JP4755629B2 - Transmission / reception device and communication method thereof - Google Patents

Description

  The present invention uses an interference cancellation technology that uses the characteristics of a TDD (Time Division Duplex) system in a priority system (Primary system) in a new system (Secondary system) in a wireless communication system that operates a plurality of systems at the same frequency. Thus, the present invention relates to a transmission / reception apparatus and a communication method thereof that significantly improve the surface frequency utilization efficiency when the entire system is considered without reducing the communication efficiency of the primary system.

  In recent years, with the widespread use of mobile phones, wireless LANs, and the like, techniques for performing transmission as fast as possible in a limited frequency band have been studied. In recent years, MIMO (Multiple Input Multiple Output) technology has attracted attention as means for realizing high-speed transmission in a limited band. MIMO uses array antennas for the transmitting side and the receiving side, respectively, and on the transmitting side, different data is transmitted for each antenna, and on the receiving side, different signals are restored by some interference cancellation / decoding technology. By doing so, it is a technique that remarkably improves the transmission speed at the same frequency as compared with transmission / reception between single antennas. Already introduced in wireless LAN systems and the like.

  However, in the MIMO technology, the number of transmission / reception antennas is a key for high-speed transmission. Therefore, in order to realize very high frequency utilization efficiency, a considerable number of antenna elements are required. When considering a small terminal, an increase in the number of antenna elements is undesirable because it increases the hardware scale.

  Cognitive radio technology has attracted attention as a means for effectively using frequencies by a method different from the MIMO technology (see, for example, Non-Patent Document 1). The cognitive radio technology is a technology in which a radio device recognizes a surrounding radio wave environment, selects an appropriate frequency band and uses it, thereby effectively utilizing an available frequency band. Since cognitive radio can effectively use frequencies and time that have not been attracting attention, the frequency per unit area can be greatly improved.

  FIG. 18 is a conceptual diagram for explaining the outline of the cognitive radio technology. In FIG. 18, 1-1 and 1-2 are two priority systems (Primary systems), and 2-1 to 2-6 are a plurality of cognitive systems (Secondary systems). Reference numeral 3 denotes a communicable area of the primary system. Reference numerals 4-1 and 4-2 denote antenna directivities of the primary systems 1-1 and 1-2, respectively.

In cognitive radio, the primary systems 1-1 and 1-2 that originally use a certain communication band and the frequencies and times that are not used by the primary systems 1-1 and 1-2 are monitored, and this information is obtained. There are secondary systems 2-1 to 2-6 that perform communication based on the above. Basically, the primary systems 1-1 and 1-2 can use a preferentially assigned communication band, and the secondary systems 2-1 to 2-6 can perform communication by themselves. By interfering with the primary systems 1-1 and 1-2, the efficiency of the primary systems 1-1 and 1-2 should not be reduced. In addition, the primary systems 1-1 and 1-2 cannot normally recognize the existence of the secondary systems 2-1 to 2-6.
S. Haykin, “Cognitive radio: Brain-empowered wireless communications”, vol.23, no.2, pp.201-220, Feb. 2005.

In cognitive radio, communication is usually performed by the following means.
(Procedure 1) The Secondary systems 2-1 to 2-6 detect times or frequencies that are not used by the Primary systems 1-1 and 1-2.
(Procedure 2) The Secondary systems 2-1 to 2-6 confirm whether or not to interfere with the receivers of the Primary systems 1-1 and 1-2 through communication performed by themselves.
(Procedure 3) If the Secondary systems 2-1 to 2-6 determine that there is no problem in the procedure 2, the communication is performed at the frequency or time detected in the procedure 1.

  The above is the communication procedure in cognitive radio. However, first, a problem occurs when the procedure 1 is performed. For example, consider TDD. In a TDD system, a station receives at a certain timing and does not transmit during that time. On the other hand, no signal is received during transmission. As hardware, a time division switch (TDD switch) is arranged between the transmission device and the reception device. Therefore, for example, even if interference from the primary system 1-1 is not detected at a certain time, if transmission is performed at that time, interference is given to the primary system 1-2.

  Further, even if the receivers of the secondary systems 2-1 to 2-6 determine that no signal has arrived at “a certain frequency” or “a certain time”, the state fluctuates with time. The signal may not be detected correctly due to the possibility or the presence of a hidden terminal. Therefore, in cognitive radio, signal detection with very high accuracy is required.

  As a means for improving this, a detection method using signal cyclostationary has been proposed. For example, Reference 1 (Cabric, D, et al., “Implementation issues in spectrum sensing for cognitive radios”, Conference Record of the Thirty-Eighth Asilomar Conference, vol.1, pp.772-776, 7-10. Nov. 2004.). In this method, signal detection is possible even at a very low CNR (Carrier to Noise Ratio) if the carrier frequencies of the primary systems 1-1 and 1-2, or the symbol rate and modulation scheme are known in advance. . However, this method requires a very large amount of time and the number of signal samples for detection, so that it is difficult to cope with a case where the propagation environment of the primary systems 1-1 and 1-2 changes. Occurs.

  Next, a problem also occurs in the above procedure 2. As described above, in principle, the primary systems 1-1 and 1-2 cannot recognize the secondary system. For example, even if the secondary systems 2-1 to 2-6 determine that the signal level from the transmitter of the primary system 1-1 is low at a certain frequency and determine that this frequency can be used, transmission is performed as is at that frequency. May cause interference to the primary system 1-2. Therefore, the interference given by the Secondary systems 2-1 to 2-6 is most surely determined by the receivers of the Primary systems 1-1 and 1-2.

  However, the primary systems 1-1 and 1-2 cannot recognize the existence of the secondary systems 2-1 to 2-6. Therefore, in order to realize this, the secondary systems 2-1 to 2-6 regularly observe a certain signal generated by the primary systems 1-1 and 1-2, and the primary systems 1-1 and 1-2 have A method of grasping the existence is considered.

  Even if this is not cognitive radio, it can be considered as the same principle as carrier sense in the conventional radio system. The carrier sense is disclosed in, for example, Document 2 (Morikura, Kubota, “Revised 802.11 High-Speed Wireless LAN Textbook”, Chapter 4, Impress, 2005). When the secondary systems 2-1 to 2-6 approach the receivers of the primary systems 1-1 and 1-2, the primary system 1 is received by receiving signals transmitted from the primary systems 1-1 and 1-2. -1, 1-2 are grasped, and the secondary systems 2-1 to 2-6 can perform the procedure 2 based on the magnitude of the signal power.

  However, when cognitive radio is considered, this accuracy is required to be very high. Therefore, it is effective to perform carrier sensing at all frequencies of the primary systems 1-1 and 1-2. However, if this is performed, it is extremely effective for interference detection (communication signal detection of the primary systems 1-1 and 1-2). This causes a problem that it takes a lot of time.

  The present invention has been made in consideration of such circumstances, and an object thereof is a transmission / reception apparatus capable of performing efficient cognitive radio with a simple configuration and avoiding interference with a primary system. And providing a communication method thereof.

  In order to solve the above-described problem, the present invention provides a plurality of antenna elements, a plurality of transmission / reception branching means connected to each of the plurality of antenna elements, and a transmission connected to each of the plurality of transmission / reception branching means. And a receiving unit connected to each of the plurality of transmitting / receiving branching units, a first node that is an interference source from another system and a second node that communicates with the first node A weighting unit that weights transmission / reception signals by the transmission unit and the reception unit based on a reception signal having a large reception power among reception signals received at two different time intervals by the reception unit from the node; A communication quality judging means for judging the communication quality of the received signal received using the weighting by the weighting means; and the communication quality judging means determines the communication quality. When it is determined that the threshold value is not exceeded, the first node is switched to another node, and the other node is set as a new first node, and the switching unit is switched by the switching unit. Power measuring means for measuring received power of two received signals obtained at two different time intervals from a first node and a second node communicating with the first node, and measured by the power measuring means A determination means for determining which of the received power is greater, and a time interval of the received signal determined by the determination means as a reception timing by the reception means, and the reception power is determined to be small. And a transmission / reception condition determining means for setting a time interval of the received signal as a transmission timing by the transmission means.

  In order to solve the above-described problem, the present invention provides a plurality of antenna elements, a plurality of transmission / reception branching means connected to each of the plurality of antenna elements, and a transmission connected to each of the plurality of transmission / reception branching means. And a receiving means connected to each of the plurality of transmitting / receiving branching means, an interference wave power measuring means for measuring interference wave power from a node of another system, and the interference wave power measuring means Determining means for determining whether or not the interference wave power measured by means of (1) exceeds a predetermined threshold value, and when the determination means determines that the interference wave power exceeds a predetermined threshold value, Search means for searching for another node in the other system whose power does not exceed the predetermined threshold as a first node, the first node searched by the search means, and the first node Weighting of transmission / reception signals by the transmission unit and the reception unit based on a reception signal having a large reception power among the reception signals received at two different time intervals by the reception unit from the second node that communicates A transmission / reception condition in which the time interval of the received signal from the first node is a transmission timing by the transmission unit, and the time interval of the reception signal from the second node is a reception timing by the receiving unit A transmission / reception apparatus comprising: a determination unit;

  According to the present invention, in the above invention, the transmission / reception condition determining unit determines that the received power is large by the determining unit when the first node and the second node communicate at different frequencies. The frequency of the reception signal is a reception frequency by the reception unit, and the frequency of the reception signal determined that the reception power is small is a transmission frequency by the transmission unit.

  According to the present invention, in the above invention, the transmission / reception condition determining unit determines that the received power is large by the determining unit when the first node and the second node communicate with different codes. The code of the received signal is a code by the receiving means, and the code of the received signal determined that the received power is small is the code by the transmitting means.

  In order to solve the above-described problem, the present invention provides a plurality of antenna elements, a plurality of transmission / reception branching means connected to each of the plurality of antenna elements, and a transmission connected to each of the plurality of transmission / reception branching means. And a communication method by a transmission / reception apparatus including a reception unit connected to each of the plurality of transmission / reception branching units, and communicates with the first node and the first node as an interference source from another system Based on a reception signal having a large reception power among reception signals received from the second node at two different time intervals by the reception unit, weighting is performed on the transmission / reception signal by the transmission unit and the reception unit. A weighting step, a communication quality judging step for judging the communication quality of the received signal received using the weighting, and the communication quality exceeds a predetermined threshold value. If it is determined that the first node is switched to another node, the other node becomes a new first node, the switched first node, and the first node A power measuring step of measuring received power of two received signals obtained at two different time intervals from a second node communicating with the node; a determining step of determining which of the measured received powers is greater; Transmission / reception condition determination using the time interval of the received signal determined to have a large received power as the reception timing by the receiving unit and the time interval of the received signal determined to have a low received power as the transmission timing by the transmitting unit Including a step.

  In order to solve the above-described problem, the present invention provides a plurality of antenna elements, a plurality of transmission / reception branching means connected to each of the plurality of antenna elements, and a transmission connected to each of the plurality of transmission / reception branching means. And a reception method connected to each of the plurality of transmission / reception branching means, in a communication method by a transmission / reception apparatus, an interference wave power measurement step of measuring interference wave power from a node of another system, and the measurement A determination step for determining whether or not the interference wave power has exceeded a predetermined threshold; and if it is determined that the interference wave power has exceeded a predetermined threshold, the interference wave power is A search step of searching for another node of the other system that does not exceed the threshold as a first node, the searched first node, and a second node communicating with the first node; The weighting step for weighting the transmission / reception signal by the transmission means and the reception means based on the reception signal having a large reception power among the reception signals received at two different time intervals by the reception means; A transmission / reception condition determining step in which a time interval of a reception signal from one node is set as a transmission timing by the transmission unit and a time interval of a reception signal from the second node is a reception timing by the reception unit. Is a communication method.

  According to the present invention, among the received signals obtained from two different time intervals, the weight value for the transmission / reception signal at the time of transmission and reception is determined based on the information of the received signal having a large received power, and the communication quality is When it is determined that the predetermined threshold value is not exceeded, the first node is switched to another node, the other node is set as a new first node, the first node, the first node, The received power of two received signals obtained at two different time intervals is measured from a second node that communicates, and the time interval of the received signals determined to have a large received power is used as the reception timing by the receiving means. The time interval of the received signal determined to have low power is used as the transmission timing by the transmission means. Therefore, efficient cognitive radio can be performed while avoiding interference with the primary system and even when the direction of communication between the terminal and the access point is the same as that between the primary system and the access point. The advantage that it can be obtained.

  According to this invention, when the interference wave power from the node of the other system exceeds a predetermined threshold, the other node of the other system whose interference wave power does not exceed the predetermined threshold is A received signal having a large received power out of received signals received at two different time intervals from the searched first node and the second node communicating with the first node. Based on the above, the transmission means and the reception means weight the transmission / reception signal, the time interval of the reception signal from the first node is set as the transmission timing by the transmission means, and the time interval of the reception signal from the second node is received. The reception timing by the means. Therefore, the secondary system is communicated without causing interference to the primary system, and even when the interference waves having substantially the same reception level are provided at the same distance from the plurality of primary systems to the terminal. The advantage that it can be obtained.

  According to the present invention, when the first node and the second node communicate at different frequencies, the frequency of the received signal determined to have a large received power is set as the received frequency by the receiving means, and the received power is small. The frequency of the received signal determined to be the transmission frequency by the transmission means. Therefore, even if it is the communication system divided | segmented according to a frequency, the advantage that communication of a Secondary system can be performed, without giving interference to a Primary system is acquired.

  According to this invention, when the first node and the second node communicate with different codes, the code of the received signal determined to have a large received power is used as the code by the receiving means, and the received power is small. The determined code of the received signal is used as the code by the transmission means. Therefore, even if it is the communication system divided | segmented by a code | symbol, the advantage that communication of a Secondary system can be performed, without giving interference to a Primary system is acquired.

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

A. First Embodiment FIG. 1 is a block diagram showing a configuration of an array antenna transmission / reception apparatus according to a first embodiment of the present invention. In FIG. 1, an array antenna transmission / reception apparatus 9 has, as a basic configuration, N antennas 10-1 to 10-N and transmission / reception separating means (switches) 11- connected to the antennas 10-1 to 10-N. 1 to 11-N, transmitters 12-1 to 12-N, and receivers 13-1 to 13-N. This corresponds to a basic array antenna apparatus. In the first embodiment, since digital signal processing is basically assumed, the memory 14 is arranged after the receiving devices 13-1 to 13-N. However, according to the principle of the present invention to be described later, control is possible regardless of analog or digital, and the present invention is not limited to digital signal processing.

  As shown in FIG. 1, the secondary system according to the first embodiment is characterized by having a primary system interference removal unit 15. The primary system interference canceling unit 15 has a mechanism for detecting signals of a time interval T1 and a time interval T2 transmitted by the primary system. In the first embodiment, as shown in FIG. 1, it can be realized by the signal detection devices 15-1 and 15-2. Moreover, in this 1st Embodiment, it has the power comparison part 15-3 which compares these signal powers, and the signal selection part 15-4 which selects the signal with higher electric power. This is because control is performed on a signal having a high reception power among the signals at the time interval T1 or T2.

  The reception weight calculation unit 15-5 uses the signal selected by the signal selection unit 15-4 in FIG. 1 to determine a weight (weight value) for weighting the array antenna. Details of the operation of the reception weight calculation unit 15-5 will be described with reference to the flowchart of FIG. The weight information obtained by the reception weight calculation unit 15-5 is supplied by the branching unit 16 to the reception signal weight multiplication unit 17 and the transmission signal weight multiplication unit 18. The reception signal weight multiplication unit 17 multiplies the reception signal by the weight and outputs it as an output signal. The transmission signal weight multiplication unit 18 multiplies the transmission signal by the weight and supplies it to the transmission devices 12-1 to 12-N.

  The transmission / reception timing determination unit 19 determines whether or not the communication quality is equal to or lower than the threshold value α based on the comparison result by the power comparison unit 15-3 in the communication using the reception weight from which the interference is removed, When the value is less than or equal to the value α, transmission / reception timing with a base station (node) of another Primary system is determined, and the transmission / reception separating means 11-1 to 11-N are switched at the transmission / reception timing, and the communication quality is a threshold value. A search is made for a base station (node) of another Primary system that is greater than or equal to α.

FIG. 2 is a block diagram showing a configuration of the reception weight multiplication unit 17 according to the first embodiment. As shown in FIG. 2, the reception weight multiplication unit 17 multiplies the received signals y _{1 to} y _N and the weights w ₁ ^{* to} w _N ^* obtained by the reception weight calculation unit 15-5 of the reception signal by a multiplier 17-1. Multiply by −1 to 17-1-N, and combine by adder 17-2. Here, the received signals y _{1 to} y _N mean a signal in which an interference wave from the Primary system and a communication signal of the Secondary system are superimposed after the Secondary system starts communication.

FIG. 3 is a block diagram showing a configuration of the transmission weight multiplication unit 18 according to the first embodiment. Also on the transmission side, transmission is performed using the weights w ₁ ^{* to} w _N ^* obtained by the reception weight calculation unit 15-5. The transmission signal S is first branched into N signals equal to the number of antennas by the branching means 18-1. With respect to the N branched signals S, S,..., S, the multipliers 18-2-1 to 18-2-N use the first to Nth weights w ₁ ^{* to} w _N ^* . Multiply The transmission weight multiplication unit 18 does not perform synthesis. This is because the antenna directivity is synthesized in space because the antennas 10-1 to 10-N can perform spatial power synthesis.

  FIG. 4 is a conceptual diagram for explaining the communication system (TDD) in the first embodiment. As shown in FIG. 4, assuming a situation where there is a pair of primary system 100-1 and primary system 100-2, primary system 100-1 and primary system 100-2 use different time intervals. Communicate. Further, an environment is assumed in which the Secondary system 101 exists between the Primary system 100-1 and the Primary system 100-2.

  In the time interval T1 transmitted by the primary system 100-1, the primary system 100-2 performs reception. On the other hand, in the time interval T2 that the primary system 100-1 receives, the primary system 100-2 performs transmission. This is one of the common communication forms and is called TDD. The transmission / reception operation is normally repeated continuously at regular intervals. Therefore, the time interval at which the primary system 100-1 receives and the primary system 100-2 transmits is defined as “T1,” and the time interval at which the primary system 100-1 transmits and the primary system 100-2 receives is defined as “T2.” There is no problem.

  In the first embodiment, in the secondary system 101, among the signals obtained from different time intervals of the primary system, a signal having a higher power (primary system closer to the access point (AP: base station) 101-1 of the secondary system) is used. Communication is performed by calculating the weight using the transmission signal of the system 100-2 and multiplying the transmission / reception signal by the weight. That is, the access point 101-1 of the secondary system is received by the nearby primary system 100-2 (the transmission signal of the remote primary system 100-1 is compared with the signal transmitted by the access point 101-1 of the secondary system). The primary system 101-1 transmits the signal only to the terminal 101-2 of the secondary system, while the nearby primary system 101-1 is transmitting (the access point 101-1 of the secondary system is transmitted by the primary system 101-1). The signal from the terminal 101-2 of the Secondary system is received. For this reason, the secondary system 101 can implement cognitive wireless communication without performing any control on the terminal 101-2 side only by performing predetermined control at the access point 101-1.

  Further, in the first embodiment, in addition to the above-described TDD communication, TDI (Time Division Multiple Access) is used. That is, the TDMA-TDD system is adopted.

  FIG. 5 is a conceptual diagram for explaining the communication system (TDMA) in the first embodiment. In the first embodiment, it is assumed that there are a plurality of primary systems, as shown in FIG. Corresponding to the example shown in FIG. 4, this corresponds to a case where a plurality of primary systems 100-2 (# 1) to 100-2 (# 4) exist for one primary system 100-1.

The primary system 100-1 and the primary system 100-2 (# 1) communicate at time intervals t _1D and t _1U , and the primary system 100-1 and the primary system 100-2 (# 2) are time intervals. Communication is performed at t _2D and t _2U , and the Primacy system 100-1 and the Primary system 100-2 (# 3) communicate at the time intervals t _3D and t _3U , and the Primitive system 100-1 and the Primary system 100- 2 (# 4) communicates at time intervals t _4D and t _4U .

Then, the secondary systems 101, 101,... Communicate with each other using, for example, the downlink timing t _1D and the uplink timing t _1u between the primary system 100-1 and the primary system 100-2 (# 1). It shall be.

At this time, when the downlink timing t _1D and the uplink timing t _1u described above are used, there is no problem for the access point in the Secondary system 101, but there is a problem under certain conditions for the terminal in the Secondary system 101. Occurs.

  FIG. 6 is a conceptual diagram for explaining the problem of interference cancellation in cognitive radio when an array antenna is used only for access point 101-1 described above. Problems can be roughly classified into the following two as shown in FIGS. 6 (a) and 6 (b).

(A) Problem 1: The communication direction between the terminal 101-2 and the access point 101-1 and between the primary system 100-2 (# 2) and the access point 101-1 are in the same direction.

  Interference removal using an array antenna can be realized by directing a directivity null in the direction of the interference wave. In the example of Fig.6 (a), the case where the terminal 101-2 is located in the direction is shown. In this case, there arises a problem that communication from the terminal 101-2 to the access point 101-1 or from the access point 101-1 to the terminal 101-2 cannot be performed correctly.

  This shows a case where the angular spread of the propagation channel is small, but when the angular spread is large, the terminal 101-2 is not positioned in the null direction, but the Primary system 100-2 (# 2). The same problem occurs when the propagation channel response between the access points 101-1 and the terminal 101-2-access point 101-1 is very close.

(B) Problem 2: When the distance from the primary systems 100-2 (# 1) and 100-2 (# 2) is substantially the same for the terminal 101-2, the interference waves have substantially the same reception level.

  In this case, a problem occurs on the terminal 101-2 side. The terminal 101-2 side cannot perform interference removal using an array antenna. That is, in the case as shown in FIG. 6B, the worst case is when the interference waves from the primary systems 100-2 (# 1) and 100-2 (# 2) have the same level. In this case, when the interference level with respect to the terminal 101-2 from both exceeds the allowable value of the terminal 101-2, communication on the terminal 101-2 side becomes difficult.

In this case, if there is no problem for the access point 101-1 and the target terminal 101-2, if another timing (for example, the timings t _2D and t _{2U in} FIG. 5) is used again, the Secondary system can be used without any problem. 101 communication can be continued. That is, if the information of the plurality of primary systems 100-1, 100-2 (# 1) to 100-2 (# 4) is used, the probability that the secondary system 101 can communicate can be increased. In this example, a plurality of Primary 100-1 and 100-2 (# 1) to 100-2 (# 4) perform communication by dividing time, but are divided not only by TDMA but also by frequency. FDMA (Frequency Division Multiple Access) and CDMA (Code Division Multiple Access) divided by codes have been proposed to be used in commercial systems, and the present invention can also be applied to such systems.

  Therefore, in the first embodiment, in the communication using the reception weight from which the interference is removed by the transmission / reception timing determination unit 19, when the communication quality becomes equal to or lower than the threshold value α, the transmission / reception timing with other Primary systems is set. The transmission / reception separating means 11-1 to 11-N are sequentially switched to find another primary system whose communication quality is equal to or higher than the threshold value α, and communication is performed using the timing (time slot) used in the primary system. I am doing it.

A-1. Basic Operation Next, FIG. 7 is a flowchart for explaining the operation of the array antenna transmitting / receiving apparatus 9 according to the first embodiment. First, in the access point 101-1, the signal powers P (T1) and P (T2) that arrive at the time intervals T1 and T2 are measured using the signal detection devices 15-1 and 15-2 (step S1). At this point in time, the secondary system 101 has not yet started communication, so the only incoming signals are the interference waves of the primary systems 100-1 and 100-2.

  In addition, the values of the time intervals T1 and T2 are generally disclosed since they are basic parameters of the wireless system, and it is easy for the Secondary system 101 to know these values in advance. is there. The value of one section of the TDD system is, for example, 625 μsec in the PHS system. This fact is disclosed in Reference 3 (Personal Handy phones system ARIB standard (RCR STD-28), ver. 2 Association of Radio Industries and Businesses, Tokyo, Dec. 1995).

  Next, the power comparison unit 15-3 determines whether or not the signal power P (T1) is greater than the signal power P (T2) (step S2). The magnitude relationship between the signal powers P (T1) and P (T2) is determined by the positional relationship of the Secondary system 101. For example, in the example illustrated in FIG. 4, the Secondary system 101 exists in the vicinity of the Primary system 100-2, and thus there is a high possibility that the power that arrives at the time interval T <b> 2 will be high.

  This is because the received power is basically inversely proportional to the propagation loss, and the propagation loss is known to be proportional to the distance between transmission and reception. Therefore, as in the first embodiment, if signals transmitted from the primary systems 100-1 and 100-2 at the time intervals T1 and T2 are received, the received power of either one increases and the presence of an interference wave exists. Can be estimated with relatively high accuracy.

  In this way, in this first embodiment, it is possible to detect the arrival of communication signals of the primary systems 100-1 and 100-2 by using a very simple method. That is, this operation solves the problem with respect to (Procedure 1) described above. In addition, when the received power is equal to or lower than a predetermined threshold value at both time intervals, the radio waves from the primary system 100-1 and the primary system 100-2 are considerably small. Then, unless the Secondary system 101 transmits with higher power than the Primary systems 100-1 and 100-2, the interference from the Secondary system 101 to the Primary systems 100-1 and 100-2 hardly causes a problem.

  Then, according to the magnitude relationship between the signal powers P (T1) and P (T2), the signal having the larger signal power is extracted using the signal selection unit 15-4 (steps S3 and S4). That is, when the signal power P (T1) is larger, the signals X (i) and (i = 1 to M) that arrive at the signal power P (T1) are extracted (step S3). On the other hand, when the signal power P (T2) is larger, the signals X (i) and (i = 1 to M) arriving at the signal power P (T2) are extracted (step S4).

  In the example shown in FIG. 4, a signal having a time interval T <b> 2, that is, a signal coming from the primary system 100-2 is extracted. Here, X (i) is given by the following equation (1).

Here, i represents a sample on the i-th time axis, and x _k (i) represents a received signal of the k-th antenna at time i. T represents transposition. Here, it is assumed that the number of acquired data per antenna is M. Therefore, the signal to be extracted is N antenna data × M sample data, that is, NM data.

  Next, with respect to the signal extracted using the signal selection unit 15-4, the reception weight calculation unit 15-5 calculates a correlation matrix from the reception signal X using the following equation (2) (step S5).

  Here, H represents a complex conjugate transpose. This correlation matrix includes only interference components from the Primary system 100-1 or 1002 because the Secondary system 101 has not yet started communication. Therefore, if a weight for removing such a signal can be formed, the interference signal can be completely removed. Specifically, a power minimization method is known. This fact is disclosed in Reference 4 (Kikuma, Adaptive Signal Processing by Array Antenna, Science and Technology Publishers, 1998). In the power minimization method, the weight is calculated according to the following equation (3) (step S6).

  As can be seen from the above equation (3), in the power minimization method, information of only the correlation matrix of the primary systems 100-1 and 100-2 is used. Actually, in addition to the calculation using Equation (3), as a method for further reducing the amount of calculation, the weight may be calculated sequentially by a method such as RLS (Recursive Least Square) or LMS (Least Mean Square). Is possible.

In addition to the power minimization method, there is a method based on eigenvalue decomposition in Equation (2) as a method for obtaining the weight of interference removal. If the equation (2) is decomposed into the eigenvalues shown in the following equation (4), the eigenvector e _i (i = 1 to K) corresponding to the signal power and the eigenvector e _i (i = K + 1 to N) corresponding to the noise power can be obtained. . The correlation matrix, eigenvalues, and eigenvectors have the following relationship (4).

Here, the signal subspace is orthogonal to the noise subspace. If the incoming signal is a K wave, the eigenvector corresponding to the eigenvalues from K + 1 to N becomes the eigenvector corresponding to the noise subspace. Therefore, the directivity of the eigenvector corresponding to the minimum eigenvalue which is _{one of} λ _{K + 1} ,..., Λ _N forms a null in the signal direction.

Therefore, it is also possible to use eigenvector e _N for the minimum eigenvalue obtained by eigenvalue decomposition as weight (vector) w. In addition, as a method for obtaining the eigenvector corresponding to the minimum eigenvalue, eigenvalue decomposition can be directly performed, but it is also possible to obtain a sequential update method such as a power method for the inverse matrix of the correlation matrix. be able to.

  Next, the secondary system 101 starts communication using the weight information. The branch means 16 in FIG. 1 branches the weight w and supplies it to the reception weight multiplication unit 17 and the transmission weight multiplication unit 18.

  The reception weight multiplication unit 17 calculates reception weight multiplication in one of the time intervals T1 and T2 based on the magnitude relationship between the signal power P (T1) and the signal power P (T2). That is, the reception weight multiplication unit 17 determines whether or not the signal power P (T1) is larger than the signal power P (T2) (step S7), and if P (T1)> P (T2) The time interval T1 is selected (step S8), and if P (T1) <P (T2), the time interval T2 is selected (step S9), and the received signal (signal transmitted from the terminal of the Secondary system + Primary) 2 is multiplied by the weight previously used in the reception weight calculation unit 15-5 using the following equation (5) to calculate the output signal Z (step S10). ).

  Thus, when P (T1)> P (T2), reception is performed at the time interval T1, while when P (T1) <P (T2), reception is performed at the time interval T2. That is, the reception of the Secondary system 101 is performed using a time interval in which the reception power increases. In the example of FIG. 4, since P (T2)> P (T1), the base station in the Secondary system 101 receives at the time interval T2 and transmits at the time interval T1. On the other hand, the terminal side transmits at time interval T2 and receives at time interval T1.

  On the other hand, the transmission weight multiplication unit 18 calculates transmission weight multiplication in one of the time intervals T1 and T2 based on the magnitude relationship between the signal power P (T1) and the signal power P (T2). That is, the transmission weight multiplication unit 18 determines whether or not the signal power P (T1) is larger than the signal power P (T2) (step S11), and if P (T1)> P (T2) The time interval T2 is selected (step S12). If P (T1) <P (T2), the time interval T1 is selected (step S13), and the reception weight calculation unit for the N-branched transmission signal is selected. The weight obtained in 15-5 is multiplied using the following equation (6) (step S14).

  Thus, when P (T1)> P (T2), transmission is performed at the time interval T2, while when P (T1) <P (T2), transmission is performed at the time interval T1. That is, the transmission of the Secondary system 101 is performed using a time interval in which the reception power is small. Note that the transmission weight multiplication unit 18 does not require a synthesis process as described above.

  Next, phenomena and effects in the Secondary system 101 according to the first embodiment will be described with reference to FIG. First, in the time interval T1, transmission is performed on the base station side of the secondary system 101, and reception is performed on the terminal side. On the base station side, if the non-directional transmission is performed from the base station at the time interval T1, as in the prior art, interference is given to the primary system 100-2.

  However, in the first embodiment, since transmission can be performed using a weight that forms a directional null in the direction of the Primary system 100-2, no interference is given to the Primary system 100-2. Moreover, since the Primary system 100-1 is transmitting and does not receive a signal, the interference with the Primary system 100-1 does not need to be considered here.

  That is, interference from the secondary system 101 to the primary system 100-2 due to the start of communication of the secondary system 101 can be avoided, so that the problem in (procedure 2) described above can be solved. On the other hand, since the signal is received at the time interval T1 with a small amount of interference on the terminal side, the amount of interference to the terminal side of the secondary system 101 is automatically set without any control on the terminal side. It becomes possible to reduce. Since miniaturization and simplification are desirable in the terminal, this is a very important advantage that the amount of interference can be reduced without performing any control.

  Next, in the time interval T2, reception is performed on the access point (base station) 101-1 side of the secondary system 101, and transmission is performed on the terminal 101-2 side. Since the access point 101-1 holds a weight capable of removing interference in advance, if the received signal is multiplied by the received signal, the interference wave can be completely removed, and good communication quality can be maintained. Can do.

  In the example illustrated in FIG. 4, it is assumed that the service areas of the primary systems 100-1 and 100-2 are larger than the service area of the secondary system 101. Therefore, since the signal of the terminal 101-2 of the Secondary system 101 is weaker than the signal of the Primary system 100-2, the amount of interference with the Primary system 100-1 is small, and the Primary system 100-2 is transmitting. Therefore, it is not necessary to consider interference with the Primary 100-2.

A-2. First Additional Operation Next, a first additional operation for solving the above-described problem 1 in the first embodiment will be described.
FIG. 8 is a flowchart for explaining the operation of the array antenna transceiver 9 according to the first embodiment.
FIG. 9 is a conceptual diagram showing an effect of the second additional operation that solves the problem 1.

First, N = 1 is set, and the access point 101-1 uses the timing of the primary system 100-2 (#N: N = 1) (in the example of FIG. 5, timings t _1U and t _1D ) (step S20). When the timing of the primary system 100-2 (# 1) is used, a signal from the terminal 101-2 is received using the reception weight from which interference is calculated, which is calculated by the above-described operation. At this time, if the problem shown in FIG. 6A occurs, the communication quality greatly deteriorates. Therefore, the communication quality determination unit 100 determines whether or not the communication quality is lower than the threshold value α (step S22). If the communication quality is equal to or higher than the threshold value α, that is, if the desired communication quality is obtained. As it is, communication is performed using the reception weight from which interference is calculated, which is calculated by the above-described operation (step S23). The threshold value α can be uniquely determined based on the communication quality determined by the Secondary system 101.

  On the other hand, when the communication quality is lower than the threshold value α, a flow of searching for another primary system is started. That is, first, it is determined whether or not N is smaller than the maximum value M (the maximum number of primary systems) (step S24). If N is smaller than M, that is, if not all primary systems are searched, N = N + 1 (step S25), a different primary system terminal 100-2 (#N: N = 2) is selected, and the access point 101-1 has this primary system 100-2 (#N: N = 2). The received powers P (T1) and P (T2) in the time interval T1 transmitted by and the time interval T2 transmitted by the Primary system communicating with the Primary system 100-2 (#N) are measured (step S26).

  Next, based on the magnitude relationship between the two received powers, the primary system 100-2 (#N) to be subjected to interference cancellation by the access point 101-1 and the transmission timing and reception timing are determined. That is, it is determined whether or not the received power P (Tl) is greater than the received power P (T2) (step S27). If the received power P (Tl) is greater, the time interval T1 is set. A weight for removing the incoming interference wave is generated (step S28), and the access point 101-1 determines the time interval T2 as the transmission timing and the time interval T1 as the reception timing (step S29). In this case, on the terminal 101-2 side, the time interval T1 is the transmission timing, and the time interval T2 is the reception timing.

  On the other hand, when the received power P (T2) is greater than or equal to the received power P (Tl), a weight for removing the interference wave that arrives at the time interval T2 is generated (step S30), and the access point 101-1 The interval T1 is determined as transmission timing, and the time interval T2 is determined as reception timing (step S31). In this case, on the terminal 101-2 side, the time interval T1 is the reception timing, and the time interval T2 is the transmission timing.

  Access point 101-1 uses the same directivity for transmission and reception. Thereafter, the process returns to step S21 to determine the communication quality, and thereafter the above-described operation is repeated until the desired communication quality is obtained.

  According to the first embodiment described above, it is possible to easily realize interference detection from the Primary system without reducing the efficiency of the Primary system at all. In addition, the communication of the secondary system 101 can be started without causing interference to the primary system. That is, the problem in the conventional cognitive radio can be solved. Further, by the operation shown in FIG. 8 described above, as shown in FIG. 9, the primary system (shown in FIG. 9) is not in the same direction as the interference from the primary system with respect to the access point 101-1, for the terminal 101-2. In the example, the terminal 100-2 (# 3)) is automatically selected, and the problem 1 in FIG. 6A can be solved.

A-3. Second Addition Operation Next, a second addition operation for solving the above-described problem 2 in the first embodiment will be described.
FIG. 10 is a flowchart for explaining the operation of the array antenna transceiver 9 according to the first embodiment.
FIG. 11 is a conceptual diagram showing an effect of the second additional operation for solving the problem 2.

  Since the problem 2 described above is a problem whether or not the interference wave power arriving on the terminal 101-2 side exceeds the threshold value, in the operation illustrated in FIG. The interference wave power from the incoming primary system is measured (step S40). Next, it is determined whether or not the interference wave power is smaller than the threshold value β (step S41). If the interference wave power exceeds the threshold value β, the process proceeds to the next step. If not, the communication starts because there is no problem (step S45). The threshold value β is a value that can be uniquely determined by the performance of the terminal 101-2 of the Secondary system 101, like the previous threshold value α.

  If the interference wave power exceeds the threshold value β, the terminal 101-2 searches for the Primary system 100-2 (#K) in which the received interference wave power is equal to or less than the threshold value β (step S42). ). Then, the terminal 101-2 notifies the searched primary system 100-2 (#K) to the access point 101-1.

  Next, the access point 101-1 calculates a weight for removing a signal (referred to as time interval T2 ') from the Primary system communicating with the Primary system 100-2 (#K) (referred to as time interval T1'). (Step S43). That is, the access point 101-1 determines that the primary system 100-2 (#K) is a primary system sufficiently far from the access point 101-1, and communicates with the primary system 100-2 (#K). Apply interference cancellation to the Primary system.

  Finally, the access point 101-1 transmits the time interval T1 ', determines the time interval T2' as the reception timing (step S44), and starts communication (step S45). For the access point 101-1, the time interval T2 'can operate without any problem because interference can be removed. Further, since the terminal 101-2 is transmitting at the time interval T2 ′ and receiving at the time interval T1 ′, the interference wave reaching the terminal 101-2 has a primary system 100- whose interference wave power is equal to or less than the threshold value β. 2 (#K), and the above problem 2 on the terminal 101-2 side can be solved. In the example illustrated in FIG. 11, the Primary system 100-2 (# 4) is selected instead of the Primary system 100-2 (# 1).

  In addition, the 1st addition operation | movement shown in FIG. 8 and the 2nd addition operation | movement shown in FIG. 10 can complement the problem which cannot be solved by each performing both. For example, although the problem 2 is solved by executing the second additional operation, the problem 1 may newly occur. In such a case, both the problem 1 and the problem 2 can be avoided by executing the first additional operation in addition to the second additional operation.

B. Second Embodiment Next, a second embodiment of the present invention will be described. In the second embodiment, an OFDM (Orthogonal Frequency Division Multiplexing) system is used in the secondary system, which is different from the first embodiment.

  FIG. 12 is a block diagram showing a configuration of an array antenna transmission / reception apparatus according to the second embodiment of the present invention. In the figure, parts corresponding to those in FIG. In FIG. 12, GI (Guard Interval) removing units 20-1 to 20-F and FFT (Fast Fourier Transform) calculating units 21-1 to 21-F are provided on the receiving side after the memory. On the other hand, on the transmitting side, an S / P (serial / parallel) conversion unit 22 that divides the number of transmission signals into the number of OFDM subcarriers, an IFFT (Inverse Fast Fourier Transform) calculation unit 23, a GI addition unit 24, Is provided.

  An OFDM system having a reception function and a transmission function described here has recently been adopted in a wireless LAN system or the like, and is an indispensable technique indispensable for broadband transmission. This fact is described in, for example, the above-mentioned document 2. Therefore, it is very important that the second embodiment can be applied to the OFDM system.

  In the ODFM, in the case of performing the above-described interference cancellation, generally, a method is employed in which a weighting value is calculated and combined for each subcarrier signal after FFT on the receiving side. In order to realize this by the method described in the first embodiment, GI removal and IFFT are performed on the received signal from the primary system, and the signal of the primary system is divided into subcarrier units. It is necessary to obtain the above-described interference removal weight for each carrier.

  However, the Primary system does not always use OFDM, and even if the Primary system is an OFDM system, the number of subcarriers and the subcarrier band are not necessarily the same as those of the Secondary system. Further, when the number of subcarriers is F, in order to obtain the weight by the primary system interference removal unit 15 for each subcarrier, calculation of F times as described in FIG. 1 is required. In an actual system, the number of F is from several tens to several hundreds, so a huge amount of calculation is required for the process of calculating the weight for each subcarrier. In the second embodiment, in order to solve this problem, the primary system interference canceling unit 15 is exactly the same as the configuration of FIG. 1, and the reception weight multiplying unit 17a is different from the configuration of FIG.

FIG. 13 is a block diagram showing a configuration of the reception weight multiplication unit 17a according to the second embodiment. In FIG. 13, first, the weights w ₁ ^{* to} w _N ^* obtained by the primary system interference canceling unit 15 are simply set to the number of subcarriers F by branching means 17 a-1-1 to 17 a-1 -N. Divide into Thereafter, the divided weights are multiplied for each subcarrier by multipliers 17a-2-1 to 17a-2-1-N,..., 17a-2-F-1 to 17a-2-F-N. . That is, the same weight is multiplied between subcarriers. The outputs of the multipliers 17a-2-1 to 17a-2-1-N,..., 17a-2-F-1 to 17a-2-F-N are respectively added to the corresponding adders 17a-3. -1 to 17a-3-F are added and supplied to the parallel / serial converter 17a-4. The parallel / serial conversion unit 17a-4 converts the addition result (parallel) from the adders 17a-3-1 to 17a-3-F into serial data, and outputs it as an output signal.

  In the primary system, when assuming a base station such as FWA (Fixed wireless Access) or a mobile phone, the base station or the receiving station is installed on the rooftop of the building. It is known that the spread is quite small (within a few degrees). On the other hand, when the Secondary system is applied to a situation where the antenna is arranged in a low place and the system is a narrow area such as a wireless LAN, the spread of the angular distribution of the propagation path is considerably large (several tens of times). It is known that the degree is more than 360 degrees. A propagation environment with a narrow angular spread is equivalent to a radio wave coming from a certain direction. In this case, even if the weight of interference removal is obtained by averaging the entire subcarriers, or if the weight of interference removal is obtained for each subcarrier, there is no significant difference. Using this property, the second embodiment multiplies the same weight between subcarriers.

  The multipliers 17a-2-1 to 17a-2-N,..., 17a-F-1 to 17a-FN have functions added to the configuration of FIG. Compared with the increase in the calculation amount in the interference removal unit 15, the influence is considerably small.

  The operation of the array antenna transmission / reception apparatus according to the second embodiment is the same as that of the first embodiment described above, and a description thereof will be omitted.

  According to the second embodiment described above, even in the OFDM system, cognitive radio can be realized without greatly increasing the amount of computation of the secondary system. It is also possible to solve the problem of interference removal in cognitive radio when an array antenna is used only for access point 101-1.

C. Third Embodiment Next, a third embodiment of the present invention will be described. The third embodiment is characterized in that the Primary system also uses the OFDM system. However, the number of subcarriers and the bandwidth of the Secondary system do not necessarily need to match those of the Primary system. In the first or second embodiment described above, it is not assumed that the propagation environment of the Primary system changes every moment.

  However, for example, in FIG. 4, when it is assumed that the primary system 100-2 is a mobile station, the propagation environment between the primary systems changes with time. Here, when communication is started, the interference between the primary system and the desired signal of the secondary system is actually mixed, so that there is not much difference between the interference power and the desired power, or the desired power is less than the interference power. If this value is too large, simple interference removal according to the first or second embodiment described above becomes difficult. Therefore, in the third embodiment, even when the propagation environment of the primary system changes due to time fluctuation, stable interference detection of the primary system is realized.

  FIG. 14 is a block diagram showing a configuration of an array antenna transmitting / receiving apparatus according to the third embodiment of the present invention. In the figure, parts corresponding to those in FIG. As shown in FIG. 14, in the interference detection method according to the third embodiment, the operation in the signal detectors 15-1a and 15-2a arriving at the time interval T1 or T2 is performed before and after starting the communication of the Secondary system. Different.

  Here, FIG. 15 is a block diagram showing a configuration of the signal detection device 15-1a shown in FIG. Since the configuration of the signal detection device 15-2a is the same as that of the signal detection device 15-1a, the description thereof is omitted. In FIG. 15, the signal detectors 15-1a and 15-2a arriving at the time interval T1 or T2 perform GI removal by the GI removal units 15-1a-1-1-1 to 15-1a-1-N before starting communication. An FFT calculation is performed by the FFT calculation units 15-1a-2-1 to 15-1a-2-N. This is the same as the normal OFDM demodulation, but actually uses regular arithmetic processing as in the Secondary system, so it is written in a different place in the block diagram, but GI removal and FFT in the Secondary system. You may divert a calculation part. Therefore, even if the FFT calculation is repeated, the hardware scale does not increase.

  The subcarrier extraction unit 15-1a-3 extracts all incoming subcarriers. Next, the subcarrier average processing unit 15-1a-4 averages the signal for each subcarrier. That is, all subcarriers are detected, the signal for each subcarrier is used as a correlation matrix, and these signals are averaged. This signal is equivalent to averaging in the frequency direction, and can be said to be almost equivalent to the correlation matrix averaged with the time axis information described in FIG. That is, the same interference removal as in FIG. That is, calculations other than the correlation matrix averaged in the frequency direction are the same as those in FIG. In other words, signal selection and reception weight calculation itself are the same as in FIG.

  Next, processing after the start of communication will be described. Even after the start of communication, in the signal detectors 15-1a and 15-2a arriving at the time interval T1 or T2, the GI removal unit 15-1a-1-1-1 to 15-1a-1-N performs the GI removal and FFT calculation unit. The FFT calculation by 15-1a-2-1 to 15-1a-2-N is performed in the same manner as the processing described above. However, after the communication starts, the signal of the Secondary system is superimposed here, so that the above-described interference cancellation may not operate properly. Therefore, in the third embodiment, interference can be easily and effectively removed even in such an environment by appropriately using the subcarrier information extracted by the subcarrier extraction unit 15-1a-3. Is proposing.

  FIG. 16 shows the relationship between the actual subcarrier arrangement (band βHz), the actual communication band (band αHz), and the guard band band (band γHz) in the OFDM system when the characteristics of the primary system and the secondary system are the same. It is a conceptual diagram shown in a different case (FIG. 16B) from (FIG. 16A). First, in the case of FIG. 16A, the spectrums of signals in the Secondary system and the Primary system appear to be exactly the same.

  However, in the relationship between the actual communication band (band αHz) and the actual subcarrier arrangement (band βHz), the relationship between the FFT point number L and the subcarrier F is always designed to satisfy L> F. That is, α> β. Ideally, L-point subcarriers can be arranged, but the information of subcarriers at both ends is set to 0 in order to avoid interference with adjacent channels. This band is called a guard band, and in FIGS. 16A and 16B, the band is γHz.

  Considering the features described above, it means that an environment for extracting only interference waves can be created even during communication. Originally, the antenna pattern for interference cancellation can be formed, and it is sufficient that the fluctuation can be derived. First, subcarrier information in the vicinity of the guard band described above can be used. In the secondary system, if the subcarrier (1) and the information of (F) are transmitted without being transmitted, the signal from the secondary system is not received by this subcarrier. In this case, if attention is paid to subcarriers (1) and (F), comparison of interference levels between time intervals T1 and T2 and calculation of interference removal can be performed based on information of received signals of the subcarriers. Since these are accurately performed in advance for the start of communication, it is only necessary to check the fluctuations in the interference detection and the interference removal after the start of communication. Therefore, the initial accuracy is not necessary.

  In the third embodiment, when the status of the primary system changes due to environmental changes such as movement, it is necessary to recheck the interference amount of the primary system. Usually, in a TDD system, a guard interval (non-communication section) is provided in order to avoid a time collision between users. By providing this section in the Secondary system and checking the signal strength of the Primary system that arrives in this section, it is possible to check the interference amount of the Primary system. The check may be performed every time reception is performed, but may be performed at a frequency of about once when receiving the secondary system several times to several tens of times.

  Therefore, in the signal detection devices 15-1a and 15-2a in the primary system interference removal unit 15, the subcarrier extraction units 15-1a-3 and 15-2a-3 receive subcarriers (1) and ( F) Pick up only. Thereafter, the correlation matrix of the two subcarriers is averaged. The subsequent processing is the same as the processing before starting communication. In the case of FIG. 16B, since the subcarrier arrangement band and the guard band band are different, in the secondary system, for example, transmission is not performed as 0 because of subcarriers (1) and (F). However, only the interference wave arrives at the carrier at the end of the communication band β2 in FIG.

  Other than the method described above, there is a method in which only the interference wave is received by the primary system interference removal unit 15 during communication. In the OFDM system, a signal called a pilot subcarrier is constantly transmitted to ensure carrier synchronization. For example, in IEEE 802.11a, 4 carriers out of 52 subcarriers are used for this carrier. Since the position of this subcarrier is known in advance by standardization or the like, it can be considered that it is recognized also in the Secondary system. If this subcarrier is not transmitted in the secondary system, the primary system interference canceling unit 15 selects and focuses only this carrier during communication, and only the interference component is obtained in the same manner as described above. Is obtained.

  It is also possible to focus on data in the time axis direction without focusing on the subcarrier. In a normal communication system, first, a base station and a terminal send a known preamble signal to each other. Thereafter, normal data is transmitted. Therefore, in the secondary system, it is possible not to transmit in the preamble section of this primary system. In this case, the signal arrives from the primary system only in the preamble section of the primary system, and the signal of the section of the secondary system arrives in the subsequent section. Also in this case, after detecting the signal in the preamble section, it is possible to obtain a weight for obtaining interference cancellation by the same procedure as that before the start of communication.

  The operation of the array antenna transmission / reception apparatus according to the third embodiment is the same as that of the first embodiment described above, and a description thereof will be omitted.

  According to the third embodiment described above, even when an OFDM system is used for the primary system, it is possible to realize cognitive radio without greatly increasing the amount of computation of the secondary system. It is also possible to solve the problem of interference removal in cognitive radio when an array antenna is used only for access point 101-1.

  Next, effects of the first to third embodiments described above will be described. The calculation was performed in an environment assuming the configuration shown in FIG. The calculation assumes an environment in which the base station and a plurality of terminals communicate as the primary systems 100-1 and 100-2. The primary systems 100-1 and 100-2 are operated in a TDMA-TDD system. The Secondary system 101 calculates the communication quality when moving within the service areas of the Primary systems 100-1 and 100-2 assuming a wireless LAN environment. The calculation parameters are shown in Table 1.

  The secondary system assumes a communication range that takes into account the 54 Mbps transmission of IEEE802.11a to be about 23 m. Therefore, it is assumed that the terminal moves within this range. The SNR of the Secondary system is set to 20 dB at the zone end. Table 2 shows the propagation loss equation.

  The propagation loss is described in, for example, Reference 5 (S. Ichitsubo, et al., “2 GHz-Band Propagation Loss Prediction in Urban areas; antenna heights ranging from ground to building roof”, IEICE Technical Report, AP96-15, May, 1996. ) Was used. In this path model, a path loss for an arbitrary antenna height of 30 m or less can be given. The antenna height of the primary system base station is 30 m, and the height of the primary system mobile station is 2 m. In addition, the antenna height of the Secondary system was 20 m, and the frequency was 2.4 GHz. The number of antenna elements of the base station of the secondary system is set to 2, which is the minimum number of elements. Interference cancellation is not performed on the terminal side of the Secondary system. The number of antenna elements is one.

  FIG. 17 is a conceptual diagram showing communication capacity (bits / s / Hz) with respect to the number of nodes in the primary system according to the present invention. As shown in the figure, when the number of nodes is 1, the characteristics are greatly deteriorated compared to the case where there is no interference on both the AP side and the terminal side (ideal value). This is because when the number of nodes is 1, the problem described in FIG. 6 cannot be solved. On the other hand, as is clear from the figure, it can be confirmed that when the number of nodes is increased, the capacity is increased, and even when the number of nodes is 3 to 4, characteristics almost ideal can be obtained.

  As described above, in the present invention, when there are a plurality of systems, paying attention to the timing of the TDMA-TDD system, the base station side performs simple interference removal, and among the plurality of Primary nodes, the above-mentioned problem By selecting a node that eliminates the problem, the Secondary system can perform communication while maintaining good quality without performing any control on the terminal side. That is, the surface frequency utilization efficiency can be improved in the entire system.

It is a block diagram which shows the structure of the array antenna transmission / reception apparatus by 1st Embodiment of this invention. It is a block diagram which shows the structure of the reception weight multiplication part 17 by this 1st Embodiment. It is a block diagram which shows the structure of the transmission weight multiplication part 18 by this 1st Embodiment. It is a conceptual diagram which shows the structure of the communication system (TDD) in this 1st Embodiment. It is a conceptual diagram which shows the structure of the communication system (TDMA) in this 1st Embodiment. It is a conceptual diagram for demonstrating the problem of the interference removal in a cognitive radio at the time of using an array antenna only for an access point. It is a flowchart for demonstrating operation | movement of the array antenna transmission / reception apparatus 9 by this 1st Embodiment. It is a flowchart for demonstrating the 1st addition operation | movement of the array antenna transmission / reception apparatus 9 by this 1st Embodiment. It is a conceptual diagram which shows the effect by the 2nd addition operation | movement in this 1st Embodiment. It is a flowchart for demonstrating the 2nd addition operation | movement of the array antenna transmission / reception apparatus 9 by this 1st Embodiment. It is a conceptual diagram which shows the effect by the 2nd addition operation | movement in this 1st Embodiment. It is a block diagram which shows the structure of the array antenna transmission / reception apparatus by 2nd Embodiment of this invention. It is a block diagram which shows the structure of the reception weight multiplication part 17a by this 2nd Embodiment. It is a block diagram which shows the structure of the array antenna transmission / reception apparatus by 3rd Embodiment of this invention. It is a block diagram which shows the structure of the signal detection apparatus 15-1a. It is a conceptual diagram which shows the relationship between actual subcarrier arrangement | positioning (band | zone (beta) Hz), an actual communication band (band | zone (alpha) Hz), and a guard band band (band | zone (gamma) Hz) in an OFDM system. It is a conceptual diagram which shows the transmission capacity which can communicate with respect to the number of nodes of the Primary system by this invention. It is a conceptual diagram for demonstrating the outline | summary of a cognitive radio | wireless technique.

Explanation of symbols

10-1 to 10-N antenna (multiple antenna elements)
11-1 to 11-N transmission / reception separating means (multiple transmitting / receiving branching means)
12-1 to 12-N transmitter (transmitter)
13-1 to 13-N Receiver (Receiver)
14 Memory 15 Primary System Interference Rejection Unit 15-1, 15-2 Signal Detection Device 15-3 Power Comparison Unit (Power Measurement Unit, Interference Wave Power Measurement Unit)
15-4 Signal selection unit 15-5 Reception weight calculation unit (weighting means)
16 branching means 17 received signal weight multiplication section (weighting means)
18 Transmission signal weight multiplier (weighting means)
17-1-1-1 to 17-1-N multiplier 17-2 adder 18-1 branching means 18-2-1 to 18-2-N multiplier 100-1, 100-2 Primary system 101 Secondary system 17a reception Signal weight multiplier (weighting means)
20-1 to 20-F GI removal unit 21-1 to 21-F FFT calculation unit 22 S / P conversion unit 23 IFFT calculation unit 24 GI addition unit 17a-1-1 to 17a-1-N branching unit 17a-2 -1-1 to 17a-2-F-N multiplier 17a-3-1 to 17a-3-F adder 17a-4 parallel / serial converter 15-1a, 15-2a Signal detection device 22-1 to 22 -F Subcarrier extraction unit 15-1a-1-1 to 15-1a-1-N GI removal unit 15-1a-2-1 to 15-1a-2-N FFT calculation unit 15-1a-3 Subcarrier extraction Unit 15-1a-4 subcarrier averaging processing unit 19 transmission / reception timing determination unit (determination means, communication quality determination means, switching means, transmission / reception condition determination means, search means)

Claims (8)

A plurality of antenna elements, a plurality of transmission / reception branching means connected to each of the plurality of antenna elements, a transmission means connected to each of the plurality of transmission / reception branching means, and connected to each of the plurality of transmission / reception branching means A transmission / reception apparatus comprising:
Of the received signals received at two different time intervals by the receiving means from the first node that is an interference source from another system and the second node that communicates with the first node, Weighting means for weighting transmission / reception signals by the transmission means and the reception means based on a large received signal;
Communication quality determining means for determining communication quality of a received signal received using weighting by the weighting means;
When the communication quality determining means determines that the communication quality does not exceed a predetermined threshold, the first node is switched to another node, and the other node is set as a new first node. When,
Power measuring means for measuring received power of two received signals obtained at two different time intervals from the first node switched by the switching means and the second node communicating with the first node When,
Determining means for determining which received power measured by the power measuring means is greater;
The time interval of the received signal for which the received power is determined to be large by the determining means is the reception timing by the receiving means, and the time interval of the received signal for which the received power is determined to be low is the transmission timing by the transmitting means. A transmission / reception apparatus comprising: a transmission / reception condition determination unit. A plurality of antenna elements, a plurality of transmission / reception branching means connected to each of the plurality of antenna elements, a transmission means connected to each of the plurality of transmission / reception branching means, and connected to each of the plurality of transmission / reception branching means A transmission / reception apparatus comprising:
Interference wave power measurement means for measuring interference wave power from a node of another system;
Determination means for determining whether or not the interference wave power measured by the interference wave power measurement means exceeds a predetermined threshold;
When the determination means determines that the interference wave power has exceeded a predetermined threshold, the other node in the other system in which the interference wave power does not exceed the predetermined threshold is searched as the first node. Search means to
Of the received signals received at two different time intervals by the receiving means from the first node searched by the searching means and the second node communicating with the first node, the reception power is large. Weighting means for weighting transmission / reception signals by the transmission means and the reception means based on a received signal;
A transmission / reception condition determining unit that sets a time interval of a reception signal from the first node as a transmission timing by the transmission unit and a time interval of a reception signal from the second node as a reception timing by the reception unit. A transmitting / receiving apparatus characterized by the above.   When the first node and the second node communicate with each other at different frequencies, the transmission / reception condition determining unit determines the frequency of the received signal determined by the determining unit as having a large received power. The transmission / reception apparatus according to claim 1, wherein the transmission frequency of the reception signal determined to be a reception frequency and the reception power is determined to be low is a transmission frequency by the transmission unit.   When the first node and the second node communicate with each other at different frequencies, the transmission / reception condition determining unit determines the frequency of the received signal determined by the determining unit as having a large received power. The transmission / reception apparatus according to claim 2, wherein the transmission frequency of the reception signal determined to be a reception frequency and the reception power is determined to be small is a transmission frequency by the transmission means.   When the first node and the second node communicate with different codes, the transmission / reception condition determining means uses the receiving means to determine the sign of the received signal determined by the determining means that the received power is large. The transmission / reception apparatus according to claim 1, wherein a code of the reception signal determined to have a low reception power is used as a code by the transmission unit.   When the first node and the second node communicate with different codes, the transmission / reception condition determining means uses the receiving means to determine the sign of the received signal determined by the determining means that the received power is large. 3. The transmission / reception apparatus according to claim 2, wherein a code of the received signal determined to have a low received power is used as a code by the transmission means. A plurality of antenna elements, a plurality of transmission / reception branching means connected to each of the plurality of antenna elements, a transmission means connected to each of the plurality of transmission / reception branching means, and connected to each of the plurality of transmission / reception branching means In a communication method by a transmission / reception device comprising a receiving means,
Of the received signals received at two different time intervals by the receiving means from the first node that is an interference source from another system and the second node that communicates with the first node, A weighting step for weighting transmission / reception signals by the transmission unit and the reception unit based on a large reception signal;
A communication quality determination step of determining a communication quality of a received signal received using the weighting;
When it is determined that the communication quality does not exceed a predetermined threshold value, the switching step of switching the first node to another node and setting the other node as a new first node;
A power measurement step of measuring received power of two received signals obtained at two different time intervals from the switched first node and a second node communicating with the first node;
A determination step of determining which of the measured received power is greater;
Transmission / reception condition determination using the time interval of the received signal determined to have a large received power as the reception timing by the receiving unit and the time interval of the received signal determined to have a low received power as the transmission timing by the transmitting unit A communication method comprising: steps. A plurality of antenna elements, a plurality of transmission / reception branching means connected to each of the plurality of antenna elements, a transmission means connected to each of the plurality of transmission / reception branching means, and connected to each of the plurality of transmission / reception branching means In a communication method by a transmission / reception device comprising a receiving means,
An interference wave power measurement step for measuring interference wave power from a node of another system;
A determination step of determining whether or not the measured interference wave power exceeds a predetermined threshold;
When it is determined that the interference wave power has exceeded a predetermined threshold, a search step of searching for another node of the other system whose interference wave power does not exceed the predetermined threshold as a first node When,
Of the received signals received at two different time intervals by the receiving means from the searched first node and the second node communicating with the first node, a received signal having a large received power A weighting step for weighting transmission / reception signals by the transmission means and the reception means,
A transmission / reception condition determining step in which a time interval of the reception signal from the first node is set as a transmission timing by the transmission unit, and a time interval of the reception signal from the second node is a reception timing by the reception unit. A communication method characterized by the above.

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