JP2010066235A - Distance measuring device and distance measuring method, communication device, and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To calculate a distance without causing large errors based on a free space propagation loss of received signal electric power even if under multi-path propagation surroundings. <P>SOLUTION: In a distance measuring device, a packet can be received by a receiver, a delay profile can be obtained using a correlation machine using a known reference signal of the packet. Only the direct wave electric power of its delay profile and predicted wave electric power are required. The distance can be obtained from the free space propagation loss using its direct wave electric power. Actually, when the sampling clock of the receiver is not so high, although delay waves are contained also in the direct wave and the predicted wave, since many of other delay waves are removed, accuracy can be enhanced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a distance measuring device, a distance measuring method, a communication device, and a computer program using radio, and in particular, a distance measuring device and a distance measuring method for measuring a distance based on the strength of a signal coming from a measurement object. , Communication device, computer program.

  More specifically, the present invention relates to a distance measuring device, a distance measuring method, a communication device, a computer, and a computer for calculating a distance based on a free space propagation loss of a received power of a signal whose transmission power transmitted from an object to be measured is known. The present invention relates to a program, and more particularly to a distance measuring device, a distance measuring method, a communication device, and a computer program for calculating a distance based on a free space propagation loss of received signal power in a multipath propagation environment.

  A wireless network is attracting attention as a system free from wiring in the conventional wired communication system. For example, wireless LAN (Local Area Network) standards such as IEEE (The Institute of Electrical and Electronics Engineers) 802.11a / b, g are representative. According to the wireless LAN, flexible Internet connection is possible. In addition to replacing the existing wired LAN, Internet connection means can be provided in public places such as hotels, airport lounges, stations, and cafes.

  In many wireless communications, data transmission is performed in a multipath environment in which a direct wave and a plurality of reflected / delayed waves arrive at the receiving device. Therefore, delay distortion occurs due to multipath, and communication errors occur. May be caused. Therefore, in wireless LAN standards such as IEEE 802.11a / g, OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme, which is one of the multicarrier schemes, is employed. In the OFDM transmission system, transmission data is distributed and transmitted to a plurality of carriers whose frequencies are orthogonal to each other, so that the bandwidth of each carrier is narrow, the frequency utilization efficiency is very high, and it is resistant to frequency selective fading interference. is there.

  Wireless LANs are already widely used, but recently, they are used not only for information devices such as personal computers (PCs) but also for small and light CE (Consumer Electronics) devices such as digital cameras, music players, and mobile phones. It is becoming common to install a wireless LAN function. Many wireless communications allow flexible connections with omnidirectional antennas. On the other hand, when a wireless LAN is mounted on a portable device, the antenna is required to be small, and a directional antenna is used to connect to a specific communication partner holding the device at a relatively close distance. An application such as Such an application requires a technique for detecting or estimating the distance to a communication partner that transmits and receives radio waves, and the arrival angle of radio waves.

  As a distance measurement method that can be realized relatively easily, a method using received signal power or RSSI (Receive Signal Strength Indicator), or from the arrival time of a packet (or round-trip time of a packet) between communication terminals with packet synchronization. A method for calculating the distance can be given. In the former method, when terminal A receives a packet transmitted by terminal B, which is a measurement target, the received signal power of the packet is measured. If the transmission power transmitted by terminal B is known in advance, the amount of power attenuation between terminal A and terminal B can be acquired. Since the power attenuation can be predicted as a free space propagation loss, the distance from the terminal A to the terminal B can be measured from the value. The free propagation loss is expressed by the following formula (1). Where d is the distance between terminals and λ is the wavelength of the radio wave used.

  2. Description of the Related Art Conventionally, a method is known in which a radio wave is transmitted from a terminal wirelessly, the strength of the radio wave is received by a plurality of base stations, and the position of the terminal is detected based on the same principle as triangulation.

  For example, as one of the position measurement network systems using a wireless LAN, the base station that configures the wireless LAN learns in advance the relationship between the RSSI of radio waves emitted by the wireless terminal and the position. There is known a RADAR system that measures the RSSI of a radio wave and measures the position of a wireless terminal.

  In addition, a position detection system that uses a received signal intensity pattern when a radio wave is received from a wireless device arranged indoors has been proposed (for example, see Patent Document 1). In this position detection system, wireless devices are placed at various locations in the room, and received signal strength patterns of radio waves transmitted from the wireless devices are measured and stored in advance, and received signal strengths of radio waves transmitted from the wireless devices are stored. The pattern is actually measured, a pre-measured received signal strength pattern similar to the actually measured received signal strength pattern is detected, and the position of the wireless device corresponding to the detected received signal strength pattern is The position is detected.

  The method of measuring the distance based on the free propagation loss of the received signal power can obtain the distance fairly accurately in a propagation environment where no reflected wave exists. However, since the actual propagation environment is a multipath propagation environment in which reflected waves exist, the distance cannot be calculated based on the above equation (1).

  FIG. 2 shows a delay profile in a multipath propagation environment. In the example shown in the figure, a state in which a plurality of reflected waves (indirect waves) whose reception power gradually decreases following the direct wave sequentially arrives is shown. The received power observed by the receiver measures the power including a multipath component composed of these many reflected waves. For this reason, even for signals transmitted with the same transmission power from the same distance, a loss value different from the free space propagation loss is obtained according to the situation of the reflected wave at that location. In other words, in a multipath propagation environment, it can be understood that even if an attempt is made to obtain a distance using received power, it becomes inaccurate due to the power of the multipath.

  Under such a multipath propagation environment, the phase relationships of the reflected waves that overlap each other differ depending on the location where the incoming radio wave from the measurement object is received, and they are strengthened or weakened. For this reason, the received power fluctuates greatly even if the reception location is slightly changed. Such a phenomenon that the reception amplitude fluctuates is called “fading”.

  In the delay profile shown in FIG. 2, actually, the reflected waves whose arrival time differences are close to the sampling clock of the receiver or less are displayed as one reflected wave. In other words, if one line in the figure is interpreted as a combination of a plurality of reflected waves, each line fluctuates up and down due to fading when the receiving location moves. The received signal power is shifted due to the presence of reflected waves in addition to the direct wave, and the value fluctuates due to a minute position shift, and further errors occur. For this reason, even if the distance is obtained by free space propagation loss based on the received power in a multipath propagation environment, a large error occurs.

Japanese Patent No. 3809528

  An object of the present invention is to provide an excellent distance measuring device, distance measuring method, communication device, and computer program capable of accurately measuring a distance based on the strength of a signal coming from a measurement object. .

  A further object of the present invention is to provide an excellent distance measurement device and distance measurement capable of accurately calculating a distance based on a free space propagation loss of a received power of a signal whose transmission power transmitted from a measurement object is known. To provide a method, a communication device, and a computer program.

  A further object of the present invention is to provide an excellent distance measurement device and distance measurement capable of calculating a distance without causing a large error based on a free space propagation loss of received signal power even in a multipath propagation environment. To provide a method, a communication device, and a computer program.

The present application has been made in consideration of the above problems, and the invention according to claim 1
A delay profile generation unit that generates a delay profile by performing a correlation operation on a known reference signal included in a packet received from a measurement object;
A direct wave power acquisition unit that acquires received signal power of a direct wave estimated based on the generated delay profile;
A distance discriminating unit that discriminates a distance to the measurement object based on a propagation loss composed of a difference between the estimated direct wave reception signal power and transmission signal power;
It is a distance measuring device characterized by comprising.

  The invention according to claim 2 of the present application is the distance measuring device according to claim 1, further comprising a propagation loss table describing a relationship between transmission signal power and the propagation loss, wherein the distance determining unit A corresponding distance is extracted by referring to the estimated received signal power of the direct wave on the propagation loss table.

  The invention according to claim 3 of the present application further includes a plurality of antenna branches that receive the packet transmitted from the measurement object, and the delay profile generation unit generates a delay profile for each antenna branch. The plurality of delay profiles are averaged.

  Further, in the invention according to claim 4 of the present application, assuming that packets are transmitted from the measurement object on a plurality of channels, the reception branch includes an RF reception circuit for each channel, and the delay profile is provided. The generation unit is configured to generate a delay profile for each channel of the reception branch and average the plurality of delay profiles.

  Further, in the invention according to claim 5 of the present application, the direct wave power acquisition unit converts the received signal into a frequency domain, and applies the high resolution algorithm to the frequency domain to transmit the packet from the measurement object. A delay time from reception to reception is acquired, and a received signal power of a direct wave corresponding to the acquired delay time is acquired from the delay profile.

  In the invention according to claim 6 of the present application, the direct wave power acquisition unit estimates a delayed wave having the maximum received signal power in the delay profile as a direct wave, but the received signal power is maximum. When the delayed wave is an incoming wave after a predetermined time has elapsed from the first incoming wave, it is determined that there is no direct wave, and when it is determined that there is no direct wave, the distance determining unit does not determine the distance, or The distance is determined with a warning.

The invention according to claim 7 of the present application is
A delay profile generation step for generating a delay profile by correlating a known reference signal included in a packet received from a measurement object;
A direct wave power acquisition step of acquiring a received signal power of a direct wave estimated based on the generated delay profile;
A distance determination step of determining a distance to the measurement object based on a propagation loss consisting of a difference between the estimated direct wave reception signal power and transmission signal power;
A distance measuring method characterized by comprising:

The invention according to claim 8 of the present application is
A transmission / reception unit for transmitting / receiving packets to / from a communication partner;
A data processing unit that performs data processing of a packet transmitted to the communication partner and a packet received from the communication partner;
A delay profile generation unit that generates a delay profile by performing a correlation operation on a known reference signal included in the received packet;
A direct wave power acquisition unit that acquires received signal power of a direct wave estimated based on the generated delay profile;
A distance discriminating unit that discriminates a distance to a communication partner based on a propagation loss formed by a difference between the estimated direct wave reception signal power and transmission signal power;
A communication device comprising:

The invention according to claim 9 of the present application is
A computer program written in a computer-readable format to execute a process for measuring a distance on the computer based on the strength of a signal coming from a measurement object,
A delay profile generator for generating a delay profile by performing a correlation operation on a known reference signal included in a packet received from a measurement object;
A direct wave power acquisition unit that acquires a received signal power of a direct wave estimated based on the generated delay profile;
A distance discriminating unit that discriminates a distance to the measurement object based on a propagation loss formed by a difference between the estimated direct wave reception signal power and transmission signal power;
It is a computer program to function as.

  The computer program according to claim 9 of the present application defines a computer program described in a computer-readable format so as to realize predetermined processing on a computer system. In other words, by installing the computer program according to claim 9 of the present application in the computer system, a cooperative action is exhibited on the computer system, and the same as the distance measuring device according to claim 1 of the present application. An effect can be obtained.

  According to the present invention, it is possible to provide an excellent distance measuring device, distance measuring method, communication device, and computer program capable of accurately measuring a distance based on the strength of a signal coming from a measurement object. .

  Further, according to the present invention, an excellent distance measuring apparatus and distance that can accurately calculate the distance based on the free space propagation loss of the received power of the signal for which the transmission power transmitted from the measurement object is known A measurement method, a communication device, and a computer program can be provided.

  Further, according to the present invention, even in a multipath propagation environment, it is possible to calculate the distance without causing a large error based on the free space propagation loss of the received signal power, and an excellent distance measurement device and distance A measurement method, a communication device, and a computer program can be provided.

  According to the first, second, seventh, eighth, and ninth aspects of the present application, the power of only the direct wave is extracted from the delay profile acquired by using the known reference signal included in the packet received from the measurement object. Using this, the distance can be obtained from the propagation loss table. Actually, when the sampling clock of the receiver is not very high, a delayed wave may be included in the wave estimated as the direct wave by the direct wave power acquisition unit, but many other delays are included. Since the wave is removed, the accuracy is considerably improved.

  According to the invention described in claim 3 of the present application, when there are a plurality of receiving antenna branches for performing MIMO or diversity reception, it is obtained for each antenna due to the fading effect depending on the difference in antenna position. Although the delay profile fluctuates, by averaging the plurality of delay profiles, it becomes possible to suppress the fluctuation of the received signal power due to the influence of fading as much as possible, and an accurate distance measurement can be performed. In addition, by averaging multiple delay profiles, it is possible to average the effects of fading due to delayed waves present in the sampling clock and to stabilize the power of the direct wave more accurately, so accurate distance measurement is possible. It becomes possible.

  In the invention according to claim 4 of the present application, the reception branch includes an RF reception circuit for each channel on the assumption that packets are transmitted from the measurement object on a plurality of channels. The delay profile obtained for each channel varies because the influence of fading differs for each channel, but by averaging these multiple delay profiles, it becomes possible to suppress fluctuations in the received signal power due to the effect of fading as much as possible. Accurate distance measurement can be performed. For example, in a multipath communication environment in which two communication systems such as IEEE802.11a using 5 GHz band and IEEE802.11b using 2.4 GHz band coexist, a direct wave reception signal obtained for each channel used in each communication system. By averaging the power, the power of the direct wave can be further stabilized, so that accurate distance measurement is possible.

  According to the invention described in claim 5 of the present application, the direct wave power acquisition unit is configured to acquire the received signal power of the direct wave using a high resolution algorithm. As a high resolution algorithm, MUSIC, ESPRIT algorithm, etc. are known, and the received signal is changed to a frequency domain signal by performing an FFT (Fast Fourier Transform) operation on the frequency domain signal. By adapting the ESPRIT algorithm, the arrival position of the received signal can be estimated even during the sampling clock. And the electric power of a direct wave can be calculated | required correctly using the formula which calculates | requires the electric power with respect to this arrival time.

  According to the invention described in claim 6 of the present application, the direct wave power acquisition unit can estimate a delayed wave having the maximum received signal power in the delay profile as a direct wave. Further, when the delayed wave with the maximum received signal power is an incoming wave after a predetermined time has elapsed from the first incoming wave, it is determined that there is no direct wave, and when it is determined that there is no direct wave, the distance determining unit Can determine the distance without warning or with a warning.

  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. 3 shows a configuration example of a computer equipped with a wireless communication function.

  A CPU (Central Processing Unit) 1 executes a program stored in a ROM (Read Only Memory) 2 or a hard disk drive (HDD) 11 under a program execution environment provided by an operating system (OS). . For example, the received packet synchronization process described later or a part of the process can be realized in a form in which the CPU 1 executes a predetermined program.

  The ROM 2 permanently stores program codes such as POST (Power On Self Test) and BIOS (Basic Input Output System). A RAM (Random Access Memory) 3 is used to load a program stored in the ROM 2 or the HDD 11 when the CPU 1 executes it, or to temporarily hold work data of the program being executed. These are connected to each other by a local bus 4 directly connected to a local pin of the CPU 1.

  The local bus 4 is connected via a bridge 5 to an input / output bus 6 such as a peripheral component interconnect (PCI) bus.

  A keyboard 8 and a pointing device 9 such as a mouse are input devices operated by a user. The display 10 includes an LCD (Liquid Crystal Display) or a CRT (Cathode Ray Tube), and displays various information as text and images.

  The HDD 11 is a drive unit incorporating a hard disk as a recording medium, and drives the hard disk. The hard disk is used for installing programs executed by the CPU 1 such as an operating system and various applications, and for storing data files and the like.

  The communication unit 12 is a wireless communication interface according to, for example, IEEE802.11a / n, and operates as an access point or a terminal station in the infrastructure mode, or operates in the ad hoc mode, and is in the communication range. Execute communication with the communication terminal. In this embodiment, the communication unit 12 uses the received power of the direct wave estimated from the delay profile obtained by correlating the known reference signal of the received packet to the transmitter based on the free space propagation loss. The distance is measured (described later).

  Here, the IEEE 802.11a / g standard supports a modulation scheme that achieves a communication speed of 54 Mbps at the maximum, but a next-generation wireless LAN standard capable of realizing a higher bit rate is required. As a wireless communication technique for realizing high-throughput wireless data transmission, a multi-antenna technique in which a communication device includes a plurality of antennas can be cited.

  As an example of the multi-antenna technique, an adaptive array antenna is widely known. This is a system that supports communication by obtaining appropriate antenna directivity in transmission and reception by controlling the gain of each antenna element. For the array antenna, the main lobe is directed only in the desired direction and unnecessary radio waves are not radiated by the low side lobe in the undesired direction, and the main lobe is directed in the desired mobile station direction for interference. There is a method for improving the SINR (signal-to-noise interference power ratio) by pointing null toward the mobile station.

  In addition, as another example of the multi-antenna technique, a diversity technique that uses a plurality of antennas arranged so as to reduce the correlation between signals and combines or switches a plurality of received signals including the same information to improve characteristics. And degradation due to flat fading can be solved.

  Further, as another example of the multi-antenna technique, MIMO (Multi-Input Multi-Output) communication has attracted attention. MIMO realizes higher quality communication by performing beam forming between a transmitter (Beamformer) and a receiver (Beamforme) each having a plurality of antenna elements. The beam forming here is a method in which each transmitting antenna is digitally weighted to change the directivity of the antenna. The transmit antenna weight can be obtained by analyzing the forward channel matrix H from the transmitter to the receiver. According to the MIMO communication system, it is possible to increase the transmission capacity according to the number of antennas without increasing the frequency band, thereby achieving an improvement in communication speed. Also, since spatial multiplexing is used, the frequency utilization efficiency is good. MIMO is a communication method using channel characteristics, and is different from a transmission / reception adaptive array. For example, IEEE 802.11n, which is an extension standard of IEEE 802.11, employs a MIMO communication system.

  FIG. 1 schematically shows a configuration example in the communication unit 12 equipped in the computer shown in FIG. The illustrated communication device includes a multi-antenna and performs MIMO reception or diversity reception. In the illustrated example, the number of transmission / reception antennas is two for convenience of explanation, but the gist of the present invention is not limited to a specific number of antennas.

  The illustrated communication device is assumed to be used for a plurality of communication systems using different channels such as IEEE802.11a and IEEE802.11b. Since IEEE802.11a uses a frequency channel of 5 GHz band and IEEE802.11b uses a frequency channel of 2.4 GHz band (well-known), each transmission / reception branch provided for each transmission / reception antenna is an RF for 5 GHz band. Each is provided with a combination of a transmitting / receiving unit and an RF transmitting / receiving unit for 2.4 GHz band.

  The transmission / reception antenna 101 is connected to the RF transmission / reception circuit unit 103 via the antenna switch 102. The RF transmission / reception circuit unit 103 includes, as a reception system, a low noise amplifier (LNA), an orthogonal demodulator (IQ demodulator) that down-converts a reception signal in the RF frequency band, and an AD converter in which the power of the reception signal is in a subsequent stage Equipped with an AGC (Automatic Gain Control) amplifier that normalizes to fit within the dynamic range of (Analog to Digital Converter: ADC), an analog low-pass filter (LPF) that removes signal components other than the desired band, etc. Also, as a transmission system, an analog LPF that removes signal components other than the desired band from the analog transmission signal after DA conversion, a quadrature modulator (IQ modulator) that upconverts to a transmission signal in the RF frequency band, Power amplifier for power-amplifying the signal (Power Amplifier) (not shown either) composed like. When the communication device operates as an object for measuring the distance from the communication partner, the power amplification amplifier amplifies the known reference signal of the packet so that the transmission signal power becomes known to the communication partner.

  Further, as described above, the communication device is assumed to be used in a multipath communication environment in which IEEE802.11a using the 5 GHz band and IEEE802.11b using the 2.4 GHz band coexist. The transmission / reception circuit unit 103 includes a 5 GHz band RF transmission / reception unit 103A and a 2.4 GHz band RF transmission / reception unit 103B.

  Each of the RF transmission / reception processing units 103A and 103B is connected to an AD converter (ADC) 105A and a DA converter (DAC) 105B via a switch 104.

  The transmission data processing unit 108 divides the transmission data stream passed from the higher-level processing unit 109 into packets, performs processing such as encoding, and then passes them to the DA converter 105B. In a communication system that employs the OFDM modulation scheme, OFDM modulation processing such as IFFT (Inverse FFT: Inverse Fast Fourier Transform) calculation is performed. Further, in a communication system employing the MIMO communication method, a plurality of transmission data streams are distributed to each transmission branch, and beam forming or spatial multiplexing processing is performed.

  Further, the synchronization processing unit 106 determines rough reception timing (temporary reception timing) based on packet discovery, frequency offset correction, noise estimation, and provisional reception timing for the reception signal digitally converted by the AD converter 105A. Processing such as extraction of more accurate reception timing used is performed. The temporary reception timing can be determined based on the autocorrelation calculation of the known burst-like reference signal at the head of the packet. In addition, accurate reception timing can be determined based on cross-correlation calculation of known reference signals.

  In the frame format in IEEE802.11a / g, a preamble section (STF: Short Training Field) consisting of a short training sequence (STS) that can be used for temporary reception timing determination and frequency offset, and accurate reception timing. A preamble section (LTF: Long Training Field) consisting of a long training sequence (LTS) that is cut by use for extraction is defined, but detailed description thereof is omitted in this specification.

  The received data processing unit 107 performs decoding processing of the portion (information field) after the synchronization processing, and reproduces the original data. In a communication system employing the OFDM modulation scheme, OFDM demodulation processing such as FFT operation is performed. Also, in a communication system that employs the MIMO communication scheme, spatial separation processing is performed by multiplying the reception data stream for each reception branch by a reception weight matrix.

  The delay profile generator 110 generates a delay profile (see FIG. 2) by performing a cross-correlation operation on the known reference signal added to the head of the packet. The delay profile can be generated using the result of the cross-correlation calculation at the time of timing detection in the synchronization processing unit 106, and based on the gain value of the AGC amplifier (described above) at the time of reception and the magnitude of the digital signal, The received signal power of each delayed wave of the delay profile can be converted. A method for generating a delay profile by cross-correlation calculation is also described in, for example, Japanese Patent Application Laid-Open No. 2004-221940 (paragraph numbers 0201 to 0202, FIG. 29) already assigned to the present applicant. Then, detailed description is abbreviate | omitted.

  The direct wave power acquisition unit 111 estimates a direct wave from the delay profile generated by the delay profile generation unit 110 and acquires the received signal power of the estimated direct wave.

  For example, the direct wave power acquisition unit 111 can estimate a delayed wave having the maximum received signal power in the delay profile as a direct wave. However, it should be determined that there is no direct wave when the delayed wave having the maximum received signal power is an incoming wave after a predetermined time has elapsed from the first incoming wave.

  The distance discriminating unit 112 calculates the distance to the measurement object that is the transmission source of the packet based on the propagation loss that is the difference between the direct wave received signal power and the transmitted signal power estimated by the direct wave power acquiring unit 111. Determine.

  The transmission signal power of the packet transmitted from the measurement object is known (described above). Accordingly, the free propagation loss consisting of the difference between the direct wave received signal power and the transmitted signal power can be calculated from the above equation (1). The propagation loss table 113 includes a ROM stored in a table format describing the relationship between known transmission signal power and propagation loss. A configuration example of the propagation loss table 113 is shown below.

  The distance determination unit 112 refers to the reception signal power of the direct wave estimated by the direct wave power acquisition unit 111 on the propagation loss table 113 to extract the corresponding distance. A specific example of determining the distance is shown below.

Step 1: The measurement object transmits a packet at 0 dBm in the 5 GHz band.
Step 2: The communication device receives the packet, creates a delay profile in the delay profile generation unit 110, and the direct wave power acquisition unit 111 obtains received signal power corresponding to the direct wave. For example, it is determined that the received signal power of the direct wave is −65.5 dBm.
Step 3: If there is a propagation loss with 0 dB of 65.5 dBm from the table in Table 1, the received power becomes -65.5 dBm, so the distance determination unit 112 estimates that there is a distance of 9 meters to the measurement object. .

  Further, as described above, the direct wave power acquisition unit 111 may determine that “there is no direct wave” in the delay profile. In such a case, the distance determination unit 112 may perform distance determination without performing distance determination or with a warning.

  The communication apparatus shown in FIG. 1 has a multi-antenna configuration including a plurality of transmission / reception antennas, and performs MIMO communication, adaptive array, or diversity reception. In such a case, a packet transmitted from the measurement object can be received and processed by each antenna branch. The delay profile generation unit 110 generates a delay profile for each reception branch, and averages the plurality of delay profiles.

  Although it is predicted that the delay profile obtained for each antenna branch varies due to the influence of fading depending on the difference in antenna position, the delay profile generator 110 averages the plurality of delay profiles, thereby fading. It is possible to suppress fluctuations in received signal power as much as possible. As a result, the latter distance determination unit 112 can perform more accurate distance determination. Also, by averaging multiple delay profiles, it is possible to average the effect of fading due to delayed waves present in the sampling clock and stabilize the power of the direct wave, so accurate distance determination is possible. It becomes possible. The direct waves received for each branch are all in phase, but since the phases of the reflected waves are not aligned, the reflected waves are suppressed by averaging.

  Further, as described above, the communication device shown in FIG. 1 is assumed to be used in a multipath communication environment in which IEEE802.11a using the 5 GHz band and IEEE802.11b using the 2.4 GHz band coexist. The RF transmission / reception circuit unit 103 for each branch includes an RF transmission / reception unit 103A for 5 GHz band and an RF transmission / reception unit 103B for 2.4 GHz band.

  The delay profile generator 110 generates a delay profile by cross-correlation of known reference signals for each frequency channel of 5 GHz band and 2.4 GHz pair in each reception branch, and averages a plurality of delay profiles for each frequency channel. It tries to become.

  Since the influence of fading is different for each channel to be used, the delay profile obtained for each frequency channel varies. The delay profile generation unit 110 averages the plurality of delay profiles, thereby making it possible to suppress fluctuations in received signal power as much as possible due to the influence of fading, and the distance determination unit 112 in the subsequent stage performs more accurate distance determination. be able to. Thus, in a multipath communication environment in which two communication systems coexist, the direct wave power is further stabilized by averaging the direct wave received signal power obtained for each channel used in each communication system. Therefore, accurate distance determination can be performed. Although the direct waves received for each branch are all in phase, since the phases of the reflected waves are not aligned, the reflected waves are suppressed by averaging (same as above).

  In the above description, the direct wave power acquisition unit 111 estimates a delayed wave having the maximum received signal power in the delay profile as a direct wave (however, the delayed wave having the maximum received signal power is If it is an incoming wave after a lapse of a predetermined time from the first incoming wave, it is determined that there is no direct wave). There is a method in which a delay time τ until reception is acquired, and a received signal power of a direct wave corresponding to the acquired delay time τ is acquired from a delay profile.

  The communication device shown in FIG. 1 is applied with a multi-antenna technique and includes an array antenna that receives a packet from a measurement target, and can apply a high-resolution algorithm such as a MUSIC or ESPRIT algorithm.

  Here, MUSIC ((Multiple Signal Classification) algorithm and ESPRIT (Estimation of Signal Parameters via Rotational Invariance Technique) algorithm are known in the industry as a technique for detecting the angle of arrival of radio waves. The eigenvalues and eigenvectors of the correlation matrix obtained from the array antenna reception signal are obtained, and the angle spectrum is calculated, and the ESPRIT method also obtains the eigenvalues and eigenvectors of the correlation matrix obtained from the array antenna reception signal as in the MUSIC method. The difference is that the arrival angle of the radio wave is estimated based on the rotation invariant relationship between the antennas.

  The delay time estimation using the MUSIC or ESPRIT algorithm is described in, for example, “Adaptive signal processing by array antenna” written by Nobuyoshi Kikuma (1998, Science and Technology Publication). The system configuration for estimating the delay time is as follows.

(1) Transmitter A that generates radio waves (equivalent to a measurement object)
(2) Transmit antenna B that transmits the radio wave generated by transmitter A toward the target
(3) Receiving antenna C that receives radio waves reflected by the target
(4) A receiver D that generates a reception signal by subjecting the reception wave of the reception antenna C to band limitation and phase detection.
(5) A / D converter E that AD converts the received signal generated by the receiver D and outputs a digital signal
(6) An FFT processing unit F that performs an FFT operation process, which is a fast Fourier transform process, on the digital signal output from the A / D converter E to obtain a frequency spectrum of the received signal.
(7) A division signal generation unit G that generates a division signal by dividing the frequency spectrum of the reception signal obtained by the FFT processing unit F by the frequency spectrum of the transmission wave.
(8) A high resolution estimation processing unit H that estimates the delay time of the target signal by performing a high resolution delay time estimation process on the division signal generated by the division signal generation unit G

  For example, when 128-point FFT is used, 128 pieces of data can be acquired. By averaging this 100 times, a 128 × 128 covariance matrix can be obtained. For this covariance matrix, a delay spectrum is drawn by MUSIC or ESPRIT algorithm, and its arrival time is accurately estimated. As for the received signal power corresponding to the arrival time, if the arrival time of the wave is obtained by delay time estimation, S is obtained as shown in the following equation (2) using the mode vector corresponding to the direct wave. Since the received power of the incoming wave enters the diagonal matrix of S, the power corresponding to the direct wave can be accurately obtained.

  As a result, by using the power of only the direct wave accurately, it becomes difficult to be affected by fading, and an accurate distance can be obtained. This type of high resolution algorithm is practically implemented in software by the upper processing unit 109.

  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 the present specification, the embodiment applied to a communication device including a multi-antenna has been mainly described, but the gist of the present invention is not limited to the multi-antenna technology. Of course, the present invention can be suitably applied to a single antenna communication technique.

  In addition, when the present invention is applied to the multi-antenna technology, a plurality of delay profiles are averaged by using the fact that the delay profile varies for each antenna due to the influence of fading that depends on the difference in antenna position. Thus, fluctuations in received signal power due to fading can be suppressed as much as possible. The gist of the present invention is not limited to a specific multi-antenna technique, and can be suitably applied to any of MIMO, adaptive array, and diversity.

  In this specification, a combination of IEEE802.11a using 5 GHz band and IEEE802.11b using 2.4 GHz band is taken up as a communication system using different channels, but the gist of the present invention is that of a specific communication system. It is not limited to the combination.

  The scope of application of the present invention is not limited to wireless LAN standards such as IEEE802.11a / n, and the present invention can be applied to various digital wireless technologies.

  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 illustrating a configuration example of a communication device according to an embodiment of the present invention. FIG. 2 is a diagram showing a delay profile in a multipath propagation environment. FIG. 3 is a diagram illustrating a configuration example of a computer having a wireless communication function.

Explanation of symbols

1 ... CPU
2 ... ROM
3 ... RAM
4 ... Local bus 5 ... Bridge 6 ... I / O bus 7 ... I / O interface 8 ... Keyboard 9 ... Pointing device (mouse)
10 ... Display 11 ... HDD
DESCRIPTION OF SYMBOLS 12 ... Communication part 101 ... Antenna 102 ... Antenna switch 103 ... RF transmission / reception circuit part 103A ... RF transmission / reception circuit part for 5 GHz band 103B ... RF transmission / reception circuit part for 2.4 GHz band 104 ... Switch 105A ... AD converter (ADC), 105B ... DA converter (DAC)
DESCRIPTION OF SYMBOLS 106 ... Synchronization processing part 107 ... Reception data processing part 108 ... Transmission data processing part 109 ... High-order processing part 110 ... Delay profile generation part 111 ... Direct wave power acquisition part 112 ... Distance discrimination | determination part 113 ... Propagation loss table

Claims (9)

A delay profile generation unit that generates a delay profile by performing a correlation operation on a known reference signal included in a packet received from a measurement object;
A direct wave power acquisition unit that acquires received signal power of a direct wave estimated based on the generated delay profile;
A distance discriminating unit that discriminates a distance to the measurement object based on a propagation loss composed of a difference between the estimated direct wave reception signal power and transmission signal power;
A distance measuring device comprising: The transmission signal power of the packet transmitted from the measurement object is known,
A propagation loss table describing the relationship between the known transmission signal power and the propagation loss;
The distance determining unit refers to the estimated direct wave received signal power on the propagation loss table, and extracts a corresponding distance.
The distance measuring device according to claim 1. A plurality of reception antennas for receiving the packets sent from the measurement object and a plurality of reception branches for each reception antenna;
The delay profile generation unit generates a delay profile for each reception branch, and averages the plurality of delay profiles.
The distance measuring device according to claim 1. It is assumed that packets from the measurement object are transmitted on a plurality of channels, and the reception branch includes an RF reception circuit for each channel,
The delay profile generation unit generates a delay profile for each channel of the reception branch, and averages the plurality of delay profiles.
The distance measuring device according to claim 1. An array antenna for receiving the packet transmitted from the measurement object;
The direct wave power acquisition unit converts a received signal into a frequency domain, applies a high resolution algorithm to the frequency domain, and acquires a delay time from when the packet is transmitted from the measurement object to when it is received. Acquiring the received signal power of the direct wave corresponding to the acquired delay time from the delay profile;
The distance measuring device according to claim 1. The direct wave power acquisition unit estimates a delayed wave having the maximum received signal power in the delay profile as a direct wave, but after the delayed wave having the maximum received signal power has elapsed for a predetermined time from the first incoming wave. When it is an incoming wave, it is determined that there is no direct wave,
When it is determined that there is no direct wave, the distance determination unit does not determine the distance or performs distance determination with a warning.
The distance measuring device according to claim 1. A delay profile generation step for generating a delay profile by correlating a known reference signal included in a packet received from a measurement object;
A direct wave power acquisition step of acquiring a received signal power of a direct wave estimated based on the generated delay profile;
A distance determination step of determining a distance to the measurement object based on a propagation loss consisting of a difference between the estimated direct wave reception signal power and transmission signal power;
A distance measuring method comprising: A transmission / reception unit for transmitting / receiving packets to / from a communication partner;
A data processing unit that performs data processing of a packet transmitted to the communication partner and a packet received from the communication partner;
A delay profile generation unit that generates a delay profile by performing a correlation operation on a known reference signal included in the received packet;
A direct wave power acquisition unit that acquires received signal power of a direct wave estimated based on the generated delay profile;
A distance discriminating unit that discriminates a distance to a communication partner based on a propagation loss formed by a difference between the estimated direct wave reception signal power and transmission signal power;
A communication apparatus comprising: A computer program written in a computer-readable format to execute a process for measuring a distance on the computer based on the strength of a signal coming from a measurement object, the computer comprising:
A delay profile generator for generating a delay profile by performing a correlation operation on a known reference signal included in a packet received from a measurement object;
A direct wave power acquisition unit that acquires a received signal power of a direct wave estimated based on the generated delay profile;
A distance discriminating unit that discriminates a distance to the measurement object based on a propagation loss formed by a difference between the estimated direct wave reception signal power and transmission signal power;
A computer program that functions as a computer.

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