JP2013176008A - Communication system, base station, mobile station, and communication control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system, base station, mobile station, and communication control method that achieve beam forming by the mobile station.SOLUTION: A communication system 100 according to the invention is a communication system 100 employing a TDD system. The communication system 100 comprises a base station 101 and a mobile station 103 for performing radio communication with the base station 101 by use of an adaptive array system. The base station 101 allocates usage uplink radio resources which the mobile station 103 uses for uplink communication with the station 101 to the mobile station 103, and allocates radio resources of which at least part of a frequency band is common to the usage uplink radio resources to the mobile station 103 as reference signal downlink radio resources which the station 101 uses for transmission of a reference signal. When the mobile station 103 receives the reference signal from the base station 101, it performs beam forming by use of the received reference signal when it transmits a radio signal by use of the usage uplink radio resources.

Description

  The present invention relates to a communication system, a base station, a mobile station, and a communication control method.

  LTE (Long Term Evolution) systems, XGP (eXtended Global Platform) systems, and the like are attracting attention as next-generation communication systems that realize improved communication performance.

  Conventionally, various techniques for improving communication services in the LTE system have been proposed (see, for example, Patent Document 1). In the base station described in Patent Document 1, scheduler, line termination, and channel encoding / decoding are processed in a time division manner by the same device. As a result, the processing load is made uniform at various data rates and sector configurations, and the processing capability of the device is utilized to the maximum. Therefore, the reduction in the number of parts and the high flexibility of operation are achieved.

  Also, in an XGP system that employs TDD (Time Divisional Duplex), a base station that implements an adaptive array antenna including a plurality of antennas is known in order to improve communication quality (for example, patents). Reference 2). An AAS (Adaptive Antenna System) function using an adaptive array antenna enables communication on a wireless channel where strong interference is expected.

  The AAS function is to calculate an antenna weight and perform beam forming or null steering using the calculated antenna weight. Beam forming is a function of concentrating radio waves of a base station on a transmission destination, that is, directing a beam. Null steering is a function of directing a directivity valley (null) in the direction of the interference station so that the radio wave does not fly in the direction in which the interference station exists and does not receive the radio wave from that direction. That is, the base station directs a null to a certain interfering station and directs a beam to the desired mobile station, thereby allocating the radio channel used by the interfering station to the desired mobile station and communicating with the desired mobile station. be able to.

JP 2008-99079 A JP 2007-318670 A

  Since it has been proposed to adopt the TDD scheme (TD-LTE system) not only for the XGP system but also for the LTE system, it is assumed that the AAS function is also used in the system. In this case, the base station receives beam forming and null steering by receiving SRS (Sounding Reference Signal) from the mobile station.

  However, since it is not assumed that the mobile station uses the AAS function, the base station does not transmit a signal corresponding to SRS to the mobile station. Therefore, the mobile station in the TD-LTE system cannot perform beam forming, which is one of AAS functions.

  Accordingly, an object of the present invention made in view of the above problems is to provide a communication system, a base station, a mobile station, and a communication control method for realizing beam forming by a mobile station.

In order to solve the above-described problems, the invention of the communication system according to the first aspect is as follows:
In a communication system employing a TDD (Time Division Duplex) method, the communication system includes a base station and a mobile station that performs wireless communication with the base station using an adaptive array method.
The base station
The mobile station assigns a used uplink radio resource used by the mobile station for uplink communication with the mobile station to the mobile station, and the mobile station uses a reference signal as a radio resource that shares at least part of the frequency band with the used uplink radio resource. Assigned to the mobile station as a downlink radio resource for reference signal used for transmission of
The mobile station
When the reference signal is received from the base station, the communication system performs beam forming using the received reference signal when transmitting the radio signal using the used uplink radio resource.

  The invention according to the second aspect is that, in the communication system according to the first aspect, the base station periodically changes the used uplink radio resource and the reference signal downlink radio resource allocated to the mobile station. It is a feature.

The invention according to the third aspect is a base station used in the communication system according to the first or second aspect,
The mobile station refers to a radio resource that is allocated to the mobile station used uplink radio resources used by the mobile station for uplink communication with the mobile station, and that shares at least part of the frequency band with the used uplink radio resources. It is a base station comprising a base station control unit that is allocated to the mobile station as a reference signal downlink radio resource used for signal transmission.

The invention according to a fourth aspect is a mobile station used in the communication system according to the first or second aspect,
A mobile station communication unit that receives the reference signal via a plurality of antennas;
A mobile station comprising: a mobile station control unit that performs beam forming using the reference signal received by the mobile station communication unit when transmitting a radio signal using the used uplink radio resource.

  As described above, the solution of the present invention has been described as an apparatus. However, the present invention can be realized as a method, a program, and a storage medium storing the program, which are substantially equivalent thereto, and the scope of the present invention. It should be understood that these are also included.

For example, a communication control method according to a fifth aspect that implements the present invention as a method is:
A communication control method in a communication system that employs a TDD (Time Division Duplex) method and includes a base station and a mobile station that performs wireless communication with the base station using an adaptive array method,
The base station allocating used uplink radio resources used by the mobile station in uplink communication with the mobile station to the mobile station;
The base station assigning to the mobile station a reference signal downlink radio resource used by the base station for transmitting a reference signal, a radio resource that shares at least a part of a frequency band with the used uplink radio resource;
When the mobile station receives the reference signal from the base station, the communication control method includes a step of performing beam forming using the received reference signal when transmitting a radio signal using the used uplink radio resource. It is.

  According to the communication system, the base station, the mobile station, and the communication control method according to the present invention configured as described above, the mobile station can perform beamforming, and the mobile station Can be delivered to the station.

FIG. 1 is a schematic configuration diagram of a communication system according to an embodiment of the present invention. FIG. 2 is a functional block diagram showing a schematic configuration of the base station according to the embodiment of the present invention. FIG. 3 is a functional block diagram showing a schematic configuration of the mobile station according to the embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration of a TDD frame according to an embodiment of the present invention. FIG. 5 is a diagram illustrating types of configurations of TDD frames according to an embodiment of the present invention. FIG. 6 is a diagram showing details of the configuration of the TDD frame according to an embodiment of the present invention. FIG. 7 is a flowchart showing processing of the base station according to the embodiment of the present invention. FIG. 8 is a flowchart showing processing of the mobile station according to the embodiment of the present invention. FIG. 9 is an explanatory diagram showing the relationship between the frequency bands of the reference signal downlink radio resources and the used uplink radio resources according to the embodiment of the present invention. FIG. 10 is an explanatory diagram showing hopping of reference signal downlink radio resources according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a communication system according to an embodiment of the present invention. The communication system 100 includes a base station 101 and a mobile station 103. The communication system 100 is a system in which a TDD (Time Division Duplex) method is adopted, and is, for example, an LTE system or an XGP system. The mobile station 103 is, for example, a mobile phone terminal or an XGP terminal. The mobile station 103 has a plurality of antennas (array antennas), and can wirelessly communicate with the base station 101 using an adaptive array system (AAS). In the present embodiment, the mobile station 103 can perform beam forming by an adaptive array method. Hereinafter, in the present embodiment, it is assumed that the communication system 100 is a TD-LTE system.

  FIG. 2 is a functional block diagram showing a schematic configuration of the base station according to the embodiment of the present invention. The base station 101 of this embodiment includes a base station communication unit 111, a base station baseband unit 113, and a base station control unit 115. Base station communication section 111 and base station baseband section 113 are connected to base station control section 115.

  The base station communication unit 111 transmits and receives radio signals (data) to and from the mobile station 103 via an antenna. The base station communication unit 111 performs amplification and down-conversion with low noise on the received radio signal (reception signal) and sends the signal to the base station baseband unit 113. In addition, the base station communication unit 111 performs up-conversion and amplification on the signal from the base station baseband unit 113 to generate a radio signal. Then, the base station communication unit 111 transmits the radio signal to the mobile station 103 via the antenna.

  The base station baseband unit 113 demodulates the received signal and extracts a baseband signal by performing AD conversion, fast Fourier transform, and the like on the received signal from the base station communication unit 111. Base station baseband section 113 then sends the baseband signal to base station control section 115. The base station baseband unit 113 modulates the baseband signal by performing inverse fast Fourier transform, DA conversion, or the like on the baseband signal generated by the base station control unit 115. Then, the modulated baseband signal is sent to the base station communication unit 111.

  The base station control unit 115 controls and manages the entire base station 101 including each functional block of the base station 101. The base station control unit 115 is configured as software executed on any suitable processor such as a CPU (Central Processing Unit), or by a dedicated processor (for example, DSP (Digital Signal Processor)) specialized for each process. It can also be configured.

  The base station control unit 115 allocates to the mobile station 103 a radio resource that is a combination of a time-axis slot and a frequency-axis carrier in order to realize radio communication between the base station 101 and the mobile station 103. More specifically, the base station control unit 115 allocates the used downlink radio resource, the used uplink radio resource, and the reference signal downlink radio resource to the mobile station 103. The used downlink radio resource is a radio resource used by the base station 101 in downlink communication with the mobile station 103. The used uplink radio resource is a radio resource used by the mobile station 103 in uplink communication with the base station 101.

  The reference signal downlink radio resource is a radio resource used by the base station 101 to transmit a reference signal to the mobile station 103, and is distinguished from the use downlink radio resource. The base station control unit 115 controls the base station baseband unit 113 and the base station communication unit 111 so that a known reference signal is generated and transmitted to the mobile station 103. This reference signal is used by the mobile station 103 to obtain a transmission weight for realizing beamforming, and is composed of a plurality of complex symbols. The reference signal corresponds to, for example, an SRS that can be transmitted by the mobile station 103 in the LTE system. As will be described later, the mobile station 103 can perform beamforming by controlling the transmission directivity of the array antenna ANT based on the reference signal received from the base station 101. Other processes performed by the base station control unit 115 will be described later.

  FIG. 3 is a functional block diagram showing a schematic configuration of the mobile station according to the embodiment of the present invention. The mobile station 103 of this embodiment includes a mobile station communication unit 121 having an array antenna ANT, a mobile station baseband unit 123, a storage unit 124, and a mobile station control unit 125. The mobile station communication unit 121, the mobile station baseband unit 123, and the storage unit 124 are connected to the mobile station control unit 125.

  The array antenna ANT is composed of a plurality of antennas, and can realize transmission directivity control such as beam forming. For example, the array antenna ANT is an adaptive array antenna.

  The mobile station communication unit 121 transmits and receives radio signals to and from the base station 101 via the array antenna ANT. The mobile station communication unit 121 performs amplification and down-conversion with low noise on the received radio signal (reception signal) and sends the signal to the mobile station baseband unit 123. In addition, the mobile station communication unit 121 performs up-conversion and amplification on the signal from the mobile station baseband unit 123 to generate a radio signal. The mobile station communication unit 121 transmits the radio signal to the base station 101 via the array antenna ANT.

  The mobile station baseband unit 123 demodulates the received signal and extracts the baseband signal by performing AD conversion, fast Fourier transform, and the like on the received signal from the mobile station communication unit 121. Then, the mobile station baseband unit 123 sends a baseband signal to the mobile station control unit 125. Further, the mobile station baseband unit 123 modulates the baseband signal by performing inverse fast Fourier transform, DA conversion, or the like on the baseband signal generated by the mobile station control unit 125. Then, the modulated baseband signal is sent to the mobile station communication unit 121.

  The storage unit 124 stores various information and also functions as a work memory.

  The mobile station control unit 125 controls and manages the entire mobile station 103 including each functional block of the mobile station 103. The mobile station control unit 125 is configured as software executed on any suitable processor such as a CPU (Central Processing Unit) or by a dedicated processor (for example, a DSP (Digital Signal Processor)) specialized for each process. It can also be configured.

  In the present embodiment, the mobile station control unit 125 includes a reception signal processing unit 127 and a transmission signal processing unit 129.

  The reception signal processing unit 127 obtains a plurality of reception weights for controlling the reception directivity at the array antenna ANT based on the reference signal received from the base station 101. Then, the reception signal processing unit 127 combines a plurality of reception signals each having a plurality of reception weights, and acquires data (control data and user data) from the combined reception signals.

  The transmission signal processing unit 129 generates baseband signals to be transmitted to the base station 101 by the number of antennas that constitute the array antenna ANT. Further, the transmission signal processing unit 129 obtains a plurality of transmission weights for controlling the transmission directivity at the array antenna ANT based on the reception weight obtained by the reception signal processing unit 127. Then, transmission signal processing section 129 sets a plurality of transmission weights for the generated plurality of baseband signals, and sends the signals to mobile station baseband section 123. As described above, the mobile station control unit 125 performs beam forming using the reference signal received by the mobile station communication unit 121. Other processes performed by the mobile station control unit 125 will be described later.

  Here, the TDD frame 131 used between the base station 101 and the mobile station 103 in the TDD communication system 100 will be described with reference to FIGS. FIG. 4 is a diagram illustrating a configuration of a TDD frame according to an embodiment of the present invention. FIG. 5 is a diagram illustrating types of configurations of TDD frames according to an embodiment of the present invention. FIG. 6 is a diagram showing details of the configuration of the TDD frame according to an embodiment of the present invention.

  The TDD frame 131 is specified in two dimensions including a time axis and a frequency axis. The frequency bandwidth (system bandwidth) of the TDD frame 131 is 10 MHz, for example, and the time length of the TDD frame 131 is 10 ms. The base station 101 identifies the time and frequency from the TDD frame 131 and determines the used uplink radio resource, the used downlink radio resource, and the reference signal downlink radio resource to be allocated to the mobile station 103.

  As shown in FIG. 4, the TDD frame 131 is composed of two half frames 133. Each half frame 133 is composed of five subframes 135. That is, the TDD frame 131 is composed of ten subframes 135. The time length of the subframe 135 is 1 ms. In the present embodiment, the ten subframes 135 constituting the TDD frame 131 are referred to as the 0th to 9th subframes 135 in order from the top.

  The subframe 135 includes a downlink subframe 135D dedicated to downlink communication, an uplink subframe 135U dedicated to uplink communication, and a special subframe 135S in which switching from downlink communication to uplink communication is performed. The base station 101 transmits data to the mobile station 103 in the downlink subframe 135D, and the mobile station 103 transmits data to the base station 101 in the uplink subframe 135U.

  In the LTE system, in the configuration of the TDD frame 131, seven types of combinations of the uplink subframe 135U, the downlink subframe 135D, and the special subframe 135S are defined. FIG. 5 shows these seven types of configurations. In the communication system 100, one of the seven types of configurations is used. In FIG. 5, “D” means a downlink subframe 135D, “U” means an uplink subframe 135U, and “S” means a special subframe 135S. In the present embodiment, it is assumed that the first configuration is used.

  In FIG. 4, each subframe 135 includes two slots 137 in the time direction. Each slot 137 is composed of seven symbol periods 139. Therefore, each subframe 135 includes 14 symbol periods 139 in the time direction. This symbol period 139 is one symbol period of an OFDM symbol in an OFDMA (Orthogonal Frequency Division Multiple Access) system adopted in downlink communication of the LTE system. Also, the symbol period 139 is one symbol period of DFTS (Discrete Fourier Transform Spread) -OFDM symbol in SC (Single Carrier) -FDMA system adopted in uplink communication of the LTE system.

  Here, the TDD frame 131 having the first configuration will be described in more detail with reference to FIG.

  The special subframe 135S includes a downlink pilot time slot (DwPTS) 141, a guard time (GP) 143, and an uplink pilot time slot (UpPTS) 145 in the time direction.

  In the downlink pilot time slot 141, the base station 101 can perform downlink communication with the mobile station 103. Also. In the uplink pilot time slot 145, the mobile station 103 can perform uplink communication with the base station 101. The guard time 143 is a no-signal period necessary for switching from downlink communication to uplink communication, and is not used for communication.

  In the LTE system, a plurality of combinations of time lengths of the downlink pilot time slot 141, the guard time 143, and the uplink pilot time slot 145 are defined. In the example of FIG. 6, 11 symbol periods 139 are defined as the time length of the downlink pilot time slot 141, and one symbol period 139 is defined as the time length of the guard time 143. Two symbol periods 139 are defined as the time length.

  In the present embodiment, the mobile station 103 transmits data to the base station 101 in each symbol period 139 of the uplink pilot time slot 145. The base station 101 transmits a reference signal in the last two symbol periods of the downlink pilot time slot 141. Hereinafter, a symbol period in which the reference signal is transmitted in the downlink pilot time slot 141 is referred to as a reference signal transmission period 147 (147-1 and 147-2). Hereinafter, a period in which the uplink pilot time slot 145 and the two uplink subframes 135U that follow the uplink pilot time slot 145 are combined is referred to as an uplink period 151.

  Note that the period during which the reference signal is transmitted is not limited to the last two symbol periods of the downlink pilot time slot 141, and the base station 101 can transmit one of the downlink subframe 135D and the downlink pilot time slot 141. A reference signal can be transmitted in the symbol period. Further, the base station 101 can transmit data to the mobile station 103 in the symbol period 139 in which the reference signal is not transmitted in the downlink subframe 135D and the downlink pilot time slot 141.

  Here, a period from the beginning of the reference signal transmission period 147-1 of the special subframe 135S to the beginning of the reference signal transmission period 147-1 of the next special subframe 135S is referred to as a unit period 149. The base station 101 can assign the used uplink radio resource, the used downlink radio resource, and the reference signal downlink radio resource to the mobile station 103 every unit period 149. In the communication system 100, it is assumed that the unit period 149 is repeated.

  In the present embodiment, the base station 101 transmits the reference signal to the mobile station 103 at least once per unit period 149, for example, by assigning the reference signal downlink radio resource. That is, in each unit period 149, the base station 101 transmits the reference signal in one or both of the reference signal transmission periods 147-1 and 147-2 included in the unit period 149. Note that the base station 101 can also transmit the reference signal once every plurality of unit periods 149.

  Next, a series of operations of the communication system 100 until the mobile station 103 according to the present embodiment performs beam forming will be described with reference to FIGS. FIG. 7 is a flowchart showing processing of the base station according to the embodiment of the present invention. FIG. 8 is a flowchart showing processing of the mobile station according to the embodiment of the present invention. FIG. 9 is an explanatory diagram showing the relationship between the frequency bands of the reference signal downlink radio resources and the used uplink radio resources according to the embodiment of the present invention. FIG. 10 is an explanatory diagram showing hopping of reference signal downlink radio resources according to an embodiment of the present invention. Hereinafter, it is assumed that there are two mobile stations 103A and 103B communicating with the base station 101.

  In order to communicate with the mobile stations 103A and 103B, the base station control unit 115 of the base station 101 determines a used downlink radio resource, a used uplink radio resource, and a reference signal downlink radio resource, and allocates these radio resources to the mobile station 103A. And 103B. At this time, the base station control unit 115 assigns the used uplink radio resource and the reference signal downlink radio resource with the following relevance.

  First, the base station control unit 115 allocates used uplink radio resources to the mobile stations 103A and 103B (step S101). For example, as shown in FIG. 9, the base station control unit 115 allocates the used uplink radio resources 153a and 153b to the mobile stations 103A and 103B so that the mobile stations 103A and 103B can transmit data in the uplink period 151, respectively. . Note that, as shown in FIG. 9, the used uplink radio resources 153a and 153b are specified in two dimensions including a time axis and a frequency axis.

  Subsequently, the base station control unit 115 allocates the reference signal downlink radio resources to the mobile stations 103A and 103B so that at least a part of the used uplink radio resources and the frequency band are common (step S102). For example, in FIG. 9, the base station control unit 115 allocates the reference signal downlink radio resource 155a having the same frequency band as the used uplink radio resource 153a to the mobile station 103A in the first reference signal transmission period 147-1. Also, the base station control unit 115 allocates the reference signal downlink radio resource 155b having the same frequency band as the used uplink radio resource 153b to the mobile station 103B in the second reference signal transmission period 147-2.

  Then, the base station control unit 115 controls the base station baseband unit 113 so as to modulate the reference signal. After that, the base station control unit 115 controls the base station communication unit 111 to transmit the modulated reference signal to the mobile station 103A using the reference signal downlink radio resource 155a (step S103). Also, the base station control unit 115 controls the base station communication unit 111 to transmit the modulated reference signal to the mobile station 103B using the reference signal downlink radio resource 155b (step S103).

  Note that the present invention is not limited to the base station control unit 115 using all the plurality of subcarriers constituting the reference signal downlink radio resource when transmitting the reference signal. For example, the base station control unit 115 can use every other subcarrier in the frequency direction among a plurality of subcarriers constituting the reference signal downlink radio resource. That is, the subcarriers used are comb-shaped in the reference signal downlink radio resources. As a result, the base station control unit 115 can assign unused subcarriers of the same reference signal downlink radio resource to other mobile stations and transmit reference signals to other base stations. Therefore, it is possible to transmit a reference signal to two mobile stations using a certain downlink radio resource for reference signal, so that it is possible to improve the utilization efficiency of limited radio resources.

  Next, processing of the mobile station 103 (103A and 103B) will be described. In the following description, when it is necessary to distinguish between the mobile stations 103A and 103B, a is added to the reference symbol of the functional block related to the mobile station 103A, and b is added to the reference symbol of the functional block related to the mobile station 103B. I will explain. In the description of matters common to both the mobile stations 103A and 103B, a and b are not added to the reference symbols.

  First, when receiving the reference signal via the array antenna ANT, the mobile station communication unit 121 sends the reference signal to the mobile station baseband unit 123 (step S201). The reference signal demodulated by the mobile station baseband unit 123 is sent to the reception signal processing unit 127. The reception signal processing unit 127 calculates a reception weight from the reference signal and sends the reception weight to the transmission signal processing unit 129. . The transmission signal processing unit 129 calculates a transmission weight that realizes beamforming based on the reception weight (step S202). Then, the mobile station control unit 125 can store transmission weight information in the storage unit 124.

  Thereafter, in the uplink period 151, the transmission signal processing unit 129 sets the transmission weight stored in the storage unit 124 to the data signal to be transmitted to the base station 101, and generates a transmission signal. The mobile station control unit 125a of the mobile station 103A controls the mobile station communication unit 121a to transmit the generated transmission signal to the base station 101 using the used uplink radio resource 153a. Since the reference signal downlink radio resource 155a and the used uplink radio resource 153a have the same frequency band, transmission of a transmission signal in which a transmission weight based on the reference signal is set means execution of beamforming (step S203). . Note that if at least part of the frequency band of the reference signal downlink radio resource and the used uplink radio resource is common, the beamforming can be realized, although the accuracy is lower than when both frequency bands are the same. is there.

  Similarly to the mobile station 103A, the mobile station control unit 125b of the mobile station 103B controls the mobile station communication unit 121b to transmit the generated transmission signal to the base station 101 using the used uplink radio resource 153b. To do.

  FIG. 9 shows reference signal downlink radio resources in one special subframe 135S, but the base station 101 periodically and aperiodically allocates reference signal downlink radio resources and uses to the mobile station 103. The uplink radio resource can be changed. For example, as shown in FIG. 10, the base station 101 changes (hops) the reference signal downlink radio resources every unit period 149, that is, every special subframe 135S for each of the mobile stations 103A and 103B. be able to.

  In FIG. 10, the base station 101 transmits a reference signal to the mobile station 103A using the reference signal downlink radio resource 155a in a certain unit period 149, and in the next unit period, the reference signal downlink radio resource 155a Transmits a reference signal using different reference signal downlink radio resources 157a. Further, the base station 101 transmits a reference signal to the mobile station 103B using the reference signal downlink radio resource 155b in a certain unit period 149, and is different from the reference signal downlink radio resource 155b in the next unit period. The reference signal is transmitted using the reference signal downlink radio resource 157b.

  The base station control unit 115 of the base station 101 changes the used downlink radio resource in accordance with the change of the reference signal downlink radio resource, and at least a part of the frequency band of the reference signal downlink radio resource and the used downlink radio resource is changed. Both radio resources are allocated to the mobile station 103 so as to be common.

  Note that, when the reference signal downlink radio resource is hopped, the mobile station control unit 125 of the mobile station 103 stores the transmission weight obtained from the reference signal every time the mobile station communication unit 121 receives the reference signal. 124 can be stored.

  As described above, in this embodiment, the base station control unit 115 of the base station 101 allocates the used uplink radio resources 153a or 153b used by the mobile stations 103A and 103B for uplink communication with the own station 101 to the mobile stations 103A and 103B. The mobile stations 103A and 103B use the radio resource 155a or 155b that shares at least a part of the frequency band with the used uplink radio resource 153a or 153b as the reference signal downlink radio resource used by the own station 101 for transmitting the reference signal. Assign to. Thereby, the mobile stations 103A and 103B can obtain the transmission weight based on the reference signal that shares a part of the frequency with the radio resource that can be used at the time of data transmission, and can realize beam forming. As a result, the strength of signals transmitted from the mobile stations 103A and 103B to the base station 101 is increased, and the mobile stations 103A and 103B can deliver signals with good communication quality to the base station 101.

  In the present embodiment, the base station control unit 115 of the base station 101 can periodically change (hop) the used uplink radio resources and the reference signal downlink radio resources allocated to the mobile stations 103A and 103B. Thereby, when the communication quality of a certain frequency band is poor, it is possible to avoid the frequency band having the poor communication quality being continuously assigned as the used uplink radio resource and the reference signal downlink radio resource.

  Further, by hopping the reference signal downlink radio resource, the mobile station control unit 125 can cause the storage unit 124 to store transmission weights for realizing beam forming not only in a certain frequency band but also in a plurality of frequency bands. Thereby, even when the base station 101 changes the used uplink radio resource and does not transmit the reference signal corresponding to the changed used uplink radio resource, the mobile station control unit 125 may be able to execute beam forming. That is, if the mobile station control unit 125 has previously received a reference signal that shares a part of the frequency band with the changed used uplink radio resource, the mobile station control unit 125 reads the transmission weight of the reference signal from the storage unit 124. Can perform beam forming.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention.

  For example, functions included in each member, each means, each step, etc. can be rearranged so as not to be logically contradictory, and a plurality of means, steps, etc. can be combined or divided into one. Is possible.

  In the above description of the embodiment of the present invention, the mobile station 103 is described as performing beamforming as transmission directivity control. However, the mobile station 103 may be able to perform not only beamforming but also null steering. is there. For example, when there are a plurality of base stations around a mobile station and the transmission timings of these base stations are synchronized, the reference signal received by the mobile station from one base station is the interference from other base stations. It will reflect the effect of the waves. Therefore, the transmission signal processing unit can calculate a transmission weight that realizes not only beamforming but also null steering.

  In the above description of the embodiment of the present invention, the base station 101 transmits the reference signal and the mobile station 103 executes the transmission directivity control. However, the mobile station transmits the reference signal (SRS). Then, the base station can perform transmission directivity control in the same manner as described above.

  In the above description of the embodiment of the present invention, it has been described that reference signals are transmitted to different mobile stations 103A and 103B for different reference signal transmission periods 147-1 and 147-2. It is not limited to. For example, the base station control unit can also transmit a reference signal to a certain mobile station using the same frequency band over a plurality of reference signal transmission periods.

  In the above description of the embodiment of the present invention, the minimum unit of time of the reference signal downlink radio resource is described as being a symbol period (reference signal transmission period 147-1 or 147-2). Is not limited to this embodiment. For example, the base station control unit can also allocate a reference signal downlink radio resource having only half the symbol period to the mobile station.

  In the above description of the embodiment of the present invention (particularly, FIG. 9), the mobile station 103 receives the reference signal in the first special subframe 135S of the TDD frame 131, and then performs the beam in the second uplink period. Although it is described that the forming is performed, the present invention is not limited to this mode. For example, the mobile station can also perform beam forming in the uplink period immediately after the reference signal or in the third and subsequent uplink periods.

100 communication system 101 base station 103 mobile station 111 base station communication unit 113 base station baseband unit 115 base station control unit 121 mobile station communication unit 123 mobile station baseband unit 124 storage unit 125 mobile station control unit 127 received signal processing unit 129 Transmission signal processor 131 TDD frame 133 Half frame 135 Sub frame 135 U Up sub frame 135 D Down sub frame 135 S Special sub frame 137 Slot 139 Symbol period 141 Down pilot time slot 143 Guard time 145 Up pilot time slot 147 Reference signal transmission period 147 − 1, 147-2 Reference signal transmission period 149 Unit period 151 Up period 153a, 153b Used uplink radio resources 155a, 155b, 157a, 157b For reference signal Ri radio resources ANT array antenna

Claims (5)

In a communication system employing a TDD (Time Division Duplex) method, the communication system includes a base station and a mobile station that performs wireless communication with the base station using an adaptive array method.
The base station
The mobile station assigns a used uplink radio resource used by the mobile station for uplink communication with the mobile station to the mobile station, and the mobile station uses a reference signal as a radio resource that shares at least part of the frequency band with the used uplink radio resource. Assigned to the mobile station as a downlink radio resource for reference signal used for transmission of
The mobile station
A communication system that, when receiving the reference signal from the base station, performs beam forming using the received reference signal when transmitting a radio signal using the used uplink radio resource.   The communication system according to claim 1, wherein the base station periodically changes the used uplink radio resource and the reference signal downlink radio resource allocated to the mobile station. A base station used in the communication system according to claim 1 or 2,
The mobile station refers to a radio resource that is allocated to the mobile station used uplink radio resources used by the mobile station for uplink communication with the mobile station, and that shares at least part of the frequency band with the used uplink radio resources. A base station comprising a base station controller that is assigned to the mobile station as a reference signal downlink radio resource used for signal transmission. A mobile station used in the communication system according to claim 1 or 2,
A mobile station communication unit that receives the reference signal via a plurality of antennas;
A mobile station comprising: a mobile station control unit that performs beam forming using the reference signal received by the mobile station communication unit when transmitting a radio signal using the used uplink radio resource. A communication control method in a communication system that employs a TDD (Time Division Duplex) method and includes a base station and a mobile station that performs wireless communication with the base station using an adaptive array method,
The base station allocating used uplink radio resources used by the mobile station in uplink communication with the mobile station to the mobile station;
The base station assigning to the mobile station a reference signal downlink radio resource used by the base station for transmitting a reference signal, a radio resource that shares at least a part of a frequency band with the used uplink radio resource;
When the mobile station receives the reference signal from the base station, the communication control method includes a step of performing beam forming using the received reference signal when transmitting a radio signal using the used uplink radio resource. .

Images