JP2008306661A - Communication system and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain cognitive radio without undergoing any interference from a Primary system, even if the number of terminal antenna element is 1. <P>SOLUTION: Transfer functions between an AP and a terminal and between a Primary system and the terminal are estimated by utilizing a training interval of the Primary system. Then, the access point AP transmits a first signal to a communication terminal TS1, in a communication interval of the Primary system with use of directivity, so that a received signal is substantially zero with respect to a communication terminal TS2. The communication terminal TS2 estimates the interference wave, arriving at the communication interval of the Primary system based on the received signal and transfer function, and transmits the interference wave information to the communication terminal TS1 by using the next signal interval. The communication terminal TS1 estimates the interference signal from the Primary system based on the interference wave information and the transfer function, and further estimates the desired signal, based on an estimated value of the interference signal, the first signal, and the transfer function. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In a wireless communication system that operates a plurality of systems at the same frequency, the present invention enables a new system (Secondary system) that does not have priority to efficiently grasp information from a conventional system (Primary system) that has priority. The present invention relates to a communication system and a communication method in which a terminal that is not performing communication is used as a virtual array antenna.

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). This cognitive radio technology is a technology for effectively utilizing an available frequency band by recognizing the surrounding radio wave environment and selecting and using an appropriate 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. 8 is a conceptual diagram for explaining the outline of the cognitive radio technology. In FIG. 8, 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 (Time Division Duplex). 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.

  Also, for example, even if the receivers of the secondary systems 2-1 to 2-6 determine that a signal has not 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.). As shown in FIG. 9, when such a method is introduced into a base station of a secondary system, it becomes possible to detect signals of the high-performance primary systems 1-1 and 1-2. That is, the communication contents grasping unit 3-1 provided in the base station 3 of the Secondary systems 2-1, 2-2,... Grasps the signal contents from the Primary systems 1-1, 1-2 to avoid interference or cancel interference. The part 3-2 avoids or cancels the interference.

  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.

  As another means for avoiding interference from the primary systems 1-1 and 1-2, an adaptive array using an array antenna is known. FIG. 10 is a block diagram showing a basic configuration of an adaptive array. As shown in FIG. 10, the adaptive array 5 performs appropriate weighting on signals input to the plurality of antennas 6-1 to 6-N by the multipliers 7-1 to 7-N by the control circuit 9. This is a technique for removing the interference wave by combining with the adder 8. Various methods for setting the weighting have been proposed, and details are disclosed in, for example, Document 2 (Kikuma, Adaptive Signal Processing with Array Antenna, Science and Technology Publishers, 1998).

  However, the base station 3 of the secondary systems 2-1, 2-2,... Shown in FIG. 9 removes interference using the adaptive array configuration shown in FIG. Even so, in the cognitive radio, the terminal 4 must also remove the interference wave. In a terminal mounted on a PC card, removing interference using a plurality of array antennas reduces the number of antennas in the terminal 4 as much as possible from the viewpoint of reduction in hardware scale and power consumption. It is desirable. Ideally, it is desirable that the number of antennas be one. That is, it is difficult to use the configuration as shown in FIG. 10 in the terminal of the Secondary system.

  As a method for solving this problem, a distributed array antenna has been proposed. For example, reference 3 (Shidong Zhou, Ming Zhao, Xibin Xu, Jing Wang and Yan Yao, “Distributed wireless communication system: a new architecture for future public wireless access”, IEEE Communications Magazine, vol. 41, no. 3 , pp.108--113, March 2003. ”and the like.

  FIG. 11 is a conceptual diagram showing an environment to which a distributed array antenna is applied. FIG. 12 is a conceptual diagram showing the configuration of a distributed array antenna. As shown in FIG. 11, terminals # 1 and # 2 have one antenna. FIG. 11 assumes an environment in which the access point 10 communicates with the terminal # 1. At that time, interference of the same frequency comes from the Primary system 11. Terminal # 2 is not communicating. The feature of the distributed array is that, in the case shown in FIG. 11, a terminal # 2 that is not communicating (referred to as an idle terminal) is used to manually operate the information of the terminal # 2, thereby providing a virtual The purpose is to form an array antenna. In FIG. 11, h represents a channel response between the transmitting station and the receiving station. Ideally, this can be achieved using the configuration of FIG. Signals x1 and x2 received by terminal # 1 and terminal # 2 are given by the following equations (1) and (2).

  Here, hS1 is a channel response between the access point 10 of the Secondary system and the terminal # 1, and S is a signal transmitted by the access point 10. hI1 is a channel response between the transmission station 11 of the primary system and the terminal # 1, and i is a signal transmitted by the transmission station 11 of the primary system, which is an interference for the terminal of the secondary system. N1 is thermal noise.

  Here, hS2 is a channel response between the access point 10 of the Secondary system and the terminal # 2, and S is a signal transmitted by the access point 10. hI2 is a channel response between the primary system transmitting station 11 and the terminal # 2, and i is a signal transmitted by the primary system transmitting station 11, which is an interference for the secondary system terminal. N2 represents thermal noise.

  Here, the signal transmitted from the terminal # 2 to the terminal # 1 can be given by the following equation (3).

  Signals x1 and x2 that can be given by Equations (1) and (3) correspond to reception signals input to the two antennas shown in FIG. Equations (1) and (3) are given as functions of the desired signal component s and the interference signal component i, respectively. In this case, for example, it is known that the desired signal s can be decoded by the following formula (4).

  In the above mathematical formula (4), tilde (˜) s is a decoding result of the desired signal. This is well known as an algorithm called Zero forcing. As a method of decoding a desired signal from Equations (1) and (3), in addition to this method, MMSE (Minimum Mean Square), SIC (Successive Methods such as Interference Cancellation) and MLD (Maximum Likelihood Detection) are known.

  Thus, if a distributed array is used, interference cancellation is ideally possible even with one terminal antenna. However, when interference waves from the continuous primary system arrive, the following problems occur. This problem will be described with reference to FIG. In FIG. 12, the time for transmitting a signal from the terminal # 2 to the terminal # 1 is ignored, but actually, the terminal # 2 cannot realize reception and transmission at the same time using the same frequency. That is, as shown in FIG. 13, terminal # 2 actually receives a signal using time t1, and transmits the information to terminal # 1 using time t2. Here, considering the interference wave from the continuous primary system, the interference wave i 'also arrives during the time t2, and this must actually be considered. That is, x21 is more strictly given by the following formula (5).

  Here, since a new interference component hI1i ′ is generated in Equation (5), the desired signal cannot be decoded using Equations (1) and (5). That is, when continuous interference waves are taken into account, there is a problem that the desired signal cannot be decoded with the conventional distributed array.

  Next, a problem also occurs in the above procedure 2. As described above, in principle, the primary systems 1-1 and 1-2 shown in FIG. 8 cannot recognize the secondary systems 2-1 to 2-6. 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, for example, in Reference 4 (Morikura, Kubota, “Revised 802.11 High-Speed Wireless LAN Textbook”, Chapter 4, Impress, 2004). 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 considering cognitive radio, if the primary systems 1-1 and 1-2 eventually generate intentional signals for notifying their existence, it is necessary to provide a mechanism other than normal communication. This leads to hardware complexity. Further, it is necessary to newly provide a frequency and time for transmitting this signal. This causes a problem that it becomes a factor of reducing the communication utilization efficiency of the primary systems 1-1 and 1-2.

  The present invention has been made in consideration of such circumstances, and the object thereof is to prevent deterioration of the characteristics of the secondary system and the number of terminal antenna elements, for example, one element even under interference conditions in a continuous primary system. Even so, it is to provide a communication system and a communication method capable of realizing cognitive radio.

  In order to solve the above-described problem, the present invention performs communication between a base station and at least one first communication terminal in an environment in which interference waves from other systems arrive continuously. In a communication system using a second communication terminal that is not communicating as a distributed array antenna, the base station includes two or more antenna elements, and the first communication terminal includes one antenna element. And the second communication terminal transmits the received interference wave to the first communication terminal using a signal interval that is known between communication stations of the other system. System.

  In order to solve the above-described problem, the present invention performs communication when performing communication between a base station and a first communication terminal in an environment where interference waves from other systems arrive continuously. In a communication system using a second communication terminal that has not been used as a distributed array antenna, a training section of the other system is used to transmit an interference wave of the other system between the base station and the first communication terminal. Transfer function estimation means for estimating a transfer function between the first communication terminal, between the base station and the second communication terminal, and between a transmission station of the interference wave of the other system and the second communication terminal; In the communication section of the other system, the first direction from the base station to the first communication terminal using directivity such that the received signal from the base station to the second communication terminal is almost zero. The first sender to send the signal And interference wave estimation for estimating an interference wave from the other system arriving at the communication section of the other system based on a received signal and the transfer function at the second communication terminal in the communication section of the other system And second transmission using a signal section having the same signal sequence that arrives after the training section from the second communication terminal to the first communication terminal after temporarily stopping transmission from the base station. An interference signal for estimating an interference signal in the communication section of the other system based on the second transmission means for transmitting the signal of the second signal, the second signal received by the first communication terminal, and the transfer function A communication system further comprising: estimation means; and desired signal estimation means for estimating a desired signal based on the estimated value of the interference signal, the first signal, and the transfer function.

  According to the present invention, in the above invention, the modulation system conversion means for converting the modulation signal of the interference wave estimated by the interference wave estimation means into a modulation system having a larger number of multivalues, and the estimation by the interference signal estimation means An inverse conversion unit that inversely converts the estimated value of the interference signal that has been converted into an original modulation signal before being converted by the modulation method conversion unit, and supplies the estimated signal to the desired signal estimation unit as the estimated value of the interference signal. It is characterized by doing.

  In order to solve the above-described problem, the present invention performs communication when performing communication between a base station and a first communication terminal in an environment where interference waves from other systems arrive continuously. In a communication method using a second communication terminal that has not been performed as a distributed array antenna, the base station includes two or more antenna elements, and the first communication terminal includes one antenna element. The second communication terminal transmits the interference wave received from the other system to the first communication terminal using a signal interval that is known between communication stations of the other system. Communication method.

  In order to solve the above-described problem, the present invention performs communication when performing communication between a base station and a first communication terminal in an environment where interference waves from other systems arrive continuously. In a communication method in which a second communication terminal that is not used is used as a distributed array antenna, a training section of the other system is used to transmit an interference wave between the base station and the first communication terminal and an interference wave of the other system. A transfer function estimation step for estimating a transfer function between the first communication terminal, between the base station and the second communication terminal, and between a transmission station of the interference wave of the other system and the second communication terminal; In the communication section of the other system, the first direction from the base station to the first communication terminal using directivity such that the received signal from the base station to the second communication terminal is almost zero. The first transmission station that transmits the signal And an interference that estimates an interference wave from the other system that arrives in the communication section of the other system based on the received signal and the transfer function in the second communication terminal in the communication section of the other system. A signal estimation step and a signal section having the same signal sequence that arrives after the training section from the second communication terminal to the first communication terminal after temporarily stopping transmission from the base station. Based on the second transmission step of transmitting the second signal, the second signal received by the first communication terminal, and the transfer function, an interference signal in the communication section of the other system is estimated. A communication control method comprising: an interference signal estimation step; and a desired signal estimation step for estimating a desired signal based on the estimated value of the interference signal, the first signal, and the transfer function.

  According to the present invention, in the above invention, between the interference wave estimation step and the second transmission step, the modulation signal of the interference wave estimated in the communication section is converted into a modulation scheme having a larger number of multivalues. Between the modulation scheme conversion step, and between the interference signal estimation step and the desired signal estimation step, the inverse of inversely converting the estimated value of the estimated interference signal into the original modulation signal before being converted in the modulation scheme conversion step. A conversion step.

  According to the present invention, in the above invention, when the transfer function estimating step has the training interval as L and the number of the first communication terminals as M and the number of the second communication terminals as M in the training interval, Dividing into L + M + 1, and using the divided training sections 1 to L, the directivity is controlled so that the signal to the second communication terminal becomes almost zero, and the first from the base station From the first to the Lth first communication terminal using the first section transmission step for transmitting a signal to the Lth first communication terminal and the sections L + 1 to M + L of the divided training sections The directivity is controlled so that the signal of the base station becomes almost zero, and the transmission of the base station is stopped in the second section transmission step of transmitting the signal from the base station to the second communication terminal and the section M + L + 1. , A third interval transmission step of transmitting a signal from the second communication terminal to the first communication terminal, and based on the received signal in each interval in the first to third interval transmission steps, The transfer function is estimated.

  According to the present invention, a second communication terminal that is not performing communication is used as an element on one side of a distributed array antenna, and communication is performed in a training section that is known among interference waves from other continuous systems. The interference wave information is transmitted from the second communication terminal that is not present to the first communication terminal that is performing communication. Therefore, even in the interference condition in the continuous primary system, there is an advantage that cognitive radio can be realized even if the number of terminal antenna elements is one element without degrading the characteristics of the secondary system.

  In addition, according to the present invention, the training interval of the other system is used, between the base station and the first communication terminal, between the interference wave transmitting station and the first communication terminal of the other system, and between the base station and the second communication. Estimate the transfer function between the terminals and between the transmission station of the interference wave of the other system and the second communication terminal, and the received signal from the base station to the second communication terminal becomes almost zero in the communication section of the other system The first signal is transmitted from the base station to the first communication terminal using such directivity, and the other system is based on the received signal and the transfer function in the second communication terminal in the communication section of the other system. The same signal sequence that arrives after the training interval from the second communication terminal to the first communication terminal after estimating interference waves from other systems that arrive in the communication interval of A second signal is transmitted using a signal interval having Based on the second signal received by the communication terminal and the transfer function, the interference signal in the communication section of the other system is estimated, and based on the estimated value of the interference signal, the first signal, and the transfer function, the desired signal Is estimated. Therefore, even in the interference condition in the continuous primary system, there is an advantage that cognitive radio can be realized even if the number of terminal antenna elements is one element without degrading the characteristics of the secondary system.

  Further, according to the present invention, the estimated modulation signal of the interference wave is converted into a modulation scheme having a larger multi-value number, and the estimated value of the estimated interference signal is converted into the original modulation signal before conversion. Reverse conversion. Therefore, in general, an interference signal can be transferred from the second terminal to the first terminal within the training period of the primary system, which is shorter than the data period, and cognitive radio can be realized more effectively. The advantage that it can be obtained.

  Further, according to the present invention, in the training section, when the number of first communication terminals is L and the number of second communication terminals is M in the training section, the training section is divided into L + M + 1 pieces. 1 to section L, the directivity is controlled so that the signal to the second communication terminal becomes almost zero, the signal is transmitted from the base station to the first communication terminal, and the divided training section section L + 1 Use the section M + L to control the directivity so that the signal to the first communication terminal becomes almost zero, and transmit the signal from the base station to the second communication terminal. In the section M + L + 1, the transmission of the base station , And a signal is transmitted from the second communication terminal to the first communication terminal, and the transfer function is estimated based on the received signal in each section in the first to third section transmission steps. Therefore, even in an interference condition in a continuous primary system, there is an advantage that cognitive radio can be realized even if the number of terminal antenna elements is one element without degrading the characteristics of the secondary system. .

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

A. First Embodiment FIG. 1 is a flowchart for explaining a communication method according to a first embodiment of the present invention. FIG. 2 is a conceptual diagram showing an example of the frame format of the communication signal of the Primary system in the first embodiment.

  A major feature of the present invention is that it utilizes the nature of the frame format of the communication signal of the Primary system. The frame format shown in FIG. 2 is widely used in mobile communication systems using FDD (Frequency Division Duplex). In the FDD system, assuming a certain communication, the first communication station transmits at frequency f1 and receives at frequency f2. Conversely, the second communication station receives at frequency f1 and transmits at frequency f2. The signal is basically transmitted continuously. FIG. 2 shows the transmission timing of the base station, and the base station communicates with a plurality of terminals by dividing time. At this time, since each terminal has to receive a signal only in a certain section, it is necessary to ensure timing from the base station and carrier synchronization.

  The preamble PR shown in FIG. 2 is used as information for that purpose. The preamble PR is also called a synchronization word. The preamble PR is generally not only recognized between the terminal and the base station in the Primary system, but is also publicly available. Therefore, in the same way that the secondary system can recognize in advance which frequency a certain primary system uses, in what modulation system and in what bit pattern this signal pattern is. The Secondary system can recognize in advance whether there is any. In general, the same preamble PR is used for a plurality of terminals, and the period is also the same. Therefore, it is easy for the Secondary system to recognize the preamble PR in advance.

  In the present invention, assuming the environment as shown in FIG. 13, the terminal # 2 in the idle terminal must transmit the information on the interference wave received at time T1 at time T2 different from time T1. Even if it is not, if the time T2 is set within the training section, the interference information in the training section is known, so that the interference wave newly arrived at the time T2 does not become an unknown signal for the terminal # 1. The control flow will be described below.

  In FIG. 1, first, a channel response (hereinafter referred to as a transfer function) between an AP and a terminal and between an interference (Primary system) and a terminal is estimated using the training section of the Primary system (PR1 in FIG. 2) (steps). Sa1). FIG. 3 shows a detailed implementation example. As shown in FIG. 3, here, communication is performed with a terminal TS1-Rx (hereinafter simply referred to as TS1) having a single antenna element that communicates with an access point AP-Tx (hereinafter simply referred to as AP). Consider a terminal TS2-Rx (hereinafter simply referred to as TS2) that has not gone. Also, assume an environment in which interference waves arrive continuously from a base station P-Tx (hereinafter simply referred to as P) of the Primary system.

  As shown in FIG. 3, first, the preamble PR1 is divided into three sections # 1, # 2, and # 3. In this example, since there is one terminal TS1 that performs communication and one terminal TS2 that does not perform communication, the number of divisions is 3, but this number of divisions is L for the number of terminals that perform communication, and no communication is performed. If the number of terminals is M, L + M + 1 division numbers are required.

  As described above, the terminals TS1 and TS2 can recognize the signal divided into three. These three divided signals are iP1, iP2, and iP3, respectively. In this section, a known signal SP is transmitted from the access point AP to the terminals TS1 and TS2. Also, a known signal sP is transmitted from the terminal TS2 to the terminal TS1.

  In FIG. 3, in section # 1, the directivity is controlled so that the signal to terminal TS2 becomes 0, and signal sP is transmitted. In section # 2, the directivity is controlled so that the signal to terminal TS1 becomes 0, and signal sP is transmitted. In section # 1 and section # 2, terminal TS2 is in the reception mode and does not transmit a signal. In section # 3, the access point AP stops transmitting signals and transmits signals from the terminal TS2 to the terminal TS1. With the above procedure, the received signals obtained in the sections # 1, # 2, and # 3 are given by the following equations.

  From the above equations (6) to (10), first, since iP2 is known in equation (8), the transfer function hI1 between the received signals x1, P2 and iP2 and the interference wave from the primary system to the terminal TS1. Is required. If this result is substituted into Equation (6), since sP and iP1 are known in Equation (6), the transfer function hS1 between the access point AP and the terminal TS1 is obtained. Similarly, a transfer function hI2 between the interference wave from the primary system and the terminal TS1 is obtained from Expression (7), and this result is substituted into Expression (9) to transfer the transfer function between the access point AP and the terminal TS1. hS2 is determined. Furthermore, in Formula (10), hI1 is obtained, and sP and iP3 are known, so that the transfer function h21 between the terminal TS2 and the terminal TS1 can be obtained. As described above, transfer functions between all transmissions and receptions can be obtained.

  Next, in FIG. 1, a signal is transmitted from the access point AP to the terminal TS1 in the data section of the primary system (step Sa2). It is assumed that the desired signal and the interference signal in this section are given by sD and iD, respectively. These desired signal sD and interference signal iD cannot be recognized in advance by terminals TS1 and TS2. At this time, the access point AP transmits a signal by controlling the directivity so that the received signal to the terminal TS2 becomes zero. That is, transmission is performed using the directivity (shaded portion) indicated by (section # 1) in FIG. In this case, the received signals obtained by the terminals TS1 and TS2 can be given by the following mathematical formulas (11) and (12).

  Here, since hI2 has already been obtained in the equation (12), the interference signal iD can be estimated by the following equation (13) at the terminal TS2 (step Sa3).

A tilde (˜) iD represents an interference signal in the estimated data section.
As a next procedure, as shown in FIG. 1, a signal is transmitted from the terminal TS2 to the terminal TS1 using a section after the next training section (after PR2 in FIG. 2) (step Sa4). At this time, no signal is transmitted from the access point AP. As a result, the terminal TS1 obtains a received signal represented by the following equation (14). Here, iP is an interference signal after the training section PR2 known by the terminal TS1.

  In the above formula (14), except for the tilde (˜) iD, it is estimated or known in step Sa1, so that the tilde (˜) iD can also be estimated by the terminal TS1 (step Sa5). If this estimated value is a tilde (˜) iD ′, this can be given by the following equation (15) from the equation (14).

  Finally, this result is substituted into the equation (11) of the received signal of the terminal TS1 obtained in the data section, and the desired signal is estimated (step Sa6). By transforming Equation (11), the estimated value tilde (˜) SD of the desired signal can be given by Equation (16) below.

  As described above, in the first embodiment, even in an environment where there is an interference wave from a continuous primary system such as an FDD signal, the desired signal is obtained by using the training section and idle terminal of the primary system. Can be estimated. In this case, since the interference wave can be reduced not only by the access point AP but also by one terminal antenna, when assuming a system such as FDD, interference can be canceled using the frequency transmitted by the Primary system. During transmission of the Secondary system, no interference is given to the Primary system. That is, the problem of interference with the primary system described in the conventional problem can be avoided.

  In the description so far, for the sake of simplicity of explanation, the case where there is only one communication terminal has been described, but the present invention is not limited to the case where there is only one communication terminal. Rather, the effect of the present invention is particularly effective when there are a plurality of communication terminals. This is because the communication terminal receives the same interference signal, and therefore, it is possible to simultaneously transfer the interference signal from the non-communication terminal (TS2) to the plurality of communication terminals, so that the communication terminal is simultaneously connected to the access point AP. This is because there is an advantage that a plurality of terminals can be relieved simultaneously with a single transfer of interference waves.

B. Second Embodiment Next, a second embodiment of the present invention will be described.
Although the method according to the first embodiment described above enables continuous interference cancellation using a distributed array, in practice, as shown in FIG. 2, the data interval of the primary system is generally much larger than the training interval. Use a long time. In order to ensure synchronization between the base station and the terminal, a training interval of a certain length is necessary, but if this is made too long, the communication efficiency is lowered. For example, in GSM (Global System for Mobile Communications), which is a typical example of a mobile communication system, the ratio of the data interval to the training interval is about 4: 1 to 5: 1. That is, as described above, in order to transmit data from the terminal TS2 to the terminal TS1 in the training section, some device is required in the actual system. Means for solving this will be described below.

  4A to 4C are conceptual diagrams illustrating an example of modulation scheme rearrangement in the communication method according to the second embodiment. As described above, the primary system is a system in which services have been started, and when these systems have been operated for a long time, the modulation scheme used therein is generally a modulation scheme with low frequency utilization efficiency. It is. In such a system, modulation schemes such as GMSK (Gaussian filtered Minimum Shift Keying), BPSK (Binary Phase Shift Keying), and QPSK (Quartered Phase Shift Keying) are employed. The data that can be sent per 1 symbol) is 1 to 2 bits.

  On the other hand, in a recently developed system such as a wireless local area network (LAN), not only an inefficient modulation method such as BPSK but also a modulation method with very high frequency utilization efficiency such as 16QAM (16 Quadrature Amplitude Modulation) and 64QAM. Can also be used. In 16QAM, the data that can be transmitted per one data transmission is 4 bits, and in 64QAM, the data that can be transmitted per one data transmission is 6 bits. That is, if transmission using such a high-performance modulation method can be realized in the Secondary system, a signal can be transmitted from the terminal TS2 to the terminal TS1 even in a training period shorter than the data period.

  The example shown in FIG. 4 shows the remapping of the modulation signal from BPSK shown in FIG. 4A to 16QAM shown in FIG. If the interference signal obtained by the terminal TS2 in step Sa3 in FIG. 1 is BSPK, this signal is temporarily changed to another modulation method by the terminal TS2. For example, as shown in FIG. 4C, if the obtained signal pattern is a pattern of 1, -1, 1, 1 at four times t1 to t4, the newly placed mapping is The information is rearranged at the position of 16QAM shown in 4 (c), and the information can be transmitted at a time only at time t1.

  The modulated signal rearranged in this way is transmitted from the terminal TS2 to the terminal TS1. In step Sa5 of FIG. 1 described above, an operation opposite to the previous procedure is performed on the interference signal obtained by the terminal TS1. That is, in this example, the 16QAM signal is reconverted into BSPK. By these operations, the interference wave of this BPSK signal is once converted to 16QAM, but finally returns to the original BPSK signal, and step Sa6 in FIG. 1 can be realized without any problem. The reduction rate required for this data transmission is, for example, 1/4 when converting a BPSK or GMSK signal to 16QAM and 1/6 when converting to 64QAM. When QPSK is converted to 64QAM, it becomes 1/3. Therefore, the remapping of the modulation signal according to the second embodiment plays an effective role in efficiently transmitting the interference signal from the idle terminal to the communication terminal.

  As shown in FIG. 4C, if the data can be transmitted and received between the ends by performing multi-level modulation or the like, it is possible to exchange information of the interference signal in a short training section. The amount of multi-level modulation used between the ends depends on the distance between terminals, that is, the reception level. Therefore, depending on the selection of the multi-level modulation value, the entire data section of the Primary system cannot always be used for data transmission of the Secondary system, and this section needs to be determined.

  FIG. 5 is a flowchart for explaining a method procedure for determining a data section according to the second embodiment. As a means for estimating an approximate reception level between terminals, the reception level when a signal is transmitted from the terminal TS2 (non-communication terminal) to the terminal TS1 (communication terminal) in the transfer function estimation section described in FIG. It is obtained by obtaining (step Sb1). Also, how much multi-level modulation can be used corresponds to the reception level of the system, and from this correspondence, a modulation method used for transmission / reception from terminal TS2 (non-communication terminal) to terminal TS1 (communication terminal) Is determined (step Sb2).

  FIGS. 6A and 6B are conceptual diagrams illustrating an example of a relationship between a reception level and usable modulation schemes in IEEE 802.11a. As shown in FIGS. 6A and 6B, there is a certain relationship between the reception level and the usable modulation schemes. Therefore, the modulation method used for communication can be selected according to the reception level. For example, if the reception level is -82 dBm, BPSK (R = 1/2) can be selected as the modulation method, and if the reception level is -79 dBm, QPSK (R = 1/2) can be selected as the modulation method.

  The reception level obtained here determines the number of modulation levels that can be remodulated shown in FIG. Therefore, according to the reception level of the signal transmitted from the terminal TS2 (non-communication terminal) to the terminal TS1 (communication terminal), the modulation method used by the primary system, and the training length, the access point AP actually uses the data of the primary system. It is possible to determine how long a signal can be sent to a terminal in a section. Specifically, the data section length of the Secondary system can be determined by the following formula (17).

  As described above, the data section length from the access point AP of the Secondary system to the terminal TS1 can be determined in accordance with the transfer function estimation from the terminal TS2 to the terminal TS1.

Next, a transfer function estimation method will be described.
If the transfer function estimation method described with reference to FIG. 3 is used, the transfer function can be estimated by effectively using the training interval of the Primary system. In practice, however, this interval is a terminal that does not perform communication as much as possible. I want to use it as time to transmit interference information from TS2 to terminal TS1 during communication. The following method aims to improve this point, and this method makes it possible to estimate the transfer function in the data section. The method will be described below.

  During communication from the terminal TS2 to the terminal TS1, a transfer function (time t ′) between the transmission station of the primary system and the terminal station TS1, and a transfer function between the terminal station TS2 and the terminal station TS1 (this estimation is not necessary). Is necessary to estimate iD), iD transmitted from the terminal station TS2 to the terminal station TS1 can be estimated. Thereafter, when the data signal is decoded by the terminal station TS1, a transfer function (estimated using times t and iD) between the transmitting station of the primary system and the terminal station TS1 is estimated. The data signal simultaneously estimates the transfer function between the secondary system transmitting station and the terminal station.

B. Third Embodiment Next, a third embodiment of the present invention will be described.
In the first and second embodiments described above, the primary system is assumed to be a modulation scheme with low frequency use efficiency such as BPSK or GMSK. However, when the Primary system is a relatively new system, it is conceivable to use multi-level modulation such as QAM. Further, it is considered that the primary system is not a digital signal but an analog signal such as a television broadcast. In such an environment, the data transmission time equivalent to that shown in FIG. 4 can be shortened by quantizing the data.

  FIG. 7 is a conceptual diagram showing a configuration example using a dedicated distributed array instead of an idle terminal according to the third embodiment. As described above, when transmitting and receiving interference signal information between the ends, it is desirable to complete the exchange in as short a time as possible, so it is desirable to use multilevel modulation as the method. The use of such multi-level modulation is based on the premise that the distance between terminals is quite close. As a specific example, the communication distance for transmitting a 64QAM signal in IEEE802.11a which is a wireless LAN standard is about 23 m in an indoor environment, which can be said to be quite short.

  Therefore, as shown in FIG. 7, the communication terminal 2 is not used as a distributed array, but a high gain antenna dedicated to interference reception or a plurality of antennas for a distributed array is used. As a method for improving the gain of the antenna without reducing the beam width in the horizontal plane, a method of narrowing the beam width in the vertical plane using a collinear array is used. If such an antenna is used as an interference wave receiving antenna, it is possible to increase the reception level of a signal transmitted to the communication terminal 1 as compared to the communication terminal 2. That is, there is a high possibility that information of interference signals can be transmitted by multi-level modulation.

  According to the first to third embodiments described above, a communication terminal that is not performing communication is used as an element on one side of a distributed array antenna, and is known by all stations among interference waves from a continuous Primary system. By using the training section and transmitting the interference information from the communication terminal that is not communicating to the communicating terminal during this training section, the characteristics of the Secondary system are deteriorated even in the interference condition in the continuous Primary system. Even if the number of terminal antenna elements is one element, cognitive radio can be realized.

4 is a flowchart for explaining a communication method according to the first embodiment of the present invention; It is a conceptual diagram which shows an example of the frame format of the communication signal of a Primary system in this 1st Embodiment. It is a conceptual diagram for demonstrating the method to estimate a transfer function in this 1st Embodiment. It is a conceptual diagram which shows the example of the rearrangement of the modulation system with the communication method by 2nd Embodiment of this invention. It is a flowchart for demonstrating the method procedure for determining a data area by this 2nd Embodiment. It is a conceptual diagram which shows an example of the relationship between the reception level and usable modulation system in IEEE802.11a. It is a conceptual diagram which shows the structural example which uses a dedicated distributed array instead of an idle terminal by this 3rd Embodiment. It is a conceptual diagram for demonstrating the outline | summary of a cognitive radio | wireless technique. It is a conceptual diagram for demonstrating the detection method using the periodic steadiness (Cyclostationary) of a signal. It is a block diagram which shows the basic composition of an adaptive array. It is a conceptual diagram which shows the environment to which a distributed array antenna is applied. It is a conceptual diagram which shows the structure of a distributed array antenna. It is a conceptual diagram for demonstrating the problem at the time of using a distributed array antenna.

Explanation of symbols

AP access point (base station)
TS1 communication terminal (first communication terminal)
TS2 communication terminal (second communication terminal)
PR1 to PR3 Preamble section (training section)

Claims (7)

When communicating between a base station and at least one first communication terminal in an environment where interference waves from other systems continuously arrive, a second communication terminal that is not communicating is distributed. In a communication system used as an array antenna,
The base station comprises two or more antenna elements,
The first communication terminal includes one antenna element,
The communication system, wherein the second communication terminal transmits the received interference wave to the first communication terminal using a signal interval that is known between communication stations of the other system. When communication is performed between the base station and the first communication terminal in an environment where interference waves from other systems continuously arrive, the second communication terminal that is not performing communication is used as the distributed array antenna. In a communication system,
Utilizing the training section of the other system, between the base station and the first communication terminal, between the interference wave transmitting station and the first communication terminal of the other system, the base station and the second communication terminal And transfer function estimating means for estimating a transfer function between the transmission station of the interference wave of the other system and the second communication terminal,
The first signal from the base station to the first communication terminal using directivity such that the reception signal from the base station to the second communication terminal becomes almost zero in the communication section of the other system. First transmitting means for transmitting
An interference wave estimation means for estimating an interference wave from the other system that arrives in the communication section of the other system based on a received signal and the transfer function in the second communication terminal in the communication section of the other system; ,
The transmission from the base station is temporarily stopped, and the second signal is transmitted from the second communication terminal to the first communication terminal using the signal section having the same signal sequence that arrives after the training section. A second transmitting means for transmitting;
Interference signal estimation means for estimating an interference signal of a communication section of the other system based on the second signal received by the first communication terminal and the transfer function;
A desired signal estimation means for estimating a desired signal based on the estimated value of the interference signal, the first signal, and the transfer function. A modulation system conversion means for converting the modulation signal of the interference wave estimated by the interference wave estimation means into a modulation system having a larger number of multi-values;
The estimated value of the interference signal estimated by the interference signal estimating means is inversely converted to the original modulated signal before being converted by the modulation method converting means, and supplied to the desired signal estimating means as the estimated value of the interference signal. The communication system according to claim 2, further comprising: an inverse conversion unit. When communication is performed between the base station and the first communication terminal in an environment where interference waves from other systems continuously arrive, the second communication terminal that is not performing communication is used as the distributed array antenna. In the communication method,
The base station comprises two or more antenna elements,
The first communication terminal includes one antenna element,
The second communication terminal transmits the interference wave received from the other system to the first communication terminal using a signal interval that is known between communication stations of the other system. Communication method. When communication is performed between the base station and the first communication terminal in an environment where interference waves from other systems continuously arrive, the second communication terminal that is not performing communication is used as the distributed array antenna. In the communication method,
Utilizing the training section of the other system, between the base station and the first communication terminal, between the interference wave transmitting station and the first communication terminal of the other system, the base station and the second communication terminal And a transfer function estimation step for estimating a transfer function between an interference wave transmitting station of the other system and the second communication terminal;
The first signal from the base station to the first communication terminal using directivity such that the reception signal from the base station to the second communication terminal becomes almost zero in the communication section of the other system. A first transmission step of transmitting
An interference wave estimation step of estimating an interference wave from the other system that arrives in the communication section of the other system based on a received signal and the transfer function in the second communication terminal in the communication section of the other system; ,
The transmission from the base station is temporarily stopped, and the second signal is transmitted from the second communication terminal to the first communication terminal using the signal section having the same signal sequence that arrives after the training section. A second transmitting step for transmitting;
An interference signal estimation step of estimating an interference signal of a communication section of the other system based on the second signal received by the first communication terminal and the transfer function;
A desired signal estimating step of estimating a desired signal based on the estimated value of the interference signal, the first signal, and the transfer function. A modulation method conversion step for converting the modulation signal of the interference wave estimated in the communication section into a modulation method having a larger number of multi-values between the interference wave estimation step and the second transmission step;
An inverse conversion step of inversely converting the estimated value of the estimated interference signal into an original modulation signal before being converted in the modulation scheme conversion step between the interference signal estimation step and the desired signal estimation step; The communication method according to claim 5. The transfer function estimation step includes:
In the training section, when the number of the first communication terminals is L and the number of the second communication terminals is M, the training section is divided into L + M + 1 pieces, and the divided training sections 1 to 5 L is used to control the directivity so that the signal to the second communication terminal becomes almost zero, and the base station transmits a signal from the first to the Lth first communication terminal. A section transmission step of
Using the divided training sections L + 1 to M + L, the directivity is controlled so that the signal from the first to the Lth first communication terminal becomes almost zero, and the second from the base station A second section transmission step of transmitting a signal to the communication terminal;
Section M + L + 1 includes a third section transmission step of stopping transmission of the base station and transmitting a signal from the second communication terminal to the first communication terminal,
6. The communication method according to claim 5, wherein the transfer function is estimated based on a received signal in each section in the first to third section transmission steps.

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