Patent Description:
A cellular system includes a base station, which is provided in each cell to communicate with a terminal having communication functionality, such as a mobile phone, located in that cell. Such cellular system undergoes an increase in transmission capacity requirement with an increase in the number of users and with an increase in the complexity of content. A cellular system uses, as one method to increase the transmission capacity, a method that increases the total available bandwidth by means of a frequency reuse technique, in which neighboring base stations in cells subjected to strong interference from each other use different frequencies from each other, while base stations in cells subjected to sufficiently low interference from each other use the same frequency. In addition, consideration is made to a recent cellular system to use, additionally to the conventional frequency, a frequency band such as a millimeter wave that is higher than the conventional frequency to provide a wider frequency band. Moreover, consideration is also made to a cellular system that forms a cell using a narrow-band multi-beam configuration to increase the signal-to-noise ratio to communicate using multilevel transmission. Furthermore, a satellite communication system, which uses an artificial satellite operating in cosmic space, or the like, to allow communication between two points with a terminal on a ship or aircraft on the earth, utilizes a multi beam configuration, in which the artificial satellite reuses the same frequency or the same polarized wave in areas subjected to sufficiently low inter-beam interference during data transmission thus to increase the transmission capacity.

A cellular system and a satellite communication system can expect an increase in the data transmission capacity by use of a multi-beam configuration, which will improve the efficacy of frequency reuse. On the other hand, use of a multi-beam configuration requires transmitters provided in a base station, an artificial satellite, a relay station, and the like to simultaneously form multiple beams to be emitted to terminals, thereby increasing the numbers of frequency converters and of amplifiers in association with the multiple-beam emission. This presents a problem in increases in the weight, in the power consumption, and in cost. Non-Patent Literature <NUM> discloses a beam hopping technique that switches beams emitted to multiple locations in the time domain. A beam hopping technique is a technique that performs so-called time division emission, in which a group called cluster is formed using multiple beams covering the coverage area, and beams emitted to multiple locations are switched from one to another within the cluster in the time domain. Time division emission in a beam hopping technique is controlled with a period corresponding to a frame. In a beam hopping technique, a beam emitted changes from slot to slot, the slots being generated by division of a frame. That is, since the beams corresponding to one frame are emitted to one cluster during a control period, use of a beam hopping technique results in the number of beams simultaneously emitted to terminals by a transmitter being the same as the number of clusters. This can prevent increase in the numbers of frequency converters and of amplifiers in association with beam emission as compared to when all beams are simultaneously emitted to terminals.

Patent Literature <NUM> discloses a method and apparatus for operating one or more satellites in a non-geosynchronous orbit (NGSO) satellite constellation. The satellite may allocate a first frequency band to a first beam, and may allocate a second frequency band to a second beam. Then, if the first beam is disabled, the satellite may re-map the first frequency band from the first beam to the second beam.

Patent Literature <NUM> discloses a method and system for operating a multibeam satellite system involving positioning a plurality of service beams associated with a plurality of service beam coverage areas and positioning a feeder beam associated with a feeder beam coverage area. Each of the plurality of service beam coverage areas uses a color. The at least near service beam coverage area uses at least one color from the plurality of colors. The feeder beam uses at least one color, excluding the at least one color used by the at least one near service beam coverage area.

Patent Literature <NUM> discloses a method for determining beamforming weights used onboard a satellite and ground-based beamforming weights used in a ground-based station as part of a satellite communication system.

Patent Literature <NUM> discloses an intelligent digital beam former in conjunction with a satellite based array antenna providing a plurality of dynamically controllable antenna beams for communication with subscriber units on earth's surface. Interference is mitigated placing a null in the transmit and receive antenna patterns at the location of the interfering signal by adjusting digital beam forming coefficients.

Non-Patent Literature <NUM>: Digital Video Broadcasting (DVB), Implementation guidelines for the second generation system for Broadcasting, Interactive Services, News Gathering and other broadband satellite applications; Part <NUM> - S2 Extensions (DVB-S2X).

Patent Literature <NUM>: <CIT>; Patent Literature <NUM>: <CIT>; Patent Literature <NUM>: <CIT>; Patent Literature <NUM>: <CIT>.

However, the beam hopping technique described in Non-Patent Literature <NUM> switches the beams within a cluster in the time domain for emission. This limits the maximum value of the transmission capacity of each cluster to the transmission capacity when one beam is constantly emitted. If terminals are heterogeneously located within the coverage area of a transmitter, the traffic demands requested by the respective terminals may be imbalanced among clusters. In this case, a cluster having traffic demands greater than a maximum transmission capacity per cluster will suffer from a deficiency in slots to be assigned. In contrast, a cluster having traffic demands less than the maximum transmission capacity will have excess slots to be assigned. This will require as many beams as the traffic demands exceeding the maximum transmission capacity to be emitted in another control period even though a cluster exists that has excess slots to be assigned. This presents a problem in reductions in time efficiency and in use efficiency of frequency in association with data transmission.

The present invention has been made in view of the foregoing, and it is an object of the present invention to provide a relay station that limits or prevents a reduction in time efficiency and a reduction in use efficiency of frequency in association with data transmission.

The invention is set forth in the appended set of claims.

The present invention provides an advantage in being capable of limiting or preventing a reduction in time efficiency and a reduction in use efficiency of frequency in association with data transmission.

A relay station, a control station, a data transmission system, a data transmission method, a control circuit, and a recording medium according to examples of the disclosure referred to as embodiments will be described in detail below with reference to the drawings.

<FIG> is a diagram illustrating an example of configuration of a data transmission system according to a first embodiment. A data transmission system <NUM> is, for example, a cellular system or a satellite communication system. The data transmission system <NUM> includes a relay station <NUM>, a gateway <NUM>-<NUM>, a gateway <NUM>-<NUM>, and a control station <NUM>. In <FIG>, a dotted line indicates wireless communication, and a solid line indicates wired communication. The gateway <NUM>-<NUM> and the gateway <NUM>-<NUM> are connected to a public network <NUM> to provide a service of another communication system (not illustrated) outside the data transmission system <NUM> to terminals <NUM> through the Internet and through the relay station <NUM>. Note that if no service of another communication system is to be used, and communication will thus be complete within the data transmission system <NUM>, the gateway <NUM>-<NUM> and the gateway <NUM>-<NUM> do not need to be connected to the public network <NUM>. In addition, although <FIG> illustrates two gateways being installed, the number of the gateways is not limited to two, and multiple gateways may be installed for redundancy. The gateway <NUM>-<NUM> and the gateway <NUM>-<NUM> are each referred to as gateway <NUM> when no distinction needs to be made. The control station <NUM> controls beam hopping operation performed by the relay station <NUM>.

Emission areas <NUM>-<NUM> to <NUM>-p and emission areas <NUM>-<NUM> to <NUM>-q each represent an emission area, on the ground, of a beam that the relay station <NUM> can emit. The relay station <NUM> forms a cluster <NUM>-<NUM> including the emission areas <NUM>-<NUM> to <NUM>-p. Similarly, the relay station <NUM> forms a cluster <NUM>-<NUM> including the emission areas <NUM>-<NUM> to <NUM>-q. The emission areas <NUM>-<NUM> to <NUM>-p and the emission areas <NUM>-<NUM> to <NUM>-q are each referred to as emission area <NUM> when no distinction needs to be made. Note that the number of the emission areas <NUM> is not limited to the number illustrated as the emission areas <NUM>-<NUM> to <NUM>-p and the emission areas <NUM>-<NUM> to <NUM>-q. In addition, although the cluster <NUM>-<NUM> and the cluster <NUM>-<NUM> are illustrated in the present embodiment, the number of clusters is not limited to two. The cluster <NUM>-<NUM> and the cluster <NUM>-<NUM> are each referred to as cluster <NUM> when no distinction needs to be made.

A terminal <NUM>-<NUM> is located in the emission area <NUM>-<NUM>, and the relay station <NUM> emits a beam onto the emission area <NUM>-<NUM> to transmit data to the terminal <NUM>-<NUM>. Similarly, a terminal <NUM>-r is located in the emission area <NUM>-p, and the relay station <NUM> emits a beam onto the emission area <NUM>-p to transmit data to the terminal <NUM>-r. The terminals <NUM>-<NUM> to <NUM>-r are each referred to as terminal <NUM> when no distinction needs to be made. Note that <FIG> illustrates the emission area <NUM>-<NUM> as including the terminal <NUM>-<NUM> only, but the emission area <NUM>-<NUM> may include multiple terminals <NUM>. Note that in a case in which the data transmission system <NUM> is a cellular system, a device including both the relay station <NUM> and the control station <NUM> is called base station. In addition, in a case in which the data transmission system <NUM> is a satellite communication system, the relay station <NUM> will be a repeater installed in an artificial satellite.

<FIG> is a diagram illustrating a frame according to the first embodiment. The present embodiment is described on an assumption that one frame includes ten slots. Note that the number of slots in one frame is not limited to ten in the present embodiment. The time division emission to each of the clusters <NUM> in a beam hopping technique is controlled with a period corresponding to the frame illustrated in <FIG>. In addition, the relay station <NUM> changes the emission area <NUM> to irradiate at every slot generated by division of the frame.

An operation of the relay station <NUM> and the control station <NUM> according to the present embodiment will now be described. Note that the gateway <NUM> and the terminal <NUM> have no particular features in the present embodiment, and such features are conceivable to persons skilled in the art. Detailed description of the configuration thereof will therefore be omitted. <FIG> is a diagram illustrating functional blocks of the relay station <NUM> according to the first embodiment. The relay station <NUM> includes a reception unit <NUM>, a switching unit <NUM>, a beam formation unit <NUM>, a transmission unit <NUM>, and a control unit <NUM>. The reception unit <NUM> receives data transmitted by the gateway <NUM>. The switching unit <NUM> assigns the slots generated by division of a frame to the emission areas <NUM>. The beam formation unit <NUM> forms the emission areas <NUM> and the clusters <NUM>. The transmission unit <NUM> transmits data to the terminal <NUM>. A detailed operation of these functional units will be described later herein.

<FIG> is a diagram illustrating functional blocks of the control unit <NUM> according to the first embodiment. The control unit <NUM> includes a first transmission-reception unit <NUM>, a first storage unit <NUM>, a first time management unit <NUM>, a switching control unit <NUM>, and a beam formation control unit <NUM>. The first transmission-reception unit <NUM> receives data transmitted by the control station <NUM>, and transmits the data to the first storage unit <NUM>. The first storage unit <NUM> stores the data transmitted by the first transmission-reception unit <NUM>. The first time management unit <NUM> synchronizes the time with the control station <NUM>. The switching control unit <NUM> generates data needed by the switching unit <NUM> to assign the slots to the emission areas <NUM>. The beam formation control unit <NUM> generates data needed by the beam formation unit <NUM> to form the emission areas <NUM>. A detailed operation of these functional units will be described later herein.

<FIG> is a diagram illustrating functional blocks of the control station <NUM> according to the first embodiment. The control station <NUM> includes a second transmission-reception unit <NUM>, a second storage unit <NUM>, a second time management unit <NUM>, a line quality monitoring unit <NUM>, a traffic monitoring unit <NUM>, a resource control unit <NUM>, and a cluster control unit <NUM>. The second transmission-reception unit <NUM> receives data from the gateway <NUM>, and transmits the data received to the second storage unit <NUM>. The second storage unit <NUM> stores the data transmitted by the second transmission-reception unit <NUM>. The second transmission-reception unit <NUM> also transmits data needed for control of the relay station <NUM> to the relay station <NUM>. The second transmission-reception unit <NUM> is also referred to as transmission-reception unit. The second time management unit <NUM> synchronizes the time with the relay station <NUM>. The line quality monitoring unit <NUM> monitors line quality of the lines for communication used by the terminals <NUM>. The traffic monitoring unit <NUM> monitors the traffic amounts requested by the terminals <NUM>. The resource control unit <NUM> adds up the requested numbers of slots of the respective emission areas <NUM>. The cluster control unit <NUM> changes the combination of the emission areas <NUM> that constitute the cluster <NUM>. A detailed operation of these functional units will be described later herein.

The reception unit <NUM>, the switching unit <NUM>, the beam formation unit <NUM>, the transmission unit <NUM>, the control unit <NUM>, the second transmission-reception unit <NUM>, the second storage unit <NUM>, the second time management unit <NUM>, the line quality monitoring unit <NUM>, the traffic monitoring unit <NUM>, the resource control unit <NUM>, and the cluster control unit <NUM> according to the first embodiment are implemented in a processing circuitry that is an electronic circuit for performing corresponding processes.

This processing circuitry may be a dedicated hardware element or a control circuit including a memory and a central processing unit (CPU) that executes a program stored in the memory. As used herein, the term memory means, for example, a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read-only memory (ROM), or a flash memory; a magnetic disk, an optical disk, or the like. In a case in which this processing circuitry is a control circuit including a CPU, this control circuit is, for example, a control circuit <NUM> configured as illustrated in <FIG>.

As illustrated in <FIG>, the control circuit <NUM> includes a processor 300a, which is the CPU, and a memory 300b. In the case of implementation in the control circuit <NUM> illustrated in <FIG>, functionality is implemented by the processor 300a by reading and executing a program corresponding to an intended process stored in the memory 300b. The memory 300b is also used as a temporary memory during processes performed by the processor 300a.

An operation of the relay station <NUM> and the control station <NUM> will now be described in detail. <FIG> is a diagram illustrating an example arrangement of the emission areas <NUM> covered by the relay station <NUM> according to the first embodiment. The chart of <FIG> uses the vertical axis as representing an x-direction and the horizontal axis as representing a y-direction. The emission areas <NUM> are assigned indices. For example, the emission area at the bottom left corner in <FIG> is assigned an index of <NUM>-<NUM>. In addition, the left-side value and the right-side value of the index assigned to an emission area <NUM> are respectively referred to as x value and y value. The x value decreases in the positive x-direction, and the y value increases in the positive y-direction. For example, the emission area at the bottom left corner in <FIG> has an x value of <NUM>, and a y value of <NUM>.

Formation of the clusters <NUM> each using the emission areas <NUM> results in a coverage area of the data transmission system <NUM> having a planar arrangement, i.e., an arrangement extending in two independent directions. In such arrangement, emission of beams to respective neighboring emission areas <NUM> at the same time, at the same frequency, or using the same polarized wave will cause the beams to interfere with each other. Accordingly, the resource control unit <NUM> assigns the beams such that the polarized wave of the beam emitted to an emission area <NUM> having an odd-numbered x value and the polarized wave of the beam emitted to an emission area <NUM> having an even-numbered x value, of the indices assigned to the emission areas <NUM>, are perpendicular to each other. Note that the term polarized wave includes a linearly polarized wave and a circularly polarized wave. Alternatively, the resource control unit <NUM> assigns beams having different frequencies respectively to an emission area <NUM> assigned an odd-numbered x value and to an emission area <NUM> assigned an even-numbered x value. Assignment of different polarized waves or different frequencies to beams emitted to respective emission areas <NUM> depending on the x value as described above results in a combination of beams having the same frequency or having the same polarized wave arranged only in the y-direction. Accordingly, by use of time division emission using a beam hopping technique, the irradiated location that will cause interference between multiple beams at a level of a certain value or lower can be determined only along a line in the y-direction, that is, one-dimensionally. Then, the beam formation unit <NUM> emits a beam having a polarized wave and a frequency assigned by the resource control unit <NUM> to the terminal <NUM>.

<FIG> is a diagram illustrating an example of relationships between the emission areas <NUM> and the clusters <NUM> according to the first embodiment. One emission area <NUM> belongs to multiple ones of the clusters <NUM>. <FIG> illustrates the emission areas <NUM> as emission areas B1 to B16. <FIG> also illustrates that there are clusters C1 to C3, and the clusters <NUM> are formed to each include eight of the emission areas <NUM>. The emission areas B1 to B8 belong to the cluster C1. The emission areas B5 to B12 belong to the cluster C2. The emission areas B9 to B16 belong to the cluster C3. That is, the emission areas B5 to B8 belong to two clusters: the cluster C1 and the cluster C2; and the emission areas B9 to B12 belong to two clusters: the cluster C2 and the cluster C3. Note that <FIG> illustrates the clusters <NUM> as being configured such that the same number of emission areas <NUM> belong to each of the clusters <NUM>, and the same number of emission areas <NUM> redundantly belong to each of the clusters <NUM>, but this is merely an example. The numbers of the emission areas <NUM> belonging to the respective clusters <NUM>, or the numbers of the emission areas <NUM> belonging redundantly to the respective clusters <NUM>, may differ by each cluster <NUM>. In addition, a distance w1 represents the distance between emission areas <NUM>. The present embodiment assumes that the distance w1 between emission areas <NUM> is a fixed distance that inhibits mutual overlapping of the emission areas <NUM>. Note that although <FIG> illustrates a case in which the emission areas B1 to B16 are linearly arranged, but the arrangement is not limited thereto. The emission areas B1 to B16 may also be linearly arranged along a curved line to form the clusters <NUM>.

<FIG> is a diagram illustrating an example of locations of the terminals <NUM> and the beam patterns according to the first embodiment. In <FIG>, a location <NUM> and a location <NUM> represent the locations of the respective terminals <NUM>. A beam pattern <NUM> and a beam pattern <NUM> represent the beam patterns of the respective beams emitted by the relay station <NUM>. In addition, a coordinate point <NUM> and a coordinate point <NUM> represent the center coordinate points of the respective emission areas <NUM>. The present embodiment assumes that the relay station <NUM> emits a beam limitedly to the center coordinate point of each of the emission areas <NUM>.

<FIG> is a diagram illustrating an example of slot assignment according to the first embodiment. <FIG> illustrates an example of slot assignment for the configuration of the clusters <NUM> illustrated in <FIG>. <FIG> includes the beam number, the requested number of slots of each beam, the cluster number, the requested number of slots of each cluster, and the number of slots assigned to each beam. One frame is assumed to include ten slots similarly to the frame illustrated in <FIG>. The beam numbers are similar to the numbers of the emission areas B1 to B16 illustrated in <FIG>. The cluster numbers are similar to the numbers of the clusters C1 to C3 illustrated in <FIG>. In addition, one cluster is assigned one frame, i.e., ten slots, illustrated in <FIG> per control period. The requested number of slots of each beam represents the number of slots requested by the terminal(s) <NUM> located in that emission area <NUM>. For example, the number of slots requested by the terminal(s) <NUM> located in the emission area B1 is <NUM>, and the number of slots requested by the terminal(s) <NUM> located in the emission area B5 is <NUM>. The number of slots requested by the terminal(s) <NUM> is calculated based on the traffic amount requested by the terminal(s) <NUM>. The requested number of slots of each cluster represents the sum of the requested numbers of slots of the respective emission areas <NUM> for each of the clusters <NUM>. The number of slots assigned to each beam represents the number of slots assigned by the control station <NUM> with respect to the requested number of slots of each beam. As illustrated in <FIG>, the cluster C2 includes the emission areas B5 to B12 belonging to either the cluster C1 or the cluster C3. Thus, when the requested number of slots of the cluster C1 is greater than <NUM>, assignment of as many slots as the number of deficient slots for the cluster C1 to the emission areas B5 to B8 belonging to the cluster C2 can compensate the deficiency of slots to be assigned to the cluster C1.

<FIG> is a flowchart illustrating an example control operation of the control station <NUM> according to the first embodiment. The control station <NUM> provides control based on the flowchart illustrated in <FIG> in a per slot basis to determine which slot is to be assigned to which emission area <NUM>, and informs the relay station <NUM> of the result. Note that the control station <NUM> may provide the control based on the flowchart illustrated in <FIG> on a per frame basis to determine slot assignment, and inform the relay station <NUM> of the result.

The second transmission-reception unit <NUM> receives control information from a gateway <NUM>, and stores the control information in the second storage unit <NUM>. The control information is information needed for calculation of the requested number of slots of the emission area <NUM>, and specifically includes the traffic amount requested by each of the terminals <NUM> and the line quality during communication between that terminal <NUM> and the gateway <NUM> through the relay station <NUM>. The traffic monitoring unit <NUM> regularly adds up the traffic demand requested by a terminal <NUM> stored in the second storage unit <NUM>, and performs operation such as averaging of the added-up traffic demand. The line quality monitoring unit <NUM> regularly adds up the line quality associated with a terminal <NUM> stored in the second storage unit <NUM>, and performs operation such as averaging of the added-up line quality. The resource control unit <NUM> calculates the number of slots needed by the terminal <NUM> to transmit data based on the traffic demand and on the line quality, and sums up the required numbers of slots of the respective terminals <NUM> located in each of the emission areas <NUM>, thus to calculate the requested number of slots for each of the emission areas <NUM> (step S1).

The resource control unit <NUM> sums up the requested numbers of slots of the respective emission areas <NUM> on a per cluster <NUM> basis to calculate the requested number of slots of each of the clusters <NUM> (step S2). Note that the combination of the emission areas <NUM> that form each of the clusters <NUM> follows a predetermined rule as illustrated in <FIG>. In addition, the combination of the emission areas <NUM> that form each of the clusters <NUM> may be modified by the cluster control unit <NUM>. For example, when the data transmission system <NUM> changes the coverage area currently in operation, there may be a change in the location to be irradiated with a beam, and therefore the configuration of the clusters <NUM> is then changed to compensate for the change in the locations to be irradiated with the beams. After the calculation of the requested number of slots of each of the clusters <NUM>, the resource control unit <NUM> determines a priority order of the clusters <NUM> for performing slot assignment determination (step S3). Slot assignment determination, as used herein, is an operation of determining whether a beam is allowed to be emitted to an emission area <NUM> that is a candidate for slot assignment. Examples of the method of determining a priority order include to sort the clusters <NUM> in a descending order of the requested number of slots of each of the clusters <NUM> and to set the result of the sorting as the priority order for the slot assignment determination. By use of the descending order of the requested number of slots of each of the clusters <NUM> as the priority order, a reduction can be achieved in the probability of occurrence of deficiency in assignment of slots to a cluster <NUM>. The resource control unit <NUM> determines a priority order of the emission areas <NUM> belonging to each of the clusters <NUM> (step S4). For example, one example is that the resource control unit <NUM> sorts the requested numbers of slots of the respective emission areas <NUM> in a descending order and sets the result of the sorting as the priority order for the slot assignment determination. By use of the descending order of the requested number of slots of each of the emission areas <NUM> as the priority order, a reduction can be achieved in the probability of occurrence of deficiency in assignment of slots to an emission area <NUM>. Thus, the priority orders are determined for performing the slot assignment determination on a per cluster <NUM> basis and on a per emission area <NUM> basis.

After the determination of the priority orders on a per cluster <NUM> basis and on a per emission area <NUM> basis, the resource control unit <NUM> performs the slot assignment determination on the emission area <NUM> assigned high priority (step S5). In a case in which an emission area <NUM> is neighboring to another emission area <NUM> that belongs to another cluster <NUM> and is already assigned to the same slot, a beam will be emitted to that neighboring emission area <NUM> at the same time and at the same frequency. This will increase interference between beams in these emission areas <NUM>. The resource control unit <NUM> therefore determines not to assign the slot to this emission area <NUM>. In this case, slot assignment determination is performed using the emission area <NUM> assigned next higher priority as the candidate for assignment. If it is determined that the slot can be assigned, then assignment determination is performed on an emission area <NUM> belonging to the next higher priority cluster <NUM>. When assignment determination has been performed on all the clusters <NUM>, the process is terminated. The information indicating which slot is to be assigned to which emission area <NUM> determined in the slot assignment determination is referred to herein as slot assignment information.

After the determination of which emission area <NUM> is to be assigned to which slot(s), the control station <NUM> informs the relay station <NUM> of control information including the slot assignment information. Upon reception of the control information by the first transmission-reception unit <NUM>, the control unit <NUM> stores the control information in the first storage unit <NUM>. In addition, the switching control unit <NUM> generates, based on the slot assignment information, information for use by the switching unit <NUM> to assign the slots to the emission areas <NUM> irradiated with beams, and transmits this information to the switching unit <NUM>. Moreover, the beam formation control unit <NUM> generates information for use by the beam formation unit <NUM> to form the beams, and informs this information to the beam formation unit <NUM>. In this operation, in a case in which the switching unit <NUM> is a channelizer, the information generated by the switching control unit <NUM> is switching information for controlling the switching unit of the channelizer. Moreover, the information generated by the beam formation control unit <NUM> may be determined depending on the means for forming a beam. Examples of the means for forming a beam include means for forming a beam using a single feed, means for forming a beam using multiple feeds, means using an analog phased array, and means using digital beam forming.

Note that, in the present embodiment, the emission areas <NUM> irradiated with beams are switched on a per slot basis, thereby requiring the gateways <NUM>, the relay station <NUM>, and the terminals <NUM> to be synchronized with the time of the control station <NUM> to transmit data based on the slot assignment information determined by the control station <NUM>. To this end, the control unit <NUM> includes the first time management unit <NUM>, and the control station <NUM> includes the second time management unit <NUM>. The method of time management may be performed, for example, such that the control station <NUM>, the relay station <NUM>, the gateways <NUM>, and the terminals <NUM> each receive a signal from a satellite positioning system for time keeping, or such that the control station <NUM> and the relay station <NUM> synchronize with each other, and the relay station <NUM> transmits a notification signal including time information to the gateways <NUM> and to the terminals <NUM> to synchronize the time.

As described above, the data transmission system <NUM> according to the present embodiment allows one emission area <NUM> to belong to multiple ones of the clusters <NUM> during the process of data transmission by a terminal <NUM> through the relay station <NUM>, in which the control station <NUM> determines which emission area <NUM> is irradiated using which slot(s) on a per cluster <NUM> basis, thereby enabling data to be transmitted from multiple ones of the clusters <NUM> to any one of the emission areas <NUM>. Accordingly, beams are emitted on a per cluster <NUM> basis, and at the same time, when the slots are deficient in a certain one of the clusters <NUM>, an emission area <NUM> belonging to multiple ones of the clusters <NUM> can be assigned as many slots as the number of deficient slots. This enables the present embodiment to prevent increase in the numbers of frequency converters and of amplifiers in association with beam emission, of the relay station <NUM> while a desired number of slots can be assigned to each of the emission areas <NUM>. This can in turn limit or prevent a reduction in time efficiency and a reduction in use efficiency of frequency in association with data transmission, of the relay station <NUM>.

The first embodiment has been described in which one emission area <NUM> belongs to multiple ones of the clusters <NUM>, and the control station <NUM> determines which emission area <NUM> is irradiated using which slot(s) on a per cluster <NUM> basis, thereby enabling data to be transmitted from multiple ones of the clusters <NUM> to any one of the emission areas <NUM>. However, the relay station <NUM> according to the first embodiment emits a beam to the emission area <NUM>, specifically to a location that is selected, from a fixed arrangement, to inhibit multiple beams to overlap each other. This limits the location irradiated with a beam. This results in a lower signal to interference and noise power ratio (SINR) of a beam emitted by the relay station <NUM> when the terminal <NUM> is located at the boundary between one emission area <NUM> and another emission area <NUM> than when the terminal <NUM> is located in the center of an emission area <NUM>. This requires the relay station <NUM> to use, during modulation of a signal, a transmission scheme that provides lower line quality to reduce the code rate, which will in turn cause a reduction in frequency use efficiency. In the present embodiment, the coordinate point to be irradiated with a beam is segmented, and the center coordinate point to be irradiated with the beam is determined to maximize the system throughput based on information such as the location of the terminal <NUM>, thereby to improve the frequency use efficiency.

A data transmission system 10a according to a second embodiment includes a control station 103a in place of the control station <NUM> of the data transmission system <NUM>. In addition, the control station 103a includes a resource control unit 166a in place of the resource control unit <NUM>. The other part of the configuration is similar to the configuration of the data transmission system <NUM>. Note that components having the same functionality in the present embodiment as the components of the first embodiment are designated by the same reference characters as the first embodiment, and duplicate description thereof will be omitted. A graphical illustration of the data transmission system 10a will also be omitted. In the present embodiment, the resource control unit 166a determines the location to be irradiated with each beam in each slot differently from the first embodiment.

<FIG> is a diagram illustrating an example of locational relationships between the clusters <NUM> and the emission areas <NUM> according to the second embodiment. As illustrated in <FIG>, the present embodiment uses a distance w2 to represent the distance between the emission areas <NUM> in smaller segmentation than when the distance w1 is used in the first embodiment. That is, the number of candidates for the location to be irradiated with a beam illustrated in <FIG> is <NUM>, which is the same as the number of beams for the cluster <NUM>; but in <FIG>, the number of candidates for the location to be irradiated with a beam can be increased depending on the value of the width of the distance w2. Note that the granularity of the distance w2 depends on accuracy of formation of the emission areas <NUM> by the beam formation unit <NUM>. In this regard, digital beam forming can provide beam forming with high accuracy.

An advantage of segmentation of the location to be irradiated with a beam will next be described. <FIG> is a diagram illustrating an example of locations of the terminals <NUM> and the beam patterns according to the second embodiment. In <FIG>, the location to be irradiated with a beam is limited to the center coordinate point of a beam, thereby preventing the terminal <NUM> located at the location <NUM> from receiving data at a maximum SINR of the beam. This reduces the power received by the terminal <NUM>, thereby causing the terminal <NUM> to communicate using a modulation scheme and a code rate that provide relatively low line quality. This reduces frequency use efficiency of the terminal <NUM>. In the present embodiment, the resource control unit 166a segments the location to be irradiated with a beam with granularity of the distance w2 as illustrated in <FIG>, and can thus select a coordinate point <NUM> and a coordinate point <NUM>, which are each the center coordinate point of a beam where the terminal <NUM> can receive data at a maximum SINR of the beam at the location <NUM> and at the location <NUM>. Thus, the present embodiment can improve the power received by the terminal <NUM> located at the location <NUM>, and increase the frequency use efficiency of the terminal <NUM>.

<FIG> is a diagram illustrating another example of locations of the terminals <NUM> and the beam patterns according to the second embodiment. The resource control unit 166a determines, as illustrated in <FIG>, a coordinate point <NUM> of the center of a beam to match the null point of the beam pattern <NUM> with the location <NUM> where the beam pattern <NUM> has the maximum SINR. The term null point refers to a point where the gain of a beam is low. This indeed results in a certain amount of reduction in the SINR of the beam pattern <NUM> at the location <NUM>, but can significantly reduce interference between the beam pattern <NUM> and the beam pattern <NUM> at the location <NUM>. Note that although <FIG> illustrates the beam pattern <NUM> and the beam pattern <NUM> as having the same beam pattern, the beam pattern <NUM> may have a different profile as long as the null point matches with the location <NUM> where the beam pattern <NUM> has the maximum SINR. In this case, such configuration can be achieved by informing the relay station <NUM> from the control station 103a of the location to be irradiated with the beam and the location of the null point to allow the beam formation unit <NUM> of the relay station <NUM> to form the beam to direct the null point to the specified location. In addition, the second transmission-reception unit <NUM> transmits the center coordinate point and the null point determined by the resource control unit 166a to the relay station <NUM>.

An operation of the control station 103a will now be described. <FIG> is a flowchart illustrating an example control operation of the control station 103a according to the second embodiment. In the first embodiment, the resource control unit <NUM> calculates the requested number of slots of each of the emission areas <NUM>, while in the present embodiment, the resource control unit 166a calculates the requested number of slots at each beam location (step S11). As used here, the term beam location refers to a location given in units of the distance w2, which is the resolution of the center coordinate point of each of the emission areas <NUM> illustrated in <FIG>. In the example of <FIG>, it is the sum of the requested numbers of slots of the respective terminals <NUM> located in each of the approximate quarters generated by division of the emission area <NUM>. The resource control unit 166a calculates the sum of the requested numbers of slots at the respective beam locations of each of the clusters <NUM> (step S12), and determines a priority order of each of the clusters <NUM> for the slot assignment determination similarly to the first embodiment (step S13). The resource control unit 166a determines a priority order of the beam locations in each of the clusters <NUM> (step S14). The resource control unit 166a performs the slot assignment determination on a beam location that is the candidate for assignment based on the priority order (step S15). Note with respect to the slot assignment determination that in the first embodiment, the determination can be made based on whether the slot has already been assigned to the neighboring emission area <NUM>; in the present embodiment, however, due to the segmentation of the location to be irradiated with a beam, the resource control unit 166a estimates the amount of interference between beams based on the beam pattern and on the distance from the emission area <NUM> that has a slot already assigned thereto, and thereafter determines the slot assignment to achieve the highest line quality, that is, the maximum SINR.

<FIG> is a diagram illustrating an example of beam locations according to the second embodiment. The second embodiment has been described in which the beam locations are determined one-dimensionally using the distance w2 as illustrated in <FIG>, but as illustrated in <FIG>, the beam locations may be determined two-dimensionally using the distance w2 and a distance w3. In the two-dimensional determination, use of different polarized waves for the emission area <NUM>-<NUM> and for the emission area <NUM>-<NUM> for transmission, or use of different frequencies for the emission area <NUM>-<NUM> and for the emission area <NUM>-<NUM> for transmission prevents interference between the emission areas <NUM> even when the center location of one of the emission areas <NUM> is changed.

<FIG> is a diagram illustrating another example of beam locations according to the second embodiment. As illustrated in <FIG>, multiple beams may be emitted to the same coordinate point simultaneously. For example, multiplex transmission of a beam to the emission area <NUM>-<NUM> and to the emission area <NUM>-<NUM> using different polarized waves enables data to be transmitted to a terminal <NUM> with a double transmission capacity.

As described above, in the present embodiment, the control station 103a segments the center coordinate point to be irradiated with the beam, and determines the center coordinate point to maximize the system throughput based on information such as the location of the terminal <NUM>. This enables the frequency use efficiency to be improved as compared to when the center coordinate point is limited, and in turn, can limit or prevent a reduction in time efficiency and a reduction in use efficiency of frequency in association with data transmission.

The configurations described in the foregoing embodiments are merely examples of various aspects of the present invention.

Claim 1:
A control station (103a) for controlling a relay station (<NUM>), wherein the control station comprises:
a resource control unit (166a) to perform assignment of a polarized wave and a frequency of a beam to be emitted by the relay station (<NUM>), the resource control unit further configured to make a determination of assignment information indicating which slot is assigned to which one of a plurality of emission areas (<NUM>) for each of a plurality of clusters (<NUM>) to be formed by the relay station, each cluster to be formed from two or more of the emission areas (<NUM>), wherein one of the emission areas (<NUM>) belongs to multiple ones of the clusters (<NUM>); and
a transmission-reception (<NUM>) unit to transmit, to the relay station (<NUM>), the assignment information as well as a center coordinate point to be irradiated with the beam and a null point of a beam pattern of the beam,
characterized in that the resource control unit (166a) is configured to
calculate a requested number of slots for each of a plurality of beam locations, wherein beam location refers to a location of the center coordinate point given in units of a distance equal to a resolution of the center coordinate point of each of the emission areas (<NUM>),
calculate the requested number of slots, as the sum of the requested numbers of slots at the respective beam locations, of each of the clusters (<NUM>),
determine a priority order of the clusters (<NUM>) by sorting the clusters (<NUM>) in a descending order of the requested number of slots of each of the clusters (<NUM>),
determine a priority order of the beam locations belonging to each of the clusters (<NUM>) by sorting the requested number of slots for each of the beam locations in a descending order, and
determine the assignment information by performing slot assignment determination based on the priority order of the clusters (<NUM>) and the priority order of the beam locations for each of the clusters (<NUM>), wherein, for a beam location that is a candidate for assignment, the resource control unit (166a) estimates the amount of interference between beams based on the beam pattern and on the distance from an emission area (<NUM>) that has a slot already assigned thereto, and thereafter determines slot assignment to achieve a maximum signal to interference and noise power ratio (SINR).