JP4337551B2 - Wireless communication system, wireless communication apparatus, wireless communication method, and computer program - Google Patents

Description

  The present invention relates to a radio communication system, a radio communication apparatus and a radio communication method, and a computer program that realize simultaneous communication with a plurality of counterparts by applying a multiple access technology and increase communication capacity, and in particular, a plurality of antennas. A wireless communication system, a wireless communication apparatus, and a wireless communication that realize space division multiple access by adaptively performing addition and synthesis by appropriately weighting each antenna element in an adaptive array antenna composed of elements The present invention relates to a method and a computer program.

  More particularly, the present invention relates to a radio communication system, a radio communication apparatus and a radio communication method, and a computer program that learn and evaluate each antenna weight using a reference signal with a small number of symbols, and in particular, learning of weights. The present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program that perform appropriate evaluation regardless of variations in SINR between subcarriers.

  By connecting multiple computers and configuring a LAN, you can share information such as files and data, share peripheral devices such as printers, and exchange information such as e-mail and data / content transfer Can be done.

  Conventionally, it has been common to use an optical fiber, a coaxial cable, or a twisted pair cable to connect to a wired LAN. In this case, however, a line laying work is required, and it is difficult to construct a network easily. The cable routing becomes complicated. In addition, even after LAN construction, the movement range of the device is limited by the cable length, which is inconvenient.

  Therefore, a wireless LAN has attracted attention as a system that releases users from wired LAN connection. According to the wireless LAN, 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, recently, in order to establish a small-scale wireless network between a plurality of electronic devices existing around a person and perform information communication, introduction of a personal area network (PAN) has been studied.

  One standard for wireless networks is IEEE (The Institute of Electrical and Electronics Engineers) 802.11 (for example, see Non-Patent Document 1), HiperLAN / 2 (for example, Non-Patent Document 2 or Non-Patent Document 2 or Non-Patent Document 2). (See Patent Document 3), IEEE 302.15.3, Bluetooth communication, and the like. As for the IEEE802.11 standard, there are various wireless communication systems such as the IEEE802.11a standard, the IEEE802.11b standard, etc., depending on the wireless communication system and the frequency band to be used.

  Recently, the penetration rate of wireless LAN has increased, and in addition to information devices such as PCs and PDAs, wireless LANs have also been used in portable devices such as mobile phones and digital cameras. The application includes uploading image data taken with a camera-equipped mobile phone or digital camera to a PC via a wireless LAN.

  Here, in a wireless communication environment in which a plurality of communication stations exist within one communication range, a multiple access technique for detecting which signal belongs to which user and controlling access is necessary. In particular, it is an important issue in order to expand communication capacity with less resources.

  As one of multiple access technologies, a system that realizes space division multiplexing called SDMA (Space Division Multiple Access) has been developed. For example, an adaptive array antenna composed of a plurality of antenna elements is used, and each antenna element is appropriately weighted and added and combined to adaptively form beams and nulls (that is, directivity is changed). By changing adaptively, simultaneous communication with a plurality of opponents can be realized (for example, see Non-Patent Document 4). According to the space division multiple access communication system, frequency utilization efficiency can be improved and communication capacity can be increased.

  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 unit, and its value is calculated by a digital signal processing unit. 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.

  For example, spatial multiplexing is performed in the downlink, and time division multiplexing is performed in the uplink. In this case, the adaptive array antenna is mounted on an access point (hereinafter referred to as AP), and each station (hereinafter referred to as STA) is mounted with one antenna.

  As a specific method of weight learning in an adaptive array antenna, the AP receives a reference signal transmitted in a time division manner from each STA, and calculates a transfer function between each STA and the plurality of antennas of the AP. For example, if there are three STAs and four antennas are mounted on the AP, three transfer functions composed of 4 × 1 vectors are obtained. The antenna weight can be obtained by solving the general inverse matrix of the channel matrix composed of the three transmissions.

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) Nobuyoshi Kikuma, “Adaptive signal processing by array antenna” (Science Description Publishing, ISBN 4-87653-054-8)

  Usually, the reference signal for acquiring the transfer function is about 2 symbols. If an IEEE802.11a PHY header is substituted, the reference signal becomes two symbols. It is necessary to know how effective the learned weight is and how much SINR can be secured by using the weight. This is because the learning AP has to determine what modulation method to transmit data to each STA in response to the result.

  In the case of the multi-carrier system, the SINR can be obtained for each carrier. Here, SINR is a ratio of a desired signal and an interference signal (= S / (I + N)). For example, IEEE802.11a employs an OFDM modulation scheme, and there are 52 carriers of SINR. In normal multi-carrier transmission, there is no interference component I, and the noise component N is constant due to thermal noise or the like, so there is no need to grasp SINR. On the other hand, since interference components appear in SDMA, it is necessary to grasp SINR.

  However, there is a problem of how to integrate and handle a plurality of SINRs. For example, the average SINR for 52 carriers is not the total SINR.

  Here, let us consider the case where the SINR is 20 dB and 10 dB, and these two carriers are used in an integrated manner.

  For example, when the desired signal is 1 and the interference signal is 0.01, the SINR is 20 dB (10 × log (S / IN)). When the desired signal is 0.1 and the interference signal is 0.01, the SINR is 10 dB. When these two are integrated by simple addition, the desired signal is 1.1 and the interference signal is 0.02, and the SINR is 10 log (1.1 / 0.02) = 17.4 dB. In other words, when the SINR of 20 dB and the SINR of 10 dB are integrated, SINR of 17.4 dB is obtained.

  On the other hand, when the desired signal is 1 and the interference signal is 0.01, the SINR is 20 dB, and the SINR with the desired signal of 1 and the interference signal of 0.1 is 10 dB. However, the interference signal becomes 0.11 at 2.0, and the integrated SINR becomes 10 log (2.0 / 0.11) = 12.59 dB.

  As described above, when SINR is calculated by integrating SINRs of 20 dB and 10 dB by simple addition of signal levels, integration is performed according to a ratio of a desired component and an interference component of the SINR signal between carriers. The SINR value changes in any way, and it is unclear which one should be true. In the above-described example, a good SINR and a bad SINR are integrated and dragged by a bad SINR.

  For example, when spatial multiplexing is performed in the downlink, the SINR is unduly lowered when the signal power of each subcarrier is integrated.

  The present invention takes into account the technical problems as described above, and an object of the present invention is to add and synthesize an adaptive array antenna composed of a plurality of antenna elements by appropriately weighting each antenna element. It is to provide an excellent wireless communication system, wireless communication apparatus, wireless communication method, and computer program capable of realizing space division multiple access by performing adaptively.

The present invention has been made in consideration of the above-mentioned problems. The first aspect of the present invention is that an adaptive array antenna is used, and the directivity of each antenna is adaptively changed, so that a transmitting station and a plurality of receiving stations are received. A wireless communication system for space division multiplex connection of a downlink with a station,
Two reference signals are transmitted from multiple receiving stations,
On the transmitting side, the weight of each antenna is learned using one reference signal, and the SINR that can be secured on each receiving side is evaluated based on the weight of each antenna learned using the other reference signal.
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.

  The present invention provides, for example, a wireless communication system in which a downlink performing communication from an access point to a station is spatially multiplexed in a wireless communication environment in which an access point having an adaptive array antenna communicates with a plurality of stations. Can be applied.

  According to the present invention, the first reference symbol is learned from the two reference symbols included in the preamble of the packet, the second reference symbol is evaluated, and the second reference symbol is learned at the same time.・ Evaluate with symbols. Then, after these two evaluation results are integrated and evaluated, a highly reliable estimation is performed by actually learning using both the first reference symbol and the second reference symbol. SINR can be obtained.

  Then, at the transmitting side, the power of the received signal from each receiving side is further measured, and the power evaluation result of the array output using each learned antenna weight and the power information are used at each receiving side at the time of downlink. SINR can be estimated. Based on the SINR estimation result, the downlink modulation scheme can be determined.

  The radio communication system according to the present invention can employ a so-called RTS / CTS scheme in order to ensure communication quality. In this case, the transmission side transmits RTS by space division, and each reception side returns CTS by time division.

  In such a case, the transmitting side can acquire the power of the CTS received by time division from each receiving side. In addition, the weight of each antenna can be learned using one of the two reference signals included in the CTS, and the SINR that can be secured on each receiving side can be evaluated using the other reference signal. Then, based on the power information and the SINR information, a modulation scheme is determined at the time of data packet transmission, and the data packet is transmitted by space division multiplexing with the obtained weight according to the determined modulation scheme. it can.

A second aspect of the present invention is a wireless system that uses an adaptive array antenna, adaptively changes the directivity of each antenna, and spatially multiplex-links a downlink between a transmitting station and a plurality of receiving stations. A communication system,
Adopting multi-carrier method, when learning weight of each antenna and evaluating SINR for each sub-carrier,
Obtain the desired signal power and interference signal power for each subcarrier, and convert the signal level while maintaining the ratio of the desired signal and interference signal for each subcarrier so that the interference power of each subcarrier is the same. And then integrating the SINR of each subcarrier,
This is a wireless communication system.

  When a multi-carrier scheme such as the OFDM modulation scheme is adopted, the array weight can be learned for each subcarrier. In normal multi-carrier transmission, there is no interference component I, and the noise component N is constant due to thermal noise or the like, so there is no need to grasp SINR. On the other hand, since interference components appear in SDMA, it is necessary to grasp SINR.

  However, when the SINR varies from subcarrier to subcarrier, there is a problem in that a good SINR and a bad SINR are integrated and dragged to a bad SINR. For example, when spatial multiplexing is performed in the downlink, the SINR is unduly lowered when the signal power of each subcarrier is integrated.

  Therefore, in the present invention, when performing SINR evaluation, desired signal power and interference signal power are acquired for each subcarrier, and desired for each subcarrier so that the magnitude of interference power for each subcarrier is the same. After converting the signal level while maintaining the ratio of the signal and the interference signal, the SINR of each subcarrier is integrated. As a result, it is possible to solve the problem that a good SINR and a bad SINR are integrated and dragged to a bad SINR.

  In addition, a dedicated signal for power estimation is prepared so that desired power and interference power can be known for each subcarrier on the downlink STA side. On the STA side, when the desired power and interference power are known, the SINRs are integrated after adjusting the signal level of each subcarrier so that the interference power becomes the same level. As a result, it is possible to solve the problem that a good SINR and a bad SINR are integrated and dragged to a bad SINR.

Further, the third aspect of the present invention uses a adaptive array antenna, adaptively changes the directivity of each antenna, and performs processing for space division multiple connection with a plurality of opponents on a computer system. A computer program written in a computer-readable format for execution,
A learning step of learning the weight of each antenna using one reference signal of two reference signals from a plurality of receiving stations;
An evaluation step for evaluating the SINR that can be secured at each receiving side with the weight of each antenna learned using the other reference signal;
A power acquisition step of acquiring the power of the received signal from each receiving station;
An estimation step for estimating the SINR at each receiving station based on the power information obtained in the power acquisition step and the SINR information obtained in the evaluation step;
A modulation scheme determining step for determining a modulation scheme in downlink based on the SINR estimated in the estimating step;
A computer program characterized by comprising:

According to a fourth aspect of the present invention, there is provided a computer system for processing in a wireless communication environment using an adaptive array antenna and adaptively changing the directivity of each antenna to perform space division multiple access. A computer program written in a computer-readable format for execution on
A power acquisition step of acquiring desired signal power and interference signal power for each subcarrier;
SINR evaluation step of integrating the SINR of each subcarrier after converting the signal level while maintaining the ratio of the desired signal and the interference signal for each subcarrier so that the magnitude of the interference power of each subcarrier is the same. ,
A computer program characterized by comprising:

  The computer program according to each of the third and fourth aspects of the present invention defines a computer program described in a computer-readable format so as to realize predetermined processing on the computer system. In other words, by installing the computer program according to each of the third and fourth aspects of the present invention in the computer system, a cooperative action is exhibited on the computer system, and 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 and second aspects of the present invention can be obtained.

  According to the present invention, in an adaptive array antenna constituted by a plurality of antenna elements, appropriate weighting is performed on each antenna element, and addition and synthesis is performed adaptively, thereby realizing space division multiple access. An excellent wireless communication system, wireless communication apparatus and wireless communication method, and computer program can be provided.

  According to the present invention, when performing spatial multiplexing using an array antenna, it is possible to perform evaluation of the SINR value on the downlink side using only 2 OFDM symbols as a learning reference signal. A modulation scheme can be assigned.

  In addition, according to the present invention, when the weight learning is performed for each subcarrier when performing spatial multiplexing using an array antenna, when the SINR varies for each subcarrier, the signal is transmitted on the downlink side. It is possible to correctly receive and prevent an unreasonable decrease in SINR.

  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.

  FIG. 1 schematically shows a network configuration of a wireless LAN according to an embodiment of the present invention.

  The AP has a plurality of antennas, and the STA has one antenna. This is a system that communicates with a plurality of STAs using the same frequency from the AP at the same time. Hereinafter, communication from the STA to the AP is referred to as “uplink”, and communication from the AP to the STA is referred to as “downlink”. Communication using the same frequency at the same time is called space division multiple access (SDMA). In the industry, uplink space division multiple access and downlink space division multiple access are conceivable, but the present invention aims to realize downlink space division multiple access with a narrow dynamic range AP. .

  The access point may also be connected to a wired network such as Ethernet (registered trademark) to communicate with other access points.

  In the wireless network system according to the present invention, transmission control using a plurality of channels effectively is performed by a transmission (MAC) frame having a gradual time division multiple access structure, and each communication station is provided with a CSMA (Carrier). Information can also be transmitted directly and asynchronously according to an access procedure based on Sense Multiple Access (carrier detection multiple access).

  In the case of the latter access procedure, at this time, the RTS / CTS method can be adopted as means for avoiding collision and improving communication quality.

  In this case, prior to transmission of the net information, the transmission source communication station transmits RTS (Request to Send), and if the reception destination communication station can receive the RTS and receive data, the response As CTS (Clear to Send). Then, data transmission is executed after a connection is established between the transmitting and receiving stations by exchanging RTS / CTS information.

  The peripheral station that has received either the RTS signal or the CTS signal refrains from data transmission processing during the data transmission period described in these packets. Therefore, the communication station that becomes a hidden terminal from the transmission side or the reception side avoids the data transmission collision by receiving either the RTS signal or the CTS signal, and thus the hidden terminal problem can be solved. In the following, an embodiment will be described in which data is transmitted by the RTS / CTS method in a space division multiple access wireless network.

  A data transmission / reception procedure in the wireless network according to the present invention will be described with reference to FIG.

  In the figure, an access point AP is a master station that mainly transmits a large amount of data, for example, a communication station such as a video server that performs streaming transmission of moving image data. On the other hand, the other communication stations STA1, STA2, and STA3 are slave stations that mainly receive data, and correspond to a content reproduction device such as a television / monitor that reproduces content such as moving image data received from the master station. Station. Here, consider a case where the access point AP transmits different data simultaneously to each of the slave stations STA1, STA2, and STA3.

  First, the access point AP transmits an RTS packet dedicated to spatial multiplexing transmission (SMT). This STS-dedicated RTS packet includes the addresses of the target slave stations (STA1, STA2, and STA3 in the illustrated example). The slave station that has received the RTS packet returns the CTS packet in a time division manner according to the address order described in the RTS packet.

  The CTS returned by each slave station in a time division manner is transmitted in a time division manner with a frame interval for the MIFS (Momentary IFS) time. The time interval is set to this value to ensure that the access point AP can receive these CTSs.

  When the access point AP receives these CTSs in a time division manner, the access point AP calculates a weight vector for space division multiple access of each slave station, sets the optimum transmission beam pattern for each, and sets the net data Send the frame (SMT).

  When each slave station receives a data frame from the access point AP, each slave station returns an ACK in the same manner as when returning a CTS packet.

  A Duration field is prepared in the header of the MAC field or PHY frame of each of the RTS packet, the CTS packet, the data packet, and the ACK packet, and a NAV (Network Allocation Vector) is set based on this value.

  In the example shown in FIG. 2, in the RTS, the time between the end of transmission of the RTS and all the CTSs is set as the NAV.

  For CTS, the time until CTS, the subsequent data frame and all ACKs are transmitted is set as NAV. Therefore, the time when the set time of the NAV specified by the CTS ends is the same time in each of the slave stations STA1, STA2, and STA3.

  In the data frame, the time until all subsequent ACKs are transmitted is set as the NAV.

  In ACK (+ CTS), as in the case of CTS, the time until the subsequent data frame and all ACKs are completely transmitted is set. Therefore, the set value of the NAV designated by this ACK is the same time in each of the slave stations STA1, STA2, and STA3.

  A peripheral station that has received one of RTS, CTS, and data sets up a NAV according to Duration described in the MAC header of the packet, and stops transmission processing until the transmission of the ACK packet is completed.

  The access point is adjusted so that a plurality of CTSs received from each station in a time division manner can be received at a constant size by adaptively setting the LNA gain of the analog unit. When a plurality of CTSs are received in a time division manner, a transfer function (also referred to as a “direction vector”) for each station is acquired from the data received in the time division manner.

  FIG. 3 shows a frame format of each packet used in the data transmission / reception procedure shown in FIG.

  As shown in the upper part of the figure, the header of the CTS packet returned in time division from each STA in response to the RTS packet from the AP includes a synchronous AGC signal and two reference signals (reference symbols).

  As shown in the lower part of the figure, the data packet transmitted from the AP to each STA has a synchronous AGC signal for each STA, two reference signals, and a power measurement signal as a header. Contains. The synchronous AGC signal and the two reference signals are space division multiplexed. On the other hand, a dedicated power measurement signal is prepared for each STA and is time-division multiplexed.

  The AP that has received a plurality of CTSs in a time division manner acquires transfer functions for the respective STAs using two reference signals included in the header of the CTS packet as shown in FIG.

Usually, the average of these two reference signals is taken, the accuracy of transfer function acquisition is increased, and the weight for each STA is obtained by obtaining a general inverse matrix as follows using the transfer function with the increased accuracy. Obtain w ₁ , w ₂ , and w ₃ . However, there is no means for evaluating how much SINR can be obtained for the downlink side with the obtained weight.

  Here, the weight itself is obtained using a transfer function obtained from the average of two reference signals. However, when evaluating SINR, the weight is obtained with one reference signal, and the remaining one reference signal is used. Evaluate how much SINR is obtained. The modulation method of the data packet on the downlink side is determined using the estimated SINR.

  I will explain a little more in detail. When the AP receives a CTS from each STA in a time division manner, the AP measures each received power. For example, as shown in the table below, it is assumed that reception has been possible from each STA with power of −60 dBm, −70 dBm, and −80 dBm.

  In the AP, a transfer function for each STA is acquired based on the reception power of one eye reference signal. Then, the remaining one reference signal is evaluated, and it is evaluated as the SINR on the downlink side.

In the SINR estimation processing, when the weights w ₁ , w ₂ , and w ₃ for each STA are used, the signal level for the transfer function acquired from each STA can be calculated as follows.

  For example, if the weight for STA1 is used, the signal of the transfer function of STA1 that is a signal from STA1 is received, but the signals from other STA2 and STA3 are received only with small power, that is, a state where null is directed. It is.

  Since each transfer function is a signal that has passed through AGC (Auto Gain Control), the magnitude of the signal is normalized. Therefore, in order to obtain the SINR on the downlink side, conversion must be performed using the power of the received CTS packet, −60 dBm, −70 dBm, and −80 dBm.

The desired signal for STA1 can be received at 0 dB−60 dB = −60 dB since the power to STA1 using the weight w ₁ is 0 dB. On the other hand, the interference signal to STA1 when the weight w ₂ is used can be calculated as −10 dB−60 dB = −70 dB. Further, the interference signal to STA1 when the weight w ₃ is used can be calculated as −30 dB−60 dB = −90 dB.

  Therefore, the SINR at STA1 in the downlink is as follows. That is, since the desired signal is −60 dB and the interference signals are −70 dB and −90 dB, an SINR of about 10 dB can be obtained.

  In this way, it is possible to learn using the first reference signal, evaluate with the remaining one reference signal, and estimate it as the SINR on the downlink side.

  As described above, learning is performed using the first reference signal, evaluation is performed using the remaining one reference signal, and it can be estimated as the SINR on the downlink side. Furthermore, it is necessary to know how effective the learned weight is and how much SINR can be secured by using the weight. This is because the learning AP has to determine what modulation method to transmit data to each STA in response to the result.

  Here, in the case of multi-carrier, after unifying the magnitude of the interference component in each carrier (that is, the level of the desired signal is also converted at the same ratio), the sum of the interference signals is taken, What is necessary is just to obtain the total SINR by summing the desired signals (see FIG. 4). In this way, when weight learning is performed for each subcarrier, even if the SINR varies from subcarrier to subcarrier, the signal is correctly received on the downlink side, and the SINR is unduly reduced. Can be prevented.

  In this way, on the AP side, the SI side estimated based on the reference signal added to the CTS from each STA is used to determine which modulation method is used, and the AP side modulates each modulation method. Three pieces of data are spatially multiplexed and transmitted.

  Here, as shown in FIG. 2, the data packet transmitted from the AP to each STA includes a synchronous AGC signal for each STA, two reference signals, and a power measurement signal in the header. The three data and preamble are weighted by the array antennas for STA1, STA2, and STA3, respectively, and are space division multiplexed. Also, a dedicated power measurement signal is prepared for each STA and is time-division multiplexed.

  Therefore, each STA can receive a power measurement signal sent in time division after the preamble before receiving data. In other words, the STA can calculate a desired signal and an interference signal addressed to itself for each subcarrier by using this time-division power measurement signal area.

  For example, in the case of STA1, the signal received in the power measurement signal area for STA1 is the power of the desired signal, and the signals received in the power measurement signal areas for STA2 and STA3 interfere with STA1. Signal.

  Thus, each STA can know the power of the desired signal and the interference signal for each subcarrier by using the power measurement signal inserted in the preamble in a time division manner. Next, when receiving the data part, the data part is mixed with the interference signal and the desired signal (which is quite small) and cannot be separated, but the ratio of the desired signal and the interference signal is known for each subcarrier. The magnitude of each signal can be adjusted so that the level of the interference signal for each subcarrier is the same.

  The signals after the adjustment can be collectively regarded as one signal, and the power can be integrated for integration. Without such adjustment, the interference component of a specific subcarrier is considered to be unduly large and adversely affects the signals of other subcarriers.

  FIG. 5 schematically shows a functional configuration example of a wireless communication apparatus operating as an AP in the wireless network according to the present invention. The AP has a plurality (two in the illustrated example) of antennas 101, and includes a transmission / reception RF unit 102, a transmitter, and a receiver for each antenna.

  The transmission / reception RF unit 102 includes a low noise amplifier (LNA) and an automatic gain controller (AGC) that amplify the received signal, and a power amplifier (PA) that amplifies the power of the transmission signal.

  Each transmitter side includes an encoder 111, a transmission weight multiplication unit 112, an IFFT 113, a guard interval insertion unit 114, and a D / A converter 115.

  The encoder 111 encodes transmission data sent from an upper layer of the communication protocol with an error correction code. At this point, a known data sequence may be inserted as a pilot symbol into the modulation symbol sequence according to the pilot symbol insertion pattern and timing. A pilot signal having a known pattern is inserted for each subcarrier or at intervals of several subcarriers.

  The transmission weight multiplier 112 multiplies the encoded transmission signal by the weight of each STA obtained based on the received reference signal.

  The IFFT 113 converts the data into parallel data corresponding to the number of parallel carriers and combines them, and performs inverse Fourier transform for the FFT size according to a predetermined FFT size and timing. The guard interval insertion unit 114 provides guard interval sections before and after one OFDM symbol in order to remove intersymbol interference. The time width of the guard interval is determined by the state of the propagation path, that is, the maximum delay time of the delayed wave that affects the demodulation.

  The transmission signal converted into parallel data is serially converted into a time-axis signal while maintaining orthogonality of each carrier on the frequency axis, and converted to an analog baseband signal by the D / A converter 115. Further, after being up-converted to an RF frequency band by the RF unit, it is transmitted from the antenna 101 to the channel.

  On the other hand, the receiver side includes an A / D converter 115, an OFDM symbol synchronization processing unit 121, an FFT 122, a transfer function acquisition unit 123, a power acquisition unit 124, a SINR evaluation unit 125, and a decoder (not shown). ).

  The signal received from the antenna 101 is down-converted from the RF frequency band to the baseband signal by the RF unit 102 and converted into a digital signal by the A / D converter 115.

  The received signal as serial data is converted into parallel data according to the synchronization timing detected by the OFDM symbol synchronization processing unit 121 and collected. Here, signals for one OFDM symbol including up to the guard interval are collected. Then, the signal corresponding to the effective symbol length is Fourier-transformed by the FFT 122 to extract the signal of each subcarrier. Thereafter, the time axis signal is converted into a frequency axis signal.

  The received signal is further error-corrected and decoded by a decoder (not shown), becomes received data, and is passed to the upper layer of the communication protocol. The decoder uses, for example, a Viterbi decoding method, and reproduces a data string that is most likely, that is, most probabilistically probable from data mixed with noise.

  The transfer function acquisition unit 123 acquires a transfer function using two reference signals included in the headers of CTS or other packets received in time division from each STA.

  The power acquisition unit 124 measures the power of the CTS or other signal received in a time division manner from each STA and stores it.

  The SINR evaluation unit 125 calculates the weight to each STA from the transfer function obtained by using two reference signals included in the header of the CTS or other packet received in a time division manner from each STA, and further on the downlink side And evaluate how much SINR is secured. The weight obtained here is set in the transmission weight multiplier 112. Also, the modulation scheme of data to be transmitted to each STA is determined by the SINR evaluation for downlink.

  FIG. 6 schematically shows a functional configuration example of a wireless communication apparatus operating as an STA in the wireless network according to the present invention. The access point AP includes one antenna 201, a transmission / reception RF unit 202, a transmitter, and a receiver.

  The transmission / reception RF unit 202 includes a low noise amplifier (LNA) and an automatic gain controller (AGC) that amplify the received signal, and a power amplifier (PA) that amplifies the power of the transmission signal.

  The transmitter side includes an encoder 211, an IFFT 212, a guard interval insertion 213 unit, and a D / A converter 214.

  The encoder 211 encodes transmission data sent from an upper layer of the communication protocol with an error correction code.

  In IFFT 212, the data is converted into parallel data corresponding to the number of parallel carriers, and is subjected to inverse Fourier transform for the FFT size according to a predetermined FFT size and timing.

  The guard interval insertion unit 213 provides guard interval sections before and after one OFDM symbol in order to remove intersymbol interference.

  The transmission signal converted into parallel data is serially converted into a time-axis signal while maintaining orthogonality of each carrier on the frequency axis, and converted to an analog baseband signal by the D / A converter 214. Further, after being up-converted to an RF frequency band by the RF unit 202, the signal is transmitted from the antenna 201 to the channel.

  On the other hand, the receiver side includes an A / D converter 214, an OFDM symbol synchronization processing unit 221, an FFT 222, and a decoder 223.

  The signal received from the antenna is down-converted from the RF frequency band to the baseband signal by the RF unit 202, and converted to a digital signal by the A / D converter.

  The received signal as serial data is converted into parallel data and collected according to the synchronization timing detected by the OFDM symbol synchronization processing unit 221.

  Then, the FFT 222 performs Fourier transform on the signal for the effective symbol length, and takes out the signal of each subcarrier. Thereafter, the time axis signal is converted into a frequency axis signal.

  The received signal is further error-corrected and decoded by the decoder 223, becomes received data, and is passed to the upper layer of the communication protocol.

  Next, an operation procedure in the data communication system including the AP shown in FIG. 5 and a plurality (three) of STAs shown in FIG. 6 will be described with reference to FIG. However, it is assumed that access control by CSMA / CA applying the RTS / CTS procedure is performed between the AP and each STA.

Step 1:
The RTS specifying the STAs of the three transmission partners is transmitted from the AP.

Step 2:
Each STA designated as a transmission partner returns a CTS in a time division manner. Reference signals for 2 OFDM symbols are added to the head of this CTS. That is, the first OFDM symbol is the first reference signal, and the second OFDM symbol is the second reference signal.

Step 3:
When the AP receives the CTS sent in time division, the AP measures the power of each CTS and stores it.

Step 4:
When the AP receives the CTS sent in time division, the AP calculates the weight of the adaptive array using the first reference signal of each CTS. Further, the weights calculated here are evaluated by the second reference signal of each CTS, the degree of SINR on the AP side for each STA is evaluated, and stored in Table 1.

Step 5:
When the AP receives the CTS sent in time division, the AP calculates the weight of the adaptive array using the second reference signal of each CTS. Further, the weight calculated here is evaluated by the first reference signal of each CTS, and the degree of SINR on the AP side for each STA is evaluated and stored in Table 2.

Step 6:
Average the SINR information in Table 1 and Table 2 to increase accuracy.

Step 7:
The AP that receives the CTS sent in time division takes the average of the first reference signal and the second reference signal of each CTS, and calculates the weight of the adaptive array using the reference signal with increased accuracy. Save this.

Step 8:
From the power information obtained in step 3 and the SINR information obtained in step 6, the SINR on the STA side on the downlink side is estimated.

Step 9:
The modulation scheme is determined based on the SINR estimated in step 8, and the spatially multiplexed data is transmitted with the weight obtained in step 7.

Step 10:
Each STA that has received the data returns an ACK.

  FIG. 8 schematically shows another functional configuration example of a wireless communication apparatus operating as an AP in the wireless network according to the present invention. The AP has a plurality (two in the illustrated example) of antennas 101, and includes a transmission / reception RF unit 102, a transmitter, and a receiver for each antenna.

  The transmission / reception RF unit 102 includes a low noise amplifier (LNA) and an automatic gain controller (AGC) that amplify the received signal, and a power amplifier (PA) that amplifies the power of the transmission signal.

  Each transmitter side includes an encoder 111, a transmission weight multiplication unit 112, an IFFT 113, a guard interval insertion unit 114, a D / A converter 115, and a power measurement signal insertion unit 116. .

  The encoder 111 encodes transmission data sent from an upper layer of the communication protocol with an error correction code. At this point, a known data sequence may be inserted as a pilot symbol into the modulation symbol sequence according to the pilot symbol insertion pattern and timing. A pilot signal having a known pattern is inserted for each subcarrier or at intervals of several subcarriers.

  The power measurement signal insertion unit 116 generates a signal for measuring desired power and interference power on the STA side, and inserts the signal into, for example, a data packet header in a time division manner (see FIG. 3).

  The transmission weight multiplier 112 multiplies the encoded transmission signal by the weight of each STA obtained based on the received reference signal.

  The IFFT 113 converts the data into parallel data corresponding to the number of parallel carriers and combines them, and performs inverse Fourier transform for the FFT size according to a predetermined FFT size and timing. The guard interval insertion unit 114 provides guard interval sections before and after one OFDM symbol in order to remove intersymbol interference. The time width of the guard interval is determined by the state of the propagation path, that is, the maximum delay time of the delayed wave that affects the demodulation.

  The transmission signal converted into parallel data is serially converted into a time-axis signal while maintaining orthogonality of each carrier on the frequency axis, and converted to an analog baseband signal by the D / A converter 115. Further, after being up-converted to an RF frequency band by the RF unit, it is transmitted from the antenna 101 to the channel.

  On the other hand, the receiver side includes an A / D converter 102, an OFDM symbol synchronization processing unit 121, an FFT 122, a transfer function acquisition unit 123, a power acquisition unit 124, an SINR evaluation unit 125, and a decoder (not shown). ).

  The signal received from the antenna 101 is down-converted from the RF frequency band to the baseband signal by the RF unit 102 and converted into a digital signal by the A / D converter 115.

  The received signal as serial data is converted into parallel data according to the synchronization timing detected by the OFDM symbol synchronization processing unit 121 and collected. Here, signals for one OFDM symbol including up to the guard interval are collected. Then, the signal corresponding to the effective symbol length is Fourier-transformed by the FFT 122 to extract the signal of each subcarrier. Thereafter, the time axis signal is converted into a frequency axis signal.

  The received signal is further error-corrected and decoded by a decoder (not shown), becomes received data, and is passed to the upper layer of the communication protocol. The decoder uses, for example, a Viterbi decoding method, and reproduces a data string that is most likely, that is, most probabilistically probable from data mixed with noise.

  The transfer function acquisition unit 123 acquires a transfer function using two reference signals included in the headers of CTS or other packets received in time division from each STA.

  The power acquisition unit 124 measures the power of the CTS or other signal received in a time division manner from each STA and stores it.

  The SINR evaluation unit 125 calculates the weight to each STA from the transfer function obtained by using two reference signals included in the header of the CTS or other packet received in a time division manner from each STA, and further on the downlink side And evaluate how much SINR is secured. Here, the signal level is converted while maintaining the ratio of the desired signal and the interference signal for each subcarrier so that the magnitude of the interference power of each subcarrier is the same, and then the SINR of each subcarrier is integrated. As a result, it is possible to solve the problem that a good SINR and a bad SINR are integrated and dragged to a bad SINR.

  The weight obtained by the SINR evaluation unit 125 is set in the transmission weight multiplication unit 112. Also, the modulation scheme of data to be transmitted to each STA is determined by the SINR evaluation for downlink.

  FIG. 9 schematically shows another functional configuration example of a wireless communication apparatus operating as an STA in the wireless network according to the present invention. The access point AP includes one antenna 201, a transmission / reception RF unit 202, a transmitter, and a receiver.

  The transmission / reception RF unit 202 includes a low noise amplifier (LNA) and an automatic gain controller (AGC) that amplify the received signal, and a power amplifier (PA) that amplifies the power of the transmission signal.

  The transmitter side includes an encoder 211, an IFFT 212, a guard interval insertion 213 unit, and a D / A converter 214.

  The encoder 211 encodes transmission data sent from an upper layer of the communication protocol with an error correction code.

  In IFFT 212, the data is converted into parallel data corresponding to the number of parallel carriers, and is subjected to inverse Fourier transform for the FFT size according to a predetermined FFT size and timing.

  The guard interval insertion unit 213 provides guard interval sections before and after one OFDM symbol in order to remove intersymbol interference.

  The transmission signal converted into parallel data is serially converted into a time-axis signal while maintaining orthogonality of each carrier on the frequency axis, and converted to an analog baseband signal by the D / A converter 214. Further, after being up-converted to an RF frequency band by the RF unit 202, the signal is transmitted from the antenna 201 to the channel.

  On the other hand, the receiver side includes an A / D converter 214, an OFDM symbol synchronization processing unit 221, an FFT 222, a decoder 223, a power acquisition unit 224, and a signal level adjustment unit 225.

  The signal received from the antenna is down-converted from the RF frequency band to the baseband signal by the RF unit 202, and converted to a digital signal by the A / D converter.

  The received signal as serial data is converted into parallel data and collected according to the synchronization timing detected by the OFDM symbol synchronization processing unit 221.

  Then, the FFT 222 performs Fourier transform on the signal for the effective symbol length, and takes out the signal of each subcarrier. Thereafter, the time axis signal is converted into a frequency axis signal.

  The power acquisition unit 224 acquires the power of the desired signal and the interference signal on the downlink side. As described above, from the AP side, dedicated power measurement signals are prepared for each STA, and these are transmitted in a time division manner in the header portion of the data packet (see FIG. 3). The acquisition unit 224 can acquire the desired signal power and the interference signal power for each subcarrier using the power measurement signal addressed to the own station as a desired signal and the power measurement signal addressed to another station as an interference signal.

  When the signal level adjustment unit 225 knows the desired power and the interference power, it adjusts the signal level of each subcarrier so that the interference power becomes the same level, and then integrates these SINRs. As a result, it is possible to solve the problem that a good SINR and a bad SINR are integrated and dragged to a bad SINR.

  Thereafter, the received signal is error-corrected and decoded by the decoder 223, becomes received data, and is passed to the upper layer of the communication protocol. The decoder uses, for example, a Viterbi decoding method, and reproduces a data string that is most likely, that is, most probabilistically probable from data mixed with noise.

  Next, an operation procedure in the data communication system including the AP shown in FIG. 8 and a plurality (three) of STAs shown in FIG. 9 will be described with reference to FIG. However, it is assumed that access control by CSMA / CA applying the RTS / CTS procedure is performed between the AP and each STA.

Step 11:
The RTS specifying the STAs of the three transmission partners is transmitted from the AP.

Step 12:
Each STA designated as a transmission partner returns a CTS in a time division manner. Reference signals for 2 OFDM symbols are added to the head of this CTS. That is, the first OFDM symbol is the first reference signal, and the second OFDM symbol is the second reference signal.

Step 13:
When the AP receives the CTS sent in time division, the AP measures the power of each CTS and stores it.

Step 14:
When the AP receives the CTS sent in time division, the AP calculates the weight of the adaptive array using the first reference signal of each CTS. Further, the weight calculated here is evaluated by the second reference signal of each CTS.

  In the evaluation method performed here, the ratio of the desired signal and the interference signal can be obtained for each of the 52 subcarriers of OFDM, but the size of the interference signal is the same for each subcarrier. The operation of converting the signal level is performed (let's produce FIG. 4). After the interference level of each subcarrier becomes the same, the desired power and the interference power are integrated for each subcarrier to obtain a total SINR.

Step 15:
A modulation scheme is determined based on the SINR obtained in step 14, and data is transmitted using the weight obtained in step 14. At the head of this data, a power measurement signal corresponding to each STA is added in a time division manner.

Step 16:
Each STA can measure the ratio and power of a desired signal and an interference signal for each subcarrier by receiving three power measurement signals.

Step 17:
When the STA performs data reception, based on the information obtained in step 6, digitally adjust the magnitude of the signal of each subcarrier so that the level of the interference signal for each subcarrier is the same, The signal is decoded as one OFDM signal by one Viterbi decoder or the like.

  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. That is, the present invention has been disclosed in the form of exemplification, and the contents described in the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims section described at the beginning should be considered.

FIG. 1 is a diagram schematically showing a network configuration of a wireless LAN according to an embodiment of the present invention. FIG. 2 is a diagram showing a data transmission / reception procedure in the wireless network according to the present invention. FIG. 3 is a diagram showing an example of a frame format. FIG. 4 is a diagram showing how the signal level is converted so that the magnitude of the interference component in each carrier is unified. FIG. 5 is a diagram schematically showing a functional configuration example of a wireless communication apparatus operating as an access point in the wireless network according to the present invention. FIG. 6 is a diagram schematically showing a functional configuration example of a wireless communication apparatus operating as an STA in the wireless network according to the present invention. FIG. 7 is a flowchart showing an operation procedure in the data communication system including the AP shown in FIG. 5 and the plurality of STAs shown in FIG. FIG. 8 is a diagram schematically showing another functional configuration example of a wireless communication apparatus operating as an access point in the wireless network according to the present invention. FIG. 9 is a diagram schematically showing another functional configuration example of a wireless communication apparatus operating as an STA in the wireless network according to the present invention. FIG. 10 is a flowchart showing an operation procedure in the data communication system including the AP shown in FIG. 8 and the plurality of STAs shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Antenna 102 ... Transmission / reception RF part 111 ... Encoder 112 ... Transmission weight multiplication part 113 ... IFFT
DESCRIPTION OF SYMBOLS 114 ... Guard interval insertion part 115 ... D / A, A / D converter 116 ... Power measurement signal insertion part 121 ... OFDM symbol synchronization processing part 122 ... FFT
DESCRIPTION OF SYMBOLS 123 ... Transfer function acquisition part 124 ... Power acquisition part 125 ... SINR evaluation part 201 ... Antenna 202 ... Transmission / reception RF part 211 ... Encoder 212 ... IFFT
213 ... Guard interval insertion unit 214 ... D / A, A / D converter 221 ... OFDM symbol synchronization processing unit 222 ... FFT
223 ... Decoder 224 ... Power acquisition unit 225 ... Signal level adjustment unit

Claims (12)

A wireless communication system that uses a plurality of antennas, adaptively changes the directivity of each antenna, and spatially multiplex-links downlinks of a transmitting station and a plurality of receiving stations,
Two reference signals are respectively transmitted from a plurality of receiving stations,
On the transmitting side, using one of the reference signals of the two reference signals transmitted from each of said plurality of receiver learns the weight of each antenna, using the other reference signals, the weight of each antenna learned To evaluate the SINR that can be secured on each receiving side,
A wireless communication system. In a wireless communication environment in which an access point having a plurality of antennas communicates with a plurality of stations, a downlink performing communication from the access point to the station is spatially multiplexed.
The wireless communication system according to claim 1. On the transmission side, the SINR on each reception side in the downlink is estimated using the power evaluation result of the output using each antenna weight learned and the power result of the reception signal from each reception side.
The wireless communication system according to claim 1. A modulation scheme at the time of downlink is determined based on the estimation result of the SINR.
The wireless communication system according to claim 3. The RTS / CTS method is adopted in which the transmission side transmits RTS (Request to Send: transmission request), and each reception side returns CTS (Clear to Send: reception ready) in response to the RTS to start data transmission.
The transmitting side transmits RTS by space division, and each receiving side returns CTS by time division.
The wireless communication system according to claim 3. On the sending side,
Obtain the power of CTS received from each receiving side,
The weight of each antenna is learned using one of the two reference signals included in the CTS, and the SINR that can be secured on each receiving side is evaluated using the other reference signal.
Based on the power information and the SINR information, a modulation scheme is determined at the time of data packet transmission,
In accordance with the determined modulation scheme, a data packet is transmitted by space division multiplexing with the obtained weight.
The wireless communication system according to claim 5. A wireless communication device that uses a plurality of antennas, adaptively changes the directivity of each antenna, and performs space division multiplex connection with a plurality of counterparts,
A transmission means for transmitting a radio signal;
Receiving means for receiving a radio signal;
Learning means for learning the weight of each antenna using one reference signal of two reference signals respectively transmitted from a plurality of receiving stations;
Evaluation means for evaluating SINR that can be secured on each receiving side with the weight of each learned antenna , using the other reference signal of the two reference signals respectively transmitted from the plurality of receiving stations ;
A wireless communication apparatus comprising: Power acquisition means for acquiring the power of the received signal from each receiving station;
Estimation means for estimating SINR at each receiving station based on power information obtained by the power acquisition means and SINR information obtained by the evaluation means;
The wireless communication apparatus according to claim 7, further comprising: A modulation scheme determining means for determining a modulation scheme in downlink based on the SINR estimated by the estimating means;
The transmitting means transmits a data packet by space division multiplexing with the obtained weight according to the determined modulation method.
The wireless communication apparatus according to claim 8. RTS (Request to Send: transmission request) is transmitted, and RTS / CTS method is used to start data transmission by receiving CTS (Clear to Send: reception ready) from each receiving side.
The power acquisition means acquires CTS power received from each receiving side,
The learning unit learns the weight of each antenna using one of the two reference signals included in the CTS, and the evaluation unit evaluates the SINR that can be secured on each receiving side using the other reference signal. ,
The wireless communication apparatus according to claim 8. A wireless communication method for using a plurality of antennas, adaptively changing the directivity of each antenna, and performing space division multiplex connection with a plurality of counterparts,
A learning step of learning the weight of each antenna using one reference signal of two reference signals respectively transmitted from a plurality of receiving stations;
An evaluation step for evaluating SINR that can be secured on each receiving side with the weight of each learned antenna , using the other reference signal of the two reference signals respectively transmitted from the plurality of receiving stations ;
A power acquisition step of acquiring the power of the received signal from each receiving station;
An estimation step for estimating the SINR at each receiving station based on the power information obtained in the power acquisition step and the SINR information obtained in the evaluation step;
A modulation scheme determining step for determining a modulation scheme in downlink based on the SINR estimated in the estimating step;
A data transmission step of transmitting data by space division multiplexing with the obtained weight according to the determined modulation method;
A wireless communication method comprising: A computer that is written in a computer-readable format to execute processing on a computer system using a plurality of antennas, adaptively changing the directivity of each antenna, and performing space division multiplex connection with a plurality of counterparts. A program,
A learning step of learning the weight of each antenna using one reference signal of two reference signals respectively transmitted from a plurality of receiving stations;
An evaluation step for evaluating SINR that can be secured on each receiving side with the weight of each learned antenna , using the other reference signal of the two reference signals respectively transmitted from the plurality of receiving stations ;
A power acquisition step of acquiring the power of the received signal from each receiving station;
An estimation step for estimating the SINR at each receiving station based on the power information obtained in the power acquisition step and the SINR information obtained in the evaluation step;
A modulation scheme determining step for determining a modulation scheme in downlink based on the SINR estimated in the estimating step;
A computer program comprising:

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