JP2012060543A - Wireless communication apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate a weight suitable for a null steering.SOLUTION: According to an embodiment, a wireless communication apparatus 100 comprises a determination part 107 which: calculates a first cross-correlation in a first sub-carrier range including a plurality of sub-carriers in a band; calculates a second cross-correlation in a second sub-carrier range including a plurality of sub-carriers different from the first sub-carrier range in the band; determines the first sub-carrier range as a sub-carrier for weight calculation in the case where the first cross-correlation is smaller than the second cross-correlation; and determines the second sub-carrier range as a sub-carrier for weight calculation in the case where the first cross-correlation is not less than the second cross-correlation. A wireless communication apparatus 100 comprises a calculation part 104 which calculates the weight from a plurality of reception signals of the sub-carrier for weight calculation in a training period.

Description

  Embodiments of the present invention relate to adaptive array antenna technology.

  Conventionally, adaptive array antenna technology has been devised in wireless communication systems such as cellular systems. The adaptive array antenna technology performs signal processing on a plurality of antennas provided in a wireless communication apparatus and adaptively controls the directivity of the plurality of antennas. So-called null steering can be realized using adaptive array antenna technology. Null steering aims at increasing the directivity of adjacent base stations in the direction of each desired signal, and decreasing the directivity in the direction of each interference signal. That is, by appropriately performing null steering, adjacent base stations can share the same frequency (band) while suppressing deterioration in reception performance due to interference.

  For example, the base station can perform null steering using received training symbols. The training symbol is a known signal arranged at the head of the data. The training symbol is included in a training sequence that is uniquely determined by a base station ID (BSID) and a use band.

  Null steering of MMSE (Minimum Mean Square Error) standards (LMS (Least Mean Square), RLS (Recursive Least Mean), etc.) is realized using the correlation between training symbols for desired signals and training symbols for interference signals. Is done. The base station generates null by performing control to reduce directivity with respect to a signal having a low correlation with a training symbol related to a desired signal. Specifically, the base station calculates a weight for reducing directivity for a signal having a low correlation with a training symbol related to a desired signal, and uses the weight to reduce a frequency domain received signal from multiple antennas (or to multiple antennas). Applies to frequency domain transmission signals). The weight of each subcarrier can be calculated individually for all subcarriers, or can be calculated for some subcarriers and then interpolated for the remaining subcarriers. According to the latter method, the amount of calculation can be reduced.

JP 2010-56714 A JP 2008-301359 A JP 2007-295314 A

Nobuyoshi Kikuma, "Adaptive signal processing by array antenna", Science and Technology Publishing

  A base station that performs null steering of the MMSE scheme calculates a weight that lowers directivity for a signal having a low correlation with a training symbol related to a desired signal. Therefore, for example, if weights are calculated based on subcarriers having a high correlation between a training symbol related to a desired signal and a training symbol related to an interference signal, it becomes difficult to distinguish the desired signal and the interference signal, and null steering is not performed appropriately. . That is, in order to appropriately perform null steering, it is desirable that the correlation between the training symbols between the desired signal and the interference signal is low in the subcarriers used for weight calculation.

  The embodiment aims to calculate a weight suitable for null steering.

  According to one embodiment, a wireless communication device calculates a first cross-correlation in a first subcarrier range that includes a plurality of subcarriers in a band, and a plurality of different first subcarrier ranges in the band The second cross-correlation in the second sub-carrier range including the sub-carrier is calculated, and when the first cross-correlation is smaller than the second cross-correlation, the first sub-carrier range is determined as the weight calculation sub-carrier. And a determination unit that determines the second subcarrier range as a weight calculation subcarrier when the first cross-correlation is greater than or equal to the second cross-correlation. The wireless communication apparatus calculates a weight from a plurality of received signals of weight calculation subcarriers in a training period, and weights and combines a plurality of received signals after the training period using a weight, Application section to obtain.

Explanatory drawing of the radio | wireless communications system containing the radio | wireless communication apparatus which concerns on 1st Embodiment. 1 is a block diagram illustrating a wireless communication device according to a first embodiment. The graph which illustrates the cross correlation characteristic of two types of training signal pairs. Explanatory drawing of the weight calculated by the 1st weight calculation part of FIG. Explanatory drawing of operation | movement of the subcarrier determination part for weight calculation of FIG. The block diagram which illustrates the radio communications equipment concerning a 2nd embodiment. FIG. 6 is a block diagram illustrating a wireless communication apparatus according to a third embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. In addition, although embodiment assumes the adaptive array antenna technique applied to an OFDMA (Orthogonal Frequency Division Multiple Access) system (especially next-generation PHS system), it can be applied suitably also to another radio | wireless communications system. For example, the embodiment can be similarly applied to adaptive array antenna technology in the frequency domain in a single carrier wireless communication system.

  In addition, the embodiment assumes a case where geographically adjacent wireless communication apparatuses share a band. However, the embodiment can be similarly applied to an SDMA (Spatial Division Multiple Access) system in which the same wireless communication apparatus accommodates a plurality of wireless communication terminals in the same band.

  Furthermore, in the following description, “training symbol (sequence, signal)” is used in the same meaning as “preamble signal”. That is, “training symbol” or the like indicates a known signal arranged at the head of data. However, it goes without saying that the data can be easily extended even when it is transmitted at a portion other than the beginning of the data.

(First embodiment)
FIG. 1 shows an example of a wireless communication system including a wireless communication apparatus 100 according to the first embodiment. The wireless communication system of FIG. 1 includes a wireless communication device 100, a wireless communication device 200, a wireless communication terminal 300, and a wireless communication terminal 400. In FIG. 1, a circle centered on the wireless communication device 100 and the wireless communication device 200 represents each cell. It is assumed that the wireless communication device 100 and the wireless communication device 200 are geographically adjacent. Note that the number of wireless communication devices in the wireless communication system is not limited to two, and the following description can be easily expanded when the number of wireless communication devices is three or more. In the embodiment, the “wireless communication apparatus” has a function of accommodating a “wireless communication terminal”. That is, the “wireless communication device” refers to a so-called base station or a similar device. In the following description, for simplification, it is assumed that the wireless communication device 100 and the wireless communication device 200 are base stations.

  In FIG. 1, the wireless communication apparatus 200 already accommodates the wireless communication terminal 400 existing in the cell in a specific band (for example, subchannel) A. Here, it is assumed that the wireless communication apparatus 100 has decided to accommodate the wireless communication terminal 300 in the cell in the band A (that is, share the band A with the wireless communication apparatus 200). In such a situation, the wireless communication device 100 executes null steering that increases the directivity with respect to the wireless communication terminal 300 that transmits the desired signal while reducing the directivity with respect to the wireless communication terminal 400 that transmits the interference signal.

  Hereinafter, null steering by the wireless communication device 100 will be described using Expressions (1) to (12). This null steering method is based on Non-Patent Document 1. Each formula is defined by focusing on any one subcarrier for the sake of simplicity. In each equation, each signal is expressed in baseband.

When the wireless communication terminal 300 and the wireless communication terminal 400 are connected to the wireless communication device 100 and the wireless communication device 200 in the same band, the received signal of the wireless communication device 100 is defined by the following formula (1). Unless otherwise noted, lowercase bold characters in the formulas represent vertical vectors, uppercase bold characters represent matrices, and the rest represent scalars.

In Expression (1), N represents the number of antennas of the wireless communication apparatus 100, and it is assumed that N = 2 in the following description. However, [] ^T represents transposition. Further, a training symbol used in the band A by the wireless communication device 100 and the wireless communication device 200 is defined by the following formula (2).

In the above equation, x ₁₀₀ represents a training symbol used by the wireless communication device 100 and the wireless communication terminal 300, and x ₂₀₀ represents a training symbol used by the wireless communication device 200 and the wireless communication terminal 400. Further, the propagation path matrix between the wireless communication terminal 300 and the wireless communication terminal 400 and the wireless communication device 100 is defined by the following mathematical formula (3).

In the above equation, h ₁₁ is a propagation path response from the wireless communication terminal 300 to the first antenna of the wireless communication apparatus 100, h ₁₂ is a propagation path response from the wireless communication terminal 400 to the first antenna of the wireless communication apparatus 100, h ₂₁ represents a propagation path response from the wireless communication terminal 300 to the second antenna of the wireless communication apparatus 100, and h ₂₂ represents a propagation path response from the wireless communication terminal 400 to the second antenna of the wireless communication apparatus 100. The reception signal of the wireless communication device 100 during the training period is expressed by the following mathematical formula (4).

In Equation (4), the vector n in represents the noise vector in the wireless communication device 100, the following equation using the noise component n ₂ in the first noise component n ₁ and a second antenna in the antenna (5) Can be defined.

According to Non-Patent Document 1, in order for the wireless communication apparatus 100 to direct null toward the wireless communication terminal 400 connected to the wireless communication apparatus 200 while directing directivity to the wireless communication terminal 300 using the MMSE norm, The weight vector w shown in the following formula (6) is used.

In Equation (6), R _yy represents the correlation matrix of the received signal, and r _yd represents the correlation vector between the received signal and the desired signal. The correlation matrix R _yy of the received signal can be rewritten as the following formula (7).

In Equation (7), E () represents an ensemble average, and () ^H represents a complex transpose. The correlation between the noise component and the received signal component can be regarded as zero. Further, if it is assumed that the propagation path (propagation path response) does not change in the ensemble section, it can be rewritten as the following formula (8) of the formula (7).

In Expression (8), R _xx represents a correlation matrix of a transmission signal (a training symbol in a training period), and ideally becomes a unit matrix. Further, σ _n ² represents noise variance, and I represents a unit matrix having the same size as the number of antennas. Further, the correlation r _yd between the received signal and the desired signal is expressed by the following mathematical formula (9).

In Expression (9), d represents a desired signal (desired training symbol), and “·” is an operator representing the product of each element of the vector and the scalar. Desired signal d with respect to the wireless communication device 100 is a training symbol _{x 100.} Also in Equation (9), the correlation between the desired signal and the noise component can be regarded as zero, so Equation (9) can be rewritten as Equation (10) below.

If the training symbols used by the wireless communication device 100 and the wireless communication device 200 are uncorrelated in the interval in which the ensemble average is calculated, r _xd is expressed by the following equation (11).

That is, under the above conditions, r _yd is expressed by the following formula (12).

In Expression (6), it is known that the matrix R _yy ⁻¹ has an effect of directing nulls to each component included in the received signal, and the matrix r _yd has an effect of directing gain to each of the components. If the matrix r _yd matches the above equation, the wireless communication apparatus 100 can direct null to the interference signal from the wireless communication terminal 400 while improving the directivity for the desired signal from the wireless communication terminal 300. That is, the wireless communication device 100 can separate a desired signal and an interference signal. On the other hand, the higher the correlation between the interference training symbol x ₂₀₀ and the desired training symbol x ₁₀₀ is, the more the component related to the propagation path response (h ₁₂ or h ₂₂ ) of the interference signal is added to each component of the matrix r _yd . It becomes difficult for the wireless communication apparatus 100 to separate the desired signal and the interference signal.

The weight vector w shown in Expression (6) can be defined for each subcarrier in the band A (excluding subcarriers where signals such as DC (Direct Current) carrier and guard carrier are not transmitted / received). That is, if the band A is composed of 24 subcarriers, a maximum of 24 weight vectors can be defined. When the sub-carrier k (k is a variable representing the sub-carrier number) represents the weight vector allocated to at w _k, apply the weight vector w _k according refers to calculation of the equation (13) below.

In Equation (13), y _k represents the frequency component vector of subcarrier _k of received signal vector y, and z _k represents the frequency component of subcarrier _k of the combined received signal.

  As illustrated in FIG. 2, the wireless communication apparatus 100 includes an AD (analog-digital) conversion unit 101, a filter unit 102, an FFT unit 103, a first weight calculation unit 104, a second weight calculation unit 105, and weight application. Unit 106 and weight calculation subcarrier determination unit 107.

  The AD conversion unit 101 converts N analog reception signals received by a plurality (N) of antennas (not shown) into N digital reception signals. The filter unit 102 suppresses out-of-band components (typically, out-of-band interference) in each of the N digital received signals.

  The FFT unit 103 performs FFT on the N received signals in the time domain output from the filter unit 102 to obtain N received signals in the frequency domain. The N received signals in the frequency domain are input to the first weight calculation unit 104 and the weight application unit 106. For example, the reception signal in the training period is input to the first weight calculation unit 104, and the reception signal in the subsequent period is input to the weight application unit 106.

  First weight calculation section 104 calculates a group weight assigned to each of one or more subcarrier groups obtained by dividing all subcarriers in the band. Note that the method for dividing all subcarriers into a plurality of subcarrier groups is not particularly limited. For example, all subcarriers may be equally divided or unequally divided.

  In the following description, for the sake of simplicity, it is assumed that all subcarriers are divided into four equal parts as shown in FIG. In FIG. 4, the horizontal axis represents time, and the vertical axis represents frequency (subcarrier). That is, the first weight calculation unit 104 performs group weight A assigned to the subcarrier group A (F1,..., F6) and group weight assigned to the subcarrier group B (F7,..., F12). B, a group weight C assigned to the subcarrier group C (F13,..., F18) and a group weight D assigned to the subcarrier group D (F19,..., F24) are calculated. However, according to the physical resource unit (PRU) illustrated in FIG. 4, since signals are not transmitted and received in F1 and F13, F1 and F13 are not subjected to weight calculation and allocation.

  Of course, all subcarriers may be divided so that each subcarrier group is composed of one subcarrier. According to this division, the first weight calculation unit 104 calculates the weights of all subcarriers. By calculating the weights of all subcarriers, the calculation amount increases, but an appropriate weight can be obtained even in an environment where frequency selective fading is intense.

  Specifically, the first weight calculation unit 104 is notified of a plurality of (for example, five) weight calculation subcarriers for calculating each group weight from the weight calculation subcarrier determination unit 107. First weight calculation section 104 calculates a group weight based on a plurality of received signals of weight calculation subcarriers. That is, the first weight calculation unit 104 calculates the group weight by substituting the average of the ensembles in the above equations with the average in the frequency direction (subcarrier direction). Note that received signals of subcarriers belonging to another subcarrier group may be used to calculate the group weight of a specific subcarrier group. For example, when the group weight A of the subcarrier group A is calculated, it is allowed to use the received signal of the subcarrier F6 belonging to the subcarrier group B.

  Second weight calculation section 105 interpolates and generates weights for all subcarriers based on the group weight calculated by first weight calculation section 104. For example, the second weight calculator 105 performs interpolation generation of the weights of all subcarriers by performing zero-order interpolation, first-order interpolation, or least square criterion based on the group weight. The interpolation based on the first-order interpolation or the least-square criterion increases the amount of calculation compared with the zero-order interpolation, but can generate an appropriate weight in consideration of frequency selective fading generated by multipath. When the first weight calculation unit 104 calculates the weights of all subcarriers, the second weight calculation unit 105 is not necessary.

  The weight applying unit 106 applies the weight for each subcarrier from the second weight calculating unit 105 to the N received signals in the frequency domain from the FFT unit 103 to obtain a combined received signal. Specifically, the weight application unit 106 performs weighted combining according to Equation (13) for all subcarriers.

  The weight calculation subcarrier determination unit 107 determines the weight calculation subcarrier for each group based on the cross-correlation between the desired training signal 11 used by the wireless communication terminal 300 and the interference training signal 12 used by the wireless communication terminal 400. Determine your career. The weight calculation subcarrier determination unit 107 notifies the first weight calculation unit 104 and the second weight calculation unit 105 of the determined weight calculation subcarriers of each group.

Here, the desired training signal 11 is known in the wireless communication apparatus 100. On the other hand, the interference training signal 12 is not necessarily known in the wireless communication device 100. However, the training sequence in the next-generation PHS system is uniquely determined by the BSID and the used band. Specifically, if the lower 5 bits of the BSID are A and the upper 5 bits next to A are B, the core sequence for determining the training symbols and the phase rotation amount in each subchannel are expressed by the following equation (14). Is done.

In Equation (14), x _t represents 12 types of core sequences called core-sequence numbers, and y _t (m) represents the amount of phase rotation in subchannel m called offset value number. N represents the total number of subchannels. For example, in a system in which n = 9 subchannels are used, when the BSID of the wireless communication apparatus 200 is “88”, core-sequence number = 1 and offset value number = 4. When the BSID of the wireless communication apparatus 100 is “98”, core-sequence number = 3 and offset value number = 5.

  Therefore, if the BSID of the wireless communication apparatus 200 that accommodates the wireless communication terminal 400 is known in the wireless communication apparatus 100, the interference training signal 12 can be uniquely derived. In addition, as long as the interference training signal 12 can be acquired, derived, or estimated by any method for other wireless communication systems, the wireless communication apparatus 100 according to the present embodiment can be applied.

  The weight calculation subcarrier determination unit 107 averages and evaluates the cross-correlation between the desired training signal 11 and the interference training signal 12 in the frequency direction. Here, in the next-generation PHS system, since the guard interval is 3.33 μsec, the spectral null period is 303 kHz in consideration of the multipath maximum delay time. Since the subcarrier interval is 37.5 kHz, the number of subcarriers that can be considered that the propagation path response does not change is about 3 to 5. Therefore, in the following description, it is assumed that the cross-correlation of training symbols for three subcarriers is evaluated. For example, the cross-correlation in the subcarrier F2 is evaluated by the average of the cross-correlations of the subcarriers F1-F3. Alternatively, the cross-correlation in subcarrier F2 may be evaluated by a weighted average of the cross-correlations of subcarriers F1-F3.

  FIG. 3 illustrates the cross-correlation characteristics of training signal pair 1 and training signal pair 2. Here, the training signal pair refers to a pair of a training signal used by the wireless communication apparatus 100 in the shared band and a training signal used by the wireless communication apparatus 200 in the shared band. In FIG. 3, the horizontal axis represents a subcarrier number (ie, frequency), and the vertical axis represents cross-correlation. The cross-correlation is standardized so that the maximum value is 1. As illustrated in FIG. 3, in the next-generation PHS system, the correlation characteristics tend to vary greatly depending on the training signal pair. For example, the training signal pair 1 has a relatively large variation in cross-correlation, and the training signal pair 2 has a relatively small variation in cross-correlation. In the following description, it is assumed that the cross-correlation characteristics of the training signals used in band A by radio communication apparatus 100 and radio communication apparatus 200 match the cross-correlation characteristics of training signal pair 1 in FIG.

  The weight calculation subcarrier determination unit 107 regards a plurality of subcarriers around one subcarrier included in each subcarrier group as the first subcarrier range. When the size of the subcarrier group is large, the propagation path response of the subcarrier occupying near one end in the subcarrier group may be significantly different from the propagation path response of the subcarrier occupying near the other end. Therefore, this first subcarrier range is typically a plurality of subcarriers that occupy near the center in each subcarrier group. Of course, the above description is merely an example, and is not intended to limit the position of the first subcarrier range. Depending on the size of the subcarrier group or the communication environment, the propagation path response of the subcarrier occupying near one end in the subcarrier group can be regarded as unchanged compared to the propagation path response of the subcarrier occupying near the other end.

  For example, the weight calculation subcarrier determining unit 107 sets F3 as the center subcarrier of the first subcarrier range of the subcarrier group A, F8 as the center subcarrier of the first subcarrier range of the subcarrier group B, and subcarriers. The central subcarrier of the first subcarrier range of group C is determined as F15, and the central subcarrier of the first subcarrier range of subcarrier group D is determined as F21.

For example, when the first subcarrier range centered on the subcarrier F8 is determined as the weight calculation subcarrier, the first weight calculation unit 104 calculates the correlation matrix R according to the following equations (15) and (16). ₈ and the correlation vector r ₈ are calculated, and the group weight vector w ₈ is derived using Equation (6).

  However, as is clear from FIG. 5 (the cross-correlation characteristics shown in FIG. 5 are the same as the cross-correlation characteristics of pair 1 shown in FIG. 3), the first sub-center centered on F8 and F21. The cross correlation in the carrier range is relatively high. Therefore, when the first subcarrier range centering on these is adopted as the weight calculation subcarriers of group B and group D, it is difficult to distinguish between the desired signal and the interference signal, and there is a possibility that null steering may not be performed appropriately. is there.

  Therefore, the weight calculation subcarrier determining unit 107 searches for a subcarrier range indicating a lower cross-correlation from the vicinity of the subcarriers F8 and F21. For example, the cross correlation in the second subcarrier range centered on the subcarrier F9 is lower than the first subcarrier range centered on the subcarrier F8, and the second subcarrier range centered on the subcarrier F22. The cross-correlation at is lower than the first subcarrier range centered on subcarrier F21. Therefore, the weight calculation subcarrier determination unit 107 determines the second subcarrier range centered on the subcarrier F9 instead of the subcarrier F8 as the weight calculation subcarrier of the subcarrier group B, and sets the subcarrier F21. Instead, the second subcarrier range centered on the subcarrier F22 is determined as the subcarrier for weight calculation of the subcarrier group D. By not adopting a subcarrier range showing a high cross-correlation as a weight calculation subcarrier, it becomes easy to distinguish between a desired signal and an interference signal, and null steering is easily performed appropriately.

For example, when the second subcarrier range centered on the subcarrier F9 is determined as the weight calculation subcarrier, the first weight calculation unit 104 replaces the following formulas (15) and (16) with the following: Correlation matrix R ₉ and correlation vector r ₉ are calculated according to Equation (17) and Equation (18), and group weight vector w ₉ is derived using Equation (6).

The first weight calculation section 104, when calculating the correlation matrix R _k or correlation vector r _k, may be weighted in accordance with the position of the subcarrier. Specifically, as the distance from the center of the weight calculation subcarrier increases, the correlation becomes smaller due to the influence of multipath, and thus weighting in consideration of such influence is effective. For example, the correlation matrix R _k and the correlation vector r _k can be calculated by the following formulas (19) and (20).

In Equation (19) and Equation (20), α _k represents a weighting factor corresponding to subcarrier k. Although the amount of calculation increases by weighting, an appropriate weight can be obtained even in an environment where frequency selective fading is severe.

  Hereinafter, various methods for determining weight calculation subcarriers will be exemplified. The weight calculation subcarrier determination unit 107 determines the weight calculation subcarrier by using these methods or other methods not illustrated alone or in combination. In any method, the weight calculation subcarrier determining unit 107 refers to the first cross-correlation between the desired training signal 11 and the interference training signal 12 in the first subcarrier range, and this first mutual correlation is determined. A subcarrier range indicating a second cross-correlation below the correlation is determined as a weight calculation subcarrier. Note that the correlation between the desired training signal 11 and the interference training signal 12 in each subcarrier range may be calculated by the weight calculation subcarrier determination unit 107 or may be calculated by other elements not shown. .

  The first method uses a predetermined threshold (for example, “0.7”). That is, the weight calculation subcarrier determination unit 107 compares the cross-correlation in the first subcarrier range with the threshold value. If the cross-correlation is equal to or less than the threshold, weight calculation subcarrier determination section 107 determines the first subcarrier range as the weight calculation subcarrier as it is. On the other hand, if the cross-correlation in the first subcarrier range exceeds a predetermined threshold, the weight calculation subcarrier determination unit 107 searches for a subcarrier range indicating a cross-correlation that is equal to or lower than the threshold, and determines the searched subcarrier range. It is determined as a subcarrier for weight calculation.

  The second method uses a predetermined search range (for example, a plurality of subcarriers including two subcarriers before and after the first subcarrier range). That is, weight calculation subcarrier determination section 107 searches for cross-correlation in a subcarrier range included in a predetermined number of subcarriers before and after the first subcarrier range as necessary, and determines weight calculation subcarriers. To do. The size of the search range is typically determined according to the number of subcarriers that can be considered that the propagation path response does not change compared to the first subcarrier range. Alternatively, the size of the search range may be determined according to the size of the subcarrier group. Further, the search range may be set beyond the subcarrier group corresponding to the first subcarrier range. On the other hand, the search range may be a part or all of the subcarriers of the corresponding subcarrier group regardless of the position of the first subcarrier range. The search may be performed unconditionally, or may be performed only when a predetermined condition such that the cross-correlation in the first subcarrier range is equal to or greater than a threshold is satisfied.

  According to an example of a combination of the first technique and the second technique, the weight calculation subcarrier determining unit 107 determines that the first subcarrier range is the first subcarrier range when the cross-correlation in the first subcarrier range exceeds the threshold. The subcarrier numbers of all the subcarriers are changed in the order of (+1, -1, +2, -2), for example, and a subcarrier range showing a cross correlation below the threshold is searched. When the weight calculation subcarrier determining unit 107 searches for a subcarrier range indicating a cross-correlation equal to or lower than the threshold, the subcarrier range is determined as a weight calculation subcarrier. On the other hand, if all the subcarrier ranges within the search range exhibit a cross-correlation that is equal to or greater than the threshold, the weight calculation subcarrier determination unit 107 determines the subcarrier range that exhibits the minimum cross-correlation within the search range as the weight calculation subcarrier. Alternatively, the first subcarrier range may be determined as the weight calculation subcarrier as it is.

  Further, according to another example of the combination of the first method and the second method, the weight calculation subcarrier determining unit 107 determines that the first subcarrier determination unit 107 receives the first correlation when the cross-correlation in the first subcarrier range exceeds the threshold. Both the sub-correlation of the sub-carrier range obtained by adding all the sub-carrier numbers in the sub-carrier range of +1 and the cross-correlation of the sub-carrier range obtained by subtracting the sub-carrier number of −1 are searched. If one of the subcarrier ranges shows a cross-correlation less than or equal to the threshold, the weight calculation subcarrier determination unit 107 determines this subcarrier range as the weight calculation subcarrier. If both subcarrier ranges show a cross-correlation less than or equal to the threshold value, the weight calculation subcarrier determining unit 107 calculates the cross-correlation of the subcarrier range obtained by adding all subcarrier numbers of the first subcarrier range +2, and Further search is made for both of the cross-correlation in the subcarrier range with the carrier number minus 2. The cross-correlation of the subcarrier ranges obtained by +2 (or -2) of all subcarrier numbers in the first subcarrier range is equal to or less than the threshold value, and the subcarrier ranges obtained by subtracting the subcarrier number -2 (or +2) If the correlation exceeds the threshold value, weight calculation subcarrier determination section 107 determines a subcarrier range obtained by adding +1 (or -1) to the subcarrier number as a weight calculation subcarrier. According to this determination method, the weight calculation subcarrier can be determined in consideration of the local tendency of the cross-correlation characteristics.

  As described above, the wireless communication apparatus according to the first embodiment refers to the first cross-correlation between the training signals in the first subcarrier range, and the second cross-correlation below the first cross-correlation. A subcarrier range indicating the correlation is determined as a subcarrier for weight calculation. The radio communication apparatus according to the present embodiment calculates group weights based on weight calculation subcarriers. Therefore, according to the radio communication apparatus according to the present embodiment, null steering is easily performed appropriately, so that it is possible to suppress deterioration in reception performance due to interference.

  Note that the above description assumes a single interfering user for simplicity. In practice, however, there may be multiple interfering users. In such a case, the embodiment can be extended and applied by the following method.

  As an example, the wireless communication apparatus according to the present embodiment can narrow down interference users based on received power. Specifically, the wireless communication apparatus may evaluate the cross-correlation of the training signal with the desired user for a single interfering user having the largest received power among the plurality of interfering users.

  Alternatively, the wireless communication apparatus according to the present embodiment may individually evaluate the cross-correlation of training signals between a plurality of interfering users and a desired user. Specifically, the wireless communication apparatus may determine the weight calculation subcarrier based on whether or not all of the plurality of cross-correlations are equal to or less than a threshold value. In addition, the wireless communication device may derive a single cross-correlation by averaging (weighted) a plurality of cross-correlations and evaluate the single cross-correlation.

(Second Embodiment)
As illustrated in FIG. 6, the wireless communication device 110 according to the second embodiment includes an AD conversion unit 101, a filter unit 102, an FFT unit 103, a first weight calculation unit 104, a second weight calculation unit 105, Weight application section 106, weight calculation subcarrier determination section 107, broadcast signal reception section 111, base station ID detection section 112, neighboring base station ID list storage section 113, data reception section 114, and training signal estimation section 115 Including. 6, the same parts as those in FIG. 2 are denoted by the same reference numerals, and in the following description, different parts between FIG. 6 and FIG. 2 will be mainly described.

  The notification signal receiving unit 111 receives a notification signal from another wireless communication device around the wireless communication device 110 (for example, geographically adjacent). Generally, a base station stores identification information (for example, BSID) of the base station in a broadcast signal.

  The base station ID detection unit 112 acquires a notification signal from the notification signal reception unit 111 and detects the BSID stored in the notification signal. The BSID detected by the base station ID detection unit 112 is registered in the neighboring base station ID list. The peripheral base station ID list is stored in the peripheral base station ID list storage unit 113. The peripheral base station ID list is used by a training signal estimation unit 115 to be described later in order to refer to identification information of other wireless communication devices around the wireless communication device 110. Normally, the arrangement of base stations is not changed in a short period of time, so that the detected identification information can be used for a long period of time (for example, several days or more).

  When the band A in which the interference signal exists is shared with other radio communication apparatuses, the radio communication device 110 receives the interference signal in the band A during the training period before accommodating the radio communication terminal in the band A. The data is received by the unit 114.

  The training signal estimation unit 115 calculates the correlation between the interference signal received by the data reception unit 114 and at least one candidate training signal, and estimates the candidate training signal having the highest correlation as the interference training signal 12. Here, the candidate training signal is a training signal uniquely determined by each piece of identification information registered in the neighboring base station ID list and the band A (see, for example, Expression (14)).

  As described above, the wireless communication device according to the second embodiment detects the identification information of other peripheral wireless communication devices in advance, and the candidate training signal uniquely determined by each of the identification information and the use band The interference training signal is estimated from Therefore, according to the radio communication apparatus according to the present embodiment, even when the interference training signal is unknown, the cross-correlation between the training signals according to the first embodiment is appropriately evaluated, and the weight calculation subcarrier is determined. can do.

  In the above description, identification information of other wireless communication devices in the vicinity is detected from the notification signal. However, such identification information may of course be detected by other methods. For example, some wireless communication systems stipulate that the handover destination base station is notified of the identification information of the handover destination base station at the time of user handover. With respect to such a wireless communication system, it is possible to detect the identification information of neighboring base stations by referring to the user's past handover history.

(Third embodiment)
As illustrated in FIG. 7, the wireless communication device 120 according to the third embodiment includes an AD conversion unit 101, a filter unit 102, an FFT unit 103, a first weight calculation unit 104, a second weight calculation unit 105, A weight application unit 106, a weight calculation subcarrier determination unit 107, a weight application unit 121, an IFFT (Inverse FFT) unit 122, a filter unit 123, and a DA (digital-analog) conversion unit 124 are included. In FIG. 7, the same parts as those in FIG. 2 are denoted by the same reference numerals, and in the following description, different parts between FIG. 7 and FIG. 2 will be mainly described. The wireless communication device 120 also uses each weight calculated by the second weight calculation unit 105 for directional transmission. The wireless communication device 120 is suitable for a time division duplex (TDD) system that uses the same frequency in the uplink and downlink.

  The weight applying unit 121 applies the weight for each subcarrier from the second weight calculating unit 105 to the transmission signal in the frequency domain, and obtains N weighted transmission signals. Note that the weight application unit 121 may perform the calibration or similar processing described in Patent Document 3 before applying the weight to the transmission signal.

  The IFFT unit 122 performs IFFT on the N weighted transmission signals in the frequency domain output from the weight application unit 121 to obtain N weighted transmission signals in the time domain. N weighted transmission signals in the time domain are input to the filter unit 123.

  The filter unit 123 suppresses out-of-band components in each of the N weighted transmission signals in the time domain. The DA conversion unit 124 converts N digital signals output from the filter unit 123 into N analog signals, and outputs them to a subsequent stage for transmission from N antennas (not shown).

  As described above, the wireless communication apparatus according to the third embodiment uses the weight calculated according to the first embodiment or the second embodiment for directional transmission. Therefore, according to the wireless communication apparatus according to the present embodiment, it is possible to direct null to the interfering user when transmitting a signal to the desired user, so that interference can be reduced.

  The processing of each of the above embodiments can be realized by using a general-purpose computer as basic hardware. The program for realizing the processing of each of the above embodiments may be provided by being stored in a computer-readable storage medium. The program is stored in the storage medium as an installable file or an executable file. The storage medium may be a computer-readable storage medium such as a magnetic disk, optical disk (CD-ROM, CD-R, DVD, etc.), magneto-optical disk (MO, etc.), semiconductor memory, etc. Any form may be used. Further, the program for realizing the processing of each of the above embodiments may be stored on a computer (server) connected to a network such as the Internet and downloaded to the computer (client) via the network.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Desired training signal 12 ... Interference training signal 100, 110, 120, 200 ... Wireless communication apparatus 101 ... AD conversion part 102 ... Filter part 103 ... FFT part 104 ... First weight calculation unit 105 ... second weight calculation unit 106 ... weight application unit 107 ... weight calculation subcarrier determination unit 111 ... broadcast signal reception unit 112 ... base station ID detection Unit 113 ... Neighboring base station ID list storage unit 114 ... Data receiving unit 115 ... Training signal estimation unit 121 ... Weight application unit 122 ... IFFT unit 123 ... Filter unit 124 ... DA converter 300, 400 ... wireless communication terminal

Claims (6)

Calculating a first cross-correlation in a first subcarrier range including a plurality of subcarriers in a band, and a second subcarrier range including a plurality of subcarriers different from the first subcarrier range in the band A first cross-correlation is calculated, and when the first cross-correlation is smaller than the second cross-correlation, the first sub-carrier range is determined as a weight calculation sub-carrier, and the first cross-correlation is determined. A determination unit that determines the second subcarrier range as the weight calculation subcarrier when a correlation is equal to or greater than the second cross-correlation;
A calculation unit for calculating weights from a plurality of received signals of the weight calculation subcarriers in a training period;
A wireless communication apparatus comprising: a first applying unit that obtains a combined received signal by weighted combining a plurality of received signals after the training period has elapsed using the weights.   The radio communication apparatus according to claim 1, wherein the determination unit determines the weight calculation subcarrier from a search range including a predetermined number of subcarriers before and after the first subcarrier range.   The determination unit compares the first cross-correlation with a predetermined threshold, and determines the first subcarrier range as the weight calculation subcarrier if the first cross-correlation is equal to or less than the threshold. The wireless communication apparatus according to claim 1. A storage unit for storing identification information of another wireless communication device geographically adjacent to the wireless communication device;
The wireless communication apparatus according to claim 1, further comprising: an estimation unit that estimates the interference training signal based on identification information of the other wireless communication apparatus and a received signal from an interference user.   Identification information of the other wireless communication device is obtained from at least one of (a) a notification signal transmitted by the other wireless communication device and (b) a user's handover history from the wireless communication device to the other wireless communication device. The wireless communication apparatus according to claim 4, further comprising a detection unit for detecting.   The wireless communication apparatus according to claim 1, further comprising a second applying unit that applies the weight to a transmission signal to obtain a plurality of weighted transmission signals.

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