JP6585414B2 - Terminal, communication system and communication method therefor - Google Patents

Description

  The present invention relates to a terminal, a communication system, and a communication method thereof that perform time-division duplex wireless communication using a part of a frequency band shared with other systems.

  2. Description of the Related Art Conventionally, an FPU (Field Pick-up Unit) is known as a device used in a wireless communication system that performs video transmission such as live television broadcasts and emergency reports. This FPU is used for transmission of materials in the broadcasting field, transmits a UL (Up Link) signal of main line information from a mobile station (terminal) on the relay site side to a base station on the broadcasting station side, and transmits a base on the broadcasting station side. The DL (Down Link) signal of the return information is transmitted from the station to the mobile station on the relay site side. Video captured by the camera is file-transmitted in real time, transmitted as a UL signal from the mobile station to the base station, stored in a storage medium, and played back.

  The highest speed desired in the FPU is the UL signal of the main line information, which is video information used in broadcasting. The FPU employs a time division duplex (TDD) system in which the UL signal transmission period is longer than the DL signal transmission period in order to increase the UL signal transmission rate. In time division duplexing, a guard time is provided between the UL transmission period and the DL transmission period in order to absorb delay due to radio wave propagation (see Patent Document 1).

  In FPU, since wireless communication is performed using a part of the frequency band shared with other systems such as transceivers, it is necessary to constantly monitor the presence or absence of interference in the frequency band in use and prevent interference with other systems. . The FPU base station measures the reception level (interference amount) of each subcarrier, and when the reception level exceeds a predetermined threshold, another system starts using the frequency band (interference has occurred). The frequency of the local signal of the synthesizer is changed so that the use of the subcarrier is stopped and another subcarrier is used (see Patent Document 2).

Japanese Patent Laid-Open No. 9-51327 JP 2012-29253 A

  When the frequency of the local signal is changed, the synthesizer takes time until the changed frequency is stabilized. Conventionally, since no preamble, control signal, or data is transmitted on all subcarriers until the frequency becomes stable after the frequency change, the non-transmission period becomes longer, and the transmission efficiency decreases.

  An object of the present invention is to provide a terminal, a communication system, and a communication method thereof that can suppress a decrease in transmission efficiency when a synthesizer changes the frequency of a local signal.

  A terminal according to the present invention is a terminal that transmits and receives an OFDM signal to and from a base station using a part of a carrier frequency in a frequency band shared with other systems, and indicates a subcarrier selected by the base station An OFDM signal obtained by performing orthogonal frequency division multiplexing on a signal including a receiving unit that receives the OFDM signal including information, a synthesizer that generates a local signal having a frequency of the selected subcarrier, and a preamble and a control signal An OFDM signal generation unit that generates a signal, and a transmission unit that wirelessly transmits the OFDM signal using a local signal having a frequency of the selected subcarrier, and the base station is in communication When a change of some subcarriers is selected, the synthesizer transmits the subkey at the preamble transmission start timing. The frequency of the local signal is changed in accordance with the change of the rear, and the OFDM signal generation unit changes the frequency after the change in the switching period including at least the time until the synthesizer is stabilized after the frequency of the local signal is changed. The OFDM signal is generated so that the preamble is transmitted from an unmodified subcarrier without transmitting the preamble from a subcarrier.

  A communication system according to the present invention is a communication system including a base station and a terminal that transmit and receive an OFDM signal using a part of a carrier frequency in a frequency band shared with other systems, and the base station transmits and receives data. A subcarrier selection unit that selects a subcarrier to be used, a control signal generation unit that generates a downlink control signal including information indicating the selected subcarrier, a downlink preamble, and a downlink signal that includes the downlink control signal An OFDM signal generation unit that performs orthogonal frequency division multiplexing processing to generate a downlink OFDM signal, and a transmission unit that transmits the downlink OFDM signal to the terminal. A receiving unit for receiving the OFDM signal including information indicating the selected subcarrier; and a local signal having a frequency of the selected subcarrier. An OFDM signal generator for generating an OFDM signal by performing orthogonal frequency division multiplexing on a signal including a synthesizer, a preamble, and a control signal; and the OFDM using a local signal of the frequency of the selected subcarrier A transmission unit that up-converts a signal and wirelessly transmits the signal, and when the base station selects a change of some of the subcarriers in communication by the subcarrier selection unit, the synthesizer of the terminal At the preamble transmission start timing, the frequency of the local signal is changed in accordance with the change of the subcarrier, and the OFDM signal generation unit of the terminal stabilizes at least the synthesizer after the frequency of the local signal is changed. In the switching period including the time until Without transmitting amble to generate the OFDM signal to transmit the preamble from the unmodified subcarrier.

A communication method according to the present invention is a communication method between a base station and a terminal that transmits and receives an OFDM signal using a part of carrier frequencies in a frequency band shared with other systems, and the base station transmits and receives data. Select a subcarrier to be used, generate a downlink control signal including information indicating the selected subcarrier, and perform orthogonal frequency division multiplexing on the downlink preamble and the downlink signal including the downlink control signal. Generating a downlink OFDM signal, transmitting the downlink OFDM signal to the terminal, the terminal receiving the downlink OFDM signal including information indicating a subcarrier selected by the base station, and selecting the selected Local signal of the subcarrier frequency is generated, and orthogonal frequency division multiplexing processing is performed on the upstream signal including the upstream preamble and the upstream control signal. An OFDM signal for transmission, up-converting the uplink OFDM signal using a local signal of the frequency of the selected subcarrier and wirelessly transmitting, and changing some of the subcarriers that the base station is communicating with When the terminal changes the frequency of the local signal in accordance with the change of the subcarrier at the transmission start timing of the uplink preamble, and at least until the synthesizer is stabilized after changing the frequency of the local signal The uplink OFDM signal is generated such that the uplink preamble is not transmitted from the subcarrier after the change, and the uplink preamble is transmitted from the unmodified subcarrier in the switching period including the above time.

  According to the present invention, when a part of subcarriers in communication is changed, a preamble and a control signal can be transmitted on unchanged subcarriers, so that a reduction in transmission efficiency can be suppressed.

The block diagram which shows the structure of the base station which concerns on Embodiment 1 of this invention. The block diagram which shows the structure of the terminal which concerns on Embodiment 1 of this invention. The figure explaining the frame structure and subcarrier selection of the radio | wireless communications system which concerns on Embodiment 1 of this invention. The flowchart which shows the frequency change operation | movement of the terminal which concerns on Embodiment 1 of this invention. The figure which shows the state of the preamble of IEEE802.11 standard etc. The figure explaining the frame structure and subcarrier selection of the radio | wireless communications system which concerns on Embodiment 1 of this invention. The block diagram which shows the internal structure of the synthesizer part of the terminal which concerns on Embodiment 2 of this invention. The figure explaining the frame structure and subcarrier selection of the radio | wireless communications system which concerns on Embodiment 2 of this invention. The figure explaining the frame structure and subcarrier selection of the radio | wireless communications system which concerns on Embodiment 2 of this invention.

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

(Embodiment 1)
<Base station configuration>
FIG. 1 is a block diagram showing a configuration of base station 100 according to Embodiment 1 of the present invention. As shown in FIG. 1, the base station 100 includes a control signal generation unit 101, a pilot symbol generation unit 102, a preamble generation unit 103, a modulation unit 105, a timing control unit 106, a switching unit 107, an S / P unit 108, IFFT unit 109, GI addition unit 110, radio transmission unit 111, radio reception unit 112, level measurement unit 113, subcarrier selection unit 114, synthesizer unit 115, and synchronous detection unit 116 GI removal section 117, FFT section 118, channel estimation section 119, channel compensation section 120, P / S section 121, and demodulation section 122. The timing control unit 106, the switching unit 107, the S / P unit 108, the IFFT unit 109, and the GI addition unit 110 constitute an OFDM (orthogonal frequency division multiplexing) signal generation unit 151.

  Control signal generating section 101 generates a control signal including selected subcarrier information output from subcarrier selecting section 114 and outputs the control signal to switching section 107. The control signal includes information indicating the length of the guard time, Ack / Nack, link adaptation information, and the like.

  Pilot symbol generating section 102 generates a pilot symbol known by terminal 200 (see FIG. 2) and outputs the pilot symbol to switching section 107.

  The preamble generation unit 103 generates a preamble that is known to the terminal 200 (see FIG. 2) and outputs the preamble to the switching unit 107. In the terminal 200, the preamble is used for AGC (Automatic Gain Control), timing detection, AFC (Automatic Frequency Control), and the like.

  Modulation section 105 modulates transmission data (DL data) and outputs the transmission signal to switching section 107. Note that transmission data before modulation is subjected to encoding processing such as error correction encoding and interleaving.

  The timing control unit 106 transmits the preamble output from the preamble generation unit 103 and the pilot output from the pilot symbol generation unit 102 to the switching unit 107 so that the OFDM signal has a predetermined frame configuration (see FIG. 3). The timing at which the symbol, the control signal output from the control signal generation unit 101, and the transmission signal output from the modulation unit 105 are output to the S / P unit 108 is controlled. In particular, when the timing control unit 106 receives flag information indicating that the subcarrier is to be changed from the subcarrier selection unit 114, the timing control unit 106 sets the frequency change timing so as to change the frequency at the preamble transmission start timing of the terminal 200. An instruction signal for instructing is output to the synthesizer unit 115.

  Based on the control of the timing control unit 106, the switching unit 107 includes a preamble output from the preamble generation unit 103, a pilot symbol output from the pilot symbol generation unit 102, a control signal output from the control signal generation unit 101, and a modulation unit One of the transmission signals output from 105 is output to the S / P unit 108. Note that the switching unit 107 outputs nothing to the S / P unit 108 during the guard time and UL signal sections.

  The S / P unit 108 converts the signal sequence output in series from the switching unit 107 into n (n is an integer of 2 or more) parallel signal sequences (serial / parallel), and outputs them to the IFFT unit 109.

  The IFFT unit 109 performs an IFFT (inverse Fourier transform process) on the parallel signal (the signal on the frequency axis) output from the S / P unit 108, whereby an OFDM signal superimposed on n subcarriers ( DL signal) is generated and output to the GI adding unit 110.

  The GI adding unit 110 adds a GI (guard interval) obtained by copying a part of the effective symbol waveform to the OFDM symbol output from the IFFT unit 109 at the head of the effective symbol, and outputs it to the radio transmission unit 111. .

  The wireless transmission unit 111 performs wireless transmission processing such as amplification and filtering on the OFDM signal output from the GI addition unit 110. Then, the wireless transmission unit 111 up-converts the signal after the wireless transmission process using the local signal output from the synthesizer unit 115 to obtain a wireless signal. Then, the wireless transmission unit 111 transmits a wireless signal (DL signal) from the antenna.

  The wireless reception unit 112 performs wireless reception processing such as amplification and filtering on the wireless signal (UL signal) received by the antenna. Further, the wireless reception unit 112 down-converts the signal after the wireless reception processing using the local signal output from the synthesizer unit 115 to obtain a baseband OFDM signal. Radio receiving section 112 then outputs the OFDM signal to level measuring section 113 and synchronous detection section 116.

  Level measurement section 113 measures the guard level reception level (interference amount) and outputs the measurement value to subcarrier selection section 114.

  The subcarrier selection unit 114 continuously selects, as a subcarrier, a frequency at which the measurement value of the reception level of the guard time is equal to or lower than the threshold value in the subcarrier in use. In addition, when there is a frequency at which the measured value of the reception level of the guard time exceeds the threshold, the subcarrier selection unit 114 determines that another system has started using the frequency (interference has occurred), and The use of the frequency is stopped, and the subcarrier is changed to use another subcarrier. Subcarrier selection section 114 then outputs selected subcarrier information indicating the selected subcarrier to control signal generation section 101 and synthesizer section 115. Further, the subcarrier selection unit 114 outputs flag information indicating that the subcarrier is changed to the timing control unit 106.

  The synthesizer unit 115 generates a local signal having the frequency of the subcarrier selected by the subcarrier selection unit 114 and outputs the local signal to the radio transmission unit 111 and the radio reception unit 112. When changing the subcarrier, the synthesizer unit 115 generates a local signal of the frequency of the subcarrier newly selected by the subcarrier selection unit 114 at the timing instructed by the timing control unit 106.

  The synchronous detection unit 116 performs synchronous detection processing using the preamble of the OFDM signal output from the wireless reception unit 112, and outputs the OFDM signal to the GI removal unit 117 at a predetermined timing.

  GI removal section 117 removes the guard interval from each symbol of the OFDM signal output from synchronous detection section 116, and outputs the result to FFT section 118.

  FFT section 118 performs an FFT (Fourier transform process) on the OFDM signal output from GI removal section 117 to extract a signal sequence superimposed on each subcarrier, and sends pilot symbols to channel estimation section 119. The control signal and the received signal (data symbol) are output to the channel compensation unit 120.

  The channel estimation unit 119 performs channel estimation for each subcarrier by calculating the correlation between the pilot symbol output from the FFT unit 118 and a known pilot pattern, and the channel compensation value as an estimation result is calculated by the channel compensation unit 120. Output to.

  Channel compensation section 120 compensates for channel fluctuations in the control signal and the received signal (data symbol) using the channel estimation value, and outputs the control signal and the received signal to P / S section 121.

  The P / S unit 121 converts the n signal sequences output in parallel from the channel compensation unit 120 into a serial signal sequence (parallel / serial), and outputs the control signal and the received signal to the demodulation unit 122.

  The demodulator 122 demodulates the control signal to obtain control information. The demodulator 122 demodulates the received signal to obtain received data (UL data). The demodulated received data is subjected to decoding processing such as deinterleaving, error correction decoding, and error detection.

<Terminal configuration>
FIG. 2 is a block diagram showing a configuration of terminal 200 according to the present embodiment. As shown in FIG. 2, terminal 200 includes radio reception section 201, synchronous detection section 202, GI removal section 203, FFT section 204, channel estimation section 205, channel compensation section 206, and P / S section. 207, demodulation section 208, synthesizer section 210, control signal generation section 211, pilot symbol generation section 212, preamble generation section 213, modulation section 215, timing control section 216, switching section 217, S / P unit 218, IFFT unit 219, GI adding unit 220, and wireless transmission unit 221 are mainly configured. The timing control unit 216, the switching unit 217, the S / P unit 218, the IFFT unit 219, and the GI adding unit 220 constitute an OFDM signal generation unit 251.

  The wireless reception unit 201 performs wireless reception processing such as amplification and filtering on the wireless signal (DL signal) received by the antenna. Further, the wireless reception unit 201 down-converts the signal after the wireless reception processing using the local signal output from the synthesizer unit 210 to obtain a baseband OFDM signal. Radio receiving section 201 then outputs the OFDM signal to synchronous detection section 202. Here, the wireless reception unit 201 performs AGC, timing detection, AFC, and the like at the frequency at which the preamble is transmitted, and reflects these measurement results in the received signals at other frequencies. The wireless reception unit 201 can also perform AGC, timing detection, AFC, and the like using the previous measurement result.

  The synchronous detection unit 202 performs synchronous detection processing using the preamble of the OFDM signal output from the wireless reception unit 201, and outputs the OFDM signal to the GI removal unit 203 at a predetermined timing.

  GI removal section 203 removes the guard interval from each symbol of the OFDM signal output from synchronous detection section 202, and outputs the result to FFT section 204.

  FFT section 204 performs an FFT (Fourier transform process) on the OFDM signal output from GI removal section 203 to extract a signal sequence superimposed on each subcarrier, and sends pilot symbols to channel estimation section 205. The control signal and the received signal (data symbol) are output to the channel compensation unit 206.

  The channel estimation unit 205 performs channel estimation for each subcarrier by calculating a correlation between the pilot symbol output from the FFT unit 204 and a known pilot pattern, and a channel estimation value as an estimation result is calculated by the channel compensation unit 206. Output to.

  Channel compensation section 206 compensates for channel fluctuations in the control signal and the received signal (data symbol) using the channel estimation value, and outputs the control signal and the received signal to P / S section 207.

  P / S section 207 converts n signal sequences output in parallel from channel compensation section 206 into a serial signal string (parallel / serial), and outputs a control signal and a received signal to demodulation section 208.

  The demodulator 208 demodulates the control signal to obtain control information. Demodulation section 208 then outputs selected subcarrier information in the control information to synthesizer section 210 and timing control section 216. The demodulator 208 demodulates the reception signal to obtain reception data (DL data). The demodulated received data is subjected to decoding processing such as deinterleaving, error correction decoding, and error detection.

  Synthesizer section 210 generates a local signal having the frequency of the subcarrier indicated by the selected subcarrier information output from demodulation section 208 and outputs the local signal to radio reception section 201 and radio transmission section 221. When changing the subcarrier, the synthesizer unit 210 generates a local signal of the frequency of the subcarrier newly indicated by the selected subcarrier information at the timing instructed by the timing control unit 216.

  The control signal generation unit 211 generates a control signal and outputs it to the switching unit 217. The control signal includes information indicating the length of the guard time, Ack / Nack, and the like.

  Pilot symbol generation section 212 generates a pilot symbol that base station 100 is known to output to switching section 217.

  The preamble generation unit 213 generates a preamble that is known to the base station 100 and outputs the preamble to the switching unit 217.

  Modulation section 215 modulates transmission data (UL data) and outputs the transmission signal to switching section 217. Note that transmission data before modulation is subjected to encoding processing such as error correction encoding and interleaving.

  The timing control unit 216 outputs the preamble output from the preamble generation unit 213 and the pilot output from the pilot symbol generation unit 212 to the switching unit 217 so that the OFDM signal has a predetermined frame configuration (see FIG. 3). The timing at which the symbol, the control signal output from the control signal generation unit 211, and the transmission signal output from the modulation unit 215 are output to the S / P unit 218 is controlled. In particular, when the selected subcarrier information is input, the timing control unit 216 outputs an instruction signal for instructing the frequency change timing to the synthesizer unit 210 so as to change the frequency at the preamble transmission start timing. In addition, the timing control unit 216 outputs a preamble and a control signal in the changed subcarrier in a predetermined period (hereinafter referred to as “switching period”) including at least a time until the synthesizer is stabilized after changing the frequency. Instead, the switching unit 217 is controlled to set the guard time.

  Based on the control of the timing control unit 216, the switching unit 217 includes a preamble output from the preamble generation unit 213, a pilot symbol output from the pilot symbol generation unit 212, a control signal output from the control signal generation unit 211, and a modulation unit One of the transmission signals output from 215 is output to the S / P unit 218. Note that the switching unit 217 outputs nothing to the S / P unit 218 during the guard time and DL signal sections.

  The S / P unit 218 converts the signal sequence output in series from the switching unit 217 into n parallel signal sequences (serial / parallel), and outputs the signal sequence to the IFFT unit 219.

  The IFFT unit 219 performs an IFFT (inverse Fourier transform process) on the parallel signal (the signal on the frequency axis) output from the S / P unit 218, whereby an OFDM signal superimposed on n subcarriers ( DL signal) is generated and output to the GI adding unit 220.

  GI adding section 220 adds a GI (guard interval) obtained by copying a part of the effective symbol waveform to the OFDM symbol output from IFFT section 219 to the head of the effective symbol, and outputs the result to radio transmitting section 221. .

  The wireless transmission unit 221 performs wireless transmission processing such as amplification and filtering on the OFDM signal output from the GI addition unit 220. Then, the wireless transmission unit 221 up-converts the signal after the wireless transmission processing using the local signal output from the synthesizer unit 210 to obtain a wireless signal. Then, the wireless transmission unit 221 transmits a wireless signal (DL signal) from the antenna.

<Frame configuration and subcarrier selection>
Next, frame configuration and subcarrier selection in the wireless communication system of the present embodiment will be described in detail with reference to FIG. 3 (the horizontal axis in FIG. 3 is time). FIG. 3 shows a case where base station 100 and terminal 200 are communicating using two subcarriers. FIG. 3 shows a case where the first synthesizer S1 and the second synthesizer S2 of the terminal 200 generate local signals having frequencies corresponding to the respective subcarriers.

  As shown in FIG. 3, in the radio communication system (FPU) of the present embodiment, a time division duplex (TDD) in which a UL section (UL signal transmission section) is longer than a DL section (DL signal transmission section). Time Division Duplex) method is adopted. Note that the FPU may not transmit data symbols (no data section is provided) in the DL section. Further, the FPU may transmit only the UL signal without transmitting the DL signal (without providing a DL section) in a predetermined frame.

  A guard time (GT) in which no signal is transmitted is provided between the UL section and the DL section. A preamble is transmitted at the beginning of the UL section, a control signal is transmitted next, and then data is transmitted. Note that pilot symbols are inserted into the data at predetermined intervals.

  In FIG. 3, in a state where the first synthesizer S1 is set to the frequency f1 and the second synthesizer S2 is set to the frequency f2, the base station 100 changes from the subcarrier of the frequency f2 to the subcarrier of the frequency f4. Is selected. In this case, the terminal 200 changes the set frequency of the second synthesizer S2 from f2 to f4 at the timing t0. Also, terminal 200 does not transmit a preamble or control signal in the switching period Tx in the subcarrier (f2 → f4) to be changed, and sets it as a guard time. Note that the terminal 200 transmits a preamble and a control signal in the switching period Tx in the subcarrier (f1) that is not changed.

<Terminal frequency change operation>
Next, frequency changing operation of terminal 200 according to the present embodiment will be described in detail with reference to FIG.

  When terminal 200 changes the frequency used by base station 100 for communication and inputs selected subcarrier information indicating that (ST301: YES), terminal 200 changes the frequency in the synthesizer corresponding to the selected subcarrier information. A later frequency is set (ST302). Terminal 200 transmits a preamble and a control signal from only the unchanged frequency (ST303). Then, after the synthesizer of the changed frequency is stabilized (ST304), terminal 200 transmits UL data from all frequencies being used for communication (ST307).

  Terminal 200 does not change the frequency unless the selected subcarrier information is input (ST301: NO) (ST305). In this case, terminal 200 transmits a preamble and a control signal from all frequencies used for communication (ST306), and transmits UL data (ST307).

<Effect>
Thus, according to the present embodiment, when changing some of the subcarriers used for communication, the preamble and the control signal can be transmitted on the unmodified subcarriers. The decrease can be suppressed.

  In general, since the control information has a small amount of information, even if the control signal is transmitted using only some of the subcarriers, it is possible to transmit the amount of control information necessary for communication on all the subcarriers.

  Further, the base station 100 can perform AGC, timing detection, AFC, and the like using the previous measurement result. For this reason, the base station 100 can maintain desired quality even if AGC, timing detection, AFC, and the like are performed on all subcarriers using preambles transmitted from some subcarriers.

  In the present embodiment, when switching period Tx is shorter than the preamble transmission period (when the synthesizer stabilizes within the preamble transmission period), terminal 200 transmits only the preamble after timing t0. Instead, a control signal may be transmitted.

  Further, when a plurality of identical preambles are continuously transmitted as in the IEEE802.11 standard (see FIG. 5), as shown in FIG. 6, the terminal 200 transmits the preamble after the switching period Tx has elapsed. The number may be reduced and transmitted. For example, when eight identical preambles are transmitted continuously, four preambles can be transmitted at the frequency f4.

(Embodiment 2)
In Embodiment 2, when terminal 200 communicates with base station 100 using n (n is a natural number) subcarriers, subcarriers are changed using (n + 1) synthesizers. The case will be described. In the second embodiment, the configurations of base station 100 and terminal 200 are the same as those shown in FIGS. 1 and 2 used in the description of the first embodiment, and thus the description thereof is omitted.

<Internal configuration of synthesizer>
FIG. 7 is a block diagram showing an internal configuration of synthesizer section 210 of terminal 200 according to the present embodiment. As illustrated in FIG. 7, the synthesizer unit 210 includes (n + 1) synthesizers 210a-1 to 210a-n + 1 and a local switching unit 210b.

  Each of synthesizers 210a-1 to 210a-n generates a local signal having a frequency indicated in the selected subcarrier information. Further, when the synthesizers 210a-1 to 210a-n receive the instruction signal from the timing control unit 216, the synthesizers 210a-1 to 210a-n are configured to generate a local signal having a frequency of the subcarrier newly indicated by the selected subcarrier information at the instructed timing. To switch the frequency of the local signal.

  The synthesizer 210a-n + 1 generates a local signal having a spare frequency that is not used for data communication. Note that the backup frequency is known between base station 100 and terminal 200, and is notified from base station 100 to terminal 200 by the selected subcarrier information at the start of communication.

  The local switching unit 210b is configured to transmit the local signal generated by the synthesizers 210a-1 to 210a-n to the wireless transmission unit 111 and the wireless reception unit during normal times (when the synthesizers 210a-1 to 210a-n are stable). To 112. Further, when the instruction signal is input from the timing control unit 216, the local switching unit 210b replaces the local signal of the frequency switching target synthesizer 210a-i (i is any integer from 1 to n) during the switching period. The local signal of synthesizer 210a-n + 1 is output. In addition, the local switching unit 210b outputs the local signal of the synthesizer 210a-i that is in a stable state after the switching of the frequency, instead of the local signal of the synthesizer 210a-n + 1, at the timing when the switching period has elapsed. .

<Frame configuration and subcarrier selection>
Next, frame configuration and subcarrier selection in the wireless communication system of this embodiment will be described in detail with reference to FIG. 8 (the horizontal axis in FIG. 8 is time). FIG. 8 shows a case where base station 100 and terminal 200 communicate using two subcarriers (when n = 2). In FIG. 8, the first synthesizer S1 and the second synthesizer S2 of the terminal 200 generate local signals having frequencies corresponding to the subcarriers, and the third synthesizer S3 generates local signals having a spare frequency. Shows the case.

  In FIG. 8, in a state where the first synthesizer S1 is set to the frequency f1, the second synthesizer S2 is set to the frequency f2, and the third synthesizer S3 is set to the standby frequency f3, the base station 100 has the frequency f2. Suppose that it has selected changing from a subcarrier to the subcarrier of the frequency f4. In this case, the terminal 200 changes the set frequency of the second synthesizer S2 from f2 to f4 at the timing t0. Also, terminal 200 (local switching unit 210b) does not transmit a preamble or control signal in the switching period Tx in the subcarrier (f2 → f4) to be changed, and sets it as a guard time. Instead, in the switching period T, the terminal 200 transmits a preamble and a control signal using the subcarrier (f3) of the backup frequency with the local signal of the third synthesizer S3. Terminal 200 transmits a preamble and a control signal even in switching period T on subcarrier (f1) that is not changed.

<Effect>
As described above, according to the present embodiment, when the subcarrier is changed, the preamble and the control signal can be transmitted on the subcarrier of the backup frequency, so that a decrease in transmission efficiency can be suppressed.

  In addition, this Embodiment is applicable also when changing all the subcarriers during communication simultaneously, as shown in FIG. In FIG. 9, it is assumed that the terminal 200 changes the setting frequency of the first synthesizer S1 from f1 to f4 and changes the setting frequency of the second synthesizer S2 from f2 to f5 at the timing t0. In this case, terminal 200 (local switching unit 210b) does not transmit a preamble or control signal in the switching period Tx in the subcarrier (f1 → f4, f2 → f5) to be changed, and sets the guard time. Instead, in the switching period T, the terminal 200 transmits a preamble and a control signal using the subcarrier (f3) of the backup frequency with the local signal of the third synthesizer S3.

  In the present embodiment, depending on communication conditions, only one frequency may be used for communication. Also in such a case, similarly, in the switching period T, the terminal 200 transmits a preamble and a control signal on the subcarrier (f3) of the backup frequency using the local signal of the third synthesizer S3.

  As described above, in this embodiment, even when all subcarriers in communication are changed simultaneously (including the case where only one frequency can be used for communication), the preamble and control are performed on the subcarriers of the backup frequency. Since a signal can be transmitted, a decrease in transmission efficiency can be suppressed.

  In addition, this invention is not limited to the said embodiment, It can change suitably in the range which does not deviate from the summary of invention, such as replacing suitably the component to what has an equivalent effect.

  The present invention is suitable for use in a wireless communication system that transmits and receives an OFDM signal using a part of a frequency band shared with other systems, such as an FPU. In addition to the FPU, in the event of a disaster, a large-scale event, traffic jams on expressways and general roads, public vehicles such as trains and buses are congested, robots, etc. In the case of performing communication (communication method generally called MtoM communication or DtoD communication) or the like, a plurality of communication traffic is expected. Therefore, even in such a case, the present invention is suitable.

100 base station 101, 211 control signal generation unit 102, 212 pilot symbol generation unit 103, 213 preamble generation unit 105, 215 modulation unit 106, 216 timing control unit 107, 217 switching unit 108, 218 S / P unit 109, 219 IFFT Unit 110, 220 GI addition unit 111, 221 radio transmission unit 112, 201 radio reception unit 113 level measurement unit 114 subcarrier selection unit 115, 210 synthesizer unit 116, 202 synchronous detection unit 117, 203 GI removal unit 118, 204 FFT unit 119, 205 Channel estimation unit 120, 206 Channel compensation unit 121, 207 P / S unit 122, 208 Demodulation unit 151, 251 OFDM signal generation unit 200 Terminal 210a Synthesizer 210b Local switching unit

Claims (6)

A terminal that transmits and receives an OFDM signal to and from a base station using a part of a carrier frequency in a frequency band shared with another system,
A receiver that receives the OFDM signal including information indicating a subcarrier selected by the base station;
A synthesizer for generating a local signal having a frequency of the selected subcarrier;
An OFDM signal generator for generating an OFDM signal by performing orthogonal frequency division multiplexing on a signal including a preamble and a control signal;
A transmitter that up-converts and wirelessly transmits the OFDM signal using a local signal of the frequency of the selected subcarrier;
Comprising
When the base station has selected to change some of the subcarriers in communication,
The synthesizer changes the frequency of the local signal in accordance with the change of the subcarrier at the transmission start timing of the preamble,
The OFDM signal generation unit does not transmit the preamble from the subcarrier after the change in the switching period including at least a time until the synthesizer is stabilized after the frequency of the local signal is changed, Generating the OFDM signal to transmit the preamble from a carrier;
Terminal. When the switching period is longer than the preamble transmission period, the OFDM signal generation unit does not transmit the preamble and the control signal from the changed subcarrier in the switching period, and the unchanged subcarrier. Generating the OFDM signal to transmit the preamble and the control signal from:
The terminal according to claim 1. When a plurality of the same preambles are continuously transmitted and the switching period is shorter than the transmission period of the preamble, the OFDM signal generation unit, after the switching period has elapsed, To reduce the number of preambles and transmit
The terminal according to claim 1. The synthesizer generates a local signal having a frequency of the selected subcarrier and a local signal having a spare frequency that is not used for data communication.
When the base station has selected to change some of the subcarriers in communication,
The synthesizer changes the frequency of the local signal in accordance with the change of the subcarrier at the transmission start timing of the preamble, and the spare frequency instead of the local signal of the frequency of the changed subcarrier in the switching period. Output the local signal to the transmitter,
In the switching period, the OFDM signal generation unit does not transmit the preamble from the changed subcarrier, and transmits the preamble from the unmodified subcarrier and the spare frequency subcarrier. Generate
The terminal according to claim 1. A communication system comprising a base station and a terminal that transmit and receive an OFDM signal using a part of a carrier frequency in a frequency band shared with another system,
The base station is
A subcarrier selector for selecting a subcarrier used for data transmission and reception;
A control signal generator for generating a downlink control signal including information indicating the selected subcarrier;
An OFDM signal generation unit that generates an OFDM signal for downlink by performing orthogonal frequency division multiplexing on the downlink signal including the downlink preamble and the downlink control signal;
A transmitter for transmitting the downlink OFDM signal to the terminal;
Comprising
The terminal is
A receiver that receives the OFDM signal including information indicating a subcarrier selected by the base station;
A synthesizer for generating a local signal having a frequency of the selected subcarrier;
An OFDM signal generator for generating an OFDM signal by performing orthogonal frequency division multiplexing on a signal including a preamble and a control signal;
A transmitter that up-converts and wirelessly transmits the OFDM signal using a local signal of the frequency of the selected subcarrier;
Comprising
When the base station selects a change of some subcarriers in communication by the subcarrier selection unit,
The synthesizer of the terminal changes the frequency of the local signal in accordance with the change of the subcarrier at the transmission start timing of the preamble,
The OFDM signal generation unit of the terminal does not transmit the preamble from the subcarrier after the change in the switching period including at least the time until the synthesizer is stabilized after the frequency of the local signal is changed, Generating the OFDM signal to transmit the preamble from a modified subcarrier;
Communications system. A communication method between a base station and a terminal that transmits and receives an OFDM signal using a part of carrier frequencies in a frequency band shared with other systems,
The base station is
Select the subcarrier used for data transmission and reception,
A downlink control signal including information indicating the selected subcarrier is generated;
Downlink preamble, and downlink signal including the downlink control signal are subjected to orthogonal frequency division multiplexing processing to generate a downlink OFDM signal,
Transmitting the downlink OFDM signal to the terminal;
The terminal is
Receiving the downlink OFDM signal including information indicating the subcarrier selected by the base station;
Generating a local signal of the frequency of the selected subcarrier;
An uplink OFDM signal is generated by performing orthogonal frequency division multiplexing on an uplink signal including an uplink preamble and an uplink control signal,
Up-converting the uplink OFDM signal using a local signal having a frequency of the selected subcarrier, and wirelessly transmitting,
When the base station has selected to change some of the subcarriers in communication,
The terminal is
Change the frequency of the local signal according to the change of the subcarrier at the transmission start timing of the uplink preamble,
In the switching period including at least the time until the synthesizer is stabilized after changing the frequency of the local signal, the uplink preamble is not transmitted from the changed subcarrier, and the uplink preamble is not transmitted from the unmodified subcarrier. Generating the uplink OFDM signal to transmit,
Communication method.

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