JP2004254335A - Radio base station and radio terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system in which communication efficiency and receiving characteristics are improved and broadcasting and communications are merged. <P>SOLUTION: A radio base station CS is a radio base station for radio communications with a plurality of radio terminals PS1-PS3 through an orthogonal frequency division multiplex system, and is provided with a conversion means for applying batch conversion into time signals to both a first subcarrier band which is assigned for two-way communications with the respective radio terminals and a second subcarrier band which is assigned for multi-address information to be provided to the plurality of radio terminals only outgoing direction in full bandwidth assignable to the radio terminals PS1-PS3, and a transmission means for multiplexing the time signals batch-converted by the conversion means, and transmitting the result to the radio terminals PS1-PS3. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a wireless communication system for transmitting a signal using an orthogonal frequency division multiplexing (OFDM) method.

  In recent years, high-speed wireless data communication systems indoors or outdoors have been required, but multipath interference in which transmitted signals are received through various paths due to reflection or shadowing by buildings or the like becomes a major problem. . When multipath interference occurs, a signal is strengthened or weakened depending on the phase relationship of signals received through a plurality of propagation paths. Even in the same multipath propagation environment, there is a case where the signals are combined in the same phase and a case where the signals are combined in the opposite phase depending on the frequency, and a distortion called frequency selective fading occurs in the frequency spectrum of the received wave. In particular, as the bit rate increases, the occupied bandwidth of the signal greatly increases. Therefore, severe distortion such as a plurality of notches in the band occurs due to frequency selective fading. When frequency selective fading occurs, signal processing of a receiver in a high-speed wireless communication system becomes very difficult.

  Therefore, a multicarrier transmission scheme has been proposed in which the influence of frequency selective fading is small and the speed of signal processing can be reduced.

  In the multicarrier transmission scheme, a transmission data sequence is divided into a plurality of parts, and signals are transmitted using subcarriers having different frequencies. At this time, the signal of each subcarrier can be reduced, and the signal processing speed can be reduced.

  In multicarrier transmission, since each subcarrier signal has a narrow band, even if frequency selective fading occurs, it appears that each subcarrier is subjected to flat fading. Therefore, the reception characteristics are improved by preventing the signal from being transmitted on the subcarrier with the notch or by performing frequency hopping.

  One of the multi-carrier transmission systems is an orthogonal frequency division multiplexing (OFDM) system. This OFDM system is a system in which subcarriers are set up at the minimum interval orthogonal to each other. In theory, thousands of subcarriers can be set up in a transmission band of several ΜHz, and the number of users increases. Can respond. In addition, by setting up a large number of subcarriers, the transmission rate of each subcarrier can be significantly reduced, and at the time of modulation and demodulation, digital signal processing of a similar algorithm such as fast inverse Fourier transform or fast Fourier transform is performed. In order to collectively modulate and demodulate a plurality of subcarrier signals, these digital signal processing units can be integrated. Therefore, it can be said that the {FD} system is a transmission system suitable for high-speed data communication and the like used in a moving body moving at high speed.

  However, the {FD} method has the following problems.

  First, when an integrated digital signal processing circuit that modulates and demodulates thousands of subcarriers at once is installed in a portable wireless terminal, the circuit scale is large, though not as large as that of a multicarrier transmission method other than OFDM. As a result, there is a problem that the entire apparatus is enlarged and portability is impaired.

  Second, when a notch in the frequency axis direction caused by frequency selective fading enters, the reception characteristics of the subcarrier signal in that portion deteriorate extremely, and the reception characteristics of a radio terminal using the subcarrier signal are reduced. There is a problem that characteristics are extremely deteriorated.

  The present invention has been made to solve such a problem, and a first object of the present invention is to reduce the size of a digital signal processing circuit of a wireless terminal.

  A second object of the present invention is to provide a wireless communication system capable of improving communication efficiency and reception characteristics.

  In order to achieve the above object, the wireless base station of the present invention is a wireless base station that performs wireless communication with a plurality of wireless terminals by the orthogonal frequency division multiplexing method, and among the total bandwidth that can be allocated to the wireless terminals, A first subcarrier band allocated for performing bidirectional communication with each wireless terminal and a second subcarrier band allocated for broadcast information provided to only a plurality of wireless terminals only in the downlink direction are combined. There is provided a conversion means for collectively converting the time signals into time signals, and a transmission means for multiplexing the time signals collectively converted by the conversion means and transmitting the multiplexed time signals to each wireless terminal.

  Further, the wireless base station of the present invention is a wireless base station that wirelessly communicates with a plurality of wireless terminals according to the orthogonal frequency division multiplexing method, and according to the type of information to be transmitted among the total bandwidth that can be allocated to the wireless terminals. Subcarrier allocating means for allocating a subcarrier signal for communicating with the wireless terminal from the divided subcarrier band, and collectively dividing the subcarrier signals of the plurality of divided subcarrier bands. And a transmitting means for multiplexing the batch-converted time signal and transmitting the multiplexed time signal to each wireless terminal.

  In the case of the present invention, in addition to the first subcarrier band allocated for communication performed by the base station with each wireless terminal, the base station is allocated for transmitting broadcast information addressed to a plurality of wireless terminals. Since the second subcarrier band is also collectively converted into a time signal, multiplexed, and transmitted, a system in which broadcasting and communication are integrated can be constructed.

  Further, the wireless terminal of the present invention is a wireless terminal that performs wireless communication with at least one or more broadcast information transmitting base stations or two-way communication base stations by an orthogonal frequency division multiplexing method, and a signal from the base station. And receiving means for receiving a part or all of the received signal, and converting means for converting the received signal received by the receiving means in the opposite manner to converting means for converting the subcarrier signal into a time signal at each base station at once. And demodulation means for demodulating a part or all of the subcarrier bands obtained by the conversion means.

  Further, the wireless terminal of the present invention is a wireless terminal that performs wireless communication with at least one or more broadcast information transmitting base stations or two-way communication base stations by an orthogonal frequency division multiplexing method, and a signal from the base station. Receiving means for receiving a part or all of the received signal, and a converting means for converting the received signal received by the receiving means, and a converting means for converting the subcarrier signal into a time signal at each base station in reverse. And demodulating means for selectively demodulating a subcarrier signal in a subcarrier band obtained by the converting means according to the type of information.

  In the case of the present invention, the wireless terminal demodulates part or all of the band of the signal transmitted from the broadcast information transmitting base station or the two-way communication base station to obtain a desired signal. Even in the integrated system, the wireless terminal can receive a desired signal.

  According to the present invention, in addition to the first subcarrier band allocated by the base station for communication performed with each wireless terminal, the base station allocates the first subcarrier band to transmit broadcast information addressed to a plurality of wireless terminals. Since the second subcarrier band is also collectively converted into a time signal and multiplexed and transmitted, a system that combines broadcasting and communication can be constructed.

  Further, according to the present invention, the wireless terminal demodulates part or all of the band of the signal transmitted from the broadcast information transmitting base station or the bidirectional communication base to obtain a desired signal. Even in a system in which communication is integrated, a desired signal can be received on the wireless terminal side.

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

  FIG. 1 is a diagram showing a configuration of a wireless communication system of a first embodiment according to the present invention. In the figure, CS is a base station, and PS1 to $ S3 are wireless terminals. Two-way communication is performed between these wireless terminals PS1 to # S3 and the base station CS using $ FDM signals of different bands.

  As shown in FIG. 2, the base station CS includes a subcarrier allocating unit 1, an OFDM transmitting / receiving unit 2, an antenna 3, a propagation environment measuring unit 4, a setting control unit 5, a setting notifying unit 6, and the like. When there is an access request from any one of the plurality of wireless terminals PS1 to $ S3, for example, the wireless terminal PS1 or the like, the subcarrier allocating unit 1 assigns a plurality of subcarriers that can be allocated to each of the wireless terminals PS1 to $ S3. The subcarrier signals are allocated to the wireless terminal PS1 by the number corresponding to the amount of information communicated by the wireless terminal PS1 among the signals. For example, when the amount of information to be communicated is large, a plurality of subcarrier signals are allocated, and when the amount of information to be communicated is small, only one is allocated. The OFDM transmission / reception unit 2 transmits and receives OFDM signals transmitted from the wireless terminals PS1 to # S3 via the antenna 3. The propagation environment measuring unit 4 measures a propagation environment when a known information symbol is received or an access request is made. The setting control unit 5 transmits, based on at least one of the number of wireless terminals already accessing the terminal itself and the propagation environment at that time when the access request is made, a transmission band used for wireless communication with the wireless terminal that made the access request. , The control condition for controlling at least one of the occupied bandwidth and the modulation method. The setting notification unit 6 returns (notifies) the control conditions determined by the setting control unit 5 to the wireless terminal that has made the access request.

  As shown in FIG. 3, the wireless terminal includes an OFD transmission / reception unit 7, a setting control unit 8, an antenna 9, and the like. The OFD transmission / reception unit 7 transmits and receives the FDM signal transmitted from the base station CS via the antenna 3. That is, the OFD transmission / reception unit converts a signal to be transmitted into a time signal, transmits the signal from the antenna 9, and converts a signal received by the antenna 9 into a data sequence.

  The OFDM transmission / reception unit 2 of the base station CS and the $ FDM transmission / reception unit 7 of the wireless terminals PS1 to $ S3 include a reception unit 10 and a transmission unit 11, as shown in FIG. The receiving unit 10 includes a reception processing unit 15, a fast Fourier transform (FFT) 16, and a demodulation unit 17. The reception processing unit 15 performs reception processing such as frequency conversion, A / D conversion, synchronization establishment, and guard time removal on the signal input to the reception unit 10. The fast Fourier transform unit (FFT) 16 collectively converts the time signal obtained by the reception processing into each subcarrier signal. The demodulation unit 17 converts only a desired signal among the subcarrier signals into a digital data sequence and outputs the digital data sequence. The transmission unit 11 includes a modulation unit 12, a fast inverse Fourier transform unit (IFFT) 13, and a transmission processing unit 14. The modulator 12 modulates an input signal to the transmitter 11 to generate a subcarrier signal. The fast inverse Fourier transform unit 13 converts a subcarrier signal into a time signal. The transmission processing unit 14 performs transmission processing such as adding a guard time, D / Α conversion, and frequency conversion, and outputs the result. Although the configuration of the OFDM transmission / reception unit 2 of the base station CS and the configuration of the OFDM transmission / reception unit 7 of the wireless terminal are the same, the settings of the components constituting the OFDM transmission / reception unit 7 may be different. For example, it is a transmission bandwidth that can collectively process transmission and reception signals.

  Hereinafter, the operation of the wireless communication system according to the first embodiment will be described with reference to FIGS. FIG. 5 is a diagram showing bands (subcarriers) allocated by the base station CS, and FIG. 6 is a process of generating a ΟFDM signal transmitted from the base station CS to any wireless terminal, for example, the wireless terminal PS1, that is, the base station CS. FIG. 7 shows a state from when a transmission subcarrier signal is generated to when radio terminal PS1 obtains a reception subcarrier signal. FIG. 7 shows a process of generating an ΟFDM signal transmitted from radio terminal PS1 to base station CS, that is, radio terminal FIG. 11 is a diagram illustrating a state from when a transmission subcarrier signal is generated in PS1 to when a base station CS obtains a reception subcarrier signal.

  In the case of the wireless communication system according to the first embodiment, the received signal received by the antenna 3 is converted into a subcarrier signal by the ΟFDM transmission / reception unit 2. Subcarrier allocating section 1 allocates the subcarrier signal obtained by ΔFDM transmitting / receiving section 2 to a signal corresponding to each wireless terminal. Here, when the received signal is, for example, an access request from the wireless terminal PS1, in the base station CS, the propagation environment measuring unit 4 measures the propagation environment from the received signal and outputs the measurement result to the setting control unit 5. Further, subcarrier allocating section 1 outputs the number of wireless terminals performing communication to setting control section 5. The setting control unit 5 determines (sets) a band used for communication with each of the wireless terminals PS1 to PS3, a subcarrier modulation method, and the like based on a propagation environment, the number of wireless terminals, and the like. The allocating unit 1 is controlled.

  As shown in FIG. 5, the subcarrier allocating unit 1 allocates the band 52 of the wireless terminal PS2 and the wireless terminal PS3 of the wireless terminal PS2 that are communicating according to the state of the available channel and the amount of information from the total bandwidth 50 that can be allocated by itself. A band 51 different from the band 53 is allocated. That is, a required number of subcarrier signals different from those of the wireless terminals PS2 and PS3 are allocated. Note that the wireless terminal PS1 and the other wireless terminals PS2 and # S3 may have different subcarrier modulation schemes, signal transmission bandwidths, and the like. Between the signal transmission band used for communication between the base station CS and each of the wireless terminals PS1 to # S3, there is a guard section in which no signal is transmitted, and this guard section prevents signals of respective users from interfering with each other. I have.

  The setting notification unit 6 converts the content set by the setting control unit 5 into a setting notification signal for the wireless terminal PS1 that communicates with the base station CS. The setting notification signal output from the setting notifying unit 6 is input to the subcarrier allocating unit 1 and, together with the signal allocated to each subcarrier in the band of the base station CS as shown in FIG. The signal is collectively converted into a time signal and transmitted from the antenna 3 using a part of the ΟFDM signal. This setting notification signal is transmitted on a dedicated channel for the setting notification signal, for example. Before the sub-carrier for data transmission is allocated to the radio terminal PS1, the sub-carrier for data transmission set by the base station CS from the base station CS to the radio terminal PS1 using the dedicated channel for the setting notification signal, A setting notification signal for notifying the wireless terminal PS1 of the modulation method and the like is transmitted. After the subcarriers for data transmission are set and data transmission is started, for example, the base station CS uses one of the subcarriers allocated for data transmission to transmit other data in the OFDM signal. The setting notification signal may be transmitted together with the signal, or the ΔFDM symbol for the setting notification signal may be transmitted periodically using the allocated subcarriers. Here, the operation of generating a signal to be transmitted from the base station CS to the wireless terminal PS1 will be described in detail.

  As shown in FIG. 6A, the base station CS transmits a signal using M subcarriers having a carrier interval Δf. The M subcarriers also include a guard section for preventing interference. Among them, the number of subcarriers that can be used for signal transmission to the wireless terminal PS1 is m including the guard section in which no signal is transmitted. The M subcarriers including the m subcarriers addressed to the wireless terminal PS1 are converted into signals in the time direction as shown in FIG. 6B by the fast inverse Fourier transform, and an effective symbol of ΟFDM is generated. The generated effective symbols are M sample values with a time interval of 1 / MΔf, and are converted to ΟFDM symbols by D / Α conversion of the transmission processing unit with a guard time added. FIG. 6C shows an OFDM symbol after D / A conversion. OFDM symbols are converted to radio frequency and transmitted.

  When the wireless terminal PS1 receives the ΟFDM symbol, the base station CS converts the symbol into a baseband signal having the center frequency of the center of the m subcarriers transmitted to the wireless terminal PS1, and the Α / D conversion of the reception processing unit 15 After the sample point of the received signal is obtained, the guard time is removed. At this time, the sampling interval of the received analog signal is 1 / mΔf, which is M / m times longer than the sampling interval obtained after the fast inverse Fourier transform of the base station CS as shown in FIG. That is, the sampling speed of the wireless terminal $ S1 is lower than the sampling speed of the fast inverse Fourier transform unit of the base station CS. The fast Fourier transform unit of the wireless terminal ΡS1 performs fast Fourier transform using m sample points after removing the guard time, and allocates it to the wireless terminal ΡS1 at the base station CS as shown in FIG. M subcarrier signals can be obtained. ΡS1 demodulates a digital data sequence by demodulating each subcarrier.

  In the wireless terminal PS1, when the OFDM transmission / reception unit 7 receives the setting notification signal transmitted from the base station CS via the antenna 9, the OFDM transmission / reception unit 7 converts the reception signal input to the reception unit 10 into a reception processing unit 15. It performs reception processing such as frequency conversion, A / D conversion, establishment of synchronization, and removal of guard time, and outputs a time signal to the fast Fourier transform unit 16. The fast Fourier transform unit 16 collectively converts the input time signal into a subcarrier signal, and the demodulation unit 17 converts the digital signal into a digital data sequence, that is, a setting notification signal.

  The setting control unit 8 sets the operating environment of the wireless terminal PS1 itself, that is, the items such as the band and the subcarrier modulation method, based on the input setting notification signal, and thereafter communicates in the operating environment.

  When a signal to be communicated, such as voice, is input to the transmission unit 11 of the OFDM transmission / reception unit 7, the input signal is modulated by the modulation unit 12, and a subcarrier signal is generated. The subcarrier signal is converted into a time signal by the high-speed inverse Fourier transform unit 13, and is output after transmission processing such as guard time addition, D / Α conversion, and frequency conversion is performed by the transmission processing unit 14.

  Here, an operation of generating a signal transmitted from the wireless terminal PS1 to the base station CS will be described.

  In ΡS1, as shown in FIG. 7A, a signal is transmitted using m ′ subcarriers with a carrier interval Δf ′. The m ′ subcarrier also includes a guard section for preventing interference. Here, as the subcarrier transmitted from the radio terminal PS1 to the base station CS, the same subcarrier as the subcarrier transmitted from the base station CS to ΡS1 may be used in a time division manner, so that Δf ′ = Δf. . When the same subcarrier is used for transmission and reception, m ′ = m.

  FIG. 7A shows a subcarrier signal generated by the wireless terminal PS1. Each subcarrier interval is Δf ′, and there are m ′ subcarriers including the guard section. The subcarrier signal is subjected to fast inverse Fourier transform by a fast inverse Fourier transform unit (IFFT) 13 having m ′ points and converted into a discrete signal in the time direction represented by m ′ sample values as shown in FIG. Is done. At this time, the sample interval is 1 / m'Δf '. The signal in FIG. 7B is D / A converted, added with a guard time, and converted into an OFDM transmission symbol as shown in FIG. 7C. Each wireless terminal generates a ΟFDM symbol having the same symbol length. The ΔFDM symbols generated by each of the wireless terminals PS1 to PS3 are frequency-converted to different radio frequencies, and transmitted to the base station CS.

  Since the base station CS simultaneously receives the OFDM symbols transmitted from the wireless terminals PS1 to PS3, the received baseband signals obtained by the frequency conversion in the base station CS are transmitted from all the wireless terminals PS1 to PS3. ΟFDM symbols are added with shifted frequencies, as shown in FIG. The base station CS performs A / D conversion on the received symbol to obtain the waveform of FIG. The sampling rate of A / D conversion is 1 / M′Δf ′, and when a plurality of wireless terminals PS1 to PS3 communicate with the base station CS using different frequencies, M ′> m ′. That is, the base station CS performs sampling at intervals shorter than the sampling intervals of the wireless terminals PS1 to PS3. In other words, each of the wireless terminals PS1 to PS3 performs sampling at intervals wider than the sampling interval of the base station CS.

  By setting the sampling speed of each of the wireless terminals PS1 to PS3 to be lower than the sampling speed of the base station CS, the digital signal processing circuit (the high-speed inverse Fourier transform unit (IFFT) 13 and the high-speed The size of the Fourier transform unit (FFT) 16) can be made smaller than the size of the base station CS.

  The M ′ sample values thus obtained are converted into Μ ′ subcarrier signals by the Μ ′ point fast Fourier transform unit (FFT) 16. The converted subcarrier signal includes m ′ subcarrier signals transmitted from the wireless terminal PS1, as shown in FIG. 7 (f). Therefore, subcarrier allocating section 1 of base station CS in FIG. 2 can extract the subcarrier signal transmitted from wireless terminal PS1.

  As described above, according to the wireless communication system of the first embodiment, when an access request is issued from the wireless terminal PS1 to the base station CS, the base station CS itself allocates all subcarriers that can be assigned to each of the wireless terminals PS1 to PS3. Of the signals, a number of subcarriers corresponding to the information amount of the radio terminal PS1 are allocated to the radio terminal PS1, and the allocated subcarrier signals are collectively converted into a time signal, multiplexed, and transmitted. Subcarriers can be efficiently allocated according to the availability of channels and the amount of information of PS3.

  Also, since the sampling frequency when the wireless terminal PS1 converts the received signal from the base station CS into the subcarrier signal is set lower than the sampling frequency when the base station CS converts the subcarrier signal into the time signal at once. In addition, the scale of digital signal processing circuits such as the fast inverse Fourier transform (IFFT) 13 and the fast Fourier transform (FFT) 16 of the wireless terminal PS1 can be reduced.

  Furthermore, the sampling frequency when the wireless terminal PS1 converts the subcarrier signal into a time signal at a time is set lower than the sampling frequency when the base station CS converts the received signal from the wireless terminal PS1 into a subcarrier signal. Therefore, the scale of digital signal processing circuits such as the fast inverse Fourier transform unit (IFFT) 13 and the fast Fourier transform unit (FFT) 16 of the wireless terminal PS1 can be reduced.

  Next, a wireless communication system according to a second embodiment of the present invention will be described with reference to FIG. The configuration of the wireless communication system of the second embodiment is almost the same as that of the first embodiment, and the base station CS divides the subcarrier band according to the type of information (for wireless communication or for broadcasting). The only thing that is different. FIG. 8 is a diagram showing the operation of the wireless communication system according to the second embodiment. In particular, subcarrier allocation in the case where the base station CS collectively converts broadcast subcarriers and communication subcarriers into time signals. This is one example. In this case, the base station CS has a first band for performing general two-way wireless communication with the wireless terminals PS1 to PS4 among all the bands 80 that can be allocated to the wireless terminals PS1 to PS4. In addition to performing wireless communication using different subcarrier signals in 81, broadcasting using subcarrier signals in a second band 82 different from the first band 81, ie, downlink to a plurality of wireless terminals, is performed. The broadcast information provided only in the direction is also collectively converted into a time signal, multiplexed, and transmitted. Further, OFDM signals having different frequencies may be transmitted from a plurality of base stations.

  On the other hand, the wireless terminals PS1 to PS4 can receive information using the subcarrier signals allocated to the wireless terminals even when wireless communication has already been performed.

  The wireless terminals PS1 to PS4 can receive a broadcast by partially receiving only a desired signal from subcarrier signals allocated for broadcast. As described above, according to the wireless communication system of the second embodiment, in addition to the subcarriers that the base station CS allocates for communication with the individual wireless terminals PS1 to PS4, each of the wireless terminals PS1 to PS4 The sub-carrier signal allocated to transmit the broadcast information addressed thereto is also collectively converted into a time signal, multiplexed and transmitted, while the wireless terminals PS1 to PS4 side receive the band of the signal transmitted from the base station CS. Among them, since a desired signal is received by selectively demodulating a part thereof, each of the wireless terminals PS1 to PS4 can receive the desired signal even in a system in which broadcasting and communication are integrated. For example, the wireless terminal PS1 can receive content such as a broadcast, and the other wireless terminals PS2 to PS4 can receive normal wireless signals.

FIG. 1 is a diagram showing a schematic configuration of an OFD wireless communication system according to one embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a base station in the OFD wireless communication system of FIG. 1. FIG. 2 is a block diagram illustrating a configuration of a wireless terminal of the OFD wireless communication system of FIG. 1. FIG. 4 is a block diagram showing an internal configuration of an OFD transmission / reception unit of the base station of FIG. 2 and the wireless terminal of FIG. 3; FIG. 4 is a diagram illustrating an example of a total bandwidth of a base station and a band allocated to each wireless terminal. FIG. 5 is a diagram illustrating a change in an OFDM signal transmitted from a base station to a wireless terminal. FIG. 4 is a diagram illustrating a change in an OFDM signal transmitted from a wireless terminal to a base station. The figure which shows the subcarrier signal of the base station containing the band for communication and the band for broadcasting.

Explanation of reference numerals

  DESCRIPTION OF SYMBOLS 1 ... Subcarrier allocation part, 2 ... OFDM transmission / reception part, 3 and 9 ... Antenna, 4 ... Propagation environment measurement part, 5 ... Setting control part, 6 ... Setting notification part, 7 ... OFDM transmission / reception part, 8 ... Setting control part, DESCRIPTION OF SYMBOLS 10 ... Reception part, 11 ... Transmission part, 12 ... Modulation part, 13 ... IFFT, 14 ... Transmission processing part, 15 ... Reception processing part, 16 ... FFT, 17 ... Demodulation part, CS ... Base station, PS1-PS4 ... Wireless Terminal.

Claims (4)

A wireless base station that wirelessly communicates with a plurality of wireless terminals using an orthogonal frequency division multiplexing method,
A first subcarrier band to be allocated to perform bidirectional communication with each wireless terminal among a total bandwidth that can be allocated to the wireless terminals, and a broadcast provided to the plurality of wireless terminals only in a downlink direction. Conversion means for collectively converting the second subcarrier band allocated for information into a time signal,
A transmission unit for multiplexing the time signal batch-converted by the conversion unit and transmitting the multiplexed time signal to each wireless terminal. A wireless base station that performs wireless communication with a plurality of wireless terminals using an orthogonal frequency division multiplexing method,
Of the total bandwidth that can be allocated to the wireless terminal, the wireless terminal is divided into a plurality of subcarrier bands according to the type of information to be transmitted, and a subcarrier signal that communicates with the wireless terminal is allocated from the divided subcarrier band. Subcarrier allocating means;
Conversion means for collectively converting the divided subcarrier signals of the plurality of subcarrier bands into a time signal,
A transmitting unit for multiplexing the batch-converted time signal and transmitting the multiplexed time signal to each wireless terminal. A wireless terminal that performs wireless communication by orthogonal frequency division multiplexing with at least one or more broadcast information transmitting base stations or bidirectional communication base stations,
Receiving means for receiving some or all of the signals from the base station,
A conversion unit that converts the reception signal received by the reception unit, and a conversion unit that converts the subcarrier signal into a time signal in a batch at each of the base stations.
A radio terminal, comprising: demodulation means for demodulating part or all of the subcarrier bands obtained by the conversion means. A wireless terminal that performs wireless communication by orthogonal frequency division multiplexing with at least one or more broadcast information transmitting base stations or bidirectional communication base stations,
Receiving means for receiving a part or all of the signal from the base station,
A conversion unit that converts the reception signal received by the reception unit, and a conversion unit that converts the subcarrier signal into a time signal in a batch at each of the base stations.
A radio terminal, comprising: a demodulation unit for selectively demodulating a subcarrier signal in a subcarrier band obtained by the conversion unit in accordance with a type of information.

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