JP6659455B2 - Base station, communication system and MCS selection method - Google Patents

Description

  The present invention relates to a base station, a communication system, and a handover method for performing MIMO communication using a part of a carrier frequency of a frequency band shared with another system.

  2. Description of the Related Art Conventionally, an FPU (Field Pick-up Unit) has been known as a device used for a wireless communication system that performs video transmission such as live television broadcasting or emergency news. The FPU is used for transmitting materials in the broadcasting field, and performs wireless communication using a part of a frequency band shared with another system such as a transceiver. For this reason, it is necessary for the FPU to constantly monitor the presence or absence of interference in the frequency band in use to prevent interference with other systems. The base station of the FPU measures the reception level (interference amount), and when the reception level (interference amount) exceeds a predetermined threshold, another system starts using the frequency band (interference has occurred). Is determined, and the mobile station stops using the frequency band and transitions the frequency band to use another frequency band.

  Conventionally, in a MIMO (Multiple-Input Multiple-Output) communication system in which a plurality of data are spatially multiplexed and transmitted using a plurality of antennas for transmission and reception of wireless communication, a substream (antenna element) A communication method of selecting an MCS (Modulation and Coding Scheme) for each communication is known (see Patent Document 1).

JP-T-2004-529267

  However, a document that discloses a technique of combining MIMO communication with wireless communication using a part of a frequency band shared with other systems, such as FPU, and a frequency band in MIMO communication that selects MCS for each substream. There is no document disclosing a method of selecting the MCS after the transition.

  An object of the present invention is to reduce the deterioration of communication quality after transitioning a frequency band when combining MIMO communication for selecting an MCS for each substream with wireless communication using a part of a frequency band shared with another system. It is an object of the present invention to provide a base station, a communication system, and an MCS selection method that can prevent such a situation.

  A base station according to the present disclosure is a base station that performs wireless communication with a mobile station using a part of a carrier frequency of a frequency band shared with another system, and that receives a MIMO-transmitted signal from the mobile station. A receiving unit that receives a signal transmitted from the mobile station by MIMO, a level measuring unit that measures an interference level and a signal level of the frequency band, and a frequency that is used for communication with the mobile station based on the interference level. A frequency selection unit that selects a band and determines whether or not a transition of the frequency band is necessary; an MCS selection unit that selects an MCS of each subframe based on a signal level of the frequency band selected by the frequency selection unit; At the time of the transition, the control signal including information indicating the frequency band selected by the frequency selection unit and information indicating the MCS selected by the MCS selection unit is transferred. A transmitting unit for transmitting to the station, the MCS selecting unit selects the lowest MCS among the MCSs of the respective substreams before the frequency transition at the time of the frequency transition, and immediately after the frequency transition, selects the selected MCS. Apply to all substreams.

  In the communication system according to the present disclosure, the mobile station and the base station perform radio communication using a part of a carrier frequency of a frequency band shared with another system, and the base station transmits a signal transmitted by MIMO from the mobile station. A communication system for receiving MIMO, wherein the base station receives a signal transmitted from the mobile station by MIMO, a level measuring unit for measuring an interference level and a signal level of the frequency band, and the frequency band. A frequency band used for communication with the mobile station is selected based on the interference level, and a frequency selection unit that determines whether or not the frequency band needs to be changed, and a signal level of the frequency band selected by the frequency selection unit. An MCS selection unit that selects an MCS of each subframe based on the information indicating a frequency band selected by the frequency selection unit during a frequency transition; and A transmitting unit that transmits a control signal including information indicating the MCS selected by the CS selecting unit to the mobile station, wherein the MCS selecting unit performs, during frequency transition, the MCS of each substream before the frequency transition. , Select the lowest MCS immediately after the frequency transition, apply the selected MCS to all substreams, and the mobile station receives a control signal from the receiving unit; A transmission unit that encodes and modulates transmission data of the frame and performs MIMO transmission of the signal in a frequency band included in the control signal.

  The MCS selection method according to the present disclosure performs wireless communication with a mobile station using a part of a carrier frequency of a frequency band shared with another system, and performs MCS reception of a signal transmitted from the mobile station by MIMO. A selection method, comprising measuring an interference level and a signal level of the frequency band, selecting a frequency band to be used for communication with the mobile station based on the interference level, and selecting a frequency band based on the interference level. It is determined whether or not the transition is necessary. At times other than the frequency transition, the MCS of each subframe is selected based on the signal level of the selected frequency band. At the time of the frequency transition, the MCS of each substream before the frequency transition is selected. Selects the lowest MCS, and applies the selected MCS to all substreams immediately after the frequency transition.

  According to the present disclosure, it is possible to prevent deterioration of communication quality immediately after a frequency band when combining MIMO communication selecting an MCS for each substream with wireless communication using a part of a frequency band shared with another system. it can.

1 is a block diagram illustrating a configuration of a communication system according to an embodiment of the present invention. FIG. 1 is a block diagram showing a configuration of a base station according to one embodiment of the present invention. FIG. 1 is a block diagram illustrating a configuration of a control station according to an embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a mobile station according to one embodiment of the present invention. FIG. 4 is a flowchart showing an MCS selection operation of the base station according to one embodiment of the present invention. The figure which shows the 1st specific example of MCS selection at the time of frequency transition concerning one Embodiment of this invention. The figure which shows the 2nd specific example of MCS selection at the time of frequency transition concerning one Embodiment of this invention. The figure which shows the 3rd example of MCS selection at the time of frequency transition concerning one Embodiment of this invention. The figure which shows the specific example of MCS selection at the time of the handover concerning one Embodiment of this invention FIG. 4 is a diagram illustrating a configuration example of a control signal at the time of frequency transition according to an embodiment of the present invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate.

<Communication system configuration>
The configuration of the communication system 1 according to Embodiment 1 of the present invention will be described in detail below with reference to FIG. As shown in FIG. 1, the communication system 1 includes a plurality of base stations 100, a control station 200, and a mobile station 300.

  Each base station 100 connects to the control station 200 by wire or wirelessly. Further, each base station 100 performs wireless communication with the mobile station 300 using a part of the frequency band shared with other systems. Further, each base station 100 has a MIMO antenna in which a plurality of antennas are arranged near each other, and receives a wireless signal transmitted from mobile station 300 by MIMO.

  The mobile station 300 performs MIMO communication with the base station 100 using the frequency band specified by the communication partner base station 100. Also, the mobile station 300 has a MIMO antenna and transmits a radio signal to the base station 100 by MIMO. Further, the mobile station 300 performs handover between the base stations 100 based on an instruction from the control station 200. The types of handover include hard handover in which the communication interface before switching is disconnected and connection is made in the communication interface after switching, or connection in the communication interface after switching, while handover before switching is performed during handover. There is a soft handover that maintains the connection at the communication interface. The present invention can be applied to both hard handover and soft handover.

<Configuration of base station>
The configuration of base station 100 according to the present embodiment will be described in detail below with reference to FIG. As shown in FIG. 2, base station 100 includes a MIMO antenna 101, a radio reception unit 102, a signal separation unit 103, a demodulation unit 104, a decoding unit 105, a P / S conversion unit 106, a level measurement unit 107, a frequency selection unit 108, an MCS selection unit 109, a control station communication unit 110, a control signal generation unit 111, a synthesizer unit 112, an encoding unit 113, a modulation unit 114, a multiplexing unit 115, It has a wireless transmission unit 116 and an antenna 117.

  The MIMO antenna 101 includes m (m is a plurality of) antenna elements 151, and receives a wireless signal transmitted from the mobile station 300 by MIMO.

  Radio receiving section 102 has as many receiving sections 152 as the number m of antenna elements of MIMO antenna 101, and uses a local signal output from synthesizer section 112 to receive a radio signal received by each antenna element of MIMO antenna 101. Is down-converted, and a radio reception process such as amplification and filtering is performed to obtain a baseband signal. Then, wireless reception section 102 outputs the baseband signal to signal separation section 103. When the received signal is an OFDM signal, which is one type of a multicarrier signal, the wireless reception unit 102 performs an OFDM reception process such as an FFT process and a P / S conversion process in addition to the above-described wireless reception process.

  The signal separating unit 103 converts the baseband signal output from the wireless receiving unit 102 into n (n) signals of the MIMO antenna 311 (see FIG. 4) of the mobile station 300 using a method such as MMSE (Minimum Mean Square Error). Are separated into signals (substreams) transmitted from each of the plurality of antenna elements, and output to the demodulation section 104 and the level measurement section 107.

  The demodulation section 104 has the same number of demodulation sections 154 as the number n of substreams, demodulates the baseband signal output from the signal separation section 103 for each substream, obtains demodulated data, and outputs the demodulated data to the decoding section 105. .

  The decoding unit 105 has the same number of decoding units 155 as the number n of substreams, and decodes demodulated data output from the demodulation unit 104 to obtain received data. Decoding section 105 outputs the received data to P / S conversion section 106.

  P / S conversion section 106 converts the same number of parallel reception data strings as the number of substreams into a serial reception data string, and outputs the serial reception data string to control station communication section 110.

  Level measurement section 107 measures the reception level (interference level) of the unused frequency band at the start of communication and when instructed by frequency selection section 108, and outputs the measured value to frequency selection section 108. The reception levels in the unused frequency bands are all interference levels.

  Also, during communication with mobile station 300, level measurement section 107 measures the reception level (interference level) of the guard time of the frequency band in use (the frequency band selected by frequency selection section 108) and measures the measured value. Is output to the frequency selection unit 108. Note that the guard level reception levels are all interference levels.

  Further, level communication section 107 measures the reception level (signal level) of each substream (each antenna element of MIMO antenna 311 of mobile station 300) separated by signal separation section 103 during communication with mobile station 300. Then, the measured value is output to MCS selection section 109 and control station communication section 110. The reception level of the used frequency band is a signal in which the interference level is mixed with the signal level which is the original desired signal, but the measurement result here is the same as the measured value of the signal level. I do.

  At the start of communication, the frequency selection unit 108 selects, from among the unused frequency bands, one whose measured value of the interference level output from the level measurement unit 107 is less than the first threshold. Here, the selected frequency band is a frequency band shared with another system and an unused frequency band not used by another system.

  Further, during communication with the mobile station 300, the frequency selection unit 108 compares the measured value of the interference level of the guard time output from the level measurement unit 107 with the first threshold. Then, when the interference level is less than the first threshold, the frequency selection unit 108 selects again the frequency band currently in use. On the other hand, if the interference level is equal to or higher than the first threshold, the frequency selection unit 108 determines that the frequency band needs to be shifted, and instructs the level measurement unit 107 to receive the unused frequency band (interference level) And selects a frequency band in which the measurement value output from the level measurement unit 107 is less than the first threshold.

  When base station 100 is the handover destination, frequency selection section 108 selects the frequency band of the handover source base station.

  Then, frequency selection section 108 outputs frequency information indicating the selected frequency band to level measurement section 107, MCS selection section 109, control station communication section 110, control signal generation section 111, and synthesizer section 112.

  The MCS selection unit 109 applies MCS (modulation method and MCS) to be applied to each substream (antenna element) of the mobile station 300 based on the measured signal level output from the level measurement unit 107 during communication with the mobile station 300. Coding rate) is selected such that the higher the reception level, the higher the transmission rate. Then, MCS selection section 109 outputs MCS information indicating the selected modulation scheme and coding rate to control station communication section 110 and control signal generation section 111.

  However, at the time of frequency transition (when a new frequency band is selected by the frequency selection unit 108), the MCS selection unit 109 selects the lowest MCS among the MCS of each substream before the frequency transition, and Immediately after the transition, the selected MCS is applied to all substreams.

  When the base station 100 is the handover destination, the MCS selection unit 109 selects the lowest MCS among the MCSs of the substreams of the handover source base station, and immediately after the handover, replaces the selected MCS with all substreams. Apply to stream.

  Control station communication section 110 transmits the received data output from P / S conversion section 106 to control station 200, and outputs the data transmitted from control station 200 to encoding section 113.

  Also, the control station communication unit 110 receives the frequency information output from the frequency selection unit 108, the MCS information output from the MCS selection unit 109, and the measured value of the reception level of the baseband signal output from the level measurement unit 107. Is transmitted to the control station 200. Then, after transmitting the reception quality information, control station communication section 110 receives a handover instruction signal instructing execution of handover from control station 200, and controls each section to execute handover. Also, when the base station 100 is the handover destination, the control station communication unit 110 outputs the frequency information of the handover source base station to the frequency selection unit 108 and the MCS information of the handover source base station to the MCS selection unit 109. Output.

  At the time of frequency transition, control signal generation section 111 generates a control signal including frequency information output from frequency selection section 108 and MCS information output from MCS selection section 109 and outputs the control signal to multiplexing section 115.

  Synthesizer section 112 generates a local signal of the center frequency of the band selected by frequency selecting section 108 and outputs the signal to wireless receiving section 102 and wireless transmitting section 116.

  Encoding section 113 encodes the transmission data output from control station communication section 110 and outputs the transmission data to modulation section 114.

  Modulating section 114 modulates the encoded data output from encoding section 113 and outputs a modulated signal to multiplexing section 115.

  Multiplexing section 115 multiplexes the modulated signal output from modulating section 114 with the control signal output from control signal generating section 111 to generate a baseband signal, and outputs the baseband signal to radio transmitting section 116.

  Radio transmitting section 116 performs radio transmission processing such as amplification and filtering on the baseband signal output from multiplexing section 115. Then, radio transmitting section 116 up-converts the signal after the radio transmission processing using the local signal output from synthesizer section 112 to obtain a radio signal. Then, wireless transmission section 116 transmits a wireless signal (DL signal) from antenna 117.

<Configuration of control station>
Next, the configuration of control station 200 according to the present embodiment will be described in detail below with reference to FIG. As shown in FIG. 3, the control station 200 includes a receiving unit 201, a handover control unit 202, an instruction signal generating unit 203, and a transmitting unit 204.

  Receiving section 201 outputs received data of a signal received from each base station 100 to an upper station (not shown).

  The handover control unit 202 determines whether or not a handover is required based on the reception quality information of each base station 100 output from the reception unit 201, and selects the handover destination base station 100 when the handover is required. A signal indicating the result is output to instruction signal generation section 203.

  The instruction signal generation unit 203 refers to the selection result output from the handover control unit 202 and performs handover to the base station 100 of the handover source (first base station) and the base station 100 of the handover destination (second base station). Is generated and output to the transmitting unit 204. The instruction signal generation unit 203 includes the frequency information and the MCS information of the handover source base station 100 in the handover instruction signal to be transmitted to the handover destination base station 100.

  Transmitting section 204 transmits transmission data to base station 100 that is communicating with mobile station 300. Further, transmitting section 204 transmits the handover instruction signal output from instruction signal generating section 203 to handover source and handover destination base stations 100.

<Configuration of mobile station>
The configuration of mobile station 300 according to the present embodiment will be described below in detail with reference to FIG.

  The mobile station 300 includes an antenna 301, a radio reception unit 302, a demodulation unit 303, a decoding unit 304, a control signal extraction unit 305, a synthesizer unit 306, an S / P conversion unit 307, and an encoding unit 308. , A modulation unit 309, a radio transmission unit 310, and a MIMO antenna 311.

  Radio receiving section 302 uses the local signal output from synthesizer section 306 to down-convert the radio signal received by antenna 301, and further performs radio reception processing such as amplification and filtering to obtain a baseband signal. Then, wireless reception section 302 outputs the baseband signal to demodulation section 303.

  Demodulation section 303 demodulates the baseband signal output from wireless reception section 302 to obtain a control signal and demodulated data. Demodulation section 303 outputs demodulated data to decoding section 304 and outputs a control signal to control signal extraction section 305.

  Decoding section 304 decodes the demodulated data output from demodulation section 303 to obtain received data.

  Control signal extraction section 305 extracts frequency information and MCS information included in the control signal output from demodulation section 303, outputs frequency information to synthesizer section 306, and encodes MCS information into encoding section 308 and modulation section 309.

  The S / P conversion unit 307 converts the serial transmission data sequence (stream data) into the same number of parallel transmission data sequences as the number of substreams, and outputs the result to the encoding unit 308.

  The encoding unit 308 has the same number of encoding units 358 as the number n of substreams, and encodes each substream output from the S / P conversion unit 307 at the encoding rate of each substream indicated in the MCS information. The transmission data is encoded and output to modulation section 309.

  Modulating section 309 has the same number of modulating sections 359 as the number of substreams, and each code output from encoding section 308 in the modulation scheme (QPSK, 16QAM, 64QAM, etc.) of each substream indicated in the MCS information. The modulated data is modulated, and a modulated signal is output to the wireless transmission unit 310.

  The wireless transmission section 310 has the same number of wireless transmission sections 360 as the number n of substreams, and performs wireless transmission processing such as amplification and filtering on the modulated signal (baseband signal) output from the modulation section 309. Then, radio transmitting section 310 up-converts the signal after the radio transmission processing using the local signal output from synthesizer section 306 to obtain a radio signal. When transmitting an OFDM signal, the wireless transmission unit 310 performs an OFDM transmission process such as an S / P conversion process and an IFFT process, in addition to the above wireless transmission process.

  The MIMO antenna 311 includes n antenna elements 361, and performs MIMO transmission of a radio signal output from the radio transmission unit 310 to the base station 100.

<Base station MCS selection operation>
Next, an MCS selection operation of base station 100 according to the present embodiment will be described in detail below with reference to FIG.

  First, the level measurement unit 107 measures the interference level of the frequency band in use and the signal level of each substream (S1).

  Next, the frequency selection unit 108 determines whether frequency transition is necessary by comparing the interference level of the frequency band in use with the first threshold (S2).

  If the interference level of the frequency band being used is less than the first threshold (S2: NO), the frequency selection unit 108 determines that frequency transition is not necessary because no interference with another system has occurred, Continue to select the frequency band in use. In this case, MCS selection section 109 selects the MCS of each substream (antenna element) of mobile station 300 based on the measured signal level (S3).

  On the other hand, when the interference level of the frequency band in use is equal to or higher than the first threshold (S2: YES), the frequency selection unit 108 determines that frequency transition is necessary because interference with another system has occurred. Then, a new frequency band is selected (S4). In this case, the MCS selection unit 109 selects the lowest MCS among the MCSs of each substream before the frequency transition, and applies the selected MCS to all substreams immediately after the frequency transition (S5).

<Specific example of MCS selection at frequency transition>
Next, a specific example of MCS selection at the time of frequency transition will be described with reference to FIGS. 6 to 8 show a case where the number n of antenna elements (the number of substreams) of the MIMO antenna 311 of the mobile station 300 is “4”.

  FIG. 6 shows an example in which the frequency band f1 is shifted to the frequency band f3. In FIG. 6, before frequency transition, antenna # 1 has a modulation scheme of 64 QAM and a coding rate of １ ／, and antenna # 2 has a modulation scheme of 64 QAM and a coding rate of 、 and antenna # 3 Indicates that the modulation scheme is 16QAM and the coding rate is 1/2, and that the antenna # 4 has the modulation scheme of 16QAM and the coding rate of 1/2.

  In this case, the MCS selection unit 109 determines the lowest MCS among the MCSs of the respective substreams before the frequency transition, that is, the MCS of the antennas # 3 and # 4 (the modulation scheme is 16QAM and the coding rate is 1/2). After selection, immediately after the frequency transition, the selected MCS is applied to the MCS of all substreams.

  FIG. 7 shows an example in which two frequency bands f1 and f2 are simultaneously shifted to frequency bands f3 and f4, and an MCS is commonly selected for all frequency bands. In FIG. 7, before the frequency transition, the frequency band f1 and antenna # 1 have a modulation scheme of 64 QAM and a coding rate of 、, and the frequency band f1 and antenna # 2 have a modulation scheme of 64 QAM and a coding rate of 1 / 2, the frequency band f1 and antenna # 3 have a modulation scheme of 16 QAM and a coding rate of 1/2, and the frequency band f1 and antenna # 4 have a modulation scheme of 16 QAM and a coding rate of 1/2. . The frequency band f2 and antenna # 1 have a modulation scheme of 64 QAM and a coding rate of 、, and the frequency band f2 and antenna # 2 have a modulation scheme of 64 QAM and a coding rate of 、 and have a frequency band of f2 and antenna # 3 have a modulation scheme of 64 QAM and a coding rate of 1/2, and the frequency band f2 and antenna # 4 have a modulation scheme of 64 QAM and a coding rate of 1/2.

  In this case, the MCS selection unit 109 determines the lowest MCS among the MCSs of the substreams before the frequency transition, that is, the MCS of the frequency band f1 and the antennas # 3 and # 4 (the modulation scheme is 16QAM and the coding rate is 1 / 2) and apply the selected MCS to the MCS of all substreams immediately after the frequency transition.

  FIG. 8 shows an example in which two frequency bands f1 and f2 are simultaneously shifted to frequency bands f3 and f4, and an MCS is selected independently for each frequency band (f1 → f3, f2 → f4). In FIG. 8, before the frequency transition, the frequency band f1, antenna # 1 has a modulation scheme of 64 QAM and a coding rate of 、, and the frequency band f1 and antenna # 2 has a modulation scheme of 64 QAM and a coding rate of 1 / 2, the frequency band f1 and antenna # 3 have a modulation scheme of 16 QAM and a coding rate of 1/2, and the frequency band f1 and antenna # 4 have a modulation scheme of 16 QAM and a coding rate of 1/2. . The frequency band f2 and antenna # 1 have a modulation scheme of 16 QAM and a coding rate of １ ／, and the frequency band f2 and antenna # 2 have a modulation scheme of 16 QAM and a coding rate of 、 and a frequency band of f2, antenna # 3 has a modulation scheme of QPSK and a coding rate of 、, and frequency band f2 and antenna # 4 have a modulation scheme of QPSK and a coding rate of ２.

  In this case, the MCS selection unit 109 determines the lowest MCS among the MCSs of the respective substreams before the frequency transition of each frequency band, that is, in the frequency band f1, the MCS of the antennas # 3 and # 4 (the modulation scheme is 16QAM, The coding rate is 1/2), and in the frequency band f2, the MCS of the antennas # 3 and # 4 (modulation method is QPSK and the coding rate is 1/2) is selected. The MCS selected in f1 is applied to the MCS of all substreams in the frequency band f3, and the MCS selected in the frequency band f2 is applied to MCS of all substreams in the frequency band f4.

<Specific example of MCS selection at handover>
Next, a specific example of MCS selection at the time of handover will be described with reference to FIG. Note that FIG. 9 shows a case where the number n of antenna elements (the number of substreams) of the MIMO antenna 311 of the mobile station 300 is “4”.

  FIG. 9 shows an example in which a handover is performed in the frequency band f1. In FIG. 9, before handover, antenna # 1 has a modulation scheme of 64 QAM and a coding rate of 、, antenna # 2 has a modulation scheme of 64 QAM and a coding rate of 、, and antenna # 3 has a modulation rate of 、. It is assumed that the modulation scheme is 16QAM and the coding rate is 1/2, and that the antenna # 4 has the modulation scheme of 16QAM and the coding rate of 1/2.

  In this case, the MCS selection unit 109 selects the lowest MCS among the MCSs of the respective substreams before the handover, that is, the MCS of the antennas # 3 and # 4 (the modulation scheme is 16QAM and the coding rate is 1/2). Then, immediately after the frequency transition, the selected MCS is applied to the MCS of all substreams. The present invention can be applied to a case where a handover is performed while communication is performed using a plurality of frequency bands simultaneously. In this case, MCS can be selected in common for all frequency bands, or MCS can be selected for each frequency band, as in the case of performing frequency transition when communication is performed using a plurality of frequency bands simultaneously. You can also.

<Configuration of control signal>
Next, a configuration example of a control signal at the time of frequency transition generated by the control signal generation unit 111 will be described with reference to FIG.

  When one frequency band is shifted as shown in FIG. 6, as shown in FIG. 10A, the control signal includes various control information (Ack / Nack, MIMO-related information, other control information) in addition to various control information. , The frequency information output from the frequency selection unit 108 and the MCS information output from the MCS selection unit 109 are inserted.

  In the present embodiment, at the time of frequency transition, one MCS selected by MCS selecting section 109 is applied to all substreams, so control signal generating section 111 inserts only one system of MCS information into the control signal. It is sufficient to suppress an increase in the information amount of the control signal.

  When a plurality of frequency bands are simultaneously shifted as shown in FIGS. 7 and 8, as shown in FIGS. 10B and 10C, in addition to various types of control information, frequency information, MCS Information and identification information is inserted. This identification information is 1-bit information indicating whether to select the MCS commonly for all frequency bands as shown in FIG. 7 or to select the MCS independently for each frequency band as shown in FIG.

  In the case of FIG. 7, one MCS selected by the MCS selection unit 109 is applied to the substreams of all the frequency bands. Therefore, as shown in FIG. 10B, the control signal generation unit 111 Only information needs to be inserted into the control signal. In addition, in the case of FIG. 8, one MCS is applied to each frequency band selected by the MCS selection unit 109 to all substreams of each frequency band. Therefore, as shown in FIG. 10C, the control signal generation unit 111 Inserts the MCS information for the number of frequency bands into the control signal.

<Effect>
As described above, according to the present embodiment, in the case where MIMO communication that selects MCS for each substream is combined with wireless communication that uses a part of the frequency band shared with another system, The lowest MCS among the MCSs of the previous substreams is selected, and the selected MCS is applied to all substreams immediately after the frequency transition. As a result, it is possible to prevent deterioration of communication quality immediately after the frequency transition. Further, in the present embodiment, at the time of handover, the lowest MCS among the MCSs of each substream before handover is selected, and immediately after handover, the selected MCS is applied to all substreams. As a result, it is possible to prevent deterioration of communication quality immediately after the handover.

  Although a case has been described with the above embodiment where both base station 100 and mobile station 300 each transmit data, the present invention is not limited to this. In a downlink, the base station transmits data to the mobile station. , And only the control signal is transmitted, and the mobile station transmits data to the base station on the uplink.

  Further, in the above embodiment, the case where the number of antenna elements n (the number of sub-streams) is “4” has been described, but the present invention is not limited to this, and the number of antenna elements n (the number of sub-streams) is Can be applied to

  Further, in the above embodiment, the case where the modulation scheme is QPSK, 16QAM, 64QAM and the coding rate is 1/2 has been described, but the present invention is not limited to this, and the present invention is not limited to this. Can be applied.

  Further, in the above embodiment, the case where communication is performed using two frequency bands f1 and f2 at the same time has been described. However, the present invention is not limited to this, and the case where communication is performed using more frequency bands at the same time. Can be applied to

  Further, the present invention is not limited to the above-described embodiment in terms of the type, arrangement, number, and the like of the members, but deviates from the gist of the invention, for example, by appropriately replacing its constituent elements with those having equivalent functions and effects. It can be changed appropriately within a range not to be performed.

  INDUSTRIAL APPLICABILITY The present invention is suitable for use in a base station that performs wireless communication using a part of a carrier frequency of a frequency band shared with another system.

Reference Signs List 100 base station 101, 311 MIMO antenna 102, 302 wireless receiving section 103 signal separating section 104, 303 demodulating section 105, 304 decoding section 106 P / S conversion section 107 level measuring section 108 frequency selecting section 109 MCS selecting section 110 control station communication Unit 111 Control signal generating unit 112, 306 Synthesizing unit 113, 308 Encoding unit 114, 309 Modulating unit 115 Multiplexing unit 116, 310 Wireless transmitting unit 117, 301 Antenna 200 Control station 201 Receiving unit 202 Handover control unit 203 Instruction signal generating unit 204 Transmitter 300 Mobile station 305 Control signal extractor 307 S / P converter

Claims (6)

A base station that performs wireless communication with a mobile station using a part of a carrier frequency of a frequency band shared with another system, and receives a MIMO-transmitted signal from the mobile station,
A receiving unit that receives a signal transmitted from the mobile station by MIMO,
A level measuring unit that measures an interference level and a signal level of the frequency band,
A frequency selection unit that selects a frequency band to be used for communication with the mobile station based on the interference level, and determines whether or not a transition of the frequency band is necessary.
An MCS selection unit that selects an MCS of each subframe based on a signal level of a frequency band selected by the frequency selection unit;
At the time of frequency transition, information indicating the frequency band selected by the frequency selection unit, and a transmission unit that transmits a control signal including information indicating the MCS selected by the MCS selection unit to the mobile station,
With
The MCS selector selects the lowest MCS among the MCSs of the respective substreams before the frequency transition at the time of the frequency transition, and applies the selected MCS to all the substreams immediately after the frequency transition.
base station. The MCS selector selects the lowest MCS among the MCSs of the respective sub-streams of all frequency bands before the frequency transition when simultaneously transiting a plurality of frequency bands, and immediately after the frequency transition, all the selected MCSs Applied to a substream of
The base station according to claim 1. The MCS selector selects the lowest MCS among the MCSs of each substream before the frequency transition for each frequency band when simultaneously transiting a plurality of frequency bands, and selects for each frequency band immediately after the frequency transition. Applying the MCS to all substreams in each frequency band,
The base station according to claim 1. The MCS selector selects the lowest MCS among the MCSs of each substream before handover at the time of handover, and applies the selected MCS to all substreams immediately after handover.
The base station according to claim 1. A communication system in which a mobile station and a base station perform wireless communication using a part of a carrier frequency of a frequency band shared with another system, and the base station receives a MIMO signal from the mobile station. ,
The base station comprises:
A receiving unit that receives a signal transmitted from the mobile station by MIMO,
A level measuring unit that measures an interference level and a signal level of the frequency band,
A frequency selection unit that selects a frequency band to be used for communication with the mobile station based on the interference level of the frequency band, and determines whether the transition of the frequency band is necessary.
An MCS selection unit that selects an MCS of each subframe based on a signal level of a frequency band selected by the frequency selection unit;
At the time of frequency transition, information indicating the frequency band selected by the frequency selection unit, and a transmission unit that transmits a control signal including information indicating the MCS selected by the MCS selection unit to the mobile station,
With
The MCS selection unit, at the time of frequency transition, selects the lowest MCS among the MCS of each sub-stream before the frequency transition, and immediately after the frequency transition, applies the selected MCS to all sub-streams,
The mobile station comprises:
A receiving unit that receives the control signal,
A transmitting unit that performs encoding and modulation on transmission data of each subframe based on the MCS of the control signal, and performs MIMO transmission of a signal in a frequency band included in the control signal;
Comprising,
Communications system. An MCS selection method of a base station that performs wireless communication with a mobile station using a part of a carrier frequency of a frequency band shared with another system and receives a signal MIMO-transmitted from the mobile station by MIMO,
Measuring the interference level and signal level of the frequency band,
Select a frequency band used for communication with the mobile station based on the interference level,
Determine the need for transition of the frequency band based on the interference level,
Other than at the time of frequency transition, select the MCS of each sub-frame based on the signal level of the selected frequency band,
At the time of the frequency transition, the lowest MCS among the MCSs of the respective substreams before the frequency transition is selected, and immediately after the frequency transition, the selected MCS is applied to all the substreams.
MCS selection method.

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