JP6585415B2 - 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 A receiving unit that receives the OFDM signal including information, a synthesizer unit that generates a local signal having a frequency of the selected subcarrier, and an OFDM that generates an OFDM signal by performing orthogonal frequency division multiplexing on an uplink signal A signal generation unit, a GI addition unit for adding a guard interval to the OFDM signal, and up-converting and wirelessly transmitting the OFDM signal to which the guard interval is added using a local signal having a frequency of the selected subcarrier. comprising a transmitter, a, before starting communication with the base station, from said base station, the subcarrier frequency Is notified guard interval timing to be changed, the synthesizer section, for each subcarrier, has two synthesizer to generate a local signal of a frequency of one sub-carrier currently in communication from one synthesizer, the When the base station has selected to change the subcarrier in communication, the guard interval after the local synthesizer generates a local signal of the frequency of the changed subcarrier and the time until the other synthesizer becomes stable has elapsed. The output of the local signal is switched.

A communication system according to the present invention is a communication system between a base station and a terminal that transmits and receives an OFDM signal using a part of a carrier frequency in a frequency band shared with another system, 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, and a downlink signal by performing orthogonal frequency division multiplexing processing on the downlink signal An OFDM signal generation unit that generates an OFDM signal for transmission and a transmission unit that transmits the OFDM signal for downlink to the terminal, and the terminal includes information indicating a subcarrier selected by the base station A receiving unit that receives an OFDM signal, a synthesizer unit that generates a local signal having a frequency of the selected subcarrier, and an upstream signal. An OFDM signal generation unit that generates an OFDM signal by performing frequency division multiplexing processing, a GI addition unit that adds a guard interval to the OFDM signal, and the guard interval using a local signal having a frequency of the selected subcarrier. A transmission unit that up-converts the added OFDM signal and wirelessly transmits the signal, and before the base station starts communication with the terminal, the base station sets a guard interval of timing for changing the frequency of the subcarrier to the terminal. The synthesizer unit of the terminal has two synthesizers for each subcarrier, and generates a local signal of the frequency of one subcarrier currently in communication from one synthesizer, and the base station If the subcarrier selection unit selects to change the subcarrier in communication, the other synthesizer To generate a local signal of a frequency of subcarriers the changed from The, the other synthesizer in the guard interval after a lapse of time to stabilize, to switch the output of the local signal.

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, perform orthogonal frequency division multiplexing on the downlink signal to generate a downlink OFDM signal, and generate the downlink OFDM signal. An OFDM signal is transmitted to the terminal, and the terminal receives the downlink OFDM signal including information indicating the subcarrier selected by the base station, and generates a local signal having a frequency of the selected subcarrier. Then, an uplink OFDM signal is generated by performing orthogonal frequency division multiplex processing on the uplink signal, a guard interval is added to the OFDM signal, and the selection is performed. Was up-converts the OFDM signal in which the guard interval is added using a local signal of the frequency subcarrier transmitted by radio, the base station, before starting communication with the terminal, to change the frequency of the subcarrier The timing guard interval is notified to the terminal, and the terminal has two synthesizers for each subcarrier, and generates a local signal of a frequency of one subcarrier currently in communication from one synthesizer, When the base station has selected to change the subcarrier in communication, the guard interval after the local synthesizer generates a local signal of the frequency of the changed subcarrier and the time until the other synthesizer becomes stable has elapsed. The output of the local signal is switched.

  According to the present invention, since a signal can be transmitted without interruption even when changing a subcarrier, it is possible to suppress a decrease in transmission efficiency when the synthesizer changes the frequency of a local signal.

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 block diagram which shows the internal structure of the synthesizer part 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 explaining the frame structure and subcarrier selection of the radio | wireless communications system 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 figure explaining the frame structure and subcarrier selection of the radio | wireless communications system which concerns on Embodiment 1 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 to the switching unit 107 and the pilot output from the pilot symbol generation unit 102 so that the OFDM signal has a predetermined frame configuration (see FIG. 4). 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.

  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. Details (internal configuration) of the synthesizer unit 210 will be described later.

  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. 4). 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 changes the frequency so that the frequency is changed so that the frequency is changed at least within the GI after the time until the synthesizer stabilizes. Is output to the synthesizer unit 210.

  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.

<Internal configuration of synthesizer>
Next, the internal configuration of synthesizer section 210 of terminal 200 of the present embodiment will be described using the block diagram of FIG. As shown in FIG. 3, the synthesizer unit 210 includes two synthesizers 210 i-1 and 210 i-2 and one local switching unit for each subcarrier i (i is any integer from 1 to n). And a synthesizer unit 210i composed of 210i-3.

  One of the synthesizers 210i-1 and 210i-2 generates a local signal having a frequency of the current subcarrier i. In addition, when the selected subcarrier information is newly input, the other of the synthesizers 210i-1 and 210i-2 generates a local signal having a frequency of the subcarrier i indicated by the selected subcarrier information.

  The local switching unit 210 i-3 switches the synthesizer 210 i that connects the wireless transmission unit 111 and the wireless reception unit 112 based on the instruction signal input from the timing control unit 216. Specifically, the local switching unit 210i-3 includes the wireless transmission unit 111 and the wireless reception unit 112, and one of the synthesizers 210i-1 and 210i-2 that generate local signals of the current frequency of the subcarrier i. Connect. Further, when the instruction signal is input from the timing control unit 216, the local switching unit 210i-3 connects the wireless transmission unit 111 and the wireless reception unit 112 to the other of the synthesizers 210i-1 and 210i-2 at the instructed timing. To do.

<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. 4 (the horizontal axis in FIG. 4 is time). FIG. 4 shows a frame configuration in one of the subcarriers used by base station 100 and terminal 200 for communication.

  As shown in FIG. 4, 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. A GI is added to the head of each symbol. In some cases, a preamble is transmitted in the UL period, a pilot symbol is transmitted next, and then a control signal is transmitted. Further, the pilot symbols may be inserted into the UL data after the control signal at regular time intervals.

  The first synthesizer S1 and the second synthesizer S2 shown in FIG. 4 correspond to the synthesizers 210i-1 and 210i-2 in FIG.

  In FIG. 4, first, it is assumed that the first synthesizer S1 generates a local signal of the current subcarrier frequency f2. In this case, the terminal 200 outputs the local signal of the frequency f2 generated from the first synthesizer S1 to the wireless transmission unit 111 and the wireless reception unit 112.

  Thereafter, in this state, it is assumed that base station 100 has selected to change from a subcarrier of frequency f2 to a subcarrier of frequency f4. In this case, terminal 200 sets the frequency of second synthesizer S2 to f4 at timing t0 during the guard time after receiving DL data.

  Then, the terminal 200 transmits the local signal of the frequency f4 generated from the second synthesizer S2 to the wireless transmission unit 111 and the wireless reception unit 112 within the GI after the switching period Tx until the second synthesizer S2 is stabilized. Change the frequency to output. For example, as shown in FIG. 4, when the second synthesizer S2 is stabilized before the head control signal, the frequency may be changed in the GI of the head control signal. If the frequency is changed in the GI of the first control signal, only the preamble is transmitted at the frequency before the change and all the control signals are transmitted from the frequency after the change, so that the communication quality of the control signal does not deteriorate at all.

  In this case, the preamble used for AGC, synchronization detection, and AFC is transmitted at the frequency before the change, but the base station 100 performs AGC, timing detection, AFC, and the like using the previous measurement result. Therefore, necessary performance can be obtained.

<Terminal frequency change operation>
Next, the 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 sets the changed frequency in one synthesizer. . When the synthesizer is stabilized (ST302: YES), terminal 200 changes the frequency in a predetermined GI transmission section (ST303: YES) (ST304). Here, when base station 100 notifies terminal 200 of GI at the timing of changing the frequency before starting communication, terminal 200 is the GI transmission section at the notified timing in ST303. Determine whether or not. Further, when notifying each other of the timings at which the frequency is changed between the base station 100 and the terminal 200, the terminal 200 determines the GI transmission section with the later timing as the predetermined GI transmission section. Alternatively, since the time required for frequency setting is generally known, terminal 200 may set a fixed GI transmission interval in advance and determine whether the set GI transmission interval is set.

  Terminal 200 does not change the frequency unless the selected subcarrier information is input (ST301: NO) (ST305). Also, even if the selected subcarrier information is input (ST301: YES), terminal 200 does not change the frequency until the synthesizer in which the changed frequency is set (ST302: NO) (ST306). Also, terminal 200 inputs selected subcarrier information (ST301: YES), and even after the synthesizer that sets the changed frequency is stabilized (ST302: YES), it is not a predetermined GI transmission section (ST303: NO). ), The frequency is not changed (ST307).

<Effect>
Thus, according to the present embodiment, when preparing two preambles for each subcarrier and changing the subcarrier, from the synthesizer that does not generate a local signal of the current subcarrier frequency, A local signal having a frequency of the changed subcarrier is generated, and the frequency is changed in the GI after the synthesizer is stabilized. As a result, even when the subcarrier is changed, the signal can be transmitted without interruption, so that it is possible to suppress a decrease in transmission efficiency when the synthesizer changes the frequency of the local signal.

  In addition, by changing the frequency within the GI, it is possible to prevent deterioration in communication performance. Since the signal becomes discontinuous at the timing of changing the frequency, it is necessary to change the frequency except when transmitting / receiving a signal necessary for reception processing. Since the GI is not necessary for the reception process, the communication performance does not deteriorate if the frequency is changed within the GI.

  Furthermore, the communication quality can be satisfied by changing the frequency in the GI of the control signal having high error tolerance. The control signal is usually more resistant to errors than data, for example, by setting a small number of modulation levels. For this reason, if the frequency is changed in the GI of the control signal, the communication quality required for data transmission / reception with low error tolerance is satisfied, and the decrease in transmission efficiency when the synthesizer changes the frequency of the local signal can be suppressed. it can.

  FIG. 4 shows an example in which the frequency is changed in the GI of the first control signal. However, the present embodiment is not limited to this, and in another GI after the synthesizer in which the changed frequency is set is stabilized. The frequency may be changed. For example, as shown in FIG. 6, the frequency may be changed in the GI of the mth control signal (m is a natural number).

  Further, when it takes a long time for the synthesizer to stabilize, such as when an inexpensive synthesizer is used, and the frequency change cannot be made in time for the GI of the control signal, as shown in FIG. In this case, the frequency may be changed. Even in this case, since the UL data can be transmitted at the changed frequency, the communication quality necessary for data transmission / reception is not satisfied.

  As shown in FIG. 8, when pilots are transmitted from all subcarriers at a specific time, it is necessary to change the frequency in the pilot symbol GI. This is because if the frequency is changed, the propagation path characteristics are also different, and therefore it is necessary to transmit the pilot symbols used for propagation path estimation, the subsequent control information, and the UL data from the same frequency.

  Moreover, in this Embodiment, you may make it the base station 100 notify GI of the timing which changes a frequency with respect to the terminal 200 before a communication start. Note that the amount of information necessary for this notification is 3 bits or less (in the case of 3 bits, the timing can be changed up to 8 OFDM symbols), and therefore the amount of signal to be increased is small. Here, the terminal 200 may notify the base station 100 of information indicating the GI at which the frequency is changed, or the terminal 200 and the base station 100 may notify each other. For example, the terminal 200 and the base station 100 can notify each other of the information and select the one that takes time to set the frequency.

  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 210i Synthesizer unit 210i-1, 210i-2 Synthesizer 210i-3 local switching unit

Claims (7)

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 unit for generating a local signal having a frequency of the selected subcarrier;
An OFDM signal generation unit that generates an OFDM signal by performing orthogonal frequency division multiplexing on the upstream signal;
A GI adding unit for adding a guard interval to the OFDM signal;
A transmitter that up-converts and wirelessly transmits an OFDM signal to which the guard interval is added using a local signal of the frequency of the selected subcarrier;
Comprising
Before starting communication with the base station, the base station is notified of the guard interval of the timing to change the frequency of the subcarrier,
The synthesizer unit has two synthesizers for each subcarrier,
Generate a local signal with the frequency of one subcarrier currently communicating from one synthesizer,
When the base station selects the change of the subcarrier in communication, the local signal of the frequency of the changed subcarrier is generated from the other synthesizer,
In the guard interval after the time until the other synthesizer stabilizes, the output of the local signal is switched.
Terminal. The synthesizer unit switches the output of the local signal within the guard interval of the control signal.
The terminal according to claim 1. The synthesizer unit switches the output of the local signal within the guard interval of the leading control signal.
The terminal according to claim 2. The synthesizer unit switches the output of the local signal within the guard interval of the leading upstream data.
The terminal according to claim 1. The synthesizer unit switches the output of a local signal within a guard interval of a pilot symbol.
The terminal according to claim 1. A communication system between a base station and a terminal that transmits and receives 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;
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 unit for generating a local signal having a frequency of the selected subcarrier;
An OFDM signal generation unit that generates an OFDM signal by performing orthogonal frequency division multiplexing on the upstream signal;
A GI adding unit for adding a guard interval to the OFDM signal;
A transmitter that up-converts and wirelessly transmits an OFDM signal to which the guard interval is added using a local signal of the frequency of the selected subcarrier;
Comprising
The base station, before starting communication with the terminal, notifies the terminal of the guard interval of the timing to change the frequency of the subcarrier,
The synthesizer part of the terminal is
Each subcarrier has two synthesizers,
Generate a local signal with the frequency of one subcarrier currently communicating from one synthesizer,
When the base station selects the change of the subcarrier in communication by the subcarrier selection unit, the local signal of the frequency of the changed subcarrier is generated from the other synthesizer,
In the guard interval after the time until the other synthesizer stabilizes, the output of the local signal is switched.
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;
A downlink OFDM signal is generated by performing orthogonal frequency division multiplexing on the downlink 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 upstream OFDM signal is generated by performing orthogonal frequency division multiplexing on the upstream signal,
Adding a guard interval to the OFDM signal;
Up-converting the OFDM signal with the guard interval added using a local signal having a frequency of the selected subcarrier, and transmitting the radio signal,
The base station, before starting communication with the terminal, notifies the terminal of the guard interval of the timing to change the frequency of the subcarrier,
The terminal
Each subcarrier has two synthesizers,
Generate a local signal with the frequency of one subcarrier currently communicating from one synthesizer,
When the base station selects the change of the subcarrier in communication, the local signal of the frequency of the changed subcarrier is generated from the other synthesizer,
In the guard interval after the time until the other synthesizer stabilizes, the output of the local signal is switched.
Communication method.

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