JP4654625B2 - Wireless communication system, wireless communication apparatus, wireless communication method, and computer program - Google Patents

Description

  The present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program for performing mutual communication between a plurality of wireless stations such as a wireless LAN (Local Area Network), and more particularly to a plurality of antennas. The present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program that perform data communication using spatial multiplexing by giving arbitrary antenna weights to each other.

  More specifically, the present invention relates to a radio communication system and a radio communication system that perform multi-antenna communication using more appropriate antenna characteristics by performing calibration so that each antenna obtains an appropriate antenna weight in a communication station having a multi-antenna configuration. The present invention relates to a communication apparatus, a wireless communication method, and a computer program. In particular, even in a communication environment where a plurality of communication stations coexist, even during the operation period of a communication system, the influence of interference waves or interference waves from peripheral stations. The present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program in which a communication station having a multi-antenna configuration performs accurate calibration without receiving a signal.

  Information network sharing and device resource sharing can be efficiently realized by computer networking such as a LAN. Here, wireless communication has attracted attention as a system that releases users from the conventional wired LAN connection. According to wireless communication, most of the wired cables can be omitted in a work space such as an office, so that a communication terminal such as a personal computer (PC) can be moved relatively easily.

  In recent years, the demand for wireless LAN systems has increased remarkably with the increase in speed and cost. In particular, the introduction of a personal area network (PAN) has been studied in order to construct a small-scale wireless network between a plurality of electronic devices existing around a person and perform information communication. For example, different radio communication systems and radio communication apparatuses are defined using frequency bands that do not require a license from a supervisory agency, such as 2.4 GHz band and 5 GHz band.

  As a standard for wireless networks, IEEE (The Institute of Electrical and Electronics Engineers) 802.11 (for example, refer to Non-Patent Document 1), HiperLAN / 2 (for example, Non-Patent Document 2 or Non-Patent Document) 3), IEEE802.15.3, Bluetooth communication, and the like. As for the IEEE 802.11 standard, there are extended standards or higher standards such as IEEE 802.11a (for example, refer to Non-Patent Document 4), b, g..., Depending on a wireless communication system or a frequency band to be used.

  Here, in a wireless communication environment where a plurality of communication stations exist within one communication range, in order to increase the communication capacity with a small amount of resources, it is necessary to detect which signal belongs to which user and access. Multiple access control technology to control is needed.

  As one of the multiple access control technologies, a system that realizes spatial multiplexing called SDMA (Space Division Multiple Access) has been developed. For example, in an adaptive array antenna constituted by a plurality of antenna elements, reception beam forming is adaptively performed by appropriately weighting and adding and combining received signals received by the respective antenna elements (that is, By changing the directivity adaptively, simultaneous communication with a plurality of opponents can be realized and the communication capacity can be increased (for example, see Non-Patent Document 5).

  A basic adaptive array antenna configuration is realized by having an RF unit independently for each antenna, and multiplying a signal from each RF unit by a weighting factor for each antenna. Each weighting factor is usually realized by a digital part, and its value is calculated by a digital signal processing part. As a specific weight calculation method, a least square method (RLS (Recursive Least Squares) algorithm) or the like is representative. When the RLS algorithm is operated, learning is performed by simultaneously receiving a desired wave and an interference wave as inputs and further inputting a known desired wave signal as a teacher signal of the RLS algorithm. The adaptive array antenna after learning changes to a characteristic that receives only a desired wave and does not receive an interference wave.

  The IEEE802.11a standard supports a modulation scheme that achieves a communication speed of 54 Mbps at the maximum, but a wireless standard capable of realizing a higher bit rate is required. For example, IEEE802.11n is examining MIMO (Multi-Input Multi-Output) communication as one of high-speed wireless LAN technologies with effective throughput exceeding 100 MBPS. MIMO communication includes a plurality of antenna elements on both the transmitter side and the receiver side, and realizes a spatially multiplexed transmission path (hereinafter also referred to as “MIMO channel”), thereby expanding the transmission capacity and enabling communication. A technology that achieves speed improvements. Since MIMO communication uses spatial multiplexing, frequency utilization efficiency is good.

  In MIMO transmission, whether to exchange channel information between transmission and reception according to the antenna configuration is an implementation issue. For example, it is possible to create an ideal spatial orthogonal channel between transmission and reception by transmitting the channel information from the transmission side to the reception side only, or by transmitting the preamble information from the reception side to the transmission side. There is also a closed-loop type MIMO transmission system. As an example of the former, V-BLAST (Vertical Bell Laboratories Layered Space Time) (for example, refer to Patent Document 2) can be cited. As the latter example, an SVD-MIMO scheme using singular value decomposition (SVD) of a propagation path function is known (see, for example, Non-Patent Document 6).

  SDMA and MIMO communication are similar in that spatial multiplexing is performed by giving an arbitrary antenna weight to each of the transmitter and the receiver, and the communication capacity of the transmission path is increased. In this type of multi-antenna communication system, it is extremely important for the communication device to set an appropriate antenna weight for each antenna branch.

  For example, in a communication system in which one or more terminal stations (STAs) perform communication under the control of a control station called an access point (AP), when the AP and the STA start communication, the AP transmits to the STA, and the STA transmits to the AP. Each transmits a training signal. Then, a weight value for multiplying each antenna branch is calculated from the training signals received by both the AP and the STA so that spatial multiplexing can be performed.

  If the weight value can be calculated in this way, the received signal can be multiplexed (MIMO) or separated (SDMA) by multiplying each antenna branch by the weight value. That is, in the MIMO communication, a plurality of MIMO channels with higher orthogonality are secured, and the communication capacity increases. In the case of SDMA, the adaptive array antenna can minimize the influence of the interference wave and can receive only the desired wave.

  Next, when obtaining the weight value at the time of transmission, the error value of the transfer function between the transmission unit and the reception unit is corrected (hereinafter referred to as “calibration”) from the weight value obtained at the time of reception.

  The basic calibration operation in a multi-antenna system is that each antenna branch alternately becomes a starting branch, broadcasts calibration data, and receives and calibrates the other antenna branches. It is one of.

  For example, each antenna branch is alternately set as a base branch, the transmission circuit and the reception circuit of only the origin branch are controlled, and the transmission setting gain and the reception setting gain are adjusted to be smaller than those during normal communication, and the forward transfer function The information and the reverse transfer function information are measured, and a calibration coefficient of the transmission path characteristic with respect to the starting branch is obtained. Further, by dividing the obtained calibration coefficients using the antenna branch other than the origin branch as a reference branch, the gain adjustment component of the origin branch can be removed, and a calibration coefficient having an appropriate transmission path characteristic can be obtained. (For example, see Patent Document 2). In this case, it is possible to realize calibration of the array antenna for both transmission and reception having an appropriate transmission and reception characteristic by performing a proper calibration process with a simple configuration and at a low cost.

  The calibration processing is necessary for securing a plurality of highly orthogonal MIMO channels in MIMO communication or removing the influence of interference waves in SDMA. Therefore, it is desired to perform calibration at any time not only at the start of communication but also during operation of the communication system, that is, when each communication station is operating.

  However, in the above method of broadcasting a calibration signal from the starting branch, the communication station that performs calibration eliminates the interference wave from the peripheral station that is performing the communication operation and transmits the calibration signal between its own antennas. It is necessary to send and receive with.

  Patent Document 2 described above discloses a self-contained calibration process itself based on an operation of transmitting and receiving a calibration signal between a start branch and another branch in a communication device having a multi-antenna configuration. No mention is made of the system operation of how to eliminate the interference wave of the peripheral station and broadcast the calibration signal during the operation period of the communication system.

  IEEE802.11a, which is a conventional wireless LAN standard, does not define a function for a communication station to broadcast a calibration signal. On the other hand, it is unclear whether or not the communication station adopts a function of broadcasting a calibration signal in IEEE802.11n that increases the speed of a wireless LAN by MIMO transmission. In addition, since IEEE802.11n uses the same frequency of 5 GHz band as IEEE802.11a, it does not cause malfunction of these conventional terminals in a communication environment where IEEE802.11a conventional terminals coexist, that is, with conventional terminals. Preferably, it is a system operation that broadcasts calibration signals in a compatible form.

Japanese Patent Laid-Open No. 10-84324 JP 2003-264492 A International Standard ISO / IEC 8802-11: 1999 (E) ANSI / IEEE Std 802.11, 1999 Edition, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layers (PH) ETSI Standard ETSI TS 101 761-1 V1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part1: BasicControl ETSI TS 101 761-2 V1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part2: Radio Link Control (LC) Supplement to IEEE Standard for Information technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5GHZ Band Nobuyoshi Kikuma, “Adaptive signal processing by array antenna” (Science Description Publishing, ISBN 4-87653-054-8) http: // radio3. ee. uec. ac. jp / MIMO (IEICE_TS). pdf (as of October 24, 2003)

  An object of the present invention is to provide an excellent radio communication system, radio communication apparatus, radio communication method, and computer program capable of suitably performing data communication using spatial multiplexing by a communication station having a multi-antenna configuration. It is in.

  A further object of the present invention is to perform calibration so that each antenna obtains an appropriate antenna weight in a communication station having a multi-antenna configuration, and can realize multi-antenna communication using more appropriate antenna characteristics. A wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program are provided.

  A further object of the present invention is to perform calibration by a communication station having a multi-antenna configuration by alternately setting each antenna branch as a starting branch and receiving a calibration signal broadcast from the starting branch at another antenna branch. It is an object to provide an excellent wireless communication system, wireless communication apparatus, wireless communication method, and computer program.

  A further object of the present invention is to provide a multi-antenna communication without being affected by interference waves or interference waves from neighboring stations even during the operation period of the communication system in a communication environment in which a plurality of communication stations coexist. An object of the present invention is to provide an excellent wireless communication system, wireless communication apparatus and wireless communication method, and computer program that enable a station to perform accurate calibration by broadcasting a calibration signal.

The present invention has been made in consideration of the above problems, and the first aspect thereof is
The RTS / CTS method is used in combination with the RTS / CTS method in which the data transmission source communication station transmits the transmission request packet RTS and the data transmission destination communication station starts to transmit data in response to receiving the confirmation notification packet CTS. A wireless communication system in which a plurality of communication stations including communication stations perform communication operations,
The communication station of the multi-antenna configuration is
A plurality of antenna elements for transmitting and receiving signals;
A radio unit for processing radio signals to be transmitted and received based on a predetermined transfer function;
A modulation / demodulation unit for modulating / demodulating transmission / reception frames;
A control unit for controlling frame processing and transmission / reception calibration operation in the radio unit,
The control unit transmits an RTS signal or a CTS that describes a transmission waiting period for transmitting and receiving a calibration signal between the antenna and the branch, and performs calibration while the peripheral station stops transmission during the transmission waiting period . Do the
This is a wireless communication system.

  However, “system” here refers to a logical collection of a plurality of devices (or functional modules that realize specific functions), and each device or functional module is in a single housing. It does not matter whether or not.

  In a multi-antenna communication apparatus, it is desired to perform calibration at any time not only at the start of communication but also during operation of the communication system, that is, while each communication station is operating. However, in the technique of broadcasting the calibration signal from the starting branch, in order to perform more accurate calibration, the interference signal from the peripheral station is eliminated and the calibration signal is transmitted and received between the antennas of the own station. There is a need.

  On the other hand, according to the present invention, since a communication station having a multi-antenna configuration performs calibration using the reserved band after the band is reserved, it is affected by interference waves or interference waves from peripheral stations. Therefore, accurate calibration can be performed by transmitting and receiving a calibration signal between the antenna and the branch.

Communication station of a multi-antenna configuration, by connecting a training signal for calibration control frame for securing the band may be performed at the same time transmitting and receiving calibration and transmission of the control frame.

  Also, in a communication system in which random access to obtain transmission rights after the communication station monitors the media clear state for a predetermined period of time, the communication station with the multi-antenna configuration checks the media clear state and then performs random access. A transmission right can be acquired according to the procedure, and a control frame for calibration can be transmitted.

  Further, communication using an RTS / CTS method in which a data transmission source communication station transmits a transmission request packet RTS and starts data transmission in response to receiving a confirmation notification packet CTS from the data transmission destination communication station. In the system, a communication station having a multi-antenna configuration transmits an RTS signal or a CTS signal that describes a transmission standby period for transmitting and receiving a calibration signal between antennas and branches, and the peripheral station stops transmission during the transmission standby period. Calibration may be performed during the operation.

  In the calibration method in which the starting branch is alternately set and the calibration signals are transmitted to each other, the time required for calibration becomes longer depending on the number of antenna elements. Therefore, the transmission standby period Duration described in the RTS signal or the CTS signal may be determined according to the number of antenna elements that require calibration.

  A communication station with a multi-antenna configuration generates a control frame when a predetermined condition is satisfied, modulates and demodulates the control frame, up-converts it to a radio signal, sends it omni-directionally, and completes transmission of the control frame. Perform transmission / reception calibration.

  Here, a communication station having a multi-antenna configuration may perform transmission / reception calibration on the condition that a certain period has elapsed. Also, for the calibration operation, the transmission / reception calibration should be performed on the condition that the congestion level of the media is not more than a predetermined value so that the normal communication operation of the peripheral station is prevented and the transmission efficiency is not lowered. Also good.

The second aspect of the present invention is
Computer-readable so that processing for performing transmission / reception calibration in a wireless communication apparatus having a plurality of antenna elements that perform communication operations and perform signal transmission / reception in a communication environment in which a plurality of communication stations coexist is executed on a computer. A computer program written in a format,
In the communication environment, there is an RTS / CTS method in which a data transmission source communication station transmits a transmission request packet RTS and starts data transmission in response to receiving a confirmation notification packet CTS from the data transmission destination communication station. Used together
For the computer
A procedure for transmitting an RTS signal or a CTS signal in which a transmission waiting period for transmitting and receiving a calibration signal between the antenna and the branch is described;
A procedure for performing transmission and reception calibration while the peripheral station stops transmission in the transmission waiting period ;
Is a computer program characterized in that

The computer program according to the second aspect of the present invention defines a computer program described in a computer-readable format so as to realize predetermined processing on the computer. Other words, cooperative operation in the computer by the computer program according to the second aspect to install on the computer of the present invention is exhibited, it operates as a wireless communication device. By activating a plurality of such wireless communication devices to construct a wireless network, the same operational effects as those of the wireless communication system according to the first aspect of the present invention can be obtained.

  According to the present invention, there are provided an excellent radio communication system, radio communication apparatus, radio communication method, and computer program capable of suitably performing data communication using spatial multiplexing by a communication station having a multi-antenna configuration. Can do.

  Further, according to the present invention, calibration is performed so that each antenna obtains an appropriate antenna weight in a communication station having a multi-antenna configuration, and multi-antenna communication using more appropriate antenna characteristics can be realized. A wireless communication system, a wireless communication device, a wireless communication method, and a computer program can be provided.

  Further, according to the present invention, a communication station having a multi-antenna configuration alternately sets each antenna branch as a starting branch, receives a calibration signal broadcast from the starting branch at another antenna branch, and performs calibration. An excellent wireless communication system, wireless communication apparatus, wireless communication method, and computer program that can be performed can be provided.

  Further, according to the present invention, in a communication environment in which a plurality of communication stations are mixed, even in the operation period of the communication system, the multi-antenna configuration is not affected by the interference wave or the interference wave from the peripheral station. An excellent wireless communication system, wireless communication apparatus, wireless communication method, and computer program in which a communication station performs accurate calibration by broadcasting a calibration signal can be provided.

  According to the present invention, the communication station that performs calibration can secure a band necessary for broadcasting the calibration signal from the starting branch, so even in a communication environment in which a plurality of communication stations are mixed. A communication station having a multi-antenna configuration can perform accurate calibration by broadcasting a calibration signal without being affected by interference waves or interference waves from neighboring stations.

  In addition, according to the present invention, a communication station that performs calibration can broadcast a calibration signal after securing a band based on the RTS / CTS procedure. Thus, an accurate calibration process can be performed while eliminating the influence of the interference wave. Since IEEE802.11a also employs the RTS / CTS procedure, even in a communication environment in which IEEE802.11a-based conventional terminals coexist, an extended standard or a higher-standard communication station can communicate with these conventional terminals. The calibration signal can be broadcast in a compatible form.

  For example, a communication station that performs calibration temporarily stops transmission of peripheral stations by transmitting a CTS (CTS-to-Self) signal addressed to itself, and performs calibration without receiving interference from other stations. Can be performed. Since the IEEE802.11a-based conventional terminal can also recognize the CTS signal, transmission can be waited for the calibration process without causing a malfunction.

  Other objects, features, and advantages of the present invention will become apparent from more detailed description based on embodiments of the present invention described later and the accompanying drawings.

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

A. System Configuration The communication propagation path assumed in the present invention is wireless, and a network is constructed among a plurality of communication stations. The communication assumed in the present invention is a storage and exchange type traffic, and information is transferred in units of packets.

  In one embodiment of the present invention, for example, a conventional communication station conforming to IEEE802.11a and a communication station using a MIMO communication scheme conforming to IEEE802.11n corresponding to its extended standard or higher standard, or the same frequency channel in the 5 GHz band is used. A communication environment is assumed in which multi-antenna communication stations such as MIMO or SDMA operate in a mixed manner.

  A communication station having a multi-antenna configuration can realize efficient data transmission by spatial multiplexing. However, it is necessary to perform a calibration process for correcting an error in the transfer function between the transmission unit and the reception unit in each antenna branch every predetermined period. Here, it is assumed that a communication station having a multi-antenna configuration alternately sets each antenna branch as a starting branch, and receives a calibration signal broadcast from the starting branch at another branch to perform calibration.

  First, a communication operation in the IEEE 802.11 communication system will be described.

  In IEEE 802.11, CSMA is adopted as a basic media access procedure, and before the transmitter transmits anything, a back-off timer is monitored over a random time while monitoring the media state for a predetermined frame interval. The transmission right is given only when there is no transmission signal during this period. In IEEE 802.11, four types of frame intervals (IFS: Inter Frame Space), SIFS (Short IFS), PIFS (PCF IFS), and DIFS (DCF IFS), are defined in order from the shortest.

  When a normal packet is transmitted according to the CSMA procedure, the DCF (called Distributed Coordination Function) must first monitor the media status for only DIFS after transmission of some packet, and there must be no transmission signal during this period. For example, a transmission right is given when random backoff is performed and there is no transmission signal during this period.

  Further, when an exceptionally urgent packet such as ACK is transmitted, it is allowed to transmit the packet after a shorter frame interval called SIFS. As a result, a packet with a high degree of urgency can be transmitted before a packet transmitted in accordance with a normal CSMA procedure.

  In short, the reason why different types of frame interval IFS are defined is that priority is given to packet transmission right contention depending on whether the IFS is SIFS, PIFS, or DIFS, that is, the length of the frame interval.

  FIG. 1 illustrates a communication procedure based on CSMA / CA. In the illustrated example, it is assumed that there are four communication stations # 0 to # 3 in the communication environment.

  Each communication station having transmission data monitors the media state for a predetermined frame interval DIFS (DCF (Distributed Coordination Function) Inter Frame Space) since the last packet detection, during which the media is cleared, that is, there is a transmission signal. Otherwise, random back-off is performed, and when there is no transmission signal during this time, a transmission right is given.

  In the illustrated example, after monitoring the media state for the frame interval DIFS, the communication station # 0 that has set a random backoff shorter than other peripheral stations acquires the transmission right and starts data transmission to the communication station # 1. be able to.

  At the time of this data transmission, the source communication station # 0 stores information on the use of the NAV (Network Allocation Vector) in the Duration field of the MAC frame header (MAC header), and the data communication transaction ends. The time until is written.

  The communication station # 1, which is the transmission destination of this data frame, performs an operation of receiving data addressed to itself for the duration of Duration described in the MAC header. When the data reception is completed, an ACK packet is returned to the data transmission source communication station # 0.

  Further, the communication stations # 2 and # 3 other than the data transmission destination that received the data frame decode the description in the Duration field of the MAC header, and the medium is occupied without monitoring the medium until the transaction ends. The transmission is stopped by recognizing This work is referred to as “performing a NAV” by a peripheral station. The NAV is valid for the period indicated in the Duration field. For example, a period until the receiving communication station # 1 returns an ACK packet is designated as Duration.

  In this way, according to the CSMA / CA scheme, a single communication station acquires a transmission right while avoiding contention, and a peripheral station stops the data transmission operation during the period of data communication operation. Can be avoided.

  In IEEE 802.11, in order to solve the hidden terminal problem, the RTS / CTS communication method is used in combination with random access control based on CSMA. In the RTS / CTS method, in response to a data transmission source communication station transmitting a transmission request packet RTS (Request To Send) and receiving a confirmation notification packet CTS (Clear To Send) from the data transmission destination communication station. Start data transmission. The hidden terminal for the transmitting station receives the CTS and sets the transmission stop period to avoid collision with the data packet, the hidden terminal for the receiving station receives the RTS and stops the transmission period, and the ACK To avoid collisions.

  FIG. 2 shows an operation example of the RTS / CTS procedure. However, in the wireless communication environment, it is assumed that there are four communication stations # 0 to # 3 in the communication environment. Communication station # 2 can communicate with adjacent communication station # 0, communication station # 0 can communicate with adjacent communication stations # 1 and # 2, and communication station # 1 can communicate with adjacent communication station # 0. , # 3 can communicate with each other, and the communication station # 3 can communicate with the adjacent communication station # 1. However, communication station # 2 is a hidden terminal for communication station # 1, and communication station # 3 is a hidden terminal for communication station # 0.

  Each communication station having transmission data monitors the media state for a predetermined frame interval DIFS since the last packet detection, and during this time the media is cleared, i.e. if there is no transmission signal, a random backoff is performed, Further, when there is no transmission signal during this period, a transmission right is given.

  In the illustrated example, after monitoring the media state for the frame interval DIFS, the communication station # 0 that has set a random backoff shorter than other peripheral stations acquires the transmission right and starts data transmission to the communication station # 1. be able to.

  That is, a transmission request packet (RTS) is transmitted from the communication station # 0 that transmits data to the communication station # 1. On the other hand, the communication station # 1, which is the reception destination, returns a confirmation notification (CTS) to the communication station # 0 with a shorter frame interval SIFS. Then, in response to receiving the CTS packet, the communication station # 0 starts transmission of the data packet with a frame interval SIFS. Further, when the reception of the data packet is completed, the communication station # 1 returns an ACK packet with a frame interval SIFS. Since SIFS is shorter than DIFS, communication station # 1 can transmit a CTS packet prior to another station that obtains a transmission right by waiting for DIFS + random backoff according to the CMSA / CA procedure.

  At this time, the communication station # 2 and the communication station # 3, which are positions that can be hidden terminals from both the communication station # 0 and the communication station # 1, detect the use of the transmission path by receiving RTS or CTS and perform this communication. Control is performed so that transmission is not performed until the processing is completed.

  Specifically, the communication station # 2 detects that the data transmission starting from the communication station # 1 is started based on the RTS packet, decodes the description in the Duration field of the MAC header of the RTS packet, Thereafter, until the transmission of the subsequent data packet is completed (period until the ACK is completed), it is possible to recognize that the transmission path is already used and to establish the NAV.

  In addition, the communication station # 3 detects that the data transmission to be received by the communication station # 1 is started based on the CTS packet, decodes the description of the Duraton field in the MAC header of the CTS packet, and subsequently continues the data -Until the packet transmission is completed (a period until the ACK is completed), it is possible to recognize that the transmission path is already used and to establish a NAV.

  As described above, when the hidden terminal receives at least one of RTS and CTS, the transmission stop period of the own station is set only during a period in which data transmission based on the RTS / CTS procedure is expected to be performed, thereby avoiding a collision. be able to.

  However, as described above, when the period until the end of the RTS / CTS procedure (that is, the period until the ACK) is specified as Duration, even if the RTS / CTS procedure breaks down in the middle, the peripheral station is not until the end. It must wait and waste communication resources. Therefore, a mechanism called Short NAV is also conceivable. In Short NAV, RTS, CTS, and data packets are reserved as Duration only until the end of the next packet. For example, the RTS packet secures the duration until the end of the CTS packet, the CTS packet until the end of the data packet, and the data packet until the end of the ACK packet. Therefore, when the RTS / CTS procedure fails midway, the peripheral station does not need to wait until the end of the transaction.

B. Calibration In a wireless communication environment in which a plurality of communication stations exist within one communication range, a spatial multiple access technique realized by a multi-antenna configuration is applied to expand communication capacity with a small amount of resources. .

  For example, in SDMA, adaptive beam forming is adaptively performed by appropriately weighting and adding and combining received signals received by each antenna element in an adaptive array antenna, and simultaneous communication with a plurality of partners. And the communication capacity can be increased. Also, in MIMO communication, by providing a plurality of antenna elements on both the transmitter side and the receiver side and obtaining a plurality of spatially multiplexed MIMO channels, transmission capacity can be expanded and communication speed can be improved. .

  In this type of multi-antenna communication system, the communication device sets an appropriate antenna weight for each antenna branch. Further, when obtaining a weight value at the time of transmission, it is necessary to perform correction of an error in the transfer function between the transmission unit and the reception unit, that is, calibration from the weight value obtained at the time of reception.

  Each antenna branch alternately becomes a starting branch, broadcasts calibration data, and is received by another antenna branch, whereby transmission / reception calibration can be performed.

  FIG. 3 schematically shows a configuration of a multi-antenna wireless communication apparatus having a calibration function. The wireless communication apparatus performs spatial multiplexing communication using a communication method such as SDMA or MIMO. However, regardless of which spatial multiplexing method is employed, the calibration function according to the present invention can be applied, and the spatial multiplexing method itself is not directly related to the mode of the present invention. The book does not explain any more.

  The illustrated wireless communication apparatus 10 includes a plurality of antenna elements 11 that transmit and receive signals, a wireless unit 12 that processes wireless signals to be transmitted and received based on a predetermined transfer function, and a modem unit 13 that performs modulation and demodulation of transmission and reception frames. A weight multiplier 14 for multiplying the transmission / reception signal for each antenna branch by a weight value; and a weight-multiplied received signal for each antenna branch for parallel / serial conversion to assemble a frame, or a transmission frame for an antenna branch A P / S and S / P converter 15 that performs serial / parallel conversion on each transmission signal, a codec 16 that encodes and decodes transmission / reception frames, and a controller 17 that controls the overall operation of the apparatus 10. Consists of. It should be noted that transmission data is given from the upper layer of the communication protocol to the codec unit 16, and the received data decoded by the codec unit 16 is passed to this upper layer, but the upper layer protocol itself is not directly related to the gist of the present invention. Not shown.

  In the present embodiment, the control unit 17 controls the transmission / reception calibration operation in the wireless unit 12 in addition to the transmission / reception frame processing.

  When the predetermined condition is satisfied, the control unit 17 instructs the control frame generation unit 18 to generate a control frame. The control frame generation unit 18 generates a control frame including a training signal for performing transmission / reception calibration. This control frame is serial / parallel converted to the transmission signal for each antenna and branch, multiplied by the weight value for each antenna, modulated and demodulated by the modulation / demodulation unit 13, and transmitted in a non-directional manner from the radio unit 12 and each antenna element 11 over a wide range. Is done. The control frame received by the antenna element 11 is decoded by the codec unit 16, extracted by the control frame extraction unit 19, and passed to the control unit 17. Then, after completing the transmission of the control frame, the control unit 17 instructs the wireless unit 12 to perform transmission / reception calibration.

  Calibration operation. For example, each branch is alternately set as a base branch, the transmission circuit and the reception circuit of only the starting branch are controlled, and the transmission setting gain and the reception setting gain are adjusted so as to be smaller than those during normal communication, and forward transfer function information and The reverse transfer function information is measured, and the calibration coefficient of the transmission path characteristic with respect to the starting branch is obtained. Further, by dividing the obtained calibration coefficients using the antenna branch other than the origin branch as a reference branch, the gain adjustment component of the origin branch can be removed, and a calibration coefficient having an appropriate transmission path characteristic can be obtained. (For example, see Patent Document 2). According to such a calibration operation, it is possible to realize calibration of an array antenna for both transmission and reception having an appropriate transmission / reception characteristic by performing a proper calibration process with a simple configuration and at a low cost.

  The wireless communication device 10 calculates the weight value of each antenna branch after power-on and performs transmission / reception calibration. Thereafter, the normal communication system is operated. However, the calibration is performed at certain time intervals due to the influence of heat generated by the communication operation, especially considering the variation of the circuit transfer function of the radio unit 12 composed of analog circuits. Is preferably performed.

  Here, in the above-described method of broadcasting a calibration signal from the origin branch to another antenna branch, the wireless communication device that performs calibration eliminates the interference wave from the peripheral station that is performing the communication and performs calibration. If the calibration signal is not transmitted and received between the antennas of the local station, accurate calibration processing cannot be performed.

  Therefore, in the present embodiment, when performing calibration, the wireless communication device 10 secures a band and transmits and receives calibration signals between antennas and branches using a period in which the peripheral station has stopped transmitting. To perform the calibration process.

  For example, after transmitting a control frame for securing a band, the wireless communication device 10 can execute a calibration process after securing the band. Then, by connecting the training signal for calibration to the control frame, transmission / reception calibration can be executed simultaneously with the transmission of the control frame.

  For example, in a communication system that performs random media access control based on CSMA as illustrated in FIG. 1, the wireless communication device 10 may transmit a control frame for executing calibration processing by random access. Yes. That is, the media state is monitored for a predetermined frame interval DIFS since the last packet detection. If the media is cleared during this period, that is, if there is no transmission signal, random backoff is performed. If it does not exist, it is possible to obtain a transmission right and transmit a control frame.

  Here, in the Duration field of the MAC header of the transmission frame, the time until the end of the data communication transaction is recorded as information on the use of the NAV. In normal data transmission, the duration until the ACK packet is returned from the data transmission destination communication station to the data transmission source communication station is described in Duration.

  On the other hand, in the control frame for performing the calibration process, the Duration field describes a transmission standby period during which a calibration signal is transmitted and received between the antenna and the branch. As a result, it is possible to transmit and receive the calibration signal between the antennas of the own station while eliminating the interference wave from the peripheral station during the communication operation.

  In the calibration method in which the start branch is alternately set and the calibration signals are transmitted to each other, the time required for calibration becomes longer according to the number of antenna elements. Therefore, the transmission standby period Duration may be determined according to the number of antenna elements that require calibration.

  In the communication system using the RTS / CTS procedure as shown in FIG. 2, the radio communication apparatus 10 may transmit a control frame for executing the calibration process in the form of an RTS signal or a CTS signal. it can.

  When a control frame is transmitted as an RTS signal, the media state is monitored for a predetermined frame interval DIFS since the last packet detection, and during this time the media is cleared, that is, if there is no transmission signal, random backoff is performed. In addition, when there is no transmission signal during this period, a transmission right can be obtained and a control frame as an RTS signal can be transmitted.

  Also, when transmitting as a CTS signal, the media state is monitored for a shorter frame interval SIFS since the last packet detection. If the media is cleared during this period, that is, if there is no transmission signal, the transmission right is obtained and the CTS is acquired. A control frame as a signal is transmitted.

  In the normal RTS / CTS procedure, the communication station transmits a CTS signal triggered by the reception of the RTS signal addressed to itself. Here, however, the CTS signal can be transmitted without receiving the RTS addressed to itself. May be defined separately. Since the CTS signal for performing calibration is transmitted from the starting branch of the own station to another antenna branch, that is, a CTS signal addressed to the own station, it is also referred to as “CTS-to-selt” below.

  FIG. 4 shows a frame configuration example of an RTS or CTS-to-self signal transmitted as a control frame. As shown, the frame includes a frame control field, a duration field, a receiver address field, and a frame check sequence (FCS) field.

  In the frame control field, information indicating the type of the frame, that is, RTS or CTS-to-self is described.

  In the Duration field, a period in which a communication station other than the reception destination that received the frame should stop the transmission operation is described.

  In the case of a normal RTS or CTS signal, the period until the transaction performed in accordance with the RTS / CTS procedure is completed (that is, the period until the ACK is transmitted from the data receiving destination), or the next packet resulting from RTS or CTS The period until the transmission of (in the case of Short NAV (described above)) is described.

  On the other hand, in the case of RTS or CTS-to-self transmitted to execute calibration, the Duration field describes a transmission waiting period for transmitting and receiving a calibration signal between the antenna branches. The As a result, it is possible to transmit and receive the calibration signal between the antennas of the own station while eliminating the interference wave from the peripheral station during the communication operation. In the calibration method in which the start branch is set alternately and the calibration signals are transmitted to each other, the time required for calibration increases depending on the number of antenna elements, so the number of antenna elements that need to be calibrated The duration may be determined according to the above (same as above).

  In Receiver Address, in normal data transmission, a data transmission destination (in the case of RTS) or an RTS transmission source (in the case of CTS) is described. In this case, since there is no data transmission partner and the communication station that is the transmission source of the control frame is used alone, the address of the own station is described.

  Information for error correction of the frame is described in the frame check sequence field.

  Furthermore, calibration training data is connected. Thereby, transmission / reception calibration can be executed simultaneously with the transmission of the control frame.

  The wireless communication device 10 calculates the weight value of each antenna branch after power-on and performs transmission / reception calibration. Further, after that, it is preferable to perform calibration at certain time intervals in consideration of fluctuations in the circuit transfer function of the wireless unit 12 due to the influence of heat generated by the communication operation.

  On the other hand, due to the calibration operation, the normal communication operation of the peripheral station may be hindered, and transmission efficiency may be reduced. Therefore, the wireless communication device 10 may perform transmission / reception calibration on the condition that the degree of media congestion is not more than a predetermined value.

  FIG. 5 shows a processing procedure for starting the calibration operation in the form of a flowchart.

  The channel usage is monitored, and the number of times the NAV is set by the peripheral station per time is counted (step S1).

  When the time to start calibration arrives, it is determined whether or not the counted number of NAV settings is less than a predetermined threshold value n (step S2).

  If the number of NAV settings is greater than the threshold value n, it is determined that the channel is congested, and the execution of calibration is postponed (step S3).

  If the number of NAV settings is equal to or less than the threshold value n, it is determined that the channel is not congested, and calibration is executed (step S4).

  IEEE802.11a, which is a conventional wireless LAN standard, does not define a function for a communication station to broadcast a calibration signal. In IEEE802.11n using the same 5 GHz frequency band as that of IEEE802.11a, it is unclear whether or not a communication station for increasing the speed of a wireless LAN by using MIMO transmission adopts a function of broadcasting a calibration signal.

  According to the present invention, the communication station that performs calibration secures a band based on the RTS / CTS procedure, and broadcasts the calibration signal using the transmission standby period of the peripheral station, thereby eliminating the influence of interference waves. However, accurate calibration processing can be performed. Here, since the RTS / CTS procedure is adopted also in IEEE802.11a, even in a communication environment where IEEE802.11a-based conventional terminals coexist, the communication stations of the extended standard or the higher standard will The calibration signal can be broadcast in a form compatible with the terminal.

  The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiment without departing from the gist of the present invention.

  In this specification, an embodiment in which the present invention is applied to a system that uses an RTS / CTS procedure and an access method based on CSMA in a wireless network that conforms to the IEEE 802.11 standard has been described. It is not limited to. For example, even a system that uses an RTS / CTS procedure in combination with a random access method other than CSMA, or a random access system that complies with regulations other than IEEE802.11, includes a communication system including a communication station with a multi-antenna configuration. The present invention can be similarly applied to the present invention.

  In short, the present invention has been disclosed in the form of exemplification, and the description of the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims should be taken into consideration.

FIG. 1 is a diagram showing a communication procedure based on CSMA / CA. FIG. 2 is a diagram illustrating an operation example of the RTS / CTS procedure. FIG. 3 is a diagram schematically illustrating a configuration of a multi-antenna wireless communication apparatus having a calibration function. FIG. 4 is a diagram illustrating a frame configuration example of an RTS or CTS-to-self signal. FIG. 5 is a flowchart showing a processing procedure for starting the calibration operation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Wireless communication apparatus 11 ... Antenna element 12 ... Radio | wireless part 13 ... Modulator / demodulator 14 ... Weight multiplication part 15 ... P / S and S / P conversion part 16 ... Codec part 17 ... Control part 18 ... Control frame generation part 19 ... Control Frame extractor

Claims (10)

The RTS / CTS method is used in combination with the RTS / CTS method in which the data transmission source communication station transmits the transmission request packet RTS and the data transmission destination communication station starts to transmit data in response to receiving the confirmation notification packet CTS. A wireless communication system in which a plurality of communication stations including communication stations perform communication operations,
The communication station of the multi-antenna configuration is
A plurality of antenna elements for transmitting and receiving signals;
A radio unit for processing radio signals to be transmitted and received based on a predetermined transfer function;
A modulation / demodulation unit for modulating / demodulating transmission / reception frames;
A control unit for controlling frame processing and transmission / reception calibration operation in the radio unit,
The control unit transmits an RTS signal that describes a transmission standby period for transmitting and receiving a calibration signal between the antenna and the branch, and performs calibration while the peripheral station stops transmission during the transmission standby period . ,
A wireless communication system. A wireless communication device that performs a communication operation in a communication environment in which a plurality of communication stations coexist,
A plurality of antenna elements for transmitting and receiving signals;
A radio unit for processing radio signals to be transmitted and received based on a predetermined transfer function;
A modulation / demodulation unit for modulating / demodulating transmission / reception frames;
A control unit for controlling frame processing and transmission / reception calibration operation in the radio unit,
Under the communication environment, there is an RTS / CTS system in which a data transmission source communication station transmits a transmission request packet RTS and starts data transmission in response to receiving a confirmation notification packet CTS from the data transmission destination communication station. Used together
The control unit transmits an RTS signal that describes a transmission standby period for transmitting and receiving a calibration signal between the antenna and the branch, and performs calibration while the peripheral station stops transmission during the transmission standby period . ,
A wireless communication device. The control unit determines a transmission standby period according to the number of antenna elements that need calibration.
The wireless communication apparatus according to claim 2 . A wireless communication method for performing transmission / reception calibration in a wireless communication apparatus having a plurality of antenna elements that perform communication operations and perform transmission / reception of signals in a communication environment in which a plurality of communication stations coexist ,
Under the communication environment, there is an RTS / CTS system in which a data transmission source communication station transmits a transmission request packet RTS and starts data transmission in response to receiving a confirmation notification packet CTS from the data transmission destination communication station. Used together
Transmitting an RTS signal that describes a transmission waiting period for transmitting and receiving a calibration signal between the antenna and the branch; and
Performing transmission and reception calibration while the peripheral station stops transmission in the transmission waiting period ; and
A wireless communication method comprising: Computer-readable so that processing for performing transmission / reception calibration in a wireless communication apparatus having a plurality of antenna elements that perform communication operations and perform signal transmission / reception in a communication environment in which a plurality of communication stations coexist is executed on a computer. A computer program written in a format,
In the communication environment, there is an RTS / CTS method in which a data transmission source communication station transmits a transmission request packet RTS and starts data transmission in response to receiving a confirmation notification packet CTS from the data transmission destination communication station. Used together
For the computer
A procedure for transmitting an RTS signal that describes a transmission waiting period for transmitting and receiving a calibration signal between an antenna and a branch;
A procedure for performing transmission and reception calibration while the peripheral station stops transmission in the transmission waiting period ;
A computer program for executing The RTS / CTS method is used in combination with the RTS / CTS method in which the data transmission source communication station transmits the transmission request packet RTS and the data transmission destination communication station starts to transmit data in response to receiving the confirmation notification packet CTS. A wireless communication system in which a plurality of communication stations including communication stations perform communication operations,
The communication station of the multi-antenna configuration is
A plurality of antenna elements for transmitting and receiving signals;
A radio unit for processing radio signals to be transmitted and received based on a predetermined transfer function;
A modulation / demodulation unit for modulating / demodulating transmission / reception frames;
A control unit for controlling frame processing and transmission / reception calibration operation in the radio unit,
The control unit transmits a CTS signal that describes a transmission standby period for transmitting and receiving a calibration signal between the antenna and the branch, and performs calibration while the peripheral station stops transmission during the transmission standby period . ,
A wireless communication system. A wireless communication device that performs a communication operation in a communication environment in which a plurality of communication stations coexist,
A plurality of antenna elements for transmitting and receiving signals;
A radio unit for processing radio signals to be transmitted and received based on a predetermined transfer function;
A modulation / demodulation unit for modulating / demodulating transmission / reception frames;
A control unit for controlling frame processing and transmission / reception calibration operation in the radio unit,
Under the communication environment, there is an RTS / CTS system in which a data transmission source communication station transmits a transmission request packet RTS and starts data transmission in response to receiving a confirmation notification packet CTS from the data transmission destination communication station. Used together
The control unit transmits a CTS signal that describes a transmission standby period for transmitting and receiving a calibration signal between the antenna and the branch, and performs calibration while the peripheral station stops transmission during the transmission standby period . ,
A wireless communication device. The control unit determines a transmission standby period according to the number of antenna elements that need calibration.
The wireless communication apparatus according to claim 7 . A wireless communication method for performing transmission / reception calibration in a wireless communication apparatus having a plurality of antenna elements that perform communication operations and perform transmission / reception of signals in a communication environment in which a plurality of communication stations coexist ,
In the communication environment, there is an RTS / CTS method in which a data transmission source communication station transmits a transmission request packet RTS and starts data transmission in response to receiving a confirmation notification packet CTS from the data transmission destination communication station. Used together
Transmitting a CTS signal that describes a transmission waiting period for transmitting and receiving a calibration signal between the antenna and the branch; and
Performing transmission and reception calibration while the peripheral station stops transmission in the transmission waiting period ; and
A wireless communication method comprising: Computer-readable so that processing for performing transmission / reception calibration in a wireless communication apparatus having a plurality of antenna elements that perform communication operations and perform signal transmission / reception in a communication environment in which a plurality of communication stations coexist is executed on a computer. A computer program written in a format,
Under the communication environment, there is an RTS / CTS system in which a data transmission source communication station transmits a transmission request packet RTS and starts data transmission in response to receiving a confirmation notification packet CTS from the data transmission destination communication station. Used together
For the computer
A procedure for transmitting a CTS signal that describes a transmission waiting period for transmitting and receiving a calibration signal between the antenna and the branch;
A procedure for performing transmission and reception calibration while the peripheral station stops transmission in the transmission standby period ;
A computer program for executing

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