JP2015023555A - Communication device, communication system and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication device, a communication system and a communication method capable of estimating an abrupt channel change.SOLUTION: The communication device processes a communication signal in which each symbol constituting a frame, including a preamble part and a data part, is transmitted through a plurality of subcarriers. The plurality of subcarriers for transmitting the data part includes at least one or more pilot subcarriers to transmit a known signal. The communication device includes: a channel estimation unit for estimating a channel on the basis of each of the plurality of known signals transmitted at mutually different timing; and a channel variation estimation unit for estimating a channel variation on the basis of correlation between channels estimated based on each of the plurality of known signals transmitted at the mutually different timing.

Description

  The present invention relates to a communication device, a communication system, and a communication method.

  Conventionally, various methods for realizing high-speed transmission in wireless communication have been proposed, and in particular, a MIMO (Multiple-Input and Multiple-Output) scheme capable of realizing high frequency utilization efficiency has attracted attention. MIMO is a spatial multiplexing transmission technology that uses a plurality of antennas to simultaneously transmit and receive a plurality of data at the same frequency. Since a plurality of data can be transmitted simultaneously, it is theoretically said that the communication speed can be increased in proportion to the number of antennas. Further, since data can be transmitted at the same frequency, it is not necessary to secure a wide frequency band for multiplexing, and the frequency utilization efficiency is excellent.

  In addition, as an example of a communication method applying MIMO, MIMO-OFDM (Multiple-Input and Multiple-Frequency Frequency Division) is introduced in wireless LAN (Local Area Network) such as IEEE 801.11n. .

Consideration of antenna arrangement suitable for 2x2 MIMO sensor using real propagation channel. IEICE technical report RCS2011-5, 20111.4

  On the other hand, in MIMO transmission, transmission characteristics vary depending on antenna conditions used in the configuration on the transmission side and the configuration on the reception side (for example, an access point and a communication terminal connected to the access point) and the surrounding propagation environment. It is known to be greatly affected.

  For this reason, for example, in transmission using the MIMO-OFDM scheme, a known channel, called a long preamble, is transmitted and received between the transmitting side configuration and the receiving side configuration, thereby transmitting a propagation channel (hereinafter simply referred to as “channel”). Is sometimes estimated).

  For example, Non-Patent Document 1 discloses an example of a technique for estimating channel fluctuations using a long preamble. In the example shown in Non-Patent Document 1, channel estimation is performed based on a plurality of long preambles having different transmission timings. That is, in order to estimate channel fluctuation, it is necessary to wait until at least the next long preamble is received after receiving one long preamble.

  However, the long preamble is included only in a section (hereinafter, sometimes referred to as a “preamble part”) located at the beginning of a transmission frame in order to ensure communication efficiency, and a section for transmitting data (hereinafter, (Sometimes referred to as “data part”). For this reason, it is difficult to receive a long preamble during the transmission period of the data part, and it may be difficult to estimate abrupt channel fluctuation as the transmission period of the data part becomes longer.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved communication apparatus, communication system, and the like that can estimate abrupt channel fluctuations. And providing a communication method.

  In order to solve the above-described problem, according to an aspect of the present invention, there is provided a communication apparatus that processes a communication signal in which each symbol constituting a frame including a preamble part and a data part is transmitted by a plurality of subcarriers. The plurality of subcarriers for transmitting the data part include at least one or more pilot subcarriers for transmitting a known signal, and channels based on each of the plurality of known signals transmitted at different timings A channel estimation unit for estimating channel variation based on a correlation between the channels estimated based on each of the plurality of known signals transmitted at different timings. A communication device is provided.

  The plurality of subcarriers includes a plurality of pilot subcarriers, and the channel estimation unit estimates the channel based on the known signals corresponding to the pilot subcarriers for each of the plurality of pilot subcarriers. The channel fluctuation estimation unit, for each of the plurality of pilot subcarriers, based on the correlation between the channels estimated based on each of the plurality of known signals transmitted at different timings, May be estimated.

  The communication signal is transmitted from a plurality of transmission antennas and received by each of a plurality of reception antennas, and the channel estimation unit includes a plurality of transmission antennas configured between the plurality of transmission antennas and the plurality of reception antennas. The channel is estimated for each propagation path, and the channel fluctuation estimation unit estimates the channel between the channels estimated based on the plurality of known signals transmitted at the different timings through the plurality of propagation paths. The channel fluctuation may be estimated based on the correlation.

  The different timings may be successive timings.

  A reception processing unit that demodulates the received communication signal may be provided.

  A reception antenna that receives the communication signal may be provided, and the reception processing unit may demodulate the communication signal received by the reception antenna.

  You may provide the transmission process part which transmits the said communication signal to a transmission antenna.

  The transmission antenna may be provided.

  In order to solve the above-described problem, according to another aspect of the present invention, a transmitter that transmits each symbol constituting a frame including a preamble part and a data part as a communication signal using a plurality of subcarriers, A plurality of subcarriers for transmitting the data portion include at least one pilot subcarrier for transmitting a known signal, and the receiving apparatuses are different from each other. A channel estimator for estimating a channel based on each of the plurality of known signals transmitted at timing; and a correlation between the channels estimated based on each of the plurality of known signals transmitted at different timings. And a channel fluctuation estimation unit that estimates channel fluctuation based on the communication system. It is subjected.

  In order to solve the above problem, according to another aspect of the present invention, a communication method for processing a communication signal in which each symbol constituting a frame including a preamble part and a data part is transmitted by a plurality of subcarriers. The plurality of subcarriers for transmitting the data portion includes at least one pilot subcarrier for transmitting a known signal, and each of the plurality of known signals transmitted at different timings. And estimating a channel fluctuation based on a correlation between the channels estimated based on each of the plurality of known signals transmitted at different timings. A featured communication method is provided.

  As described above, according to the present invention, there are provided a communication device, a communication system, and a communication method capable of estimating a rapid channel fluctuation.

It is the figure which showed the schematic structure of the flame | frame used by an OFDM system. It is an example of the frame structure of the communication signal used with the communication system which concerns on this embodiment. It is the block diagram which showed an example of the structure of the communication system which concerns on embodiment of this invention. It is a figure for demonstrating the estimation of the channel in the communication system which concerns on this embodiment. It is the block diagram which showed another example of the communication system which concerns on this embodiment. It is the figure which showed an example of the measurement environment which concerns on an Example. It is the figure which showed an example of the measurement result which concerns on an Example, the comparative example 1, and the comparative example 2. FIG.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Embodiment>
[Overview]
First, the outline of channel estimation and the problems of the communication system 1 according to this embodiment will be summarized, and then the outline of the communication system 1 according to this embodiment will be described.

First, a channel estimation method in transmission based on the MIMO scheme will be described taking the case of the MIMO-OFDM scheme as an example. Note that the OFDM scheme (orthogonal frequency division multiplexing) is a multicarrier transmission scheme in which the frequency of each subcarrier is set so that the subcarriers are orthogonal to each other within a symbol interval. For example, in the MIMO-OFDM scheme, the channel h _ij between the j-th transmission antenna and the i-th reception antenna is estimated by (Equation 1) shown below.

In (Expression 1), s _j (k) represents a transmission signal transmitted from the jth transmission antenna by the kth subcarrier. R _ij (k) indicates a received signal transmitted from the j-th transmission antenna by the k-th subcarrier and received by the i-th reception antenna.

In general, it is difficult to derive the transmission signal s _j (k) in the configuration on the reception side. For example, known signals are transmitted and received between the configuration on the transmission side and the configuration on the reception side. Thus, in the configuration on the receiving side, the channel h _ij can be estimated based on the known signal.

  Here, an outline of channel estimation based on the conventional scheme will be described. First, a schematic configuration of a frame used in the OFDM scheme will be described with reference to FIG. FIG. 1 is a diagram showing a schematic configuration of a frame used in the OFDM scheme, and shows a case where attention is paid to subcarriers c1 and c2 among a plurality of subcarriers for transmitting a frame.

  In FIG. 1, reference numeral d102 indicates a section in which one short preamble (SP) signal is transmitted. Reference numeral d104 indicates a section for transmitting h long preamble (LP) signals (h is an integer of 2 or more). Note that a section including the short preamble and the long preamble indicated by reference numerals d102 and d104 corresponds to a preamble signal section, that is, a preamble portion.

  The long preamble signal is a code pattern known in the system. The long preamble signal may be composed of, for example, an orthogonal code such as an M sequence (M is the number of transmission antennas) or a Hadamard sequence, and the length thereof is determined by the length of the orthogonal code (for example, OFDM) Number of signal symbols). The long preamble signal is repeatedly transmitted h times. Note that the value of h is appropriately set depending on the number of antenna control patterns in the applied communication system. Note that the example shown in FIG. 1 shows a case where two long preamble signals are transmitted (when h = 2).

  Reference numeral d110 indicates a section for transmitting data, that is, a data portion. The data length of the data part d110 becomes variable, and the example shown in FIG. 1 shows an example in which the data part d110 includes U symbols.

  As described above, channel estimation is performed using a known signal between the configuration on the transmission side and the configuration on the reception side. In the conventional method, a long signal is used as a known signal used for channel estimation. The preamble is used.

  However, the long preamble is included only in the section (for example, the preamble portion) located at the beginning of the transmission frame to ensure communication efficiency, and is included in the data portion for transmitting data as shown in FIG. Absent. That is, during the transmission period of the data part, it is difficult for the receiving side configuration to receive the long preamble. Therefore, even if a sudden channel change occurs during the transmission period of the data part, it is difficult for the receiving side configuration to estimate the channel change.

  Therefore, the communication system 1 according to the present embodiment is intended to enable rapid channel fluctuation estimation even in the transmission period of the data portion. Specifically, the communication system 1 according to the present embodiment estimates channel fluctuation based on a known signal included in the data part. Therefore, hereinafter, the outline of the communication system 1 according to the present embodiment will be described with reference to FIG. 2, taking as an example a case where a frame configuration defined in IEEE 802.11a typically used in the OFDM scheme is applied. To do. FIG. 2 is an example of a frame configuration of a communication signal used in the communication system 1 according to the present embodiment, and shows an example of a frame d10 defined by IEEE802.11a.

  As shown in FIG. 2, the frame d10 includes a short preamble d102, a long preamble d104, a signal field d112, and a data part d114.

  Short preamble d102 includes 10 short training symbols assigned to each of 12-wave subcarriers c10. In the example shown in FIG. 2, the data length of the short training symbol is 800 ns, and the data length of the short preamble d102 is 8 μs.

  The long preamble d104 includes two long training symbols assigned to 52 subcarriers. In the example shown in FIG. 2, the data length of the long training symbol is 4 μs, and the data length of the long preamble d104 is 8 μs.

  Signal field d112 includes one OFDM symbol assigned to each of the 52 subcarriers. The signal field is used for transmission of information for decoding received data, such as the length and delay of a packet, by the configuration on the receiving side. In the example shown in FIG. 2, the data length of one OFDM symbol is 4 μs, and the data length of the signal field d112 is 4 μs.

  The area after the signal field d112 corresponds to the data part d114. The data part d114 includes 52 subcarriers, and among the 52 subcarriers, the four subcarriers indicated by reference symbols c12a to c12d are known signals (hereinafter referred to as “pilot signals”). Used to send Hereinafter, each of the four subcarriers c12a to c12d used for transmitting the pilot signal may be referred to as a “pilot subcarrier”. Pilot subcarriers c12a to c12d are inserted for synchronization supplementation. In addition, when each of the pilot subcarriers c12a to c12d is not particularly distinguished, it may be described as “pilot subcarrier c12”.

  The communication system 1 according to the present embodiment estimates channel variation by using pilot subcarriers c12a to c12d among a plurality of subcarriers for transmitting the data part d114. As a result, the communication system 1 according to the present embodiment enables rapid channel fluctuation estimation even during the transmission period of the data part d114. Hereinafter, details of the communication system 1 according to the present embodiment will be described.

[Constitution]
First, the configuration of the communication system 1 according to the present embodiment will be described with reference to FIG. FIG. 3 is a block diagram illustrating an example of a configuration of the communication system 1 according to the embodiment of the present invention, and illustrates an example of a MIMO wireless communication system. In the present embodiment, description will be made assuming that the communication system 1 is an orthogonal frequency division multiplexing (MIMO-OFDM) system represented by IEEE 802.11n.

  As illustrated in FIG. 3, the communication system 1 according to the present embodiment includes a transmission device 50, a plurality of transmission antennas Tx1 and Tx2, a plurality of reception antennas Rx1 and Rx2, and a reception device 10. In the example illustrated in FIG. 3, the propagation paths h11, h12, h21, and h22 are established between the transmission antennas Tx1 and Tx2 connected to the transmission device 50 and the reception antennas Rx1 and Rx2 connected to the reception device 10. An example of 2 × 2 MIMO for forming is shown. However, the example illustrated in FIG. 3 is merely an example, and the configuration of the communication system 1 according to the present embodiment is not limited to 2 × 2 MIMO, and the number of transmission antennas and reception antennas is not particularly limited. The receiving apparatus 10 according to the present embodiment includes a reception processing unit 102, a channel estimation unit 104, and a channel fluctuation estimation unit 106.

  The transmission device 50 is a device that transmits m signals from m transmission antennas (m ≧ 2). For example, in the example shown in FIG. 3, since the number of transmission antennas is two, the transmission device 50 transmits signals of two systems (m = 2).

  The transmission device 50 generates a data frame (data portion) having a predetermined frame format suitable for wireless transmission from transmission data input from the outside, and adds a preamble portion to the head of each generated frame. Transmitting apparatus 50 arranges a pilot signal at a predetermined position in the frequency direction of the data frame. This pilot signal is transmitted by the pilot subcarrier c12.

  The transmitting device 50 modulates the two systems of signals to which the preamble signal is added, converts the frequency into a signal of a predetermined radio frequency band, amplifies the signal to a predetermined level, and outputs it. The two output signals thus output are transmitted as RF (Radio Frequency) signals by the transmission antennas Tx1 and Tx2, respectively.

The receiving apparatus 10 receives m signals transmitted from the transmitting apparatus 50 using n (n ≧ 2) receiving antennas. That is, there are n × m transmission paths between the transmission device 50 and the reception device 10. Here, when the transfer function when transmitted from the i-th transmitting antenna and received by the j-th receiving antenna is h _ji , an n-by-m matrix with this as the (j, i) component is a channel matrix. It is. Hereinafter, the channel matrix is denoted as H.

  For example, in the example illustrated in FIG. 3, the number of reception antennas is two. Therefore, the reception device 10 receives two signals (m = 2) transmitted from the transmission device 50 (n = 2). Are received by the receiving antennas Rx1 and Rx2. In this case, 2 × 2 transmission paths, that is, propagation paths h11, h12, h21, and h22 exist between the transmission apparatus 50 and the reception apparatus 10.

  The reception processing unit 102 acquires m systems of RF signals received by each of the n reception antennas. The reception processing unit 102 filters each acquired RF signal in a predetermined band for each reception system, and performs amplification, frequency conversion, and the like to convert it into a baseband signal.

  The reception processing unit 102 extracts pilot subcarriers c12a to c12d from the converted baseband signal, and converts each of the extracted pilot subcarriers c12a to c12d into digital signals. In this way, reception processing section 102 demodulates the pilot signal from each of pilot subcarriers c12a to c12d extracted for each reception system.

  For example, in the example shown in FIG. 3, the reception processing unit 102 uses two RF signals received by the two reception antennas Rx1 and Rx2 as bases corresponding to the reception antennas Rx1 and Rx2, respectively. Convert to band signal. Then, the reception processing unit 102 extracts pilot subcarriers c12a to c12d from the baseband signals corresponding to the reception antennas Rx1 and Rx2. The reception processing unit 102 demodulates the pilot signal from each of the pilot subcarriers c12a to c12d extracted corresponding to each of the reception antennas Rx1 and Rx2.

The reception processing unit 102 is a channel estimation unit for each symbol transmission timing of the received signal (that is, pilot signal) demodulated for each pilot subcarrier c12 extracted from the baseband signal for each reception system in symbol units. Sequentially output to 104. Hereinafter, the received signal demodulated in units of symbols for each pilot subcarrier c12 may be described as a received signal r _i ^(t) (k) at each symbol transmission timing. Note that “i” indicates the number of the receiving antenna (that is, the receiving system), and “k” indicates the number for identifying each of the pilot subcarriers c12a to c12d. “T” indicates a transmission timing at which the demodulated symbol is transmitted.

For example, in the case of 2 × 2 MIMO illustrated in FIG. 3, the reception processing unit 102 sets r ₁ ⁽ corresponding to the reception antenna Rx1 as the reception signal r _i ⁽¹⁾ (k) corresponding to the transmission timing t = 1. ¹⁾ ₍₁₎ ^{~r 1 (1)} (4), and outputs _r ² corresponding to the receiving antenna Rx2 (1) ₍₁₎ ^{~r 2 (1)} and (4) to the channel estimation unit 104. Then, the reception processing unit 102, a received signal _r ⁱ which corresponds to the transmission timing ^{t = 2 (2) (k} ), r 1 (2) (1) corresponding to the receiving antenna Rx1 ^{~r 1 (2) (4} ) And r ₂ ⁽²⁾ (1) to r ₂ ⁽²⁾ (4) corresponding to the receiving antenna Rx ² are output to the channel estimation unit 104.

The channel estimation unit 104 sequentially acquires the reception signal r _i ^(t) (k) from the reception processing unit 102 for each transmission timing of the reception signal (symbol). Channel estimation section 104 estimates channel h _ij for each propagation path for each pilot subcarrier c12 based on received signals r _i ^(t) (k) having different transmission timings. Hereinafter, details of the processing related to the calculation of the channel h _ij by the channel estimation unit 104 will be described.

First, referring to FIG. FIG. 4 is a diagram for explaining channel estimation in the communication system 1 according to the present embodiment, and schematically shows received signals (pilot signals) received for each antenna when there are two receiving antennas. Show. Data 1-1 to 1-U in FIG. 4 indicate reception signals received by the reception antenna Rx1, and correspond to the reception signals r ₁ ^(t) (k). Similarly, Data 2-1 to 2-U indicate reception signals received by the reception antenna Rx2, and correspond to the reception signal r ₂ ^(t) (k).

The channel estimation unit 104 uses the received signals r _i ^(t) (k) transmitted at different transmission timings for estimating the channel h _ij for each propagation path. For example, in the case of the example illustrated in FIG. 4, the channel estimation unit 104 divides Data 1-1 and Data 2-1 transmitted at the transmission timing t11 and Data 1-2 and Data 2-1 transmitted at the transmission timing t12. Based on this, the channel h _ij is estimated. The channel h _ij estimated at this time indicates the channel for each propagation path in the time during which Data 1-1, Data 2-1, Data 1-2, and Data 2-2 are propagated.

Similarly, the channel estimation unit 104, based on Data1-3 and Data2-3 transmitted at the transmission timing t21, and Data1-4 and Data2-4 transmitted at the transmission timing t22, the channel h _{ij at} another time. Is estimated. Note that the reception signals r _i ^(t) (k) used for estimating the channel h _ij need only have different transmission timings, and the transmission timings corresponding to the reception signals r _i ^(t) (k) are not necessarily continuous. May be.

Here, the principle of channel estimation in the communication system 1 according to the present embodiment will be described. Received signals r _i ^(t) (k) transmitted at two different transmission timings are defined by (Expression 2) to (Expression 6) shown below.

In the above (Expression 2) to (Expression 6), k represents a number for identifying each of the pilot subcarriers c12a to c12d. Further, as shown in (Equation 3), R (k) represents a received signal matrix formed by received signals r _i ^(t) (k) transmitted at two different transmission timings. H (k) represents a channel matrix. As shown in (Equation 4), each element of the channel matrix H (k) is a channel h _ij for each propagation path corresponding to each pilot subcarrier c12. (K) is shown. Further, N (k) shown in (Equation 6) indicates thermal noise.

Further, as shown in (Equation _{5), S} p (k) is the received signal _r ⁱ which constitutes the received signal matrix R (k) ^(t) corresponding to the (k), the transmitted signal _s ^{pi (t)} The transmission signal matrix formed by (k) is shown. For example, the transmission signal _s ^{p1 (2) (k)} corresponds to the received signal ^{_{r 1 (2) (k)}} . Similarly, the transmission signal _s ^{p2 (1) (k)} corresponds to the received signal ^{_{r 2 (1) (k)}} . Note that the transmission signal s _pi ^(t) (k) indicates a pilot signal at the time of transmission, and needless to say, is a known signal.

In addition, (Equation 2) shown above shows the case of 2 × 2 MIMO, and the received signal matrix R (k), the channel matrix H (k), and the transmitted signal according to the number of transmitting antennas and receiving antennas. Needless to say, the number of elements of each of the matrix _Sp (k) and the thermal noise N (k) changes.

  Based on (Equation 2) above, the channel matrix H (k) is estimated based on (Equation 3) shown below.

As shown in the above (Expression 7), the propagation environment in the real space is strictly affected by the thermal noise N (k), but the norm (geometric vector) of the channel matrix H (k) is the thermal noise N It is much larger than the norm of (k) and the thermal noise N (k) can be ignored. That is, the channel estimation unit 104 estimates the channel matrix H (k) based on the reception signal matrix R (k) and the transmission signal matrix _Sp (k). Thereby, channel h _ij (k) for each propagation path corresponding to each pilot subcarrier c12 is estimated.

As described above, channel estimation section 104 sequentially estimates channel h _ij (k) for each propagation path corresponding to each pilot subcarrier c12, and channel fluctuation estimation section 106 estimates estimated channel h _ij (k). Are output sequentially.

The channel fluctuation estimation unit 106 sequentially acquires, from the channel estimation unit 104, the channel h _ij (k) for each propagation path corresponding to each estimated pilot subcarrier c12. The channel fluctuation estimation unit 106 calculates a correlation coefficient ρ based on the correlation of the channels h _ij (k) estimated for different times (in other words, different transmission timings), and the calculated correlation coefficient ρ Based on this, channel fluctuation is estimated. Details of the channel fluctuation estimation unit 106 will be described below.

The channel fluctuation estimation unit 106 compares the correlations between the channels h _ij (k) estimated for different times. As a specific example, the channel fluctuation estimation unit 106 uses the channel h _ij (k) estimated based on the received signals r _i ^(t) (k) corresponding to the transmission timings t11 and t12 shown in FIG. Obtained from the estimation unit 104. Next, the channel fluctuation estimation unit 106 acquires from the channel estimation unit 104 the channel h _ij ′ (k) estimated based on the reception signals r _i ^(t) (k) corresponding to the transmission timings t21 and t22.

The channel fluctuation estimation unit 106 calculates the correlation coefficient ρ by comparing the correlation between the channel h _ij (k) and the channel h _ij ′ (k) obtained sequentially from the channel estimation unit 104. Specifically, the correlation coefficient ρ is calculated by (Equation 8) shown below.

In (Expression 8), channel h _ij (k) corresponds to a reference channel (propagation channel response), and channel h _ij ′ (k) is estimated for a time different from channel h _ij (k). Correspond to the selected channel. H _ij ^* (k) represents a complex conjugate of the channel h _ij (k). Further, “v” indicates the number of pilot subcarriers c12. “M” indicates the number of reception antennas, and “n” indicates the number of transmission antennas. For example, in 2 × 2 MIMO, when four pilot subcarriers c12 are used, v = 4, m = 2, and n = 2.

When there is no change in the propagation environment, that is, when the channel h _ij (k) and the channel h _ij ′ (k) are equal, the correlation coefficient ρ = 1, and when the propagation environment changes, depending on the degree of change The correlation coefficient ρ decreases.

Therefore, the channel fluctuation estimation unit 106 estimates the channel fluctuation by sequentially calculating the correlation coefficient ρ based on the channels h _ij (k) sequentially obtained from the channel estimation unit 104 and monitoring the calculated correlation coefficient ρ. It becomes possible to do. Note that the channel h _ij (k) and the channel h _ij ′ (k) used for calculating the correlation coefficient ρ need only correspond to different times, and the channel h _ij (k) and the channel h _ij ′ (k) ) Does not necessarily have to be continuous.

  Moreover, although the example shown above demonstrated the example applied to the radio system of a MIMO system, as shown to (Formula 8), the communication system 1 which concerns on this embodiment is not necessarily limited to a MIMO system. That is, as a configuration of the communication system 1, it goes without saying that any of SISO (single input and multiple output), SIMO (single input and multiple-output), and MISO (multiple-input and single output) can be applied. Further, the number of pilot subcarriers c12 is not limited as long as a communication signal used in the communication system 1 according to the present embodiment includes at least one pilot subcarrier c12.

  Further, in the example described above, the example in which the reception device 10 includes the channel estimation unit 104 and the channel fluctuation estimation unit 106 has been described. However, the channel estimation unit 104 and the channel fluctuation estimation unit 106 are separated from the reception device 10. It may be provided as a body.

  Further, each receiving antenna (for example, receiving antennas Rx1 and Rx2) may be incorporated as a part of the receiving device 10. Similarly, each transmission antenna (for example, transmission antennas Tx1 and Tx2) may be incorporated as a part of the transmission device 50.

  Further, the transmission device 50 and the reception device 10 may be configured integrally. For example, FIG. 5 is a block diagram illustrating another example of the communication system 1 according to the present embodiment, and illustrates a configuration of the communication system 1a in which the transmission device 50 and the reception device 10 are integrally configured. In the example illustrated in FIG. 5, the transmission processing unit 502 corresponding to the transmission device 50 described above, and the reception processing unit 102, the channel estimation unit 104, and the channel fluctuation estimation unit 106 included in the reception device 10 described above are included in the communication device. 10a is integrally formed.

  The series of operations described above can be configured by a program for causing the CPU of the device that operates each configuration of the transmission device 50 and the reception device 10 to function. This program may be configured to be executed via an OS (Operating System) installed in the apparatus. In addition, the position of the program is not limited as long as the apparatus including the configuration for executing the above-described processing can be read. For example, the program may be stored in a recording medium connected from the outside of the apparatus. In this case, it is preferable to connect the recording medium storing the program to the apparatus so that the CPU of the apparatus executes the program.

  As described above, the communication system 1 according to the present embodiment uses the pilot subcarriers to estimate the channel for each propagation path based on the pilot signal included in the data part, and the channel estimated for different times. Channel fluctuation is estimated based on the correlation. Therefore, the communication system 1 according to the present embodiment can estimate the channel variation even when a sudden channel variation occurs during the transmission period of the data portion. Further, according to the communication system 1 according to the present embodiment, it is possible to perform channel estimation based on at least two OFDM symbols among OFDM symbols transmitted as a data part. Therefore, the communication system 1 according to the present embodiment can estimate the channel fluctuation with higher time resolution (that is, at shorter intervals) than when the channel fluctuation is estimated based on the long preamble. Become.

<2. Example>
Next, as an example, an example in which the communication system 1 according to the present embodiment is applied to a security system for detecting intrusion of a person into a predetermined area will be described. Specifically, the propagation environment fluctuates due to human intrusion, breathing, heart movement, and the like. Therefore, the communication system 1 according to the embodiment detects the intrusion of a person into the area by monitoring the channel fluctuation in the predetermined area to be monitored.

Phase Specifically, the communication system 1 according to the embodiment, with sequentially estimate the channel h _{ij (k),} which is estimated to based correlation number ρ estimated channel h _{ij (k),} which is sequentially estimated By comparing the relation number ρ with a predetermined threshold, channel fluctuations are monitored. At this time, if a person enters the area to be monitored, the propagation environment changes, and the estimated correlation coefficient ρ decreases. Therefore, the communication system 1 can determine whether or not a person has entered a region to be monitored depending on whether or not the sequentially estimated correlation coefficient ρ is less than a predetermined threshold. .

  Below, the measurement result of the detection probability at the time of detecting a person's intrusion using the communication system 1 which concerns on an Example is demonstrated with a comparative example.

  First, the measurement environment will be described with reference to FIG. FIG. 6 is a diagram illustrating an example of a measurement environment according to the embodiment. As shown in FIG. 6, an indoor space p1 having a width of 6 m in the vertical direction W1, a width of 7.8 m in the horizontal direction W2, and a height of 2.6 m was used. Further, in the indoor space p1, the transmission antennas Tx1 and Tx2 are arranged in the vicinity of both ends of the vertical direction W1 in one of the horizontal directions W2, and the reception antennas Rx1 and Rx2 are arranged in the vicinity of both ends of the vertical direction W1 in the other 2 ×. 2 MIMO configuration.

  As a signal used for channel fluctuation estimation, a wireless LAN signal conforming to the IEEE 802.11n standard was used. The antenna element interval is 32λ.

  In the measurement environment as described above, when a person is moving in the direction indicated by p11 to p15, the probability of detecting the movement of the person is measured.

  Note that, in the same measurement environment, even when the channel fluctuation is estimated by a method different from that of the communication system 1 according to the example, the measurement is performed as Comparative Example 1 and Comparative Example 2. Therefore, the measurement conditions of Examples, Comparative Example 1, and Comparative Example 2 will be described below.

  First, in the embodiment, channel fluctuation is estimated using four pilot subcarriers included in a plurality of subcarriers for transmitting the data portion. In this case, channel fluctuation is estimated every 2 OFDM symbol intervals, that is, every 8 [μs].

  In Comparative Example 1, the communication signal adjusted so that only the long preamble is transmitted continuously without including the data portion is used, and the channel fluctuation is estimated using the 56-wave long preamble. The first comparative example is a signal intentionally generated assuming ideal conditions, and channel fluctuation is estimated every 1 OFMD symbol interval, that is, every 4 [μs].

  In Comparative Example 2, the data portion was inserted so that the long preamble was transmitted every 0.1 [s] interval, and the channel fluctuation was estimated using the 56-wave long preamble. In this case, the channel fluctuation is estimated every long preamble interval, that is, every 0.1 [s].

  Under the above measurement conditions, the SNR of a signal used for channel fluctuation estimation was varied between 1 and 30 [dB], and the probability of detecting human movement in each case was measured. In addition, since the intervals at which the channel fluctuation is estimated are different in the example, the comparative example 1, and the comparative example 2, the measurement time is adjusted for each so that the number of samples becomes equal.

  The measurement results of Example, Comparative Example 1, and Comparative Example 2 are shown in FIG. FIG. 7 is a diagram illustrating an example of measurement results according to Example, Comparative Example 1, and Comparative Example 2. In FIG. 7, reference numeral g10 indicates a measurement result based on the measurement conditions shown as the example. Reference sign g21 indicates the measurement result based on the measurement condition shown as Comparative Example 1, and reference sign g22 indicates the measurement result based on the measurement condition indicated as Comparative Example 2.

  As can be seen from the comparison of the measurement results g10 and g21, according to the communication system 1 according to the example, it is understood that the channel fluctuation can be estimated with the same accuracy as in the comparative example 1. In other words, by using four-wave pilot subcarriers, it is possible to detect human intrusion with the same detection probability as when using an ideal communication signal and using a 56-wave long preamble. Become.

  In addition, as shown in the measurement result g22, when channel fluctuation is estimated by a 56-wave long preamble using a communication signal having a condition close to the actual environment in which the data portion is inserted, the SNR of the signal is increased. Even if it was set, the detection probability did not reach 100%. On the other hand, as shown by the measurement result g10, according to the communication system 1 according to the embodiment, an overall detection probability higher than the measurement result g22 can be realized, and the SNR is 20 [dB] or more. In some cases, a detection probability of 100% could be realized.

  As described above, the communication system 1 according to the above-described embodiment sequentially monitors channel fluctuations in a predetermined area to be monitored, for example, to detect an intrusion of a person into the area to be monitored. It becomes possible. Note that the application example to the security system shown in the examples is merely an example, and the application field of the communication system 1 according to the above-described embodiment is not particularly limited as long as the channel fluctuation needs to be estimated.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

1, 1a Communication system 10 Reception device 10a Communication device 50 Transmission device 102 Reception processing unit 104 Channel estimation unit 106 Channel fluctuation estimation unit 502 Transmission processing unit

Claims (10)

A communication device for processing a communication signal in which each symbol constituting a frame including a preamble part and a data part is transmitted by a plurality of subcarriers,
The plurality of subcarriers for transmitting the data portion includes at least one or more pilot subcarriers for transmitting a known signal;
A channel estimation unit that estimates a channel based on each of the plurality of known signals transmitted at different timings;
A channel fluctuation estimator for estimating a channel fluctuation based on a correlation between the channels estimated based on each of the plurality of known signals transmitted at different timings;
A communication apparatus comprising: The plurality of subcarriers includes a plurality of the pilot subcarriers,
The channel estimation unit estimates the channel based on the known signal corresponding to each of the pilot subcarriers for each of the plurality of pilot subcarriers,
The channel fluctuation estimation unit calculates the channel fluctuation based on the correlation between the channels estimated based on each of the plurality of known signals transmitted at the different timing for each of the plurality of pilot subcarriers. The communication device according to claim 1, wherein the communication device is estimated. The communication signal is transmitted from a plurality of transmission antennas and received by a plurality of reception antennas,
The channel estimation unit estimates the channel for each of a plurality of propagation paths configured between the plurality of transmission antennas and the plurality of reception antennas,
The channel fluctuation estimation unit is configured to determine the channel fluctuation based on the correlation between the channels estimated based on each of the plurality of known signals transmitted at the different timings through each of the plurality of propagation paths. The communication device according to claim 1, wherein the communication device is estimated.   The communication apparatus according to claim 1, wherein the different timing is a continuous timing.   The communication apparatus according to claim 1, further comprising a reception processing unit that demodulates the received communication signal. A receiving antenna for receiving the communication signal;
The communication apparatus according to claim 5, wherein the reception processing unit demodulates the communication signal received by the reception antenna.   The communication apparatus according to claim 5, further comprising a transmission processing unit configured to transmit the communication signal to a transmission antenna.   The communication apparatus according to claim 7, comprising the transmission antenna. A transmission device that transmits each symbol constituting a frame including a preamble portion and a data portion as a communication signal by a plurality of subcarriers;
A receiving device for receiving the communication signal,
The plurality of subcarriers for transmitting the data portion includes at least one or more pilot subcarriers for transmitting a known signal;
The receiving device is:
A channel estimation unit that estimates a channel based on each of the plurality of known signals transmitted at different timings;
A channel fluctuation estimator for estimating a channel fluctuation based on a correlation between the channels estimated based on each of the plurality of known signals transmitted at different timings;
A communication system comprising: A communication method for processing a communication signal in which each symbol constituting a frame including a preamble part and a data part is transmitted on a plurality of subcarriers,
The plurality of subcarriers for transmitting the data portion includes at least one or more pilot subcarriers for transmitting a known signal;
Estimating a channel based on each of the plurality of known signals transmitted at different timings;
Estimating channel variations based on correlations between the channels estimated based on each of the plurality of known signals transmitted at the different timings;
A communication method comprising:

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