JP2007300421A - Radio station, radio communication system, and radio communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system and a radio communication method which use frequency bands assigned to other systems to communicate and can suppress interferences produced at the other systems and continue self-communication. <P>SOLUTION: A radio terminal 11-1 selects candidate frequency bands A to C to be used for communication with a radio terminal 11-2 among frequency bands 1-L. A slot 7 to which the radio terminal 11-1 transmits data has a carrier sense CS section 701 where carrier sense CS for the candidate frequency bands A to C is performed and a transmission section 702 where data are transmitted. The radio terminal 11-1 performs the carrier sense CS in the candidate frequency bands A to C in the carrier sense SC section and then transmits the data in the transmission section 702 by using an "empty" candidate frequency band. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio station, a radio communication system, and a radio communication method.

  Improve frequency utilization efficiency by temporarily sharing a frequency band that is not allocated to itself with other systems compared to a conventional wireless communication system that performs communication using only the license band allocated to itself. A wireless communication system using cognitive radio technology has been proposed (see, for example, Non-Patent Document 1).

  The system 1 using this cognitive radio technology performs a carrier sense in a frequency band other than the license band LB1 allocated to itself (for example, the license band LB2 allocated to the system 2), and the license that is not used by the system 2 Band LB2 is detected. The system 1 dynamically allocates a part of the detected license band LB2 to the communication between its wireless devices, and temporarily shares the license band LB2 with the system 2 to improve frequency use efficiency. ing.

  However, since the wireless communication system using this cognitive wireless technology is premised on sharing the license band LB2, it is not always in an environment where the frequency channel used for communication can always be used. Further, since interference between the wireless devices belonging to the system 2 should not be given, the interference with the wireless device using the license band LB2 is found even if the wireless device belonging to the system 1 is communicating. If you do, you must stop communication immediately.

  Therefore, as a wireless communication system that shares a license band without interfering with other wireless devices, a license band assigned to the wireless communication system is shared by a plurality of base stations, and communication with wireless terminals is performed while avoiding interference with each other. There is known a wireless communication system that dynamically allocates frequency channels to (see, for example, Patent Document 1).

In the wireless communication system described in Patent Document 1, the base station periodically detects the usage status of the license band using the broadband receiving means. The base station analyzes the signal received by the wideband receiving means to measure the amount of interference in each frequency channel so that the frequency channel with a large amount of interference is not used for the next communication. As a result, even if there are a plurality of base stations sharing one license band, it is possible to communicate with the wireless terminal without interfering with each other.
J. et al. Mitola III et al., “Cognitive Radio; Making Software Radios More Personal”, IEEE Personal Communications Magazine, August. 1999 JP 2002-300630 A

  However, the base station BS1 belonging to the wireless communication system described in Patent Literature 1 periodically detects the usage status of the license band. Therefore, even if this base station BS1 interferes with another base station BS2, this interference cannot be detected until the license band usage state is detected next, and this interferes with the other base station BS2. There is a problem of continuing.

  In addition, since the frequency channel that is considered to be interfering as a result of detecting the usage status of the license band cannot be used until it is detected that there is no interference next, the frequency channel that is considered to be interfering Increases, it becomes difficult for the base station BS1 to continue communication with the wireless terminal.

  The present invention has been made in order to solve the above-described problems of the prior art, and can suppress interference given to other communication and continuously perform its own communication. The purpose is to provide.

  In order to achieve the above object, a radio station according to the present invention is a radio station that transmits a signal to a communication partner in a fixed time slot. Carrier sense means for performing a second carrier sense in M frequency bands (L ≧ M ≧ 2) in the first carrier sense section of the time slot, and the first carrier sense As a result, the M frequency bands that are not used are selected from the L frequency bands, and the transmission frequency band that is not used from the M frequency bands is selected as a result of the second carrier sense. And a transmission means for transmitting a signal using the transmission frequency band determined by the control unit in a transmission section subsequent to the carrier sense section.

  The wireless communication system of the present invention is a wireless communication system in which a first wireless station and a second wireless station communicate with each other using a fixed time slot, and the first wireless station includes the time slot. Carrier sensing means for performing carrier sensing of M (M ≧ 2) frequency bands in the first carrier sensing section, and determining the transmission frequency band from the frequency bands not used as a result of the carrier sensing And a first transmission means for transmitting a known signal sequence and data using the transmission frequency band determined by the control unit in a transmission period following the carrier sense period. The second radio station receives the signals of the M frequency bands in the detection interval of the time slot, and selects one of the M frequency bands in the reception interval following the detection interval. Based on the correlation value between the receiving means for receiving the signal in the waveband and the signal received by the receiving means in the detection interval and the signal of the same series as the known signal, the receiving means receives in the receiving interval. And a second control unit that determines a frequency band.

  The wireless communication method of the present invention is a wireless communication method in which a first wireless station and a second wireless station communicate with each other using a fixed time slot, and the first wireless station includes carrier sense means. However, in the carrier sense section at the beginning of the time slot, M (M ≧ 2) carrier senses of frequency bands are performed, and the first control unit is in a frequency band that is not used as a result of the carrier sense. The transmission frequency band is determined from the first transmission means, and the first transmission means transmits the known signal sequence and data using the transmission frequency band determined by the control unit in the transmission period following the carrier sense period. , A signal is transmitted to the second radio station, and the second radio station receives a signal of the M frequency bands in a detection period of the time slot, and a second control unit To the receiving means Therefore, based on the correlation value between the signal received in the detection section and a signal of the same series as the known signal, the receiving means determines the frequency band received in the reception section, and the receiving means A signal transmitted from the first radio station is received by receiving a signal in a frequency band determined by the control unit in a reception section following the section.

  According to the wireless communication system and the wireless communication method of the present invention, it is possible to suppress interference given to other communication and continue its own communication.

  Embodiments of the present invention will be described below with reference to the drawings.

  A radio communication system according to the first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a diagram illustrating an outline of a wireless communication system according to the present embodiment.
A wireless communication system (hereinafter referred to as system 1) according to the present embodiment is a system that performs communication by temporarily using a frequency band that is not allocated to itself. The system 1 performs communication by sharing a part of the license band LB2 assigned to a wireless communication system (hereinafter, referred to as a system 2) different from the system 1 with the system 2, for example.

  First, an outline of the system 2 will be described. For example, a base station 20 and a wireless terminal 21 belong to the system 2 shown in FIG. The base station 20 and the wireless terminal 21 communicate with each other in the communication area 22 of the base station 20 using a frequency channel obtained by dividing the license band LB2 into a certain bandwidth h.

  On the other hand, the wireless terminals 11-1 and 11-2 belong to the system 1. The wireless terminals 11-1 and 11-2 communicate with each other while using a part of the frequency band of the license band LB2 within the communication area 22.

  Next, the frequency band used for communication by the wireless terminals 11-1 and 11-2 will be described with reference to FIGS. FIG. 2 is a diagram showing frequency bands that can be used in communication of the system 1.

  The wireless terminals 11-1 and 11-2 divide the license band LB2 into frequency bands 1 to L having a bandwidth M, select N candidate frequency bands from any one of the frequency bands 1 to L, Communication is performed using this candidate frequency band. The bandwidth M may be the same as or different from the bandwidth h of the frequency channel used by the base 20.

  The frequency bands 1 to L do not need to be continuous as shown in FIG. 2, and may be arbitrarily selected from the license band LB2, for example, as shown in FIG. As shown in FIG. 4, not only the license band LB2 assigned to the system 2, but also the frequency band including the license band LB3 assigned to the system 3, for example, may be divided into L pieces.

  Next, with reference to FIG. 5, candidate frequency bands used for communication between the wireless terminals 11-1 and 11-2 will be described. FIG. 5 is a diagram illustrating frequency band candidates used for communication between the wireless terminals 11-1 and 11-2. Here, a case will be described in which the wireless terminal 11-1 selects a candidate frequency band, but this selection may be performed by the wireless terminal attempting to start communication, or may be performed by the wireless terminal 11-2.

  First, before starting communication, the wireless terminal 11-1 performs carrier sense CS of the frequency bands 1 to L and detects the usage status. Next, the wireless terminal 11-1 selects N candidate frequency bands to be used for communication based on the detection result. In the following description, as shown in FIG. 5, N = 3, and the wireless terminal 11-1 selects candidate frequency bands A, B, and C from frequency bands 1 to L as a result of carrier sense CS. Details of the method of selecting the candidate frequency bands A, B, and C will be described later. The carrier sense CS determines whether each frequency band is “in use” or “empty” by determining a threshold value of received power of a signal in each frequency band. Here, received power is used for carrier sense CS, but received field strength or the like may be used.

  Next, the configuration of the wireless terminal 11-1 will be described with reference to FIG. FIG. 6 is a block diagram illustrating a configuration of the wireless terminal 11-1. Note that the configuration of the wireless terminal 11-2 is the same as that of the wireless terminal 11-1, and a description thereof will be omitted.

  The wireless terminal 11-1 includes an antenna 110, an analog RF signal processing unit 120 including a transmission system RF wireless unit 121, a reception system RF wireless unit 122, an A / D conversion unit 123, and a D / A conversion unit 124. It has a digital signal processing unit 130 connected to the signal processing unit 120, a control unit 140 that controls each unit, and a storage unit 150 connected to the control unit 140.

Next, details of each part will be described.
First, the reception RF radio unit 122 included in the analog signal processing unit 120 performs processing such as frequency conversion on the signal received by the antenna 110 and converts the signal into a reception analog signal. The subsequent A / D conversion unit 123 converts the reception analog signal input from the reception system RF radio unit 122 into a reception digital signal and outputs it to the digital signal processing unit 130.

  The digital signal processing unit 130 processes the reception digital signal input from the A / D conversion unit 123 to obtain reception data. The digital signal processing unit 130 converts transmission data into a transmission digital signal and outputs the transmission data to the D / A conversion unit 124.

  The D / A conversion unit 124 converts the transmission digital signal input from the digital signal processing unit 130 into a transmission analog signal and outputs it to the transmission RF radio unit 121. The transmission RF radio unit 121 performs processing such as frequency conversion on the transmission analog signal input from the D / A conversion unit 124 to convert it into a transmission signal, and transmits it from the antenna 110.

  The control unit 140 also controls the analog signal processing unit 120 and the digital signal processing unit 130 to switch between transmission and reception, and determines a frequency band to be used for communication based on information stored in the storage unit 150. To do. The storage unit 150 connected to the control unit 140 stores past usage history and the like of each frequency band 1 to L.

  Here, the configuration of the frame 6 used in communication between the wireless terminals 11-1 and 11-2 will be described with reference to FIGS. The wireless terminals 11-1 and 11-2 perform communication using a TDD (Time Division Duplex) method. In this communication, it is assumed that the wireless terminal 11-1 requests the wireless terminal 11-2 to start communication, and the time synchronization of communication by the TDD scheme is a communication request first transmitted by the wireless terminal 11-1. Assume synchronization with the slot timing of the signal.

  FIG. 7 is a diagram illustrating a temporal configuration of the frame 6 used by the wireless terminals 11-1 and 11-2 for communication. First, the wireless terminal 11-1 transmits a signal using the slot 7. Next, the wireless terminal 11-2 that has received this signal transmits a signal using the slot 8 that follows the slot 7. The slot 7 and the slot 8 are combined into a frame 6, and the wireless terminals 11-1 and 11-2 repeat the frame 6 to perform communication.

Next, details of the slot 7 will be described with reference to FIGS.
FIG. 8 is a diagram illustrating a temporal configuration of the slot 7 used for transmission by the wireless terminal 11-1. The slot 7 used for transmission by the wireless terminal 11-1 has a carrier sense CS section 701 for detecting whether or not the candidate frequency bands A, B, and C are usable, and a transmission section 702 for transmitting a signal. The radio terminal 11-1 time-divides the carrier sense CS section 701 and performs carrier sense CS in order from the candidate frequency band A. As a result of the carrier sense CS, the wireless terminal 11-1 that has detected an unused “free” frequency band (candidate frequency band C in FIG. 7) transmits a signal in the transmission section 702 using this frequency band C. To do. The signal transmitted in this transmission section 702 is composed of a known signal sequence and data.

  Next, FIG. 9 is a diagram showing a temporal configuration of the slot 7 used for reception by the wireless terminal 11-2. The slot 7 used for reception by the wireless terminal 11-2 has a standby interval 711, a detection interval 712 for detecting a known sequence transmitted by the wireless terminal 11-1, and a reception interval 713 for receiving data following the known sequence. is doing. The wireless terminal 11-2 stands by while the wireless terminal 11-1 is performing carrier sense CS. Therefore, the slot 7 used for reception by the wireless terminal 11-2 has a standby section 711 having the same time length as the carrier sense CS section 701.

  Next, the wireless terminal 11-2 time-divides the detection section 712, and calculates a correlation value between the received signal and the same signal sequence as the known sequence held in advance from the candidate frequency band A. The wireless terminal 11-2 detects the frequency band (candidate frequency band C in FIG. 9) having the maximum correlation value based on the calculation result, and the wireless terminal 11-1 uses the candidate frequency band C. It is determined that a signal has been transmitted. Therefore, the wireless terminal 11-2 receives a signal in the candidate frequency band C and obtains data following the known sequence.

Next, operations of the wireless terminals 11-1 and 11-2 will be described.
First, the operation when the wireless terminal 11-1 transmits and receives data will be described with reference to FIG. The operation of the wireless terminal 11-2 is the same as that of the wireless terminal 11-1, and thus the description thereof is omitted.

  When transmission data such as application data or control data generated by the control unit 140 is transmitted, the transmission data is subjected to processing such as error correction coding in the digital signal processing unit 130 and is transmitted in a predetermined modulation method. Modulated and output to the D / A converter 124 as a transmission digital signal. Next, the D / A conversion unit 124 converts the input transmission digital signal into a transmission analog signal and outputs it to the transmission RF radio unit 121. The transmission RF radio unit 121 performs radio processing such as orthogonal modulation, up-conversion, band limitation, and power amplification on the input transmission analog signal to generate a radio signal. The generated radio signal is transmitted to the radio terminal 11-2 via the antenna 110.

  Note that the frequency band of the radio signal processed by the transmission RF radio unit 121 is determined by notification from the control unit 140.

  Next, a case where the wireless terminal 11-1 receives data will be described. A radio signal received by the antenna 110 is input to the reception system RF radio unit 122. The reception RF radio unit 122 performs radio processing such as power amplification, band limitation, down-conversion, and orthogonal demodulation on the input radio signal, generates a reception analog signal, and outputs the received analog signal to the A / D conversion unit 123. . The A / D conversion unit 123 converts the received reception analog signal into a reception digital signal and outputs it to the digital signal processing unit 130. Next, the digital signal processing unit 130 demodulates the input received digital signal and performs processing such as error correction decoding to obtain received data. Note that the frequency band of the radio signal processed by the reception RF radio unit 122 is determined by notification from the control unit 140.

  Next, a process until the wireless terminal 11-1 and the wireless terminal 11-2 start communication will be described with reference to FIG. FIG. 10 is a diagram illustrating a sequence until the wireless terminal 11-1 and the wireless terminal 11-2 start communication. Note that FIG. 10 illustrates an example in which communication is started by, for example, the wireless terminal 11-1 requesting the wireless terminal 11-2 to start wireless communication, but the wireless terminal 11-2 is wireless. The terminal 11-1 may be requested to start wireless communication.

  First, the control unit 140 of the wireless terminal 11-1 sequentially performs carrier sense CS from the frequency band 1 to all of the frequency bands 1 to L before starting communication with the wireless terminal 11-2 (step S101). . Therefore, the control unit 140 first instructs the reception system RF radio unit 122 to measure the received power in the frequency bands 1 to L. The reception RF radio unit 122 measures the received power in each frequency band 1 to L in accordance with this instruction. Next, the control unit 140 compares the received power measured by the reception RF radio unit 122 with a predetermined threshold Th1. As a result of the comparison, the control unit 140 determines that the frequency band in which the received power is equal to or greater than the threshold Th1 is “in use”, and determines that it is “empty” if the frequency band is less than the threshold Th1.

  The control unit 140 selects N frequency bands from among the frequency bands determined to be “free” as candidate frequency bands to be used for communication. At this time, when there are N or more frequency bands determined to be “free”, the control unit 140 refers to the past use history of the frequency bands 1 to L stored in the storage unit 150 and uses the frequency band in the past. Those with the highest number of times are selected as candidate frequency bands in order. The N candidate frequency bands may be preferentially selected from those having a high frequency band, for example, or may be selected randomly. Here, it is assumed that the number of candidate frequency bands to be selected is N = 3, and candidate frequency bands A, B, and C are selected from frequency bands 1 to L (step S102).

  Next, the control unit 140 of the wireless terminal 11-1 selects one of the candidate frequency bands A, B, and C as a frequency band used for requesting the start of communication, and notifies the transmission system RF wireless unit 121 of the selected frequency band. To do. Here, it is assumed that the candidate frequency band A is selected (step S103).

  The control unit 140 measures the received power of the candidate frequency band A with respect to the reception-system RF radio unit 122 in order to perform the carrier sense CS of the candidate frequency band A in the carrier sense CS section 701 (see FIG. 7) of the slot 7. Instruct. The reception RF radio unit 122 measures the received power in the candidate frequency band A according to the instruction from the control unit 140 and notifies the result. The control unit 140 determines that the candidate frequency band A is “empty” if the reception power measured by the reception system RF radio unit 122 is equal to or less than a predetermined value, and sends a communication start request signal to the transmission system RF radio unit 121. And instructing to transmit information of candidate frequency bands A, B, and C. Receiving the instruction, the transmission-system RF radio unit transmits a signal using the slot 7 in FIG. 7 (step S104). The wireless terminal 11-2 as the communication partner knows that the number of candidate frequency bands is N = 3, but does not know which frequency band is selected from the frequency bands 1 to L. Therefore, the wireless terminal 11-1 also transmits information on the candidate frequency bands A, B, and C together with the communication start request signal. The communication start request signal and information on the candidate frequency bands A, B, and C are repeatedly transmitted until a communication permission signal transmitted by the wireless terminal 11-2 is detected.

  On the other hand, since the wireless terminal 11-2 does not know which frequency band is used to transmit the communication start request signal, the wireless terminal 11-2 determines whether the communication start request signal is transmitted for all the frequency bands 1 to L. This is determined by whether or not a known sequence arranged at the head of the communication start request signal has been detected. The wireless terminal 11-2 includes a matched filter or the like in the reception-system RF wireless unit 122, and uses this to calculate the correlation value between the same signal sequence as the known sequence stored in advance and the leading sequence of the received signal. calculate. Next, the control unit 140 of the wireless terminal 11-2 compares the calculated correlation value with a predetermined threshold Th2, and determines that the frequency band that is equal to or higher than the threshold Th2 is the frequency band in which the communication start request signal is transmitted. (Step S105).

  The wireless terminal 11-2 receives the communication start request signal transmitted using the frequency band determined in step S105 (candidate frequency band A in FIG. 10). The wireless terminal 11-2 detects the synchronization of the slot 7 using the known sequence of the communication start request signal, and receives the communication start request signal and the information of the candidate frequency bands A, B, and C following the known sequence (step S106).

  The wireless terminal 11-2 that has received the communication start request signal in step S106 transmits a communication permission signal using a slot (slot 8 in FIG. 7) following the slot 7 to which the communication start request signal is transmitted (step S107). ). For this transmission, the candidate frequency band A used by the wireless terminal 11-1 for transmitting the communication start request signal is used.

  Next, the wireless terminal 11-1 observes the slot 8 following the slot 7 that has transmitted the communication start request signal, and detects whether or not the communication permission signal is received in the slot 8 (step S108). After the wireless terminal 11-1 receives the communication permission signal transmitted by the wireless terminal 11-2, any one of the candidate frequency bands A, B, and C is used between the wireless terminals 11-1 and 11-2. Communication was performed.

  Next, communication performed between the wireless terminals 11-1 and 11-2 after the start of communication will be described with reference to FIG. FIG. 11 is a diagram illustrating a communication sequence performed between the wireless terminals 11-1 and 11-2. Although the case where the wireless terminal 11-1 transmits data to the wireless terminal 11-2 will be described here, communication is performed in the same manner when the wireless terminal 11-2 transmits data.

  First, the control unit 140 of the wireless terminal 11-1 performs carrier sense CS for the candidate frequency bands A, B, and C. First, the control unit 140 compares the received power of each candidate frequency band A, B, C measured by the reception RF radio unit 122 with a predetermined threshold Th3. Next, the control unit 140 determines that the candidate frequency band whose received power is greater than or equal to the threshold Th3 is “in use”, and determines that the candidate frequency band that is less than the threshold Th3 is “free” (step S201).

  The control unit 140 selects one candidate frequency band determined to be “free”, and notifies the transmission system RF radio unit 121 of the selected candidate frequency band (step S202). Here, it is assumed that the candidate frequency band C is selected.

  Next, the transmission-system RF wireless unit 121 of the wireless terminal 11-1 transmits a known sequence and data in the transmission section 702 (see FIG. 8) using the candidate frequency band C (step S203). After the transmission, the control unit 140 of the wireless terminal 11-1 sets the usage frequency of the candidate frequency band used for the transmission in step S203 among the usage histories of the frequency bands 1 to L stored in the storage unit 150 to “1”. ”And the usage history is updated (step S204).

  On the other hand, the radio terminal 11-2 on the receiving side is on standby (step S205) while the radio terminal 11-1 is performing carrier sense CS (the standby section 711 in FIG. 9). After waiting, signals in candidate frequency bands A, B, and C are received, and a known sequence is detected (step S206). The control unit 140 of the radio terminal 11-2 calculates a correlation value between the signal received using the matched filter of the reception-system RF radio unit 122 and the same signal sequence as the known sequence held in advance, and the calculated correlation The value is detected by threshold determination. Here, a known sequence is detected from the signal in the candidate frequency band C.

  The wireless terminal 11-2 continues to receive the signal of the candidate frequency band C in which the known sequence is detected in step S206, and receives data in the reception section 713 (see FIG. 9) following the detection section 712 (step S207). ).

  Here, with reference to FIG. 12, when there are a plurality of candidate frequency bands detected as “free” in step S202, a method of selecting one of the plurality of candidate frequency bands will be described. FIG. 12 is a diagram illustrating a result of the carrier sense CS performed by the wireless terminal 11-1. The wireless terminal 11-1 performs the carrier sense CS, and after obtaining the result as shown in FIG. 12A, performs the carrier sense CS again and obtains the result as shown in FIG. And

  First, as a result of the carrier sense CS performed by the wireless terminal 11-1, when the candidate frequency band C is detected as “free” as shown in FIG. 12A, the wireless terminal 11-1 Data is transmitted using C, the use history of frequency bands 1 to L in the storage unit 150 is updated, and the use of candidate frequency band C is stored.

  Next, as a result of the carrier sense CS being performed by the wireless terminal 11-1, when the candidate frequency bands A and C are detected as “free” as shown in FIG. 12B, the wireless terminal 11-1 stores Referring to unit 150, candidate frequency band C used for the previous transmission is preferentially selected.

  In FIG. 12B, the one used for the previous transmission is preferentially used from among a plurality of candidate frequency bands detected as “free”. For example, as shown in FIG. If the candidate frequency bands A and B are detected as “free” as a result of the carrier sense CS, the candidate frequency band C used in the previous transmission is “in use”, and therefore cannot be selected. Therefore, in this case, either one of the candidate frequency bands A and B may be selected at random, or the candidate frequency band with the lower reception power may be selected. Alternatively, the candidate frequency band may be selected on the basis that the time detected as “free” is closest to the transmission section 702.

  As described above, according to the first embodiment, the radio terminal 11-1 does not perform carrier sense CS of all usable frequency bands at the head of the slot, but selects candidate frequencies from all the frequency bands. Since carrier sense CS is performed by selecting bands A, B, and C, carrier sense CS in a frequency band used for signal transmission can be performed at short time intervals called slots, and interference generated during communication can be detected immediately. . Further, by not using the candidate frequency band in which the interference is detected for signal transmission, it is possible to suppress interference given to communication between the base station 20 and the wireless terminal 21 belonging to the system 2. Further, the radio terminal 1-2 is based on the correlation value between the received signal of the candidate frequency bands A, B, and C notified from the radio terminal 1-1 at the start of communication and the same series signal as the known signal stored in advance. In order to detect the frequency band used for signal transmission, the radio terminal 1-1 does not need to notify the radio terminal 1-2 of the frequency band used for signal transmission in advance, and different candidate frequency bands for each slot. It becomes possible to transmit a signal. Furthermore, by selecting a plurality of candidate frequency bands used for communication between the wireless terminals 11-1 and 11-2, even if one candidate frequency band is used for communication of the system 2, the wireless terminal 11 -1 and 11-2 can use the remaining unused frequency bands, and can continue without interrupting communication.

  Next, a radio communication system according to the second embodiment of the present invention will be described with reference to FIGS.

  FIG. 13 is a diagram illustrating an outline of the wireless communication system according to the present embodiment. The wireless communication system according to the present embodiment is the same as the system 1 shown in the first embodiment in that it is a system that performs communication by temporarily using a frequency band that is not allocated to itself. The wireless terminals belonging to the communication system do not communicate with each other, but the base station 10 and the plurality of wireless terminals 11-3, 11-4,.

  Further, frequency bands 1 to L and candidate frequency bands used for communication between the base station 10 and the plurality of wireless terminals 11-3, 11-4,... Are the same as the frequency bands shown in FIGS. The configuration and operation of the base station 10 and the plurality of wireless terminals 11-3, 11-4,... Are the same as those of the wireless terminal 11-1 shown in FIG. . In the following description, the number of the plurality of wireless terminals 11-3, 11-4,... Is “3”, but is not limited to this, and the number of wireless terminals is an arbitrary number. Good.

  Next, a frame configuration used for communication between the base station 10 and the plurality of wireless terminals 11-3 to 11-5 will be described with reference to FIG. FIG. 14 is a diagram illustrating a temporal configuration of a frame used for communication by the base station 10 and the plurality of wireless terminals 11-3 to 11-5.

  In this frame, the base station 10 transmits control information to the plurality of radio terminals 11-3 to 11-5, and the control downlink slot 70 and the base station 10 transmit data to the radio terminals 11-3 to 11-5. User downlink slots 71 to 73 for transmission, and user uplink slots 81 to 83 for the wireless terminals 11-3 to 11-5 to transmit data to the base station 10 are provided. User downlink slots 71 to 73 and user uplink slots 81 to 83 correspond to each other. For example, the wireless terminal 11-3 that has received data in the user downlink slot 71 uses the user uplink slot 81 to Send data to the station. Since the time structure of each slot is the same as that of the slot 7 shown in FIGS. 8 and 9, the same reference numerals are given and description thereof is omitted.

  Next, the operation until the base station 10 starts wireless terminal 11-3 to 11-5 communication will be described with reference to FIG. FIG. 15 is a diagram illustrating a sequence until the base station 10 and the wireless terminal 11-3 start communication. The base station 10 communicates with the wireless terminals 11-3 to 11-5. Here, a sequence until communication with the wireless terminal 11-3 is started will be described. Note that the steps in which the base station 10 selects the candidate frequency bands A, B, and C are the same as steps S101 and S102 shown in FIG.

  The base station 10 that has selected the candidate frequency bands A, B, and C transmits control information using the control downlink slot 70 (step S303). This transmission is performed in the carrier sense CS section 701 of the control downlink slot 70. Any one of the detected “free” candidate frequency bands is used. Alternatively, one of the candidate frequency bands A, B, and C is determined in advance as a frequency band to be used for transmission of control information, and carrier sense CS of the determined candidate frequency band is performed to detect “free”. The control information may be transmitted only when it is done. The control information transmitted using the control downlink slot 70 includes information on the candidate frequency bands A, B, and C, whether the user downlink slots 71 to 73 and the user uplink slots 81 to 83 are used. (Hereinafter referred to as slot allocation information) and information on candidate frequency bands used when the wireless terminals 11-3 to 11-5 transmit a communication start request signal.

  On the other hand, the wireless terminal 11-3 tries to detect control information for all the frequency bands 1 to L (step S304). This is because the wireless terminal 11-3 knows the number of candidate frequency bands, but does not know which one of the frequency bands 1 to L the base station 10 has selected. The wireless terminal 11-3 calculates the correlation value of the same signal sequence as the received signal and the known sequence of the control information using a matched filter or the like included in the reception-system RF wireless unit 122, and determines the correlation value as a threshold value. Detect control information.

  Subsequently, the wireless terminal 11-3 that has detected the control information uses the candidate frequency band information used when transmitting information on the candidate frequency bands A, B, and C, slot allocation information, and a communication start request signal from the control information. Is obtained (step S305). The slot allocation information obtained at this time does not use all of the user downlink slots 71 to 73 and the user uplink slots 81 to 83, and the frequency band used for transmitting the communication start request signal includes candidate frequencies. Assume that band A has been designated.

  Next, the wireless terminal 11-3 selects an unused one from the user uplink slots 81 to 83, and transmits a communication start request signal using the candidate frequency band A using the selected slot ( Step S306). Here, since all of the user uplink slots 81 to 83 are not used, the wireless terminal 11-3 selects, for example, the slot 81 having a small slot number.

  On the other hand, the base station 10 observes a signal transmitted using the candidate frequency band A in the user uplink slots 81 to 83, and detects a communication start request signal transmitted by the wireless terminal 11-3 ( Step S307).

  The base station 10 that has detected the communication start request signal transmits a communication permission signal using the user downlink slot 71 corresponding to the transmitted user uplink slot 81 (step S308). After the wireless terminal 11-3 receives this communication permission signal, the base station 10 and the wireless terminal 11-3 communicate using any one of the candidate frequency bands A, B, and C.

  The communication sequence between the base station 10 and the wireless terminal 11-3 is the same as the sequence shown in FIG.

  As described above, according to the second embodiment, even when the base station and the plurality of wireless terminals 11-3 to 11-5 communicate, the base station 10 and the wireless terminal 11-3 Thus, by performing carrier sense CS of the candidate frequency band used for transmission, it is possible to suppress interference given to communication of the system 2. Moreover, even if one candidate frequency band is used for communication of the system 2 by selecting a plurality of candidate frequency bands used for communication between the base station 10 and the wireless terminals 11-3 to 11-5. The base station 10 and the wireless terminals 11-3 to 11-5 can use the remaining candidate frequency bands that are not used, and can continue without interrupting communication.

  Next, a radio communication system according to a third embodiment of the present invention is described with reference to FIG.

  The radio communication system according to the present embodiment is the same as the radio communication system according to the first embodiment except that the time configuration of the detection section 712 of the slot 7 shown in FIG. The description is omitted.

  The time structure of the slot 7 according to the present embodiment will be described with reference to FIG. FIG. 16 is a diagram illustrating a temporal configuration of the slot 7 used for reception by the wireless terminal 11-2.

  The slot 7 used for reception by the wireless terminal 11-2 includes a standby interval 711, a detection interval 712 for detecting correlation of a known sequence transmitted by the wireless terminal 11-1, and a reception interval 713 for receiving data following the known sequence. Have.

  The wireless terminal 11-2 stands by in the carrier sense CS section 701 of the wireless terminal 11-1. Therefore, the slot 7 used for reception by the wireless terminal 11-2 has a standby section 711 having the same time length as the carrier sense CS section 701. Next, the wireless terminal 11-2 time-divisions the detection section 712, calculates the correlation value of the received signal and the same signal sequence as the known sequence held in advance from the candidate frequency band A, and the calculated correlation value and The threshold value Th3 is compared. When the correlation value is equal to or greater than Th3, it is determined that the signal is transmitted using the candidate frequency band, and the next candidate frequency band is not detected, and data is received in the subsequent reception section.

  For example, as shown in FIG. 16, the known sequences are detected in the candidate frequency band B as a result of detecting the known sequences in order from the candidate frequency band A. In this case, detection of a known sequence in the next candidate frequency band C is not performed, and a signal in the candidate frequency band B is received.

  As described above, according to the third embodiment, the same effects as those of the first embodiment can be obtained, and when a known sequence is detected in, for example, the candidate frequency band B in the detection section 712 of the slot 7, By omitting the detection in the candidate frequency band C, it is possible to omit the frequency switching process of the reception-system RF radio unit 122 and to simplify the control at the time of reception.

  Here, the wireless communication system using the slot shown in FIG. 16 instead of the slot 7 shown in FIG. 9 of the wireless communication system according to the first embodiment has been described, but the wireless communication according to the second embodiment is described. Similarly, in the system, the slot shown in FIG. 16 may be used instead of the slot 7 shown in FIG.

  Next, a radio communication system according to the fourth embodiment of the present invention will be described with reference to FIG.

  The radio communication system according to the present embodiment is the same as the radio communication system according to the second embodiment, except for the time configuration of user uplink slots 81 to 83 used by the radio terminal 11-3 to transmit a communication start request signal. Therefore, the same configuration and operation are denoted by the same reference numerals and description thereof is omitted.

  With reference to FIG. 17, the time structure of the user uplink slot used by the wireless terminal 11-3 for transmission of the communication start request signal will be described. FIG. 17 is a diagram illustrating a temporal configuration of the user uplink slot 81 used by the wireless terminal 11-3 to transmit a communication start request signal. The frequency band used for transmitting the communication start request signal is designated in advance by the base station 10. Here, description will be made assuming that the candidate frequency band A is designated.

  The wireless terminal 11-3 performs carrier sense CS of the candidate frequency band A using the carrier sense CS section 701, confirms that this candidate frequency band A is not used, and then transmits a communication start request signal. To do. At this time, for example, as shown in FIGS. 17A to 17C, the wireless terminal 11-3 prepares three carrier sense CS sections 701 having different lengths in advance, and randomly selects one of them. The carrier sense CS of the candidate frequency band A is selected and selected. Since the time length of the user uplink slot 81 is constant, if the carrier sense CS section 701 is short, the subsequent transmission section 702 becomes long. Therefore, when the carrier sense CS section 701 is short, the signal length is adjusted by transmitting dummy data after the communication start request signal.

  As described above, according to the fourth embodiment, the same effect as that of the second embodiment can be obtained, and a plurality of wireless terminals 11-3 to 11-5 can use the same user uplink slot 81 to communicate simultaneously. Even when a start request signal is to be transmitted, a plurality of wireless terminals 11-3 to 11-5 can be simultaneously set to “free” by simultaneously selecting carrier sense CS sections 701 having different lengths. If there is, the probability of detection is reduced, and collision of communication start request signals can be reduced.

  In addition, this invention is not limited to the said Example as it is, A component can be deform | transformed and embodied in the range which does not deviate from the summary in an implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiments. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a diagram showing an outline of a wireless communication system according to a first embodiment of the present invention. The figure which showed the frequency band which can be used by communication of the system 1 which concerns on 1st Example of this invention. The figure which showed the modification of the frequency band which can be used by communication of the system 1 which concerns on 1st Example of this invention. The figure which showed the modification of the frequency band which can be used by communication of the system 1 which concerns on 1st Example of this invention. The figure which showed the candidate of the frequency band used for communication between the radio | wireless terminals 11-1 and 11-2. The block diagram which shows the structure of the radio | wireless terminal 11-1 which concerns on 1st Example of this invention. The figure which shows the time structure of the flame | frame 6 which the radio | wireless terminals 11-1 and 11-2 based on 1st Example of this invention use for communication. The figure which shows the time structure of the slot 7 which the radio | wireless terminal 11-1 based on 1st Example of this invention uses for transmission. The figure which shows the time structure of the slot 7 which the radio | wireless terminal 11-2 based on 1st Example of this invention uses for reception. The figure which shows the sequence until the radio | wireless terminal 11-1 and the radio | wireless terminal 11-2 which concern on 1st Example of this invention start communication. The figure which shows the sequence of the communication performed between the radio | wireless terminals 11-1 and 11-2 based on 1st Example of this invention. The figure which shows the result of the radio | wireless terminal 11-1 which performed carrier sense CS based on 1st Example of this invention. The figure which shows the outline of the radio | wireless communications system which concerns on 2nd Example of this invention. The figure which shows the time structure of the flame | frame which the base station 10 which concerns on 2nd Example of this invention and several radio | wireless terminals 11-3 to 11-5 use for communication. The figure which shows the sequence until the base station 10 and radio | wireless terminal 11-3 based on 2nd Example of this invention start communication. The figure which shows the time structure of the slot 7 which the radio | wireless terminal 11-2 based on 3rd Example of this invention uses for reception. The figure which shows the time structure of the uplink slot 81 for users which the radio | wireless terminal 11-3 based on 4th Example of this invention uses for transmission of a communication start request signal.

Explanation of symbols

10, 20 ... base stations 11-1, 11-2, 11-3, 11-4, 11-5, 21 ... wireless terminal 22 ... communication area 110 ... antenna 120 ... analog Signal processing unit 121 ... Transmission system RF wireless unit 122 ... Reception system RF wireless unit 123 ... A / D conversion unit 124 ... D / A conversion unit 130 ... Digital signal processing unit 140 ... Control unit 150 ... storage unit 6 ... frames 7, 70, 71, 72, 73, 81, 82, 83, 8 ... slot 701 ... carrier sense CS section 702 ... transmission section 711 ... Standby section 713 ... Detection section 714 ... Reception section

Claims (15)

In a radio station that transmits a signal to a communication partner in a certain time slot,
The first carrier sense of L frequency bands (L ≧ 2) is performed before the start of communication, and the second of M (L ≧ M ≧ 2) frequency bands is performed in the first carrier sense section of the time slot. Carrier sense means for performing carrier sense of
As a result of the first carrier sense, the M frequency bands that are not used are selected from the L frequency bands, and as a result of the second carrier sense, the frequency bands are selected from the M frequency bands. A control unit for determining an unused transmission frequency band;
A radio station, comprising: a transmission unit configured to transmit a signal using the transmission frequency band determined by the control unit in a transmission period subsequent to the carrier sense period.   The control unit is used for the previous transmission as the transmission frequency band to be used for transmission from among a plurality of frequency bands detected as unused as a result of performing carrier sense of the M frequency bands. The radio station according to claim 1, wherein the selected frequency band is selected.   The radio station further includes a storage unit that stores the number of times the M frequency bands are used for signal transmission, and the control unit selects the transmission frequency band from the M frequency bands. 2. The radio station according to claim 1, wherein a frequency band that is used frequently is preferentially selected with reference to the storage unit.   The control unit according to claim 1, wherein the control unit randomly selects one carrier sense interval from a plurality of carrier sense intervals having different time lengths, and performs carrier sense of the M frequency bands. The radio station to list.   The radio station further includes a storage unit that stores the number of times the L frequency bands are used for signal transmission, and the control unit selects the M frequency bands from the L frequency bands. 2. The radio station according to claim 1, wherein the frequency band that is used frequently is preferentially selected by referring to the storage unit. A wireless communication system in which a first wireless station and a second wireless station communicate using a fixed time slot,
The first radio station is
Carrier sensing means for performing carrier sensing of M frequency bands (M ≧ 2) in the first carrier sensing section of the time slot;
As a result of the carrier sense, a first control unit that determines the transmission frequency band from among unused frequency bands;
A first transmission means for transmitting a known signal sequence and data using the transmission frequency band determined by the control unit in a transmission section subsequent to the carrier sense section, the second radio station,
Receiving means for receiving the signal of the M frequency bands in the detection section of the time slot and receiving a signal of one frequency band from the M frequency bands in the reception section following the detection section; A second control unit for determining a frequency band received by the receiving unit in the receiving section based on a correlation value between the signal received by the receiving unit in the detection section and a signal of the same sequence as the known signal; A wireless communication system comprising:   The receiving means time-divides the detection section into M, sequentially receives the signals of the M frequency bands, and the control means and the frequency band signals received by the receiving means in the detection sections The wireless communication system according to claim 6, wherein a correlation value between the known signal and a signal of the same series is calculated.   When the second control unit determines that one of the M frequency bands is a frequency band to be received in the reception section, the reception unit omits reception of signals in the remaining frequency bands. The radio communication system according to claim 7, wherein the radio communication system is characterized.   The first control unit, as a result of performing carrier sense of the M frequency bands, among the plurality of frequency bands detected as not being used, as the transmission frequency band used for transmission, The radio communication system according to claim 6, wherein a frequency band used for transmission is selected.   The first wireless station further includes a storage unit that stores the number of times the M frequency bands have been used for signal transmission, and the control unit selects the transmission frequency band from the M frequency bands. 7. The radio communication system according to claim 6, wherein, when selecting, the storage unit is referred to, and a frequency band that is frequently used is preferentially selected.   The first control unit performs carrier sense of L (L ≧ M) frequency bands by the first carrier sense means before starting communication, and is used from among the L frequency bands. 7. The wireless communication system according to claim 6, wherein M frequency bands not selected are selected.   The first radio station further includes a storage unit that stores the number of times the L frequency bands are used for signal transmission, and the control unit includes the M frequencies from the L frequency bands. The radio communication system according to claim 11, wherein when selecting a band, the storage unit is referred to, and a frequency band that is frequently used is preferentially selected.   The first radio station notifies the second radio station of a communication start request signal and information on M frequency bands selected by the first control unit. Wireless communication system.   The first radio station transmits information on the M frequency bands selected by the first control unit and information on a communication start frequency band used for transmission of a communication start request signal to the second radio station. When the second radio station notifies the first radio station of the communication start request signal, the second control unit randomly selects a plurality of carrier sense intervals having different time lengths. The wireless communication system according to claim 9, wherein one carrier sense section is selected and carrier sense of the communication start frequency band is performed. A wireless communication method in which a first wireless station and a second wireless station communicate with each other using a fixed time slot,
The first radio station is
Carrier sensing means performs carrier sensing of M (M ≧ 2) frequency bands in the first carrier sensing section of the time slot,
The first control unit determines the transmission frequency band from the frequency bands that are not used as a result of the carrier sense,
By transmitting a known signal sequence and data using the transmission frequency band determined by the control unit in a transmission section that the first transmission means follows the carrier sense section,
Transmitting a signal to the second radio station;
The second radio station is
A receiving means receives the signals of the M frequency bands in the detection section of the time slot,
Based on the correlation value between the signal received in the detection interval by the receiving means and the signal of the same sequence as the known signal, the second control unit determines a frequency band that the receiving means receives in the receiving interval. Decide
The receiving means receives a signal in a frequency band determined by the control unit in a reception section that follows the detection section,
A wireless communication method comprising receiving a signal transmitted by the first wireless station.

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