that assignment of subchannels in uplink time slots and assignment of time slots in downlink time slots are made symmetrical. In each of the uplink time slot and the downlink time slot, the radio resource allocation unit 38 allocates at least two subchannels to the terminal device 12.

  Here, how to assign subchannels will be described. The radio resource allocation unit 38 determines at least two subchannels to be allocated to the terminal device 12 so that the number of time slots including at least two subchannels is reduced. To reduce the number of time slots means to make the number of time slots close to 1. That is, the radio resource allocation unit 38 identifies the number of subchannels to be allocated, and identifies a time slot having a larger number of free subchannels than the identified number. Also, the radio resource allocation unit 38 confirms the amount of interference in the empty subchannel of the identified time slot, and determines whether the empty subchannel can be allocated to the terminal device 12. If the allocation is possible, the radio resource allocation unit 38 allocates the empty subchannel to the terminal device 12. On the other hand, if assignment is not possible, the same processing is executed for another time slot, and subchannels to be assigned are determined so that the number of time slots is reduced.

  The radio resource allocation unit 38 may further allocate subchannels as follows. Here, among the at least two subchannels assigned to the terminal device 12, subchannels in which data that requires real-time performance beyond a predetermined threshold (hereinafter referred to as “real-time data”) are arranged, And sub-channels in which data that does not require real-time performance beyond a predetermined threshold (hereinafter referred to as “non-real-time data”) are included. Further, the radio resource allocation unit 38 determines at least two subchannels to be allocated to the terminal device 12 so that the number of time slots including subchannels in which real-time data is arranged is preferentially reduced. That is, the radio resource allocation unit 38 first executes the above-described processing on the real time data. Thereafter, similar processing is performed on the non-real time data based on the remaining subchannels. As a result, non-real time data is more likely to span multiple time slots compared to real time data. However, since the radio resource allocation unit 38 only needs to release the subchannel to which the non-real time data is allocated according to the subchannel allocation status by the other base station apparatus 10, the influence on the real time data can be reduced.

  Further, the radio resource allocation unit 38 transmits an allocation notification from the modem unit 24 to the terminal device 12 via the RF unit 20. The assignment notification includes information on the assigned subchannel and time slot. The radio resource assignment unit 38 causes the RF unit 20 to cause the modem unit 24 to execute communication with the terminal device 12 to which the subchannel is assigned. At that time, the radio resource allocation unit 38 performs time alignment on the terminal device 12. Since a known technique may be used for the time alignment process, a description thereof is omitted here.

  The control channel determination unit 32 assigns control signals to subchannels. Here, the control signal is a signal including information used for controlling communication with the terminal device 12 as described above. Such a control signal is more important than a data signal. The control channel determination unit 32 selects a control signal for a predetermined subchannel while referring to the storage unit 30. In addition, the control channel determination unit 32 notifies the radio resource allocation unit 38 of the selected subchannel. The radio resource allocation unit 38 allocates a subchannel to the control signal according to the notification from the control channel determination unit 32. The storage unit 30 stores information on subchannels assigned to the terminal device 12 and information on control channels in cooperation with the radio control unit 28.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it is realized by a program having a communication function loaded in the memory. Describes functional blocks realized by collaboration. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  FIG. 5 shows the configuration of the terminal device 12. The terminal device 12 includes an RF unit 50, a modem unit 52, an IF unit 54, a radio control unit 56, and a storage unit 58.

  Since the RF unit 50 and the modem unit 52 execute the same processing as the RF unit 20 and the modem unit 24, description thereof is omitted here. As reception processing, the IF unit 54 receives the demodulation result from the modem unit 52 and outputs the demodulation result to a display or a speaker (not shown). The IF unit 54 inputs data from a button or a microphone (not shown) as a transmission process. The IF unit 54 assigns data to the subchannel. The IF unit 26 outputs the multicarrier signal to the modem unit 52.

  The wireless control unit 56 controls the operation of the IF unit 54 from the RF unit 50. Before executing communication with the base station apparatus 10, the radio control unit 56 receives a control signal transmitted from each base station apparatus 10. The control signal is assigned to one subchannel of one time slot among a plurality of downlink time slots included in the superframe. Further, as described above, the control signal includes information such as the identification number of the base station apparatus 10 that has transmitted the control signal and the number of empty subchannels. The wireless control unit 56 stores the acquired information in the storage unit 58. The radio control unit 56 selects the base station apparatus 10 that should request subchannel allocation while referring to the storage unit 58. For example, the radio control unit 56 selects the base station apparatus 10 having a large number of free subchannels. The storage unit 58 also stores reception power when a control signal is received, and the radio control unit 56 may select the base station apparatus 10 corresponding to the control signal with large reception power.

  The radio control unit 56 transmits an allocation request to the selected base station apparatus 10 via the modem unit 52 and the RF unit 50. Further, the radio control unit 56 receives an assignment notification from the base station apparatus 10 via the RF unit 50 and the modem unit 52. Since the assignment notification includes information on the assigned time slot and subchannel, the radio control unit 56 performs communication operation from the RF unit 50 to the IF unit 54 in the assigned time slot and subchannel. Let it run. Note that the radio control unit 56 may communicate with each of the plurality of base station apparatuses 10 by assigning subchannels from each of the plurality of base station apparatuses 10. On the other hand, the radio control unit 56 may receive a rejection instead of the allocation notification. At that time, the radio control unit 56 selects another base station device 10 and transmits an allocation request to the selected another base station device 10.

  After the start of communication, the radio control unit 56 receives a time alignment instruction from the base station apparatus 10 via the RF unit 50 and the modem unit 52. The time alignment instruction is information such as “make the transmission timing earlier than the present” or “make the transmission timing 1 nsec earlier than the present”. The radio control unit 56 derives the transmission timing in accordance with the time alignment instruction. In addition, the radio control unit 56 instructs the modem unit 52 and the RF unit 50 to perform transmission at the derived transmission timing.

  FIGS. 6A to 6B show uplink transmission / reception timings in the communication system 100. FIG. FIG. 6A shows the configuration of the communication system 100 to be described. The communication system 100 includes a first base station apparatus 10a, a second base station apparatus 10b, and a terminal apparatus 12 that are collectively referred to as a base station apparatus 10. As illustrated, the base station apparatus 10 performs communication with the first base station apparatus 10a and the second base station apparatus 10b. Here, it is assumed that the terminal apparatus 12 is present at a position that is close to the first base station apparatus 10a and the second base station apparatus 10b at an equal interval, and that the distance between the both is close to some extent. For example, the service area formed by the first base station apparatus 10a and the service area formed by the second base station apparatus 10b have an overlapping part, and the terminal apparatus 12 exists in the overlapping part. Furthermore, the terminal device 12 shall not exist in the edge part of each service area.

  FIG. 6B shows the timing of the packet signal transmitted from the terminal apparatus 12 and the packet signal received by the base station apparatus 10 in the situation of FIG. The horizontal axis represents time. The top row shows a packet signal transmitted from the terminal device 12 to the first base station device 10a. Moreover, the lower part shows the packet signal received by the 1st base station apparatus 10a. Here, although a reception window is illustrated, the reception window corresponds to an uplink time slot including a subchannel assigned to the terminal device 12 in the base station device 10.

  As illustrated, the packet signal transmitted from the terminal apparatus 12 is received by the first base station apparatus 10a with a delay of “D1”. The received packet signal is contained in the reception window. The third row shows a packet signal transmitted from the terminal device 12 to the second base station device 10b. Moreover, the lower stage shows the packet signal received by the second base station apparatus 10b. As illustrated, the packet signal transmitted from the terminal apparatus 12 is received by the second base station apparatus 10b with a delay of “D2”. The received packet signal is contained in the reception window.

  FIGS. 7A to 7B show other transmission / reception timings of the uplink in the communication system 100. FIG. FIG. 7A shows a configuration of the communication system 100 in a situation different from that in FIG. In FIG. 7A, as illustrated, the terminal device 12 is located in the vicinity of the first base station device 10a, but the distance between the terminal device 12 and the second base station device 10b is the same as that of the terminal device 12 and the first base station. It is larger than the distance from the station apparatus 10a. FIG. 7B shows the timing of the packet signal transmitted from the terminal device 12 and the packet signal received by the base station device 10 in the situation of FIG. The configuration of FIG. 7B is the same as the configuration of FIG.

  The top row shows a packet signal transmitted from the terminal device 12 to the first base station device 10a. Moreover, the lower part shows the packet signal received by the 1st base station apparatus 10a. As illustrated, the packet signal transmitted from the terminal apparatus 12 is received by the first base station apparatus 10a with a delay of “D1 ′”. The received packet signal is contained in the reception window. On the other hand, the third row shows a packet signal transmitted from the terminal device 12 to the second base station device 10b. Moreover, the lower stage shows the packet signal received by the second base station apparatus 10b. As illustrated, the packet signal transmitted from the terminal apparatus 12 is received by the second base station apparatus 10b with a delay of “D2 ′”. The received packet signal does not fit in the reception window.

  That is, in communication, a delay occurs according to the distance. For this reason, if the transmission timings from the plurality of terminal apparatuses 12 to the base station apparatus 10 are the same, the reception timings at the base station apparatus 10 vary due to delay. As a result, the base station apparatus 10 cannot receive a signal with a large delay without error. In order to solve this, the second base station apparatus 10b outputs a time alignment instruction to the terminal apparatus 12 so as to advance the transmission timing. When receiving the instruction from the second base station apparatus 10b, the terminal apparatus 12 changes the transmission timing and transmits the next packet signal.

  FIGS. 8A to 8C show subchannels assigned by the base station apparatus 10. FIG. 8A shows the configuration of the uplink time slot in the frame. This is a combination of the uplink time slot in the frame shown in FIG. 2A and the subchannel shown in FIG. Unlike FIG. 2B, in order to simplify the drawing, it is assumed in FIG. 8 that eight subchannels are included in one time slot. In the eighth subchannel, control signals are arranged from the first uplink time slot to the fourth uplink time slot. Further, in the first uplink time slot and the second uplink time slot, the fifth subchannel to the seventh subchannel are assigned by the first base station apparatus 10a. On the other hand, the first base channel to the fourth subchannel of the first uplink time slot and the third subchannel to the fourth subchannel of the second uplink time slot are assigned by the second base station apparatus 10b.

  For this reason, the first uplink time slot and the second uplink time slot are assigned subchannels by the first base station apparatus 10a and the second base station apparatus 10b. If the first base station device 10a and the second base station device 10b are located away from the terminal device 12 as in the second base station device 10b of FIG. Receives time alignment instructions from the first base station apparatus 10a and the second base station apparatus 10b. As a result, the terminal device 12 does not know which instruction to follow. That is, when the terminal apparatus 12 communicates with a plurality of base station apparatuses 10, the transmission timing is the same if there are the same instructions from the plurality of base station apparatuses 10, but the transmission timings are different if there are different instructions. become. For example, the instructions are inconsistent such that one of the two instructions is an instruction to transmit later than the current transmission timing and the other is an instruction to transmit earlier than the current transmission timing. Therefore, the operation of the terminal device 12 cannot be determined uniquely.

  FIG. 8 (b) also shows the configuration of the uplink time slot in the frame, as in FIG. 8 (a). FIG. 8B shows a case where the radio resource assignment unit 38 of FIG. 4 assigns subchannels. As illustrated, the second subchannel to the seventh subchannel in the first uplink time slot are allocated by the first base station apparatus 10a, and the second subchannel to the seventh subchannel in the second uplink time slot are Allocation is performed by the second base station apparatus 10b. If the first base station device 10a and the second base station device 10b are located away from the terminal device 12 as in the second base station device 10b of FIG. Receives time alignment instructions from the first base station apparatus 10a and the second base station apparatus 10b. At that time, the terminal apparatus 12 follows the instruction from the first base station apparatus 10a in the first uplink time slot and follows the instruction from the second base station apparatus 10b in the second uplink time slot. As a result, the operation of the terminal device 12 is uniquely determined for each time slot.

  FIG.8 (c) shows the case where the subchannel is allocated only from the 1st base station apparatus 10a. “RT” in the figure corresponds to the aforementioned real-time data, and “NRT” corresponds to the aforementioned non-real-time data. As shown in the figure, RTs are arranged from the second subchannel to the sixth subchannel in the first uplink time slot, and NRT is assigned to the seventh subchannel extending from the first uplink time slot to the third uplink time slot. Has been placed. In such a situation, when the subchannel is allocated by another base station apparatus 10, the terminal apparatus 12 may release the NRT of the second uplink time slot and the third uplink time slot. As a result, a subchannel by another base station apparatus 10 is assigned to any one of the second uplink time slot to the fourth uplink time slot. Thus, even if the terminal device 12 releases the subchannel in which the NRT is arranged, the terminal device 12 does not release the subchannel in which the RT is arranged, so that the influence on the user can be reduced.

  The operation of the communication system 100 configured as above will be described. FIG. 9 is a sequence diagram showing an assignment procedure by the communication system 100. The terminal device 12 transmits an allocation request to the first base station device 10a (S10). The first base station apparatus 10a allocates a subchannel to the terminal apparatus 12 (S12), and transmits the result to the terminal apparatus 12 as an allocation notification (S14). The terminal device 12 transmits an allocation request to the second base station device 10b (S16). The second base station apparatus 10b allocates a subchannel to the terminal apparatus 12 (S18), and transmits the result to the terminal apparatus 12 as an allocation notification (S20). Through the above processing, the terminal apparatus 12 is assigned subchannels from the first base station apparatus 10a and the second base station apparatus 10b.

  FIG. 10 is a flowchart showing an allocation procedure by the base station apparatus 10. If the radio resource allocation unit 38 does not receive an allocation request (N in S50), the radio resource allocation unit 38 stands by. When an allocation request is received (Y in S50), if there is a subchannel that can be allocated in a specific time slot (Y in S52), the radio resource allocation unit 38 allocates a subchannel in the time slot (S54). ). On the other hand, if there is no subchannel that can be allocated in a specific time slot (N in S52), the radio resource allocation unit 38 allocates a subchannel in another time slot (S56). The radio resource allocation unit 38 transmits the allocated result as an allocation notification (S58).

  Hereinafter, the operation of the terminal device 12 will be described in more detail. Up to now, the base station apparatus 10 has assigned a plurality of subchannels to the terminal apparatus 12 so that the number of time slots is reduced. However, depending on the situation of empty subchannels, different subchannels included in one time slot may be assigned by different terminal apparatuses 12. At that time, the terminal apparatus 12 may receive different time alignment instructions from the plurality of base station apparatuses 10. Below, the process of the terminal device 12 in such a situation is demonstrated. Here, the configuration of the terminal device 12 is the same type as the configuration of FIG.

  The RF unit 50 and the modulation / demodulation unit 52 communicate with each of the plurality of base station devices 10 by allocating different subchannels included in one time slot from the plurality of base station devices 10. Here, it is assumed that the subchannels are assigned as shown in FIG. The radio control unit 56 receives a time alignment instruction from each of the plurality of base station apparatuses 10 via the RF unit 50 and the modem unit 52. The radio control unit 56 determines the transmission timing based on the received multiple time alignment instructions, and instructs the modem unit 52 and the RF unit 50 to perform transmission at the determined transmission timing. Here, the radio control unit 56 selects any one of a plurality of time alignment instructions, and determines the transmission timing based on the selected time alignment instructions. For example, the wireless control unit 56 selects the earliest transmission timing or the latest transmission timing among a plurality of time alignment instructions.

  FIG. 11 is a flowchart showing a transmission timing instruction procedure by the terminal device 12. When receiving a plurality of time alignment instructions (Y in S100), the wireless control unit 56 derives each transmission timing (S102). Further, the wireless control unit 56 selects the last transmission timing (S104). On the other hand, when a plurality of time alignment instructions are not received (N in S100), that is, when one time alignment instruction is received, the wireless control unit 56 determines the transmission timing based on the time alignment instruction. Derived (S106). The radio control unit 56 instructs the transmission / reception unit 52 and the RF unit 50 on the transmission timing (S108).

  Next, processing executed by the terminal apparatus 12 in a situation where the terminal apparatus 12 receives different time alignment instructions from the plurality of base station apparatuses 10 will be described. The radio control unit 56 receives a time alignment instruction from each of the plurality of base station apparatuses 10 via the RF unit 50 and the modem unit 52. The radio control unit 56 derives the transmission timing based on each of the received plurality of time alignment instructions. That is, the radio control unit 56 derives a plurality of transmission timings. In addition, the wireless control unit 56 determines one transmission timing by executing statistical processing such as averaging for a plurality of transmission timings. Further, the radio control unit 56 instructs the modem unit 52 and the RF unit 50 to perform transmission at the determined transmission timing.

  FIG. 12 is a flowchart illustrating another instruction procedure of transmission timing by the terminal device 12. When receiving a plurality of time alignment instructions (Y in S120), the wireless control unit 56 derives each transmission timing (S122). Further, the wireless control unit 56 determines the transmission timing by executing statistical processing based on each transmission timing (S124). On the other hand, when a plurality of time alignment instructions are not received (N in S120), that is, when one time alignment instruction is received, the wireless control unit 56 determines the transmission timing based on the time alignment instruction. Derived (S126). The radio control unit 56 instructs the transmission / reception unit 52 and the RF unit 50 on the transmission timing (S128).

  Next, processing executed by the terminal device 12 in a situation where the terminal device 12 receives different time alignment instructions from the plurality of base station devices 10 will be described. The radio control unit 56 receives a time alignment instruction from each of the plurality of base station apparatuses 10 via the RF unit 50 and the modem unit 52. The radio control unit 56 estimates the base station device 10 at a close position among the plurality of base station devices 10 with which the RF unit 50 and the modem unit 52 are communicating. Here, the estimation is performed based on the transmission rate used with each base station apparatus 10. The transmission rate is determined by, for example, a combination of a modulation scheme, a coding rate, and the like. Generally, the transmission rate becomes higher as the propagation environment is improved. In addition, the base station apparatus 10 located closer to each other has a better propagation environment.

  Therefore, the radio control unit 56 selects the base station device 10 having the highest transmission rate and estimates that the base station device 10 is closest. Note that the radio control unit 56 may select the base station apparatus 10 having the largest received power without using the transmission rate. The radio control unit 56 determines the transmission timing based on the estimated time alignment instruction from the base station apparatus 10. Further, the radio control unit 56 instructs the modem unit 52 and the RF unit 50 to perform transmission at the determined transmission timing.

  FIG. 13 is a flowchart showing yet another instruction procedure of the transmission timing by the terminal device 12. When receiving a plurality of time alignment instructions (Y in S140), the radio control unit 56 selects the base station apparatus 10 having a high transmission rate (S142). Further, the radio control unit 56 selects a time alignment instruction from the selected base station apparatus 10 (S144). Further, the wireless control unit 56 derives the transmission timing based on the selected time alignment instruction (S146). On the other hand, when a plurality of time alignment instructions are not received (N in S140), that is, when one time alignment instruction is received, the wireless control unit 56 determines the transmission timing based on the time alignment instruction. Derived (S148). The wireless control unit 56 instructs the modulation / demodulation unit 52 and the RF unit 50 on the transmission timing (S150).

  According to the embodiment of the present invention, since at least two subchannels to be allocated to the terminal device are determined so that the number of time slots including at least two subchannels is reduced, a predetermined time slot is determined in the terminal device. Can be reduced. In addition, since the number of base station devices to which a predetermined time slot is allocated in the terminal device is reduced, duplication of instructions can be avoided even when receiving time alignment instructions from a plurality of base station devices. In addition, since it is an instruction for another time slot, it is possible to reliably execute an instruction for time alignment to a terminal apparatus to which subchannels can be allocated from a plurality of base station apparatuses. Further, since real-time data is preferentially allocated to a predetermined time slot with respect to non-real-time data, the time slot to which real-time data is allocated can be easily used exclusively.

  In addition, since the time slot to which real-time data is allocated is exclusively used for a predetermined base station apparatus, it is possible to follow a time alignment instruction from the predetermined base station apparatus. Further, when a subchannel is allocated by another base station apparatus, the subchannel to which the non-real time data is allocated is released, so that the subchannel to which the real time data is allocated can be continuously used. Moreover, since the subchannel to which real-time data is allocated is continuously used, the influence on the user can be reduced.

  Even when a time alignment instruction is received from each of the plurality of base station apparatuses, any one is selected, so that the time alignment instruction can be reliably executed. Moreover, since the rear transmission timing is selected, the influence of interference can be reduced. In addition, since the transmission timing is determined by statistical processing, transmission timing suitable for each of the plurality of base station apparatuses can be used. In addition, since the base station apparatus existing in the close position is estimated and the instruction from the base station apparatus is followed, a line with a high transmission rate can be maintained.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

It is a figure which shows the structure of the communication system which concerns on the Example of this invention. It is a figure which shows the frame structure in the communication system of FIG. It is a figure which shows the frame structure in the communication system of FIG. It is a figure which shows the frame structure in the communication system of FIG. It is a figure which shows arrangement | positioning of the subchannel in the communication system of FIG. It is a figure which shows the structure of the base station apparatus of FIG. It is a figure which shows the structure of the terminal device of FIG. FIGS. 6A to 6B are diagrams illustrating transmission / reception timings of the uplink in the communication system of FIG. FIGS. 7A and 7B are diagrams showing other transmission / reception timings of the uplink in the communication system of FIG. It is a figure which shows the subchannel allocated by the base station apparatus of FIG. It is a figure which shows the subchannel allocated by the base station apparatus of FIG. It is a figure which shows the subchannel allocated by the base station apparatus of FIG. It is a sequence diagram which shows the allocation procedure by the communication system of FIG. It is a flowchart which shows the allocation procedure by the base station apparatus of FIG. It is a flowchart which shows the instruction | indication procedure of the transmission timing by the terminal device of FIG. It is a flowchart which shows another instruction | indication procedure of the transmission timing by the terminal device of FIG. 6 is a flowchart showing still another instruction procedure of transmission timing by the terminal device of FIG. 5.

Explanation of symbols

  10 base station devices, 12 terminal devices, 20 RF units, 22 baseband processing units, 24 modulation / demodulation units, 26 IF units, 28 radio control units, 30 storage units, 32 control channel determination units, 38 radio resource allocation units, 50 RF Unit, 52 modulation / demodulation unit, 54 IF unit, 56 radio control unit, 58 storage unit, 100 communication system.

Claims (3)

A base station apparatus that forms a frame by time multiplexing of a plurality of time slots while forming a time slot by frequency multiplexing of a plurality of subchannels,
An allocating unit that allocates at least two subchannels to the terminal device;
A communication unit that performs communication while performing time alignment for a terminal device that has allocated at least two subchannels in the allocation unit,
The at least two subchannels include a subchannel in which data requiring real-time property is arranged and a subchannel in which data not requiring real-time property is arranged,
The allocating unit determines at least two subchannels to be allocated to a terminal device so that the number of time slots including subchannels in which data requiring the real-time property is arranged is preferentially reduced. A characteristic base station apparatus. A time slot is formed by frequency multiplexing of a plurality of subchannels, a frame is formed by time multiplexing of a plurality of time slots, and at least two subchannels are allocated to a terminal device;
Performing communication while executing time alignment for a terminal device to which at least two subchannels are allocated, and
The at least two subchannels include a subchannel in which data requiring real-time property is arranged and a subchannel in which data not requiring real-time property is arranged,
The allocating step determines at least two subchannels to be allocated to the terminal apparatus so that the number of time slots including subchannels in which the data requiring the real-time property is arranged is preferentially reduced. A characteristic communication method. A time slot is formed by frequency multiplexing of a plurality of subchannels, a frame is formed by time multiplexing of a plurality of time slots, and at least two subchannels are allocated to a terminal device;
Performing communication while executing time alignment for a terminal device to which at least two subchannels are allocated, and
The at least two subchannels include a subchannel in which data requiring real-time property is arranged and a subchannel in which data not requiring real-time property is arranged,
The allocating step determines at least two subchannels to be allocated to the terminal apparatus so that the number of time slots including subchannels in which the data requiring the real-time property is arranged is preferentially reduced. A program to be executed by a computer.

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