JP4230932B2 - Transmission radio station, reception radio station, radio communication system, and radio communication method - Google Patents

Description

  The present invention has a hierarchical cell structure (so-called cell-in-cell structure) and performs wireless data communication using orthogonal carrier frequency bands (for example, OFDM (Othgonal Frequency Division Multiplexing) transmission or OFCDM). The present invention relates to a transmitting radio station, a receiving radio station, the radio communication system, and a radio communication method in (Othgonal Frequency Code Division Multiplexing).

  In FIG. 1, one or more transmitting radio stations covering a certain area 90, and signals from the transmitting radio stations can be received. A wireless transmission system using a transmission wireless station that forms a small cell 80 with a small Equivalent Isotropically Radiated Power (EIRP). In the present specification, one or more transmitting radio stations covering a certain area 90 are referred to as “large cell transmitting radio stations”, and EIRP is smaller than the large cell transmitting radio station and forms a small cell 80. The radio station will be described as “small cell transmission radio station”. Further, as shown in FIG. 1, it is assumed that the large cell transmission radio station uses the frequency band f1, and the small cell transmission radio station uses the frequency band f2.

  FIG. 2 shows a functional block configuration of a transmission radio station 1 and a reception radio station 11 with a small conventional EIRP. As shown in the figure, in the receiving radio station 11, in order to receive the data transmitted from each transmitting base station, only the frequency band f1 and the filter 12 that cuts off the frequency band f2 and only the frequency band f2 are received. And the desired frequency band separated by the switch 14 must be selected and input to the receiving unit 15. This is to prevent a signal in a frequency band not to be received at the time of demodulation from causing interference and deteriorating the reception quality.

On the other hand, a technique related to a symbol synchronization method has been conventionally proposed. For example, a technique related to a symbol synchronization method in a relay station in the broadcasting field is disclosed in Patent Document 1 below.
Japanese Patent Laid-Open No. 7-283806

  However, wireless communication related to mobile communication has a characteristic that is not found in other fields of communication in which a receiving wireless station such as a mobile terminal moves between various cells and areas. For this reason, it is necessary to perform a handover for switching the transmission radio station that is a communication partner of the reception radio station. At the time of this handover, the receiving radio station 11 of FIG. 2 needs to demodulate the received signal after switching from the previous frequency band to the desired frequency band in the switch 14, so that the frequency band f1 is changed to the frequency band f2. Alternatively, it has been difficult to realize a smooth handover from the frequency band f2 to the frequency band f1.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a transmitting radio station, a receiving radio station, a radio communication system, and a radio communication method capable of realizing a smooth handover. .

To achieve the above object, a transmitting radio station according to the present invention arranges symbols to be transmitted on a frequency axis and transmits signals to radio terminals in an area using one or a plurality of carrier frequency bands. And at least one when detecting a carrier frequency band signal of a different transmission scheme, and a signal detection means for detecting at least one carrier frequency band signal of a transmission scheme different from the local station. one of the basis of the received signal, and symbol synchronization detection means for detecting a symbol synchronization for transmitting, in a DFT section 1 symbols of the signal based on the symbol detected synchronization small cell sending radio station transmits, large cell sending radio station the symbol transmission timing symbol boundary of the signal is performed so that there from, the signal transmission for transmitting a signal to be transmitted And having a stage. Note that the above transmission scheme includes various transmission schemes such as a scheme that divides by a frequency band and a scheme that divides by a spread code. A symbol refers to transmission data after being modulated, and includes control information for synchronization, for example, in addition to actual data. The above carrier frequency band means a carrier frequency or a subcarrier frequency, and the transmitting radio station according to the present invention may transmit data using only one carrier. Moreover, said radio | wireless terminal means all the terminals which are located in an area and can perform radio | wireless communication, and is a concept containing a transmitting radio station other than a receiving radio station (for example, mobile station) and an own station. In addition, in “detection of carrier frequency band signal”, when the transmitting radio station itself detects a carrier frequency band signal,
This includes both cases where the transmitting radio station detects the carrier frequency band signal by receiving the synchronization request signal from the receiving radio station.

  In the transmitting radio station, when the signal detecting means detects at least one carrier frequency band signal having a transmission method different from that of the own station, the symbol synchronization detecting means detects symbol synchronization to be transmitted based on at least one received signal. The signal transmission means transmits a signal to be transmitted based on the symbol transmission timing derived based on the detected symbol synchronization. Thereby, the signal transmission means outputs the signal at the optimum symbol transmission timing (that is, it does not interfere with each other) by the correlation between at least one carrier frequency band signal of a transmission method different from that of the own station and the signal of the own station. It becomes possible to transmit. Along with this, the receiving radio station can simultaneously receive and demodulate signals in a plurality of carrier frequency bands, so there is no need to perform “frequency switching processing” at the time of handover as in the prior art, and smoothness is achieved. Handover can be realized.

  In addition, the following effects are also obtained. Since the setting of the guard band can be made small or unnecessary, the frequency can be effectively used. Further, since signals from a plurality of transmitting radio stations can be received simultaneously, multilink transmission can be executed by the means. In addition, it is possible to freely arrange a new transmission radio station without considering the influence of interference with other existing transmission radio stations forming a small cell. Furthermore, since the receiving part of the receiving radio station that receives a plurality of frequency bands can be made common, it is possible to reduce the volume of the receiving radio station and reduce the manufacturing cost.

  Note that the signal detection means may detect that a carrier frequency band signal having a smaller equivalent isotropically radiated power (EIRP) than the local station is received, for example.

  The transmission radio station may further include the following configuration requirements. That is, the transmission radio station according to the present invention has a frequency interval detection unit that detects a frequency interval based on a received signal from a radio terminal, and is orthogonal to the transmission carrier frequency of the radio terminal based on the detected frequency interval. Thus, it further has a frequency setting means for setting the transmission carrier frequency. Note that the above-mentioned “wireless terminal” means, for example, another transmitting wireless station that transmits a carrier frequency band signal having a larger equivalent isotropic radiated power than the transmitting wireless station according to the present invention, and is located in the area. It is a concept including any terminal (for example, a mobile station) capable of wireless communication.

  Further, the transmitting radio station according to the present invention includes a reception quality measuring unit that measures reception quality based on a received signal from a wireless terminal, and a spreading factor setting unit that sets a spreading factor based on the reception quality obtained by the measurement. Furthermore, it is characterized by having. The above-mentioned “wireless terminal” also means, for example, another transmitting wireless station that transmits a carrier frequency band signal having a larger equivalent isotropic radiated power than the transmitting wireless station according to the present invention, and is within the area. It is a concept that includes all terminals (for example, mobile stations) that can be wirelessly communicated.

The wireless communication system configured to include the transmitting wireless station and the receiving wireless station can be described as follows. That is, the radio communication system according to the present invention arranges symbols to be transmitted on the frequency axis and transmits signals to radio terminals in the area using one or a plurality of carrier frequency bands, and A radio communication system having a hierarchical cell structure configured to include a receiving radio station for receiving a signal, wherein the transmitting radio station detects at least one carrier frequency band signal having a transmission scheme different from that of the own station. when, different in the case of detecting the carrier frequency band signal transmission method, based on at least one received signal, and symbol synchronization detection means for detecting a symbol synchronization for transmitting and based on the symbol detected synchronization small cell sending radio station symbol but performed as in DFT section 1 symbols of the signal to be transmitted, there is no symbol boundary of the signal from the large cell sending radio station More Shin timing, and a signal transmitting means for transmitting a signal to be transmitted, the receiving radio station, characterized by having a simultaneous reception control means for receiving and demodulating a signal of a plurality of carrier frequency bands at the same time .

  In the transmitting radio station, when the signal detecting means detects at least one carrier frequency band signal having a transmission method different from that of the own station, the symbol synchronization detecting means detects symbol synchronization to be transmitted based on at least one received signal. The signal transmission means transmits a signal to be transmitted based on the symbol transmission timing derived based on the detected symbol synchronization. In the receiving radio station, the simultaneous reception control means can simultaneously receive and demodulate signals in a plurality of carrier frequency bands. As a result, the transmitting radio station transmits a signal at an optimum symbol transmission timing (that is, it does not interfere with each other) with each correlation between at least one carrier frequency band signal of a transmission method different from that of the own station and the signal of the own station. It is possible to transmit, and the receiving radio station can simultaneously receive and demodulate signals of multiple carrier frequency bands, eliminating the need for “frequency switching processing” during handover as in the past. Smooth handover can be realized.

  In addition, the following effects are also obtained. Since the setting of the guard band can be made small or unnecessary, the frequency can be effectively used. Further, since signals from a plurality of transmitting radio stations can be received simultaneously, multilink transmission can be executed. In addition, it is possible to freely arrange a new transmission radio station without considering the influence of interference with other existing transmission radio stations forming a small cell. Furthermore, since the receiving part of the receiving radio station that receives a plurality of frequency bands can be made common, it is possible to reduce the volume of the receiving radio station and reduce the manufacturing cost.

  The above wireless communication system may further include the following configuration requirements. That is, in the wireless communication system according to the present invention, when the receiving wireless station moves into a small cell in the hierarchical cell structure, the receiving wireless station receives a signal from the transmitting wireless station of the large cell that covers the area. Can be received, and information indicating that a signal from a transmission radio station of a small cell can be received is transferred to a data transfer device (for example, a location where location registration of the reception radio station is realized in the network). Registration means for registration in a registration management server or a router in the network), and the data transfer apparatus selects a transmission radio station that transmits the data according to the type of data to be transmitted to the reception radio station. It is characterized by selecting.

  That is, when the receiving radio station moves into a small cell in the hierarchical cell structure, the receiving radio station can receive a signal from a transmitting radio station of a large cell covering the area, and Information indicating that a signal from a transmitting radio station of a scale cell can be received is registered in the data transfer device, and the data transfer device performs the data transfer according to the type of data to be transmitted to the receiving radio station. Multicast information is transmitted from the large cell transmitting wireless station to the receiving wireless station, and individual information having a high data rate such as image data is transmitted from the small cell transmitting wireless station. It is possible to realize appropriate data transmission control according to the type of data.

  Note that the following modes can be employed for symbol synchronization. That is, a radio communication system according to the present invention includes a plurality of transmission radio stations that use different carrier frequency bands and a symbol synchronization reference source that transmits a symbol synchronization reference signal. Based on the symbol transmission timing based on the reference signal from the symbol synchronization reference source, the symbol of the signal to be transmitted by each transmitting radio station is transmitted in synchronization.

  In addition, the wireless communication system according to the present invention includes a plurality of transmission wireless stations that use different carrier frequency bands, and the plurality of transmission wireless stations cooperate with each other using wired or wireless transmission, and each transmission The radio station transmits a symbol of a signal to be transmitted in synchronization. At this time, it is desirable that the plurality of transmission radio stations cooperate with each other and be set so that the transmission carrier frequencies of signals to be transmitted by the respective transmission radio stations are orthogonal to each other.

A radio communication system according to the present invention arranges a symbol to be transmitted on a frequency axis and transmits a signal to a radio terminal in an area using one or a plurality of carrier frequency bands, and a signal from the transmission radio station. A wireless communication system having a hierarchical cell structure configured to include a receiving wireless station for receiving, wherein the receiving wireless station makes a request for symbol synchronization to the transmitting wireless station, and a plurality of carrier frequency bands Simultaneous reception control means for simultaneously receiving and demodulating the signal, and when the transmitting radio station receives a request for symbol synchronization from the receiving radio station, it performs symbol synchronization for transmission based on at least one received signal. a symbol synchronization detection means for detecting, the small cell sending radio station based on the symbol detected synchronization in DFT section 1 symbols of the signal to be transmitted, from the large cell sending radio station More symbol transmission timing symbol boundary of No. is performed so as not to exist, and having a signal transmitting means for transmitting a signal to be transmitted.

  In this radio communication system, when the synchronization request means of the receiving radio station requests symbol synchronization from the transmitting radio station, the symbol synchronization detecting means transmits based on at least one received signal in the transmitting radio station. The symbol synchronization is detected, and the signal transmission means transmits a signal to be transmitted based on the symbol transmission timing derived based on the detected symbol synchronization. In the receiving radio station, the simultaneous reception control means can simultaneously receive and demodulate signals in a plurality of carrier frequency bands. As a result, the transmitting radio station transmits a signal at an optimum symbol transmission timing (that is, it does not interfere with each other) with each correlation between at least one carrier frequency band signal of a transmission method different from that of the own station and the signal of the own station. It is possible to transmit, and the receiving radio station can simultaneously receive and demodulate signals of multiple carrier frequency bands, eliminating the need for “frequency switching processing” during handover as in the past. Smooth handover can be realized.

  In addition, the following effects are also obtained. Since the setting of the guard band can be made small or unnecessary, the frequency can be effectively used. Further, since signals from a plurality of transmitting radio stations can be received simultaneously, multilink transmission can be executed. In addition, it is possible to freely arrange a new transmission radio station without considering the influence of interference with other existing transmission radio stations forming a small cell. Furthermore, since the receiving part of the receiving radio station that receives a plurality of frequency bands can be made common, it is possible to reduce the volume of the receiving radio station and reduce the manufacturing cost.

The present invention can be described as the invention related to the wireless communication method as follows. A radio communication method according to the present invention is a transmission radio station which arranges symbols to be transmitted on a frequency axis and transmits a signal to radio terminals in an area using one or a plurality of carrier frequency bands in a radio communication system having a hierarchical cell structure And a signal detection step in which the transmitting radio station detects at least one carrier frequency band signal having a transmission scheme different from that of the own station, and a carrier frequency band signal having a transmission scheme different from that of the transmitting station. when detecting, based on at least one received signal, and symbol synchronization detection step of detecting a symbol synchronization for transmitting the signal the transmission radio station, the small cell sending radio station based on the symbol detected synchronization sends in DFT section 1 symbol, the symbol transmission symbol boundaries of a signal from the large cell sending radio station is carried out such that there More timing, and having a signal transmission step of transmitting a signal to be transmitted.

  The radio communication method according to the present invention is a transmission in which symbols to be transmitted are arranged on a frequency axis and a signal is transmitted to radio terminals in the area using one or a plurality of carrier frequency bands in a radio communication system having a hierarchical cell structure. A wireless communication method in a receiving wireless station that receives a signal from a wireless station, and when the local station moves into a small cell in a hierarchical cell structure, the local station transmits a large-scale cell covering the area A registration step of registering information indicating that a signal from a small-sized cell transmission radio station can be received in a data transfer apparatus in a wireless communication system, and a plurality of carrier frequencies And a simultaneous reception step of simultaneously receiving and demodulating the band signals.

A radio communication method according to the present invention includes a transmission radio station that arranges symbols to be transmitted on a frequency axis and transmits a signal to a radio terminal in an area using one or a plurality of carrier frequency bands; A radio communication method in a radio communication system having a hierarchical cell structure configured to include a receiving radio station that receives a signal, wherein the receiving radio station makes a request for symbol synchronization to the transmitting radio station; A symbol synchronization detection step of detecting symbol synchronization to be transmitted based on at least one received signal when the transmission radio station receives a symbol synchronization request from the reception radio station; and a symbol synchronization detected by the transmission radio station based have been the small cell sending radio station is performed as in the DFT section 1 symbols of the signal to be transmitted, there is no symbol boundary of the signal from the large cell sending radio station Symbol More transmission timing, and having a signal transmission step of transmitting a signal to be transmitted.

  The present invention can also be described as the invention relating to a wireless communication program as follows. A radio communication program according to the present invention is a transmission radio station that arranges symbols to be transmitted on a frequency axis and transmits a signal to radio terminals in an area using one or a plurality of carrier frequency bands in a radio communication system having a hierarchical cell structure A wireless communication program to be executed by a computer equipped with a signal detecting step for detecting at least one carrier frequency band signal having a transmission method different from that of the own station, and detecting a carrier frequency band signal having a different transmission method A symbol synchronization detection step for detecting symbol synchronization to be transmitted based on at least one received signal, and a signal transmission step for transmitting a signal to be transmitted based on a symbol transmission timing derived based on the detected symbol synchronization. It is characterized by having.

  The radio communication program according to the present invention is a transmission that arranges symbols to be transmitted on a frequency axis and transmits a signal to radio terminals in an area using one or a plurality of carrier frequency bands in a radio communication system having a hierarchical cell structure. A wireless communication program to be executed by a computer provided in a receiving wireless station that receives a signal from a wireless station. When the local station moves into a small cell in a hierarchical cell structure, the local station covers the area. Information indicating that a signal from a transmitting radio station in a large-scale cell can be received and that a signal from a transmitting radio station in a small-cell can be received is registered in a data transfer apparatus in the radio communication system A registration step; and a simultaneous reception step of simultaneously receiving and demodulating signals in a plurality of carrier frequency bands.

  As described above, according to the present invention, the transmitting radio station is optimal (that is, interferes with each other) in each correlation between at least one carrier frequency band signal of a transmission method different from that of the own station and the signal of the own station. It is possible to transmit a signal at a symbol transmission timing that does not reach. Along with this, the receiving radio station can simultaneously receive and demodulate signals in a plurality of carrier frequency bands, so there is no need to perform “frequency switching processing” at the time of handover as in the prior art, and smoothness is achieved. Handover can be realized.

  Moreover, since the setting of the guard band can be made small or unnecessary, the frequency can be effectively used. Further, since signals from a plurality of transmitting radio stations can be received simultaneously, multilink transmission can be executed. In addition, it is possible to freely arrange a new transmission radio station without considering the influence of interference with other existing transmission radio stations forming a small cell. Furthermore, since the receiving part of the receiving radio station that receives a plurality of frequency bands can be made common, it is possible to reduce the volume of the receiving radio station and reduce the manufacturing cost.

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

[First Embodiment]
3 is a functional block configuration diagram of the small cell transmission radio station 101 and the reception radio station 111 in FIG. 3, and the received symbols from the large cell transmission radio station and the transmission symbols of the small cell transmission radio station in the first embodiment of the present invention. Will be described with reference to a diagram showing a timing relationship between Also, a case will be described where the large cell transmission radio station uses the frequency band f1, and the small cell transmission radio station uses the frequency band f2. The “carrier frequency band” according to the present invention means a carrier frequency or a subcarrier frequency, and the transmitting radio station may transmit data using only one carrier.

  The small cell transmission radio station 101 receives the frequency band f1 or a part of the frequency band f1 when the power is turned on or periodically or continuously, so that the symbol synchronization detection unit 105 The symbol timing of the data being transmitted is detected. A specific method of the detection can be realized by using a general method executed by a receiving radio station that receives an OFDM signal. The symbol synchronization detection unit 105 corresponds to a signal detection unit and a symbol synchronization detection unit according to the present invention.

  For example, as shown in FIG. 8, the symbol synchronization detection unit 105 delays the input signal of the plurality of different transmission schemes by the length of one symbol DFT section, and does not delay the delayed signal. A correlator 302 that performs guard interval length (GI) correlation using the signal, a maximum correlation value detector 303 that detects a timing at which the correlation value is maximum, and a plurality of signals with different transmission schemes. A timing deriving unit 304 for deriving optimum (non-interfering) timing can be employed. In this symbol synchronization detection unit 105, a guard interval length (GI) is correlated using a signal delayed by the length of one symbol DFT section and a signal not delayed, and the timing at which the correlation value is maximum is detected. Further, it is possible to derive an optimum timing (not causing interference) with respect to a plurality of signals of different transmission schemes by respective correlations. In general, the signal from the large cell transmission radio station is considered to have temporally fluctuated power and phase due to the influence of fading, etc. By doing so, the accuracy of symbol synchronization can be improved.

  Then, the symbol synchronization detection unit 105 outputs the detected timing to the transmission unit 102. The transmitter 102 modulates the data input from the data input terminal 4 into an OFDM transmission signal, and transmits the modulated signal in synchronization with the timing input from the symbol synchronization detector 105. As shown in FIG. 4, the timing synchronization is performed so that the symbol boundary of the signal from the large cell transmission radio station does not exist within the DFT section of one symbol of the signal transmitted by the small cell transmission radio station. . Therefore, the allowable synchronization deviation is the guard interval length (GI). In synchronization, a delay occurring between the antenna 3A and the symbol synchronization detection unit 105 is taken into consideration.

  Note that the small cell transmission radio station 101 can adopt a configuration that can support not only OFDM transmission but also OFCDM transmission. In this case, the small cell transmission radio station 101 further includes a reception quality measurement unit 104 and a spreading factor setting unit 103 indicated by broken lines in FIG. Such a configuration will be described later with reference to FIG.

  Here, the configuration of the small cell transmission radio station 101 will be described in more detail.

  FIG. 9A shows a configuration related to transmission of an OFDM signal in the small cell transmission radio station 101. The symbol synchronization detection unit 105 shown in the figure has the configuration shown in FIG. 8 described above, and the symbol boundary of the signal from the large cell transmission base station is within one symbol DFT interval from the received signal from the large cell transmission radio station. Symbol synchronization is derived so that it does not exist.

  On the other hand, transmission carrier setting section 102A sets subcarriers to be transmitted based on the number of transmission carriers and the usage status of subcarriers given from a control signal from a control section (not shown). The symbol sequence to be transmitted by the lower cell transmitting radio station (which means “the transmitting radio station of the lower cell in the hierarchical cell structure” and corresponds to the small cell transmitting base station in FIG. 1) is the serial / parallel converter 102B. Thus, based on the set carrier information, the symbol series is serial / parallel (S / P) converted into parallel data for all or part of the number of subcarriers. Then, the symbol series converted to parallel data is time / frequency converted into multi-carrier components orthogonal on the frequency axis by inverse FFT (IFFT) calculation in IFFT section 102C. Finally, the guard interval is inserted into the symbols of the subcarriers converted into multicarriers by the guard interval (GI) insertion unit 102D. The insertion of the guard interval is realized by copying the signal waveform corresponding to the FFT sample in the end of each symbol or symbol series to the head of each symbol. The GI insertion unit 102D outputs the modulated signal to the symbol transmission control unit 102E, and the symbol transmission control unit 102E transmits the symbol sequence modulated based on the symbol synchronization timing output from the symbol synchronization detection unit 105. To do.

  FIG. 9B shows a configuration relating to transmission of the OFCDM signal in the small cell transmission radio station 101. The symbol synchronization detection unit 105 shown in the figure has the configuration shown in FIG. 8 described above, and the symbol boundary of the signal from the large cell transmission base station is within one symbol DFT interval from the received signal from the large cell transmission radio station. Symbol synchronization is derived so that it does not exist.

  The received signal from the large cell transmission radio station is also input to the reception quality measuring unit 104 and the reception quality is measured. Based on the measured reception quality, spreading factor setting section 103 determines whether or not to spread the signal to be transmitted by the lower cell transmission radio station, and if spreading, sets the spreading factor and sets the spreading code. Output to the generation unit 102F. The spreading code generation unit 102F assigns a spreading code from the set spreading factor. It should be noted that general spreading code allocation or the method described in Japanese Patent Application Laid-Open No. 10-290211 may be used which selects and allocates different spreading codes for users with different transmission speeds. Applicable.

  On the other hand, a symbol sequence (transmission signal) to be transmitted by the small cell transmission radio station 101 is input to the multiplexing unit 102G, and pilot bits for channel estimation are multiplexed by the multiplexing unit 102G. In addition, transmission carrier setting section 102A sets subcarriers to be transmitted based on the spreading factor from spreading ratio setting section 103 and the number of transmission carriers and the usage status of subcarriers given from a control signal from a control section (not shown). To do. The serial / parallel conversion unit 102B performs serial / parallel (S / P) conversion of the symbol series into parallel data corresponding to (all or part of the number of subcarriers / spreading ratio) based on the set carrier information. The symbol series converted into parallel data by the serial / parallel conversion described above has continuous subcarriers and a time axis on the time axis based on the relationship between the number of spreading factors (SF) and the number of subcarriers used by the copy unit 102H. Copied. Specifically, when the spreading factor SF is larger than the number of subcarriers, it is copied on the subcarrier and the time axis, and when the spreading factor SF is smaller than the number of subcarriers, it is copied to a part of the subcarriers. Is done. At this time, copying of the same symbol to SF subcarriers can be realized by repeatedly reading a symbol series input to the memory.

  After that, SF consecutive identical symbol sequences are spread (scrambled) by combining section 102I with a spreading code of spreading factor SF uniquely assigned. Then, the dimension for performing the FFT operation is determined according to the number of subcarriers input from the control signal, and the spread symbol sequence corresponding to the number of subcarriers is determined by the inverse FFT (IFFT) operation in the IFFT unit 102C. Time / frequency conversion into multi-carrier components orthogonal on the axis. Finally, a guard interval is inserted into each subcarrier symbol converted into multicarriers by the guard interval insertion unit 102D. The insertion of the guard interval is realized by copying the signal waveform corresponding to the FFT sample in the end of each symbol or symbol series to the head of each symbol. The GI insertion unit 102D outputs a modulated signal to the symbol transmission control unit 102E, and the symbol transmission control unit 102E transmits a symbol sequence modulated based on the symbol synchronization timing output from the symbol synchronization detection unit 105. .

  Next, the configuration and operation of the reception radio station 111 will be described.

  As shown in FIG. 3, in the reception radio station 111, the signal from the antenna 16 is input to the symbol timing detection unit 18 via the filter 112 that passes both frequency bands f1 and f2 and is received. Symbol timing (timing for performing FFT operation, also referred to as FFT window timing) is detected from the multicarrier signal.

  In the present embodiment, two frequency bands f1 and f2 have been described, but the same applies to three or more frequency bands. The filter 112 is used to block radio waves of another system that is difficult to synchronize. The signals in the frequency band f1 and the frequency band f2 that have passed through the filter 112 are demodulated after being subjected to DFT (Discrete Fourier Transform) processing collectively by the receiving unit 15. The configuration of the receiving unit 15 will be described later with reference to FIG.

  The signal demodulated by the receiving unit 15 is output from the data output terminal 17. The data output at this time can be data transmitted only in the frequency band f1, only the frequency band f2, or the frequency bands f1 and f2. That is, according to the present invention, signals in a plurality of frequency bands can be received simultaneously, so that a smooth handover can be executed.

  In addition, when a small cell transmission radio station is installed in a mobile body such as a train or a bus and the mobile body is used as a cell of the small cell transmission radio station, Even when the reception power from the large cell transmission radio station greatly fluctuates with respect to the reception power, interference can be reduced by performing symbol synchronization as described above, so that the large cell transmission radio station and the small cell transmission radio It becomes possible to simultaneously demodulate the signals from the stations.

  Here, the configuration of the reception radio station 111 (particularly the reception unit 15) will be described in more detail.

  FIG. 10A shows a configuration related to transmission of an OFDM signal in the receiving radio station 111. As shown in the figure, the received signal from the large cell transmission radio station has both frequencies of frequency band f1 and frequency band f2 (or three frequency bands fn if three or more are received from the large cell transmission radio station). Symbol timing (timing for performing FFT operation, also referred to as FFT window timing) is detected from the received multicarrier signal that is input to the symbol timing detection unit 18 through the filter 112 that passes the band. The symbol timing can be detected by detecting the correlation in the guard interval section. The guard interval removing unit 15A removes the guard interval signal from the symbol timing detected by the symbol timing detecting unit 18 as described above. Thereafter, the removed signal is subjected to discrete Fourier transform (DFT) based on the estimated FFT window timing in the FFT unit 15B, and parallel / serial (P / S) converted in the parallel / serial conversion unit 15C. Input to the demodulator 15D. Note that the demodulation unit 15D may be configured to select and demodulate some signals from signals of a plurality of carrier frequency bands of different transmission schemes.

  The filter 112 is intended to remove signals in frequency bands other than signals in a plurality of frequency bands that are desired to be received at the same time. However, a specific upper cell transmission radio station (“transmission radio station of an upper cell in a hierarchical cell structure” ”And corresponding to the large cell transmission radio station in FIG. 1), signals other than the necessary frequency band can be removed by selecting the frequency band. Needless to say. At that time, the filter 112 sets a frequency band for filtering by a control signal from a control unit (not shown), and a frequency band for performing FFT calculation changes. By notifying the unit 15B, it is possible to perform an FFT operation in a necessary frequency band.

  FIG. 10B shows a configuration related to the transmission of the OFCDM signal in the receiving radio station 111. As shown in the figure, both frequency bands of a frequency band f1 and a frequency band f2 (in the case of receiving three or more from the large cell transmission radio station, each frequency band fn) are received signals from the large cell transmission radio station. The symbol timing (which is the timing for performing the FFT operation, also referred to as the FFT window timing) is detected from the received multicarrier signal. The symbol timing can be detected by detecting the correlation in the guard interval section. The guard interval removing unit 15A removes the guard interval signal from the symbol timing detected by the symbol timing detecting unit 18 as described above. Thereafter, the removed signal is subjected to discrete Fourier transform (DFT) based on the estimated FFT window timing in the FFT unit 15B, and in the channel estimation unit 15E, the channel impulse response (channel fluctuation) of each subcarrier is Estimated using pilot symbols. The in-phase addition unit 15G performs in-phase addition (that is, despreading) of the SFCD sub-carrier component OFCDM symbols on the frequency axis from the channel estimation value of each sub-carrier and the spreading code used for spreading, thereby obtaining an information symbol sequence. Is generated. The despread (total number of subcarriers / spreading factor) information symbols are parallel / serial (P / S) converted by the parallel / serial converter 15C and input to the demodulator 15D. Note that the demodulation unit 15D may be configured to select and demodulate some signals from signals of a plurality of carrier frequency bands of different transmission schemes.

  The filter 112 is intended to remove signals in frequency bands other than signals in a plurality of frequency bands that are desired to be received at the same time, but when receiving a signal from a specific upper cell transmission radio station, the frequency band It goes without saying that signals other than the necessary frequency band can be removed by selecting. At that time, the filter 112 sets a frequency band for filtering by a control signal from a control unit (not shown), and a frequency band for performing FFT calculation changes. By notifying the FFT unit 15B, it is possible to perform an FFT operation in a necessary frequency band.

  By the way, the processing in the transmitting radio station and the receiving radio station of the present embodiment described above can also be understood as processing of a radio communication program executed by a computer provided in each radio station. Hereinafter, processing in the transmitting radio station (FIG. 11) and processing in the receiving radio station (FIG. 12) will be described in order.

  An outline of processing in the transmitting radio station can be expressed as shown in FIG. As shown in the figure, the transmitting radio station monitors whether or not one or a plurality of carrier frequency band signals having a transmission method different from that of the own station has been received (S01: signal detection step), and a carrier having a different transmission method is received. When reception of a frequency band signal is detected, symbol synchronization to be transmitted is detected from the received signal (S02: symbol synchronization detection step). Then, based on the detected symbol synchronization, a symbol transmission timing at which a carrier frequency band signal of a different transmission method and a signal from the own station do not interfere with each other is derived, and a signal to be transmitted is transmitted at the symbol transmission timing. (S03: Signal transmission step).

  On the other hand, for the receiving radio station, the following characteristic processing executed when the own station moves into a small cell in the hierarchical cell structure can be regarded as processing of the radio communication program. As shown in FIG. 12, the reception radio station is able to receive information from the large cell transmission radio station and information indicating that the signal from the small cell transmission radio station can be received. Registration is performed in a transfer device (for example, a location registration management server that realizes location registration of a receiving radio station in the network or a router in the network) (S11: registration step). For example, the data transfer apparatus that has received the information selects the transmission radio station that transmits the data according to the type of data to be transmitted to the reception radio station, thereby providing the multicast information to the reception radio station. It is possible to perform data transmission control according to the type of data, such as transmitting from a large cell transmission radio station and transmitting individual information having a high data rate such as image data from a small cell transmission radio station. Needless to say, the determination is not limited to the above embodiment, although it is possible to select a transmission radio station based on the amount of data, traffic characteristics (for example, non-real time, real time), and the like.

  The receiving radio station that has transmitted signals of a plurality of carrier frequency bands simultaneously receives and demodulates the signals of the plurality of carrier frequency bands (S12: simultaneous reception step).

  For example, as shown in FIG. 7, when the receiving radio station moves to a place where a signal from the small cell transmitting radio station can be received, the fact that it has moved into the cell of the small cell transmitting radio station # 3 By notifying the above-described data transfer device via the transmission radio station # 1 or the small cell transmission radio station # 3, the large cell transmission radio is always used when in the cell of the small cell transmission radio station. It becomes possible to receive data from the station and the small cell transmission radio station.

  Therefore, in the case of transmission of multicast information for transmitting the same information to a plurality of receiving radio stations located in a wide area, the multicast information is transmitted from the large cell transmitting radio station, and large-capacity information for a specific receiving radio station In the case of the transmission, the large-capacity information can be transmitted independently from the small cell transmission radio station.

  As described above, the processing in the transmitting radio station and the receiving radio station according to the present embodiment can be understood as processing of a radio communication program executed by a computer provided in each radio station.

  Next, the effect of this embodiment will be described with reference to the spectrum from the large cell transmission radio station after the DFT of the reception radio station in FIG. 5 and the spectrum from the small cell transmission radio station.

  The setting of the DFT section in the receiving radio station is synchronized with the signal from the small cell transmitting radio station. Further, no guard band is provided between the frequency band used by the large cell transmission radio station and the frequency band used by the small cell transmission radio station. That is, the intervals of all subcarrier frequencies are the same. Since the cell radius of the large cell is larger than the cell radius of the small cell, the equivalent isotropically radiated power (EIRP) of the large cell transmitting radio station is larger than the EIRP of the small cell transmitting radio station. . Therefore, in the receiving radio station located in the small cell existing in the vicinity of the large cell transmitting radio station, the radio wave from the large cell transmitting radio station is received with higher power as shown in FIG.

  A rectangular spectrum whose normalized frequencies are shown as 0 to 1 is a spectrum after DFT processing of a signal from a small cell transmission radio station. Further, the spectrum that is rectangular in the normalized frequency range of −1 to 0 is the spectrum after the DFT process is performed on the signal from the large cell transmission radio station. Thus, it can be seen that the amount of interference leaking into the frequency band used by the small cell transmission radio station can be greatly reduced by performing the synchronization of the present invention. In addition, even if synchronization is performed, the interference that leaks into the frequency band exists because of distortion in the amplifier. Since the interference due to such distortion is the same as the state in which the thermal noise has increased, the interference can be reduced by performing diffusion modulation together with the interference due to the distortion.

  The receiving radio station is provided with a synchronization request means for requesting symbol synchronization to the transmitting radio station, and the transmitting radio station detects symbol synchronization by using a symbol synchronization request from the synchronization request means of the receiving radio station as a trigger. Also, an embodiment in which transmission timing control is performed can be adopted. In this aspect, as described above, the receiving radio station can simultaneously receive and demodulate signals in a plurality of carrier frequency bands, and thus needs to perform “frequency switching processing” at the time of handover, as in the past. Therefore, smooth handover can be realized. Moreover, since the setting of the guard band can be made small or unnecessary, the frequency can be effectively used. Further, since signals from a plurality of transmitting radio stations can be received simultaneously, multilink transmission can be executed. In addition, it is possible to freely arrange a new transmission radio station without considering the influence of interference with other existing transmission radio stations forming a small cell. Furthermore, since the receiving part of the receiving radio station that receives a plurality of frequency bands can be made common, it is possible to reduce the volume of the receiving radio station and reduce the manufacturing cost.

  In addition, the transmission radio station according to the present invention is not limited to a base station, and may be a mobile station. When applied to a pervasive network with a multi-hop connection between a plurality of mobile stations, a single mobile station ( The synchronization request means (corresponding to the receiving radio station) requests symbol synchronization from another mobile station (corresponding to the transmitting radio station), and the other mobile stations perform symbol synchronization detection and transmission timing control. Autonomous transmission timing control can be realized.

  Furthermore, the accuracy (stability) of symbol synchronization in the small cell transmission radio station is such that the small cell transmission radio station is fixedly installed, the antenna gain is higher than that of the reception radio station, and the small cell The antenna installation environment of the transmitting radio station is better than the antenna installation environment of the receiving radio station, which is considered to be higher than the accuracy (stability) of symbol synchronization at the receiving radio station. In addition, it is expected that the environment between the small cell transmitting radio station and the receiving radio station will have a better visibility in many situations than between the large cell transmitting radio station and the receiving radio station. In other words, the accuracy (stability) of symbol synchronization at the receiving radio station is higher when symbol synchronization is performed on a small cell transmission radio station than when symbol synchronization is performed on a large cell transmission radio station. Is considered higher.

  From the above, the receiving radio station can receive a signal from the large cell transmitting radio station more stably by executing symbol synchronization with the small cell transmitting radio station (that is, for the small cell transmitting radio station). Synchronizing the symbol will equivalently synchronize the symbol to the large cell).

[Second Embodiment]
Next, a second embodiment will be described using the functional block configuration diagram of the transmitting radio station and the receiving radio station in FIG. In the present embodiment, a description is given of a transmission radio station using the frequency band f3 and a transmission radio station using the frequency band f4. The transmitting radio station is applicable to either a large cell transmitting radio station or a small cell transmitting radio station. Although the case where two frequency bands are used will be described, the same applies to the case where three or more frequency bands are used.

  The transmission unit 202 of the transmission radio station 201 and the transmission unit 202 of the transmission radio station 221 perform symbol synchronization of transmission symbols by a signal output from the symbol synchronization reference source 230. That is, the data input from the data input terminal 4 of the transmission wireless station 201 and the data input from the data input terminal 4 of the transmission wireless station 221 are transmitted in synchronization with each other. Symbol synchronization at this time is performed so that there is no symbol boundary of a signal transmitted by another transmitting radio station within one symbol DFT interval, as shown in FIG. The symbol synchronization reference source 230 in FIG. 6 (particularly, the part that transmits the synchronization request signal to the transmission unit 202) corresponds to the “synchronization request unit” according to the present invention. Further, in this description, the symbol synchronization reference source is provided independently, but in addition to this, a symbol synchronization reference source is provided in one of the transmission radio stations, and a transmission radio station having no symbol synchronization reference source is A method of synchronizing with a transmitting radio station having a symbol synchronization reference source may be adopted. In addition, a symbol synchronization reference source is provided in all the transmission radio stations, and the symbol synchronization reference source of the local station and the symbol synchronization reference source of another transmission radio station cooperate with each other using wired or wireless, and the symbol A method of performing synchronization may be employed. At this time, it is desirable that the transmitting radio stations cooperate with each other and set so that the transmission carrier frequencies of signals to be transmitted by the transmitting radio stations are orthogonal to each other. That is, the transmitting radio station detects the frequency interval based on the received signal from the other transmitting radio station, and the orthogonal relationship with the transmission carrier frequency of the other transmitting radio station based on the detected frequency interval. So that the transmission radio station has an optimal correlation with each of the carrier frequency band signal of the transmission method different from the own station and the signal of the own station. It is possible to transmit signals at symbol transmission timings that do not interfere with each other. An example of the frequency setting will be described later.

  In the reception radio station 211, the signal from the antenna 16 is input to the reception unit 15 via the filter 112 that passes both the frequency bands f3 and f4. The signal demodulated and demodulated by the receiving unit 15 is output from the data output terminal 17. The data output at this time can be data transmitted only in the frequency band f3, only in the frequency band f4, or in the frequency bands f3 and f4.

  As described in the first and second embodiments, the following effects can be obtained by applying the present invention. In other words, the transmitting radio station can transmit a signal at the optimum symbol transmission timing (which does not interfere with each other) with the correlation between the carrier frequency band signal of the transmission method different from the own station and the signal of the own station. The receiving radio station can receive and demodulate signals in multiple carrier frequency bands at the same time, eliminating the need for “frequency switching” at the time of handover as in the past, and realizing a smooth handover. can do.

  Moreover, since the setting of the guard band can be made small or unnecessary, the frequency can be effectively used. Further, since signals from a plurality of transmitting radio stations can be received simultaneously, multilink transmission can be executed. In addition, it is possible to freely arrange a new transmission radio station without considering the influence of interference with other existing transmission radio stations forming a small cell. Furthermore, since the receiving part of the receiving radio station that receives a plurality of frequency bands can be made common, it is possible to reduce the volume of the receiving radio station and reduce the manufacturing cost.

Here, an example of the frequency setting will be described with reference to FIGS. A received signal from another transmitting radio station such as a large cell transmitting radio station is multiplied by a signal from the local oscillator 317 by multipliers 311A and 311B, and then passed through a low-pass filter 312A and 312B, respectively. (R _I , r _Q ) is converted ((π / 2) phase-converted signal is input to multiplier 311B). The baseband signals (r _I , r _Q ) and the baseband signals (r _−I , r _−Q ) delayed by the delay units 313A and 313B for delaying by one symbol DFT interval length, respectively. Become. Next, multiplication and addition are performed on the baseband signal (r _I , r _Q ) that is not delayed and the delayed baseband signal (r _-I , r _-Q ), respectively. This process corresponds to a process of multiplying a complex vector signal that is not delayed by the complex conjugate of the delayed complex vector signal.

  As shown in FIG. 14A, since a part of the OFDM signal is copied to the guard interval part, when the multiplication timings coincide with each other (when the signal is multiplied by the copy portion of the signal), On the complex plane described in FIG. 14B, a vector that does not vary with time is obtained. Accordingly, in the integrators 314A and 314B that integrate the vectors by the guard interval length, the same vectors are added, so that the magnitude of the vector after the integration becomes a value equal to or larger than the set threshold value. On the other hand, when the timings of multiplication do not match (when multiplying a signal and a portion other than the copy portion of the signal), on the complex plane described in FIG. Become. Therefore, since the integration is not performed in the same phase, the magnitude of the vector after the integration becomes a value equal to or smaller than the threshold value. The timing at which the magnitude of the post-integration vector is greater than or equal to the threshold and becomes the maximum value is the symbol timing for DFT.

However, if the frequency of the local oscillator 317 is not the same as the frequency of any subcarrier signal of the OFDM signal, even if the symbol timings match, the 1-symbol DFT set in the delay units 313A and 313B Since the phase is rotated by the difference in frequency during the section length, the angle formed with the I axis shown in FIG. 15B is not a vector whose angle with the I axis shown in FIG. Yields a vector of θ [rad]. In FIG. 13, θ [rad] is obtained by searching the relationship between the amplitude of each signal after integration stored in the Tan memory 315 and θ. Then, the frequency difference calculation unit 316 calculates the following equation (1) to obtain the value (Δf) of the shifted frequency.
Δf [Hz] = (1 / 2π) × (θ / T) (1)

  In this equation (1), Δf [Hz] is the minimum value of the difference between the frequency of the local oscillator 317 and the frequency of each subcarrier signal of the OFDM signal, and θ [rad] is the deflection angle of the post-integration vector. T [sec] is a delay time (1 symbol DFT interval length) set in the delay units 313A and 313B.

  Then, the local oscillator 317 is tuned by correcting the obtained frequency deviation. The state in which the frequency is tuned is a state in which the local oscillator 317 of the local station is tuned to the transmission frequency of a signal from another transmitting radio station, and therefore the local oscillator 317 is set to the transmission frequency of the signal transmitted by the local station. By using it, the transmission carrier frequencies of the signals from the respective transmission radio stations are orthogonal.

  The small cell transmission radio station in the first and second embodiments may be a wireless LAN or a wireless communication network in another small area.

It is a figure for demonstrating the radio | wireless communications system comprised from one or more transmitting radio stations which cover the area of a certain range, a transmitting radio station with small EIRP, and a receiving radio station. It is a functional block block diagram of the transmission radio station and reception radio station with the conventional small EIRP. It is a functional block block diagram of a transmission radio station and reception radio station with small EIRP of 1st Embodiment. It is a figure which shows the timing relationship of the reception symbol from the transmission radio station which covers the area of a certain range, and the transmission symbol of a transmission radio station with a small EIRP. It is a figure of the spectrum from the large cell transmission radio station after the DFT of the receiving radio station, and the spectrum from the small cell transmission radio station. It is a functional block block diagram of the transmitting radio station and receiving radio station of 2nd Embodiment. It is a figure for demonstrating position registration when EIRP moves into the cell of a small transmitting radio station. It is an example of the structure which implement | achieves a symbol synchronous detection part. (A) is a functional block diagram showing a configuration related to transmission of an OFDM signal in a small cell transmission radio station, and (b) is a functional block diagram showing a configuration related to transmission of an OFCDM signal in the small cell transmission radio station. (A) is a functional block diagram showing a configuration related to reception of an OFDM signal in a receiving radio station, and (b) is a functional block diagram showing a configuration related to reception of an OFCDM signal in the receiving radio station. It is a flowchart which shows an example of a process of the radio | wireless communication program in a transmission radio station. It is a flowchart which shows an example of a process of the radio | wireless communication program in a receiving radio station. It is a figure for demonstrating an example of a frequency setting. (A) is a figure which shows a copy of a part of OFDM signal, (b) is a figure which shows a vector when the timing to multiply match, (c) is a vector when the timing to multiply does not match FIG. (A) is a figure which shows a vector when the timing to multiply and a frequency synchronize, (b) is a figure which shows a vector when the timing to multiply and a frequency do not synchronize.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 101, 201, 221 ... Transmission radio station, 11, 111, 211 ... Reception radio station 2, 102, 202 ... Transmission part, 3, 3A, 16 ... Antenna, 4 ... Data input terminal, 12, 13, 112 , 212 ... filter, 14 ... switch, 15 ... receiver, 15A ... guard interval remover, 15B ... FFT unit, 15C ... parallel / serial converter, 15D ... demodulator, 15E ... channel estimator, 15F ... spread code Setting unit, 15G ... In-phase addition unit, 17 ... Data output end, 18 ... Symbol timing detection unit, 80 ... Cell, 90 ... Area, 102A ... Transmission carrier setting unit, 102B ... Serial / parallel conversion unit, 102C ... IFFT unit, 102D: guard interval insertion unit, 102E: symbol transmission control unit, 102F: spreading code generation unit, 102G: multiplexing unit, 102H Copy unit, 102I. Synthesis unit, 103 ... Spreading factor setting unit, 104 ... reception quality measurement unit, 105 ... symbol synchronization detection unit, 230 ... symbol synchronization reference source, 301 ... delay unit having a length of one symbol DFT section, 302 ... Guard interval length sliding correlator, 303 ... Maximum correlation value detector, 304 ... Timing derivation unit, 311A, 311B ... Multiplier, 312A, 312B ... Low pass filter, 313A, 313B ... Delayer, 314A, 314B ... Integrator 315 ... Tan memory, 316 ... frequency difference calculation unit, 317 ... local oscillator.

Claims (9)

A transmitting radio station in a radio communication system having a hierarchical cell structure, wherein symbols to be transmitted are arranged on a frequency axis and a signal is transmitted to a radio terminal in an area using one or a plurality of carrier frequency bands,
Signal detection means for detecting at least one carrier frequency band signal of a transmission method different from that of the own station;
Symbol synchronization detection means for detecting symbol synchronization to be transmitted based on at least one received signal when detecting a carrier frequency band signal of the different transmission method;
Based on the detected symbol synchronization in DFT section 1 symbol signals the small cell sending radio station transmits, by the symbol transmission timing symbol boundaries of a signal from the large cell sending radio station is carried out so as not to exist, transmits A transmitting radio station comprising: a signal transmitting means for transmitting a signal to be transmitted. A frequency interval detecting means for detecting a frequency interval based on a received signal from another transmitting radio station ;
The transmission radio station according to claim 1, further comprising frequency setting means for setting a transmission carrier frequency so as to be orthogonal to the transmission carrier frequency of the radio terminal based on the detected frequency interval. Reception quality measuring means for measuring reception quality based on a reception signal from a wireless terminal;
The transmission radio station according to claim 1, further comprising spreading factor setting means for setting a spreading factor based on reception quality obtained by measurement. A transmission radio station that arranges symbols to be transmitted on the frequency axis and transmits a signal to a radio terminal in the area using one or a plurality of carrier frequency bands, and a reception radio station that receives a signal from the transmission radio station A wireless communication system having a structured hierarchical cell structure,
The transmitting radio station is
Signal detection means for detecting at least one carrier frequency band signal of a transmission method different from that of the own station;
Symbol synchronization detection means for detecting symbol synchronization to be transmitted based on at least one received signal when detecting a carrier frequency band signal of the different transmission method;
In DFT section 1 symbol of based on the detected symbol synchronization small cell sending radio station signal to be transmitted, more symbol transmission timing when the symbol boundary of the signal from the large cell sending radio station is carried out so as not to exist, Signal transmitting means for transmitting a signal to be transmitted,
The receiving radio station is
A wireless communication system comprising a simultaneous reception control means for simultaneously receiving and demodulating signals in a plurality of carrier frequency bands. The radio communication system is configured to include a plurality of transmission radio stations using different carrier frequency bands,
The wireless communication system according to claim 4, wherein the plurality of transmission wireless stations cooperate with each other using wired or wireless transmission, and transmit symbols of signals to be transmitted by the transmission wireless stations in synchronization with each other. 6. The radio communication system according to claim 5, wherein the plurality of transmitting radio stations are set so as to cooperate with each other so that transmission carrier frequencies of signals to be transmitted by the transmitting radio stations are orthogonal to each other. A transmission radio station that arranges symbols to be transmitted on the frequency axis and transmits a signal to a radio terminal in the area using one or a plurality of carrier frequency bands, and a reception radio station that receives a signal from the transmission radio station A wireless communication system having a structured hierarchical cell structure,
The receiving radio station is
Synchronization request means for requesting symbol synchronization to the transmitting radio station;
Simultaneous reception control means for simultaneously receiving and demodulating signals of a plurality of carrier frequency bands,
The transmitting radio station is
Symbol synchronization detecting means for detecting symbol synchronization to be transmitted based on at least one received signal when receiving a symbol synchronization request from the receiving radio station;
In DFT section 1 symbol of based on the detected symbol synchronization small cell sending radio station signal to be transmitted, more symbol transmission timing when the symbol boundary of the signal from the large cell sending radio station is carried out so as not to exist, A wireless communication system, comprising: signal transmission means for transmitting a signal to be transmitted. In a wireless communication system with a hierarchical cell structure, a wireless communication method in a transmitting wireless station that arranges symbols to be transmitted on a frequency axis and transmits a signal to wireless terminals in an area using one or a plurality of carrier frequency bands,
A signal detection step in which the transmitting radio station detects at least one carrier frequency band signal of a transmission method different from that of the own station;
A symbol synchronization detecting step of detecting symbol synchronization to be transmitted based on at least one received signal when the transmitting radio station detects the carrier frequency band signal of the different transmission method;
The sending radio station is performed as the small cell sending radio station based on the symbol detected synchronization in DFT section 1 symbols of the signal to be transmitted, there is no symbol boundary of the signal from the large cell sending radio station more symbol transmission timing, the wireless communication method and a signal transmission step of transmitting a signal to be transmitted. A transmission radio station that arranges symbols to be transmitted on the frequency axis and transmits a signal to a radio terminal in the area using one or a plurality of carrier frequency bands, and a reception radio station that receives a signal from the transmission radio station A wireless communication method in a configured wireless communication system having a hierarchical cell structure,
A synchronization request step in which the receiving radio station makes a request for symbol synchronization to the transmitting radio station;
A symbol synchronization detecting step of detecting symbol synchronization to be transmitted based on at least one received signal when the transmitting radio station receives a request for symbol synchronization from the receiving radio station;
The transmitting radio station is performed as the small cell sending radio station based on the symbol detected synchronization in DFT section 1 symbols of the signal to be transmitted, there is no symbol boundary of the signal from the large cell sending radio station more symbol transmission timing, the wireless communication method and a signal transmission step of transmitting a signal to be transmitted.

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